广东长坑金矿床成矿流体特征及成矿机制初探

摘要

Changkeng Gold Deposit is a large Carlin deposit.Fluid inclusions and geochemistry of hydrogen and oxygen isotopes are studied to find out the fluid mineralization process of the deposit.The gold precipitation can be di-vided into three main stages as follows:quartz-pyrite-phyllic stage,polymetallic sulphide stage,and quartz-carbon-ate stage.Petrographical study shows that there are two types of fluid inclusions:liquid-phase inclusion and gas-liq-uid-phase inclusion.The homogenization temperature of the gold ore-forming fluid ranges 158-282℃,with the peak values within the range of 190-220 ℃.The ice-point temperatures of fluid inclusions in the gold deposit range from-0.2 ℃to -6.6 ℃.The salinity varies from 0.35 %to 9.88 %.As the mineralization process proceeds,the tem-perature and salinity of the ore-bearing hydrothermal fluids steadily decrease.H and O isotopic study shows theδD of quartz in the deposit is from -78 ‰to -46 ‰whileδ18 OH2O ranges from -2.16 ‰to 8.01 ‰; the metallogenic hydrothermal fluids mainly consist of magmatic hydrothermal fluids and are mixed with meteoric water.The mixing of magmatic water with meteoric water results in the precipitation of ore-forming materials.%长坑金矿床为大型卡林型金矿床。通过研究流体包裹体及氢氧同位素地球化学，旨在查明该矿床的流体成矿过程。金矿成矿阶段分为黄铁矿－石英－绢云母阶段、石英－多金属硫化物阶段和碳酸盐阶段。岩相学研究表明，长坑金矿床的流体包裹体主要有液相水溶液包裹体和气液二相水溶液包裹体。测温结果显示：金矿床流体包裹体冰点温度为－6．6～－0．2℃，相应盐度为0．35％～9．88％，均一温度的变化范围为158～282℃，成矿峰值温度为190～220℃；随着成矿作用的进行，成矿流体的温度、盐度持续稳定的降低。氢氧同位素研究表明：金矿床石英的δD值为－78‰～－46‰，δ18 OH2O值变化于－2．16‰～8．01‰，成矿热液主要为岩浆热液，伴随着成矿过程进行，有不同程度的大气降水混入。混合作用是引起成矿流体中矿质发生沉淀富集的主要成矿机制。