Abstract:
Skarn magnetite deposits of the Valer'yanovskii volcanoplutonic belt (Tyumen-Kustanai depression and regions east of the middle and southern Urals) were studied with applications to the problem of the relationship of basaltoid magmatism to ore formation, and the physicochemical parameters of the evolution of basaltoid magma that controlled the petrochemical and geochemical characteristics of ore-bearing comagmatic volcanic and plutonic complexes and their potential ore content were established. Iron-bearing magmatic systems related to basaltoids are regarded as regularly evolving systems completely or partially open with respect to volatile components in their upper parts and relatively closed in the lower parts (peripheral and transitional magma chambers). In the upper part of the system, the processes of postmagmatic mineralization are widespread and often give rise to large-scale magnetite deposits with diverse mineralogy and geochemistry (scapolite, skarn proper, and hydrous silicate subtypes), whereas magmatic-stage ore-forming processes take place in the lower parts and form only low-grade disseminated ores. The main factors of ore concentration in iron-bearing complexes and their potential ore content are the character of magmatic differentiation (including magmatic separation of basaltoid magma into fluid-saturated ore and silicate components) in deep-seated environments and physicochemical characteristics of fluid-magma differentiation occurring under hypabyssal crustal conditions in peripheral chambers (intrusion chambers). It was shown that the type and character of petrochemical trends in the FeO*-MgO coordinates are controlled by the water fluid content of melt: the higher is the initial content of water, the more distinct is the calc-alkaline direction in the evolution sequence, and the higher is the potential ore content of volcanoplutonic complexes.