辽宁榛子沟铅锌矿床热液叠加成矿作用特征及成矿流体来源

Characteristics of Hydrothermal Superimposed Mineralization and Source of Ore-Forming Fluids in Zhenzigou Pb-Zn Deposit,Liaoning Province

榛子沟铅锌矿矿床是青城子矿田代表性矿床之一,矿体赋存于高家峪组和大石桥组之中,呈层状、似层状和脉状产出,受地层、岩浆和构造联合控制。矿床的形成经历了海底喷流、变质变形和热液叠加三期成矿作用,其中热液叠加成矿作用对脉状矿体的形成与层状矿体的局部热液改造起到了重要作用,可划分为I黄铁矿-方铅矿-闪锌矿-石英和Ⅱ黄铁矿-方铅矿-石英-方解石两个阶段。流体包裹体和碳、氢、氧同位素研究表明:I阶段石英中发育气液两相和少量的富气相、CO2三相流体包裹体,成矿流体属中高温、低盐度、低密度的CO_2-H_2O-NaCl体系热液,含H_2O、CO_2、CH_4和N_2,流体包裹体的δDH_2O-SMOW为-96.5‰和-95.4‰、δ^(18 )OH_2O-SMOW为-0.62‰和0.04‰、δ^(13)C为-4.8‰和-4.4‰,具有大气降水与岩浆水混合流体的特点;Ⅱ阶段石英中主要发育气液两相包裹体,成矿流体属低温、低盐度和低密度的H_2ONaCl体系热液,流体包裹体δDH2O-SMOW为-88.4‰^-80.0‰、δ18 OH2O-SMOW为-7.93‰^-5.57‰,具有大气降水的特点,δ^(13) C为-12.6‰^-7.9‰,具有岩浆水特点。综合分析表明,热液叠加成矿期成矿流体来源于岩浆水与大气降水的混合热液,且成矿后期大气降水的混入比例增加。

Zhenzigou Pb - Zn deposit is a representative one of Qingchengzi Pb - Zn ore field. The deposit mainly occurs in Gaojiayu and Dashiqiao Formation, and is controlled by strata,magmatism, and tectonism with the main ore types being stratiform, stratoid, and veined ore bodies. The deposit experienced three metallogenic episodes such as submarine exhalation, metamorphism or deformation, and hydrothermal superposition. Hydrothermal superposition mineralization played an important role in the formation of the veined ore bodies and the local hydrothermal transformation of stratiform ore bodies. It can be classified into two stages： pyrite-galena-sphalerite quartz（stage I）and pyrite-galenaquartz-calcite（stage II）. According to the fluid inclusions and C- D- O isotope research, aqueous twophase is developed in stage I with minor vapor-rich and COe-bearing three phase in the quartz fluid inclusions, and the ore-forming fluids are of middle-low temperature,low salinity, and low density CO2 - H2O- NaCl system with enrichment of H2O,CO2 , CH4 , and N2. The 8DH2O-SMOW ,δ^18OH2O-SMOW and δ^13C of the fluid inclusions in the quartz are -96. 5‰ and -95.4‰, -0. 62‰ and 0.04‰,-4.8‰ and -4.4‰ respectively, which shows some characteristics of a fluid mixture of meteoric water and magma water. In stage II, aqueous two-phase fluid inclusions are developed in quartz; and the ore-forming fluids are of the low temperature,low salinity and low density H2O- NaCl system, containing a small amount of CO2, CH4 , and N2. The δDH2O-SWOW and δ^18OH2O-SMOW Of the fluid inclusions in the quartz are -88.4‰-80.0‰ and -7.93‰-5.57‰ respectively, which shows the characteristics of meteoric water with δ^13C of -12. 6‰-7. 9‰, a characteristics of magma water. Based on the above, we can infer that in the early mineralization stage, the ore-forming fluids were the mixture of meteoric water and magmatic water in Yanshan period, and in the late mineralization stage the blending proportion of meteoric water increased.