西藏邦铺钼铜多金属矿床硫、铅同位素 地球化学特征

摘 要]西藏邦铺钼铜多金属矿床位于西藏冈底斯斑岩铜矿带东段,是典型的大型斑岩型矿床,以钼、铜为主,共生铅、锌。本文通过硫、铅同位素研究,获得含矿岩浆岩的硫同位素δ³⁴S( -0.48‰～12.2‰,平均3.80‰)与硫化物矿物的硫同位素δ³⁴S( -1.5‰～ +4.3‰,平均0.98‰) 组成一致,具有典型的岩浆硫特点(δ³⁴S=0译);含矿岩浆岩铅同位素²⁰⁶Pb/²⁰⁴Pb、²⁰⁷Pb/²⁰⁴Pb²⁰⁸Pb/²⁰⁴Pb 比值分别变化于38.857～39.857、15.620～15.704、18.684 ～ 18.768 之间,方铅矿铅同位素组成²⁰⁶Pb/²⁰⁴Pb、²⁰⁷Pb/²⁰⁴Pb、²⁰⁸Pb/²⁰⁴Pb 比值分别变化于18.752～18.825、15.712 ～ 15.718、39.348～39.463 之间,显示其具有正常铅同位素的特点,可能同源,具有相同的演化历史或起源;特征值及铅同位素图解显示其具有壳幔混合特征,以壳源为主,可能主要来源于参加造山带的上部地壳。

Geochemical Characteristics of Sulfur and Lead Isotopes from the Bangpu Mo-Cu Polymetallic Deposit,Tibet

The Bangpu molybdenum-copper deposit in Tibet,which is located in the eastern part of the Gangdese porphyry copper belt,is a large-scale porphyry deposit,dominated by Mo and Cu with associated Pb-Zn.Sulfur and lead isotopic studies show that δ34S from ore-bearing magmatic rocks(0.48‰～12.2‰,averaged 3.80‰) are in accordance with that of sulfide minerals(-1.5‰～+4.3‰,averaged 0.98‰),sharing typical magmatic sulfur characteristics(δ34S=0‰).Lead isotopes of 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb from ore-bearing magmatic rocks vary from 38.857～39.857,15.620～15.704,and 18.684～18.768,respectively,while those from galena vary from 18.752～18.825,15.712～15.718 and 39.348～39.463,which indicates its normal lead characteristics with the same homologous evolutionary history or the same source.The eigenvalue and lead isotopic diagram show that they are characterized by mixed crustal and mantle materials,dominated by crust origin,probably originated from the upper crust involving orogeny.