Ilmenite Alteration and Its Adsorption and Catalytic Reduction in U Enrichment in Sandstone-Hosted U Deposits from the Northern Ordos Basin, North China

Minerals

Chuang Zhang¹  Hong-Xu Liu¹  De-Ru Xu²  Bo Ding²  Lin-Fei Qiu² 

[1] CNNC Key Laboratory of Uranium Resource Exploration and Evaluation Technology, China Beijing Research Institute of Uranium Geology, Beijing 100029, China;State Key Laboratory Breeding of Nuclear Resource and Environment, East China University of Technology, Nanchang 330013, China;

关键词: sandstone-hosted U deposits;    altered ilmenite;    colloidal pyrite;    adsorption and catalytic reduction;    Ordos Basin;   

DOI  :  10.3390/min12020167

来源: DOAJ

【 摘 要 】

Detrital ilmenite and its altered minerals are common in sandstone-hosted U deposits in the northern Ordos Basin, north China. Petrographic observation, SEM-EDS, EMPA, and LA-MC-ICP-MS were utilized to characterize the spatial relationship between altered ilmenite and the U minerals, and to investigate the U enrichment mechanism and alteration processes of ilmenite. Ilmenite was completely or partially altered to leucoxene and anatase along its rim and crack in ore-bearing sandstone. Framboidal and cement pyrite of BSR and TSR origin were identified around altered ilmenite. Two U phases closely related to altered ilmenite contain Ti-coffinite (I) and coffinite (II). These data indicate that ilmenite alteration and the associated processes of U enrichment can be divided into two stages. Stage one involves U pre-enrichment and adsorption, with stage two involving U enrichment via TiO₂ (leucoxene and anatase) catalytic reduction. Ilmenite was altered into porous leucoxene that can adsorb U as uraniferous leucoxene and Ti-coffinite (I) and framboidal pyrite directly by reactions with H₂S, produced by sulfate-reducing bacteria during synsedimentary and early diagenesis stages. Altered ilmenite can enrich U in the form of coffinite (II) through a catalytic reduction reaction which is triggered by β and γ radiation produced by previously adsorbed U during the uplift of ore-bearing bed in the Late Cretaceous period. In addition, cement pyrite can also reduce U⁶⁺ into U⁴⁺ which deposits on its surface in the form of coffinite (II). These results demonstrate a new mechanism, mediated by adsorption and catalytic reduction, to enrich U in sandstone-hosted U deposits.

【 授权许可】

Unknown