Feasibility Study and Technical Report - Pretivm

Table 16.8Rock Mass PropertiesUnitUCS(MPa) GSI *Unit Weight **(kN/m 3 ) mi mb SErm(GPa)VOK FZ 89 60 26.3 12 1.110 0.0023 5.13VOK WRZ 50 63 28.6 17 1.879 0.0037 0.77VOK D1 116 72 27.2 17 3.211 0.0144 9.76VOK D2 95 70 27.1 19 3.186 0.0106 9.02VOK D3 73 85 27.3 26 10.647 0.103 14.37WZ FZ 77 57 26.3 12 0.928 0.0015 4.27WZ WRZ 37 62 28.6 17 1.771 0.0032 0.73WZ FR 116 85 27.3 21 8.599 0.103 16.77Notes:*GSI are calculated from median rock mass parameters for each unit, where GSI = RMR '76.**Unit weights are based on average results of specific gravity testing when possible.The Hoek-Brown failure criteria were estimated assuming a disturbance factor ('D') of 0.8 for allunits.The Hoek-Brown curves were derived using a sigma3 maximum for a tunnel depth of 650 m.16.5.3 BRUCEJACK FAULT ZONEThe Brucejack Fault lineament is currently the only known major structure that intersectsthe proposed mining footprint. It is a northerly striking anastomosing fault zone locatedalong the western margin of the study area and extends north to the Iskut River Fault. Inplaces the lineament appears to be several sub-vertical to moderately (greater than 60°)dipping fault strands braided together. The zone has normal faulting with variabledisplacement estimated at 500 to 800 m (ERSi 2010).At the time this report was prepared, Pretivm had not yet developed a structural geologymodel for the Project. BGC reviewed drillhole data and core photographs in relation tothe Brucejack Fault surface used in the PEA (Silver Standard 2010) to characterize theproperties of the Fault Zone and review its proximity to the proposed mine workings.BGC's work focused on identifying the orientation, thickness, and rock masscharacteristics of the Fault Zone. These interpretations were combined with the PEA faultsurface to develop an updated 3D Brucejack Fault Zone surface, which was provided toPretivm and the mine planning group to assist with ongoing project planning.The Brucejack Fault Zone is comprised of a core of highly fractured rock with a zone ofless fractured, fault-disturbed rock mass on either side. The width of the fault zonevaries with depth and along strike from approximately 5 to 40 m. It is considered to becontinuous along strike, and dips slightly to the east above the 1,325 m elevation, anddips slightly west below the 1,325 m elevation. For design purposes, the median RQD,Joint Condition, and point lead index Is50 value (ISRM 1985) are 62%, 16, and 3.5 MPa,respectively, compared to the ”excellent” median RQD value (91%) and median Is50value of 6.5 MPa in the surrounding undisturbed VOK D2 rock mass.Pretium Resources Inc. 16-28 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC