缅甸茂奇钨锡矿床电气石花岗岩地球化学、锆石年代学、Hf同位素组成及地质意义

Geochemistry, zircon U-Pb geochronology, Hf isotopes of tourmaline granite in Mawchi tungsten-tin deposit, Myanmar and their geological implications

中文关键词:锆石U-Pb定年  Hf同位素  元素地球化学  茂奇钨锡矿床  缅甸

keywords:zircon U-Pb dating  Hf isotope  element geochemistry  Mawchi tungsten-tin deposit  Myanmar

中文摘要:缅甸东部克耶邦茂奇钨锡矿床位于东南亚锡钨成矿带西缘，地处印支板块与滇缅泰马地块交汇部位，是该区重要的钨锡多金属矿床之一。矿体主要赋存于始新世花岗岩与石炭系—下二叠统茂奇群变质沉积岩的北西-南东向断裂系统中，成矿作用与中始新世花岗岩密切相关。文章对与成矿相关的电气石花岗岩进行了LAICP-MS锆石U-Pb定年及Hf同位素分析，结果表明，花岗岩锆石U-Pb加权平均年龄为（43.20±0.49）Ma（MSWD=2.3），属中始新世。锆石ε_Hf（t）值为-6.0～-3.5，二阶段模式年龄(T_DM2)为1.56～1.72 Ga，指示其源区为中元古代地壳物质部分熔融。岩石地球化学特征显示其为强分异的过铝质花岗岩，具高Ga/Al比值和显著的稀土元素四分组效应，并表现为Rb、U、Th、Pb富集，Ba、Sr、Nb、P、Ti亏损。结合区域构造演化，文章认为茂奇钨锡矿床形成于新特提斯洋俯冲消减后的陆内伸展阶段，是中元古代地壳部分熔融、岩浆高分异演化以及W-Sn元素富集成矿的响应。

Abstract:The Mawchi tin-tungsten deposit in Kayah State, eastern Myanmar, is situated at the western margin of the Southeast Asia Sn-W metallogenic belt, where is the junction of the Indochina plate and the Sibumasu block, representing one of the significant tungsten-tin polymetallic deposits in the region. The ore bodies primarily occur within the NW-SE trending fault systems between Eocene granites and metamorphosed sedimentary rocks of the Carboniferous—Early Permian Mawchi Group, with mineralization closely related to the Middle Eocene granites.This study presents LA-ICP-MS U-Pb dating and Hf isotope analyses of zircons in tourmaline granite which is genetically linked to mineralization at Mawchi. The results yield a zircon U-Pb weighted mean age of（43.20±0.49）Ma（MSWD=2.3）, indicating a Middle Eocene age. Zircon ε_Hf（t） values range from -6.0 to -3.5, with T_DM2 of 1.56～1.72 Ga, suggesting derivation from partial melting of Mesoproterozoic crustal material. Petrogeochemical data indicate a strongly fractionated peraluminous granite, characterized by high Ga/Al ratios and a pronounced rare earth element tetrad effect, with enrichments in Rb, U, Th, Pb and depletions in Ba, Sr, Nb, P, Ti. In conjunction with regional tectonic evolution, it is interpreted that the Mawchi tungsten-tin deposit formed during the intracontinental extensional stage following the subduction of the Neo Tets Ocean, representing a response to partial melting of Mesoproterozoic crust, highly fractionated magmatic evolution, and the enrichment and mineralization of tungsten-tin elements.