Abstract
Sulfide minerals host most of the world’s supplies of metals such as Cu, Ni, Co, Zn, Pb, or Mo, and understanding their crystallization, dissolution, and textural evolution is key to understanding the formation of mineral deposits, metal recovery via metallurgy, and their environmental impact. Despite the prominence of hydrothermally formed sulfide minerals, the interpretation of textures in sulfide petrology relies mainly on comparison with results from experiments conducted under dry conditions. Here, we show experimentally that the exsolution of chalcopyrite (CuFeS2) lamellae from a bornite (Cu5FeS4)-digenite (Cu9S5) solid solution (bdss) is a back-reaction, which occurred during low temperature annealing (150 °C) following initial replacement of parent chalcopyrite by bdss at 300 °C. The back-reaction is rapid (days), and its progress is catalyzed by small amounts of fluid present in the porosity within the bdss. This porosity initially results from the formation of bdss via the replacement of parent chalcopyrite by an interface-coupled dissolution-reprecipitation mechanism. During annealing, bdss first breaks down into bornite and digenite via solid-state exsolution. The bornite-digenite assemblage then exsolves chalcopyrite in local patches. We discovered strikingly similar textures in iron oxide copper gold (IOCG) deposits from South Australia; in these samples, the fluid-driven nature of the exsolution reaction is reflected by the fact that the chalcopyrite lamellae propagate around cracks and fractures within bornite. As in our experiments, most of this natural bornite formed via replacement of chalcopyrite. These reactions are controlled by kinetic factors (e.g., relative nucleation rates of Cu-Fe-sulfides; presence of porosity) rather than equilibrium thermodynamics, but result in final assemblages and textures that may not be distinguishable from those evolving from equilibrium processes under dry conditions.
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References
Altree-Williams A, Pring A, Ngothat Y, Brugger J (2015) Textural and compositional complexities resulting from coupled dissolution-reprecipitation reactions in geomaterials. Earth-Science Review, in press
Brugger J, Etschmann B, Liu W, Testemale D, Hazemann J-L, Emerich H, Van Beek W, Proux O (2007) An XAS study of the structure and thermodynamics of Cu (I) chloride complexes in brines up to high temperature (400 °C, 600bar). Geochim Cosmochim Acta 71:4920–4941
Bruker A (2005) TOPAS V3: general profile and structure analysis software for powder diffraction data. User’s manual, Bruker AXS, Karlsruhe
Cook NJ, Ciobanu CL, Danyushevsky LV, Gilbert S (2011) Minor and trace elements in bornite and associated Cu–(Fe)-sulfides: a LA-ICP-MS studyBornite mineral chemistry. Geochim Cosmochim Acta 75:6473–6496
Holwell DA, Adeyemi Z, Ward LA, Smith DJ, Graham SD, McDonald I, Smith JW (2017) Low temperature alteration of magmatic Ni-Cu-PGE sulfides as a source for hydrothermal Ni and PGE ores: a quantitative approach using automated mineralogy. Ore Geol Rev 91:718–740
Hoshino K, Watanabe M (1997) Exsolution mechanism of chalcopyrite from bornite solid solution. Neues Jahrbuch Fur Mineralogie-Monatshefte 145–154
Milke R, Neusser G, Kolzer K, Wunder B (2013) Very little water is necessary to make a dry solid silicate system wet. Geology 41:247–250
Ramdohr P (1980) The ore minerals and their intergrowths, 2nd edn. International series in earth science, 35. London: Pergamon Press
Robb L (2013) Introduction to ore-forming processes. John Wiley & Sons
Schwartz GM (1931) Textures due to unmixing of solid solutions. Econ Geol 26:739–763
Shvarov YV, Bastrakov E (1999) HCh: a software package for geochemical equilibrium modelling (user’s guide). Australian Geological Science Organisation (AGSO) record 1999/25, 60 pp.
Skirrow RG, Bastrakov EN, Barovich K, Fraser GL, Creaser RA, Fanning CM, Raymond OL, Davidson GJ (2007) Timing of Iron Oxide Cu-Au-(U) Hydrothermal Activity and Nd Isotope Constraints on Metal Sources in the Gawler Craton, South Australia. Econ Geol 102(8):1441–1470
Sugaki A, Shima H, Kitakaze A, Harada H (1975) Isothermal phase relations in the system Cu-Fe-S under hydrothermal conditions at 350 degrees C and 300 degrees C. Econ Geol 70(4):806–823
Vaughan DJ (2006) Sulfide mineralogy and geochemistry: introduction and overview. Rev Mineral Geochem 61(1):1–5
Zhao J, Brugger J, Chen G, Ngothai Y, Pring A (2014a) Experimental study of the formation of chalcopyrite and bornite via the sulfidation of hematite: mineral replacements with a large volume increase. Am Mineral 99:343–354
Zhao J, Brugger J, Ngothai Y, Pring A (2014b) The replacement of chalcopyrite by bornite under hydrothermal conditions. Am Mineral 99:2389–2397. https://doi.org/10.2138/am-2014-4825
Zhao J, Brugger J, Grguric BA, Ngothai Y, Pring A (2017) Fluid-enhanced coarsening of mineral microstructures in hydrothermally synthesized bornite–digenite solid solution. ACS Earth and Space Chemistry 1(8):465–474
Acknowledgements
We thank Aoife McFadden and Benjamin Wade (Adelaide Microscopy) for their assistance with FESEM and EPMA. We thank Dr. Kathy Ehrig (BHP Billiton) for Fig. 1. We are grateful to A. Deditius, R. Linnen (associate editor) and Georges Beaudoin (Chief editor) for insightful comments that helped improve this contribution.
Funding
This work has been made possible by the financial support of the Australian Research Council (DP1095069 and DP170101893).
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Li, K., Brugger, J. & Pring, A. Exsolution of chalcopyrite from bornite-digenite solid solution: an example of a fluid-driven back-replacement reaction. Miner Deposita 53, 903–908 (2018). https://doi.org/10.1007/s00126-018-0820-6
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DOI: https://doi.org/10.1007/s00126-018-0820-6