RTH Mineralization in Rift Formations of the Ishlya Graben (Western Slope of the Southern Urals)

Rift formations of the Ishiya graben, widespread on the western slope of the Southern Urals, are represented by alternating terrigenous rocks (carbonaceous shales, silestones, silestones) with a volcano-plutonic association (gabbrodolerites, basic effusives with a small amount of pyroclastic material). In the rocks of the Ishiya graben, complex rare earth mineralization was discovered, represented by allanite-(Ce), REE-containing epidote, monazite-(Ce), xenotime-(Y), chevkinite-(Ce), fergusonite-(Nb), rare earth fluorocarbonates (bastnaesite-(Ce), hydroxyblastnaesite-(Ce), parisite-(Ce), synchysite-(Ce)), which is characterized by a wide variety of morphological types of mineralization and the presence of complex associations. Based on the analysis of the chemical composition of metamorphic minerals, the P–T parameters of rock metamorphism were established (T = 250-600°C, P = 2-10 kbar), the chemical composition of the fluid phase and its temperature (CaCl + NaCl; T = 180-408°C, for primary inclusions and FeCl; T = 121-248°C for secondary ones), as well as the hematization temperature (465-593°C) and re-equilibration of the ilmenite-titanomagnetite association (T = 501-576°C at oxygen fugacity from -23.15 to -21.25) were determined. It is shown that in the natural environment, the processes of rare earth mineral formation are diverse and multifactorial, with the chemistry of the local-scale mineral formation environment being of great importance. Based on the comparative analysis of the chemical composition of monazite and xenotime, it was established that neither the configuration of the normalized graphs nor the chemical composition of the minerals found in the rocks of the Ishiya graben and the Shatak complex correspond to analogs from alluvial deposits. Thus, it can be stated that the primary source of rare-earth phosphates from channel and alluvial deposits are the Riphean-Vendian metamorphosed rocks of the eastern subzone of the Bashkir meganticlinorium.