The Geochemistry of the Dykes in the Carletonville Goldfield Alida Litthauer Submitted in accordance with the requirements for the degree of Magister Scientiae in the Faculty of Natural and Agricultural Sciences, Department of Geology at the University of the Free State. November 2009 Supervisor: Prof. W.A. van der Westhuizen Co-supervisor: Prof.M. Tredoux Declaration I declare that the dissertation hereby handed in for the qualification Magister Scientiae at the University of the Free State, is my own independent work and that I have not previously submitted the same work for a qualification at/in another University/faculty. Signed at Bloemfontein on the day of 2009. Alida Litthauer ii Acknowledgements The Author would like to thank the following: • AngloGold Ashanti for the funding of the project. • Mark Watts (Field Office), Rob Burnett, Katarien Deysel (Tau Tona) and Michelle Pienaar (Mponeng) for their assistance regarding sampling and the providing of information and mine plans. • Hannes Moller, Tau Tona rock engineering. • My supervisor, Professor Willem van der Westhuizen and co-supervisor, Professor Marian Tredoux for their support and guidance during the project. • Professor Gerhard Beukes for his help with the mineralogical part of the study. • Professor Anton le Roex, Fayrooza Rawoot and Christel Tinguely at UCT Department of Geology for their help with the REE analysis. • Thandeka Klaas and Jonas Choane for their help with sample preparation for XRF analysis. • Daniel Radikgomo for the preparation of thin sections. • My parents for their constant help and support and for the proofreading of this thesis. • My husband, Michael, for his unfailing support throughout the last 18 months. • My friends and fellow musicians for much-needed distraction. Finally, I want to thank the Lord, Jesus Christ for the ability to do research and the strength to complete this project. iii Abstract Numerous dykes traverse the Witwatersrand Supergroup rocks in the Carletonville Goldfield. The aim of this study was to investigate a classification system for the dykes. Samples were obtained from Tau Tona and Mponeng mines as well as from AngloGold Ashanti’s field office. The mineralogical investigation revealed that most dykes, with the exception of the Brazil dyke, are altered. The most abundant minerals are chlorite, actinolite, epidote, quartz and albitised and/or saussuritised feldspar, corresponding to a greenschist metamorphic facies mineral composition. Veins are commonly filled with quartz, calcite, epidote and chlorite, with sulphides and Fe oxides occurring occasionally. However, mineralogical heterogeneity as a result of different degrees of alteration, were found between samples from the same dyke. This heterogeneity may be an important consideration where rock engineering is concerned as it could cause different sections of the same dyke to have different physical properties Geochemical separation of the dykes into different groups was achieved by means of Bowen’s (1984) TiO2 v Zr and Zr/P v P/Ti plots as well as Linton’s (1992) discriminant plot. These same plots were employed in order to classify the dykes according to geochemical data taken from literature for four igneous events, namely, the Ventersdorp Supergroup, Transvaal Supergroup, Bushveld Igneous Complex and Karoo Supergroup, as well as geochemical data for dykes from the East Rand Proprietary Mine. Rare Earth Element patterns from the dykes were compared to literature data for the above-named igneous events in order to obtain a better classification. iv Table of Contents Declaration .................................................................................................................. ii Acknowledgements .................................................................................................... iii Abstract ...................................................................................................................... iv Table of Contents ....................................................................................................... v List of Tables .............................................................................................................. ix List of Figures ............................................................................................................. x Chapter 1: Introduction ............................................................................................... 1 1.1 The Purpose of the Study ................................................................................ 1 1.2 The Study Area ................................................................................................ 1 1.3 Igneous Provinces with Possible Relevance to the Study Area ....................... 3 1.3.1 The Ventersdorp Supergroup .................................................................... 3 1.3.2 The Transvaal Supergroup ........................................................................ 7 1.3.3 Bushveld-Age intrusives ............................................................................ 9 1.3.4 The Pilanesberg Alkaline Province .......................................................... 11 1.3.5 The Karoo Dolerite Suite .......................................................................... 14 1.4 Previous Work ............................................................................................... 15 1.4.1 Dykes in the Witwatersrand Basin ........................................................... 15 1.4.2 The Ventersdorp Supergroup .................................................................. 18 1.4.3 Transvaal Supergroup ............................................................................. 22 Chapter 2: Sampling and Analytical Techniques ...................................................... 24 2.1 Sampling ....................................................................................................... 24 2.2 Sample Preparation and Analytical Techniques ............................................ 24 v Chapter 3: Mineralogy ............................................................................................. 26 3.1 Introduction .................................................................................................... 26 3.2 Petrographic Study ........................................................................................ 26 3.2.1 The Peggy Dyke ...................................................................................... 26 3.2.2 The Georgette Dyke ................................................................................. 30 3.2.3 The Skelm Dyke....................................................................................... 30 3.2.4 The Soll Dyke .......................................................................................... 34 3.2.5 The Kudu Dyke ........................................................................................ 35 3.2.6 The Sill ..................................................................................................... 36 3.2.7 The Jeans Dyke ....................................................................................... 37 3.2.8 The Friday Dyke....................................................................................... 37 3.2.9 The Lib Dyke ............................................................................................ 40 3.2.10 The Little Tumi Dyke ............................................................................ 40 3.2.11 The PE Dyke ....................................................................................... 41 3.2.12 Ventersdorp Lava ................................................................................ 42 3.2.13 The Amigo Dyke .................................................................................. 43 3.2.14 The Bank Dyke .................................................................................... 45 3.2.15 The Speckled Dyke ............................................................................. 46 3.2.16 The Twin Dyke ..................................................................................... 47 3.2.17 The Brazil Dyke ......................................................................................... 47 3.2.18 The CLA Dyke ..................................................................................... 50 3.2.19 The KEN Dyke ........................................................................................... 51 3.2.20 The Swannie Dyke ..................................................................................... 53 vi 3.2.21 The “Unknown” Samples ...................................................................... 53 3.3 Discussion ................................................................................................... 58 3.4 Normative Mineralogy .................................................................................... 59 3.5 Conclusion ..................................................................................................... 62 Chapter 4: Geochemistry I ....................................................................................... 63 4.1. Major and Trace Element Statistics ............................................................... 63 4.1.1 Major Element Oxides .............................................................................. 63 4.1.2 Trace Elements ........................................................................................ 66 4.2 Element Mobility ............................................................................................ 67 4.3 Chemical Variation Between Chill and Central Zones of Dykes .................... 72 4.3 Rock Classification ........................................................................................ 79 4.4 Geotectonic Classification ............................................................................. 82 4.5 Conclusions ................................................................................................... 85 Chapter 5: Geochemistry II ...................................................................................... 88 5.1 Grouping of Dykes According to Their Geochemistry .................................... 88 5.2 Classification According to Literature Data .................................................... 95 5.3 Rare Earth Elements ................................................................................... 103 5.3.1 Discussion of REE Patterns .......................................................................... 104 5.3.2 Classification of dykes according to REE data from literature ................... 106 5.4 Discussion ................................................................................................... 111 5.5 Conclusion ................................................................................................... 115 Chapter 6: The Engineering Aspects of the Dykes ................................................. 116 6.1 Introduction .................................................................................................. 116 vii 6.2 The Dangers Posed by Dykes ..................................................................... 116 6.3 A Case Study ............................................................................................... 117 6.4 Dykes from this Study .................................................................................. 118 6.5 Concluding Remark ..................................................................................... 121 Chapter 7: Conclusions and Recommendations ................................................... 122 7.1 Conclusion ................................................................................................... 122 7.2 Recommendations ....................................................................................... 124 8: References ......................................................................................................... 125 Appendix A: Sampling Localities ............................................................................ 134 Appendix B: Mineralogy ......................................................................................... 137 Appendix C: Chemistry ........................................................................................... 154 Appendix D: Standards .......................................................................................... 175 viii List of Tables Table 3.1 Average CIPW norms for the dykes. Major element data taken from Table C.1. n = number of analyses. .............................................................................................................................. 60 Table 4.1. A summary of the classifications of the dykes according to four plots. ......................... 86 Table 5.1. Grouping of dyke samples according to the three plots and approximate strike derived from the locality maps in Chapter 2. ..................................................................................................... 94 Table 5.2. The importance of the components, including the proportion of variance and cumulative proportion of each component. All values were rounded to three decimals. Values were generated by GCDkit (Janousek et al., 2007). ...................................................................................... 98 Table 5.3. The coefficients of each variable used in principle component analysis, generated by GCDkit (Janousek et al., 2007). ............................................................................................................ 98 Table 6.1. The compressional strength of the three most common lithologies in Tau Tona and Mponeng (supplied by H. Moller, AngloGold Ashanti). ....................................................................... 116 ix List of Figures Figure 1.1. The Witwatersrand Basin with the location of the Carletonville Goldfield. Adapted from McCarthy (2006). .................................................................................................................................... 2 Figure 1.2. Outcrops and the estimated extent of the Ventersdorp Supergroup (adapted from Van der Westhuizen et al., 2006). .................................................................................................................. 4 Figure 1.3. The stratigraphy of the Ventersdorp Supergroup (adapted from Van der Westhuizen et al., 2006). ......................................................................................................................................... 6 Figure 1.4. The Transvaal Basin of the Transvaal Supergroup (adapted from Eriksson et al., 2006). ......................................................................................................................................... 7 Figure 1.5. The Distribution of the Bushy Bend lavas (adapted from Eriksson et al., 1994). ........... 8 Figure 1.6. The Pilanesberg Alkali Province (adapted from Verwoerd, 2006). ............................... 13 Figure 1.7. The location of Karoo basalts and dolerites relevant to the study area (adapted from Duncan and Marsh, 2006). .................................................................................................................... 15 Figure 1.8. A: Ti v Zr, B: Ti/Zr v Ti/P, C: Zr/P v P/Ti plots used by Bowen (1984a) to distinguish between different formations. ................................................................................................................ 19 Figure 1.9. Distinguishing between different formations in the Klipriviersberg Group with Fn2 v Fn1. Discriminant functions from Linton (1992) and data from Bowen (1984a) ................................. 21 Figure 3.1. PEG1. ................................................................................................................................. 26 Figure 3.2. PEG1, showing altered plagioclase, chlorite, epidote and hornblende with an altered rim. Hb=Hornblende, Fsp=Feldspar, Cl=Chlorite, Ep=Epidote. ........................................................... 27 Figure 3.3. PEG1 with chlorite, altered plagioclase and remnants of unaltered biotite. Bi=Biotite. ...... 27 Figure 3.4. PEG2. ................................................................................................................................. 28 Figure 3.5. PEG2 with large amounts of quartz and smaller amounts of chlorite and epidote. The large black areas are holes in the thin section. Qz=Quartz. ................................................................. 28 Figure 3.6. PEG5. ............................................................................................................................ 28 Figure 3.7. PEG5 with large euhedral plagioclase crystals, chlorite and biotite. ............................ 29 Figure 3.8. PEG5 with plagioclase, chlorite and epidote. ................................................................ 29 Figure 3.9. GEOR1. ......................................................................................................................... 30 Figure 3.10. GEOR2 with quartz, altered feldspar and some opaques. ........................................... 30 x Figure 3.11. SKE1. ............................................................................................................................ 30 Figure 3.12. SKE1 showing pyrite (square crystal) and altered sphene (higher relief and not quite as dark in B). Py=Pyrite, Sph=Sphene. ..................................................................................................... 31 Figure 3.13. An epidote vein in SKE1. .............................................................................................. 31 Figure 3.14. Darker veins iron oxide in SKE1. .................................................................................. 32 Figure 3.15. SKE5. ................................................................................................................................ 33 Figure 3.16. SKE5 consisting of intergrown chlorite and epidote. ..................................................... 33 Figure 3.17. The chlorite nodule in SKE5. ......................................................................................... 33 Figure 3.18. SKE3. ............................................................................................................................ 32 Figure 3.19. An epidote vein in SKE3. Albite twinning in the plagioclase crystals is still visible. ...... 32 Figure 3.20. SOL2. ............................................................................................................................ 34 Figure 3.21. Euhedral plagioclase microphenocrysts in a fine matrix. .............................................. 34 Figure 3.22. SOL3. ................................................................................................................................ 34 Figure 3.23. Alteration in SOL3. ........................................................................................................ 35 Figure 3.24. Vein consisting of quartz, chlorite and sulphides. ......................................................... 35 Figure 3.25. KUD1. ............................................................................................................................ 35 Figure 3.26. KUD1 with chlorite nodules and an epidote-quartz vein. .............................................. 36 Figure 3.27. SIL1. .............................................................................................................................. 36 Figure 3.28. Scattered needle-like plagioclase crystals in SIL1. ....................................................... 36 Figure 3.29. JEA1. ............................................................................................................................. 37 Figure 3.30. Epidote, quartz and altered plagioclase in JEA1. Cal=Calcite. ..................................... 37 Figure 3.31. FRI1. .............................................................................................................................. 37 Figure 3.32. Intergrown epidote and chlorite along with quartz in FRI1. ........................................... 38 Figure 3.33. Prehnite in FRI1. Pre=Prenite. ...................................................................................... 38 Figure 3.34. FRI4. .............................................................................................................................. 38 Figure 3.35. Chlorite, epidote, quartz and sphene in FRI4. .............................................................. 39 xi Figure 3.36. FRI7. .............................................................................................................................. 39 Figure 3.37. Intergrown epidote and chlorite, quartz and sphene. .................................................... 39 Figure 3.38. LIB1. .............................................................................................................................. 40 Figure 3.39. LIB1 consists mostly of chlorite. Albite and small amounts of quartz are present along with a large percentage of opaque minerals. ........................................................................................ 40 Figure 3.40. LIT1. .................................................................................................................................. 40 Figure 3.41. Large albite crystals in LIT1. ......................................................................................... 41 Figure 3.42. PE1. ............................................................................................................................... 41 Figure 3.43. Large amounts of quartz and chlorite in PE1. ............................................................... 41 Figure 3.44. LAV1. ............................................................................................................................. 42 Figure 3.45. Fine crystalline Ventersdorp lava with visisble albite and epidote. ............................... 42 Figure 3.46. AMI3. ............................................................................................................................. 43 Figure 3.47. Altered plagioclase, chlorite, iron oxides and opaque minerals in AMI3. A small quartz vein is present. ...................................................................................................................................... 44 Figure 3.48. AMI5. ............................................................................................................................. 44 Figure 3.49. A pyroxene cluster in a matrix of chlorite and opaque minerals in AMI5. Px=Pyroxene. . ....................................................................................................................................... 44 Figure 3.50. BAN1. ............................................................................................................................ 45 Figure 3.51. Saussuritised plagioclase, large opaque crystals, chlorite and remnants of unaltered pyroxene in BAN1. ................................................................................................................................ 45 Figure 3.52. SPE1. ............................................................................................................................ 46 Figure 3.53. Large altered remains of plagioclase in fine matrix in SPE1. ....................................... 46 Figure 3.54. TWI1. ............................................................................................................................. 47 Figure 3.55. TWI1 containing a stringer-like quartz vein and a quartz and sulphide nodule. ........... 47 Figure 3.56. BRA2. ............................................................................................................................ 47 Figure 3.57. The relatively unaltered BRA2 with microphenocrysts of pyroxene in a medium to fine matrix of plagioclase, pyroxene, chlorite and opaque minerals. .................................................... 48 Figure 3.58. BRA3. ............................................................................................................................ 48 xii Figure 3.59. Slightly altered plagioclase and pyroxene in BRA3. ..................................................... 49 Figure 3.60. BRA4. ............................................................................................................................ 49 Figure 3.61. The unaltered BRA4. Large volumes of sulphides are present. ................................. 49 Figure 3.62. CLA3. ............................................................................................................................ 50 Figure 3.63. A large altered sphene crystal in CLA3. Other minerals are chlorite, epidote and quartz. Calcite is found in veins. ......................................................................................................... 50 Figure 3.64. CLA4. ............................................................................................................................ 50 Figure 3.65. Chlorite, quartz, epidote and remnants of unaltered pyroxene in CLA4. ...................... 51 Figure 3.66. A large opaque mineral in along with chlorite, quartz and remnants of pyroxenes in CLA7. ....................................................................................................................................... 51 Figure 3.67. KEN1. ............................................................................................................................ 51 Figure 3.68. Alteration in KEN1. Chlorite and quartz are identifiable optically. .............................. 52 Figure 3.69. KEN2. ............................................................................................................................ 52 Figure 3.70. A chloritised pyroxene cluster in saussuritised plagioclase and opaque minerals in KEN2. ....................................................................................................................................... 52 Figure 3.71. SWA2. ........................................................................................................................... 53 Figure 3.72. Chlorite, quartz, calcite, sphene, epidote and opaque minerals in SWA2 .................... 53 Figure 3.73. UNK1. ............................................................................................................................ 53 Figure 3.74. One of the chlorite nodules rimmed by quartz and stained by iron oxide in UNK1. ..... 54 Figure 3.76. UNK4A. ......................................................................................................................... 54 Figure 3.77. Vein containing chlorite, quartz and opaque minerals in UNK4A. ................................ 55 Figure 3.78. UNK6. ............................................................................................................................ 55 Figure 3.79. Altered remains of plagioclase in a fine matrix of chlorite, along with quartz and calcite in UNK6. ....................................................................................................................................... 55 Figure 3.80. UNK7. ............................................................................................................................ 56 Figure 3.81. Large saussuritised euhedral plagioclase crystals, remnants of biotite, and chlorite. .. 56 Figure 3.82. Large patches of calcite along with plagioclase and remnants of pyroxene. ................ 56 xiii Figure 3.83. 120A2 from Unknown 8. ................................................................................................ 57 Figure 3.84. Altered feldspar, chlorite, epidote and sericite in 120A2. Ser=Sericite. ....................... 57 Figure 3.85. 120B2 from Unknown 9. ................................................................................................ 57 Figure 3.86. Altered feldspar, and chlorite in 120B2. The fracture is filled with chlorite and iron oxides/ hydroxides. ............................................................................................................................... 58 Figure 4.1. Box plots for SiO2 and TiO2, showing small SiO2 ranges in most of the dykes, but large ranges for SiO2 and TiO2 in the Sill. Concentrations in wt%. ............................................................. 64 Figure 4.2. Box plots for Al2O3 and total Fe2O3 showing some variation for both oxides. Concentrations in wt%. ......................................................................................................................... 64 Figure 4.3. Box plots showing little variation in MnO and more variation in MgO. Concentrations in wt%. ....................................................................................................................................... 65 Figure 4.4. Box plots for CaO and P2O5, showing large CaO ranges for all dykes, but small differences in P2O5 concentrations. Concentrations in wt%. ............................................................... 65 Figure 4.5. Box plots showing large variation in Na2O K2O concentrations. Concentrations in wt%. ....................................................................................................................................... 65 Figure 4.6. Box plots showing little variation in Cr contents, but some variation in Ni contents. .... 66 Figure 4.7. Box plots showing large variation in both Rb and Sr concentrations. ........................... 67 Figure 4.8. Box plots showing some variation for both Y and Zr. .................................................... 67 Figure 4.9. Plots used to determine element mobility. All samples were included and separated according to their MgO content. ............................................................................................................ 71 Figure 4.10. SiO2 and Al2O3 mobility plots showing the smaller groups made by samples from the same dykes. ....................................................................................................................................... 72 Figure 4.11. Element concentrations in the chill zones and central zone of the Bank dyke in borehole number DPH 3885, showing enrichment of compatible elements in the chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. ............................................................... 73 Figure 4.12. Element concentrations in the chill zones and central zone of the Bank dyke in borehole number DPH 3880 showing enrichment of Cr and Ni in the chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. .......................................................................... 74 Figure 4.13. Element concentrations in the chill zones and central zone of the Brazil dyke in borehole number DPH 3881, showing Cr enrichment in the chill zones and Ni enrichment in chill zone 1. The unit for the major element oxides is wt% and for Cr and Ni, ppm. .......................................... 74 xiv Figure 4.14. Element concentrations in the chill zones and central zone of the Brazil dyke in borehole number DPH 3884, showing Cr enrichment in chill zone 1 and Ni enrichment in both chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. ................................... 75 Figure 4.15. Element concentrations in the chill zones and central zone of the CLA, showing enrichment of compatible elements in the chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. ......................................................................................................................... 75 Figure 4.16. Element concentrations in the chill zones and central zone of the Friday dyke, showing enrichment in MgO, Cr and Ni. The unit for the major element oxides is wt% and for Cr and Ni, ppm. . ....................................................................................................................................... 76 Figure 4.17. Element concentrations in the chill zones and central zone of the Speckled dyke, showing an enrichment Cr, Ni and Sr in the central zone. The unit for the major element oxides is wt% and for Cr, Ni and Sr, ppm. ........................................................................................................... 76 Figure 4.18. Element concentrations in the chill zones and central zone of the Swannie dyke, showing enrichment of Cr and Ni in the chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. ................................................................................................................................ 77 Figure 4.19. Element concentrations in the chill zones and central zone of the “Unknown 8” dyke, showing enrichment of Cr and Ni in the central zone. The unit for the major element oxides is wt% and for Cr and Ni, ppm. ......................................................................................................................... 77 Figure 4.20. Element concentrations in the chill zones and central zone of the “Unknown 9” dyke, showing Cr and Ni enrichment in the central zone and chill zone 2. The unit for the major element oxides is wt% and for Cr and Ni, ppm. .................................................................................................. 78 Figure 4.21. AFM classification diagram (Irvine and Baragar, 1971), dividing igneous rocks into tholeiitic and calc.alkaline series. The majority of the dyke samples are classified as tholeiitic. ........ 80 Figure 4.22. Jensen cation plot (1976) classifies most samples as high-Fe tholeiite basalts. The Speckled dyke is classified as a komatiitic basalt. ................................................................................ 80 Figure 4.23. Winchester and Floyd’s Zr/TiO2 v Nb/Y diagram (1977) classifies the majority of samples as sub.alkaline basalt to andesite. The Peggy dyke is classified as alkali basalt. ............... 81 Figure 4.24. The R1-R2 diagram by De la Roche et al. (1980) gives a more felsic classification than the other plots. Some samples, including the Speckled dyke, are not plotted due to the absence of alkalis, causing a shift to the right on the x-axis.................................................................................... 82 Figure 4.25. Ti – Zr – Y diagram for tectonic classification (after Pearce and Cann, 1973). LAT=Low K tholeiites, MORB=Ocean floor basalts, WPB=within plate basalts. .................................. 83 xv Figure 4.26. Ti – Zr (after Pearce and Cann, 1973). Acronyms are the same as for the previous figure. ................................................................................................................................... 83 Figure 4.27. Total Fe – MgO – Al2O3 (after Pearce et al., 1977) classifies the majority of the dykes as having a continental origin. .............................................................................................................. 84 Figure 5.1. Dyke samples on a plot of TiO2 (wt%) v Zr (ppm) (after Bowen, 1984a) showing the grouping of dykes. ................................................................................................................................. 89 Figure 5.2. Dyke samples on a plot of Zr/P v P/Ti (after Bowen, 1984a) showing the division of dykes into three groups. ........................................................................................................................ 90 Figure 5.3. The grouping of dyke samples on the discriminant plot developed by Linton (1992). Fn1=0.0172Y-0.06078Zr+20.8084TiO2-11.4636; Fn2=-0.24892Y+0.16017Zr-11.7088TiO2-0.07079. 91 Figure 5.4. Data from various igneous provinces with possible relevance to the study area on, A: TiO2 (wt%) v Zr (ppm); B: Zr/P v P/Ti; C: disciminant plots. A and B is derived from (Bowen, 1984a) and C from Linton, 1992). Fn1=0.0172Y-0.06078Zr+20.8084TiO2-11.4636 and Fn2=- 0.24892Y+0.16017Zr-11.7088TiO2-0.07079......................................................................................... 97 Figure 5.5. The separation of Bushveld (Harmer and Sharpe, 1985 and Davies and Tredoux, 1985) and Loraine-Edenville (Bowen, 1984a) rocks achieved by principle component analysis (Le Maitre, 1968). ....................................................................................................................................... 99 Figure 5.6. The geochemistry of dykes from ERPM compared to literature data fields derived from Fig. 5.4A. 1a: Alberton, Rietgat, Goedgenoeg, Orkney and Alanridge Formations (Ventersdorp Supergroup); 1c: Loraine-Edenville Formation (Ventersdorp Supergroup); 2: Lesotho Formation (Karoo); 3: Lebombo Basalts (Karoo); 4: Hekpoort Lavas (Transvaal Supergroup); 5: Bushy Bend Lavas (Transvaal Supergroup); 6: Bushveld Igneous Complex. ........................................................ 100 Figure 5. 7. The geochemistry of dykes from ERPM (McCarthy et al., 1990) compared to literature data fields derived from Fig. 4.4C. 1: Ventersdorp Supergroup; 2: Bushveld Igneous Complex; 3: Hekpoort Formation; 4: Bushy Bend Lavas; 5: Lesotho Formation Basalts; 6: Lebombo Basalts. .... 101 Figure 5.8. The geochemistry of dykes from the study area compared to all literature data fields on TiO2 (wt%) v Zr (ppm). 1: Ventersdorp Supergroup; 2: Bushveld Igneous Complex; 3: Hekpoort Formation; 4: Bushy Bend Lavas; 5: Lesotho Formation Basalts; 6: Lebombo Basalts. ERPM dyke data (McCarthy et al., 1990): “V-dorp”: Ventersdorp; “Lor-Ed”: Loraine-Edenville: “Bush”: Bushveld Type; “Epi”: Epidiorite; “Ilm-di”: Ilmenite-diabase. .............................................................................. 102 Figure 5.9. The geochemistry of dykes from the study area compared to all literature data fields on Linton’s (1992) discriminant plot. 1: Ventersdorp Supergroup; 2: Bushveld Igneous Complex; 3: Hekpoort Formation; 4: Bushy Bend Lavas; 5: Lesotho Formation Basalts; 6: Lebombo Basalts. ERPM dyke data (McCarthy et al., 1990): “V-dorp”: Ventersdorp; “Lor-Ed”: Loraine-Edenville: “Bush”: Bushveld Type; “Epi”: Epidiorite; “Ilm-di”: Ilmenite-diabase. .............................................................. 103 xvi Figure 5.10. The REE patterns of the dykes. REE data normalised to C1 chondrite after Anders and Grevesse (1989). ......................................................................................................................... 105 Figure 5.11. Fields derived from REE data for the Ventersdorp (Marsh et al., 1992), Bushveld (Maier and Barnes, 1998) and Karoo (Elburg and Goldberg, 2000), mafic rocks. ............................. 106 Figure 5.12. Dyke REE data from this study compared to literature REE data. Karoo (Elburg and Goldberg, 2000), Ventersdorp (Marsh et al., 1992) and Bushveld (Maier and Barnes, 1998). .......... 107 Figure 5. 13. REE patterns of the CLA dyke, SIL1 and UNK6 compared to Busveld REE data (Maier and Barnes, 1998). .................................................................................................................. 108 Figure 5.14. Dykes with similar (likely Ventersdorp) REE patterns compared to data from Marsh et al. (1992). ..................................................................................................................................... 108 Figure 5.15. REE patterns from the Soll dyke compared to the average REEs in low Ti/Zr Karoo basalt (Elburg and Goldberg, 2000). ................................................................................................... 109 Figure 5.16. REE patterns of the, hitherto, unclassified dykes compared to the REE fields of Ventersdorp (Marsh et al., 1992) and Bushveld (Maier and Barnes, 1998) and Karoo rocks (Elburg and Goldberg, 2000). .......................................................................................................................... 110 Figure 5. 17. A comparison of the unclassified dykes with an REE field derived from syenites from the Democratic Republic of Congo (Makutu et al., 2004) and the Palabora Complex, South Africa (Govindaraju, 1994). ........................................................................................................................... 110 Figure 6.1. Comparison of Fe2O3, CaO and Sr concentrations in BRA2, 3 and 4 indicating a depletion in CaO and Sr, and a slight apparent enrichment in Fe2O3 in BRA2 and 3 relative to BRA4. Fe2O3 and CaO concentrations are given in wt% and Sr is given in ppm) ......................................... 119 xvii Chapter 1: Introduction 1.1 The Purpose of the Study The dykes in the Witwatersrand Basin pose numerous problems for the mining industry and are probably the greatest hazard associated with deep level mining. They are largely impermeable and create water compartments that can lead to the flooding of the mine when they are breached. However, the greatest concern is related to mining stability, as the dykes tend to cause seismic events when they are negotiated. These events, termed rock bursts, can cause major damage to mine property and injuries or fatalities to mining personnel, especially when such an event occurs during a shift. Lenhardt (1988) showed that the dykes in the Western Deep Levels mining area (now Tau Tona, Mponeng and Savuka Mines) are responsible for 82% of the high magnitude seismic events in that region. In many instances dykes intrude in a fault zone so that the displacement happens even before the dyke emplacement. These zones can stay active over a long time and can be reactivated. In some instances this requires a new establishment to be made on the other side of the dyke (pers. comm.: H. Moller, 2009). According to Greeff (1988b), a study of the relationship between the composition (geochemistry and mineralogy) of the dykes and their physical aspects, e.g. rock mechanics and porosity, would provide useful information for geologists and rock engineers at the mines. An investigation into the mineralogy of the dykes as well as their joints and veins could therefore be an aid in understanding the behaviour of these rocks. An attempt will be made to correlate the dykes with overlying lavas, where applicable, or with other stratigraphic units. A classification system, according to which individual dykes can be geochemically “finger-printed”, will be investigated, as well as relationships between chemistry, mineralogy and rock mechanics properties. 1.2 The Study Area The West Wits Line is situated on the north-western edge of the Witwatersrand Gold Field (Fig. 1.1), between the West Rand Fault in the east and the Potchefstroom Gap in the west (McCarthy, 2006). The West Wits Line is divided into two sections by the Bank Fault with the western section lying between Carletonville and Fochville (Robb, 2005). This section is sedimentologically distinct from the West Rand Gold 1 Field and is also referred to as the Carletonville Goldfield. Stratigraphically, the Carletonville Goldfield falls in the Central Rand Group (SACS, 2006). Folding that developed during Central Rand times, and before Ventersdorp times, indicates regional compression. However, this compressional regime was replaced by one of tension, resulting in block faulting during Middle Ventersdorp times (McCarthy, 2006). Figure 1.1. The Witwatersrand Basin with the location of the Carletonville Goldfield. Adapted from McCarthy (2006). The entire Carletonville Goldfield was affected by pre-Ventersdorp erosion which was terminated by the outpouring of the lavas of the Ventersdorp Supergroup. The lower-most formation of the Ventersdorp Supergroup, the Venterspost Formation, is also known as the Ventersdorp Contact Reef (VCR), and is a major source of gold on many of the mines (McCarthy, 2006). It occurs in the Klerksdorp and 2 Carletonville Goldfields, the area north of the Loraine goldmine and, possibly, further east and northeast of the Central Rand Group Basin. AngloGold Ashanti’s West Wits operations are situated in the West Wits Line near Carletonville, and encompass the Tau Tona, Mponeng and Savuka mines (see fold- out map in Appendix A). Mponeng (formerly South Shaft or Shaft 1) is the youngest of the three former Western Deep Levels mines with its main shaft being completed in 1986 (www.mining-technology.com). Only two of the seven gold-bearing conglomerates in the lease area are economically viable and only one, the VCR, is currently being mined. The deepest operating stope is just over 3.3 km deep (www.anglogoldashanti.com). Tau Tona mine started operations in 1962 (www.mining-technology.com). Two reef horizons, namely the VCR and the Carbon Leader Reef (CLR), are currently being mined. The vertical separation between the VCR and the CLR varies between 900 m and 1 200 m with the VCR stratigraphically at the top. Mining operations take place at depths ranging from 1.8 km to 3.9 km (www.anglogoldashanti.com). 1.3 Igneous Provinces with Possible Relevance to the Study Area Apart from the Ventersdorp Supergroup, there are four other igneous provinces that could post date the Witwatersrand Supergroup. They are the Transvaal Supergroup, intrusives related to the Bushveld Igneous Complex, intrusives related to the Pilanesberg Alkaline Complex, and Karoo-age intrusives. However, Harris and Watkins (1990) exclude the Transvaal Supergroup from this list. No reason is given for this exclusion. 1.3.1 The Ventersdorp Supergroup After the stabilisation of the Kaapvaal Craton, a series of four basins, namely the Dominion Group, the Witwatersrand and Ventersdorp Supergroups and the Transvaal Basin, developed on it between 3 000 and 2 100 Ma ago. The Ventersdorp Supergroup is the second last of these basins and was preceded by the Witwatersrand Supergroup, which it overlies. The Ventersdorp Supergroup covered most of the area of the older Dominion Group, as well as the Witwatersrand Supergroup, and its elliptical basin occupies an area of approximately 300 000 km2 3 with a northeast axis of 750 km (Fig. 1.2). However, the true extent of the Ventersdorp Supergroup is difficult to determine due to poor exposures, as well as the presence of Transvaal and Karoo Supergroup cover. Borehole information indicates that the extent of the supergroup is much greater than indicated by its surface expression (Winter, 1976). A region around Bothaville, between the Klerksdorp and Welkom Gold fields, has been shown, by deep core drilling, to represent an area where a consistently recognised lithological succession is best developed. This region has been chosen as the type area of the Ventersdorp Supergroup (Winter, 1976). Figure 1.2. Outcrops and the estimated extent of the Ventersdorp Supergroup (adapted from Van der Westhuizen et al., 2006). 4 The Ventersdorp Supergroup (Fig. 1.3) comprises the Klipriviersberg Group at the base, followed by the Platberg Group, the sedimentary Bothaville Formation and the volcanic Allanridge Formation. The Klipriviersberg Group is essentially volcanic and represents a flood basalt sequence covering 100 000 km2 and is, on average, between 1 500 and 2 000 m thick. It is further divided into the Venterspost Formation, Westonaria, Alberton, Orkney, Jeanette, Loraine and Edenville Formations. The Platberg Group is mostly absent from the northeastern part of the Ventersdorp depository and outcrops inconsistently over the rest of the area with varying thickness. The Platberg Group is subdivided into the sedimentary Kameeldoorns Formation, the intermediate to felsic volcanic rocks of the Goedgenoeg Formation, the Makwassie Formation quartz-feldspar porphyry, and the Rietgat Formation. The sedimentary Bothaville Formation has a greater lateral distribution than the Platberg Group. The volcanic Allanridge Formation forms the upper-most unit of the Ventersdorp Supergroup, and extruded over large areas. It covers the underlying rocks in the Northern Cape, Free State, and North West Provinces and outcrops extensively in the vicinity of Vryburg, Mafikeng, Warrenton, Bloemhof, the West Rand, west of Kimberley and along the Orange River close to Hopetown (Van der Westhuizen et al., 2006). Some factors can influence the determination of age by changing the isotopic systems. Metamorphism, where rocks are subjected to high temperatures and the migration of fluids, tends to reset some of the isotopic systems. These factors cause the ages obtained to be younger than the true ages. Greenschist metamorphism affected the Rb-Sr ratios of the Ventersdorp Supergroup in such a way that it gives younger ages than other techniques. Whole-rock Pb-isotope studies yield well-constrained ages, but these probably reflect a metamorphic or hydrothermal event at about 2 370 Ma, which caused alteration of the rocks. The most accurate ages, around 2 700 Ma, are probably those obtained from U-Pb dating of zircons (Van der Westhuizen et al., 2006). Ventersdorp Supergroup Rocks have undergone extensive alteration due to greenschist facies metamorphism. This has been attributed to autohydrothermal processes at low temperatures, which caused the formation of secondary minerals. The original igneous textures have been retained and give an indication of the original mineralogy, although the original minerals have been destroyed. Variations 5 in isotopic ratios can also be attributed to this alteration (Van der Westhuizen et al., 2006). Figure 1.3. The stratigraphy of the Ventersdorp Supergroup (adapted from Van der Westhuizen et al., 2006). 6 1.3.2 The Transvaal Supergroup The late Archaean/early Proterozoic Transvaal Supergroup is preserved in three structural basins, namely the Griqualand West Basin, Transvaal Basin (Fig. 1.4), and the Kanye Basin in Botswana. The Transvaal Basin is the most relevant to the study area and is subdivided into the Chuniespoort and Pretoria Groups. The Chuniespoort Group is purely sedimentary, but four units in the Pretoria Group consist completely or partially of lava. These units are the Bushy Bend Member of the Timeball Hill Formation, the Hekpoort Formation, The Machadodorp Member of the Silverton Formation and parts of the Rayton Formation. Of these the Bushy Bend lavas and Hekpoort Formation volcanics are the most relevant to the study area (Eriksson et al., 2006). Figure 1.4. The Transvaal Basin of the Transvaal Supergroup (adapted from Eriksson et al., 2006). 1.3.2.1 The Bushy Bend Lavas The Busy Bend lavas were identified in 1993 by Eriksson et al. (1994). The lavas are situated approximately 10 km southeast of the town of Stilfontein and about 10 km northwest of the sharp bend in the Vaal River known as Bushy Bend (Fig. 1.5). 7 They have been identified over an area of approximately 30 km by 10 km, but a larger distribution is possible. The lavas are fine-crystalline to amygdaloidal, and it can be assumed that they erupted subaerially. The lava contains small plagioclase phenocrysts and former clinopyroxene in a fine-crystalline matrix consisting of the same material. The lava has undergone epidotisation and sericitisation, with pyroxenes having been altered to amphibole. Brecciated lava and veinlets of calcite and quartz occur throughout the succession, pointing to later hydrothermal activity, with the base of the succession being extensively epidotised. The lavas have a wide range of silica contents equivalent to that of picro-basalt to andesite. The wide range in concentrations of elements such as SiO2, Fe2O3, and alkalis can be at least partly attributed to alteration (Eriksson et al. 1994). Unfortunately very little geochemical data are available for the Bushy Bend lavas. Figure 1.5. The Distribution of the Bushy Bend lavas (adapted from Eriksson et al., 1994). 8 1.3.2.2 The Hekpoort Volcanics The Hekpoort Formation has a thickness of up to 500 m in the Potchefstroom Basin and an average thickness of 300 m in the southern and middle parts of the main Transvaal Basin. Burger and Coertze (1973-1974) determined a Rb-Sr age of 2 224±21 Ma for the Hekpoort lavas. The formation consists of tuffs, pyroclastic material and microporphyritic to amygdaloidal lavas. The lavas consist of altered plagioclase and altered skeletal crystals of pyroxene and secondary minerals such as amphibole, chlorite, clinozoisite, epidote and quartz. Traces of biotite, cummingtonite, muscovite, iron oxides and sulphides are present locally. Secondary quartz veins are also present (Rezcko et al., 1995). Oberholzer (1995) classified the lavas as tholeiitic, although he states that this result is probably due to the removal of alkalis. If the alkalis were present the lavas would probably be classified as calc-alkaline. 1.3.3 Bushveld-Age intrusives 1.3.3.1 The Losberg Complex The Losberg Complex is considered to be coeval with the Rustenburg Layered Suite (Cawthorn et al., 2006) and has a Rb-Sr age of 2 041±41 Ma (Anhaeusser, 2006). The subhorizontal layered mafic intrusive is situated 105 km south of Rustenburg and 70 km west of Johannesburg in the shale and quartzite of the Pretoria Group of the Transvaal Supergroup. The intrusive is approximately 130 m thick and has been divided into three units. The intrusive consists of a zone of harzburgite (18 m thick), consisting of orthopyroxene-olivine cumulate, at the base; a quartz norite zone (10 m thick), consisting of a plagioclase-orthopyroxene-clinopyroxene cumulate; and a quartz gabbro zone (102 m thick), consisting of a plagioclase-clinopyroxene cumulate. The rocks formed immediately below the roof of the complex include chill-phase gabbro and some late-phase augite granophyre (Anhaeusser, 2006). 1.3.3.2 Sills in the Fochville/Losberg and Vredefort Dome Areas Numerous sills intruded below the cumulate rocks of the Bushveld Igneous Complex. It is generally accepted that more than one magma injection was responsible for the development of the Bushveld Complex and each magma injection may have its own 9 suite of associated sills. These sills occur throughout the Transvaal Supergroup surrounding the Bushveld Complex, and some might even have intruded at greater depth into the Witwatersrand Supergroup and the Vredefort Dome area (Cawthorn, et al. 1981), as discussed below. Cawthorn et al. (1981) investigated these sills in the area from Rustenburg to Fochville and identified six different types: metadolerites, hypersthene microgabbros, norites and pyroxenites, contaminated norites, quench-textured micropyroxenites and dolerites. In a hypersthene microgabbro sill close to the Losberg Complex just south of Fochville, hypershenes occur as prismatic blades and is occasionally rimmed by or intergrown with augite. Pleochroic hornblende occurs as a minor phase and was interpreted to be of igneous rather than metamorphic origin. The norite and pyroxenite sills are most common in the immediate vicinity of the Bushveld Complex; one such a sill is found near the northern margin of the granitic basement rocks exposed in the Vredefort Dome. One example of a quench-textured micropyroxenite is found below the Losberg Complex. This sill contains a few crystals of olivine that have been altered to serpentine. The other sill types are not represented in the immediate Fochville/Losberg area. A number of Neoarchaean to Mesoproterozoic mafic and ultramafic intrusives were emplaced in the core and collar rocks of the Vredeford Dome (Anhaeusser, 2006). Many of these are tholeiitic and are regarded to be of Bushveld age (Coetzee et al. 2006). Most of these tholeiitic intrusives are found in the Witwatersrand rocks in the collar of the dome. The intrusives can be subdivided into three types, the Wittekopjes norite, Parsons Rust dolerite-norite and the Reebokkop dolerite on farms with similar names. All three these types show a negative correlation between Mg- numbers and Al2O3, TiO2, CaO, Na2O, P2O5, Zr, and Nb concentrations. This indicates a crystallisation of olivine and orthopyroxene at the expense of clinopyroxene and plagioclase and the concentration of incompatible elements in the melt during fractional crystallisation. The latter is further confirmed by a strong positive correlation between Zr and the concentration of other incompatible elements. The rocks also show a positive correlation between Mg-numbers and Cr concentrations, which is typical for mafic rocks. The Wittekopjes norite has a more primitive composition than the other two intrusives as it has a higher MgO content and Mg-number. The Wittekopjes norite has an interesting feature in that the 10 amount of silica decreases with a decrease in MgO and Cr concentration upwards in the sill. This phenomenon can possibly be ascribed to the crystallisation of large amounts of enstatite that depleted the magma of silica and is similar to that observed in the lowermost unit of the Bushveld Complex. The three intrusives show parallel REE patterns with an increase in REE concentrations with decreasing Mg-number. The intrusives are slightly enriched in LREE with HREE having an approximately chondritic abundance (Coetzee et al., 2006). This pattern has been described as tholeiitic by Barker (1983). The intrusives were compared with high-Mg noritic layered intrusives and dyke swarms prominent during the late Archaean and early Proterozoic. When comparison of major elements was done, the composition of the Wittekopjes norite is in-between that of the ultramafic and micropyroxenite sills of the Bushveld Complex. The Parsons Rust dolerite-norite and Reebokkop dolerite overlaps with the Bushveld’s micropyroxenite sill and norite intrusives in the Witwatersrand Basin. When trace elements are compared, Ti/Zr ratios are similar to that of Bushveld sills, which is lower than that of modern tholeiitic rocks. REE patterns of the tholeiites do not show the same degree of LREE enrichment as the Bushveld micropyroxenite and ultramafic sills. It is possible that this flatter pattern was caused by the crystallisation of orthopyroxene from melts with highly fractionated REE patterns (Coetzee et al., 2006). Another reason could be that not all siliceous high-Mg basalts show a high degree of LREE enrichment (Sun et al., 1989). A good correlation was also observed between the tholeiitic group and the ultramafic Bushveld sills, except for lower P2O5 and TiO2 contents in the Bushveld sills (Coetzee et al., 2006). 1.3.4 The Pilanesberg Alkaline Province Between 1 450 and 1 200 Ma ago widespread alkaline volcanic and plutonic activity took place during a period of relative tectonic stability on the Kaapvaal Craton. This event gave rise to the Pilanesberg Alkaline Province that consists of predominantly silica-undersaturated rocks, and probably ended with the eruption of the Premier group of kimberlite pipes. Alkali igneous complexes are roughly circular bodies in plan, only a few kilometres in diameter, and ideally consist of concentric rings or arcs of rocks such as nepheline syenite (foyaite), carbonatite, pyroxenite, ijolite and 11 syenite (Verwoerd, 2006). Alkali rocks contain Na and/or K in excess amounts necessary to form ordinary feldspar and pyroxene, due to a deficiency of silica. Peralkaline rocks contain alkalis in excess of alumina and are distinguished by non- aluminous alkaline minerals like aegirine and arfvedsonite. Carbonatite is the most silica deficient of the alkaline rocks and often intrudes at a late stage in the history of the complex. Carbonatites can also erupt from closely related fissures and diatremes. Many alkaline complexes contain volcanic and plutonic components. They represent either conduits or, in the case of layered bodies, relatively shallow magma chambers. The Pilanesberg in the North West Province is one of the largest and best-known alkaline ring complexes in the world. Smaller occurrences, dykes, necks, plugs, maars and volcanic complexes form part of the same petrogenetic province. Some of these smaller occurrences include dyke swarms, the Pienaars River Subprovince, the Goudini Complex, The Spitskop Complex, the Mogashoa Suite, the Glenover Complex, and the Stukpan Complex (Fig. 1.6) (Verwoerd, 2006). Of these, the dyke swarms and the Stukpan Complex are probably most relevant to the study. The Pilanesberg Dyke Swarm is a set of northwest-trending dykes that cut through the northeastern half of the Pilanesberg Complex and extends over a distance of at least 350 km from Botswana to the Vaal River and fans out from a width of 40 km on the Botswana border to about 120 km south of Johannesburg. The dykes are considered to be part of the Pilanesberg Province on the basis of petrology and age. Many of these dykes are composite, with marginal zones of fine-grained dolerite intruded while still hot by slightly younger syenite and nepheline syenite in the centre. The dykes have been traced magnetometrically in more detail north of the Pilanesberg than further south. Some of these dykes, like the Maanhaarrand near Magaliesburg, form prominent outcrops. Some other dykes that have been named are the Robinson, Venterspost and Gemspost dykes in the Witwatersrand gold mines, and the Pretoria dyke that runs through the Fountains valley and Wonderboompoort (Verwoerd, 2006). 12 Figure 1.6. The Pilanesberg Alkali Province (adapted from Verwoerd, 2006). The Stukpan Complex is situated in the Free State Goldfield 20 km east of Bothaville and about 180 km southwest of Johannesburg. It is overlain by Karoo strata and a dolerite sill approximately 200 m thick. The complex was discovered in 1982 when a prominent magnetic and gravity anomaly was tested by drilling. Geophysical modelling indicates that it could be the largest carbonatite occurrence in South Africa. The pipe penetrates Witwatersrand and Ventersdorp Supergroup rocks and has been dated at ~1 354 Ma. The only available samples are from drill core. These include Na-amphibole-rich calcite carbonatite, minor dolomite carbonatite and fenitised Ventersdorp lava and tuff. The carbonatite has a high Sr content but is extraordinarily poor in Ba, Nb, Zr, Y and REE (Verwoerd, 2006). 13 1.3.5 The Karoo Dolerite Suite The Karoo Igneous Province is one of the world’s classic continental flood basalt provinces. 40Ar/39Ar dating confirmed that the Karoo igneous event was short-lived, approximately 1 – 3 Ma, and indicates an age of 183±2 Ma for the Lebombo Group. The low-Ti basalts of the Central Area are slightly younger than the low-Ti basalts of the Lebombo Group (Fig. 1.7) (Duncan and Marsh, 2006). The Karoo Dolerite Suite represents the feeder system to the flood basalt eruptions. It is best developed in the main Karoo Basin and occurs as a network of dykes, sills and saucer-shaped sheets. The sills range from a few metres to 200 m or more in thickness. The dykes are generally 2 – 10 m wide and 5 – 30 km long. The sheets and sills show some differentiation caused by processes such as flow differentiation and gravity settling, but the dykes are compositionally homogeneous and their geochemistry correlates well with that of the overlying lavas. Most of the dykes do not show strong systematic orientation, but there are two well developed linear dyke swarms, namely the Rooi Rand dyke swarm trending north-south in the southern Lebombo, and the Okavango dyke swarm trending east-southeast across northeastern Botswana (Duncan and Marsh, 2006). Similar to other continental flood basalt provinces, the Karoo basalts are relatively siliceous, with SiO2 contents in excess of 52%, and evolved in terms of their Mg- number. Basalts in equilibrium with normal mantle olivine would be expected to have a Mg number of ~70, whereas the Karoo mafic rocks have typical Mg-numbers of 50 – 60. This possibly indicates that the flood basalts were derived by fractionation from mantle-derived picritic precursors (Duncan and Marsh, 2006). The vast majority of Karoo basaltic rocks can be classified as tholeiitic based on petrographic as well as geochemical characteristics. An important geochemical feature of the Karoo Igneous Province is the compositional provinciality amongst the basalt. The Karoo basalts and picrites in Zimbabwe can be distinguished from those in Lesotho and Swaziland (southern Lebombo mountains) by their K, Ti, P, Ba, Sr and Zr, with the former having unusually high concentrations of these elements compared to other tholeiites. 14 Figure 1.7. The location of Karoo basalts and dolerites relevant to the study area (adapted from Duncan and Marsh, 2006). This observation gave rise to the concept of a northern high-Ti-Zr province and a southern low-Ti-Zr province. It is now recognised that these high-Ti basalts are not only confined to the northern part of the igneous province, but are also associated with the rift-related conditions of the Lebombo, Mwenezi-Save, Tuli, and Hwange- Victoria Falls areas. The Botswana dyke swarm also predominantly falls in this group. The Lesotho formation falls in the low-Ti-Zr group (Duncan and Marsh, 2006). 1.4 Previous Work 1.4.1 Dykes in the Witwatersrand Basin McCarthy et al. (1990) used petrographic and geochemical techniques in order to identify feeder dykes to the Klipriviersberg Group volcanics on East Rand Proprietary Mines Ltd (ERPM), and to subdivide the dykes further into feeders of the different 15 Formations in this group. The orientation of the different feeder dykes were then used to determine changes in stress states along the northern margin of the Witwatersrand Basin, especially during Klipriviersberg times. In a detailed study of the intrusives on ERPM mine by Jeffery (1975) (in McCarthy et al., 1990) and Fumerton (1975) (in McCarthy et al., 1990), five major dyke events were recognised. These five events were confirmed by McCarthy et al. (1990) and are represented by the following rock types: (1) Norite, occuring mainly on the western portions of the mine as shallow-dipping dykes and sills, consists of orthopyroxene, lesser clinopyroxene and plagioclase, and is considered, by the authors, to be of Bushveld age, similar to the sills described by Cawthorn et al. (1981). (2) Ilmenite diabase, consisting of pyroxene and plagioclase that are variably altered to tremolite, chlorite and saussurite, with skeletal boxworks of ilmenite that has been altered to leucoxene. These rocks are considered to be pre-Transvaal in age, but Jeffery (1975) suggested that they could be of Bushveld age. (3) Epidiorite, consisting almost entirely of actinolite in a ground mass of chlorite, calcite and minor opaque minerals. Cawthorn et al. (1981) considered them to be equivalents of the pre-Bushveld metadolerites that occur as sills in the Transvaal Supergroup. (4) Aplitic dykes that, according to Jeffery (1975) (in McCarthy et al., 1990), post- date Ventersdorp diabases. (5) Ventersdorp diabases that are distinguished from all other intrusives by their greater degree of alteration, and are typically dark green to grey in colour, with some containing large feldspar phenocrysts. They consist almost entirely of extremely altered plagioclase and augite that is largely altered to amphibole, chlorite and serpentine. Sphene, apatite, secondary quartz, ilmenite and magnetite occur as secondary minerals. McCarthy et al. (1990) found that the Alberton and Orkney Formation dykes have a strike direction of around 30°. The Jeanette and Loraine dykes show a more complex distribution and have strikes varying between 105° and 165°, as well as the 30° orientation. The ilmenite diabase dykes are commonly oriented in the 135°-160° 16 direction, but some exhibit the 30° strike. The epidiorite dykes show a 120° strike, parallel to some of the ilmenite diabase and Ventersdorp dykes. The epidiorite dykes are, however, not widely distributed. In order to correlate Klipriviersberg Group dykes with their respective Formations, the authors (McCarthy et al., 1990) found discriminant anlysis using TiO2, Zr, and Y to be the most useful. This is the same plot used by Linton (1992) which is discussed below. Meier et al. (2009) studied the dykes in the Klerksdorp Goldfield, specifically in Kopanang Mine, in order to assess the possibility of metamorphic-hydrothermal ore formation in the Witwatersrand Basin. Their study included structural, mineralogical and geochemical investigations. The Vaal Reef, which is the main reef mined in Kopanang, is displaced by numerous dykes and faults. Sharp, unsheared dyke contacts indicate that magma emplacement occurred during or after reef displacement, and that magma intruded into active or pre-existing faults. Sigmoidal veins, containing chlorite and quartz in some dyke contacts, show that these contacts were subjected to partly ductile deformation during metamorphism. This confirms a premetamorphic emplacement of the dykes. This is similar to the conclusions drawn by Harris and Watkins (1990), who compared intrusives from Welkom, Klerksdorp, Evander and Carletonville mines, and compared them to a known Ventersdorp intrusive, the Conera Sill. All the dykes in their study were of the same metamorphic facies as the Conera Sill, and were therefore assumed to be of the same age. The authors subsequently assumed that metamorphism and alteration affected the intrusives and country rock as a single package. The mineralogical investigations of the two studies yielded approximately the same results, but Meier et al. (2009) noted that some samples were almost completely replaced by carbonates. This indicates that significant amounts of CO2 were present in the hydrothermal fluid responsible for the alteration of the rocks. Meier et al. (2009) compared the chemistry of dykes with that of overlying lava flows from the Klipriviersberg Group. By comparing immobile elements, including REEs, they showed that the dykes believed to be of Ventersdorp age are on a single fractionation trend which overlaps the Jeanette and Loraine-Edenville Formations of the Klipriviersberg Group. Younger dykes from elsewhere in the Witwatersrand Basin, such as the ilmenite diabase and epidiorite dykes, as well as Bushveld aged 17 intrusives, showed distinct geochemical differences from Klipriviersberg dykes and lavas. 1.4.2 The Ventersdorp Supergroup Bowen (1984a) classified the volcanic rocks of the Witwatersrand Triad (i.e. the Dominion Group, Witwatersrand Supergroup and Ventersdorp Supergroup) as primarily subalkaline tholeiitic rocks. She distinguished geochemically between the Klipriviersberg Group, the Platberg Group and the Pniel sequence, as well as their smaller subdivisions. Three chemically distinct units were identified in the Klipriviersberg Group, namely the Alberton Formation, Orkney Formation, and the Loraine and Edenville Formations together. In the Platberg Group, the Goedgenoeg Formation, at the base of the group, and the Rietgat Formation, at the top, are chemically similar, but are separated by the chemically distinct Makwassie Formation. Due to the subjection of the rocks to low grade greenschist metamorphism, some elements, namely Na, K, Mn, Ba and Rb, cannot be used to make any petrogenetic deductions as they are too mobile in metamorphic processes. Ti, P, Nd, Zr, Y and the light REEs were found to have been little affected by these processes (Bowen, 1984a) and are therefore much more useful. Bowen (1984a) used several techniques to distinguish between the different rock units. The simplest of these was orthogonal discrimination which assesses the range of each major and trace element, as well as that for each interelement ratio for every geochemical unit. The element ranges of each formation are then compared with those of every other formation. If the ranges of an element from two different units do not overlap it means that this element could possibly be used to discriminate between the two units. The significance of the difference in ranges is determined by calculating the so-called “orthogonal discriminator” (OD). The OD is obtained by dividing the difference between the minimum value of the highest range and the maximum value of the lowest range (i.e. the separation between the ranges) by the minimum value of the highest range. A value between 0 and 1 is obtained. A value of 0 indicates that the ranges are immediately adjacent to one another. The greater the separation between ranges, the closer the OD will be to 1, with a value of 1 only being reached if a particular element is absent from one of the formations. 18 Figure 1.8. A: Ti v Zr, B: Ti/Zr v Ti/P, C: Zr/P v P/Ti plots used by Bowen (1984a) to distinguish between different formations. A more detailed explanation of orthogonal discrimination can be found in Bowen (1984a). This method was successful in distinguishing all stratigraphic units geochemically from one another, except the Dominion Group basalts from those of the Allanridge, Loraine-Edenville, Orkney and Loraine Formations. The use of three discrimination plots, Ti/Zr vs Ti/P, Zr/P vs P/Ti and TiO2 vs Zr, (Figure 1.8 A, B, and C) could separate all the units from one another. The third technique was discriminant analysis. This method could assess the success of the parameters defining the groups and could classify unknown samples (Bowen, 1984a). The conclusions of Bowen (1984b), who investigated the petrogenesis of these same rocks, are summarized below: 19 The Loraine-Edenville rocks are the most primitive of the Klipriviersberg Group succession and are classified as magnesian tholeiites to tholeiitic andesites. The lavas probably evolved from the fractional crystallisation of Mg-rich orthopyroxene, possibly accompanied by a small amount of chromite. This was followed by the crystallisation of an augite dominated extract from the residual liquid. The Alberton and Orkney Formations are more evolved than the Loraine-Edenville Formation, with the Orkney Formation being intermediate between the other two. The three groups are probably consanguineous, but they do not form a continuous differentiation sequence. Enrichment in siderophile elements in the Orkney Formation requires that the Alberton and Orkney Formations’ fractionation paths diverged after reaching evolved Loraine-Edenville compositions. This enrichment could be due to variable roles of oxides or minerals such as plagioclase, which tend to exclude siderophile elements, in the late stages of differentiation. These two groups either formed independently from a common parent, or by varying degrees of partial melting of the same source which was progressively more depleted in incompatible elements. Concerning the Platberg Group, Bowen (1984b) suggested that the Makwassie Formation was derived from a crustal melt, and that the chemically indistinguishable Goedgenoeg and Rietgat Formations formed due to a mixing of this crustal melt with an unrepresented basic magma. The Allanridge Formation lavas seem to have evolved independently from both the Platberg and Klipriviersberg Groups. The idea that the Allanridge lavas represent a separate magmatic episode is supported by the fact that it is separated from both the other two formations by the mature, flat-lying sediments of the Bothaville Formation. The Allanridge lavas are also more evolved than both the Platberg and Klipriviersberg Groups, although it is possible that the lavas were derived by the fractional crystallisation of Klipriviersberg type magma. However, Bowen (1984b) considered source heterogeneity with the Allanridge lavas evolving along a similar path, although independently, to be a more feasible explanation. Linton (1992) compared Klipriviersberg Group samples with mid-ocean ridge basalts, continental arc basalts, island arc basalts, Archaean basalts, ocean island basalts, continental rift basalts, and continental flood basalts. The lavas proved to be chemically similar to Archean basalts. TiO2, Al2O3, Fe2O3+FeO2, MnO, P2O5 and Y are similar in content. Cr displays similar values and depletion in Archaean Basalt 20 and Ni displays similar values and enrichment in Archaean Basalt. The Klipriviersberg lavas also display affinities to MORB, CRB, and CFB. Linton (1992) also managed to distinguish between the different units of the Klipriviersberg Group by means of discriminant function analysis (D.F.A), using the incompatible elements TiO2, Y, and Zr. In Fig. 1.9 some of Bowen’s data (1984a) was plotted using Linton’s D.F.A. functions (Fn1= 0.01720*Y-0.06078*Zr+20.8084*TiO2.11.4636 Fn2= 0.24892*Y+0.16017*Zr-11.7088*TiO2-0.07079). All samples plotted correctly except for one Rietgat Formation sample that was misclassified as a Makwassie Formation sample. Allanridge Fn1 Figure 1.9. Distinguishing between different formations in the Klipriviersberg Group with Fn2 v Fn1. Discriminant functions from Linton (1992) and data from Bowen (1984a) Winter (1995) investigated the stratigraphy and geochemistry of the Alberton Formation. The Alberton Formation overlies the Venterspost Formation. The lava is aphanitic and severely altered, more so than the other Klipriviersberg lavas, with none of the original minerals or textures being preserved, and has a grey-green colour. The Edenville Formation lavas are similarly altered. Both the Alberton and Edenville Formations are in direct contact with sedimentary formations, namely Venterspost Formation sediments and the Kameeldoorns Formation respectively. Winter (1995) states this as the reason why these two lava formations are the most altered. The mineral assemblage, epidote, chlorite, albite, and sulphides, is characteristic of propylitic alteration, with some areas showing excessive silicification 21 Fn2 (lighter areas) or chloritisation and epidotisation (darker areas). The original composition of Alberton Formation feldspars has been destroyed and their current composition is Ab95 – Ab97, indicating that the rocks have undergone sodium metasomatism (Winter, 1995). Ca-plagioclase has been completely altered to Na- plagioclase, epidote-bearing assemblages and chlorite. Pyroxene has been altered to chlorite and actinolite, consistent with greenschist facies metamorphism. The presence of actinolite and carbonates and the absence of prehnite and pumpellyite suggest the metamorphic fluids responsible for the alteration had a high CO2 content (Winter, 1995). Winter (1995) proposed that, in most cases, the chemical state of the lavas still reflects original magmatic compositions, except in the lower Alberton, which has been subjected to more intense hydrothermal alteration. Using various techniques, Winter (1995) determined that Zr, Y, Nb, V, Ni, Cr, Co, Zn, Al2O3, TiO2, Fe2O3 and MgO were least to moderately mobile during alteration. Winter (1995) classified the rocks of the Alberton and lower Orkney Formations as tholeiitic basaltic-andesites with a calc-alkaline affinity. However, some trends between elements, such as Ti and Zr, are not consistent with a strictly calc-alkaline provenance. Winter (1995) also determined that the lavas were erupted in a within- plate tectonic environment. 1.4.3 Transvaal Supergroup 1.4.3.1 Hekpoort Volcanics Oberholzer (1995) classified the Hekpoort lavas using mainly Ti, Zr, Nb, Y and REEs by means of the classification systems of Winchester and Floyd (1977) and Jensen (1976). According to the Winchester and Floyd system the lavas were classified as andesitic, while the Jensen system classified them as calc-alkaline. However, the Irvine and Baragar (1971) AFM diagram classifies the lavas as tholeiitic. Oberholzer (1995) also compared the geochemistry of the Hekpoort Formation with that of other similar deposits. These include the Ventersdorp mafic volcanics. The Hekpoort lavas were found to have a higher SiO2 and MgO content than the Ventersdorp lavas, with the exception of the Loraine-Edenville Formation that has a higher MgO content. However, the most notable difference lies in the much lower alkali content of the Hekpoort lavas. The low alkali content of the Hekpoort lavas can be attributed 22 to the high degree of alteration to which the rocks were submitted. Only the Loraine-Edenville Formation has higher Cr and Ni contents than the Hekpoort lavas. Data from some of the studies discussed will be used in subsequent chapters in order to find a geochemical classification system for the dykes in the Carletonville Goldfields. 23 Chapter 2: Sampling and Analytical Techniques 2.1 Sampling A total of 94 samples were obtained from Tau Tona and Mponeng. 85 samples were taken from the core yards of Tau Tona and Mponeng and the remaining five were taken underground on 104 level in Tau Tona (Appendix A). Where possible, the chill zones and central zones of dykes were sampled. In some cases chill zones were visibly contaminated with country rock. These were not sampled. Care was also taken to take samples with minimal veining. It is important to note that the nature of the study area imposes limits on sampling methods as well as the number of samples that could be taken. As it is only possible to sample very few dykes underground, most of the sampling relies on the availability of dykes in drill core. For this reason some dykes will be represented by more samples than others, and in some cases only one sample per dyke was available. Mine plans and locality maps were obtained from the geology offices at the respective mines (Fold-out maps in Appendix A). 2.2 Sample Preparation and Analytical Techniques Thin sections for petrographic study were made from 45 samples. Powder X-ray diffraction was excecuted on 31 samples on a Siemens D5000 XRD (Appendix B). XRD films were used in cases where single mineral identification was required. These were made on a Phillips PW1051 X-ray diffractometer using a Debye- Scherrer camera. Samples were crushed in a jaw crusher and pulverised in a carbon steel mill. The powdered samples were then used in geochemical analyses as well as for mineralogical investigation. For major element analysis, fusion discs were made according to the method developed by Norrish and Hutton (1969). According to this method approximately 3 g of sample is dried overnight at 100°C in a porcelain crucible, after which the sample is weighed, ignited at 1 000°C and weighed again. 0.28 g of this sample is then mixed with 0.02 g of NaNO3 and 1.5 g of Spectroflux (Li2B4O7 = 47%, Li2CO3 = 36.7%, La2O3 = 16.3%). The mixture is then melted in platinum crucibles at 950°C and formed into a fusion disc. Analyses for trace elements and sodium were executed on pressed powder briquettes that were made 24 by compressing a mixture of 8 g of powdered sample and 3 g of Hoechst Wax Micro powder at 20 tons. Major and trace element geochemistry was affected by means of X-ray fluorescence spectrometry (XRF) on a Panalytical Axios X-ray spectrometer using SuperQ software. The standards used for calibration include certified reference materials as well as in-house standards. Rare Earth Element analysis was carried out by means of ICP-MS at the Department of Geology at the University of Cape Town. For REE analysis 50 mg of pulverised samples were digested in Teflon beakers using 4 ml of a concentrated 4:1 HF/HNO3 solution at 50-60°C for at least 24 hours. After digestion the samples were dried in the beakers at ±75°C. Once dry, 2 ml HNO3 was pipetted into the beakers and once again left to dry. The last step was then repeated. 4 ml of the internal standard solution (ISS) was added to each sample and the samples were treated by ultra sound for 1 hour. The ISS consists of 10ppb In, Re, Rh and Bi in 5% HNO3. Each sample was diluted to 50 ml with ISS and weighed. 1 ml of this solution was weighed, diluted further to 10 ml and weighed again, ultimately reaching a 10 000 times dilution. The whole procedure was also followed with the external standard (BHVO2) as well as a total procedural blank (tpb) to which no sample was added. All results are included in Appendix C. A list of the standards is included in Appendix D. 25 Chapter 3: Mineralogy 3.1 Introduction A mineralogical investigation of some of the dykes in Tau Tona was conducted by Greeff (1988a) as part of an investigation of the dykes after seismic events originating at the Peggy Dyke. He examined a large number of thin sections of different dykes, including the Bank, Speckled, Twin, Peggy and CLA dykes as well as Ventersdorp lava samples. In this study, at least one thin section per dyke was made and X-ray powder diffraction was carried out, mostly on the same samples from which thin sections were made. The XRD patterns are included in Appendix B. The thin sections themselves were electronically scanned and are included, as it often provides a better idea of features such as the rock textures and veining. Thin sections have dimensions of 44 mm x 25 mm, but some of the images have been cropped in the length. Where applicable, results from this study are compared to those from Greeff (1988a). For each set of photomicrographs, A was taken in plane polarized light, and B with crossed nicols. The modal compositions were estimated using XRD peak sizes in conjunction with thin section observations (Appendix B), as point counting is problematic due to the intergrown nature of minerals. Minerals were labelled where possible and abbreviations are given in the captions. 3.2 Petrographic Study 3.2.1 The Peggy Dyke Figure 3.1. PEG1. 26 A B Ep Cl Hb Fsp 1000µm 1000µm Figure 3.2. PEG1, showing altered plagioclase, chlorite, epidote and hornblende with an altered rim. Hb=Hornblende, Fsp=Feldspar, Cl=Chlorite, Ep=Epidote. A B Bi Cl 1000µm 1000µm Figure 3.3. PEG1 with chlorite, altered plagioclase and remnants of unaltered biotite. Bi=Biotite. PEG1 (Fig. 3.1) is a medium to coarse crystalline rock. It contains chlorite, epidote, remnants of biotite that are in the process of being chloritised, saussuritised feldspar which was identified as albite by means of XRD, sphene, some actinolite and a few crystals of brown hornblende (Fig. 3.2 and 3.3). The large hornblende crystal at bottom centre of Fig. 3.2 is in the process of being chloritised at the rim. This particular sample is cut by a vein of approximately 2 – 3 mm wide. The vein consists of chlorite, small quartz crystals and larger patches of calcite. 27 Figure 3.4. PEG2. A B Qz 500µm 500µm Figure 3.5. PEG2 with large amounts of quartz and smaller amounts of chlorite and epidote. The large black areas are holes in the thin section. Qz=Quartz. PEG2 (Fig. 3.4) is more coarse crystalline than PEG1 and contains less dark minerals. The sample contains far more quartz, which in PEG1 was restricted to veins. PEG2 contains remnants of biotite being chloritised, as well as epidote and some iron oxide staining (Fig. 3.5), albite, and illite-montmorillonite. Figure 3.6. PEG5. 28 A B 1000µm 1000µm Figure 3.7. PEG5 with large euhedral plagioclase crystals, chlorite and biotite. PEG5 (Fig. 3.6) is medium to coarse crystalline. Euhedral, saussuritised plagioclase is present, along with chlorite, biotite, hornblende and epidote (Figs. 3.7 and 3.8). Albite twinning is still visible in the plagioclase crystals, but these are too altered to identify specifically by optical means. XRD analysis indicated albite. A B 1000µm 1000µm Figure 3.8. PEG5 with plagioclase, chlorite and epidote. Greeff (1988a) included two Peggy dyke samples in his petrographic study of the dykes. He makes no mention of epidote, biotite, sphene or amphiboles. He does, however, mention rutile in one sample, which was not found in any of the samples in this study. He also makes no mention of albite, or any other plagioclase. One of Greeff’s samples contains large patches of calcite, whereas all calcite in the Peggy dyke samples from this study is located in veins. It is clear from both studies, as 29 well as from a comparison of the two, that the Peggy dyke is mineralogically rather heterogeneous, with all the samples being medium to coarse crystalline. 3.2.2 The Georgette Dyke Figure 3.9. GEOR1. GEOR1 (Fig. 3.9) contains microphenocrysts of feldspar that have been almost completely altered to chlorite. The sample also contains quartz, epidote, actinolite and altered sphene (Fig. 3.10). A B Fsp Qz Fsp 1000µm 1000µm Figure 3.10. GEOR2 with quartz, altered feldspar and some opaques. 3.2.3 The Skelm Dyke Figure 3.11. SKE1. 30 The Skelm dyke (Fig. 3.11) is medium crystalline and consists of epidote, chlorite, actinolite, altered albite and illite-montmorillonite, and quartz both in small veins and in the rock itself. Altered sphene and pyrite are present and the difference can be seen in Fig. 3.12. The rock is fractured in places with the bulk of the epidote being situated in the fractures (Fig. 3.13). Some of the fractures contain iron oxides and opaque minerals (Fig. 3.14). A B Sph Py 1000µm 1000µm Figure 3.12. SKE1 showing pyrite (square crystal) and altered sphene (higher relief and not quite as dark in B). Py=Pyrite, Sph=Sphene. A B Fsp Qz Ep Cl 1000µ 1000µm Figure 3.13. An epidote vein in SKE1. 31 A B 1000µm 1000µm Figure 3.14. Darker veins iron oxide in SKE1. Figure 3.15. SKE3. SKE3 (Fig. 3.18) is very similar to SKE1 in that both are fine to medium crystalline and both contain epidote-filled veins. In SKE3 (Fig. 3.19) some quartz is also present in the veins, but epidote remains volumetrically dominant. Chlorite, epidote and sphene are present along with altered plagioclase, of which the twinning is still visible. A B 1000µm 1000µm Figure 3.16. An epidote vein in SKE3. Albite twinning in the plagioclase crystals is still visible. 32 Figure 3.17. SKE5. SKE5 is medium to fine crystalline (Fig. 3.15). It contains altered plagioclase, intergrown chlorite and epidote, quartz, some iron oxide staining and opaque minerals (Fig. 3.16). Nodules consisting entirely of chlorite are also present. These chlorite nodules are suspected to be altered pyroxene phenocrysts (Fig. 3.17). A B Cl Ep Fsp 1000µm 1000µm Figure 3.18. SKE5 consisting of intergrown chlorite and epidote. A B 1000µm 1000µm Figure 3.19. The chlorite nodule in SKE5. 33 3.2.4 The Soll Dyke Figure 3.20. SOL2. A B Fsp Fsp 1000µm 1000µm Figure 3.21. Euhedral plagioclase microphenocrysts in a fine matrix. SOL2 (Fig. 3.20) is fine crystalline and contains euhedral microphenocrysts as well as finer crystals of plagioclase. Both types have been altered almost completely, and albite twinning is no longer visible (Fig. 3.21). The matrix is fine crystalline and consists mostly of chlorite. Small quartz crystals are also present together with opaque minerals. Figure 3.22. SOL3. 34 A B 1000µm 1000µm Figure 3.23. Alteration in SOL3. SOL3 (Fig. 3.22) is altered and consists mostly of chlorite and quartz with small amounts of epidote being present together with opaque minerals (Fig. 3.23). The veins consist of quartz, chlorite and sulphides (Fig. 3.24). Sulphides are mostly confined to the veins. A B Qz 1000µm 1000µm Figure 3.24. Vein consisting of quartz, chlorite and sulphides. 3.2.5 The Kudu Dyke Figure 3.25. KUD1. 35 KUD1 (Fig. 3.25) is fine crystalline and consists of albite, chlorite, epidote and quartz with microphenocrysts that have been altered to chlorite and smaller amounts of epidote (Fig. 3.26). Few small crystals of opaque minerals are present. Veins are filled with either epidote and quartz or calcite and quartz, the latter being the younger. A B Ep Cl Qz 1000µm 1000µm Figure 3.26. KUD1 with chlorite nodules and an epidote-quartz vein. 3.2.6 The Sill Figure 3.27. SIL1. A B Fsp 500µm 500µm Figure 3.28. Scattered needle-like plagioclase crystals in SIL1. 36 SIL1 (Fig. 3.27) is fine crystalline and consists of scattered needle-like altered plagioclase crystals in a matrix of chlorite and opaque minerals (Fig. 3.28). The vein consists of calcite. 3.2.7 The Jeans Dyke Figure 3.29. JEA1. JEA1 (Fig. 3.29) contains chlorite as the dominant mineral. The chlorite is dark green in places, indicating a high iron content (Nesse, 2004). Epidote is also present along with sphene, quartz and some opaque minerals (Fig. 3.30). Large calcite crystals are also present. Veins are filled with chlorite. One extremely altered nodule, consisting of clay minerals with sulphide minerals on its rim is present. A B Qz Cl Ep Cal 500µm 500µm Figure 3.30. Epidote, quartz and altered plagioclase in JEA1. Cal=Calcite. 3.2.8 The Friday Dyke Figure 3.31. FRI1. 37 FRI1 (Fig. 3.31) consists of intergrown chlorite and epidote as well as quartz, sphene, and prehnite (Figs. 3.32 and 3.33). A B Qz Cl Ep 500µm 500µm Figure 3.32. Intergrown epidote and chlorite along with quartz in FRI1. A B Cl Pre Ep 200µm 200µm Figure 3.33. Prehnite in FRI1. Pre=Prenite. Figure 3.34. FRI4. FRI4 (Fig. 3.34) is medium crystalline and consists of chlorite, epidote, altered plagioclase, small amounts of quartz and sphene (Fig. 3.35). 38 A B Sph 1000µm 1000µm Figure 3.35. Chlorite, epidote, quartz and sphene in FRI4. Figure 3.36. FRI7. FRI7 (Fig. 3.36) is more fine crystalline than FRI 1 and 4 and consists of intergrown chlorite and epidote as well as some actinolite, quartz sphene and saussuritised feldspar (Fig. 3.37). A B 500µm 500µm Figure 3.37. Intergrown epidote and chlorite, quartz and sphene. 39 3.2.9 The Lib Dyke Figure 3.38. LIB1. LIB1 (Fig. 3.38) is medium to fine crystalline and consists mostly of chlorite, but albite and small amounts of quartz are also present, along with some opaque minerals (Fig. 3.39). A B 1000µm 1000µm Figure 3.39. LIB1 consists mostly of chlorite. Albite and small amounts of quartz are present along with a large percentage of opaque minerals. 3.2.10 The Little Tumi Dyke Figure 3.40. LIT1. LIT1 (Fig. 3.40) is medium to coarse crystalline with large albite crystals. Chlorite, epidote, actinolite, small amounts of quartz and opaque minerals can be identified optically (Fig. 3.41). Illite-montmorillonite was identified by means of XRD. 40 A B Fsp 1000µm 1000µm Figure 3.41. Large albite crystals in LIT1. 3.2.11 The PE Dyke Figure 3.42. PE1. PE1 (Fig. 3.42) is medium crystalline and consists of chlorite, small amounts of epidote, actinolite, altered sphene, large amounts of quartz (Fig. 3.43), and lath-like crystals of what is suspected to have been plagioclase, but is now completely chloritised. A B Cl Qz 1000µm 1000µm Figure 3.43. Large amounts of quartz and chlorite in PE1. 41 3.2.12 Ventersdorp Lava Figure 3.44. LAV1. The lava sample (Fig. 3.44) is fine crystalline and consists of large amounts of chlorite intergrown with some epidote and actinolite (Fig. 3.45). Albite is also present along with some iron oxides. Hydrobiotite (sericite) was identified by means of XRD. A B 500µm 500µm Figure 3.45. Fine crystalline Ventersdorp lava with visisble albite and epidote. Greeff (1988a) studied numerous Ventersdorp lava samples. They differed greatly in both mineralogy and texture. All samples containd plagioclase, chlorite, epidote, quartz and opaque minerals. Minerals that are present in some samples are actinolite, calcite, pyroxene, rutile, sphene and remnants of biotite. One occurrence of zeolite and a few of apatite are found. Greeff never specifies from which units of the Ventersdorp Supergroup his samples were obtained, therefore the heterogeneity in mineralogy and texture could be the result of the sampling of different flows or even different stratigraphic units. However, the Alberton Formation is the hanging wall for Ventersdorp Contact reef and it would be fair to assume that Greeff’s samples are from this formation. The mineralogical and textural descriptions given 42 by Greeff support this assumption. Winter (1995) found that, with the exception of the Alberton Formation, it is very difficult to recognise specific stratigraphic units of the Klipriviersberg group by means of petrography alone. Winter (1995) divided the Alberton Formation into three units. The lower units (1 and 2) are highly altered with very little of the original mineralogy or textures being preserved. The rocks consist of microcrystalline quartz, chlorite, actinolite, feldspar (ranging from albite to orthoclase), sericite, and carbonates. The degree of alteration decreases with increase in distance from the Ventersdorp-Witwatersrand contact. Winter found that the rocks of Unit 3 are considerably better preserved than in units 1 and 2. Plagioclase and clinopyroxene exist as major minerals along with minor secondary phases of actinolite, chlorite, epidote, carbonate, sericite, rutile and sulphides. Plagioclase and pyroxene exist, both as phenocrysts and in the matrix. 3.2.13 The Amigo Dyke Figure 3.46. AMI3. AMI3 (Fig. 3.46) is medium crystalline and consists of altered plagioclase, chlorite, iron oxides and opaque minerals. A small quartz vein cuts the sample (Fig. 3.47). XRD analysis was conducted on AMI1 and only chlorite and quartz were detected. 43 A B Fsp 1000µm 1000µm Figure 3.47. Altered plagioclase, chlorite, iron oxides and opaque minerals in AMI3. A small quartz vein is present. AMI5 (Fig. 3.48) consists of a fine mass intergrown chlorite and epidote along with some opaque minerals. Scattered throughout the sample are clusters of pyroxene crystals (Fig. 3.49). Remnants of plagioclase crystals are also present as well as large pyrite nodules. Some plagioclase remnants are contained within these nodules (Fig. 3.48). Figure 3.48. AMI5. A B Px Px 1000µm 1000µm Figure 3.49. A pyroxene cluster in a matrix of chlorite and opaque minerals in AMI5. Px=Pyroxene. 44 3.2.14 The Bank Dyke Figure 3.50. BAN1. BAN1 (Fig. 3. 50) is medium to coarse crystalline and consists of altered plagioclase and some less altered pyroxene although some pyroxenes have been chloritised (Fig. 3.51). Some quartz is also present along with opaque minerals and epidote. Actinolite and sericite were both detected by means of XRD in BAN2. A B Fsp Cl Px Fsp 1000µm 1000µm Figure 3.51. Saussuritised plagioclase, large opaque crystals, chlorite and remnants of unaltered pyroxene in BAN1. Greeff’s (1988a) description of the Bank dyke is very similar to what was found in this study. He did detect hornblende, and, in one sample, biotite, which were not found in this study. Opaque minerals in both studies were found to be large and skeletal. Greeff found that they are associated with pyroxenes. 45 3.2.15 The Speckled Dyke Figure 3.52. SPE1. The SPE1 sample (Fig. 3.52) consists of large altered remnants of plagioclase in a fine matrix of chlorite, opaque minerals and quartz (Fig. 3.53). A network of calcite and quartz veins is present (Fig. 3.52). The calcite veins appear to be the youngest. Greeff’s study (1988a) of the Speckled dyke is in many ways similar to this study. He did, however, find pyroxene and biotite in some of his samples. Opaque minerals vary in size from tiny specks to large crystals. His findings indicate a somewhat heterogenous mineralogy, with some samples containing no feldspar. This heterogeneity is probably due to differences in degrees of alteration in the dyke. The dyke originally contained large amounts of euhedral plagioclase, and their skeletal remains can still be observed, even though the feldspars are now occasionally absent. A B Fsp Fsp Fsp 1000µm 1000µm Figure 3.53. Large altered remains of plagioclase in fine matrix in SPE1. 46 3.2.16 The Twin Dyke Figure 3.54. TWI1. TWI1 (Fig. 3.54) is fine-crystalline and consists of quartz, chlorite, opaque minerals and illite (detected by means of XRD). Veins are filled with dark minerals (Fig. 3.54), possibly iron oxides or stringer-like and filled with quartz (Fig. 3.55), with the dark veins being the oldest. Quartz nodules containing sulphides are present, A B Qz 1000µm 1000µm Figure 3.55. TWI1 containing a stringer-like quartz vein and a quartz and sulphide nodule. Greeff (1988a) studied only one Twin dyke sample. He found biotite and rutile in addition to the minerals found in this study. 3.2.17 The Brazil Dyke Figure 3.56. BRA2. 47 BRA2 (Fig. 3.56) is relatively unaltered, with some chloritisation being present in the smaller crystals of the matrix. The plagioclase crystals are fresh enough for their compositions to be determined by means of the Michel-Lévy method, and were found to have a labradoritic composition (An50 – An70). Clinopyroxene is present as microphenocrysts and are also largely unaltered (Fig. 3.57). Smaller unaltered plagioclase crystals are present in the matrix along with chlorite and sulphides. Quartz, albite and a small amount of actinolite was identified by means of XRD. A B Fsp Px 1000µm 1000µm Figure 3.57. The relatively unaltered BRA2 with microphenocrysts of pyroxene in a medium to fine matrix of plagioclase, pyroxene, chlorite and opaque minerals. Figure 3.58. BRA3. BRA3 (Fig. 3.58) is from the chill zone of the Brazil dyke. It contains clinopyroxene and slightly altered plagioclase microphenocrysts in a matrix of slightly altered plagioclase and chlorite (Fig. 3.59). Large sulphide nodules are also present. The sample also contains a large altered patch, consisting of chlorite, albite and pyrophyllite, and is cut by a quartz vein (Fig. 3.56). Albite and pyrophyllite were identified by means of XRD (film technique). 48 A B Fsp Px 1000µm 1000µm Figure 3.59. Slightly altered plagioclase and pyroxene in BRA3. Figure 3.60. BRA4. BRA4 (Fig. 3.60) is medium crystalline with only minor alteration. Clinopyroxene is present along with plagioclase, which was once again identified as labradorite, and small amounts of quartz (Fig. 3.61). Large volumes, up to ±10%, of sulphide minerals are present. BRA4 can be classified mineralogically as a dolerite. A B Fsp Px 1000µm 1000µm Figure 3.61. The unaltered BRA4. Large volumes of sulphides are present. 49 3.2.18 The CLA Dyke Figure 3.62. CLA3. CLA3 (Fig. 3.62) is medium crystalline and consists of altered remnants of plagioclase, chlorite, epidote, quartz and some altered sphene (Fig. 3.63). Calcite is present in veins. A Qz B Sph Ep 1000µm 1000µm Figure 3.63. A large altered sphene crystal in CLA3. Other minerals are chlorite, epidote and quartz. Calcite is found in veins. CLA4 (Fig. 3.64) consists of saussuritised feldspar, chlorite, epidote, altered sphene, quartz, and some sulphides. Small remnants of pyroxene are present (Fig. 3.65). Figure 3.64. CLA4. 50 A B 1000µm 1000µm Figure 3.65. Chlorite, quartz, epidote and remnants of unaltered pyroxene in CLA4. CLA7 consists of altered plagioclase chlorite and epidote, quartz, large opaque mineral crystals and remnants of original pyroxenes (Fig. 3.66). A B Qz Px 1000µm 1000µm Figure 3.66. A large opaque mineral in along with chlorite, quartz and remnants of pyroxenes in CLA7. Greeff (1988a) studied one CLA dyke sample. In addition to the minerals found in this study Greeff also found biotite and apatite. Sphene and pyroxene were absent from his sample. All the CLA dyke samples were found to be highly altered. 3.2.19 The KEN Dyke Figure 3.67. KEN1. 51 KEN1 (Fig. 3.67) is extremely altered so that only skeletal remains of plagioclase are visible. The sample consists mostly of chlorite and quartz with smaller amounts of iron oxides and opaque minerals (Fig. 3.68). A B 1000µm 1000µm Figure 3.68. Alteration in KEN1. Chlorite and quartz are identifiable optically. KEN2 (Fig. 3.69) consists of saussuritised plagioclase with some slightly chloritised clinopyroxene clusters occurring. Small amounts of chlorite are present along with some opaque minerals and a quartz vein (Fig. 3.70). Figure 3.69. KEN2. A B Fsp Px 500µm 500µm Figure 3.70. A chloritised pyroxene cluster in saussuritised plagioclase and opaque minerals in KEN2. 52 3.2.20 The Swannie Dyke Figure 3.71. SWA2. SWA2 (Fig. 3.71) is medium crystalline and consists of chlorite, epidote, actinolite, quartz, calcite and altered sphene (Fig. 3.72). Feldspar is almost completely absent and opaque minerals make up less than 1% of the total rock volume. A B Qz Sph Cal Ep Cl 500µm 500µm Figure 3.72. Chlorite, quartz, calcite, sphene, epidote and opaque minerals in SWA2 3.2.21 The “Unknown” Samples Figure 3.73. UNK1. UNK1 (Fig. 3.73) is medium to fine crystalline and consists of chlorite, both scattered and in nodules, and quartz with some iron oxide staining (Fig. 3.74). Veins are filled with quartz and calcite. 53 A B Qz Cl 1000µm 1000µm Figure 3.74. One of the chlorite nodules rimmed by quartz and stained by iron oxide in UNK1. UNK2 consists of large completely altered plagioclase crystals, chlorite, small amounts of epidote and large crystals of opaque minerals (Fig. 3.75). Veins are filled with calcite. A B Fsp Cl 500µm 500µm Figure 3.75. Highly altered plagioclase and chlorite and opaque minerals in UNK2. UNK4A (Fig. 3.76) is fine crystalline and consists of chlorite, albite, epidote and quartz with a vein containing chlorite, quartz, calcite and opaque minerals (Fig. 3.77). Figure 3.76. UNK4A. 54 A B Cl Qz 1000µm 1000µm Figure 3.77. Vein containing chlorite, quartz and opaque minerals in UNK4A. UNK6 (Fig. 3.78) is medium to fine crystalline. The altered remains of plagioclase are still present along with chlorite, quartz and some calcite (Fig. 3.79). Sulphide nodules surrounded by quartz also occur. Figure 3.78. UNK6. A B Fsp Cal Qz 1000µm 1000µm Figure 3.79. Altered remains of plagioclase in a fine matrix of chlorite, along with quartz and calcite in UNK6. 55 UNK7 (Fig. 3.80) is medium to coarse crystalline and contains chlorite, large saussuritised plagioclase crystals (Fig. 3.81), small remnants of altered pyroxene and biotite, large calcite crystals and some opaque minerals (Fig.3.82) as well as illite-montmorillonite. UNK7 is mineralogically very similar to the Peggy dyke samples. Figure 3.80. UNK7. A B Bi Fsp 1000µm 1000µm Figure 3.81. Large saussuritised euhedral plagioclase crystals, remnants of biotite, and chlorite. A B Cal Fsp 1000µm 1000µm Figure 3.82. Large patches of calcite along with plagioclase and remnants of pyroxene. 56 Figure 3.83. 120A2 from Unknown 8. 120A2 (Fig. 3.83) is one of three samples that belong to a previously unknown dyke labelled Unknown 8 in this study. It consists predominantly of saussuritised feldspar, chlorite intergrown with actinolite, and smaller amounts of quartz and epidote (Fig. 3.84). Muscovite and small sphene crystals are found in lesser amounts. The sample is cut by a quartz vein. XRD analysis indicates the presence of montmorillonite. A B Fsp Ep Ser 1000µm 1000µm Figure 3.84. Altered feldspar, chlorite, epidote and sericite in 120A2. Ser=Sericite. Figure 3.85. 120B2 from Unknown 9. 120B2 (Fig. 3.85) is from the dyke labelled Unknown 9 in this study. It is medium to fine crystalline and consists predominantly of completely altered feldspar, chlorite 57 and quartz. Small opaque minerals, possibly chalcopyrite, are present and fractures are filled with chlorite and iron oxides/hydroxides (Fig. 3.86). A B 1000µm 1000µm Figure 3.86. Altered feldspar, and chlorite in 120B2. The fracture is filled with chlorite and iron oxides/ hydroxides. 3.3 Discussion The chlorite + actinolite + epidote + albite + quartz mineral assemblage is characteristic of greenschist facies metamorphism in metabasites, but either chlorite or actinolite may be absent. Greenschist facies metamorphism has a lower temperature limit of 400°C. However, it is possible for greenschist facies assemblages to form at lower temperatures in the presence of CO2-rich fluids, with laumontite, prehnite and pumpellyite reacting with CO2 to form calcite, epidote, quartz and chlorite (Yardley, 1989). Sphene is the most common Ti-rich mineral in metabasites in the greenschist facies, but ilmenite and rutile can occur instead. The formation of the different minerals depends on the bulk-rock geochemistry as well as CO2 potential. Sphene is stable when the mole fraction of CO2 is less than 0.1 (Miyashiro, 1994). In constrast to higher-grade metamorphism, the principal effect during low-grade metamorphism is the hydration of anhydrous minerals (Robinson and Bevins, 1999). According to Schiffman and Day (1999) low-grade metamorphic rocks such as metabasites can display compositional heterogeneity that can be visible in outcrop, hand specimen, or even on thin section scale. Such “meta-domains” occur as a result of original heterogeneity being enhanced by fluid-rock interaction, which is 58 controlled by the porosity and permeability of the rock. For example, fractured sections of metabasite dykes may become enriched in calcium due to the filling of voids. This process can clearly be seen in many of the dykes where veins have become calcite-filled. Compositional heterogeneity can clearly be seen in dykes such as the Peggy and Speckled dykes. Similar heterogeneity is found in the Alberton Formation according to Winter (1995), and can also be seen in the “Ventersdorp lava” samples studied by Greeff (1988b). The heterogeneity usually occurs as a result of variable degrees of alteration. Good examples would be the Peggy dyke, where some samples contain hornblende and biotite and others do not, and the CLA dyke where remnants of pyroxenes were found in this study, but not in Greeff’s study. The composition of the primary minerals of mafic rocks determines which secondary minerals will form during low-grade metamorphism, e.g. olivine and orthopyroxenes are pseudomorphed by Mg-smectite, serpentine and talc. The absence of serpentine and talc in all samples indicate that no olivine was present. Ca and Al are released from plagioclase and contribute towards the formation of calcite, prehnite, pumpellyite, epidote, and sphene, causing these minerals to form in veins, vesicles and within the primary plagioclase itself. The removal of Ca from the plagioclase means that the resulting plagioclase has an albitic composition. The replacement of clinopyroxene by actinolite and lesser chlorite (uralitisation) is characteristic of greenschist metamorphism. The formation of actinolite requires, at least in part, the decomposition of significant amounts of chlorite, and forms after chlorite, albite, epidote and quartz have formed. Primary ilmenite and magnetite can be pseudomorphed by low Ti-magnetite or sphene, which is able to form as a result of aluminium being released in the process of albitisation (Schiffman and Day, 1999). 3.4 Normative Mineralogy CIPW norms were calculated in GCDkit (Janousek et al., 2007) using major element data (See Appendix C), and averages for each dyke are given in Table 3.1. The major element concentrations were recalculated to 100% volatile free. FeO and Fe2O3 were calculated from total Fe (given as Fe2O3 in Appendix C) using a 59 Fe2O3/FeO ratio of 0.15 (Middlemost, 1989). The normative mineralogy for each sample is included in Appendix B. It should be kept in mind that CIPW norms assume the absence of water, and therefore no biotite or hornblende is calculated. This is clearly not an accurate reflection of many of the rocks, as primary biotite and hornblende is visible, e.g. in the Peggy dyke. The fact that some elements have probably been mobilised during greenschist metamorphism will also have an influence on the normative mineralogy. The observed plagioclase contents of the samples correlate reasonably well with the calculated norm, although all anorthite has been converted to albite (one of the constituents of saussurite (Nesse, 2004)). In the case of the Jeans dyke (JEA1), plagioclase has been converted to calcite. Samples with large amounts of modal chlorite do not necessarily have high normative pyroxene percentages. However, pyroxene is not the only source of chlorite during alteration, and biotite and hornblende can also be altered to chlorite. The presence of normative corundum is likely due to the apparent enrichment of aluminium as a result of the depletion of elements such as Na, K and Ca. Table 3.1. Average CIPW norms for the dykes. Major element data taken from Table C.1. n = number of analyses. Peggy Georgette Skelm Soll Kudu Sill Jeans Friday n=6 n=3 n=5 n=3 n=1 n=2 n=3 n=9 Quartz 1.65 27.19 11.82 34.31 20.44 23.02 14.62 17.04 Corundum 0 2.15 0.00 9.07 0 5.67 4.01 5.66 Orthoclase 7.92 0.06 0.33 0 0.06 0.62 0 0 Albite 35.94 7.36 14.05 5.50 16.75 5.37 5.64 1.29 Anorthite 11.15 21.39 29.44 7.76 30.54 15.90 25.07 22.04 Diopside 18.11 3.75 9.69 0.00 2.7 8.97 4.54 3.91 Hypersthene 19.70 34.52 26.90 37.13 25.44 33.54 37.11 38.94 Olivine 0 0 0 0 0 0 0 0 Magnetite 2.47 1.95 2.90 2.94 2.00 2.68 3.02 3.74 Ilmenite 2.61 1.52 4.02 2.98 1.69 3.41 4.66 5.83 Apatite 0.48 0.19 0.93 0.44 0.38 0.96 1.40 1.73 60 Table 3.1. (continued). Lib Lit. Tumi PE Lava Amigo Bank Speckled Twin n=1 n=1 n=2 n=1 n=4 n=7 n=5 n=2 Quartz 16.73 7.54 11.94 5.13 23.53 5.81 32.87 43.62 Corundum 0 0 0.65 0.55 8.90 0.08 9.15 14.26 Orthoclase 0 4.08 0 6.62 0.03 1.98 0 11.85 Albite 10.32 21.15 6.81 34.61 6.33 16.22 0 1.27 Anorthite 29.94 22.16 31.50 24.97 13.18 28.81 7.16 0.21 Diopside 1.28 8.36 2.51 0 0 10.79 0 0 Hypersthene 30.78 26.66 35.31 23.96 37.44 27.99 47.35 25.40 Olivine 0 0 0 0 0 0 0 0 Magnetite 3.38 3.28 3.35 1.87 3.14 3.03 2.57 2.02 Ilmenite 5.21 4.85 6.08 1.96 6.14 5.42 0.92 1.22 Apatite 2.04 1.99 1.93 0.36 1.44 0.81 0.14 0.20 Table 3.1. (continued). Brazil CLA Ken Swannie UNK1 UNK2 UNK3 UNK4 n=8 n=9 n=7 n=3 n=1 n=1 n=1 n=2 Quartz 9.98 15.63 7.21 20.40 7.66 2.301 20.62 16.74 Corundum 1.62 6.85 2.07 9.21 0 0.405 0 1.68 Orthoclase 1.00 0 0.33 0 0 0 5.73 0 Albite 14.20 4.23 13.61 0 8.12 4.739 14.47 12.06 Anorthite 25.28 22.07 26.28 11.87 31.41 37.611 33.14 27.75 Diopside 8.35 3.81 9.30 3.36 12.87 0 8.29 6.30 Hypersthene 29.66 41.71 33.31 43.39 28.97 42.028 11.81 26.28 Olivine 0 0 0 0 0 0 0 0 Magnetite 3.15 3.06 3.12 4.15 3.34 4.132 0.96 2.75 Ilmenite 5.70 2.39 4.71 5.97 5.97 6.84 1.92 4.24 Apatite 0.87 0.31 0.72 1.84 1.80 2.084 0.43 0.79 Table 3.1. (continued). UNK6 UNK7 UNK8 UNK9 n=1 n=1 n=3 n=3 Quartz 3.98 5.73 17.33 24.84 Corundum 9.22 0 0.90 4.58 Orthoclase 0 4.61 4.49 7.21 Albite 31.56 32.24 19.26 6.88 Anorthite 0.19 11.29 24.57 21.90 Diopside 0 10.08 9.23 0 Hypersthene 54.73 29.55 20.24 30.30 Olivine 0 0 0 0 Magnetite 3.18 2.71 1.87 2.12 Ilmenite 1.16 2.57 1.75 1.81 Apatite 0.17 0.45 0.39 0.340 61 Silica concentrations show the same apparent increase, but some silica may also have been added to the system in the form of veins, resulting in normative quartz. No modal rutile was observed. 3.5 Conclusion The petrographic study of the dykes revealed that all the dykes, with the exception of the Brazil dyke, have undergone low-grade metamorphism. Primary mafic minerals such as pyroxenes have mostly been converted to chlorite, actinolite and epidote, and feldspars have been albitised. In some instances, remnants of the original minerals can still be seen, e.g. in the Peggy dyke where hornblende and biotite are still present, the Amigo Dyke where clusters of largely intact clinopyroxene phenocrysts occur, and in the CLA dyke where small amounts of pyroxene remain unaltered. In comparing dyke samples from this study with each other and with those from Greeff (1988a) it becomes clear that compositional heterogeneity exists within the dykes themselves. The heterogeneity is likely the result of differences in the degree of alteration along dykes, but original heterogeneity could have made a significant contribution. Veins are a common feature in most of the dykes and are mostly filled with calcite and quartz, but some include epidote, chlorite, iron oxides and sulphides in veins. An interesting case is the Skelm dyke, where veins are filled almost exclusively with epidote. The Brazil dyke is unusual in the sense that it shows much less alteration than any of the other dykes, and, apart from small amounts of chloritisation, displays an almost intact primary mineralogy. The Friday dyke is the only case where prehnite was identified, and the Jeans dyke, as well as Unknown 7, contains large patches of calcite outside veins and in the rock itself. Apart from these few “odd” characteristics it would be very difficult to identify most of the dykes by using petrographic methods alone. It would be advisable to compile a library of petrographic data including numerous samples from each dyke in order to obtain a clearer picture of the petrographic characteristics of each dyke. This could in turn lead to a better understanding of the mechanisms involved in their alteration and, possibly, to an identification system based on mineralogy. 62 Chapter 4: Geochemistry I 4.1. Major and Trace Element Statistics 4.1.1 Major Element Oxides In a study on the dykes in the Central Welkom Goldfield, Rompel (1995) found that very little chemical variation is present within a specific dyke, and that dykes can be traced according to their chemical composition along their strike. Therefore, if chemical variation does occur, it may indicate that the elements have been mobilised by low-grade metamorphism to varying degrees. Rompel (1995) also found that individual dykes could be fingerprinted according to their chemistry, and therefore, large variation, especially in those elements that are regarded as immobile, would indicate different origins for samples. Box and whisker diagrams, such as those plotted in Figs. 4.1 to 4.5, are very useful when examining the element variations within and between dykes. The plot represents the median as the solid black rectangle in the box. In cases where only one sample is present (e.g. Ventersdorp lava), this rectangle is the only feature plotted. The dashed lines (“whiskers”) indicate the maximum and minimum, non- outlier, values in the range. According to convention, the whiskers can be no longer than 1.5 times the length of the box, and any data values that are not contained in this range are seen as outliers, and marked as circles. The box represents the range between the upper and lower quartiles of the data. The quartiles are values halfway between the maximum/minimum values and the median (Verzani, 2005). The box plots were constructed using GCDkit (Janousek et al., 2007), an R-based geochemistry software package. The most notable feature in the box plots is the extreme range in SiO2, TiO2, MgO, and CaO concentrations in the Sill (Figs. 4.1, 4.3 and 4.4). This may indicate that, what was assumed to be a single intrusive is in reality two different intrusives. This possibility will be investigated further in Chapter 5. At first glance there seems to be great variation in P2O5 concentrations, but this is due to the large scale of the plot (Fig. 4.4). CaO (Fig. 4.4), Na2O and K2O (Fig. 4.5) show large ranges in almost all the dykes. These large ranges are probably due to the mobilisation of the elements in question during metamorphism, a possibility that is further strengthened by the 63 absence of K2O in eight of the dykes. However, the heterogeneous nature of alteration, as well as the fact that not all dykes are equally altered may cause elements such as K2O to be removed from some dykes or even from some sections of the dykes and not from other. This possibility will be investigated further in a following section. Figure 4.1. Box plots for SiO2 and TiO2, showing small SiO2 ranges in most of the dykes, but large ranges for SiO2 and TiO2 in the Sill. Concentrations in wt%. Figure 4.2. Box plots for Al2O3 and total Fe2O3 showing some variation for both oxides. Concentrations in wt%. 64 Figure 4.3. Box plots showing little variation in MnO and more variation in MgO. Concentrations in wt%. Figure 4.4. Box plots for CaO and P2O5, showing large CaO ranges for all dykes, but small differences in P2O5 concentrations. Concentrations in wt%. Figure 4.5. Box plots showing large variation in Na2O K2O concentrations. Concentrations in wt%. 65 4.1.2 Trace Elements Of the trace elements, only Cr, Ni, Sr, Rb, Zr and Y (concentrations given in ppm) are included in the statistical investigation because they are used in subsequent geochemical classifications. Cr contents for all the dykes fall in a relatively small range (Fig. 4.6). Two exceptions are the Sill and the Speckled dyke, with the Speckled dyke having not only a much wider range of Cr concentrations, but also much higher Cr concentrations than any of the other dykes. In the CLA dyke CLA5 plots as an outlier with a much higher Cr content than the other CLA samples. The dykes’ Ni contents (Fig. 4.6) are much more varied than the Cr contents. The Sill, Soll, Georgette and Jeans dykes have very large Ni ranges and CLA5 is once again an outlier, indicating either the presence of a cumulate effect or the sampling of a different intrusive. Figure 4.6. Box plots showing little variation in Cr contents, but some variation in Ni contents. Sr concentrations vary greatly within dykes, and similar variation is found in Rb concentrations (Fig. 4.7). Sr and Rb largely mirror the behaviour of Ca and K respectively, due to their chemical similarity to these elements (White, 2007). This is reflected in the box plots. Y and Zr display very similar trends (Fig. 4.8): The largest ranges in both elements are in the Sill, but large ranges of both elements are present in the Amigo and Skelm dykes as well. The Little Tumi and Lib dykes have the highest Zr concentrations, exceeding 450 ppm. 66 Figure 4.7. Box plots showing large variation in both Rb and Sr concentrations. Figure 4.8. Box plots showing some variation for both Y and Zr. 4.2 Element Mobility Since most of the dykes have undergone greenschist metamorphism it is likely that certain elements have been redistributed. Bowen (1984a) noted that K, Na, Mn, Rb and Ba were extremely mobile in the Ventersdorp lavas and cannot be used to make any deductions on their geochemistry. In his study on the geochemistry of the Klipriviersberg group, Linton (1992) used the following technique, first introduced by Palmer et al. (1986) (in Linton, 1992), to test element mobility: An immobile element is selected as the divisor for element ratios. A second immobile element is used as the numerator for the x-axis. The unknown element is used as the y-axis 67 numerator. Zr (as divisor) and Ti (as x-axis numerator) are popular choices as their analytical precision is good and both are regarded as being immobile. In addition, both are highly incompatible in basalts and fractionation does not produce dramatic fluctuations in their concentrations (Linton, 1992). In order to take the possible influence of fractionation and partial melting into account, Linton (1992) divided his lava samples into three groups based on their Mg content. This technique was also applied to the samples in this study. If the element in question was immobile, samples from the different MgO groups should plot more or less together. On the other hand, if vertical scatter occurs in the plots it would indicate mobility of the element. In Linton’s study (1992), samples in the same Mg range clustered together to form three distinct groups, a trend which was not observed in this study where the distinction is more complex. This can be ascribed to the fact that the dyke samples are more than likely related to different stratigraphic units. The plots (Fig. 4.9 A to M) indicate that the mobility of an element appears to be related to its Mg content. SiO2 (A), Fe2O3 (B), MnO (C), CaO (E), Na2O (F) and Y (M) show the most scatter in the >9% MgO range. Al2O3 (D) and K2O (H) are most scattered in the <6% MgO range, and Cr and Ni being the most scattered in the intermediate range MgO. K2O is completely absent from the 6 – 9% MgO range. This may indicate that the intermediate MgO rocks are older than the rocks with higher and lower MgO contents, and that they have therefore been subjected to longer periods of metamorphism. TiO2 and Zr mobility is impossible to determine in the ratio plots, but if the box plots show similar variation for these elements as for Y, and it is therefore likely that they have also been mobilised (Fig 4.1 and 4.8) and that using their ratios as x-axis values may lead to misleading conclusions. The mobility of these elements will be discussed in Chapter 5. When the ratio plot patterns from this study are compared with those done by Linton it would seem that the dyke chemistry has been changed far more than that of the Ventersdorp lavas studied by Linton. However, this is possibly an unwarranted conclusion to make as it is not known to what extent the different possible origins of the dykes can influence the plots, even though most primary magmatic effects have been compensated for by separating groups on the grounds of MgO content. In some plots, notably in the SiO2 and Al2O3 ones (Fig. 4.10), smaller groups form 68 within larger groups; these smaller groups are mostly made up of samples from the same dykes. In a study such as this where individual intrusives are investigated it probably makes more sense to use box plots to determine which elements have been mobilised. The reasoning behind this is that the ratio plots give a generalised view of which elements were mobile, but the box plots give an indication of which elements were mobile in individual dykes. The ratio plot also can mask effects of Ti and Zr mobility because they may not be as immobile as normally assumed. Another advantage of the box plots is that they show where outliers are present e.g. in CLA dyke (Fig. 4.1, 4.3 and 4.6). An outlier may indicate that multiple sampling of supposedly the same intrusive has resulted in the sampling of an unrelated intrusive which is in close proximity. A B 69 C D E F G H 70 I J K L M Figure 4.9. Plots used to determine element mobility. All samples were included and separated according to their MgO content. 71 Figure 4.10. SiO2 and Al2O3 mobility plots showing the smaller groups made by samples from the same dykes. 4.3 Chemical Variation between Chill and Central Zones of Dykes The chill zones of intrusives are regarded to have a geochemistry that is equivalent to that of the unfractionated magma due to a quick cooling rate which 'locks in' the original chemistry. However, it is more likely that fractionation of mantle-compatible elements into the chill zone will occur with its formation. In this study there are 10 cases where both chill zones of the dykes and central zones were sampled, making it possible to compare the chemistry of the different zones. It is most useful to compare the concentrations of compatible elements especially since many incompatible elements are present in concentrations that would make comparison statistically meaningless, or were below the detection limit of the XRF spectrometer. If fractionation did occur, the chill zones will have a higher compatible element concentration than the central zones, as these elements, especially Ni and Cr tend to partition into olivine and early pyroxenes (Rollinson, 1993). MgO, CaO, Cr and Ni were used in the comparison, as well as SiO2 which should display an opposite trend to those of the above-mentioned compatible elements. The expected trends are clearly seen in the Bank dyke, especially in the samples from borehole DPH3885 (Fig. 4.11) where all compatible elements have higher concentrations in the chill zones than in the centre. The samples from DPH3880 (Fig. 4.12) show the same trend, where the fractionation of both Ni and Cr are even more pronounced. Approximately the same trend with the fractionation of compatible elements into chill 72 zones is seen in the Brazil (Fig. 4.13 and 4.14), CLA (Fig. 4.15), Friday (Fig. 4.16) and Swannie (Fig.4.18) dykes, although Ni and Cr do not show the same tendency in the Brazil 1 (DPH3881) and Brazil 2 (DPH3884) dykes respectively. The Speckled dyke (Fig. 4.17) displays exactly the opposite trend with the central zone being more enriched in incompatible elements than the chill zones. The same trend is seen in Unknown 8 (Fig. 4.19), especially in Ni and Cr concentrations. Unknown 9 (Fig. 4.20) does not conform perfectly to either scenario, but has a centre that is slightly enriched in Cr and slightly depleted in SiO2. In the other dykes SiO2 does not always display a trend opposite to that of the compatible elements, but does so in the Brazil 2, CLA, Speckled and Unknown 9. Possible reasons for this will be discussed below. Figure 4.11. Element concentrations in the chill zones and central zone of the Bank dyke in borehole number DPH 3885, showing enrichment of compatible elements in the chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. 73 Figure 4.12. Element concentrations in the chill zones and central zone of the Bank dyke in borehole number DPH 3880 showing enrichment of Cr and Ni in the chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. Figure 4.13. Element concentrations in the chill zones and central zone of the Brazil dyke in borehole number DPH 3881, showing Cr enrichment in the chill zones and Ni enrichment in chill zone 1. The unit for the major element oxides is wt% and for Cr and Ni, ppm. 74 Figure 4.14. Element concentrations in the chill zones and central zone of the Brazil dyke in borehole number DPH 3884, showing Cr enrichment in chill zone 1 and Ni enrichment in both chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. Figure 4.15. Element concentrations in the chill zones and central zone of the CLA, showing enrichment of compatible elements in the chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. 75 Figure 4.16. Element concentrations in the chill zones and central zone of the Friday dyke, showing enrichment in MgO, Cr and Ni. The unit for the major element oxides is wt% and for Cr and Ni, ppm. Figure 4.17. Element concentrations in the chill zones and central zone of the Speckled dyke, showing an enrichment Cr, Ni and Sr in the central zone. The unit for the major element oxides is wt% and for Cr, Ni and Sr, ppm. 76 Figure 4.18. Element concentrations in the chill zones and central zone of the Swannie dyke, showing enrichment of Cr and Ni in the chill zones. The unit for the major element oxides is wt% and for Cr and Ni, ppm. Figure 4.19. Element concentrations in the chill zones and central zone of the “Unknown 8” dyke, showing enrichment of Cr and Ni in the central zone. The unit for the major element oxides is wt% and for Cr and Ni, ppm. 77 Figure 4.20. Element concentrations in the chill zones and central zone of the “Unknown 9” dyke, showing Cr and Ni enrichment in the central zone and chill zone 2. The unit for the major element oxides is wt% and for Cr and Ni, ppm. A possible explanation for this “inverse” trend in chemistry in the Speckled dyke and to a certain extent in Unknown 9 can be found in a study executed on a lava flow near the Katse dam in Lesotho (De Bruiyn, et al. 2000). Both the top and bottom sections of the flow have a tholeiitic composition, but the central zone is picritic. Some olivine crystals in this zone contain microscopic melt inclusions that probably represent quenched parental liquid, which was apparently intermediate in composition between those of the contact zones and the central part. Geochemical modelling indicated that approximately 28% olivine had to be separated from the parental magma in order to yield the tholeiitic base and top zones. The separation of the olivine was likely achieved by means of flow differentiation. When a fluid containing suspended particles flows though a conduit, the particles will migrate toward the region with the highest flow rate, i.e. away from the walls of the conduit. Bhattacharji (1967) was first to apply this principle, which was originally observed in blood vessels, to magmas. His experimental work showed that early minerals would concentrate in the centre of dykes and sills in which high flow rates are present, but would settle once the rate decreases. This means that the mantle- 78 compatible element-rich pyroxenes and, possibly, olivines would move from the chill zone into the central zone of the intrusive. If this principle is used to explain the “inverse” chemistry of the Speckled and Unknown 8 dykes it would mean that these dykes had higher flow rates than the dykes with compatible elements concentrated in their chill zones. This trend may be useful as an identification tool for these two dykes, however, there may be other dykes in the study are which were not included in this study, that display the same trend. An interesting feature of Unknown 9 is the concentration of Cr and Ni in only one chill zone. This concentration of mantle- compatible elements may lead one to suspect the presence of a cumulate layer of early minerals. However, the dyke is almost perfectly vertical (pers. comm. K. Deysel, 2009) which eliminates the possibility of gravitational settling of early minerals to the chill zone. Two likely explanations exist, the first is that the dyke changed from slow flowing to fast flowing as different magma pulses intruded, and the second involves different cooling rates for the two sides of the dyke, resulting in the partitioning of compatible elements in the chill zone with the quicker cooling rate. However, a more detailed study of this dyke is required in order to obtain any definite answers. 4.3 Rock Classification Since any mineralogical classification is made impossible by the severe alteration of the primary igneous minerals to chlorite actinolite and other clay minerals, a logical next step would be to classify the dykes with existing geochemical plots. Both classifications for rock names and for tectonic settings were used. These plots are ideally used with unaltered rocks, and the fact that the dykes are altered may cause some misclassification. It could, however, still give a preliminary idea of which dykes are related to which igneous event. The Irvine and Baragar (1971) AFM diagram (Fig. 4.21) distinguishes between calc- alkaline and tholeiitic rocks. The Ventersdorp lava sample, Unknown 3 and PEG3 and 6 plot in the Calc-alkaline series and PEG2, 4 and 5 plot on the line between the two series. All other samples plot in the tholeiite field. 79 Figure 4.21. AFM classification diagram (Irvine and Baragar, 1971), dividing igneous rocks into tholeiitic and calc.alkaline series. The majority of the dyke samples are classified as tholeiitic. Figure 4.22. Jensen cation plot (1976) classifies most samples as high-Fe tholeiite basalts. The Speckled dyke is classified as a komatiitic basalt. 80 In the Jensen (1976) cation plot most of the samples plot in the high-Fe tholeiite basalt field, with a few exceptions (Fig. 4.22). The Speckled dyke, SIL1 and GEOR3 plot in the komatiitic field. The CLA, KEN1, and other two Georgette samples are classified as High-Mg tholeiite basalts. The Ventersdorp lava sample, Twin dyke, Unknown 8, Lib dyke and PEG6 are classified as basalts, although TWI2 plots more in the andesite field. Unknown 3 is classified as an andesite. A few samples plot on the boundaries between fields. The remainder of the samples are classified as high-Fe tholeiite basalt. According to the Winchester and Floyd (1977) Zr/TiO2 vs. Nb/Y system most samples are classified as subalkaline basalt (Fig. 4.23). PEG 1-5, SOL3, GEOR 3 and UNK7 plot in the alkaline basalt field, with CLA9 being classified as a trachy- andesite. While most of the Friday dyke samples are classified as subalkaline basalts FRI4 and 5 encroach slightly into the andesite/basalt field. Unknown 1 and 2, the Skelm dyke, JEA 1 and 3 and Unknown 8 also fall in this field. Unknown 9, JEA2, the Kudu dyke, Lib and Little Tumi dykes are classified as andesites. Figure 4.23. Winchester and Floyd’s Zr/TiO2 v Nb/Y diagram (1977) classifies the majority of samples as sub.alkaline basalt to andesite. The Peggy dyke is classified as alkali basalt. 81 Figure 4.24. The R1-R2 diagram by De la Roche et al. (1980) gives a more felsic classification than the other plots. Some samples, including the Speckled dyke, are not plotted due to the absence of alkalis, causing a shift to the right on the x-axis. When the classification system by De la Roche et al. (1980) (Fig. 4.24) is used, there is a general shift towards more felsic classifications with samples from the CLA, Friday and Swannie dykes as well as SOL1 being classified as rhyodacites. This plot also tends to separate samples from the same dyke into widely different groups, e.g. The Friday (andesi-basalt and dacite), CLA (andesi-basalt and rhyodacite) and Brazil (andesi-basalt and dacite). The Peggy dyke plots towards the more alkaline part of the plot. 4.4 Geotectonic Classification In the Ti – Zr – Y diagram (Fig. 4.25) most of the samples, including the Ventersdorp lava sample are classified as “within plate basalt”. Most CLA and some Speckled dyke samples fall in the MORB – island arc basalt – low alkali tholeiite field, and one CLA sample plots outside any field. In the Ti- Zr diagram (Fig. 4.26) many samples, including the Brazil dyke, cannot be classified due to excessively high Ti or Zr concentrations. While most of the classified samples plot either as calc-alkaline basalts (Unknown 8 and 9, Kudu dyke and Ventersdorp lava) or low alkali tholeiites (Speckled and Georgette dykes and Unknown 6) the CLA, Peggy and Soll dykes plot 82 as MORB. This may be an indication that these dykes are related to the Ventersdorp lavas as Linton (1992) classified some Ventersdorp rocks as MORB. Figure 4.25. Ti – Zr – Y diagram for tectonic classification (after Pearce and Cann, 1973). LAT=Low K tholeiites, MORB=Ocean floor basalts, WPB=within plate basalts. Figure 4.26. Ti – Zr (after Pearce and Cann, 1973). Acronyms are the same as for the previous figure. 83 Figure 4.27. Total Fe – MgO – Al2O3 (after Pearce et al., 1977) classifies the majority of the dykes as having a continental origin. The FeOt – MgO – Al2O3 diagram (Fig. 4.27) can be used for rocks with a SiO2 range of 51 – 56%. Most of the dyke samples fall in this range, but there are a few exceptions. One limiting factor of this diagram is that it was drawn up using analyses from relatively modern rocks. Caution should therefore be exercised when using this diagram on older rocks as in the case in this study. Most samples plot as continental flood basalts. GEOR1 and 2, SIL1 and JEA2 plot as ocean ridge and ocean floor basalts. Unknown 3, the Ventersdorp lava sample, Unknown9 and Unknown 8A, PEG6, TWI1 and the Lib dyke are classified as orogenic basalts. The Speckled dyke, Swannie, Amigo, CLA and Ken dykes and SIL2 are classified as ocean island basalts. 84 4.5 Conclusions Box plots show large variations in certain elements in some of the dykes. The most remarkable of these is the Sill, with large ranges in SiO2, TiO2, MgO, CaO, Ni and Cr, possibly indicating different and maybe unrelated origins for the two samples. Another significant observation is that CLA9 plots as an outlier with regard to most of the elements, and may have a different origin from the other CLA samples. Variation in element concentrations can be attributed to these elements becoming mobile during greenschist metamorphism. A test for mobility, where the element in question over Zr is plotted against Ti/Zr, indicates that CaO, K2O, Na2O, Rb and Sr were the most mobile, as one would expect from their known geochemistry. MgO, Ni and Cr seem to have been the least affected by greenchist metamorphism. When these plots are compared to those from Linton (1992), it seems that the dykes’ chemistry have been more affected by alteration than the lavas studied by Linton. The fact that samples from the same dykes often group together in the plots could indicate that the scatter of the plots are influenced by the fact that the dykes are most probably from different stratigraphic units. Some elemental variations occur between the central and chill zones of dykes. When compatible element concentrations are compared in chill and central zones, the chill zones mostly have higher concentrations of compatible elements than the central zones. The opposite trend is seen in the Speckled dyke and in Unknown 8 and to a certain extent in Unknown 9. This “inverse” chemistry is possibly as a result of fast-flowing magma in the dyke, causing the first-formed crystals to migrate to the centre of the dyke. The results of the geochemical classifications are best summarised in table form (Table 4.1). Geotectonic plots seem to be very susceptible to the alteration of the rocks plotted. Some samples, notably the CLA, Peggy and Soll dykes to be classified as mid- ocean ridge basalts, which may indicate that they are related to the Ventersdorp lavas as Linton’s study (1992) classified some Ventersdorp rocks as MORB. It is possible that these geotectonic plots only serve to show even further how altered 85 these rocks are and that any plots, such as those used in geochemical and tectonic classification should be treated with circumspection. Table 4.1. A summary of the classifications of the dykes according to four plots. AFM Jensen Cation Zr/TiO2 v Nb/Y R1-R2 Peggy Calc-alkaline High-Fe Alkali basalt Latite/lati- tholeiite basalt andesite/andesi- basalt Georgette Tholeiite Komatiitic Alkali NC basalt/High- basalt/Sub- Mg tholeiite alkaline basalt basalt Skelm Tholeiite High-Fe Andesite/Basalt Andesite tholeiite basalt Bank Tholeiite High-Fe Sub- andesi- tholeiite basalt alkaline basalt basalt/andesite CLA Tholeiite High-Mg Sub- rhyodacite/andesi- tholeiite basalt alkaline basalt basalt Brazil Tholeiite High-Fe Sub- andesi- tholeiite basalt alkaline basalt basalt/dacite Speckled Tholeiite Komatiitic Sub- NC basalt alkaline basalt Twin Tholeiite Basalt Sub- NC alkaline basalt Kudu Tholeiite High-Fe Andesite/Basalt NC tholeiite basalt Friday Tholeiite High-Fe Sub- dacite/andesite tholeiite basalt alkaline basalt Jeans Tholeiite High-Fe Andesite/Basalt andesite tholeiite basalt Soll Tholeiite High-Fe Sub- andesite tholeiite basalt alkaline basalt 86 Sill Tholeiite Komatiitic Sub- andesi-basalt/NC basalt/High- alkaline basalt Fe tholeiite basalt Ken Tholeiite High-Fe Sub- andesi-basalt tholeiite basalt alkaline basalt Swannie Tholeiite High-Fe Andesite rhyodacite tholeiite basalt Amigo Tholeiite High-Fe Sub- dacite tholeiite basalt alkaline basalt LIB Tholeiite Basalt Andesite andesite Little Tumi Tholeiite High-Fe Andesite andesite tholeiite basalt PE Tholeiite High-Fe Andesite/Basalt andesite tholeiite basalt Ventersdorp Calc-alkaline Basalt Sub-alkaline andesite Lava basalt 87 Chapter 5: Geochemistry II 5.1 Grouping of Dykes According to Their Geochemistry Dykes sharing the same origin should have approximately the same geochemistry and it is theoretically possible to divide them into groups according to their geochemistry. In order to be considered viable for use in the geochemical investigation of the dykes, the element in question must have been immobile and unaffected by primary magmatic processes such as fractionation in basaltic magma. The merits of Ti and Zr in this regard have already been discussed in the previous chapter. Y has similar behaviour, with regards mobility and primary magmatic processes, to that of Ti and Zr as all three are High Field Strength Elements (HFSEs), i.e. they form small, highly charged cations (Rollinson, 1993). As previously mentioned, Bowen (1984a) successfully separated the rocks of the Witwatersrand Triad by means of TiO2 v Zr, Zr/P v P/Ti plots and the discriminant plot devised by Linton (1992) gave a good geochemical separation of the Klipriviersberg Group rocks. These three plots were employed in the separation of the dykes into chemically distinct groups. In the TiO2 v Zr plot (Fig. 5.1), all CLA dyke samples, except CLA9, group together along with one Georgette sample (GEOR3) and SOL3 from the Soll dyke. All Peggy samples, as well as Unknown 7, plot together except PEG6 which is slightly removed from the other Peggy samples and plots in the same group as Unknowns 3, 8 and 9, the Kudu dyke, and the Ventersdorp lava. The two Sill samples plot in completely different groups, one with the Speckled dyke and the other in the Friday dyke group on PE dyke sample PE1. SOL1 and SOL2 plot close together, but SOL3 plots closer to the CLA group. The Brazil dyke samples plot together along with most of the Ken and Bank dyke samples and the two Amigo dyke samples AMI3 and AMI5. Only BAN1 of the Bank dyke plots outside this field. The Friday, PE, Swannie, Unknown 1 and Unknown 2 dykes, as well as two Amigo samples (AMI1 and AMI2) and two Jeans samples (JEA1 and JEA3) plot in one field along with Skelm dyke sample SKE2 and SIL2. Skelm dyke samples 1 and 3 plot in the same field as the two Unknown4 samples and Friday dyke sample FRI4. The Speckled, Unknown6, and Twin dykes, along with Georgette samples GEOR1 and GEOR2 as well as SIL1 88 plot in the field with the lowest TiO2 and Zr values. The Lib and Little Tumi dykes plot together away from any of the other fields. These two dyke samples are distinguished from the other dykes by their high Zr content. Figure 5.1. Dyke samples on a plot of TiO2 (wt%) v Zr (ppm) (after Bowen, 1984a) showing the grouping of dykes. When the Zr/P v P/Ti plot is used (Fig. 5.2), the dyke samples plot into three groups with only five outliers (PEG1, JEA2, GEOR3, LIT1 and LIB1) that do not plot in any of the fields. The CLA9 sample was omitted from the plot as it has a Zr/P ratio >5 due to a high Zr content and low P content. The Peggy, Speckled, Twin, Skelm, Georgette, Kudu, Unknown3, Unknown4, Unknown6, Unknown7, Unknown 8 and Unknown 9 and the Ventersdorp lava group together. Included in this group are also SIL1, FRI4, and SOL3. The CLA, Brazil, Ken, Soll, and Bank dykes plot in the group below, along with Amigo dykes samples AMI3 and AMI5 and SPE4 from the Speckled dyke. The Friday, Jeans, Swannie, Unknown1, Unknown2 and PE dykes plot in the field with the highest P/Ti and lowest Zr/P ratios. The Amigo dyke 89 samples AMI1 and AMI2, Skelm dyke sample SKE2 and SIL2 are also in this field. The Lib and Little Tumi dykes once again plot together in their own field. Figure 5.2. Dyke samples on a plot of Zr/P v P/Ti (after Bowen, 1984a) showing the division of dykes into three groups. When the samples are plotted on Linton’s discriminant plot (Fig. 5.3) they form essentially the same groups as in the TiO2 v Zr plot. The CLA samples (excluding CLA9) group together with KEN 1 and 4, and the Speckled, Georgette and Twin dykes group together with SIL1 and UNK6. Unknown 8 and 9 group together with the Peggy dyke, Ventersdorp lava, the Kudu dyke, SKE5, GEOR3 and SOL3, Unknown3 and Unknown7. SKE1 and 3, Unknown 4 and FRI4 form a group. The Bank, Brazil and Amigo dykes group together with the Ken dyke, and the Friday and Swannie dykes, SKE2, SIL2, AMI1 and 2, and Unknown 2 group together. 90 Figure 5.3. The grouping of dyke samples on the discriminant plot developed by Linton (1992). Fn1=0.0172Y-0.06078Zr+20.8084TiO2-11.4636; Fn2=-0.24892Y+0.16017Zr- 11.7088TiO2-0.07079. When the dyke samples are plotted onto these immobile, High Field Strength Element (HFSE) plots, samples from the same dyke mostly plot together. The Soll, Peggy, Amigo, Jeans, Georgette and Skelm dykes as well as the Sill, are exceptions, although to a lesser extent in the case of the Peggy dyke. It may be that the HFSEs are not entirely immobile, but mobility of these elements would likely not cause large variation between samples. On the other hand, large variations in geochemistry, such as that between the two Sill samples, probably indicate that the samples actually represent two different intrusives. Intrusives are mapped mostly by using data derived from drill core, and to some extent, by means of underground mapping. If very little data is available for an area it is more difficult to make correct deductions, and mine plans are constantly updated as more data becomes available. Thus, before any conclusions regarding sample scatter due to element mobility can be made, one should first look at the sample localities to determine whether any samples have been misnamed: 91 • FRI4 always plots away from the rest of the Friday dyke samples and groups with two Skelm dyke and the two UNK4 samples (Figs. 5.1, 5.2 and 5.3). When one refers to Fig. 2.2 it is clear that FRI4 really belongs to the Skelm dyke. • KEN1 and 4 plot with the CLA dyke samples (Figs. 5.1 and 5.3), but on the locality map they are very close to KEN2 and 3 and not near the CLA dyke (Fig. 2.4). • Similarly, CLA9 is completely removed from all the other samples on the plots (Figs. 5.1 and 5.3), but it was sampled very close to CLA4 and 5 (Fig. 2.4). • Skelm dyke samples SKE1 and 3 were sampled close to each other (Fig. 2.4), but SKE5 (Fig. 2.2) was sampled a few hundred meters away. SKE2 is not indicated on the map. The physical distance between SKE5 and SKE1 and 3 is reflected in their chemistry where SKE1 and 3 plot together, but SKE 2 and 5 plot in different groups (Figs. 5.1 and 5.3). This difference in chemistry may indicate the sampling of two different intrusives, and that SKE2 is from the same dyke as SKE5. • Similar situations as in the Skelm dyke can be observed in the Jeans dyke (Fig. 5.1 and 5.3). JEA1 and 3 were sampled in Tau Tona in the Pretorius Fault (Fig. 2.4) and JEA2 was sampled a considerable distance away in Mponeng (Fig. 2.9). This once again raises the possibility of the sampling of two different dykes. • Likewise, GEOR3 (Fig. 2.12) was sampled a considerable distance away from GEOR1 and 2 (Fig. 2.8) and has a completely different geochemistry (Figs 5.1 and 5.3). It should be noted, however that there are three Georgette dykes that cut each other, often hampering the accuracy of labelling. • According to the maps (Figs. 2.9 and 2.13), UNK2 and 3 seem likely to be from the Jeans dyke in Mponeng. UNK2 and 3 are chemically similar to JEA2 (Fig 5.3). This confirms that the three samples are from the same source. • The Soll dyke samples were taken close to each other (Fig. 2.3), but the chemically distinct SOL3 (Figs. 5.1 and 5.3) was taken in a fault cutting the Soll dyke. The possible local influence of the fault on the geochemistry of the dyke will be discussed in a later section. 92 • UNK1 (Fig. 2.2) seems to be a Peggy dyke sample according to the map, but not according to the geochemistry (Figs. 5.1, 5.2 and 5.3). • The UNK4 samples are known to be from an unnamed dyke in Mponeng (Fig. 2.10). • UNK6 and 7 are not indicated on the maps, but, according to their geochemistry, UNK7 could be a Peggy dyke sample, and UNK6 can be either from the Speckled dyke or the Georgette dyke (Figs. 5.1, 5.2 and 5.3). • Unknown 8 and 9 are possibly the same unnamed dyke as they are geochemically similar (Figs, 5.1, 5.2 and 5.3) and were sampled close together (Fig. 2.2). From a structural point of view the dykes can also be grouped according to strike. The fact that the positions and strikes are inferred from borehole data means it is often difficult to determine the exact strike of a dyke from a mine plan. In addition, dykes are not perfectly linear, resulting in a gentle oscillation of the strike. McCarthy et al. (1990) overcame the problem of oscillating strikes by dividing strike directions into 15° intervals. Table 5.1 shows the grouping of the dykes according to the three plots, as well as according to strike. The largest group in the Zr/P v P/Ti plot encompasses three strike groups which, for the sake of clarity, were placed in the table consecutively. Therefore, the strike intervals do not appear in exact numerical order. Unknown 1, 2, 3, 5, 6 and 7 and the Ventersdorp lava sample were excluded from the table as they cannot be linked to a specific strike and the links between the unknown samples and known dykes have already been discussed in the previous paragraph. Unknown 4, 8 and 9 were included as they are unnamed dykes and not samples with an unknown origin. When the grouping in the plots is compared to the strike grouping, a very good correlation is found between geochemistry and strike (Table 5.1). This may indicate that dykes with the same strike were possibly formed as a result of the same magmatic event, agreeing well with the conclusions drawn by McCarthy et al. (1990). However, when confronted with such a long period of time (Ventersdorp to Karoo), one should be careful of drawing such conclusions as later magmas may have intruded into weak areas created by earlier tectonic regimes. If the results regarding 93 dyke strikes in the ERPM mine from McCarthy et al., (1990) are applied to this study, the Lib and Jeans dyke can be classified as Ventersdorp dykes. Ilmenite diabase dykes as well as Loraine and Jeanette dykes may all have strikes varying between 105° and 165°. Dykes from this study that may be classified as ilmenite diabase dykes are, the Bank, CLA, Brazil, Ken, Amigo and Soll dykes. It is doubtful as to whether the 90 – 105° strike of the Peggy, Georgette and Speckled dykes classifies them as belonging to either the Loraine or Jeanette Formations of the Ventersdorp Supergroup. Table 5.1. Grouping of dyke samples according to the three plots and approximate strike derived from the locality maps in Chapter 2. Grouping Strike Grouping Grouping Grouping In according to according to according to according to Linton’s degrees(°) Strike TiO2 v Zr Zr/P v P/Ti (Fig. 4.1) (Fig. 4.2) discriminant plot (Fig. 4.3) 0 - 15° Kudu, Skelm, Skelm 1 and 3, Skelm 1 and 3, Unknown 4 Unknown 4 Unknown 4, Speckled, Peggy, FRI4. Unknown 8 and Georgette, Twin, 9, Peggy, Unknown 8 and Unknown 4, 8 and 60 – 75° Unknown 8 Kudu, CLA, 9, Peggy, Kudu, and 9 GEOR3, Soll, 9, FRI4, SOL3, SOL3, Skelm 5, Skelm 5 Kudu, Sill1, Skelm, JEA2 Peggy, Speckled, Twin Speckled, 90 – 105° Georgette, Georgette, Sill1, Georgette, Sill1, Speckled Twin Twin Sill, Friday, 15 – 30° PE, Little Tumi, Friday, PE, CLA, Soll Swannie Jeans, Jeans, Friday, PE, Swannie, Sill2, Sill2, Swannie, Amigo 1 and 2, Friday, Jeans, Skelm 2, Amigo 30 – 45° Lib, Jeans SKE2 PE, Sill2, Swannie, Skelm 2, Amigo 1 and 2 Bank, CLA, CLA, Ken, Brazil, Bank, Brazil, 150–165° Brazil, Ken, Bank, Brazil, Ken Soll, Bank, Amigo Ken, Amigo 3 Amigo, Soll 3 and 5 and 5 94 None of the dykes sampled in this study can be classified as epidiorites, as no dykes with 120° strike were sampled. McCarthy et al., (1990) did, however, not include any Bushveld, Pilanesberg or Karoo dykes in their study. This prevents any definite conclusions, regarding dyke ages based on strike, to be made at this stage in the study. The similarity in strike of the Jeans and Lib dykes is not reflected in their geochemistry. The Lib dyke never plots close to the Jeans dyke in any of the three plots used (Figs. 5.1, 5.2 and 5.3), but is chemically similar to the Little Tumi dyke. If the two dykes do share a common origin, it seems plausible that one of them was emplaced in a re-activated weak zone created by tectonism in the Witwatersrand rocks. 5.2 Classification According to Literature Data As was previously mentioned, the dykes in the Carletonville mines, as in the ERPM mine (McCarthy et al., 1990), are related to a number of igneous events. Although a cumulate effect can be found in dykes, resulting in the enrichment of mantle- compatible elements such as Cr and Ni, their chemistry should be similar to the lavas for which they acted as feeder channels (McCarthy et al., 1990). In an attempt to correlate the dykes with other igneous events, geochemical data from literature were collected for the following: • Ventersdorp Supergroup (Bowen, 1984a), • The Hekpoort lavas (Oberholzer, 1995) and the Bushy Bend lavas (Eriksson, 1994), • Tholeiites and basalts from the Marginal Zone and sills of the Bushveld Complex (Davies and Tredoux, 1985), • Marginal Rocks from the Eastern Bushveld Complex (Harmer and Sharpe, 1985), • The Losberg Complex (Danchin and Ferguson, 1970) and Bushveld-aged sills in the Vredefort Dome (Coetzee et al., 2006) and Fochville areas (Cawthorn et al., 1981). • Karoo dolerites (Erlank, 1984, Sweeney, et al., 1994 and Elburg and Goldberg, 2000). 95 Sufficient data for the Pilanesberg alkaline complex is unavailable, but these rocks should be easily recognisable from their geochemical characteristics, as alkali rocks usually contain very small amounts of compatible elements such as MgO, CaO, TiO2, Ni and Cr and unusually high concentrations of K2O, N2O, Zr, Y and REEs (Gerasimovsky, 1974). The geochemical data of all these igneous events, excluding Pilanesberg, were plotted on the same plots used for the mine data, namely TiO2 v Zr, Zr/P v P/Ti (Bowen, 1984a), and Linton’s discriminant plot (1992) (Fig. 5.4). As these plots employ only incompatible elements, they cannot be affected by the cumulate effect previously mentioned. In the TiO2 v Zr plot (Fig. 5.4A) it is possible to distinguish between Bushveld samples, high-Ti-Zr Karoo basalts and most of the Klipriviersberg rocks. As expected, the Losberg rocks (Danchin and Ferguson, 1970) and Vredefort tholeiites (Coetzee et al., 2006) group with the Bushveld rocks. The Lorraine-Edenville rocks form a separate small group within the Bushveld field. Very little separation is found between the Hekpoort lavas and the Bushveld rocks, as well as between the Lesotho formation basalts, the Bushy Bend lavas and the Alberton and Orkney Formation. In the Zr/P v P/Ti plot (Fig. 5.4B) very little separation is found between many of the groups, excluding the Makwassie Formation and the Goedgenoeg and Rietgat Formations. This plot is therefore not useful for determining to which igneous provinces the dykes are related. On Linton’s discriminant plot (1992) (Fig. 5.4C), essentially the same kind of separation is achieved as in the TiO2 v Zr plot (Fig. 5.4A). Using the literature data on the plots, fields can be derived that can in turn be used to classify the Carletonville mine samples. The Loraine-Edenville rocks are indistinguishable from the Bushveld rocks on these plots. In order to obtain a better separation between the two groups, principle component analysis (Le Maitre, 1968) was attempted. Principle component analysis defines a new set of orthogonal axes, or eigenvectors, which gives the maximum spread of the data in the direction of these vectors. Each eigenvector has an 96 associated eigenvalue which indicates the proportion of total variance represented by the vector (Table 5.2). (ppm) Figure 5.4. Data from various igneous provinces with possible relevance to the study area on, A: TiO2 (wt%) v Zr (ppm); B: Zr/P v P/Ti; C: disciminant plots. A and B is derived from (Bowen, 1984a) and C from Linton, 1992). Fn1=0.0172Y-0.06078Zr+20.8084TiO2- 11.4636 and Fn2=-0.24892Y+0.16017Zr-11.7088TiO2-0.07079. The number of vectors equals the number of variables, and each variable is assigned a coefficient (Table 5.3). The sum of the squares of these coefficients equals 1. The first eigenvector will contain the most information, with subsequent functions containing less (Le Maitre, 1968 and Rolllinson, 1993). Principle 97 (Wt%) component analysis was executed in GCDkit (Janousek et al., 2007). The best separation was obtained when Rb, Sr and SiO2 were used, although SiO2 only occurs in the third component, and therefore only Rb and Sr were plotted. Table 5.2. The importance of the components, including the proportion of variance and cumulative proportion of each component. All values were rounded to three decimals. Values were generated by GCDkit (Janousek et al., 2007). Component 1 Component 2 Component 3 Standard deviation 1 44.591 59.511 3.665 Proportion of 0.855 0.145 0.000 Variance Cumulative 0.855 0.999 1.000 Proportion Table 5.3. The coefficients of each variable used in principle component analysis, generated by GCDkit (Janousek et al., 2007). Component 1 Component 2 Component 3 SiO2 1.00 Rb -0.813 -0.583 Sr 0.583 -0.813 This plot, however, still does not separate the groups perfectly (Fig. 5.5). The Eastern BIC (Harmer and Sharpe, 1985) rocks and, to a certain extent, tholeiitic rocks (Davies and Tredoux, 1985) from the Marginal Zone of the BIC can be separated from the Loraine-Edenville rocks (Bowen, 1984a), but there is still significant overlap between the Loraine-Edenville rocks and the basaltic Bushveld rocks (Davies and Tredoux, 1985). It should also be mentioned that Rb and Sr are potentially not reliable, due to their mobility; this plot should therefore be used with circumspection where altered rocks, such as those encountered in this study, are concerned. 98 Figure 5.5. The separation of Bushveld (Harmer and Sharpe, 1985 and Davies and Tredoux, 1985) and Loraine-Edenville (Bowen, 1984a) rocks achieved by principle component analysis (Le Maitre, 1968). Chemical compositions from dykes from ERPM mine that have already been grouped according to the stratigraphy (McCarthy et al., 1990) were also plotted on the same systems for the purpose of comparison. When the geochemistry of the dykes from ERPM (McCarthy et al., 1990) are plotted on TiO2 v Zr (Fig. 4.6) the Bushveld 1, 2 and 3 type dykes, as well as the Loraine and Jeanette dykes plot in the Bushveld and Loraine-Edenville fields and are chemically indistinguishable. The Alberton Formation dykes plot in the Ventersdorp field, but the Westonaria and Orkney Formation dykes enlarge this field, causing it to overlap with the fields of the Hekpoort and Lesotho Formations. The ilmenite diabase, epidiorite and Bushveld 4 dykes form three separate groups that encroach into the Lebombo basalt field (Fig. 5.6). 99 (ppm) Figure 5.6. The geochemistry of dykes from ERPM compared to literature data fields derived from Fig. 5.4A. 1a: Alberton, Rietgat, Goedgenoeg, Orkney and Alanridge Formations (Ventersdorp Supergroup); 1c: Loraine-Edenville Formation (Ventersdorp Supergroup); 2: Lesotho Formation (Karoo); 3: Lebombo Basalts (Karoo); 4: Hekpoort Lavas (Transvaal Supergroup); 5: Bushy Bend Lavas (Transvaal Supergroup); 6: Bushveld Igneous Complex. On Linton’s discriminant plot (1992) (Fig. 5.7), the Alberton, Orkney and Westonaria Formation dykes all plot in the Ventersdorp field. The Bushveld 1, 2 and 3 and Loraine and Jeanette dykes form a tight group that mostly coincides with the Bushveld field. The ilmenite diabase and Bushveld 4 dykes once again form two separate groups that overlap with the Lebombo basalt field. The epidiorite dykes do not plot in any of the fields. When the mine samples are plotted on the TiO2 v Zr plot (Fig. 4.8), the Georgette, Twin and Speckled dykes as well as Unknown 6 are classified as Lorraine-Edenville rocks, with SIL1 plotting in the Bushveld field. The PE, Friday, Swannie, Skelm, Jeans, Soll, some Peggy samples and Unknown 1, 2 and 4. Apart from the Ventersdorp lava sample, Unknown 7, JEA 3, Unknown3 and two Peggy samples are grouped as Klipriviersberg rocks, with 3 of the other Peggy samples plotting in the Lebombo Basalt field and one as an Epidiorite. Unknown 3, 8 and 9 and SKE5 plot as Ventersdorp dykes. The CLA dyke is classified as a Type 4 Bushveld dyke, 100 (Wt%) but the Soll dyke and GEOR3 plot very close to this field, although SOL3 plots away from the other two Soll dyke samples. The Brazil, Ken and Amigo dykes form their own separate field, and the Lib and Little Tumi samples are separated from all other samples and fields as a result of their high Zr, but moderate TiO2 contents. The rest of the dyke samples all plot as Lebombo Basalts. Fn1 Figure 5. 7. The geochemistry of dykes from ERPM (McCarthy et al., 1990) compared to literature data fields derived from Fig. 4.4C. 1: Ventersdorp Supergroup; 2: Bushveld Igneous Complex; 3: Hekpoort Formation; 4: Bushy Bend Lavas; 5: Lesotho Formation Basalts; 6: Lebombo Basalts. 101 Fn2 (ppm) Figure 5.8. The geochemistry of dykes from the study area compared to all literature data fields on TiO2 (wt%) v Zr (ppm). 1: Ventersdorp Supergroup; 2: Bushveld Igneous Complex; 3: Hekpoort Formation; 4: Bushy Bend Lavas; 5: Lesotho Formation Basalts; 6: Lebombo Basalts. ERPM dyke data (McCarthy et al., 1990): “V-dorp”: Ventersdorp; “Lor-Ed”: Loraine-Edenville: “Bush”: Bushveld Type; “Epi”: Epidiorite; “Ilm-di”: Ilmenite-diabase. In Linton’s discriminant plot (Fig. 5.9), the Speckled dyke and SIL1 are classified as either Lorraine-Edenville or Bushveld rocks, with the Georgette and twin dykes and UNK6 sample plotting in the Bushveld/Loraine-Edenville dyke field. Unknown 8 and 9, the Ventersdorp lava sample, the Kudu dyke and Unknown 4 are classified as Ventersdorp rocks. The Friday, Amigo, Jeans, PE and Swannie dykes are classified as high Ti-Zr Karoo dolerites, along with Unknown 1 and 2 and the CLA dyke and Ken 1 and 4 are classified as Type 4 Bushveld dykes, and SOL 1 and 2 could be either Bushveld rocks or high-Ti-Zr Karoo dolerite. The Brazil, Ken, Amigo and Bank dykes plot in a field of their own, except for two Bank dyke samples and one Brazil dyke sample that plot in the Ilmenite-Diabase field. The Lib and Little Tumi Dykes once again plot away from the other fields. 102 (Wt%) Figure 5.9. The geochemistry of dykes from the study area compared to all literature data fields on Linton’s (1992) discriminant plot. 1: Ventersdorp Supergroup; 2: Bushveld Igneous Complex; 3: Hekpoort Formation; 4: Bushy Bend Lavas; 5: Lesotho Formation Basalts; 6: Lebombo Basalts. ERPM dyke data (McCarthy et al., 1990): “V-dorp”: Ventersdorp; “Lor- Ed”: Loraine-Edenville: “Bush”: Bushveld Type; “Epi”: Epidiorite; “Ilm-di”: Ilmenite- diabase. 5.3 Rare Earth Elements The Rare Earth Elements (REEs) all have very similar chemical and physical properties as they all form stable trivalent ions of similar size. The differences in chemical behaviour result from the small but steady decrease in size with increase in atomic number. These small differences cause REEs to become fractionated relative to each other (Rollinson, 1993). The light REEs (LREEs) are incompatible in the mantle and become concentrated in melts during partial melting. Consequently, the mantle becomes LREE depleted (White, 2007). For this reason rocks containing olivine and ortho- and clinopyroxene are more enriched in the 103 heavy REEs. However, the REEs are all incompatible in these minerals in basaltic and andesitic liquids, and are only slightly fractionated. Extreme depletion of the HREE could indicate the presence of garnet in the source. The middle REEs, Sm to Ho, are highly compatible in hornblende and even a moderate amount of this mineral can cause enrichment of these elements. Clinopyroxene has a similar effect on the MREEs although the effect is not so pronounced (Rollinson, 1993). The REEs are highly insoluble and immobile and REE patterns generally remain unchanged during low-grade metamorphism and weathering. As a result it is possible to derive the pre-metamorphic history of rocks from REE patterns (White, 2007). 5.3.1 Discussion of REE Patterns REE concentrations were normalised using the C1 chondrite values published by Anders and Grevesse (1989). REE with even atomic numbers are more stable, and therefore more abundant than REE with odd atomic numbers. This will result in a zigzag pattern when “raw” REE data is plotted according to increasing atomic number. It is for this reason that REE data has to be normalised. The REE concentrations of chondritic meteorites are the most popular choice for normalising values for two reasons. The first is that they are thought to be relatively unfractionated samples of the solar system, and normalising with chondrite values will not only eliminate the variation between odd and even atomic number elements, but will also allow the identification of any REE fractionation relative to chondritic meteorites. The second reason is that element concentrations can be determined by analysis rather than by estimation, as is the case with primitive mantle values (Rollinson, 1993). The dykes show a variety of REE patterns (Fig. 5.10). At a first glance it seems that the dykes can be divided into three groups based on their LREE content: The CLA, and Unkown 6 dykes and the SIL1 have either virtually no LREE enrichment or a slight depletion, others have intermediate LREE content (Ventersdorp lava and the Twin, Georgette, Amigo and Soll dykes), and a third group is highly enriched by LREEs (the Little Tumi and Lib dykes). The CLA and Unknown 6 dykes, as well as the sill have an almost chondritic pattern with the CLA dyke having a very slight 104 negative Eu anomaly. The implications of these flat patterns will be discussed subsequently. Figure 5.10. The REE patterns of the dykes. REE data normalised to C1 chondrite after Anders and Grevesse (1989). The two Georgette dyke samples have very similar patterns. Both show some enrichment in the LREEs, but GEOR2 has a very large positive Eu anomaly, reflecting the large amount of plagioclase in the sample (Fig. 3.10) (Rollinson, 1993). This Eu anomaly is not accompanied by unusually high CaO, Na2O or K2O concentrations, but all three element oxides were shown to have been mobile (Fig. 4.9 E, F and H) and may therefore have been removed from the sample. Eu, on the other hand is immobile (White, 2007) and would not have been removed. In numerous cases the REE patterns overlap to such an extent that the different samples become indistinguishable from one another. These include, PE1 and Unknown 2; Kudu, Unknown8 and 9(120A) and (120B); and, to a lesser extent, Ken 105 and Brazil. The most variation is found on the LREE side of the diagram with the least fractionation having taken place in the HREEs. 5.3.2 Classification of dykes according to REE data from literature REE data for the Ventersdorp Supergroup, specifically from the Alberton, Orkney and Loraine-Edenville formations (Marsh, et al., 1992), Bushveld-aged dykes and sills (Maier and Barnes, 1998) and both high and low Ti-Zr Karoo basalts (Elburg and Goldberg, 2000) were collected for the purpose of comparison with data from this study. The data were chondrite normalised using the values published by Anders and Grevesse (1989), plotted, and converted to fields that cover a range of REE data for each igneous province (Fig. 5.11), by tracing the highest and lowest values for each element. Dotted lines indicate the absence of element data. Figure 5.11. Fields derived from REE data for the Ventersdorp (Marsh et al., 1992), Bushveld (Maier and Barnes, 1998) and Karoo (Elburg and Goldberg, 2000), mafic rocks. The REE data from this study was then plotted over these fields in order to obtain a classification (Fig. 5.12). 106 Figure 5.12. Dyke REE data from this study compared to literature REE data. Karoo (Elburg and Goldberg, 2000), Ventersdorp (Marsh et al., 1992) and Bushveld (Maier and Barnes, 1998). When REE data from this study are compared to literature data (Fig. 5.11 and 5.12), CLA5, SIL1 and UNK6 are classified as Bushveld intrusives, confirming the classification of both the TiO2 v Zr and Linton discriminant plots. Although AMI1 is over all more enriched in REEs than CLA dyke, it has a pattern very similar to that of the Bushveld intrusives (Fig. 5.13). LAV1 plots in the Ventersdorp field and corresponds exactly to the Alberton Formation REE pattern (Fig. 5.12). The greatest variation in REE content in the different volcanic formations in the Ventersdorp Supergroup is found in the LREEs, with very little variation in HREEs. For the Allanridge, Goedgenoeg, Rietgat and Makwassie Formations only La, Ce and Nd data are available (Bowen, 1984a), but this is adequate to show that these rocks are considerably more LREE enriched than the Loraine-Edenville, Orkney and Alberton Formations. LAV1 shows a very slight negative Eu anomaly. The data from Marsh et al. (1992) does not include Gd, making it difficult to draw any conclusions about the presence of Eu anomalies from 107 their data. However, it is probably safe to assume that such an anomaly is present to a greater or lesser extent in all the mafic Ventersdorp rocks. When these criteria are used in the identification of Ventersdorp-age dykes, the Little Tumi, Lib, PE, Friday, Jeans, Swannie, Skelm, Kudu and Unknown 8 and 9 dykes, as well as the Unknown 1, 2, and 4 samples are classified as Ventersdorp dykes (Fig. 5.14). Figure 5. 13. REE patterns of the CLA dyke, SIL1 and UNK6 compared to Busveld REE data (Maier and Barnes, 1998). Figure 5.14. Dykes with similar (likely Ventersdorp) REE patterns compared to data from Marsh et al. (1992). 108 The Soll dyke’s REE pattern matches that of the low-Ti-Zr Karoo basalt, although SOL1 does not fit exactly into the low-Ti-Zr basalt field and SOL2 plots completely outside of this field (Fig. 5.15). None of the samples fit the high-Ti-Zr Karoo basalt field. 50 40 30 Average Low Ti/Zr 20 SOL1 10 SOL2 0 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Yb Lu Figure 5.15. REE patterns from the Soll dyke compared to the average REEs in low Ti/Zr Karoo basalt (Elburg and Goldberg, 2000). The remaining 10 samples seem to belong to three different groups (Fig. 5.16). The Brazil, Bank and Ken samples plot below the high-Ti-Zr Karoo Basalt field, but run almost perfectly parallel to it, and it seems likely that they may belong to this group. The Peggy dyke and its two matching Unknown samples, UNK 3 and 7 are difficult to place. Lenhard (1988) identified the Peggy dyke as being of Ventersdorp age, but its REE pattern is considerably steeper than that of the other Ventersdorp dykes. However, these samples do not fit in any of the other fields, and the other element plots (Figs. 5.8 and 5.9) classify the Peggy dyke as having a Ventersdorp, or close to Ventersdorp, chemical composition. It is therefore likely that Lenhard’s classification (1988) of the Peggy dyke is correct. The two Twin and Georgette dyke samples clearly fall in a group of their own. The only remaining mafic igneous event in the region, other than those which have been considered up until now, is the Pilanesberg Alkaline Complex and its related intrusives. Comparison of dyke samples with Pilanesberg geochemistry is hindered by the aparent lack of available data. In order to test the possibility of the Twin and Georgette dykes belonging to the Pilanesberg Complex, REE data from two syenite dykes from the Noqui Alkaline Province in the Democratic Republic of Congo (Makutu et al., 2004), as well as one syenite sample from the Palabora Complex in South Africa, NIM-S (Govindaraju, 1994), were used to derive an REE field for syenites (Fig. 5.17). Apart from the large positive Eu anomaly in GEOR2, the Twin 109 and Georgette dykes fit the syenite field perfectly. This classification is a “best-fit” for the data available and should not be seen as a definite classification. Figure 5.16. REE patterns of the, hitherto, unclassified dykes compared to the REE fields of Ventersdorp (Marsh et al., 1992) and Bushveld (Maier and Barnes, 1998) and Karoo rocks (Elburg and Goldberg, 2000). Figure 5. 17. A comparison of the unclassified dykes with an REE field derived from syenites from the Democratic Republic of Congo (Makutu et al., 2004) and the Palabora Complex, South Africa (Govindaraju, 1994). 110 5.4 Discussion Differences in geochemistry between dykes of the same age, or even samples from the same dyke, could be the result of differences in grade of metamorphism and alteration conditions between dykes or in different locations along one dyke, an argument which is strengthened by the variations in mineralogy discussed in Chapter 3. In order to understand how such differences in alteration could have come about, one needs to take a closer look at fluid flow in the Witwatersrand Supergroup. Various types of fluids that contributed to metamorphism and alteration were present during the diagenesis and metamorphism of the Witwatersrand Supergroup. These are: connate waters that were trapped in pore spaces and bound in clay minerals, and were expelled during compaction and diagenesis; metamorphic fluids produced when hydrous minerals are broken down at higher temperatures and pressures; retrograde fluids that are present after peak metamorphism; meteoric or surface waters that invade the basin along permeable horizons; and magmatic fluids from the intrusives (Phillips et al., 1990). Connate water from the original Witwatersrand sediments can be disregarded when one considers the influence of fluids on the dykes, as, during compaction, this water would have moved to the margin of the basin towards areas of lower pressure (Phillips et al., 1990). The movement of metamorphic fluid is controlled by deformation zones, and especially by microscopic and even sub-microscopic dislocations along grain boundaries. Meteoric waters can invade the Witwatersrand Basin at any time, especially in areas where it crops out (Phillips et al., 1990). Meteoric water influx and movement occurs along permeable horizons and may be channelled parallel to impermeable lithologies. Dykes that extend all the way to the surface can therefore act as conduits for meteoric water to enter the lower parts of the basin. The role of retrograde fluids is negligible, as mineralogical studies indicate that only minimal retrograde metamorphism has occurred both in the Witwatersrand rocks themselves and in the intrusives (Phillips et al., 1990). The extent of the effect of magmatic fluids is debatable. The majority of the magmas that intruded into the Witwatersrand Supergroup were mafic, and could therefore not have had high water contents. As a result, the influence of magmatic fluids was very localised and concentrated around the intrusives (Phillips et al., 1990). For the 111 magmatic water of an intrusive to have any effect on an older intrusive, the two must be situated very close together, or even cut each other. Magmatic fluids could therefore be responsible for the alteration of a small part of a dyke, but leave most of it intact (Phillips et al., 1990). According to Onstott et al., (2006) the fracture water in the Witwatersrand Basin represents a mixture of paleo-meteoric water and 2.0 – 2.3 Ga old hydrothermal fluid. The hydrothermal fluid was highly saline and had temperatures of 250 - 300°C. The meteoric water had a low salinity, high CO2 content, and was approximately 10k – >1.5 Ma old. Mixing of these two components has probably been occurring for at least the past 100 Ma (Onstott et al., 2006). The misclassification of some dyke samples as other dykes and the reasons there for have been discussed. However, a simple misnaming during logging or sampling cannot always account for scatter. While the chemical differences between samples from the “same” dyke that were taken a considerable distance apart could be explained by them being, in reality, from more than one intrusive, it still does not explain cases such as the Ken and CLA dykes where samples were taken close to one another. For that, one needs to look at possible element mobility. Even though the HFSEs, that include Ti, Zr, Y and the REEs, are generally regarded as being mobile, it has been found in numerous studies on the weathering and metasomatism of igneous rocks that this is not always the case. One such a study was conducted on weakly altered to completely kaolinitised andesites and dacites from the Erenler Dağı Volcanics in Konya, Turkey (Karakaya, 2009). These rocks were weakly to highly altered by hydrothermal fluids and then weathered by surface conditions. It was found that Zr and Y remain immobile in weakly to moderately altered rocks, but that their concentrations decreased significantly in the kaolinitised rocks. The Light and Middle REE contents were found to decrease slightly with weak to moderate alteration, but would increase in the completely weathered rock, but in general REE patterns of moderately altered rocks were sub-parallel to that of the parent rock, but with a slight overall depletion. Experimental and field data has shown that HFSE can occur in a wide range of temperature and pressure conditions. Zr and Ti solubility is largely enhanced with increasing P and T (Jiang et al., 2005). High temperature alteration at the Strange 112 Lake peralkaline complex of North-Eastern Canada resulted in a depletion of HFSE and HREE, while these elements were significantly enriched in areas of low temperature alteration (Salvi and Williams-Jones, 1996). Both very high and very low pH conditions can result in the mobilisation of Ti and Zr. Furthermore, the presence of F- and OH- can result in the formation of Zr-F-OH complexes that lead to the solubility of Zr over much wider pH ranges (Jiang et al., 2005). Onstott et al. (2006) reported very low (µM) F concentrations in the Witwatersrand fracture water, but the F concentrations may have been significantly higher before large-scale mixing with meteoric water occured. In extreme pH conditions, both Ti and Zr can become mobile in low temperature fluids (270-300°C) (Jiang et al., 2005). The mobility of HFSEs in such high pH environments can likely be due to hydroxy and carbonatohydroxo complexing. Sulphate can also act as a complexing agent, but the only data available are from high temperature and pressure environments and more experimental work is needed to test the significance of the influence of sulphate on HFSE mobility (Jiang et al., 2005). The exact role of complexing ions and their effect on the intrusives in the Witwatersrand Supergroup is difficult to assess. The Witwatersrand Supergroup is made up of a number of different lithologies, and the geochemistry and mineralogy of each will influence the chemistry of the fluids in contact with them to a certain extent. This, in turn, could result in different effects on the intrusives. According to Phillips et al. (1990), metamorphic fluids in general had temperatures in excess of 200°C and a neutral to moderately acidic pH. They state that the absence of evaporate minerals mean that chloride and sulphate were not significant, but that fluid inclusion studies confirm the presence of CO2 and CH4 (Phillips et al., 1990). However, one should not exclude the possibility that the highly saline, ancient hydrothermal fluids (Onstott et al., 2006) may have had some effect on at least the older dykes before being diluted gradually by meteoric water. The absence of evaporate minerals may possibly be attributed to the later influx of the meteoric water. Whether more extreme pH conditions than those reported by Phillips et al. (1990) could have been present on small scale would require a very detailed investigation of the Witwatersrand rocks which is beyond the scope of this study. The relatively small differences in geochemistry in e.g. the Peggy dyke are possibly the result of element mobility, as the origin of these samples is reasonably certain 113 and the scatter is more than what one would expect for incompatible elements in a single mafic intrusive, especially compared to other intrusives such as the Friday, Bank and Brazil dykes. Whether large differences in geochemistry over large distances, such as those found in the Jeans dyke, are the result of element mobility or of the sampling of two different intrusives will only become clear if more sampling is done at closer distances along the dyke. The anomalous geochemistry of CLA9 cannot be attributed to either element mobility or distance as all other CLA dyke samples are chemically similar to each other and CLA9 was taken from the same section of drill core as CLA4 and 5. It is, however from the chill zone of the dyke and the most plausible explanation for its anomalous geochemistry would be contamination by the country rock. No other intrusive cuts or comes close enough to the CLA dyke in this particular location for contamination by another dyke to be considered a possibility (Fig 2.4). There is no clear reason why the chemistry of KEN1 and 4 are similar to that of the CLA dyke and further sampling is required in for this issue to be resolved. The Soll dyke offers proof for the mobilisation of HFSEs by fluids. SOL3 was sampled in a fault, which would act as a conduit for fluids, and is slightly depleted in TiO2, Zr and Y relative to SOL1 and 2. If these elements were mobile it becomes increasingly possible that the REEs could have been mobile as well. As REE mobility tends to result in a general depletion of REEs while preserving the inherent REE pattern (Karakaya, 2009), this should not affect the allocation of dykes to igneous provinces, although it would influence the allocation of Ventersdorp-age dykes to the different formations within the Supergroup. A small possibility of HREE enrichment exists (Salvi and Williams-Jones, 1996), but as no other HFSEs seem to be significantly enriched, the importance of HREE enrichment is minimal. The well constrained geochemistry of the Brazil, Bank and (to a somewhat lesser extent) Ken dykes, indicates a lesser presence of fluids. The fresh appearance of the Brazil dyke confirms this. This is an indication that these dykes are the youngest of the intrusives. Although Onstott et al. (2006) state that the dykes with a north-south strike, of which the Bank dyke is one, belong to the Pilanesberg Complex, they do not provide reasons for this statement. 114 5.5 Conclusion The absence of data concerning the strike of dykes other than those of the epidiorites, ilmenite-diabases and early Ventersdorp aged dykes hinder the classification of dykes by the use of strike. The fact that dykes with different origins may have the same strike, due to the intrusion of younger magmas into older weak zones, is an additional problem. The use of the HFSE Ti, Zr and Y, and the REEs was moderately successful in firstly grouping the dykes among themselves, and secondly in grouping them with other igneous events. Dykes from the Ventersdorp Supergroup (Peggy, Unknown 8 and 9, Kudu and Skelm dykes, and the Jeans dyke in Mponeng, Bushveld Igneous Complex (Speckled and CLA dykes and the sill) and Karoo Igneous Province (Brazil, Bank, Ken and possibly Soll dykes) are present, with the possibility of the Twin and Georgette dykes belonging to the Pilanesberg Complex. Some classifications remain inconclusive, e.g. the Friday and Swannie dykes, that are classified as Ventersdorp dykes in the REE plots, but as high-Ti-Zr Karoo basalts in the other HFSE plots. The variable alteration of the dykes is, in some cases, reflected in their geochemistry, and proof was found that the HFSEs are not entirely immobile. This mobility makes the classification of the dykes more difficult as it causes scatter between samples from the same dyke, and less adherence to the geochemistry of their allocated igneous provinces. The extreme variation in geochemistry between some samples from the same dyke that were taken a considerable distance apart warrants sampling in between in order to determine if the samples are, in reality, from the same dyke. 115 Chapter 6: The Engineering Aspects of the Dykes 6.1 Introduction The preceding chapters have, to a greater extent, been purely academic. In practise, the presence of a dyke poses problems during mining. Not only do they impede the rate of mining due to displacement of the ore body, but larger dykes require haulages traversing them to be given special treatment, as they are susceptible to rock bursts (Brink, 1979). According to Gill et al. (1993) “a rockburst is a sudden rock failure characterised by the breaking up and expulsion of rock from its surroundings, accompanied by a violent release of energy”. Gill et al. (1993) defined two broad classes of rock bursts: Type I, resulting from fault-slip events, and Type II, resulting from the failure of the rock mass itself, which includes strain bursts and pillar bursts (Gill et al., 1993). Most of the large seismic events in the mines are recorded close to geological structures. Of these structures, the dykes are considered to be the most hazardous (Chichowicz, 1997). These events are completely random and are very seldom related to blasting (pers. comm. H. Moller, 2009). 6.2 The Dangers Posed by Dykes The reasons for seismic activity in these areas are related to stress changes in the area, rock properties (particularly rock strength), and the challenges posed by mining in very hard rock such as the dykes (Table 6.1). The deep mine environment is a high stress environment, and the excavations made during mining introduce additional, tensional stresses. In some cases the stresses are not transferred well across major geological structures, causing amplification of stress between the structure and the face. This, in turn leads to a high probability of seismic activity. Table 6.1. The compressional strength of the three most common lithologies in Tau Tona and Mponeng (supplied by H. Moller, AngloGold Ashanti). Strength (uni-axial Material compressive tests) Dyke 300MPa (or higher) Quartzite 200MPa Shale 150MPa 116 Of all the many different properties of country rock and dykes which can result in different strain rates in the same time window during mining, different rock strengths are the most important (pers. comm. H. Moller, 2009). When a dyke and adjacent country rock are subjected to the same change in stress, they behave differently and so doing, create a mechanism to shear free from each other, resulting in a Type I rock burst (Gill et al., 1993). The nature of the contact between country rock and dyke also determines the size of the seismic event will take place. Two very different types of contacts can both result in seismic events: A welded contact will be broken when stress applied exceeds its strength, and a soft contact with a wavy form that will not allow free movement, will require rock material to be sheared off before movement can take place. During the mining process, the highest stress environment is found immediately ahead of the advancing face. Under normal circumstances, this will induce fracturing in the rock which aids in the redistribution of stresses ahead of the mining face. Most dykes are very hard which means that they will not fracture easily. This results in the build-up of extremely high stress ahead of the mining face, up to the point where the rock fails. The freedom offered by the nearby excavation causes the rock to buckle and burst into the working area (pers. comm. H. Moller, 2009). Jeffery (1975) found that the thickness of the dyke is a contributing factor, and that dykes with thicknesses of ±15m or more are more likely to cause rockbursts than smaller dykes. The intrusion of dykes altered areas in the surrounding Witwatersrand quartzite and shales by means of contact metamorphism, resulting in a hardened, brittle rock. This rock is blocky and makes it difficult to support the roof of the excavation. The major concern in such an area is fall of ground induced by gravity and seismic activity. Similar blocky conditions are created in dykes as they respond to the stress changes induced by mining. These blocks are usually much larger than in the case of metamorphosed country rock and fall of ground occurrences are generally much more severe (pers. comm. H. Moller, 2009). 6.3 A Case Study The physical properties of rocks are affected by their degree of alteration, and therefore by their mineralogy and chemistry. A study by Moon and Jayawardane (2004) investigated the relationship between chemistry, mineralogy and 117 geomechanical characteristics very comprehensively, using rocks from an abandoned basalt quarry at Karamu, near Hamilton, New Zealand. The quarry provided a complete weathering sequence from fresh to completely weathered basalt and the authors identified five weathering zones: fresh, slightly weathered, moderately weathered, highly weathered and completely weathered. At an early stage of weathering a significant decrease in CaO, MgO, FeO, Na2O, K2O, Rb and Sr took place, accompanied by a significant relative increase in Fe2O3 and Zr. Very little textural change took place between fresh and moderately weathered basalt, and indeed very little mineralogical change occurred between fresh and slightly altered rocks, with the formation of clay minerals, such as smectite, kaolinite and illite, only becoming significant in moderately weathered rocks. However, the greatest decrease in dry density and increase in porosity, and the accompanying decrease in strength, occurred between fresh and slightly weathered rock. The authors attributed this dramatic loss of intact strength to microfractures that develop due to cation substitution. The loss of Ca2+, Fe2+, and Mg2+ and their substitution by the significantly smaller H+ and Al3+ cations creates imbalances in the crystal lattices, which in turn leads to the formation of microfractures. Surface weathered rocks can therefore lose strength before any mineralogical changes become apparent (Moon and Jayawardane, 2004). 6.4 Dykes from this Study The minerals formed in the dykes because of the greenschist metamorphic environment of the Witwatersrand basin are considerably different from those formed in the surface weathering environment studied by Moon and Jayawardane (2004). However, the chloritisation and saussuritisation of primary mafic minerals will result in the same style of weakening of the rocks by reducing the cohesion between primary minerals as secondary minerals form along crystal boundaries (Pusch, 1995). Dykes that have lost a significant amount of strength in fact are less problematic than those that appear to be perfectly intact. Detailed mineralogy has been discussed in Chapter 2 and will not be repeated here, except to remind the reader that the dykes can be broadly divided into three groups based on their degree of alteration: completely altered - where all primary minerals 118 have been altered, mostly altered but still containing some primary minerals (specifically pyroxenes), and largely unaltered. The Brazil dyke is the only dyke in this study to belong to the last group. The only significant alteration in this dyke is found close to veins and fractures and very few of these are present. During sample preparation it was found that the rock is very hard compared to the other dykes and does not break easily. However, if the findings of Moon and Jayawardane (2004) are taken into account, the very slight alteration observed in some of the Brazil dyke samples would already have reduced the strength of the rock significantly. A chemical trend similar to that found by Moon and Jayawardane (2004) is seen in the Brazil dyke, especially regarding Ca and Sr concentrations. These elements are significantly depleted in the two slightly weathered samples (BRA2 and 3) compared to the fresh (BRA 4) sample. Fe2O3 shows a slight enrichment in these samples (Fig. 6.1). The strength of the Brazil dyke would therefore be variable. Figure 6.1. Comparison of Fe2O3, CaO and Sr concentrations in BRA2, 3 and 4 indicating a depletion in CaO and Sr, and a slight apparent enrichment in Fe2O3 in BRA2 and 3 relative to BRA4. Fe2O3 and CaO concentrations are given in wt% and Sr is given in ppm) Dykes in the second group include the CLA, Ken and Amigo dyke. As the primary pyroxenes occur either as small scattered remains or as clusters, it is unlikely that they will affect rock strength significantly, and these rocks will likely have properties similar to that of the completely altered dykes. All the other dykes in the study are completely weathered. 119 The Jeans dyke should be mentioned in particular as it contains large patches of calcite. Such a rock may react differently under the stresses than one that consists dominantly of chlorite and quartz. Both minerals have low hardness and excellent cleavage – the result of weak atomic cohesion (Wenk and Bulakh, 2004) – but calcite is more brittle than chlorite. The calcite crystals are also considerably larger than the chlorite crystals with larger cleavage planes. This nature of the calcite crystals would likely make the rock more susceptible to Griffith-type failure, depending on the orientation of the crystals. Griffith cracks can form from microscopic or even sub-microscopic defects under tensional stress. When such stress exists for a prolonged period of time, these microscopic cracks can grow until they intersect lower order discontinuities (i.e. larger cracks and joints), resulting in a significant reduction of rock strength (Pusch, 1995). The time required for significant Griffith cracks to form is probably much longer than that taken to negotiate dykes during mining and they would likely not reduce the strength of the dyke to an extent where the risk of a rock burst is diminished. It could, however, become significant in the already excavated dyke and may contribute to the formation of the blocky conditions previously mentioned, creating stability problems. The extent of the contribution of calcite towards instability depends on the distribution of calcite in the rock. This would only be possible to assess if more, closely spaced samples of the dyke are examined. During mining operations, the problem of rock bursts is overcome partly by the preconditioning technique. This involves the drilling of a single row of additional, longer holes that are blasted in conjunction with the usual blast holes. This serves to weaken the rock ahead of the face, decreasing the risk of rock bursts (pers. comm. H. Moller, 2009). The parts of the Jeans dyke containing calcite should respond very well to preconditioning, and even normal blasting should contribute to the weakening of the rock, as rock around blasted areas is damaged to several tens of centimetres from the blast (Pusch, 1995). Another important feature of the dykes, from an engineering perspective, is veining. Veins are filled with a variety of minerals, namely quartz, epidote, calcite, mixtures of quartz and chlorite and, less commonly, sulphides and iron oxides/hydroxides (see Chapter 3). These veins are classified as 4th order discontinuities (Pusch, 1995) and are responsible for the bulk hydraulic conductivity of the rock and provided 120 pathways for hydrothermal fluids. These discontinuities can expand and soften, creating unstable wedges or block sliding. These joints would generally contribute significantly to the weakening of the rock, but pure quartz veins can be welded and behave very much the same as unfractured rock (Pusch, 1995). The Twin dyke is the only case in this study where a pure quartz vein was found. In all other instances quartz occurred in combination with chlorite, calcite, epidote or sulphides. Veins in the Skelm dyke consist almost exclusively of epidote, which has also been fractured. The orientation of the joints and veins will, however, be a major factor in the weakening of the rock, regardless of their composition. 6.5 Concluding Remark It has been shown in this study that dyke alteration is heterogeneous and it would be dangerous to assign properties to dykes on the basis of only a few samples. Gill et al. (1993) confirmed that using data from areas in which the geology is considered comparable to the area in question can lead to the inaccurate evaluation of the mechanical properties of the rock mass. It is therefore essential to assess each case on its own merit. Dyke – country rock contacts have not been included in this study, but since the dykes themselves have been subjected to a variety of conditions, resulting in the varying mineralogy, it should be safe to assume that the dyke contacts are also not the same everywhere, especially since the dykes passed through more than one lithology during intrusion. 121 Chapter 7: Conclusions and Recommendations 7.1 Conclusion The mineralogical investigation of the dykes in Tau Tona and Mponeng revealed that most dykes, with the exception of the Brazil dyke, are altered. The most abundant minerals are chlorite, actinolite, epidote, quartz and albitised and/or saussuritised feldspar, corresponding to a greenschist metamorphic facies mineral composition. In the Jeans dyke feldspars were converted to calcite. The most common vein minerals are quartz, calcite, epidote and chlorite, with sulphides and Fe oxides occurring occasionally. Veins usually consist of a combination of these minerals, but veins in the Skelm dyke consist almost exclusively of epidote. Often, dyke alteration is very heterogeneous with different samples from the same dyke containing different minerals, e.g. primary pyroxene may be present in some samples, but not in others. This heterogeneity is similar to that reported by Winter, (1995) for the Alberton Formation and is likely due to the different lithologies traversed by the dykes, resulting in differences in fluid flow. Similar heterogeneity is found in the chemistry of the dykes, notably in the more mobile elements such as Ca, Na, Mg, Rb and Sr, resulting in a wide range of element concentrations in some of the dykes. Evidence was also found for the mobility of traditionally immobile elements such as Ti, Zr and Y. In the Peggy dyke, the scatter produced on plots employing these elements can only be explained by their mobility, as Ti, Zr and Y are mantle incompatible and not greatly affected by the primary magmatic processes in basaltic magmas. Further evidence for their mobility is found in the Soll dyke, where a sample taken from a fault was significantly depleted in these elements. It is uncertain whether large differences in chemistry between samples from the same dyke, such as those found in the Jeans and Skelm dyke, are the result of element mobility or of the sampling of different dykes, and more, closely spaced sampling is required in order to resolve this issue. A different type of heterogeneity was found where both chill- and central zones of dykes were sampled from the same drill core. It was found that the mantle compatible elements Cr and Ni are significantly enriched in the chill zones. Exceptions are found in the Speckled dyke and in Unknown 8 and 9, where the central zones are enriched in Cr and Ni. This may be the result of flow 122 differentiation during dyke intrusion, which resulted in the migration of first-formed, chill zone crystals to the centre of the dyke, but more detailed sampling of the dykes in question is required in order to determine if this enrichment of the central zone is present everywhere these dykes. Bowen’s (1984a) TiO2 v Zr and Zr/P v P/Ti plots as well as Linton’s (1992) discriminant plot proved useful in dividing the dykes into groups according to chemistry. These groups correlated reasonably well with groups formed by dykes with similar strike, which may indicate that dykes with similar strike may share a common origin. However, dykes with different ages and origins may have the same strike due to the intrusion of younger dykes into older weak zones and conclusions regarding the relationship between strike and origin cannot be made until more detailed work has been done. The Lib and Little Tumi dykes that are chemically similar to each other, but different from all the other dykes in the study, do not strike in the same direction, and either one may have intruded into a weak zone created by earlier tectonic events. Geochemical data for igneous rocks from the Ventersdorp Supergroup, Transvaal Supergroup, Bushveld Igneous Complex and Karoo Supergroup, as well as for dykes from the ERPM mine were collected and plotted on the same three plots employed for the geochemical separation of the dykes from this study. However, the Zr/P v P/Ti plot was unable to separate the data from different igneous provinces in a satisfactory way, and was discarded. The Loraine-Edenville rocks proved to be chemically indistinguishable from most of the Bushveld rocks even when principal component analysis was attempted, with the Loraine-Edenville rocks forming a group of their own within the Bushveld field. Over all, the classifications in the TiO2 v Zr and discriminant plots correlate well. The Georgette, Twin and Speckled dykes as well as Unknown 6 and SIL1 are classified as Loraine-Edenville/Bushveld dykes. The CLA dyke is classified as a Bushveld Type 4 dyke. The PE, Friday, Swannie, Skelm, Jeans, Soll, and Unknown 1, 2 and 4 plot as Lebombo basalts. The Brazil, Ken, Amigo and Bank dykes plot in a field of their own, and the Little Tumi and Lib dykes always plot away from the other samples in their own group. Unknown 3, 7, 8 and 9, JEA3, and two Peggy samples 123 are grouped as Ventersdorp dykes, although the Peggy samples do show some scatter. This is likely due to the mobility of the elements used for classification. 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Pearson. 248 pp. 133 Appendix A: Sampling Localities Table A - 1. Sample names and localities Sample Dyke Name Mine Borehole Depth AMI1 Amigo Tau Tona DPH 3887 AMI2 Amigo Tau Tona DPH 3887 AMI3 Amigo Tau Tona LIB TT 2002 315 AMI5 Amigo Tau Tona DPH 3923 391.8 BAN1 Bank Tau Tona DPH 3885 BAN3 Bank (chill) Tau Tona DPH 3885 28.4 BAN4 Bank Tau Tona DPH 3880 67.7 BAN5 Bank (chill) Tau Tona DPH 3880 41 BAN6 Bank (chill) Tau Tona DPH 3880 71.1 BAN7 Bank Tau Tona DPH 3885 35.2 BAN8 Bank (chill) Tau Tona DPH 3885 52.7 BRA1 Brazil (chill) Tau Tona DPH 3881 184.3 BRA2 Brazil Tau Tona DPH 3881 187.2 BRA3 Brazil (chill) Tau Tona DPH 3884 195.65 BRA4 Brazil Tau Tona DPH 3884 195 BRA5 Brazil (chill) Tau Tona DPH 3881 186.75 BRA6 Brazil (chill) Tau Tona DPH 3884 192.37 Underground BRA7 Brazil (chill) Tau Tona Sampling 104 Underground BRA8 Brazil Tau Tona Sampling 104 CLA1 CLA (chill) Tau Tona DPH 3883 196.9 CLA2 CLA (chill) Tau Tona DPH 3883 162 CLA3 CLA Tau Tona DPH 3883 177.7 CLA4 CLA Tau Tona DPH 3884 90.36 CLA5 CLA Tau Tona DPH 3884 97.9 CLA6 CLA (chill) Tau Tona DPH 3882 85.45 CLA7 CLA Tau Tona DPH 3882 76.55 CLA8 CLA Tau Tona DPH 3884 87.77 CLA9 CLA (chill) Tau Tona DPH 3884 83.33 FRI1 Friday Tau Tona DPH 3887 230 FRI2 Friday Tau Tona DPH 3887 234 FRI3 Friday Tau Tona LIB TT 2002 210 FRI4 Friday Tau Tona LIB 120 730 FRI5 Friday Tau Tona DPH 3887 FRI6 Friday (chill) Tau Tona DPH 3887 FRI7 Friday Tau Tona DPH 3923 203.82 FRI8 Friday (chill) Tau Tona DPH 3923 193.85 FRI9 Friday (chill) Tau Tona DPH 3923 206.5 GEOR1 Georgette Mponeng DBH 1890 11 GEOR2 Georgette Mponeng DBH 1890 48 134 GEOR3 Georgette Mponeng GBH 2928 110.55 JEA1 Jeans Tau Tona LIB TT 2002 505 JEA2 Jeans Mponeng GBH 2919 27 JEA3 Jeans Tau Tona LIB TT 2002 KEN1 Ken Tau Tona DPH 3883 200.45 KEN2 Ken Tau Tona DPH 3884 223.65 KEN3 Ken Tau Tona DPH 3884 223.35 KEN4 Ken Tau Tona DPH 3883 203.9 Underground 104 KEN5 Ken Tau Tona sampling level Underground 104 KEN6 Ken Tau Tona sampling level Underground 104 KEN7 Ken Tau Tona sampling level KUD1 Kudu Tau Tona LIB TT 2002 870 LAV1 Lava sample Mponeng DBH 1884 16 LIB1 LIB Mponeng GBH 2919 33.8 LIT1 Little Tumi Mponeng GBH 2919 103.5 PE1 PE Mponeng GBH 2922 103.5 PE2 PE (chill) Mponeng GBH 2922 31 PEG1 Peggy Tau Tona UD36 2871 PEG2 Peggy (Maggie) Tau Tona DPH 3964A PEG3 Peggy (Chill zone) Tau Tona DPH 3964A 2909 PEG4 Peggy Tau Tona UD 36 2623 PEG5 Peggy Mponeng DBH 1884 70 PEG6 Peggy Mponeng DBH 1884 21 SIL1 Sill Tau Tona LIC 118 47 SIL2 Sill Tau Tona LIB 120 282 SKE1 Skelm Tau Tona LIB TT 2002 SKE2 Skelm Tau Tona DPH 3905 90 SKE3 Skelm Tau Tona LIB TT 2002 420 SKE5 Skelm Tau Tona LIC 118 850 SOL1 Soll Tau Tona DPH3935 SOL2 Soll Tau Tona DPH 3935 242 SOL3 Soll Tau Tona DPH 3961 115 SPE1 Speckled Tau Tona DPH 3867 157.5 SPE2 Speckled Tau Tona DPH3867 161.3 SPE3 Speckled (chill) Tau Tona GBH 3997 SPE4 Speckled Tau Tona GBH 3997 88 SPE5 Speckled (chill) Tau Tona GBH 3997 90 SWA1 Swannie (chill) Tau Tona GBH 3994A 63 SWA2 Swannie Tau Tona GBH 3994A 50 SWA3 Swannie (chill) Tau Tona GBH 3994A 44 TWI1 Twin Tau Tona DPH 3924 288.4 TWI2 Twin Tau Tona DPH 3924 287.9 135 UNK1 Unknown1 Tau Tona LIC 118 130 UNK2 Unknown2 Mponeng GBH 2919 63 UNK3 Unknown3 Mponeng GBH 2939 1.8 UNK4A Unknown4 Mponeng GBH 2918 0.5 UNK4B Unknown4 (chill) Mponeng GBH 2918 1.3 UNK6 Unknown6 Tau Tona/Mponeng GBH 3953 74.1 UNK7 Unknown7 Tau Tona/Mponeng DPH 3964A 204.64 120A1 LIB120(1) chill Tau Tona LIB120 594 120A2 LIB120(1)mid Tau Tona LIB120 600 120A3 LIB120(1) chill Tau Tona LIB120 606 120B1 LIB120(2) chill Tau Tona LIB120SE2 348 120B2 LIB120(2) mid Tau Tona LIB120SE2 351 120B3 LIB120(2) chill Tau Tona LIB120SE2 356 136 Appendix B: Mineralogy X-ray Diffraction Scans 137 138 139 140 141 142 143 144 145 UNK4 146 Table B.1. Approximate modal mineral quantities. PEG2 PEG4 GEOR1 SKE1 SOL2 SIL1 JEA1 >40% Albite Albite Actinolite Illite- Quartz Chlorite Mont. Chlorite 20 – Actinolite Actinolite Chlorite Albite Quartz 40% Chlorite 10 – Illite- Epidote Albite 20% Mont. Quartz Chlorite Biotite Actinolite 5 – 10% Epidote Illite- Quartz Quartz Opaque Calcite Chlorite Mont. Opaque minerals Epidote Epidote minerals <5% Sphene Opaque Opaque Opaque Opaque minerals minerals minerals minerals Sphene Sphene Sphene 147 Table B.1 (Continued). FRI1 LIB1 LIT1 PE1 LAV1 AMI1 BAN4 >40 Chlorite Illite- Actinolite Quartz % Mont. Chlorite 20 – Chlorite Albite Chlorite Albite Albite 40% Albite Quartz 10 – Quartz Quartz Quartz Actinolit Chlorite Chlorite 20% Actinolit e Actinolite e Chlorite 5 – Prehnit Opaque Epidote Hydrobiotit Hydrobiotit 10% e mineral e e Illite- Epidote s Mont. Opaque mineral s <5% Sphene Opaque Opaque Opaque Opaque minerals minerals mineral minerals s Table B.1 (Continued). SPE2 TWI1 TWI2 BRA1+2 CLA3 CLA5 KEN1 >40% Quartz Quartz Quartz Quartz Quartz Chlorite Chlorite Chlorite 20 – Albite Quartz 40% Chlorite 10 – Chlorite Illite- Chlorite Albite 20% Illite- Mont. Pigeonite Mont. Quartz 5 – Chlorite Actinolite Epidote Sphene 10% <5% Opaque Opaque Opaque Opaque Sphene Opaque minerals minerals minerals minerals minerals 148 Table B.1 (Continued). KEN4 SWA2 UNK3 UNK4 UNK6 UNK7 UNK8 UNK9 >40% Quartz Chlorite Chlorite Albite Albite Chlorite Quartz 20 – Quartz Quartz Albite Illite- Actinolite Quartz 40% Albite Chlorite Mont. Chlorite Quartz 10 – Chlorite Chlorite Quartz Albite 20% Actinolit Illite- e Mont. 5 – Illite- Illite- Epidote Chlorite Chalco-pyrite 10% Mont. Mont. Opaque minerals <5% Opaque Opaque Sphene Opaque Sphene Sphene Opaque minerals minerals minerals minerals Sphene CIPW Norms Table B - 2. CIPW norms PEG1 PEG2 PEG3 PEG4 PEG5 PEG6 Quartz 2.60 0.57 0.10 1.81 3.24 1.59 Corundum 0.00 0.00 0.00 0.00 0.00 0.00 Orthoclase 8.33 3.61 7.15 11.17 8.45 8.81 Albite 22.85 43.24 35.37 32.07 40.87 41.21 Anorthite 12.64 8.28 14.34 9.90 9.40 12.35 Diopside 26.97 17.08 20.55 17.09 11.95 14.99 Hypersthene 20.34 21.36 17.56 21.84 20.25 16.82 Olivine 0.00 0.00 0.00 0.00 0.00 0.00 Magnetite 2.86 2.62 2.23 2.70 2.47 1.96 Ilmenite 2.81 2.83 2.28 2.98 2.81 1.92 Apatite 0.62 0.43 0.45 0.45 0.57 0.36 149 Table B - 2 (Continued). GEOR1 GEOR2 GEOR3 SKE1 SKE5 SKE2 SKE3 Quartz 15.95 14.25 51.37 11.60 15.45 9.39 10.84 Corundum 0.00 0.00 6.44 0.00 0.00 0.00 0.00 Orthoclase 0.18 0.00 0.00 0.71 0.00 0.00 0.59 Albite 14.39 7.70 0.00 13.71 25.13 4.23 13.12 Anorthite 28.41 32.72 3.03 29.13 25.44 33.56 29.64 Diopside 8.74 2.51 0.00 10.64 7.15 8.58 12.37 Hypersthene 29.03 39.74 34.78 25.99 22.86 33.34 25.42 Olivine 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Magnetite 1.93 1.93 2.00 3.13 1.97 3.39 3.09 Ilmenite 1.20 1.01 2.34 4.28 1.69 5.93 4.18 Apatite 0.19 0.17 0.21 0.83 0.38 1.73 0.76 Table B - 2 (Continued). SOL1 SOL2 SOL3 KUD1 SIL1 SIL2 Quartz 27.86 14.99 60.08 20.44 38.23 7.80 Corundum 15.46 3.96 7.80 0.00 11.33 0 Orthoclase 0.00 0.00 0.00 0.06 0.00 1.24 Albite 0.00 16.50 0.00 16.75 0.00 10.75 Anorthite 0.22 22.84 0.23 30.54 2.24 29.56 Diopside 0.00 0.00 0.00 2.70 0.00 17.93 Hypersthene 48.79 35.26 27.34 25.44 45.14 21.94 Olivine 0.00 0.00 0.00 0.00 0.00 0 Magnetite 4.00 2.74 2.07 2.00 2.22 3.13 Ilmenite 3.33 3.27 2.34 1.69 0.91 5.91 Apatite 0.50 0.50 0.33 0.38 0.14 1.78 Table B - 2 (Continued). LIB1 LIT1 PE1 PE2 LAV1 JEA1 JEA2 JEA3 Quartz 16.73 7.541 10.72 13.155 5.125 12.611 19.066 12.20 Corundum 0 0 0 1.3 0.549 0 12.029 0 Orthoclase 0 4.078 0 0 6.619 0 0 0 Albite 10.323 21.154 5.585 8.039 34.608 3.892 8.885 4.15 Anorthite 29.941 22.157 32.809 30.199 24.967 33.571 7.487 34.15 Diopside 1.279 8.363 5.02 0 0 7.405 0 6.21 Hypersthene 30.784 26.653 34.643 35.975 23.958 32 46.62 32.72 Olivine 0 0 0 0 0 0 0 0 Magnetite 3.378 3.277 3.523 3.175 1.87 3.262 2.436 3.36 Ilmenite 5.206 4.845 5.89 6.27 1.957 5.681 2.679 5.62 Apatite 2.037 1.99 1.895 1.966 0.355 1.658 0.829 1.71 150 Table B - 2 (Continued). FRI1 FRI2 FRI3 FRI4 FRI5 FRI6 FRI7 FRI8 FRI9 Quartz 13.49 26.73 13.98 11.37 19.75 14.42 12.42 15.26 25.96 Corundum 0 14.127 0 0 10.22 0 0 12.15 14.48 Orthoclase 0 0 0 0 0 0 0 0 0 Albite 0 0 0 10.66 0 0.25 0.68 0 0 Anorthite 35.28 0.66 35.83 34.35 10.86 35.99 35.14 9.72 0.57 Diopside 10.99 0 6.75 1.55 0 4.63 11.26 0 0 Hypersthene 29.89 46.34 33.23 33.82 47.29 34.21 29.89 49.24 46.52 Olivine 0 0 0 0 0 0 0 0 0 Magnetite 3.35 4.05 3.31 3.22 4.16 3.38 3.38 4.71 4.12 Ilmenite 5.49 6.35 5.47 4.33 6.08 5.59 5.62 6.99 6.57 Apatite 1.68 1.99 1.61 0.81 1.87 1.68 1.73 2.18 1.99 Table B - 2 (Continued). AMI1 AMI2 AMI3 AMI5 Quartz 32.07 34.86 15.23 11.96 Corundum 15.08 14.67 3.32 2.51 Orthoclase 0 0 0 0.12 Albite 0 0 12.52 12.78 Anorthite 0.42 0.44 24.67 27.20 Diopside 0 0 0 0 Hypersthene 40.99 39.12 34.45 35.18 Olivine 0 0 0 0 Magnetite 3.19 3.00 3.13 3.23 Ilmenite 6.35 6.33 5.80 6.08 Apatite 2.13 1.8 0.88 0.95 Table B - 2 (Continued). BAN1 BAN3 BAN4 BAN5 BAN6 BAN7 BAN8 Quartz 2.43 3.56 2.69 11.11 12.54 2.52 5.78 Corundum 0 0 0 0 0.59 0 0 Orthoclase 2.66 0.65 3.96 0.95 0.12 3.19 2.31 Albite 19.46 17.18 20.82 9.48 12.27 19.97 14.39 Anorthite 28.10 27.10 24.96 33.60 32.12 26.91 28.90 Diopside 14.62 16.80 14.35 1.55 0 14.77 13.41 Hypersthene 25.30 25.60 26.20 33.21 32.50 25.76 27.35 Olivine 0 0 0 0 0 0 0 Magnetite 2.71 3.03 3.20 3.19 2.87 3.12 3.12 Ilmenite 4.09 5.28 5.59 6.02 6.08 5.38 5.59 Apatite 0.69 0.81 0.69 0.92 0.95 0.76 0.88 151 Table B - 2 (Continued). SPE1 SPE2 SPE3 SPE5 TWI1 TWI2 Qua rtz 13.93 28.35 48.33 40.89 41.34 45.90 Corundum 1.53 12.88 10.10 12.11 14.70 13.77 Orthoclase 0 0 0 0 10.17 13.53 Albite 0 0 0 0 1.02 1.52 Anorthite 27.24 0.63 0.27 0.50 0.16 0.27 Diopside 0 0 0 0 0 0 Hypersthene 53.77 53.92 38.54 43.16 28.93 21.88 Olivine 0 0 0 0 0 0 Magnetite 2.62 3.07 2.06 2.54 2.29 1.75 Ilmenite 1.00 1.06 0.78 0.87 1.24 1.197 Apatite 0.14 0.17 0.12 0.14 0.21 0.19 Table B - 2 (Continued). BRA1 BRA2 BRA3 BRA4 BRA5 BRA6 BRA7 BRA8 Quartz 14.53 17.87 10.93 4.51 3.85 21.40 2.05 4.70 Corundum 4.599 3.569 0.994 0 0 3.786 0 0 Orthoclase 0.06 0 0 0.36 0.77 0 3.49 3.37 Albite 14.3 10.15 14.05 16.08 16.42 13.37 16.16 13.03 Anorthite 19.56 23.81 28.77 27.58 27.36 21.51 25.73 27.89 Diopside 0 0 0 16.104 17.263 0 17.206 16.249 Hypersthene 36.55 34.16 35.24 25.67 24.84 29.69 25.67 25.44 Olivine 0 0 0 0 0 0 0 0 Magnetite 3.42 3.19 3.23 3.10 3.06 2.86 3.22 3.07 Ilmenite 6.10 5.80 5.93 5.43 5.38 5.89 5.66 5.43 Apatite 0.95 0.90 0.90 0.81 0.83 0.92 0.85 0.83 Table B - 2 (Continued). CLA1 CLA2 CLA3 CLA4 CLA5 CLA6 CLA7 CLA8 CLA9 Quartz 19.61 21.95 5.99 10.68 20.56 1.99 3.16 9.58 47.14 Corundum 17.97 17.15 0 0 15.17 0 0 0 11.35 Orthoclase 0 0 0 0 0 0 0 0 0 Albite 0 0 4.57 0 6.26 14.55 12.69 0 0 Anorthite 0.36 0.49 40.39 42.05 0.44 35.45 35.64 43.47 0.38 Diopside 0 0 5.89 3.16 0 9.84 7.92 7.44 0 Hypersthene 55.43 53.77 38.57 37.73 51.46 33.28 35.18 33.30 36.67 Olivine 0 0 0 0 0 0 0 0 0 Magnetite 4.06 3.76 2.58 2.54 4.22 2.54 2.45 2.41 2.99 Ilmenite 2.62 2.81 2.41 2.39 2.58 2.62 2.36 2.07 1.60 Apatite 0.36 0.38 0.33 0.31 0.38 0.38 0.33 0.28 0.02 152 Table B - 2 (Continued). KEN1 KEN2 KEN3 KEN4 KEN5 KEN6 KEN7 Quartz 7.70 3.02 13.08 4.64 7.68 7.96 6.36 Corundum 2.99 0 0 11.50 0 0 0 Orthoclase 0 0 0.06 0 0.77 0.77 0.71 Albite 17.6 17.01 0 27.33 10.07 10.83 12.44 Anorthite 25.61 28.33 37.27 0.36 31.11 31.20 30.05 Diopside 0 16.82 10.96 0 12.40 10.69 14.24 Hypersthene 42.70 25.18 28.03 52.96 28.51 28.96 26.81 Olivine 0 0 0 0 0 0 0 Magnetite 2.78 2.90 2.99 3.9 3.13 3.10 3.06 Ilmenite 2.64 5.61 5.38 2.68 5.49 5.64 5.51 Apatite 0.36 0.88 0.85 0.36 0.85 0.88 0.85 Table B - 2 (Continued). UNK1 UNK2 UNK3 UNK4A UNK4B UNK6 UNK7 Quartz 7.66 2.30 20.62 7.59 25.90 3.98 5.73 Corundum 0 0.41 0 0 3.35 9.22 0 Orthoclase 0 0 5.73 0 0 0 4.61 Albite 8.12 4.74 14.47 24.12 0 31.57 32.24 Anorthite 31.41 37.61 33.14 24.10 31.4 0.19 11.29 Diopside 12.87 0 8.29 12.60 0 0 10.08 Hypersthene 28.97 42.03 11.81 24.32 28.23 54.73 29.55 Olivine 0 0 0 0 0 0 0 Magnetite 3.34 4.13 0.96 2.97 2.52 3.18 2.71 Ilmenite 5.97 6.84 1.92 4.07 4.41 1.16 2.57 Apatite 1.80 2.08 0.43 0.76 0.83 0.17 0.45 Table B - 2 (Continued). 120A1 120A2 120A3 120B1 120B2 120B3 Quartz 20.92 12.33 18.73 24.53 17.78 32.23 Corundum 2.70 0 0 0.74 1.06 11.94 Orthoclase 0 0 13.48 12.29 0 9.34 Albite 30.63 26.49 0.68 1.44 17.69 1.52 Anorthite 18.62 22.76 32.34 32.13 29.22 4.35 Diopside 0 13.41 14.29 0 0 0 Hypersthene 22.95 21.12 16.65 24.90 30.14 35.85 Olivine 0 0 0 0 0 0 Magnetite 1.94 1.97 1.70 1.77 2.06 2.54 Ilmenite 1.9 1.62 1.75 1.81 1.79 1.84 Apatite 0.43 0.33 0.40 0.40 0.38 0.40 153 Appendix C: Chemistry Major Elements Table C – 1. Major Element Concentrations (wt%). Bdl = below detection limit. Sample SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 LOI Sum AMI1 50.13 14.15 15.65 0.04 7.96 1.18 bdl bdl 3.10 0.84 4.97 97.88 AMI2 53.46 14.19 15.19 0.03 8.02 1.04 bdl bdl 3.20 0.73 5.21 100.52 AMI3 49.02 13.89 15.53 0.18 5.46 5.12 1.39 bdl 2.87 0.35 5.74 99.55 AMI5 47.98 14.19 16.21 0.20 5.55 5.69 2.54 0.02 3.03 0.38 4.76 100.55 BAN1 49.89 14.43 14.41 0.20 5.66 9.64 2.09 0.53 2.12 0.29 1.68 100.94 BAN3 48.51 13.24 15.98 0.22 5.63 9.99 1.96 0.19 2.77 0.34 1.06 99.90 BAN4 49.02 13.37 16.29 0.22 4.86 8.50 3.18 0.64 2.82 0.28 1.80 100.99 BAN5 49.77 14.10 16.60 0.17 5.43 7.54 1.54 0.15 3.11 0.39 2.76 101.57 BAN6 50.08 14.28 14.67 0.15 5.79 6.79 2.22 0.02 3.09 0.38 3.19 100.67 BAN7 48.86 13.81 15.87 0.21 5.01 9.05 2.84 0.52 2.73 0.31 1.55 100.76 BAN8 49.25 13.43 16.07 0.21 5.44 9.28 1.96 0.38 2.86 0.36 1.40 100.64 BRA1 49.28 13.91 17.27 0.18 5.60 4.27 1.57 0.01 3.07 0.38 4.24 99.78 BRA2 51.49 13.95 16.48 0.17 5.40 5.18 1.74 bdl 2.99 0.37 3.66 101.45 BRA3 48.39 13.49 16.22 0.21 5.62 5.94 1.46 0.00 2.93 0.36 4.11 98.73 BRA4 49.55 13.40 16.51 0.23 5.52 9.96 2.30 0.06 2.88 0.34 2.03 102.80 BRA5 49.52 13.46 16.29 0.21 5.55 10.21 2.23 0.13 2.86 0.35 1.83 102.65 BRA6 54.34 14.06 14.86 0.14 4.79 4.78 2.15 bdl 3.06 0.38 3.47 102.02 BRA7 46.61 12.69 16.34 0.24 5.18 9.41 1.46 0.57 2.86 0.34 3.44 99.13 BRA8 47.73 12.94 15.74 0.22 5.31 9.67 1.43 0.55 2.77 0.34 2.24 98.94 CLA1 46.66 17.35 20.55 0.18 9.80 0.26 bdl bdl 1.32 0.14 5.86 101.74 CLA2 48.40 16.65 19.05 0.31 10.06 0.30 bdl bdl 1.42 0.16 5.86 101.94 CLA3 46.74 14.59 12.66 0.19 8.55 9.09 0.39 bdl 1.18 0.13 7.07 100.49 CLA4 47.01 14.32 12.48 0.17 7.86 8.75 1.16 bdl 1.17 0.12 3.96 96.92 CLA5 49.58 15.98 21.53 0.22 7.78 0.29 bdl bdl 1.32 0.15 5.33 101.87 CLA6 47.98 15.15 12.86 0.18 7.72 9.35 1.13 bdl 1.32 0.15 7.23 102.97 CLA7 49.30 15.24 12.74 0.17 8.46 9.14 1.84 bdl 1.21 0.14 2.65 100.80 CLA8 48.84 15.58 12.41 0.16 7.68 10.50 1.50 bdl 1.07 0.12 3.00 100.77 CLA9 63.65 11.07 15.23 0.14 5.51 0.09 bdl bdl 0.81 0.01 4.04 100.07 FRI1 48.39 12.61 17.24 0.21 5.28 10.42 bdl bdl 2.82 0.69 4.35 101.78 FRI2 49.05 13.85 20.65 0.27 7.52 1.19 bdl bdl 3.22 0.81 4.91 101.03 FRI3 48.48 12.78 17.06 0.22 5.82 9.57 0.13 0.01 2.80 0.66 3.60 101.13 FRI4 49.62 14.17 16.57 0.22 4.86 7.55 1.30 bdl 2.22 0.33 3.85 100.68 FRI5 46.17 13.47 21.07 0.32 7.25 3.11 bdl bdl 3.06 0.75 5.12 100.26 FRI6 47.60 12.62 17.20 0.31 5.36 8.97 0.31 bdl 2.82 0.68 5.29 101.15 FRI7 47.05 12.52 17.36 0.24 5.13 10.47 0.09 bdl 2.86 0.71 4.46 100.90 FRI8 42.39 15.02 24.05 0.59 6.53 3.06 0.12 bdl 3.56 0.88 5.05 101.26 FRI9 47.94 14.17 21.14 0.40 7.27 1.17 0.05 bdl 3.36 0.82 5.01 101.32 154 Sample SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 LOI Sum GEOR1 57.74 13.10 10.11 0.14 7.48 7.89 1.84 0.03 0.62 0.08 2.39 101.43 GEOR2 53.08 12.61 9.50 0.15 9.91 6.84 1.28 bdl 0.50 0.07 7.99 101.89 GEOR3 69.95 7.39 10.38 0.12 8.16 0.71 bdl bdl 1.20 0.09 3.81 101.58 JEA1 47.36 12.35 16.30 0.21 5.54 8.96 0.12 bdl 2.83 0.67 5.35 99.64 JEA2 51.82 15.87 12.36 0.13 11.42 1.90 1.71 bdl 1.36 0.34 5.37 102.26 JEA3 47.49 12.73 17.02 0.21 5.30 8.91 0.62 bdl 2.83 0.68 4.60 100.33 KEN1 50.69 14.97 13.92 0.34 8.54 5.08 bdl bdl 1.31 0.15 6.28 100.99 KEN2 47.33 13.29 14.91 0.21 5.92 9.97 2.25 bdl 2.86 0.36 4.58 101.64 KEN3 47.68 13.21 15.25 0.23 5.53 10.27 1.36 0.01 2.73 0.35 3.02 99.63 KEN4 48.28 16.00 19.45 0.37 9.06 0.26 bdl bdl 1.33 0.14 5.68 100.14 KEN5 48.83 13.29 16.32 0.21 5.69 9.57 1.37 0.13 2.85 0.36 3.17 101.78 KEN6 48.55 13.30 15.98 0.22 5.56 9.10 1.60 0.10 2.89 0.36 2.87 100.53 KEN7 48.36 13.25 15.84 0.21 5.55 9.73 1.43 0.12 2.83 0.35 2.69 100.36 KUD1 58.63 14.17 10.35 0.14 4.82 6.88 2.47 0.01 0.87 0.16 3.15 101.65 LAV1 56.73 17.73 9.94 0.13 4.32 5.26 5.38 1.13 1.03 0.15 1.16 102.96 LIB1 50.59 12.47 17.13 0.20 3.47 7.18 1.60 bdl 2.63 0.83 5.22 101.23 LIT1 50.97 12.78 17.07 0.22 3.52 7.43 2.86 0.68 2.51 0.82 2.78 101.63 PE1 47.50 12.71 18.04 0.20 5.53 8.61 0.92 bdl 3.01 0.78 3.39 100.65 PE2 48.06 13.29 15.99 0.23 6.13 6.85 1.33 bdl 3.15 0.79 4.13 99.91 PEG1 51.70 10.24 14.61 0.18 5.24 9.06 4.11 1.36 1.43 0.25 3.38 101.56 PEG2 55.39 11.99 13.74 0.15 4.58 5.95 5.73 0.61 1.47 0.18 1.25 101.04 PEG3 55.37 13.55 11.88 0.14 4.86 8.16 4.45 1.22 1.21 0.19 0.79 101.81 PEG4 55.01 11.81 14.36 0.16 4.50 6.42 3.66 1.95 1.58 0.20 1.18 100.82 PEG5 56.87 12.87 12.98 0.13 3.61 5.04 5.68 1.43 1.47 0.24 0.87 101.19 PEG6 56.99 14.06 10.31 0.14 4.10 6.26 5.03 1.48 1.01 0.15 0.75 100.28 SIL1 57.65 10.99 10.59 0.24 10.17 0.48 bdl bdl 0.44 0.06 5.12 95.21 SIL2 44.53 11.94 15.06 0.16 4.04 10.19 1.29 0.19 2.82 0.68 9.09 99.98 SKE1 51.61 13.24 16.28 0.23 3.95 8.71 1.78 0.12 2.21 0.34 2.99 101.46 SKE2 45.86 12.43 16.98 0.23 5.96 9.27 0.67 bdl 2.96 0.69 5.56 100.53 SKE3 51.36 13.32 16.11 0.22 4.17 9.20 1.84 0.10 2.17 0.32 2.93 101.74 SKE5 58.33 13.97 10.24 0.16 4.77 6.95 4.03 bdl 0.87 0.16 1.39 100.83 SOL1 51.10 14.98 20.39 0.17 7.69 0.31 bdl bdl 1.69 0.20 5.40 101.52 SOL2 51.77 14.75 13.73 0.18 6.17 4.63 2.52 bdl 1.63 0.20 5.78 101.32 SOL3 72.07 7.63 10.58 0.02 5.07 0.22 bdl bdl 1.19 0.13 3.24 99.93 SPE1 49.63 10.43 12.53 0.52 12.06 5.06 bdl bdl 0.46 0.06 9.82 100.20 SPE2 54.25 12.37 15.36 0.18 11.45 0.21 bdl bdl 0.53 0.07 5.66 99.79 SPE3 66.88 9.85 10.52 0.13 8.82 0.11 bdl bdl 0.40 0.05 4.34 100.55 SPE4 34.71 10.48 13.90 1.09 15.70 9.62 bdl bdl 0.43 0.05 15.08 100.48 SPE5 58.50 11.20 12.22 0.12 8.68 0.17 bdl bdl 0.42 0.06 4.78 95.45 SWA1 46.10 13.25 20.93 0.34 7.73 1.11 bdl bdl 3.05 0.77 5.44 97.95 SWA2 47.35 12.18 18.16 0.21 5.00 9.94 bdl bdl 2.85 0.70 4.73 100.81 155 Sample SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 LOI Sum SWA3 46.67 13.03 23.11 0.24 6.70 1.07 bdl bdl 3.00 0.74 5.26 99.82 TWI1 62.91 16.65 11.98 0.05 4.71 0.14 0.08 1.70 0.65 0.09 3.97 102.93 TWI2 66.49 16.50 9.19 0.04 3.60 0.15 0.18 2.27 0.62 0.08 3.58 102.72 UNK1 44.95 12.20 16.43 0.26 5.19 9.71 0.90 bdl 2.92 0.70 7.34 100.60 UNK2 40.23 14.11 20.42 0.25 5.59 8.16 0.52 bdl 3.36 0.82 6.51 99.98 UNK3 55.89 15.06 4.73 0.11 3.72 8.44 4.09 0.91 0.95 0.17 7.56 101.63 UNK4A 50.61 12.84 14.90 0.20 4.00 7.87 2.31 bdl 2.03 0.31 6.53 101.55 UNK4B 51.43 14.14 12.71 0.14 4.55 6.46 3.30 bdl 2.20 0.33 6.09 101.29 UNK6 51.84 14.52 15.84 0.10 11.54 0.12 bdl bdl 0.57 0.06 5.74 99.92 UNK7 55.12 11.02 14.02 0.19 5.95 4.86 4.50 0.76 1.32 0.19 4.28 102.21 120A1 58.88 14.76 9.77 0.09 3.51 3.81 5.01 bdl 0.95 0.17 2.69 99.56 120A2 57.50 13.27 10.28 0.14 5.29 7.90 3.51 bdl 0.84 0.14 1.70 100.55 120A3 53.19 13.24 8.20 0.33 4.15 9.36 0.01 2.09 0.85 0.15 9.33 100.91 120B1 56.97 14.20 8.81 0.39 4.47 6.33 0.26 1.96 0.90 0.16 7.09 101.54 120B2 54.99 14.30 10.21 0.16 5.75 5.74 3.52 bdl 0.89 0.15 5.10 100.72 120B3 58.47 15.15 13.05 0.25 6.67 1.08 0.10 1.55 0.95 0.17 4.09 101.53 156 Major Element Summary Amigo Bank n N A Mean S D Min Max n N A Mean SD M in M ax SiO2 4 0 53.19 2.23 50.68 55.86 SiO2 7 0 50.65 0.75 49.38 51.86 TiO2 4 0 3.23 0.14 3.05 3.34 TiO2 7 0 2.85 0.36 2.12 3.20 Al2O3 4 0 14.96 0.20 14.80 15.23 Al2O3 7 0 14.16 0.48 13.39 14.77 Fe2O3 4 0 16.61 0.52 15.90 17.12 Fe2O3 7 0 16.05 0.97 14.36 16.97 MnO 4 0 0.12 0.10 0.03 0.21 MnO 7 0 0.20 0.02 0.16 0.23 MgO 4 0 7.16 1.53 5.82 8.57 MgO 7 0 5.56 0.33 5.06 6.00 CaO 4 0 3.46 2.64 1.09 6.01 CaO 7 0 8.85 1.11 7.00 9.96 Na2O 2 2 1.50 0.02 1.48 1.51 Na2O 7 0 1.92 0.51 1.12 2.46 K2O 1 3 0.02 NA 0.02 0.02 K2O 7 0 0.33 0.24 0.02 0.67 P2O5 4 0 0.61 0.26 0.37 0.9 P2O5 7 0 0.34 0.05 0.29 0.40 B razil CLA n NA M ean SD Min Max n N A M ean S D Min M ax SiO2 8 0 50.83 2.26 48.51 55.14 SiO2 9 0 51.95 5.33 48.66 66.04 TiO2 8 0 3.00 0.14 2.83 3.21 TiO2 9 0 1.26 0.19 0.84 1.48 Al2O3 8 0 13.83 0.56 13.21 14.56 Al2O3 9 0 15.76 1.84 11.49 18.10 Fe2O3 8 0 16.62 0.87 15.08 18.08 Fe2O3 9 0 16.17 3.92 12.69 22.31 MnO 8 0 0.21 0.04 0.14 0.25 MnO 9 0 0.20 0.05 0.15 0.33 MgO 8 0 5.49 0.30 4.86 5.86 MgO 9 0 8.52 1.41 5.72 10.47 CaO 8 0 7.59 2.58 4.47 10.13 CaO 9 0 5.55 5.05 0.09 10.74 Na2O 8 0 1.68 0.25 1.20 1.94 Na2O 4 5 1.13 0.57 0.54 1.72 K2O 5 3 0.27 0.28 0.01 0.59 K2O 0 9 NA NA NA NA P2O5 8 0 0.37 0.02 0.34 0.40 P2O5 9 0 0.13 0.05 0.01 0.16 F riday Georgette n NA Mean SD M in M ax n N A M ean SD Min Max SiO2 9 0 49.36 2.07 44.33 51.49 SiO2 3 0 62.23 8.07 56.78 71.50 TiO2 9 0 3.07 0.41 2.28 3.68 TiO2 3 0 0.80 0.38 0.53 1.23 Al2O3 9 0 13.99 0.97 12.93 15.71 Al2O3 3 0 11.43 3.36 7.55 13.49 Fe2O3 9 0 19.78 2.79 17.04 24.91 Fe2O3 3 0 10.34 0.24 10.17 10.61 MnO 9 0 0.31 0.12 0.22 0.6 MnO 3 0 0.14 0.02 0.12 0.16 MgO 9 0 6.4 1.12 5.05 7.8 MgO 3 0 8.84 1.57 7.57 10.60 CaO 9 0 6.34 4.07 1.22 10.74 CaO 3 0 5.34 4.01 0.73 7.98 Na2O 3 6 0.46 0.7 0.03 1.26 Na2O 2 1 1.31 0.56 0.91 1.70 K2O 0 9 NA NA NA NA K2O 1 2 0.03 NA 0.03 0.03 P2O5 9 0 0.73 0.17 0.34 0.92 P2O5 3 0 0.08 0.01 0.07 0.09 157 Jeans Ken n NA Mean SD M in Max n NA M ean SD Min M ax SiO2 3 0 51.20 2.32 49.69 53.87 SiO2 7 0 50.24 1.61 48.77 53.52 TiO2 3 0 2.45 0.90 1.41 2.99 TiO2 7 0 2.48 0.74 1.39 2.97 Al2O3 3 0 14.29 1.92 13.06 16.50 Al2O3 7 0 14.41 1.38 13.50 16.94 Fe2O3 3 0 15.96 2.71 12.85 17.81 Fe2O3 7 0 16.52 1.91 14.70 20.59 MnO 3 0 0.19 0.05 0.14 0.22 MnO 7 0 0.27 0.08 0.21 0.39 MgO 3 0 7.76 3.57 5.54 11.87 MgO 7 0 6.81 1.72 5.69 9.60 CaO 3 0 6.92 4.29 1.97 9.47 CaO 7 0 7.94 3.82 0.27 10.63 Na2O 3 0 0.67 0.33 0.46 1.05 Na2O 6 1 1.88 0.76 1.19 3.23 K2O 0 3 NA NA NA NA K2O 4 3 0.10 0.06 0.01 0.13 P2O5 3 0 0.59 0.21 0.35 0.72 P2O5 7 0 0.30 0.11 0.15 0.37 Kudu L ib n N A M ean SD Min Max n N A Mean S D Min M ax SiO2 1 0 59.84 NA 59.84 59.84 SiO2 1 0 52.69 NA 52.69 52.69 TiO2 1 0 0.89 NA 0.89 0.89 TiO2 1 0 2.74 NA 2.74 2.74 Al2O3 1 0 14.46 NA 14.46 14.46 Al2O3 1 0 12.98 NA 12.98 12.98 Fe2O3 1 0 10.57 NA 10.57 10.57 Fe2O3 1 0 17.84 NA 17.84 17.84 MnO 1 0 0.14 NA 0.14 0.14 MnO 1 0 0.21 NA 0.21 0.21 MgO 1 0 4.92 NA 4.92 4.92 MgO 1 0 3.62 NA 3.62 3.62 CaO 1 0 7.02 NA 7.02 7.02 CaO 1 0 7.47 NA 7.47 7.47 Na2O 1 0 1.98 NA 1.98 1.98 Na2O 1 0 1.22 NA 1.22 1.22 K2O 1 0 0.01 NA 0.01 0.01 K2O 0 1 NA NA NA NA P2O5 1 0 0.16 NA 0.16 0.16 P2O5 1 0 0.86 NA 0.86 0.86 L ittle Tumi P E n NA M ean SD Min M ax n N A Mean SD Min Max SiO2 1 0 51.77 NA 51.77 51.77 SiO2 2 0 49.69 1.00 48.98 50.40 TiO2 1 0 2.55 NA 2.55 2.55 TiO2 2 0 3.20 0.14 3.10 3.30 Al2O3 1 0 12.98 NA 12.98 12.98 Al2O3 2 0 13.52 0.58 13.11 13.93 Fe2O3 1 0 17.33 NA 17.33 17.33 Fe2O3 2 0 17.69 1.29 16.77 18.60 MnO 1 0 0.22 NA 0.22 0.22 MnO 2 0 0.23 0.02 0.21 0.24 MgO 1 0 3.58 NA 3.58 3.58 MgO 2 0 6.07 0.52 5.70 6.43 CaO 1 0 7.55 NA 7.55 7.55 CaO 2 0 8.03 1.20 7.18 8.87 Na2O 1 0 2.5 NA 2.5 2.5 Na2O 2 0 0.81 0.21 0.66 0.95 K2O 1 0 0.69 NA 0.69 0.69 K2O 0 2 NA NA NA NA P2O5 1 0 0.84 NA 0.84 0.84 P2O5 2 0 0.82 0.02 0.80 0.83 158 Peggy Sill n N A M ean S D Min M ax n N A M ean S D M in Max SiO2 6 0 55.69 1.47 53.47 57.38 SiO2 2 0 56.41 10.39 49.06 63.76 TiO2 6 0 1.37 0.22 1.01 1.57 TiO2 2 0 1.80 1.86 0.48 3.11 Al2O3 6 0 12.52 1.26 10.60 14.15 Al2O3 2 0 12.65 0.71 12.15 13.15 Fe2O3 6 0 13.07 1.74 10.37 15.11 Fe2O3 2 0 14.16 3.46 11.71 16.60 MnO 6 0 0.15 0.02 0.14 0.18 MnO 2 0 0.22 0.06 0.17 0.26 MgO 6 0 4.54 0.61 3.63 5.42 MgO 2 0 7.85 4.79 4.46 11.24 CaO 6 0 6.86 1.58 5.06 9.37 CaO 2 0 5.88 7.57 0.53 11.23 Na2O 6 0 4.25 0.90 2.70 5.11 Na2O 1 1 1.27 NA 1.27 1.27 K2O 6 0 1.34 0.42 0.61 1.89 K2O 1 1 0.21 NA 0.21 0.21 P2O5 6 0 0.20 0.04 0.15 0.26 P2O5 2 0 0.41 0.49 0.06 0.75 Skelm Soll n NA M ean SD M in Max n N A M ean S D M in Max SiO2 4 0 53.09 4.56 48.39 59.33 SiO2 3 0 60.69 11.98 53.01 74.50 TiO2 4 0 2.12 0.92 0.89 3.12 TiO2 3 0 1.57 0.29 1.23 1.75 Al2O3 4 0 13.58 0.46 13.12 14.21 Al2O3 3 0 12.99 4.42 7.88 15.54 Fe2O3 4 0 15.32 3.34 10.42 17.91 Fe2O3 3 0 15.52 5.19 10.94 21.15 MnO 4 0 0.21 0.04 0.16 0.24 MnO 3 0 0.13 0.10 0.02 0.19 MgO 4 0 4.85 1.02 4.02 6.29 MgO 3 0 6.57 1.37 5.24 7.97 CaO 4 0 8.77 1.19 7.07 9.79 CaO 3 0 1.81 2.66 0.23 4.88 Na2O 4 0 1.66 1.01 0.50 2.97 Na2O 1 2 1.95 NA 1.95 1.95 K2O 2 2 0.11 0.01 0.10 0.12 K2O 0 3 NA NA NA NA P2O5 4 0 0.39 0.24 0.16 0.73 P2O5 3 0 0.19 0.04 0.14 0.21 Speckled S wannie n NA M ean S D Min Max n NA M ean SD M in Max SiO2 5 0 57.25 10.95 40.45 69.25 SiO2 3 0 49.37 0.20 49.14 49.51 TiO2 5 0 0.49 0.06 0.41 0.56 TiO2 3 0 3.14 0.16 2.96 3.28 Al2O3 5 0 11.86 1.09 10.20 13.11 Al2O3 3 0 13.56 0.82 12.64 14.23 Fe2O3 5 0 14.12 2.24 10.89 16.29 Fe2O3 3 0 21.94 2.86 18.84 24.49 MnO 5 0 0.46 0.49 0.14 1.27 MnO 3 0 0.28 0.07 0.22 0.36 MgO 5 0 12.46 3.69 9.13 18.30 MgO 3 0 6.86 1.57 5.19 8.30 CaO 5 0 3.46 4.92 0.12 11.21 CaO 3 0 4.22 5.29 1.14 10.32 Na2O 0 5 NA NA NA NA Na2O 0 3 NA NA NA NA K2O 0 5 NA NA NA NA K2O 0 3 NA NA NA NA P2O5 5 0 0.06 0.01 0.05 0.07 P2O5 3 0 0.78 0.05 0.73 0.82 159 Twin Unknown1 n N A Mean S D M in Max n N A M ean S D Min M ax SiO2 2 0 65.32 2.49 63.56 67.08 SiO2 1 0 48.24 NA 48.24 48.24 TiO2 2 0 0.64 0.01 0.63 0.65 TiO2 1 0 3.14 NA 3.14 3.14 Al2O3 2 0 16.73 0.13 16.64 16.82 Al2O3 1 0 13.09 NA 13.09 13.09 Fe2O3 2 0 10.69 2.01 9.27 12.11 Fe2O3 1 0 17.63 NA 17.63 17.63 MnO 2 0 0.05 0.01 0.04 0.06 MnO 1 0 0.27 NA 0.27 0.27 MgO 2 0 4.20 0.80 3.63 4.76 MgO 1 0 5.57 NA 5.57 5.57 CaO 2 0 0.16 0.01 0.15 0.16 CaO 1 0 10.42 NA 10.42 10.42 Na2O 2 0 0.15 0.04 0.12 0.18 Na2O 1 0 0.96 NA 0.96 0.96 K2O 2 0 2.01 0.40 1.72 2.29 K2O 0 1 NA NA NA NA P2O5 2 0 0.09 0.01 0.08 0.09 P2O5 1 0 0.76 NA 0.76 0.76 U nknown2 Unknown3 n N A M ean SD Min Max n N A M ean S D M in Max SiO2 1 0 43.08 NA 43.08 43.08 SiO2 1 0 59.42 NA 59.42 59.42 TiO2 1 0 3.6 NA 3.6 3.6 TiO2 1 0 1.01 NA 1.01 1.01 Al2O3 1 0 15.11 NA 15.11 15.11 Al2O3 1 0 16.01 NA 16.01 16.01 Fe2O3 1 0 21.86 NA 21.86 21.86 Fe2O3 1 0 5.03 NA 5.03 5.03 MnO 1 0 0.27 NA 0.27 0.27 MnO 1 0 0.11 NA 0.11 0.11 MgO 1 0 5.99 NA 5.99 5.99 MgO 1 0 3.95 NA 3.95 3.95 CaO 1 0 8.74 NA 8.74 8.74 CaO 1 0 8.97 NA 8.97 8.97 Na2O 1 0 0.56 NA 0.56 0.56 Na2O 1 0 1.71 NA 1.71 1.71 K2O 0 1 NA NA NA NA K2O 1 0 0.97 NA 0.97 0.97 P2O5 1 0 0.88 NA 0.88 0.88 P2O5 1 0 0.18 NA 0.18 0.18 Unknown4 Unknown6 n N A Mean S D Min M ax n N A Mean S D M in M ax SiO2 2 0 53.65 0.53 53.27 54.02 SiO2 1 0 55.05 NA 55.05 55.05 TiO2 2 0 2.23 0.13 2.14 2.32 TiO2 1 0 0.61 NA 0.61 0.61 Al2O3 2 0 14.19 0.95 13.52 14.86 Al2O3 1 0 15.42 NA 15.42 15.42 Fe2O3 2 0 14.52 1.65 13.35 15.68 Fe2O3 1 0 16.81 NA 16.81 16.81 MnO 2 0 0.18 0.04 0.15 0.21 MnO 1 0 0.1 NA 0.1 0.1 MgO 2 0 4.50 0.40 4.21 4.78 MgO 1 0 12.25 NA 12.25 12.25 CaO 2 0 7.54 1.05 6.79 8.28 CaO 1 0 0.13 NA 0.13 0.13 Na2O 1 1 2.85 NA 2.85 2.85 Na2O 1 0 3.73 NA 3.73 3.73 K2O 0 2 NA NA NA NA K2O 0 1 NA NA NA NA P2O5 2 0 0.34 0.02 0.32 0.35 P2O5 1 0 0.07 NA 0.07 0.07 160 Unknown7 Unknown8 n N A Mean SD M in M ax n N A Mean S D M in Max SiO2 1 0 56.28 NA 56.28 56.28 SiO2 3 0 59.41 2.06 58.04 61.78 TiO2 1 0 1.35 NA 1.35 1.35 TiO2 3 0 0.92 0.08 0.85 1.00 Al2O3 1 0 11.25 NA 11.25 11.25 Al2O3 3 0 14.47 1.00 13.49 15.48 Fe2O3 1 0 14.32 NA 14.32 14.32 Fe2O3 3 0 9.88 0.81 8.95 10.44 MnO 1 0 0.19 NA 0.19 0.19 MnO 3 0 0.20 0.14 0.09 0.36 MgO 1 0 6.08 NA 6.08 6.08 MgO 3 0 4.53 0.85 3.68 5.37 CaO 1 0 4.96 NA 4.96 4.96 CaO 3 0 7.41 3.16 3.99 10.21 Na2O 1 0 3.81 NA 3.81 3.81 Na2O 3 0 2.28 1.92 0.08 3.62 K2O 1 0 0.78 NA 0.78 0.78 K2O 1 2 2.28 NA 2.28 2.28 P2O5 1 0 0.19 NA 0.19 0.19 P2O5 3 0 0.16 0.02 0.14 0.18 Unknown9 V entersdor p la va n NA M ean S D M in Max n NA Mean S D M in M ax SiO2 3 0 59.60 1.01 58.46 60.38 SiO2 1 0 56.43 NA 56.43 56.43 TiO2 3 0 0.95 0.02 0.94 0.97 TiO2 1 0 1.03 NA 1.03 1.03 Al2O3 3 0 15.27 0.25 15.05 15.54 Al2O3 1 0 17.64 NA 17.64 17.64 Fe2O3 3 0 11.19 2.05 9.34 13.39 Fe2O3 1 0 9.89 NA 9.89 9.89 MnO 3 0 0.28 0.13 0.17 0.42 MnO 1 0 0.12 NA 0.12 0.12 MgO 3 0 5.89 1.07 4.73 6.84 MgO 1 0 4.3 NA 4.3 4.3 CaO 3 0 4.63 3.07 1.10 6.70 CaO 1 0 5.23 NA 5.23 5.23 Na2O 3 0 0.81 1.11 0.17 2.09 Na2O 1 0 4.09 NA 4.09 4.09 K2O 2 1 1.83 0.35 1.58 2.08 K2O 1 0 1.12 NA 1.12 1.12 P2O5 3 0 0.17 0.01 0.16 0.17 P2O5 1 0 0.15 NA 0.15 0.15 161 Trace Elements Table C – 2. Trace Element Concentrations (ppm). Bdl = below detection limit. Sample S Sc V Cr Co Ni Cu Zn Ga Ge AMI1 861.37 31.45 279.35 54.30 13.85 44.85 75.96 92.53 21.27 bdl AMI2 168.25 29.78 305.35 127.90 10.86 48.17 49.89 93.21 19.21 bdl AMI3 345.66 26.94 389.19 89.85 40.34 54.65 103.84 111.10 20.03 0.39 AMI5 49.02 24.02 390.74 93.89 23.85 49.69 74.83 95.07 21.59 bdl BAN1 495.32 31.90 274.87 23.41 33.04 40.22 92.66 110.19 24.92 0.86 BAN3 565.24 27.57 310.19 37.85 37.61 42.84 87.47 112.24 22.27 0.99 BAN4 528.33 28.60 308.03 20.51 31.02 30.20 117.62 119.00 24.10 1.21 BAN5 902.06 28.28 399.84 83.97 40.97 54.26 92.51 118.22 22.34 bdl BAN6 931.61 29.52 395.58 86.72 46.94 50.73 89.82 104.78 21.86 bdl BAN7 470.26 30.46 307.84 17.51 36.73 35.21 78.65 127.23 26.30 1.01 BAN8 612.27 32.10 323.89 28.73 35.09 43.45 88.77 111.58 23.09 0.02 BRA1 701.91 29.03 345.22 26.31 27.80 43.01 96.52 123.90 23.86 0.86 BRA2 845.00 31.94 333.13 17.66 33.56 41.76 90.48 113.18 22.99 0.32 BRA3 437.86 24.63 387.75 78.02 33.23 51.07 88.25 120.02 23.22 bdl BRA4 482.95 29.24 320.08 25.17 34.54 36.70 88.11 113.11 23.54 0.42 BRA5 522.54 30.97 310.39 18.50 36.58 38.52 88.12 110.67 23.52 0.05 BRA6 1339.72 27.88 346.32 21.11 25.86 42.03 95.46 106.29 23.42 1.20 BRA7 432.80 27.14 359.47 92.27 43.24 48.85 85.45 107.96 23.10 bdl BRA8 334.53 26.85 301.89 63.44 35.22 39.82 75.56 85.30 18.06 0.04 CLA1 61.69 21.45 237.48 66.11 35.00 209.51 55.61 166.88 18.61 bdl CLA2 442.33 34.84 270.93 77.56 32.91 135.54 345.58 522.63 17.73 0.01 CLA3 180.55 32.36 196.26 58.97 37.65 126.38 78.21 126.77 15.16 bdl CLA4 308.56 36.49 221.74 79.91 38.60 122.85 62.12 88.69 14.96 0.64 CLA5 55.90 30.63 252.93 66.23 25.32 155.15 28.87 169.24 17.46 0.99 CLA6 176.28 37.76 226.15 66.18 34.75 102.66 61.70 107.83 13.84 0.33 CLA7 289.05 31.69 210.96 82.78 42.15 130.73 64.67 85.14 14.85 1.09 CLA8 276.08 31.88 205.16 84.62 39.65 164.73 56.84 82.07 15.89 1.00 CLA9 51.64 11.37 118.69 1040.05 28.51 271.15 36.30 101.23 13.36 bdl FRI1 137.15 30.90 249.78 30.70 30.83 62.59 70.68 131.76 19.05 1.26 FRI2 116.39 32.16 275.84 31.60 26.43 77.82 48.95 449.00 22.18 0.22 FRI3 131.65 32.29 252.15 33.62 35.16 65.53 65.05 153.76 17.50 0.26 FRI4 406.56 26.95 274.63 14.83 43.06 52.47 117.03 174.24 18.87 bdl FRI5 687.51 33.02 292.52 33.01 39.37 56.03 62.23 382.08 21.42 bdl FRI6 508.71 28.87 254.68 29.95 36.68 58.78 69.41 255.83 19.07 0.58 FRI7 320.27 28.53 237.98 29.06 31.37 55.20 65.66 149.05 18.82 0.82 FRI8 91.30 36.57 328.04 38.38 4.37 143.75 86.64 425.45 23.87 0.24 FRI9 67.10 37.51 306.08 31.87 22.54 75.72 26.54 846.40 22.49 0.14 GEOR1 420.52 30.46 159.84 185.80 44.93 223.31 93.39 77.50 13.10 1.10 GEOR2 16.44 29.72 162.07 159.46 34.29 192.55 50.89 63.82 12.12 0.08 GEOR3 2021.17 15.48 127.85 252.67 56.55 618.93 190.82 319.79 11.01 0.62 JEA1 228.53 34.02 289.09 24.97 30.38 61.65 79.75 149.89 19.36 0.44 JEA2 9.26 24.41 164.73 192.59 33.29 355.94 21.54 108.05 18.94 0.90 JEA3 620.26 34.15 305.95 25.91 34.31 61.87 73.28 123.06 19.46 bdl KEN1 44.56 30.63 225.98 61.00 35.25 117.47 59.00 217.15 17.34 bdl KEN2 469.21 30.24 334.73 17.49 28.97 43.24 87.56 117.51 22.45 0.27 KEN3 653.60 29.74 321.93 23.28 34.62 44.25 99.44 108.37 22.41 bdl KEN4 862.69 36.95 261.94 65.96 31.72 127.20 198.52 345.40 17.68 bdl 162 Sample S Sc V Cr Co Ni Cu Zn Ga Ge KEN5 368.29 30.24 376.90 88.43 38.62 47.79 89.14 104.49 21.62 0.04 KEN6 206.16 29.53 382.03 81.89 40.93 50.18 85.94 108.05 22.10 0.61 KEN7 939.79 28.41 380.67 74.79 46.86 47.67 87.17 105.01 20.98 bdl KUD1 37.37 23.18 155.50 27.57 35.31 92.29 90.01 70.19 17.41 bdl LAV1 15.51 23.51 159.71 36.16 37.00 110.35 40.82 85.20 19.07 bdl LIB1 662.40 36.73 137.78 9.65 28.77 29.44 54.80 119.97 20.35 0.78 LIT1 478.53 32.85 146.22 9.08 28.26 32.36 52.51 144.51 20.14 0.23 PE1 1338.16 30.75 216.86 28.11 36.18 52.94 98.45 153.41 19.31 0.34 PE2 2297.68 26.59 241.83 36.27 37.37 42.67 122.11 255.93 17.54 0.12 PEG1 64.76 16.86 127.99 139.09 56.67 167.21 252.59 112.03 14.45 bdl PEG2 130.19 17.29 113.53 27.09 39.82 140.23 325.98 106.68 16.70 0.18 PEG3 78.17 18.30 133.81 23.74 38.52 117.88 159.44 93.79 18.36 0.79 PEG4 147.04 11.98 108.51 20.12 38.24 126.03 381.11 110.12 17.10 0.44 PEG5 93.97 7.51 73.23 15.64 30.21 88.74 255.31 96.85 17.78 0.14 PEG6 7.97 20.05 143.59 21.80 34.79 100.82 35.35 86.31 15.71 0.15 SIL1 55.98 32.14 193.28 585.37 58.51 437.63 138.79 174.84 10.61 bdl SIL2 223.63 36.83 291.57 118.55 39.94 66.16 77.74 53.51 14.73 bdl SKE1 84.96 33.19 285.37 7.55 28.00 43.28 117.89 154.22 18.73 0.87 SKE2 455.55 35.41 237.73 25.45 33.03 58.67 71.03 152.17 17.73 1.10 SKE3 102.20 35.16 291.25 9.84 32.27 48.42 121.85 134.20 19.89 1.52 SKE5 48.68 22.86 187.39 185.51 42.40 110.71 99.47 77.74 14.28 bdl SOL1 258.65 33.48 275.84 22.75 34.47 68.90 590.40 299.69 18.23 0.90 SOL2 311.60 29.47 253.96 22.46 35.10 63.60 81.97 81.00 16.71 0.29 SOL3 2888.86 20.15 138.72 276.35 68.77 1015.77 314.85 77.36 15.01 0.64 SPE1 155.04 28.22 207.29 2904.30 42.64 497.45 61.78 120.38 9.61 bdl SPE2 1859.48 36.31 197.16 546.01 58.52 365.20 146.85 208.69 13.45 bdl SPE3 11.15 20.43 152.46 1769.71 40.98 316.74 21.66 89.27 10.14 0.20 SPE4 61.18 31.80 185.83 2912.73 79.86 457.54 52.81 94.70 8.74 bdl SPE5 7.39 21.60 186.99 2144.68 36.82 389.70 18.66 90.40 10.92 0.53 SWA1 384.86 27.52 286.85 137.93 31.37 74.02 186.66 369.80 18.75 0.76 SWA2 54.63 28.27 248.23 102.05 37.76 64.57 62.33 121.59 16.83 bdl SWA3 1775.56 26.31 288.89 117.14 64.55 159.98 328.54 375.13 16.74 bdl TWI1 134.67 33.94 210.16 136.51 53.65 214.55 142.97 95.93 16.16 0.39 TWI2 51.27 29.45 196.22 125.20 34.05 149.93 51.73 72.84 15.36 bdl UNK1 129.11 34.07 263.83 98.84 38.20 48.44 52.31 180.25 16.91 0.16 UNK2 61.34 34.01 319.18 118.47 41.36 59.58 55.33 146.45 19.29 bdl UNK3 121.38 25.87 137.00 8.45 20.56 60.30 248.66 40.36 12.96 bdl UNK4A 476.54 33.13 281.66 16.05 30.35 39.40 143.16 123.18 17.27 0.15 UNK4B 276.47 35.41 311.79 20.47 28.97 43.79 69.31 83.60 19.26 0.18 UNK6 155.26 29.60 212.40 609.04 63.89 370.36 33.43 150.14 15.28 0.74 UNK7 247.91 8.94 105.60 32.50 42.29 151.34 310.56 118.92 16.05 bdl 120A1 1293.05 18.26 171.69 34.71 50.11 63.60 137.89 80.15 15.51 bdl 120A2 33.36 25.32 193.35 224.40 53.43 132.85 83.45 75.13 15.31 bdl 120A3 65.46 18.86 143.60 31.36 27.47 57.10 184.38 180.06 12.75 bdl 120B1 100.22 22.81 188.39 61.50 34.60 74.04 93.85 217.30 15.51 bdl 120B2 123.79 18.55 185.70 134.19 43.03 92.27 66.11 71.53 14.19 bdl 120B3 52.39 21.98 209.50 130.84 44.34 108.30 85.58 186.77 17.35 0.33 163 Sample Rb Sr Y Zr Nb Sb Ba Hf Ta Pb AMI1 1.10 8.81 51.09 312.76 19.87 48.88 bdl 5.96 7.54 0.02 AMI2 0.45 8.05 41.69 321.81 18.42 bdl bdl bdl 9.41 4.13 AMI3 5.27 95.86 29.58 164.78 14.72 bdl 0.94 6.51 10.48 6.17 AMI5 3.49 231.92 28.42 168.34 14.30 bdl 64.52 2.20 12.41 3.31 BAN1 16.46 413.79 28.12 151.02 13.66 43.86 320.54 6.78 4.54 3.74 BAN3 3.16 360.67 27.78 157.03 15.24 46.63 176.25 7.57 8.57 4.56 BAN4 28.42 288.77 31.43 168.75 15.56 61.80 225.10 6.79 2.42 6.26 BAN5 5.12 296.71 29.84 174.00 15.25 bdl 155.45 bdl 7.01 5.05 BAN6 1.39 294.53 30.52 180.68 15.47 bdl 87.11 11.06 6.17 8.10 BAN7 20.04 448.63 31.35 178.89 16.66 52.66 257.19 4.70 2.37 5.02 BAN8 10.89 336.62 28.85 160.10 15.47 48.61 245.51 3.82 4.67 2.46 BRA1 0.75 183.80 29.19 171.16 16.35 49.10 47.16 2.19 3.70 15.22 BRA2 1.90 231.02 28.91 167.27 16.02 39.45 53.17 7.52 4.80 30.08 BRA3 0.86 207.65 28.14 169.84 14.05 bdl 66.62 4.18 8.49 28.86 BRA4 1.52 381.54 28.98 166.41 15.10 54.38 131.78 5.08 6.40 2.38 BRA5 4.17 390.98 28.80 167.56 14.86 49.43 190.96 3.48 3.75 5.98 BRA6 1.63 250.93 30.73 175.86 16.42 56.25 54.72 6.80 1.98 10.29 BRA7 23.39 455.04 29.05 173.10 13.16 bdl 358.61 4.30 5.90 6.18 BRA8 17.15 336.95 23.93 138.15 12.11 bdl 254.58 3.88 9.05 4.79 CLA1 0.67 3.96 29.82 75.67 7.02 61.71 bdl bdl 0.98 1.55 CLA2 0.02 4.02 17.95 81.53 6.93 42.84 bdl 0.37 9.87 8.38 CLA3 0.31 256.14 22.27 73.09 6.52 55.29 bdl 5.42 2.74 14.66 CLA4 bdl 226.86 22.48 67.65 5.82 49.82 5.60 bdl 5.84 2.38 CLA5 0.44 4.45 18.61 74.22 7.29 64.50 bdl 4.09 6.33 1.77 CLA6 0.23 299.06 22.22 75.38 6.09 52.99 bdl 2.87 2.34 7.61 CLA7 0.62 272.73 24.71 75.46 6.57 40.56 6.40 1.47 7.68 2.27 CLA8 0.21 320.01 22.88 63.09 6.09 45.14 0.26 2.02 4.96 2.97 CLA9 0.19 2.45 9.08 234.12 10.58 bdl bdl 6.04 9.84 bdl FRI1 1.28 397.28 51.92 260.93 17.97 55.21 27.78 6.29 5.95 10.91 FRI2 0.12 10.96 35.41 310.79 19.87 53.89 bdl 4.21 8.13 8.05 FRI3 1.12 351.29 50.24 252.91 16.64 43.02 3.71 4.08 6.17 11.62 FRI4 1.43 283.99 42.83 230.50 15.27 43.40 33.61 2.95 6.13 8.43 FRI5 0.22 8.23 64.15 285.40 19.85 50.26 bdl 10.11 3.20 17.37 FRI6 0.57 323.02 50.83 262.30 17.46 49.16 bdl 8.99 7.39 9.05 FRI7 0.88 471.47 54.15 272.43 18.20 48.66 1.22 8.76 8.42 18.20 FRI8 1.01 11.46 35.09 323.05 21.60 53.05 bdl 7.48 4.26 7.62 FRI9 0.44 10.13 42.82 318.86 20.70 53.44 bdl 0.09 16.00 10.98 GEOR1 3.57 314.85 12.24 62.78 5.57 50.18 166.53 2.41 0.68 2.84 GEOR2 0.87 119.23 11.72 52.59 4.88 37.23 17.01 2.02 5.06 27.36 GEOR3 0.25 14.04 10.33 85.64 15.07 43.55 bdl 1.11 6.70 15.43 JEA1 1.99 397.27 50.35 273.67 16.54 48.33 bdl 9.95 9.32 6.02 JEA2 0.75 117.35 33.78 206.73 13.59 48.27 1.94 4.93 7.89 3.66 JEA3 0.76 438.06 51.35 284.35 16.46 48.66 bdl 5.73 6.59 6.90 KEN1 0.43 138.17 25.58 74.69 6.61 51.18 bdl 1.05 7.51 95.45 KEN2 0.88 298.57 29.39 164.96 16.65 48.67 39.59 2.25 2.98 9.08 KEN3 2.86 363.98 27.88 162.07 15.88 54.08 75.78 9.95 3.13 5.84 KEN4 0.79 4.70 19.18 77.18 6.92 58.24 bdl bdl 9.26 12.85 KEN5 5.31 329.98 27.55 166.99 14.59 bdl 407.39 2.94 12.14 3.92 KEN6 5.42 339.08 27.57 170.17 14.05 bdl 337.04 5.01 10.51 3.28 KEN7 4.96 343.79 27.60 167.15 13.96 bdl 415.46 4.30 8.38 4.75 KUD1 bdl 777.98 18.58 131.53 8.24 46.59 38.30 3.28 5.57 7.30 164 Sample Rb Sr Y Zr Nb Sb Ba Hf Ta Pb LAV1 15.05 778.25 16.81 115.91 7.85 46.54 722.83 0.23 7.16 4.03 LIB1 0.34 334.10 60.62 462.27 24.68 45.31 bdl 9.05 2.27 bdl LIT1 77.85 642.24 59.58 451.25 23.70 51.37 637.23 9.66 5.16 2.88 PE1 bdl 269.08 56.83 285.70 18.81 51.57 bdl 9.22 11.60 7.82 PE2 0.12 143.85 60.93 300.74 20.01 47.93 bdl 7.41 4.07 16.67 PEG1 62.60 579.55 15.94 139.22 17.54 bdl 452.02 6.51 12.87 7.03 PEG2 27.53 1284.80 14.79 119.37 17.79 53.69 593.32 7.81 5.31 6.62 PEG3 24.18 856.08 19.72 128.68 19.58 49.10 587.45 4.14 3.23 7.03 PEG4 73.10 674.11 17.93 144.27 20.47 54.59 406.56 4.60 2.93 0.85 PEG5 47.18 718.15 18.49 167.03 22.48 52.45 528.18 3.87 6.76 3.84 PEG6 35.25 972.05 19.09 135.00 10.74 46.78 595.86 6.06 5.46 1.90 SIL1 0.91 7.65 11.22 39.36 4.21 42.77 bdl 2.31 6.84 250.68 SIL2 15.56 601.14 55.37 289.02 17.64 bdl 243.10 2.20 8.96 6.49 SKE1 18.11 394.59 46.99 252.80 15.94 57.13 613.87 4.33 6.22 6.57 SKE2 0.47 348.12 52.50 267.96 16.80 49.76 bdl 4.92 bdl 23.52 SKE3 14.86 296.00 44.72 240.27 16.22 37.61 453.76 10.60 7.93 10.52 SKE5 0.21 938.84 16.21 120.83 6.24 bdl 66.14 9.38 7.73 8.71 SOL1 bdl 4.23 32.33 110.64 8.43 52.40 bdl 1.34 6.62 0.42 SOL2 0.49 111.10 31.21 109.54 8.51 41.75 4.99 3.11 4.46 SOL3 0.43 11.28 14.00 93.98 16.31 37.78 bdl 3.66 6.28 54.87 SPE1 bdl 26.89 9.57 42.56 4.30 bdl bdl 1.89 11.00 5.26 SPE2 0.40 4.12 9.34 48.33 4.79 48.65 bdl 0.50 4.98 2.29 SPE3 0.09 4.09 5.56 37.09 3.24 bdl bdl bdl 6.50 0.60 SPE4 0.76 62.44 9.52 32.95 3.23 bdl bdl 1.98 9.31 1.26 SPE5 0.35 3.39 10.39 41.85 3.23 bdl bdl bdl 7.69 1.01 SWA1 0.52 17.76 46.52 288.38 16.90 bdl bdl 3.80 9.08 35.27 SWA2 4.01 357.44 48.19 259.99 15.54 bdl 115.40 10.46 8.26 9.75 SWA3 0.65 15.79 32.19 275.92 16.14 bdl bdl 12.45 17.22 80.58 TWI1 48.59 17.13 11.31 74.64 5.72 45.08 379.04 2.59 7.21 bdl TWI2 63.09 17.64 12.62 69.77 5.13 44.33 471.15 2.19 2.45 bdl UNK1 0.11 295.01 47.38 254.77 14.29 bdl bdl 4.56 12.64 37.04 UNK2 0.55 335.10 59.33 309.81 17.51 bdl bdl 5.79 15.65 4.17 UNK3 39.77 278.75 20.45 136.72 8.79 43.68 220.82 2.52 3.33 1.22 UNK4A 0.83 305.71 41.43 214.48 14.72 48.06 0.93 10.71 3.06 3.83 UNK4B 0.36 256.94 41.78 245.33 16.18 52.42 bdl 6.46 6.95 1.43 UNK6 0.61 2.76 10.68 51.44 4.92 39.76 bdl bdl 3.44 0.97 UNK7 48.02 457.16 17.97 154.41 21.27 46.27 788.53 4.46 6.34 4.63 120A1 0.54 255.36 19.51 148.40 8.39 bdl 17.90 3.50 5.13 2.13 120A2 1.75 631.22 16.31 123.66 6.84 bdl 184.78 6.52 7.56 9.85 120A3 66.12 126.77 20.67 115.53 7.02 bdl 760.80 4.87 9.59 20.48 120B1 77.28 100.52 19.52 136.65 8.10 bdl 1014.34 3.51 9.12 19.64 120B2 0.33 245.79 16.25 129.68 7.39 bdl 29.19 1.65 9.93 3.56 120B3 56.78 26.50 24.28 145.67 7.62 bdl 667.33 7.21 5.87 51.52 165 Sample Bi Th U Sample Bi Th U AMI1 4.50 9.79 1.44 KUD1 3.44 7.91 0.81 AMI2 2.95 9.52 bdl LAV1 3.82 7.16 0.73 AMI3 4.60 8.30 bdl LIB1 4.52 12.29 1.70 AMI5 3.04 6.60 bdl LIT1 4.55 13.22 1.66 BAN1 3.42 9.45 bdl PE1 5.64 11.48 0.99 BAN3 3.13 11.28 bdl PE2 2.99 10.81 bdl BAN4 2.92 10.53 bdl PEG1 6.67 6.39 bdl BAN5 4.01 7.67 bdl PEG2 4.25 9.46 bdl BAN6 4.81 4.62 bdl PEG3 3.58 10.19 bdl BAN7 5.78 10.97 0.65 PEG4 2.46 11.26 0.62 BAN8 2.67 8.28 bdl PEG5 3.44 10.99 bdl BRA1 4.68 10.45 bdl PEG6 4.30 7.84 bdl BRA2 6.31 9.83 0.57 SIL1 7.15 7.79 0.26 BRA3 6.34 6.76 bdl SIL2 11.07 7.56 bdl BRA4 3.97 9.69 bdl SKE1 4.07 10.86 0.93 BRA5 5.06 10.42 bdl SKE2 4.12 12.00 bdl BRA6 2.95 10.59 bdl SKE3 6.13 10.91 bdl BRA7 4.61 7.76 bdl SKE5 3.45 3.48 bdl BRA8 3.89 5.48 bdl SOL1 4.13 11.21 bdl CLA1 2.52 9.75 0.3 SOL2 4.85 9.91 0.27 CLA2 5.37 10.11 bdl SOL3 3.10 11.29 0.77 CLA3 4.35 7.57 bdl SPE1 4.55 8.75 bdl CLA4 4.52 9.26 bdl SPE2 2.02 9.96 bdl CLA5 5.85 9.46 0.18 SPE3 5.15 6.06 bdl CLA6 3.29 7.74 bdl SPE4 3.44 6.22 bdl CLA7 3.99 7.33 bdl SPE5 3.64 6.95 bdl CLA8 4.06 8.41 bdl SWA1 4.57 10.36 bdl CLA9 2.89 14.28 bdl SWA2 4.21 7.76 0.85 FRI1 3.33 11.05 0.85 SWA3 2.64 9.22 bdl FRI2 5.07 12.92 bdl TWI1 1.39 9.31 0.60 FRI3 1.94 8.40 bdl TWI2 3.39 8.98 0.55 FRI4 2.53 12.71 bdl UNK1 5.14 5.47 0.90 FRI5 2.69 13.56 bdl UNK2 4.45 7.24 1.03 FRI6 4.01 10.01 bdl UNK3 2.71 11.01 0.95 FRI7 5.81 10.12 bdl UNK4A 4.10 11.81 0.96 FRI8 1.07 14.42 bdl UNK4B 5.67 11.49 bdl FRI9 1.37 14.11 bdl UNK6 0.92 10.44 0.49 GEOR1 2.40 8.20 0.40 UNK7 4.08 13.61 0.67 GEOR2 1.49 9.87 bdl 120A1 2.54 9.34 bdl GEOR3 2.41 11.74 0.73 120A2 4.51 6.27 0.82 JEA1 5.16 9.74 0.63 120A3 1.31 8.33 bdl JEA2 4.31 12.59 bdl 120B1 2.73 11.40 bdl JEA3 3.83 8.93 bdl 120B2 3.56 8.48 0.86 KEN1 4.25 8.80 bdl 120B3 4.52 7.85 bdl KEN2 4.08 14.10 bdl KEN3 1.69 11.11 bdl KEN4 1.83 10.56 bdl KEN5 5.10 8.62 bdl KEN6 4.82 5.74 bdl KEN7 5.08 7.41 0.59 166 Summary of Selected Trace Elements Amigo Bank N S td N Mea Std n A Mean dev Min Max n A n dev Min Max S 4 0 356 358 49 861 S 7 0 644 192 470 932 Sc 4 0 28 3 24 31 Sc 7 0 30 2 28 32 V 4 0 341 57 279 391 V 7 0 331 48 275 400 Cr 4 0 91 30 54 128 Cr 7 0 43 30 18 87 Co 4 0 22 13 11 40 Co 7 0 37 5 31 47 Ni 4 0 49 4 45 55 Ni 7 0 42 8 30 54 Cu 4 0 76 22 50 104 Cu 7 0 92 12 79 118 Zn 4 0 98 9 93 111 Zn 7 0 115 7 105 127 Rb 4 0 3 2 0 5 Rb 7 0 12 10 1 28 Sr 4 0 86 106 8 232 Sr 7 0 349 63 289 449 Y 4 0 38 11 28 51 Y 7 0 30 1 28 31 Zr 4 0 242 87 165 322 Zr 7 0 167 11 151 181 Hf 3 1 5 2 2 7 Hf 6 1 7 3 4 11 Brazil CLA Std Std n NA Mean dev Min Max n NA Mean dev Min Max S 8 0 637 328 335 1340 S 9 0 204.7 135.5 51.64 442.33 Sc 8 0 28 2 25 32 Sc 9 0 29.83 8.35 11.37 37.76 V 8 0 338 28 302 388 V 9 0 215.6 43.27 118.69 270.93 Cr 8 0 43 30 18 92 Cr 9 0 180.3 322.54 58.97 1040.1 Co 8 0 34 5 26 43 Co 9 0 34.95 5.4 25.32 42.15 Ni 8 0 43 5 37 51 Ni 9 0 157.6 52.51 102.66 271.15 Cu 8 0 88 6 76 97 Cu 9 0 87.77 97.81 28.87 345.58 Zn 8 0 110 12 85 124 Zn 9 0 161.2 139.49 82.07 522.63 Rb 8 0 6 9 1 23 Rb 8 1 0.34 0.22 0.02 0.67 Sr 8 0 305 100 184 455 Sr 9 0 154.4 145.25 2.45 320.01 Y 8 0 28 2 24 31 Y 9 0 21.11 5.67 9.08 29.82 Zr 8 0 166 12 138 176 Zr 9 0 91.13 53.87 63.09 234.12 Hf 8 0 5 2 2 8 Hf 7 2 3.18 2.09 0.37 6.04 167 F rida y G e orgette N S td N n A Mean dev Min Max n A Mean Std dev Min Max S 9 0 274.07 219.61 67.1 687.51 S 3 0 819.4 1060.2 16.44 2021.2 Sc 9 0 31.87 3.55 26.95 37.51 Sc 3 0 25.22 8.44 15.48 30.46 V 9 0 274.63 29.64 237.98 328.04 V 3 0 149.9 19.15 127.85 162.07 Cr 9 0 30.34 6.41 14.83 38.38 Cr 3 0 199.3 48.05 159.46 252.67 Co 9 0 29.98 11.5 4.37 43.06 Co 3 0 45.26 11.13 34.29 56.55 Ni 9 0 71.99 28.33 52.47 143.75 Ni 3 0 344.9 237.79 192.55 618.93 Cu 9 0 68.02 24.72 26.54 117.03 Cu 3 0 111.7 71.74 50.89 190.82 Zn 9 0 329.73 230.63 131.76 846.4 Zn 3 0 153.7 144 63.82 319.79 Rb 9 0 0.79 0.47 0.12 1.43 Rb 3 0 1.56 1.77 0.25 3.57 Sr 9 0 207.54 194.07 8.23 471.47 Sr 3 0 149.4 152.65 14.04 314.85 Y 9 0 47.49 9.38 35.09 64.15 Y 3 0 11.43 0.99 10.33 12.24 Zr 9 0 279.69 32.13 230.5 323.05 Zr 3 0 67 16.92 52.59 85.64 Hf 9 0 5.88 3.29 0.09 10.11 Hf 3 0 1.85 0.67 1.11 2.41 Jeans Ken S td Std n NA Mean dev Min Max n NA Mean dev Min Max S 3 0 286.02 309.53 9.26 620.26 S 7 0 506 332 45 940 Sc 3 0 30.86 5.59 24.41 34.15 Sc 7 0 31 3 28 37 V 3 0 253.26 77.13 164.73 305.95 V 7 0 326 62 226 382 Cr 3 0 81.16 96.51 24.97 192.59 Cr 7 0 59 28 17 88 Co 3 0 32.66 2.04 30.38 34.31 Co 7 0 37 6 29 47 Ni 3 0 159.82 169.84 61.65 355.94 Ni 7 0 68 37 43 127 Cu 3 0 58.19 31.9 21.54 79.75 Cu 7 0 101 45 59 199 Zn 3 0 127 21.2 108.05 149.89 Zn 7 0 158 92 104 345 Rb 3 0 1.17 0.71 0.75 1.99 Rb 7 0 3 2 0 5 Sr 3 0 317.56 174.58 117.35 438.06 Sr 7 0 260 136 5 364 Y 3 0 45.16 9.87 33.78 51.35 Y 7 0 26 3 19 29 Zr 3 0 254.92 42.07 206.73 284.35 Zr 7 0 140 44 75 170 Hf 3 0 6.87 2.7 4.93 9.95 Hf 6 1 4 3 1 10 168 Kudu Lib Std S td n NA Mean dev Min Max n NA Mean dev Min Max S 1 0 37.37 NA 37.37 37.37 S 1 0 662.4 NA 662.4 662.4 Sc 1 0 23.18 NA 23.18 23.18 Sc 1 0 36.73 NA 36.73 36.73 V 1 0 155.5 NA 155.5 155.5 V 1 0 137.8 NA 137.78 137.78 Cr 1 0 27.57 NA 27.57 27.57 Cr 1 0 9.65 NA 9.65 9.65 Co 1 0 35.31 NA 35.31 35.31 Co 1 0 28.77 NA 28.77 28.77 Ni 1 0 92.29 NA 92.29 92.29 Ni 1 0 29.44 NA 29.44 29.44 Cu 1 0 90.01 NA 90.01 90.01 Cu 1 0 54.8 NA 54.8 54.8 Zn 1 0 70.19 NA 70.19 70.19 Zn 1 0 120 NA 119.97 119.97 Rb 0 1 NaN NA NA NA Rb 1 0 0.34 NA 0.34 0.34 Sr 1 0 777.98 NA 777.98 777.98 Sr 1 0 334.1 NA 334.1 334.1 Y 1 0 18.58 NA 18.58 18.58 Y 1 0 60.62 NA 60.62 60.62 Zr 1 0 131.53 NA 131.53 131.53 Zr 1 0 462.3 NA 462.27 462.27 Hf 1 0 3.28 NA 3.28 3.28 Hf 1 0 9.05 NA 9.05 9.05 Little Tum i P E S td Std n NA Mean dev Min Max n NA Mean dev Min Max S 1 0 478.53 NA 478.53 478.53 S 2 0 1818 678.48 1338.2 2297.7 Sc 1 0 32.85 NA 32.85 32.85 Sc 2 0 28.67 2.94 26.59 30.75 V 1 0 146.22 NA 146.22 146.22 V 2 0 229.3 17.66 216.86 241.83 Cr 1 0 9.08 NA 9.08 9.08 Cr 2 0 32.19 5.77 28.11 36.27 Co 1 0 28.26 NA 28.26 28.26 Co 2 0 36.77 0.84 36.18 37.37 Ni 1 0 32.36 NA 32.36 32.36 Ni 2 0 47.8 7.26 42.67 52.94 Cu 1 0 52.51 NA 52.51 52.51 Cu 2 0 110.3 16.73 98.45 122.11 Zn 1 0 144.51 NA 144.51 144.51 Zn 2 0 204.7 72.49 153.41 255.93 Rb 1 0 77.85 NA 77.85 77.85 Rb 1 1 0.12 NA 0.12 0.12 Sr 1 0 642.24 NA 642.24 642.24 Sr 2 0 206.5 88.55 143.85 269.08 Y 1 0 59.58 NA 59.58 59.58 Y 2 0 58.88 2.9 56.83 60.93 Zr 1 0 451.25 NA 451.25 451.25 Zr 2 0 293.2 10.63 285.7 300.74 Hf 1 0 9.66 NA 9.66 9.66 Hf 2 0 8.31 1.28 7.41 9.22 Peggy Sill Std Std n NA Mean dev Min Max n NA Mean dev Min Max S 6 0 87 50 8 147 S 2 0 139.8 118.55 55.98 223.63 Sc 6 0 15 5 8 20 Sc 2 0 34.49 3.316 32.14 36.83 V 6 0 117 25 73 144 V 2 0 242.4 69.502 193.28 291.57 Cr 6 0 41 48 16 139 Cr 2 0 352 330.09 118.55 585.37 Co 6 0 40 9 30 57 Co 2 0 49.23 13.131 39.94 58.51 Ni 6 0 123 28 89 167 Ni 2 0 251.9 262.67 66.16 437.63 Cu 6 0 235 123 35 381 Cu 2 0 108.3 43.169 77.74 138.79 Zn 6 0 101 10 86 112 Zn 2 0 114.2 85.793 53.51 174.84 Rb 6 0 45 20 24 73 Rb 2 0 8.235 10.359 0.91 15.56 Sr 6 0 847 255 580 1285 Sr 2 0 304.4 419.66 7.65 601.14 Y 6 0 18 2 15 20 Y 2 0 33.3 31.219 11.22 55.37 Zr 6 0 139 16 119 167 Zr 2 0 164.2 176.54 39.36 289.02 Hf 6 0 5 2 4 8 Hf 2 0 2.255 0.078 2.2 2.31 169 Skelm Soll Std S td n NA Mean dev Min Max n NA Mean dev Min Max S 4 0 173 190 49 456 S 3 0 1153 1503.5 258.65 2888.9 Sc 4 0 32 6 23 35 Sc 3 0 27.7 6.839 20.15 33.48 V 4 0 250 48 187 291 V 3 0 222.8 73.667 138.72 275.84 Cr 4 0 57 86 8 186 Cr 3 0 107.2 146.5 22.46 276.35 Co 4 0 34 6 28 42 Co 3 0 46.11 19.624 34.47 68.77 Ni 4 0 65 31 43 111 Ni 3 0 382.8 548.21 63.6 1015.8 Cu 4 0 103 23 71 122 Cu 3 0 329.1 254.51 81.97 590.4 Zn 4 0 130 36 78 154 Zn 3 0 152.7 127.33 77.36 299.69 Rb 4 0 8 9 0 18 Rb 2 1 0.46 0.042 0.43 0.49 Sr 4 0 494 299 296 939 Sr 3 0 42.2 59.77 4.23 111.1 Y 4 0 40 16 16 52 Y 3 0 25.85 10.275 14 32.33 Zr 4 0 220 67 121 268 Zr 3 0 104.7 9.317 93.98 110.64 Hf 4 0 7 3 4 11 Hf 2 1 2.5 1.64 1.34 3.66 Speckled Swannie Std S td n NA Mean dev Min Max n NA Mean dev Min Max S 5 0 418.85 807.54 7.39 1859.48 S 3 0 738.4 913.3 54.63 1775.6 Sc 5 0 27.67 6.73 20.43 36.31 Sc 3 0 27.37 0.99 26.31 28.27 V 5 0 185.95 20.64 152.46 207.29 V 3 0 274.7 22.91 248.23 288.89 Cr 5 0 2055.49 977.69 546.01 2912.73 Cr 3 0 119 18.02 102.05 137.93 Co 5 0 51.76 17.73 36.82 79.86 Co 3 0 44.56 17.6 31.37 64.55 Ni 5 0 405.33 72.31 316.74 497.45 Ni 3 0 99.52 52.57 64.57 159.98 Cu 5 0 60.35 51.9 18.66 146.85 Cu 3 0 192.5 133.2 62.33 328.54 Zn 5 0 120.69 50.8 89.27 208.69 Zn 3 0 288.8 144.87 121.59 375.13 Rb 4 1 0.4 0.28 0.09 0.76 Rb 3 0 1.73 1.98 0.52 4.01 Sr 5 0 20.19 25.64 3.39 62.44 Sr 3 0 130.3 196.69 15.79 357.44 Y 5 0 8.88 1.9 5.56 10.39 Y 3 0 42.3 8.8 32.19 48.19 Zr 5 0 40.56 5.83 32.95 48.33 Zr 3 0 274.8 14.23 259.99 288.38 Hf 3 2 1.46 0.83 0.5 1.98 Hf 3 0 8.9 4.53 3.8 12.45 T win Unknown 1 S td S td n NA Mean dev Min Max n NA Mean dev Min Max S 2 0 92.97 58.97 51.27 134.67 S 1 0 129.1 NA 129.11 129.11 Sc 2 0 31.7 3.17 29.45 33.94 Sc 1 0 34.07 NA 34.07 34.07 V 2 0 203.19 9.86 196.22 210.16 V 1 0 263.8 NA 263.83 263.83 Cr 2 0 130.85 8 125.2 136.51 Cr 1 0 98.84 NA 98.84 98.84 Co 2 0 43.85 13.86 34.05 53.65 Co 1 0 38.2 NA 38.2 38.2 Ni 2 0 182.24 45.69 149.93 214.55 Ni 1 0 48.44 NA 48.44 48.44 Cu 2 0 97.35 64.52 51.73 142.97 Cu 1 0 52.31 NA 52.31 52.31 Zn 2 0 84.39 16.33 72.84 95.93 Zn 1 0 180.3 NA 180.25 180.25 Rb 2 0 55.84 10.25 48.59 63.09 Rb 1 0 0.11 NA 0.11 0.11 Sr 2 0 17.39 0.36 17.13 17.64 Sr 1 0 295 NA 295.01 295.01 Y 2 0 11.96 0.93 11.31 12.62 Y 1 0 47.38 NA 47.38 47.38 Zr 2 0 72.2 3.44 69.77 74.64 Zr 1 0 254.8 NA 254.77 254.77 Hf 2 0 2.39 0.28 2.19 2.59 Hf 1 0 4.56 NA 4.56 4.56 170 Unknown2 Unknown3 S td S td n NA Mean dev Min Max n NA Mean dev Min Max S 1 0 61.34 NA 61.34 61.34 S 1 0 121.4 NA 121.38 121.38 Sc 1 0 34.01 NA 34.01 34.01 Sc 1 0 25.87 NA 25.87 25.87 V 1 0 319.18 NA 319.18 319.18 V 1 0 137 NA 137 137 Cr 1 0 118.47 NA 118.47 118.47 Cr 1 0 8.45 NA 8.45 8.45 Co 1 0 41.36 NA 41.36 41.36 Co 1 0 20.56 NA 20.56 20.56 Ni 1 0 59.58 NA 59.58 59.58 Ni 1 0 60.3 NA 60.3 60.3 Cu 1 0 55.33 NA 55.33 55.33 Cu 1 0 248.7 NA 248.66 248.66 Zn 1 0 146.45 NA 146.45 146.45 Zn 1 0 40.36 NA 40.36 40.36 Rb 1 0 0.55 NA 0.55 0.55 Rb 1 0 39.77 NA 39.77 39.77 Sr 1 0 335.1 NA 335.1 335.1 Sr 1 0 278.8 NA 278.75 278.75 Y 1 0 59.33 NA 59.33 59.33 Y 1 0 20.45 NA 20.45 20.45 Zr 1 0 309.81 NA 309.81 309.81 Zr 1 0 136.7 NA 136.72 136.72 Hf 1 0 5.79 NA 5.79 5.79 Hf 1 0 2.52 NA 2.52 2.52 Unknown4 Unknown 6 S td Std n NA Mean dev Min Max n NA Mean dev Min Max S 2 0 376.5 141.47 276.47 476.54 S 1 0 155.3 NA 155.26 155.26 Sc 2 0 34.27 1.61 33.13 35.41 Sc 1 0 29.6 NA 29.6 29.6 V 2 0 296.73 21.31 281.66 311.79 V 1 0 212.4 NA 212.4 212.4 Cr 2 0 18.26 3.13 16.05 20.47 Cr 1 0 609 NA 609.04 609.04 Co 2 0 29.66 0.98 28.97 30.35 Co 1 0 63.89 NA 63.89 63.89 Ni 2 0 41.59 3.1 39.4 43.79 Ni 1 0 370.4 NA 370.36 370.36 Cu 2 0 106.23 52.22 69.31 143.16 Cu 1 0 33.43 NA 33.43 33.43 Zn 2 0 103.39 27.99 83.6 123.18 Zn 1 0 150.1 NA 150.14 150.14 Rb 2 0 0.59 0.33 0.36 0.83 Rb 1 0 0.61 NA 0.61 0.61 Sr 2 0 281.32 34.49 256.94 305.71 Sr 1 0 2.76 NA 2.76 2.76 Y 2 0 41.6 0.25 41.43 41.78 Y 1 0 10.68 NA 10.68 10.68 Zr 2 0 229.91 21.81 214.48 245.33 Zr 1 0 51.44 NA 51.44 51.44 Hf 2 0 8.59 3.01 6.46 10.71 Hf 0 1 NaN NA NA NA Unknown7 Unknown8 S td S td n NA Mean dev Min Max n NA Mean dev Min Max S 1 0 247.91 NA 247.91 247.91 S 3 0 464 718 33 1293 Sc 1 0 8.94 NA 8.94 8.94 Sc 3 0 21 4 18 25 V 1 0 105.6 NA 105.6 105.6 V 3 0 170 25 144 193 Cr 1 0 32.5 NA 32.5 32.5 Cr 3 0 97 110 31 224 Co 1 0 42.29 NA 42.29 42.29 Co 3 0 44 14 27 53 Ni 1 0 151.34 NA 151.34 151.34 Ni 3 0 85 42 57 133 Cu 1 0 310.56 NA 310.56 310.56 Cu 3 0 135 51 83 184 Zn 1 0 118.92 NA 118.92 118.92 Zn 3 0 112 59 75 180 Rb 1 0 48.02 NA 48.02 48.02 Rb 3 0 23 38 1 66 Sr 1 0 457.16 NA 457.16 457.16 Sr 3 0 338 262 127 631 Y 1 0 17.97 NA 17.97 17.97 Y 3 0 19 2 16 21 Zr 1 0 154.41 NA 154.41 154.41 Zr 3 0 129 17 116 148 Hf 1 0 4.46 NA 4.46 4.46 Hf 3 0 5 2 4 7 171 Unknown9 Ventersdorp lava Std S td n NA Mean dev Min Max n NA Mean dev Min Max S 3 0 92 36 52 124 S 1 0 15.51 NA 15.51 15.51 Sc 3 0 21 2 19 23 Sc 1 0 23.51 NA 23.51 23.51 V 3 0 195 13 186 210 V 1 0 159.7 NA 159.71 159.71 Cr 3 0 109 41 62 134 Cr 1 0 36.16 NA 36.16 36.16 Co 3 0 41 5 35 44 Co 1 0 37 NA 37 37 Ni 3 0 92 17 74 108 Ni 1 0 110.4 NA 110.35 110.35 Cu 3 0 82 14 66 94 Cu 1 0 40.82 NA 40.82 40.82 Zn 3 0 159 77 72 217 Zn 1 0 85.2 NA 85.2 85.2 Rb 3 0 45 40 0 77 Rb 1 0 15.05 NA 15.05 15.05 Sr 3 0 124 112 26 246 Sr 1 0 778.3 NA 778.25 778.25 Y 3 0 20 4 16 24 Y 1 0 16.81 NA 16.81 16.81 Zr 3 0 137 8 130 146 Zr 1 0 115.9 NA 115.91 115.91 Hf 3 0 4 3 2 7 Hf 1 0 0.23 NA 0.23 0.23 172 Rare Earth Elements Table C – 3. Rare Earth Element Concentrations (ppm). La Ce Pr Nd Sm Eu Gd Tb Dy Ho PEG4 30.43 67.81 8.28 32.82 5.90 1.75 4.82 0.62 3.34 0.58 GEOR1 6.77 14.3 1.80 7.28 1.63 0.65 1.77 0.28 1.83 0.39 GEOR2 6.28 15.69 2.17 9.44 1.87 1.91 1.80 0.27 1.73 0.39 SKE1 24.60 54.28 6.82 28.76 6.60 1.81 7.12 1.12 7.23 1.44 SOL1 10.07 23.85 3.22 14.87 4.03 1.22 4.91 0.79 5.27 1.09 SOL2 6.31 14.60 1.86 7.75 1.78 0.43 2.20 0.33 1.99 0.40 KUD1 20.97 43.34 5.03 19.55 3.95 1.12 3.71 0.53 3.15 0.58 SIL1 2.44 5.17 0.67 3.05 0.94 0.44 1.47 0.26 1.79 0.40 JEA1 26.26 61.68 8.00 35.54 8.43 2.48 9.01 1.41 8.86 1.77 FRI1 28.75 65.63 8.45 37.01 8.70 2.37 9.51 1.49 9.45 1.90 LIB1 44.79 99.28 12.10 50.18 10.79 2.77 11.02 1.67 10.41 2.06 LIT1 47.20 101.70 12.14 50.11 10.58 2.81 10.83 1.64 10.10 1.99 PE1 32.32 75.97 9.67 42.01 9.83 2.70 10.44 1.63 10.38 2.08 LAV1 13.28 29.91 3.75 15.99 3.66 1.03 3.59 0.53 3.23 0.61 AMI1 7.29 17.82 2.37 11.21 3.90 0.85 5.43 0.84 5.36 1.13 BAN7 22.57 52.46 6.96 31.14 7.21 2.38 7.02 1.01 5.90 1.09 TWI1 10.7 25.9 2.60 9.88 1.86 0.40 1.66 0.23 1.35 0.27 TWI2 5.70 15.5 1.48 5.77 1.25 0.32 1.52 0.23 1.46 0.29 BRA2 20.5 47.6 6.43 29.2 6.75 2.50 6.51 0.92 5.35 0.97 CLA5 1.79 5.49 0.56 2.71 0.90 0.18 1.40 0.24 1.71 0.36 UNK1 31.6 69.5 8.76 37.5 8.74 2.33 9.30 1.45 9.26 1.85 UNK2 32.5 76.4 9.78 43.0 10.1 2.60 10.9 1.70 10.8 2.21 UNK3 25.0 51.0 5.89 23.8 5.03 1.42 4.63 0.62 3.33 0.61 UNK4A 23.4 52.6 6.55 27.9 6.45 1.76 6.90 1.10 7.06 1.45 UNK6 0.63 1.63 0.21 1.00 0.40 0.10 0.75 0.14 0.97 0.23 REPL 34.2 72.1 8.42 33.3 5.84 1.64 4.64 0.61 3.28 0.59 KEN8 20.5 47.3 6.31 29.0 6.75 2.65 6.57 0.92 5.30 0.98 SWA2 25.1 60.3 7.94 35.5 8.39 2.29 9.03 1.40 8.91 1.81 120A2 20.4 42.9 4.98 19.8 3.99 1.12 3.73 0.54 3.18 0.61 120B2 21.2 44.4 5.16 20.4 4.08 1.12 3.74 0.54 3.16 0.60 173 Er Tm Yb Lu PEG4 1.57 0.20 1.24 0.17 GEOR1 1.16 0.17 1.14 0.17 GEOR2 1.31 0.20 1.32 0.20 SKE1 4.34 0.61 3.99 0.58 SOL1 3.30 0.46 3.14 0.46 SOL2 1.19 0.17 1.13 0.17 KUD1 1.64 0.22 1.42 0.20 SIL1 1.22 0.19 1.24 0.20 JEA1 5.23 0.73 4.82 0.68 FRI1 5.63 0.77 5.15 0.74 LIB1 6.07 0.84 5.61 0.80 LIT1 5.87 0.81 5.27 0.73 PE1 6.21 0.86 5.65 0.81 LAV1 1.74 0.23 1.46 0.21 AMI1 3.59 0.54 3.93 0.62 BAN7 2.97 0.39 2.49 0.36 TWI1 0.89 0.14 bdl 0.15 TWI2 0.90 0.14 1.00 0.15 BRA2 2.66 0.34 2.19 0.31 CLA5 1.09 0.16 1.20 0.18 UNK1 5.51 0.77 5.12 0.75 UNK2 6.45 0.91 5.89 0.85 UNK3 1.71 0.25 1.64 0.23 UNK4A 4.22 0.60 3.93 0.58 UNK6 0.75 0.12 0.91 0.15 REPL 1.60 0.21 1.31 0.19 KEN8 2.66 0.35 2.18 0.31 SWA2 5.24 0.75 4.78 0.69 120A2 1.67 0.22 1.37 0.19 120B2 1.70 0.24 1.55 0.22 174 Appendix D: Standards The following standards were used during the calibration of the XRF spectrometer: AC-E ASK1 ASK-2 ASK-3 BE-N BHVO-1 USGS BR DT-N FK-N GA GH GS-N GSP-1 JA-1 JA2 JB1 JB1A JB-3 JG-1 JG-2 JG-3 JP-1 JR-2 MA-N MICA-FE MICA-MG NIM-G NIM-L NIM-N NIM-P 175 NIM-S SARM39 SARM46 SARM48 SARM51 SARM9 SY-2 and SY-3 Details concerning all standards may be found in Govindaraju (1994). The standard used during ICP-MS analysis for REEs was BHVO2. 176   A plan of Tau Tona Mine. Numbered blocks indicate areas sampled.       Below 120 Level localities (Block 1). Dykes are green and faults are purple. Soll 112 Level localities (Block 2).     100/104 Level Localities (Block 3). Underground Sampling on 104 level (Block 4).   A Plan of Mponeng Mine indicating the localities of the boreholes sampled.   The boreholes are represented by red dots and the dykes are (in this figure and henceforth) depicted in green.                                    Sample localities from borehole number DBH1884. Sample localities from borehole number DBH 1880.                 Localities of samples from borehole number GBH 2918. Localities of samples from borehole number GBH 2919         Localities of samples from borehole number GBH 2922. Localities of samples from borehole number GBH 2928. Localities of samples from borehole number GBH 2939. UD4 85 2m 85 1.0 55 0.85 UD6 UD9-D1 UD9 7565 UD3 LIB8 LOG 12m 0.2m LIB12 LIB4 85 1M 85 LIBTT2002 LIBTT2002-D2 UD1 UD1 UD10 UD32-D8 B2-D1 UD32-D7 B2 UD32-D6 LIB13 UD32 LIB6 LIB13-D4 LIB2 LIB13-D7 B1 LIB13-D5 LIC118 LIBB120 UD14-D1 LIB120SE2 LIB120SE B5 LIB120Q B5 UD36 UD14 B3 LIB18 LIB11 LIB17 LIB17B UD31 75^ LIB1 UD12 UD36-D5 LIB17B-D2 UD55 UD36 -D6 LIB17B-D1 74^ GBH2788 1m UD37-D2 70^ 73^ UD 37-D5 70^ UD 37-D1 80^ 3m MYLONITE IN A FORM OF A SILL 77^ 0.2M UD 37-D4 UD3 7-D3 LIB14 UD 37-D6 85^ 0.3m 48^ UD37 0.25m 0.4m 68^ 75^ 0.4m UD30 0.48m GBH1000 LVB6 UD2-D2 GBH1000-D6 LIB31 LVB5 LVB4 LVB7 LVBA1 LVBH-D4 UD33-D15 LIB34 LIB16B UD54 LVBI-D7 UD13 UD33-D10 UD33-D14 UD29 UD33 UD28 LVBA2 LIB19B LIB19 UD49-D6 LVBA3 UD49-D3 UD49 LIB27 L IB25 UD52 UD25-D8 LIB23 L IB20 LIB21 LIB24 UD25-D10 UD48 UD21 LIB30B LIB35 LIB28 LIB29 LIB30 LIB 29A ELANDSFONTEIN UD42 135 IQ REFERENCE Carletonville Lease Boundaries Inter - Mine Boundaries UD51 Welverdiend GFI MINING SOUTH AFRICA Boreholes UD 9 (PROPRIETARY) LIMITED CLR Intersection Dykes (DRIEFONTEIN GOLD MINE) UD35 Fault Loss Contours UD53 DURBAN ROODEPOORT DEEP TAUTONA UD50 (BLYVOORUITZICHT) SAVUKA UD46 MPONENG HARMONY (ELANDSKRAAL) Fochville As at 30 June, 2009 SCALE 1 : 30 000 0 1 2 3 4 500 0 500 1000 1500 2000 KILOMETRES Metres