吐哈盆地八仙口地区砂岩型铀矿微量元素的特征

Characteristics of Trace Elements in Sandstone Type Uranium in Baxiankou Area,Tuha Basin

天山造山带上的伊犁和吐哈盆地是中国重要的砂岩型铀矿产区,吐哈盆地八仙口地区是近年来铀矿勘查的重要地段,铀矿化具有矿带窄、厚度不大、品位较低和钙质含量较高等特点。八仙口地区微量元素地球化学变化规律研究薄弱,制约了矿化规模成因的分析。以氧化流体蚀变空间分带研究为基础,开展微量元素分布规律和特征元素在不同蚀变分带的定量迁移富集研究,并通过与伊犁蒙其古尔矿床的对比,揭示八仙口地区氧化流体作用下铀的富集过程与富集规模成因。研究认为,U与Re等变价元素在矿化带内同步富集指示氧化还原是最主要成矿作用;Sc、Co、Ni、Th等不易变价元素和稀土元素(rare earth element,REE)在氧化带内富集而矿带内亏损与地下水性质有关,高矿化度地下水造成的水解和黏土化,增强了氧化带内碎屑颗粒对溶液中离子的吸附;上新世以来天山快速的隆升造成吐哈盆地极端干旱气候出现,造成微量元素和稀土元素在不同蚀变带内再分配。在铀矿化成因分析中可加强对其中变价与不变价元素变化量的表征,在找矿过程中需对氧化带渗入阶段的古气候加以重视。

The Yili and Tuha Basins on the Tianshan Orogenic belt are important sandstone type uranium mineral areas in China.The Baxiankou area located in the Tuha Basin is an important area for uranium exploration in recent years,but uranium mineralization here is characterized by narrow ore belts,small thickness,low grade,and high calcium content.The study of trace element geochemical changes in Baxiankou area is weak,which restricts the analysis of the genesis of mineralization scale.Based on the study of the spatial zoning of oxidation fluid alteration,the quantitative migration and enrichment of trace element distribution patterns and characteristic elements in different alteration zones were carried out.Through comparison with the Mengqigur deposit in Yili Basin,the enrichment process and origin of uranium enrichment scale under the action of oxidation fluid in the Baxiankou area were revealed.The results show that the synchronous enrichment of variable valence elements such as U and Re within the mineralization zone indicates that oxidation-reduction is the main mineralization process.The enrichment of non volatile elements such as Sc,Co,Ni,Th,and REE in the oxidation zone and the depletion in the ore zone are related to the properties of groundwater.The hydrolysis and clay formation caused by high salinity groundwater enhance the adsorption of ions in the solution by debris particles in the oxidation zone.Since Pliocene,the rapid uplift of Tianshan Mountains caused the extreme arid climate in Tuha Basin,resulting in the redistribution of trace elements and rare earth elements in different alteration zones.In the analysis of the genesis of uranium mineralization,it is necessary to strengthen the characterization of the changes in valence and constant valence elements,and pay more attention to the ancient climate during the infiltration stage of the oxidation zone during the ore exploration process.