Nickel potential of the Molopo Farms Complex in the area of Jwaneng- Makopong shear zone

Abstract

The Molopo Farms Complex (MFC), located in southern Botswana, is likely to have had the same origin as the Bushveld Complex. It has been a subject of several economic studies which reported Ni-Cu-PGE mineralisation associated with a suite of well-layered ultramafic rocks. Following previous studies and self-gathered data, Kalahari Key Minerals Exploration Company (KKME) has proceeded with exploration in the Jwaneng-Makopong shear zone in the MFC, where a gravimetric and electromagnetic anomaly was detected, motivating the drilling of two boreholes, KKME – 1/6 and KKME – 1/14.

Whole rock and initial petrographic data in borehole KKME – 1/6 indicated several mineralised portions with an anomalous Ni enrichment. This prompted further studies to understand the characteristics and potential of the Ni mineralisation. Borehole KKME – 1/6 is characterised by variably alternating sequences of mostly heavily serpentinised orthopyroxenite and harzburgite. Nickel mineralisation is observed in both orthopyroxenite and harzburgite in relatively narrow zones comprised of interstitial sulphide blebs or disseminated sulphide grains. There is a predominance of Ni-rich sulphides, mainly pentlandite and heazlewoodite, as well as a Ni-Fe alloy, awaruite, and a Ni arsenide, orcelite, locally associated with a disseminated chromite-enriched layer.

XRF data showed the existence of high Ni enrichment (28174 ppm Ni) in sample IMK – 05149, as well as a general enrichment of ~2000 Ni ppm. With the help of the TIMA, it was possible to calculate the Ni deportment, where results indicate that the overwhelming majority of Ni is present in ore minerals, especially in the most enriched samples, however, a base Ni amount was calculated to belong to the silicates and oxides (non-recoverable) around ~1000 – 1500 ppm Ni. The TIMA results show that a minor Ni proportion occurs within the gangue minerals, but the anomalous enrichment is attributed to the ore assemblages where Ni is recoverable. The textural and compositional characteristics of the mineralisation, as well as its assemblages, are suggestive of complete replacement of the primary magmatic sulphides and late formation of the present minerals, indicating a secondary origin for this mineralisation. The main serpentinisation event is suggested to have been the main contributor of ore mineral formation which implies a strong relevance of the alteration events and processes for the formation of the mineralisation in this study, and, by extension, the studied area of the Jwaneng- Makopong shear zone of the MFC.