赣南草桃背铀矿床中绿泥石地球化学特征及成矿指示意义

赣南草桃背铀矿床位于会昌地区河草坑铀矿田，是一个大型火山岩容矿的铀矿床，成因机制存在较大争议。矿床内发育有大面积的花岗岩和火山岩，矿体主要赋存在火山隐爆角砾岩和震碎花岗岩中。文章以该矿床内花岗岩、火山岩及矿石中广泛发育的蚀变矿物绿泥石为研究对象，采用电子探针及LA-ICP-MS原位微区分析技术对其矿物化学组成进行分析。分析结果表明，花岗岩和矿石中的绿泥石主要为富铁的鲕绿泥石和蠕绿泥石，火山岩中的绿泥石则为相对富镁的密绿泥石。各类绿泥石阳离子置换关系主要以Fe、Mg置换为主，同时存在一定的Tschermak（TK）和二八—三八面体（DT）替换机制。矿石中绿泥石具有相对较高含量的Ti、Li、Be、B、Zn、Ga、Ge、Sn、Cs、U、Rb和Ba等元素，并显示出较低的Th/U比值。矿石中绿泥石的结晶温度区间为201~269℃，平均值为242℃，属于中低温热液作用的产物。矿石中绿泥石的氧逸度（log f O₂）变化于-48.4~-41.2之间，平均值为-44.5，硫逸度（log f S₂）变化于-7.5~+2.8之间，平均值为-1.8，草桃背铀矿床的铀矿化主要形成于低氧逸度、高硫逸度的环境。

Geochemical Characteristics and Metallogenic Indications of Chloritein the Caotaobei Uranium Deposit in Southern Jiangxi Province

The Caotaobei uranium deposit is a large-scale volcanic-hosted uranium deposit in the Hecaokeng ore field in Huichang area, southern Jiangxi Province. Granites and volcanic rocks occur in the deposit, and the orebodies are mainly hosted by the cryptoexplosive breccia and shattered granites. Chlorite, a widely developed alteration mineral in the granites, volcanic rocks and ores, is taken as the research object in this paper, and its chemical compositions are analyzed by EPMA and LA-ICPMS. The results show that the chlorite in the granites and the ores is mainly iron-rich chamosite and prochlorite, while the chlorite in the volcanic rocks is mainly magnesium-rich pycnochlorite. Ionic substitution mechanisms of Fe ? Mg, Tschermak (TK) and di-trioctahedral (DT) are likely important for chemical variations of the chlorite at the Caotaobei uranium deposit. Chlorite in the ores has relatively high contents of Ti, Li, Be, B, Zn, Ga, Ge, Sn, Cs, U, Rb and Ba, and shows low Th/U ratios. Crystallization temperatures of the chlorite in the ores are calculated to be 201-269℃ with an average value of 242℃, indicating the mediumlow temperatures for ore-forming fluids. The oxygen fugacity (log f O₂) of chlorite in the ores varies from -48.4 to -41.2 with an average value of -44.5; the sulfur fugacity (log f S₂) varies from -7.5 to +2.8 with an average value of -1.8. The uranium mineralization in the Caotaobei deposit was formed in an environment of low oxygen fugacity and high sulfur fugacity.