American Mineralogist, Volume 59, pages 378-380, 1974

AccessoryThorianite from the Massifsof AlkalineRocks and Garbonatitesof the TurjaPeninsula (Kola Peninsula)

ANonnr G. Burnxn, ArExsEr A. Mlznrov

Department ol Mineralogy, Leningrad State Uniuersity Leningrad, U.,S.S.R.

Abstract

Thorianite has been discovered in altered melilite rocks of the Turja peninsula (White Sea). Physical properties (n - 2.14; d - 8.4; a - 5.603 A) indicate that this mineral belongs to the thorian end member of the isomorphous group of UO.ThO.CeOz minerals.

Introduction related to carbonatitesin alkalic-ultrabasicmassifs, Thorianite is a comparativelyrare mineral of the being generallyformed from the alterationof melilite CeOz structural type. It occurs mainly in placer de- rocks (Kranck, 1928; Orlova, 1959; Epshtein, posits, accompaniedby zircon, ilmenite, and thorite. Anikejeva, and Michajlova, L961). In the Central It has been found in pegmatitesin bedrock and is massif of the Turja peninsula, these rocks are de- also observedas an accessorymineral in some gran- veloped in turjaites and uncompahgrites,their form ites,syenites, carbonatites, and marbles.This present being that of pockets and irregular bodies and their occfr,crence,in altered melilite rocks of the Turja thicknessfluctuating from 1 to 100 m. As a rule, pen',usula(northern coast of the White Sea), repre- the calcite-diopside-hornblenderocks are medium- sen[sa ratherpeculiar association. to fine-grained aggregatesof zeolites, calcite, and apatite, including short prismatic and xenomorphic Occurrence grainsof diopside(c A y - 38o; 2V = 62"). fhe alkalic massifsof the Turja peninsulabelong Perovskite occurs as an accessorymineral. Evenly ro the Caledonianalkalic-ultrabasic formation of the scatteredin this polymineralicaggregate are rounded Baltic shield (Dmitriev, Shatilov,and Bulakh, 1970; grains of magnetiteand large (1-3 cm) poikilitic Kukharenko,Bulakh, and Ilyinsky, 197l). Two large crystals of hornblende.The hornblendehas the fol- massifsand a number of small satellitesare known lowing optical characteristics:(-)2V : 69J4"; within the limits of the Turja peninsulaand occupy c A y = 2l-23",y : 1.670;I = I.662;" = 1.651. a total area of about 40 km2. The Central massif The average composition of the rock (in volume which is the largestone, has a zonal structure.Its percent) is: hastingsitichornblende, 50; magnetite, border zone is formed by alkalic rocks of the 10; diopside,10; fine-grainedaggregate of zeolites, ijolite-melteigiteseries. The inner zone, however, calcite,and apatite, 30. containsnot only ijolites and melteigitesbut also al- The calcite-garnet-vesuvianiterocks are denseand kalic pyroxenites,turjaites, uncompahgrites, okaites, massive.They arecomposed of a fined-grained(0.2- and melilitholites. Where these rocks predominate, 0.3 mm) garnet-vesuvianite-phlogopite-calciteagge- they alternate with each other in a complicated gate in which megacrysts( l-2 cm) of garnet and manner.Veins and vertical,stock-shaped bodies of magnetite are uniformly distributed. Calcite also carbonatite and of apatite-forsterite-magnetiteand occursin separatepockets. Perovskite is an acces- apatite-calcite-magnetiterocks have also been re- sory mineral.The averagecomposition of the rock ported from the core of the massif (Bulakh et o/, (in volume percent) is: vesuvianite,30; garnet 1972, 1973a). The proterozoic sandstonesand (andraditeand melanite-andradite),30; magnetite, granodiorites surrounding the massifs are strongly 10;calcite,20; phlogopite,10. fenitized(Yevdokimov and Bulakh, 1972). Thorianite occurswith pyrochlore as an accessory Morphology and PhysicalProperties in the original calcite-diopside-hornblendeand cal- Thorianiteusually occurs in areasof calcitesegre- cite-garnet-vesuvianiterocks which are gene,tically gation as an impregnatio'nof fine (0.2-0.3 mm and 378 MINERALOGICAL NOTES 379

is usually enriched in uranium, sornetimesto such degreethat it forms varieties intermediate in com- position between ThOz and UOz @.s., in carbe natitesfrom the Lulecopemassif, Africa). Evidently, such a change from essentiallypure thorianite in the phlogopite-bearing,calcite-garnet-vesuvianite and other early metasomatitesto the uraniferousvarieties in the later carbonatites is in complete agreement with the generalgeochemical characteristic of thorium , 0,2uu , snfl u1a1iurn-a gradual decreasein the ratio Th/U with time in natural evolutionaryseries of rocks and Frc. 1. Crystalhabits of thorianitefrom theTurja peninsula. minerals. tendency thorium USSR. This of and uranium has been clearly recognized in the formation of the alkalic massifsof the Turja peninsula (Bulakh et al, smaller) round grains or as idiomorphic crystals. 1,973b). The latter are cubes modified by very narrow rhombic-dodecahedral and sometimes octahedral Acknowledgments faces(Fig. I ). We would like to express our thanks to Miss T. The ,thorianite is light orange in color, is trans- Kochurova and Mr. A. Iskoz-Dolinin for their help in lucent in small grains,and has a slightly gleasylustre. translatingthe article into English. In thin section it is transparentand light brown or References gray. It is opticallyisotropic, n = 2.14 I 0.01. The specificgravity is 8.4 + 0.4. Bul,xH, A. G., D. N. Durrnrev, L. N. KezerrNov, AND A. A. KursmtNro (1972) New findings on carbonatites X-ray diffraction study shows the thorianite to be on the Kola peninsula. Dokl. Akad. Naa&. SSSR, 205, slightly metamict.The mineral powder gave the fol- 446-448 (in Russian). lowing reflections in the range 27-55o2d (onoN-l V. N. KenplrENKov, eNo G. F. ANestesnNro diftractorneter,Cu radiation, recording rate of 0.5"/ (1973a) The accessory minerals of carbonatites of the min., NaCl standardfor d-spacings):1ll-80-3.234; Central massif of the Turja peninsula. ln, Minerals and (in 2OO-22-23O4 (hkl- Paragenesesof Rocks,Nauka,T-17 Russian). ; 22o-4t-r.9807; 11 3-30- 1.69 O A. A. Mlzlrov, A. A. SlrunrN, eNo A. V. relative intensity-d-spacingin A). The cell edgea is Brcnrrlnov (1973b) Distribution of uranium and tho- 5.603:t 0.005A. rium in alkalic rocks of the Turja peninsula (Murmansk All the data obtained-namely, index of refrac- province). Geoch.9, 1404-1407(in Russian). tion, specific gravity, and unit cell size-indicate Durrnrtv, D. N., S. V. Srnrrrov, eNo A. G. Burexu (1970) New data on the geology of massifs of alkalic-ultrabasic this that mineral correspondsto the thorian end rocks and carbonatites of the Turja peninsula (Kola member of the isomorphous group of UOr-ThO2- peninsula). Dokl. Akad. Nazft. ,S,S.SR,193, 1356-1f59 CeOr. (in Russian). EpsHTErN,Ye. M., L. T. ANrxr.rnvA, ANDA. F. Mrcnl.novl Conc'lusions (1961) On the metasomaticrocks and phlogopite content the intrusive. Trudy NIIGA, 122, l2O-2lO (in Prior to its discovery in apomelilite rocks from of Guly Russian). the Turja peninsula,thorianite had beenobserved at KllusrrN, Yu. L. (1964) Accessory rare-metal mineralogy the Kola peninsula only in the Kovdor massif, in of the carbonatites of the Kola peninsula. In, Mineralogy phlogopite-bearingrocks (Krasnova et al, 1967), and Genetic Characteristics of Alkalic Massifs, Nedra, andin carbonatites(Kapustin, 1964). The thorianite pp. l2E-129 (in Russian). H. (1928) Turjaite and the ijolite stem of in the altered melilite rocks of the Turja peninsula KRANcK, E. Turja, Kola. Fennia, 51, no. 5, 104pp. (in English). resemblesthat from the phlogopite-bearingrocks of Kne,sNove, N. I., N. F. KlnrnNro, O. M. Rttusrevl- the Kovdor massif. In both cases the mineral is Konsmov^1. lxo V. V. FsenurrNr (1967) Thorianite essentiallythe thorian end member. This peculiarity from phlogopite-bearing rocks of Kovdor massif. Min- of composition of thorianite from the phlogopite- eral. Geochem. 2, 19-27, Leningrad University (in Rus- . bearing and calcite-garnet-vesuvianiterocks sian) distin- KurnenExxo, A. A., A. G. But-lxn, G. A. IrvtNsrt, N. F. guishes it from thorianite in carbonatites from a Snrxxlnrv, eNn M. P. Onrove (1971) Metallogenic number of other massifs.In theselatter the mineral characteristics of alkalic formations of the eastern part of 380 MINERALOGICAL NOTES

the Baltic Shield. ?rrdy Leningrad. Obshch. Yestestoois- Yrworruov, M. D., eNo A. G. Buurn (1972) T\e pytateley,72,no.2, Nedra,278 pp. (in Russian). aposandstonefenites of the Turja peninsula. Vestnik Onrove, M. P. (1959) On the genesisof the turjaites of Leningrad. Uniuersiteta, 12r 3242 (in Russian). the Salmagor massif, Kola peninsula. Materialy Vses. Geol. Inst. VSEGEI, n. ser. 26, 36-43. Gostoptekhisdat. Manuscript receioed,May 21,1973; accepted (in Russian). for publication,NouemberS, 1973.

Phofogrophldentificof ion Contest

Photographer ldentification No. l. Richardl. Gibson Humankidney stone; carbonate-apatite, Car. (PO,,CO*OH).(OH),;whewellite, CaC,Oo H,O;and weddellite,CaCrOn ' 2 H,O. No. 2. J. H. Berg' Snowflaketroctolite, Labrador. Spheroids of radiallygrown plagioclasein granularlay- ereddunite plus anorthosite, from the un- metamorphosedHettasch layered intru- sron. No. 3. S. A. Morse' Snowflaketroctolite, Labrador. Spheroids of radiallygrown plagioclaseset in olivine (here hornblendizedby a later granite) plus plagioclase. No. 4. PeterR. Buseckand Electronmicrophotograph of clinoenstatite. Sumiolijima No. 5. P. R. Buseckand S. lijima Electronmicrophotograph of idocrase. No.6. P. R. Buseckand S. lijima Electronmicrophotograph of beryl and cor- dierite. No. 7. P. R. Buseckand S. lijima Electronmicrophotograph of orthoenstatite: a-b and a-gsections. No. 8. Hans Nissen Scanningelectron microphotograph of opal.

lResearch under the Nain Anorthosite Project supportedbyNSF grantGA32134.