Peculiarities of behavior of trace elements during fractional crystallization of sulfide magmas

摘要

The behavior of elements of copper-nickel ores during fractional crystallization of sulfide magma, which is composed of more than 20 significant major and trace elements, is considered on the basis of the theory of the direct crystallization of multicomponent melts. During this process, the trajectory of variation of composition of the t-component melt moves consecutively along the elements of the liquidus surface, which corresponds to the crystallization from 1 to t phases with formation of the primary zoning of the orebody. The composition of ores gradually varies inside the zone and changes strongly when it transits from one zone to another. The zonal distribution of major ore elements is superimposed by zoning of the accompanying and trace elements including PGEs, gold, and silver. The peculiarities of the behavior of trace elements, which are cocrystallized with major ore-forming elements or form individual microphases, are analyzed. The last portions of sulfide magma is enriched in Pt, Pd, Au, and other noble metals, which are crystallized from the melt at the final stage of formation of the orebody as an assemblage of minerals of these elements.