Timing of supergene enrichment of low-grade sedimentary manganese ores in the Kalahari Manganese Field,South Africa |
| |
| Institution: | 1. Helmholtz Institute Freiberg for Resource Technology, Halsbrücker Str. 34, 09599 Freiberg, Germany;2. Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa;1. Université Paris Sud, IPN, in2p3, 91405 Orsay, France;2. Université Paris Sud, UMR GEOPS-CNRS 8148, 91405 Orsay, France;1. Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany;2. Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, CEP 70910-900 Brasília, DF, Brazil;3. Instituto de Geociências, Universidade de São Paulo, Rua do Lago 562, 05508-080 São Paulo, SP, Brazil;1. Department of Earth Sciences, Utrecht University, P.O. Box 80.115, 3508 TC Utrecht, The Netherlands;2. Geology Department, Rhodes University, Drosty Road, Grahamstown 6139, South Africa;3. GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany;1. Royal Museum for Central Africa, Geodynamics and Mineral Resources, Leuvensesteenweg 13, B-3080 Tervuren, Belgium;2. Ghent University, Department of Geology, Mineralogy and Petrology, Krijgslaan 281 S8, B-9000 Gent, Belgium;3. Scottish Universities, Environmental Research Centre, Isotope Geoscience Unit, Rankine Avenue, G75 OQF East Kilbride, United Kingdom |
| |
| Abstract: | Low-grade carbonate-rich manganese ore of sedimentary origin in the giant Kalahari Manganese Field, South Africa, is upgraded to high-grade todorokite–manganomelane manganese ore by supergene alteration below the unconformity at the base of the Cenozoic Kalahari Formation. Incremental laser-heating 40Ar/39Ar dating of samples from the supergene altered manganese ore suggest that chemical weathering processes below the Kalahari unconformity peaked at around 27.8 Ma, 10.1 Ma and 5.2 Ma ago. Older ages are dominant in the upper part of the weathering profile, while younger ages are characteristic of the deeper part of the profile. Younger ages partially overprint older ages in the upper part of the weathering profile and demonstrate the downward progression of the weathering front by as little as 10 cm per million years. The oldest age obtained in the weathering profile, namely 42 Ma, is considered a minimum estimate for the onset of the post African I cycle of weathering and erosion that followed the break up of Gondwanaland and formation of the Cretaceous to early Cenozoic African land surface. The youngest ages, recorded at around 5 Ma, in turn, correspond well to the Pliocene transition from humid to arid climatic conditions in Southern Africa. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
