Skip to main content Accessibility help
×
Home

Placer platinum-group minerals in the Shetland ophiolite complex derived from anomalously enriched podiform chromitites

  • Hazel M. Prichard (a1), Saioa Suárez (a1) (a2), Peter C. Fisher (a1), Robert D. Knight (a1) and John S. Watson (a3)...

Abstract

Highly anomalous platinum-group element (PGE) concentrations in the podiform chromitites at the Cliff and Harold's Grave localities in the Shetland ophiolite complex have been well documented previously. The focus of this study is alluvial platinum-group minerals (PGM) located in small streams that drain from the PGE-rich chromitites. The placer PGM assemblage at Cliff is dominated by Pt-arsenides (64%) and Pd-antimonides (17%), with less irarsite–hollingworthite (11%) and minor Pd-sulfides, Pt–Pd–Cu and Pt–Fe alloys and laurite. Gold also occurs with the PGM. Alluvial PGM have average sizes of 20 µm × 60 µm, with sperrylite the largest grain identified at 110 µm in diameter, matching the range reported for the primary PGM in the source rocks. The placer assemblage contains more Pt-bearing and less Pd-bearing PGM compared with the rocks. The more resistant sperrylite and irarsite–hollingworthite grains which are often euhedral become more rounded further downstream whereas the less resistant Pd-antimonides which are commonly subhedral may become striated and etched. Less stable phases such as Pt- and Pd-oxides and other Ni-Cu-bearing phases located in the rocks (i.e. Ru-pentlandite, PtCu, Pd–Cu alloy) are absent in the placer assemblage. Also the scarce PGM (PdHg, Rh- and Ir-Sb) and Os in the rocks are absent. At Harold's Grave only three alluvial PGM (laurite, Ir, Os) and Au were recovered reflecting the limited release of IPGM from chromite grains in the rocks. In this cold climate with high rainfall, where erosion dominates over weathering, the PGM appear to have been derived directly from the erosion of the adjacent PGE-rich source rocks and there is little evidence of in situ growth of any newly formed PGM. Only the presence of dendritic pure Au and Pd-, Cu-bearing Au covers on the surface of primary minerals may indicate some local reprecipitation of these metals in the surficial conditions.

Copyright

Corresponding author

Footnotes

Hide All

Associate Editor: Brian O'Driscoll

This paper is published as part of a thematic set in memory of Professor Hazel M. Prichard

Footnotes

References

Hide All
Aiglsperger, T., Proenza, J.A., Font-Bardia, M., Baurier-Aymat, S., Galí, S., Lewis, J.F. and Longo, F. (2016). Supergene neoformation of Pt-Ir-Fe-Ni alloys: multistage grains explain nugget formation in laterites. Mineralium Deposita, 52, 10691083.
Augé, T., Legendre, O. and Maurizot, P. (1998) The distribution of Pt and Ru-Os-Ir minerals in the New Caledonia ophiolite. Pp. 141154 in: International Platinum (Laverov, P.N. and Distler, V.V., editors). Theophrastus publications, St. Petersburg, Athens.
Bacuta, G.C.J., Lipin, B.R., Gibbs, A.K. and Kay, R.W. (1988) Platinum-group element abundance in chromite deposits of the Acoje ophiolite block, Zambales ophiolite complex, Philippines. Pp. 381382 in: Geo-Platinum Symposium Volume (Prichard, H.M., Potts, P.J., Bowles, J.F.W. and Cribb, S.J., editors). Elsevier.
Badanina, I.Y., Malitch, K.N., Lord, R.A. and Meisel, T.C. (2013) Origin of primary assemblage in chromitite from a mantle tectonite at Harold's Grave (Shetland Ophiolite Complex, Scotland). Mineralogy and Petrology, 107, 963970.
Badanina, I.Y., Malitch, K.N., Lord, R.A., Belousova, E.A. and Meisel, T.C. (2016) Closed-system behaviour of the Re–Os isotope system recorded in primary and secondary platinum-group mineral assemblages: evidence from a mantle chromitite at Harold's Grave (Shetland Ophiolite Complex,Scotland). Ore Geology Reviews, 75, 174185.
Bowles, J.F.W. (1986) The development of platinum-group minerals in laterites. Economic Geology, 81, 12781285.
Bowles, J.F.W. (1988) Further studies of the development of platinum-group minerals in the laterites of the Freetown Layered Complex, Sierra Leone. Pp. 273280 in: Proceedings of the symposium Geo-Platinum 87. (Prichard, H.M., Potts, P.J., Bowles, J.F.W. and Cribb, S.J., editors). Elsevier Applied Science, London.
Bowles, J.F.W. (1995) The development of platinum-group minerals (PGM) in laterites: mineral morphology. Chronique de la Recherche Minière, 520, 5563.
Bowles, J.F.W., Giże, A.P. and Cowden, A. (1994 a) The mobility of the platinum-group elements in the soils of the Freetown Peninsula, Sierra Leone. The Canadian Mineralogist, 32, 957967.
Bowles, J.F.W., Giże, A.P., Vaughan, D.J. and Norris, S.J. (1994 b) The development of platinum-group minerals in laterites; an initial comparison of the organic and inorganic controls. Transactions of the Institute of Mining and Metallurgy, B Applied Earth Science, 103, 5356.
Bowles, J.F.W., Giże, A.P., Vaughan, D.J. and Norris, S.J. (1995) Organic controls on platinum-group element (PGE) solubility in soils: initial data. Chronique de la Recherche Minière, 520, 6573.
Bowles, J.F.W., Lyon, I.C., Saxton, J.M. and Vaughan, D.J. (2000) The origin of platinum group minerals from the Freetown Intrusion, Sierra Leone, inferred from osmium isotope systematics. Economic Geology, 95, 539548.
Bowles, J.F.W., Prichard, H. M., Suárez, S. and Fisher, P.C. (2013) The first report of platinum-group minerals in magnetite-bearing gabbro, Freetown layered Complex, Sierra Leone: occurrences and genesis. The Canadian Mineralogist, 51, 455473.
Bowles, J.F.W., Suárez, S., Prichard, H.M. and Fisher, P.C. (2017) Weathering of PGE sulfides and Pt–Fe alloys in the Freetown Layered Complex, Sierra Leona. Mineralium Deposita, 52, 11271144.
Bowles, J.F.W., Suárez, S., Prichard, H.M. and Fisher, P.C. (2018) The mineralogy, geochemistry and genesis of the alluvial platinum-group minerals of the Freetown Layered Complex, Sierra Leone. Mineralogical Magazine, 82(S1), S223S246.
Bridges, J.C., Prichard, H.M., Neary, C.R. and Meireles, C.A. (1993) Platinum-group element mineralization in the chromite-rich rocks of the Braganca massif, northern Portugal. Transactions Institute Mining Metallurgy, B Applied Earth Science, 102, 103113.
Brough, C.P., Prichard, H.M., Neary, C.R., Fisher, P.C. and McDonald, I. (2015) Geochemical variations within podiform chromitite deposits in the Shetland Ophiolite: Implications for petrogenesis and PGE concentration. Economic Geology, 110, 187208.
Cabral, A.R. and Kwitko-Ribeiro, R. (2004) On the rossettes of “native palladium” from Minas Gerais, Brazil: evidence from Gongo Soco. The Canadian Mineralogist, 42, 683–674.
Cabral, A.R., Beaudoin, G., Choquette, M., Lehmann, B. and Polônia, J.C. (2007) Supergene leaching and formation of platinum in alluvium: evidence from Serro, Minas Gerais, Brazil. Mineralogy and Petrology, 90, 141150.
Cabral, A.R., Tupinanbá, M., Lehmann, B., Kwitko-Ribeiro, R. and Vymazalová, A. (2008) Arborescent palladiniferous gold and empirical Au2Pd and Au3Pd in alluvium from southern Serra do Espinhaço, Brazil. Neues Jahrbuch für Mineralogie Abhandlungen, 148/3, 329336.
Cabral, A.R., Lehmann, B., Tupinambà, M., Schlosser, S., Kwitko-Ribeiro, R. and Abreu, F.R. (2009) The platiniferous Au-Pd belt of Minas Gerais, Brazil, and genesis of its botroidal Pt-Pd aggregates. Economic Geology, 104, 12651276.
Cabral, A.R., Radtke, M., Munnik, F., Lehmann, B., Reinholz, U., Riesemeier, H., Tupinambá, M. and Kwitko-Ribeiro, R. (2011) Iodine in alluvial platinum–palladium nuggets: Evidence for biogenic precious-metal fixation. Chemical Geology, 281, 125132.
Cabri, L.J. and Harris, D.C. (1975) Zoning of Os-Ir alloys and the relation of the geological and tectonic environment of the source rocks to the bulk Pt:Pt+Ir+Os ratio for placers. The Canadian Mineralogist, 13, 266274.
Cabri, L.J., Harris, D.C. and Weiser, T.W. (1996) Mineralogy and petrology of platinum-group mineral (PGM) placer deposits of the world. Exploration and Mining Geology, 5, 73176.
Corrivaux, L. and Laflamme, J.H.G. (1990) Minéralogie des éléments du groupe du platine dans les chromitites de l'ophiolite de Thetford mines, Québec. The Canadian Mineralogist, 28, 579595.
Derbyshire, E.J., O'Driscoll, B., Lenaz, R., Gertisser, R. and Kronz, A. (2012) Compositionally heterogeneous podiform chromitite in the Shetland Ophiolite Complex (Scotland): Implications for chromitite petrogenesis and late stage alteration in the upper mantle portion of a supra-subduction zone ophiolite. Lithos, 162–163, 279300.
Escayola, M., Garuti, D., Zaccarini, F., Proenza, J., Bédard, J.H. and Van Staal, C. (2011) Chromitite and platinum-group-element mineralization at Middle Arm Brook, Central Advocate Ophiolite Complex, Baie Verte Peninsula, Newfoundland, Canada. The Canadian Mineralogist, 49, 15231547.
Flinn, D. (1985) The Caledonides of Shetland. Pp. 11591172 in: The Caledonide Orogeny – Scandinavia and Related Areas (Gee, D.G. and Sturt, B.A., editors.). John Wiley and Sons Ltd.
Fuchs, W.A. and Rose, A.W. (1974) The geochemical behavior of platinum and palladium in the weathering cycle in the Stillwater Complex, Montana. Economic Geology, 69, 332346.
Garrels, R.M. and Christ, C.L. (1965) Solutions, Minerals, and Equilibria. Harper & Row, Publishers, New York, 450 pp.
González-Jiménez, J.M., Griffin, W.L., Proenza, J.A., Gervilla, F., O'Reilly, S.Y., Akbulut, M., Pearson, N.J. and Arai, S. (2014). Chromitites in ophiolites: How, where, when, why? Part II. The crystallization of chromitites. Lithos, 189, 140158.
Grammatikopoulos, T.A., Kapsiotis, A., Zaccarini, F., Tsikouras, B., Hatzipanagiotou, K. and Garuti, G. (2007). Investigation of platinum-group minerals (PGM) from Pindos chromitites (Greece) using hydroseparation concentrates. Minerals Engineering, 20, 11701178.
Hough, R., Noble, R. and Reich, M. (2011) Natural gold nanoparticles. Ore Geology Review, 42, 5561.
Kim, W.-S. and Chao, G.Y. (1991) Phase relations in the system Pd-Sb-Te. The Canadian Mineralogist, 29, 401409.
Kozlu, H., Prichard, H.M., Melcher, F., Fisher, P.C., Brough, C. and Stueben, D. (2014) Platinum group element (PGE) mineralisation and chromite geochemistry in the Berit ophiolite (Elbistan/Kahramanmaraş), SE Turkey. Ore Geology Reviews, 60, 97111.
Leake, R.C., Bland, D.J., Styles, M.T. and Cameron, D.G. (1991) Internal structure of Au-Pd-Pt grains from south Devon, England in relation to low temperature transport and deposition. Transactions of the Institute of Mining and Metallurgy, B Applied Earth Science, 100, B159178.
Lord, R.A., Prichard, H.M. and Neary, C.R. (1994) Magmatic PGE concentrations and hydrothermal upgrading in the Shetland ophiolite complex. Transactions Institute Mining Metallurgy, B Applied Earth Science, 103, B87162.
Moreno, T., Prichard, H., Lunar, R., Monterrubio, S. and Fisher, P. (1999). Formation of a secondary platinum-group minerals assemblage in chromitites from the Herbeira ultramafic massif in Cabo Ortegal, NW Spain. European Journal of Mineralogy, 11, 363378.
Moreno, T., Gibbons, W., Prichard, H.M. and Lunar, R. (2001). Platiniferous chromitite and the tectonic setting of ultramafic rocks in Cabo Ortegal, NW Spain. Journal of the Geological Society, 158, 601614.
Mota-e-Silva, J., Prichard, H.M., Suárez, S., Ferreira Filho, C.F. and Fisher, P.C. (2016) Supergene alteration of platinum-group minerals and the formation of Pd-Cu-O and Pd-I-O compounds in the Limoeiro Ni-Cu-(PGE) deposit, Brazil. The Canadian Mineralogist, 54, 755778.
Oberthür, T., Weiser, T.W. and Gast, L. (2003) Geochemistry and mineralogy of platinum-group elements at Hartley Platinum Mine, Zimbabwe Part 2. Supergene redistribution in the oxidized Main Sulfide Zone of the Great Dyke, and alluvial platinum group minerals. Mineralium Deposita, 38, 344355.
Oberthür, T., Weiser, T.W., Melcher, F., Gast, L. and Wöhrl, C. (2013) Detrital platinum-group minerals in rivers draining The Great Dyke, Zimbabwe. The Canadian Mineralogist, 51, 197222.
Ohnenstetter, M., Johan, Z., Coherie, A., Fouillac, A., Guerrot, C., Ohnenstetter, D., Chaussidon, M., Rouer, O., Makovicky, E., Makovicky, M., Rose-Hansen, J., Karup-Moller, S., Vaughan, D., Tumer, G., Pattrick, R.A.D., Gize, A.P., Lyon, I. and McDonald, I. (1999) New exploration methods for platinum and rhodium deposits poor in base-metal sulfides. Transactions Institute Mining Metallurgy, B Applied Earth Science, 108, 119150.
Orberger, B., Fredrich, G. and Woermann, E. (1988) Platinum-group element mineralisation in the ultramafic sequence of the Acoje ophiolite block, Zambales, Philippines. Pp. 391–380 in: Geo-Platinum Symposium Volume (Prichard, H.M., Potts, P.J., Bowles, J.F.W. Cribb, S.J., editors). Elsevier.
O'Driscoll, B. and González-Jiménez, J.M. (2016) Petrogenesis of the platinum-group minerals. Pp. 489578 in: Highly Siderophile and Strongly Chalcophile Elements in High-Temperature Geochemistry and Cosmochemistry, (Harvey, J. and Day, J.M.D., editors). Reviews in Mineralogy & Geochemistry, 81. Mineralogical Society of America and the Geochemical Society, Chantilly, Virginia, USA.
Ottemann, J. and Augustithis, S.S. (1967) Geochemistry and Origin of “Platinum-Nuggets” in Lateritic Covers from Ultrabasic Rocks and Birbirites of W. Ethiopia. Mineralium Deposita, 1, 269277.
Pedersen, R.B., Johannesen, G.M. and Boyd, R. (1993) Stratiform PGE mineralisations in the ultramafic cumulates of the Leka ophiolite complex, central Norway. Economic Geology, 88, 782803.
Prichard, H.M. (1985) The Shetland Ophiolite. Pp 11731184 in: The Caledonide Orogeny – Scandinavia and Related Areas (Gee, D.G. and Sturt, B.A., editors.). John Wiley and Sons Ltd.
Prichard, H.M. and Brough, C.P. (2009) Potential of ophiolite complexes to host PGE deposits. Pp. 277290 in: New Developments in Magmatic Ni-Cu and PGE Deposits (Li, C. and Ripley, E.M., editors.). Geological Publishing House, Beijing.
Prichard, H.M. and Lord, R.A. (1993) An overview of the PGE concentrations in the Shetland ophiolite complex. Pp. 273294 in: Magmatic Processes and Plate Tectonics (Prichard, H.M., Alabaster, T., Harris, N.B., Neary, C.R., editors). Vol. 76, Geological Society of London.
Prichard, H.M. and Lord, R.A. (1994) Evidence for the mobility of PGE in the secondary environment in the Shetland ophiolite complex. Transactions Institute Mining Metallurgy, B Applied Earth Science, 103, 7986.
Prichard, H.M. and Tarkian, M. (1988) Platinum and palladium minerals from two PGE-rich localities in the Shetland Ophiolite Complex. The Canadian Mineralogist, 26, 979990.
Prichard, H.M., Neary, C.R. and Potts, P.J. (1986) Platinum-group minerals in the Shetland Ophiolite. Pp. 395414 in: Metallogeny of the Basic and Ultrabasic Rocks (Gallagher, M.J., Ixer, R.A., Neary, C.R. and Prichard, H.M., editors). Transactions Institute Mining Metallurgy.
Prichard, H.M., Potts, P.J., Neary, C.R., Lord, R.A. and Ward, G.R. (1988) Development of techniques for the determination of the platinum-group elements in ultramafic rock complexes of potential economic significance: mineralogical studies. Commission of the European Communities. Report EUR 11631, 163 pp. ISBN 92-825-9245-6.
Prichard, H.M., Ixer, R.A., Lord, R.A., Maynard, J. and Williams, N. (1994) Assemblages of platinum-group minerals and sulfides in silicate lithologies and chromite-rich rocks within the Shetland Ophiolite. The Canadian Mineralogist, 32, 271294.
Prichard, H.M., , J.H.S. and Fisher, P.C. (2001) Platinum-group mineral assemblages and chromite composition in the altered and deformed Bacuri complex, Amapa, North Eastern Brazil. The Canadian Mineralogist, 39, 377396.
Prichard, H.M., Economou-Eliopoulos, M. and Fisher, P.C. (2008 a) Platinum-group minerals in podiform chromitite in the Pindos ophiolite complex, Greece. The Canadian Mineralogist, 46, 329341.
Prichard, H.M., Neary, C.R., Fisher, P.C. and O'Hara, M.J. (2008 b) PGE-rich podiform chromitites in the Al'Ays Ophiolite complex, Saudi Arabia: An example of critical mantle melting to extract and concentrate PGE. Economic Geology, 103, 15071529.
Prichard, H.M., Barnes, S.J., Dale, C.W., Godel, B., Fisher, P.C. and Nowell, G.M. (2017) Paragenesis of multiple platinum-group mineral populations in Shetland ophiolite chromitite: 3D X-ray tomography and in situ Os isotopes. Geochimica et Cosmochimica Acta, 216, 314334.
Reith, F., Zammit, C.M., Shar, S.S., Etschmann, B., Bottrill, R., Southam, G., Ta, C., Kilburn, M., Oberthür, T., Bail, A.S. and Brugger, J. (2016) Biological role in the transformation of platinum group mineral grains. Nature Geoscience, 9, 294298.
Salpéteur, I., Martel-Jantin, B. and Rakotomanana, D. (1995) Pt and Pd mobility in ferralitic soils of the West Andriamena area (Magadascar). Evidence of a supergene origin of some Pt and Pd minerals. Chronique de la Recherche Minière, 520, 2745.
Suárez, S., Prichard, H.M, Velasco, F., Fisher, P.C. and McDonald, I. (2010) Alteration of platinum-group minerals and dispersion of platinum-group elements during progressive weathering of the Aguablanca Ni-Cu deposit (SW Spain). Mineralium Deposita, 45, 331350.
Takeno, N. (2005) Atlas of Eh-pH diagrams. Intercomparison of thermodynamic databases. Geological Survey of Japan Open File Report No.419, 287 p.
Tarkian, M. and Prichard, H.M. (1987) Irarsite-hollingworthite solid-solution series and other associated Ru-, Os-, Ir-, and Rh bearing PGM's from the Shetland Ophiolite Complex. Mineralium Deposita, 22, 178184.
Weiser, T.W. (2002) Platinum-group minerals (PGM) in placer deposits. Pp. 721–756 in: The Geology, Geochemistry, Mineralogy and Mineral Beneficiation of Platinum-Group Elements. (L.J. Cabri, editor). Canadian Institute of Mining, Metallurgy and Petroleum, special volume 54.
Williams, P.A. (1990) Oxide Zone Geochemistry. Ellis Horwood Series in Inorganic Chemistry, 286 pp.
Wood, S.A. and Vlassopoulos, D. (1990) The dispersion of Pt, Pd, and Au in surficial media about two PGE-Cu-Ni prospects in Quebec. The Canadian Mineralogist, 28, 649663.
Zaccarini, F., Pushkarev, E., Garuti, G., Krause, J., Dvornik, G.P., Stanley, C. and Bindi, L. (2013) Platinum group minerals (PGM) nuggets from alluvial-eluvial placer deposits in the concentrically zoned mafic-ultramafic Uktus complex (Central Urals, Russia). European Journal of Mineralogy, 25, 519531.

Keywords

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed