内蒙古林西县大井铜多金属矿床的硫、碳和铅同位素及成矿物质来源

S, C,and Pb isotopes and sources of metalloge netic elements of the Dajing Cu-polymetallic deposit in Linxi County, Inner Mongolia, China

内蒙古自治区林西县大井铜多金属矿床是大兴安岭南段的一个大型 Cu-Sn-Ag-Zn-Pb矿床。该矿床的黄铜矿、黄铁矿、闪锌矿和方铅矿等硫化物的δ34 S值变化为 -1.8‰至 + 3 .8‰ ,平均为 + 0 . 65‰。大约为 -5‰的δ13 C值与峰值为～ + 1‰的δ34 S值的很窄分布表明成矿流体中的碳和硫来源于深部岩浆 ,并且排除了上二叠统林西组地层提供一部分硫和碳的可能性。硫化物矿石的 2 0 6 Pb/ 2 0 4 Pb,2 0 7Pb/ 2 0 4 Pb和 2 0 8Pb/ 2 0 4 Pb比值分别在 18.2 57～ 18.3 68,15.476～ 15.60 9和 3 7.916～3 8.3 55范围内 ,其模式年龄为 12 2～ 2 0 9Ma。黑色页岩含有较高的放射成因铅 ,其 2 0 8Pb/ 2 0 4 Pb比值为 18.473～ 2 0 .156,与矿石完全不同。然而 ,矿石、基性 -超基性岩脉和附近花岗岩体的长石铅中 2 0 6 Pb/ 2 0 4 Pb,2 0 7Pb/ 2 0 4 Pb和 2 0 8Pb/ 2 0 4 Pb比值是相近的 ,它们在 2 0 8Pb/ 2 0 4 Pb-2 0 6 Pb/ 2 0 4 Pb和 2 0 7Pb/ 2 0 4 Pb-2 0 6 Pb/ 2 0 4 Pb图上落在同一条直线上。这条铅同位素混合线两个端元分别为上地幔和造山带 ,即混合了上地幔与前中生代形成的造山带物质。这些证据都强烈地支持了成矿物质来源于深源岩浆。因此 ,大井矿床是一个典型的与次火山岩有关的岩浆

The Dajing Cu-polymetallic ore deposit in Linxi county, Inner Mongolia Autonomous Region, China, is a large-scale Cu-Sn-Ag-Zn-Pb deposit in the southern section of the Da Hinggan area. The delta(34)S values of chalcopyrite, pyrite, sphalerite, and galena sulfides collected from the Dajing ore deposit range from -1.8parts per thousand to +3.8parts per thousand with an average of +0.65parts per thousand. The narrow distributions of the delta(13)C values round -5parts per thousand and the delta(34)S values with similar to+1parts per thousand peak value indicate that the sulfur and carbon of the ore-forming fluid are derived from a hypomagma and exclude the possibility that the,hosted Upper Permian Linxi Formation strata provide a certain amount of sulfur and carbon. The Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 ratios of sulfide ores range respectively within 18.257similar to18.368, 15.476similar to15.609, and 37.916similar to38.355 with the model ages of 122similar to209 Ma. But, the black shale contains higher radiogenic lead with the Pb-208/Pb-204 ratios of 18.473similar to20.156, differing from the ores. However, the Pb-206/Pb-204, Pb-207/(204)Pn and Pb-208/Pb-204 ratios of the ore, basic-ultrabasic dike and feldspar leads are similar and lie on the same lines in the diagrams of Pb-208/Pb-204 vs. Pb-206/Pb-204 and Pb-207/Pb-204 vs. Pb-206/Pb-204. The analysed feldspars were separated from granite in the neighborhood of the Dajing ore deposit. For the mixing lines, the two end members are respectively upper mantle and orogenic belt that means mixing the matters of the upper mantle and of orogenic belt prior to the Mesozoic. All the evidences strongly support that the metallogenic elements were carried by the hypomagma. Therefore, the Dajing ore deposit is a typical magmatic-hydrothermal vein type of ore deposit associated with subvolcanic rocks.