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The replacement of chalcopyrite by bornite under hydrothermal conditions

  • Jing Zhao , Joël Brugger , Yung Ngothai and Allan Pring EMAIL logo
Published/Copyright: November 12, 2014
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American Mineralogist
From the journal American Mineralogist Volume 99 Issue 11-12

Abstract

We report the replacement of chalcopyrite by bornite under hydrothermal conditions in solutions containing Cu(I) and hydrosulfide over the temperature range 200-320 °C at autogenous pressures. Chalcopyrite was replaced by bornite under all studied conditions. The reaction proceeds via an interface coupled dissolution-reprecipitation (ICDR) mechanism and via additional overgrowth of bornite from the bulk solution. Initially, the reaction is fast and results in a bornite rim of homogeneous thickness. Reaction rates then slow down, probably reflecting healing of the porosity, and the reaction proceeds predominantly along twin boundaries of the chalcopyrite.

The composition of the bornite product is generally Cu-rich, corresponding to the bornite-digenite (Cu5FeS4-Cu9S5; Bn-Dg) solid solution (bdss). The Cu and Fe contents were controlled principally by temperature, with solution pH having only a small effect. The percentage of Cu in bdss decreased and the percentage of Fe increased with increasing reaction temperature: at 200 °C a composition of Bn47Dg53 was obtained; at 300 °C the composition was Bn90Dg10 and at 320 °C it was near-stoichiometric bornite. The influence of temperature rather than solution chemistry on the composition of bdss, as well as the homogeneity of the bornite product grown both via replacement of chalcopyrite and from the bulk solution as overgrowth, are interpreted to reflect buffering of the bornite activity in bdss via solids (e.g., reaction chalcopyrite + 2 chalcocite = bornite).

Only the end-member compositions of the bdss are found in nature, indicating that the products obtained are metastable, and illustrating the importance of reaction mechanism for controlling the chemistry of the mineral product. The unique features of the chalcopyrite to bornite reaction investigated here are related to interaction between a solution controlled ICDR reaction with solid-state diffusion processes driving porosity healing.

Keywords : Chalcopyrite; bornite; mineral replacement reaction; diffusion; hydrothermal; bornitedigenite solid solution
Received: 2013-12-1
Accepted: 2014-6-7
Published Online: 2014-11-12
Published in Print: 2014-11-1

© 2014 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2014-4825
Keywords for this article
Chalcopyrite; bornite; mineral replacement reaction; diffusion; hydrothermal; bornitedigenite solid solution

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  1. Highlights and Breakthroughs Merrillite and apatite as recorders of planetary magmatic processes
  2. Highlights and Breakthroughs Comparing clays from Mars and Earth: Implications for martian habitability
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  5. Synthesis and structure of carbonated barium and lead fluorapatites: Effect of cation size on A-type carbonate substitution
  6. Optical absorption spectroscopy study of the causes for color variations in natural Fe-bearing gahnite: Insights from iron valency and site distribution data
  7. Si-magnetite nano-precipitates in silician magnetite from banded iron formation: Z-contrast imaging and ab initio study
  8. Ordering kinetics in synthetic Mg(Al,Fe3+)2O4 spinels: Quantitative elucidation of the whole Al-Mg-Fe partitioning, rate constants, activation energies
  9. Experimental study of phlogopite reaction rim formation on olivine in phonolite melts: Kinetics, reaction rates, and residence times
  10. Etch-pit size, dissolution rate, and time in the experimental dissolution of olivine: Implications for estimating olivine lifetime at the surface of Mars
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  12. A large spectral survey of small lunar craters: Implications for the composition of the lunar mantle
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  15. Determining hematite content from NUV/Vis/NIR spectra: Limits of detection
  16. The role of water in generation of group II kimberlite magmas: Constraints from multiple saturation experiments
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