The Selebi-Phikwe copper-nickel deposit, located in north-eastern Botswana, is hosted by the Phikwe Complex. The Phikwe Complex is within the Central Zone of the Limpopo Mobile Belt which has been subjected to two episodes of regional metamorphism. The Phikwe Complex consists of various types of gneisses such as granite gneiss, hornblende gneiss, biotite gneiss, pelitic schist, amphibolite and meta-sedimentary rocks. It is generally accepted that Ni-Cu mineralisation is hosted in metamorphosed gabbronorites, pyroxenites and peridotites. Previous studies investigated Ni-Cu mineralisation in the Selebi-Phikwe ores from geological, mineralogical and geochemical aspects to discuss petrogenesis of these ores and host rocks, including the Ni-Cu mineralisation. Apart from (Wakefield 1976), relationship between sulphide mineralisation and metamorphism on the Selebi-North sulphides has been rarely investigated. Therefore, the aim of this study is to discuss the formation process of sulphide ores, taking into consideration the effect of metamorphism on the Selebi-North sulphide deposits. The objectives are i) to identify and study the textural relationship between ore and rock-forming minerals, ii) to determine the geochemical composition of host rock and Ni-Cu mineralisation and iii) to determine the pressure-temperature conditions at the Selebi-North area. After collecting samples from the Selebi-North underground mine, petrographic, geochemical, and mineralogical works were conducted using a petrographic microscope, an Inductively Coupled Plasma-Optical Emission Spectrometer and Electron Probe Micro Analyzer. The collected and identified samples were mica-free amphibolite, mica-rich amphibolite, biotite schist and Ni-Cu ore. Petrographic investigations revealed that minerals present in mica-free amphibolite are amphibole, plagioclase, quartz and disseminated sulphides and oxides. Mica-rich amphibolite is composed of amphibole, plagioclase, biotite, quartz, oxides and disseminated sulphides. Furthermore, biotite schist is primarily composed of biotite, plagioclase, quartz, disseminated sulphides and oxides. Sulphide minerals present in all types of ores consist of pyrrhotite, pentlandite, chalcopyrite and pyrite. Silicate minerals and magnetite are also observed in these ores. Based on the amount of ore minerals, ore is classified into disseminated, semi massive and massive.Disseminated to semi-massive ores often show sulphides along the foliation and schistose plane, implying that the ore and host rock were subjected to metamorphism. Three different occurrences of mineralisation were observed in the ores i) sulphides along the gneissic fabric, ii) sulphide veinlets cutting across the gneissic fabric and iii) mineralisation associated with sericite and biotite alteration. Pyrrhotite is the predominant sulphide in massive ores and often contain lamellae of pentlandite. Pentlandite occurs dominantly associated with the pyrrhotite grain as lamellae and loop textures and along the grain boundaries of pyrrhotite (Figure 12 F and G). Chalcopyrite commonly occurs in relatively higher abundance in close proximity to amphibolite silicates in semi-massive ore and at the margins of pyrrhotite in massive ore (Figure 12A-close proximity with silicates and G chalcopyrite exsolved from sulphides). Furthermore, chalcopyrite has been observed to infill cracks and cleavage planes along silicate minerals. Minor pyrite occurs predominantly in sheared areas. Magnetite occurs mainly as subhedral and euhedral and sometimes with sulphide inclusions, indicating that sulphur was saturated during magnetite crystallization in the magma. Whole rock geochemical analysis shows that the host rocks of the Ni-Cu mineralisation are characterised by slight enrichment of the LREE and displays a negative Eu anomaly. On the basis of the trace element data, it indicates that ores and rocks in Selebi-North were formed in island arc basalt, a subduction setting. The Selebi-Phikwe deposits has been documented to be subjected to two episodes of metamorphism that occurred at 2.7-2.6 and 2.0Ga.The pressure-temperature conditions prevailing at Selebi-North were determined to be 706-711 °C and 6.2-7.3 kbar. During these metamorphic conditions, pentlandite is postulated to have been not been melted.

Thesis (MSc in Geological Sciences)---Botswana International University of Science and Technology, 2023