Other
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59.2709k&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 59, Issue 13, pp.2709-2723
Other
1
Scientific paper
Compositions of hydrothermal chlorite and fine-grained white mica from the inner and outer alteration halos in the Koongarra U deposit were analyzed by electron microprobe and analytical electron microscopy. Analyses show that although chlorite and white mica compositions vary considerably outside the main ore zone, they are uniform inside the ore zone. Ore-zone chlorite has a ratio of Fe/(Fe + Mg) of 0.25 and low octahedral occupancy (average 5.5 per formula unit), which may represent a mixture of diand trioctahedral chlorite. White mica has a typical K + Na atomic content of 0.85 per formula unit. These compositions were used to calculate the activity ratios a Fe +2 / a H + 2 , a Mg +2 / a H + 2 , a K + / a H + , and a Na + / a H + for the hydrothermal fluids associated with deposition of uraninite. Hydrothermal apatite analyses in conjunction with salinities suggested from fluid inclusion studies were used to calculate the pH of the fluids during the pre-ore alteration. The calculated pH values range from 4.8 to 6.0. Finally, the coexistence of chlorite with quartz and hematite was used to calculate oxygen fugacities. The calculated values are about 2 log units higher than for the hematite-magnetite buffer at 200°C. Consequently, the oxidation state of the fluid lay in the hematite field and U was probably transported as uranyl complexes.
Komninou A.
Sverjensky Dimitri A.
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