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Publication Type:

Journal Article


Ore Geology Reviews, Volume 135, p.104221 (2021)






fluid inclusion, Hydrothermal fluid evolution, Orogenic gold, Timing of gold mineralization


Although many aspects of orogenic gold systems are well understood, considerable debate surrounds the chemistry of the ore-forming fluids and their relevance to mineralization. This may in part relate to the lack of both regional-scale studies and a uniform approach in studying fluid inclusions in these complex and protracted hydrothermal ore systems. In order to address this problem, over 30 orogenic-type deposits covering a variety of geological settings were systematically studied using the fluid inclusion assemblage (FIA) protocol integrated with microthermometry in the gold-endowed Abitibi greenstone belt, Canada. A diversity of fluid inclusion types are documented (i.e., carbonic CO2-CH4, aqueous-carbonic, aqueous), in addition to complex textural features, in particular decrepitation clusters which are rarely reported in the literature or the deposits studied; together these data provide new insight to these ore systems. Furthermore, we note that the fluid composition is significantly affected by the proximity of carbon-rich sedimentary units which are capable of producing a carbonic-only fluid. In later stages of hydrothermal evolution, variable XCO2 in aqueous-carbonic inclusions reflects variable degrees of fluid-rock interaction. Pressure cycling is an integral part of these systems, but petrographic evidence of in situ fluid unmixing is lacking, and cannot be accounted for gold mineralization. Vein-style gold is not related to fluid chemistry and, where best constrained with petrography (i.e., visible Au near fluid inclusions), P-T estimates based on fluid inclusion microthermometry link the mineralization to the later, low-pressure (<1.5 kbar) stages of deposit evolution. Accordingly, gold is coeval with quartz vein formation in epizonal deposits whereas it postdates quartz in the ore dominant mesozonal ore systems.