内蒙古根河三道桥铅锌银矿床C-H-O-S同位素和U-Pb定年研究及其意义

C-H-O-S isotopes and U-Pb geochronology constraints on the genesis of Sandaoqiao Pb-Zn-Ag deposit,Inner Mongolia

内蒙古根河三道桥大型铅锌银矿床位于大兴安岭得尔布干成矿带中北段,矿体主要呈脉状赋存于火山岩地层中。氢氧同位素研究表明,成矿期石英和绢云母的δD值变化范围为-149.1‰~-156.7‰,δ^(18)OH_(2)O值变化范围为-13.6‰~3.4‰;成矿后期石英δD值变化范围为-131.9‰~-147.7‰,δ^(18)OH_(2)O值变化范围为-16.5‰~-18.2‰。碳同位素分析结果表明,与矿化有关的方解石δ^(13)C值变化范围为-1.8‰~-3.1‰,δ^(18)O值变化范围为5.3‰~8.6‰。原位S同位素分析结果表明,硫化物的δ^(34)S值变化范围为2.3‰~5.6‰,与其西南侧下护林矽卡岩型铅锌银矿床中的硫化物的δ^(34)S值(1.2‰~5.9‰)基本一致。上述同位素组成特征指示成矿物质主要来源于岩浆热液,在上升到地壳浅部时有一定量的大气降水混入。锆石U-Pb年代学研究表明,矿化的闪长玢岩脉年龄为(136.0±0.7)Ma(MSWD=0.44);未矿化、穿切硫化物微细脉的闪长玢岩脉的锆石U-Pb年龄为(120.8±0.6)Ma(MSWD=0.49)。结合前人相关研究进展,认为三道桥铅锌银矿床形成于136.0~120.8 Ma期间(早白垩世),为伸展构造背景下与浅成侵入岩有关的中温热液型铅锌银矿床。

The Sandaoqiao Pb-Zn-Ag deposit in the Inner Mongolia belongs to the northern section of the De'erbugan metallogenic belt,and the vein-type orebodies were hosted by the Jurassic volcanic rocks.H-O isotope research indicates that theδD values of quartz and muscovite from the mineralization stage range from 149.1‰to-156.7‰,and theδ^(18)OH_(2)O values vary from-13.6‰to 3.4‰;theδD values of quartz from the late mineralization stage range from 131.9‰to-147.7‰,and theδ^(18)OH_(2)O values vary from-16.5‰to-18.2‰.The C isotope study shows that theδ^(13)C values associated with mineralization of calcite range from-1.8‰to-3.1‰,and theδ^(18)O values range from 5.3‰to 8.6‰.The in-situδ^(34)S values of the Sandaoqiao sulfides changed from 2.3‰to 5.6‰,which was basically consistent with theδ^(34)S values(1.2‰to 5.9‰)of sulfides in the southwestern Xiahuling skarn-type Pb-Zn-Ag deposit.Collectively,the main source of ore-forming materials is magmatic hydrothermal fluids,which have a certain amount of meteoric water and sea water mixed in as they rise to the shal⁃low part of crust.The zircon U-Pb dating shows that the intrusive age of the mineralized diorite porphyrite dike is(136.0±0.7)Ma(MSWD=0.44),while the intrusive age of the non-mineralized diorite porphyrite dike that cross cut sulfide veinlets is(120.8±0.6 Ma)(MSWD=0.49).In summary,the Sandaoqiao Pb-Zn-Ag deposit formed in 136.0-120.8 Ma,which is an epithermal deposit occurred in the extensional setting.