Hostname: page-component-78c5997874-xbtfd Total loading time: 0 Render date: 2024-11-10T09:23:18.644Z Has data issue: false hasContentIssue false
  • English
  • Français

Non-metamict uranoan pyrochlore and uranpyrochlore from tuff near Ndale, Fort Portal area, Uganda

Published online by Cambridge University Press:  05 July 2018

D. D. Hogarth  and
J. E. T. Horne
D. D. Hogarth
Affiliation:
Department of Geology, University of Ottawa and Ottawa-Carleton Geoscience Centre, Ottawa, Canada K1N 6N5
J. E. T. Horne
Affiliation:
Formerly of the Atomic Energy Division, Geological Survey of Great Britain
Get access Rights & Permissions [Opens in a new window]

Abstract

A thin (100 m) cover of flat-lying, Recent, calcite-rich tuff at Ndale near Fort Portal, Uganda, unconformably overlies steeply dipping Precambrian metamorphic rocks. It is locally radioactive owing to uranium-rich pyrochlore minerals and lesser amounts of zircon, monazite, titanite, and an unidentified thorium phosphate. In one concentrate, four grains of uranpyrochlore and one grain of uranoan pyrochlore showed a positive linear correlation of Ti with U, and negative linear correlations of Ti with Na, F and Sr. Ta remained high and relatively constant [11 anal., ave. 14.5 (0.6)% Ta2O5]. In the same concentrate the composition of a separate grain of uranoan pyrochlore did not plot on these lines and Ta was comparatively low [2 anal., ave. 4.5 (0.3)% Ta2O5]. The data suggest two separate paths of differentiation. However, zoned grains were not observed. Unit cells were cubic with a = 10.351 ± 0.002 Å for a grain with 12.9% UO2tot and 10.333 ± 0.002 Å for a grain with 26.6% UO2tot. On heating in air the cell size decreased, possibly due to oxidation of U4+. The crystalline nature of these minerals can be attributed to a very young (4000–5000 yr) geological age.

Keywords

Fort PortalNdaleUgandatuffpyrochloreuranpyrochloreuraniumtantalumtitaniumnon-metamictradioactivity
Type
Research Article
Information
Mineralogical Magazine , Volume 53 , Issue 370 , April 1989 , pp. 257 - 262
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.)

Footnotes

*

Present address: 58 Westend, Kemsing, nr Sevenoaks, Kent TN15 6QB.

References

Barker, D. S. and Nixon, P. H. (1983) EOS 64 (45), 896.Google Scholar
Brooker, E. J. and Nuffield, E. W. (1952) Am. Mineral. 37, 363-85.Google Scholar
Campbell, C. B. and Home, J. E. T. (1953) Geol. Surv. Museum, Atomic Energy Div. Rep. 150.Google Scholar
Combe, A. D. (1938) Uganda Geol. Surv., Ann. Rep. 14.Google Scholar
Combe, A. D. and Holmes, A. (1945) Trans. Roy. Soc. Edin. 61, 361.Google Scholar
Hogarth, D. D. (1961) Can. Mineral. 6, 610-33.Google Scholar
Hogarth, D. D. (1977) Am. Mineral. 62, 403-10.Google Scholar
Hogarth, D. D. (in press) In Carbonatites: petrogenesis and processes (Bell, K., ed.). (London, Allen and Unwin).Google Scholar
Holmes, A. (1950) Am. Mineral. 35, 772-91.Google Scholar
Holmes, A. (1956) Nederl. Geol-Minjb. Gen. Verh., Geol. Ser. 16, 139-66.Google Scholar
Kapustin, Yu. L. and Polyakov, A. I. (1982) Zap. Vses. Mineral. Obshch. 111, 639-55. [in Russian].Google Scholar
von Knorring, O. and Dubois, C. G. B. (1961) Nature 192, 1064-5.CrossRefGoogle Scholar
Laplante, R. (1980) Etude de la minéralization en Nb-Ta-U du complex igné alcalin du Crevier, Compté Roberval, Lac St. Jean P. Q. M.Sc. (Appl.) thesis, Dép. Génie Minéral, Ecole Polytechnique, Montreal, Canada.Google Scholar
Livingstone, D. A. (1967) Ecol. Monogr. 37, 25-52.CrossRefGoogle Scholar
Logachev, N. A. (1974) In East-African rift system 1, Major Features of Structure and Stratigraphy V. V. (Beloussov, E. E., Milanovskii, and Logachev, N. A., eds.). Nauka, Moscow, 62-236 [in Russian].Google Scholar
Newman, H. and Campbell, C. B. (1952) Symposium on the Mineralogy of Uranium (New York). Unpub. printed proceedings, 5-8.Google Scholar
Nixon, P. H. and Homing, G. (1973) Overseas Geol. Min. Res. No. 41, 168-179.Google Scholar
Osmaston, H. A. (1965) D.Phil. thesis, Oxford.Google Scholar
Rucklidge, J. C. and Gasparrini, E. L. (1969) Specifications of a computor program for processing electron microprobe analytical data: EMPADR VII. Geol., Univ. Toronto, Toronto, Canada.Google Scholar