Dissolution of Pyrochlore and Microlite in Alkaline, Subaluminous, and Peraluminous Granitoid Melts

Abstract

The represented experimental data on the Ta and Nb contents in acidic magmatic melts of different compositions, when dissolving pyrochlore and microlite at T = 650–850 °C and P = 100–400 MPa, make it possible to obtain quantitative characteristics to create physico-chemical models of the genesis of Ta–Nb deposits. At pyrochlore dissolution in granitoid melts at P = 100 MPa, the highest Nb content (0,7–1,9 wt.%) is obtained in alkaline melts, it decreases to 0,06–0,38 wt.% in sub-aluminous melts, and then slightly increases to 0,11–0,41 wt.% in high-alumina melts. An increase in temperature increases the dissolution of pyrochlore, and an increase in pressure decreases its. In high-alumina granite melts the pyrochlore is unstable. At the microlite dissolves with the increase in the alumina-rich melt, the Nb/Ta ratio in the melt increases approximately doubles.