Surface transformations of platinum grains from Fifield, New South Wales, Australia

Campbell, S.Gordon, Reith, Frank, Etschmann, Barbara, Brugger, Joel, Martinez-Criado, Gema, Gordon, Robert A and Southam, Gordon (2015) Surface transformations of platinum grains from Fifield, New South Wales, Australia. American Mineralogist, 100 5-6: 1236-1243. doi:10.2138/am-2015-4905

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Author Campbell, S.Gordon
Reith, Frank
Etschmann, Barbara
Brugger, Joel
Martinez-Criado, Gema
Gordon, Robert A
Southam, Gordon
Title Surface transformations of platinum grains from Fifield, New South Wales, Australia
Journal name American Mineralogist
ISSN 1945-3027
0003-004X
Publication date 2015-05-01
Year available 2015
Sub-type Article (original research)
DOI 10.2138/am-2015-4905
Open Access Status Not yet assessed
Volume 100
Issue 5-6
Start page 1236
End page 1243
Total pages 985
Place of publication Chantilly, United States
Publisher Mineralogical Society of America
Language eng
Abstract A growing literature is demonstrating that platinum (Pt) is transformed under surface conditions; yet (bio)geochemical processes at the nugget-soil-solution interface are incompletely understood. The reactivity of Pt exposed to Earth-surface weathering conditions, highlighted by this study, may improve our ability to track its movement in natural systems, e.g., focusing on nanoparticles as a strategy for searching for new, undiscovered sources of this precious metal. To study dissolution/re-precipitation processes of Pt and associated elements, grains of Pt-Fe alloy were collected from a soil placer deposit at the Fifield Pt-field, Australia. Optical- and electron-microscopy revealed morphologies indicative of physical transport as well as chemical weathering. Dissolution “pits,” cavities, striations, colloidal nano-particles, and aggregates of secondary Pt platelets as well as acicular, iron (Fe) hydroxide coatings were observed. FIB-SEM-(EBSD) combined with S-m-XRF of a sectioned grain showed a fine layer of up to 5 mm thick composed of refined, aggregates of 0.2 to 2 mm sized crystalline secondary Pt overlying more coarsely crystalline Pt-Fe-alloy of primary magmatic origin. These results confirm that Pt is affected by geochemical transformations in supergene environments; structural and chemical signatures of grains surfaces, rims, and cores are linked to the grains’ primary and secondary (trans)formational histories; and Pt mobility can occur under Earth surface conditions. Intuitively, this nanophase-Pt can disperse much further from primary sources of ore than previously thought. This considerable mineral reactivity demonstrates that the formation and/or release of Pt nanoparticles needs to be measured and incorporated into exploration geochemistry programs.
Keyword Platinum
Weathering
Fifield Pt-Province
Secondary mineralization
Australia
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Earth Sciences Publications
Official 2016 Collection
 
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