内蒙古甲生盘铅锌硫矿床铅同位素组成及其对成矿物质来源的示踪意义

Lead isotope composition of the Jiashengpan lead-zinc-sulfur deposit in Inner Mongolia and its tracing significance for ore-forming materials

甲生盘铅锌硫矿床位于华北地台北缘狼山—渣尔泰山成矿带内,赋矿地层为中元古代渣尔泰山群的一套黑色岩系。铅同位素测试结果表明,甲生盘矿床铅同位素组成分为两组：A组以低放射性成因铅为特征,其同位素组成206Pb/204Pb为15.889~16.257,207Pb/204Pb为15.158~15.455,208Pb/204Pb为35.112~36.271;B组以相对高放射性成因铅为特征,其同位素组成206Pb/204Pb为17.871~18.990,207Pb/204Pb为15.509~15.672,208Pb/204Pb为37.525~38.770。矿石硫化物明显分为早期沉积的层纹状、浸染状细粒硫化物和后期脉状产出的粗粒硫化物,均含有A、B两组铅特征,前者以A组特征为主,后者以B组特征为主。根据铅构造模式图解及μ值等铅同位素参数综合分析：A组铅来自上地壳中的造山带,并且有幔源铅的补偿,成矿物质来自于古老的基底地层;B组铅主要来源于上地壳,部分受矿体北翼花岗岩侵入体的影响,成矿物质主要来自赋矿围岩;矿床铅具有多来源混合铅结构特征。

The Jiashengpan lead-zinc-sulfur deposit is located in the Langshan-Zhaertaishan mineralization belt on the northern margin of the North China Platform.Its ore bodies are hosted in black shale strata of the Mesoproterozoic Zhaertaishan Group.Lead isotopic composition of sulfides in ores can be classified into two groups（Group A and Group B）.Group A is characterized by lower radiogenic lead with 206Pb/204Pb ranging from 15.889 to 16.257,207Pb/204Pb ranging from 15.158 to 15.455,and 208Pb/204Pb ranging from 35.112 to 36.271,whereas Group B is characterized by higher radiogenic lead with 206Pb/204Pb ranging from 17.871 to 18.990,207Pb/204Pb ranging from 15.509 to 15.672,and 208Pb/204Pb ranging from 37.525 to 38.770.It is evident that the sulfides in ores can be divided into the early depositional ones having fine-grained,layered and disseminated features and the later ones having coarse-grained and veinlike features.Both of them contain lead isotope compositions of Group A and Group B,but the former consists mainly of the features of Group A whereas the latter consists mainly of the features of Group B.Based on tectonic patterns of lead isotope and related parameters,it can be concluded that the lead of Group A was mainly derived from the upper crust and the orogenic belt with the participation of some mantle-derived lead.The ore-forming materials of Group A were derived from the old basement strata during the main ore-forming period,whereas the lead of Group B was mainly derived from the late hydrothermal event with some influence of the Varisian granite to the north of the ore bodies.The lead of the Jiashengpan ore deposit has a multi-source mixing structure.