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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.
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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