中国驱龙和伊朗诺春斑岩铜矿梳状石英层成因研究

Comb quartz layers, also named as unidirectional solidification textures (UST), refer to a special igneous texture that are present in layers and multilayered sequences consisting of euhedral, prismatic quartz crystals and aplite substrates. Such textures generally occur at the top and/or margin of shallow granite porphyries, and are often associated spatially with porphyry-type Mo, W and Cu deposits. Comb quartz layers are usually thought to form during the magmatic-hydrothermal transition, but their genesis still remains the subject of much debate. Two hypotheses have been proposed to account for formation of such textures. One concept proposes that these textures have grown from pockets of exsolved magmatic fluid located between the magma and its crystallized border, but the other proposes that they have precipitated directly from a crystallizing silicate melt. To test these hypotheses, as well as to investigate nature and source of primitive ore-forming fluids in porphyry Cu systems, comb-layered quartz from Qulong and Now Chun porphyry Cu deposits have been selected for the following studies using recently-emerged in situ analysis techniques (e.g., LA-ICPMS, SHRIMP, and Cameca IMS 1280). Features to be studied include: (1) their distribution, occurrence and petrographic characteristics; (2) their spatial and genetic relationships with Cu mineralization; (3) characteristics of melt/fluid inclusions (e.g., composition, formation temperature, Cu content) in comb-layered quartz; and (4) their elemental and oxygen isotopic geochemistry. The aims of this study are to: (1) document nature and variation of initial ore-forming fluids in the two deposits; (2) clarify genesis of comb quartz layers; and (3) identify source of ore-forming fluids for porphyry Cu system.

梳状石英层，又称单向固结结构，指的是由自形、棱柱状石英与细粒-等粒花岗岩互层生长而形成的一种特殊结构岩石；常产于含矿斑岩体顶部及边缘，与斑岩矿床关系密切。已有的研究显示，梳状石英层形成于岩浆-热液过渡阶段，记录着斑岩矿床早期成矿流体生成、聚集及排泄等过程，但其成因却有争议，存在岩浆和热液两种起源假说。为查明梳状石英层的成因，同时也为了调查斑岩铜矿早期成矿流体性质及来源，项目选择西藏驱龙及伊朗诺春斑岩铜矿床中的梳状石英层开展立典式研究，拟在详细的岩相学、特别是阴极发光岩相学基础之上，采用激光消融等离子质谱、离子探针等原位分析技术，全面开展梳状石英层熔体/流体包裹体、微量元素及氧同位素地球化学等特征的调查，以期查明梳状石英层的成因机制，约束斑岩铜矿早期成矿流体性质及来源，完善斑岩铜矿成矿理论。

梳状石英层，又称单向固结结构，指的是由自形、棱柱状石英与细粒–等粒花岗岩互层生长而形成的一种特殊结构岩石；常产于含矿斑岩体顶部及边缘，与斑岩矿床关系密切。已有的研究显示，梳状石英层形成于岩浆-热液过渡阶段，记录着斑岩矿床早期成矿流体生成、聚集及排泄等过程，但其成因却有争议，存在岩浆和热液两种起源假说。为查明梳状石英层的成因，项目选择西藏驱龙和伊朗诺春斑岩铜矿床、内蒙古毕力赫金矿床中的梳状石英层开展立典式研究。调查结果显示：（1）驱龙矿床梳状石英层中发育大量原生流体包裹体，原生石英具有较高的形成温度（760-800℃），且δ18O值变化于+6.2 ~ +7.6‰之间，提出驱龙矿床梳状石英层为初始岩浆热液成因；诺春矿床梳状石英层显示与驱龙矿床类似的特征，也为岩浆热液成因；（2）毕力赫矿床梳状石英层发育大量熔融包裹体、缺乏原生的流体包裹体，石英结晶温度950oC以上，梳状石英层为岩浆成因；进而确定梳状石英层既可为热液成因，也可为岩浆成因，其存在并非一定指示流体饱和。研究过程中还揭示：（1）毕力赫矿床为岩浆型金矿床，这是一种新的金矿类型，中等还原条件下岩浆分异结晶导致Au的不断富集是矿床形成的关键；（2）以驱龙为代表的碰撞型斑岩铜矿，其成矿斑岩岩浆中的水主要来自大陆板片俯冲脱水和镁质碱性岩浆的混合注入；（3）岩浆过程中金属和S的预富集可能是超大型斑岩铜矿床形成的关键因素。. 项目在SEG Special Publication、Economic Geology、Journal of Petrology、CMP等国际主流期刊发表论文10篇，项目成果受到国内外关注和认可，产生了重要影响。