Cu isotope fractionation during bornite dissolution: An in situ X-ray diffraction analysis

Journal Article · Wed Oct 24 00:00:00 EDT 2012 · Ore. Geol. Rev.

DOI:https://doi.org/10.1016/j.oregeorev.2011.01.001· OSTI ID:1047300

Wall, Andrew J; Mathur, Ryan; Post, Jeffrey E; Heaney, Peter J ^[1]

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1. Juniata

Low-temperature ore deposits exhibit a large variation in {delta}{sup 65}Cu ({approx}12{per_thousand}), and this range has been attributed, in part, to isotope fractionation during weathering reactions of primary minerals such as chalcocite and chalcopyrite. Here, we examine the fractionation of Cu isotopes during dissolution of another important Cu ore mineral, bornite, using a novel approach that combines time-resolved X-ray diffraction (XRD) and isotope analysis of reaction products. During the initial stages of bornite oxidative dissolution by ferric sulfate (< 5 mol% of total Cu leached), dissolved Cu was enriched in isotopically heavy Cu ({sup 65}Cu) relative to the solid, with an average apparent isotope fractionation ({Delta}{sub aq - min} = {delta}{sup 65}Cu{sub aq} - {delta}{sup 65}Cu{sub min}{sup 0}) of 2.20 {+-} 0.25{per_thousand}. When > 20 mol% Cu was leached from the solid, the difference between the Cu isotope composition of the aqueous and mineral phases approached zero, with {Delta}{sub aq - min}{sup 0} values ranging from - 0.21 {+-} 0.61{per_thousand} to 0.92 {+-} 0.25{per_thousand}. XRD analysis allowed us to correlate changes in the atomic structure of bornite with the apparent isotope fractionation as the dissolution reaction progressed. These data revealed that the greatest degree of apparent fractionation is accompanied by a steep contraction in the unit-cell volume, which we identified as a transition from stoichiometric to non-stoichiometric bornite. We propose that the initially high {Delta}{sub aq - min} values result from isotopically heavy Cu ({sup 65}Cu) concentrating within Cu{sup 2+} during dissolution. The decrease in the apparent isotope fractionation as the reaction progresses occurs from the distillation of isotopically heavy Cu ({sup 65}Cu) during dissolution or kinetic isotope effects associated with the depletion of Cu from the surfaces of bornite particles.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: NSFDOE - BASIC ENERGY SCIENCES
• OSTI ID: 1047300
• Journal Information: Ore. Geol. Rev., Vol. 42, Issue (1) ; 11, 2011
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CHALCOPYRITE
CONTRACTION
COPPER 65
DEPOSITS
DISSOLUTION
DISTILLATION
FRACTIONATION
ISOTOPE EFFECTS
ISOTOPES
ISOTOPE SEPARATION
KINETICS
MINERALS
ORES
PARTICLES
RANGE
SULFATES
SURFACES
TEMPERATURE RANGE 0065-0273 K
VARIATIONS
WEATHERING
X-RAY DIFFRACTION