西秦岭三个典型金矿床稳定同位素地球化学特征  

Stable isotope geochemistry of three typical gold deposits in the West Qinling

作　　者：冯建忠[1] 汪东波[2] 王学明[3] 邵世才[1] 

机构地区：[1]北京矿产地质研究所,北京100012 [2]中国地质科学院地质研究所,北京100037 [3]中国地质调查局发展研究中心,北京100037

出　　处：《中国地质》2004年第1期78-84,共7页Geology in China

基　　金：国家重点基础研究项目(G1999043213);国家科技攻关项目(96-914-01-04)联合资助。

摘　　要：据八卦庙金矿、李坝金矿、小沟里金矿稳定同位素研究,金矿床δ34S比正常沉积岩变化范围窄,比岩浆-火山岩型矿床宽,硫源是海水硫酸盐还原硫与深部热液来源硫所组成的混合硫。石英包裹体流体氢、氧同位素分布于岩浆水、大气降水的重叠过渡区,更靠近岩浆水区,岩浆水的同位素特征更明显。八卦庙金矿石英脉3He/4He高于地壳3He/4He值(n×10-8),低于地幔3He/4He值(n×10-5),为壳-幔混合源。上述同位素地球化学证据表明,金成矿与岩浆岩有一定的成因关系。岩浆岩与金矿床空间关系密切,矿区内脉岩发育,脉岩为矿体的上下盘。含矿岩石中发育斑点构造,斑点为黄铁矿、磁黄铁矿、毒砂、绿泥石、石英、绢云母、黑云母、堇青石、红柱石、电气石、碳酸盐等热变质矿物和热液交代矿物,表明花岗岩为成矿提供热动力。据八卦庙金矿、李坝金矿、小沟里金矿稳定同位素地球化学研究,结合成矿地质背景分析和区域成矿地质特征对比,认为凤太、西成、礼岷地区金矿与微细浸染型(卡林型)金矿有明显的差别,该区金矿类似于岩浆热液矿床。Stable isotope study indicates that theδ 34 S values of the Baguamiao gold deposit,Liba gold deposit and Xiaogouli gold deposit have a narrower range than those of sediment-hosted deposits and a wider range than those of magmatic or volcanic-hosted deposits.The sulfur was derived from mixing of the sulfur source of seawater sulfate reduction and the deep magmatic sulfur source.Theδ 18 O andδD values of fluid inclusions fall in the overlapped,transitional field of magmatic water and meteoric water but are closer to the magmatic water field and show more pronounced isotopic features of magmatic water.The 3 He/ 4 He ratio of Au-bearing quartz veins is higher than that(n×10 -8 )of the crust and lower than that(n×10 -5 )of the mantle,implying a crust-mantle mixing source for He.The aforesaid isotope geochemical evidence indicates that there is a certain genetic relation between gold mineralization and magmatism.Magmatic rocks are spatially closely related to gold deposits.Dikes are well developed in the area.They act as the hanging walls and footwalls.The spots or stains in host rocks are thermometamorphic minerals and hydrothermal alteration minerals such as pyrite,pyrrhotite,arsenopyrite,chlorite,quartz,sericite,biotite,cordierite,andalusite,tourmaline and carbonates,indicating that granites provided thermodynamic forcing for mineralization.Based on the stable isotope geochemistry of the Baguamiao,Liba and Xiaogouli gold deposits,combined with the metallogenic environment and regional metallogenic characteristics,the authors suggest that gold deposits in the Fengtai-Xicheng-Limin area are notably different from finely disseminated(Carlin type)gold deposits in that the former are genetically similar to magmatic hydrothermal deposits.

关 键 词：金矿床 稳定同位素 地球化学 成矿地质 

分 类 号：P597[天文地球—地球化学]