Serendibite in the Tayozhnoye Deposit of the Aldan Shield' Eastern

American Mineralogist, Volume 76, pages 1061-1080, I99I

Serendibitein the Tayozhnoyedeposit of the Aldan Shield' easternSiberia, U.S.S.R.

Eow.c.RDS. Gnrw Department of Geological Sciences,I 10 Boardman Hall, University of Maine, Orono, Maine 04469, U.S'A. Nmor,ay N. Prnrsnv, Yr-nonvrrnA. BonoNrKHrN,SnncBv Yn. Bonrsovsrrv Institute of the Geology of Ore Deposits, Petrology, Mineralogy, and Geochemistry of the U.S.S.R. Academy of Sciences(IGEM)' Staromonetnyyper., 35 Moscow 109017,U.S.S.R. MlnrrN G. Y.q,res Department of Geological Sciences,I l0 Boardman Hall, University of Maine, Orono, Maine 04469, U.S.A. Nrcrror..ts Mlngunz AerospaceCorporation, P.O. Box 92957,l-os Angeles,California 90009, U.S.A.

AssrRAcr The Tayozhnoye iron ore deposit contains the world's most extensive development of serendibite, approximately Car(Mg,Fe'z*)r(Al,Fe3*)orBr5Si3O20. The Tayozhnoye serendibite is found (l) as grains, up to a few centimeters,in magnesianskarns with clinopyroxene, potassium pargasite,spinel, anorthite, uvite, phlogopite, and, locally, anhydrite and (2) as rare grains, 0.02-0.4 mm, in olivine-rich orthosilicate rock with clinohumite, K-rich pargasite,uvite, spinel, magnetite,ludwigite, and sinhalite. Basedon electron and ion microprobe analyses,serendibite contains variable Fe (5.9-13.8 wto/oas FeO) and relatively constantB (1.4-1.6 B atoms per formula unit). Olivine contains l.l-1.4 wto/oBrOr, 0.3- 0.6 wto/oF; clinohumite,0.4-1.2 wto/oBrO., 1.0-4.3 wto/oF. The sequenceof mineral formation is (l) formation of skarns containing spinel [] + anorthite + clinopyroxene and plagioclase* clinopyroxene (local orthopyroxene)during upper amphibolite to granulite-facies metamorphism (to 850 "C, 4-5 kbar); (2) introduction of B to form ludwigite, serendibite, and tourmaline (sodian uvite and uvite) at 600-700 "C; (3) replacement of earlier formed serendibite to form poikilitic uvite, calcite, spinel [2], and rare clintonite, and formation of serendibite + pargasite;and (4) low-temperature alteration to chlorite, clinozoisite, grossular, margarite, and aluminous uvite. A review of the nine localities reported worldwide for serendibite,together with T-X(COr) and p(COr)-p(B,OJ diagrams in the model system CaO-MgO-AlrO3-SiOr-BrO3-CO2-HrO,indicate that serendibite is a mineral characteristically found in silica-undersaturatedskarns metamorphosed in the 'C) presenceof HrO-rich fluids at relatively high temperatures(600-825 and low to intermediate pressures(< l0 kbar).

INtnooucuoN formed suggeststhat pressure and temperature are less critical than other factors in determining the stability range Serendibite, a borosilicate of the aenigmatite group of this mineral. The absence of serendibite in quartz- and approximately Car(Mg,Fe2*)3(Al,Fer*)orB, ,SirOro,has bearing rocks indicates that it may be restrictedto certain been reported from nine localities worldwide (Table l, assemblagesor bulk compositions. Furthermore, seren- Appendix l, also Deer er al., 1978). Typical associated dibite is typical of metasomatic deposits. This study of minerals include clinopyroxene, spinel, pargasite,phlog- the Tayozhnoye deposit, which has the most extensively opite (biotite), plagioclase,and calcite, but quartz is con- developed serendibite of the nine localities listed, at- spicuously absent. Estimated conditions of formation tempts to identify the parameters defining the stability cover a wide range of pressuresat relatively high tem- limits of serendibite. peratures, 1-9.5 kbar, 600-825 "C. Serendibite typically We believe that it is particularly appropriate to report occurs in zoned metasomatic deposits (skarns) between our results on the Tayozhnoye serendibite in a volume contrasting rock types, generallymarble and a feldspathic honoring J. B. Thompson. Thompson strongly influenced rock. the senior author's contribution to this study. In his class Serendibite is a rare mineral compared to other Ca- lectures, Thompson emphasized the importance of the Mg-Fe-Al borosilicates,especially calcic tourmaline. The composition of a given mineral in understandingits pet- wide range of P-T conditions over which serendibitehas rologic role. While Thompson concentratedon the com- 0003-004x/91/0506-1 06 1 $02.00 106l 1062 GREW ET AL.: SERENDIBITE

TABLe1. Worldserendibite localities

Locality Critical associated minerals' Associated rocks*' P. f conditions

1. Gangapitiya,Sri Lanka Cpx, Spl, Pl, Scp Qtz-Fsp granulite marble 2. Johnsburg,NY, U.S.A. Cpx, Spl, Cal, Scp, Phl, Snh, Spr, Gdd,Tur, Prg, Kfs Kfs rockt 6.5-8 kbar Dol marble 720-740rc 3. Riverside,CA, U.S.A. Cpx, Pl, Cal, Spl, Bt, Tur, Czo, Cln Tonalite 1 kbar Dol marble 755-825 qC 4. Tayozhnoye,U.S.S.R. Cpx, Spl, Prg, Cal, Pl, Ol, Chu, Anh, Lud, Snh, Tur, Qtz-Fsp rocks 4-5 kbar Czo, Ep, Mag, Cln, scheelite Dol marbles 600-700'c 5. Handenidistrict, Tanzania Snh, Spl, Tur, Tr In Cal marble 6. Melville Peninsula,NWT, Canada Cpx, Tur, Cal, Czo, Cln, Spl Granite 4.9-5.4 kbar Cal marble 700-749 "C 7. lanapera, Madagascar Pf, Gpx, Hbl,Zo, Czo, Tur, Grs, Crn, Spl Serpentinite 7-9.5 kbar clinopyroxenite 750J00 "c 8. lhosy, Madagascar Pl, Scp, Cpx, Prg, Tur, Spl, Cal, Crn Leptynite 4 kbal marble 700.c 9. Russell,NY, U.S.A. Cpx, Cal, Prg, Scp, Tur, Gdd, Phl,Spl In calc-silicate 6.7-7.4 kbal 660-750 rc

Nofe.'Sources ot intormationon serendibitelocalities: 1. Coomaraswamy(1902), Prior and Coomaraswamy(1903); sample BM87O5O.2. Larsen and Schaller(1932); Schaller and Hildebrand(1955); Grew et al. (1991).3. Richmond(1939); Harvard Min. Mus.-simpteg+As2 from New City Quarryand samples Grew collected at nearby locality discoveredby D.M. Morton. P-f conditions are those deduced by Wiechmann(1988) tor met;somati3m in the nearby Crestmore quarries. 4. Shabynin and Pertsev (1956); Pertsev and Nikitina (1959); Pertsev (1971); Pertsev and Boionikhin (1986, 1988); Pertsev and Kulakovsky (1987, 1988); this study. 5. von Knorring (1967); Bowden et al. (1969), sample collected by P. Bowden.6. Hutcheon et at. (1977);Henderson (1983); U.S. Nat. Mus. sample136851. 7 and 8. Nicollet(1988, 1990a, 1990b); C. Nicollet'ssamples 261g and 320. 9. Grew et al. (1990a). * Mineral abbreviationsare given in Appendix 1. '- Underliningmeans that serendibite-bearingskarns occur along contacts between rock types indicated. t In addition, rare Srd in the Kfs rock itselt.

mon rock-forming minerals, he also encouragedthe study consists of dolomite marble, magnesian skarns, and ul- ofthe rarer ones,as these,he believed, could also lead to tramafic orthosilicate rocks, as well as gneissessimilar to petrologic insight. Moreover, Thompson introduced his those in the underlying and overlying units. Kulakovsky students to the thinking of academician D. S. Korzhin- (1985),Kulakovsky and Pertsev(1986), and Pertsevand skii. Korzhinskii's students,Pertsev among them, had al- Kulakovsky (1988) interpreted the orthosilicate rocks, ready worked on the Tayozhnoye deposit over 30 years which consist largely of olivine and humite-group min- ago (e.g.,Shabynin and Pertsev, 1956).Thompson en- erals, to be tectonically emplaced serpentinite that was couraged the senior author to carry out researchin col- subsequently metamorphosed during the high-grade laboration with Korzhinskii's students as part of the in- events. The marbles, skarns,and ultramaflc rocks are the teracademy exchangeprogram, which supported the senior hosts for Fe and B mineralization, largely magnetite and author's researchin the U.S.S.R. ludwigite, respectively. The overlying unit consists of gneissesand quartzitescontaining sillimanite, biotite, and, in places, cordierite; these commonly contain abundant Gnor,ocrcal oYERvrEw tourmaline. The Precambrian crystalline rocks are cut by The Tayozhnoye iron ore deposit and nearby deposits postmetamorphic Mesozoic syenite porphyries. of the Irglier field are part of the Precambrian meta- The Tayozhnoye deposit lies in a steeplyplunging (70") morphic complex of the Aldan Shield. This field is lo- sigmoidal fold that in map pattern forms an overtipped cated about 550 km south of Yakutsk. Major rock units "U" roughly 2 km x 2 km in area and opening to the are (l) a dominantly mafic gneiss unit, largely migma- southeast.The north limb of this asymmetric fold is at- tized, underlying the magnetite deposits, (2) a heteroge- tenuated and pinchesout, while the thickened south limb neousunit 300-320 m thick with magnetite deposits,and can be followed to other depositsin the Leglier field. The (3) an overyling gneissunit >500 m thick (e.g.,Maraku- fold developed during two periods of deformation, the shev, 1958; Pertsev,l97l; Shabynin,1974).Unmigma- second of which was associatedwith the main Fe min- tized mafic gneissesin the underlying unit are dominantly eralization. The deformation involved plastic flow of car- hypersthene + biotite + clinopyroxene and clinopyrox- bonate rocks and considerablefaulting (Kulakovsky and ene I hornblende * plagioclase,locally with almandine Pertsev, 1986, 1987; Pertsev and Kulakovsky, 1987, * hyperstheneand rare cordierite, whereas migmatized l 988). gneissesin the underlying unit are largely biotite granitic Three cycles of metamorphism are recognized, each gneiss,injection granites, and alaskite. The middle unit involving a prograde and a retrograde stage(Pertsev and GREW ET AL.: SERENDIBITE r063

Kulakovsky, 1987). Geochronologic data suggesta Pro- TleLe 2. Mineral content of the samples analyzed terozoic(l.9 + 0.05 Ga) agefor the most intensiveevent Magnesianskarns Orthosilicaterocks in this part of the shield. Conditions during the prograde 5678 first cycles attained conditions of the 1234 stagesof the two 5151 5152 Tzh 516 485t upper-amphibolite facies and granulite facies (4-5 kbar, 858' 650-850 "C). Granitization that produced alaskite and 255 372 28 4A 4V 4Zh the most extensivedevelopment of magnesianskarns ac- Srd-' X X XXTtTTfT companied the prograde stage of the second cycle, fol- spl T X TXXXXX cpx X x TX lowed by the main Fe and B mineralization at 600-700 Prg T TTTX 'C during the early alkali phase of the retrograde stage. An x Rare andalusite formed independently of sillimanite dur- Phl T XXT_T_ Tur X X TXTTT_ ing the retrograde stage of the first cycle. Secondary Cal T X XT prehnite and pumpellyite could have been causedby Me- Anh X+ XXXX sozoic hydrothermal activity accompanying the syenite ol Chu TXTT porphyries (Marakushev, I 958). Mag X TXXXX B mineralization is local by comparison with Fe min- Po T_XT Py T$ T$ X- eralization; ludwigite, (Mg,Fe'z+)rFe3*BOr,is the most ccp TTTT widespreadB mineral in both the orthosilicate rocks and Ap T T- the dolomitic marbles. Less widespread are suanite, Zrn T_TTT Lud T-T- MgrBrOr, and sinhalite, MgAlBOo, in the marbles and Other (T) Cln Qzo Grs Mgs Snh serendibite and tourmaline in magnesianskarns. The term chl Mrg chl Tms "magnesian" refers to skarns with forsterite, clinopyrox- Ttn(?) ene, or spinel ("calc-silicate" ofother authors), which are : : * hedenbergiteassemblages Note: X exceeds 1% modal; T trace' distinct from the andradite ' From sections of core no. 485 at 858.2 m and 858.4 m depth' Letters of calcareousskarns (e.9., Marakushev, 1958).The source refer to individualslices of these sections. of the B for ludwigite, serendibite,and tourmaline in the " Mineral abbreviationsare given in Appendix 1 grains too small to analyze. and associatedskarns, as well as for tour- t Srd ore deposits t Partly altered to gypsum. maline in the overyling gneiss, is unknown. Possible $ Unidentifiediron sulfide (Py or Po). sourcesinclude (l) a sedimentary origin for the main B mineralization in the deposit (Serdyuchenko,1959); (2) a sedimentary origin for the tourmaline in the gneisswith using a full ZAF-correction method (Boronikhin and Tse- metasomatic introduction into the iron ores of B remo- pin, 1980); (2) the Institute of Geology, Yakutsk Filial, bilized from the gneisses[a possibility that Marakushev U.S.S.R. Academy of Sciences(five analyses)on Cameca (1958)considered to be oversimplifiedl,and (3) a meta- Camebax-micro at 20 kV and 40 nA; and (3) the Uni- somatic origin for all the B, introduced through hydro- versity of Maine on a MAC 400s at 15 kV and 20 nA, thermal activity associatedwith the alaskitesand granit- using Bence-Albeecorrections as describedby Yates and ization (e.g., Shabynin, 1974 Pertsev and Kulakovsky, Howd (1988). Ion microprobe analyseswere carried out 1987). Regardlessof the ultimate origin of the B, in this on the AerospaceCorporation ARL ion microprobe mass paper we treat the B in the serendibite-bearingrocks as analyzer. Uncertainties of I o reported by Grew et al. having been introduced metasomatically. (1990b) for this ion microprobe are +l2o/o of the measured value for BrOr, +24o/oof that for LirO, and + 330/o of that for F. Mnrnons In general,the tabulated compositions combine aver- The samples studied in thin section and analyzed on agesofseveral electron microprobe analysesand one ion the electron and ion microprobes were largely obtained microprobe analysis obtained at one spot on one grain of from drill cores;a few are from surfaceworkings (trench- each mineral per thin section. More spots or grains were es). Serendibite was found in about 15 of the approxi- analyzed per thin section in casesofzoning (phlogopite, mately 400 holes drilled. About 60 thin sections of ser- tourmaline), textural variation (clinopyroxene in no. endibite-bearing rocks were examined. Minerals were 5152),or modal variation (orthosilicateminerals, no. 458/ analyzedin eight thin sections(Table 2). In addition, gar- 858. 4A). net in sample8527, which Pertsevand Boronikhin (1988, Twenty-one spots were analyzed by both the IGEM sample l) studied in detail, and clintonite in sample and University of Maine (UM) microprobes. In many 136851(Melville Peninsula)were analyzedfor compar- cases,the values for the major constituents (SiOr, AlrO3, ative purposes. FeO, MgO, CaO, KrO) are within a I wto/oof one anoth- Electron microprobe analyseswere conductedat (t) the er. Differences are greatestfor AlrO, and SiOr, particu- Institute of Geology of Ore Deposits, Petrology, Miner- larly for phlogopite, in which casethe values of SiO, and alogy, and Geochemistry GGEM) of the U.S.S.R. Acad- AlrO, obtained at IGEM are systematically higher than emy of Scienceson a Cameca MS-46 at 20 kV, 30 nA, those obtained at UM. In other cases,the differencesdo 1064 GREW ET AL.: SERENDIBITE

Cal

Fig. l. Photomicrographsof magnesianskarns in plane lighr. by tourmaline. Sample 5152. (C) Serendibitewith inclusions of (A) Potassiumpargasite (Prg) enclosed in serendibite(Srd), which spinel (Spl, lighter gray) and pargasite.Matrix to serendibite is is embayedby tourmaline (Tur) containing calcite (Cal). Banding phlogopite and pargasite;calcite and clinopyroxeneare also pres- in serendibiteis polysynthetictwinning. The island ofserendibite ent in the section. Sample 347l. {D) Serendibitesurrounded by is part oflarge grain. Sample5 152.(B) Aluminous (l I wtoloAIrOr) mantle of poikilitic tourmaline with magnetite (Tur + Mag) in clinopyroxene (Cpx) included in serendibite,which is embayed plagioclase(Pl) + phlogopite (Phl) matrix.

not appear to be systematic,although values of MgO ob- two zones where the boundary is gradational, that is, in tained at IGEM tend to be lower than those obtained at assemblagesof clinopyroxene * spinel + calcic plagio- UM. clase (seealso Shabynin and Pertsev, 1956; Pertsev and Tabulated data include one analysis for each of the Nikitina, 1959).Serendibite is also presentin magnesian spots analyzed,while the discussionand figuresgenerally skarnsrich in pargasite,phlogopite, calcite, or, rarely, an- considerall ofthe analyses. hydrite. In some cases,the skarn serendibiteforms irregular massesand rough crystals up to several ceritimeters Pntnocnlprry across, nearly black in color, but blue in powder or on Two fundamentally distinct paragenesesare character- the rough surlhces of drill cores. In thin section, seren- istic ofthe Tayozhnoye serendibite:(l) magnesianskarns dibite is polysynthetically twinned (Fig. lA), is strongly and (2) orthosilicate rocks, the former being by far the pleochroic in blue, green, and yellow-brown, and shows most widespread. anomalous interference colors (Pertsev and Nikitina, I 959). Magnesian skarns Larger serendibite grains are poikilitic with inclusions In general,magnesian skarns include four zonesdevel- ofclinopyroxene (Fig. lB), apatite,spinel (Fig. lC), par- oped between dolomitic marbles and an aluminosilicate gasite (Figs. lA, lC), plagioclase,phlogopite, and seren- rock such as biotite gneissor granitic migmatite: (l) cal- dibite in grains differing in orientation from the host. cite, (2) spinel + forsterite, (3) spinel * clinopyroxene, Microveinlets and patchesof fine-grained secondaryma- and (4) clinopyroxene * plagioclase.Serendibite has been terial cut the serendibite. Serendibite is found in direct found only in the two zones with clinopyroxene; most contact with clinopyroxene, plagioclase,pargasite, phlog- commonly, it is found along the boundary betweenthese opite, calcite, and anhydrite, although it is more com- GREW ET AL.: SERENDIBITE 1065

0.1mm

I Prgr

0.4mm 0.4mm t cal iT !fltgr-,m \'€.1, )- t- t 'zf

Fig' 2' Photomicrographsof magnesianskarns in plane light. (A) Secondarytourmaline (Tur) with inclusions of garnet (Grt), spinel (Spl), (cal), calcite and relict serendibite (Srd). Sample 8530. (B) Clintonite (Cln) flake adjacent to serendibiteembayed by poikilitic tourmaline. Sample 5151. (C) Symplectite of serendibite(dark) in pargasite(prg). Sample 8908. (D) Tourmaline, calcite, spinel, plagioclase and (Pl) mostly replacedby fine-grainedaggregate of clinozoisite and margarite at maryin of embayedserendibite. Sample5152.

monly overgrown by a mantle of poikilitic tourmaline ite occurs in the tourmaline mantle at its contact with (e.g., Fig. 1D). serendibitein sample5l5l (Fig. 2B). Tourmaline is found in the zones containing clinopy_ A third variety of tourmaline is deep blue, zoned, fine roxene + plagioclase and clinopyroxene + spinel. In feld_ grained, and, locally, somewhat fibrous. This variety is spathic rocks with biotite and either clinopyroxene, or- found in serendibite-bearingrocks in associationwith cli- thopyroxene, or both, in the spinel-free zone, primary nozoisite, epidote, muscovite, margarite, and rarely chlo- tourmaline (a sodian uvite) appearsinstead of serendibite rite. and forms friable aggregatesof equant polygonal grains Clinopyroxene is the dominant constituent in many of that are unzoned and dark bluish brown in the <.rvibra- the serendibite-bearingskarns and is present in all but a tion direction. This tourmaline does not occur with ser- few of them. Olive-green (locally brown) in hand speci- endibite. In serendibite-bearingrocks, a second variety men, it is nearly colorless in thin section. A few grains of tourmaline poikilitic forms margins (Fig. lD) around show anomalous interference colors. In more altered serendibite,in some cases,so extensivelythat it becomes samples, clinopyroxene is turbid and riddled with fine a major constituent of the rock. This variety is typically inclusions. gray-blue with green a cast, and locally zoned in color Calcic plagioclase (anorthite in analyzed samples) is intensity, but overall is lighter in color than the primary much less common than clinopyroxene or spinel and is tourmaline. Tourmaline in the maryins generally has an replaced to a considerableextent by muscovite (in part, irregular outline and embays associatedminerals, but in sericitic), margarite tufts, rare thomsonite, and clinozois- placesis euhedral against calcite. It is commonly riddled ite, and in placeswith deep-bluetourmaline (e.g.,sample with fine inclusions, most abundantly, serendibite relics 5I 52). and (Fig. spinel 2A), less commonly clinopyroxene, cal_ Garnet replacesplagioclase and locally forms selvages cite,anhydrite (sample 5 16/ 37z),and magnetite.Clinton_ betweenclinopyroxene and plagioclaseor pseudomorphs r066 GREW ET AL.: SERENDIBITE

Prg

0.1mm

(A) Serendibite(Srd) enclosed Fig. 3. photomicrographs of a magnesianskarn (A) and orthosilicate rocks (B-D) in plane light' (?) itand opaque (most likely in spinel (Spl) in pargasrre(prg). Sample 5158. (B) Serendibite with selvageof serpentine between betweenmagnetite (Mag) magnetite)in matrix of clinohumite (chu) with spinel. Sample 485/858, 6. (C) Thin margin of serendibite Sample 485/858' 4Zh' and clinohumite. Sample 485/858, 44. (D) Pargasite-utgitrr around olivine (Ol, high relief) in magnetite.

of plagioclase. In sample 516/372, garnet and chlorite with serendibite,as well as after serendibitein association replace clinopyroxene. with tourmaline. Pargasiteand phlogopite occur in many of the skarns Orthosilicate rocks and are dominant in a few. Pargasiteis pale blue-gray. Phlogopite is pale brown, and in sample Tzh 255, it is Serendibite was found in orthosilicate rocks from one zonedwith brown coresand nearlycolorless margins. Both interval 0.4 m long in a single core drill (no. 485 at a minerals locally contain relics of clinopyroxene. In par- depth 858.2-858.6 m), an occurrencefirst describedby ticular, pargasite typically penetratesand isolates clino- Pertsev and Boronikhin (1986)' The serendibite-bearing pyroxene. In these rocks, clinopyroxene contains appar- interval differs from other orthosilicate rocks in that ol- ent inclusions of pargasite that may result from ivine is more abundant than clinohumite and in that spi- penetration ofpargasite into clinopyroxene from outside nel and pargasite are more common. Rare relics of cli- the plane of the section. Pargasite also forms margins nopyroxene occur in olivine associatedwith tourmaline around spinel, isolating it from clinopyroxene. A sym- at 865 m in the same drill hole (Pertsevand Boronikhin, plectitic intergrowth with serendibitein one section (Fig. 1986), but no clinopyroxene was found in sectionscon- 2C) suggestscoeval development of these two minerals. taining serendibite. grains Green spinel is presentin almost all of the serendibite- Serendibiteis lound only in traceamounts in or bearing skarns. Textural relations suggestthat several selvages0.02-0.4 mm acrossthat are generallyfound be- generationsare present.Most abundant is spinel included tween magnetite or spinel on the one hand, olivine or in tourmaline formed from serendibite breakdown (Fig. clinohumite on the other (Figs' 3B, 3C) or between mag- 2D). In some cases,spinel is enclosedor overgtown by netite and spinel. Lesscommonly, serendibiteis included serendibite (Fig. lC). Spinel overgrowths around large in spinel, clinohumite, or olivine. Blue-gray tourmaline serendibite grains have not been found, but small seren- appears as margins around ludwigite (locally in sample dibite inclusions are not unusual in spinel (Fig. 3A)- Thus 485/858, 4V), magnetite,or spinel;it appearsless com- spinel developed prior to, and, in some cases,coevally monly as isolated grains in olivine. Pargasite,also blue- GREW ET AL.: SERENDIBITE t067

Tler-e 3. Metamorphic history in the Tayozhnoye deposit

Mineralsin magnesianskarns' Stage e f conditions and orthosilicaterocks

I Progressive 4-5 kbar,750-850'C Spl, Pl, Cpx, Opx, Ol,-- Ap, Zrn, Cal tl Retrogressive,early alkaline phase 600-700.c Srd, Tu(1), Lud,.' Mag, Cal ill Retrogressive,acid phase 450-600rc Tu(2), Prg, Phl,Cal, Anh, Srd, Snh," Chu.. IV Retrogressive,late alkaline phase 400rc Ms, Czo, Mrg, Tu(3), Chl, Grt, Srp(?),-'Mgs" Nofe; Adapted from Pertsev and Kulakovskv, 1997. Clinopyroxene+ plagioclaseand clinopyrbxene *'Occurs,. + spinel zones onty. only in the orthosilicaterocks. Srp(?) and Mgs are rare in the samples examined in this study.

gray in thin section, forms distinctive margins around third generation of tourmaline, the blue variety. Garnet olivine in sample 485/858, aZh Fig.3D). No reaction formation and scheelitemineralization (Pertsev and Bo- relationships were found among serendibite,tourmaline, ronikhin, 1988) may belong to this stage.The orthosili- and pargasite. cate rocks examined in this study were virtually unaf- In sample 485/858, 4V sinhalite forms a symplectite fected by the fourth stage. with magnetite adjacent to ludwigite and selvagesbe- Thomsonite probably formed during the Mesozoic tween ludwigite and magnetite. event when the syenite porphyries were emplaced. Olivine forms subequantgrains (0.5-7 mm across)in placesclouded with opaque dust. In a few sections,some Crrnvrrc.ql, coMposlTroN olivine grains have pleochroic brown patchesassociated Serendibite with oriented acicular inclusions that are fine and abun- The Tayozhnoye serendibitescontain traces ofF, con- dant. siderable Fe, and relatively constant B (Table 4). In for- Clinohumite is locally abundant, in which caseit forms mulae normalized to 14 cations and 20 O atoms, the B inequant grains, 0.5-3 mm long, having a preferred ori- contentsrange from 1.43-1.59atoms, close to the 1.50- entation. In the other sections,clinohumite forms grains, in part pleochroic in yellow, rarely as large as I mm long and interstitial to the much larger olivine grains. Olivine Trsle 4. Analyses of serendibite and clinohumite are both virtually free of alteration; ser- 123 pentine is rare. Magnesite, probably a late mineral formed coevally with Electron microprobe analyses-wto/o sio, 22.54 22.OO 24.79 24.86 25.17 25.02 serpentine, occurs with tourmaline in sample 485/g5g, Tio, 0.09 0.27 0.18 0.33 0.08 0.04 4F^. Al,o3 34.18 31.31 31.34 30.23 28.59 28.07 FeO 5.88 13.34 7.23 7.O7 9.98 9.80 Metarnorphic history MnO 0.13 0.23 0.20 0.16 0.12 0.09 MgO 13.63 11.17 14.42 14.95 14.95 14.55 't5.21 Textures in the serendibite-bearingskarns suggesta CaO 15.76 14.60 15.20 15.42 15.40 four-stage Na,O 0.05 0.08 0 0 O.02 0 metamorphic history (Table 3). The first stage lon microprobeanaly3es-wt% representsoriginal skarn formation under conditions of Li,O 0.001 0.005 0.001 0.001 0.006 0.00s the upper amphibolite facies and the hornblende-granu- BeO 000.001 00 0.001 BrO" 7.80 6.77 7.54 7.06 7.04 7.42 lite facies.Fe (mostly as magnetite)and B mineralization F 0.02 0.o2 0.o2 0.03 0..14 0.08 accompanied the second stage while temperatures re- SrO 0 0.001 0.001 0.001 mained high. During the Total 100.07 99.79 100.91 100.10 101.44 100.26 third stage,fluids were intro- Formulaenormalized to 14 cationsand 20 O atoms duced as temperaturesdecreased, resulting in the break- Si 2.659 2.688 2.919 2.955 2.977 2.988 down of serendibiteto tourmaline, as well as the formation B 1.588 1.426 1.533 1.448 1.437 1.530 AI 1.753 of additional 1.886 1.548 1.597 1.586 1.482 serendibite,typically with pargasite,phlog- Total 6.000 6.000 6.000 6.000 6.000 6.000 opite, or calcite. The serendibite + pargasiteassemblages Ti 0.008 0.025 0.016 0.029 0.007 0.004 AI 2.999 suggestthat the second and third stagesmay not be dis- 2.622 2.802 2.638 2.399 2.469 Fe3* 0.339 0.662 0.247 0.348 0.617 0.538 crete, but may be the beginning and end of a continuum. Fe2* 0.241 0.701 0.465 0.354 0.370 o.441 Thus the anhydrous assemblageSrd + Cpx + Spl + pl Mn 0.013 0.024 0.020 0.016 0.012 0.009 Mg 2.397 was stabilized in some rocks during 2.034 2.532 2.649 2.636 2.591 introduction of the Li 0 0.002 0 0 0.003 0.002 B-bearing fluids (2nd stage), whereas Srd + prg is an Total 5.997 6.070 6.082 6.034 6.044 6.054 intermediate assemblage,and Tur + Spl + Cal is an ex- Ca 1.992 1.911 1.918 1.964 1.951 1.946 ample of Na 0.011 0.019 0 0 0.005 0 a third stage assemblageforming from seren- Total 2.003 1.930 1.918 1.964 1.956 1.946 dibite (mineral abbreviations are in Appendix l). During F 0.008 0.008 0.006 0.012 0.053 0.029 the fourth stage, fluids were introduced at low tempera- Note: Fe measured as FeO and Fe3+lFe2+is calculated from stoichi- tures, resulting in the alteration of plagioclaseto musco- ometry. Totals corrected for F : O. All electron microprobe analyses vite, clinozoisite, and margarite, and the formation of a obtainedat UM. 1068 GREW ET AL.: SERENDIBITE

SiOe Serendibite 2A Qza Tavozhnoye o O Magnesianskarns S 2c-D T tr Orthosilimterocks o o o Johnsburg N A Russell o (Mg,Fe,Mn)O V lhosy ldeal r (0 07) X (Na) = Na,r(Ca+Na) 7B <- (Mg,Fe,Mn)O T 037 0.35

:44 or,'#,Jf o o N lu-7.o,,-,r______--______(u.u6) \ a 6 o

031 (Al,FelzOg------+ zqalA6\ Fig. 4. Composition of serendibitein terms of molecular pro- 06 0.8 portions of (Mg,Fe,Mn)O, (Al,Fe)'O,, and SiO,. Tayozhnoye 00 0.2 0.4 Feror 29O compositions normalized to 20 O atoms, 14 cations to estimate Per Fe3*and Fe2*contents, whereas Fe is assumedto be FeO in the Fe-poor Johnsburg, Russell, and Ihosy compositions. For Tay- Fig. 5. Compositionsof Tayozhnoyeuvite in termsof Fe,.,, ozhnoye, unfilled symbols refer to UM analyses,filled symbols Mg, and Al atoms per 29 O atoms(ideal formulation of threeB refer to IGEM analyses,numbers refer to samplesin Table 2. atomsand four OH-). Linesindicating l:l substitutionare for For Johnsburg,numbers correspond to samplesas follows: I : referenceonly. Numbersrefer to samplesin Table2, lettersto Sl-3 core,2 : S1-3rim, 3 : 5231,4 : 18964,5 : Sl-4,and 6 : individual grains, where 2C'L and 2C-D refer to lighter and 84-5 (Grew et a1.,1991). For Russell, I and 2 refer to two grains darkerzones in grainC of sample5 I 52.Unfilled symbols : UM in the analyzed section (Grew et a1., 1990a).For Ihosy, 320 : analyses,filled symbols: IGEM analyses,stippled symbols : sample320 (Nicollet, 1988, 1990b).Spacing between Tschermak Instituteof Geology,Yakutsk, analyses. Ideal uvite-feruvite solid substitution lines calculatedfrom NaSiCa-'Al-,. The numbers solutionis Ca(Mg,Fe'?*)3MgAl5Si6B30r?(OH)o. in parentheseswith arrows are rangesof X(Na) for Tayozhnoye (except sample 3, IGEM) and for Johnsburg samples l-4. Dots from NaSiCa-'Al-, probably arise as marked 111 and 434 indicate ratios of (Mg,Fe,Mn)O, (Al,Fe)tOr, tions estimated ratio of Fe3*/Fe2* and SiO,. much from uncertainty in the estimated as from analytical elTors. 1.54 atoms measured for Johnsburg serendibite by Grew Tourmaline et al. ( I 99 I ). In addition, the B contents of I .59 and | .43 atoms in samples 5l5l and 5152 (nos. I and 2) measured The blue-graytourmaline in serendibite-bearingskarns : with the ion microprobe agree with the 1.61 and 1.46 B and orthosilicate rocks is uvite with X.. Cal(Ca + Na) atoms obtained in crystal structural refinements of seren- : 0.89-1.0 (Table 5). Uvite from the magnesianskarns dibite in these samples (P. K. Sen Gupta and G. H. Swi- deviates from the ideal formula for uvite-feruvite solid hart, unpublished data; see also Sen Gupta et al., 1989). solution, Ca(Mg,Fe't)rMgAlsSi6B3O"(OH,Do (Dunn et : Calculated Fe3* contents arc 35-630/o of the total Fe. The al., 1977 Grice and Robinson, 1989) in that Mg * Fe dominant compositional variation in the Tayozhnoye 3.5 and Al increasesfrom 5.3 to 5.8 with increasing Fe serendibite is related to a Tschermak-type substitution: (Fig. 5). On the other hand, uvite from the orthosilicate (Mg,Fe'?*)Si(Al,Fe'*)-, (Fig. a). Tayozhnoye serendibite rocks has (Mg + Fe) and Al contents closer to the values compositions plot in an elongated area oriented parallel of 4 and 5 in the ideal uvite formula. Association with to one for the Johnsburg serendibite compositions, but magnetite and Fe3+-bearingserendibite suggeststhat a displaced to lower SiOr. This displacement is approxi- substantial proportion of the Fe in the uvite is ferric. mately that calculated for 100/osubstitution of Ca by Na Inasmuch as the uvite compositionsplot closeto or above from the exchange NaSiCa-,Al-', which is also charac- the uvite-feruvite join in Figure 6, we infer that Fe3*sub- teristic of aenigmatite (Deer et al., 1978). Discrepancies stitutes for Mg on the I site rather than for Al on the Z between the plotted serendibite compositions and posi- site [site notation XY3Z6S|6B3Or,(OH)0,Deer et al., 1986]. GREW ET AL.: SERENDIBITE 1069

Tleu 5. Analyses of tourmaline

1- 2' 3- 4' 5. 6' 7' UM UM UM UM IGEM UM UM UM Electronmicroprobe analyses-wt"6 sio, 35.40 35.87 31.93 35.72 36.41 37.20 36.34 3s.90 Tio, 0.0s 0.05 0.02 0.35 0.43 0.09 0.06 0 Al,o3 29.30 29.33 38.59 28.69 28.10 25.24 26.48 26.64 FeO 4.67 4.83 6.89 2.94 2.45 3.68 2.79 3.14 MnO 0 0.01 0.04 0.01 0 0 0.00 0.0s Mgo 11.53 11.54 5.39 13.29 13.07 15.21 14.43 15.45 CaO 5.28 4.97 2.95 5.29 5.22 5.69 5.69 5.57 Naro 0.17 0.25 1.28 o.25 0.08 o.14 0.03 0.08 l(ro 0.01 0.02 0 00 0 0.04 0.06 lon microprobeanalyses-wt06 LirO 0 0.001 0.001 00 0.002 0 0.001 B,O" 9.90 9.79 11.24 9.72 10.02 11.81 9.69 11.15 SrO 0.007 0.003 0.02 0.04 0.03 0.0071 0.009 0.02t BaO 0 0 00 F 0.27 0.32 0.01 0.70 0.75 1.32 0.s9 1.56 Calculated-wtc6 H.O 3.50 3.48 3.71 3.31 3.29 3.13 3.33 2.97 Total 99.98 100.33 'l02.o7 100.02 99.53 102.96 99.23 101.93 Formulaefor 29 O atoms Si 5.858 5.915 5.160 5.883 5.989 5.936 6.033 5.798 B 2.828 2.787 3.134 2.763 2.845 3.253 2.777 3.108 Ti 0.006 0.006 0.002 0.043 0.053 0.011 0.007 0 AI 5.715 5.701 7.350 5.569 5.447 4.747 5.181 5.071 Fe 0.646 0.666 0.931 0.405 0.337 0.491 0.387 o.424 Mn 0 0.001 0.00s 0.001 0 0 0 0.007 Mg 2.845 2.837 1.299 3.263 3.205 3.618 3.571 3.720 Li 0 0.001 0.001 0 0 0.001 0 0 Ca 0.936 0.878 0.511 0.934 0.920 0.973 1.012 0.964 Na 0.055 0.080 0.401 0.080 0.026 0.043 0.010 0.025 K 0.002 0.004 0 0 0 0 0.008 0.012 Sr 0.001 0 0.001 0.004 0.003 0.001 0.001 0.002 Total 18.892 18.876 18.795 18.945 18.825 19.074 18.987 19.131 r 0.141 0.167 0.005 0.365 0.390 0.666 0.310 0.797 OH 3.859 3.833 3.995 3.635 3.610 3.334 3.690 3.203 /Vote.'AllFe as FeO; (OH + F) assumed to equal 4. Totals corrected for F : O. UM and IGEM indicatethe electron microprobeused. ' Blue-gray uvite. t* Blue, aluminous uvite. lon microprobevalues are averagesof two spots. t Also 0.001 wt% Rb,O.

This substitution is consistent with the inverse relation Clinopyroxene and clinoamphibole between Mg and Fe in uvite from the skarns (Fig. 5). Clinopyroxene is aluminous diopside with close to one Becausethe ratio of Fe3+/Fe2+has not been determined, Ca atom per formula unit (Table 6). In sample 5152 (no. inferring a substitution schemefor Mg, Fe, and Al is not 2), it is heterogeneous:the difference between taiAl and possible. tulAl (corrected for Ti) and Fe,o,increase with AI,o,,a re- Zoning in the uvite appearsto be related to Ti and Fe lation suggestingincorporation ofFe through the substi- contents, which were found in one caseto be higher in a tution r6rFe3,rotAlMg_,Si_,. darker zone (TiO, : : 0.51 wto/0,Fe as FeO 4.53 wto/o) The clinoamphiboles are pargasiteand potassium par- than in : the adjacent lighter-colored zone (TiO, 0.33 gasitewith X": W(K + Na) : 0.42-0.63 in the ortho- wto/0,Fe : as FeO 3.14 wto/o)(Figs. 5 and 6). silicate rocks and X" : 0.62-0.74 in sample 5152 : Blue tourmaline is an aluminous uvite with X(Ca\ (no. 2), a skarn (Table 7; Fig. lA). This potassium par- 0.54-0.56 and differs markedly from the earlier formed gasite also contains 0.39-0.57 wto/oCl (IGEM probe). uvite in the same sample (no. 2) in its higher Al (Fig. 6) Pargasite& increaseswith increasinEXr. [: Fe,.,/(Fe,", (Table and lower Si and F contents 5). BecauseLi con- + Mg)l and with decreasingI41Al (Fig. 7), trends reported tents are negligible in the aluminous uvite, the extra Al in other K-rich amphibole samplesfrom silica-undersat- appears to be incorporated by a Tschermak substitution, urated skarns (Shimazaki et al.. 1984: Matsubara and I4Al r4rAl : rlr(Mg,Fe) r4tsi + + (Henry and Guidotti, Motoyoshi, 1985). I 985). BrO, contents determined with the ion microprobe are Phlogopite, clintonite, margarite, and chlorite 9.69-l l.8l wo/0, that is, within the expected analytical Phlogopite is relatively Ti poor and Si rich; zoning in uncertainty of + 1.5 wto/o(Grew et al., 1990b) of the cor- coarseflakes in sample Tzh 255 (no. 3) is correlatedwith respondingideal BrO. contentsof 10.3-10.9wto/o (for three Ti and Fe, with darker cores slightly richer in these con- B atoms per formula unit). stituents than lighter margins (Table 8). 1070 GREW ET AL.: SERENDIBITE

z-3 2A Pargasites o 2A

! 28 U' .j6 (D As2B o, X 5n tu

Al osFe,o,os Al os Mg os Tavozhnoye 7 O O Magn"sianskarn I rock Fig. 6. Al-Fe,.,-Mg diagram (in atomic proportions) for uvite ! I ortho.ilicate from the Tayozhnoyedeposit (adaptedfrom Henry and Guidotti, Antarctica 1985). The triangles 2D refer to the blue aluminous uvite asso- n Skarn(1-2) and 4 (4) ciated with margarite and clinozoisite in sample 5152 (no. 2). Nodule Otherwise, symbols are the sameas in Figure 5. None of the 393 2A tourmaline compositionscompiledby Henry and Guidotti (1985) 0.3 plot in lhe field marked here as No Tur. t g'o ,L l^o" 28 J LL V.Z 8 q) il ! tr 5 I Enr TABLE6, Analyses of clinopyroxene o v.' 4 't 2. A UM UM UM IGEM IGEM 0.0 Electron o/c microprobe analyses-nrt 0.3 0.4 0.5 0.6 0.8 sio, 51.01 44.57 51.45 51.09 48.98 Tio, 0.25 0.86 0.49 0.38 o.72 Atomicl((K+Na) Al,o3 4.78 10.95 3.59 5.61 5.67 FeO 2.55 6.85 3.50 3.03 2.82 Fig.7. Compositionsof pargasiteand potassium pargasite in MnO 0.19 0.22 0.12 0.18 0.10 Fe/(Fe+ Me,)(Fe,",), tot41 (calculated Mgo 16.23 11.56 15.82 15.35 15.24 termsof theatomic ratio of CaO 25.20 24.57 24.56 24.53 24.43 as8 - Si andignoring B) andthe atomicratio of K/(K + Na"J. Naro 0.12 0.10 0.17 0.30 0 Sourcesofdata: (1) Magnesianskarn and orthosilicate rock, this lon microprobe analyses-YYt06 study,numbers refer to sampleslisted in Table2,letters refer to Liro 0.002 individualgrains, ofwhich 28 wasanalyzed at two ditrerentspots B.o" 0.096 : SrO 0.005 at IGEM; unfilledsymbols : UM data,filled symbols IGEM F 0.009 data.(2) Skarn and nodule, from Matsubara and Motoyoshi (1985), Total 100.33 99.79 99.70 100.511 98.96 numbersrefer to analyseslisted in their Table l. Formulaenormalized to 6 O atoms Si 1.861 1.675 1.893 1.860 ',t.820 AI 0.139 0.319 0.107 0.140 0.180 B 0.006 Total 2.000 2.000 2.0 2.O 2.O Ti 0.007 0.024 0.014 0.010 0.020 Clintonite formed from serendibitebreakdown in sam- AI 0.067 0.166 0.049 0.101 0.068 ple 5151 (no. 1) (Tayozhnoye)and in sample 136851 Fe 0.078 0.21s 0.108 0.092 0.088 (Melville Peninsula) are similar compositionally, except Mn 0.006 0.007 0.004 0.006 0.003 Mg 0.883 0.648 0.868 0.833 0.844 in F content(Table 8), and are low in Si (Si: 2.31-2.39) Total 1.041 1.060 1.043 1.042 1.023 and intermediate in Fe,", (Fe : 0.20-0.28) compared to Ca 0.985 0.990 0.968 0.957 1.012 : - Na 0.008 0.007 0.012 0.021 0 clintonite overall (Si 2.22-2.72, Fez* + Fe3* 0.66 Total 0.993 0.997 0.980 0.978 1.012 per 22 O atoms, Guggenheim,1984). Total cat, 4.034 4.057 4.023 4.020 4.035 Margarite is close to the end-member in composition r 0.001 except for 4 molo/oparagonite solid solution (Table 8). ivofe; All Fe as FeO. UM and IGEM indicate the electron microprobe Chlorite closely associatedwith garnet in sample 516/ useo. - Enclosedin serendibite. 372 (no.4) is lessmagnesian than phlogopitein the same .' In matrix to serendibite. thin section (Table 8). This Fe-Mg fractionation is the f Total includes 0.04 wto/" K,O. reverseof that for most biotite + chlorite pairs (e.g.,Al- GREW ET AL.: SERENDIBITE l07l

Trau 7. Analysesof pargasite 2 578 UM UM IGEM UM Electronmicroprobe analyses-wtcr sio, 38.85 42.59 44.92 42.27 Tio, 0.54 o.o2 0.03 0.04 Al203 19.29 15.52 13.58 14.96 Cr2og 0.03 FeO 9.34 6.34 5.63 6.59 MnO 0.16 0.03 0.15 0.06 Mgo 13.66 't7.52 17.08 17.50 CaO 11.75 13.35 13.44 13.28 E Naro 0.90 1.13 1.77 0.83 o KrO 3.5s 2.00 1.93 2.10 d 0.39- 0.13 U) lon microprobeanalyses-urtoA Li,O 0 0.005 0.003 B.o" 0.050 0.059 0.085 Rbro 0.005 0.006 SrO 0.02 0.03 0.036 BaO 0.04 0.01 0.01 F 0.45 1.94 0.98 Calculated-wt% H"o 1.73 1.24 2.07 1.61 Total 100.45 100.97 100.73 99.95 Formulaenormalized to 23 O atoms si 5.698 5.942 6.394 6.102 AI 2.289 2.044 1.606 1.877 B 0.013 0.014 0.021 oo 01 oz Total 8.0 8.0 8.0 8.0 Batoms Ti 0.060 0.002 0.003 0.004 AI 1.046 0.508 o.672 0.668 Fig.8. B andSi contentsof olivineand clinohumite in terms 0.003 FE 1.146 0.740 0.670 0.796 of ideal formulations:4MgrSiOo and MgSioO,u(OH)r.Unfilled Mn 0.020 0.004 0.018 0.007 symbols: UM data,filled symbols : IGEM data,numbers refer Mg 2.987 3.644 3.625 3.766 to samplesin Table2, lettersto individualgrains. Li 0 0.003 0.002 Total 5.259 4.901 4.991 5.243 Ca 1.847 1.995 2.050 2.054 Na 0.256 0.306 0.489 0.232 bee, 1968) and implies that the late-formed chlorite did K 0.664 0.356 0.350 0.387 not equilibratewith phlogopite. Rb 0 0.001 Sr 0.002 0.002 0.003 Ba 0.002 0.001 0.001 Olivine and clinohumite Total 2.77'l 2.661 2.889 2.677 Olivine (XF" : 0.ll-0.15) is unique in its high BrO3 Total cat. 16.030 15.562 15.880 15.920 F 0.209 0.846 o.447 (l.l- 1.4 wto/o)and F (0.33-0.60 wto/o)contents (Table 9), cl 0.097 0.031 constituents rarely sought in olivine and then generally OH 1.694 1.154 1.969 1.553 detectedonly at the trace level (e.g.,Steele et al., 1981; Note.'All Fe as FeO. OH + F + Cl assumedto equal 2. Totals corrected Kohn et al., 1989),even in association for O : F, O : Cl. UM and IGEM indicate the electron microprobe used. with kornerupine . (Grew, 1988). Clinohumite (Xr. : 0.08-0.11) conrains Measured at IGEM. 0.37-1.2 wto/oBrOr, matchingthe maximum reportedin a humite-group mineral (chondrodite, Hinthorne and Ribbe, 1974).ln formulae normalized to 16 and 17 O atoms, respectively, B + Si is approximately equal to 4 below the detection limit of the electron microprobe at for both olivine and clinohumite (Fig. 8). An inverse re- UM (i.e., less than 0.1 wtoloAlrO3), solid solution of sin- lation of B and Si is reported in some minerals with a halite, (Mg,Fe)AlBOo,a mineral isostructural with oliv- variable B content, such as chondrodite (Hinthorne and ine, is unlikely. One schemeconsistent with available an- Ribbe, 1974) and sillimanite (Grew and Hinthorne, 1983), alylical data involves F or hydroxyl: B(F,OH)Si_,O-,, as but to date only in kornerupine has extensive B-Si mis- proposedby Hinthorne and Ribbe (1974) and Deer et al. cibility been demonstrated for a single tetrahedral site (1982,p.400). B contentsin olivine are equal to or ex- (e.g.,Moore and Araki, 1979). ceed F contents (atomic basis, Table 9), allowing that D. R. Veblen (personalcommunication, 1990) has ex- some hydroxyl is probably also presentto balancecharge. amined homogeneouspatches of olivine with the trans- mitting electron microscope and found no B-rich inclu- Plagioclase,clinozoisite, garnet, and thomsonite sions.Thus B is incorporated in the olivine itself. Pending Plagioclasein samples8527 and,5152is anorthite, Anee further study by Veblen, which is now in progress,infer- (Pertsevand Boronikhin, 1988;this study,Table 10). ring a substitutional schemefor B incorporation is pre- Secondaryclinozoisite derived from plagioclaseis vari- mature. Becausethe Al,O" contents of the olivine are able in FerO. content (Table l0). t072 GREWET AL.: SERENDIBITE

TABLE8, Analysesof micasand chlorite

2 33 4 4 5 7 Cln Cln' Mrg Ph(cr- Ph(M)t Phl chl Phl Phl UM UM IG UM UM UM UM UM UM Electronmicroprobe analyses-wtc/o sio, 16.82 16.47 30.86 38.88 39.03 38.s3 27.55 40.26 40.68 Tio, 0.02 0.02 0.01 0.53 0.44 0.65 0.02 0.01 0.05 Alro3 43.25 44.79 51.04 16.78 16.61 16.39 23.95 14.60 14.U CrrO" 0.01 FeO 2.35 1.74 0.18 3.87 3.46 2.66 7.04 2.70 2.57 MnO 0.05 0 0.03 0.13 0.o7 0 0.11 0 0.04 Mgo 19.68 19.34 0.06 24.02 24.05 24.46 28.54 25.93 25.67 CaO 12.54 13.38 13.09 0 0.05 0.13 0.27 0.02 0.05 Na"O 0.09 0.37 0.31 0.35 0.45 0.2'l 0.26 0.34 KrO 0.01 0.01 0.10 10.68 10.60 10.48 10.42 10.54 lon microprobeanalyses-wt7" Li,O 0.002 0.024 0.001 0.001 0.002 0.o44 0.017 BeO 0.002 0 BrO" 0.009 0.01 0.02 0.01 0.007 0.02 0.008 Rb,O 0.15 0.16 0.21 0.16 0.14 SrO 0.003 0.01 0.004 0.005 0.005 0.004 0.003 BaO 0.001 0.054 0.05 0.28 0.16 0.16 F 0.14 1.09 0.94 1.01 1.00 2.20 1.70 Calculated-wt% HrO 4.15 3.77 4.54 3.77 3.72 3.70 12.53 3.17 3.41 Total 99.06 100.56 100.23 99.78 99.29 98.29f 100.01 99.03$ 99.00$ Formufae toJ 22 O atoms (micas), 28 O atoms (chlorite) Si 2.387 2.305 4.074 5.533 5.569 5.543 5.273 5.735 5.792 AI 5.610 5.692 3.926 2.462 2.429 2.455 2.727 2.261 2.206 Be 0.001 0 B 0.002 0.003 0.005 0.002 0.002 0.004 0.002 Total 8.000 8.000 8.000 8.000 8.0 8.0 8.0 8.0 8.0 Ti 0.002 0.002 0.001 0.057 0.047 0.070 0.003 0.001 0.00s AI 1.623 1.694 4.016 0.352 0.364 0.324 2.676 0.190 0.200 Cr 0.001 Fe o.279 0.204 0.020 0.461 0.413 0.320 1.127 0.322 0.306 Mn 0.006 0 0.003 0.016 0.008 0 0.018 0 0.005 Mg 4.163 4.O34 0.012 5.095 5.115 5.246 8.144 5.507 5.449 Li 0.001 0.013 0.001 0 0.001 0.025 0.010 Total 6.O74 5.947 4.053 5.982 5.947 5.961 11.968 6.045 5.975 Ca 1.907 2.006 1.852 0 0.008 0.020 0.055 0.003 0.008 Na 0.025 0.100 0.079 0.097 0.124 0.059 o.o72 0.094 K 0.002 0.002 0.017 1.939 1.929 1.923 1.894 1.915 Rb 0.014 0.015 0.019 0.015 0.013 Sr 0 0.001 0 00 0 0 Ba 0 0.003 0.003 0.016 0.009 0.009 Total 1.934 2.109 1.948 2.053 2.079 2.037 0.055 1.993 2.039 Total cat. 16.008 16.056 14.001 16.035 16.026 15.998 20.023 16.038 16.014 F 0.063 0.484 0.423 0.456 0.455 0.991 0.766 OH 3.937 3.516 4.0 3.577 3.544 3.545 16.000 3.009 3.234 Nofe.'All Fe as FeO. Totals corrected for F : O. UM, IGEM, and lG indicatethe electron microprobeused. t Sample136851, Melville Peninsula, Canada. .. Core. t Margin. + Cl present in amounts <0.270. $ Cl not detected.

Secondarygarnet associatedwith chlorite in 516/372 content per formula unit given for thomsonite, is needed (no. 4) is largely grossular-andradite,while that in sample to bring the analytical total to l00o/0. 8527, an anorthite-clinopyroxeneskam containing scheelite and rare serendibite(Pertsev and Boronikhin, 1988), Sinhalite and ludwigite is nearly pure grossular (this study, Table l0). Si values An analysis of sinhalite in an overgrowth around lud- below 6 per 24 O atoms and low analytical totals suggest wigite in 485/858, 4V (no. 7) ga:vea reasonableanalytical some 4H+ : Si4* (hydrogrossular)substitution in these total assumingan ideal B content, (Mg,Fe'?*)AlBOo(Table garnets. I l). However, analyticaltotals for ludwigite are high (103- Analysis of a fine-grained fibrous mineral occurring with l}4wo/o, Table I l). Ludwigite analyseswere recalculated clinozoisite, margarite, and blue tourmaline formed from from (Mg,Fe'z*)r(Fe3t,Al)BOr,the formula derived from anorthite breakdown in sample 5152 (no. 2) yields a stoi- single-crystalX-ray studies (Takeuchi et al., 1950; Nor- chiometry close to NaCarAlrSi,Oro (Table 10), the for- restam et al., 1989), and we have no explanation for the mula for thomsonite. However, more than 6HrO, the HrO high analytical totals. Ludwigite in sample 485/858, 28 GREW ET AL.: SERENDIBITE 1073

TAELE9. Analysesof olivineand clinohumite 55666778 Ol Chu Ot. Chu Chu Ot. Chu Ol IGEM IGEM UM UM UM UM UM IGEM Eleclronmicroprobe analyses-wtc6 sio, 37.94 36.11 38.02 35.16 34.54 Tio, 38.48 36.12 39.85 0 0.15 0.01 0.07 0.05 0.o2 0.02 0.03 Al2o3 0 0.06 0.08 0.05 0.04 o.02 0.04 0 Cr,O. 0 0 FeO 14.45 8.97 11.64 7.98 7.88 I 1.33 1036 12.97 MnO 0.29 0.21 0.27 0.33 0.16 0.27 0.25 Mgo 0.30 46.75 50.01 48.72 51.77 51.79 49.07 49.34 45.63 CaO 0 0 0.05 0.07 0.05 0.04 0.02 Naro 0 0 0 0 lon microproJanatyses-rrt;6 LirO 0.002 0.001 0.001 0.001 0.001 't.1 0.001 0.001 0.001 B,O" 1.14 o.37 1.11 1.10 3 1.35 0.86 1.11 F 0.60 3.46 0.33 4.26 1.88 0.55 1.05 0.39 Calculated-wt06 H"O 1.11 0.76 1.86 2.27 Total 100.92 98.99 100.09 99.76 98.59 100.90 99.89 100.1 2 Formulae per 4 oxygens (Ot), 17 orygens (Chu) Si 0.943 3.941 0.940 3.794 3.761 0.942 3.911 B 0.986 0.049 0.070 0.047 0.204 0.212 0.057 0.161 0.o47 Total 0.992 4.011 0.987 3.998 3.973 0.999 4.072 1.033 Ti 0 0.012 0 0.006 0.004 0 0.002 AI 0.001 0 0.008 0.002 0.006 0.005 0.001 0.005 0 Cr 0 0.000 Fe 0.301 0.819 o.241 arzo azre o.zsz Mn ogge 0.268 0.006 0.019 0.006 0.030 0.015 0.006 0.023 0.006 Mg 1.734 8.138 1.796 8.327 8.406 1.791 7.963 1.680 Ca 0 0 0.001 0.008 0.006 0.001 0.002 0 Na 0 0 0 Li 0 0 oo- 0 ;o- 0 Total 2.041 8.996 2.046 9.097 9.154 2.031 8.933 1.955 Total cat. 3.033 13.007 3.033 13.095 13.'127 3.030 13.005 2.988 F o.047 1.194 0.026 1.455 o.647 0.043 0.360 0.031 OH 0.806 0.545 1.353 1.640 Note: Fe as FeO. In clinohumite, assumed formula is (Mg,Fe).(Si,B).Or6(OH,F)r.Totals corrected for F : O. UM and IGEM indicate the electron microprobe used. 'Ni sought but not detected

(no. 5) is lessmagnesian than other Tayozhnoyeludwigite (20-29 wto/oMgO, Lisitsyn et al., 1985; pertsev and Bo- ronikhin, 1986), whereasthe range of AlrO, contents in the newly analyzed samples (0.4-3.2 wt0/0,Table I l) overlaps the range reported by these authors, 0.49-2.7 wtoloAlrOr. I g3 o Magnetite, spinel, and magnesite 6 Magnetite o in the orthosilicate rocks approachesend_ ?4 member FerOoin composition with MgO the most abun_ o dant impuriry (0.93-1.56 wr0/0,Table l2). 8 Spinel is a magnesian spinel-hercynite with variable amounts of FerO, estimated by stoichiometry (Table l2). Spinel associated with tourmaline in three magnesian skarnscontains less zinc (0.15-0.38 wto/oZnO) than spinel in the orthosilicate rocks (0.53-0.88 wto/o). A single carbonategrain adjacent to the analyzedtour- 01 05 1.0 maline in 485/858,28 is ferroanmagnesite, (Mg.nrFeoor_ Atomic F/OH Fig. Mno oouCaooor)CO.. 9. Distribution of F and hydroxyl in Tayozhnoye fer- romagnesian silicates plotted in a sequenceofincreasing ratio of Element distribution F/OH oftourmaline on a semilogarithmicdiagram (adapted from Albee, 1968). OH contents have been calculated from ideal Assuming ideal F * OH contents, the ratio of F/OH formulations as follows, neglecting Cl in pargasite: OH + F : 4 increasesPhl < Prg < Tur, (except Chu Chu in no. 7, Fig. (Phl), OH + F : 2(Chu and Prg) and OH + F : I (Tur, from 9). Phl < Prg is the reverseof experimentally determined Deer et al., 1986). Sample referencesare taken from Table 2. to14 GREW ET AL.: SERENDIBITE

TABLE10. Analysesof plagioclase,clinozoisite, thomsonite, and TABLE1 1, Analysesof sinhaliteand ludwigite garnet 5777 Lud Lud"" Snh'- 22248527". Lud' UM IGEM UM UM Pl Czo. Tms Grt Grt UM IG UM UM IGEM wtoh 0.25 microprobeanalyses-wt7c sio, Electron 0.15 0.37 0.30 43.08 37.76 35.65 35.95 38.74 Tio, sio, 0.41 3.15 1.63 40.39 Tio, 0.03 0t 1.00 0.05 Alro3 Crro" 0.06 At,os 36.58 28.89 30.53 15.63 21.89 34.19 8'13 0.50 FerOJ 34.98 32.75 Fe,O" 6.78 23.57 31.00 4.13 0t FeO 35.87 FeO 0.16 0.11 o.22 0.18 0 MnO 0:2 0t 0.14 0.45 MnO 0.08 0.08 ZnO 0-04 MgO 0 0t 25.33 20 36 29.19 13.49 37.16 37'23 MgO 16.16 CaO 20.25 23.51 o.22 Na,O 0.11 0.03 3'67 0 Na"O 0 KrO 0.01 K,O 0.01 0 0.01 16.81 16.28 27.43 lon microptobeanalyses-wto/o BrO.*. 15.66 Total 103.35 102.78 103.93 101 .14 Li,o0-0- Formulaefor lour cations,five O atoms(Lud); four O atoms(Snh) B.O" O.O2 0.08 0.009 0.07 Si SrO 0.04 0.004 0.010 0-008 BaO0-0t Ti Ar 0.018 0.128 0.068 1'005 Total 100.25 99.03 96.41+ 98.09 98.94 0.002 (Pl),12.5 O atoms(Czo), Formulaetor eightO atoms 0.849 0.916 20 O atoms(Tms), 12 O atoms(Grt) Fe3t 0.974 Fe,t 1.110 0.679 o.922 0.073 5l 1.994 2.956 4.967 2.871 2.957 Mn 0 003 0.006 0.005 0 B 0.001 0.019 Zn 0.001 Ti 0.002 0 0.060 0.003 Mg 0.891 1.301 1.080 0.919 AI 1.996 2.666 5.014 1.471 1.969 Na 0.015 Fe 0.006 0.399 0 0.489 0.029 K 0 Mn 0.007 0 0.009 0-029 B 1.000 1.000 1.000 1.000 Mg 0 0 0.010 0.009 Total 4.000 4.000 3.999 2.997 Ca 1.004 1.972 2.014 3.180 3.045 Na 0.010 0.005 0.992 0 Notei CaO : 0. Sb and Sn sought but not detected in ludwigite (UM)' K 0.001 0 0.002 0 UM and IGEM indicatethe electron microprobe used' Sr 0.001 0.006 * Fine prisms in olivine. Total 5.013 8.007 13.014 8.090 8.041 * Rounded ludwigite grain mantled in part by sinhaliteand magnetite' Calculated from stoichiometry and assuming 18 per formula unit' Note; All Fe as FeO in Pl, as FerO3in Grt and Czo. UM, IGEM,and lG t except Snh, where all Fe assumed as FeO. indicate the electron microprobe used. t All Mn as MnrO3.At two other spots, Fe2O3: 5.96, 3.48 wt%. Total includes 1.91 wt% HrO calculatedfrom ideal formulation, .. Sample 8527, Pertsev and Boronikhin (1988). t Not analyzed at UM, but found to be zero in an analysisdone at lG. minerals are near the limit of detection; only tourmaline in scan on ion microprobe. Be, Ba, and F were not detected and pargasite incorporate significant amounts. Among * fncludes 12.91 wlo/"HrO calculatedassuming 6HrO per 20 O atoms. serendibitelocalities overall, the ratio of Na/Ca increases (exceptwhere Na/Ca < 0.01), as follows: Pl' Cpx < Srd << Scp, Prg, Tur (Fig. l0), a sequenceconsistent with the (Henry partitioning between phlogopite and pargasite(Westrich, ratio of Na/Ca increasingPl < Tur in pelitic rocks reversalin Tur-Prg relations l98l). Kd [: @/OH)Tur/(F/OH)Phl] is4.4-6.4 (17 in no. and Guidotti, 1985).The 7), substantiallyabove the Ko valuesof 0.75- 1.7for tour- with decreasingratio of Na/Ca is causedby the modest maline + biotite pairs in eight kornerupine-bearingsam- decreasein the ratio of Na/Ca in pargasiteas compared ples (Grew et al., 1990b).Possibly the enhancedfraction- to the hundredfold decreasein the Na/Ca ratio in tour- Na/ ation of F into tourmaline relative to biotite is causedby maline, which parallels the decreasesin the ratio of sodic the substitution of Fe3* for Mg in tourmaline on the I Ca in serendibite and clinopyroxene in the more site, which is bonded to O(1). The enhancedfractionation samples.Contrasting site occupanciescould explain these while ofF is suggestedby the site occupanciesin buergerite,in trends. In pargasite,Ca is restricted to the M(4) site, present which the l site is more than 600/ooccupied by Fe3*and Na vies with K on the A site and little, if any' Na is for the O(l) site is occupiedby F (Barton, 1969;Tippe and on the M(4) site. On the other hand, Na substitutes Hamilton. 197l). The contents of Fe3*in the octahedral Ca on one site in tourmaline and clinopyroxene. In ser- layer in associatedbiotite are probably less than that in endibite, Na substitutesfor Ca on two sites,but the ratios (P. the Ysite of tourmaline;Guidotti and Dyar (1991)report of CalNa are similar at 3.4 and 4.6 on the two sites that r6tFe3+: l0-l3o/o 31d [+llis:+: 8o/oof the total Fe in K. Sen Gupta and G. H. Swihart, unpublished data on a biotite associatedwith magnetite in pelitic rocks. The as- Johnsburgserendibite; see also SenGupta et al., 1989). sociation of Fe3*and F in tourmaline implies that "Fe-F Fe-Mg distribution is lessregular than F-OH or Na-Ca avoidance" (e.g.,Munoz, 1984,p. 472) applies only to distribution (Fig. I l), probably becauseFe3+ and Fe2+can- Fe2* and not to Fe3*. An "Fe3*-F attraction" deserves not be distinguished in electron microprobe analyses. consideration as a factor in F-OH distribution. Within the limitations imposed by ambiguitiesin the ratio In general,Na contents of the Tayozhnoye calc-silicate of Fe2*/Fe3*,the sequenceof increasing Mg/Fe2* ratio is GREW ET AL.: SERENDIBITE 1075

V5 tv6 v3 tv5 v2 tv7

0 001 0 005 01 005 01 05 10 Atomic NeLiCaratio

quenceof ing ratio of MglFe in serendibiteor olivine on a semilogarithmic diagram (adapted from Albee, 1968). Num- bering in column and plotting of maximum and minimum values follow the same system as in Figure 10. The only compositions lows:A: Sl-4,B : 523t,C: Sl-3,D:84-5, andE: 18964. plotted are thosefor which Mg/Fe2*is inferred to difer little from In caseswhere more than one analysis is available, only the the ratio of Mg,/Fe,".(O1, Chu, Phl; all minerals u.ith MglFe > maximum and minimum ratios of Na/Ca are plotted. Arrows at 9), or for which the ratio of Mg/Fe2t can be estimated from left side indicate Na is below detection in theseminerals. Na/Ca stoichiometry (Srd, Spl with MglFe < 9). For VII, 7 wro/oB,Ol < 0.02 are approximate becauseof the difiiculty of analyzing was assumedin calculating Mg/Fst* in serendibite. small quantities of NarO (< 0.2 wto/o).Localities II_VI (top half ofdiagram) are arrangedaccording to decreasingratio ofNa/Ca in serendibite;locality IV (Tayozhnoye,bottom half), according to the ratio of Na,/Cain tourmaline.

TABLE12. Analysesof spineland magnetite

124566788 Spl spt spt Mas spt Spt Mag UM .qpl _spl UM IGEM IGEM IGEM IGEM IGEM IGEM IGEM

wtch sio, 0.00 0.00 0.16 Tio, 0.34 0.11 0.00 0.13 0.04 0.06 0.03 0.03 0.03 0.13 0.00 0.00 o.12 Alr03 64.31 62.74 68.64 66.22 66.52 0.66 65.26 65.74 0.45 Cr"O. o.o2 0.06 0.03 0.04 Vro" 0.00 0.03 FerO3 4.01 4.49 0.00 1.67 0.80 68.49 4.40 2.76 69.63 FeO 8.65 13.06 10.69 14.00 13.55 28.25 9.95 13.24 29.90 MnO 0.52 0.86 0.27 0.15 0.17 0.31 0.14 0.17 0.30 ZnO 0.27 0.15 0.38 0.58 0.53 0.19 0.88 0.78 Mgo 21.20 18.12 20.68 18.42 18.57 1.56 20.82 18.77 0.93 CaO 0.00 0.00 0.00 0.04 0.00 0.00 0.00 Naro 0.00 0.00 0.11 0.00 0.00 KrO 0.00 0.00 0.05 0.00 0.00 Total 99.02 99.57 100.69 |01.10 100.33 99.97 101.76 101.46 101.46 Formulae for four O atoms and three cationg Ti 0.001 0.001 0.001 0.001 0.001 0.004 0.000 0.000 0.003 AI 1.922 1.909 2.OO2 1.966 1.984 0.030 1.917 1.948 0.020 Cr 0.000 0.001 0.001 0.001 Fe3* o.077 0.087 0.000 0.032 0.015 1.963 0.083 0.052 1.973 Total 2.000 1.999- 2.003 2.000 2.000 1.997 2.001 2.000 1.996 Fer* 0.183 0.282 o.221 0.295 o.287 0.900 o.207 0.278 os42 Mn 0.011 0.019 0.006 0.003 0.004 0.010 0.003 0.004 0.010 Zn 0.005 0.003 0.007 0.011 0.010 0.00s 0.016 0.014 Mg 0.801 0.697 0.763 0.692 0.700 0-089 0.773 0.703 0.052 Total 1.000 1.001 0.997 1.001 1.001 1.004 0.999 0.999 1.004 Total cat. 3.000 3.000 3.000 3.001 3.001 3.001 3.000 3.000 3.000 Note' Fe3+lFe2+calculated from . stoichiometry.UM and IGEM indicatethe electron microprobeused. Includes0.001 V3*. t076 GREW ET AL.: SERENDIBITE

1988; Nicol- Spl < Srd, Ol < Prg < Tur < Cpx, Phl and Ol < Chu. anorthite (Atnr-nn,Pertsev and Boronikhin, of a Thus the sequencefor serendibite localities in general, let, 1988; this study, Table 7). With the exception 1991)'sodic including more Fe-rich assemblages,differs little from the few specimensfrom Johnsburg(Grew et al., seren- sequenceGrew et al. (1991) inferred for the Fe-poor plagioclaseis not found with serendibite. Sodian with scapolite Johnsburgassemblages. aiUit" ut Russell and Johnsburg occurs lX(Ca): 0.59-0.75,Grew et al., 1990a,l99l)' DrscussroN The Johnsburg and Tayozhnoye serendibite samples a meta- Featuresof serendibite parageneses developed through metasomatism. By analogy, somatic origin was inferred for Russell serendibite(Grew Serendibitemostly occurs in rocks containing substan- et al., 1990a) and such an origin appearsto be plausible tial CaO, (Mg,Fe)O, AlrOr, and SiOr, that is, aluminous for the skarn rocks formed between two contrasting li- calc-silicateassemblages such as magnesian skarns. Seren- thologies at the other localities listed in Table I (Deer et dibite has not been found with quartz (seealso Hutcheon at., tgZ8). von Knorring (1967)and Bowdenet al' (1969) et al., 1977), nor has it been found in carbonate rocks describedthe Handeni assemblageas a skarn in marble, such as marble. Only two Ca-poor parageneseshave been leaving open the possibility of a metasomatic origin, reported: the orthosilicate rocks from Tayozhnoye and a whereasNicollet (1988, 1990a)suggested that the seren- rock rich in potassium feldspar from Johnsburg. dibite-bearing rocks at the two Madagascarlocalities are In most cases,calc-silicate rocks containing serendibite metarodingitesinto which B could have been introduced from other localities are similar in mineralogy to the mag- prior to, rather than during, metamorphism. nesianskarns from Tayozhnoye,and relationshipsamong the minerals have many features in common. In partic- Petrogeneticgrids for serendibiteparagenesis ular, poikilitic tourmaline mantles around serendibiteare characteristic of Tayozhnoye skarns, Johnsburg, River- side.Handeni. and Russell.However, in contrastto coeval development of pargasiteand serendibite in some Tay- ozhnoye skarns, pargasite formed later than serendibite in the Russell and Johnsburg skarns (Grew et al-, 1990a, l99l), whereastourmaline appearsto have precededser- endibite in the Melville skarn (Hutcheon et al., 1977)-The Ianapera rock differs from the other skarns in that serendibite apparently crystallized in an equilibrium assemblage Srd + Tur + Cpx + An + Hbl * Czo-r Zo * Grs (Nicollet, 1988, 1990a).The last three minerals,as well mobile components, that is, the skarns behave as open least during as tourmaline, are clearly secondary in Tayozhnoye, systemswith regard to these constituents,at 1957)' In ad- Johnsburg, and Riverside skarns. formation of serendibite (seeKorzhinskii, Serendibite-bearingskarns range from highly magne- dition, we have only considered paragenesesassociated to be rea- sian compositions (Johnsburg, Russell, Ihosy) to those with HrO-rich fluids. This assumption appears intermediate in the ratio ofMg/Fe; the most Fe-rich seren- sonablefor the early stagesof metamorphism duringwhich justified during dibite has a (Fe3* * Fe'z*)/Mg: 1.08 (Ianapera, Mada- serendibiteformed. It is for the later stages gascar,Nicollet, 1988,1990a). The Johnsburgand Russell which clintonite and grossular+ chlorite formed, because of paragenesesare distinctive in their relatively high ratios clintonite and grossular + chlorite are characteristic of Na/Ca and associationwith scapolite,thereby implying HrO-rich fluids (Rice, 1983). CaO-MgO- that serendibiteis not restrictedto Na-poor compositions, bisposition ofthe phasesin the tetrahedron is illus- at least at intermediate pressures. AlrO3-SiO, (inert components) or chemography is unambiguous Minerals associatedwith serendibite have some dis- traled in Figure 12. The chemography and seren- tinctive compositional features,several of which are char- except for the relative positions of tourmaline with spinel and acteristic of high-temperature, silica-undersaturated mag- dibite, which appearto be nearly colinear for tourmaline nesian (calc-silicate)skarns' Clinopyroxenes are moderately quartz.Had FerO. contentsbeen estimated a coffe- (2-5 wto/oAI.O.) to extremelyaluminous, reaching l8 wto/o and combined with AlrO. (thereby deducting as was done for in the Ianapera sample (Nicollet, 1988)' In the Johnsburg sponding amount of FeO added to MgO), compositions clinopyroxene samples,a significant part of the AlrO, is serendibite and spinel, then tourmaline incorporatedas NaAlSirOu(Grew et al., l99l), whereas in the Tayozhnoye,Melville, and Ianaperaclinopyroxene samples,it is incorporatedlargely as Cuter4lt+t(AlSi)O. and Q4toJfsr+r+r(AlSi)O6 (Hutcheon etal., 19771'Nicollet, 1988; this study, Table 6). Hornblendes are pargasitic hornblende, pargasite, and in the Ianapera sample, the Na and l4). phasesin an isother- equivalent to magnesio-sadanagaite,for which Nicollet The invariant point involving six for a (1988)reports Si : 5.341per formula unit. Plagioclaseis mal. isobaric p(BzOJ-p(COr) diagram applicable GREW ET AL.: SERENDIBITE 1077

(SRD)

P2 ----+ t

;

Mgo AlzOe (FeO) (FezOs) Yn€ \I/u/o x VO Fig. 12. CompositionsofTayozhnoye clinopyroxene (Cpx), uvite(Tur), serendibite (Srd), spinel (Spl), and anorthite (An) are plottedin termsof MgO, SiO,,AlrO3, and CaO(projected from calcite).For Cpxand Tur, Feis assumedto beFeO and combined (cAL) with MgO. For Srd and Spl, the ratio of Fe3+/Fe2+has been estimatedfrom stoichiometry,FerO, is combinedwith AlrOr, [(BzOe)-+ andFeO is combinedwith MgO.CaTs is thecalcium_Tschermak Fig. 13. Diagramof p(CO)-p(BrO,)for invariantpoint in- component,6utotfrrr (AlSi)O6. volving six phases(Spl, Srd, Cpx, An, Tur, Cal) for the model systemof four inert components(CaO, MgO, AlrO., SiOr)and threeperfectly mobile components (COr, BrO3, HrO). p, refers specified HrO activity (Fig. 13) should be applicable to to low to intermediatepressures; P, refersto high pressures(see the seven serendibite localities for which p-Iconditions text).In compatibilitydia$ams, solid lines join phasescoexisting have been estimated, becauseestimated temperatureslie with calcite;dashed lines join phasesnot coexistingwith calcite. in a relatively narrow range (600-825 "C, Table l). In addition, synthesis experiments in the COr-free system nopyroxene and tourmaline, whereasspinel partitions Fe2* CaO-MgO-AIrO3-SiOr-BrOr-HrO have been carried out relative to serendibite(Fig. I l). Most likely, any increase over a similar temperatureinterval, 600-800.C, but with in the serendibitestability field causedby additional Fer* wider a range of pressures(1.8-20 kbar, G. Werding, N. or Fe3+is small compared to effectsof other variables. N. Pertsev,and W. Schreyer,unpublished data). The ex- Figure I 3 can also be used to deducethe effect of pres- periments show that tourmaline coexistswith serendibite sure on serendibite-tourmaline relations according to over the rangeofpressures and temperaturesstudied. Fig_ Korzhinskii's depth-faciesprinciple, whereby p(CO,) in- ure 13 indicates that this assemblagewould be stable at creaseswith pressure[Pertsev, l97l,Fig.36, applied this high p(B,O) and low &(CO,), that is, between the uni- principle to the distribution of borates using the p(COr)- variant reactions (An) and (Cal). These conditions ap- p(BrOJ diagraml. At lower pressures,P,, serendibiteap- parently were not attained at the peak metamorphic tem- pears first as p(BrOr) increases,whereas tourmaline re- peratures at the localities listed in Table l, exceptIanapera quires much greater,apparently unattainable, p(BrOr) in and Melville Peninsula. At the other localities, there is order to be stabilizedwith calcite. At the higher pressures, little evidence for stable high-temperatureSrd * Tur as- Pr,Ihe sequencewith increasingp@rOr) is reversed;tour- semblages, although secondary Tur * Srd assemblages maline appearsfirst and is stable with spinel and calcite. are common (seebelow). Consequently,p(BrOr) probably We are not aware of any reports of high-temperature pro- did not exceedthat for the invariant point, except at the grade tourmaline + calcite * spinel assemblages.Tour- Ianapera and Melville Peninsula localities. maline * spinel assemblagesare not common (e.g.,pert- At low p(CO) in silica-undersaturated,spinel-bearing sev, l97l); one example is the Tayozhnoye orthosilicate rocks, serendibiteappears with increasingp(BrOr), where- rock (Pertsevand Boronikhin, 1986;this study).However, as p(COr), at high tourmaline + calcite should appear. carbonate is rare in theserocks and in the one caseana- The relative abundance ofTur + Cal in the absenceof lyzed, turned out to be magnesite.Thus p(COr), and cor- (e.g., povondra spinel Dunn et al., 1977;Deeret al., 1986: responding pressures,may not exceed those of the in- and Novak, 1986) compared to serendibite is causedby variant point. In summary, serendibite + anorthite + factors other than p(COr), namely silica saturation,NarO, clinopyroxene assemblages,including those at Tayozh- or both; NarO is preferentially fractionated inro rour_ noye, Ihosy, and Riverside, formed at relatively low p(BrO.) maline and stabilizesit (Fig. l0). and p(COr) (correspondingto moderate to relatively low The effect of Fe on tourmaline-serendibite relations is pressures)in the field between the univariant reactions less obvious. Serendibite partitions Fe,", relative to cli- (Tur) and (Cal). 1078 GREW ET AL.: SERENDIBITE

maline mantles at Tayozhnoye and Johnsburg (Grew et al., l99l; this study,Figs. 2A, 2D). This assemblage,apparently unstableat high temperatures,appears to be stable at lower temperaturesas a breakdown product of serendibite.

CoNcr,usror',1 We now return to the question of what factors control o the paragenesisof serendibite. This mineral is restricted (g rocks formed at relatively high q) to silica-undersaturated (600-825 and low to intermediate pres- E temperatures "C) o sures(<10 kbar). Low CO, activities are critical, as Ni- l,M collet ( 1988)noted. Introduction of HrO-rich fluids at high would create favorable conditions for ser- tqPt I temperatures *_ryH endibite if B were available. At lower temperatures,CO, (SPL) activities in aqueousfluids are sufficiently high to convert serendibite to its carbonated equivalent, tourmaline * tCPXl spinel + calcite, which is commonly observedas a breakdown of serendibite. Metasomatic skarns, developed be- (cPX) tween contrasting rock types, provide a suitable environ- ment for serendibite; at seven of the nine localities, serendibitehas developedin this setting, and field dataat ------> X(COz) the remaining two do not preclude a similar origin. Kor- Fig. 14. Diagramof T-X(COJ for the sameinvariant point zhinskii (1955) proposed a model whereby magnesian as in Figure13, hereshown as [Zo]. The two invariantpoints skarns, such as those in the Tayozhnoye deposit' formed involving zoisite,[SpU and [Cpx], are not complete;reactions while granitizing, dominantly aqueousfluids invade a con- involving Zo with Srd or Tur are not shown.In compatibility tact betweenmarble and quartzofeldspathicrock. At higlr join phases with calcite;dashed diagrams,solid lines coexisting temperatures,silica-undersaturated, spinel-bearing zones linesjoin phasesnot coexistingwith calcite.The inferredcon- in the skarns would be suitable sites for serendibite for- ditionsfor Tayozhnoye(T, includingpossible retrograde paths mation, while tourmaline would form in more siliceous, asbroad arrows), Ianapera, Madagascar (I) and Melville Penin- This combination of silica-undersatu- sula(M) arealso shown. spinel-free zones. rated skarns,metamorphosed at fairly high temperatures during influx of B-bearing aqueous fluids, is not com- A secondperspective on serendibitepetrogenesis is pro- monly encountered in metamorphic terrains, and thus vided by a T-X(COr) diagram ofthe sameinvariant point, serendibiteis a rare mineral. which is labeled lZolin Figure 14. We suggestthat this invariant point lies in the stability field of An + Cal. This Acxxowr,rncMENTs assem- assemblageis reported in the Ihosy, Madagascar We thank the following individuals and institutions for samples: the blage(Nicollet, 1988),and calcite,in most casessecond- A.E. Fersman Mineralogical Museum of the U.S.S'R. Academy of Sci- ary, occurswith anorthite and tourmaline in sample 5152 ences,for three samples(including 5 15 I and 5 I 58, latter is alsono' 412M), (Tayozhnoye). Assemblageswith primary zoisite or cli- M. Maleev. Sofia, for 5152, British Museurn (Natural History) for BM of Natural History for 136851, T' Frisch for (Ianapera, possibly Melville Peninsula) would 87050, National Museum nozoisite the Handeni specimen,Harvard Mineralogical Museum for 94852, and have beenstable with more H,O-rich fluids. Rice (1983) C. Nicollet for 261gand 320. We also thank A.A. Godovikov, P' Dunn, calculated that the univariant reaction, Zo : An * Cal, and C.A. Francis for information regardingthe museum samples.In ad- decreasesfrom X(CO,) : 0.3 at 500 "C to 0'04 at 750'C dition, we are grateful to N.V. Irskova for assistance with the electron Yakutsk; P.K. SenGupta and G'H' : 5 kbarl and that clintonite and grossular + microprobe at the Institute ofceology, tP(fluid) providing unpublished crystallographic data on serendibite zoisite sta- Swihart for chlorite forms at T-X(COr) conditions of the from samples515l and 5152; D.R. Veblen for unpublished information bility field. Thus Figure 14 can be used to infer possible on olivine; and D.M. Morton for assistancein collectingat fuverside' retrograde paths (broad arrows) for Tayozhnoye. Seren- This paper has been much improved as a result of the critical reviews Guidotti, and D'J' Henry' dibite crystallized at high temperatures in the field be- by D M. Burt, J.V. Chernosky,P.C. Grew, C'V. wassupponedby U.S. National ScienceFoundation Grant reactions (Cal) and (Tur). Meta- This research tween the univariant DPP-8613241 to the University of Maine and by the interacademyex- morphic evolution was one of decreasingtemperature and changeprogram betweenthe U.S.S'R. and U.S'A. It was carriedout within X(CO,), so that in some cases,T-X(COr) conditions at- the framework of IGCP Project 235, "Metamorphism and Geodynamics'" tained those in the zoisite stability field. The paths first cut across the univariant reaction (Cal), stabilizing the Rrrnnr,Ncrs CITED + Tur, as indicated by the serendibite assemblageSrd Albee. A.L. (1968)Metamorphic zonesin northern Yermont' lnE-anZnn' relics in tourmaline (Fig. 2A). Then the paths cut the W.S. White, J.B. Hadley, and J.B. Thompson, Jr', Eds', Studies of univariant reactions (Spl) and (Cpx), stabilizing Tur * Appalachian geology: Northern and maritime, p' 329-341 ' Wiley, New Cal + Spl, an assemblagefound in some poikilitic tour- York. GREW ET AL.: SERENDIBITE t079

Banon, Randolf, (1969) Jr. Refinementofthe crystalstructure ofbuergerite Kulakovsky, A.L. (1985) Platinoids in rocks and ores ofthe Tayozhnoye and the absolute orientation of tourmalines. Acta Crystallographica, skarn-magnetitedeposit (Central Aldan). Doklady Akademii Nauk SSSR, B25, 1524-1533. 281, 129-133 (in Russian) Boronikhin, V.A., and Tsepin, (1980) A.I. A univenal program for the Kulakovsky, A.L., and Pertsev,N.N. (1986) Regenerationof magnesium real-time calculation ofcorrections and statistical processingof mea_ orthosilicatesand severalaspects in the genesisofrich iron ores ofthe surementsduring quantitative electron microprobe analysis.In Appa- Tayozhnoye deposit (Central Aldan). Geologiya Rudnykh Mestorozh_ ratus and methods of X-ray analysis, 23, p. 204-217. kningrad (in deniy, 28 (2),36-46 (in Russian). Russian). -(1987) Allochthonous carbonate rocks of the central Al&n pre_ Bowden,P., von Knorring, Oleg,and Bartholemew,R.W. (l969). Sinhalite cambrian. Izvestiya Akademii Nauk SSSR, Seriya Geologicheskaya, and serendibitefrom Tanzania.Mineralogical Magazine, 37, 145_146- 1987(l), 52-6E (in Russian). Coomaraswamy,A.K. (1902) The crystallinelimestones of Ceylon. euar_ Larsen,E.S., and Schaller,W.T. (1932) Serendibitefrom Warren County, terly Joumal of the Geological Societyof London, 5g, 399_422. New York, and its paragenesis.American Mineralogist, 17,457_465. Deer, W.A., Howie, R.A., and Zussman,J. (1978) In Rock_formingmin- Lisitsyn, A.Ye., Rudnev, V.Y., Gaft, A.L., Dobrovol'skaya, N.V., Dara, erals, vol. 24: Single-chain (2nd silicates edition), 66g p. Longman, O.M., and Tkacheva,T.V. (1985) New data on ludwigite and ascharite London. of the Tayozhnoyeskarn-magnetite (southernyakutil). - deposit Zapiski (1982) In Rock-forming minerals,vol. lA: Orthosilicates(2nd edi_ VsesoyuznogoMineralogischeskogo Obshchestva, I 985(I ), 62-7 3 (in tion), 919 p. Longman, London. Russian). -(1986) In Rock-forrning minerals, vol. lB: Disilicates and ring Marakushev, A.A. (1958) Petrology ofthe Tayozhnoye iron-ore deposit silicates(2nd edition), p. york. 629 Longman and Wiley, New in the Archean of the Aldan Shield. Trudy Dal'nevostochnogoFiliala Dunn, P.J Appleman, , D., Nelen, J.A., and Norberg, J. (1977) Uvite, a imeni V.L. Komarova Akademii Nauk SSSR,Seriya Geologicheskaya, new (old) common member ofthe tourmaline group and its implications vol. 5, l2l p. Magadan Press,Magadan (in Russian). for collectors.Mineralogical Record, 8, 100-108. Matsubara, S-, and Motoyoshi, Yoichi (1985) Potassium pargasitefrom Grew, E.S.(1988) Kornerupine at the Sar-e-Sang,Afghanistan, whiteschist Einstiidingen, Liitzow-Holm Bay, East Antarctica. Mineralogical Mag- locality: Implications for tourmaline-kornerupinedistribution in meta_ azine. 49. 703-707 . morphic rocks. American Mineralogist, 73, 345_357. Moore, P.B., and Araki, T. (1979) Kornerupine: A detailed crystal-chem- Grew, E.S.,and Hinthorne, J.R. (1983)Boron in sillimanite. Science.221. ical study. Neues Jahrbuch Iiir Mineralogie Abhandlungen, 134,317- 547-549. 336. Grew, E.S., Yates, M.G., and delorraine, W. (1990a) Serendibitefrom Munoz, J.L. (1984)F-OH and CI-OH exchangein micas with applications the northwest Adirondack york, Lowlands,in Russell,New USA. Min_ to hydrotherrnal ore deposits. In Mineralogical Society ofAmerica Re- eralogicalMagazing, 54, 135-137. views in Mineralogy, 13,469-493. Grew, E.S.,Chemosky, J.V., Werding, G., Abraham, K., Marquez, Nich_ Nicollet, Christian (l 988) M6tabasitesganulitiques,anorthosites et roches olas, and Hinthorne, (1990b) J.R. Chemistry ofkomerupine and as_ associ6esde la cro0te inlErieure. Exemples pris i Madagascar et dans sociated minerals, a wet chemical, ion microprobe, and X-ray study le Massif Central frangais.Arguments en faveur d'un m6tarnorphisme emphasizingLi, Be, petrology, B and F contents.Journal of 3 I, I 025_ associ6ii I'extension lithosphdrique. ThCse d'Etat, Universit6 Blaise 1070. Pascal,Clermont-Ferrand (in French). Grew, E.S.,Yates, M.G., p.B., Swihart, G.H., Moore, and Marquez, Nich_ - ( I 990a) Crustal evolution of the granulites of Madagascar. In D. olas (1991) The paragenesis york, ofserendibite at Johnsburg,New Vielzeufand Ph. Vidal, Eds., Granulites and crustal evolution, p. 291- USA: An example of boron enrichment in the granulite facies.In L.L. 310. NATO ASI Series,Kluwer Academic Publishers,Dordrecht. Perchuk, Ed., Progress in metamorphic and magmatic petrology: A -(1990b) Occurrencesof grandidierite, serendibite,and tourmaline memorial volume in honorof D.S. Korzhinskiy, p. 247-2g5. Cambridge near Ihosy, southern Madagascar.Mineralogical lN4agazine,54,l3l- University Press,Cambridge, United Kingdom. I JJ. Grice, J.D., and Robinson, (1989) G.W. Feruvite, a new member of the Nonestam, R., Dahl, S., and Bovin, J.-O. (1989) The crystal structure of tourmaline group, and its crystal structure.Canadian Mineralogist, 27, magnesium-aluminumludwigite, Mgr,, Alo,,FeorrTio orsbo o,BOr, a r99-203. combined single crystal X-ray and HREM study. Zeitschrift fiir Kris- Guggenheim,Stephen (1984) The brittle micas. In Mineralogical Society tallographie 187, 201-21 l. of America Reviews in Mineralogy, 13, 6l-104. Pertsev,N.N. (1971) Paragenesesofboron minerals in magnesianskarns, Guidotti, C V., and Dyar, M.D. (1991) Ferric iron in metamorphic biotite 192 p Nauka, Moscow (in Russian). and its petrologic and crystallochemicalirnplications. American Min- Pertsev,N.N., and Boronikhin, V.A. (1986) Sinhalite, tourmaline, seren- eralogist,7 1 - 6, 6 | 175. dibite and ludwigite in magnetite ore ofthe Tayozhnoye deposit (Central Henderson, (1983) J.R. Structure and metamorphism of the Aphebian Aldan). In A.A. Godovikov, Ed., New data on minerals,A.E. Fersman Penrhyn Group and its Archean basementcomplex in the Lyon inlet Mineralogical Museum of the USSR Academy of Sciences,33, p. 143- area, Melwille Peninsula, Districr of Franklin. Geological Survey of 147. Nauka, Moscow (in Russnn). CanadaBulletin, 324,50 p. - (1988) Scheelitemineralization in skarn-magnetitedeposits of rhe Henry, D.J., and Guidotti, C.V. (1985) Tourmaline as a petrogeneticin_ central Aldan. MineralogicheskiyZhlurnal, l0(l),94-97 (in Russian). dicator mineral: An example from the staurolite-gade metapelites of Pertsev,N.N., and Kulakovsky, A.L. (1987)Metasomatic quartzites, poly- NW Maine. American Mineralogist, 70, l-15. metamorphism and deformation in the Tayozhnoye iron-ore deposit Hinthome, J.R., and Ribbe, P.H. (1974) Determination of boron in chon- (Central Aldan). In D.S. Korzhinskiy, L.L. perchuk, and N.N. pertsev, drodite by ion microprobe mass analysis.American Mineralogist, 59, Eds-, Regularities of metamagmatism, metasomatism ano meramor- ll23-t126. phism, p. l0l-l18. Nauka, Moscow(in Russian). Hutcheon, I., Gunter, A.E., and kcheminant, A.N. (1977) Serendibite - (1988) Iron bearingcomplex ofthe central Aldan: polyrnetamorph- from Penrhyn peninsula, Group Marble, Melville District of Franklin. ism and structural evolution, 237 p. Nauka, Moscow (in Russian). CanadianMineralogist, 15, 108-l 12. Pertsev,N.N., and Nikitina, I.B. (1959) New data on serendibite.Zapisk:t Kohn, S.C.,Henderson, C.M.B., and Mason,R-A. (1989)Element zoning VsesoyuznogoMineralogicheskogo Obshchestva, 88 (2), 169-172 (in trends in olivine phenocrysts from a supposed primary high_magnesian Russian). andesite:An electron-and ion-microprobe study.Contributions to Min- Povondra, P., and Novak, M. (1986) Tourmalines in metamorphosed eralogyand Petrology, 103, 242-252. carbonate rocks from western Moravia, Czechoslovakia. Neues Jahr- Korzhinskii, D.S. (1955) Oulline of metasomatic processes.In Funda- buch filr Mineralogie Monarshefte, 1986(6), 273-282 mental problems in the study of magmatogenicore deposits(2nd edi_ Prior, G.T., and Coomaraswamy,A.K. (1903) Serendibite,a new boro- tion), p. 335-453. U.S.S.R.Academy of Sciences,Moscow (in Russian). silicate from Ceylon. Mineralogical Magazine, 13, 224-227 . - (l 957) The physico-chernical basisfor the analysisofmineral para_ Rice, J.M ( I 983) Metamorphism of rodingites:Part l. phaserelations in geneses, p. 184 U.S.S.R. Academy of Sciences,Moscow (in Russian; a portion of the system CaO-MgO-AIrO,-SiO,-CO,-H,O. American york) also 1959 hanslation, ConsultantsBureau. New Journalof Science.283-A. l2l-l 50. 1080 GREW ET AL.: SERENDIBITE

( equilibria betweenmica-amphibole Richmond, G.M. (1939) Serendibite and associatedminerals from the Westrich,H.R. I 98 I ) F-OH exchange pairs. Contributions to Mineralogy and Petrology, 78' 318- New City Quarry, Riverside, Califomia. American Mineralogist, 24' mineral 72s-726. 323. (1988) Mineral assemblagezoning in the Crestmore Schaller.W.T., and Hildebrand, F.A' (1955) A secondoccurrence of the Wiechmann. M.J. (Califomia) aureole.Eos, 69' 514' mineral sinhalite(2MgO'AlrO, B'O,). American Mineralogist,40, 453- contact metasomatic (1988) Contact metamorphism of the Black 457. Yates, M.G., and Howd, F.H. Hancock County, Maine. Maritime Sediments SenGupta, P.K., Swihan, G.H., and Van Derveer, D.G' (1989) A restudy Hawk Zn-Pb-Cu deposit, ofthe metal occupancies in serendibite. Geological Society ofAmerica and Atlantic GeologY,24,267-279. Abstracts with Progmms, 2l (6), 4120. l, 1990 Serdyuchenko,D.P. (1959) The origin ofthe Archean iron ores ofSouth M,+ruscnrrr RECEIvEDFeorulnv ll, 1991 Yakutiya. Izvestiya Akademii Nauk SSSR,Seriya Geologicheskaya,E, MnNuscnrvr AcCEPTEDFEsnuARv 34-49. Shabynin, L.l. (1974) Ore deposits in magnesianskam formations, 287 p- Nedra. Moscow (in Russian). ABBREITATIoNS Shabynin,L.L, and Pertsev,N.N. (1956) Warwickite and serendibitefrom AppnNorx 1. MrNnw. Vsesolr:znogo Miner- : magnesian skams of southern Yakutiya. Zapiski Anh : anhydrite, An : anorthite, Ap : apatite, Bt biotite, 85 (4), 515-528 (in Russian). : alogicheskogoObshchestva, Cal : calcite, Ccp : g6.1..tyrite, Chl : chlorite, Chu clino- Shimazaki, Hidehiko, Bunno, Michiaki, and Ozawa, Tohru (1984) Sa- : humite, Cpx : clinopyroxene, Czo : clinozoisite, Cln clin- danagaite and magnesio-sadanagaite,new silica-poor members of calcic : Di : diopside, Dol : dolomite' Ep : amphibole from Japan. American Mineralogist, 69, 465-47 1. tonite, Crn comndum, : : garnet' grandidierite Steele,I.M., Hervig, R.L., Hutcheon,I.D., and Smith, J.V. (1981)Ion epidote, Fsp 1"16tout,Grt Gdd: [(Mg' : : microprobe techniquesand analysesof olivine and low-Ca p)'roxene. Fe)AlrBSiOJ, 66 : grossular, Hbl hornblende, Kfs Po- : American Mineralogist, 66, 526-546. tassium feldspar, Lud : ludwigite [(Mg,Fe'?*)rFe3*BOr],Mgs Takeuchi, Y., Watanabe,T., and Ito, T. (1950) The crystal structuresof magnesite,Mag:.u*.,ite, Mrg: margarite,Ms: muscovite, warwickite, ludwigite and pinakiolite. Acta Crystallogaphica, 3, 98- Ol: olivine, Opx: orthopyroxene,Prg: p:Irgasite,Phl: phlog- 107. opite, Pl: plagioclase,Po: pyrrhotite, Py: pyrite,Qtz: qtuartz' A., and Hamilton, w.C. (1971) A neutron-diffraction study of the : Tippe, Spr : sapphirine, scp : scapolite,Srd : serendibite,Srp Ser- ferric tourmaline, buergerite.American Mineralogist, 56' 101-113. : pentine, Snh : sinhalite Spl : spinel, Tms von Knorring, O. (1967) A skarn occurrenceofsinhalite from Tanzama. [(Mg,Fe)AlBOJ, : Tr : tremolite, Tur : tourmaline, Research Institute of African Geology of the University of I-eeds I I th thomsonite, Ttn titanite, : Annual Report (1965-1966), p. 40. I-eeds,England. Zo zoisite, Zrn: zircon.