Evolution of the compositions of ore minerals in high-potassium basalts and associated rocks of Permo-Triassic volcanogenic series of the Maimecha-Kotui province (northern Siberian Platform)

The ranges of temperatures and -lg P-O2 equilibrium for the pairs of coexis ting titanomagnetite and ilmenite in high-potassium basalts and associated subalkalic basic rocks of the Maimecha-Kotui province were estimated using an improved ilmenite-magnetite geothermometer - 700-1180 degreesC and 10-20 , respectively. Their highest values, approaching magmatic ones, have been determined for olivine tholeiitic basalts (T = 1000-1320 degreesC, -lg P-O2 - 8.2-12.6). These parameters for potassic basalts and subalkaline basalts suggest that the formed under the magmatic to postmagmatic conditions, the latter being evidently predominant. In postmagmatic fluids, of major impor tance were, possibly, increased activity of alkalies and, hence, O-2 in the evolution of compositions of coexisting ore mineral phases discussed in th is work.