江西相山矿田铀铅锌多金属成矿流体演化与成矿机制

The Xiangshan uranium deposit is the largest volcanic rock type uranium deposit, which is located in Jiangxi Province, China, has a history of 60 years of research and exploitation. The predecessors have done a lot of research works to this deposit and obtained many achievements, but the major questions remain to be answered about the deposit, such as the age of the uranium deposit and the relationship between the ore deposit and volcanic - intrusive igneous complexes etc. In the early stage, most of scholars paid more attention to the theoretical system of “ the ore-forming materials came from shallow and deposited in the shallow ”. In recent years, more and more people paid attention to subvolcanic rock in the deep and found plenty of mineral veins of the lead zinc and silver, these promote “ prospecting ore in the deep”. Although the discovery of new mineral ore increases the difficulty of mineralization on the Xiangshan uranium deposit, it helps us find a breakthrough in solving scientific problems. For example, the Olympic dam uranium deposit, is the largest uranium deposit in the world, is a Cu-Au-U polymetallic deposit. Sylvialake volcanic rock type uranium deposit in Canada is also associated with Pb-Zn-Mo. By the study about lead-zinc mine in the deep of Xiangshan uranium deposit, we can use the new-found lead-zinc ore deposit and the advanced test technology to study the the genesis of the deposit. For example, by the spatial relationship between ore bodys and surrounding rock, and the Ar-Ar dating method, we can obtain metallogenic epoch and stage of the uranium deposit and lead-zinc ore. By the temperature measurement, component analysis and traditional isotope test of fluid inclusions, we can finding out the nature and origin and evolution process of metallogenic fluid of Xiangshan uranium polymetallic deposit. By the Fe isotope technique of the alteration minerals of surrounding rock, gangue minerals of uranium deposits and lead-zinc ore , we can find the material sources, the evolution of ore source and its relationship with metallogenic fluid. In the end, we determine whether uranium deposits and lead-zinc ore belong to the same metallogenic system, and evolve the metallogenic mechanism of uranium lead and zincpolymetallic ore.

相山铀矿田是我国最大的火山岩型铀矿，已经有了60多年的开采、研究历史，但是对铀矿床的成矿时限及矿床成因等方面依然存在诸多争论。早期，多数学者多注重“浅源浅成”的理论体系。近年，随着人们对相山矿田次火山岩重视程度的加深以及矿田西部牛头山-河元背矿区深部铅锌银矿的发现，促进了“深部找矿”工作。新矿种的发现虽然增大了矿田成矿作用的复杂性，但是亦找到了解决科学问题的突破口。申请者利用矿体与围岩等的空间关系以及Ar-Ar法测年技术限定铀矿床和铅锌矿的成矿年代及成矿期次，通过流体包裹体测温、成分分析及传统同位素测试技术阐述铀矿床和铅锌矿的成矿流体性质、来源及其演化过程，利用Fe同位素技术对围岩蚀变矿物、铀矿床和铅锌矿的脉石矿物进行测试，查明铀矿床和铅锌矿的成矿金属元素的来源、演化规律及其与成矿流体的耦合关系。最终判断两者是否同属于一个成矿系统，进而反演铀铅锌多金属的成矿机制。

江西相山是中国最大的火山岩型铀矿床的产地，该矿田已有近60年的勘探开采历史，前人已做了大量的矿床特征和成因的研究工作，但这些研究往往是以U（Th）这一类放射性金属矿种单独开展的。近年，在矿田西部的牛头山-河元背矿区的深部陆续有大量的铅锌银矿脉被发现。深部的铅锌银与铀有着一定的共生关系，那么，铀与铅锌银之间有着何种关系？笔者通过对两种矿体及其围岩开展了精确年代学、同位素地球化学、岩石地球化学以及流体包裹体成分分析等技术，最终判断两者同属一套成矿系统。具体成果如下： .1.利用SIMS/LA-ICPMS锆石原位微区测年技术，获得相山赋矿火山-侵入杂岩体不同阶段和不同岩性的准确年龄。测年数据与矿田地质特征所反映的岩浆活动演化顺序高度一致。 .2.利用蚀变矿物进行39Ar-40Ar法测年得到高精度的矿田铀铅锌多金属矿化年龄。铅锌矿的形成时间为137.5Ma～138.3Ma之间，代表了矿田中生代成矿活动开始。铀矿床的成矿时间为132.6±1.3 Ma、122.8±1.1 Ma，具有两个阶段成矿特点。 .3.确定了含矿岩石的性质及其起源。含矿火山侵入杂岩属于弱过铝质钙碱性系列，表现富钾、富碱，贫钙、贫镁的特征。火山-侵入岩具有一致的起源，均系同一岩浆房的岩浆演化产物，起源于板内拉张环境中上地壳的熔融并有不同比例幔源基性岩浆的加入，且从早期到晚岩浆房内的幔源基性岩浆成分有增多的趋势。 .4.典型矿床研究表明，相山矿田铅锌银矿与铀矿床均为火山-岩浆热液矿床，二者的成矿流体与成矿物质大部分来自于赋矿火山-侵入杂岩岩浆，成矿流体具有低-中盐度，变质水和大气水参与了成矿作用。后期，深部（幔源）富铀流体物质的加入是矿田形成铅锌银与铀两种不同矿化类型的重要原因。成矿作用主要发生于岩浆期后，从铅锌矿到铀矿床成矿温度逐渐降低，铀矿化持续时间更长而展现出两阶段矿化特点。 .5.厘定了相山矿田矿化系统结构，构建了相山矿田铀铅锌银矿多金属成矿模式。相山矿田的铀与铅锌银矿化的物质结构、成矿期次、空间结构特征以及保存与改造条件指示他们属于同一矿化系统，是矿田火山-岩浆热液成矿系统活动于不同阶段的产物。