Relationships between regolith materials, petrophysical properties, hydrologeology and supergene Ni enrichment at the Cawse Ni-laterite deposits, Western Australia: Implications for exploring with AEM

Abstract

In the Eastern Goldfields of Western Australia, airborne electromagnetic (AEM) data have been acquired over areas prospective for nickeliferous laterite deposits, although their application in exploring for this style of mineralisation is not well understood. In part, this can be attributed to a lack of detail concerning relationships between supergene Ni enrichment and the petrophysical, particularly electrical, properties associated with prospective regolith materials and settings. This issue was addressed using a combination of multi-parameter borehole geophysical techniques and lab analysis of mineralogy, geochemistry and soluble salt content for 24 drill holes in a zone of known mineralisation associated with the Cawse lateritic Ni deposits, located in the Eastern Goldfields, W.A. The regolith associated with supergene Ni enrichment exhibited a complex vertical conductivity structure. In places, elevated conductivities were coincident with Ni-Mn-Co mineralisation. These correlations were noted to occur at hydromorphic barriers associated with structural discontinuities or in places where regolith textural changes were marked. The observed regolith electrical structure was indicative of contemporary groundwater processes, with higher conductivities associated with concentrations of soluble salts. Results suggest that AEM data could be used as an exploration tool particularly to locate structurally controlled conductivity contrasts that may be associated with Ni enrichment.