哀牢山南段长安金矿床成矿物质来源:来自S、Pb同位素的证据  

Origin of Metallogenic Materials of the Chang'an Gold Deposit in the Southern Ailaoshan Belt: Evidence from Sulfur and Lead Isotopic Composition

作　　者：李士辉[1,2] 张静[1] 杨立强[1] 王欢[1] 

机构地区：[1]地质过程与矿产资源国家重点实验室中国地质大学地球科学与资源学院,北京100083 [2]内蒙古第十地质矿产勘查开发院,内蒙古赤峰024000

出　　处：《现代地质》2013年第4期879-887,共9页Geoscience

基　　金：国家重点基础研究发展规划项目(2009CB421006);中央高校基本科研业务费专项(2652013017;2010ZD11)

摘　　要：哀牢山南段长安金矿床是三江造山带哀牢山成矿带南段大型矿床之一,就位于甘河断裂的脆性破碎带内,赋矿岩石以下奥陶统砂岩和碎屑岩为主。目前已知各地质体内黄铁矿的硫同位素δ34S值变化范围为-3.49‰～+3.57‰,峰值集中在+1‰～+3‰;矿石与其他围岩及岩浆岩脉的硫同位素组成的对比表明,成矿热液中硫最可能源自于地层,或者部分混染了喜山期岩浆热液中的硫。矿石铅同位素组成为:208Pb/204Pb=38.722～40.649,207Pb/204Pb=15.604～15.813,206Pb/204Pb=18.788～19.761。结果显示其变化范围相对较小,说明矿石相对富集放射成因铅;矿石铅来源于成熟度较高的上地壳,显示矿床铅更可能源自区内的白云岩、碎屑岩、粉砂岩等沉积岩类。蚀变岩和岩浆岩类的铅主要显示出造山带铅源特点,暗示矿石铅源与矿区内岩浆岩相关性较小,应主要来自赋矿围岩。区内新生代岩浆活动为矿床的进一步叠加富集提供了热源和部分成矿物质。The Chang’an deposit is one of large gold deposits in the Southern Ailaoshan metallogenic belt in Sanjiang region,and the occurrence of ore bodies is controlled by the brittle fractured zone of Ganhe fault. The orehosted rocks are dominated by Lower Ordovician sandstone and clastic rocks. The δ34 S values of pyrites in the magmatite and ores range from 3. 49‰ to ＋ 3. 57‰,concentrating between ＋ 1‰ and ＋ 3‰. The comparative study on sulfur isotopic compositions of the ores,wall rocks and magmatic dikes suggests that the sulfur in ore-forming fluid was most probably sourced from the ore-hosted strata and partly mixed with that in the Himalayan period magmatic hydrothermal fluid. The Pb isotopic values of the ore vary in a narrow range,i. e. , 208 Pb /204 Pb = 38. 722 40. 649,207 Pb /204 Pb = 15. 604 15. 813 and 206 Pb /204 Pb = 18. 788 19. 761,respectively,showing that the gold ores are relatively rich in radiogenic lead. It is suggested that the ore lead was sourced from the upper crust with higher maturity,indicating that the lead and other ore-forming elements should be mainly derived from the Devonian dolomite and clastic rocks,the Ordovician sandstone in mining area. At the same time,the lead isotopic compositions of altered rock and magmatite mainly show the characteristics of orogenetic belt. Comprehensive research proves that the metallogenic materials only have a little relationship to the magmatite. That is to say,the ore-forming materials were mainly sourced from the ore-hosted wall rocks, and the Cenozoic magmatism provided the heat source and part metallogenic materials for the further enrichment of the Chang’an gold deposit.

关 键 词：硫、铅同位素 成矿物质来源 长安金矿床 哀牢山成矿带 

分 类 号：P618.5[天文地球—矿床学]