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TitleOre Fluid Characteristics of Orogenic Gold Deposits: An Overview
AbstractOrogenic gold deposits collectively account for significant amount of world gold (more than 25000 tons gold) production. There have been worldwide intense studies on these deposits, for the past three decades, on various aspects of regional-and mine-scale structures, host rock metamorphism, ore mineralogy, alteration geochemistry and physico-chemical conditions pertaining to nature and evolution of the ore fluid, and transport-precipitation mechanisms of gold. Ore fluid compositions in orogenic gold deposits are very well understood from wide range of fluid inclusion, petrological and geochemical studies. A comprehensive review shows that the nature of ore fluids responsible for Archaean lode-gold systems are generally neutral to weakly alkaline, low to moderate-salinity aqueous-gaseous with high CO2 (+CH4) (0.05 to 0.25 XCO2) for deposits ranging from sub-greenschist to upper-amphibolite facies conditions, capable of carrying Au, Ag, As and Sb but with limited capacity to transport base metals. In spite of all these studies the source of gold-carrying fluids and controls on its composition still remain potential unknowns.