西秦岭寒武系金矿床中硫同位素组成及其地质意义

SULFUR ISOTOPIC COMPOSITION AND ITS GEOLOGICAL SIGNIFICANCE OF THE CAMBRIAN GOLD DEPOSITS IN WESTERN QINLING,CHINA

西秦岭寒武系硅岩建造中的金矿床 ,是我国境内发现的一种新的独特类型的层控金矿床。矿床中硫同位素组成的证据表明 ,含矿硅岩建造中沉积黄铁矿的δ3 4S值变化范围较大 ,并以富集重硫为特征。说明含矿硅岩建造中沉积黄铁矿的硫 ,主要来自封闭 -半封闭盆地海水硫酸盐的细菌分解。从东部的牙相金矿点至西部的拉尔玛金矿床 ,沉积黄铁矿的δ3 4S值有不断升高的趋势 ,表明盆地深度可能由东而西逐渐变浅。矿床中热液硫化物和重晶石的硫同位素组成变化范围也很宽。这些热液矿物的δ3 4S值虽有较大差别 ,但它们都有共同的硫源 ,即由寒武系硅岩建造的沉积硫所供给。

The gold deposits in Cambrian silicolite formation of western Qinling mountain are a new unique type of stratabound gold deposit which were discovered in China’s territory. The evidence of sulfur isotopic composition in silicolite formation of the deposits shows that the δ 34 S values vary in a wide range but they are characterized by enrichment in heavy sulfur. It is clear that the sulfur of sedimentary pyrite in ore-forming silicolite formation is meanly derived from sea-water sulfate by bacterium fractionation in a close or half-close basin. From eastern Yaxiang gold occurrence to western La’erma gold deposit the trend of δ 34 S value of sedimentary pyrite is upwards which means the depth of the basin was becoming shallow from east to west. The sulfur isotopic composition of hydrothermal minerals and barite vary in a wide range too. The sulfur of these minerals was derived from a same source and supplied by sedimentary sulfur of Cambrian silicolite formation although they are in different δ 34 S values.