Feasibility Study and Technical Report - Pretivm

pump box will be pumped to the hydrocyclones for classification. Approximately 67% ofthe hydrocyclone underflow will return by gravity to the ball mill, while 33% of thehydrocyclone underflow will flow by gravity to the centrifugal concentration circuit. Thecirculating load to the ball mill will be approximately 300%. The particle size of thehydrocyclone overflow, or the product of the primary grind circuit, will be 80% passing74 µm. The pulp density of the hydrocyclone overflow slurry will be approximately 33%solids. Steel balls will be manually added into the mills on a batch basis as grindingmedia.The gravity concentration process will recover nugget gold particles from thehydrocyclone underflow. Tailings from gravity concentration will return to thehydrocyclone feed pump box by gravity. The gravity concentrate will be pumped to thegold room for further upgrading by tabling. Tailings from the tabling will be recycled backto the centrifugal gravity concentrator feed well, while the concentrate from the table willbe further upgraded by smelting. The gravity concentration circuit will have a securityenclosure and CCTV cameras; access will be restricted to authorized personnel only.Dilution water will be added to the grinding circuit as required. A particle size analyzerwill be installed to monitor and optimize the operation efficiency, in conjunction with anautomatic sampling system and the required instrumentation such as solid density,pressure, and flow rate meters.ROUGHER AND SCAVENGER FLOTATIONThe pulp from the primary grinding circuit will be subjected to conventional flotation torecover the free gold, silver, and their bearing minerals from the materials beingprocessed. The feed rate for the flotation circuit will be 122 t/h of ore. Flotationreagents will be added to the flotation circuits as defined through testing. The flotationreagents include PAX as collector and MIBC as frother. The mass recovery of the rougherconcentrate is approximately 20% of the flotation feed. The concentrates produced fromthe rougher flotation circuit will be sent to the regrind circuit and subsequently to thecleaner flotation circuit. The rougher flotation tailings will be further floated by scavengerflotation, along with the tailings from the first cleaner flotation circuit. The scavengerconcentrate will be returned to the preceding rougher flotation head. Rougher andscavenger flotation will be carried out at the natural pH level (without slurry pHadjustment). The rougher/scavenger flotation circuit will consist of:• four 100 m 3 rougher flotation tank cells• two 100 m 3 scavenger flotation tank cells.The tailings from the flotation circuit will be discharged to the tailings thickener.Depending on the mining operation requirement, the thickener underflow will be pumpedto the paste backfill plant for excavated stope backfilling underground and/or toBrucejack Lake for storage.Automatic sampling systems will be installed to collect the samples required for processoptimization and metallurgical accounting.Pretium Resources Inc. 17-8 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC