Geochemical Specifics of Highly Differentiated Topaz-Bearing Granite of the Salmi Batholith

Abstract

Two varieties of highly differentiated topaz-bearing granite of the Salmi Batholith are distinguished: Li-siderophyllite topaz-bearing granite (Li-Sdph) (Lupikko dome) and Li–F-topaz-zinnwaldite granite (Li–F-Znwl) (Uksinskii dome). Their geochemical patterns and their place in the evolution of the compositions of A-type granite magma derivatives are shown using indicators of crystallization differentiation and the mineragenic potential; the likely regime of the volatile components (water activity in the melt and F accumulation) is discussed. The physicochemical conditions of the formation of Li–F granite were studied. The solidus temperature was determined experimentally by the method of rock powder melting (570–640°C under water saturated and dry conditions). Based on the temperatures of rock formation obtained and the data on the composition of micas, the F content in the fluid in equilibrium with micas (~0.24–0.34 mol/dm³ HF) was estimated. This similarity of the evolutionary trends for granite magmatism of the studied rocks and commercial Ta–Nb objects of Eastern Transbaikalia (S-type granite) is shown.