Hostname: page-component-78c5997874-s2hrs Total loading time: 0 Render date: 2024-11-19T04:16:57.541Z Has data issue: false hasContentIssue false
  • English
  • Français

Replacement phenomena in tantalum minerals from rare-metal pegmatites in South Africa and Namibia

Published online by Cambridge University Press:  05 July 2018

Joy R. Baldwin
Joy R. Baldwin*
Affiliation:
Department of Geology, University of St Andrews, St Andrews, Fife, KY16 9ST, Scotland
Get access Rights & Permissions [Opens in a new window]

Abstract

Manganotantalite replacement by (1) microlite and (2) ferrotantalite, and changes in composition of uranoan microlite from rare-metal pegmatites in South Africa and Namibia have been investigated with the electron microprobe. A uranmicrolite from Karibib, Namibia contained 14.35% UO2, 1.03% PbO, 56.12% Ta2O5, 13.18% Nb2O5, 0.58% Fe2O3, 6.87% CaO, 0.54% SrO, 0.59% MnO, 0.86% Na2O and 0.47% F. Analyses along traverses across a 1.3 mm uranoan microlite, Tantalite Valley, Namibia, revealed two essentially distinct compositions: a more hydrated rim area of 200 µm radius containing 7% higher Ta2O5, 10% lower CaO and 1.3% lower F than a main central area of slightly variable composition. Back-scattered electron images reveal zoning and distinctive subspheroidal structures. New data and structural features are given for radioactive uranoan microlite from Namaqualand, South Africa. These crystals contain remnants of a bismuth phase and are in various stages of replacement. In the microlites replacing manganotantalite, the microlite reflects the composition of the replaced mineral. At Rubicon Mine, Karibib, a narrow marginal zone of mangantantalite is replaced by ferrotantalite along cleavages; a zone of intermediate composition is apparent. Detailed traverses have been completed across all of these crystals.

Keywords

microlitemanganotantaliteferrotantaliteSouth AfricaNamibiareplacement
Type
Non-silicate Mineralogy
Information
Mineralogical Magazine , Volume 53 , Issue 373 , December 1989 , pp. 571 - 581
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1989

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

Brandenberger, E. (1931) Kristallogr. 76, 322-34.Google Scholar
Borodin, L. S. and Nazarenko, I. I. (1957) Geochem. 4, 330-49.Google Scholar
Eid, A. S. (1976) Unpubl. M.Ph. thesis. Univ. of Leeds.Google Scholar
Gevers, T. W. (1937) Trans. Geol. Soc. S. Africa 39, 331-75.Google Scholar
Ginzburg, A. I. and Gorzhevskaya, S. A. (1960) [Geol. Mest. Redk. Elem., Vses Nauchn-lssled. Inst. Mineral Syr'ya, no. 10, 5-10]. Chem. Abstr. 58, 3202.Google Scholar
Guimaraes, C. P. (1939) Annaes. Acad. Brasil. Ciencias. 11, 347-350.Google Scholar
Harris, P. M. (1966) Mineral. Mag. 35, 277-290.Google Scholar
Hogarth, D. D. (1961) Can. Mineral. 6, 610-633.Google Scholar
Hogarth, D. D. (1977) Am. Mineral. 62, 403-10.Google Scholar
Kornetova, V. A. and Kazakova, M. E. (1964) [Tr. Mineral. Muz., Akad. Nauk. SSSR, no. 15, 219-22]. Chem. Abstr. 61, 14369.Google Scholar
Machatschki, F. (1932) [Chem. Erde, 7, 56-76], M.A. 5,185.Google Scholar
Mihalik, P. G. V. (1967) Unpubl. M.Sc. thesis. Univ. of Witwatersrand, Johannesburg, S.A.Google Scholar
Sweatman, T. and Long, J. V. P. (1969) J. Petrol. 10, 332-379.CrossRefGoogle Scholar
Van der Veen, A. H. (1963) Nederlands Geol. Mijnbouwkd. Gen. Verh., Geol. Ser. 22, 188pp.Google Scholar
Von Gaertner, H. R. (1930) Neues Jahrb. Mineral. 61, 1-30.Google Scholar
Von Knorring, O. and Fadipe, A. (1981) Bull. Mineral. 104, 496-507.Google Scholar
Von Knorring, O. and Condiffe, E. (1984) Mineral. Mag. 48, 443-8.CrossRefGoogle Scholar