新疆喀喇昆仑多宝山铅锌矿床矿物学、地球化学及成因

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

新疆喀喇昆仑多宝山铅锌矿床赋存于上白垩统铁隆滩组灰岩段中,明显受构造控制,矿体形态呈不规则囊状、脉状、透镜状等。成矿阶段可分为3期:早期硫化物成矿阶段(方铅矿、闪锌矿、方解石)、中期交代成矿阶段(菱锌矿、铁氧化物、白铅矿、石膏)与晚期氧化阶段(水锌矿)。硫化物阶段方铅矿的δ34 S为-14‰^-0.6‰,表明S可能来源于海相硫酸盐岩的还原。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δ18 C PDB为3.5‰~5.7‰,δ18 O SMOW为22.1‰~27.1‰,来源于碳酸盐岩地层的溶解作用。交代成矿阶段菱锌矿的δ18 C PDB为2.9‰~3.8‰,δ18 O SMOW为16.9‰~20.3‰;白铅矿的δ18 C PDB为2.7‰~4.4‰,δ18 O SMOW为15.8‰~20.3‰,C、O同位素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流体包裹体的3 He/4 He值为0.72~0.93 R/Ra,40 Ar/36 Ar值为302.1~350.7,方铅矿流体包裹体的3 He/4 He值为1.17 R/Ra,40 Ar/36 Ar值为298.1,交代成矿阶段菱锌矿流体包裹体的3 He/4 He值为0.22~0.46 R/Ra,40 Ar/36 Ar值为292.6~295.8,白铅矿流体包裹体的3 He/4 He值为0.40~0.59 R/Ra,40 Ar/36 Ar值为292.9~295.4,两个阶段成矿流体均为地壳流体与大气降水混合流体。综上所述,多宝山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,交代成矿阶段为直接交代成因,后期发生叠加氧化作用。

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.Theδ34 S 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.Theδ18 C PDB values of calcite are from 3.5‰to 5.7‰and theδ18 O SMOW,from 22.1‰to 27.1‰are which indicate the dissolution of carbonate.Theδ18 C PDB andδ18 O SMOW values of the smithsonite are from 2.9‰to 3.8‰and 16.9‰to 20.3‰,respectively.Theδ18 C PDB andδ18 O 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 40 Ar/36 Ar 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 40 Ar/36 Ar ratios of the fluid inclusions in the galena are 1.17 R/Ra and 298.1,respectively.The 3He/4He and 40 Ar/36 Ar 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 40 Ar/36 Ar 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.