吉林小西南岔金-铜矿床成矿流体地球化学特征及矿床成因研究

小西南岔金-铜矿床产于海西期花岗闪长岩-石英闪长岩体之中,其矿化类型以石英大脉及石英细脉带型金-铜矿化为主,局部地段叠加发育有石英脉型辉钼矿化。流体包裹体研究结果表明,矿区金-铜矿脉及辉钼矿脉石英中均主要发育含NaCl子矿物三相、气相-富气相及气液两相三种类型的原生流体包裹体,同类包裹体均一温度、盐度等参数相近,显示两类矿化成矿流体具有相似的地球化学性质,氢-氧同位素研究结果反映它们均主要来源于岩浆热液。辉钼矿Re-Os同位素定年研究表明区内辉钼矿化主要发生于109Ma±,而金-铜矿脉石英的40Ar-39Ar同位素定年结果表明金-铜矿化则主要发生于123.35±0.8Ma。结合矿区已有的岩浆岩年代学研究成果,提出小西南岔矿区金-铜矿化主要与燕山晚期细粒(花岗)闪长岩活动有关,而辉钼矿化则与其后侵位的隐伏花岗斑岩活动有关的认识。

Study on the geochemical characteristics of ore-forming fluids and genesis of Xiaoxinancha gold-copper deposit, Jilin Province.

Xiaoxinancha gold-copper deposit occurred in granodiorite-quartz diorite intrusions of Hercynian epoch. The mineralization of it mainly composed of large quartz vein type and fine quartz veinlet type, with molybdenite-quartz veins superimposed only locally. Fluid inclusion study shows that quartz in both of gold-copper ore veins and in molybdenite-quartz veins contain the same kinds of fluid inclusions, which include NaCl daughter mineral-bearing, gaseous and gas-rich as well as aqueous two-phase fluid inclusions. The similarity of homogenization temperature and salinity of the same kind of fluid inclusions reveals that the geochemical nature of ore-forming solutions of gold-copper and molybdenum mineralization have much in common. Hydrogen-oxygen isotopes of fluid inclusions imply they both came from magmatic fluids. Re-Os isotopic dating of molybdenite shows that molybdenum mineralization happened in ca. 109Ma, whereas ⁴⁰Ar-³⁹Ar isotopic dating of quartz in gold-copper veins reveals that gold-copper mineralization happened in 123.35±0.8Ma. Combined with the results of chronological study of magmatic intrusions in the mining area, the conclusion were made that the origin of gold-copper mineralization mainly related with fine grained granodiorite intrusion of late phase of Yanshan, while the origin of molybdenum mineralization mainly related with granite porphyry of late phase of Yanshan, which successively emplaced after fine grained granodiorite intrusion in the mining area.