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Article Dans Une Revue Contributions to Mineralogy and Petrology Année : 2014

Hypersaline fluids generated by high-grade metamorphism of evaporites: fluid inclusion study of uranium occurrences in the Western Zambian Copperbelt

Aurélien Eglinger
Alexandre Tarantola
Anne-Sylvie André-Mayer
Olivier Vanderhaeghe
Marie-Christine Boiron
Jean Dubessy
  • Fonction : Auteur
Antonin Richard

Résumé

In the Pan-African Lufilian belt (Western Zambian Copperbelt), uranium mineralizations, preferentially scattered in kyanite +/- talc micaschists (metamor-phosed evaporitic sediments) or concentrated along transposed quartz veins provide an opportunity to (1) understand the time/space relationship between the ore minerals and the deformation of the host rocks, (2) identify the different fluid events associated with specific stages of quartz deformation and (3) characterize the ore fluid geochemistry in terms of fluid origin and fluid/rock interactions. In the U occurrences studied in Lolwa and Mitukuluku (Domes region, Western Zambian Copperbelt), two mineralizing stages are described. The first generation of ore fluids (53-59 wt% CaCl2, 13-15 wt% NaCl; N-2-H-2 in the gas phase of fluid inclusions) circulated during the high-temperature quartz recrystallization, at 500-700 degrees C. This temperature is in agreement with the P-T conditions recorded during the crustal thickening related to continental collision at ca. 530 Ma. LA-ICPMS analyses show the presence of uranium within this fluid, with a concentration mode around 20 ppm. The second generation of ore fluid (21-32 wt% NaCl, 19-21 wt% CaCl2; CO2-CO in the gas phase of fluid inclusions) percolated at lower temperature conditions, at the brittle-ductile transition, between 200 and 300 degrees C. This temperature could be related to the exhumation of the high-grade metamorphic rocks at ca. 500 Ma. The formation of H-2 and CO is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions. Finally, a late fluid (14-16 wt% NaClequiv) circulated in the brittle domain but seems unrelated to U (re-)mobilization event.
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Dates et versions

hal-01292782 , version 1 (23-03-2016)

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Citer

Aurélien Eglinger, Clément Ferraina, Alexandre Tarantola, Anne-Sylvie André-Mayer, Olivier Vanderhaeghe, et al.. Hypersaline fluids generated by high-grade metamorphism of evaporites: fluid inclusion study of uranium occurrences in the Western Zambian Copperbelt. Contributions to Mineralogy and Petrology, 2014, 167 (2), ⟨10.1007/s00410-014-0967-9⟩. ⟨hal-01292782⟩
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