新疆喀喇昆仑火烧云超大型铅锌矿床矿物学、地球化学及成因

近年来，青藏高原北缘喀喇昆仑铅锌找矿取得重大突破，新发现的火烧云超大型铅锌矿床已成为中国最大的铅锌矿床，矿石矿物以菱锌矿、白铅矿、水锌矿为主，也是世界第二大非硫化物铅锌矿床。矿体呈似层状产出，埋藏浅，主要为褐色块状矿石，Pb+Zn平均品位近30%。可分为3个成矿阶段。早期铅锌硫化物成矿阶段（方铅矿、闪锌矿、方解石）、中期铅锌非硫化物成矿阶段（菱锌矿、锰氧化物→菱锌矿、白铅矿、石膏）与晚期表生氧化阶段（水锌矿）。硫化物阶段方铅矿的δ34S为-18.9‰~-4.2‰，非硫化物阶段热液石膏的δ34S为-20.6‰~-7.5‰，继承了硫化物阶段矿物的硫同位素特征。Pb同位素组成集中，具有地壳来源特征，二叠系—白垩系可能提供了金属成矿物质。方解石的δ18CPDB为0.6‰~3.1‰，δ18OSMOW为15.3‰~24.6‰，菱锌矿的δ18CPDB为-2.7‰~4.5‰，δ18OSMOW为10.4‰~26.1‰，来源于碳酸盐岩的溶解作用；白铅矿的δ18CPDB为-7.7‰~4.3‰，δ18OSMOW为9.3‰~24.3‰，同位素发生漂移，可能是与大气降水的混入有关。硫化物成矿阶段方解石中流体包裹体的3He/4He值为0.05~0.39 R/Ra，40Ar/36Ar值为296.2~428.9，方铅矿中流体包裹体的3He/4He值为0.03 R/Ra，40Ar/36Ar值为290.0，成矿流体可能为中温、低盐度、中低密度的还原性壳源流体；非硫化物成矿阶段菱锌矿中流体包裹体的3He/4He值为0.10~0.43 R/Ra，40Ar/36Ar值为290.6~295.3；白铅矿中流体包裹体的3He/4He值为0.08 R/Ra，40Ar/36Ar值为293.5，成矿流体可能为中低温、低盐度、中密度的壳源流体与大气降水混合流体。综上所述，火烧云超大型铅锌矿床是盆地边缘褶皱逆冲+构造流体+次生交代成矿系统的产物，硫化物成矿阶段为构造热液成因，非硫化物成矿阶段为围岩交代成因，后期发生叠加氧化作用，形成大量水锌矿。

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.