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Discovery of the Flatreef (interpreted as the down dip, sub-horizontal extension of the Platreef in Transvaal, South Africa), has opened new avenues for enquiry that allow the study of a magmatic stratigraphy less affected by footwall interaction. A study has been carried out of the Sr isotope composition of plagioclase through a 280 m thick intersection of the Flatreef and its footwalls and hanging walls as intersected by borehole UMT-393 drilled on the Macalacaskop farm. Comparison of the Sr-isotopic composition and the anorthite content of plagioclase across this intersection with data from the Merensky and Bastard cyclic units elsewhere in the Bushveld Complex supports the proposition that the Flatreef is a correlative of the Upper Critical Zone-Main Zone transition, including the Merensky and Bastard cyclic units. The available data suggest that the sulphides of the Flatreef and its correlatives in the remainder of the Bushveld Complex originally formed in a deeper staging chamber. During continued magma ascent some of the sulphides were entrained and deposited in the Flatreef., Discovery of the Flatreef (interpreted as the down dip, sub-horizontal extension of the Platreef in Transvaal, South Africa), has opened new avenues for enquiry that allow the study of a magmatic stratigraphy less affected by footwall interaction. A study has been carried out of the Sr isotope composition of plagioclase through a 280 m thick intersection of the Flatreef and its footwalls and hanging walls as intersected by borehole UMT-393 drilled on the Macalacaskop farm. Comparison of the Sr-isotopic composition and the anorthite content of plagioclase across this intersection with data from the Merensky and Bastard cyclic units elsewhere in the Bushveld Complex supports the proposition that the Flatreef is a correlative of the Upper Critical Zone-Main Zone transition, including the Merensky and Bastard cyclic units. The available data suggest that the sulphides of the Flatreef and its correlatives in the remainder of the Bushveld Complex originally formed in a deeper staging chamber. During continued magma ascent some of the sulphides were entrained and deposited in the Flatreef.

The in-situ major element, trace element, and Sr-isotopic compositions of plagioclase in the broadly gabbroic cumulates from the Upper and Main Zones of the Northern Limb of the Bushveld Complex, as obtained from the Bellevue (BV-1) and Moordkopje (MO-1) drill cores have been determined by means of electron microprobe and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS). The results show the existence of inter and intra-crystal initial 87Sr/86Sr disequilibrium of coexisting plagioclase, a phenomenon which has received rather rudimentary attention not only in the Bushveld Complex, but in other layered intrusions as well. This disequilibrium is particularly striking in samples from the Lower Main Zone, an interval which also records a lack of differentiation, as exemplified by the An% of plagioclase. In the rest of the stratigraphy, up to the top of the Rustenburg Layered Suite, there is less, if any, inter and intra-crystal initial 87Sr/86Sr disequilibrium of plagioclase coupled to more prominent differentiation trends. These results are in support of a model for the petrogenesis of this part of the Bushveld Complex, which involves the Lower Main Zone forming through the repeated intrusion of crystal mushes derived from a deeper seated, sub-compartmentalized staging chamber, into the Bushveld main magma chamber, with fractionation processes being key in the formation of the Upper Main and Upper Zones. Based on the initial 87Sr/86Sr composition of plagioclase, the Northern Limb of the Bushveld Complex can also be divided into a putative integration and differentiation stages, similar to the Western Limb of the Bushveld Complex. The integration stage in the Western Limb included the Lower, Critical, and Lower Main Zones, whereas the differentiation stage included the Upper Main and Upper Zones. The integration stage in this study incorporates the lower reaches of the Lower Main Zone, with the rest of the stratigraphy up to the top of the Upper Zon, National Research Foundation (NRF)

The formation of the Merensky reef still remains controversial despite of its economic importance and decades of research. Remaining questions like, the variability of the Merensky reef and how this effects the platinum distribution (e.g. whether the grade or distribution of platinum is influenced by the presence or not of pegmatoidal Merensky reef, whether PGE distribution are more associated with sulphides or with chromites) are still unanswered. Data were generated in order to address some of these questions. This study was undertaken in the south-western portion of the Western lobe of the Bushveld Complex on intersections of pegmatoidal and non-pegmatoidal Merensky reef from Impala Platinum Mine. The two non-pegmatoidal reefs correspond to the normal Merensky ‘A’ type reef and the pegmatoidal reef corresponds to the Merensky ‘B’ type reef according to the classification by Leeb-du Toit (1986). The core was analysed in 2 cm intervals. Samples were analysed by optical microscopy. Quantitative analysis was done using scanning electron microproscopy and electron microprobe analysis. Major elements and trace elements were determined by using ICP-MS (inductively coupled plasma mass spectrometry). Platinum-group elements (PGE) were determined by Ni-S fire assay with an ICP-MS finish and sulphur by an Eltra Infrared Analyser. Macroscopic investigation of the drillcores identified an anorthositic footwall with an overlying basal chromitite stringer and a pyroxenite hangingwall for the two non-pegmatoidal reefs. The pegmatoidal reef consists of an anorthositic footwall, a bottom chromitite stringer, a pegmatoidal layer with an overlying top chromitite stringer and a pyroxenite hangingwall. Microscope analysis showed one sulphide inclusion visible in a chromitite grain which displayed a negative crystal shape imposed by the crystal structure of the host chromite. This could indicate the presence of sulphide liquid in the system at a very early stage. This might be an indic, Inkaba YeAfrica Project, Impala Platinum Mine

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