胶东地区石英原位微区结构－成分特征及其对金成矿过程的限定

Jiaodong area is the biggest reservoir of gold in China, with reserves of as much as 5,000 ton. The mineralization process occurred explosively in the Mesozoic era. There are still several debatable interpretations on the classification and origin of the gold deposit in the area. As a common mineral in various rocks and ores, quartz recorded plentiful information geological activities. Further investigation on the quartz is helpful to disclose the critical linkage between the rock-forming and ore-forming processes. Selecting two typical sections in the Jiaodong gold deposit, we will apply cutting-edge microbeam analytical techniques, including CL + SEM, EPMA, LA-ICPMS and SIMS, to study in situ compositional and structural features of the quartz in various alteration zones. With these integrated information, we’ll discuss the characteristics of the ore-forming fluid and distribution pattern of the elements, and try to constrain the relationship between the gold mineralization and local granitic bodies, such as the Linglong granite and the Guojialing granodiorite.

胶东地区是我国最大的金矿产地，黄金总储量达5000吨，具有中生代爆发成矿的特点。目前有关胶东金矿成因、矿床类型的认识还存在较大的争议。石英作为各类岩石和矿石中普遍存在的矿物，记录了丰富的地质活动信息。对石英的详细研究有助于揭示成岩与成矿作用联系的关键环节。本项目拟选择胶东金矿两个典型剖面，采用CL+SEM、EPMA、LA-ICPMS和SIMS等现代微束分析技术，观测不同蚀变带上石英的微区原位结构－成分特征，探讨成矿流体的特征、元素在蚀变带上的分布规律，从而限定玲珑花岗岩和郭家岭花岗闪长岩与金成矿的关系。

将石英作为一种“矿物探针”，根据石英的阴极荧光结构、光谱波长和强度的变化，对胶东金矿中生代成岩成矿体系中的石英，进行了成因类型的准确甄别，厘定了岩浆石英、热液石英的生长期次和生长特征。结合石英及共生矿物的原位微量元素－氧同位素成分、石英流体包裹体研究，提出成矿流体多期活动、成矿过程中存在一个急剧降压过程的新认识；成矿流体来源于幔源岩浆的脱气、脱水作用，并在地壳浅部与大气降水发生了混合。幔源岩浆的流体不混溶作用、主成矿期的碳酸盐流体活动，是胶东金矿重要的成矿机制。本项目的工作不但为胶东金矿成因研究提供了新的视角，而且这种新的研究思路和技术路线也可为其他矿床的研究提供借鉴。