新疆东准噶尔松喀尔苏铜金矿区斑岩型矿床成因研究

Genetic study of porphyry-type deposit in Songkaersu Cu-Au ore district in eastern Junggar, Xinjiang

松喀尔苏铜金矿区位于卡拉麦里石炭纪陆相火山岩带。文章通过矿床地质、围岩蚀变、含矿斑岩、流体包裹体和同位素研究,探讨了矿床成因类型。研究表明,松喀尔苏矿床具斑岩型矿床的特征,铜金矿化体产于岩体接触带,围岩蚀变具有分带性,从岩体向围岩依次发育绢英岩化带、高岭石化带和青磐岩化带,绢英岩化带与成矿相关。含矿斑岩复式岩体系同期陆相火山活动产物,成矿作用在时间、空间和成因上与复式岩体中晚期花岗斑岩有关。花岗斑岩具有富水、富挥发性组分和岩浆爆破作用的氧化性岩浆特点,具有后碰撞花岗岩类的地球化学亲缘性,其岩浆起源于后碰撞挤压-伸展转换期的壳-幔岩浆过渡带。幔源岩浆注入、软流圈地幔底侵作用和壳-幔岩浆混合作用是形成含矿斑岩岩浆的主导因素。流体包裹体包括液相包裹体、气相包裹体和含子晶多相包裹体,激光拉曼探针分析表明,气相成分以CO2和CH4为主。成矿流体具有从高温、高盐度岩浆体系向低温、低盐度与大气降水混合的演化过程,流体沸腾或不混溶作用及温度、盐度降低是导致流体中成矿物质沉淀的主要因素。氢、氧同位素组成表明成矿流体以岩浆水为主,在成矿晚期混有大气降水。硫同位素具幔源硫的特征。铅同位素组成显示成矿作用起源于下地壳-上地幔过渡带的岩浆作用。综上所述,该矿床属于与陆相火山-侵入岩有关的斑岩型铜金矿床。

The Songkaersu Cu-Au deposit located in south Karamaili tectonic belt is related to the continental volcanic intrusive rocks in Carboniferous continental volcanic belt. Based on studying deposit geology, rock alteration, host porphyry, fluid inclusions and isotopes, this paper discusses its genesis. It has characteristics of porphyrytype deposit, and mineralization occurs in the contact zone of granite porphyry. As for rock alteration zonation, there are successively phyllic alteration zone, kaolinite zone and propylite zone from the porphyry to the wall rock, with the mineralization related to the phyllic alteration zone. Mineralization is closely related to hypabyssal phase granite porphyry in time, space and genesis; granite porphyry which is closely associated with post-collisional granitoids has oxidation magma characteristics of water- and volatile-enrichment and magma burst function, implying a crust-mantle mixing magmatic origin. The injection of mantle-derived magma, the underplating of asthenosphere mantle and the magmatic mixture interaction between the lower crust and the upper mantle were the main factors responsible for the formation of ore-bearing porphyry magma. Ore-forming fluids and H, O, S, Pb isotope studies further proved the genesis of porphyry-type deposit. Studies have shown that the different host fluid inclusions were liquid, gas and daughter-crystal-bearing gas-liquid-solid phase inclusions, and the analysis of the individual inclusions by Raman microprobe analysis shows that the gases were mainly CO2 and CH4. The evolution process of ore-forming fluids was from the high temperature and high salinity magmatic system to the low temperature and low salinity with the addition of meteoric water, corresponding basically to the mineralization stages. Fluid boiling or immiscibility and the reducing temperature and salinity were the main factors responsible for the precipitation of the metallogenic minerals. The composition of H, O isotopes shows that ore-forming fluids were mainly magmatic water, mixed with a small amount of meteoric water at the late metallogenic stage. The S isotope of pyrite and granite porphyry was the same as mantle-derived S in characteristics. Pb isotopic composition had crust - mantle mixing magmatism characteristics, suggesting that the magmatism related to mineralization formed an extrusion-stretching conversion period in a post-collision environment. Considering the background and mineral deposits, the authors hold that the deposit belongs to porphyry-type Cu-Au deposit related to continental volcanic-intrusive rocks.