Milling Process

The Rice Lake mill employs gravity concentration, flotation and carbon-in-leach circuits. Maximum capacity currently is 1,200 tons per day.

Since mills run at maximum efficiency when they are run at or near capacity, the mill is currently being run at full capacity part-time. The mill currently operates on a demand basis. Ore from the both the Rice Lake and Hinge mines is stockpiled until sufficient ore is available to allow the mill to run for a minimum of two weeks.

Mill Flow Sheet

Run-of-mine ore at minus 14 inches is fed at approximately 50 tons per hour from a coarse ore bin to a 25" x 42" jaw crusher and 4 1/4-foot short head cone crusher operating in closed circuit with a 5/8-inch screen. Screen undersize is fed from one of two fine ore bins to a 12.5' x 14', 1250 HP ball mill operating in closed circuit with a hydro cyclone classifier. The product size is 80% passing 150 microns.

2 centrifugal concentrators (Falcon and Knelson Super-Bowl) are fed with a portion of the cyclone underflow. The gravity rejects are returned to the grinding circuit while the gravity concentrate is passed over a diagonally driven shaking table for further gravity concentration. The table concentrate is taken directly to the smelting furnace; table tailings are pumped to the flotation circuit.

The grinding circuit product reports to the flotation circuit. From primary conditioners, the pulp is fed to a bank of 100 cu. ft. rougher flotation cells. Rougher concentrate, at 3 to 5 oz. Au per ton, is passed through a regrind ball mill, dewatered in a single tray thickener and pumped to the leach circuit. Rougher tailings undergo a second conditioning step and enter a bank of 100 cu. ft. scavenger flotation cells. Scavenger concentrate is returned to the primary grinding circuit with scavenger tailings pumped to the tailings management area.

Cyanide leaching of flotation concentrate takes place in two 12-foot diameter by 24-foot high mechanically agitated leach tanks. The pulp flows from the leach circuit to a six stage carbon-in-leach circuit and an Inco cyanide destruction system. Gold is removed in a pressure strip vessel where the solution is pumped up through the vessel and overflowed through an electro winning cell. The electro winning sludge and gravity concentrate are refined in an electric induction furnace to produce doré bars that are shipped out for final refining.

Tailings slurry from the flotation circuit and the carbon-in-leach circuit are combined, treated and pumped 2.5 km to the tailings management area.

Mill Recovery

Historic mill recovery has been 93% of the gold delivered to the mill. With an expanded gravity circuit, 96% recovery is possible.

Tailings Management Facility

The tailings management facility is located 2.5 km. north of the Rice Lake Mill and consists of a main tailings slurry containment basin and a final water polishing basin. Water meeting the Provincial and Federal discharge requirements, as set out in the Manitoba Conservation environmental licence, is released from the polishing basin to the natural environment.