SGA Lecture – Prof. Dr. Reiner Klemd

SGA STUDENT CHAPTER ERLANGEN
- Lecture Series - Mineral Deposits -

The SGA Student Chapter Erlangen is delighted to welcome

Prof. Dr. Reiner Klemd (FAU Erlangen-Nürnberg)

who will present a lecture entitled:

“Geology and fluid characteristics of orogenic Au-deposits in Ghana: revisited”.

 
Monday, July 6th 2026 | 17:00 -18:00
Übungsraum Geologie (01.124) - GeoZentrum Nordbayern, Schlossgarten 5, Erlangen.

As always, we provide a Zoom Link for those who cannot join the talk in person: https://fau.zoom-x.de/j/66052333207.

Abstract:

The Paleoproterozoic Birimian Supergroup in the southern part of the West African craton constitutes one of the world’s largest gold provinces with an endowment of more than 10,000 metric tons (t). Therefore, West Africa hosts the largest Paleoproterozoic gold-producing region worldwide. Ghana, the major gold-producer in Africa, produces between 150 and 170 metric tonnes per year. The gold mainly occurs in structurally-controlled lode-gold deposits, which commonly occur in the transition zones between the volcanic belts and the basin sediments of the Birimian Supergroup. In Ghana and eastern Ivory Coast, the 2.2 to 2.0 Ga Birimian terranes consist of parallel and evenly spaced, NNE-trending volcanic belts separated by sedimentary basins, while in Burkina Faso and central Ivory Coast continuity, spacing, and parallelism of Birimian volcanic belts are less clearly developed, and terrains between them are made up largely of gneisses and granitoids. The major gold deposits are lode-gold deposits that are interpreted as ‘orogenic gold deposits‘, although paleoplacer and placer deposits also occur in the volcanic belts. The volcanic belts are dominated by tholeiitic volcanic rocks, with isoclinally folded volcaniclastic and chemical sediments filling adjacent sedimentary subbasins, which are intruded by extensive, late kinematic granitoid plutons. Locally, the tholeiitic basalts are associated with calc-alkaline andesites, dacites,and rhyolites. Regional metamorphism ranging from low to high amphibolite facies conditions was dated at about 2.1 Ga. The main deformation in Ghana occurred between 2.1 and 2.09 Ga simultaneously with the regional metamorphism.

The Paleoproterozoic of West Africa appears to be best defined as filling an ocean basin developed in a rifted Archean cratonic block, while the Eburnean orogeny is thought to have been initiated at ca. 2.13 Ga. The gold mineralization mainly formed during compressional tectonics that occurred between 2.13 and 2.1 Ga, including crustal thickening associated with thrust fault systems. The Tarkwaian sediments, which host numerous paleoplacer gold deposits, were deposited between 2.11 and 2.09 Ga in long, narrow intramontane grabens, which formed as the result of rifting, preferentially, in the central portions of all five Birimian volcanic belts in Ghana.

Paleoproterozoic gold-bearing brittle-ductile quartz veins, stockworks, breccias, and disseminated orebodies occur next to major fault systems, such as areas with second-order faults, regional fold systems, and rheological differences. The quartz of the gold-bearing vein deposits and the palaeoplacers in Ghana, Ivory Coast, and Burkina Faso, predominantly contains CO₂-N₂-rich (70-80 mol%) fluid inclusions often displaying a very unusual high-density (up to 1.15 g/cm ), which is in contrast to most other orogenic gold deposits in the world. Consequently, a number of studies make the assumption that this unusual fluid composition represents an anomalous fluid property and, consequently, the gold source region. In contrast, the present study provides evidence that the (high-density) CO₂-rich fluids are a result of grain boundary migration recrystallisation during the exhumation evolution. Ductile deformation induced selective extraction of H₂O-NaCl via pipe diffusion during decreasing temperatures. The CO₂-density increase is thought to be due to isobaric cooling during the exhumation of the host rock in the orogenic and placer deposits. Thus, fluid inclusion evidence from Birimian-hosted orogenic gold deposits may very well imply that the mineralizing fluid is compatible with H₂O-CO₂-salt-rich fluids as observed in other orogenic gold deposits elsewhere in the world.