贵州小屯乡萤石-锑矿床硫同位素地球化学特征及其地质意义  

Geochemical characteristics of sulfur isotopes for the Xiaotunxiang fluorite-antimony deposit,Guizhou,China and its geological significances

作　　者：彭旎 周家喜 徐阳东[3] PENG Ni;ZHOU Jia-xi;XU Yang-dong(School of Earth Sciences,Yunnan University,Kunming 650500,China;Key Laboratory of Critical Minerals Metallogeny in Universities of Yunnan Province,Kunming 650500,China;Institute of Geophysical and Geochemical Prospecting,Bureau of Geology and Mineral Exploration and Development of Guizhou Province,Guiyang 550018,China)

机构地区：[1]云南大学地球科学学院,昆明650500 [2]云南省高校关键矿产成矿学重点实验室,昆明650500 [3]贵州省地质矿产勘查开发局地球物理地球化学勘查院,贵阳550018

出　　处：《矿物岩石地球化学通报》2023年第4期820-829,共10页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：云南省高层次人才支持项目(YNQR-QNRC-2018-104);贵州省找矿突破战略行动重大协同创新项目(黔科合战略找矿[2022]ZD004);云南大学科研启动项目(YJRC4201804);研究生科研创新基金项目(2021Z100)联合资助。

摘　　要：贵州省贞丰县小屯乡萤石矿床地处黔西南州中部,其深部发育锑矿体,是近年来新发现的锑资源。为查明锑矿体中硫的来源与演化,通过岩相学观察、全矿物消融法及原位激光剥蚀法,对锑矿体的矿物组合和辉锑矿的硫同位素组成进行了分析。结果表明,含硫矿物主要为辉锑矿,极少量为黄铁矿,脉石矿物主要有石英和萤石。辉锑矿亏损重硫同位素(δ34S为-28.40‰~-25.07‰,n=9,全矿物消融法;δ34S为-26.74‰~-22.44‰,n=12,原位激光剥蚀法),其硫同位素组成明显不同于华南锑矿带上大部分锑矿床的硫同位素组成,暗示二者硫的来源或还原硫形成机制不同。在开放体系中,细菌硫酸盐还原作用(BSR)可以产生大量显著亏损重硫同位素的还原硫,小屯乡矿床的赋矿围岩中有草莓状沉积黄铁矿和海相硫酸盐矿物发育,暗示有BSR存在。因此,本文推测该矿床的硫主要来自地层(沉积黄铁矿和海相硫酸盐),是BSR过程的产物。另外,萤石的流体包裹体测温结果(100~176℃)显示成矿温度超出细菌存活温度,故推测BSR发生在锑成矿之前。小屯乡矿床的辉锑矿与沉积黄铁矿均亏损重硫同位素,表明富锑流体与富硫流体的混合作用应是导致辉锑矿沉淀的重要机制。The Xiaotunxiang fluorite deposit in Zhenfeng County is located in the central part of SW Guizhou prefecture.The antimony ore bodies,developed in its deep part,were discovered antimony resource in recent years.In order to find out the source and evolution of sulfur in the antimony ore bodies,the mineral assemblage of antimony ore bodies and sulfur isotope compositions of stibnites were studied through the petrographic observation,and the whole-mineral ablation and in-situ laser ablation ICP-MS analyses.The results show that there are sulfide minerals including major stibnite and minor pyrite,and major gangue minerals including quartz and fluorite.The sulfur isotopes of stibnite samples are depleted in heavy sulfur isotopes(83S=-28.40‰ to-25.07‰,n=9,whole-mineral ablation analytical method;δ34S=-26.74‰ to-22.44‰,n=12,in-situ laser ablation analytical method),and they are obviously different from those of stibnites in most antimony deposits in the South China Sb metallogenic belt,suggesting that their sources of sulfur or the formation mechanisms of reduced sulfur are different.In the open system,the bacterial sulfate reduction(BSR)can produce a large amount of reduced sulfur with significant depletion of heavy sulfur isotopes.The framboids sedimentary pyrite and marine sulfate minerals,developed in the host rocks of the Xiaotunxiang deposit,further suggest the existence of BSR in the deposit.Therefore,we propose that the sulfur in this deposit was mainly sourced from the strata(sedimentary pyrite and marine sulfate)and is the product of BSR process.In addition,the methothermometric data of fluid inclusions in fluorites(100℃ to 176℃)show that the ore-forming temperatures is higher than those of the survival bacteria,so it is inferred that the BSR should have occurred before the antimony mineralization.Both stibnite and sedimentary pyrite in the Xiaotunxiang antimony deposit have depleted heavy sulfur isotopes,indicating that the mixture of Sb-rich and S-rich fluids is a key mechanism leading to the sti

关 键 词：矿物学 硫同位素 硫来源 小屯乡萤石-锑矿床 华南锑矿带 

分 类 号：P611[天文地球—矿床学] P597.2[天文地球—地质学]