American Mineralogist, Volume 66, pages 1022_1033, IggI Surinagite, taaffeite, and heryllian sapphirine from pegmatites ingranulite-facies rocks of caJey Bay,Enderby Land, fntarctica

• Main Author: Eowano S. Gnew
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Antarctic; Casey Bay; Tange Promontory; Antarc*; Antarctica; Enderby Land
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.567.1911; http://rruff.info/doclib/am/vol66/AM66_1022.pdf

Surinamite, taaffeite, berylliaa sapphirine, niobian rutile, chrysoberyl, and wagnerite occurin sillimanite-rich, medium-grained segregations in two pegmaiites ofprobable late Archean age which cut granulite-facies.rocks near Mclntyre llaia-1erzz,s,4go05,E) in casey Bay,Antarctica. Antarctic surinamite contains 30.9-32.1 wt.za sior, 33.7-37.3 wt.vo Alror,9.i-l3'4 wt.Eo Feo, 0.01-0.2 wt.vo Mro, and 16.4-1g.4 wt.vo Mgo,0.5-r wt.vo Be, and 0.66+0.2 wt'Vo H2O. Assuming water is absent, a constant BeO content of 3.5 wt.Vo, and possible Fe3*for Al substitution, surinamite analyses recast to 32 oxygens contain 22 cations. Antarctic taafeite conrains 68.5-69.3,xt.vo A12o3,9.7 w.vo Feo, 10.6-11.0 wr. % Mgo, 4.7-5.2 wt.vo zno, and ' 0.5-l wt. % Be. cell parameters sre a:5.6g04 (2)A, c: +t.tC4-(zt1,,"gg"r,;g that this taaffeite is the gR polyrype. sapphirine contains zo.i wt.co sio2, 5 l. l wt.vo Airor ani 9:-l Y.E " Be, indicating substitution of Be for Al: Be + Si: 2Al. Associared garnet contains33 to 42 mole vo pyrope and associated cordierite, I wt.7a NarO. Stable mineral assemblagesin the segregations at the time the pegrnatites crystallized are quartz-sillimanite-surinamite-biotite-orthopyroxene-garnet, quartz-surinamite-taafeite, sillimanite-garnet-biotite-su-rinamite-taaffeite-sapphirine, and siltim4nite-garnet-biotite-chrysoberyl_surinamite. Tem_peratures and pressures at the time of pegmalils emplacement are estimated to have been800-900"c and 7-8 kbar. The Archean beryllian pegmatites are 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.