ABSTRACT The Vuoriyarvi Alkaline Ultramafic Complex, northern Karelia, consists of a stock of clinopyroxenites surrounded by ijolitic rocks. It is intruded by stockworks of calcite carbonatites, associated with silicate-apatite-magnetite rocks (phoscorites), that evolve towards later calcite-dolomite carbonatites containing Sr-Ba-LREE minerals. Three main stages of emplacement of carbonatite-phoscorite associations are distinguished, characterized successively by forsterite-phlogopite, phlogopite-tetraferriphlogopite, and magnesio-arfvedso- nite-richterite as the main silicate minerals. The succession of mineral assemblages and the mineral composition trends reflect a global enrichment, from stage to stage, in fluorine, sulphur, alkali elements, Sr and Ti, while the evolution of phlogopite from VI Al-bearing compositions to tetraferriphlogopite reflects a depletion in Al. The carbonatite- phoscorite associations may represent the successive products of the fractional crystallization of an alkali-bearing carbonatite magma. The differentiation, within each association, into carbonatites and phoscorites is considered to result mainly, in the early stage, from an efficient separation between coeval cumulate products, while, in later stages, the phoscorites consist mainly of pegmatitic accumulations and replacement rocks produced by fluids related to the crystallization of the associated carbonatites.

ABSTRACT Phoscorites are plutonic ultramafic rocks, comprising magnetite, apatite and one of the silicates, forsterite, diopside or phlogopite. They almost always occur in close association with carbonatites. Common minor minerals are calcite, dolomite, phlogopite, tetraferriphlogopite and richterite. Key accessories are baddeleyite, pyrochlore, pyrrhotite and chalcopyrite. Phoscorites are rare rocks and only 21 occurrences have been found worldwide. They often form multiphase phoscorite-carbonatite complexes and field relationships include girdle, ring or arcuate zones and veins around or in the carbonatite cores of many complexes, steeply dipping veins that form stockwork pipe-like bodies, or oval, lens-like or isometric bodies up to 100s of metres wide. Five complexes in the Kola Alkaline Province: Kovdor, Vuoriyarvi, Turiy Mys, Seblyavr and Sokli, provide examples of phoscorite diversity. There is no accepted nomenclature for the subdivision of phoscorite varieties. Three possible systems are: (1) the addition of mineral prefixes; (2) the scheme of Yegorov (1993) based on modal (volume) abundances of minerals; and (3) the RHA method of Krasnova et al. (2002) based on molecular abundances of minerals calculated from whole-rock chemistry. Petrogenetic studies of phoscorite emphasize the close relationship between carbonatites and phoscorites and suggest their origin from evolving melts by crystal fractionation and/or liquid immiscibility. Isotopic studies provide evidence of a mantle origin and in some cases argue for successive melt batches.

ABSTRACT The Kovdor Phoscorite-Carbonatite Complex (PCC), a pipe-like intrusion in the alkaline silicate Kovdor pluton, Kola Peninsula, provides compelling evidence that some carbonatite parental melts may bear considerable amounts of Fe, P and Si in addition to the Ca-Mg carbonate components. These parental melt compositions, however, are not easily captured in homogeneous bodies, and instead they differentiate upon ascent and emplacement to produce different generations of vein-shaped intrusive bodies ranging from magnetite-forsterite (phlogopite)-apatite rocks (phoscorites) to carbonatites sensu stricto , that presumably separated from each other through crystal fractionation or/and liquid immiscibility. Each of at least six intrusive stages bears a specific mineralogy, which is shared by the carbonate-poor (phoscorite) and the carbonate-rich (carbonatite) members. This mineralogy evolved from nearly Al-saturated (phlogopite, Al-bearing magnetite) to strongly Al-depleted (tetraferriphlogopite, Al-free magnetite) and from calcite-dominated towards dolomite-dominated. The weighted average composition of Kovdor PCC recalculated to proportions of normative minerals (wt.%) gives: forsterite = 21.9, apatite = 14.1, magnetite = 32.8, calcite = 21.5 and other minerals = 9.7 (mainly dolomite and phlogopite).