陕西柞水银洞子银铅矿床硫同位素地质研究

SULFUR ISOTOPIC STUDIES OF THE YINDONGZI SILVER-LEAD DEPOSIT,ZHASHUI COUNTY,SHANXI

在银洞子银铅矿床中,硫同位素组成变化很大,围岩地层中硫化物的δ^(34)S/‰值为-3.2—+6.5,13号矿体的硫同位素以富集重硫为特征,硫化物和硫酸盐的δ^(34)S/‰值为+4—+28.48,而小铅矿体群的硫同位素以相对富集轻硫为特征,硫化物的δ^(34)S/‰为-3.5—+4.67,其顶板岩石为接近零的负值.研究表明,矿体和围岩中的硫主要来自封闭盆地中海水硫酸盐的还原,沉积环境经历了对H_2S的封闭—开放—封闭的过程,矿体是在海底热卤水中沉积形成的,硫化物的δ^(34)值受沉积环境和热卤水的物理化学条件所制约.

The changes of sulfur isotope composition in the Yindongzi Ag-Pb deposit are great.δ34S values of sulfides in the wall rock stratum are-3. 2‰ to +6. 5‰. Sulfur isotopes in number 13 orebody are characterized by an enrichment in heavy sulfur, with δ34S values of sulfides and sulfates being + 4‰ to +28.48‰,δ34SBaso4>δ34SFeS2>δ34Szns>δSpbs. This suggests that the sulfur isotopes between coexisting minerals reach the equilibrium distribution. Sulfur isotopes in small lead orebodies are characterized by an enrichment in light sulfur withδ34S values of sulfides being-3. 5‰ to +4. 67‰,and by the equilibrium distribution of sulfur isotopes between coexisting minerals, too. The study suggests that the sulfur in orebodies and wall rocks are mostly derived from the reduction of the sea-water sulfate in a close basin,that the sulfides and sulfates in orebodies may be submarine hot brine sedimentary,and that δ34S values of sulfides are restricted by sedimentary surroundings and physical chemistry conditions of hot brine.