赣南上窖铀矿床微量元素地球化学特征与成矿模型

Trace elements geochemical characteristics and metallogenic model of the Shangjiao uranium deposit in southern Jiangxi

通过对比研究赣南上窖铀矿床各类岩(矿)石的微量元素、稀土元素地球化学特征,讨论了上窖铀矿床的成矿物质来源与成矿模型。地质、元素地球化学资料表明:(1)印支早期花岗岩与燕山早期花岗岩较高的U含量和较低的Th/U值,反映了两者均具备为区内铀成矿提供充足铀源的能力,并且燕山早期花岗岩提供铀源的潜力更大。(2)水云母化蚀变基本不改变原岩微量元素、稀土元素的含量和配分特征,但叠加赤铁矿化时则伴随U的富集甚至矿化,出现稀土元素的活化转移,说明赤铁矿化与铀矿化关系更为密切。(3)辉绿岩的微量元素配分曲线具有幔源特征,明显区别于花岗岩和铀矿石,且蚀变辉绿岩的U含量和U/Th值明显较新鲜辉绿岩高,说明上窖铀矿床的成矿物质非源于辉绿岩;矿床大面积的赤铁矿化暗示辉绿岩为铀成矿作用提供了发生氧化还原反应的挥发分和矿化剂(CH_4、CO、CO_2、H_2S、Fe^(2+)),从而使迁移态的U6+还原成U4+并沉淀成矿。(4)铀矿石与花岗岩的微量元素配分曲线相似程度高,且为递变关系,说明上窖铀矿床的成矿物质来源于花岗岩;铀矿石的稀土元素总量明显低于花岗岩和辉绿岩,表明成矿流体具贫稀土元素的性质。根据上窖铀矿床的成矿地质背景、岩体-构造-蚀变"三位一体"控矿要素以及微量元素地球化学特征,进一步补充和完善了该矿床的成矿模型。

In this paper, the authors made a comparative study of the geochemical characteristics of trace elements and REE for various rocks such as granites and dolerites as well as uranium ores from the Shangjiao uranium deposit of southern Jiangxi. The ore-forming material source and metallogenic model of the Shangjiao uranium deposit were discussed. Based as geological and elemental geochemical data, the authors have reached some conclusions：（1） The high U content and low Th/U values of early Indosinian granites and early Yanshanian granites suggest that both granites had the capability of providing adequate sources of uranium for uranium mineralization in the study area, and the potential of early Yanshanian granites for providing the sources of uranium was even greater;（2） There was almost no change in the content of trace elements and REE and distribution patterns during hydromicazation of granites, but there occurred uranium enrichment and mineralization and REE remobilization during the superposition of hematitization. These phenomena imply that hematitization was more closely related to uranium mineralization in the study area;（3） The trace elements distribution patterns of dolerites show mantle characteristics, significantly different from features of granites and uranium ores, and the U content and U/Th ratios of altered dolerites are obviously higher than those of fresh dolerites, which suggests that the ore-forming material of the Shangjiao uranium deposit was not derived from dolerites. Large areas of hematitization imply that dolerites provided ore-forming components and volatiles（ CH4, CO, CO2, H2S and Fe2＋） for oxidation-reduction reaction of uranium mineralization, so that the migration of U^（6＋） experienced deoxidation to form U^（4＋） and precipitated mineralization material;（4） The trace elements distribution patterns of uranium ores and granites show high similarity and gradual relationship, indicating that ore-forming material was derived from granites. The total REE content of uranium ores is obviously lower than that of granites and dolerites, indicating that the ore-forming fluids were characterized by a lack of REE. In combination with the geological background of mineralization, the characteristics of magmatic-structurealteration and geochemical characteristics of trace elements, the authors have improved the metallogenic model of the deposit.