Output list
Conference presentation
Published 2014
Society of Economic Geologists (SEG) Building Exploration Capability for the 21st Century, 27/09/2014–30/09/2014, Keystone, CO, USA
Conference presentation
Coffinite and ningyoite from the natural, nuclear reactor at Bangombé, Gabon
Published 2008
Geology in China, 42, 5
Goldschmidt Conference 2008, 13/07/2008–18/07/2008, Vancouver, Canada
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