Abstract
Ore in the Kamoa-Kakula deposits (Democratic Republic of Congo) is dominated by fine-grained Cu sulfides disseminated in Cryogenian diamictite matrix and siltstone, commonly with coarsely crystalline sulfide-gangue ‘caps’ and ‘beards’ on larger clasts. In addition to sedimentary material, ore-zone matrix contains hypogene Cu-sulfides, and ore-stage haematite and sericite. The finest-grained part of ore-zone matrix consists of randomly distributed, randomly oriented, irregularly interlocking subequant matrix crystals, with equant sulfide phases in interstitial pores. Millimetric subvertical swaths of microfoliated ore-zone matrix adjacent to larger diamictite clasts are dominated by sericite and are characterised by elongation and depletion of tectosilicates, dolomite, and Cu-sulfides. Removal of material from sides of silt-sized detrital particles in foliated ore-zone matrix was accompanied by syntaxial precipitation at their tops and bottoms, indicating that during horizontal compression, fluid-mediated pressure-solution and reprecipitation produced grain elongation and alignment, mass transfer (~−30%), and Cu-depletion in microfoliated matrix. This process explains the transfer of sulfide and gangue material into low-pressure areas on the tops and bottoms of the larger clasts (‘caps’ and ‘beards’). Ore characteristics were therefore produced by two distinct events: ‘early’ disseminated ore emplaced into isotropic diamictite matrix prior to orogenic compression and ‘late’ transfer of Cu and gangue minerals from diamictite matrix into clast-caps during Lufilian (late Neoproterozoic) compression.
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Acknowledgements
Financial and logistical support from Ivanhoe Mines Ltd. and Kamoa Copper S.A., together with financial support from a Canada Natural Sciences and Engineering Research Council Collaborative Research and Development Grant to ECT. Our thanks to F. Twite for stimulating discussions, J. Marsh, K. Ross, and W. Zhe for SEM assistance, and an anonymous reviewer and Associate Editor Frimmel for helpful suggestions.
Funding
Financial and logistical support was received from Ivanhoe Mines Ltd. and Kamoa Copper S.A., together with financial support from Natural Sciences and Engineering Research Council Collaborative Research and Development Grant CRDPJ 499944-16 to ECT.
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Fieldwork (QD, ECT, DWB); petrography (QD, ECT); analytical work (ECT, QD); interpretive model (ECT, QD, DWB, DJK); geochemical analysis (DJK, ECT); writing (all authors).
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Turner, E.C., Dabros, Q., Broughton, D.W. et al. Textural and geochemical evidence for two-stage mineralisation at the Kamoa-Kakula Cu deposits, Central African Copperbelt. Miner Deposita 58, 825–832 (2023). https://doi.org/10.1007/s00126-023-01165-z
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DOI: https://doi.org/10.1007/s00126-023-01165-z