Feasibility Study and Technical Report - Pretivm

16.9.11 PORTAL STRUCTUREA portal structure (see Figure 16.30) will be constructed at the access to theunderground decline tunnels. The structure will span the area between both declinetunnels and will house the mine air heaters and ventilation fans, the conveyor drivemotor and mechanism, and an electrical substation. The main decline conveyor will exitup from the tunnel and pass through the portal structure on its way to the mill. Accessinto the portal structure will be via one of four overhead doors.The portal structure was designed to be built up against the mill site high wall and will berequired to resist roof snow loads with pressures up to 400 kg/m 3 . The roof wasdesigned with 6:12 and 7:12 pitches to better shed snow. A ridgeline roof split will alsohelp initiate snow movement from the roof.A monorail located in the ceiling of the portal structure will allow for removal of the mineair fan motor and components.Figure 16.30Portal Structure Schematic16.9.12 HEATING SYSTEM AND PROPANE STORAGEThe energy to run mine air heaters is typically derived from natural gas, propane,electricity, and diesel. With exception of natural gas, the other energy types willpotentially be available at the Project site. As part of the feasibility study, AMC examinedthe merits of alternative types of energy supply to run the heaters. Based on the resultsof the analysis and the site availability of electrical power, a hybrid electrical/propanepowered mine heating system was determined as the best outcome for the Project.CLIMATIC DATAClimactic data from site was analyzed to quantify the amount of annual power andpropane required for mine air heating. AMC was provided with a climatic data setcollected from a weather station located adjacent to Brucejack Lake, at an elevation of1,400 m.Pretium Resources Inc. 16-67 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC