Feasibility Study and Technical Report - Pretivm

FULL-WIDTH UNDERCUTSThe Project mine planners proposed full-width undercutting of select stopes. Ground supportrecommendations are provided in Table 16.10. Primary stopes should be tight-filled as bestas possible.MINING THROUGH THE BRUCEJACK FAULTThe feasibility study mine plan has development (stope access drifts) sub-parallel to theBrucejack Fault Zone. At the next level of study, it is recommended that developments near orwithin the fault zone be aligned perpendicular to the fault trend to minimize the exposure offault-disturbed rock.All developments through the Brucejack Fault Zone will require support with fully grouted #7Dywidag bolts on a 1.5 m square pattern. Full coverage (sill to sill) of welded wire mesh and75 mm of fibre-reinforced shotcrete is also recommended.Stopes should be excavated in isolation and backfilled prior to any other production openingswithin the fault zone. The rock mass within the fault zone is not competent enough to formadequate rib or sill pillar strength between stopes. In each case, stopes should beconstrained to either the host or fault disturbed rock. Excavations bridging the boundary willhave unplanned dilution along the contact.The preliminary recommendation for maximum supported back hydraulic radii is 2.5 (10 m by10 m), and maximum unsupported hanging wall hydraulic radii is 3.75 (10 m by 30 m), forstopes within the fault zone. Cable bolt support consisting of 6 m single or double strandbulbed cable bolts on a 2.5 m square spacing in the back is recommended.SURFACE RAISE LOCATIONSThe finalized raise locations should avoid fault-disturbed rock, and minimize intersection ofweathered rock. The recommended pillar thickness between a raise and nearby developmentor production openings, including the decline access ramp, is 10 m.UNDERGROUND CRUSHER AND OTHER MINE INFRASTRUCTUREThe proposed crusher excavation will require upper level access for trucks and lower levelaccess for conveyor egress. The proposed excavation will consist of an upper truck dump androck breaker level, which connects via a bin and hopper system to the lower level crusherstation.A localized set of data was reviewed to estimate the geotechnical properties of the rock massat the proposed crusher location. The rock mass is entirely within the VOK D2 geotechnicaldomain. The 25 th percentile values were used for design.The excavation was designed for a factor of safety of 2.0, as the excavation must remainoperable for the life of the mine, and opportunities for rehabilitation will be limited once themine is in production. Two levels of support are recommended:• Primary support consisting of galvanized, resin-grouted rebar (or an equivalent) andwelded wire mesh (or fibre-reinforced shotcrete). The purpose of these elements isPretium Resources Inc. 16-32 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC