Rare earth and trace elements enrichment and implications in black shales of Safaga-Qussier sector, Egypt

Abstract

The electronic revolution in recent years points out the importance of rare earth elements (REEs) and trace elements (TEs) in these strategic industries. This study aimed to assess REEs and TEs in black shales from Duwi Formation of two mines, Um Al-Huwaitat and Hamadat, located in the Safaga-Qussier region. The chemical results indicated oxic marine along with warm and humid climate conditions of this sediment deposition. Um Al-Huwaitat Mine was highly enriched with total REEs (average 255.3–325.3 ppm) than Hamadat (average 157–207.4 ppm). Thus, it revealed that the total REEs decreased from Safaga to Qussier direction. The average content of REEs has nearly the same decreasing order of elements; they are arranged in decreasing order: Ce> Y> La> Nd> Sc> Sm and Ce> Y> La> Nd> Sc> Sm for Hamadat and Um El-Huwaitat Mines, respectively. The REEs and TEs concentrations are normalized to the UCC to investigate their distribution patterns. REEs and TEs concentration in the studied samples were higher than UCC, especially Y, Sc, Cs, Co, Zn, Zr, Mo, Cd, Hf, Ta, W, Bi, Se, Br, I, Th and U. The enrichment factor showed that Um Al-Huwaitat black shale is extremely enriched with Y, Cs, Sr, Mo, Cd, W, Bi, Se, I and U; and very high enriched with Ce, Nd, Sc, Co, and Br. La, Sm, Cr, Mn, Ni, Zn, and Th revealed significant enrichment. Clay minerals, especially montmorillonite, have been the major contributor to the enrichment of shale with REEs and TEs. Such findings point towards shale mineralisation with these elements. The current results shed light on the benefit optimization of ceased phosphate mines in the study area through using the associated black shale deposits as a source of REEs and TEs.