Ashanti (Obuasi)
Ashanti belt (Birimian, southwest of the country), Ghana
Orogenic goldAu (As)
- Type
- Mesothermal, shear-hosted orogenic gold
The historic Obuasi mine, worked by the Ashanti since antiquity and industrially since 1897. Mineralisation, dated at 2.1 Ga, is hosted in Birimian (Palaeoproterozoic) metasedimentary schists along NNE-trending shear zones. The belt has produced about 1,500 tonnes of gold, in several forms: quartz veins, disseminated arsenopyrite-pyrite sulfides and Tarkwaian palaeoplacers.
δ34S in ‰ (per mil) Values of the same system
Standard : V-CDT
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| −20.9 / 7.3 ‰ | syn-sedimentary to diagenetic pyrite (Birimian host schists) Median of about -10 ‰. A very wide, negative range typical of bacterial sulfate reduction in an open marine setting. This host-rock signature carries into the ore; Oberthür et al. regard it as the preferred sulfur source for the gold mineralisation. | Oberthur et al. 1996, Gold mineralization in the Ashanti Belt of Ghana, Economic Geology … |
δ18O in ‰ (per mil) Values of the same system
Standard : V-SMOW
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 12.9 / 22.2 ‰ | hydrothermal vein carbonates Carbonates and auriferous quartz precipitated in oxygen isotope equilibrium, indicating fluid-dominated conditions during mineralisation. A fluid of metamorphic or magmatic origin. | Oberthur et al. 1996, Economic Geology 91:289-301 | ||
| 12.8 / 15.6 ‰ | auriferous vein quartz Quartz coeval with the carbonates, whose isotopic equilibrium is confirmed by quartz-carbonate Δ18O. | Oberthur et al. 1996, Economic Geology 91:289-301 |
δD in ‰ (per mil) Values of the same system
Standard : V-SMOW
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| −53 / −37 ‰ | fluid inclusions in auriferous quartz δD of waters extracted from fluid inclusions. Combined with the δ18O calculated for the fluid at equilibrium, it points to a metamorphic or magmatic origin of the gold-bearing fluid and rules out a significant meteoric contribution. | Oberthur et al. 1996, Economic Geology 91:289-301 |
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- Gounkoto Mali
- Loulo (district de Gara-Yalea) Mali
- Massawa Senegal
- Muruntau Uzbekistan
- Kalgoorlie (Golden Mile) Australia
- Victorian Goldfields Australia
Cite this page
IsoFind Atlas (2026). Ashanti (Obuasi), isotope signatures. https://www.isofind.tech/isotopes/en/deposits/ashanti-obuasi/ (accessed 2026-10-06).
@misc{isofind2026ashantiobuasiisotopesignature,
title = {Ashanti (Obuasi), isotope signatures},
author = {{IsoFind Atlas}},
year = {2026},
url = {https://www.isofind.tech/isotopes/en/deposits/ashanti-obuasi/},
note = {Accessed 2026-10-06}
}Updated : 2026-10-06