1887

oa South African Journal of Geology - The Kalahari manganese field: an enigmatic association of iron and manganese

Volume 101 Number 4
  • ISSN : 1012-0750
  • E-ISSN: 1996-8590

 

Abstract

The origin of the giant manganese deposits of the Kalahari manganese field has been highly contentious for many years. Proposed models cover a diverse spectrum of genetic processes, from large-scale epigenetic replacement mechanisms, to submarine volcanogenic-exhalative activity, to purely chemical sedimentation whereby the influence of volcanism is of reduced significance. In this paper, attention is drawn to the potential metallogenic importance of glacial processes occurring prior to the development of the Kalahari deposits, as manifested by the occurrence of an older diamictite unit (Makganyene Formation). Hence, the 'snow-ball earth' scenario as proposed for Neoproterozoic Fe-Mn formations may provide an attractive explanation for the required levels of dissolved Mn in the anoxic parts of the Kalahari palaeodepository. However, the primary source of Mn, the processes leading to the characteristic cyclic development of iron formation and Mn sediment, and the likely influence of a postulated sudden oxygenation during, or prior to, the deposition of the Kalahari ores, are aspects of a long-standing enigma that still await resolution.

Die oorsprong van die reusagtige mangaan deposits of die Kalahari mangaanveld is reeds vir baie jare hoogs omstrede. Voorgestelde modelle dek 'n uiteenlopende spektrum genetiese prosesse, van grootskaalse epigenetiese vervangingsmeganismes, tot ondersese volkanogene uitwasemingsaktiwiteit, tot suiwer chemiese afsetting waar die invloed van vulkanisme van minder betekenis is. In hierdie artikel word die aandag op die potensiële metallogeniese belangrikheid van gletserprosessse wat voor die ontwikkeling van die ontwikkeling van die Kalahari-afsettings plaasgevind het, soos aangedui deur die teenwoordigheid van 'n ouer diamiktieteenheid (Makganyene Formasie), gevestig. Dus kan die 'sneeubal aarde' scenario soos vir Neoproterozoïese Fe-Mn formasies voorgestel 'n aantreklike verklaring vir die vereiste vlakke van opgeloste Mn in die anoksiese gedeeltes van die Kalahari paleoafsettingsgebied bied. Die primêre bran van Mn, die prosesse wat tot die kenmerkende sikliese ontwikkeling van ysterformasie en Mn-afsetting lei, en die waarskynlike invloed van 'n veronderstelde skielike oksigenering tydens, of voor die afsetting van die Kalahari-ertse, is nietemin aspekte van 'n langdurige vraagstuk wat nag steeds opgelos moet word.

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1998-12-01
2020-09-24

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