The parageneses of sulphide minerals in transgressive carbonatite of the Palabora Carbonatite Complex, South Africa

Abstract

The Palabora Complex, also known as the Palabora Carbonatite Complex, is situated in the Limpopo Province, next to the town of Phalaborwa. The complex intruded the Kaapvaal Craton in early Proterozoic times. The centre of the complex is known as the Loolekop pipe and hosts the youngest rock types of the complex. These rock types are phoscorite (older), banded carbonatite (younger), and transgressive carbonatite (youngest). Transgressive carbonatite hosts one of the world’s largest copper deposits in the form of sulphide group minerals. The paragenesis of the various sulphide minerals is not well known, and a back and forth dispute exists of the formational processes (e.g. magmatic, hydrothermal, autometasomatic, etc.) which led to sulphide mineral crystallisation. This study shows that these sulphide minerals form part of different repetitive assemblages. These assemblages have distinguishable mineralogical, petrographical, geochemical, and paragenetic characteristics. Some assemblages that contain more than one generation of a certain sulphide mineral show differences in mineral chemistry (e.g. pentlandite group minerals, pyrrhotite, chalcopyrite, and sphalerite). The same assemblages that form part of transgressive carbonatite are also found in banded carbonatite. However, the sulphide mineral assemblage of phoscorite is completely different. This is indicative of different sulphide mineralisation events within the Loolekop pipe. The majority of transgressive carbonatite minerals show evidence of a magmatic origin, and most of them have been modified due to hydrothermal activity. Both processes are also responsible for sulphide mineral formation. This study also shows the discovery of sulphide minerals (e.g. heazlewoodite and shandite) and Cu-rich veinlets that have not been observed from this area in the past.