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Orbicular and spherulitic carbonatites from Sokli and Vuorijärvi
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Orbicular and spheruliitic carbonatites from Sokli and Vuorijiirvi A. V. LAPIN & H. VARTIAINEN
L1THOS
Lapin, A. V. & Vartiainen, H. 1983 01 15: Orbicular and spherulitic carbonatites from Soldi and .Vuorijiirvi. L/thos, Vol. 16, pp. 53--60. Osio. ISSN 0024-4937. The main types of spherulitic and orbicular structures in carbonatites of Sokli (Finland) and Vuorijgrvi (U.S.S.R.) are der,cribed. The structures have small-scale morphological differences although generally they show fairly similar characteristic features. All the rocks investigated are composed of two structurally different portions: regular ellipsoidal and spherical segregations containing forsterite, magnetite, phlogopite and sometimes calcite and apatite, and a substantially calcitic matrix containing some apat~e, sifica~e and opaque components. These two portions correspond to phoscorite and s6vi~e fractions separated during the crystallization of an initial melt of mixed composition. The structures described are regarded as evidence of liquid immiscibilityprocesses in the formation of s6vite and phoscorite rock .~eries which were promoted by limited solubility of ore-silicate and carbonate fractions. Crystellization differentiation by early settling of apatite, silicate and ore minerals plays a leading role in th~ fractionation of substantially sOvitic solutions that contain comparatively small amounts of silicate, c¢'e and phosphate components,
A. V. Lapin, Institute of Mineralogy, Geochemistry and Crystal Chemiswy of Rare E~ements, Moscow, U.S.S.R.; H. Varaainen, Rautaruukki Oy, SF-96100 Rovaniemi 10~ Finland; 22nd April, 1982.
In many carbonatite massifn, s6vites (caleitic carbonatites) are closely associated with the magnetite-silicate--apatite rocks known as phoscorites or camaforites. These two rocks are peneeontempor,~neous in formation and similar in geological position and mineral paragenesis (Borodin eta!. 1973; Russel et al. 1954; Vartiainen & Paarma 1979.; Vartiainen 1980). Known examples of such massifs are Palabora in South Africa; Sokli in Finland; Kovdor, Vuorijiirvi and Essei in U.S.S.R. The close association of carbonatites with phoscorites and the genetic ~e!ationship between them is one of the more interesting, but ~ess investigated problems in carbOnatite petrology. The present paper approaches this problem mainly on the basis of investigations performed on the massifs of Sokli and Vuorijiirvi, both of which belong to the alkaline rock province of Kola (Fig. 1).
Phoscofite-S6vite relatioaships in
carbonffe complexes The known modes of occurrence ef z6vitic rocks and phoscorites in carbonatite complexes, can be summ=fized as follows: (1) zonal! setting of phoscorites around a s6vitic core (Palabora); (2) interbanding of phoscorites and s6~htic rocks usually combined with brecciation ol! phoscorites by
carbonatites within large bodies (Kovdor); (3) blocks of different size and lense-like bodies of phoscorites in sOvitic cores and dikes (Sokli, Vuorijiirvi, Essei). The mineral parageneses of phoscorites and sSvites are characterized by the same main minerals, i.e. calcite, apatite, forsterite, magnetite and phlogopite. The rocks differ only in the relative proportions of these minerals and, primarily in the ratios between calcite and ore-silicatephosphate components. A full gradational series between phoscorites and s6vites anay develop during a long and tranquil evolution phase. Generally, however, owing to the complicated evolution of carbonatite complexes, phoscorites and s6vitic rocks occur in geological settings that are characterized by such strong brecciation, veining. assimilation and hydrothermal alteration that their genetic relations are, hard to establish. In every case, geological data suggest that these rocks represent magmatic suites (Lapin 1978; Vartiainen 1980) and this i,~;in agreement with the experimental data (Wyllie 1966).
Spherulitic rocks Th~~ , rocks displaying spherulitic structures are composed of regular spherical or e~iips~ida~ radia! aggregates of magnetite and forsterite embed-
A. V. Lapin & H. Vartiainen
54
LITHOS 16 (1983)
,~.
x,~ NORWAY
;INLAND ~ ~
_
(
-\
L
KOLA PENINSULA KHIBINA
~
@
. KOVDOR
A~r,
I ~e
@ _ "'x\,, • -VU0Rt_e___
\e
IIVAAR~ ~ F"J
\ o
~o
Fig. 2. Forsterite-magnetite spherulites in calcitic matrix. One nieol. Vuorij~irvi, Tuhtavaara. Scale bar, 1.0 ram.
7ORJA. . . . . . . . . . WHITE SEA
!"-"
~o KM
@ Alkolmecomplexes of the Kota provinte
big. I. Locaqon of the Sokli and Vuorijiirvi massifs in the alkaline rock p~'ovince of Kola.
ded in a carbonate-rich matrix. In the Vuorij~irvi massif th,; rocks of spherulitic struc.turt: occur in the area of Tuhtavaara, where they form blocks m,zasuring up to six metres in calcite-bearing forsterite-magnetite phoscorite. The phoscorites are intcr,~ected by s6vitic dikes. The spherulites consist of radial aggregates of forsterite and magnetite enclosed in a calcite matrix with some phlogopite. The spheruliles, which are 4--5 mm in diameter, are characterized by zonal texture (Fig. 2). The external zone cor~sists of radially oriented forsterite and magnetite grains. The same minerals, often mixed with phlogopite, make up the ,:ore, where they do not have radial orientation, but often ;how an intergrowth texture similar to a eutecfic one. Spherulites with cores consisting ~lly of magnetite are fairly common, whereas cores of apatite with minor forsterite and magnerite admixtures are more rare. The majority of the spherulites have a narrow internal concentric zone of phlogopite. In some spherulites this zone is within a radially o~iented aggregate of forsterice and magnetite and seems to have stopped the ~'adial crystallization of these minerals (Fig. 3). In c>lhers the phlogopite zone separates the external parts of the spheru!ites from the core.
The formation of the phlogopite zone is bound up with the fact that during crystallization of forsterite and magnetite the impurities of K, AI and other components that are not a part of these minerals are driven back and a zone enriched in these components is formed at the front of crystallization. In the outer parts of the spherulites some grains of olivine and magnetite were nucleated with a non-radial orientation, but these have stopped growing at an early stage giving place to the radially oriented grains. This indicates that these spherical aggregates represent spherulites which crystallized from the periphery to the centre, which in turn confirms an origin by liquid immiscibility (Grigoriev 1966). Similar spherulitic structures are encountered at Sokli in the forsterite-rich phoscorite formerly designated an olivine orbicular rock (Vartiainen 1980). The rocks of spherulitic structure were found as blocks measuring up to four metres in olivine s6vites of Stage II along the eastern border of the magmatic core. The spherulites are ellipsoidal, their long axis being 8-10 mm and their minor axis 6-8 ram. They consist mainly of forsterite and magnetite and are embedded in a s6vitic matrix with significant amounts of apatite, forsterite and magnetite (Fig. 4). Completely developed spherulites have zonal structl~re, their outer zone consisting of radially oriented grams of forsterite followed by a zone of radially oriented grains of forsterite and magnetite. The core is composed of the above minerals or of magnetite only (Fig. 5) and thus does not usually show radial orientation. Apatite often occurs in the internal parts of the sphelulites on the border between the core and the radial forsterite-mag-
LITHOS 16 (1983)
Orbicuiar and spherulitic carbonatites
55
Fig. 3. Concentric phlogopite zone (Ph) within a radial textured spherulite composed of forsterite and magnetite. One nicol. Vuorijiirvi, Tuhtavaara. Scale bat, 1.0 ram.
netite zone. The texture of the spherulites often exhibits a pulsation pattern of cT:y,stallization with a zone containing several rhythmically repeated subzones of similar composition and texture (Fig. 6). The spherulites exhibit sphe;roidal cleavage which has given rise to a conchoidal texture.
Orbicular rocks
,fig. '. Forsterite-magnetitespheruli~iesin sificos6viticmatrix. One nicol. Sokli, drill hole 434. Sc~,I!e bar, 2.0 ram.
On the basis of the texture and mineral composition of the orbicules and matrix, three types of orbicular rock can be distinguished: 1. Rocks with c|lipsoidal, essentially forsteritemagnetite orbicules of concentric zonal texture in calcite or in a calcite-magnetite matrix. 2. Rocks with ellipsoidal forstefite-tetraferriphlogopite-magnetite-calcite orbicules of concentric zonal structure in a calcite-magnetite matrix. 3. Rocks with ellipsoidai calcite-phlogopite-magnetite orbicules in a carbonate matrix. The first type occurs in the Vuonj~irv;, massif. This phoscoritic rock occurs as blocks up to 0.5 metres in diameter in silicos6vites, containing forsterite, magnetite, apatRe and phlogopite. The orbicules, which consist mainly of forsterite and magnetite, are embedded in a calcite matrix and exhibit: an ellipsoid~l form with parallel orientation ,of long axes (Fig. 7). The average length
Fig. 5. Zoned structure in forsterite-m~gnetitesphe~lite. One nicol. Soldi, drill hole 434. Scale bar, ; 0 ram. .
of the long axes is from 10 to 15 mm and that of the minor axes from 4 to 6 ram, The para|lelism of the orbicules is due to their plastic deformation (Fig. 7). TEe internal structure of the orbicules is char-
56
A. V. Lapin & H. Vartiainen
big. 6. Rhythmically repeated subzones in forsterite-magnetite sphcrulitc. One nicol. Sokli, drill hole 434. Scale bar, 1.0 ram.
t.ig. 7 ('onccr~lrically zoned forsterite-magnetite orbiculcs embcddt d in s6vitic matrix. One nicol. Vuorijarvi, Tuhtavaara. Scale bar, 2.0 mm.
Fig 8 Concentrically zoned forstefite-~etraferriphlogopitemag~lctite-calcite ~rbi,:ules in phoscoritk (calcite-magnetite) matrix. Onc nicol. Soi~li, drill hole 519. Scale bar, 2.1) ram.
LITHOS
16 (1983)
acterized by multiple alternation of concentric zones of forsterite and magnetite. The rhythmical structure is usually more evident in the outer parts of the orbicules, where the narrow monomineral forsterite and magnetite zones alternate. In the inner parts of the orbicules this feature is not so well developed and some zones have a bimineral forstefite-magnetite composition. Pyrrhotite is often present as small blebs and lenses in the magnetite zones of the orbicules. The orbicules are rimmed by a drusy magnetite zone composed of small idiomorphic magnetite crystals growing towards the interstitial calcitic aggregate. The druse rims sometimes exhibit a bipartite structure, the druses of forsterite crystals growing on the surface of the magnetite. In the centre of some orbicules there are round calcite segregations separated from the surrounding zones by a drusy magnetite rim similar to that observed on the periphery of the orbicules. Rhythmical concentric magnetite zones are sometimes present in the calcitic cores. Types 2 and 3 are encountered in the Sokli massif on the eastern border of its magmatic core and in s6vitic shoots in the metacarbonatite area. Orbicular phoscorite blocks some tens of centimetres i~i size (type 2) contain regular ellipsoidal orbicule~ with zonal texture, the long axes being from 4 to 6 mm and the short axes from 3 to 4 mm (Fig. 8). The host rock of the orbicular phoscoriJte is s6vite of the magmatic Stage II with tetraferriphlogopite. The outer zone of the orbicules, which is composed o,f forster~te, is followed by tetraferriphlogopite and magnetite zones. The core consists of calcite with an admixture of tetraferriphlogopite and magnetite (Fig. 9). The orbicules being close to each other, the volume of the matrix is small (Fig. 8) The amtrix is composed mainly of calcite an, l magnetite with subordinate forsterite and tetraferriphlogopite. It seems likely that the segregation of the orbicules was accompanied by the removal of interstitial liquid from the system resulting in a change in the initial proportions of the ~nagnetite-silicates and carbonate components of the matrix. The third orbicular rock type has been encountered in only one drill hole sectio~l at Sokli. This orbic~.dar structv-'ed s6vite occurs as a fragmentlike ,mit in magmatic s6vite of Stage IV. The orbi~0;ules atre ellipsoids often plastically deformed at their contacts. The orbicules are from 6 to 8 mm long and from 3 to 5 rnm wide. Their outer zones are composed mainly of tetraferripla-
LITHOS
Orbicular and spherulitic carbonatites 57
16 (1'~83)
Table I. Chemical comoositions in weight percentages of the spherulitic rocks of Vuorij/irvi and Sokli and of the orbicular rock of Vuorijitrvi. 4
5
6
34.50 0.48 0.85 12.23 4.92 0.88 38.92 2.02 0.15 0.26 1.48 2.64 0.18 1.98 0.19
12.38 !.30 0.85 22.13 6.10 1.05 17.46 17.67 0.42 0.65 2.48 1.72 0.20 15.68 0.16
16.54 i.92 2.49 27.88 ~9.94 0.81 21.7! 4.13 0.09 0.10 0.14 0.93 0.04 2.67 1.36
-O = S - O = F~
100.32 100.50 99.81 100.40 100.27 0.05 . . . . 0.07 0.10 0.07 0.08
100.75 0.68 -
Total
100.27 100.47 99.71
100.07
SiOz TiOz
gl203 Fe203 leo MnO MgO CaO Na20 K20 P:Os+ HzO F CO2 S, S03
1
2
3
15.73 1.52 1.15 32.64 16.05 0.78 21.57 5.04 0.12 0.37 0.26 1.08 tr. 3.92 0.09
17.10 24.03 1,72 0.85 0.84 0.22 42.40 15.43 12.78 6.60 0.78 0.78 21.06 29.26 !.42 8.57 0.13 0.30 0.20 0.53 0.14 0.14 0.69 3.25 0.18 0.2~ 0.86 8.03 0.20 0.19
100.33 100.19
Fig. 9. One orbicule from the orbicular rock of Fig, 8. Scale bar, 1.0 mm.
1. Bulk composition of spherulitic rock. Vuorij~irvi, Tuhta. vaara. 2. Forsterite-magnetite spherulites of the former rock. 3. Bulk composition of spherulitic rock. Sokli, driil hole 434.4. Forsterite-magnetite spherulites of the former .,rock. 5. S6vi~ic matrix of the former rock. 6. Bulk composition of orbicular rock. Vuorij/irvi, Tuhtavaara.
logopite and magnetite and subordinate richterite. The central pans are preGorainantly calcite with small amounts of the same minerals as in the outer zones (Fig. 10). The orbicules are enclosed in a calci~ic groundmass bearing some magnetite, tetraferciphlogopite, richterite and apatite. The outer surface of the orbicules is usually covered with druses of small crystals of magnetite crystallized from the matrix.
Chemistry The chemical composition of 0~oherulitic rocks, spherulites and carbonatite matrix is given in Table 1. The spherulite rocks of the Vuorijiirvi massif were not analysed for the carbonate matrix, but this is evidently similar to s6vitic carbonatite in composition. Fractionation of the o~esilicate and carbonate liquids in the spherulitic rocks of Vuorij~irvi is fairly complete, as demonstrated by the fact that the matrix, occupying only a small portion, has an essentially calcitic composition, whereas forstefite-magnetite
Fig. 10. Tetraferdphlogopite-magnetite-calcite orbicules in s6vitic matrix. One mcoi. Sokli, drill hole 355. Scale bar, 2.0 mm.
spherulites (Table 1/2) contain only traces of carbonates. The fractionation that took place during the evolution of the spherulitic rocks of Sokli can be illustrated in a trianga~iar diagram (Fig. 11). The calculation was done as suggested by Vartiainen (1980), except that forsterite was the only silicate minera' present. If the composition otr the whole rock is regarded as the bulk composition of the unfractionated melt, then the compositions of the spherulites and the matrix can be taken as those of i~s fractionated portmnso The spherulite composition in Fig. 11 plots near the opaques silicate, ~.e. the phoscorite apex, and the c~mposition of the matrix towards silicos6vite0, and near to the crystallization path of magmatk carbonatires. Henc,:, the chemical fractionatior~ observed in the spherulitic rock of Sokli is in accordance
58 A. V. Lapin & H. Vartiainen
Ln'nos 16 0983)
DOLOMITP:.
A
/ OPAOUES
~
~
._~
~
~
~
,
.
CALCITE
Fig. 11. Triangular diagram showing variation in weight perccntages of the principal oxides in the spherulitic rock of Sokli, calculated as proposed by Vartiainen (1980). Numbers: 3, bulk of spherulitic rock; 4, spherulites; 5, matrix; ! phoscorites of magmatic Stage i; I!, srvites and silicosrvites of magmatic Stagc ll; curve, crystallization path of the early magmatic carbonatitcs
with the crystallization differentiation of the magmatic carbonatites. The chemical composition of the orbicular rock of Vuorijfirvi is given in Table 1. It is rather similar to that of the b~dk composition of the spherulitic rock. The fractionat~on of the ore silicate and carbonate components in the orbicular rock is fairly complete, because the pre':%minant part of the carbonate material is involved in interstitial liquid of substantially calcitic composition. The orbicular rock and the spherulitic rock (Table 1/1 and 6) contain only *.races of carbonate matrix, probably owi~ag to disturbance in the initial proportions of carbonate and ore-silicate components.
Discussion The association of phoscorites arm s6vites, their pattern of geological setting in complex ultrabasic alkaline massifs, the similarity of their mineral paragenests and their close ge ~logical age indicate that, genetically, they are c!osely related. The geological data and experime,~tal result,,~ suggest a magmatic genesis for carbon~tites, i.e that they crystallized from a specific, rather mobile me~t enriched in volatile components (Wyllie 1966; Lapin 1978; unpublished C-O isotopes work, Lapin). Taking into accoun: the fact that carbonatites (s6vites) usually predominate over phoscorites in quantity, one may sappose that
the i~,:ter were formed as a result of carbonatite differentiation, i.e. ore (magnetite and other opaques) silicate-phosphate separation. When discussing the mode of differentiatioa of phoscorites and s0vites, two possible processes can be proposed: 1) gravitational settling of an apat~te-magnetite-silicate fraction from the initial carbonatite melt, (2) phoscorite and s0vite fractionation by liquid immiscibility from a carbonatite melt enriched in phosphorus, silicate arid ore components. Limited mutual solubility of a carbonate and ore-silicate-phosphate liquid (Fisher 1950) promotes the liquid immiscibility process. The spherulitic and orbicular structures in phoscorites and srvites described here give direct geological and petrographical evidence pertinent to this problem. The spherulitic and orbicular rocks have essentially two structural components: spherulites and orbicules consisting mainly of forsterite and magnetite with subordinate apatite, phlogopite and calcite; and interstitial m:,,trix. Calcite is the predominant mineral: in the matrix, which is therefore s6vitic in composition. Such structures can be attributed to the segregation of the initial melt imo essentially ore-silicate (phoscoritic) and carbonatic (s6vitic) fractions. The drops of heavier and more viscous ore-silicate liquid separate first from the initial melt and give rise to a carbonaterich, rather mobile melt with tow viscosity. The differences in viscosity and density of these liquids and their limited mutual solubility make the fractionation of the liquids possible. The separation of the ore-silicate fraction from the more mobile carbonate melt apparently creates conditions favourable for the conservation of ore silicate drops and for the development of spheruiitic and orbicular structures, which would not have been feasible under conditions of equilibrium. Consequently, the present phoscoritic spherulite/sOvitic matrix ratio need not correspond to the composition of the initial melt, which had a higher concentration of carbonate components. Petrographically this is shown in places where the orbicules are so close to each other that the carbonate ~interstitiai liquid seems to have been squeezed out by plastically deformed orbicules. On the other hand, the same structures demonstrate that dense ore-sificate drops can easily be segregated from a low-viscosiB, melt. Depending on the composition of the inifia| melts, magmatic differentiation lea& to various proportions of ore-silicate components in residu-
~I:II~ITHOS 16 (1983)
Orbicular and spherulitic carbonat;tes 59
!
al liquids. In some cases magnetite and fors~ erite undergo almost complete fraetionation and become concentrated in the ore-silicate liquid; in others a significant proportion of Iorsterite, and especially of magnetite, remains dissolved in the carbonate liquid. The limited mutual miscibility of carbonate and ore--silicate liquids is well demonstrated by the orbicular structure of phescorite. The ellipsoidal form of orbieules and the character of their plastic deformation proves that before crystallization the melt was heterogeneous and con.si:;ted of drops of more viscous ore-silicate liquid in a mobile and fiuidal calcitic liquid. Concerning; the spherulites, crystallization from the peri.. phery to the centre shows the existence of ~ boundary surface between two liquids, i.e. exist.ence of partly crysta!lized drops. Calcite segregations in the orbicules suggest that some of the carbonate material was either dissolved in drops of ore--silicate liquid, or that carbonate melt was captured during the evolution of drops. The occurrence of sulphides in the olivine nodules i~l orbicular peridotite can be attributed to sub phide !iquation, which preceded the rapid crystallization of the olivine nodules (Papunen 1980). Note that when the initial melt segregated imo ore,-silicate and carbonate liquids, apatite preferred the carbonate fraction. In some rocks, sphe~lites of forsterite-magnetite composition may almos~ totally lack apatite. Apatite, however, is present in the matrix, tt~e composition of which varies from calcitic to apatitic. It is interesting that the apatite which occurs in the matrix with calcite usually forms aggregates isolated from calcite. The chemistry of the spherulitic and orbicular rocks corroborates the geological and petrographical evidence of fractionatiot~ of ore-silicate and carbonate liquid from an ir~i~tiaI melt. The chemical composition of the sphe~'ulites and orbicules is analogous to that of pho:;corite ~nd the composition of the matrix to that of s6vite (Vuorij~trvi) or silicos6vite (Sokli, Fig. 11). Liquid immiscibility is favoured as a mechanism of separation in ore-silicate-phc~sphate and carbonate fractions from melts e,nriched in oresilicate components. When the crystallization of the ore-silicate drops comes to an end while the carbor, ate liquid still exists, fractionation proceeds most likely by crystallization differentiation. The importance of the de,,;cribed spherulitic and orbicular structures lies in the fact that
they give evidence of the early magmatic history of the phoscoritic and s6vitic rocks, evidence which is usually concealed by later crystallizat:~on and other processes. The spherulite and orbi:u!at structures are preserved only locally in non~,quilibrium conditions where the melt is kept in the liquidus area (e.g. one liquid is removed from the range of certain volume or one liquid is quickly cooled). When crystallization of magmatie system takes place under equilibrium conditions, as one liquid is exhau~,ted (a phoscolite one), crystallization proceeds according to the common sequence by the processes of crystallization differentiation. Thus liquid immisdbility does not exclude, but in coatrast implicates also participation of other mechanisms in formation of phoscorite-sOvite rock series. Crystallization differentiation probably plays an important role in fractionation of substantially carbonatic melts with rather small amounts of silicate, phosphate and ore components, qThe most obvious differentiation process for sach melts is the early settling of apatite, ore (rnagne~ite and other opaques) and silicate minerals and the separation of carbonatite liquid by means of filter-pressing. It should be emphasized that the process of crys.tallization differentiation in carbonatite melts ,.'an be quite efficient, because the carbonatite m~gmas are extremely mobile and the crystals can settle quickly. At" ".,owledgements'. - We are extremely grateful to Dr. T. A.
H/ikli for his critical reading of the manuscripl and for the numerous suggestions he made for its improvement. The map and diagra:n were drawn by Ms. M. Lantto. Mrs. Gillien H/ikli corrected the language of the manuscript. We are indebted to Prof. L. S. Borodin, Laboratory Chief of the Institute o~" Mineralogy, Geochemistry and Crystallochemistry of Rare Elements, U.S.S.R., and to Dr. J. Nuutilainen, Manager of the Exploration of Rautaruukki Co.. for giving us permission to have the paper published.
References Bor~din, L. S., Lapin, A. V. & Kharc.~c,~kov, A. G 1973: Rare metal camaphorites. Nauka, Moscow. 176 pp. (ip Russian). Fisher, R. 1950: Entmischungen in Schmeizer aus S~:hv,ermetaloxyden, Silikaten and Phosphate, lhre geochemische und lagerst~ttenkundliehe Bedeutung, Neues Jahrb. Mireral. Monatsh. 3, 315--364. Grigoriev, D. P. I S . Application of mineral ont,3geny for petrography. Trudu V';EGEI 65, 23-35 (in Russian). Lapin, A. V. 1978: On ~ m e problems of ge'le~is of carbonatires. Geol. rudn. mestor. 20, 33-45 (in Ru~si:~.n). Papunen, H. 1980: The Kylmiikosld nickel-co,per deposit in southwestern Finland. Bull. Geol. Soc. Finland 52, ~29-145. Russel, H. D., Hiemstra, S° A. & Oroenveld, Do 1954: The
60
A . V. L a p i n & H. Vartiainen
ln~neralogy and petrology of the carbonatite at Loolekop, Eastern Transvaal. Geol. Soc. S. Africa, Trans. 57, 197-208. Vartiainen, H. 1980: The petrography, mineralogy and petrochemistry of the Sokl~ c~rbonatite massif, northern Finland. Geol. Surv. Finland. Bull. 313. 126 pp. Vartiainen, H. & Paarma, H. 1979: Geological characteristics
UTnOS 16 (1983) of the Sokli carbonatite complex, Finland. Econ. Geol. 74, 1296-1306. Wyllie, P. J. 1966: Experimental studies of carbonatite problem: The origin and differentiation of carbonatite magmas, pp. 311-352 in Tuttle, O. F. & Gittins, J. (eds.), Carbonatires, John Wiley & Sons, New York.
V
Orbicular and spheruliitic carbonatites from Sokli and Vuorijiirvi A. V. LAPIN & H. VARTIAINEN
L1THOS
Lapin, A. V. & Vartiainen, H. 1983 01 15: Orbicular and spherulitic carbonatites from Soldi and .Vuorijiirvi. L/thos, Vol. 16, pp. 53--60. Osio. ISSN 0024-4937. The main types of spherulitic and orbicular structures in carbonatites of Sokli (Finland) and Vuorijgrvi (U.S.S.R.) are der,cribed. The structures have small-scale morphological differences although generally they show fairly similar characteristic features. All the rocks investigated are composed of two structurally different portions: regular ellipsoidal and spherical segregations containing forsterite, magnetite, phlogopite and sometimes calcite and apatite, and a substantially calcitic matrix containing some apat~e, sifica~e and opaque components. These two portions correspond to phoscorite and s6vi~e fractions separated during the crystallization of an initial melt of mixed composition. The structures described are regarded as evidence of liquid immiscibilityprocesses in the formation of s6vite and phoscorite rock .~eries which were promoted by limited solubility of ore-silicate and carbonate fractions. Crystellization differentiation by early settling of apatite, silicate and ore minerals plays a leading role in th~ fractionation of substantially sOvitic solutions that contain comparatively small amounts of silicate, c¢'e and phosphate components,
A. V. Lapin, Institute of Mineralogy, Geochemistry and Crystal Chemiswy of Rare E~ements, Moscow, U.S.S.R.; H. Varaainen, Rautaruukki Oy, SF-96100 Rovaniemi 10~ Finland; 22nd April, 1982.
In many carbonatite massifn, s6vites (caleitic carbonatites) are closely associated with the magnetite-silicate--apatite rocks known as phoscorites or camaforites. These two rocks are peneeontempor,~neous in formation and similar in geological position and mineral paragenesis (Borodin eta!. 1973; Russel et al. 1954; Vartiainen & Paarma 1979.; Vartiainen 1980). Known examples of such massifs are Palabora in South Africa; Sokli in Finland; Kovdor, Vuorijiirvi and Essei in U.S.S.R. The close association of carbonatites with phoscorites and the genetic ~e!ationship between them is one of the more interesting, but ~ess investigated problems in carbOnatite petrology. The present paper approaches this problem mainly on the basis of investigations performed on the massifs of Sokli and Vuorijiirvi, both of which belong to the alkaline rock province of Kola (Fig. 1).
Phoscofite-S6vite relatioaships in
carbonffe complexes The known modes of occurrence ef z6vitic rocks and phoscorites in carbonatite complexes, can be summ=fized as follows: (1) zonal! setting of phoscorites around a s6vitic core (Palabora); (2) interbanding of phoscorites and s6~htic rocks usually combined with brecciation ol! phoscorites by
carbonatites within large bodies (Kovdor); (3) blocks of different size and lense-like bodies of phoscorites in sOvitic cores and dikes (Sokli, Vuorijiirvi, Essei). The mineral parageneses of phoscorites and sSvites are characterized by the same main minerals, i.e. calcite, apatite, forsterite, magnetite and phlogopite. The rocks differ only in the relative proportions of these minerals and, primarily in the ratios between calcite and ore-silicatephosphate components. A full gradational series between phoscorites and s6vites anay develop during a long and tranquil evolution phase. Generally, however, owing to the complicated evolution of carbonatite complexes, phoscorites and s6vitic rocks occur in geological settings that are characterized by such strong brecciation, veining. assimilation and hydrothermal alteration that their genetic relations are, hard to establish. In every case, geological data suggest that these rocks represent magmatic suites (Lapin 1978; Vartiainen 1980) and this i,~;in agreement with the experimental data (Wyllie 1966).
Spherulitic rocks Th~~ , rocks displaying spherulitic structures are composed of regular spherical or e~iips~ida~ radia! aggregates of magnetite and forsterite embed-
A. V. Lapin & H. Vartiainen
54
LITHOS 16 (1983)
,~.
x,~ NORWAY
;INLAND ~ ~
_
(
-\
L
KOLA PENINSULA KHIBINA
~
@
. KOVDOR
A~r,
I ~e
@ _ "'x\,, • -VU0Rt_e___
\e
IIVAAR~ ~ F"J
\ o
~o
Fig. 2. Forsterite-magnetite spherulites in calcitic matrix. One nieol. Vuorij~irvi, Tuhtavaara. Scale bar, 1.0 ram.
7ORJA. . . . . . . . . . WHITE SEA
!"-"
~o KM
@ Alkolmecomplexes of the Kota provinte
big. I. Locaqon of the Sokli and Vuorijiirvi massifs in the alkaline rock p~'ovince of Kola.
ded in a carbonate-rich matrix. In the Vuorij~irvi massif th,; rocks of spherulitic struc.turt: occur in the area of Tuhtavaara, where they form blocks m,zasuring up to six metres in calcite-bearing forsterite-magnetite phoscorite. The phoscorites are intcr,~ected by s6vitic dikes. The spherulites consist of radial aggregates of forsterite and magnetite enclosed in a calcite matrix with some phlogopite. The spheruliles, which are 4--5 mm in diameter, are characterized by zonal texture (Fig. 2). The external zone cor~sists of radially oriented forsterite and magnetite grains. The same minerals, often mixed with phlogopite, make up the ,:ore, where they do not have radial orientation, but often ;how an intergrowth texture similar to a eutecfic one. Spherulites with cores consisting ~lly of magnetite are fairly common, whereas cores of apatite with minor forsterite and magnerite admixtures are more rare. The majority of the spherulites have a narrow internal concentric zone of phlogopite. In some spherulites this zone is within a radially o~iented aggregate of forsterice and magnetite and seems to have stopped the ~'adial crystallization of these minerals (Fig. 3). In c>lhers the phlogopite zone separates the external parts of the spheru!ites from the core.
The formation of the phlogopite zone is bound up with the fact that during crystallization of forsterite and magnetite the impurities of K, AI and other components that are not a part of these minerals are driven back and a zone enriched in these components is formed at the front of crystallization. In the outer parts of the spherulites some grains of olivine and magnetite were nucleated with a non-radial orientation, but these have stopped growing at an early stage giving place to the radially oriented grains. This indicates that these spherical aggregates represent spherulites which crystallized from the periphery to the centre, which in turn confirms an origin by liquid immiscibility (Grigoriev 1966). Similar spherulitic structures are encountered at Sokli in the forsterite-rich phoscorite formerly designated an olivine orbicular rock (Vartiainen 1980). The rocks of spherulitic structure were found as blocks measuring up to four metres in olivine s6vites of Stage II along the eastern border of the magmatic core. The spherulites are ellipsoidal, their long axis being 8-10 mm and their minor axis 6-8 ram. They consist mainly of forsterite and magnetite and are embedded in a s6vitic matrix with significant amounts of apatite, forsterite and magnetite (Fig. 4). Completely developed spherulites have zonal structl~re, their outer zone consisting of radially oriented grams of forsterite followed by a zone of radially oriented grains of forsterite and magnetite. The core is composed of the above minerals or of magnetite only (Fig. 5) and thus does not usually show radial orientation. Apatite often occurs in the internal parts of the sphelulites on the border between the core and the radial forsterite-mag-
LITHOS 16 (1983)
Orbicuiar and spherulitic carbonatites
55
Fig. 3. Concentric phlogopite zone (Ph) within a radial textured spherulite composed of forsterite and magnetite. One nicol. Vuorijiirvi, Tuhtavaara. Scale bat, 1.0 ram.
netite zone. The texture of the spherulites often exhibits a pulsation pattern of cT:y,stallization with a zone containing several rhythmically repeated subzones of similar composition and texture (Fig. 6). The spherulites exhibit sphe;roidal cleavage which has given rise to a conchoidal texture.
Orbicular rocks
,fig. '. Forsterite-magnetitespheruli~iesin sificos6viticmatrix. One nicol. Sokli, drill hole 434. Sc~,I!e bar, 2.0 ram.
On the basis of the texture and mineral composition of the orbicules and matrix, three types of orbicular rock can be distinguished: 1. Rocks with c|lipsoidal, essentially forsteritemagnetite orbicules of concentric zonal texture in calcite or in a calcite-magnetite matrix. 2. Rocks with ellipsoidal forstefite-tetraferriphlogopite-magnetite-calcite orbicules of concentric zonal structure in a calcite-magnetite matrix. 3. Rocks with ellipsoidai calcite-phlogopite-magnetite orbicules in a carbonate matrix. The first type occurs in the Vuonj~irv;, massif. This phoscoritic rock occurs as blocks up to 0.5 metres in diameter in silicos6vites, containing forsterite, magnetite, apatRe and phlogopite. The orbicules, which consist mainly of forsterite and magnetite, are embedded in a calcite matrix and exhibit: an ellipsoid~l form with parallel orientation ,of long axes (Fig. 7). The average length
Fig. 5. Zoned structure in forsterite-m~gnetitesphe~lite. One nicol. Soldi, drill hole 434. Scale bar, ; 0 ram. .
of the long axes is from 10 to 15 mm and that of the minor axes from 4 to 6 ram, The para|lelism of the orbicules is due to their plastic deformation (Fig. 7). TEe internal structure of the orbicules is char-
56
A. V. Lapin & H. Vartiainen
big. 6. Rhythmically repeated subzones in forsterite-magnetite sphcrulitc. One nicol. Sokli, drill hole 434. Scale bar, 1.0 ram.
t.ig. 7 ('onccr~lrically zoned forsterite-magnetite orbiculcs embcddt d in s6vitic matrix. One nicol. Vuorijarvi, Tuhtavaara. Scale bar, 2.0 mm.
Fig 8 Concentrically zoned forstefite-~etraferriphlogopitemag~lctite-calcite ~rbi,:ules in phoscoritk (calcite-magnetite) matrix. Onc nicol. Soi~li, drill hole 519. Scale bar, 2.1) ram.
LITHOS
16 (1983)
acterized by multiple alternation of concentric zones of forsterite and magnetite. The rhythmical structure is usually more evident in the outer parts of the orbicules, where the narrow monomineral forsterite and magnetite zones alternate. In the inner parts of the orbicules this feature is not so well developed and some zones have a bimineral forstefite-magnetite composition. Pyrrhotite is often present as small blebs and lenses in the magnetite zones of the orbicules. The orbicules are rimmed by a drusy magnetite zone composed of small idiomorphic magnetite crystals growing towards the interstitial calcitic aggregate. The druse rims sometimes exhibit a bipartite structure, the druses of forsterite crystals growing on the surface of the magnetite. In the centre of some orbicules there are round calcite segregations separated from the surrounding zones by a drusy magnetite rim similar to that observed on the periphery of the orbicules. Rhythmical concentric magnetite zones are sometimes present in the calcitic cores. Types 2 and 3 are encountered in the Sokli massif on the eastern border of its magmatic core and in s6vitic shoots in the metacarbonatite area. Orbicular phoscorite blocks some tens of centimetres i~i size (type 2) contain regular ellipsoidal orbicule~ with zonal texture, the long axes being from 4 to 6 mm and the short axes from 3 to 4 mm (Fig. 8). The host rock of the orbicular phoscoriJte is s6vite of the magmatic Stage II with tetraferriphlogopite. The outer zone of the orbicules, which is composed o,f forster~te, is followed by tetraferriphlogopite and magnetite zones. The core consists of calcite with an admixture of tetraferriphlogopite and magnetite (Fig. 9). The orbicules being close to each other, the volume of the matrix is small (Fig. 8) The amtrix is composed mainly of calcite an, l magnetite with subordinate forsterite and tetraferriphlogopite. It seems likely that the segregation of the orbicules was accompanied by the removal of interstitial liquid from the system resulting in a change in the initial proportions of the ~nagnetite-silicates and carbonate components of the matrix. The third orbicular rock type has been encountered in only one drill hole sectio~l at Sokli. This orbic~.dar structv-'ed s6vite occurs as a fragmentlike ,mit in magmatic s6vite of Stage IV. The orbi~0;ules atre ellipsoids often plastically deformed at their contacts. The orbicules are from 6 to 8 mm long and from 3 to 5 rnm wide. Their outer zones are composed mainly of tetraferripla-
LITHOS
Orbicular and spherulitic carbonatites 57
16 (1'~83)
Table I. Chemical comoositions in weight percentages of the spherulitic rocks of Vuorij/irvi and Sokli and of the orbicular rock of Vuorijitrvi. 4
5
6
34.50 0.48 0.85 12.23 4.92 0.88 38.92 2.02 0.15 0.26 1.48 2.64 0.18 1.98 0.19
12.38 !.30 0.85 22.13 6.10 1.05 17.46 17.67 0.42 0.65 2.48 1.72 0.20 15.68 0.16
16.54 i.92 2.49 27.88 ~9.94 0.81 21.7! 4.13 0.09 0.10 0.14 0.93 0.04 2.67 1.36
-O = S - O = F~
100.32 100.50 99.81 100.40 100.27 0.05 . . . . 0.07 0.10 0.07 0.08
100.75 0.68 -
Total
100.27 100.47 99.71
100.07
SiOz TiOz
gl203 Fe203 leo MnO MgO CaO Na20 K20 P:Os+ HzO F CO2 S, S03
1
2
3
15.73 1.52 1.15 32.64 16.05 0.78 21.57 5.04 0.12 0.37 0.26 1.08 tr. 3.92 0.09
17.10 24.03 1,72 0.85 0.84 0.22 42.40 15.43 12.78 6.60 0.78 0.78 21.06 29.26 !.42 8.57 0.13 0.30 0.20 0.53 0.14 0.14 0.69 3.25 0.18 0.2~ 0.86 8.03 0.20 0.19
100.33 100.19
Fig. 9. One orbicule from the orbicular rock of Fig, 8. Scale bar, 1.0 mm.
1. Bulk composition of spherulitic rock. Vuorij~irvi, Tuhta. vaara. 2. Forsterite-magnetite spherulites of the former rock. 3. Bulk composition of spherulitic rock. Sokli, driil hole 434.4. Forsterite-magnetite spherulites of the former .,rock. 5. S6vi~ic matrix of the former rock. 6. Bulk composition of orbicular rock. Vuorij/irvi, Tuhtavaara.
logopite and magnetite and subordinate richterite. The central pans are preGorainantly calcite with small amounts of the same minerals as in the outer zones (Fig. 10). The orbicules are enclosed in a calci~ic groundmass bearing some magnetite, tetraferciphlogopite, richterite and apatite. The outer surface of the orbicules is usually covered with druses of small crystals of magnetite crystallized from the matrix.
Chemistry The chemical composition of 0~oherulitic rocks, spherulites and carbonatite matrix is given in Table 1. The spherulite rocks of the Vuorijiirvi massif were not analysed for the carbonate matrix, but this is evidently similar to s6vitic carbonatite in composition. Fractionation of the o~esilicate and carbonate liquids in the spherulitic rocks of Vuorij~irvi is fairly complete, as demonstrated by the fact that the matrix, occupying only a small portion, has an essentially calcitic composition, whereas forstefite-magnetite
Fig. 10. Tetraferdphlogopite-magnetite-calcite orbicules in s6vitic matrix. One mcoi. Sokli, drill hole 355. Scale bar, 2.0 mm.
spherulites (Table 1/2) contain only traces of carbonates. The fractionation that took place during the evolution of the spherulitic rocks of Sokli can be illustrated in a trianga~iar diagram (Fig. 11). The calculation was done as suggested by Vartiainen (1980), except that forsterite was the only silicate minera' present. If the composition otr the whole rock is regarded as the bulk composition of the unfractionated melt, then the compositions of the spherulites and the matrix can be taken as those of i~s fractionated portmnso The spherulite composition in Fig. 11 plots near the opaques silicate, ~.e. the phoscorite apex, and the c~mposition of the matrix towards silicos6vite0, and near to the crystallization path of magmatk carbonatires. Henc,:, the chemical fractionatior~ observed in the spherulitic rock of Sokli is in accordance
58 A. V. Lapin & H. Vartiainen
Ln'nos 16 0983)
DOLOMITP:.
A
/ OPAOUES
~
~
._~
~
~
~
,
.
CALCITE
Fig. 11. Triangular diagram showing variation in weight perccntages of the principal oxides in the spherulitic rock of Sokli, calculated as proposed by Vartiainen (1980). Numbers: 3, bulk of spherulitic rock; 4, spherulites; 5, matrix; ! phoscorites of magmatic Stage i; I!, srvites and silicosrvites of magmatic Stagc ll; curve, crystallization path of the early magmatic carbonatitcs
with the crystallization differentiation of the magmatic carbonatites. The chemical composition of the orbicular rock of Vuorijfirvi is given in Table 1. It is rather similar to that of the b~dk composition of the spherulitic rock. The fractionat~on of the ore silicate and carbonate components in the orbicular rock is fairly complete, because the pre':%minant part of the carbonate material is involved in interstitial liquid of substantially calcitic composition. The orbicular rock and the spherulitic rock (Table 1/1 and 6) contain only *.races of carbonate matrix, probably owi~ag to disturbance in the initial proportions of carbonate and ore-silicate components.
Discussion The association of phoscorites arm s6vites, their pattern of geological setting in complex ultrabasic alkaline massifs, the similarity of their mineral paragenests and their close ge ~logical age indicate that, genetically, they are c!osely related. The geological data and experime,~tal result,,~ suggest a magmatic genesis for carbon~tites, i.e that they crystallized from a specific, rather mobile me~t enriched in volatile components (Wyllie 1966; Lapin 1978; unpublished C-O isotopes work, Lapin). Taking into accoun: the fact that carbonatites (s6vites) usually predominate over phoscorites in quantity, one may sappose that
the i~,:ter were formed as a result of carbonatite differentiation, i.e. ore (magnetite and other opaques) silicate-phosphate separation. When discussing the mode of differentiatioa of phoscorites and s0vites, two possible processes can be proposed: 1) gravitational settling of an apat~te-magnetite-silicate fraction from the initial carbonatite melt, (2) phoscorite and s0vite fractionation by liquid immiscibility from a carbonatite melt enriched in phosphorus, silicate arid ore components. Limited mutual solubility of a carbonate and ore-silicate-phosphate liquid (Fisher 1950) promotes the liquid immiscibility process. The spherulitic and orbicular structures in phoscorites and srvites described here give direct geological and petrographical evidence pertinent to this problem. The spherulitic and orbicular rocks have essentially two structural components: spherulites and orbicules consisting mainly of forsterite and magnetite with subordinate apatite, phlogopite and calcite; and interstitial m:,,trix. Calcite is the predominant mineral: in the matrix, which is therefore s6vitic in composition. Such structures can be attributed to the segregation of the initial melt imo essentially ore-silicate (phoscoritic) and carbonatic (s6vitic) fractions. The drops of heavier and more viscous ore-silicate liquid separate first from the initial melt and give rise to a carbonaterich, rather mobile melt with tow viscosity. The differences in viscosity and density of these liquids and their limited mutual solubility make the fractionation of the liquids possible. The separation of the ore-silicate fraction from the more mobile carbonate melt apparently creates conditions favourable for the conservation of ore silicate drops and for the development of spheruiitic and orbicular structures, which would not have been feasible under conditions of equilibrium. Consequently, the present phoscoritic spherulite/sOvitic matrix ratio need not correspond to the composition of the initial melt, which had a higher concentration of carbonate components. Petrographically this is shown in places where the orbicules are so close to each other that the carbonate ~interstitiai liquid seems to have been squeezed out by plastically deformed orbicules. On the other hand, the same structures demonstrate that dense ore-sificate drops can easily be segregated from a low-viscosiB, melt. Depending on the composition of the inifia| melts, magmatic differentiation lea& to various proportions of ore-silicate components in residu-
~I:II~ITHOS 16 (1983)
Orbicular and spherulitic carbonat;tes 59
!
al liquids. In some cases magnetite and fors~ erite undergo almost complete fraetionation and become concentrated in the ore-silicate liquid; in others a significant proportion of Iorsterite, and especially of magnetite, remains dissolved in the carbonate liquid. The limited mutual miscibility of carbonate and ore--silicate liquids is well demonstrated by the orbicular structure of phescorite. The ellipsoidal form of orbieules and the character of their plastic deformation proves that before crystallization the melt was heterogeneous and con.si:;ted of drops of more viscous ore-silicate liquid in a mobile and fiuidal calcitic liquid. Concerning; the spherulites, crystallization from the peri.. phery to the centre shows the existence of ~ boundary surface between two liquids, i.e. exist.ence of partly crysta!lized drops. Calcite segregations in the orbicules suggest that some of the carbonate material was either dissolved in drops of ore--silicate liquid, or that carbonate melt was captured during the evolution of drops. The occurrence of sulphides in the olivine nodules i~l orbicular peridotite can be attributed to sub phide !iquation, which preceded the rapid crystallization of the olivine nodules (Papunen 1980). Note that when the initial melt segregated imo ore,-silicate and carbonate liquids, apatite preferred the carbonate fraction. In some rocks, sphe~lites of forsterite-magnetite composition may almos~ totally lack apatite. Apatite, however, is present in the matrix, tt~e composition of which varies from calcitic to apatitic. It is interesting that the apatite which occurs in the matrix with calcite usually forms aggregates isolated from calcite. The chemistry of the spherulitic and orbicular rocks corroborates the geological and petrographical evidence of fractionatiot~ of ore-silicate and carbonate liquid from an ir~i~tiaI melt. The chemical composition of the sphe~'ulites and orbicules is analogous to that of pho:;corite ~nd the composition of the matrix to that of s6vite (Vuorij~trvi) or silicos6vite (Sokli, Fig. 11). Liquid immiscibility is favoured as a mechanism of separation in ore-silicate-phc~sphate and carbonate fractions from melts e,nriched in oresilicate components. When the crystallization of the ore-silicate drops comes to an end while the carbor, ate liquid still exists, fractionation proceeds most likely by crystallization differentiation. The importance of the de,,;cribed spherulitic and orbicular structures lies in the fact that
they give evidence of the early magmatic history of the phoscoritic and s6vitic rocks, evidence which is usually concealed by later crystallizat:~on and other processes. The spherulite and orbi:u!at structures are preserved only locally in non~,quilibrium conditions where the melt is kept in the liquidus area (e.g. one liquid is removed from the range of certain volume or one liquid is quickly cooled). When crystallization of magmatie system takes place under equilibrium conditions, as one liquid is exhau~,ted (a phoscolite one), crystallization proceeds according to the common sequence by the processes of crystallization differentiation. Thus liquid immisdbility does not exclude, but in coatrast implicates also participation of other mechanisms in formation of phoscorite-sOvite rock series. Crystallization differentiation probably plays an important role in fractionation of substantially carbonatic melts with rather small amounts of silicate, phosphate and ore components, qThe most obvious differentiation process for sach melts is the early settling of apatite, ore (rnagne~ite and other opaques) and silicate minerals and the separation of carbonatite liquid by means of filter-pressing. It should be emphasized that the process of crys.tallization differentiation in carbonatite melts ,.'an be quite efficient, because the carbonatite m~gmas are extremely mobile and the crystals can settle quickly. At" ".,owledgements'. - We are extremely grateful to Dr. T. A.
H/ikli for his critical reading of the manuscripl and for the numerous suggestions he made for its improvement. The map and diagra:n were drawn by Ms. M. Lantto. Mrs. Gillien H/ikli corrected the language of the manuscript. We are indebted to Prof. L. S. Borodin, Laboratory Chief of the Institute o~" Mineralogy, Geochemistry and Crystallochemistry of Rare Elements, U.S.S.R., and to Dr. J. Nuutilainen, Manager of the Exploration of Rautaruukki Co.. for giving us permission to have the paper published.
References Bor~din, L. S., Lapin, A. V. & Kharc.~c,~kov, A. G 1973: Rare metal camaphorites. Nauka, Moscow. 176 pp. (ip Russian). Fisher, R. 1950: Entmischungen in Schmeizer aus S~:hv,ermetaloxyden, Silikaten and Phosphate, lhre geochemische und lagerst~ttenkundliehe Bedeutung, Neues Jahrb. Mireral. Monatsh. 3, 315--364. Grigoriev, D. P. I S . Application of mineral ont,3geny for petrography. Trudu V';EGEI 65, 23-35 (in Russian). Lapin, A. V. 1978: On ~ m e problems of ge'le~is of carbonatires. Geol. rudn. mestor. 20, 33-45 (in Ru~si:~.n). Papunen, H. 1980: The Kylmiikosld nickel-co,per deposit in southwestern Finland. Bull. Geol. Soc. Finland 52, ~29-145. Russel, H. D., Hiemstra, S° A. & Oroenveld, Do 1954: The
60
A . V. L a p i n & H. Vartiainen
ln~neralogy and petrology of the carbonatite at Loolekop, Eastern Transvaal. Geol. Soc. S. Africa, Trans. 57, 197-208. Vartiainen, H. 1980: The petrography, mineralogy and petrochemistry of the Sokl~ c~rbonatite massif, northern Finland. Geol. Surv. Finland. Bull. 313. 126 pp. Vartiainen, H. & Paarma, H. 1979: Geological characteristics
UTnOS 16 (1983) of the Sokli carbonatite complex, Finland. Econ. Geol. 74, 1296-1306. Wyllie, P. J. 1966: Experimental studies of carbonatite problem: The origin and differentiation of carbonatite magmas, pp. 311-352 in Tuttle, O. F. & Gittins, J. (eds.), Carbonatires, John Wiley & Sons, New York.