Newly identified uranyl vanadate mineral formation in the Thrace Basin, NW Türkiye: Insights into identification and origin of carnotite and tyuyamunite minerals

The Thrace Basin is located in the northwest of Türkiye, bounded by the Rhodope Zones to the west, the Strandja (Istranca, Strandzha) Massif to the North, and the İstanbul Zone to the east. The Stranja Massif’s basement is composed of the Tekedere Group, which includes Paleozoic gneisses and schists, as well as the Şeytandere Metagranite, consisting of altered and unaltered metagranites. Unaltered metagranites are characterized by large feldspar crystals and are typically white and pink in color, while altered metagranites are typically yellow color. The subject of this study Şeytandere metagranites which the uraninite mineral, for the first time, was identified in unaltered metagranite samples, while carnotite and tyuyamunite minerals were identified in altered meta-granite samples. The morphologies and elemental compositions of these minerals were identified by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The SEM-EDS analyses revealed that the major elements of carnotite [K2(UO2)2(V2O8)(H2O)3] and tyuyamunite [Ca(UO2)2(V2O8)(H2O)8] are of K, U and V and Ca, U and V, respectively. In the investigated samples carnotite has a plate-like morphology, whereas tyuyamunite shows a fibrous apperance. This investigation shows that carnotite and tyuyamunite are epigentically formed from uranyl vanadate minerals in the Şeytandere metagranite. These minerals indicate uranium leaching from granitic materials and re-deposition as fine specks in open pores by circulating meteoric water. The leached uranyl ions, combined with vanadate ions, form carnotite and tyuyamunite under weathering conditions.