TY - JOUR

T1 - Sphalerite as a non-traditional critical metal source

T2 - Correlative microscopy (EPMA, EBSD, and APT) of cobalt-enriched sulfides from the sediment-hosted copper-cobalt Dolostone Ore Formation deposit, Namibia

AU - Bertrandsson Erlandsson, Viktor

AU - Gopon, Phillip

AU - Waldl, Helene

AU - Misch, David

AU - Ellmies, Rainer

AU - Melcher, Frank

PY - 2023/4/28

Y1 - 2023/4/28

N2 - Sphalerite from the sediment-hosted Dolostone Ore Formation (DOF) Cu-Co-Zndeposit, in northwestern Namibia, has previously been shown to containextremely high concentrations of the critical metal Co (up to 1 wt%). Theseconcentrations are the highest reported in sphalerite to date, and the how andwhy of sphalerite being able to incorporate such high concentrations of Co arepoorly understood. We use correlative electron probe microanalysis, electronbackscattered diffraction, and atom probe to reconstruct the likely incorporationmechanisms and modes of occurrence of such high Co concentrations in naturalsphalerite. While over twenty samples were studied, the comprehensive analyticalworkflow was executed on one representative sample to gain a detailedunderstanding of Co enrichment. The sulfides of the studied sample are Corichpyrite, chalcopyrite, Co-rich sphalerite, linnaeite, cobaltpentlandite, andcobaltite, mentioned in order of abundance. Detailed petrography of thesesulfides 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 grewduring Ore Stage 1 and was later affected by oxidizing fluids (Ore Stage two). Thisled 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 ofaccessory cobaltite along with the Co-rich sphalerite and chalcopyrite. The hyperenrichedCo-sphalerite then is the last major sink for Co in the DOF deposit. A lowFe and Co and high Zn sub-grain boundary network within the Co-rich sphaleritewas identified by EPMA and EBSD. This sub-grain network is believed to haveformed during a later, secondary metamorphic stage (Cu-Zn (-Pb) Ore Stage 4),which developed during ductile deformational mineralization styles such aspressure shadows and veins. Our APT data reconstructions show no evidencefor Co-inclusions within the Co-sphalerite, and spatial ion correlation analyses ofthe 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 nontraditional Co source in future critical metal exploration.

AB - Sphalerite from the sediment-hosted Dolostone Ore Formation (DOF) Cu-Co-Zndeposit, in northwestern Namibia, has previously been shown to containextremely high concentrations of the critical metal Co (up to 1 wt%). Theseconcentrations are the highest reported in sphalerite to date, and the how andwhy of sphalerite being able to incorporate such high concentrations of Co arepoorly understood. We use correlative electron probe microanalysis, electronbackscattered diffraction, and atom probe to reconstruct the likely incorporationmechanisms and modes of occurrence of such high Co concentrations in naturalsphalerite. While over twenty samples were studied, the comprehensive analyticalworkflow was executed on one representative sample to gain a detailedunderstanding of Co enrichment. The sulfides of the studied sample are Corichpyrite, chalcopyrite, Co-rich sphalerite, linnaeite, cobaltpentlandite, andcobaltite, mentioned in order of abundance. Detailed petrography of thesesulfides 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 grewduring Ore Stage 1 and was later affected by oxidizing fluids (Ore Stage two). Thisled 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 ofaccessory cobaltite along with the Co-rich sphalerite and chalcopyrite. The hyperenrichedCo-sphalerite then is the last major sink for Co in the DOF deposit. A lowFe and Co and high Zn sub-grain boundary network within the Co-rich sphaleritewas identified by EPMA and EBSD. This sub-grain network is believed to haveformed during a later, secondary metamorphic stage (Cu-Zn (-Pb) Ore Stage 4),which developed during ductile deformational mineralization styles such aspressure shadows and veins. Our APT data reconstructions show no evidencefor Co-inclusions within the Co-sphalerite, and spatial ion correlation analyses ofthe 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 nontraditional Co source in future critical metal exploration.

U2 - 10.3389/feart.2023.1171859

DO - 10.3389/feart.2023.1171859

M3 - Article

VL - 11.2023

JO - Frontiers of earth science

JF - Frontiers of earth science

SN - 2296-6463

M1 - 1171859

ER -