Geology and pyrite sulfur isotopes of the Suoluogou gold deposit: Implication for crustal continuum model of orogenic gold deposit in northwestern margin of Yangtze Craton, SW China

Abstract

Since the crustal continuum model was proposed mainly based on the variation of mineralization and alteration features of hypozonal, mesozonal, to epizonal deposits, genetic relationship between the different types in one ore belt still requires research. This issue was addressed by the research on the Suoluogou mesozonal orogenic gold deposit and its comparison with the hypozonal orogenic gold deposit in northwestern margin of Yangtze craton. Gold mineralization in Suoluogou is controlled by the bends of roughly EW-trending brittle fault developed in the Late Triassic strata, and it is associated with quartz, sericite, chlorite, carbonate, and sulfide alteration. Pyrite and arsenopyrite are the predominant sulfide mineral, with minor amounts of chalcopyrite, sphalerite, and galena. Four paragenetic stages are divided based on crosscutting relationship and mineral assemblage, including the pre-mineralization stage (stage Ⅰ), the hydrothermal quartz-sulfide stage (stage Ⅱ) and carbonate-quartz-sulfide stage (stage III), and the post-mineralization carbonate-pyrite stage (stage Ⅳ). The δ34S values for pyrite in stage Ⅱ vary from 6.01% to 8.59‰, and those in stage III are from 0.96% to 4.62‰. The decrease of δ34S value from stage Ⅱ to III is explained to the result of the isotope fractionation during separation of oxidised sulfur species in the brecciated space. The sulfide δ34S values in the initial gold mineralization stage of the Suoluogou deposit are similar to those of regional hypozonal orogenic deposit with derivation from metasomatized mantle in the craton margin. This similarity suggests that the mesozonal and hypozonal gold deposits formed in different depths of a crustal continuum model for the deposits sharing similar subcrustal source.