Uraniferous diagenetic xenotime in northern Australia and its relationship to unconformity-associated uranium mineralisation |
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| Authors: | Daniela A Vallini David I Groves Neal J McNaughton Ian R Fletcher |
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| Institution: | (1) Centre for Global Metallogeny, School of Earth and Geographic Sciences, University of Western Australia, Crawley, WA, 6009, Australia |
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| Abstract: | Stratabound, uraniferous diagenetic xenotime cements provide a minimum depositional age of 1,632±3 Ma for the sedimentary
Birrindudu Group in the Killi Killi Hills, Tanami Region in northern Australia. The age of xenotime formation is broadly coeval
with that recently proposed (1,650–1,600 Ma) for uranium mineralisation in the unconformity-associated deposits of the Pine
Creek Inlier, northern Australia, and Athabasca Basin, Canada. The geological setting and formation model for the uraniferous
xenotime crystals are similar to those widely proposed for unconformity-associated uranium deposits, suggesting a genetic
link between the two. However, xenotime formation in the Birrindudu Group occurred during an apparently earlier stage of diagenesis,
compared to late diagenetic formation of unconformity-associated uranium deposits. This could be explained by variations in
the thickness of sediment cover and diachronous diagenesis across the basin, at the time of the basin-wide uranium mobilisation
event, herein dated at ca. 1,630 Ma. In such a scenario, stratabound uraniferous xenotime cements could represent the remote
distal zones of a more deeply buried, uranium mineralising system. Alternatively, the xenotime layer represents a precursor
to, or a source for, later unconformity-associated ore deposition. In this case, the presence of diagenetic uraniferous xenotime
in an area prospective for unconformity-associated uranium mineralisation would be an indication of, and still provide an
approximate age for, uranium mobilisation within the cover sequence. Xenotime is a far more robust mineral than uraninite
for U–Pb geochronology and can potentially provide a more reliable and precise timeframe for uranium mineralisation and subsequent
recrystallisation events if present in the immediate uranium-ore environment. |
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| Keywords: | Uraniferous xenotime Unconformity-associated uranium Diagenesis U– Pb geochronology |
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