Geology,geochemistry and mineralogy of the lignite-hosted Ambassador palaeochannel uranium and multi-element deposit,Gunbarrel Basin,Western Australia |
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| Authors: | Email author" target="_blank">Grant?B?DouglasEmail author Charles?R?M?Butt David?J?Gray |
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| Institution: | (1) CSIRO Land and Water, Private Bag No 5, Wembley, WA, 6913, Australia;(2) CSIRO Earth Science and Resource Engineering, PO Box 1130, Bentley, WA, 6102, Australia |
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| Abstract: | The Ambassador U and multi-element deposit occurs on the SW margin of the Gunbarrel Basin, Western Australia. Low-grade, flat-lying
U mineralization averaging about 2 m thick at 0.03% U occurs in lignites at the redox front at the base of the weathering
profile within a laterally extensive palaeochannel network. Uranium is principally associated with organic matter within the
lignitic matrix, although rare discrete U minerals, such as coffinite and uraninite, are also present. The lignite is also
enriched in a suite of other elements, principally base metals and sulphur, with concentrations of 0.3 ≥ 1% Cu, Pb, Ni, Co,
Zn and total rare earth elements (REE) in some samples. Other element enrichments include: Cr, Cs, Sc, Se, Ta, Ti, Th, V and
Zr as detrital heavy minerals of Zr, Ti and REE (oxides and silicates) or authigenic minerals of Cu, Bi, Pb, Zn, Ni, Se, Hg,
Ti, Cr, Tl, V, U and REE (sulphides, vanadates, selenides, oxides, chlorides and native metals) and diffuse lignite impregnations.
The Ambassador deposit probably formed from the convergence of redox-active weathering processes to unique source/host rocks,
constrained within the palaeochannel. A proximal source of U and trace elements of lamproite/carbonatite origin is probable,
as constrained by U–Pb isotope and U–Th disequilibria studies. Uranium and other metals were precipitated syngenetically with
organic matter as it was deposited during a humid phase in the Late Eocene. Remobilization subsequently concentrated the metals
in the upper 2 m of the lignite. This may have occurred during one or more periods of weathering and associated diagenesis,
with the latest episode in the last 300,000 years. |
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