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The phoshate mineral associations of the Tsaobismund pegmatite, Namibia

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Abstract

A detailed mineralogical investigation using the classical methods of identification by X-ray diffraction and by optical properties in thin sections, has revealed thirty one phosphate minerals occurring in the Tsaobismund pegmatite. This investigation is complemented by wet chemical and, mainly, electron microprobe analyses performed on the phosphates known to be typomorphic or considered to be relevant to the hydrothermal alteration. Additionally, microprobe analyses are also given for garnet, gahnite, and ferrocolumbite associated with the phosphates. On the basis of their chemical composition, particularly in terms of their Fe, Mn, and Mg contents, three types of triphylites are distinguished. Triphylite 1 only occurs as a primary phase, triphylite 2 shows exsolution lamellae of sarcopside, and triphylite 3 is partly replaced by a fluorophosphate of the triplite-zwieselite series. These minerals constitute three generations of the parent phases, which were progressively transformed by metasomatic processes, hydrothermal alteration, and by weathering, to give finally three types of complex associations. The Li(Fe,Mn)PO4 minerals appear to be more sensitive to such transformations than those of the (Fe,Mn)2PO4F series. Four main stages of hydrothermal alteration processes have been recognized in the Tsaobismund pegmatite: (i) the Mason-Quensel sequence results from a progressive oxidation of Fe and Mn, and a concomitant Li-leaching of triphylite yielding ferrisicklerite and heterosite, successively; (ii) the metasomatic exchange of Na for Li produces alluaudite; in the present case, the formation of hagendorfite from triphylite 2 is considered to be earlier than the generation of alluaudite-Na□ occurring in the three associations; (iii) the hydration phase mainly transforms the parent Li(Fe,Mn)PO4 phase into grey hureaulite, associated with barbosalite and tavorite; (iv) the formation of fluorapatite, not particularly widespread, replaces alluaudite-Na□, as well as zwieselite s.l. The following crystallization sequence of the initially formed phosphate minerals is proposed: triphylite 1 → triphylite 2 + sarcopside (associated with garnet) → triphylite 3 + zwieselite s.l. The most prominent feature of this succession is the increase in the Mg and Zn contents in the composition of the phosphates, as well as the decrease in their Li contents. The variations of the Fe/Mn ratios in this sequence are discussed. The succession triphylite-zwieselite within weakly differentiated and Li-poor pegmatites is of general significance.

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References

  • Baldwin JR, Von Knorring O (1983) Compositional range of Mngarnet in zoned granitic pegmatites. Can Mineral 21:683–688

    Google Scholar 

  • Bergholz J, Kubanek F (1981) Zur Spurenverteilung in pegmatitischen Na-Feldspäten als Prospektionshilfe am Beispiel Tsaobismund/SWA. Min Depos 16:31–43

    Google Scholar 

  • Boury Ph (1981) Comportement du fer et du manganèse dans des associations de phosphates pegmatitiques. Mémoire de licence (inédit) Inst Minéral Univ Liège 118 p

  • Cameron EN (1955) Concepts of the internal structure of granitic pegmatites and their applications to certain pegmatites of South West Africa. Trans Geol Soc South Africa 58:46–70

    Google Scholar 

  • Cameron EN, Jahns RH, McNair AH, Page Lr (1949) Internal structure of granitic pegmatites. Econ Geol Monogr vol 2, 115 p

  • Čerńy P (1982) The Tanco pegmatite at Bernic Lake, southeastern Manitoba. Mineral Assoc Canada Short Courses Handbook 8:527–543

    Google Scholar 

  • Čerńy P, Hawthorne FC (1982) Selected peraluminous minerals. Mineral Assoc Canada Short Courses Handb 8:163–186

    Google Scholar 

  • Chapman CA (1943) Large magnesia-rich triphylite crystals in pegmatites. Am Mineral 28:90–98

    Google Scholar 

  • Clark AM, Couper AG (1979) End-member triploidite from Cornwall. Mineral Mag 43:179–180

    Google Scholar 

  • Fisher DJ (1957) Alluaudites and varulites. Am Mineral 42:661–664

    Google Scholar 

  • Fontan F (1978) Etude minéralogique et essais expérimentaux sur des phosphates de fer et de manganèse de pegmatites des Jebilet (Maroc) et des Pyrénées (France). Thèse de Doctorat d'Etat Univ Paul-Sabatier Toulouse 250 p

  • Fontan F (1981) La magniotriplite ferrifère du massif des Albères (Pyrénées-Orientales, France). Une nouvelle variété. Bull Minéral 10:672–676

    Google Scholar 

  • Fontan F, Huvelin P, Orliac M, Permingeat F (1976) La ferrisicklerite des pegmatites de Sidi-bou-Othmane (Jelibet, Maroc) et le groupe des minéraux à structure de triphylite. Bull Soc Fr Minéral Cristallogr 99:274–286

    Google Scholar 

  • Fransolet A-M (1976) L'huréaulite: ses propriétés minéralogiques et son rôle dans l'évolution des phases Li(Fe,Mn)PO4. Bull Soc Fr Minéral Cristallogr 99:261–273

    Google Scholar 

  • Fransolet A-M (1977a) Intercroissances et inclusions dans les associations graftonite-sarcopside-triphylite. Bull Soc Fr Minéral Cristallogr 100:198–207

    Google Scholar 

  • Fransolet A-M (1977b) Le problème génétique des alluaudites. Bull Soc Fr Minéral Cristallogr 100:348–352

    Google Scholar 

  • Fransolet A-M, Keller P, Fontan F (1983) Preliminary results of the investigation of the phosphate minerals from the Tsaobismund pegmatite, Namibia. Fortschr Mineral 61 (Beih 1):65–66

    Google Scholar 

  • Fransolet A-M, Abraham K, Speetjens J-M (1985) Evolution génétique et signification des associations de phosphates de la pegmatite d'Angarf-Sud, Plaine de Tazenakht, Anti-Atlas, Maroc. Bull Minéral 108:551–574

    Google Scholar 

  • Frommurze HF, Gevers TW, Rossouw PJ (1942) The geology and mineral deposits of the Karibib area, South West Africa. Expl Sheet 79 (Karibib, S.W.A.), Geol Surv South Africa, 172 p

  • Frondel C (1949) Wolfeite, xanthoxenite, and whitlockite from the Palermo mine, New Hamsphire. Am Mineral 34:692–705

    Google Scholar 

  • Gevers TW (1963) Geology along the north-western margin of the Khomas Highlands between Otjibingwe-Karibib and Okahandja, South West Africa. Trans Geol Soc South Africa 66:199–251

    Google Scholar 

  • Gevers TW, Frommurze HF (1929) The tin-bearing pegmatites of the Erongo Area, South West Africa. Trans Geol Soc South Africa 32:111–149

    Google Scholar 

  • Ginsburg AI (1960) Specific geochemical features of the pegmatitic process. 21st Intern Geol Congress Session Norden Rept Part 17:111–121

    Google Scholar 

  • Haapala I (1966) On the granitic pegmatites in the Peräseinäjoki-Alavus area, South Pohjanmaa, Finland. Bull Comm Géol Finlande 224, 98 p

  • Haughton SH, Frommurze HF, Gevers TW, Schwellnus CM, Rossouw PJ (1939) The geology and mineral deposits of the Omaruru area, South West Africa. Expl Sheet 71 (Omaruru, S.W.A.), Geol Surv South Africa, 151 p

  • Heinrich EWm (1951) Mineralogy of triplite. Am Mineral 36:256–271

    Google Scholar 

  • Huvelin P, Orliac M, Permingeat F (1972) Ferri-alluaudite calcifère de Sidi-bou-Othmane (Jebilet, Maroc). Notes Serv Géol Maroc 32: n∘241, 35–419

    Google Scholar 

  • Karnin WD (1980) Petrographic and geochemical investigations on the Tsaobismund pegmatite dyke, South West Africa, Namibia. N Jahrb Mineral Monatsh 1980:193–205

    Google Scholar 

  • Keller P (1974) Phosphatmineralien aus Pegmatiten Südwestafrikas. Aufschluss 25:577–591

    Google Scholar 

  • Keller P (1980) Giniit, Fe2+ Fe 3+4 [(H2O)2¦(OH)2¦(PO4)4], ein neues Mineral aus dem Pegmatit von Sandamab bei Usakos, Namibia. N Jahrb Mineral Monatsh 1980:49–56

    Google Scholar 

  • Keller P (1985) Neue Mineralfunde aus dem Pegmatit von Sandamab, S.W.A./Namibia. Aufschluss 36:117–119

    Google Scholar 

  • Mason B (1941a) Minerals of the Varuträsk pegmatite. XXIII. Some ironmanganese phosphate minerals and their alteration products, with special reference to material from Varuträsk. Geol Fören Förhandl 63:117–165

    Google Scholar 

  • Mason B (1941b) Minerals of the Varuträsk pegmatite. XXVII. Triplite and vivianite. Geol Foren Förhandl 63:285–288

    Google Scholar 

  • Moore PB (1971) Crystal chemistry of the alluaudite structure type: Contribution to the paragenesis of pegmatite phosphate giant crystals. Am Mineral 56:1955–1975

    Google Scholar 

  • Moore PB (1973) Pegmatites phosphates: Descriptive mineralogy and crystal chemistry. Mineral Record 4:103–130

    Google Scholar 

  • Moore PB, Ito J (1979) Alluaudites, wyllieites, arrojadites: Crystal chemistry and nomenclature. Mineral Mag 43:227–235

    Google Scholar 

  • Peacor DR (1969) Triphylite-sarcopside-graftonite intergrowths from Custer, South Dakota. Am Mineral 54:969–972

    Google Scholar 

  • Plimer IR, Blucher ID (1979) Wolfeite and barbosalite from Thackaringa, Australia. Mineral Mag 43:505–507

    Google Scholar 

  • Reuning E (1923) Pegmatite and Pegmatitmineralien in Südwestafrika. Z Kristallogr 58:448–459

    Google Scholar 

  • Roering C (1966) Aspects of the genesis and crystallization sequence of the Karibib pegmatites, South West Africa. Econ Geol 61:1064–1089

    Google Scholar 

  • Shigley JE (1982) Phosphate minerals in granitic pegmatites: A study of primary and secondary phosphates from the Stewart pegmatite, Pala, California. Ph D Thesis, Stanford Univ, 535 p

  • Smith DAM (1965) Geology of the area around the Khan and Swakop Rivers in South West Africa. Mem Geol Surv South Africa SWA Series 3, 113 p

  • Sturmann BD, Mandarino JA, Mrose ME, Dunn PJ (1981) Gormanite, Fe 2+3 Al4(PO4)4(OH)6·2 H2O, the ferrous analogue of souzalite, and new data for souzalite. Canad Mineral 19:381–387

    Google Scholar 

  • Uebel P-J (1977) Internal structure of pegmatites, its origin and nomenclature derived from petrographic studies of deeply dipping dykes in South West Africa and extended to gently dipping dykes observed in southern Norway. N Jahrb Mineral Abh 131:83–113

    Google Scholar 

  • Varlamoff N (1958) Zonéographie de quelques champs pegmatitiques de l'Afrique Centrale et les classifications de K.A. Vlassov et de A.I. Guinsbourg. Ann Soc Géol Belgique 52:B55–87

    Google Scholar 

  • Varlamoff N (1961) Matériaux pour l'étude des pegmatites du Congo et du Ruanda. Quatrième note: Pegmatites à amblygonite et à spodumène et pegmatites fortement albitisées à spodumène et à cassitérite de la région de Katumba (Ruanda). Ann Soc Géol Belgique 54:257–278

    Google Scholar 

  • Von Knorring O (1976) Mineralogical notes from southern Africa. 20th Ann Rep Res Inst Afr Geol, Univ Leeds: 53–55

  • Waldrop L (1969) The crystal structure of triplite (Mn,Fe)2FPO4. Z Kristallogr 130:1–14

    Google Scholar 

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  1. André -Mathieu Fransolet

    Present address: Institut de Minéralogie, Université de Liège, Bât. B18, Sart Tilman, B-4000, Liège 1

Authors and Affiliations

  1. Institut de Minéralogie, Université de Liège, Place du Vingt-Août, 9, B-4000, Liège, Belgium

    André -Mathieu Fransolet

  2. Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Pfaffenwaldring 55, D-7000, Stuttgart 80, Vaihingen, Federal Republic of Germany

    Paul Keller

  3. Laboratoire de Minéralogie, Université Paul-Sabatier de Toulouse, Allées Jules-Guesde 39, F-31400, Toulouse, France

    François Fontan

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  2. Paul Keller
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Fransolet, A.M., Keller, P. & Fontan, F. The phoshate mineral associations of the Tsaobismund pegmatite, Namibia. Contrib Mineral and Petrol 92, 502–517 (1986). https://doi.org/10.1007/BF00374432

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