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 Reports on the presence of hydrocarbons in igneous rocks have been on the increase and generating greater interest in the scientific community over the last 20 years. Most of the occurrences are due to the incorporation of organic material into the magmatic systems. However, reports on the presence of hydrocarbons formed by abiogenic processes have also increased in recent years, suggesting that these hydrocarbons may not be as rare as previously thought and may have implications for natural gas resources in the future. This paper reviews these occurrences and the models proposed for the generation of these hydrocarbons, in particular the nature of the hydrocarbon-bearing fluids in the alkaline complexes Khibina, Lovozero and Ilimaussaq. The origin of these hydrocarbons remains controversial, whether they are (1) derived directly from the mantle, (2) formed during late crystallization stages by respeciation of a C-O-H fluid below 500°C, or (3) formed during postmagmatic alteration processes involving Fisher-Tropsch type reactions catalysed in the presence of Fe-oxides and silicates. The reports suggest that a direct mantle origin for the hydrocarbon fluid is unlikely. A model involving near-solidus reequilibration of a C-O-H fluid to a CH 4 -rich composition is possible, although only for extreme melt compositions that have large crystallization temperature ranges (i.e. hyperagpaitic melts). The Fischer-Tropsch synthesis of hydrocarbons in igneous rocks seems to be a more applicable model for a wide variety of igneous rocks.