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Reduced Intrusion-related Gold Systems

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Reduced intrusion-related gold systems (RIRGS) are characterized by widespread arrays of sheeted auriferous quartz veins that preferentially form in the brittle carapace at the top of small plutons, where they form bulk-tonnage, low-grade Au deposits characterized by a Au-Bi-Te-W metal assemblage, such as the Fort Knox and Dublin Gulch deposits. RIRGS also include a wide range of intrusion-related mineral deposit styles (skarns, replacements, veins) that form within the region of hydrothermal infl uence surrounding the causative pluton, and are characterized by proximal Au-W-As and distal Ag-Pb-Zn metal associations, thereby generating a zoned mineral system. Plutons that generate RIRGS form in tectonic settings characterized by weak post-collisional extension behind a thickened continental margin. Such settings are also conducive to the formation of W deposits, and thereby generate a regional Au-W metallogenic association, but individual plutons can generate both W and Au deposits. Associated magmas are diverse and have characteristics of I-, S-, and A-type granitoids. The most prolifi c Au systems comprise metaluminous, moderately reduced, moderately fractionated, biotite>>hornblende>pyroxene quartz monzonites that have mixed with volatile-rich lamprophyric melts. The magmas have a reduced primary oxidation state that form ilmenite-series plutons. This reduced state causes associated sulphide assemblages to be characterized by pyrrhotite, and quartz veins that host methane-rich inclusions. RIRGS mostly form at a depth of 5 to 7 km and generate mineralizing fl uids that are low salinity, aqueous carbonic in composition and are, therefore, unlike typical porphyry Cu deposits. The RIRGS class was developed on well-studied examples in Yukon and Alaska. Other suggested Canadian examples are in southeastern British Columbia and New Brunswick; numerous global examples have been suggested, but many are controversial.
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... Intrusion-related gold deposits (IRGS) can divide into reduced and oxidized IRGS (Hart and Goldfarb 2005). Among them, the reduced type is generally characterized by Au-Bi-Te-W assemblages (Hart 2007), and the oxidized ones are Au-rich variants of the porphyry Cu-Au class (Hart 2007;Niroomand et al. 2018). The magmatic rocks in oxidized intrusion-related gold deposits commonly have high oxygen fugacity (Helt et al. 2014) and high water content (Li et al. 2018), favoring Au-Chalcophile mental association (Elshourbagi and Fan 2021). ...
... Intrusion-related gold deposits (IRGS) can divide into reduced and oxidized IRGS (Hart and Goldfarb 2005). Among them, the reduced type is generally characterized by Au-Bi-Te-W assemblages (Hart 2007), and the oxidized ones are Au-rich variants of the porphyry Cu-Au class (Hart 2007;Niroomand et al. 2018). The magmatic rocks in oxidized intrusion-related gold deposits commonly have high oxygen fugacity (Helt et al. 2014) and high water content (Li et al. 2018), favoring Au-Chalcophile mental association (Elshourbagi and Fan 2021). ...
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... Se ha establecido que los magmas oxidados presentan una estrecha relación con la mineralización aurífera y con ellos se asocian desde el punto de vista metalogénico los depósitos de oro epitermal y de skarn (Ishihara 1981;Guilbert y Park 1986;Robert et al. 2007;Sillitoe 2010). A diferencia de estos, en los magmas reducidos el oro presenta baja ley (Hart 2015). ...
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