Abstract

Weathering and groundwater dispersion were studied at the North Miitel komatiite-hosted Ni sulphide deposit to understand the near-surface signature of this economically important mineralization style. Soil chemistry, regolith chemistry and groundwater chemistry show the secondary Ni enrichment is weak, limited primarily to the residual parent material and dispersed a few hundred metres laterally and only a few metres vertically above the water table. Partial extractions of soils did not enhance the visibility of the mineralisation to geochemistry. However, a subtle Ni anomaly was observed in the interface of the carbonate/clay accumulation at c. 30–40  cm depth. The results show weathering and hydromorphic dispersion by groundwater are responsible for the large geochemical halo related to mineralisation at a depth of 10–20 m. A second mechanism involving gases or vegetation is proposed for the subtle near-surface anomaly. To successfully explore through transported cover it is essential to understand how surface anomalies form, what metals move and which sample media will best represent the buried ore signature. Here, groundwater provides the largest multielement target (Ni, Co, Pt and Pd), residual regolith is most accurately able to locate the mineralisation using Ni, and Ni in the soil clay/carbonate interface presents the easiest to collect but subtle surface geochemical signature of the primary ore which is buried 400 m below surface.

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