Chirano - Akoti, Tano, Suraw, Paboase, Obra, Sariehu, Mamnao


Main commodities: Au
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The 9 km long Chirano lode horizon, and related shear zones on the south-east margin of the Sefwi-Bibiani belt, host a series of gold deposits within the Birimian Supergroup rocks of southwest Ghana.

The mineralisation of economic significance at Chirano is predominantly hosted by albite- and carbonate-altered tonalite intrusives (as distinct from the Birimian sedimentary rocks and graphitic shear zones in mafic volcanics of the main deposits in Ghana), while weaker alterered zones containing < 1 ppm gold grades extend into adjacent Birimian mafic igneous rocks and Tarkwaian Group sediments. Pink albite alteration (albite-quartz-pyrite-hematite-rutile leucoxene-chalcopyrite gold) and later pale carbonate alteration (ankerite-sericite-quartz-pyrite-hematite-gold-Ag-Au-telluride) are characteristic of the gold deposits at and surrounding Chirano.

The mineralisation of the Chirano district was formed during a relatively late episode of small scale displacement, brittle cataclasis along the Chirano lode horizon following reverse ductile shearing associated with regional-scale shortening. This structural setting and its timing has similarities to that observed at the larger Ashanti and Bogoso deposits on the opposite side of the Kumasi basin, reflecting the structural history of the Eburnean 2 orogeny.

The following lists the main deposits in the Chirano District:

Akwaaba - 0.560 Mt @ 2.7 g/t Au
Suraw - 1.180 Mt @ 2.4 g/t Au
Akoti - South 0.830 Mt @ 1.5 g/t Au
Akoti - North 1.290 Mt @ 3.3 g/t Au
Akoti - Extended 1.030 Mt @ 3.2 g/t Au
Paboase - 4.810 Mt @ 1.9 g/t Au
Tano - 3.180 Mt @ 2.9 g/t Au
Obra South 0.670 Mt @ 2.0 g/t Au
Obra - 10.910 Mt @ 1.8 g/t Au
Sariehu - 3.490 Mt @ 1.8 g/t Au
Mamnao South - 0.670 Mt @ 2.5 g/t Au
Mamnao Central - 1.500 Mt @ 1.8 g/t Au
Mamnao North - 0.280 Mt @ 1.5 g/t Au
Total 30.400 Mt @ 2.1 g/t Au for 63.8 Tonnes (2.05 Moz) of gold.

For details of the geological setting and mineralisation see the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2004.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Allibone A, Hayden P, Cameron G, Duku F,  2004 - Paleoproterozoic Gold Deposits Hosted by Albite- and Carbonate-Altered Tonalite in the Chirano District, Ghana, West Africa: in    Econ. Geol.   v99 pp 479-497

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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