Phoscorites and Carbonatites from Mantle to Mine: the Key example of the Kola Alkaline Province

edited by 

F.Wall and A.N. Zaitsev

Contents

Chapter 1	Overview of carbonatite-phoscorite complexes of the Kola Alkaline Province in the context of a Scandinavian North Atlantic Alkaline Province	A. G. Bulakh, V. V. Ivanikov and M. P. Orlova
Chapter 2	Introduction to phoscorites: occurrence, composition, nomenclature and petrogenesis	N. I. Krasnova, T. G. Petrov, E. G. Balaganskaya, D. Garcia, J. Moutte, A. N. Zaitsev and F. Wall
Chapter 3	Timing of Kola ultrabasic, alkaline and phoscorite-carbonatite magmatism	U. Kramm and S. Sindern
Chapter 4	Kovdor – classic phoscorites and carbonatites	N. I. Krasnova, E. G. Balaganskaya and D. Garcia
Chapter 5	Carbonatites and phoscorites from the Sokli Complex, Finland	M. J. Lee, D. Garcia, J. Moutte, C. T. Williams and F. Wall
Chapter 6	The phoscorite-carbonatite complex of Vuoriyarvi, Kola Peninsula	P. I. Karchevsky and J. Moutte
Chapter 7	Sallanlatvi complex – a rare example of magnesite and siderite carbonatites	A. N. Zaitsev, M. A. Sitnikova, V. V. Subbotin, J. Fernández-Suárez and T. E. Jeffries
Chapter 8	Afrikanda: An association of ultramafic, alkaline and alkali-silica-rich carbonatitic rocks from mantle-derived melts	A. R. Chakhmouradian and A. N. Zaitsev
Chapter 9	Mineralogy of high-.eld-strength elements (Ti, Nb, Zr, Ta, Hf) in phoscoritic and carbonatitic rocks of the Kola Peninsula, Russia	A. R. Chakhmouradian and C. T. Williams
Chapter 10	Rare earth minerals in Kola carbonatites	F. Wall and A. N. Zaitsev
Chapter 11	A review and comparison of PGE, noble-metal and sulphide mineralization in phoscorites and carbonatites from Kovdor and Phalaborwa	N. S. Rudashevsky, Yu. L. Kretser, V. N. Rudashevsky and E. S. Sukharzhevskaya
Chapter 12	Stable C and O isotope compositions of carbonatite complexes of the Kola Alkaline Province: phoscorite-carbonatite relationships and source compositions	A. Demény, M. A. Sitnikova and P. I. Karchevsky
Chapter 13	Carbonatites from the Kola Alkaline Province: Origin, evolution and source characteristics	K. Bell and A. S. Rukhlov
Chapter 14	Economic deposits associated with the alkaline and ultrabasic complexes of the Kola Peninsula	S. V. Petrov

Chapter 1. Overview of carbonatite-phoscorite complexes of the Kola Alkaline

Province in the context of a Scandinavian North Atlantic Alkaline

Province

A. G. Bulakh, V. V. Ivanikov and M. P. Orlova

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, andd ykes, 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 andva rieties of alkaline complexes andd ykes. 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 series dykes; (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 liquidimm iscibility from an evolvedca rbonatedne pheline melilitite melt.

Chapter 2. Introduction to phoscorites: occurrence, composition, nomenclature

and petrogenesis

N. I. Krasnova, T. G. Petrov, E. G. Balaganskaya, D. Garcia, J. Moutte, A. N. Zaitsev and F. Wall

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 pre.xes; (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.

Chapter 3. Timing of Kola ultrabasic, alkaline and phoscorite-carbonatite magmatism

U. Kramm and S. Sindern

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 between carbonatites and associated alkali silicate rocks nor between carbonatites and phoscorites.

Chapter 4. Kovdor – classic phoscorites and carbonatites N. I. Krasnova, E. G. Balaganskaya and D. Garcia

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).

Chapter 5. Carbonatites and phoscorites from the Sokli Complex, Finland

M. J. Lee, D. Garcia, J. Moutte, C. T. Williams and F. Wall

The Sokli alkaline complex, ‘Finnish Lapland’, Finland, shows a rock association dominated by calcite carbonatites and phoscorites surrounded by altered alkaline rocks (clinopyroxenites), and cut by ultramafic lamprophyres. Calcite carbonatites and phoscorites are intimately associated on a metre scale, and they exhibit similar mineralogies.At the larger scale of the intrusive complex, variations in mineral assemblage delineate a broad concentric structure, with three main groups of calcite carbonatites and associated phoscorites evolving towards later REE-depleted dolomite carbonatites and .nally LREE-Sr-Ba-Mn-Fe-enriched dolomite carbonatites.Bu lk-rock chemical data allow additional intrusive bodies to be discriminated.The y underline the dominance of magnetite (over silicate and phosphate) in phoscorites and the general lack of gradation towards calcite carbonatite compositions. Large variations in mineral chemistry are documented as a function of intrusive stage, in particular for pyrochlore.Carbonatite and phoscorite from the same stage share many mineralogical similarities, but the zoning patterns of micas and pyrochlores record a longer-lived crystallization history in most phoscorites, thus not favouring the idea that phoscorites are cumulates and calcite carbonatites, residual liquids.The segregation between calcite carbonatite and phoscorite is more likely to be driven by immiscibility between Fe-rich and carbonate-rich melts, a possibility which is yet to be explored experimentally. The late-stage evolution towards dolomite carbonatites is best seen as an in situ differentiation of the phoscorites, complicated by hydrothermal redistribution of the REE.

Chapter 6. The phoscorite-carbonatite complex of Vuoriyarvi, Kola Peninsula

P. I. Karchevsky and J. Moutte

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-arfvedsonite- 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 ^VIAl-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.

Chapter 7. Sallanlatvi complex – a rare example of magnesite and siderite carbonatites

A. N. Zaitsev, M. A. Sitnikova, V. V. Subbotin, J. Fernández-Suárez and T. E. Jeffries

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.

Chapter 8. Afrikanda: An association of ultramafic, alkaline and alkali-silica-rich carbonatitic rocks from mantle-derived melts

A. R. Chakhmouradian and A. N. Zaitsev

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 amphibole–peridotite 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 alkali silica-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.

Chapter 9. Mineralogy of high-field-strength elements (Ti, Nb, Zr, Ta, Hf) in phoscoritic and carbonatitic rocks of the Kola Peninsula, Russia

A.R. Chakhmouradian and C.T. Williams

Complex Ti, Nb and Zr oxides (baddeleyite, zirconolite, perovskite-, pyrochlore and ilmenite-group minerals) are primary HFSE hosts in early calcite carbonatites and phoscorites. Appreciable amounts of Hf and Ta are concentrated in baddeleyite and uranoan pyrochlore, respectively. In their absence, minor Ta may be sequestered in perovskite, lueshite or ilmenite, and Hf in zirconolite. Ilmenite (as ‘exsolution’ lamellae in magnetite and discrete crystals) and perovskite are the principal Ti minerals, but a signi.cant proportion of this element is also bound in rock-forming silicates. Primary zircon is of limited significance; it is characteristically poor in Hf. Titano-, niobo- and zirconosilicates are restricted to deuteric and metasomatic parageneses developed after and at the expense of the primary HFSE minerals during the late stages of carbonatite evolution, or as a result of metasomatic overprint in the wallrocks. Depending on the activity of silica, Na and other cations in deuteric (metasomatic) fluids, these parageneses may also contain complex oxides enriched in Sr, Ba and light REE (e.g. loparite and bariopyrochlore), as well as TiO₂ polymorphs, late-stage baddeleyite, and poorly characterized Ti-Nb-Zr phases. Evolution of .fluids causes systematic changes in modal mineralogy (e.g. replacement of gittinsite by catapleiite) and/ or composition of minerals (e.g. enrichment of perovskite in REE). The activity of HFSE in these environments is determined by the nature and relative stability of their (hydroxo-)carbonate complexes.

Chapter 10. Rare earth minerals in Kola carbonatites

F. Wall and A. N. Zaitsev

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-fluocarbonates 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.

Chapter 11. A review and comparison of PGE, noble-metal and sulphide mineralization in phoscorites and carbonatites from Kovdor and Phalaborwa

N. S. Rudashevsky, Yu. L. Kretser, V. N. Rudashevsky and E. S. Sukharzhevskaya

Comparative characteristics of PGE, noble-metal and sulphide mineralization in phoscorites and carbonatites from the Kovdor and Phalaborwa deposits are given. Four typical sulphide-rich samples from Kovdor and Phalaborwa (phoscorites and carbonatites from both deposits, as well as sulphide concentrate from the Kovdor Concentrating Mill and a .flotation sulphide concentrate from the Palabora Mining Company) were studied. In Kovdor, mainly in calcite-rich areas of the phoscorites, small, drop-shaped isolated sulphide (pyrrhotite, chalcopyrite ± pentlandite) inclusions occur in calcite, as well as similar calcite inclusions in sulphide aggregates. Besides these and other rare sulphides, six Pt-bearing minerals, nine Pd-bearing minerals and four Au minerals were identified in the ‘heavy concentrates’ of the Kovdor samples. Copper-bearing minerals – bornite, chalcopyrite, minerals of the chalcosine group and cubanite – dominate within sulphides of the samples from the Loolekop deposit, Phalaborwa. Typical exsolution textures of chalcopyrite– bornite solid solution, as well as myrmekitic intergrowths of bornite and chalcosine-group minerals are usually observed. Besides these sulphides and other scarcer ore minerals, one Pt-bearing mineral, eight Pd minerals, four Au-bearing minerals, and .ve Ag-bearing minerals were identi.ed in the ‘heavy concentrates’ of the Phalaborwa samples. At Kovdor, pyrrhotite sulphide mineralization crystallized from a high-temperature sulphide-rich .uid phase, separated from the carbonatitic (or phoscoritic) magma. In contrast, the crystallization temperature of the dominant copper sulphide mineralization at Phalaborwa is considered to be medium to low. Thus, sulphide mineralization in the Kovdor Complex occurred at a higher temperature than at Loolekop, and was essentially richer in S and poorer in Cu than the Phalaborwa Complex.

Chapter 12. Stable C and O isotope compositions of carbonatite complexes of the Kola Alkaline Province: phoscorite-carbonatite relationships and source compositions

A. Demény, M.A. Sitnikova and P.I. Karchevsky

Stable C and O isotope compositions have been compiled for the Kovdor, Sokli,

Turiy Mys, Vuoriyarvi, Afrikanda, Khibiny, Sallanlatvi, Telyachiy Island, Tiksheozero and Siilinjärvi Carbonatite Complexes of the Kola-Karelia Region. Stable isotope relationships of various carbonate minerals (calcite, dolomite, rare-earth minerals) from several stages of carbonatite evolution have been investigated in order to determine primary compositions and the influence of secondary processes (Rayleigh fractionation in the fluid-carbonate-silicate system, hydrothermal alteration, degassing, crustal contamination). The phoscorite-carbonatite relationship has also been investigated. The data for some phoscorites (Sokli, Vuoriyarvi) are consistent with an origin by carbonatite-silicate liquid immiscibility, whereas those of the Turiy Mys phoscorites suggest the involvement of different sources. The primary carbon isotope compositions obtained for different complexes show a large variation at fairly constant oxygen isotope compositions. This is best explained by mantle heterogeneity, probably related to CO₂ metasomatism or by removal of a ¹²C-enriched phase in the mantle.

Chapter 13. Carbonatites from the Kola Alkaline Province: Origin, evolution and source characteristics

K. Bell and A. S. Rukhlov

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.O n 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.

Chapter 14. Economic deposits associated with the alkaline and ultrabasic complexes of the Kola Peninsula

S. V. Petrov

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 (phoscoritecarbonatite, 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-titanomagnetite- 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.