Mineralogy, Geochemistry and Genesis of Duobaoshan Zn-Pb Deposit, in Karakoram, Xinjiang

Located in Karakoram of Xinjiang, the Duobaoshan lead-zinc deposit was formed in the limestones of the Cretaceous Tielongtan Formation, and was obviously controlled by structural fracture zones. The ore bodies are irregularly sac-like, vein-like, and lenticular-shape-like. It can be divided into three metallogenic stages:the early sulfide mineralization stage, the intermediate replacement mineralization stage and the late oxidation stage. The first stage is characterized by galena, sphalerite and calcite; the second stage is represented by smithsonite, iron oxide, cerussite, and gypsum; the last stage is characterized by hydrozincite. The δ³⁴S values of the galena in the first stage range from -14‰ to -0.6‰, which shows a feature of reduced sulfur source. The lead isotope compositions are concentrated and show a crustal source feature, and the Permian-Cretaceous sedimentary rocks may be the sources of metals. The δ¹⁸C_PDB values of calcite are from 3.5‰ to 5.7‰ and the δ¹⁸O_SMOW, from 22.1‰ to 27.1‰ are which indicate the dissolution of carbonate. The δ¹⁸C_PDB and δ¹⁸O_SMOW values of the smithsonite are from 2.9‰ to 3.8‰ and 16.9‰ to 20.3‰, respectively. The δ¹⁸C_PDB and δ¹⁸O_SMOW values of the cerussite are from 2.7‰ to 4.4‰ and 15.8‰ to 20.3‰, respectively. All these values indicate the mixing of atmospheric precipitation. The ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of the fluid inclusions in the calcite are from 0.72 R/Ra to 0.93 R/Ra and 302.1 to 350.7, respectively; and the ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of the fluid inclusions in the galena are 1.17 R/Ra and 298.1, respectively. The ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of fluid inclusions in the smithsonite are from 0.22R/Ra to 0.46R/Ra and 292.6 to 295.8, respectively; the ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of fluid inclusions in cerussite are from 0.40R/Ra to 0.59R/Ra and 292.9 to 295.4, respectively. Thus, the ore-forming fluid may be the crustal fluid mixed with atmospheric precipitation. In summary, the Duobaoshan zinc-lead deposit is the product of fold thrust in the edge of the basin, structural fluids and secondary replacement system. The sulfides are formed of structural fluids, and the nonsulfides are the result of direct replacement, with oxidation occurring and hydrozincites formed at the last stage.