Geochemical and mineralogical characterization of weathered granite hosting secondary uranium mineralization: A case study from the eastern part of the Reguibat shield, Northern Mauritania

Abstract

The eastern part of the Reguibat shield hosts significant uranium deposits in Northern Mauritania. Weathered granite identified as the uranium host rock. The study area located at the extreme eastern part of the Requibat shield hosts uraniferous granites form part of neobirimian ensemble belonging to yetti complex. The present investigation concerns the petrographic, geochemical and mineralogical characterization and secondary uranium mineralization genesis. Analyses were conducted using EPMA-EDS and ICP-MS. The study area is made up of two uraniferous granites, coarse-grained porphyritic pink with a mylonitic texture and medium-grained grey granite. Paragenesis consists mainly of Qtz + K-F + Pl + Bt + Ap + Sph + Zr + Amp + Cal + Cls ± granet ± Barite ± Ilmenite. Both granites represent monzogranite weakly peraluminous and shoshonitic. REE signature illustrates a negative anomaly of Eu (Eu/Eu* = 0.1 and 0.18 average), and slight fractionation of LREE from HREE remarkable particularly for grey granite ((La/Yb)_N = 5.37–10.27). Multielement spectra show significant enrichments in U, Ta, and Pb, depletions in Ba, Nd, and Eu of pink granite. However, grey granite highlights significant enrichments in U, and Pb, while showing depletions in Nb, Eu, Zr, and Ba.

Geochemistry of the rocks highlights the emergence of the processes of fractional crystallization. Petrogenetic indicator K/Rb ratio suggests rock moderately evolved derived from fractionated magma with potential involvement of crustal material. Rock generated in deep sources of the lower crust or the upper mantle by partial melting. Grey granite similar to A-type however pink granite is S-I-type fractionated to nofractionated granite. Tectonic diagrams placed confirm syn-collisional pink granite and grey granite as within plate granite setting.

Both granites exhibit low CIA and PIA indicting low to moderate weathered rocks. Uranium bearing minerals (Carnotite and Tyuyamunite) occur as small grains size (∼ 10 μm) associated with weathering products filling voids and fractures of the granitoids. The presence of calcite, Celestine, fluorite are the indictors of uranium mineralization formation within evaporitic context in dry and low-temperature conditions.