Dissolution of pyrochlore and microlite in alkaline, sub-aluminous and high-aluminous granitoid melts

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.