THE KOVDOR PHLOGOPITE DEPOSIT, KOLA PENINSULA, RUSSIA

Abstract

The Kovdor phlogopite deposit, one of the largest on Earth, occurs in the northwestern part of the Kovdor carbonatite-bearing alkaline-ultrabasic complex, Kola Peninsula, Russia. The Main phlogopite lode is situated in the central part of a semicircular zone of phlogopite-rich rocks; its morphology is similar to some bodies of granitic pegmatites, hosted in granites, and has a zonal structure. The rocks of the marginal part are monomineralic and consist of giant crystals (up to 2 m across) of diopside, whereas near the center are zones of forsterite–phlogopite, forsterite and apatite rocks. A microtextural study of the phlogopite-bearing bodies shows a regular pattern of spatial arrangement of the main minerals. All grew from the contacts of individual vein-like bodies toward the center. The chemical composition of the main rock-forming minerals (forsterite, phlogopite, diopside) is characterized by lower contents of Ti and Fe compared to the compositions of those minerals in olivinites, but are relatively enriched compared to the same minerals in phoscorites and carbonatites. Gas extracted from phlogopite and apatite shows that hydrogen is an important component in the inclusions. Thermometric data suggest that the formation of the main minerals in the deposit took place at a high temperature, in the range 800–900°C, whereas hydrostatic pressure in the system barely exceeded 2000 bars. On the basis of its shape, structure, features of mineral growth and crystallization sequence, the Main phlogopite lode may be regarded as a peculiar alkali-ultrabasic pegmatite.