西藏冈底斯中段错杰地区花岗斑岩年代学、地球化学特征及其找矿意义

在西藏冈底斯中段错杰地区发现一套含孔雀石的花岗斑岩,为确定其形成时代、成因及其找矿意义,对该套花岗斑岩进行了岩相学、LA- ICP-MS锆石U-Pb年代学及地球化学特征研究。结果表明: 该套花岗斑岩中的锆石为岩浆成因,锆石²⁰⁶Pb/²³⁸U加权平均年龄为(13.9±0.2)Ma,侵入时代为中新世。主量元素地球化学测试结果显示花岗斑岩具有富SiO₂、富Al₂O₃、富碱、富钠的钙碱性特征。微量元素地球化学测试结果显示花岗斑岩相对富集U、Th等大离子亲石元素,亏损Nb、Yb等高场强元素,稀土总量为(47.4~141.4)×10^-6,轻稀土相对富集,具正Eu异常。经过综合分析,认为花岗斑岩形成于加厚下地壳的部分熔融,形成过程中可能发生了部分分离结晶作用。通过将花岗斑岩的地质特征与区域典型矿床进行对比,发现错杰地区花岗斑岩具有与冈底斯斑岩铜矿相似的地质特征及成矿系统,深部可能隐伏有较大的含矿斑岩体,具有较好的找矿前景。

Chronology,geochemical characteristics and prospecting significance of the granite porphyry in Cuojie area of Middle Gangdise in Tibet

A set of malachite-bearing granite porphyry was found in Cuojie area of the Middle Gangdise in Tibet. In order to determine the age, genesis and prospecting significance of the granite porphyry, the authors have conducted the petrographic, LA-ICP-MS zircon U-Pb chronology and geochemical characteristics of the granite porphyry. The results show that the zircons in the granite porphyry are of magmatic origin, with a weighted ave-rage age of ²⁰⁶Pb/²³⁸U of (13.9±0.2) Ma, and the intrusive age is Miocene. The geochemical characteristics of major elements show that the granite porphyry is characterized by high SiO₂, high Al₂O₃, rich alkali, and rich sodium calc-alkalic characteristics. The geochemical characteristics of trace elements show that the granitic porphyry is rich in large ion lithophile elements such as U, Th, and depleted in high field strength elements such as Nb and Yb. The total amount of rare earth elements is (47.4~141.4) ×10^-6, and the light rare earth elements are relatively rich with positive Eu anomaly. The granitic porphyry was formed by partial melting of the thickened lower crust, and partial separation crystallization may have occurred during the formation process, through comprehensive analysis. By comparing the geological characteristics of the granite porphyry with the typical deposits in the region, it is found that the granite porphyry in Cuojie area has similar geological characteristics and metallogenic system with the Gangdise porphyry copper deposit. And there may be a large ore-bearing porphyry buried in the deep, which briags a better prospecting prospect.