Modern Mining June 2016

WEST AFRICA

modern facility – GSR constructed it in 2005 – incorporates a four-stage crushing circuit, grinding, gravity recovery, CIL circuits and a thickener. It requires only minor upgrades – in progress and soon to be completed – to serve the needs of the underground project. Average

ventilation raise and escape way close to the start of the decline. The main decline is 5,8 m high by 5,2 m wide and is being developed using standard trackless mechanised methods. The upper stopes will be mined using longi- tudinal longhole open stoping with waste rock fill. This will enable efficient early produc- tion before a cemented rock fill preparation and delivery system is installed. The open pit will eventually mine down to the top of these upper stopes, but only towards the end of the life of mine. In the deeper, wider areas of the deposit a transverse longhole open stoping method will be used. A primary-secondary mining sequence will be implemented with the primary stopes filled with cemented rock fill and the secondary stopes with waste rock fill. The overall stoping sequence will be bottom-up to reduce the inci- dence of sill pillar development. New surface infrastructure to support the underground mining will be constructed including electrical power supply from the grid with backup genset support and surface mechanical and electrical workshops. At steady state production, Wassa Under­ ground is expected to produce an average of approximately 2 000 tonnes per day across the life of mine. The underground ore will be treated in the existing processing plant, which is located just 500 m from the open pit. This relatively

The Wassa underground mine is accessed by a twin decline system. The portals of the declines are seen here.

Channel sampling under- ground at Wassa.

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June 2016  MODERN MINING  31