青海省东昆仑大水沟金矿英云闪长岩锆石U-Pb测年、岩石地球化学及其找矿意义

大水沟金矿位于东昆仑中段,目前矿区西部共圈定金矿(化)体9条,结合化探异常和区域地质背景对比,认为该区具有良好的找矿前景。本文利用LA-MC-ICPMS锆石U-Pb定年技术,首次获得与金矿成矿有密切关系的英云闪长岩加权平均年龄为(239.5±0.9)Ma,厘定为中三叠世;岩石地球化学研究表明,英云闪长岩为钙碱性系列岩石,轻稀土富集,轻重稀土分馏明显,具弱的负铕异常,岩体明显富集大离子亲石元素(Rb、K)、活泼不相容元素Th、轻稀土元素和Pb,相对亏损高场强元素(Nb、Ta、P、Ti),Rb/Sr、Nb/Ta等特征反映出岩石具有壳幔混合岩浆的特点。结合东昆仑地区已有的年代学资料、岩石地球化学和区域地质构造演化分析,本文认为英云闪长岩形成构造环境为俯冲阶段;俯冲作用促进了幔源流体的运移,在构造有利部位沉淀形成金矿。

Zircon U-Pb dating and geochemical characteristics of the tonalite in the Dashuigou gold deposit of Eastern Kunlun Mountains, Qinghai Province

Abstract: The Dashuigou gold deposit is located in the middle segment of Eastern Kunlun, and nine orebodies were delineated in the west of the Dashuigou gold deposit. In combination with geochemical anomalies and regional geological background, the authors hold that the Dashuigou gold deposit has good ore-search prospect. Gold ore prospecting has achieved new breakthrough. LA-MC-ICPMS zircon U-Pb dating shows that the weighted mean age of tonalite, which is closely related to mineralization in the Dashuigou gold deposit, is (239.5±0.9)Ma, with MSWD being 1.3, suggesting Middle Triassic. Geochemical studies indicate that tonalite belongs to the calc-alkaline series, with obvious fractionation of REE, enrichment of LREE and slightly negative Eu anomalies. This suite of rocks are enriched in LILE (such as Rb, K), LREE and more mobile incompatible elements (such as Th), and relatively depleted in HFSE (such as Nb, Ta, Ti, P). Rb/Sr and Nb/Ta ratios reflect the characteristics of mantle-derived magma. Based on a combined study of geochronology, geochemistry and evolutionary characteristics of regional structures, the authors hold that tonalite was formed at the subduction stage. Subduction promoted the migration of mantle-derived fluids, which precipitated in favorable?parts?of?structure, forming the gold orebody.