遵义松林镍钼多金属层铀存在形式及成因探讨

The existing forms of uranium and genesis of Ni-Mo polymetallic layer in the Songlin area,Zunyi

贵州省遵义松林地区下寒武统牛蹄塘组镍钼多金属层富集U、Mo、Ni、Re、Tl等元素。本文以松林地区镍钼多金属层磷块岩为主要研究对象,在松林系统取样的基础上,开展化学分析、径迹蚀刻、扫描电镜、能谱面扫描、浸出实验等工作。结果表明下寒武统牛蹄塘组镍钼多金属层中Ni、Mo显著富集,达到工业品位,U、Re、Tl明显富集。径迹蚀刻实验揭示铀主要富集于磷块岩碎屑边缘有机碳外带,为进一步确定铀的赋存形式圈定重点观察区。该区镍钼多金属层中铀呈晶质铀矿形式赋存于溶蚀重结晶磷块岩的溶蚀孔洞、微裂隙或微孔隙中,并与中高温热液矿物针镍矿、辉砷镍矿、闪锌矿、方铅矿、磷灰石共生。浸出实验采用去离子水、H_(2)SO_(4)、NaHCO_(3)+MnO_(2)三种介质浸出样品中水溶态、酸可溶态、氧化可溶态的铀。80℃,48h条件下浸出实验结果显示多金属磷块岩由黑色褪色为浅灰色、灰色,碳质页岩实验前后颜色均为黑色。遵义地区镍钼多金属层及碳质页岩中铀主要以吸附状态或独立矿物形式存在,以类质同象形式存在的难溶铀占比较小。研究认为,该区镍钼多金属层磷块岩中铀以独立矿物形式存在并与中高温热液矿物共生,为揭示扬子陆块东缘陆源裂陷环境下发生海底喷流和热水沉积作用提供新的微观证据。

U,Mo,Ni,Re and Tl elements are enriched in the Ni-Mo polymetallic layer of the Lower Cambrian Niutitang Formation in the Songlin area of Zunyi,Guizhou Province.In this paper,the phosphorite of Ni-Mo polymetallic layer in the Songlin area is taken as the main research object.Chemical analysis,track etching,scanning electron microscopy and energy spectrum scanning,leaching experiment were carried out,based on the sampling of profile system in the Songlin area.The results show that Ni and Mo reached industrial grade,while U,Re and Tl are significantly enriched in the Niutitang Ni-Mo polymetallic layer of the Lower Cambrian.Trace etching experiments show that uranium is mainly enriched in the organic carbon extranet at the clastic edge of phosphorite block,and the key observation area is delineated for further determining the occurrence form of uranium.The uranium in the Ni-Mo polymetallic layer in this area is in the form of uraninite and occurs in the corrosion hole,micro-cracks or micro-pores of the dissolved and recrystallized phosphorite,and is symbiotically associated with medium and high temperature hydrothermal minerals such as stileite,arsenopyrite,sphalerite,galena and apatite.Deionized water,H_(2)SO_(4),NaHCO_(3)+MnO_(2)were used to leach uranium in water soluble,acid soluble and oxidized soluble state.48hours leaching experiment at 80℃shows that the color of polymetallic phosphorite fades from black to light gray,while the color of carbonaceous shale is black before and after the experiment.The uranium in the Ni-Mo polymetallic layer and carbonaceous shale in the Zunyi area mainly exists in the form of adsorption or independent minerals,while the proportion of insoluble uranium in the form of isomorphism is less.It is concluded that uranium in the polymetallic phosphorite in this area exists as an independent mineral in the middle and high temperature hydrothermal mineral symbiosis,which provides new microscopic evidence for revealing the submarine jet and hot water deposition in the marginal rifting environment of the eastern margin of the Yangtze block.