The Huize and Maoping deposits,the famous high-grade Mississippi Valley-type lead-zinc deposits in China,are located in the central south of the Sichuan-Yunnan-Guizhou lead-zinc polymetallic ore cluster area in the southwestern margin of the Yangtze block and tectonically in structural composite area of Xiaojiang fault zone,Zhaotong-Qujing hidden fault zone,and Yadu-Ziyun fault zone.This study discussed effect of sulfate evaporate salt layer on lead-zinc mineralization of the Huize and Maoping deposits using sulfur isotope compositions of sulfides and gypsum from the two deposits.δ34 SV-CDT value of the Huize ore sulfides ranges from 11.0‰ to 20.0‰ (averaging 14.7‰),with most concentrated in 13.0‰～17.0‰,roughly representing total sulfur isotopic composition.δ34 SV-CDT value of the carbonate-associated sulfate ranges from 10.4‰ to 18.6‰ (averaging 13.1‰),slightly lower than the ore sulfides.δ34 SV-CDT value of the gypsum in the Carboniferous gypsum salt layer ranges from 12.9‰ to 17.1‰ (averaging 13.6‰),which is consistent with that of the carbonate-associated sulfate.δ34 SV-CDT value of the ore sulfides in the Maoping deposit is closely related to its occurrence layers.The δ34 SV-CDT value of the ore sulfides in the Baizuo Formation (C1b) ranges from 7.1‰ to 17.5‰,with an average of 12.8‰,which is slightly lower than carbonate-associated sulfate and gypsum in Carboniferous carbonate strata.The δ34SV-CDT value of ore sulfides in the Zaige Formation (D3zg) ranges from 18.3‰ to 22.7‰,with an average of 21.1‰.The results are unlikely with the ore sulfides in the Baizuo Formation (C1b) or the Huize deposit.The δ34 SV-CDT value of the gypsum in the Zaige Formation (D3zg) ranges from 21.9‰ to 25.9‰,with an average of 23.6‰,which is slightly higher than sulfides in the Zaige Formation (D3zg).By comparing the sulfur isotopic compositions of the sulfides,sulfate and gypsum,we propose that the sulfur in the ore sulfides of Huize and Maoping lead-zinc deposits mainly came from the sulfate in the ore-bearing strata.In addition,sulfur in the ore sulfides of the Huize lead-zinc deposit mainly came from Carboniferous gypsum salt layer,with only 10％ of the sulfur from the underlying Zaige Formation gypsum salt layer;while sulfur in the Zaige Formation ore sulfides of Maoping lead-zinc deposit derived from the Zaige Formation gypsum salt layer,sulfur in the Baizuo Formation ore body mainly came from the Baizuo Formation gypsum salt layer,i.e.the gypsum was reduced in situ.Collectively,we divided the metallogenic process into two stages.At the first stage,gypsum reacted with methane and/or other organic compositions forming hydrogen sulfide gas,which preserved in interlayer fissures or karst caves companied with large scale dolomization.At the second stage,ore-forming fluids containing Pb,Zn and other metals leached from the basement rocks mixed with H2 S-rich fluids,resulting in precipitation of pyrite,galena,sphalerite and forming high-grade ores,%云南会泽和毛坪铅锌矿床位于扬子地块西南缘川-滇-黔铅锌多金属矿集区的中南部,小江断裂带、昭通-曲靖隐伏断裂带和垭都-紫云断裂带的构造复合部位,是我国著名的MVT型铅锌矿床.本文以会泽和毛坪铅锌矿为例,系统研究了矿床中矿石硫化物、矿区相关碳酸盐岩地层中微量硫酸盐(CAS)以及外围不同时代膏盐层中石膏的硫同位素组成,探讨了膏盐层在云南会泽和毛坪铅锌矿成矿中的作用.会泽矿床矿石硫化物的δ34 SV-CDT值为11.0‰～20.0‰,多数集中在13.0‰～17.0‰之间,平均14.7‰,大致代表总硫的同位素组成.石炭系碳酸盐岩地层中微量硫酸盐的δ34 SV-CDT值为10.4‰～18.6‰,平均13.1‰,较矿石硫化物的值稍低.矿区外围石炭系膏盐层中石膏的δ34 SV-CDT值为12.9‰～17.1‰,平均13.6‰,与石炭系碳酸盐岩中微量硫酸盐的δ34 SV-CDT值几乎完全一致.毛坪矿床矿石硫化物的δ34 SV-CDT值与其赋存层位密切相关,赋存于摆佐组(C,b)的矿石硫化物的δ34 SV-CDT值为7.1‰～17.5‰,平均12.8‰,较会泽矿石硫化物的值稍低,与石炭系碳酸盐岩地层中微量硫酸盐和石膏的值一致;赋存于宰格组(D3zg)的矿石硫化物的δ34SV-CDT值为18.3‰～22,7‰,平均21.1‰,与赋存于摆佐组(C1b)的矿石硫化物的值和会泽矿床矿石硫化物的值明显不同.矿区外围宰格组(D3zg)膏盐层中石膏的δ34 SV-CDT值为21.9‰～25.9‰,平均23.6‰,与毛坪矿床宰格组(D3zg)矿石硫化物的值相似.通过对比会泽、毛坪矿床中不同赋矿层位矿石硫化物、石炭系不同层位碳酸盐岩中微量硫酸盐和矿区外围不同时代膏盐层中石膏的硫同位素组成及变化规律,提出会泽、毛坪铅锌矿床矿石硫化物中的硫主要来源于赋矿层位膏盐层中石膏硫酸盐的热还原.其中会泽铅锌矿的硫绝大部分来自石炭系膏盐层,只有10％的硫来自下伏的宰格组膏盐层;毛坪铅锌矿床中赋存于宰格组的矿体,矿石硫主要来自宰格组膏盐层,而赋存于摆佐组的矿体,矿石硫主要来自摆佐组膏盐层,即膏盐层是在原地被还原的.成矿作用分为两个阶段,第一阶段石膏与甲烷等有机质发生热化学反应,全部被还原形成H2S,储存在层间裂隙或溶洞之中,同时发生大规模白云岩化;第二阶段淋滤了深部基底岩石中Pb、Zn等金属成矿物质的成矿流体与储存在层间裂隙或溶洞之中的富含H2S的流体混合,形成黄铁矿、方铅矿和闪锌矿等富集沉淀,形成高品位矿石.
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