山西中条山铜矿峪斑岩型铜矿床成矿流体特征

Characteristics of ore-forming fluids of Tongkuangyu porphyry copper deposit in Zhongtiao Mountain, Shanxi Province

铜矿峪铜矿床位于中条山铜多金属成矿带,是目前中国最古老的斑岩型铜矿床之一。基于详尽的野外地质调查,结合流体包裹体岩相学、显微测温、群包裹体成分和碳、氢、氧、硫同位素分析等研究,探讨铜矿峪铜矿床成矿流体来源、性质及其演化和成矿物质来源。铜矿峪铜矿床的成矿阶段可划分为红钠化(石英-钠长石)阶段,钾长石-石英阶段,石英-硫化物阶段,石英-碳酸盐阶段(石英-方解石-硫化物阶段和石英-铁白云石-硫化物阶段)和碳酸盐阶段。流体包裹体类型主要有富液相气液两相包裹体(Ⅰ型)、含子晶包裹体(Ⅱ型)和CO2包裹体(Ⅲ型),还有少量的富气相包裹体(Ⅳ型)和液相包裹体(Ⅴ型),成矿流体系统早期为中高温、高氧逸度、富CO2的岩浆热液,中阶段经过流体沸腾、温度降低、氧逸度降低、CO2逸失等过程演化为还原性流体,使得大量金属硫化物沉淀,最后由于大气降水的不断加入和降温等过程,形成晚期的低温、中低氧逸度、低盐度、贫CO2的大气降水热液。氢、氧同位素组成(δ18OH2O值变化范围为6.5‰～-1.10‰,δD值变化范围为-99‰～-58‰)显示,从早阶段到晚阶段,成矿流体从以原生岩浆水为主,到晚期大气降水为主。9件硫化物样品δ34S值变化于1.1‰～4.8‰,平均值为2.44‰。表明成矿物质具有深源的特征。

Located in the Zhongtiao Mountain copper metallogenic belt, the Tongkuangyu copper deposit is one of the oldest porphyry Cu （Mo） deposits in China. Through detailed field geological survey and petrographic as well as microthermometric studies of fluid inclusions, the authors investigated the origin, characteristics and evolution of ore-forming fluid and the source of ore-forming materials. The ore-forming process of the Tongkuangyu copper deposit can be divided into five stages： red albitization （quartz-albite） stage, potash feldspar-quartz stage, quartz- sulfide stage, quartz-carbonate stage （quartz-calcite-sulfide stage and quartz-sulfide-ankerite stage）, and carbon- ate stage. Quartz and calcite associated with the mineralization contain abundant fluid inclusions. According to the fluid inclusion compositions and the phases presented at room temperature, five different types of fluid inclu-sions were distinguished： liquid-vapor inclusion （Ⅰ-type）, multi - phase inclusion （Ⅱ-type）, aqueous-CO2 in- clusion （Ⅲ-type）, vapor-rich or gas inclusion （Ⅳ type） and pure liquid inclusion （Ⅴ）. Group inclusions composition and H, O, S isotopes were used to study the origin, property and evolution of the ore-forming fluids as well as ore-forming materials. On such a basis, the genesis of the Tongkuangyu copper deposit was revealed. The ore-forming fluid was magmatic fluid with medium-high temperature, high oxygen fugacity, rich CO2 at the early stage, whereas the middle stage fluids evolved into reducing fluids due to boiling, temperature decreasing, dropping of oxygen fugacity, and escaping of CO2 and led to the precipitation of metal sulfide. With the addition of atmospheric precipitation and cooling, metamorphic hydrothermal fluids with low temperature, medium-low oxygen fugacity, low salinity, and poor- CO2 were formed. The isotope composition of oxyhydrogen-oxygen （δ^18OH2O values from -6.5%0 to -1.10‰, and δDVSMOW values from -99‰ to -58‰） shows that, from the early stage of mineralization to the post-ore stage, the fluids were characterized by the evolution from mainly deep-sourced fluids to the gradual addition of shallow-sourced meteoric water. 9 samples from the Tongkuangyu copper deposit yielded a range of sulfur isotope values （1.1‰ to 4.8%0, 2.44‰ on average）, and also suggest that the ore-forming materials mainly came from deep region.