江西相山矿田邹家山铀矿床特富矿石流体包裹体特征:来自共生磷灰石-紫黑色细晶萤石等矿物制约

在相山矿田成矿流体研究中,前人一般选择成矿晚期结晶良好、透明度高的脉石矿物中的流体包裹体进行研究,其结果难以准确反映成矿流体的信息。基于此,选择江西相山矿田邹家山铀矿床特富矿石中与铀矿物紧密共生的磷灰石及其伴生微细晶透明矿物作为研究对象,通过岩相学观察、扫描电镜能谱分析及流体包裹体研究,讨论该矿床的成矿流体性质,以期为成矿流体来源的判断与成矿过程的研究提供新资料。结果表明:特富铀矿石中与铀矿物密切共生的磷灰石可分为两类。一类为含黑色矿物包裹体的微晶磷灰石(Ap1型),晶形较差,形状不规则,透明度较差,粒度小,推测为主成矿阶段产物,与之共生的主要有微晶石英和紫黑色细晶萤石,同属主成矿阶段产物; 另一类为中粗晶磷灰石(Ap2型),自形程度高,形状规则,部分呈六方柱形,粒度大,推测为成矿晚阶段产物。主成矿阶段,紫黑色细晶萤石中流体包裹体气体成分主要为H₂,微晶石英中流体包裹体气体成分主要为O₂和CO₂,指示了成矿流体中的气体组分以H₂、O₂为主,可能含有少量的CO₂,说明成矿流体具有富H₂的深源流体加入。主成矿阶段流体包裹体均一温度为270 ℃～330 ℃,盐度为5%～9% NaCl_eq,成矿晚阶段流体包裹体均一温度为180 ℃～220 ℃,盐度为4%～10% NaCl_eq,成矿温度最低为180 ℃。特富铀矿石中成矿期磷灰石及其共生脉石矿物中流体包裹体组合特征较好地指示了铀主成矿阶段的流体性质。

Characteristics of Fluid Inclusions of the Ultra-rich Ore from Zoujiashan Uranium Deposit in Xiangshan Orefield of Jiangxi,China: Insights from Paragenesis Apatite-purple Black Fine Crystal Fluorite and Other Minerals

Xiangshan uranium orefield in Jiangxi is always the focus of scholars. Most of them chose fluid inclusions in gangue minerals with good crystallization and high transparency for research. These gangue minerals are generally the products of crystallization in the late or post mineralization period, and the results are difficult to accurately reflect the information of ore-forming fluids. In view of this, the apatite and its associated fine crystal transparent mineral, which are closely associated with uranium minerals of the ultra-rich ore in Zoujiashan uranium deposit, were studied by petrographic observation, SEM-EDS analysis and fluid inclusions determining. Ore-forming fluid properties of the deposit were discussed in order to provide new information for the determination of ore-forming fluid source and the study of ore-forming process. The results show that there are two types of apatites closely associated with uranium minerals in ultra-rich uranium ore. One is microcrystalline apatite(Ap1)with inclusions of black minerals, which has poor crystal shape, irregular shape, poor transparency and small particle size, and it should be formed in main ore-forming stage. Microcrystalline quartz and purple black fine crystal fluorite are associated with microcrystalline apatite, and both are formed in main ore-forming stage. The another one is medium coarse crystalline apatite(Ap2), which has high degree of automorphism, regular shape, hexagonal column shape and large particle size, and it should be formed in late ore-forming stage. In main ore-forming stage, the gas composition of fluid inclusions in the purple black fine crystal fluorite is mainly H₂, and that of fluid inclusions in microcrystalline quartz is mainly O₂ and CO₂. It shows that the gas composition of the ore-forming fluids is mainly H₂ and O₂, and a small amount of CO₂, indicating that the ore-forming fluids have the addition of deep source fluid rich in H₂. The homogenization temperature of fluid inclusions is concentrated in 270 ℃-330 ℃, and the salinity is 5%-9% NaCl_eq in main ore-forming stage. The homogenization temperature of fluid inclusions is concentrated in 180 ℃-220 ℃, the salinity is 4%-10% NaCl_eq in late ore-forming stage, and the lowest mineralization temperature is above 180 ℃. The characteristics of fluid inclusion assemblage in apatite and its associated gangue minerals in the metallogenic stage of ultra-rich uranium ore indicate the fluid properties in the main ore-forming stage of uranium.