ABSTRACT Deposits associated with the alkaline complexes of the Kola Peninsula are very important to the economy of northwest Russia. They contain large reserves of iron ore and rare-metal minerals, as well as industrial minerals including apatite, nepheline, phlogopite, vermiculite, baddeleyite, baryte, ilmenite, titanomagnetite and olivine. The ores can be grouped into four genetic types (phoscorite-carbonatite, foidolite, mafite-ultramafite and exogenous) which are subdivided into ten economic types. At present ores are being mined within three complexes: Kovdor (complex baddeleyite-apatite-magnetite ores, technogenic (man-made) baddeleyite-apatite sands, phlogopite and vermiculite), Khibiny (nepheline-apatite ores) and Lovozero (loparite ore). The most promising mineral deposits are located in the Salmagora, Gremyakha-Vyrmes and Sallanlatvi complexes where large reserves of complex sulphide-titanomagne-tite-apatite, ilmenite-titanomagnetite and baryte ores have been detected. The development of these deposits and the development of techniques to make more efficient use of ores are the main challenges for the mining industry in the Kola region.

Abstract The tectonic position of the Palaeozoic alkaline complexes containing phoscorites and carbonatites is determined by the combination of three factors. These are (1) the presence of rift systems; (2) the presence of deep fracture zones; (3) the powerful energetic excitement of lithosphere with an epicentre in the region of the Khibiny complex, i.e. the action of a mantle plume or ‘a hot spot’. The ages of alkaline magmatism in the eastern part of the Baltic Shield are in general synchronous with the manifestation of alkaline magmatism in the whole of the North Atlantic Alkaline Province. Early Palaeozoic alkaline magmatism on the Kola Peninsula is small-scale compared with that in western Fennoscandia. It consists of diatremes and dykes of olivine melilitite-alnöite-carbonatites. The formation of the carbonatitic ultramafite-foidolite complexes started in the early Palaeozoic. The peak of alkaline magmatism, of volcanic activity, large intrusions, and dykes, took place in the late Devonian, forming the Devonian Kola Alkaline Province (KAP). As a whole, the carbonatites in their various different forms and sizes are related to six petrogenetic types and varieties of alkaline complexes and dykes. They are: (1) Proterozoic complexes of ultramafic/mafic rocks-foidolites-foidosyenites; (2) dykes and diatremes of the early Palaeozoic series of the Kandalaksha Graben; (3) Kandagubian seriesdykes; (4) Turiy series dykes; (5) Palaeozoic plutons of alkaline-ultramafic rocks; (6) agpaite nepheline syenite complexes. A quantitative model proposed for the formation of the carbonatites involves liquid immiscibility from an evolved carbonated nepheline melilitite melt.

ABSTRACT A set of criteria has been established that we use to assess whether carbonatites are generated as primary mantle melts, or whether they are the products of magma differentiation (crystal fractionation, liquid immiscibility) of a parental, carbonated silicate melt. On the basis of these criteria, in conjunction with the vast amount of published field information and geochemical data from the Kola Alkaline Province (KAP), no clear-cut pattern emerges that favours any of these processes over the others. Any evidence for liquid immiscibility seems to be restricted to some members of the dyke swarms (Kandaguba, Turiy), while robust evidence for the generation of primary carbonatitic magmas seems to be lacking. Potential candidates for primary melts include the carbonatites from Turiy Mys and the older dyke swarms associated with the Kandalaksha Deep Fracture Zone. The spatial and temporal association of most carbonatites with silicate rocks at Kola, along with the presence of olivinites, clinopyroxenites and other cumulate rocks in some complexes favour crystal fractionation as an important process in generating some of the KAP rocks. We are left with the impression that all three processes may be responsible for carbonatite generation, even within the same complex. The isotopic evidence suggests the involvement of at least three distinct mantle sources, one of which is common to all of the complexes and perhaps indicative of a deep-seated, primitive mantle at least 3 Ga old. Overall, we propose an integrated plume-related model for the Devonian alkaline and carbonatitic magmatism that characterizes much of the KAP. Low-degree partial melting within the volatile-rich, and cooler parts of a plume head accompanied by the mixing of small-volume magma batches, their subsequent differentiation, and interaction with entrained materials and continental lithosphere may help explain some of the problems associated with unravelling the genesis of carbonatite magmas.

ABSTRACT The oldest alkaline silicate rocks known are Archaean (2700–2600 Ma) lamprophyres and alkali syenites. Several Proterozoic alkaline gabbroic intrusions which in part also contain carbonatites occur between 2000 and 1800 Ma. Intensive alkaline magmatic activity formed more than 20 complexes (Kola Alkaline Province, KAP) during the Palaeozoic between 410 and 362 Ma with the majority of ages being between 382 and 362 Ma. The data show no systematic geographical distribution of ages within the KAP so that timing of magmatic activity cannot be correlated to the major tectonic structures. A distinction of the intrusions into Caledonian and Hercynian groups is not supported. A lithologically controlled variation of ages within single complexes can neither be seen betweencarbonatites and associated alkali silicate rocks nor between carbonatites and phoscorites.

ABSTRACT Sallanlatvi Alkaline Complex (~ 375 Ma), northern Karelia, contains diverse carbonatitic rocks that include calcite, dolomite, ankerite, magnesite-dolomite, siderite-ankerite and siderite carbonatites. Associated alkaline rocks belong to the melteigite-ijolite-urtite series. No ultrabasic, melilitic and nepheline syenitic rocks or phoscorites are known from Sallanlatvi. The carbonatites are considered to be polygenetic in origin: calcite, dolomite and ankerite carbonatites are magmatic, siderite carbonatite precipitated from carbo-hydrothermal fluid and magnesite-bearing carbonatites are of hydrothermal-metasomatic origin. The sequence of carbonatite formation at Sallanlatvi may be interpreted as produced by fractional crystallization of a hydrous carbonatite magma. The presence of lueshite, as well as burbankite, shortite, eitelite and bradleyite as daughter minerals in fluid inclusions and as solid inclusions in the lueshite and early crystallized magnetite from calcite carbonatites indicates initially high Na activity, water-enrichment and low fluorine during early-stage carbonatite evolution. Late-stage subsolidus processes in carbonatites include re-crystallization of carbonates, formation of chlorite, carbonate-hydroxylapatite, ancylite, strontianite and baryte.

ABSTRACT The Afrikanda pluton (Kola Peninsula) comprises predominantly olivine- and clinopyroxene-dominant cumulate ultramafic rocks, with subordinate melteigites and ijolites. On the basis of petrographic and geochemical evidence, these rocks are interpreted to have formed at mid-crustal depths from a Ca-rich melanephelinitic magma. Olivinites (+wehrlites) and clinopyroxenites precipitated from separate batches of magma, whereas the foidolites are related to the clinopyroxenites by crystal fractionation. In both cases, the parental magma was derived by partial melting of a metasomatized lithospheric source enriched in pargasite and phlogopite. The melting occurred just above the amphiboleperidotite solidus, thus producing a liquid depleted in K, Ba and Rb, but enriched in light REE , Nb, Ta and Th. Plutonic carbonatitic rocks occur predominantly as branching veins and nests in the clinopyroxenites. They show variable modal composition in terms of both principal (diopside, magnesiohastingsite and calcite) and minor (perovskite, magnetite, titanite, chlorite and ilmenite) rock-forming phases, delineating a series from calcite-amphibole clinopyroxenite to calcite carbonatite. These rocks crystallized from an alkalisilica-rich carbonatitic magma of mantle provenance. Solidification of this magma and accompanying processes (reaction with the wallrock, xenocryst assimilation, fractionation of a Na-rich fluid, and subsolidus re-equilibration) led to the formation of several distinct parageneses comprising over 50 mineral species.

ABSTRACT Carbonatites of the Devonian Kola Alkaline Province contain 25 different rare earth minerals, in quantities ranging from accessory to rock-forming proportions. In contrast, Kola phoscorites are practically devoid of rare earth minerals. The most widespread REE mineral in carbonatites is ancylite-(Ce), which is a hydrothermal mineral in nine carbonatite occurrences. Ancylite compositions vary according to locality but can also show fluid evolution, as found at Sallanlatvi. Burbankite and carbocernaite are more common than previously reported in carbonatites world-wide and occur in pegmatitic transition-environment carbonatites at Vuoriyarvi and Khibiny where they are then replaced by ancylite-(Ce) or synchysite-(Ce). The REE fluocarbonates are less common than reported in carbonatites elsewhere, although rare Ba-fluocarbo-nates are found at Khibiny and Vuoriyarvi. Carbonates of Y and the heavy REE , mckelvyite, ewaldite and donnayite, occur in low-temperature, hydrothermal carbonate-zeolite veins at the end of this sequence. Monazite-(Ce) is a common accessory phase and has variable compositions, with three main controls: high Th content and formation by hydrothermal alteration tend to produce low La/Ce ratios and greater mid- REE contents. Small differences in the probability of REE uptake on different growth surfaces result in a pivoting of REE chondrite-normalized patterns around Ce. Burbankite and carbocernaite carbonatites, in particular, yield good data on isotopic source characteristics and in general Nd ratios are more robust than those of Sr. Paragenetic sequences and changes in REE mineral composition record the final magmatic stages of carbonatite emplacement and a fluid evolution in which minerals usually become less light REE -enriched, probably reflecting the increasing water to carbon species ratio of the evolving carbonatite-derived fluid.