富铜矽卡岩钨矿的成因机制研究：以江西朱溪矿床为例

It is generally accepted that the incompatible W would not coexist with the compatible Cu in a magmatic-hydrothermal system due to their different geochemical behaviors during magmatic and magmatic-hydrothermal transitional processes. However, magmatic-hydrothermal (e.g., skarn) deposits containing both economic W and Cu are widely developed worldwide, particularly in China. The mechanism of W-Cu coexistence is still poorly understood. In this study, the newly-discovered giant Zhuxi W-Cu deposit has been selected for the following studies using recently-emerged in situ analysis techniques (e.g., LA-ICPMS). Features to be studied include: (1) origin of W-Cu-bearing granite magma and subsequent magmatic processes; (2) contents and variations of W and Cu in melt during magma evolution; and (3) enrichment mechanism of W and Cu during magmatic-hydrothermal transition. The aims of this study are to: (1) determine sources of W-Cu-rich magma; (2) document W-Cu content in melt and/or hydrothermal fluids during magmatic and magmatic-hydrothermal transitional processes; and (3) identify the mechanism of W-Cu coexistence at Zhuxi.

W是不相容元素，Cu是相容元素，两者在岩浆起源、岩浆演化及流体出溶过程中的地球化学行为截然不同。通常认为，两者很难在岩浆-热液系统中共存。然而世界范围内，特别是中国境内W-Cu共存的岩浆-热液矿床（如矽卡岩）却广泛发育，但岩浆-热液成矿系统中W、Cu共存机制尚不清楚。为此，本项目选择当前中国最大、有较好研究基础的钨矿床——朱溪钨铜矿床开展研究；拟在详细的岩相学基础之上，采用激光消融等离子质谱等原位分析技术，通过成矿花岗岩中斑晶（如石英、黑云母）矿物化学、石英斑晶及热液石榴石中熔融/流体包裹体成分的系统调查，精确追踪该矿床岩浆演化及岩浆热液过渡过程中熔体和/或流体中W-Cu含量变化，查明钨矿富铜的原因，进而揭示W-Cu的共存机制。

通常认为钨和铜因在岩浆-热液体系中地球化学行为截然不同而难以共存，但世界范围内广泛发育W-Cu共存的岩浆-热液矿床挑战了这一认知。为理解岩浆热液系统中铜钨共存机制，本项目选择超大型的朱溪钨铜矿床开展研究。三年来，通过系统的矿物学、岩石学、地球化学及流体包裹体研究，取得以下5个方面的主要进展：（1）查明了朱溪矿床的蚀变特征：发现矿床浅部以石榴石、透辉石、硅灰石、钙角闪石等钙矽卡岩矿物发育为特征，而深部却以镁橄榄石、蛇纹石等镁矽卡岩矿物发育为特征，两种蚀变均与黑云母花岗岩和花岗斑岩空间上相邻；（2）明确了成矿岩体为晚侏罗世的黑云母花岗岩及花岗斑岩，为钛铁矿系列花岗岩，具有较低氧逸度，可能起源于新元古代变质沉积岩的部分熔融；（3）确定了朱溪矿床蚀变矿化期次及特征，钙铝榴石-钙铁榴石、透辉石-钙铁辉石形成于成矿前，钨矿化与钙角闪石、绿泥石的退蚀变有关，而铜矿化晚于钨矿化，形成于石英硫化物阶段；（4）厘清了成矿流体演化特征及成矿机制，从岩浆房出溶的成矿流体具有低氧逸度特征，与偏还原的碳酸质围岩发生水岩反应导致白钨矿沉淀，而铜的沉淀则因流体降温及与大气降水混合所致；（5）综合分析提出朱溪矽卡岩矿床中的钨和铜是一期岩浆成矿热液事件不同阶段的产物，虽然低氧逸度岩浆的结晶分异会导致残余岩浆富集钨而贫化铜，但当残余岩浆体量足够大、流体饱和较早情况下，依然可以形成可观的铜矿化。