Geology

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Open Access
The allanite deposits on Vrede, Gordonia District, Cape Province
(University of the Free State, 1961-11) Hugo, Petrus Jacobus; De Villiers, J. E.; Kent, L
Allanite deposits of an unusual nature occur in two types of granulite on the farm. Vrede, portion of Cnydas West, Gordonia District, Cape Province. The granulites belong to the Archaean complex which is also represented by schists and gneisses. These rocks, which are described in detail, have been correlated with the Kaaien Series of the Kheis System. The ore bodies are characterised by their distinct banding and the close -connection between their distribution and the regional structure of the metamorphic rocks. Allanite occurs with tourmaline, apatite, zircon and monazite in bands ranging from one-sixteenth to two inches in thickness, parallel to the foliation of the granulites. The mineralisation, probably hydatopneumatolytic in nature, started with the introduction of zircon, monazite and tourmaline, after which apatite, allanite, magnetite and quartz followed in that order. The optic axial angle of the allanite is 2V=60° or more. A high magnesian variety, however, has a positive sign with 2V=40°. The range in refractive indices is: no~=1.732 - 1.757 n f3 = 1. 7 4 7 1. 7 68 n~ = 1.759 1.779 This variation is probably due to differences in chemical composition. The three analyses of allanite given have been recalculated on the basis of 13 (O, OH, F) atoms to the unit cell and the formulae obtained conform closely to the formula X₂ Y₃ Z₃ (O, OH, F) 13 developed by Machatschki. Chip sampling was done on all the deposits and the samples were radiometrically assayed against a standard uranium-thorium sample. The average values obtained are Allanite is, therefore, a prescribed material in terms of the Atomic Energy Act. The other ore minerals are all normal in their properties. A crystallising pegmatite is believed to have been the source of the mineralising, solutions giving rise to these deposits. This pegmatite and those of the surrounding area are related to a younger granitic intrusion, probably the acid granite intruded into parts of Bushmanland. The deposits opened up by 1960 occur intermittently over a total area of approximately 600 feet by 200 feet, but their extent in depth has still to be proved. Only the main deposit may perhaps be workable; if the allanite bands there extend to a depth of 200 feet, the ore reserve will be of the order of 1500 tons, assuming that the ore contains roughly 10 percent allanite.
Open Access
Die geologie van die serie Stormberg in die sisteem Karoo, suid van Bethlehem, O.V.S.
(University of the Free State, 1964-08) Kingsley, Charles Seymour; Van Biljon, W. J.
Afrikaans: 'n Gebied tussen Bethlehem en Fouriesburg, waarin alle etages van die Etage Bo-Beaufort tot die Etage Drakensberg verteenwoordig is, is gekarteer asook die veldgegewens opgeteken. Oor geskikte roetes in die gebied is monsters geneem waarop verskillende petrografiese ondersoeke gedoen is. Vanaf swaarmineraalstudies kon gevolgtrekkings gemaak word omtrent oorspronggebied en afsettingstoestande van die Serie Stormberg. Korrelgrootte en -verspreiding is in die sandstene deur sifanalise bepaal. 'n Vergelykende studie is met behulp van die mikroskoop op die sandstene sowel as op die dolerietindringings en lawavloeiings uitgevoer. Uit die resultate kon in hooftrekke die volgende afleidings gemaak word: Die oorsprongrotse van die sedimente moes hoofsaaklik vanaf granitiese stollingsgesteentes wat êrens na die suidooste geleë was afkomstig gewees het. Die afsetting van die sedimente moes in landelike meergebiede geskied het. Die Moltenolae se afsetting moes relatief vinnig onder nat toestande plaasgevind het, terwyl die Eooilae en Holkranssandsteen onder 'n geleidelike droeër-wordende klimaat gevorm is. Die laaste stadiums van afsetting van die Holkranssandsteen het gelyktydig met die eerste lawavloeiings plaasgevind. Laastens was die dolerietgange in hierdie gebied moontlik ook die toevoerkanale vir die basaltiese Drakensberglawa.
Open Access
The relationship between mineralisation and structure in the Pilgrim's Rest - Sabie gold-field
(University of the Free State, 1967) Zietsman, Andries Louis
The area that was investigated, covers the metallogenetic province of the Sabie-Pilgrim's Rest Gold-field in the Eastern Transvaal. The geological formations include the Basement Granite, Godwan Formation, Wolkberg Formation, and the Transvaal System. Diabasic and pyroxenitic sills, pre-mineralisation in age, and probably genetically related to the Bushveld Complex, are present also. Three generations of dykes can be distinguished, one before, one contemporaneous with, and the other after the mineralisation. Three types of folding are present, i.e., tectonic folds that are due to magmatic intrusion. At least two periods of tectonic folding can be distinguished, the one superimposed upon the other. The axes of the earliest folds trend approximately east, while those of the later folds trend north and northeast. Both periods of folding are due to compressional forces which can be ascribed to the intrusion of the Bushveld Complex. Both tectonic and non-tectonic faults are encountered. The tectonic faults consist of low-angle thrust-faults, low-angle gravity-faults, and high-angle normal faults. The thrusts are probably due to the same compressional forces that were responsible for the nortn- and northeast-trending folds, i.e., they are probably related to the intrusion of the Bushveld Complex as well. Evidence of gravitational gliding-tectonics is provided by the presence of low-angle gravity-faults. These structures postdate the thrust-faults. The high-angle normal faults are due to tensional stresses and they are mostly post-mineralisation in age. A remarkable directional relationship between the linear structures and the folds is noticeable. The linear features, as well as the axes of the folds are orientated in three directions, namely, north, east and northeast. The gold-bearing reefs consist of interbedded as well as, transgressive, epigenetic ore-bodies. The interbedded reefs are represented by bedding-thrusts. The localisation and development of these reefs were controlled by the presence of favourable horizons and the intrusion of sills, folding, especially superimposed folding, as well as the formation of the bedding-thrusts. The conditions necessary for the emplacement of the transgressive reefs were the presence of early planes of weakness and/or dykes which are pre-reef in age. The low-angle gravity-faults resulted in the opening of pre-existing fractures such as early high-angle faults, joints and dyke-contacts. Two distinctly different periods of mineralisation are visualised, one preceding and the other postdating the bedding-thrusts. The first period is seen as a process of contact-metasomatism, caused by the intrusion of the basic sills. This process was probably localised and controlled by the folding. The second period of mineralisation was one of fissure-filling by solutions which were introduced during two phases: an early pyrite-rich phase, which was followed by a later copper- and bismuth-rich phase. The bedding-thrusts, as well as the low-angle gravity-faults, acted as channel-ways for the mineralising solutions. The second period of mineralisation, which produced ore-minerals that are typical of mesothermal deposits, is visualised as a metal-liferous front originating from the "root" of the Bushveld Complex. The ore-minerals, including gold, are considered to have been derived from the magma-chamber itself, as well as from the adjacent sedimentary rocks. The deposits of chrysotile in the area are considered to have been localised due to a similar structural control as to that which influenced the localisation of the interbedded reefs, i.e., folding.
Open Access
Die sedimentologie van die Etage Holkranssandsteen, sisteem Karoo
(University of the Free State, 1969) Beukes, Nicolas Johannes; Visser, J. N. J.
Afrikaans: 'n Regionale, sedimentologiese studie van die Etage Holkranssandsteen is gedurende Maart 1968 tot Maart 1969, in Natal, Noordoos-Kaapland, die Vrystaat en Lesotho, voltooi. Die etage is in drie rotsstratigrafiese sones, gebaseer op 45 stratigrafiese profiele, ingedeel. Sone I bestaan uit dik- tot baie dikgelaagde, massiewe, baie fynkorrelrige sandsteen tot sanderige sliksteen. Die kontak met die Etage Rooilae is aan die basis van die deurlopende, massiewe sandsteen geneem. Dit is egter nie 'n vaste kontak nie, aangesien daar 'n geleidelike oorgang tussen die Rooilae en holkranssandsteen bestaan. Sone I bereik sy maksimum dikte in die noorde van die geboed en hier word dit veral deur 'n ligbruin of ligrooi kleur en volop kalsitiese konkresies gekenmerk. Holkranse kom algemeen in die sone voor. Hulle vorm deurdat die sandsteen wat 'n kalsitiese matriks bevat, makliker verweer. Klein, lensvormige afsettings met vlakwaterstrukture word dikwels aangetref. Sone II kan as 'n Kruisgelaagde Sone beskryf word. Dit bestaan uit kruisgelaagde en fynbelaagde, relatief growwer, skoon sandsteen tussengelaagd met massiewe, baie fynkorrelrige, vuil sandsteen. Lensvormige afsettings met kenmerkende vlakwaterstrukture is relatief skaars. Sone III bestaan hoofsaaklik uit massiewe, dik- tot baie dikgelaagde, vuil, baie fynkorrelrige sandsteen in die noorde en weste van die gebied. Na die ooste en suide gradeer die sandsteen lateraal in ligbruin en ligrooi, massiewe, dik- tot baie dikgelaagde, slikkerige sandsteen en sanderige sliksteen met volop klein kalsitiese konkresies. Lensvormige afsettings met kenmerkende vlakwaterstrukture kom algemeen voor, maar is veral opvallend op die kontak met die Drakensbergbasalt. Sandsteenlae kom tussengelaagd met die basalt voor en dui daarop dat die sedimentasie nie volledig met die eerste lawavloeiings beëindig is nie. Sedimentasie het in 'n vlak, binnelandse kom plaasgevind. Die afsetting van die Holkranssandsteen het waarskynlik vroeër in die noorde as in die suide van die gebied begin. Dit kan aan 'n geleidelike verskuiwing van klimaat (gekoppel aan Kontinentale Drywing of Poolverskuiwing) toegeskryf word. Die etage bereik sy maksimum dikte in die suidelike deel van die gebied. Die lokale veranderings in dikte is deur die uitvloei van lawas, wat sedimentasie beïnvloed het, en primêre duinstrukture veroorsaak. Die kruisgelaagde eenhede van Sone II kan aan die migrasie van duine toegeskryf word. Die brongebied van die sedimente was na die weste, noordweste en suidweste geleë en het hoofsaaklik uit sedimentêre materiaal van die Serie Beaufort bestaan. Die korrelgrootte van die kruisgelaagde sandsteen neem in die rigting van afsetting af. Die massiewe sandsteen dui op meer stabiele duine na afsetting, deurdat hulle nie herhaaldelik herwerk is nie. Strukture in die sandsteen word deur verwering of die uniformiteit in korrelgrootte verberg. Duine versadig met water het moontlik tot sandvloeiings en die vernietiging van strukture aanleiding gegee. Die korrelgrootteverspreidings van die sandstene stem met die van eoliese sedimente ooreen. Die kwartskorrels in die gesteentes is hoofsaaklik afgerond, maar die primêre afronding is deur diagenese verlaag. Die korrels besit gematte of pokdalige oppervlakke en dit word aan fisies-chemiese prosesse wat in woestyne teenwoordig is, toegskryf. Die sandstene is halfvolwasse en kan hoofsaaklik as sub-grouwakke geklassifiseer word. Die kruisgelaagde sandsteen is beter gesorteer en meer grofkorrelrig as die massiewe sandsteen. Die mineralogiese samestelling dui daarop dat die sedimente van die drie sones vanaf dieselfde brongebied afkomstig is. Seoliete kom in sommige van die sandstene voor en hulle is aan die vulkaniese aktiwiteite verwant. Die afsetting van die drie sones kan aan klimaatsveranderinge gekoppel word. Sones I en III is onder halfdroë woestyntoestande afgeset, terwyl 'n droë klimaat, soortgelyk aan die van 'n ware woestyn, tydens die afsetting van Sone II geheers het. Ten spyte van die droë klimaat het plante- en dierelewe, tot en met die uitvloei van die eerste lawas van die Etage Drakensberg, bly voortbestaan.
Open Access
A sedimentological study of the conglomerates in the Elsburg stage on the Welkom and Western holdings gold mines
(University of the Free State, 1970-12) Kleynhans, Jacob Johannes; Botha, B. J. V.; Visser, J. N. J.; Antrobus, T.
A sedimentological description of the layers of conglomerate in the Elsburg Stage of the Witwatersrand System, as disclosed by 23 boreholes and underground development on the Welkom and Western Holdings Gold Mines in the Orange Free State Goldfield, is given. The palaeocurrents in the Elsburg Stage as inferred from pebble-size distribution and preferred pebble orientation, were from two different directions. On Western Holdings Limited and the Welkom Mine area west of the Arrarat Fault, the layers of conglomerate were derived from the north-west. On the Welkom Mine area east of the Arrarat Fault, the direction of transport was from the south-west. These two different palaeocurrent directions can be explained by lateral movement along the Arrarat Fault. Thus, the eastern block of the lease area of the Welkom Gold Mining Company, which was formerly situated on the north-eastern flank of a delta fan, was displaced along the strike of the Arrarat Fault for a distance of approximately 6 000 m towards the south, while the western block (Welkom No.3 Shaft and Western Holdings Limited), was displaced towards the north. A detailed analysis regarding the composition, roundness, shape, orientation and sorting of the pebbles in the layers of conglomerate was undertaken. The sorting and roundness of the pebbles increase towards the centre of the basin, while the majority are orientated with their long axes parallel to the palaeocurrent direction. The percentage of non-durabIe pebble types also decreases in a down-current direction, while the durable types remain constant. The pebbles are mostly spheroidal, although certain types show a strong tendency to disc shaped. These features indicate that the layers of conglomerate were probably deposited on an alluvial fan bordering an inland lake or sea.
Open Access
Die geologie van die gebied Poortjie 3022B in die distrikte Britstown, Carnarvon, Prieska en Victoria-Wes, Noord-Kaapland
(University of the Free State, 1977) Van der Westhuizen, Willem Andries
Die geologiese geskiedenis van die gebied was kompleks en word gekenmerk deur verskeie diskordansies en klinodiskondansies asook vulkanisme, vervorming, metamorfose en vergletsering. Die oudste gesteentetipe is die Welgevondengraniet, 'n horst, wat as vloer beskou word. In die noordoostelike hoek van die gebied dagsoom dolomiet; kalksteen en gestreepte ysterformasie van die Sisteem Transvaal. Wes van die Doornberglineament dagsoom gesteentes bestaande uit arkoose, lawa, kalksteen en gestreepte ysterformasie wat vroeër as 'n gedeelte van die Serie Marydale beskou was, maar wat nou die Soetvleiformasie genoem word, en wat 'n ouderdom vergelykbaar met die Transvaalgesteentes het. Die geochemie van die Soetvleilawas dui 'n tholeiïetiese basaltiese samestelling aan. Die lae van die Sisteem Transvaal knyp uit teen die Welgevondengraniet en gevolglik kan die Welgevondengraniet as ‘n gedeelt e van die westelike grens van die Transvaalkom beskou word, of dit kan in hoog in die. Transvaalkom wees met 'n laterale variasie in die litologie wes van die hoog af. Wes van die Welgevondengraniet is daar 'n dik opeenvolging van metapelitiese gesteentes bestaande uit kwartsiete, gneise en amfiboliete wat met die Matsap/Kheis gekorreleer word. Die graad van metamorfose is egter eerder vergelykbaar met dié van die Namakwalandse Mobiele Gordel as met die Kheis- of Matsapdomein verder noord. Die gesteentes het drie hoofperiodes van vervorming ondergaan waarvan die eerste twee isoklinaal ko-aksiaal was, met ‘n noord-noordwestelike strekking, gevolg deur 'n periode van oopplooiing loodreg op die b-plooias van die eerste twee periodes van vervorming. Hierdie laaste periode van plooiing het koepel-en-kom strukture tot gevolg gehad. Die gesteentes wes van die Doornberglineament was aan verskeie temperatuur- en druktoestande blootgestel en gevolglik kan twee isograde deur die gebied getrek word. Daar is 'n toename in graad van metamorfose van oos na wes en die metamorfe gebiede bestaan uit baie laegraadse-, laegraadse- en 'n medium- tot hoëgraadse area. Na die tydperke waartydens vervorming en metamorfose plaasgevind het, het 'n glasiale periode begin waartydens die Serie Dwyka afgeset is. Uit die voorkoms van halietkristalle in die Étage Bo-Dwykaskalies kan afgelei word dat die afsetting van dié Serie onder vlakwatertoestande plaasgevind het en nie in 'n relatief diep see soos aanvanklik vermoed is nie. Na die afsetting van die Karoosuksessie het doleriet, en nog later, kimberliet die Karoogesteentes binnegedring. Die Karoogesteentes word grootliks deur resente materiaal soos kalkreet, sand en grond bedek. Ondergrondse water is geassosieer met verskuiwings en lineêre strukture en goeie lewerings kom voor. Geormorfologies bestaan die gebied uit groot vlaktes met inselberge. Die vernaamste erosiesiklusse was die Afrika- en na—Afrikasiklusse.
Open Access
Die geologie in die omgewing van Britstown
(University of the Free State, 1977) Lemmer, William Murray
Afrikaans: 'n Stratigrafiese kolom is met behulp van geologiese kartering en profiele vir die gebied opgestel. Die twee eenhede van die Ventersdorpgroep kan gekorreleer word met die eenhede in die Bothaville-omgewing. Die nuwe standaard onderverdeling van die Karoosupergroep wat in die gebied gebruik is, verskil van die ou indeling. Paleogeomorfologiese gegewens en primêre strukture toon dat die Dwyka-ysplate in 'n suid-suidoostelike rigting beweeg het. Verskillende afsettingsomgewings soos diep mariene, onderste wegstrand, boonste wegstrand, strandfase, delta-top en kontinentale fluviale omgewings kan in die veld vir die Ecca- en Beaufortgroepe onderskei wrod. Primêre strukture, petrografiese en paleontologiese gegewens dui op 'n diep mariene, beperkte afsettingskom vir die Prins Albertformasie. Die Whitehill- en Tierbergformasies is onder soortgelyke toestande afgeset. Die water het vlakker geword en deltas wat die begin van die Beaufortsedimentasie aandui, het vanuit die suidweste gemigreer. Kontinentale fluviale sedimente is op die sikliese deltaïese sedimente afgeset. Die kontak tussen die Ecca- en Beaufortgroepe is graderend en vir praktiese doeleindes is die basis van die eerste deurlopende sandsteenlaag aan die bokant van die Eccagroep konsekwent as 'n herkenbare en karteerbare eenheid in die veld as kontak geneem. 'n Enkele kimberliet wat nie vantevore beskryf is nie, is gevind. Die verspreiding van kalkreet word beheer deur die topografie en kom net op ou Afrika-oppervlakke voor.
Open Access
Aspects of the hydrogeochemistry of the Karoo sequence in the Great Fish River basin, Eastern Cape Province, with special reference to the groundwater quality
(University of the Free State, 1978-12) Tordiffe, Eric Arthur Wolferstan; Botha, B. J. V.
The aim of the study was to examine some of the major aspects responsible for the chemical quality of the groundwater in the Great Fish River Basin and its influence on the irrigation water. Approximately 18 000 ha of land are at present irrigated from several weirs down the river. The section of the Great Fish River Basin under discussion comprises an area of approximately 25 000 km² located between longitudes 25°E to 27°E and latitudes 31° 15'S to 33° 15'S. This area is divided into the following geomorphologic provinces: The Marginal Region (lower than 760m), the Great Escarpment (750 - 1070m), the Headbas (1070 - 1370m) and the Interior Plateau (higher than 1370m). Each of these provinces play an important part in controlling the movement and the chemical quality of groundwater in the area. Most of the annual precipitation (350 - 450 mm) occurs between February and March when evapotranspiration is at its highest. Runoff from the entire basin amounts to only 3 percent of the annual precipitation. The rest of the water either evaporates immediately because of the semi-arid climatic conditions, or is temporarily stored in the soil before it is lost to the atmosphere by means of evapotranspiration. It is also pointed out that apart from periods of extreme precipitation, the monthly evapotranspiration always exceeds the monthly precipitation. Such semi-arid climatic conditions, as well as the nature of the soils in the area prohibit a fast infiltration of meteoric water and it is therefore doubted whether as much as 5 percent of the annual precipitation over reaches the groundwater table. The area under discussion is underlain by sedimentary rocks of the Karoo Sequence beginning with the glacial deposits of the Dwyka Tillite Formation (680 m) at the bottom, followed by the marine deposits of the Ecca Group (2 340 m), the transitional deposits of the Koonap Formation (980 m) and the fluvial deposits of the Beaufort Group (4 540 m). Because the Koonap Formation represents the transition between the marine (deltaic) deposits of the Ecca Group and the fluvial deposits of the Beaufort Group, it is regarded as a separate formation not belonging to either group. The Beaufort Group on account of the environment in which the sediments were deposited, is subdivided into the Adelaide Subgroup (reducing environment) and the Tarkastad Subgroup (oxidizing environment). Red mudstone is regarded as indicative of an oxidizing environment and is present only in patches in the Middleton Formation, which forms the lower part of the Adelaide Subgroup. No red mudstone is present in the Balfour Formation, which forms the top half of this subgroup, but becomes very prominent in the Katberg and Burgersdorp Formations of the Tarkastad Subgroup. The Balfour Formation, on lithologic grounds, is subdivided into the Oudeberg Sandstone Member (180 m), The Daggaboersnek member (1 200 m), the Barberskrans Sandstone Member (190 mA) and the Elandsberg Member (320 m). It is suggested that the arenaccous units of the Beaufort Group, i.e. the Oudeberg Sandstone Member, the Barberskans Sandstone Member and the Katberg Formation represent periods of major tectonic activity in the provenance which was located to the south-east. During such activity vast amounts of coarse-grained material were transported and deposited at a relatively fast rate. Owing to the semi-arid climatic conditions, which prevail in the area, the soils tend to be rather alkaline with a high clay content and the poor development of an A-horizon. Calcrete or caliche occurs at or near the surface of most of the soils. Dolorite has intruded the sedimentary strata as concordant and conical sills, as well as near-vertical dykes. The dykes in the south of the area have an orientation of approximately 290°, coinciding with the Cape Fold Belt, whilst farther north, a prominent northerly trend with a weaker easterly trend is observed. In the extreme north, where the sedimentary strata is at its thickest, an almost random orientation is present. Various types of dolerite are encountered in the area and of particular interest is the occurrence of quartz dolorite which has intruded a sill of normal dolorite near Speelmanskop. This leucocratic body is probably the result of magmatic differentiation lower down in the cust, whilst limited differentiation whithin the body itself, both from floor to roof and in an "up-dip" direction, must have occurred. The intrusion of the dolerite is of particular importace because of the fracture zones it causes in the adjacent sedimentary rocks. Such zones are normally open to circulating groundwater. Where the dolerite itself is not fractured it may act as an impervious barrier when crossing the regional flow path of the groundwater. In such cases groundwater compartments are developed. Weathering of the provenance and of the various rock-types in the area, diagenetic processes which proceeded the deposition of the sediments in the Karoo Basin and the adsorption and ion exchange during the interaction of the surface and groundwater with the surrounding rocks, are considered to be the main geochemical factors responsible for the changes in the chemical quality of the groundwater in the area. During the chemical weathering of the rock-forming minerals cations such as Na+, K+, Mg++ are released to solution in the groundwater, whilst compounds such as SiO2O3 regroup to form residual clay minerals such as montmorillonite. Weathering of the sedimentary rocks is, however, limited because of the fact that the primary minerals which constitute such rocks have already withstood at least one cycle of weathering in the provenance. In areas where leaching is vigorous, K+ is, however, removed from illite in the mudstone with the result that this clay mineral adopts swelling features similar to montmorillonite, thus causing the rock to crumble. Dolerite in turn, because of its igneous origin, is more prone to chemical weathering. As a result of compaction the porosity and permeability of the sediments in the Karoo Basin was reduced to extremely low values. The chemistry of the interstitial waters was also altered by this process because of the diagenetic alteration of montmorillonite to illite during which K+ is removed from the water, whilst SiO2, H2O, Na+, Ca++, Mg++ and Fe++ are added to the water. During the compaction process, C1- was accumulated in the remaining water in the lower strata as result of ultra-filtration as the formation water was squeezed through clay-rich mudstone layers. Because of its small ionic radius and high electrical charge, Ca++ is adsorbed by the clay minerals in the mudrock of the area to a far greater extent than any of the other cations present. The maximum concentration of adsorbed Ca++ is observed in the Oudeberg Sandstone Member, which suggests that this unit represents a geochemical marker. A gradual increase in the CEC of the mudrock from the lower strata to this unit is furthermore observed. Sodium concentrations increase toward the south of the study area, therefore suggesting an influence of the palaeomarine environment on the adsorbed cations. Groundwater in the Great Fish River Basin is restricted mainly to joints in the sedimentary rocks and to fracture zones caused by the intrusion of dolerite. The water levels in most of the bore-holes therefore represent a pressure or piezometric surface rather than an actual water table. Such levels, however, regionally represent a surface which closely resembles the surface topography, whilst the flow of groundwater is down the regional slope and the rivers act as effluent drainage canals for the groundwater. Although the groundwater is recharged in the higher lying areas by circulating meteoric water, there appears to be no direct relationship between the seasonal precipitation and the groundwater levels. As far as the origin of the major ions in the groundwater is concerned, the cations are derived mainly from the weathering of primary rock-forming minerals, whilst the anions accumulate from non-lithologic sources. Generally, the groundwater in the areas of recharge, i.e. the higher lying areas, has a pronounced Ca++ and HCO-3-character, whilst in the stagnant low-lying areas Na+ and C1- are the predominant ions. In between the two extremes, groundwater with a prominent Mg++ and SC=4-character is encountered. This trend corresponds well with the normal metamorphism of natural waters and appears to be controlled largely by the topography of the area. Groundwater with a distinctly high Na+ and C1- -concentration also has a high salinity concentration. The pH in turn is highest in the areas of high Ca++ and HCO-3-concentrations and lowest in the areas of high Na+ and C1- -concentrations. All the water of the area is, however, oversaturated in relation to CaCO3 and, where conditions are suitable, calcrete is precipitated. Chloride is the dominant anion in the lower strata of the Karoo Sequence and is attributed mainly to the retention of this ion during the migration of the formation waters through the argillaceous material. High salinities, as a result of high Na+ and C1- -concentrations, prevail in the groundwater up to the Daggaboersnek Member. From the Barberskrans Sandstone Member upward, the concentration of these ions decrease sharply. The cation percentages in the groundwater of the upper strata, however very considerably, thus indicating the influence of chemical weathering. There is more SO=4 in the groundwater of the lower strata, which was deposited under reducing conditions, than in the upper strata, which was deposited under oxidizing conditions. This is attributed to the formation of pyrite under reducing conditions, which can later oxidize to release SO=4 to the water. During the periods of extreme precipitation a considerable amount of meteoric water infiltrates down to the groundwater level, dissolving precipitated salts on its way down. This naturally causes an increase in the salinity of the groundwater and is a result of an increase in Na+ and C1-. Seepage water in the Great Fish River contains Na+ as the main cation and increases gradually in concentration farther downstream. To the north of Cradock HCO-3 is the dominant anion but it decreases rapidly farther downstream, with a concurrent sharp increase in the C1- -concentration. The increase in the Na= and C1- -concentration coincides with an increase in the total salt load farther downstream. A similar trend is observed in the change in groundwater quality down the Great Fish River. This is conclusive proof of the influence of groundwater on the seepage water in the river. The groundwater compartments caused by dolerite intrusions also have a marked influence on the quality of the seepage water. During a single irrigation lead from Grassridge Dam the initial irrigation water reaching the consecutive weirs along the river possessed an extremely high salinity load as a result of the solution of precipitated salts in the river bed as well as the flushing of saline water from stagnant pools. The duration of the saline head increased at each consecutive weir downstream. Such conditions present a serious threat to the irrigable land along the Great Fish River and therefore measures will have to be taken to either prevent such contamination of the irrigation water or to limit the application of such contaminated water by allowing the saline head to pass the various weirs.
Open Access
Die sedimentologie van die Soutpansbergsteenkoolveld met spesiale verwysing na steenkoolvorming
(University of the Free State, 1980) Van der Berg, Hendrik Jacobus; Visser, J. N. J.
Afrikaans: Die Karoolae noord van die Soutpansberg is geleë in die Tshipise-kom wat tydens vorming deur oos-wesverskuiwings beheer is. 'n Hoë rug in die vloer verdeel die kom in die weste in 'n suidelike en 'n noordelike trog wat onderskeidelik deur kwartsiet en lawa van die Soutpansberggroep en ouer tuf onderlê word. Die kom is waarskynlik met die swak sone, geskep deur die Limpopo Mobiele Gordel, geassosieer. Na-Karooverskuiwings het 'n rol gespeel in die behoud van die Karoo-lae in die Tshipise-kom. Die Karoo-opeenvolging is litologies in 6 sones verdeel en die sedimentasie van die sones is deur middel van vertikale siklusse bestudeer. Sone 1, aan die basis, bestaan uit 'n onderse Sanderige en 'n boonste Kleiige Diamiktieteenheid. Die Sanderige Diamiktieteenheid word opgebou ui oorwegend diamiktietlae bestaande uit fragmente, enkeles geskraap en gefasetteer, van kwartsiet, lawa en tuf van wisselende grootte in 'n sanderige matriks. Dun warfagtige lae kom soms ook voor. Die eenheid word geïnterpreteer as 'n oorwegend fluvioglasiale afsetting, agtergelaat deur valleigletsers wat ooswaarts teruggetrek het. Fasiesveranderinge kom algemeen in 'n weswaartse rigting voor. Die Kleiige Diamiktieteenheid bestaan oorwegend uit koolstofryke, kleiige sedimente wat waarskynlik ook vanuit die ooste aangevoer is. Grofkorrelrige, sanderige materiaal was egter ook vanaf die sentrale rug in die weste afkomstig en is as kanaalafsettings tussen die kleiige lae afgeset is. Langs die steil afsettingshellings het moddervloeie ontstaan en 'n vermenging van grofkorrelrige en kleiige materiaal het tot die kleiige diamiktietlae aanleiding gegee. Sone 2 bestaan uit sandsteen, skalie-sliksteenassosiasie, moddersteen en steenkool, oorwegend in opwaarts fyner-wordende fluviale siklusse gerangskik. Die sedimente is hoofsaaklik deur meanderende rivieriere op die vloedvlakte as puntwal-, oewerwal- en deurbreekafsettings agtergelaat. Die sandsteen-skalieverhouding van die opeenvolging dui op 'n aanvoerrigting vanuit die noordooste. Tydens kort stabiele periodes het plantmateriaal in vloedkomme onder koel, redusereende toestande versamel en tot dun, afwisselende steenkoollae aanleiding gegee. Die baie wortelafdrukke, paleosols, tussengelaagde skalie en siklisiteit van die steenkoollae dui op 'n oorwegend in situ oorsprong vir die steenkool. Sone 3 volg diskordant op Sone 2 en bestaan uit 'n onderste grofkorrelrige Sandsteeneenheid, opgebou uit opwaarts fyner-wordende siklusse en is deur vlegstrome vanuit die suidooste afgeset. Dit gradeer in 'n Moddersteeneenheid bestaande uit dun opwaarts fynerwordende sandsteensiklusse en dik, grys tot koolstofryke, kleiige gedeeltes. Die afsettingshelling het platter geword en die eenheid is afgestet deur meanderende riviere met wye vloedvlaktes. Hoewel die litologie en sikliese ontwikkeling van Sone 4 presies met dié van Sone 2 ooreenstem, is die gesteentes van Sone 4 oorwegend rooi, pers en groen van kleur en plantmateriaal is afwesig, terwyl karbonaatryke knolle opwaarts in die sone meer algemeen word. Dit dui op afsetting deur meanderende strome vanuit die suide en suidooste tydens warm en droër klimaattoestande. Sone 5 bestaan uit 'n middelkorrelrige, goedgesorteerde sandsteen. Sone 5 bestaan uit 'n middelkorrelrige, goedgesorteerde sandsteen. Sedimentêre strukture aan die basis dui op afsetting deur water, maar hoër op kom uitsluitlik grootskaalse wig- en tafelvormige kruisgelaagdheid voor en word die lae as 'n windafsetting geïnterpreteer. Woestyntoestande het dus op daardie tydstip geheers en die heersende windrigting was vanuit die suidweste. Karoosedimentasie is deur die uitvloei van basiese lawa (Sone 6) en die indringing van dolerietplate en -gange afgesluit. Die Karoolae in die Tshipise-kom kan met dié in die hoof-Karookom gekorreleer word. (i) Die Sanderige Diamiktieteenheid word op grond van afsettingsomgewing en stratigrafiese posisie met die Dwykaformatsie gekorreleer. (ii) Die Kleiige Diamiktieteenheid verteenwoordig 'n oorgangsfase, maar word saam met Sone 2, waarin fossiele van Glossopteris en Vertebraria algemeen voorkom, met die Eccagroep gekorreleer. (iii) Sone 3 word op grond van litologie en die voorkoms van Dicroidium sp. met die Moltenoformasie gekorreleer. (iv) Sone 4 word met die Ellitoformasie gekorreleer. (v) Sone 5 word met die Clarensformasie gekorreleer. (vi) Sone 6 stem ooreen met die Drakensberggroep. Die Beaufortgroep is volgens hierdie indeling afwesig in die Tshipise-kom.
Open Access
The geology of an area west of Welkom, O.F.S.: (degree blocks 2825 A and B and 2826 A)
(University of the Free State, 1980-10) Behounek, Norbert Josef; Grobler, N. J.
Rocks present in the mapped area range from Early Precambrian (Easement granite) to the most recent deposits of aeolian sands, alluvium, gravel and calcrete. Outcrops of Ventersdorp rocks are scarce and widely scattered. Nevertheless, agglomerates and felsic lavas of the Makwas'sie Quartz Porphyry Formation, fanglomerates, .quartzites, volcanic breccias, tuff, mafic massive la.vas and pillow lavas of the Rietgat Formation, quartzites of the Bothaville Formation and plateau lavas of the Allanridge Formation could be distinguished and studied. The latter were all grouped together in accordance with the lithostratigraphic classification of Winter (1976), because of the proximity to his type area. Overlying the Ventersdorp Supergroup are shales and/or tillite of the Karoo Sequence. Bore holes drilled to the east (outside) of the mapped area proved that Dwyka glacial deposits are preserved in pre-Karoo valleys and/or valleys excavated through ice movement. Here, the Dwyka Formation consists of tillite, varved shales and a glacio-fluvial unit, viz. the sandstone-siltstone-shale unito In the western sector of the mapped area. Ventersdorp rocks are directly overlain by black, micaceous shales of the Ecca Group (Prince Albert Formation). The V/hitehill .Formation is probably not present as one continuous layer over the whole of the mapped area, and only occurs in a few isolated pockets. As a result the Prince Albert Formation is in most cases overlain by grey shales of the Tierberg Formation which grades from shales and mudstones (marine deposits) upwards into rhythmic layers of grey shales and sandstones (deltaic deposits). The transitional zone between the Ecca Group (Tierberg Formation) and the overlying Beaufort Group is exposed on the farm Basberg 416. The Beaufort Group in this area shows the typical features of a fluvial deposit, viz. coarse-grained channel-axis facies which laterally grade into finer-grained and thin-bedded hannelmarginal facies and levee mudstone deposits. The latter sediments were most probably deposited on the flood plain of a braided rivero Intrusive rocks consist of post-Karoo dolerites (sills and dykes) and the kimberiite intrusions at Rovic Diamond Mines. Nodular and laminated calcrete deposits are the most abundant calcrete deposits in the area under investigation, Aeolian sands cover large tracts of this area and occurmaiicly as aeolian sheet deposits but also as dunes of variable magnitude. The Vaal River Gravels and the alluvial sands and silts of the Yet and Sand Rivers are the most significant alluvial deposits present in the mapped area. Pans of variable shaper, and sizes have originated through the erosion of paleo river channels by subsequent wind action.
Open Access
The geology of the acid phase of the Bushveld complex, north of Pretoria: a geochemical/statistical approach
(University of the Free State, 1980-12) Bruiyn, Hendrik; Deringer, G. J.
A petrographical and geochemical study of the acid phase of the Bushveld Complex, north of Pretoria, was undertaken with the aim to identify the different rock units, to determine their interrelationships and to classify the rocks as well as describing their geochemistry. The oldest geological formation in the area is the Rooiberg Group which is subdivided into two units, namely the Kwaggasnek (lower) and Schrikkloof (upper) Formations. Petrographical, mineralogical and geochemical data are submitted for the different units. From the data it can be deduced that these units formed as products of a single parental magma, while statistical manipulation of the geochemical data indicates that these formations differ significantly from the Damwal Formation farther to the east. The gradational contact relationships between the felsites and underlying granophyre are described and explained in the text. The various granophyre occurrences of .the Rashoop Granophyre Suite are classifiedand described. The mineralogical, petrographical and geochemical data indicate a limited differentiation trend from the felsites into the granophyre. This may indicate that the granophyre in part resulted from . the rapid crystallization of the parental magma of the Rooiberg Group. A model for the origin and formation of the Rashoop Granophyre Suite, based on petrographical and-qeochernical evidence, is proposed. The granites are subdivided according to age and field relationships, as well as mineralogical, petrographical and geochemical characteristics into the Sekhukhuni, Verena, Makhutso, Klipvoor and Klipkloof granites. The mode of intrusion as well as the mineralogical, petrological and geochemical composition of each type are discussed. A petrochemical investigation of the granites indicate that the various granites, with the exception of the Klipkloof granite, represent the differentiation products of a single parental magma. A similar study on the Makhutso and.Verena granites indicates that leptite assimilation influenced the final differentiation trend in these granites, causing enrichment in certain elements and depletion in others.
Open Access
The source material of the Big Pebble Marker and Rosedale reefs in the Welkom Goldfield
(University of the Free State, 1990-06) Steenekamp, Johannes Marthinus Andries; Grobler, N. J.
English: In this study the clasts of the Big Pebble Marker (BPM) in the Aandenk Formation and the basal conglomerate of the Rosedale Member (ROM) in the Eldorado Formation, in the Welkom Goldfield, were investigated. The aim of this study was to employ a different approach to acquire an insight into the nature of the provenance of the gold-bearing conglomerates in the Welkom Goldfield. To achieve this, the quantitative and qualitative compositions of two coarse and polymictic reefs were studied. Observations were made at six underground IocaIities per reef. At each locality a clean, reasonably flat surface, of three to four square metres, with sufficient conglomerate exposure, was investigated. A modal count of the different types of clasts present was done at one thousand points per exposure with the aid of two grid frames. The long axes of at least two hundred clasts, falling on preselected lines, were measured. The long axes of the ten largest clasts in the selected area were also measured. Representative samples of the various clast types present were taken for laboratory study. Every exposure studied, was photographed. All samples were cleaned meticulously to prevent any contamination with matrix material. A total of 126 samples were analyzed for gold, major and trace elements. A selection of samples were also analyzed by means of XRD and microprobe for mineral composition. Petrographic studies were carried out on thin sections of all the samples. A few samples were investigated by means of electron microscope. Fluid inclusion studies were carried out on four quartz samples. All the field data and analytical results were processed statistically plotted on concentrations on computer. Petrographic information were standard ternary diagrams. Average gold in the different clast types were compared with world wide averages for comparable rock types. Field data indicate different transport mechanisms for the BPM and RDM. Composite or multiple provenances are also indicated for both reefs. Quartz and chert dominate the clast assemblages of both reefs, but more so in the case of the BPM. Results from the clast assemblage plots on the ternary diagrams indicate thrust belt and recycled orogenic provenances for the BPM and RDM. Clasts, derived from greenstone-type source rocks, occur predominantly in both reefs. Silica dominates the chemical composition of the majority of the clasts. On average, chert clasts from the BPM contained the highest gold concentrations (143 ppb) of all the clast types. Based on modal composition, the total c last assemblage of the BPM is approximately 6X more auriferous than that of the RDM (76 ppb vs 12 ppb). Respectively, these figures are approximately 30X and 5X higher than the figure of 2,4 ppb, which is generally accepted for a Barberton-type granite-greenstone crust.
Open Access
The development and application of key profit drivers in mineral resource management
(University of the Free State, 2002-02) Van Niekerk, Gerhardus Johannes; Van der Westhuizen, W. A.; Boer, R. H.
Every mining operation is constantly seeking for new ways to manage a broad range of business variables. Managers across the production chain find themselves torn between the initiatives to reduce costs, balancing throughput and asset utilisation improvements, maintaining product quality, and other similar performance indicators. This they do in their respective areas of responsibility, measuring against their set targets. Herein lies the dilemma: Which operational factors will maximise the profit of the organisation as a whole as opposed to the individual areas. And what is the impact of parameters outside their domains on their performance areas? Phalaborwa Mining Company has been no exception in this scenario. With time the same issues and operational challenges were presenting itself to the management team. The question had to be asked: Would a fundamentally new approach to viewing the business unearth anything new and useful to take this remarkable company to new heights? This study was launched to challenge the views of business and to offer answers to the above dilemma. The study has shown a remarkable degree of interlinkedness between production variables across the production chain. For instance, the mineralogy and petrology of the rock mined had strong effects in the milling, flotation and even smelting processes, and the status of the metal market price conditions offered exciting options to operational managers, provided the relationships are understood. Using an integrated model the magnitude and nature of interrelationships between the drivers of performance are explained. As a result it could provide the capability to "play off' costs against benefits for operating decisions. For example: How long should one keep the open pit mine operational and should it be decommissioned at the same or at a different time as the downstream units? The integrated nature of the business model clearly showed that to reach optimal performance for the whole company, decision-makers across the production chain need to plan collaboratively. It was evident that the powerful modelling approach will loose its effectiveness if the organisational thinking is not changed to a collective one. The model therefore, could only be effective if it is embedded into the planning and monitoring business cycles.
Open Access
Assessment of potential toxic influence of uranium trial mining in the Karoo uranium province
(University of the Free State, 2003) Scholtz, Nicolaas; Loock, J. C.
An assessment of uranium trial mining on four mining sites in the Karoo Uranium Province, South Africa revealed localised above-background values for U, Mo, Pb, Cu, As and Fe in surface - and ground water, soils, sediment and crops. Inadequate remedial action on cessation of mining activities in 1980 led to the presence of uranium ore in stockpiles, open pits, mining shafts, mining equipment and waste dumps within featured areas. Heavy metal contamination is suppressed by the lack of run–off and the dry climate experienced within the mining areas. However, the heavy metal content in surface water and sediment within the open pits on Rietkuil and Mooifontein is especially high. These values pose a risk for human ingestion and may cause cancer in the long term or renal damage over the short term. These pits are easily accessed, lack a fence and are used for a drinking medium by fauna and as a growth medium for flora. The easily accessed Cameron Shaft on Ryst Kuil is a matter of concern due to the possible presence of the radioactive inert gas, radon. Farm owners were unaware of the possible toxic effects of uranium and coherent heavy metals. This led to previous usage of mine water for crop irrigation, the moving and feeding of livestock as well as wildlife amongst uranium ore stockpiles, swimming in water-filled open pits and using crushed uranium ore for gravel road maintenance and construction. The presence of uranium ore in stockpiles and the coherent effects on the water, soils, sediment, fauna and flora and possibly man, prioritises the remediation and rehabilitation of the of uranium trial mining sites within the Karoo Uranium Province.
Open Access
Quantitative evaluation of minerals in coal deposits in the Witbank and Highveld Coalfields, and the potential impact on acid mine drainage
(University of the Free State, 2003-05) Pinetown, Kaydy Lavern; Van der Westhuizen, W. A.
A mineralogical and geochemical study on the coal and coal-bearing successions of the Witbank and Highveld Coalfields in the Mpumalanga Province of South Africa was proposed in order to, firstly, investigate the quantitative distribution of minerals in the lithological units, and secondly, to correlate this data with the potential of the units to contribute to acid mine drainage conditions in the region. X-ray diffraction and X-ray fluorescence techniques were used to analyse the samples from the study area. Samples from the No.1, No.2, No.4 and No.5coal seams were collected from several mines in the Witbank Coalfield, while samples from the No.4 and No.5coal seams were collected from borehole material obtained from the Highveld Coalfield. The inorganic components make up approximately 8.00 to 35.00 wt% of a coal sample. Si02 concentrations varied between 0.00 and 35.00 wt% of a sample, AI203 between 0.50 and 16.00 wt%, Fe203 between 0.03 and 10.00 wt%, and S between 0.15 and 8.00 wt%. Minor concentrations of CaO (0.00 to 8.00 wt%) and MgO (0.00 to 1.00 wt%) were present. P205 occurred in concentrations of 0.00 to 3.50 wt% and K20 was in the order of 0.00 to 1.30 wt%. Na20 values were the lowest varying between 0.00 and 0.45 wt%. The only difference in chemistry between Witbank and Highveld coals was a slight increase in Na20 (0.00 to 0.51 wt%) in the Highveld coals. These results were confirmed by the XRD investigations. The mineral components in the XRD patterns were semi-quantitatively evaluated in terms of dominant (>40% of the mineral fraction), major (10-40%), minor (2-10%), accessory (1-2%) and rare « 1%) constituents. The mineral fraction in the coals was dominated by quartz and kaolinite, with major to minor and trace amounts of calcite, dolomite and pyrite, as well as accessory phosphates phases. XRF and XRD results for the coal-bearing units were also in good agreement. Higher K20 and Na20 concentrations were obtained in the sandstones in comparison to the siltstone and carbonaceous shale samples, and were supported by the presence of feldspars and clays such as illite in XRD interpretations. A normative program designed for Australian coals and sedimentary rocks, called Sednorm, was used to calculate normative mineralogical compositions from the geochemical results. Good \ correlations were obtained for comparisons made between the chemical composition, mineralogical interpretations and normative results for the coal and sediment samples. Acid-base accounting was used to investigate the potential of the coal and coalbearing units to produce acid mine drainage conditions. The acid and neutralising potentials are largely dependant on the abundance and availability of minerals such as pyrite and calcite respectively. According to the screening criteria proposed by Usher et al. (2001), averages for Neutralising Potential Ratio (NPR) suggest that all the coal and coal-bearing units, excluding the unit between No. 1 and No. 2 coal seams, are potentially acid generating. The latter lithological unit is considered to be inconclusive. The average Net Neutralising Potential (NNP) values suggest that the NO.5 coal seam, NO.4 Upper coal seam, and between NO.4 and NO.2 coal seams are potentially acid generating. This is a result of the weathering of carbonates in these lithological units. The other units could become either acidic or neutral. In theory it is possible to calculate the AP from the analysed S by multiplying the S value by 31.25. Assuming that all sulphide-S is available for oxidation, then the total S analysed could be used to predict the AP for samples on which no acid-base determinations has been carried out. Similarly, the excellent correlation between the NP and CaO, and between the NP and combined CaO and MgO, confirms that these chemical components are largely responsible for NP values. It is then also possible to predict the NP by using the CaO and MgO concentrations for samples for which no AP or NP data is available. The application of ABA in this study offered a major contribution to understanding the complexities governing water-rock interactions. Results provided a preview of situations that might arise regarding groundwater quality in a certain area, but also offers ample time to decide on appropriate prevention or remediation programs. The potential for these lithological units to contribute to the deterioration of groundwater is evident.
Open Access
The seismo-deformation of Karoo aquifers induced by the pumping of a borehole
(University of the Free State, 2003-09) Dzanga, Panganai; Botha, J. F.; Cloot, A. H. J.
The research unequivocally showed that pump-induced seismo-deformations exist, especially in boreholes equipped with electric and diesel pumps. Central to seismo-deformations are the mechano- and the geo-acoustic effects on both the borehole water and the aquifer. These aspects of the pump instigate the proposed diaphragmatic deformation hypothesis. In an aquifer the pump vibrations manifest as Rayleigh waves. By virtue of the driving source, the waves are harmonic (White, 1965). To be effective in engineering the proposed diaphragmatic deformation on a hydrostratigraphic unit situated several metres below the ground surface, the waves propagate along the borehole. The component of the Rayleigh wave orthogonal to the unit instigates the deformation and thus oscillations are generated in drawdown curves. Oscillations are a common feature in pumping test data and the masking effect of abstraction makes them inconspicuous. However, the derivative technique when applied to the signal enhances the phenomenon. The technique suppresses the abstraction effect in the data leaving the time-dependent oscillations. The spikes obtained in some of the derivatives of the pumping test data may suggest a one-sided deformation, probably the upper lip to a hydrostratigraphic unit. Coupled with the effects of Rayleigh waves is the pressure variation on the water level caused by the sound. The humming sound of a pump in operation is capable of subjecting borehole water to constant pressure variations thus leading to inherent oscillations in the pumping test data. The conspicuousness of oscillations in the raw pumping test data (Figure 1.2) can be attributed to the high resolution of the equipment used and interferences of different wave forms existing in the system. For a borehole that is continuously in operation, the impact of seismo-deformations on the physical integrity of an aquifer can be detrimental. In hard-rock fractured Karoo aquifers, the induced seismo-deformations can be of astronomical severity. The fact that successful boreholes are drilled in the Karoo within a short distance of a failed or "dried up" borehole is a clear evidence of structural failure. Bedding fractures in particular are very susceptible (Rasmussen, 1998). The radial extent of failure depends on the strength of the vibrations which are habitually intense close to the borehole and decay exponentially-like with distance. The ultimate failure of hydrostratigraphic units after prolonged pumping, which is common in the Karoo, may be due to the evolution history of deformation that accumulates as residual strains and stresses (Botha and Cloot, 2002). The research also revealed that ground displacements are smaller when discharging than when not. According to the hypothesis, this is due to the decreasing hydrostatic pressure essential in opposing the normal stress from a pump. It is in this view that groundwater should be considered as a hydroskelatal component of an aquifer and the rationale of lowering the discharge rate should not only be seen as a process to prevent dewatering but as a mechanism for preserving the dynamic equilibrium between the normal stress emanating from a pump and the hydrostatic force offered by water. Offsetting the equilibrium can lead to irreversible plastic deformation and aquifer subsidence (Botha and Cloot, 2002). The failure of numerical models to simulate the oscillations completely indicates that the wave that triggers the proposed diaphragmatic deformation of a fracture is more complicated than the simple harmonic waveform caused by pump vibrations. The wave should be a convolution of the vibrations, sound and the natural ground roll. Besides, the pump vibrations on reaching a geological feature of interest in a multi-stratigraphic geologic terrain would have undergone multiple reflections and transmissions with the ultimate waveform being a distortion of the primary signal. The research conducted showed that pump-induced seismo-deformations should have the same status as the discharge rate in aquifer management. It is clear that the introduction of measures aimed at reducing the transmission of seismic waves to an aquifer should be a priority in order to deter the pump-induced seismo-deformations. This includes preventing the pump and the borehole casing from coming into direct contact; incorporating gadgets to tone down the frequency of the mains; and installing shock absorbers between the pump and the ground. The selection of pumps should be based on the seismological properties of the aquifer that is to be used and its hydrogeological properties.
Open Access
Geological conditions and environmental impact of the Mohale Dam, Lesotho Highlands Water Project
(University of the Free State, 2004) Letlatsa, Gerard Molatoli; Praekelt, Hermann J.; Van Tonder, Gerrit J.
Abstract not available
Open Access
A proposed method to implement a groundwater resource information project (GRIP) in rural communities, South Africa
(University of the Free State, 2005-07) Botha, Frederik Stefanus; Dennis, Ingrid
English: Groundwater forms an essential part of water supply in the Limpopo Province, South Africa. However, at planning level this message seems to be skewed and misinterpreted. Although a vast number of water supply schemes are developed using groundwater as a resource, these schemes are reported to fail and the resources are not considered sustainable. Therefore mistrust in groundwater has developed, planners effectively eliminate groundwater from integrated water resource planning and groundwater continues to be seen only as an ad hoc or emergency supply. The Groundwater Resource Information Project (GRIP) was introduced to compare available information with verified field information and it presents the information to planners and engineers in a format that is sensible and easy to incorporate, therefore presenting groundwater as an integrated sustainable and strategic resource. The work implemented during this project describes a hydrocensus - an information capturing and presentation protocol that can be introduced anywhere at any scale to give planners the opportunity to consider already developed groundwater infrastructure and incorporate it into the overarching planning. The methodology was developed to describe to the user how he/she should go about when conducting a hydrocensus to serve both the needs of water services and water resource managers. The development of groundwater in South Africa is discussed to provide a perspective on how groundwater was dealt with in the past and is looked upon now. Issues concerning groundwater resource mapping as attempted by the Department of Water Affairs and Forestry (DWAF) and the Water Research Commission (WRC) are discussed and commented on. Also discussed is the availability and format of groundwater data when creating maps and how the data are captured in the different databases. All the maps however are derived from questionable and unverified field data. The legal perspective on groundwater in terms of the National Water Act (NWA), the Water Services Act (WSA) and the Environmental Conservation Act (ECA) is also briefly discussed. The different uses of water are mentioned where groundwater may have a significant contribution. Shortcomings in the Act are also discussed. The proposed methodology spells out the so-called Groundwater Resource Information Project (GRIP) and with marketing in the 21st century becoming more important in science, the slogan “Get a GRIP on groundwater” was adopted. The methodology highlights the importance of an integrated team with various responsibilities and deliverables, the importance of field and office procedures and the involvement of the community. It describes various verification stages where a quality control officer checks field data through ad hoc site visits and where historically disadvantage individuals previously not involved with a project of this nature, can learn from more experience individuals. Information gathered clearly illustrates that vast amounts of money are spent on groundwater development and that the majority of villages in Limpopo already have boreholes in close proximity. The raw data can be used for immediate planning, operation and management purposes. The core of GRIP is, however, dissemination of information and much time was spent to develop an interface where data is captured, validated and placed on a database accessible through the World Wide Web. The data can be downloaded through various methods available on the web page and exported as an Excel spreadsheet. The data can then be imported in a GIS tool and manipulated to develop a series of planning maps, develop site -specific water supply business plans or help planning engineers with day- to-day requests. Prior to GRIP, it was difficult and time consuming for planners in Limpopo to get access to reports compiled by specialists for municipalities or consulting engineers, but through the means developed in GRIP, planning engineers are enabled to stand up in meetings and with hard evidence in hand support future groundwater development and planning, making it truly part of integrated water resource management (IWRM). This study lasted from the beginning of 2002 up to the middle of 2004. Further implementation of GRIP continues in Limpopo and the Eastern Cape and there is a strong possibility that is might be implemented in Kwazulu/Natal and the Free State. The GRIP website, other technology and legislation may change with further implementation of GRIP.
Open Access
The relationship between geological structures and dolerite intrusions in the Witbank Highveld Coalfield, South Africa
(University of the Free State, 2008-05) Du Plessis, Gideon Petrus; Praekelt, H. E.
English: The study forms part of the COALTECH 2020 research program, a collaborative study which aims to ensure the continued viability of the South African Coal Mining Industry well beyond the year 2020. It participates in the Geology and Geophysics Technology Area of the COALTECH 2020 Technology Wheel. The mission statement of this Working Group is to facilitate applied research to identify, quantify and qualify the remaining Coal Resources, starting with the Witbank-Highveld Coalfield, to enable informed decisions when defining and extracting Coal Reserves. The structural investigation of dolerites in the south-eastern part of the Witbank Coalfield contributes to Task 1.1.1; Sedimentological and Structural Model of the Witbank-Highveld Coalfield. The Witbank Coalfield in the Mpumalanga Province of South Africa is situated on the northern sector of the main Karoo basin. The main Karoo basin is described as an asymmetric depository with a stable, passive cratonic platform (Kaapvaal Craton) in the northwest and a foredeep to the south with the Cape Fold Belt on its southern margin. The study area is situated south of the prominent  15m thick Ogies Dyke, which strikes from Ogies in the west to Optimum Colliery in the east. The east-west trending pre-Karoo Smithfield Ridge, consisting of Rooiberg Felsites, bounds the study area to the south and also separates the Witbank Coalfield from the adjacent Highveld Coalfield to the south. The study was conducted on four collieries, namely Bank, Goedehoop, Koornfontein and Optimum Collieries in the south-eastern part of the Witbank Coalfield. The objective of the study is to investigate the intrusion mechanism of the dolerites and the metamorphic effect the dolerite intrusions had on the coal in order to quantify the impact on mining and coal utilisation in the south-eastern part of the Witbank Coalfield. The most important effects of dolerites on mining with a decreasing order of importance are: 1. Decrease in the safety conditions and an increase in the risk of roof failures, pillar and floor stability. 2. Increase in the overall production and mining costs with a decrease in the potential profit. 3. Decrease in saleable tonnages with a decrease in the profit margin. 4. Increase in waste product generation and an increase in the environmental risk. From the objective two separate studies were identified: the first study (A) focuses on the relationship between geological structures and dolerite intrusions and the second study (B) determines the metamorphic effect the dolerite intrusions had on the coal. The structural investigation of the relationships between geological structures and the dolerites is contained in this document. Regional scale information was acquired by using various remote-sensing techniques. The CSIR Miningtek through the COALTECH 2020 Research Program provided this state of the art information. In conclusion to the regional scale study probable relationships between certain Karoo-age dyke, sill and lineament trends that are associated with the northern main Karoo basin and surroundings could possibly provide insight into better understanding of the intrusion mechanism of dolerites in the south-eastern Witbank Coalfield. It is therefore probable that some of the Karoo-age intrusives in the south-eastern Witbank Coalfield followed older basement structures inherited by the Karoo strata and/or syn-tectonic structures related to Gondwana fragmentation which was synchronous with dolerite intrusion (Encarnación et al., 1996). The EW striking Ogies Dyke, which is the main structure in the Witbank Coalfield, most probably pre-dates its associated smaller scale dykes and sills. Conclusions for this relative age difference are summarised as being the following: Its association with EW basement Pre-Karoo diabase, which probably acted as a plane of weakness and might have triggered its earlier intrusion. Difference in geochemical and mineralogical characteristics. Absence of sills immediately to its north. Should the NS striking dykes north and south of the Ogies Dyke be favoured by cooling joints which developed as a result of its earlier intrusion, the age difference is evident. Comparing the physical appearance of the ± 20m sill (main sill) in the Witbank Coalfield with the B8 sill in the Secunda Coalfield, the two sills have a number of properties in common. However, these physical property comparisons are not precise and it is therefore suggested a detailed geochemical analysis be undertaken focussing on the mineralogy, major and trace elements. The sedimentary sequence is reconstructed by removing the main sill from the stratigraphy. The reconstruction is aimed at determining if a spatial relationship exists between the coal seams, the intra-seam strata and the main sill prior to the intrusion event. Borehole information on the elevation of the pre-Karoo basement is sparse as borehole penetration was terminated at the bottom of the coal seam of interest. The removal of the dolerite convincingly reveals the pre-Karoo basement topography, palaeo-floor and -roof morphology, as well as the width distribution of the sedimentary units. The following reconstructed sedimentary units were examined individually: No. 2 Coal Seam; Facies between the No. 2 Coal Seam and No. 4L Coal Seam; No. 4L Coal Seam; Facies between No.4L and No. 5 Coal Seam; No. 5 Coal Seam. The examination process of the data of each unit starts with the statistical analyses thereof which includes histogram and probability plots of the palaeo floor, width and palaeo roof. The investigation resulted in nearly direct linear correlation curves which disclose the existing relationships between the palaeo floor elevations of the No.2, No.4L and No.5 Coal Seams. Considering the range of correlation coefficient values of 0.81 to 0.99 for the palaeo floor elevations it convincingly reveals the co-existing relationship in the geometry of elevations throughout the entire stratigraphy of the sedimentary sequences. Several sedimentological factors contributed to the present day geometries and widths of coal and associated clastical sedimentary rocks of sequence of succession. The evidence in the relationship of the geometries of the palaeo floor and roof elevations concludes that irrespective of variable intra-seam strata and coal seam widths the pre-Karoo topography is reflected throughout the entire stratrigraphic sequence. Prior to sediment burial, plant growth took place most probably on similar structural relief of gentle attitudes. To conclude, a four-stage model is proposing how burial could have influenced widths and aerial distribution of peat and intra-seam clastic sedimentary rocks of sequence of succession. At the time of peat formation, the unconsolidated sediments had not yet undergone a great deal of lithification in that the floor structure of the peat might have been without undulations. In conclusion, a reasonable inverse relationship between the net width of the stratigraphic sequence from the palaeo floor of the No. 2 Coal Seam to the palaeo roof of the No.5 Coal Seam and the floor elevation of the main sill exists. A Quantile-Quantile-plot and the regression slope analysis of the data sets convincingly conclude the inverse relationship that exists between the floor elevation of the main sill and the net width of the almost entire sediment sequence. In this context the reasonable negative correlation coefficient of -0.57 is good. This negative correlation implies that where the main sill is present in the lower stratigraphic levels it underlies thicker sedimentary sequences and conversely where the sill had stepped up to higher stratigraphic levels it underlies the thinner sedimentary sequences. In conclusion the differential compaction of the sedimentary strata was in the main controlled by the the Pre-Karoo basement topography. This in turn resulted in the fracturing and jointing of the sedimentary rocks over the flanks of the pre-Karoo basement topography which to a large extent controlled the propagation path of the main sill. Evidence established in this study suggests the effect of basin tectonics to be the overriding controlling factor of the stratigraphic position of the main sill in the Vryheid Formation sedimentary rocks of sequence of succession of the south-eastern Witbank Coalfield. Other factors i.e. the influence of the Ogies Dyke and syn-tectonic related regional scale structures seem to have had some control in the propagation paths of the associated offshoots of the main sill.
Open Access
Petrochemical characterization of dolerites and their influence on coal in the Witbank Highveld Coalfield, South Africa
(University of the Free State, 2008-08) Du Plessis, Johannes Jochemus; Van der Westhuizen, W. A.
A study was firstly conducted on the mineralogy and geochemistry of the dolerites, secondly on sedimentological controls (syngenetic) on coal deposition and diagenesis to gain a better understanding of the environment of the coal deposition and thirdly, the metamorphic influence of dolerite intrusions (epigenetic) on coal. The Ogies Dyke is the only intrusion found in the study area at Optimum Colliery. The absence of dolerite sill intrusions in this area made it possible to study coal deposition and diagenesis. It was to investigate the behaviour of a 20m thick bifurcating dolerite sill (the Witbank sill) and its associated metamorphic influence which occurs in the other Koornfontein, Bank and Goedehoop Collieries. The most prominent structure, the Ogies Dyke, forms the northern limit of the study area and forms a very important part of the geochemical and mineralogical study. Thin section investigations revealed the involvement of plagioclase in both the Witbank and Sasolburg dolerite fractionation assemblages indicates that the fractionation processes must have occurred within the crust although within different depths. The absence of pyroxene phenocrysts in the B5 sill (Sasolburg) indicates that the fractionation took place at a pressure significantly higher than that at which the plagioclase and olivine microphenocrysts have formed. The high percentage olivine in the B4 sill (Sasolburg) indicates that these two sills originated from different magma sources. Plagioclase microphenocrysts in the B5 sill as oppose to the macrophenocrysts of the B4 sill concludes that the fractionation processes of the B5 sill must have happened deeper within the crust. This study engage with dolerites that crystallised rapidly, intermediately and slowly as the crystal sizes are directly related to magma cooling. Fine crystalline dolerites like the chilled margins and bifurcations tend to be more susceptible for alteration as opposed to the medium and coarse crystalline dolerites. The 40m thick, fine crystalline B4 sill has undergone the most alteration comparing to the B5 sill, Witbank sill and the Ogies Dyke. The differences identified during this study distinguish the Sasolburg dolerites from the Witbank sill and the Ogies Dyke. X-ray fluorescence techniques were used to analyse the dolerite samples from the study area. All the dolerites are falling in the “basic” group. The B4 – Sasol dolerite sill is a high-MgO (picritic) basalt while the rest are basalts. The chilled margins of the bifurcations have an arithmetic mean of 4.89% MgO and the Ogies Dyke has 4.9% MgO and can be classified as evolved basalts. Lower MgO and Ni values in the Witbank bifurcations comparing to the Witbank sill indicate that the bifurcations are more evolved. The basaltic and evolved basalts can further be divided into low and intermediate K2O concentrations. A higher K2O concentration is placing the Ogies Dyke in the intermediate-K2O group whilst the Witbank sill (interior and chilled margins), and the Witbank bifurcations (interior and the chilled margins) are all falling in the low-K2O group. Two of the Witbank bifurcations (interior) having intermediate-K2O concentrations and are associated with the Ogies Dyke. The picritic B4 sill (Sasol) is also classified as a low- K2O dolerite. Considering K2O and MgO element concentrations the samples are falling in three categories, from evolved to picritic with the majority in the basaltic field. Borehole information was used to conduct isopach and isopleth maps of the pre-Karoo topography, floor elevation and thickness distribution, coal parameters and statistical data of various coal seams to underpin the sedimentological controls (syngenetic) on coal deposition and diagenesis The undulated platform onto which the No. 2 Upper Coal Seam formed at the Optimum study area had a major influence on coal grade. Thicker coals were deposited in the lower lying areas while they were thinning towards palaeohigh areas. Significant values indicate that the thinner coals are higher in ash (air-dry), lower in VM (daf), lower in CV MJ/kg (air-dry) and higher in relative density comparing to the coals deposited in the lower lying areas of the palaeovalley. Lithological descriptions from boreholes and structural interpretations in geological crosssections revealed the presence of a green 20m thick, bifurcating dolerite sill that intruded into the Vryheid formation of the Karoo Supergroup. It is associated with ±20m displacement and metamorphism on coal which is putting major constraints on coal mining in general. The metamorphic influence of the coal is largely restricted to the width of the contact aureole. The nature of the aureole depends on the geometry, variation in thickness and bifurcation of the sill. It is also found that the metamorphic contact aureole is much more extensive in the displaced and uplifted coal seams comparing to those beneath the sill. Moisture (ash-free) of the proximate analyses, volatile matter (daf), CV (daf) and approximated ash yield (AD) isopleth maps show that the dolerite sill caused a localised increase in rank. Areas of high moisture (proximate analyses moisture content) correspond to devolatilised areas, which are higher in ash and therefore having lower CV’s and are adjacent to known intrusions.