Mineralogy, Geochemistry and Genesis of Giant Huoshaoyun Zn-Pb Deposit in Karakoram Area, Xinjiang, NW China

In recent years, a breakthrough has been made about the zinc and lead prospecting in Karakorum area of northern Qinghai-Tibet Plateau. The newly discovered giant Huoshaoyun zinc-lead deposit has become the largest zinc-lead deposit in China and the second largest nonsulfide zinc-lead deposit in the world. The ore bodies are layer-shaped, buried shallow with depth of 50 to 230 meters. The ores show brown color and massive structure, and the average grade of lead and zinc is nearly 30%. It can be divided into three metallogenic stages:early zinc-lead sulfide mineralization stage, intermediate zinc-lead nonsulfide mineralization stage and late oxidation stage. The first stage is characterized by galena, sphalerite and calcite; the second stage is represented by smithsonite, manganese oxide, cerussite, and gypsum; the last stage is characterized by hydrozincite. The δ³⁴S values of the galena in the first stage range from -18.9‰ to -4.2‰. The δ³⁴S values of gypsum in the second stage vary from -20.6‰ to -7.5‰, which inherits the sulfur isotope characteristics of minerals in the sulfide stage. 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 δ¹⁸CPDB and δ¹⁸OSMOW values of calcite range from 0.6‰ to 3.1‰ and from 15.3‰ to 24.6‰, respectively. The δ¹⁸CPDB and δ¹⁸OSMOW values of the smithsonite vary from -2.7‰ to 4.5‰ and from 10.4‰ to 26.1‰, respectively. All these values indicate the dissolution of carbonate. The δ¹⁸CPDB and δ¹⁸OSMOW values of the cerussite range from -7.7‰ to 4.3‰ and from 9.3‰ to 24.3‰, respectively, indicating the mixing of atmospheric precipitation. The ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of the fluid inclusions in the calcite vary from 0.05 R/Ra to 0.39 R/Ra and from 296.2 to 428.9, respectively; and the ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of fluid inclusions in the galena are 0.03 R/Ra and 290.0, respectively. Thus, the ore-forming fluid of the first sulfide metallogenic stage may be medium-temperature, low salinity, and medium-low density reducing fluid from the crust. The ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of fluid inclusions in the nonsulfide metallogenic stage range from 0.10 R/Ra to 0.43 R/Ra and from 290.6 to 295.3, respectively; the ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios of fluid inclusions in cerussite are 0.08 R/Ra and 293.5, respectively. Thus, the ore-forming fluid of the nonsulfide metallogenic stage may be medium-low temperature, low salinity, and medium density fluid from crust mixed with atmospheric precipitation. In summary, the giant Huoshaoyun zinc-lead deposit is the product of basin fold thrust in the edge of a basin, with the activities of structure fluids and secondary replacement system. The sulfides are formed with the activities of structure fluids, and the nonsulfides are the result of wall rock replacement. At the last stage, the oxidation occurred and the hydrozincites formed.