А.B. MAKEEV (IGEM RAN), B.A. MAKEEV (FTC Institute of Geology Komi SC UB RAS), S.E. BORISOVSKIY (IGEM RAN)

Thorium phosphate: New mineral phase (Middle Timan, Komi Republic)

In four places within the Middle Timan a new mineral phase thorium phosphate was found in the form of individual grains and their aggregates. The phase turned out to be X-ray amorphous. The chemical composition and some physical properties of the two varieties of the new phase have been studied. The grains of the thorium phase from the Ichetyu occurrence are characterized by high calcium, iron, sulfur, carbon contents that suggests wide isomorphism in both the cationic and anionic parts of this compound: (Th, Ca, Fe)·[(PO₄) (SO₄) (CO₃)] × NH₂O. The CHIME method was used to estimate the transformation age of this phase in the Ichetyu occurrence. It turned out to be unexpectedly very young – 52.7±6.1 Ma (Early Paleogene). It is assumed that this is the time of exhumation of the primary bedding of the Ichetyu conglobreccia layer, which became accessible to saline meteoric waters and their interaction with the unstable radioactive phase of the thorium phosphate, which resulted in the complication of its composition.
Keywords: the Middle Timan, Ichetyu, Novo-Bobrovskoe occurrences, the Mezen River, thorium phosphate, chemical composition, properties.