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Alteration of coffinite (USiO4) under reducing and oxidizing conditions

Deditius, A.P., Utsunomiya, S. and Ewing, R.C. (2006) Alteration of coffinite (USiO4) under reducing and oxidizing conditions. MRS Proceedings, 985 . pp. 47-52.

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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.

Item Type: Journal Article
Publisher: Cambridge University Press
Copyright: © Materials Research Society 2007
Notes: 2006 MRS Fall Meeting; Boston, MA; United States; 27 November 2006 through 1 December 2006
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