Geochemistry of the Palæoproterozoic Mooidraai Formation: Fe-rich limestone as end member of iron formation deposition, Kalahari Manganese Field, Transvaal Supergroup, South Africa
✍ Scribed by H. Tsikos; J.M. Moore; C. Harris
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 768 KB
- Volume
- 32
- Category
- Article
- ISSN
- 1464-343X
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✦ Synopsis
The Mooidraai Formation forms the uppermost portion of the Palasoproterozoic Transvaal Supergroup in Griqualand West, Northern Cape Province, South Africa and is developed immediately above the Mn-bearing Hotazel Formation. Though previously described as a (cherty) dolomite, the portion of the Mooidraai succession investigated here contains microcrystalline calcite as the sole carbonate constituent. Variable amounts of magnetite and quartz are commonly present in the rock, giving it a mineralogical/geochemical character that approaches, at times, that of the underlying Hotazel iron formation. Bulk rock and rare earth element data compare well with those of the Hotazel iron formation and suggest that the Mooidraai Formation constitutes the yd member of chemical precipitation that produced the cyclic Fe-Mn sequence of the Hotazel Formation. Calcite C and 0 isotope data indicate a diagenetic origin for the carbonate component with deviations from typical marine bicarbonate isotope values proportionally related to the amount of Fe present. The Mooidraai data thus support models of organic matter oxidation-ferric Fe reduction, as observed in modern 0 deficient diagenetic environments.