西藏北部舍索与拉屋铜矿床硫化物铅同位素特征

Lead isotopes in the sulfide ores from the Shesuo and Lawu copper deposits, northern Xizang

关键词:  Pb同位素  成矿物质来源  拉屋  舍索

Key words:  Pb isotope  origin of ore-forming matter  Lawu  Shesuo

摘要:

本文在系统的野外地质工作基础上,对舍索与拉屋矿床的矿石硫化物铅同位素组成进行综合分析,进而示踪其成矿物质来源。结果显示,舍索矿区矿石硫化物铅的²⁰⁶Pb/²⁰⁴Pb值为18.517~18.776,²⁰⁷Pb/²⁰⁴Pb值为15.671~15.756,²⁰⁸Pb/²⁰⁴Pb值为38.955~39.33;拉屋矿区矿石硫化物铅的²⁰⁶Pb/²⁰⁴Pb值为18.651~18.757,²⁰⁷Pb/²⁰⁴Pb值为15.707~15.823,²⁰⁸Pb/²⁰⁴Pb值为39.183~39.561。研究表明,舍索与拉屋矿床矿石硫化物铅同位素含量比值具有明显的上地壳特征,指示两个矿床成矿物质主要来自上地壳。其中舍索矿床成矿物质富集受燕山期岩浆作用影响,而拉屋矿床部分成矿物质由晚石炭纪地幔物质的喷流沉积作用提供。

Abstract:

The emphasis in the present paper is placed upon the lead isotopic compositions and their origins in the sulfide ores from the Shesuo and Lawu copper deposits, northern Xizang. The analytical results include ²⁰⁶Pb/²⁰⁴Pb ratios from 18.517 to 18.776, ²⁰⁷Pb/²⁰⁴Pb ratios from 15.671 to 15.756, ²⁰⁸Pb/²⁰⁴Pb ratios from 38.955 to 39.33 for the Shesuo copper deposit, while ²⁰⁶Pb/²⁰⁴Pb ratios from 18.651 to 18.757, ²⁰⁷Pb/²⁰⁴Pb ratios from 15.707 to 15.823, ²⁰⁸Pb/²⁰⁴Pb ratios from 39.183 to 39.561 for the Lawu copper deposit. The above-mentioned lead isotopic values for the sulfide ores indicate the upper crustal origin of the ore-forming matter in the Shesuo and Lawu copper deposits. More precisely, the ore-forming matter in the Shesuo copper deposit may come mainly from the remelted crust during the Yanshanian, while those in the Lawu copper deposit may be locally originated from the mantle matter during the Late Carboniferous. In the Shesuo-Duoba metallogenic belt in Gangdise, the skarn-type deposits could be found in the contact zones between the Lower Cretaceous carbonate-clastic rocks and moderately acidic rocks, whereas in the Nyainqentanglha area, SEDEX type deposits may be hosted in the Upper Carboniferous Laigu Formation.