Extreme closed system fractionation of volatile-rich, ultrabasic peralkaline melt inclusions and the occurrence of djerfisherite in the Kugda alkaline complex, Siberia

Djerfisherite [K-6(Cu,Fe,Ni)(25)S26Cl] has been found as a daughter mineral in melt inclusions in melilite from a Kugda melilitolite. The inclusion mineral assemblage includes pyrrhotiie, pentlandite, forsterite, diopside, monticellite, phlogopite, wollastonite, nepheline, sodalite, combeite, calcite, Na-K-Ca carbonate, and hydrated calcium silicates. The djerfisherite is Ni-rich rather than Cu-rich consistent with an ultimate upper mantle magma source. The djerfisherite-bearing assemblage formed from primary carbonate/alkali-rich, melilititic melt inclusions which underwent extreme, closed-system, magmatic to postmagmatic fractionation over a temperature range of >1000 degrees to <500 degrees C.