西藏狮泉河蛇绿混杂岩带首例石英脉型黑钨矿矿床成矿机制研究

The Jiaoxi quartz-vein type wolframite deposit, preserving a medium tungsten deposit size, is the first single wolframite deposit found on the western Bangong-Nujiang metallogenic belt, Tibet. This deposit was formed in the Shiquanhe ophiolite mélange zone, which differs from the homogeneous quartz-vein type wolframite deposits in South China. Compared with the dominant Cu-Au mineralization on the western Bangong-Nujiang metallogenic belt, the tungsten mineralization like the Jiaoxi deposit is also different and uncommon. In order to effectively understand these differences mentioned above, we need to conduct in-depth studies on the petrogenesis and metallogenesis of the Jiaoxi deposit. Based on detail studies of the Jiaoxi mineralization and alteration systems, this application will mainly focused on the ore-forming granite and the ore-forming fluids system and their relationship with the tungsten mineralization. In addition, the mineralization time and sources of ore-forming metal will also be studied in this project. Hence, geochronology, mineral geochemistry, elements and isotopic geochemistry and ore-forming fluids geochemistry analyses are carried out to constrain time of intrusion and mineralization, identify the mineralization tectonic setting, trace sources of the ore-forming metal, clarify the relationship between granite petrogenesis and the wolframite mineralization, and find out factors controlling wolframite migration and depositing during evolution of the ore-forming fluids system. Based on these studies, the main factors causing differences between the Jiaoxi wolframite and the regional copper-gold mineralization can be clarified and metallogenic differences on quartz-vein type wolframite deposits both formed in ophiolite mélange zone and South China can be also revealed. The study results can improve the metallogeny regularity of the Bangong-Nujiang metallogenic belt, promote the mineralization theories of the quartz-wolframite vein type wolframite deposits and also provide scientific basis on regional prospecting prediction of the tungsten deposits in the Bangong-Nujiang metallogenic belt.

角西钨矿系西藏班-怒成矿带西段发现的首例石英脉型黑钨矿矿床，具中型规模。矿床产于狮泉河蛇绿混杂岩带内，与华南同类钨矿所处构造位置不同，且以其独立的钨矿化区别于班-怒带优势的铜金组合。缘何在蛇绿混杂岩带内形成与铜金矿差别较大的钨矿，其与华南同类钨矿成矿机理有无差异，需对其成岩成矿机制进行系统研究。项目基于矿化蚀变体系解剖，以岩浆岩与钨成矿关系、流体演化与钨迁移沉淀过程为研究主线；通过同位素年代学、矿物化学、元素与同位素化学、成矿流体化学等手段，查明矿床成岩成矿时代、成矿物质来源及形成背景；厘定岩浆岩成因机制，研判岩石类型、性质、物源、分异演化等制约钨成矿的因素；追踪流体来源、出溶及演化过程，明确钨迁移沉淀机制。基于此，限定钨与区域铜金成矿差异之主控因素、揭示蛇绿混杂岩带与华南地区石英脉型钨矿成矿机理之差别。这对完善班-怒带成矿规律、开展区域钨矿找矿预测及丰富石英脉型钨矿成矿理论具有重要价值。

角西钨矿系班-怒成矿带西段所发现的首例石英脉型黑钨矿矿床，具中型规模。矿床产于狮泉河蛇绿混杂岩带内，以其独立的钨矿化区别于班-怒带优势的铜金组合。缘何在蛇绿混杂岩带内形成与铜金成矿差别较大的钨矿，需对其成矿机制进行系统研究。项目基于矿化蚀变体系解剖，以岩浆岩与钨成矿关系、流体演化与钨迁移沉淀过程为研究主线，开展了同位素年代学、矿物化学、岩浆岩成因与物化性质、成矿金属与流体来源、流体演化与矿质迁移沉淀机制等方面的研究，查明了钨成矿之内控机制。研究结果表明，矿床热液成矿期可划分为氧化物、硫化物和萤石-碳酸盐三个矿化阶段。成矿花岗岩类集中侵位于中新世（14.5-13.7Ma），黑钨矿沉淀时代为13.4-13.3Ma，而硫化物则形成于11.6Ma；成岩与成矿作用形成于拉萨地块与印度板块碰撞过程中的伸展动力学背景下。成岩物质源区为成熟的地壳物质并混入有约10%的幔源物质，直接成矿白云母花岗岩具典型高分异特征。成矿岩体具高温、中-高fO2和S逸度、低Cl逸度以及中-低H2O含量性质。成矿流体与金属物质主体源自高分异的白云母花岗岩，成矿流体还混有天水；而金属物质来源则还有云英岩化过程中黑云母、长石类矿物分解以及砂板岩地层物质的加入。流体混合造成的成矿热液自然降温、盐度降低以及水岩反应过程中pH值升高系钨沉淀成矿的关键机制。成岩成矿动力学背景与物质源区不同加之成矿岩体fO2、Cl-S逸度、H2O含量等物理化学条件差异系造成班-怒成矿带西段铜金与钨成矿差异之根本因素。与华南同类型矿床成岩成矿物质源自中-上地壳富矿质沉积岩部分熔融的物源相比，角西成岩成矿作用发生过程中则有明显幔源物质的加入（~10%），此为二者最显著区别。