Feasibility Study and Technical Report - Pretivm

• Further test work to identify the benefit of light classification for paste backfill bycycloning is recommended; with a view to remove clays and production of acoarser paste fill PSD to improve the filtering process and give a higher-qualitypaste fill. The estimated cost for this work is $10,000.• Further test work using locally available binders, preferably slag based cement,should be undertaken to determine the appropriate cement dosages. Local orimported cement suppliers that can supply high slag based cement as per theannual demand should be contacted. The estimated cost for this work is$35,000.26.4.1 GEOTECHNICALBGC has identified the following key risks and opportunities with regards to the rockmechanics assessment:• At the time of reporting, a structural geology model for the Project area had notbeen completely developed. BGC generated a structural model based onhistoric maps, a limited review of historic drillhole data, and a structural geologicreport generated for an adjacent property. BGC assumed that the BrucejackFault Zone is the only major structure that intercepts the proposed miningfootprint. The geotechnical reliability of the underground designs could beimproved if further geological modelling work could define the location,orientation, and geotechnical characteristics of major geologic structures.• The lack of a West Zone geology model and lack of in situ stress data limits thepotential of the MAP3D model. Additional refinement of inputs, and calibrationto underground observations, are required before quantitative characterizationof the rock mass response is possible.• The stope dimensions provided in this report assume stope-scale geologicstructures are present sub-parallel to the stope walls. As additional explorationdrillholes are drilled, a structural model is developed for the Property, andparticularly as additional underground developments are exposed, the structuraldatabase and subsequent structural domains should be reviewed to refine theassumptions inherent in the stope span recommendations. Tighter definition ofstructural domains may allow less-conservative assumptions with respect tostope-scale structure, with a subsequent increase in recommended maximumstope spans.BGC makes the following recommendations for additional rock mechanics assessmentwork:• Six to eight geotechnical drillholes should be completed, with the associateddata used to confirm the geological interpretations and the geotechnicalparameters of the rock mass for final design. The program should includepacker testing above, below and across/within faults or geologic contacts. Keyareas include the Brucejack Fault Zone, the proposed underground crusherexcavation, exhaust raise developments, and the West Zone ramp. LaboratoryPretium Resources Inc. 26-3 1291990200-REP-R0012-02.1Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC