开鲁盆地钱家店铀矿床铀的赋存状态及成因探讨

The occurrence state and origin of uranium in Qianjiadian uranium deposit,Kailu Basin

采用电子探针、能谱及背散射分析、扫描电镜、微区X射线荧光等实验方法,详细研究了钱家店铀矿床铀的赋存形式、含铀矿物类型,并对铀矿物相关的矿物组合类型及成因进行探讨。结果表明:(1)钱家店铀矿区铀的赋存形式包括铀矿物、吸附态铀以及含铀矿物三大类。其中,铀矿物类型主要为沥青铀矿,铀石次之,仅在局部可见含钛铀矿物等;吸附铀主要为高岭石吸附和有机质吸附。铀矿物常与黄铁矿、铁白云石、高岭石等密切共生,多呈胶状发育在黄铁矿、铁白云石边缘及裂隙内,也有呈粒状、球粒状独立分布,少数分布在碎屑颗粒内部。(2)研究区至少存在两期铀成矿相关流体:一期中性-弱碱性含铀流体形成的铀矿物围绕黄铁矿边缘发育,形成环边、似环边状,同时形成铁白云石为主的碳酸盐围绕黄铁矿外围发育;另一期含铀流体形成的铀矿物呈脉状充填在黄铁矿内部,无碳酸盐形成。(3)铀矿物(特别是铀石)中含有丰富的磷元素,扫描电镜也发现部分样品中存在富磷元素的微球粒状的铀石集合体,初步认为这是低温流体下微生物参与铀成矿作用的有力证据。

The Qianjiadian uranium deposit,located in the Kailu Basin on the southwestern margin of the Songliao Basin,is the second in-situ leachable sandstone-type uranium deposit which put into industrial development in China.In this paper,electron probe,energy spectrum and backscattering analysis,micro-area Xray fluorescence,X-ray electron spectroscopy and other methods were used to study the uranium-bearing mineral type,occurrence form and uranium valence state of the deposit,and discuss the formation period and process of uranium minerals.The results show that:(1)the occurrence of uranium in Qianjiadian uranium mine includes uranium minerals,adsorbed uranium and uranium bearing minerals.Uranium minerals are mainly coffinite,followed by pitchblende,with titanium bearing uranium minerals visible in some parts.The adsorption of uranium is mainly kaolinite adsorption and organic matter adsorption.Uranium minerals are often closely associated with pyrite,ankerite,kaolinite,etc.They are mostly colloidal and developed in the edges and fissures of pyrite and ankerite.They are also independently distributed in granular and spherulite forms,and a few are distributed in the interior of clastic particles.At the same time,the uranium content in uranium minerals has obvious negative correlation with the sum of"SiO2+P2O5".(2)there are at least two stages of uranium oreforming fluids in the study area.The uranium minerals formed by the neutral weak alkaline uranium bearing fluids in the first stage develop around the edge of pyrite,forming a ring and ring-like shape,and the carbonate dominated by ferruginous dolomite develops around the periphery of pyrite.The uranium minerals formed by the uranium bearing fluids in the second stage fill the interior of pyrite in a vein like manner,without carbonate formation.(3)Uranium minerals(especially coffinite)are rich in phosphorus.Some samples are also found to contain microspherical aggregate of coffinite with phosphorus rich elements by SEM,which is considered to be a strong evidence of microbial participation in uranium mineralization under low temperature fluid.