TY - JOUR
T1 - Mineralogy and mineral paragenesis of the Palaeoproterozoic manganese ores of the Avontuur deposit of the Kalahari Manganese Field, South Africa
AU - Coetzee, L. L.
AU - Gutzmer, J.
AU - Smith, A. J.B.
AU - Beukes, N. J.
N1 - Publisher Copyright:
© 2024 Geological Society of South Africa. All rights reserved.
PY - 2024/3
Y1 - 2024/3
N2 - This study provides for the first time details of the mineralogy, petrography and mineral paragenetic relationships of manganese ores of the Avontuur deposit, a prominent northern outlier of the Kalahari Manganese Field in the Northern Cape Province of South Africa. Using a combination of light and electron microscopy and X-ray powder diffractometry on an extensive suite of exploration drill core samples, it is shown that the manganese ores comprise an exceptionally fine-grained assemblage of Mn2+-silicates (friedelite, tephroite, gageite), Mn2+/Mn3+-oxides (jacobsite, hausmannite) and Mn2+-carbonates (rhodochrosite, kutnahorite, Mn-dolomite and Mn-calcite). This mineral assemblage is a product of diagenesis and very low-grade regional metamorphism. Locally, this assemblage is overprinted by contact metamorphism or supergene alteration. Despite close geochemical and textural similarities, the manganese ores of the Avontuur deposit are surprisingly different in their mineralogy compared to the carbonate-and braunite-dominated mangano-lutites of the main Kalahari deposit. Distinctly higher concentrations of both SiO2 and Fe2O3 in the mangano-lutites of the Avontuur deposit as compared to the main Kalahari Deposit provide the reason for the markedly different mineralogy. Such marked differences in bulk chemistry are tentatively attributed to systematic lateral variations in the physicochemical conditions of mineral precipitation during the deposition of the Hotazel Formation.
AB - This study provides for the first time details of the mineralogy, petrography and mineral paragenetic relationships of manganese ores of the Avontuur deposit, a prominent northern outlier of the Kalahari Manganese Field in the Northern Cape Province of South Africa. Using a combination of light and electron microscopy and X-ray powder diffractometry on an extensive suite of exploration drill core samples, it is shown that the manganese ores comprise an exceptionally fine-grained assemblage of Mn2+-silicates (friedelite, tephroite, gageite), Mn2+/Mn3+-oxides (jacobsite, hausmannite) and Mn2+-carbonates (rhodochrosite, kutnahorite, Mn-dolomite and Mn-calcite). This mineral assemblage is a product of diagenesis and very low-grade regional metamorphism. Locally, this assemblage is overprinted by contact metamorphism or supergene alteration. Despite close geochemical and textural similarities, the manganese ores of the Avontuur deposit are surprisingly different in their mineralogy compared to the carbonate-and braunite-dominated mangano-lutites of the main Kalahari deposit. Distinctly higher concentrations of both SiO2 and Fe2O3 in the mangano-lutites of the Avontuur deposit as compared to the main Kalahari Deposit provide the reason for the markedly different mineralogy. Such marked differences in bulk chemistry are tentatively attributed to systematic lateral variations in the physicochemical conditions of mineral precipitation during the deposition of the Hotazel Formation.
UR - http://www.scopus.com/inward/record.url?scp=85192575686&partnerID=8YFLogxK
U2 - 10.25131/sajg.127.0016
DO - 10.25131/sajg.127.0016
M3 - Article
AN - SCOPUS:85192575686
SN - 1012-0750
VL - 127
SP - 31
EP - 54
JO - South African Journal of Geology
JF - South African Journal of Geology
IS - 1
ER -