大兴安岭北段宝兴沟金矿床成矿流体特征及矿床成因

宝兴沟金矿床是大兴安岭北部上黑龙江成矿带内大型金矿床之一，矿体主要产于下侏罗统二十二站组砂岩与早白垩世石英闪长岩、闪长玢岩内外接触带内，其热液成矿作用可划分为：黄铁矿±毒砂-石英（Ⅰ）、多金属硫化物-石英（Ⅱ）及少硫化物-碳酸盐（Ⅲ）3个阶段。流体包裹体岩相学研究表明：Ⅰ阶段矿石主要发育气液两相（LV）、少量含CO₂三相包裹体（H_CO2）及富气相包裹体（FV）；Ⅱ阶段矿石中主要发育LV及少量H_CO2包裹体；Ⅲ阶段矿石中只发育LV包裹体。测温结果显示：Ⅰ、Ⅱ阶段包裹体总体均一温度峰值集中于225.00~300.00℃，盐度（w（NaCl））为2.00%~10.00%；Ⅲ阶段均一温度峰值集中于175.00~225.00℃，盐度为4.00%~8.00%；成矿流体为简单的含CO₂中低温、低盐度的NaCl-H₂O热液体系，总体具有从成矿早期到晚期均一温度、盐度逐渐降低的特征。氢、氧同位素分析结果显示，Ⅰ、Ⅱ阶段成矿流体δD_SMOW为-131.00‰~-108.00‰、δ¹⁸O_SMOW为1.00‰~4.00‰，Ⅲ阶段δD_SMOW为-108.00‰、δ¹⁸O_SMOW为-1.89‰，表明早期以岩浆水为主，晚期逐渐演化为与大气降水混合热液。矿石中黄铁矿（毒砂）δ³⁴S_V-CDT为1.50‰~4.20‰，显示其物质来源以深源岩浆为主。综合分析认为，区内金成矿作用与早白垩世（石英）闪长岩、闪长玢岩侵入活动有直接关系，矿床属中低温岩浆热液成因类型。

Characteristics of Ore-Forming Fluid and Genesis of Baoxinggou Gold Deposit in North of Great Xing'an Range

The Baoxinggou gold deposit is a large-scale deposit in the upper Heilongjiang metallogenic belt in the north of Great Xing'an Range. The ore bodies mainly occur in the contact zone between the sandstone of the Early Jurassic Ershierzhan Formation and the Early Cretaceous quartz diorite, diorite porphyrite. The hydrothermal mineralization can be classified into three stages:pyrite±arsenopyrite-quartz (Ⅰ), polysulfide-quartz (Ⅱ) and sulfide-poor carbonate (Ⅲ). The petrographic study of the fluid inclusions showed that there were aqueous two phases (LV type), fewer CO₂-bearing three phases (H_CO2 type),and vapor-rich phases (FV type) fluid inclusions developed in the stage I; aqueous two phases (LV type) and fewer CO₂-bearing three phases (H_CO2 type) in the stage Ⅱ; only aqueous two phases (LV type) in the stage Ⅲ. The micro-thermometric research revealed that the peak homogeneous temperature of fluid inclusions in the stageⅠandⅡ was range of 225.00-300.00℃, the salinity was range of 2.00%-10.00% NaCl, and those in the stage Ⅲ were 175.00-225.00℃ and 4.00%-8.00% NaCl correspondingly. The ore-forming fluids were of CO₂-bearing medium-low temperature and low salinity NaCl-H₂O-CO₂ system solutions; and with the progressing of mineralization, the temperature and salinity gradually decreased. The hydrogen and oxygen isotope analysis showed that the δD_SMOW of mineralization stageⅠand stageⅡvaried in the range of -131.00‰-108.00‰, δ¹⁸O_SMOW varied in the range of 1.00‰-4.00‰, and the corresponding average values in the stage Ⅲ were -108.00‰ (δD_SMOW)and -1.89‰ (δ¹⁸O_SMOW), meaning that magmatic derived solutions dominated in the early stages of mineralization, while meteoric water gradually played an important role in the later stage of mineralization. The sulfur isotope analysis showed that δ³⁴S of pyrite was range of 1.50‰-4.20‰, indicating the metals mainly from deep-sourced magmas. All these lead to the conclusion that Baoxinggou gold deposit is of medium-low temperature magmatic hydrothermal origin which is directly related to the quartz diorite and diorite porphyritic magmatism.