Feasibility Study and Technical Report - Pretivm

Table 14.2Summary Statistics of Composited Data for Mineralized Domains – West ZoneStatistic Gold g/t Silver g/tSamples 33,089 33,089Minimum 0.00 0.25Maximum 1,657 37,636Mean 1.40 30.66Standard Deviation 17 219Coefficient of Variation 11.84 7.15Variance 275 48,020Skewness 66.98 62.6514.6.2 EXTREME VALUES – GOLD AND SILVERBetween 2 and 5% of the data within the mineralized high-grade domains appear to lie ina separate higher-grade population, which contains significant extreme grades. Thetreatment of these extreme grades is discussed in Section 14.7.14.7 CONSIDERATION OF GRADE OUTLIERS AND ESTIMATION METHODAssay populations from gold deposits are generally skewed and contain high-gradeoutliers that can introduce bias to mineral resource estimates.Both West Zone and VOK exhibit extremely skewed grade populations where the highgrades and the majority of the metal are located in less than 5% of the data, withindividual raw gold grades of up to around 41,500 g/t Au. As a result of this populationdistribution, standard estimation techniques have been found to significantly oversmooth the grades.Discussions with Pretivm and analysis of the data indicated that the mineralization couldbe split into a pervasive background mineralization and a separate high-grade butdiscreet mineralization style. In order to model this style of mineralization withoutsmearing grade, Snowden separated the lower-grade "background" population from thehigher-grade population and estimated them independently. For gold in the West Zoneand VOK, a threshold of 5 g/t Au was selected to separate the two populations, based onreview of the population statistics and graphs. The silver data was treated using thesame method with a threshold of 50 g/t Ag for VOK and 300 g/t Ag for the West Zone(Figure 14.4).The relatively low skewness and the presence of only few samples with extreme grades inthe low-grade domains allowed for the estimation of grades using ordinary kriging with atop cut. A top cut of 4 g/t Au and 100 g/t Ag was selected for VOK, based on the point ofdisintegration seen on the histogram and log probability plot. A top cut of 3 g/t Au and100 g/t Ag was selected for West Zone.Pretium Resources Inc. 14-7 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC