The role of hydrothermal activity in the formation of karst-hosted manganese deposits of the Postmasburg Mn Field, Northern Cape Province, South Africa

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dc.contributor.authorFairey, Brenton J.
dc.contributor.authorTimmerman, Martin J.
dc.contributor.authorSudo, Masafumi
dc.contributor.authorTsikos, Harilaos
dc.contributor.funderAngloamericanen
dc.contributor.funderASSMANG Ltden
dc.date.accessioned2019-11-19T10:08:15Z
dc.date.available2019-11-19T10:08:15Z
dc.date.issued2019-07-03
dc.description.abstractThe Postmasburg Manganese Field (PMF), Northern Cape Province, South Africa, once represented one of the largest sources of manganese ore worldwide. Two belts of manganese ore deposits have been distinguished in the PMF, namely the Western Belt of ferruginous manganese ores and the Eastern Belt of siliceous manganese ores. Prevailing models of ore formation in these two belts invoke karstification of manganese-rich dolomites and residual accumulation of manganese wad which later underwent diagenetic and low-grade metamorphic processes. For the most part, the role of hydrothermal processes and metasomatic alteration towards ore formation has not been adequately discussed. Here we report an abundance of common and some rare Al-, Na-, K- and Ba-bearing minerals, particularly aegirine, albite, microcline, banalsite, sérandite-pectolite, paragonite and natrolite in Mn ores of the PMF, indicative of hydrothermal influence. Enrichments in Na, K and/or Ba in the ores are generally on a percentage level for most samples analysed through bulk-rock techniques. The presence of As-rich tokyoite also suggests the presence of As and V in the hydrothermal fluid. The fluid was likely oxidized and alkaline in nature, akin to a mature basinal brine. Various replacement textures, particularly of Na- and K- rich minerals by Ba-bearing phases, suggest sequential deposition of gangue as well as ore-minerals from the hydrothermal fluid, with Ba phases being deposited at a later stage. The stratigraphic variability of the studied ores and their deviation from the strict classification of ferruginous and siliceous ores in the literature, suggests that a re-evaluation of genetic models is warranted. New Ar-Ar ages for K-feldspars suggest a late Neoproterozoic timing for hydrothermal activity. This corroborates previous geochronological evidence for regional hydrothermal activity that affected Mn ores at the PMF but also, possibly, the high-grade Mn ores of the Kalahari Manganese Field to the north. A revised, all-encompassing model for the development of the manganese deposits of the PMF is then proposed, whereby the source of metals is attributed to underlying carbonate rocks beyond the Reivilo Formation of the Campbellrand Subgroup. The main process by which metals are primarily accumulated is attributed to karstification of the dolomitic substrate. The overlying Asbestos Hills Subgroup banded iron formation (BIF) is suggested as a potential source of alkali metals, which also provides a mechanism for leaching of these BIFs to form high-grade residual iron ore deposits.en
dc.description.statusPeer revieweden
dc.description.versionPublished Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.articleid408en
dc.identifier.citationFairey, B.J., Timmerman, M.J., Sudo, M. and Tsikos, H., 2019. The Role of Hydrothermal Activity in the Formation of Karst-Hosted Manganese Deposits of the Postmasburg Mn Field, Northern Cape Province, South Africa. Minerals, 9(7), (408). DOI:10.3390/min9070408en
dc.identifier.doi10.3390/min9070408en
dc.identifier.eissn2075-163X
dc.identifier.endpage28en
dc.identifier.issued7en
dc.identifier.journaltitleMineralsen
dc.identifier.startpage1en
dc.identifier.urihttps://hdl.handle.net/10468/9035
dc.identifier.volume9en
dc.language.isoenen
dc.publisherMDPIen
dc.relation.urihttps://www.mdpi.com/2075-163X/9/7/408
dc.rights© 2019 by the authors. Licensee MDPI, Basel, Switzerlanden
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/en
dc.subjectManganese oreen
dc.subjectPostmasburg manganese fielden
dc.subjectHydrothermalen
dc.subjectKarsten
dc.subjectSouth Africaen
dc.titleThe role of hydrothermal activity in the formation of karst-hosted manganese deposits of the Postmasburg Mn Field, Northern Cape Province, South Africaen
dc.typeArticle (peer-reviewed)en
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