SULFIDE MINERALIZATION IN HIGH-ALKALINE PEGMATITES OF THE KOASHVA DEPOSIT (KHIBINY MASSIF, KOLA PENINSULA)

Abstract

While studying high-alkaline pegmatites of the Koashva deposit (Khibiny Massif) in addition to widely spread sulfides (galena, sphalerite, chalcopyrite, and cobaltite), rare potassium sulfides were identified: djerfisherite, rasvumite, and potassium-sodium and sodium-bearing sulfide phases with different copper and iron content. Some of them develop after early chalcopyrite, others form independent segregations among minerals characteristic of this pegmatite type (sodalite, microcline, villiaumite, lomonosovite, and pectolite). Their chemical compositions and X-ray data suggested that potassium-sodium and sodium-bearing sulfide phases had no analogues among the known natural and synthetic compounds. The physical properties (reflectance, microhardness) of several such sulfides were investigated. The formation of sulfide mineralization was considered in connection with the development of a pegmatite complex of deposit Koashva. The development of the pegmatite complex is believed to proceed in three stages. The first magmatic stage is potassium and sodium differentiation along with crystallization of the bulk mass of urtites and the formation of potassium differentiates-rischorrite-pegmatites. The second stage consists in the separation of the most fluid-saturated phase from the melt and its accumulation in the most permeable zone, at the contact of urtites with an apatite orebody. The third stage is postmagmatic potassium and sodium separation.