Summary
Microlite occurs as a rare accessory mineral in beryl-columbite, beryl-columbitephosphate, complex spodumene, albite-spodumene and amblygonite type rare-element granitic pegmatites in the Archean Yellowknife pegmatite field of the Canadian Shield. The chemistry of microlite is variable but consistent with the accepted structural formula A2−mB2X6Y1−n pH2O, where generally A = Ca,Na; B = Ta,Nb; X = O; Y = O,OH, F; m = 0 - 2; n = 0 - 1 and p = 0 - l. The chemistry of the Yellowknife microlite is dominated by Ca, Na, Ta, and Nb with minor amounts of U, Pb, Fe, Mn, and Ti. The compositions of microlite are interpreted to reflect primary variability and effects of late-stage alteration.
Two principal types of microlite can be distinguished by their primary composition and alteration trends. U-poor microlite originated by the metasomatic replacement of pre-existing manganocolumbite, manganotantalite, and ferrotapiolite; with progressive alteration, its composition evolves from early Ca-rich, Fe,Mn-poor members to late Ca,Na-poor, Fe,Mn-enriched members. In contrast, U-bearing microlite formed from U-enriched, moderately fractionated pegmatitec fluids acting upon ferrocolumbite, manganocolumbite, and manganotantalite; with progressive alteration, its composition evolves from U,Ca,Na-enriched members to U,Ca,Na-poor, Fe,Mn-enriched members.
Zusammenfassung Primärer Zusammensetzungsbereich und Umwandlungstrends der Mikrolithe aus dem Yellowknife Pegmatitfeld, Northwest Territories, Kanada
Mikrolith kommt in den Beryll-Columbit-, Beryll-Columbit-Phosphat-, komplexen Spodumeri-, Albit-Spodumen- und Amblygonit-Typen der Seltene-Element-Granitpegmatite im archäischen Yellowknife Pegmatitfeld des Kanadischen Schildes als seltenes akzessorisches Mineral vor. Der Chemismus des Mikroliths variiert, ist aber mit der gebräuchlichen Strukturformel A2−mB2X1−mY1−n·pH2O verträglich, mit im allgemeinen A = Ca,Na, B = Ta,Nb, X = O, m=0−2, n =O−1 und p=0−1. Der Chemismus des Yellowknife Mikroliths wird durch Ca, Na, Ta und Nb dominiert, U, Pb, Fe, Mn und Ti treten in kleineren Mengen auf. Die Zusammensetzungen des Mikroliths spiegeln die primäre Variabilität sowie die Auswirkungen späterer Umwand lungen wieder.
Zwei Haupttypen des Mikroliths können nach ihrer primären Zusammensetzung und den Umwandlungstrends unterschieden werden. U-armer Mikrolith entstand durch metasomatischen Ersatz von früherem Manganocolumbit-Manganotantalit und Ferrotapiolith, mit fortschreitender Umwandlung entwickelt sich seine Zusammensetzung von frühen Ca-reichen, Fe,Mn-armen Gliedern zu späten Ca,Na-armen, Fe,Mn-angereicherten Gliedern. Im Gegensatz dazu bildete sich U-haltiger Mikrolith aus an U angerereicherten, mäßig fraktionierten pegmatitischen Fluiden, die auf Manganocolumbit-Manganotantalit einwirkten, mit fortschreitender Umwandlung entwickelt sich seine Zusammensetzung von U,Ca,Na-angereicherten Gliedern zu U,Ca,Na-armen, Mn,Feangereicherten Gliedern.
Similar content being viewed by others
References
Baldwin JR (1989) Replacement phenomena in tantalum minerals from rare-metal pegmatites in South Africa and Namibia. Mineral Mag 53: 571–581
Černý P (1989) Exploration strategy and methods for pegmatite deposits of tantalum. In:Möller P, Černý P, Saupé F (eds) Lanthanides, Tantalum and Niobium. Springer Berlin Heidelberg New York, pp. 274–302
—— (1989) Mineralogy of Niobium and Tantalum: Crystal chemical relationships, paragenetic aspects and their economic implications. In:Möller P, Černý P, Saupé F (eds) Lanthanides, Tantalum and Niobium. Springer Berlin Heidelberg New York, pp. 28–79
Fransolet A-M, Ercit TS, Chapman R (1988) Foordite SnNb2O6, new mineral species and the foordite-thoreaulite series. Can Mineral 26: 889–898
—— (1986) Fractionation trends in the Nb- and Ta-bearing oxide minerals in the Greer Lake pegmatitic granite and its pegmatite aureole, southeastern Manitoba. Amer Mineral 71: 501–517
—— (1979) Stibiobetafite, a new number of the pyrochlore group from Vezna, Czechoslovakia. Can Mineral 17: 583–588
—— (1980) The Tanco pegmatite at Bernic Lake, Manitoba. XII. Hafnian zircon. Can Mineral 18: 313–321
—— (1984) Geochemistry and petrology of feldspar crystallization in the Věžná pegmatite, Czechoslovakia. Can Mineral 22: 631–651
Colby JW (1980) Magic V-a computer program for quantitative electron-excited energydispersive analysis. In: QUANTEX- RAY Instruction Manual. Kevex Corporation, Foster City, California
Ercit TS (1986) The Simpsonite Paragenesis: The Crystal Chemistry and Geochemistry of Extreme Tantalum Fractionation. Unpubl. Ph.D. thesis, Univ. of Manitoba, Winnipeg, Manitoba, 471 pp
— (1982) The paragenesis of simpsonite. Progr. Abstr. GAC-MAC Annual Meeting Winnipeg, 7: 48
Ewing RC (1975) Alteration of metamict, rare-earth, AB2O6-type Nb-Ta-Ti oxides. Geochim Cosmochim Acta 39: 521–530
Foord EE (1982) Minerals of tin, titanium, niobium and tantalum in granitic pegmatites. In:Černý P (ed) Granitic Pegmatites in Science and Industry. Mineralogical Assoc Can Short Course Hbk 8: 187–238
Ginsburg AI (1956) On some characteristics of tantalum geochemistry and on the types of tantalum mineralization. (in Russian). Geokhim 74–83
Groat LA, Černý P, Ercit TS (1987) Reinstatement of stibiomicrolite as a valid species. Geol Fören Stock Förh 109: 105–109
Groult D, Pannetier J, Raveau B (1982) Neutron diffraction study of the defect pyrochlore TaWO5.5, H2TaWO6·H2O. J Solid State Chem 41: 277–285
Hogarth DD (1977) Classification and nomenclature of the pyrochlore group. Amer Mineral 62: 403–410
Jolliffe AW (1944) Rare element minerals in pegmatites, Yellowknife-Beaulieu area, Northwest Territories. Geol Surv Can Pap 44-12: 24 pp
von Knorring O, Condliffe E (1984) On the occurrence of niobium, tantalum, and other rare element minerals in Meldon aplite, Devonshire. Mineral Mag 48: 443–448
—— (1981) On the mineralogy and geochemistry of niobium and tantalum in some granite pegmatites and alkali granites of Africa. Bull Mineral 104: 496–507
London D (1986) Magmatic-hydrothermal transition in the Tanco rare-element pegmatite: evidence from fluid inclusions and phase-equilibrium experiments. Amer Mineral 71: 376–395
—— (1989) Vapor-undersaturated experiments in the system macusanite-H2O at 200 MPa, and the internal differentiation of rare-element pegmatites. Contrib Mineral Petrol 102: 1–17
Lumpkin GR, Chakoumkous BC, Ewing RC (1986) Mineralogy and radiation effects of microlite from the Harding pegmatite, Taos Country, New Mexico. Amer Mineral 71: 569–588
Meintzer RE (1987) The Mineralogy and Geochemistry of the Granitoid Rocks and Related Pegmatites of the Yellowknife Pegmatite Field, Northwest Territories. Unpubl Ph.D. thesis, Univ. of Manitoba, Winnipeg, Manitoba, 819 pp
— Wise MA, Černý P (1984) Distribution and structural setting of fertile granites and related pegmatites in the Yellowknife pegmatite field, District of Mackenzie. In: Current Research, Part A, Geol Surv Can Pap 84-1A: 373–381
Perrault G (1986) La composition chimique et la structure cristalline du pyrochlore d'Oka, P.Q. Can Mineral 9: 383–402
Pough FH (1945) Simpsonite and the northern Brazilian pegmatite region. Geol Soc Am Bull 56: 505–514
Rowe RB (1952) Pegmatite deposits of the Yellowknife-Beaulieu region, District of Mackenzie. Geol Surv Can Pap 52-8: 36 pp
SAS Institute, Inc (1982) SAS user's guide: Statistics, 1982 edition.Ray AA (ed). Gary, North Carolina
Smeds SA, Černý P (1989) Pollucite from the Proterozoic petalite-bearing pegmatites of Utö, Stockholm archipelago, Sweden. Geol Fören Stock Förh 111: 361–372
Van Wambeke L (1970) The alteration processes of the complex titano-niobo-tantalates and their consequences. Neues Jahrb Mineral Abh 112: 117–149
Voloshin AV, Pakhomovskyi YA (1982) Study of chemical composition and heterogeneity of microlite. In:Balkov IV, Voloshin AV, (eds) Minerals and Mineral Parageneses of Rocks of the Kola Peninsula, Kola Branch of the Academy of Sciences U.S.S.R., pp. 3–9 (in Russian)
Wise, MA (1987) Geochemistry and Crystal Chemistry of Nb, Ta and Sn Minerals from the Yellowknife Pegmatite Field, N.W.T., Unpubi Ph.D. thesis, Univ. of Manitoba, Winnipeg, Manitoba, 356 pp
— Meintzer RE, Černý P (1985) Final report on the geological field study YK 83-84/008, the Yellowknife pegmatite field: Mineralogy and geochemistry of Nb, Ta, Sn oxide minerals. In: Contributions to the Geology of the Northwest Territories 2: Geol Div Yellowknife Can Dept Indian Affairs and Northern Development EGS 1985-6, pp. 15–25
Author information
Authors and Affiliations
Additional information
With 9 Figures
Rights and permissions
About this article
Cite this article
Wise, M.A., Černý, P. Primary compositional range and alteration trends of microlite from the yellowknife pegmatite field, Northwest territories, Canada. Mineralogy and Petrology 43, 83–98 (1990). https://doi.org/10.1007/BF01164303
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF01164303