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Geochemical Controls on Uranium Release from Neutral-pH Rock Drainage Produced by Weathering of Granite, Gneiss, and Schist Skierszkan, Elliott Karl; Dockrey, John W.; Mayer, K. Ulrich; Bondici, Viorica F.; McBeth, Joyce M.; Beckie, Roger D.
Abstract
We investigated geochemical processes controlling uranium release in neutral-pH (pH ≥ 6) rock drainage (NRD) at a prospective gold deposit hosted in granite, schist, and gneiss. Although uranium is not an economic target at this deposit, it is present in the host rock at a median abundance of 3.7 µg/g, i.e., above the average uranium content of the Earth’s crust. Field bin and column waste-rock weathering experiments using gneiss and schist mine waste rock produced circumneutral-pH (7.6 to 8.4) and high-alkalinity (41 to 499 mg/L as CaCO₃) drainage, while granite produced drainage with lower pH (pH 4.7 to >8) and lower alkalinity (<10 to 210 mg/L as CaCO₃). In all instances, U release was associated with calcium release and formation of weakly sorbing calcium-carbonato-uranyl aqueous complexes. This process accounted for the higher release of uranium from carbonate-bearing gneiss and schist than from granite despite the latter’s higher solid-phase uranium content. In addition, unweathered carbonate-bearing rocks having a higher sulfide-mineral content released more uranium than their oxidized counterparts because sulfuric acid produced during sulfide-mineral oxidation promoted dissolution of carbonate minerals, release of calcium, and formation of calcium-carbonato-uranyl aqueous complexes. Substantial uranium attenuation occurred during a sequencing experiment involving application of uranium-rich gneiss drainage into columns containing Fe-oxide rich schist. Geochemical modeling indicated that uranium attenuation in the sequencing experiment could be explained through surface complexation and that this process is highly sensitive to dissolved calcium concentrations and pCO₂ under NRD conditions.
Item Metadata
Title |
Geochemical Controls on Uranium Release from Neutral-pH Rock Drainage Produced by Weathering of Granite, Gneiss, and Schist
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Creator | |
Publisher |
Multidisciplinary Digital Publishing Institute
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Date Issued |
2020-12-09
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Description |
We investigated geochemical processes controlling uranium release in neutral-pH (pH ≥ 6)
rock drainage (NRD) at a prospective gold deposit hosted in granite, schist, and gneiss. Although
uranium is not an economic target at this deposit, it is present in the host rock at a median
abundance of 3.7 µg/g, i.e., above the average uranium content of the Earth’s crust. Field bin and
column waste-rock weathering experiments using gneiss and schist mine waste rock produced
circumneutral-pH (7.6 to 8.4) and high-alkalinity (41 to 499 mg/L as CaCO₃) drainage, while granite
produced drainage with lower pH (pH 4.7 to >8) and lower alkalinity (<10 to 210 mg/L as CaCO₃).
In all instances, U release was associated with calcium release and formation of weakly sorbing
calcium-carbonato-uranyl aqueous complexes. This process accounted for the higher release of
uranium from carbonate-bearing gneiss and schist than from granite despite the latter’s higher
solid-phase uranium content. In addition, unweathered carbonate-bearing rocks having a higher
sulfide-mineral content released more uranium than their oxidized counterparts because sulfuric
acid produced during sulfide-mineral oxidation promoted dissolution of carbonate minerals, release
of calcium, and formation of calcium-carbonato-uranyl aqueous complexes. Substantial uranium
attenuation occurred during a sequencing experiment involving application of uranium-rich gneiss
drainage into columns containing Fe-oxide rich schist. Geochemical modeling indicated that uranium
attenuation in the sequencing experiment could be explained through surface complexation and that
this process is highly sensitive to dissolved calcium concentrations and pCO₂ under NRD conditions.
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Subject | |
Genre | |
Type | |
Language |
eng
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Date Available |
2021-01-06
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Provider |
Vancouver : University of British Columbia Library
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Rights |
CC BY 4.0
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DOI |
10.14288/1.0395471
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URI | |
Affiliation | |
Citation |
Minerals 10 (12): 1104 (2020)
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Publisher DOI |
10.3390/min10121104
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Peer Review Status |
Reviewed
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Scholarly Level |
Faculty
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Rights URI | |
Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
CC BY 4.0