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Surinagite, Taaffeite, and Heryllian Sapphirine from Pegmatites In American Mineralogist, Volume 66, pages 1022_1033, IggI Surinagite, taaffeite, and heryllian sapphirinefrom pegmatitesin granulite-faciesrocks of caJey Bay,Enderby Land, fntarctica Eowano S. Gnew Department of Earth and Space Sciences U niv ersity of Caldo rni a Los Angeles, Califurnia 90024 Abstrect Surinamite, taaffeite,berylliaa sapphirine,niobian rutile, chrysoberyl,and wagneriteoccur in sillimanite-rich, medium-grainedsegregations in two pegmaiitesofprobable late Archean age which granulite-facies.rocks cut near Mclntyre llaia-1erzz,s,4go05,E) in casey Bay, Antarctica. Antarctic surinamite contains 30.9-32.1wt.za sior, 33.7-37.3wt.vo Alror,9.i- l3'4 wt.Eo Feo, 0.01-0.2wt.vo Mro, and 16.4-1g.4wt.vo Mgo,0.5-r wt.voBe, and 0.66+0.2 wt'VoH2O. Assuming water is absent,a constantBeO content of 3.5 wt.Vo,and possibleFe3* for Al substitution, surinamite analysesrecast to 32 oxygenscontain 22 cations. Antarctic taafeite ,xt.vo conrains68.5-69.3 A12o3,9.7w.vo Feo, 10.6-11.0wr.% Mgo, 4.7-5.2 wt.vo zno, and'0.5-l wt.% Be. cell parameterssre a :5.6g04 (2)A, c : +t.tC4-(zt1, ,"gg"r,;g that this taaffeite gR is the polyrype.sapphirine contains zo.i wt.cosio2, 5 l. l wt.voAiror ani Be, 9:-l Y.E" indicating substitutionof Be for Al: Be + Si : 2Al. Associaredgarnet contains 33 to 42 mole vopyrope and associatedcordierite, I wt.7aNarO. Stablemineral assemblages in the segregationsat the time the pegrnatitescrystallized are quartz-sillimanite-surinamite- biotite-orthopyroxene-garnet, quartz-surinamite-taafeite, sillimanite-garnet-biotite-su- rinamite-taaffeite-sapphirine, and siltim4nite-garnet-biotite-chrysoberyl_surinamite.Tem_ peraturesand pressures at the time of pegmalils emplacementare estimatedto have been 800-900"c and 7-8 kbar. The Archean beryllian pegmatitesare interpreted to be of mag- matic origin and may be related to charnockitic plutonic rocks such as the body exposed& Tange Promontory 70 km to the west. Introduction (Kozhevnikov et al., 1975). From the Musgrave Surinamite, a rare Mg-Al-Fe silicate mineral re_ Rangesof central Australia, Hudson et at. (196i) de_ scribed a taaffeite nodule sheathed by spinel and containing minor beryllian sapphirine (Wilson and Hudson, 1967);the nodule occursin a phlogopite re_ placementzone in metapyroxenite.Teale (19g0) re_ ports taaffeiteand hdgbomiteenclosed in spinel por_ phyroblasts in a phlogopite rock from the Flinders Ranges(South Australia). The type taaffeite is a cut gemstoneof unknown provenance(Anderson el a/.. r95t). I report here a new paragenesisfor surinamite and taaffeite. These unusual minerals are present in sil_ Taaffeite,an oxide of Be, Al, Mg, and Fe, occursin limanite-rich segregationsin two pegmatitescutting metasomatic rocks and in high-grade metamorphic granulite-faciesrocks; associated minerals are garnet, terrains. In China, taaffeite occurs with chrysoberyl beryllian sapphirine, chrysoberyl, wagnerite, and so_ and spinel in lepidolite veins and in reaction skarns dian cordierite. Prior to my finds, surinamite, taaf_ in linestone cut by these veins (Beus, 1966,p. 33) feite, chrysoberyl and wagnerite had not been re- and in eastern Siberia, in nica-fluorite metasomatite ported from Antarctica (Grew, 1980a).I also present 000.3-oux/8 | /09 I 0- I 022$02.00 to22 GREW: SITRINAMITE, TAAFFEITE, BERYLLIAN SAPPHIRINE new X-ray powder and microprobe analytical data The granutite-faciesrocks of the Napier complex on taaffeite, surinamite, and on some of the associ- are cut by two generations of pegmalilss. An early ated minerals. The results of this study suggest that generation includes pegmatites dated radiometrically beryllium is an essential constituent of the Antarctic at 2500 million years (m.y.) (Grew and Manton, surinamite; de Roever (personal communication, 1979),some of which are shown in Figure l. These 1980) independently found significant beryllium in pegmatites are found at many exposuresin the Na- surinamite from the type locality. pier complex, but are nowhere abundant (see also Sheratonet al.,1980). Pegmatitesof the early genera- Geology of the pegmatltes tion form crosscuttingplanar veins up to I m across, Casey Bay and neighboring parts of Enderby Land irregular masses,some of which are associatedwith (66"30'-67"45'5and 48-53oE,Fig. l) are underlain boudinage, or pods. The last are generally 0.5-2 m by a late Archean (2500 m.y.) granulite-facies ter- thick and extend up to 4 m; they lie at a higb angle to rain, the Napier zone or complex (Ravich and Kame- the compositonal layering. The early pegmatiteshave nev, 1975,p. 2; Grew and Manton,1979; Sheratonet a granulite-facies mineralogy. Accessoryminerals in- aL, 1980).The Napier complex consistslargely of or- clude orthopyroxene, garnet, biotite, apatite' per- thopyroxene-quartz-feldspar gneisses ("charnock- rierite, zircon, sillimanite, ilmenite, rutile, monazite, itic" and "enderbitic" gneisses),pyroxene granulite, and locally cordierite, hornblende, and the rare min- garnetiferous gneisses, and subordinate aluminous erals to be described in more detail below' In a few and siliceous rocks, which are locally intruded by cases,the early pegmatites have an aureole of dark- anorthositicand charnockitic rocks (Fig. l). ened country rock a few cm thick. An example of + 6605 50"E Locolitiesfor BerylliumMinerols (Indicoted by Be) In EnderbyLond, Antorctico . ARCHEANPEGMATITES t\ cz cnanNocKtlcRocKS I ..- -.-.-.-., -Fflvf Y-+rt, ^ ANORTHOSITIC\||fvvf rfv ROCKS ,-)/ (,) t- - - - - EXPosuRE [-^ruL4 -,.. ) { ): , i(,"uLai( Mrs. /'ij 67"s {I l-f- ))^ ^ 44ut.pr,^.--.1.-._':':::6"1.-----' r,. ,r,^,:.1.-._. ../"./' l. ; A --t-sAP ":-Z /-oll-tolllngsvHorrilUiil.itn|)2"'a) 'fr .'..:.. /\ .<+ar-7iv CAStfA.AF.' ,fo^' ! | i | |( :r,'t p,oro.io,vffi'!if',,P.,ii; -$... ecf :-) (j $ 1.._€-cil--,' l' ANTARCTICA t00\ . Fig. l. Map of a portion of thc Napicr complcx in Enderby Land showing localitics for surinamite, taaficitc, and beryllian sapphirinc ncar trlclntyre IstanOin Casey lay (indicated by Bc), Archean pegmatitcs of possiblc plutonic origin (small circles) are planar veins and podiform bodies, one of which was dated by Grew and Manton (1979). Sourccs of data: intrusive charnockitic rocks (7) on Tange Promontory (Ravich and Kamcncv, 1975,p. 494 Sheraton el al., 1980),east end of CaseyBay (J. W' Sheraton, p€rsonal communication, l9E0), and north of the Tula Mouatains (Ravich and Kamcnev, l9?5, p. 4%). Spccifc localitics of Soviet samplcs provided by Ye. N. Kamenev (personal communication, l9?8) and of Shcraton et aL's (19E0)two anorthosites by J. W. Shcraton (pffsoml communication" l9E0). GREW: SURINAMITE, TAAFFEITE, BERYLLIAN SAPPHIRINE such an aureole was sampled along a sillimanite- rocks within a tectoniczone of extensivedeformation bearing pegmatitenear Mt. Pyhagoras (Fig. l). The and retrogression.Pegmatites of the later generation country rocks here are osumilite granulites.The au- are abundant. reole is darker in color than the country rock and ap- The surinamite-bearing pegmatite consists of pearsto be richer in biotite. In placesno increasein coarse-grained(>l cm) quartz, microrcline,apatite, biotite was noted in the aureole;the darker color is biotite and sillimanite, and of medium-grained due to darkening of orthopyroxeneas contact with (mostly 0.05-2 mm) dense segregationsrich in sil- the pegmatiteis approached.Near the contact,ortho- limanite, garnet, cordierite, biotite, apatite, and su- pyroxene is partly replaced by garnet or a garnet- rinamite. In hand specimen, much of the microcline quartz intergrowth. The mineralogical changessug- is red. Sillimanite crystals(up to l0 cm long and 3 cm gest an increasein Fe/Mg ratio as well as in water across)are white or brown; brown sillimanite is chat- content of the host rock; temperatureswere suffi- oyant. The medium-grainedsegregations form irreg- ciently high for osumilite to remain in some layers ular veins,masses, and stringersup to 5 cm across.In within the aureole. addition to the above listed minerals, some samples The later generationincludes pegmatites dated ra- of the medium-grained segregationscontain ortho- diometrically at 520m.y. (Grew and Manton, lg79\. pyroxene, wagnerite, pynte, ilmeno-hematite, mag- The later pegmatitesare abundant in CaseyBay but netite, or monazite(Table l). In generalthe minerals are rare elsewherein Enderby Land. They form (l) exceptsillimanite lack preferredorientation. Sillima- cross-cuttingveins up to 4 m in width and up to at nite forms a few coarse prisms 0.5 to several cm in least 350 m in extent, (2) subconcordantpods, or (3) length and bundlesof prisms (mostly 0.05 to 0.2 mm large massesseveral meters and more across.Retro- acrossand up to 0.5 cm in length); someof the bun- gressionof the country rock by the pegmatitesoc- dles appear as fans in thin section. Pleochroic haloes curred under amphibolite-faciesconditions in au- are conspicuousin biotite, which is pale green to reoles generally no more than a few meters thick. brown, and in cordierite.Microveinlets (0.02-0.2 mm Accessoryminerals include biotite, muscovite,horn- thick) of biotite or cordierite cut garnet, sillimanite, blende, sphene, magnetite, allanite, beryl, kyanite, and, rarely, surinamite. Cordierite typically forms sillimanite, garnet, staurolite,tourmaline, dumortier- aggregatesengulfing surinamite, garnet, biotite and ite, and, locally, sodian cordierite. Columbite-tan- finer-grainedsilliminals. In places,surinamite-quartz talite is present at Mount H6llingsworth (Fig. l), grain contacts are preserved. Orthopyroxene grains which is the first
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