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(1984) Manganese-Rich Red Tourmaline from The ConadianMineralogist Y ol. 22, pp. 327-331(1984) MANGANESE-RICH RED TOURMALINE FROM THE FOWLER TALC BELT, NEW YORK ROBERT A. AYUSO ANDC. ERVIN BROWN U.S. GeologicalSuney, Mail Stop 954, Reston,Virginia 22092, U.S.A. ABSTRACT The talc belt includesa sequenceof layeredrocks composedmainly of talc and tremolite and contain- Red uvite from the Arnold talc mine contains up to 4.34 ing significant amounts of serpentine and an- wt. 9o MnO as determinedby microprobe analyses.The thophyllite. This belt is part of a thick, carbonate- manganesecontent is unusually high for a lithium-poor rich metasedimentarysequence exposed in the over- tourmaline and is in grsrt contrast with the abundant, turned limb of the Balmat-Edwardssynform (Brown manganese-poordravite and uvite that occur elsewhere in & Engel 1950. the Gouverneurarea. The red uvite occurswith manganese- Locally within the talc belt are thin, bearing tremolite (hexagonite),braunite Mn7SiO12and discontinuouslayers containing manganese-bearing quartz in a carbonate-richsequence in the Balmat-Edwards minerals. Local concentrations of manganese synform. Manganese-richdravite is precludedin pegmatitic minerals, forming pods, also occur in the nearby areasbut specializedenvironments consisting of evaporitic Balmat mining district (Brown et al. 1979). rocks possiblyrepresented in this area contain bulk com- Engel (1962)first describedthe manganese-rich positions that could have led to the formation of zone of the Fowler talc belt and the occurrenceof manganese-richminerals. wine-red tourmaline coexistingwith pink to lavender manganese-bearingtremolite (hexagonite).He also Keywords: uvite, manganese, tourmaline, evaporitic rocks, Arnold mine, New York, reported the composition of red tourmaline form- ing large (2-3 cm) crystalsin quartz-rich veins in the SonlMxns Woodcock mine (Fig. l). In contrastto our results, Engel's data (Table l) pertain to tourmaline that is L'uvite rouge de la mine de talc d'Arnold (€tat de New not manganese-richbut that contains significant York, E.-U.) contient jusqu'd 4.340/ode MnO en poids amounts of iron. (analysesd la microsonde),Pour une tourmaline pauvre Tourmaline disseminatedin a rock composed en lithium, une telle teneur en manganiseest anormalement mainly of hexagoniteis exposedin a rib of unmined 6lev6e,excddant fortement celle de la dravite et de I'uvite waste-rockin the Arnold open-cut talc mine and can d'autres localitds de la r6gion de Gouverneur.L'uvite rouge be found on the wastepile of the nearby Wight mine. est accompagn6ede tr6molite manganifbre (hexagonite), C. E. B. collectedspeciments of tourmaline-bearing braunite MrySiO12et quartz, dans une s€rie carbonatdedu rock from Arnold mine synforme de Balmat-Edwards. Des roches dvaporitiques, the in 1969;the authorsand dont on soupgonnela pr6sencedans ce socle fortement J.F. Slack collectedadditional specimensin 1980and m6tamorphis6,poss6deraient le chimismeapproprid pour l98l from the dump at the Wight mine. expliquer pareille associationd'espdces manganifbres. MICRoPRoBEANALYSES (Traduit par la R6daction) Microprobe analyseswere obtained on 2-to-10-pm Mots-clds: uvite, manganbse,tourmaline, roches 6vapo- spots along closely spacedtraverses by combining ritiques, mine Arnold, New-York. wavelength-dispersionand energy-dispersiontechni- quesin an automatedtlree-channel microprobe hav- INTRoDUC"ToN ing an operatingvoltage of 15 kV and a current of Tourmaline is a common accessory mineral in 0.150nA. most rocks of the Precambrian Grenville Complex Synthetic and natural minerals used as standards in St. Lawrence County, New York. As part of a include:plagioclase for Al, Na and K, biotite for Ti, study of tourmaline compositions in tourmaline- pyroxene for Si and Mg, synthetic tephroite for Mn, bearing rocks found mainly northwest of fayalite for Fe, garnet for Ca, and synthetic Gouverneur, the authors also analyzed red tour- chlorapatite for Cl. Checkson the standardization maline from the Arnold talc mine in the talc belt near were made against wel-characterized minerals, in- Fowler (Fig. 1). Our purpose here is to present cluding buergerite,calcic amphibole, phlogopite and microprobe data for the unusually manganese-rich anorthoclase.Corrections and data reduction were tourmaline from the Arnold mine, and to sompare made according to the method of Bence& Albee its composition with that of other varieties of tour- (1968). maline (excluding Li-rich elbaite). The formula lel lqurmaline was calculatedon the 327 328 THE CANADIAN MINERALOGIST Fowrerxrf COMPOSITION OF TOURMALINE I The red tourmaline from the Arnold mins 15 ( significant in that although it contains substantial 1a. amounts of manganese, it falls within the uvite- dravite series. The ideal formula for uvite is CaMg3(AlrMg)B3Si6(O,OA3o(OH,F)'as document- ed by Dunn et al. (1977b), and that for dravite is NaMg3AI5B3SI6(O,OH)3.(OH,F)as given in Walen- ta & Dunn (1979) . Along this series, the X site is oc- cupiedin the ideal formula by Na and Ca, the Isite by Mg, and the Z site by Al and Mg (Walenta & Dunn 1979). Typical traversesacross individual grains indicate substantial composilional homogeneityfrom core to rim, in agreementwith the lack of optical zoning. However, slightly higher contentsof Mn but lower Al are found along the rim of some grains, relative to the core. In a total of 66 analyzedspots, the range of the Na2o/(Naro+Kro+cao) ratio is 0.323to 0.358, rhat of the Feo/(Feo + Mgo) ratio is 0.125 to 0.138,and that of the MnO/Al2O3ratio is 0.158 to 0.180. The calcium content in the red tourmaline is high, averaging 2.78 wt. 9o (Table 1), resulting in a O 2OOOFEET relativelylow NalCaratio and a compositionof 519o h uvite. This composition recurs throughout the 600 METEB f, Gouverneur area; it correspondsto the middle of the ffi's& uvite-dravite series@unn et al. 1977b),The Arnold in Mn compared Frc. l. Talcbelt nearFowler, New York, showingloca- specimenis substantially enriched (1977b) the tion oftourmaline-hexagoniteoccurrence CI) in Arnold to uvitetabulatedbyDunn et al. andto mine.and location of othermines that alsohave similar reddish brown tourmaline (6190uvite) from Ontario, occurrences.Adapted from Brown& Eneel(1956). which containsno trace of Mn or Li (Bruce 1917). Although microprobe analysesof tourmaline can- not yield data to completely characterizethe site oc- basis of 29 oxygen atoms, assumingthree boron cupanciesin the structure, it seemsreasonable to sug- atoms per formula unit. Averagesand approximate gestthat the compositionof the red manganiferous variationsat2o areg;venwhere appropriate (Iables uvite from the Arnold mine generally conforms to l,2). the ideal formula of uvite given by Dunn et ql. (1977b).The low Al content in the red uvite is in DsscnrprroN oF ToURMALINE-BEARINGRocKs agreementwith the addition of Mg in the Z site to compensatefor the substitutionof Na for Ca in the The tourmaline-bearingrocks are predominantly X position and to maintain charge balance (Dunn grey to pale lavenderand consist of Mn-tremolite et al. 1977a,b). Accordingto Manning (1969,1973), (hexagonite), braunite (Mn-rich opaque phase)and Mn3* may occupyboth the Y and Z sitesand is the talc. Tourmaline comprisesless than 590 of the rock. cation responsiblefor the pink color in tourmaline. Red tourmaline from the Arnold mine forms However, chargebalance in the red uvite can be ac- poikiloblastic, subhedralto anhedral grains as much complished by varying the MelAl ratio without as 3 mm in diameter arranged along discontinuous resortingto the addition of Mn3* in the Z site. Fur- bands parallel to layering. Tourmaline also forms thermore, the analytical data obtained by electron scatteredclusters surrounded by euhedral tremolile. microprobe cannot be used to adequately and The poikiloblastic tourmaline is generally crowded preciselydetermine the Mn3+/Mn2* ratio and its with randomly oriented euhedral tremolite and relation to color. Thus, availablemicroprobe data anhedralbraunite (Fig. 2). This sieve-liketexture sug- for this red uvite are insufficient to properly assess geststhat the tourmaline grew late in the paragenetic the importanceof Mn3* in producingthe red color. sequence.The red tourmaline from the Arnold mine Throughout the area northwest of Gouverneur, shows moderate absorption, and dichroism from tourmaline compositionscan be directly correlated rose to red. No optical zoning is evident. with the bulk composition and type of host rock Mn-RICH TOURMALINE FRoM Tm FowLER TALC BELT 329 TABrr 1. colPosrrroN ANDroxultlA oF rouRlalrr{E FRottrEE aRNor,DMrNE, xgE wooDcocKMrNE, AND FROM NOR1E OF @IJgERNEI'R, NEI' YO3K L23 4) lo@tlo! anoldt lloodcoc&. Noith Gourebeur SaupLe f 80-t ltrTrl 67-37 67-5L 67-90 Slo2 ct.Z 36.4r (1.08) 36.44 X7,71 (O.47) 37.24 <O.29) 34.34 (0.34) 41203 25.79 (L.O4) 25.88 30.05 (0.10) 28.90 (0.J.6) 24.88 (0.74) TLo2 1.02 (0.21) 1.68 r.77 (0.08) 0.23 (0.03) 1.13 (0.11) Feo 2.02 (0.13) D.d. 0.69 (0.19) 2.34 (0.34) 12.36 (0.19) Fa2O3 !.a1. !.d. 7.30 o.d. !.d. u.d. D.d. tr.aI. n.d. ltlo 4.34 (O.27) 0.0r. 0.01 (0.01) 0.02 (0.02) 0.04 (0.04) lgo r.2.95 (0.38) rL.77 12.52 (0.13) 12.86 (0.25) 7.83.(0.30) cao 2.78 (0.09) 1.61 1.26 (0.13) 3.55 (0.03) 2.22 (o,LO) Na2o 1.44 (0.02) a.d. 2.3r (0.02) 0.98 (0.04) 1.66 (0.13) K20 0.03 (0.L1) n.tl. 0.02 (0.03) 0.04 (0.01) 0.12 (0.03) lot€l 86.78 84.69 86.36 86.51 84.58 st s.991s.ee 6.001 e.66 6.02J e.s2 6.06I e.06, B 3.00J 3.00J 3.00J 3.00J aL 5.00J 5.13 5.63] 5.sa s.so] 5.53 ).Lt | 5.32 T1 0.13.) 0.2L) 0.03J 0.15J 0.281 o.oeI 0.32) r.821 MD 0.60I 4.Os 0 I 3.06 0 | 3.42 0.011 3.89 z-tt ) 3.10J 2.06J Ca o.49 0.221 0.6q 0.42) Na 0.46 0.96 0.7rI 0.93 0.25I 0.87 0.57| r,o2 K 0.01 o J o.ou o.o3J t Data for lou@llle h coL@ L ed 3-5 are der!.ved.
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