冈底斯带西段普觉铜多金属矿床形成时代、岩浆起源及区域勘查启示  

Mineralization age and magmatic origin of the Pujue Cu-polymetallic deposit in the western Gangdese belt:Implication for regional exploration

作　　者：赵苗 侯增谦[3] 杨竹森[1] 夏文杰[4] 官玮琦 赵晓燕 张霖原[1,2] 刘畅 ZHAO Miao;HOU ZengQian;YANG ZhuSen;XIA WenJie;GUAN WeiQi;ZHAO XiaoYan;ZHANG LinYuan;LIU Chang(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;SinoProbe Laboratory,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质科学院矿产资源研究所,自然资源部成矿作用与资源评价重点实验室,北京100037 [2]北京大学地球与空间科学学院,北京100871 [3]自然资源部深地科学与探测技术实验室,中国地质科学院地质研究所,北京100037 [4]地质过程与成矿预测全国重点实验室,中国地质大学(北京),北京100083

出　　处：《岩石学报》2025年第2期600-620,共21页Acta Petrologica Sinica

基　　金：第二次青藏科考项目(2021QZKK0302);国家自然科学青年基金项目(41903047);中国地质调查局地质调查项目(DD20230040、DD20221696)联合资助.

摘　　要：冈底斯构造岩浆带东段发育多个碰撞型的大型-超大型斑岩铜矿床,87°E以西却鲜少发育,控制其成矿差异的关键因素尚存在争议。为此,本文选取冈底斯西段新发现的普觉铜钼多金属矿床,开展了成岩成矿年代学和岩浆岩地球化学研究。结果显示普觉矿床花岗斑岩(锆石U-Pb年龄:23.6Ma±0.4Ma)与铜钼矿化年龄(辉钼矿Re-Os年龄:24.4±0.3Ma)接近,为成矿岩体,石英二长斑岩(锆石U-Pb年龄:16.4±0.3Ma)为成矿后岩体。岩浆岩地球化学结果表明花岗斑岩和石英二长斑岩属I-S型花岗岩;偏高的Sr/Y(27.57~49.62)和(La/Yb)_(N)(20.18~40.37)显示埃达克岩亲缘性,且具有富集轻稀土元素和大离子亲石元素,相对亏损重稀土元素和高场强元素Nb、Ta、P、Ti等特征。富集的(^(87)Sr/^(86)Sr)_(i)(0.708014~0.708192)、ε_(Nd)(t)(-7.7~-7.5)和ε_(Hf)(t)(-2.8~2.9)同位素组成,及锆石微量元素分析结果表明:成矿岩浆起源于新特提斯洋俯冲改造的角闪岩相下地壳发生部分熔融,但有大量古老地壳物质加入,岩浆经过高度分异演化,形成高氧逸度(△FMQ:-0.8~3.2)、低温(564~677℃)的富水特征;随后地壳持续增厚并诱发下地壳发生榴辉岩相变质及部分熔融,形成成矿后石英二长斑岩岩浆。普觉铜钼多金属矿床的发现,暗示冈底斯西段虽然岩浆源区有大量古老地壳物质加入,如果岩浆富水且具有较高氧逸度也可以形成一定规模的铜多金属矿床。The eastern segment of the Gangdese tectono-magmatic belt hosts many giant and large porphyry copper deposits,while the western segment(west of 87°E)of the belt is typically lacking of such type of deposits.However,the key factors controlling mineralization differences between the eastern and western segments are still poorly understood.To address this issue,this paper investigates geology,geochronology and geochemistry of the newly-discovered Cu-Mo polymetallic deposit at Pujue in western Gangdese.Zircon U-Pb LA-ICP-MS dating in this study shows that sample of the mineralization-associated granite porphyry has an age of 23.6±0.4Ma,and one sample of the post-mineralization quartz monzodiorite has an age of 16.4±0.3Ma.Molybdenite Re-Os dating yields an isochron age of 24.4±0.3Ma,which is identical to crystallization age of the granite porphyry and can represent age of Cu-Mo mineralization.Both the granite porphyry and quartz monzodiorite exhibits geochemical features of I-S type granites;in addition,the elevated Sr/Y(27.57~49.62)and(La/Yb)_(N)(20.18~40.37)ratios of the two suite of rocks also indicate their adakitic affinity.In combination with their geochemical features such as enrichment in LILE and depletion in HFSEs and relatively enriched(^(87)Sr/^(86)Sr)_(i)(0.708014~0.708192),ε_(Nd)(t)(-7.7~-7.5)andε_(Hf)(t)(-2.8~2.9)isotopic compositions,we propose that the granite porphyry were derived from partial melting of amphibolite facies lower crust modified by Noe-Tethys Ocean subduction,with different degree of involvement of ancient crustal material.Water-rich and oxidized nature of the granite porphyry magma reflected by high zircon△FMQ(-0.8~3.2)and low Ti-in-zircon temperature(564~677℃)was resulted from high fractionation.In contrast,the post-mineralization quartz monzodiorite was sourced from thickened eclogite-facies lower crust.In summary,the presence of the Pujue Cu-Mo polymetallic deposit in the western Gangdese implies that the western Gangdese has potential to produce water-rich and high f O 2

关 键 词：普觉 斑岩矿床 埃达克岩 岩石成因 冈底斯西段 西藏 

分 类 号：P588.13[天文地球—岩石学] P597.3[天文地球—地质学] P618.41