赣南主要钼矿成因及钨-钼共生分离机制研究

In recent years, the exploration and exploitation works of molybdenum minerals have made a series of breakthroughs in non-traditional molybdenum ore area. However, the genesis of these Mo deposits in non-traditional molybdenum ore area haven’t been explained clearly, because of the lagging scientific research works. For example, southern Jiangxi province, as a traditional tungsten ore area, in where independent large molybdenum deposit and molybdenum polymetallic deposit have also been found besides syngenetic or associated Mo deposits. There hadn’t been developed systemic study of it. It is important theoretical and practical significance to find out metallogenic mechanism of Mo deposits in southern Jiangxi province, mineralization geological background and its relationship with the tungsten mineralization through this study of these major Mo deposits. Based on the preliminary work on Yuanlingzhai Mo deposit, taking Leigongzhang and Getingkeng Mo deposit as the main research objects, the research will carry out the precise geological survey, and study the mineral association, geochemistry, chronology and ore-forming fluid. We will study the ore-forming materail sources by the characteristics of trace elements and isotopic compositions, and comparing with associated molybdenum mineralization to discuss the chemical characteristics of ore-forming fluid and precipitation mechanism of ore minerals of independent and associated Mo deposits. Meanwhile, tungsten-molybdenum paragenesis and separation has been discussed through comparative study on ore- and rock-forming of Mo deposits and W deposits in region, and ore-forming of W and Mo in the same orebody.

近年来，非传统钼矿产区钼找矿取得快速突破，科研工作却相对滞后，钼矿成因不清。如赣南地区，作为传统的钨矿产区，除共/伴生钼矿外，亦新发现了独立钼矿和以钼为主的多金属矿，但对赣南钼矿成因还未开展过系统的研究。本申请拟通过对赣南主要钼矿成因的深入研究，查明其成矿机制、地质背景及其与钨成矿的关系，具有重要的理论与实际意义。本次拟在以往对园岭寨独立大型钼矿研究基础上，以赣南雷公嶂、葛廷坑等2个新发现钼矿为主要对象，开展精细野外地质调查和系统的矿物学、地球化学、年代学、成矿流体等研究，特别是通过对具有示踪意义的微量元素和S-Pb-Hf等同位素的联合示踪，及与钨伴生钼矿研究成果的对比研究，揭示独立钼矿和伴生钼矿不同矿化阶段成矿流体的性质、来源及其演化过程；同时，通过区域上钨、钼矿成岩成矿作用和同一矿体内钨、钼成矿作用的对比，揭示钨、钼成矿作用的差异性，探讨钨钼时而分离时而共伴生的机制。

为查明赣南地区主要钼矿成因及其与钨矿的共生分离机制，在总结前人研究成果的基础上，重点对赣南主要钼矿床开展了成因矿物学、矿床地球化学及年代学研究，查明了钼、钨成矿岩体的基本特征和成矿专属性，即钼成矿一般与磁铁矿系列花岗岩类有关，而钨成矿一般与钛铁矿系列花岗岩类有关，且与钼成矿有关岩体遭受了更明显的幔源物质影响；获得了雷公嶂钼矿辉钼矿Re-Os同位素等时线年龄为156.9±3.6Ma，属赣南地区主成矿期成钼事件（162～150Ma），形成于中侏罗世岩石圈全面伸展-减薄的地球动力学环境；通过对辉钼矿成因矿物学研究，查明了主要赣南地区辉钼矿结构标型主要为2H型；通过对辉钼矿微量元素测定显示，辉钼矿富集Se、W、Bi、Pb、Sb、Zn等常见的成矿元素，暗示不成钼流体搬运的成矿元素具有一致性和普遍性；对于同一个辉钼矿集合体、同一辉钼矿晶体的不同部位，辉钼矿中微量元素含量差异性不明显，但辉钼矿集合体的中部具有更高含量的As、Sb等元素，同一辉钼矿晶体中心较边部具有更高的Fe、Co含量和较低的Sb；稀土元素配分曲线具有多样性，明显富集轻稀土，具Eu负异常、Ce正异常和Sm正异常，反映了不同辉钼矿成因或成矿流体性质的差异性，以及较高温的还原环境；成钼流体一般为富CO2和Cl-（个别还富含F-）以及一些还原性气体成分（H2、CO、CH4等）的成矿流体。赣南主要钼矿成矿流体具多期次脉动成矿特征，流体不混溶（减压沸腾）、不同流体混合为主要的成矿机制。综合本项目研究成果，初步认为钨、钼两元素以及络阴离子的某些化学性质的相似性以及两者亲硫和亲氧特性是造成两者共生分离的根本原因，即辉钼矿的形成具有更低的氧逸度、更高的温度和硫逸度。