Hostname: page-component-848d4c4894-xm8r8 Total loading time: 0 Render date: 2024-06-30T04:42:00.510Z Has data issue: false hasContentIssue false
  • English
  • Français

Clay minerals in the Namacotche Pegmatite Group from Zambezia Province, Mozambique: main constituents of late-stage secondary paragenesis

Published online by Cambridge University Press:  09 July 2018

M. A. Sequeira Braga ,
C. Leal Gomes ,
J. Duplay  and
H. Paquet
M. A. Sequeira Braga*
Affiliation:
CIG-R, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal
C. Leal Gomes
Affiliation:
CIG-R, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal
J. Duplay
Affiliation:
CGS-UMR 7517, EOST, 1 rue Blessig, 67084 Strasbourg Cedex, France
H. Paquet
Affiliation:
CGS-UMR 7517, EOST, 1 rue Blessig, 67084 Strasbourg Cedex, France
*
*E-mail: masbraga@dct.uminho.pt
Get access Rights & Permissions [Opens in a new window]

Abstract

Namacotche gem-bearing pegmatites of Alto Ligonha pegmatite district are heterogeneous, strongly fractionated, and have large Li and Ta and extremely large Cs contents. Clay samples were collected in fracture infillings and dilation cavities with gemstones and were studied using X-ray diffraction (XRD), polarized light microscope, scanning electron microscopy-energy dispersive spectroscopy, high-resolution transmission electron microscopy and chemical analyses. The <2 μm fraction contains cookeite, illite, illite-smectite and suggested irregular mixed-layer cookeite-smectite, beidellite, montmorillonite, kaolinite and goethite.The XRD patterns of chlorite and their d values suggest the presence of ‘di-trioctahedral chlorite’ similar to cookeite-Ia polytype. Cookeite chemical analyses show that Li contents range from 0.82 to 1.08 atoms per half unit cell.

A close relationship has been established between occurrences of gemstones and clay minerals. Some important textures and crystal chemistry are discussed.The main gemstones related to the Namacotche Pegmatite are: morganite (pink cesian beryl), kunzite (spodumene) and elbaite tourmaline. As the mechanisms responsible for the gemstone formation take place at low temperature, the clay minerals paragenesis cookeite ± cookeite-smectite interstratification ± beidellite + montmorillonite ± illite-smectite interstratification, represents a late-stage secondary paragenesis, generated by hydrothermal alteration.

Keywords

cookeitecookeite-smectite interstratificationbeidellitemontmorillonitehydrothermal alterationgem-bearing pegmatitesMozambique
Type
Research Article
Information
Clay Minerals , Volume 43 , Issue 4 , December 2008 , pp. 597 - 613
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bailey, S.W. (1980) Structures of layer silicates. Pp. 1–124 in: Crystal Structures of Clay Minerals and their X-ray Identification (Brindley, G.W. & Brown, G., editors). Monograph 5, Mineralogical Society, London.Google Scholar
Beaufort, D., Berger, G., Lacharpagne, J.C. & Meunier, A. (2001) An experimental alteration of montmorillonite to a di + trioctahedral smectite assemblage at 100 and 200°C. Clay Minerals, 36, 211–225.CrossRefGoogle Scholar
Brammall, A., Leech, J.G.C. & Bannister, F.A. (1937) The paragenesis of cookeite and hydromuscovite associated with gold at Ogofau, Carmarthenshire. Mineralogical Magazine, 24, 507–520.CrossRefGoogle Scholar
Çerný, P. (1970) Compositional variations in cookeite. The Canadian Mineralogist, 10, 636–647.Google Scholar
Çerný, P., Povondra, P. & Stanek, J. (1971) Two cookeites from Czechoslovakia: a boron-rich variety and a lib polytype. Lithos, 4, 7–15.CrossRefGoogle Scholar
Christidis, G.E. (2006) Genesis and compositional heterogeneity of smectites. Part III: Alteration of basic pyroclastic rocks — A case study from the Troodos Ophiolite Complex, Cyprus. American Mineralogist, 91, 685–701.Google Scholar
Christidis, G. and Dunham, A.C. (1993) Compositional variations in smectites: Part I. Alteration of intermediate volcanic rocks. A case study from Milos Island, Greece. Clay Minerals, 28, 255–273.CrossRefGoogle Scholar
Dudoignon, P., Meunier, A., Beaufort, D., Gachon, A. & Buigues, D. (1989) Hydrothermal alteration at Mururoa Atoll (French Polynesia). Chemical Geology, 76, 385–401.CrossRefGoogle Scholar
Dudoignon, P., Proust, D. & Gachon, A. (1997) Hydrothermal alteration associated with rift zones at Fangatauffa atoll (French Polynesia). Bulletin of Volcanology, 58, 583–596.CrossRefGoogle Scholar
Elsass, F., Beaumont, A., Pernes, M., Jaunet, A.M. & Tessier, D. (1998) Changes in layer organization of Na- and Ca-exchanged smectite materials during solvent exchanges for embedded in resin. The Canadian Mineralogist, 36, 1475–1483.Google Scholar
Foord, E.E., Starkey, H.C. & Taggart, J.E. Jr. (1986) Mineralogy and paragenesis of ‘pocket’ clays and associated minerals in complex granitic pegmatites, San Diego County, California. American Mineralogist, 71, 428–439.Google Scholar
Gaudin, A., Buatier, M.D., Beaufort, D., Petit, S., Grauby, O. & Decarreau, A. (2005) Characterization and origin of Fe3+-montmorillonite in deep-water calcareous sediments (Pacific Ocean, Costa Rica Margin). Clays and Clay Minerals, 53, 452–465.CrossRefGoogle Scholar
Goffe, B., Baronnet, A. & Morin, G. (1994) La saliotite, interstratifié régulier 1:1 cookéite/paragonite. Nouveau phyllosilicate du métamorphisme de haute pression et basse température. European Journal of Mineralogy, 6, 897–911.CrossRefGoogle Scholar
Gomes, C.F. (1967) Alteration of spodumene and lepidolite with formation of dioctahedral chlorite plus dioctahedral chlorite-dioctahedral montmorillonite interstratifications. Memórias e Notícias, 64, 32–57.Google Scholar
González López, J.M., Subías Pérez, I., Fernández-Nieto, C. & Fanlo González, I. (1993) Lithium-bearing hydrothermal alteration phyllosilicates related to Portalet fluorite ore (Pyrenees, Huesca, Spain). Clay Minerals, 28, 275–283.Google Scholar
Guggenheim, S., Adams, J.M., Bain, D.C., Bergaya, F., Brigatti, M.F., Drits, V.A., Formoso, M.L.L., Galan, E., Kogure, T. & Stanjek, H. (2006) Summary of recommendations of nomenclature committees relevant to clay mineralogy: report of the Association Internationale Pour l'Etude des Argiles (AIPEA) nomenclature committee for 2006. Clays and Clay Minerals, 54, 761–772.CrossRefGoogle Scholar
Güven, N. (1988) Smectites. Pp. 497–559 in: Hydrous Phyllosilicates (Bailey, S.W., editor). Reviews in Mineralogy 19, Mineralogical Society of America, Washington, D.C. CrossRefGoogle Scholar
Haymon, R.M. & Kastner, M. (1986) The formation of high temperature clay minerals from basalt alteration during hydrothermal discharge on the East Rise axis at 21°N. Geochimica et Cosmochimica Ada, 50, 1933–1939.CrossRefGoogle Scholar
Inoue, A. & Utada, M. (1991) Smectite-to-chlorite transformation in thermal metamorphosed volcano-clastic rocks in the Kamikita area, northern Honsu, Japan. American Mineralogist, 76, 628–640.Google Scholar
Kile, D.E. (2005) Mineralogy and provenance of clays in miarolitic cavities of the Pikes Peak Batholith, Colorado. The Canadian Mineralogist, 43, 1093–1105.CrossRefGoogle Scholar
Klein, C. & Hurlbut, C.S. Jr. (1985) Manual of Mineralogy, pp. 430–434. John Wiley & Sons, New York.Google Scholar
Kristmannsdottir, H. (1979) Alteration of basaltic rocks by hydrothermal activity at 100-300°C. Pp. 359–367 in: International Clay Conference Oxford (Mortland, M.M. & Farmer, V.C., editors). Developments in Sedimentology, 27, Elsevier, Amsterdam.Google Scholar
Kühnel, R.A. & Van der Gaast, S.J. (2000) Inhomogeneous clay mineral formation in volcanic rocks from Gran Canaria, Spain: preliminary results. Pp. 15–26 in: First Latin-American Clay Conference (Gomes, C.S.F., editor), Proceedings, 1, Funchal, Madeira.Google Scholar
Leal Gomes, C. (1999) Indicadores paragenéticos das mineralizações pegmatíticas na área da concessão Naípa — Zambézia — Moçambique. Pp. 121–124 in: Adas do II Congresso Ibérico de Geoquímica e XI Semana de Geoquímica, Lisboa.Google Scholar
Leal Gomes, C. (2003a) As paragéneses correspondentes à mineralização em gemas dos pegmatites LCT do Alto Ligonha — Moçambique (Análise dos locais chave, Nahia, Nahipa e Namacotche). Pp. 199–201 in: Adas do IV Congresso Iberico de Geoquímica, Coimbra.Google Scholar
Leal Gomes, C. (2003b) O papel dos fenómenos de evolução tardia na génese de gemas pegmatíticas — ilações da análise paragenética em pegmatites LCT do Alto Ligonha (Moçambique). A Geologia de Engenharia e os Recursos Geológicos. Coimbra, Imprensa da Universidade, 2, 217–228.CrossRefGoogle Scholar
Leal Gomes, C., Dias, P., Guimarães, F., Marques, J. & Ferreira, J. (2006) Contrasting styles of Bi mineralisation, equilibrium and evolution in Zambezia Pegmatite Province, Mozambique. Pp. 308–309 in: 21st Colloquium of African Geology, (Maputo, Mozambique).Google Scholar
Merceron, T., Inoue, A., Bouchet, A. & Meunier, A. (1988) Lithium-bearing donbassite and tosudite from Echassières, Massif Central, France. Clays and Clay Minerals, 36, 39–46.CrossRefGoogle Scholar
Merriman, R.J. (2000) The influence of volcanism and tectonic setting on the genesis of clay minerals. Pp. 59–70 in: First Latin-American Clay Conference (Gomes, C.S.F., editor). Proceedings, 1, Funchal — Madeira.Google Scholar
Meunier, A., Inoue, A. & Beaufort, D. (1991) Chemiographic analysis of trioctahedral smectite-to-chlorite conversion series from the Ohyu Caldera, Japan. Clays and Clay Minerals, 39, 409–415.CrossRefGoogle Scholar
Meunier, A., Mas, A., Schenato, F. & Dudoignon, P. (2000) Clay minerals in basaltic rocks: review and questions. Pp. 27–47 in: First Latin-American Clay Conference (Gomes, C.S.F., editor). Proceedings, 1, Funchal — Madeira.Google Scholar
Meunier, A., Mas, A. & Patrier, P. (2007) Textures as markers of the origin of clay minerals in basaltic rocks. Pp. 52–61 in: Euroclay2007, Invited lectures (Rocha, F., Terroso, D. & Quintela, A., editors). Aveiro, Portugal.Google Scholar
Moore, D.M. & Reynolds, R.C. Jr. (1997) X-ray Diffraction and the Identification and Analysis of Clay Minerals, pp. 226–260. Oxford University Press, New York.Google Scholar
Murnane, R. & Clague, D.A.(1983) Nontronite from a low-temperature hydrothermal system on the Juan de Fuca Ridge. Earth and Planetary Science Letters, 65, 343–352.CrossRefGoogle Scholar
Pecora, W.T., Switzer, G., Barbosa, A.L. & Myers, A.T. (1950) Structure and mineralogy of the Golconda pegmatite, Minas Gerais, Brazil. American Mineralogist, 35, 9–10, 889-901.Google Scholar
Quensel, P. (1937) Minerals of the Varuträsk Pegmatite. VI. On the occurrence of cookeite. Geologiska Föreningen i Stockholm Förhandlingar, 59, 262–268.CrossRefGoogle Scholar
Reynolds, R.C. (1980) Interstratified clay minerals. Pp. 275–281 in: Crystal Structures of Clay Minerals and their X-ray Identification (Brindley, G.W. & Brown, G., editors). Mineralogical Society, Monograph 5, London.Google Scholar
Robertson, H.E., Reynolds, R.C. & Jenkins, D.M. (1999) Hydrothermal synthesis of corrensite: a study of the transformation of saponite to corrensite. Clays and Clay Minerals, 47, 212–218.CrossRefGoogle Scholar
Sahama, Th.G., Knorring, O. v. & Lehtinen, M. (1968) Cookeite from the Muiane pegmatite, Zambézia, Mozambique. Lithos, 1, 12–17.CrossRefGoogle Scholar
Zheng, H. & Bailey, S.W. (1997) Refinement of the cookeite ‘r’ structure. American Mineralogist, 82, 1007–1013.CrossRefGoogle Scholar