新疆包古图斑岩铜矿床成矿流体及成矿物质来源——来自硫、氢和氧同位素证据

Sources of ore-forming fluids and materials of the Baogutu porphyry copper deposit in Xinjiang:Constraints from sulfur-hydrogen-oxygen isotopes geochemistry

包古图大型斑岩铜矿位于准噶尔盆地西缘。铜矿化主要呈浸染状、细脉浸染状分布于似斑状(石英)闪长岩、闪长玢岩、隐爆角砾岩和少量花岗闪长岩中。依据矿脉的穿插关系和矿物组合,成矿过程经历了黑云母-钾长石-钠长石阶段、石英-硫化物阶段和石英碳酸盐阶段。矿脉中石英的δDSMOW值介于-107‰～-86‰,δ18OSMOW值变化于11.3‰～16.2‰,δ18OH2O值为4.4‰～9.3‰,表明成矿流体来源为深源的岩浆水。硫化物的δ34S值介于-5.1‰～0.7‰,平均为-1.8‰,表明硫来源于深部岩浆或地幔。结合Ⅱ、Ⅲ和Ⅴ号含矿岩体锆石LA-ICP-MSU-Pb年龄及辉钼矿Re-Os年龄,推断包古图铜矿床成矿作用发生在晚石炭世,与中酸性斑岩体的侵入有密切成因关系。

The Baogutu large-scale porphyry copper deposit is located in the west margin of Junggar basin. Copper mineralization which mainly occurs as disseminated and veinlet-disseminated,is hosted by porphyritic (quartz) diorite,diorite porphyrite,crypto-explosive breccia,minor in granodiorite. Based on cross-cutting relationships and mineral assemblages of the ore veins,the ore-forming process underwent three stages as follows:Biotite-potassic feldspar-albite stage,quartz-sulfide stage and quartz carbonate stage. The δDSMOW values of quartz vein range from-107‰ to-86‰,and the δ18OSMOW values range from 11.3‰ to 16.2‰,with corresponding δ18OH2O values range from 4.4‰ to 9.3‰. The combined isotopic data suggested that the ore-forming fluids were derived from deep-seated source magmatic water. The δ34S values of sulfide range from-5.1‰ to 0.7‰ with an average of-1.8‰,indicating that the sulfur in the fluids was derived from deep-seated magma or the mantle. Combining LA-ICP-MS zircon U-Pb dating on the Ⅱ,Ⅲ and Ⅴ magmatic body and the Re-Os dating on molybdenite,we suggest metallogenesis of the Baogutu porphyry copper deposit took place in the Late Carboniferous,and its mineralization is closely related to the intruding of the intermediate-acid porphyry body.