浙北张家坞铀矿床矿石特征及铀的赋存状态研究

A study on ore characteristics and uranium occurrence state of the Zhangjiawu uranium deposit in the northern Zhejiang, China

浙北湖州—安吉地区位于赣杭火山岩带北西侧,中生代火山岩分布广泛,发育有一系列的中小型火山岩型铀矿(化)点。张家坞铀矿床是浙北地区最大的火山岩型铀矿床,本文通过详实的野外观察,结合光学显微镜、扫描电镜、能谱仪和电子探针等测试技术,对张家坞铀矿的矿石特征和铀的赋存状态进行深入研究。结果表明,矿石呈现红色具流纹构造,整体表现为热液作用的特征,矿石以发育有金属矿物黄铁矿、赤铁矿、金红石和闪锌矿,非金属矿物玉髓、绿泥石、磷灰石、绢云母和方解石为特征。铀的赋存主要以独立铀矿物沥青铀矿和铀石为主,少量赋存在含铀副矿物中。铀矿物颗粒细小从核部到边部依次为沥青铀矿、"铀石化"成因硅含量偏高的铀石("高硅铀石")和正常铀石。矿石和脉石矿物特征表现出成矿时可能是张扭性的构造环境和高温迅速转变为中-低温的成矿环境。从矿体、矿石、矿物、围岩蚀变特征和成矿环境等角度,推测张家坞铀矿属于中-低温热液成因铀矿床。

The Huzhou-Anji area in the northern Zhejiang is located in the northwestern Gan-Hang volcanic belt.Mesozoic volcanic rocks are widely distributed in the area. A series of small-to medium-sized volcanic type uranium deposits(occurrences) are developed. The Zhangjiawu uranium deposit is the largest volcanic-type uranium deposit in the northern Zhejiang. In this paper, through detailed field observation, combined with optical microscope, scanning electron microscope, energy spectrometer and electron probe test techniques, the ore characteristics and uranium occurrence state of the Zhangjiawu deposit have been studied in details. The results show that the ore is in red with rhyolitic structure and overall characteristics of hydrothermal activity. The ore is characterized with the developed metallic minerals including pyrite, hematite, rutile, and sphalerite, and nonmetallic minerals such as chalcedony, chlorite, apatite, sericite, and calcite.The uranium is mainly contained in independent uranium minerals of pitchblende and coffinite, and partly hosted in uranium-bearing accessory minerals. From the core to the edge of small sized uranium mineral grain, there are pitchblende, Si-rich coffinite(with high content of ’coffinitization’ genetic silicon), and normal coffinite;The characteristics of ore and gangue minerals show that the mineralization could occur in a tectonic environment of tension and torsion during and a metallogenic environment of the rapid transformation of high temperature into medium-low temperature. From the perspectives of characteristics of orebodies, ores, minerals, and wall rock alterations, and metallogenic environment, it is believed that the Zhangjiawu uranium deposit belongs to the medium-low temperature hydrothermal uranium deposit.