The genesis of high sulphidation gold: a comparative study of the Bowone-Binebase deposits and Kawah Ijen volcano, Indonesia

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High sulphidation epithermal deposits are an important source of gold that has been receiving increased attention since discovery of the giant Yanacocha deposit (Peru) in the mid-1980s with a resource of >50 million oz. gold. However, in comparison to their relatives, low sulphidation epithermal and porphyry copper deposits, high sulphidation epithermal gold deposits are poorly understood. As mining companies are become increasingly dependent on genetic models to guide their exploration strategies, there is greater need to improve our understanding of ore-forming processes. Although there is agreement that these deposits form within volcanic edifices and that condensed magmatic vapours are responsible for ground preparation, there is much less agreement on the nature of the ore fluids, the manner in which the gold is dissolved, and the timing of mineralisation. In many cases, there is evidence for late introduction of gold and for these deposits, researchers have variously proposed that the ore fluid is of magmatic origin, meteoric liquid that absorbed magmatic vapour, or magmatic vapour that contracted to liquid without passing through the two-phase region; both bisulphide and chloride complexes have been invoked as agents of gold transport. However, in some cases, there is evidence that ground preparation and gold mineralisation were pene-contemporaneous, implying that gold was transported by vapour, possibly as a hydrated chloride or sulphide species. This proposal is for a comparative study of a pair of high sulphidation deposits (Bowone-Binebase, Indonesia) in which gold mineralisation appears to have been early (associated with pyritisation), and an active volcano (Kawah Ijen, Indonesia) which shows evidence of high sulphidation alteration, including pyritisation. The objective of the research is to develop a genetic model by characterising petrographically and geochemically the mineralisation and alteration, reconstructing the physicochemical conditions of ore formation, determining the composition of Kawah Ijen fluids, and experimentally investigating their gold transporting capacity. If successful, the project will help refine existing models for high sulphidation mineralisation and strategies for its exploration.