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Yamfo-Sefwi

Ghana

Main commodities: Au
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The Yamfo-Sefwi project is located on the north-west margin of the 2.2 to 2.1 Ga Birimian Yamfo-Sefwi belt of volcanics, dominated by tholeiitic meta-volcanics and meta-sediments, near the sheared contact with the adjacent Sunyani Basin sediments. The latter are mainly volcaniclastic shales, greywackes and siltstones. Eburnian co-magmatic granitoids (the Dixcove Suite) have intruded the volcanics, notably along the contact with the Sunyani Basin sediments. The gold mineralisation has been emplaced close to the hydrothermally altered brittle-ductile shear zones at or near the volcanics-sediment contact. Three deformations are in evidence, namely an early S1 foliation, related to the shears that form many of the lithological contacts in the region; a regional F2 folding and shearing reworking earlier D1. The mineralisation at Yamfo is hosted by shearing of this phase. The third phase is a late brittle episode associated with hydraulic brecciation and minor gold. In the main Centenary Zone there are two mineralised NE trending and SE dipping shears that are mineralised. Gold is also discontinuously developed between the shears. The gold is generally hosted by sheared, altered and brecciated greywacke/siltstone in which the main alteration products are quartz-carbonate and feldspar-chlorite-pyrite. It is usually fine grained, <25 µm, and is associated preferentially with carbonate and quartz-carbonate veinlets and stockworks, together with fine grained pyrite . The mineralised shears average 20 m in thickness but may be up to 70 m wide. Narrow high grade shoots of limited extent are indicated within the main ore zones. These have grades of up to 14 g/t over narrow widths. To the south in the Kenyase Zone, the sediment-volcanic contact is occupied by a dioritic intrusive of the Dixcove Suit. Gold is hosted by the sheared contact between the intrusive and sediments and a mylonite, along with gold bearing quartz vein stockworks in the hangingwall diorite.

Within the Rank area, some 25 km to the SSE, the main contact mineralisation is less continuous, while the hangingwall stockworks are potentially more significant. A second mineralised shear, to the east of and parallel to the main zone is found within a granodiorite, with gold being associated with strong hydrothermal alteration which dip at 70 degrees to the east. Intersections have been indicated over a two km length, ranging from 10 to 130 m (average 30 m) wide, with 2 to 3.9 g/t Au.

The project is currently the property of Normandy Ghana Gold, a wholly owned subsidiary of Normandy Mining Ltd. In mid 1999, the resource estimated for he project area was 64.56 mt @ 3 g/t Au for 190 t (6.16 Moz) of gold using a 0.5 g/t Au cut-off. The project is currently in feasibility, but is as yet un-developed.

The most recent source geological information used to prepare this summary was dated: 2001.    
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.


Yamfo-Sefwi

  References & Additional Information
   Selected References:
Anonymous  1998 - Normandy Mining Limited: in   Extracts from the Normandy Mining Limited 1997 Annual Report    pp 12-14, 17, 26-28.
Anonymous  1999 - Yamfo-Sefwi: in    Register of African Gold 1999/2000    p108
Bird, D., Sylvain, J.-P.,  1999 - Discovery Case History for Yamfo-Sefwi Gold Mineralisation (Ghana): in   New Generation Gold Mines 99, Case Histories of Discovery, Perth, November 1999,  Australian Mineral Foundation, Adelaide,   Conference Proceedings, pp. 151-161.
Takyi-Kyeremeh, K., Wemegah, D.D., Preko, K. and Menyeh, A.,  2019 - Integrated geophysical study of the Subika Gold Deposit in the Sefwi Belt, Ghana: in    Cogent Geoscience,   v.5, 16p., https://doi.org/10.1080/23312041.2019.1585406


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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