S、Pb同位素对冈底斯斑岩铜矿带成矿物质来源和造山带物质循环的指示  

Implications of S and Pb isotopic compositions of the Gangdise porphyry copper belt for the ore-forming material source and material recycling within the orogenic belt

作　　者：曲晓明[1] 侯增谦[1] 李佑国[2] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]成都理工大学地球科学学院,四川成都610059

出　　处：《地质通报》2002年第11期768-776,共9页Geological Bulletin of China

基　　金：中国地质调查局地质调查项目"西藏铜金锑多金属矿产资源远景评价"(编号:200010200168)成果之一。

摘　　要：近年来发现青藏高原南部冈底斯岩浆弧中发育了一条潜力很大的斑岩型铜(钼、金)多金属成矿带。通过野外地质调查和岩石地球化学、S-Pb同位素示踪及Re-Os同位素定年研究,发现该带的铜多金属矿化与喜马拉雅晚期碰撞后地壳松弛阶段形成的晚造山花岗质斑岩体有关。本文资料显示,该带的含矿斑岩和矿石硫化物具有完全一致的S、Pb同位素组成。δ34S在-3.8‰～+2.4‰之间,具幔源硫特征;206Pb/204Pb、207Pb/204Pb及208Pb/204Pb分别变化于18.106～18.752、15.501～15.638和37.394～39.058之间,富含放射成因铅,反映了物质来源上的同一性。空间上该铜矿带铅同位素具有明显的变化规律,由成矿带东段的地壳铅经中段的造山带铅向西段的地幔铅演化,在Pb构造模式图上构成很好的等时线,在源区端元图上清楚地落在印度洋MORB与印度洋沉积物两个端元之间。化学分析结果表明,这些斑岩体高度富集大离子不相容元素Rb、K、U、Th、Sr、Pb,强烈亏损高场强元素Nb、Ta、Ti和重稀土元素Yb,缺少Eu异常。Recent study has confirmed that there exists a porphyry-type Cu (Mo ,Au )polymetallic met-allogenic belt along the Gangdise magma arc in the southern Qinghai-Tibet Plateau.Through the field in-vestigation and geochemical study,S-Pb isotopic tracing and Re-Os isotopic dating,the authors found out that Cu polymetallic mineralization of the belt was genetically related to late orogenic granitic por-phyries formed in the late Himalayan post-collision crustal relaxation period.The data of this paper demon-strate that ore sulfides of the Gangdise porphyry copper belt have the same S and Pb isotopic compositions as ore-bearing porphyries.Theirδ 34 S values vary between-3.8‰and+2.4‰and are typical of mantle S.The 206 Pb / 204 Pb,207 Pb / 204 Pb and 208 Pb / 204 Pb ratios vary in the ranges of 18.106～18.752,15.501～15.638and37.394～39.058respectively,with rich radiogenetic lead,reflecting the consistency of their material sources.Spatially Pb isotopic compositions of the copper belt show a notable regular variation from crustal Pb in the eastern segment of the belt through orogenic Pb in the central segment to mantle Pb in the western segment.They constitute a good mixing line isochron in the plumbotectonic framework diagram and fall between Indian Oceanic MORB and Indian Oceanic sediments in the end-member diagram of the source region.Chemical analysis indicates that these porphyries are highly enriched in the large ion lithophile ele-ments Rb ,K,U,Th ,Sr and Pb and strongly depleted in the high field strength elements Nb ,Ta and Ti and the heavy rare earth element Yb without any Eu anomaly.

关 键 词：成矿物质来源 青藏高原 冈底斯岩浆弧 斑岩型铜矿带 铅同位素 硫同位素 

分 类 号：P618.41[天文地球—矿床学]