Conference presentation
Coffinite and ningyoite from the natural, nuclear reactor at Bangombé, Gabon
Geology in China, Vol.42(5)
Goldschmidt Conference 2008 (Vancouver, Canada, 13/07/2008–18/07/2008)
2008
Abstract
P-rich coffinite, U(Si,P)04•H20 , from the natural nuclear reactors in Bangombe, Gabon, is an important phase that incorporates percent levels of actinides and fission products. We have examined sample BAX03 (depth 12.2-12.3m) from Bangombe in order to understand micro- and nano-scale crystalo-chemical properties of P-coffinite.
Electron microprobe analysis (EMPA) was completed only on coffinite inclusions (-100 fliil in size) in quartz to minimize the effect of alteration to U(VI)-phosphates and - sulfates. Based on the Si/P ratios three different chemical compositions; i) coffinite (<1.45 wt.% of P20 5) without uraninite inclusions, ii) P-coffinite, and iii) Si-ningyoite, (U,Ca,Ceh(P04)2•1-2H20. Phases ii) and iii) have inclusions of uraninite. The composition of coffinite i) is expressed to be CUo.79Cao.osREE+ Yo.04)o. s7(Si,.03Po.os)J.0704. The amount of (Y+REE)203 is <1.9 wt.%. Phosphorous substitutes for Si as evidenced by its negative correlation with Si (R2=0.87) and positive correlation with Y +REE (R2=0.6). The formula of P-coffinite (ii) is (Uo.7J-o. ss Cao.o6-o.uREE+ Yo.o7-o.Js)o.92- J.os(Sio. 39-o.s9Po.2s-o.4So.03-0.J2)o.s-o.9604, and the P20 s and (REE+Y)203 m·e as high as 9.3 wt.% and 8.64 wt.%, respectively. There is a positive correlation between Ca and P (R2=0.62), but no correlation among P, Y+REE and Si. The chemical formula of Si-rich ningyoite is (U~.43_u 3REE+ Y0.2_ o.3C<lo.J s-o.23)J.88-2.3(Po.7-o.sSio.6-o.sSo.J-o.3Aso-o.J)J. 32-1.6404. Silicon is positively correlated with P (R2=0.7). The EMPA elemental maps reveal homogeneous distribution of P, Si, Nd, Y and U in P-coffinite and Si-ningyoite.
These results suggest that coffinite-(i) in Bangombe is not the alteration product of uraninite. But, P-coffinite and Siningyoite precipitated at the expense of uraninite under reducing conditons. The lack of con·elation between P and Y +REE in P-coffinite and Si-ningyoite implies that these minerals may consist of nano-scale intergowths of coffinite and homogeneously disttibuted (Ca,U,Y,REE)-phosphates. This is supported by the elemental maps, as well as TEM results.
Details
- Title
- Coffinite and ningyoite from the natural, nuclear reactor at Bangombé, Gabon
- Authors/Creators
- S. Utsunomiya (Author/Creator)A.P. Deditius (Author/Creator)V. Pointeau (Author/Creator)R.C. Ewing (Author/Creator)
- Publication Details
- Geology in China, Vol.42(5)
- Conference
- Goldschmidt Conference 2008 (Vancouver, Canada, 13/07/2008–18/07/2008)
- Identifiers
- 991005545037307891
- Murdoch Affiliation
- Murdoch University
- Language
- English
- Resource Type
- Conference presentation
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