新疆阿尔泰小土尔根铜矿流体包裹体和H-O、Cu同位素特征及其成因探讨

小土尔根铜矿位于新疆阿尔泰地区诺尔特Au-Pb-Zn(-W-Mo)成矿带北部,成矿条件有利。在详细的野外考察基础上,作者系统分析了矿区的流体包裹体类型、流体成分,结合H-O、Cu同位素地球化学研究,对其成矿流体特征及来源、成矿物质来源和矿床成因进行了探讨。该矿流体包裹体类型比较简单,主要为气液两相包裹体,少量纯液相包裹体,偶见含子晶包裹体。激光拉曼光谱分析表明,成矿流体为H_2O-Na Cl-CO_2-CH_4体系。成矿流体温度介于188~421℃,盐度介于0.71%~15.53%Na Cl_(eqv),主要集中于8.0%~12.0%Na Cl_(eqv),为中?高温、中?低盐度成矿流体。H、O同位素(δD_(SMOW)值介于-72‰~-122‰,δ~(18)O_(fluid)值介于3.7‰~8.1‰)指示,成矿流体主要来源于岩浆水,随着成矿作用的进行,大气降水混入的比例略有增大。黄铜矿的δ~(65)Cu值介于-0.12‰~0.93‰,落入花岗岩δ~(65)Cu值分布范围,且分馏特征与花岗岩相似,说明成矿元素Cu来自花岗岩岩浆。结合前人成果,作者认为小土尔根铜矿应为诺尔特地区首例还原性斑岩铜矿床。

Characteristics of Fluid Inclusions and H-O,Cu Isotope Composition of Xiaotuergen Copper Deposit,Altay, Xinjiang,and its Metallogenesis

The Nurt area is located in the northern section of the Altay region which is an important metallogenic belt of nonferrous metals and precious metals in China. The Xiaotuergen copper deposit lies on the northern side of the richly endowed Nurt Au-Pb-Zn (-W-Mo) metallogenic belt. In this contribution, with the aims of deciphering the characteristics and source of the ore-forming fluid, the source of ore-forming materials, and the genesis of the deposit, we present data from detailed field observations, fluid inclusions, fluid compositions, and H-O-Cu isotopic compositions from the ore bodies in the Xiaotuergen copper deposit. Our study reveals that the primary fluid inclusions are large but simple in composition, being mainly vapor and liquid inclusions, with little pure liquid and only rare daughter mineral-bearing inclusions. Laser Raman analysis suggests that the ore-forming fluids of two stages were both rich in methane and with a certain amount of carbon dioxide, indicating that the ore-forming fluids belong to H2O-NaCl-CO2-CH4system, which is a common fluid system of reduced copper deposits. The ore-forming fluids are characterized by medium-high temperatures (188 421 ? ℃) and mid-low salinity (ranging from 0.71% to 15.53% NaCleqv, predominantly 8.0% 12.0% NaCl? eqv). Hydrogen isotopic compositions (δDSMOWfrom -72‰ to -122‰) and oxygen isotopic compositions (δ18Ofluidfrom 3.7‰ to 8.1‰) indicate the ore-forming fluids originated mainly from the magmatic fluid, and meteoric water was increasingly involved in later processes. The δ65Cu of chalcopyrite ranges from-0.12‰ to 0.93‰, is consistent with that of granites and moreover, shares similar fractionation characteristics with granites. These features argue for an origin where the chalcopyrite formed in a relatively not very hot environment and the metallogenic copper was derived from silicic magma. Previous studies showed that granodiorite-porphyry, the metallogenic parent rock for the Xiaotuergen copper deposit, was an ilmenite-series, reduced, I-type granitoid, and accompanied by abundant primary pyrrhotite but lacking primary hematite, magnetite and sulfate minerals. From these features, combined with the results of our study, we conclude that the Xiaotuergen copper deposit is the first reduced porphyry copper deposit to be recognized in the Nurt area of the Altay region.