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

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• 作者：Aurélien Eglinger (1)
  Clément Ferraina (1)
  Alexandre Tarantola (1)
  Anne-Sylvie André-Mayer (1)
  Olivier Vanderhaeghe (1)
  Marie-Christine Boiron (1)
  Jean Dubessy (1)
  Antonin Richard (1)
  Marc Brouand (2)
  
• 关键词：Uranium ; Gondwana ; Pan ; African ; Evaporite ; Metamorphic brines ; Sinjarite
• 刊名：Contributions to Mineralogy and Petrology
• 出版年：2014
• 出版时间：February 2014
• 年：2014
• 卷：167
• 期：2
• 全文大小：2,248 KB
• 作者单位：Aurélien Eglinger (1)
  Clément Ferraina (1)
  Alexandre Tarantola (1)
  Anne-Sylvie André-Mayer (1)
  Olivier Vanderhaeghe (1)
  Marie-Christine Boiron (1)
  Jean Dubessy (1)
  Antonin Richard (1)
  Marc Brouand (2)
  
  1. UMR GeoRessources 7359, CNRS-CREGU, Université de Lorraine, 54506, Vand?uvre-lès-Nancy Cedex, France
  2. AREVA, BU Mines, Paris, France
  
• ISSN：1432-0967

文摘

In the Pan-African Lufilian belt (Western Zambian Copperbelt), uranium mineralizations, preferentially scattered in kyanite?±?talc micaschists (metamorphosed 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 (53-9?wt% CaCl2, 13-5?wt% NaCl; N2–H2 in the gas phase of fluid inclusions) circulated during the high-temperature quartz recrystallization, at 500-00?°C. This temperature is in agreement with the P-em class="a-plus-plus">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 (21-2?wt% NaCl, 19-1?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?°C. This temperature could be related to the exhumation of the high-grade metamorphic rocks at ca. 500?Ma. The formation of H2 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 (14-6?wt% NaClequiv) circulated in the brittle domain but seems unrelated to U (re-)mobilization event.