西藏驱龙巨型斑岩铜钼矿岩浆-热液过渡过程中流体出溶机制研究

The mechanism of the fluid exsolution from the ore-forming magma is the essential factor that controlling the formation of the porphyry-type deposits. However, the properties of melts-exsolved fluid-volatile, their evolving paths through the magmatic-hydrothermal transition, and their key factors controlling the formation of the giant porphyry deposits have not yet been well understood and revealed. A series of geological textures recording the processes of the fluid exsolution have been developed in the giant Qulong porphyry Cu-Mo deposit, Tibet, including aplite-pegmatite clots, vein dykes, aplite, unidirectional solidification textures (USTs) and the early barren quartz veins. They are the ideal cases for investigating the key scientific question of “the processes of the magmatic-hydrothermal transition in the giant porphyry Cu deposit”. Therefore, in this proposal, we are going to focus on the fluid exsolution textures as research targets. Based on the multiple generations of quartz and coexisted mineral phases revealed by scanning electron microscope-cathodoluminescence (SEM-CL) and back-scattered electron (BSE), we will carry out in-situ trace elements and oxygen isotope (for quartz) analysis via LA-ICPMS and SIMS, and analyze the composition of the individual fluid and melt inclusions by LA-ICPMS and EPMA, respectively, to study the genesis and forming mechanism of the fluid exsolution textures at the stage of the Qulong magmatic-hydrothermal transition, to constrain the properties of melts, exsolved fluid and volatile and their evolution through the magmatic-hydrothermal transition, and to decipher the linking magmatic and hydrothermal factors between the process of the fluid exsolution and the formation of the Qulong porphyry Cu deposit. This study would lead to a better understanding on the fluid exsolving processes from the deep magma chamber in the giant porphyry Cu deposits, and shed new lights on how the processes of the magmatic-hydrothermal transition contributes to the unique mineralization processes in the giant porphyry Cu deposits.

流体出溶过程是斑岩型矿床形成的关键控制因素，然而对该过程中熔体-出溶流体-挥发分性质、演化过程和如何控制超大型斑岩矿床的形成尚不清楚。西藏冈底斯驱龙千万吨级斑岩铜钼矿中发育一系列流体出溶结构，如细晶-伟晶状团块、脉状岩脉、细晶岩、单向固结结构和早期石英脉，是研究“巨型斑岩铜矿岩浆-热液过渡过程”这一关键科学问题的理想场所。本申请拟以上述各类流体出溶结构为研究对象，在图像分析（CL和BSE）揭示石英生长世代基础上，结合石英及其共生矿物的原位主微量元素（LA-ICPMS）和氧同位素（SIMS）分析及单个流体和熔体包裹体成分的系统测试，研究驱龙岩浆-热液过渡阶段流体出溶结构的形成机制，限定熔体-出溶流体-挥发分的性质及演化过程，厘定控制驱龙巨型铜矿流体出溶过程和成矿效率的岩浆-热液因素。以上研究将有助于理解巨型斑岩铜矿深部流体出溶过程，并为岩浆-热液过渡过程如何控制巨型斑岩矿床形成提供科学依据。

研究围绕着“超大型斑岩矿床流体出溶过程的控制因素”关键科学问题，开展如下研究工作并取得如下成果：1）系统刻画西藏驱龙斑岩铜钼矿床流体出溶结构地质特征及成因，揭示出各类流体出溶结构在驱龙斑岩铜钼矿的2km内深度分布体系，揭露驱龙斑岩成矿体系中细晶岩所形成的岩浆-热液过渡阶段时间一致，均为同一岩浆房演化，而单向固结结构钛扩散模型揭示出其形成时限在30.9-52.1 k.y.之间，表明驱龙巨型斑岩铜钼成矿体系可以在短时期万年尺度内出溶大量流体，新近揭示的钾长石巨斑成因是岩浆房出溶流体与缓慢结晶的钾长石相互作用的结果；2）利用驱龙铜钼矿黑云母成分示踪早期流体性质-组成演化与热液中心，表明热液黑云母的组成的系统变化（向着矿床中心，热液黑云母的Fe, Ti, Co, Zn, Cl含量增加；而Mg, Ge, F含量减少）可以作为一个热液矿化中心的指示。；3）综合利用矿物元素-同位素研究大型-超大型斑岩成矿系统的流体出溶过程，包括含水矿物组成示踪挥发份在斑岩系统流体出溶过程中的行为，冈底斯驱龙等大型-超大型斑岩矿床中金红石结构-组成示踪成矿流体出溶-演化特征，石英元素组成制约斑状花岗岩岩浆-热液过渡阶段流体出溶过程和稀有金属成矿机制，和萤石元素-同位素组成制约斑岩成矿系统流体来源和出溶过程。