缅甸南部Hermyingyi钨锡矿床成因研究：来自黑钨矿40Ar/39Ar年代学和流体包裹体的证据

The SE Asian W-Sn belt, in the vicinity of South China, is a world-renowned metallogenic belt where widespread W-Sn mineralization are closely associated with the Late Cretaceous granitic magmatism that are distinctly differing from those took place in the Late Jurassic throughout South China. Despite much attention having been payed to South China, of equal importance with respect to W-Sn deposits in SE Asia are considerations of a bewildering range of mineralization age, sources of metals and properties of mineralizing fluids, which are not only crucial for elucidating genesis and time-space distribution of W-Sn deposits in SE Asia, but also beneficial to our exploration for Late Cretaceous W-Sn deposits in South China which are still scarce to date. Hermyingyi W-Sn deposit in Myanmar is typical of quart-vein type W-Sn deposits associated with the Late Cretaceous granitoid. Some geological knowledge have accumulated by previous research on geochronology and petrogeneis of ore-bearing granites, systematic studies regarding mineralization age, sources of mineralizing fluids as well as ore genesis remain to undertake. In this study, we wish to provide a precise geochronological constraint by direct dating fluid inclusions in wolframite using the 40Ar/39Ar technique by crushing in vacuo, combined with molybdenite Re/Os and muscovite 40Ar/39Ar ages. Infrared microthermometric studies of fluid inclusions in coexisting quartz and wolframite integrating with analysis of hydrogen and oxygen isotopes in fluid inclusions of quartz and lead isotopes of sulfides and feldspars in granites are also taken to obtain information on the sources of metals and mineralizing fluids and to gain further insight into the evolution of fluids and ore genesis.

与华南毗邻的东南亚钨锡成矿带是一条世界级的成矿带，成矿主要与晚白垩世的岩浆作用有关，但相关研究较薄弱。对其开展详细研究不但有助于深入了解该成矿带的成岩成矿特征，也将为华南晚白垩世的成岩成矿作用研究及钨锡找矿突破提供借鉴。为此，本项目选取东南亚最具代表性的缅甸Hermyingyi石英脉型钨锡矿床为研究对象，在申请人前期对该矿床晚白垩世含矿花岗岩的研究基础上，进一步开展成矿年龄测定，并深入探究成矿流体来源及成矿机制。本项目拟采用真空击碎法对Hermyingyi矿床中矿石矿物黑钨矿的流体包裹体开展40Ar/39Ar定年，结合辉钼矿Re/Os和白云母40Ar/39Ar年龄，精确厘定矿床的成矿年龄；通过开展黑钨矿的流体包裹体红外显微测温分析并与共生的石英流体包裹体研究结果对比，提供客观可靠的成矿流体信息，结合石英的H-O同位素和花岗岩及硫化物的Pb同位素来示踪成矿流体及成矿物质来源，探讨成矿机制。

与华南毗邻的东南亚钨锡成矿带内的成矿作用主要与晚白垩世岩浆活动有关，但相关研究较薄弱。对其开展详细研究不但有助于深入了解该成矿带的成岩成矿特征，也将为华南晚白垩世成岩成矿作用的研究及钨锡找矿突破提供借鉴。本项目以缅甸Hermyingyi石英脉型钨锡矿为主要研究对象，同时以我国华南石人嶂钨矿作为对比研究对象，开展了系统的成岩成矿年代学、岩石地球化学和矿床地球化学的研究，取得如下重要认识：（1）赫米英吉和当皮拉花岗岩的锆石U-Pb年龄分别为70Ma和69Ma，为晚白垩世岩浆活动的产物。综合二者的岩相学、岩石地球化学和同位素地球化学特征，我们认为赫米英吉和当皮拉花岗岩属于 A2型花岗岩，是古元古代以英云闪长岩-花岗闪长岩为主的陆壳部分熔融，以及斜长石、钾长石和黑云母等矿物的分离结晶共同作用的产物。晚白垩世（~70Ma）时，平板俯冲的新特提斯洋板片后撤引起的弧后拉张环境可能有利于赫米英吉和当皮拉 A 型花岗岩的形成；（2）通过辉钼矿 Re-Os 法测定了Hermyingyi 矿床的成矿年龄为 68.4±2.5 Ma，与二长花岗岩的成岩年龄在误差范围内一致；结合较低的辉钼矿 Re 含量(22.9~298.6ppb)和具有岩浆硫特征的 S 同位素组成(+0.2‰~+5.8‰)，我们推测 Hermyingyi 花岗岩与钨锡矿体之间具有密切的时空和成因联系；（3）石人嶂隐伏花岗岩由边缘相的斑状黑云母花岗岩和中心相的中细粒二长花岗岩组成，二者的锆石 U-Pb年龄分别为164±2Ma 和 162±4Ma。LA-ICP-MS锡石U-Pb 年龄为 164±2Ma 和 160±2Ma。 一致的成岩成矿年龄表明，石人嶂矿区的成岩成矿作用发生在晚侏罗世(~160Ma)。地球化学和同位素结果表明， 石人嶂隐伏花岗岩为高分异的 I 型花岗岩，由古元古代地壳基底部分熔融形成，并经历了矿物的分离结晶作用。该岩体形成于大陆弧环境，可能与古太平洋板块的北西向俯冲有关。 结合隐伏岩体与矿脉密切的时空关系，以及硫化物和花岗岩的Pb同位素特征，我们推测石人嶂隐伏岩体与钨成矿作用具有成因联系. 分离结晶作用和熔体-流体相互作用可能导致了石人嶂隐伏花岗岩和钨矿的形成。