Recognizing, in lateritic cover, detritus shed from the Archaean Gossan Hill Cu–Zn–Au volcanic-hosted massive sulphide deposit,Western Australia

Abstract

Cenozoic cover about the Golden Grove Gossan Hill volcanic-hosted massive sulphide (VHMS) deposit consists of lateritic colluvium, remnants of lateritic duricrust, associated lateritic soils and lateritic gravels. Clasts in these materials were investigated for features diagnostic of the mineralized system. The pebble-sized clasts showed: (a) preservation of tuffaceous and other volcanic textures with relict cassiterite (an associate of the ore zone sulphides); (b) relict micrometre-scale Cu, Zn, As or Pb sulphide inclusions in quartz; (c) micrometre-scale gold grains; (d) interpreted ferruginous pseudomorphs after base metal sulphides; and (e) elevated trace amounts of Cu, As, Zn or, more rarely, Sb or Bi in the core matrix of clasts, and in cutans on some of the clasts. All samples studied from an area extending laterally c. 600 m from the central strike of the VHMS ore system are positive, despite intensive weathering, to one or more of these diagnostic criteria. The background samples (2 km to 5 km from the ore system) are negative to all the criteria. A qualitative indication of proximity to the ore system can be derived by listing the occurrence of each of the diagnostic criteria within mineralized clasts in individual samples. A more specialized case of general models for interface sampling is proposed for exploring areas of thick transported cover in deeply weathered terrain. The model focuses on recognizing the described diagnostic criteria in basal cover from samples provided by drill core or cuttings.