Version 1
: Received: 26 August 2024 / Approved: 27 August 2024 / Online: 28 August 2024 (10:41:25 CEST)
How to cite:
Adomako-Ansah, K.; Hammond, N. Q.; Morishita, Y.; Ishiyama, D. Evolution of Auriferous Fluids in the Kraaipan-Amalia Greenstone Belts: Evidence from Mineralogical and Isotopic Constraints. Preprints2024, 2024082025. https://doi.org/10.20944/preprints202408.2025.v1
Adomako-Ansah, K.; Hammond, N. Q.; Morishita, Y.; Ishiyama, D. Evolution of Auriferous Fluids in the Kraaipan-Amalia Greenstone Belts: Evidence from Mineralogical and Isotopic Constraints. Preprints 2024, 2024082025. https://doi.org/10.20944/preprints202408.2025.v1
Adomako-Ansah, K.; Hammond, N. Q.; Morishita, Y.; Ishiyama, D. Evolution of Auriferous Fluids in the Kraaipan-Amalia Greenstone Belts: Evidence from Mineralogical and Isotopic Constraints. Preprints2024, 2024082025. https://doi.org/10.20944/preprints202408.2025.v1
APA Style
Adomako-Ansah, K., Hammond, N. Q., Morishita, Y., & Ishiyama, D. (2024). Evolution of Auriferous Fluids in the Kraaipan-Amalia Greenstone Belts: Evidence from Mineralogical and Isotopic Constraints. Preprints. https://doi.org/10.20944/preprints202408.2025.v1
Chicago/Turabian Style
Adomako-Ansah, K., Yuichi Morishita and Daizo Ishiyama. 2024 "Evolution of Auriferous Fluids in the Kraaipan-Amalia Greenstone Belts: Evidence from Mineralogical and Isotopic Constraints" Preprints. https://doi.org/10.20944/preprints202408.2025.v1
Abstract
The Kraaipan and Amalia greenstone belts in South Africa occurs in the western part of the Kaapvaal Craton. The two belts stretch discontinuously in an approximately north-south orientation over a distance of about 250 km from southern Botswana in the north to the Vaal River near Christiana in the south and are separated by a distance of about 90 km. Gold mineralization is hosted in banded iron-formation at both the Kalahari Goldridge deposit (Kalgold) in the Kraaipan greenstone belt in the north, and the Amalia deposit in the Amalia greenstone belt in the south, with the mineralization associated with quartz-carbonate veins. The footwall of these deposits is generally composed of mafic volcanic schist and hanging wall consisting of graywackes, schist and shale units.
The Kalgold and Amalia gold deposits show some variation in the redox condition of the mineralizing system, mineralization temperatures and fluid chemistry. The ore mineral assemblage is characterized by magnetite-pyrrhotite-pyrite at Kalgold, which is indicative of reducing conditions, and magnetite-hematite-pyrite assemblage at Amalia that suggest a relatively oxidizing environment. Average mineralizing temperatures determined from chlorite geothermometry were relatively higher at the Kalahari Goldridge deposit ranging from 350 to 400oC compared to 335 to 370oC (mean, 352± 18, n = 113) at Amalia. The composition of the fluids derived from fluid inclusions are indicative of low salinity H2O-CH4-CO2-rich fluids at Kalgold against relatively H2O-CO2-rich fluids at Amalia.
Evidence from strontium-carbon-oxygen isotopic ratios from carbonates suggests differences in redox conditions in the deposits could be attributed to different flow pathways by the evolving fluid from a common source (with minimum 87Sr/86Sr=0.70354) to the sites of gold deposition; with significant ore fluid interaction with thick sequence of carbonaceous meta-pelitic rock units at the Kalahari Goldridge deposit, that is absent in the Amalia deposit.
Environmental and Earth Sciences, Geophysics and Geology
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