上黑龙江盆地金矿床地质特征及成因探讨

Geological characteristics and genesis of gold deposits in Upper Heilongjiang Basin

上黑龙江盆地是近年来发现的重要岩金成矿区,文章对该区的砂宝斯、老沟等矿床进行了详细的野外调查和矿床地质特征研究,通过流体包裹体均一温度、包裹体成分群体分析、单个包裹体激光拉曼探针分析和H、O、S、Pb同位素研究,对金矿的成矿作用进行了深入探讨。研究结果表明,矿石中硫化物以黄铁矿为主,硫化物含量一般不超过3%,为少硫化物型矿石。流体包裹体主要类型为气液两相和含CO2三相包裹体,并有少量纯CO2包裹体。黄铁矿等的δ34S值为-1.6‰～9.6‰;成矿热液的δ18O值为-1.3‰～+6.6‰,δD值为-89‰～-135‰;铅同位素表现出造山带铅同位素特征。成矿流体液相中阳离子主要为Na+、K+,阴离子主要是Cl-和SO2-4,气相成分中H2O、CO2和N2占绝对优势,还含有H2、O2、CO、CH4、C2H4、C2H6、C3H8、C6H6和H2S,成矿晚期CH4含量明显增加,总体上属H2O_NaCl_CO2_CH4体系。流体包裹体的盐度w(NaCleq)平均为5.0%,属低盐度流体;均一温度为266.5～295.2℃,属中温热液矿床。上述金矿床与造山型金矿具有相似的地质_地球化学特征,矿石类型为Au_Sb组合,属标准的浅成造山型金矿床,形成于中生代蒙古—鄂霍茨克陆_陆碰撞造山环境。

Upper Heilongjiang Basin is an important gold metallogenic province found recently. Gold deposits such as Shabaosi, Laogou, Shabaosilinchang and Ergenhe are strictly controlled by nearly EW-trending Luoguhe-Ergenhe brittle-ductile shear zone, and the ore bodies normally occur in SN-, NE- and NW- trending subsidiary tensioshear fractures, which were derived from the ductile shear zone. In order to probe into the genetic types of Shabaosi, Laogou and other gold deposits as well as the ore prospecting potential in this area, the authors carried out a detailed field investigation, and studied geological characteristics of typical deposits. Meanwhile, based on the homogenization temperature, whole components, Laser Raman Microprobe analyses of fluid inclusions in quartz, and H, O, S and Pb isotopes, the authors systematically discussed the metallogenesis of the gold deposits. The results show that these gold deposits are characterized by poor sulfides with ≤3 % sulfide minerals （mainly pyrite）. Fluid inclusions in the gold deposits can be divided into aqueous two-phase type, CO2-bearing three-phase type and pure CO2 type. The sulfur, lead, hydrogen and oxygen isotopic components of typical ores and ore-forming fluids indicate that δ^34S values of sulfides （pyrite, pyrrhotite and stibnite） range from - 1.6%0 to 9.6%0, 8180 values of ore-forming fluids from - 1.3‰ to ＋ 6.6‰, while δD from - 89‰ to - 135‰. Lead isotopes of ores have characteristics of the orogenic belt. The cations of the ore-forming fluids are mainly Na^＋ and K^＋ , while the anions are chiefly Cl^- and SO4^2-. The vapor-phase components of the ore-forming fluids are composed mainly of H2O, CO2 and N2, with minor amounts of H2, O2, CO, CH4, C2H4, C2H6, C3H8, C6H6 and H2, whereas the content of CH4 evidently increased at the late ore-forming stage. The ore-forming fluids belong to H2O-NaCl-CO2-CH4 system characterized by low salinity （averagely 5.0 % ）. The homogenization temperature of fluid inclusions ranges from 266.5℃ to 295.2℃, belonging to the mesothermal type. The ore type is of Au-Sb association. Studies show that the gold deposits are similar to the orogenic gold deposits in geological and geochemical characteristics, and can hence be assigned to the epizonal orogenic subtype. The formation of the ore deposits was closely related to Mongolia-Okhotsk orogeny.