Primary & Secondary Crushing
Typical Grinding Circuit
Leach & CIP Circuit
Tailings & Dam Construction
After the formation of the Porcupine Joint Venture in 2002, ore has been fed to the Dome mill from the following main sources: Pamour Open Pit, Pamour Stockpile, the Dome underground mine and Hoyle Pond's Underground Mine. Ore is crushed in three stages to produce a product size of 80% passing ½". Primary and secondary crushing is achieved in a 400hp 42"x 65" gyratory and 400 hp 7' standard cone crusher, respectively. The latter feeds a 10' x 24' double deck screen in a closed circuit with a HP700 cone crusher. The screen undersize reports to two 4,000 tonne fine ore bins and the oversize is conveyed to a 75 tonne tertiary surge bin feeding the HP700 cone crusher. Due to limited fine ore bin capacity, an external fine ore stockpile and reclaim conveyor system provide for supplemental mill feed during extended shutdowns of the crushing plants for maintenance.
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Minus 1/2" material is fed to a grinding circuit that consists of two parallel grinding lines. Circuit A consists of a 10.5' diameter x 14' 700 hp rod mill and 13.5' x 20' 2200 hp ball mill while Circuit B consists of a 15' diameter x 20' 2200 hp rod mill and a 16' x 28.5' 4500 hp ball mill. Prior to 2005, Circuit B operated as a primary ball mill circuit. The rod mill was added in conjunction with the Pamour Pit expansion to handle the higher work index of the Pamour ore and to produce a finer grind at a total designed plant capacity of 11,000 metric tonnes per day. Gravity gold is recovered by the use of five Knelson CD-30 Concentrators fed from the cyclone underflow. In December 2002, a Consep CS6000 Acacia Reactor was commissioned to intensively leach the Knelson concentrate. The Acacia loaded solution has a dedicated electrowinning circuit. Gravity recovery accounts for up to 45% of the recovered gold, depending on ore type.
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GRINDING CIRCUIT A |
GRINDING CIRCUIT B |
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The cyclone overflows reports to a 155' thickener where the slurry density is increased to 55-60% solids. The thickener underflow feeds nine leach tanks in series, which provide about 32 hours residence time. The leach circuit was expanded during the Pamour Pit Expansion to include three new additional tanks to increase the leach residence time which was a requirement of the Pamour ore.
Lime is added to the mill discharge pump boxes, thickener feed well, as well as staged addition points in the leach circuit to maintain a pH of 11.5 during cyanide leaching. Cyanide is added to the head of the leach circuit. Staged oxygen addition maintains oxygen levels for optimum leach kinetics. After leaching, the slurry passes over a vibrating screen to remove any grit before being pumped to the CIP circuit where solution gold is absorbed by activated carbon contained in the CIP tanks. Loaded carbon is removed from the tanks and stripped. A fine carbon collection system is in place to collect any fine carbon generated during the transferring and sizing stages and is periodically shipped to a smelter for refining. The strip circuit, including acid wash and strip vessels, as well as the kiln were upgraded during the Pamour Pit Expansion to eliminate a prior bottleneck. The elution process transfers the gold from carbon into solution. The solution is passed through electrowinning cells where gold attaches itself to a cathode in the form of high-grade sludge. The cells are cleaned by power washing the sludge off the stainless mesh, and the sludge is filtered, dried and then refined in an induction furnace.
CIP tails passes over a vibrating screen to collect any carbon which may have leaked past the inter-stage screens. This carbon is collected and shipped to a smelter for refining. The final tails are sampled using an automated full stream sampler before being pumped to the tailing impoundment.
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The current No. 6 Tailing Management Area is located approximately 3 km to the south of the mill site and consists of a naturally occurring basin enclosed by topographic highs to the east and west of the facility and by construction of a series of dams within the topographic lows around the perimeter.
Construction of the No. 6 tailing facility began in 1983 and has been raised in stages over the past 24 years with engineered dams constructed using local fill materials. In 1997, an emergency spillway was constructed on the east side of the north dam to replace the old style decant structure.
Tailing slurry is pumped from the mill to the No. 6 Tailing Management Area via a 22 inch pipeline that branches into two 18 inch pipelines at the north dam to allow for the tailing material to be distributed around the perimeter of the facility to maintain beaches and a pond at the north end of the basin where the emergency spillway is located along with a mill water reclaim system.
Water reclaimed from the tailing impoundment represents approximately 60% of the total mill water used in the process. The balance comes from a freshwater source and some nominal volume from the underground. Excess water in the impoundment is treated prior to being discharged to the environment. The Effluent Treatment Plant (ETP) operates each year between May and October, and uses sulphur dioxide and air to destroy any residual cyanide and ferric sulphate and lime are used to precipitate heavy metals. A 105' diameter x 16'-9" reactor clarifier separates the precipitated sludge which is pumped back into the tailing impoundment where it is co-deposited with the tailing. The clear overflow is further treated with EDTA and carbon dioxide to control to regulatory limits.
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Dam Construction & Rehabilitation |
Dam Construction & Rehabilitation |
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Tailings Dam Construction |
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