北山成矿带老硐沟金多金属矿床S-Pb-C-O同位素特征及其对矿床成因的约束

S-Pb-C-O isotope characteristics and constraints on genesis of Laodonggou gold polymetallic deposit of Beishan metallogenic belt

老硐沟金多金属矿床是北山成矿带内蒙古段最为典型的金矿床之一,其矿床成因存在较多争议,矿床成矿物质来源方面的研究几近空白。文章基于详细的野外实地调查,选取不同成矿阶段的硫化物和方解石,开展原位S-Pb同位素和C-O同位素测试。研究结果表明,老硐沟金多金属矿床δ34S值为-0.56‰~5.54‰,^(206)Pb/^(204)Pb比值为18.326~18.390,207Pb/^(204)Pb比值为15.563~15.645,^(208)Pb/^(204)Pb比值为38.226~38.390,铅同位素μ值变化范围为9.40~9.55,ω值变化范围为35.77~36.85,方铅矿二阶段模式年龄为232~270 Ma,δ^(13)C值介于-0.04‰~2.93‰之间,表明老硐沟金多金属矿床成矿物质具有岩浆和地层混合来源性质,成矿流体以岩浆来源为主,成矿作用晚期流体中混入了地层变质水。文章从矿床稳定同位素研究方面,结合前人对北山造山带构造演化的认识,提出老硐沟金多金属矿床成因为岩浆热液型。

The Laodonggou gold polymetallic deposit is one of the most typical gold Mineral of the Beishan metallogenic belt in Inner Mongolia.There are many disputes about its genesis,and the research on the source of oreforming materials in the deposit is almost blank.Based on the on-situ investigation of the deposit,this work selected typical ore samples from different middle sections underground and conducted in-situ S-Pb and C-O isotope studies.Theδ34S of Laodonggou gold polymetallic deposit ranges from-0.56‰to 5.54‰,the^(206)Pb/^(204)Pb ranges from 18.326 to 18.390,the 207Pb/^(204)Pb ranges from 15.563 to 15.645,the^(208)Pb/^(204)Pb ranges from 38.226 to 38.390,theμof lead isotopes ranges from 9.40 to 9.55,theωranges from 35.77 to 36.85,the S-KⅡmodel age of galena is 232~270 Ma,and theδ^(13)C ranges from-0.04‰to 2.93‰.These show that the ore-forming materials of the Laodonggou gold polymetallic deposit have a mixed source of magma and strata,and the ore-forming fluid is mainly derived from magma.In the late stage of mineralization,metamorphic water from strata was mixed into the fluid.Based on the study of stable isotopes of ore deposits,combined with previous studies on the tectonic evolution of the Beishan orogenic belt,it is first proposed that the genesis of the Laodonggou gold polymetallic deposit is magmatic hydrothermal type.