Petrographic and geochemical implications for ore genesis and mineralogical composition studies of the Tarat formation hosted sandstone uranium deposit in the Tamari Prospect from Arlit, Niger

Abstract

The ongoing uranium mining activities coupled with mines development in SOMAIR open pit mine at Arlit led to the discovery of a new prospect called Tamari prospect endowed with a potential uranium ore deposit and have been subjected to a very few scientific studies but their characteristics still need to be examined in further detail investigation in order to determine the mineralogical composition, ore genesis and geochemical characteristics of the deposit. Based on detailed studies using optical microscopy, backscattered electron imaging, electron-microprobe and high resolution elemental mapping, the authors have established that detrital, authigenic and uranium ore-stage minerlization are associated with the deposit. Previous studies on the deposits documented two stages of uranium deposits one close to 190 Ma and the other close to 150 Ma. The dominant uranium ore minerals occur as uraninite. Pyrite and galena are the most dominant sulfide minerals associated with the uranium mineralization and therefore, chemical composition analysis shows that pyrite contains an average U concentration up to of 7.62 wt% and galena has an average of 27.16 wt%. The association U–Zr–Pb present in the zircon and monazite indicates that the geochemical environment responsible for this correlation should be that with a large association with lithophile elements which occur in monazite and zircon minerals that could possibly be the potential source of uranium. The impregnation of organic matter with U–Ti oxide indicates a synsedimentary or early source of uranium. Uraninite contains a high concentration of Zr (av. 5.77 wt%) suggesting a probable succession of fluid circulation that would allow either the deposition of two generations of uraninites or mineralization leaching. The excellent positive correlation of U, Fe, Ca and Mn in the mineralized pole of U–Ti oxides is related to the presence of high concentrations of complexing ligands such as carbonate, oxalate, hydroxide, fulvic and humic acids in the deposits. Uranium mineralization occurs as Iriginite (U–Mo) and the powellite (Pb–MoO4) cemented the quartz grains and kaolinite highlights a late fluid circulation.