In early 2018 Wassa transitioned into an underground-focused operation.
Mining is by underground with trackless access by decline (1:7 gradient), operated by GSWL personnel. The method is long hole open stoping (LHOS), mostly with transverse uphole stopes, in 25 m lifts, mined topdown, in primary/secondary sequence. Stable unsupported stope heights are up to 100 m and stopes are mined to full orebody width. The mine is divided into Panels, which reflect progressive stages of capital development. The Mineral Reserve includes Panels 1, 2 and 3, which lie between 150-650 m depth.
Panels 1 and 3
• Stope length is 25 m along strike with 6-10 m pillars between.
• Stope width is full width of the orebody which can be up to 35 m but is usually 15-25 m.
• Stopes are mined with uphole blastholes drilled from below. The stope lifts are extracted in a topdown sequence; each stope lift is extracted below the open stope void above. Up to four stope lifts are extracted to create a continuous excavation up to 100 m high.
• In Panels 1 and 3, the 100 m height limit usually enables full extraction of the orebody without the need for sill pillars. Where this is not the case, a sill pillar is left in the level between the sets of stopes.
• Mined voids are generally left open with some loose rock fill to dispose of waste or for opportunistic pillar recovery.
• Narrower ore zones (<15 m) are mined as longitudinal stopes with progressive placement ........
