Journal
AMERICAN MINERALOGIST
Volume 92, Issue 2-3, Pages 267-280Publisher
MINERALOGICAL SOC AMER
DOI: 10.2138/am.2007.2277
Keywords
APS minerals; florencite; goyazite; svanbergite; unconformity-type uranium deposits; Athabasca basin; clay minerals; geochernistry
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Aluminum phosphate-sulfate (APS) minerals formed around the Athabasca unconformity-type deposits and those from their Australian counterparts are chemically very similar showing the same continuum between the diagenetic Sr-rich APS minerals of the barren sandstones and the LREE-rich composition of the APS minerals in the hydrothermally altered sandstone. The P- and LREE-rich compositions were controlled by the transport and the redistribution of P and LREE elements released from the dissolution of phosphate minerals (principally monazite) in the basement rocks and in the basin during the syn-ore alteration processes. The S/Sr ratio measured in the APS minerals from unaltered sandstone away from the unconformity and any mineralization is preserved during the syn-ore alteration processes suggesting that the fluids involved in both the deep burial diagenetic processes and the syn-ore alteration system were derived from a similar diagenetic reservoir in both the Athabasca and Kombolgie regions. The trioctahedral chlorite host-rock alteration around the Australian basement-hosted U deposits, as compared to the illite and sudoite associated with the Athabasca basement-hosted, along with the more LREE-rich APS compositions in the Australian deposits, suggests that the pH and oxygen fugacity (f(o2)) of the syn-ore fluids differed in the alteration systems of the two regions at the time of the U deposition.
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