Geology and geochemistry of the Xiajiadian gold deposit in the Cambrian black rock series in the South Qinling

Abstract：Study of the Xiajiadian gold deposit, South Qinling, has led to the following understanding: microdisseminated gold deposits are hosted in gold-rich barite-chert hydrothermal sedimentary rock series, and the formation of the ore deposits has gone through synsedimentary preconcentration and a process of industrial concentration from brittle-ductile shear structural overprinting to post-hydrothermal reworking. The gold mineralization has close coupling relations to the tectonic evolution of continental subduction-collisional orogeny in the area. The ore-forming processes of this gold deposit may fall into three epochs and eight stages. The ores are composed of three types and eleven subtypes, showing complex ore-forming processes. The homogenization temperatures of fluid inclusions in ore minerals cluster at the range of 199-300℃ and the mineralization pressures range from 370×105 to 820×105 Pa, showing the features of meso- and epithermal mineralization. The salinities of the fluid inclusions were 3.27 wt.% NaClequiv. in the early mineralizing stage and 5.25 wt.% NaClequiv. in the middle and late stages. The hydrogen and oxygen isotopic compositions of the ore minerals form six samples are δ18OH O=-7.86‰ to +0.37‰ and δDH O=-80.70‰ to -66.30‰. The data points in the plot shift laterally from meteoric water to the right, suggesting that the ore fluids consisting predominantly of meteoric water have been subjected to intense reworking. The Xiajiadian gold deposit is a microdisseminated (Carlin-like type) gold deposit. The mineralization has the features of hydrothermal deposition-brittle-ductile structural overprinting-reworking of hydrothermal ore fluids dominated by meteoric water.