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金沙厂铅锌矿床位于云南省东北部,川-滇-黔铅锌成矿域的西北部,矿体主要赋存于下寒武统和上震旦统的碳酸盐地层中。该矿床的主要矿石矿物是闪锌矿和方铅矿,主要脉石矿物是重晶石、萤石和石英。闪锌矿的δ34S值分布于3.9‰～11.2‰之间,平均为5.7‰;方铅矿的δ34S值在6.0‰～9.0‰之间,平均为7.1‰;两个重晶石的δ34S值分别为34.8‰和34.5‰。重晶石的δ34S值与下寒武地层硫酸盐的一致,排除其他可能来源,认为重晶石的硫来源于下寒武统地层。硫化物的硫不可能来自细菌硫酸盐还原作用,因为流体包裹体均一温度远高于细菌的存活温度。硫酸盐热化学还原作用产生的同位素分馏至多为20‰,由此可知下寒武统地层中硫酸盐发生热化学还原作用产生的还原硫δ34S值至少应为14‰,这个值远高于该矿床硫化物δ34S值,因此这种机制不是还原硫的唯一来源。矿区周围广泛分布玄武岩,并且与岩浆有关的硫化物δ34S值比较低,所以硫化物中的硫可能来自岩浆活动。在方铅矿和闪锌矿共生的样品中,闪锌矿的δ34S值大于方铅矿的δ34S值,说明成矿流体的硫同位素局部达到平衡。利用矿物对硫同位素组成计算的硫化物平衡温度与流体包裹体均一温度一致。
The Jinshachang lead-zinc deposit is located in the northwest of the lead-zinc ore-forming area in northeastern Yunnan, Sichuan-Yunnan-Guizhou. The orebodies mainly occur in the carbonate formations of the Lower Cambrian and the Upper Sinian. The main ore minerals of this deposit are sphalerite and galena, and the main gangue minerals are barite, fluorite and quartz. The δ34S values of sphalerite range from 3.9 ‰ to 11.2 ‰, with an average of 5.7 ‰. The δ34S values of galena range from 6.0 ‰ to 9.0 ‰, with an average of 7.1 ‰. The δ34S values of the two barites are respectively 34.8 ‰ and 34.5 ‰. The δ34S value of barite is consistent with that of the Lower Cambrian strata and excludes other possible sources, suggesting that barite sulfur is derived from the Lower Cambrian stratigraphy. Sulfide sulfur is unlikely to result from bacterial sulfate reduction because the fluid inclusions have a homogenization temperature that is much higher than the bacterial survival temperature. The thermochemical reduction of sulphate gives rise to an isotopic fractionation of up to 20 ‰, indicating that the δ34S value of the reduced sulfur produced by the thermochemical reduction of sulphate in the Lower Cambrian strata should be at least 14 ‰, much higher than the deposit Sulphide δ34S values, so this mechanism is not the sole source of sulfur reduction. Basalt is widely distributed around the mines, and the δ34S value of sulphide associated with magma is relatively low, so the sulfur in sulphide may come from magmatic activity. In the samples symbiosed with galena and sphalerite, the δ34S value of sphalerite is larger than the δ34S value of galena, indicating that the sulfur isotopes of ore-forming fluid are locally in equilibrium. The calculated sulphide equilibrium temperature using the mineral composition of sulfur isotopes is consistent with the homogenization temperature of the fluid inclusions.