江苏观山高硫型铜铅金矿床稳定同位素地球化学和成因意义

Stable Isotopic Geochemistry and Genesis of the Guanshan High-Sulphidation Type Cu-Pb-Au Deposit in Jiangsu Province

江苏观山铜铅金矿是典型的高硫型浅成低温热液矿床。本文通过对观山铜铅金矿床氢、氧、碳、硫同位素组成的研究,探讨成矿溶液中水、碳、硫的来源以及成矿溶液的演化。同位素测定显示石英流体包裹体水的δD=-90‰～-70‰,δ18O水=-8.9‰～-1.1‰;热液方解石流体包裹体水的δD=-90‰～-81‰,δ18O水=0.1‰～2.3‰。氢氧同位素组成说明成矿流体主要为与围岩进行过水岩反应的循环大气降水,不排除有少量岩浆水的加入。黄铁矿与黄铜矿矿石的δ34SV-CDT=5.8‰～9.9‰,平均值为7.6‰,表明该矿成矿过程中的S很可能是沉积岩来源的硫与岩浆岩来源硫的混合。矿床中可见较多的重晶石等硫酸盐矿物,这种高价态硫的矿物的存在显示其成矿溶液具有富集34S的特征,加上成矿过程中流体的沸腾导致H2S等气体大量逸出和残余岩浆流体富集34S,使得沉淀的黄铁矿、黄铜矿等硫化物同样具有富集34S的特征;热液方解石碳同位素δ13C方解石=-4.1‰～6.1‰,平均为δ13C方解石=1.3‰,显示其中的C主要来源于流体对流循环过程中对基底岩石中碳酸盐地层的溶解。

The Guanshan Cu-Pb-Au deposit in Jiangsu Province is a high-sulphidation type epithermal poly-metallic deposit. This work studies the stable isotope compositions of ore minerals and fluid inclusions,the sources of ore-forming fluid and materials. The result shows that the δD and δ^18O of fluid inclusions in quartz veins range from -90‰ to -70‰ and -8.9‰ to -1.1‰, respectively, while those of the hydrothermal calcites are -90‰ - - 81‰ and 0.1‰ - 2.3‰, respectively, indicating that the ore-forming fluids stem mainly from cycling atmospheric precipitation and a little amount of magmatic water. The sulfur isotope of chalcopyrites and pyrites range from 5.8‰ to 9.9‰, with average 7.6‰, suggesting that the sulfur is probably derived partly from sedimentary rocks. Plenty of sulfates such as barites can be found in Guanshan implies the enrichment of ^34S in the ore-forming fluids. Along with the boiling of ore-forming fluids, it resulted in degassing of trace gases such as H2 S, and enrichment of ^34 S in the residual magmatic fluids, and deposited pyrites and chalcopyrites enriched in ^34 S. δ^18C of hydrothermal calcites are -4.1‰ - 6.1‰ with average 1. 3‰, implying that the primary source of the carbon in the ore-forming fluids is the dissolved carbonate formation in the basement rocks.