Feasibility Study and Technical Report - Pretivm

• cleaner flotation processes.A gravity concentration circuit will also be incorporated in the bulk concentrate regrindingcircuit. The final flotation concentrate will be dewatered, bagged, and trucked to thetransload facility in Terrace, BC. It will be loaded in bulk form into rail cars for shipping toa smelter located in eastern Canada. The gravity concentrate will be refined in the goldroom on site to produce gold-silver doré.A portion of the flotation tailings will be used to make paste for backfilling the excavatedstopes in the underground mine, and the balance will be stored in Brucejack Lake. Thewater from the thickener overflows will be recycled as process make-up water. Treatedwater from the water treatment plant will be used for mill cooling, gland seal service,reagent preparation, and make-up water.17.1.3 FLOWSHEET DEVELOPMENTThe process flowsheet was developed based on test work conducted mainly from 2009to 2013, as well as engineering experience. The comminution circuit design was basedon the topography of the proposed plant site and operability of the system. The sizeselection of the grinding mills was based on the amenability of the ore to grinding, asdetermined through test programs performed by different laboratories. Grindability testswere performed to determine the following hardness parameters:• BWi• RWi• CWi• Ai• SAG mill comminution breakage.The gravity circuit was selected based on the laboratory gravity concentration tests andGRG test results and related simulations.Flotation cell sizing was based on optimum flotation times, which were determined bytest work and using scale-up factors from similar operations.Various test programs evaluated the cyanidation process to extract the gold and silverfrom the test head samples and flotation concentrates. Although the mineralizationresponds reasonably well to the process, a few of the samples showed poor cyanidationresponses, which may be a result of the presence of preg-robbing constituents (graphite),potential refractory components (arsenopyrite), and slow leaching kinetics from electrumor other silver bearing minerals. However, the cyanidation process has not been used forthis study, including direct cyanide leach and carbon-in-leach procedures. Furtherstudies are required to evaluate the feasibility of the cyanidation process to recover thegold and silver from the flotation concentrate, including further test work to more fullyassess the metallurgical response of the mineralization to cyanidation.Pretium Resources Inc. 17-2 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC