Abstract The Tibetan Plateau is one of the most significant Cu poly-metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry Cu mineralization. This study investigates a new occurrence of Cu mineralization-related andesitic porphyries in the western domain of the Gangdese magmatic belt and assesses its petrologic, zircon U-Pb geochronology, whole-rock chemistry, and Sr-Nd-Hf-Pb isotope data. Zircon U-Pb dating of three ore-related porphyries yields crystallization ages of 212–211 Ma. These ages are consistent with previous molybdenite Re-Os dating, indicating a late Triassic magmatic and Cu mineralization event in the western Gangdese magmatic belt. Nb, Ta, and Ti depletion, Th and LREE enrichment, and high La/Yb and Th/Yb ratios in addition to high U/Yb ratios from zircons suggest that the magma was generated in an active continental arc setting. The porphyries have radiogenic isotopic compositions with (87Sr/86Sr)i 0.70431–0.70473, eNd(t) +1.1 to +3.8, (207Pb/204Pb)i 15.601–15.622, and (208Pb/204Pb)i 38.450–38.693, as well as high positive zircon eHf(t) values from +6.2 to +10.6 (mean value 8.3), corresponding to model ages (TDM) ranging from 509 Ma to 819 Ma (mean 646 Ma). This suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment-derived melts during the subduction of the Neo-Tethys Ocean. The mineralization-related porphyries contain amphibole and epidote, as well as high whole-rock Fe2O3/FeO and zircon Ce4+/Ce3+ ratios, suggesting hydrous and highly oxidized parent magmas. Considering the existing Cu mineralization and highly oxidized magma of the well-preserved Triassic andesitic igneous rocks in the western Gangdese belt, the subduction-related continental arc magma system is favorable for subduction-related porphyry Cu deposits. The existence of Luerma porphyry mineralization demonstrates that there are at least five generations of porphyry Cu-(Mo-Au) mineralization in the Gangdese magmatic belt, which advances the timeframe of porphyry mineralization to the late Triassic.

中文翻译：

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冈底斯西部鲁尔玛斑岩铜矿床晚三叠世安山岩的年龄和岩石成因及区域成矿意义

摘要 青藏高原是世界上最重要的铜多金属成矿区之一，保存着与俯冲和碰撞斑岩铜成矿相关的重要信息。本研究调查了冈底斯岩浆带西部地区新发现的与铜矿化相关的安山斑岩，并评估了其岩石学、锆石 U-Pb 年代学、全岩化学和 Sr-Nd-Hf-Pb 同位素数据。三个与矿石有关的斑岩的锆石 U-Pb 定年产生的结晶年龄为 212-211 Ma。这些年龄与之前的辉钼矿 Re-Os 测年一致，表明在冈底斯岩浆带西部发生了晚三叠世岩浆和铜矿化事件。Nb、Ta 和 Ti 耗尽，Th 和 LREE 富集，除了锆石的高 U/Yb 比率外，高 La/Yb 和 Th/Yb 比率表明岩浆是在活动的大陆弧环境中产生的。斑岩的放射性同位素组成为 (87Sr/86Sr)i 0.70431–0.70473，eNd(t) +1.1 至 +3.8，(207Pb/204Pb)i 15.601–15.622 和 (208Pb.4i,838Pb.4i,838 Pb well)作为从+6.2到+10.6（平均值8.3）的高正锆石eHf（t）值，对应于从509 Ma到819 Ma（平均646 Ma）的模型年龄（TDM）。这表明安山岩的岩浆作用主要来自于新特提斯洋俯冲期间被俯冲的海洋沉积物衍生的熔体改性的枯竭地幔物质。与矿化有关的斑岩含有角闪石和绿帘石，以及较高的全岩 Fe2O3/FeO 和锆石 Ce4+/Ce3+ 比值，表明含水和高度氧化的母岩浆。考虑到冈底斯带西部保存完好的三叠系安山火成岩中存在铜矿化和高度氧化的岩浆，俯冲相关大陆弧岩浆系统有利于俯冲相关斑岩铜矿床。鲁尔玛斑岩矿化的存在表明冈底斯岩浆带至少存在五代斑岩铜(Mo-Au)矿化作用，将斑岩矿化的时间框架提前至晚三叠世。