REE-, Sr-, Ca-aluminum-phosphate-sulfate minerals of the alunite supergroup and their role as hosts for radionuclides

Abstract

Aluminum-phosphate-sulfate (APS) minerals of the alunite supergroup are minor components of uranium-bearing copper ores from the Olympic Dam deposit, South Australia. They typically represent a family of paragenetically late replacement phases after pre-existing REE-bearing phosphates (fluorapatite, monazite, and xenotime). Characterization with respect to textures and composition allows two groups to be distinguished: Ca-Sr-dominant APS minerals that fall within the woodhouseite and svanbergite compositional fields; and a second REE- and phosphate-dominant group closer to florencite in composition. All phases nevertheless display extensive solid solution among end-members in the broader APS clan and show extensive compositional zoning at the grain-scale. Samples representative of the deposit (flotation concentrate and tailings), as well as those that have been chemically altered during the processing cycle (acid leached concentrate), were studied for comparison. NanoSIMS isotope mapping provides evidence that the APS minerals preferentially scavenge and incorporate daughter radionuclides of the 238U decay chain, notably 226Ra and 210Pb, both over geological time within the deposit and during ore processing. These data highlight the role played by minor phases as hosts for geologically mobile deleterious components in ores as well as during mineral processing. Moreover, Sr-Ca-dominant APS minerals exhibit preferential sorption of Pb from fluid sources, in the form of both common Pb and 210Pb, for the first time revealing potential pathways for 210Pb elimination and reduction from ore processing streams.

Multivariate Statistical Analysis of Trace Elements in Pyrite: Prediction, Bias and Artefacts in Defining Mineral Signatures

“…Laser spot size varied from 19 to 33 µm. Isotopes measured were 27 Al, 34 S, 47 Ti, 55 Mn, 57 Fe, 59 Co, 60 Ni, 65 Cu, 66 The ca. 5000 spot analyses were collected in 28 batches.…”

“…Ores of the Olympic Dam deposit display evidence for multi-stage overprinting [33,43,44,[59][60][61]66]. This has been observed for several mineral groups and is often expressed by the release of minor/trace impurities to form the same mineral with modified trace element signature and growth textures (e.g., hematite, uraninite), or formation of new minerals in close proximity to the parent phase.…”

Detection of Trace Elements/Isotopes in Olympic Dam Copper Concentrates by nanoSIMS

“…One minor, but important host for REE is the Sr-Ca-dominant aluminum phosphate-sulfates of the woodhouseite-svanbergite group. Detailed investigation of these minerals in OD samples has revealed several distinct members [37]. These phases belong to the alunite supergroup with the general formula [AB 3 (XO 4 ) 2 (OH) 6 ], where [A] may be a wide variety of mono-, bi-, or trivalent cations, [B] is almost always Al, and (XO 4 ) may be phosphate, sulfate, or a mixture thereof [49].…”

“…Rare earth elements are abundant and ubiquitous within the Olympic Dam ore [20] [20]. Additionally, woodhouseite-svanbergite group minerals, fluorapatite, zircon, fluorite, and uranium/thorium minerals are known to host low quantities of REE [35][36][37].…”

Thermal stability of the waylandite-structured nanocrystalline BiAl3(PO4)2(OH)6

“…The relevance of obtaining and studying such phosphates, in particular, lies in the prospects of using them as matrices for toxic and radioactive waste due to their structural features, thermal stability and high ability to ionic substitution of toxic Hg, As, Tl, Sb, Cr, Ni, Ca, radioactive K, Sr, Th, U, Ra, Pb and rare earths [10][11][12][13][14]. Data on the synthesis of these compounds are scanty and have a number of shortcomings.…”