陕西青山金矿床金的迁移形式与沉淀机制研究

TRANSPORTING STYLE AND DEPOSITIONAL MECHANISM OF GOLD IN THE QINGSHAN GOLD DEPOSIT,SHAANXI PROVINCE

青山金矿床是一个赋存于石炭系沉积岩中的中-小微细粒浸染型金矿床.采用原子吸收光谱、气相色谱仪等分析技术,利用地球化学热力学理论,对青山金矿床开展了成矿流体成分分析和热力学计算,解析了该矿床成矿物理化学条件及金的迁移形式和沉淀机制.结果显示,成矿流体呈弱酸性、弱还原性,为重碳酸钙亚型,可大致视为CO2-H2O-NaCl体系,来源于古大气降水,并且后期受到了大气降水的混合.成矿早期流体中的金主要以氯络合物形式[Au(Cl)4]-迁移,主成矿期与晚期流体中金以硫络合物形式[Au(HS)2]-迁移.成矿流体温度、盐度、pH值、Eh值、氧逸度等物理化学条件的变化、后期大气降水的混合、水-岩反应及硫酸盐还原菌是造成本矿床金沉淀的主要因素.

The small-medium sized Qingshan gold deposit in Shaanxi Province, hosted in the Carboniferous sedimentary rocks, is of micro-fine dissemination type. The fluid inclusion is examined by atomic absorption spectrometry and gas chromatograph. Based on geochemical thermodynamics theory, the physical-chemical conditions of mineralization and the transportation style and deposition mechanism of the deposit are studied. The result shows that the metallogenic fluid is in weakly acid and reduced, belonging to calcium bicarbonate type, generally regarded as CO2-H2O-NaC1 system, mainly derived from ancient meteoric water, and mixed with the meteoric water during later period. The gold in the metallogenic fluid transported as Au-C1 complex [Au （HS）2]- in early mineralization stage, while as Au-S complex [Au （HS）：]- in main and late stages. Change of physical-chemical conditions, such as temperature, salinity, pH, Eh and oxygen fugaeity, as well as the mixing of meteoric water, water-rock reaction and sulfate reducing bacteria are the main factors causing the precipitation of gold.