Mill processing unit operations include a gyratory crusher and coarse ore stockpile with feeders, a grinding circuit, a gravity recovery circuit, a leaching circuit, a carbon-in-leach (CIL) circuit, a carbon stripping circuit and a refinery as shown in the mill flow sheet.
Hard and transition rock is reduced in size through a primary crusher then stacked over two apron feeders for delivery to the mill grinding. Soft rock is fed by excavators through two apron feeders in parallel to the primary crusher, reporting to the grinding circuit on the same conveyor as the hard and transition rock. Ore is ground to 80% -75 microns to liberate the gold for leaching (pulp). Within the grinding circuit, a portion of the cyclone underflow reports to the gravity circuit where screens, cones and a Knelson concentrator are used to separate gravity recoverable gold (GRG). Gravity gold is then further concentrated on a Deister table, dried and refined in the induction furnace at 1,250oC.
The pulp from the cyclone overflow is thickened and then fed to leach tanks where 70% of the feed gold is leached to be recovered by activated carbon in the CIL process. Pulp leaving the CIL circuit reports to the tailing pond with trace levels of gold. The loaded carbon from the CIL process is recovered by screening and sent to the stripping circuit where gold is stripped from carbon and put into solution. The solution reports to an electro-winning process where the gold is plated onto cathodes by electrolysis, the gold sludge is washed from the cathodes, dried and finally refined in the induction furnace.
Depending on the gold mineralogy, the rock type, the ore grade, and the processing rate, recovery at Rosebel is typically in the low to mid 90% range.