云南东川大笑铅锌矿床成矿物质来源:S和Pb同位素制约  

The origin of ore-forming materials of the Daxiao Pb-Zn deposit in Dongchuan,Yunnan:Constraints from S and Pb isotopes

作　　者：潘萍[1,2] 常河 PAN Ping;CHANG He(School of Land Resources Engineering,Kunming University of Science and Technology,Kunming 650093,China;Geomatics Engineering Faculty,Kunming Metallurgy College,Kunming 650033,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093 [2]昆明冶金高等专科学校测绘学院,云南昆明650033

出　　处：《矿物学报》2020年第4期466-474,共9页Acta Mineralogica Sinica

基　　金：国家自然科学基金项目(编号:U1133602,U1812402);云南省矿产资源预测评价工程实验室项目(2010);云南省地质过程与矿产资源创新团队项目(2012)。

摘　　要：位于扬子板块西南缘的云南东川大笑铅锌矿床,赋存于中—新元古代昆阳群黑山组泥质白云岩中,呈脉状、透镜状或似层状产出。该矿床矿石矿物主要为方铅矿,闪锌矿和黄铁矿次之,脉石矿物主要有方解石、白云石和石英。矿石矿物具有粒状、交代等结构,矿石具有块状、脉状、浸染状等构造,具有后生热液成矿特征。方铅矿的δ34S值介于+6.1‰^+8.5‰,明显高于幔源岩浆硫的δ34S值(-3‰^+3‰),但位于赋矿中-新元古代变质岩/流体的δ34S值(-20‰^+20‰)范围内,所以不能排除赋矿地层的贡献。此外,与上覆震旦—二叠系沉积岩中海相硫酸盐矿物的δ34S值(+11.8‰^+28.3‰)相比,该矿床硫化物的δ34S值要明显低的多,但硫酸盐热化学还原作用(TSR,能产生高达+15‰的分馏)可以形成大笑铅锌矿床硫化物的S同位素组成特征,所以也不能排除上覆地层蒸发膏岩(层)的贡献。因此,最合理的解释是该矿床成矿流体中的S由赋矿地层和上覆地层共同提供,而TSR在还原S的形成中扮演了重要角色。单颗粒方铅矿的Pb同位素比值变化较小,其206Pb/204Pb比值范围为16.5687~16.6058,207Pb/204Pb比值范围为15.4978~15.5026,208Pb/204Pb比值范围为36.3700~36.4067,位于上地壳和造山带平均铅演化线之间,落入赋矿中—新元古代昆阳群Pb同位素组成范围内,表明该矿床成矿金属Pb具有壳源特征,且主要由赋矿地层昆阳群提供。因此,大笑铅锌矿床成矿物质具有混合特征,其中赋矿地层昆阳群提供了主要成矿物质(金属铅和部分硫),上覆盖层沉积岩提供了部分硫,其矿床类型属于后生热液型。The Daxiao Pb-Zn deposit in Dongchuan,Yunnan is located in the southwestern Yangtze Block.Its orebodies,occurred as veined,lenticular,or stratiform forms,are hosted in argillaceous dolostone of the Heishan Formation of the Meso-to Neo-Proterozoic Kunyang Group.Ore minerals of the deposit are mainly galena,and secondly sphalerite and pyrite.Gangue minerals are mainly calcite,dolomite,and quartz.Ore minerals have granular,metasomatic and other textures.Ores have massive,veined,and disseminated structures,with characteristics of the epigenetic mineralization.Theδ34S values of galena samples range from+6.1‰to+8.5‰,which are significantly higher than those of mantle-derived sulfur(-3‰to+3‰).Thus,the contribution of sulfur mainly derived from the mantle magma can be ruled out.However,theδ34S values of sulfides vary within range of Meso-and Neo-proterozoic metamorphic rocks/fluids(δ34S=-20‰to+20‰),so the contribution of sulfur derived from the ore-bearing strata cannot be ruled out.In addition,compared with the sulfur isotope compositions of marine-derived sulfate minerals in the overlying Ediacaran-Permian sedimentary rocks(δ34S=+11.8‰to+28.3‰),theδ34S values of sulfides are significantly low.However,the thermochemical sulfate reduction(TSR can result in up to+15‰isotope fractionation)could lead to the sulfur isotopic compositions of sulfides in the Daxiao Pb-Zn deposit,so the contribution of sulfur from the evaporate rocks in the overlying strata should not be ruled out.Therefore,the most reasonable explanation is that the sulfur in the ore-forming fluid of the deposit is most likely to be provided by the ore-bearing strata and the overlying sedimentary rocks,and the TSR played an important role for the formation of reduced sulfur.The Pb isotope ratios of individual particles of galena vary in small ranges with 206Pb/204Pb ratios varying from 16.5687 to 16.6058,207Pb/204Pb ratios varying from 15.4978 to 15.0026,and 208Pb/204Pb ratios varying from 36.3700 to 36.4067.Such Pb isotopic ratios are pl

关 键 词：硫化物 S和Pb同位素 成矿物质来源 流体混合 大笑铅锌矿床 

分 类 号：P571[天文地球—矿物学] P618[天文地球—地质学]