东南亚稀土找矿新启示：老挝华潘MQ矿床成矿母岩的时代与成因

New insights on rare earth element exploration in Southeast Asia: Age and genesis of parent rock of MQ deposit in Huaphan, Laos

中文关键词:锆石U-Pb定年  地球化学  S型花岗岩  离子吸附型稀土矿  长山成矿带  老挝

keywords:zircon U-Pb dating  geochemistry  S-type granite  ion-adsorption REE deposit  Truong Son Belt  Laos

中文摘要:离子吸附型稀土矿是全球重稀土的重要来源，其形成与特定花岗岩母岩的风化密切相关。该类矿床主要分布于中国华南，近年东南亚长山成矿带也显示出良好的找矿前景。老挝华潘省MQ稀土矿是长山成矿带新发现的以重稀土为主的离子吸附型矿床，其成矿母岩的形成时代与构造背景缺乏约束。文章以老挝华潘省MQ重稀土矿床花岗岩母岩为研究对象，开展锆石U-Pb年代学与全岩地球化学分析。结果表明，该岩体形成于早三叠世晚期（约247 Ma），为高硅、过铝质、高分异S型花岗岩，具有明显Eu负异常及低Sr、Zr含量，指示其来源于加厚下地壳的部分熔融。综合判定，该岩体形成于古特提斯洋闭合后，由同碰撞向后碰撞伸展阶段转换的构造过渡期。研究结果厘定了约247 Ma为长山成矿带构造体制转折的关键时期，明确了该期高分异S型花岗岩是重稀土成矿的有利母岩，为东南亚古特提斯构造域寻找同类型重稀土矿床提供了重要的地质依据与找矿启示。

Abstract:Ion-adsorption rare earth element（REE） deposits represent the global primary source of heavy rare earth elements（HREEs）, and their distribution is strictly controlled by the weathering of specific granitic parent rocks.While such deposits have predominantly been documented in South China, the Truong Son Belt in Southeast Asia has recently emerged as a new exploration hotspot. The MQ deposit in Huaphan Province, Laos, is a newly discovered ion-adsorption HREE deposit in this belt; However, the genesis and tectonic setting of the parent rocks in this region remain poorly constrained. This study focuses on the granitic parent rock of the MQ HREE deposit,employing zircon U-Pb geochronology and whole-rock geochemical analyses. The results indicate that the granitic intrusion formed in the Late Early Triassic（～247 Ma） and is a highly fractionated S-type granite characterized by high SiO₂ contents, peraluminous composition, and intense fractional crystallization, and distinctive geochemical features（e.g., significant Eu anomalies, low Sr and Zr contents）. These characteristics suggest it derived from the partial melting of thickened continental crust. Although its geochemical signature is highly similar to that of mineralized granites in South China, this study reveals that it formed in a tectonic transition from syn-collisional to post-collisional extension following the closure of the Paleo-Tethys Ocean, rather than in a subduction-related setting like the Pacific tectonic regime responsible for the South China deposits. This discovery not only identifies ～247 Ma as a critical period for tectonic transition and related magmatic-metallogenic events in the Truong Son Belt but also demonstrates that these highly fractionated S-type granites are ideal parent rocks for HREE mineralization, providing new scientific foundations and exploration implications for discovering such critical metal deposits within the Paleo-Tethyan domain in Southeast Asia.