Abstract:
An overview of world class Ni-sulphide deposits (and two examples of African Ni-sulphide deposits/resources) namely Voisey's Bay, Noril'sk, Sudbury Igneous Complex, Jinchuan, Uitkomst and Kabanga shows they have a number of features in common. These characteristics which include tectonic setting, host lithologies and morphology may be used to generate targets for new Ni-sulphide projects. After considering a combination of exploration techniques it was found that stream and soil geochemical surveys combined with airborne electromagnetic (EM) and ground EM surveys are the most appropriate for detecting Ni-sulphide deposits. It is important to discriminate between geochemical anomalies resulting from silicates and those attributable to sulphides. This may be done by identifying areas of coincident, elevated Ni and Cu anomalies or ratios such as Ni/MgO. Likewise with geophysics it is important to use a low frequency (such as 2,5 Hz) EM technique to discriminate between sulphides and conductive sediments or serpentinised ultramafics. Data from exploration programmes needs to be continuously integrated and compared to the genetic model in order to assess the targets potential and know how to further evaluate it. Critical review stages must also be built into the exploration programme in order to ensure that the effort remains focused and that the exploration expenditure remains in balance with the potential outcome. Socio-political considerations as well as infrastructure are important considerations that need an initial assessment before commencing with groundwork and will need to be evaluated in greater detail if initial results are encouraging before embarking on a major drill programme, or when changes occur during the programme. The application of geophysics, genetic models and drilling is illustrated in the case study of lnsizwa (modeled on Noril'sk). Exploration results show this Karoo aged intrusion has little potential to host an economic Ni-sulphide deposit. The application of the deep penetrating mobile metal ion (MMI) geochemistry to a conceptual target analogous to the Sudbury Igneous Complex is given in an overview of the Morokweng Project. Analytical data from a single borehole and the MMI results show that Sudbury style mineralisation is nlikely to have formed at Morokweng.
