Paleoproterozoic, turbidite-hosted, gold deposits of the Ashanti gold belt (Ghana, West Africa): Comparative analysis of turbidite-hosted gold deposits and an updated genetic model

• Published in: Ore geology reviews Vol. 39; no. 1; pp. 91 - 100
• Main Author: Berge, John
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2011
• Subjects: Graphite–gold association; Interflow (chemical) sediments; Origin of mineralizing fluids and gold; Turbidite-hosted gold deposits; Origin of mineralizing fluids and gold; Interflow (chemical) sediments; Graphite–gold association; Turbidite-hosted gold deposits
• ISSN: 0169-1368; 1872-7360
• DOI: 10.1016/j.oregeorev.2010.12.001

The Paleoproterozoic gold deposits of the Ashanti gold belt, Ghana, occur mainly as auriferous quartz veins in graphitic shears proximal to contacts between deformed and metamorphosed turbidites and tholeiitic volcanics (alternately block-faulted Tarkwaian sediments). They are suggested in this article to belong to that class of gold deposits recognized as ‘turbidite-hosted’. Hence, evidence from previous investigations of turbidite-hosted and turbidite-associated gold deposits occurring in circumstances roughly similar to the Ashanti deposits are used, where relevant, to produce an updated genetic model for the latter. Given the relatively significant amounts of graphite associated with the major Ashanti deposits, the role of non-carbonate carbon is assessed in the light of conclusions reached by work on other turbidite-hosted and turbidite-associated gold belts. Conclusions as to the origins of mineralizing fluids and temporary repositories of gold (auriferous interflow sediments) reached by work on these other belts are also analysed. A concept of the tectonic development of the Ashanti belt-Kumasi basin area, introduced in this article, is deemed to be critical to the origin of the Ashanti gold deposits. It encompasses the role of non-carbonate carbon, turbidites, and the primary sources and secondary repositories of Au and As in the genesis of the major Ashanti gold deposits. It examines the significance of the intimate relationship between calc alkaline volcanism and the basin sediments, the occurrences of felsic metasandstones in transition-zone sediments, and TTG granitic material and fragments of chemical sediments in turbidites: all of which are incompatible with one or the other of existing concepts of tectonic development in the area. ► Development of a new tectonic concept crucial to an updated gold-deposit genetic model. ► Pre-orogenic non-carbonate carbon/orogenic gold-associated carbon relations clarified. ► Ashanti belt auriferous chemical sediments are placed in a global context. ► Conclusions drawn for the first time as to the primary origin of Ashanti belt gold. ► Likely significance of turbidites to a turbidite-hosted gold system explained.