Use of immobile trace elements in gold exploration in the Neoarchean Sandstone Greenstone Belt, Yilgarn Block, Western Australia

Exploration in the Sandstone Greenstone Belt (SSGB), with its widespread complex regolith cover, is extremely difficult as targeted orogenic gold deposits have no consistent parameters that allow direct geophysical detection, and gold and ore-metal surface geochemistry reflects variations from in situ to highly transported responses. Based on aeromagnetic interpretations, the gold deposits of the SSGB can be viewed within broad litho-structural frameworks, and NNW-NW and NNE-NE–trending domains, with more favourable orientation with respect to the inferred principal maximum stress during the time of gold mineralisation, can be defined. Fault jogs and high-angle corridors of cross faults further constrain more-prospective zones. However, the aeromagnetic data cannot identify relatively small volumes of critical host rocks which can localize ore-fluid flux and fluid-rock reactions that control the deposition of gold mineralisation. In the SSGB, these critical host rocks include thin granodiorite intrusions within ultramafic schists or specific mafic bodies in mafic-ultramafic sequences. A reconnaissance study using the immobile trace elements, Ti and Zr, demonstrates that these critical rock types can be readily recognized at surface and in drill chips. In particular, Ti–Zr geochemistry identifies previously unknown 20-km-long differentiated dolerite units with granophyric zones that localize gold mineralisation. A combination of aeromagnetic interpretation of structures and major Domains, plus the location of critical host units using Ti–Zr geochemistry, allows production of an exploration targeting map for this district with definition of priority targets based on a mineral system approach. Thus, in the SSGB, for gold exploration under regolith cover that represents in situ weathering of those host rocks, rather than later cover sequences, immobile trace element geochemistry provides an effective, low-cost methodology, as an adjunct to conventional ore-metal geochemistry, and should be used in other orogenic gold provinces worldwide.