Feasibility Study and Technical Report - Pretivm

units is not exclusively based on lithology. Therefore, all units of the geological model areconsidered to be entirely PAG, except unit Office P1.KINETIC TESTINGKinetic tests are used to predict the long-term weathering characteristics of mine wasteunder accerlerated weathering conditions (simulated with humidity cells) and undersubaqueous conditions (simulated with custom column experiments).In total, 21 humidity cells (19 for waste rock and 2 for tailings solids) and 5 subaqueouscolumns (2 for waste rock and 3 for tailings) were constructed. The results from thekinetic tests indicate that, under optimal weathering conditions, some waste rockmaterial at the site has the potential to generate ARD within one year; however, the onsetto ARD for the majority of the waste rock will take tens of years before the available acidneutralization potential in the material is consumed. At lower pH values (e.g. a pH valueof less than 5) the mobility of most metals (copper, zinc, iron) should increase.Concentrations of most dissolved metals should remain low under a circumneutral pH.The weathering of waste stored beneath a water cap (subaqueous columns) is expectedto be significantly less due to the overlying water column. Waste material depositedsubaqueously is generally characterized by a neutral pH and low dissolved metalconcentrations, except dissolved arsenic. The tailings solids are not expected togenerate ARD.SUMMARYThe preceding discussion of the ARD/ML assessment indicates that site waste rock isprimarily PAG material and, although ARD and ML processes can be significant underoptimal weathering conditions, these processes are reduced in a subaqueousenvironment. The selected management strategies for the Project mine waste shouldprevent the potential for ARD, thereby reducing the potential for ML at the site. Thisincludes the subaqueous disposal of waste rock in Brucejack Lake and storage of wasterock material in the underground workings. Although ML can be minimized byappropriate management strategies, its impact on the downstream receivingenvironment has been evaluated by water quality predictions outlined in Section 20.1.5.20.1.5 WATER QUALITYBGC developed a site-specific water quality model for the Project using GoldSimsimulation software, an environmental and engineering statistical program. The waterquality model was used to predict the water quality of Brucejack Lake and thedownstream receiving environment during mine operations. The predictions werecalibrated and validated against baseline data and compared to regulation standardsand other criteria developed for similar mine discharge waters.The predictions represent the probable observed water qualities during miningoperations and were calculated based on information provided to BGC at the time ofmodelling and reporting. Where possible, BGC (2013) used conservative assumptions toestimate dissolved parameters in an attempt to account for data gaps. However, as withPretium Resources Inc. 20-11 1291990200-REP-R0012-02.1Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC