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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

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1945-3027
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Volume 100, Issue 5-6

Issues

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

S. Gordon Campbell
  • Department of Earth Sciences, The University of Western Ontario, London, Ontario N6A 5B7, Canada
  • Other articles by this author:
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/ Frank Reith
  • Centre for Tectonics, Resources and Exploration, School of Earth and Environmental Sciences, The University of Adelaide, North Terrace, South Australia 5000, Australia
  • CSIRO Land and Water, Environmental Biogeochemistry, PMB2, Glen Osmond, South Australia 5064, Australia
  • Other articles by this author:
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/ Barbara Etschmann
  • Division of Mineralogy, South Australian Museum, Adelaide, South Australia 5000, Australia
  • School of Chemical Engineering, The University of Adelaide, North Terrace, Adelaide, South Australia 5005, Australia
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/ Joël Brugger
  • Division of Mineralogy, South Australian Museum, Adelaide, South Australia 5000, Australia
  • School of Geosciences, Monash University, Clayton, Victoria 3800, Australia
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/ Gema Martinez-Criado / Robert A. Gordon / Gordon Southam
Published Online: 2015-05-12 | DOI: https://doi.org/10.2138/am-2015-4905

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-μ-XRF of a sectioned grain showed a fine layer of up to 5 μm thick composed of refined, aggregates of 0.2 to 2 μm 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.

Keywords: Platinum; weathering; Fifield Pt-Province; secondary mineralization; Australia

About the article

Received: 2014-01-27

Accepted: 2014-12-01

Published Online: 2015-05-12

Published in Print: 2015-05-01


Citation Information: American Mineralogist, Volume 100, Issue 5-6, Pages 1236–1243, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-4905.

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© 2015 by Walter de Gruyter Berlin/Boston.

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