西藏铁格隆南超大型Cu(Au、Ag)矿床S、Pb同位素地球化学研究

摘要

西藏铁格隆南矿床位于多龙矿集区北侧,是近年来在班公湖—怒江成矿带西段发现的首例与高硫化型浅成低温热液成矿作用有关的超大型斑岩-浅成低温热液型铜(金银)矿床.本文在矿石学研究的基础上,对铁格隆南矿床中代表性岩(矿)石样品进行了S、Pb同位素分析,探讨成矿物质来源.铁格隆南矿床硫化物及硫盐矿物的 δ34S值在–9.8‰~6.8‰之间,平均为–1.8‰,其频率直方图具有"塔式"分布特征,总体体现出地幔岩浆硫特征,但已受到少数地壳硫的混染.矿石(206Pb/204Pb=17.959~18.653,207Pb/204Pb=15.606~15.707,208Pb/204Pb=37.926~39.007)与含矿花岗闪长斑岩(206Pb/204Pb=18.527~18.681,207Pb/204Pb=15.564~15.632,208Pb/204Pb=38.697~38.724)以及安山岩(206Pb/204Pb=18.543~18.572,207Pb/204Pb=15.529~15.538,208Pb/204Pb=38.654~38.672)的初始铅组成基本一致,表明三者具有相同的来源;结合铅构造模式图及其源区判别图分析,矿床的铅主要为和岩浆作用有关的上地壳与地幔混合的俯冲带铅.铁格隆南Cu(Au、Ag)矿床的S、Pb同位素组成共同指示成矿物质主要来源于深部岩浆,这种岩浆可能主要起源于班公湖—怒江洋盆俯冲板片部分熔融与地幔物质混熔,并受到少量地壳物质的混染.斑岩成矿系统理论及矿床成矿系列的"缺位理论"指示,多龙矿集区西南部可能存在一个规模较大的斑岩-浅成低温热液-隐爆角砾成矿系统,同时北东部有寻找矽卡岩型矿床的潜力.%The Tiegelongnan ore deposit, located in the north of the Duolong ore concentration area, is the first superlarge porphyry-epithermal copper (gold-silver) deposit related to high sulfidation discovered in the western part of the Bangong Co–Nujiang metallogenic belt in recent years. In this paper, S, Pb isotopes of the typical rock (mineral) samples in the Tiegelongnan deposit were analysed to identify the source of metallogenic materials. Theδ34S values of the Tiegelongnan deposit vary from –9.8‰ to 6.8‰ with the average value being –1.8‰, and the frequency histogram shows the tower appearance, generally representing the trait of mantle sulfur, mixed with a small quantity of crustal sulfur. The initial constituents of Pb in minerals of the Tiegelongnan deposit (206Pb/204Pb=17.959~18.653,207Pb/204Pb=15.606~15.707,208Pb/204Pb=37.926~39.007) is almost the same as those of ore-bearing granodiorite porphyry (206Pb/204Pb=18.527~18.681,207Pb/204Pb=15.564~15.632,208Pb/204Pb=38.697~38.724) and andesite (206Pb/204Pb=18.543~18.572,207Pb/204Pb=15.529~15.538,208Pb/204Pb=38.654~38.672), indicating that they were derived from the same place. Combined with the analyses of structure-pattern map and source-discrimination map of Pb isotopes, it is suggested that the Pb of the Tiegelongnan deposit mainly originated from upper crust-mantle mixed subduction zone which was connected with magmatism. Therefore, judging from the components of sulfur and lead isotopes in the Tiegelongnan copper (gold-silver) deposit, it can be concluded that the metallogenic materials primarily originated from hypomagma, which was generated from partial melted mantle material mixed with some subduction plates of Bangong Co–Nujiang oceanic basin, with the addition of a small amount of crustal materials.