Sphalerite as a non-traditional critical metal source: Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, Namibia

Sphalerite from the sediment-hosted Dolostone Ore Formation (DOF) Cu-Co-Zn deposit, in northwestern Namibia, has previously been shown to contain extremely high concentrations of the critical metal Co (up to 1 wt%). These concentrations are the highest reported in sphalerite to date, and the how and...

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Main Authors: Viktor Bertrandsson Erlandsson, Phillip Gopon, Helene Waldl, David Misch, Rainer Ellmies, Frank Melcher
Format: Article
Language:English
Published: Frontiers Media S.A. 2023-04-01
Series:Frontiers in Earth Science
Subjects:
Online Access:https://www.frontiersin.org/articles/10.3389/feart.2023.1171859/full
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author Viktor Bertrandsson Erlandsson
Phillip Gopon
Helene Waldl
David Misch
Rainer Ellmies
Frank Melcher
author_facet Viktor Bertrandsson Erlandsson
Phillip Gopon
Helene Waldl
David Misch
Rainer Ellmies
Frank Melcher
author_sort Viktor Bertrandsson Erlandsson
collection DOAJ
description Sphalerite from the sediment-hosted Dolostone Ore Formation (DOF) Cu-Co-Zn deposit, in northwestern Namibia, has previously been shown to contain extremely high concentrations of the critical metal Co (up to 1 wt%). These concentrations are the highest reported in sphalerite to date, and the how and why of sphalerite being able to incorporate such high concentrations of Co are poorly understood. We use correlative electron probe microanalysis, electron backscattered diffraction, and atom probe to reconstruct the likely incorporation mechanisms and modes of occurrence of such high Co concentrations in natural sphalerite. While over twenty samples were studied, the comprehensive analytical workflow was executed on one representative sample to gain a detailed understanding of Co enrichment. The sulfides of the studied sample are Co-rich pyrite, chalcopyrite, Co-rich sphalerite, linnaeite, cobaltpentlandite, and cobaltite, mentioned in order of abundance. Detailed petrography of these sulfides indicates that they formed through three stages during the main Cu-Co-Zn ore stage of the DOF. Cobalt was initially contained in pyrite that grew during Ore Stage 1 and was later affected by oxidizing fluids (Ore Stage two). This led to remobilization and growth of linnaeite (Co2+Co3+2S4). A later change in fO2 (Ore Stage three) led to the breakdown of linnaeite and the further growth of accessory cobaltite along with the Co-rich sphalerite and chalcopyrite. The hyper-enriched Co-sphalerite then is the last major sink for Co in the DOF deposit. A low Fe and Co and high Zn sub-grain boundary network within the Co-rich sphalerite was identified by EPMA and EBSD. This sub-grain network is believed to have formed during a later, secondary metamorphic stage (Cu-Zn (-Pb) Ore Stage 4), which developed during ductile deformational mineralization styles such as pressure shadows and veins. Our APT data reconstructions show no evidence for Co-inclusions within the Co-sphalerite, and spatial ion correlation analyses of the data suggest that Co occurs in the sphalerite through simple substitution of Zn. This study demonstrates that sphalerite may contain significant concentrations of the Co through simple substitution, potentially representing an important non-traditional Co source in future critical metal exploration.
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spelling doaj.art-e51391c919b94731ad9c0989bb01a4a82023-05-05T09:10:38ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632023-04-011110.3389/feart.2023.11718591171859Sphalerite as a non-traditional critical metal source: Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, NamibiaViktor Bertrandsson Erlandsson0Phillip Gopon1Helene Waldl2David Misch3Rainer Ellmies4Frank Melcher5Department of Applied Geosciences and Geophysics, Montanuniversität Leoben, Leoben, AustriaDepartment of Applied Geosciences and Geophysics, Montanuniversität Leoben, Leoben, AustriaChristian Doppler Laboratory for Advanced Coated Cutting Tools, Montanuniversität Leoben, Leoben, AustriaDepartment of Applied Geosciences and Geophysics, Montanuniversität Leoben, Leoben, AustriaGecko Namibia, Swakopmund, NamibiaDepartment of Applied Geosciences and Geophysics, Montanuniversität Leoben, Leoben, AustriaSphalerite from the sediment-hosted Dolostone Ore Formation (DOF) Cu-Co-Zn deposit, in northwestern Namibia, has previously been shown to contain extremely high concentrations of the critical metal Co (up to 1 wt%). These concentrations are the highest reported in sphalerite to date, and the how and why of sphalerite being able to incorporate such high concentrations of Co are poorly understood. We use correlative electron probe microanalysis, electron backscattered diffraction, and atom probe to reconstruct the likely incorporation mechanisms and modes of occurrence of such high Co concentrations in natural sphalerite. While over twenty samples were studied, the comprehensive analytical workflow was executed on one representative sample to gain a detailed understanding of Co enrichment. The sulfides of the studied sample are Co-rich pyrite, chalcopyrite, Co-rich sphalerite, linnaeite, cobaltpentlandite, and cobaltite, mentioned in order of abundance. Detailed petrography of these sulfides indicates that they formed through three stages during the main Cu-Co-Zn ore stage of the DOF. Cobalt was initially contained in pyrite that grew during Ore Stage 1 and was later affected by oxidizing fluids (Ore Stage two). This led to remobilization and growth of linnaeite (Co2+Co3+2S4). A later change in fO2 (Ore Stage three) led to the breakdown of linnaeite and the further growth of accessory cobaltite along with the Co-rich sphalerite and chalcopyrite. The hyper-enriched Co-sphalerite then is the last major sink for Co in the DOF deposit. A low Fe and Co and high Zn sub-grain boundary network within the Co-rich sphalerite was identified by EPMA and EBSD. This sub-grain network is believed to have formed during a later, secondary metamorphic stage (Cu-Zn (-Pb) Ore Stage 4), which developed during ductile deformational mineralization styles such as pressure shadows and veins. Our APT data reconstructions show no evidence for Co-inclusions within the Co-sphalerite, and spatial ion correlation analyses of the data suggest that Co occurs in the sphalerite through simple substitution of Zn. This study demonstrates that sphalerite may contain significant concentrations of the Co through simple substitution, potentially representing an important non-traditional Co source in future critical metal exploration.https://www.frontiersin.org/articles/10.3389/feart.2023.1171859/fullcobaltsphaleritedolostone ore formationsubstitution mechanismsEBSDEPMA
spellingShingle Viktor Bertrandsson Erlandsson
Phillip Gopon
Helene Waldl
David Misch
Rainer Ellmies
Frank Melcher
Sphalerite as a non-traditional critical metal source: Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, Namibia
Frontiers in Earth Science
cobalt
sphalerite
dolostone ore formation
substitution mechanisms
EBSD
EPMA
title Sphalerite as a non-traditional critical metal source: Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, Namibia
title_full Sphalerite as a non-traditional critical metal source: Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, Namibia
title_fullStr Sphalerite as a non-traditional critical metal source: Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, Namibia
title_full_unstemmed Sphalerite as a non-traditional critical metal source: Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, Namibia
title_short Sphalerite as a non-traditional critical metal source: Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, Namibia
title_sort sphalerite as a non traditional critical metal source correlative microscopy epma ebsd and apt of cobalt enriched sulfides from the sediment hosted copper cobalt dolostone ore formation deposit namibia
topic cobalt
sphalerite
dolostone ore formation
substitution mechanisms
EBSD
EPMA
url https://www.frontiersin.org/articles/10.3389/feart.2023.1171859/full
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