Abstract
The Tuwaishan deposit is an orogenic gold deposit that is structurally controlled by the NE-trending Gezhen shear zone in the western part of Hainan Island, south China. It is part of a belt of numerous similar deposits hosted in Mesoproterozoic granitoids and lesser Paleoproterozoic to Mesoproterozoic schists. The Tuwaishan gold orebodies comprise auriferous quartz veins and disseminated gold in sulfidized granitic mylonite. The veins consist of early quartz-pyrite-arsenopyrite-pyrrhotite with minor gold, middle stage quartz-gold-base metal sulfides, and barren late quartz-carbonate. New 40Ar/39Ar dating of muscovite from wallrock schists yielded a minimum age of 356.8 ± 0.9 Ma, suggesting the youngest possible age estimate for amphibolite facies regional metamorphism of the Baoban Group country rocks. The 40Ar/39Ar dating of sericite from auriferous quartz veins yielded a weighted mean age of 243.4 ± 2.3 Ma, representing the ore-forming age of the Tuwaishan gold deposit. The formation of the shear-hosted gold deposits along the Gezhen gold belt was likely related to the Early to Middle Triassic convergence between the Indochina and South China Blocks. Based on the widely accepted metamorphic devolatilization model for orogenic gold deposit formation, most Au tends to be released into the ore-forming fluid in the source region when country rocks were firstly metamorphosed from greenschist to amphibolite facies. Therefore, it is highly unlikely that the immediate country rocks of the Baoban Group, which were at amphibolite facies by early Carboniferous, were the source for fluids and metals along the Gezhen shear zone.
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