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Rapid exsolution behaviour in the bornite–digenite series, and implications for natural ore assemblages

Published online by Cambridge University Press:  05 July 2018

B. A. Grguric  and
A. Putnis
B. A. Grguric
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
A. Putnis
Affiliation:
Institut für Mineralogie, Universität Münster, Corrensstrasse 24, D-48149 Münster, Germany
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Abstract

Intermediate compositions along the bornite–digenite join exsolve during quenching from above-solvus temperatures. This involves vacancy clustering and cation ordering processes, and is facilitated by fast cation diffusion rates in the presence of a large (10–25%) metal vacancy population. Samples of six different compositions across the bornite–Cu9S5 join, synthesised from component elements in sealed quartz capsules, were water-quenched from 600°C and analysed using high-resolution neutron powder diffraction (HRPD). Time-of-flight spectra measured at room temperature showed all intermediate compositions had exsolved into mixtures of bornite and low digenite with a 5.0a superstructure. No evidence for the presence of any other phase was found. Variations in the lattice parameters of the exsolved bornite phase were observed for different bulk compositions across the join, and ascribed to variations in the degree of order. Bornite exsolved from digenite-rich compositions may not be fully ordered due to the much lower solvus temperatures at the Cu-rich end of the solid solution. As only slight differences were observed between the diffraction patterns of a visibly exsolved and a rapidly quenched sample of the same bulk composition, the formation of optically-visible exsolution lamellae on {100} is ascribed to a process of coalescence of sub-microscopic domains initially formed during the quenching process. The rapid kinetics of exsolution at geologically low temperatures, explains the lack of authenticated natural occurrences of intermediate compositions in the solid solution in nature, and the limited degree of stoichiometric variation observed in end-members.

Keywords

bornitedigeniteexsolutioncation ordering
Type
Research Article
Information
Mineralogical Magazine , Volume 63 , Issue 1 , February 1999 , pp. 1 - 12
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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Footnotes

*

Present address: WMC Mount Keith Operations, P.O. Box 238, Welshpool Delivery centre, W.A. 6986, Australia

References

Barton, P.B. (1970) Sulfide Petrology. Mineral. Soc. Amer. Spec. Papers, 3, 187–98.Google Scholar
Barton, P.B. and Skinner, B.J. (1979) Sulfide mineral stabilities. In Geochemistry of Hydrothermal Ore Deposits (Barnes, H.L., ed.), Wiley, 798 p.Google Scholar
Berger, R. and Bucur, R.V. (1996) Potentiometric measurements of copper diffusion in polycrystalline chalcocite, chalcopyrite and bornite. Solid State Ionics, 89, 269–78.CrossRefGoogle Scholar
Bird, D.K., Brooks, C.K., Gannicott, R.A. and Turner, P.A. (1991) A gold-bearing horizon in the Skaergaard intrusion, East-Greenland. Econ. Geol., 86, 1083–92.CrossRefGoogle Scholar
Brett, R. (1964) Experimental data from the system Cu-Fe-S and their bearing on exsolution textures in ores. Econ. Geol., 59, 1241–69.CrossRefGoogle Scholar
Brett, R. and Yund, R.A. (1964) Sulfur-rich bornites. Amer. Mineral., 49, 1084–98.Google Scholar
Bucur, R.V. and Berger, R. (1995) Electrochemical potentiometric determination of the diffusion coeffi-cient of copper in low digenite, a copper sulfide. Solid State Ionics, 76, 291–6.CrossRefGoogle Scholar
David, W.I.F., Akporiaye, D.E., Ibberson, R.M. and Wilson, C.C. (1988) The high resolution powder diffractometer at ISIS. ISIS Facility Technical Report, Rutherford-Appleton Laboratory, Chilton, U.K.Google Scholar
van Dyck, D., Conde-Amiano, C. and Amelinckx, S. (1980) The diffraction pattern of crystals presenting a digenite type of disorder. Physica Status Solidi, 58, 451–68.CrossRefGoogle Scholar
Grace, J. and Putnis, A. (1976) Thermal decomposition and cation mobility in bornite. Econ. Geol., 71, 1058–9.CrossRefGoogle Scholar
Grguric, B.A. and Putnis, A. (1998) Compositional controls on phase transition temperatures in bornite: a DSC study. Canad. Mineral., 36, 215–27.Google Scholar
Grguric, B.A., Putnis, A., and Harrison, R.J. (1998) An investigation of the phase transitions in bornite (Cu5FeS4) using neutron diffraction and differential scanning calorimetry. Amer. Mineral., 83, 1231–9.CrossRefGoogle Scholar
Guibert, J.M. and Park, C.F. Jr (1986) The Geology of Ore Deposits. W.H. Freeman and Co., New York, 985 p.Google Scholar
Haynes, D.W., Cross, K.C., Bills, R.T., and Reed, M.H. (1995) Olympic Dam ore genesis: a fluid mixing model. Econ. Geol., 90, 281–307.CrossRefGoogle Scholar
Holland, T.J.B. and Redfern, S.A.T. (1997) Unit cell re®nement from powder diffraction data: the use of regression diagnostics. Mineral. Mag., 61, 65–77.CrossRefGoogle Scholar
Ibberson, R.M., David, W.I.F. and Knight, K.S. (1992) The high resolution powder diffractometer (HRPD) at ISIS – a user guide. Rutherford-Appleton Laboratory Report RAL-92-031.Google Scholar
Johnson, M.W. and David, W.I.F. (1985) The high resolution powder diffractometer at the SNS. Rutherford-Appleton Laboratory Report RAL-85-112.Google Scholar
Kanazawa, Y., Koto, K., and Morimoto, N. (1978) Bornite (Cu5FeS4): stability and crystal structure of the intermediate form. Canad. Mineral., 16, 397–404.Google Scholar
Knight, K.S. (1996) A neutron powder diffraction determination of the thermal expansion tensor of crocoite (PbCrO4) between 60 K and 290 K. Mineral. Mag., 60, 963–72.CrossRefGoogle Scholar
Koto, K. and Morimoto, N. (1975) Superstructure investigation of bornite, Cu5FeS4, by the modified partial Patterson function. Acta Crystallogr., B31, 2268–73.CrossRefGoogle Scholar
Kullerud, G. (1960) The Cu9S5-Cu5FeS4 join. Carnegie Inst. Washington Yearb., 59, 114–6.Google Scholar
Meyer, C., Shea, E.P. and Goddard, C.C. Jr. (1968) Ore deposits at Butte, Montana. In Ore Deposits of the United States, 1933-1967 (Ridge, J.D., ed.), American Institute of Mining, Metallurgical and Petroleum Engineers, New York.Google Scholar
Morimoto, N. and Gyobu, A. (1971) The composition and stability of digenite. Amer. Min., 56, 1889–909.Google Scholar
Morimoto, N. and Koto, K. (1970) Phase relations of the Cu-S system at low temperatures: stability of anilite. Amer. Mineral., 55, 106–17.Google Scholar
Morimoto, N. and Kullerud, G. (1961) Polymorphism in bornite. Amer. Mineral., 46, 1270–82.Google Scholar
Morimoto, N. and Kullerud, G. (1966) Polymorphism on the Cu5FeS4-Cu9S5 join. Zeits. Kristallogr., 123, 235–54.CrossRefGoogle Scholar
Pierce, L. and Buseck, P.R. (1978) Superstructuring in the bornite-digenite series: a high-resolution electron microscopy study. Amer. Mineral., 63, 1–16.Google Scholar
Pósfai, M. and Buseck, P.R. (1994) Djurleite, digenite, and chalcocite: intergrowths and transformations. Amer. Mineral., 79, 308–15.Google Scholar
Putnis, A. and Grace, J. (1976) The transformation behaviour of bornite. Contrib. Mineral. Petrol., 55, 311–5.CrossRefGoogle Scholar
Ramdohr, P. (1969) The Ore Minerals and Their Intergrowths. Pergamon Press, 1174 p.Google Scholar
Roseboom, E.H. Jr. (1966) An investigation of the system Cu-S and some natural copper sulfides between 258 and 700°C. Econ. Geol., 61, 641–72.CrossRefGoogle Scholar
Wager, L.R. Vincent, E.A. and Smales, A.A. (1957) Sulphides in the Skaergaard intrusion, East Greenland. Econ. Geol., 52, 855–903.CrossRefGoogle Scholar
Yund, R.A. and Hall, H.T. (1970) Kinetics and mechanism of pyrite exsolution from pyrrhotite. J. Petrol., 11, 381–404.CrossRefGoogle Scholar