Reflected-Light Microscopy of Uraniferous Bitumens

P. A. Eakin* and A. P. Gize
Dept. of Geology, Queen's University of Belfast, Belfast BT7 1NN, U.K.
Dept. of Geology, The University, Manchester M13 9PL, U.K.
*Present address: UG Isotech Ltd., Aston Way, Middlewich, Cheshire CW10 0HT, U.K.

Abstract: Uraniferous bitumens from Great Britain, Scandinavia and South Africa have been studied by oil-immersion reflected-light microscopy and categorised into those formed either by replacement of preexisting uraninite and pitchblende or by complexation/reduction mechanisms in pre-existing hydrocarbons. The former are characterised by displaying normal replacive textures, and containing high concentrations of non-mineral-bound uranium, or later, occasionally exotic, uraniferous fracture- filling phases. Uraniferous bitumens formed during complexation/reduction reactions display monotonous mineralogies and ordered mineral-inclusion distributions.

Radiolytic alteration of uraniferous bitumens induces both chemical and mechanical alteration. Early alteration is marked by the generation of mobile hydrocarbons during ‘cracking reactions’ with subsequent within-sample migration to form globular bitumens and dendritic interspersions of mineral-rich and -poor uraniferous bitumen. Mobile hydrocarbons may act as lubricants during mechanical deformation. Advanced organic alteration is characterised by well-documented increased reflectance around uraniferous grains, and by fracturing of the bitumens.

Keywords: bitumens • uranium • reflected-light microscopy • hydrocarbons

Mineralogical Magazine; March 1992 v. 56; no. 382; p. 85-99; DOI: 10.1180/minmag.1992.056.382.10
© 1992, The Mineralogical Society
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