Discovery of Trogtalite ( <scp> CoSe ₂ </scp> ) in the Qianjiadian Sandstone‐Type Uranium Deposit in China

ABSTRACT Cobalt (Co), selenium (Se) and uranium (U) are strategic and critical elements with significant global demand. Typically, cobalt is mainly recovered as a by‐product from sulfide and sulfoarsenide minerals associated with copper, nickel, and iron, while its occurrence as independent minerals, particularly trogtalite (cubic CoSe 2 ), is rare. This study reports the presence of trogtalite in a sandstone‐type uranium deposit in China. It was identified in the Qianjiadian deposit in the southwestern Songliao Basin, through electron probe microanalysis (EPMA) and Raman spectroscopy analysis (wavenumber 188 cm −1 ). The trogtalite occurs as cubic or polyhedral microcrystals, distributing as detrital mineral dispersed in the clay matrix or enclosed in detrital quartz or feldspar in uranium‐mineralized sandstones from Upper Cretaceous Yaojia Formation. The sandstone also contains selenides, including clausthalite, ferroselite, and krut'aite, which are typical cobalt mineralization associations found in the deposits in Argentina and Congo. The uranium‐mineralized rocks in the Qianjiadian deposit are enriched in Se, suggesting the co‐enrichment of Se and U during the mineralization. Thus, Se serves as an indicator of uranium mineralization in this deposit.