Feasibility Study and Technical Report - Pretivm

CONCENTRATE REGRINDINGThe flotation concentrate from the rougher flotation circuit will be forwarded to theregrinding circuit. The major equipment in the circuit includes:• one 2,440 mm diameter by 4,270 mm long (EGL) ball mill, driven by a 265 kWmotor• one centrifugal gravity concentrator• two cyclone feed pumps• four 250 mm hydrocyclones.The rougher flotation concentrate will be reground to 80% passing 35 to 40 µm in theball mill, in closed circuit with hydrocyclones and one centrifugal gravity concentrator.The discharge from the ball mill and the tailings from the gravity concentrator will reportto the hydrocyclone feed pump box, from where the slurry will be pumped to thehydrocyclones for classification. Approximately 50% of the hydrocyclone underflow willreturn by gravity flow to the ball mill, while the balance will report by gravity flow to thecentrifugal gravity concentration circuit. The ball mill circulating load will beapproximately 150%. The pulp density of the hydrocyclone overflow slurry will beapproximately 22% solids. Steel balls will be manually added into the mills on a batchbasis as grinding media.The gravity concentrator will recover metallic gold grains from the hydrocycloneunderflow. The tailings from the gravity concentration will return to the hydrocyclone feedpump box by gravity flow. The gravity concentrate will be sent to the gold room for furtherupgrading by tabling. Similar to the gravity concentration in the primary grinding circuit,this gravity concentration area will also be in a secure area and monitored by CCTVcameras.The particle size of the hydrocyclone overflow will be automatically sampled andmonitored. An instrumentation system, similar to that used for the primary grindingcircuit, will be installed for the regrinding circuit to optimize the grinding efficiency andcontrol the regrind particle size.CLEANER FLOTATIONThe reground concentrates will undergo three stages of cleaning by flotation in order toproduce a final gold-silver bearing concentrate.The major equipment in the cleaner flotation circuit includes:• four 30 m 3 tank cells for the first cleaner flotation• two 30 m 3 tank cells for the first cleaner/scavenger flotation• one 30 m 3 tank cell for the second cleaner flotation• one 30 m 3 tank cells for the third cleaner flotation.Pretium Resources Inc. 17-9 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC