Landscape evolution and geochemical dispersion of the DeGrussa Cu-Au deposit, Western Australia

Sedimentary systems associated with ore deposits may act as mechanical dispersion agents of pathfinder elements at local and regional scales. The DeGrussa Cu-Au Volcanogenic Massive Sulfide (VMS) deposit (12.4 Mt @ 4.7% Cu and 1.8 g/t Au) was discovered in a deeply weathered landscape in Western Australia. The DeGrussa deposit is geochemically characterized as being enriched in Cu, Zn, Au and Ag, as well as significant enrichments in In, Mo, Se, Te, Bi, As, Cd and Co, and depletions in Nb, Hf, Th, REE, Cr, Ni, V, Sc and Ba. The Cenozoic palaeochannel sedimentary package that overlies the DeGrussa deposit displays elevated Cu, Zn, Au, and Ag concentrations, as well as significant enrichments in Cr, Ni, V, Sc, In, Mo, Se, Te, Bi, As, Cd and Co, and a remarkable depletion in REE. The palaeochannel sedimentary package shows similarities in its chemical signature to the DeGrussa deposit and associated basement rocks. However, due to the complexity of the landscape evolution and weathering impacts, there is uncertainty regarding the source(s) of this anomalous signature. It may represent (1) the geochemical signature of the immediately underlying basement rocks and/or the DeGrussa deposit; (2) concentration related to the weathering intensity experienced by the sediments, (3) concentration related to the cannibalistic nature of the sedimentary system, resulting in the reworking of previous deposits, or (4) a combination of the above. The Cenozoic channel clay deposits display strikingly depleted values of total REE (TREE) content, which has been interpreted to indicate that the palaeochannel clay units were mostly derived from weathering of proximal dolerite, with no mixing with other weathering products. This, in combination with high Mo, In and Se, and elevated Cu, Zn, Au, and Ag concentrations, may represent the relics of the DeGrussa footprint. Chromium Ni, V, and Sc are interpreted as being sourced mainly from the mafic basement units. Despite the geochemical signatures reported, this study has discovered that the metal geochemical footprint observed in the palaeochannel sedimentary package represents the footprint of the DeGrussa deposit. Hence the geochemistry of the transported cover can be used as an efficient tool for mineral exploration in specific landscape contexts, since the cover can preserve key elemental vectors of the mineral deposit and the geochemical signature of the basement rocks.