Hostname: page-component-cd9895bd7-7cvxr Total loading time: 0 Render date: 2024-12-26T06:24:01.475Z Has data issue: false hasContentIssue false
  • English
  • Français

A silver-palladium alloy from the Bahia lateritic gold deposit, Carajas, Brazil

Published online by Cambridge University Press:  05 July 2018

Weisheng Zang ,
William S. Fyfe  and
Robert L. Barnett
Weisheng Zang
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
William S. Fyfe
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
Robert L. Barnett
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
Get access Rights & Permissions [Opens in a new window]

Abstract

A silver-palladium alloy with structural formula close to AgPd has been found in laterite from the Bahia lateritic gold deposit. The alloy occurs in a void of an iron oxide nodule, associated with goethite and hematite. The angular shape and protuberances of the alloy grains suggest crystal growth in a lateritic environment, indicating that the alloy is a secondary mineral precipitated during lateritisation. The oxidation of sulphides of the parent rocks probably favoured the migration of palladium and silver as transient thiosulphate and sulphite complexes. Destruction of the thiosulphate and sulphite ligands could result in precipitation of both palladium and silver as an alloy. Eh-pH phase diagrams for Pd-H2O-C1 and Ag-H2O-C1 systems show that both palladium and silver are stable in lateritic environments under lower redox potentials. Such an environment may exist at the top of the ferruginous zone due to the abundant organic matter near the surface.

Keywords

silver-palladium alloythiosulphate complexchloride complexlateriteBahia gold depositBrazil
Type
Research Article
Information
Mineralogical Magazine , Volume 56 , Issue 382 , March 1992 , pp. 47 - 51
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2014

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Baas Becking, L. G. M., Kaplan, I. R., and Moore, D. (1960) Limits of the natural environment in terms of pH and oxidation-reduction potentials. J. Geol., 68, 243–84.CrossRefGoogle Scholar
Breemen, N. V. and Wielemaker, W. G. (1974) Buffer intensities and equilibrium pH of minerals and soils. Soil Sci. Soc. Amer., Proc., 38, 61–6.CrossRefGoogle Scholar
Bowles, J. F. W. (1986) The development of platinum-group minerals in laterites. Econ. Geol. 81, 1278–85.CrossRefGoogle Scholar
Bowles, J. F. W. (1987) Further studies of the development of platinum-group minerals in the laterites of the Freetown layered complex, Sierra Leone. In Geo-platinum 87 (Prichard, H. M., Potts, P. J., Bowles, J. F. W., and Cribb, S. J., eds.). Elsevier Applied Science, London and New York, pp. 273-80.Google Scholar
Fuchs, W. A. and Rose, A. W. (1974) The geochemical behaviour of platinum and palladium in the weathering cycle in the Stillwater Complex, Montana. Econ. Geol., 69, 332–46.CrossRefGoogle Scholar
Karakaya, I. and Thompson, W. T. (1986) Ag-Pd (silverpalladium). In Binary Alloy Phase Diagrams (Massalski, T. B., ed.). Amer. Soc. Metals, Metals Park, Ohio, pp. 54-5.Google Scholar
Keays, R. R. and Davison, R. M. (1976) Palladium, iridium and gold in the ores and host rocks of nickel sulphide deposits in Western Australia. Econ. Geol., 71, 1214–28.CrossRefGoogle Scholar
Kharkar, D. P., Turekian, K. K., and Bertine, K. K. (1968) Stream supply of dissolved silver, molyb-denum, antimony, selenium, chromium, cobalt, rubidium and cesium to the oceans. Geochim. Cosrno-chim Acta, 32, 285–98.CrossRefGoogle Scholar
Lottermoser, B. G. (1988) Supergene, secondary mon-azite from the Mt Weld carbonatite laterite, Western Australia. Neues Jahrb. Mineral., Mh., 67-70.Google Scholar
Mann, A. W. (1984) Mobility of gold and silver in lateritic weathering profiles: some observation from Western Australia. Econ. Geol., 79, 38–49.CrossRefGoogle Scholar
Plimer, I. R. and Williams, P. A. (1987) New mech-anisms for the mobilzation of the platinum-group elements in the supergene zone. In Geoplatinum 87, (Prichard, H. M., Potts, P. J., Bowles, J. F. W., and Cribb, S. J., eds.). Elsevier Applied Science, London and New York, pp. 83-92.Google Scholar
Stallard, R. F. (1980) Major element geochemistry of the Amazon River system. Ph.D. dissertation, MIT/ Woods Hole Oceanographic Inst., WHOI-80-29, 366 PP.Google Scholar
Stallard, R. F. and Edmond, J. M. (1981) Geochemistry of the Amazon: 1. Precipitation chemistry and the marine contribution to the dissolved load at the time of peak discharge. J. Geophys. Res., 86 (C10), 9844-58.Google Scholar
Travis, G. A., Keays, R. R., and Davison, R. M. (1976) Palladium and iridium in the evaluation of nickel gossans in Western Australia. Econ. Geol., 71, 1229–43.CrossRefGoogle Scholar
Wagman, D. D., Evans, W. H., Parker, V. B., Schumm, R. H., Halow, I., Bailey, S. M., Churney, K. L., and Nuttall, R. L. (1982) The NBS tables of chemical thermodynamic properties. J. Phys. Chem. Ref. Data, 11, Supplement No. 2.Google Scholar
Webster, J. G. (1986) The stability of gold and silver in the system Au-Ag-O2-H2O at 25 °C and 1 atm. Geochim. Cosmochim. Acta, 50, 1837–45.CrossRefGoogle Scholar
Westland, A. D. (1981) Inorganic chemistry of the platinum-group elements. I. Platinum-group Elements: Mineralogy, Geology, Recovery (Cabri, L. J., ed.). Canad. Inst. Mining. Metall. Spec. Vol. 23, 7–18.Google Scholar