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Alteration of coffinite (USiO4) under reducing and oxidizing conditions

By A.P. Deditius, S. Utsunomiya and R.C. Ewing

Abstract

Samples of natural coffinite (USiO4·nH2O) from Grants uranium region, New Mexico were investigated in order to understand the alteration process of coffinite under reducing and oxidizing conditions. Alteration of the primary coffinite under reducing conditions was promoted by organic acids and as a result secondary coffinite precipitated. Subsequently oxidizing fluids altered the coffinite, and (Na,K)-boltwoodite and jáchymovite precipitated with no rare earth elements. Based on the charge balance calculation we suggest that the amount of U6+ in the coffinite is less than 0.2 [apfu] and U6+ is accommodated in the structure via substitution: U4+ + Si4+ ⇔ U6+ + 2(OH)-. The high and variable analysis total of electron microprobe indicates that H2O is not an essential component in coffinite structure. The U-Pb ages of coffinite formation vary from 36.6-0 Ma suggesting that the coffinite has precipitated continuously in this period and organic matter can preserve reducing conditions even when oxidizing conditions dominate

Publisher: Cambridge University Press
Year: 2006
OAI identifier: oai:researchrepository.murdoch.edu.au:25778
Provided by: Research Repository
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