西藏拿若铜（金）矿床硫、铅同位素组成及成矿物质来源

Sulfur and lead isotope composition and tracing for sources of ore-forming materials in the Naruo Cu(Au) deposit, in Tibet

关键词:  硫同位素  铅同位素  成矿物质来源  拿若铜(金)矿  班怒成矿带

Key words:  sulfur isopote  lead isotope  ore-forming source  Naruo Cu(Au) deposit  Bannu metallogenic belt

摘要:

为探讨多龙矿集区拿若铜（金）矿床的成矿物质来源，研究矿床成矿机制，本文在详细的野外地质调查和矿石学研究基础上对矿石样品进行硫和铅同位素分析，并对成因意义进行讨论。研究结果表明，17件金属硫化物的δ³⁴S值变化于－2.3‰~2.3‰之间，均值为－0.1‰；其中13件黄铁矿δ³⁴S值变化范围为－2.3‰~2.3‰，均值为0.2‰；4件黄铜矿的δ³⁴S值变化范围为－1.5~－0.8‰，均值为－1.1‰。δ³⁴S值频率直方图总体具有塔式分布特征，平均值接近于零，具幔源硫特征。金属硫化物的²⁰⁸Pb/²⁰⁴Pb介于38.209~38.854之间，平均值为38.635；²⁰⁷Pb/²⁰⁴Pb变化范围为15.541~15.665，平均值为15.605；²⁰⁶Pb/²⁰⁴Pb为17.942~18.580，平均值为18.461，具有正常铅的特征。铅同位素μ值变化范围为9.40~9.57，均小于9.58，表明矿床铅主要来自幔源物质。拿若矿床的硫和铅同位素特征与多龙矿集区斑岩型矿床类似，成矿物质主要来源于岛弧环境下幔源物质，可能存在壳源物质的混入。

Abstract:

On the basis of detailed field geological survey and mineralogical research, in order to discuss the source of ore-forming materials from the Naruo copper (gold) deposit in the Duolong ore-concentrated area and study the metallogenic mechanism, we analyzed the sulfur and lead isotope from the orebody, discussed the significance. The results show that the δ³⁴S values of the seventeen metal sulfides vary from -2.3‰ to 2.3‰, with an average of 0.13‰. The δ³⁴S values of thirteen pieces of pyrite vary from -2.3‰ to 2.3‰, with an average of 0.17‰. δ³⁴S values of four pieces of chalcopyrite vary from -1.5‰ to 0.8‰, with an average of -1.1‰. The δ³⁴S histogram is distributed approximately in a tower shape, with an average nearly zero, which indicates a mantle source. ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb isotopic composition of metal sulfides respectively are 38.209~38.854, 15.541~15.665 and 17.942~18.58, with average of 38.635, 15.605 and 18.641. These data show the normal lead characteristics. Lead isotope μ values range from 9.40 to 9.57, less than 9.58. The feature shows that lead mainly comes from mantle material. Sulfur and lead isotopic characteristics of theNaruo deposit are identical with those of other porphyry deposits in the Duolong ore-concentrated area. The ore-forming materials of theNaruo deposit was mainly derived from mantle materials in an island arc environment, and there may be a mix of shell-derived materials.