壳幔相互作用对W-Mo矿床形成的制约：以江南古陆阳储岭斑岩型W-Mo矿床为例

It is generally accepted that the W and Mo-bearing granitic magmas are mainly derived from partial melting of crustal materials, however, the possibility that Mo-bearing granitic magmas could be derived from the melting of mantle or juvenile lower crust cannot be excluded. The mantle-crust interaction is commonly involved in the formation of the W-Mo mineralization, during which the mantle-derived mafic magmas likely provide the heat that triggers the partial melting of crustal materials. Nevertheless, it is still lack of strong evidence to support the hypothesis that the mantle-derived mafic magmas also provide metallogenic materials for the W-Mo mineralization related granitic magma. The intense interaction of mafic and felsic magmas is recorded in the ore-related granitic rocks of the Yangchuling W-Mo deposit. Both macroscopic and microscopic evidence shows that the W and Mo mineralization closely related to felsic and dioritic magmas, respectively. Therefore, the Yangchuling deposit is a window to explore the possible contribution of mantle-crust interaction processes to the genesis of W-Mo deposits. This project plans to focus on the detail in-situ microanalysis of minerals in the mineralization-related granitic rocks of the Yangchuling deposit. Zircon Hf-O isotopes will be used to define the magma source of the W and Mo mineralization related granitic magma. The elemental compositions of the growth zoning of plagioclase, hornblende and titanite will be studied for the purpose of reconstruction of magma processes. The W, Mo concentration of apatite, and the growth zoning of hornblende and titanite will also be studied to reveal the dynamic variation of W, Mo concentration in the magma system during the magma processes. This study will shed light on the controls of mantle-crust interaction performed on the W-Mo mineralization.

成钨、成钼岩浆均可以来自地壳物质的重熔，但也不排除成钼岩浆来自地幔或新生下地壳。W-Mo矿床的形成常伴随壳幔相互作用，幔源岩浆除了为W-Mo矿床成矿岩浆的形成提供热源外，是否还提供了成矿物质？目前仍然缺乏有力证据。阳储岭斑岩型W-Mo矿床的矿区内基性、酸性岩浆相互作用的痕迹十分明显，并且宏观和微观证据均显示W、Mo矿化分别与酸性和偏基性岩石密切相关。因此，阳储岭矿床是研究解析壳幔相互作用对W-Mo矿床成矿作用制约的一个窗口。本项目拟对阳储岭矿床成矿相关岩体内的单矿物开展精细的矿物学原位微区研究，根据锆石Hf-O同位素厘定分别与W、Mo矿化作用密切相关的岩体岩浆源区性质；从斜长石、角闪石、榍石的环带成分变化探索其生长过程中所经历的岩浆过程，并结合角闪石、榍石环带及磷灰石的W、Mo元素含量揭示岩浆体系内W、Mo元素浓度在岩浆过程中的动态变化；论证壳幔相互作用对W-Mo矿床成矿作用的制约。

江南古陆钨矿带的WO3资源量超过了600 万吨，是近年来新发现的一个世界级钨矿带。该钨矿带上钨多金属矿床可划分为与壳源S型花岗岩相关的还原型钨矿床(以朱溪W矿床为代表)，以及与壳幔混源的I型花岗岩相关的氧化型钨矿床(以阳储岭W-Mo矿床为代表)。成钨、成钼岩浆均可以来自地壳物质的重熔，但也不排除成钼岩浆来自地幔或新生下地壳。鉴于江南古陆钨矿带上的W-Mo矿床的成矿相关岩体无一例外地伴随着强烈的壳幔相互作用，幔源岩浆除了为W-Mo矿床成矿岩浆的形成提供热源外，是否还提供了成矿物质？该问题尚未得到前人研究的关注。本项目为厘定以阳储岭矿床为代表的W-Mo矿床的成矿岩浆形成机制，查明幔源岩浆是否为W-Mo矿床的成矿过程中提供了成矿物质，对阳储岭成矿相关岩体开展了精细的镜下观察及一系列矿物学微区研究：1) 对花岗闪长斑岩、二长花岗斑岩及其所含的暗色包体中的锆石进行了SIMS原位U-Pb同位素分析，发现这些成矿相关岩石为同期岩浆作用的产物，形成于150 Ma左右。2) 对偏基性岩脉、花岗闪长斑岩、及二长花岗斑岩的斜长石斑晶进行微区原位电子探针主量元素定量分析和定性扫面、LA-ICP-MS微量元素分析、LA-MC-ICP-MS Sr同位素分析，结合成矿相关岩体全岩Sr-Nd同位素和锆石Hf-O同位素组成特征，厘定了阳储岭成矿相关岩浆形成过程中，发生了多次的基性岩浆注入事件。3) 电子探针和LA-ICP-MS Mo元素含量测试显示暗色包体内的白钨矿相对于其寄主岩石二长花岗斑岩内的白钨矿具有显著较高的Mo含量，鉴于二长花岗斑岩及暗色包体内的锆石记录了相似的氧逸度，说明氧逸度不是影响两类白钨矿Mo含量的根本因素，而是由于形成暗色包体的偏基性岩浆相对于形成二长花岗斑岩的偏酸性岩浆具有显著较高的Mo含量；结合矿区内偏基性岩脉、暗色包体以及煌斑岩脉中广泛出现辉钼矿的客观地质事实，厘定了幔源岩浆为阳储岭矿床Mo成矿作用提供了主要金属来源。这些研究成果有助于正确认识斑岩-矽卡岩型W-Mo矿床的成因机制，拓宽了过去认为Mo成矿作用通常仅与壳源岩浆作用相关的认识。