APPENDIX 3.0-E Feasibility Geotechnical Pit Slope Evaluation Kitsault Project British Columbia, Canada

Transcription

1 KITSAULT MINE PROJECT ENVIRONMENTAL ASSESSMENT APPENDICES APPENDIX 3.0-E Feasibility Geotechnical Pit Slope Evaluation Kitsault Project British Columbia, Canada VE51988 Appendices

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3 A V A N T I K I T S A U L T M I N E L T D KITSAULT MOLYBDENUM PROJECT FEASIBILITY STUDY REPORT C.1 F E A S I B I L I T Y GEOT E C H N I C A L PIT S L O P E E VA L U AT I O N SRK NOV 20 Project No APPENDIX C 1 January 2011

4 Feasibility Geotechnical Pit Slope Evaluation Kitsault Project British Columbia, Canada Report Prepared for Avanti Mining Inc. Report Prepared by November 20

5 Feasibility Geotechnical Pit Slope Evaluation Kitsault Project British Columbia, Canada Avanti Mining Inc DTC Parkway Suite 405 Greenwood Village, CO SRK Consulting (U.S.), Inc. Suite 3000, 7175 West Jefferson Avenue Denver, Colorado, USA Tel: Fax: Web site: SRK Project Number 2CA November 20 Author Michael Levy, P.E., P.G.

6 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page i Table of Contents 1 Introduction and Background Program Objectives and Work Program Program Objectives Work Program Geologic Setting Local Geology Major Geologic Structures Field Data Collection Geotechnical Core Logging Geotechnical Logging Procedures Core Drilling Method Discontinuity Orientation Point Load Testing Geotechnical Observations of Existing Pit Packer Testing Laboratory Testing Unconfined Compressive Strength and Elastic Properties Triaxial Compressive Strength Testing Direct Shear Testing Direct Tensile Strength Testing Unit Weight Measurements Geotechnical Model Data Analysis Intact Rock Strength Discontinuity Frequency Discontinuity Shear Strength Discontinuity Orientation Rock Mass Classification Geotechnical Domains Hornfels Domain Intrusives Domain Rock Mass Shear Strength Groundwater Design Sectors Interramp/Overall Slope Stability Modeling Model Methodology Results of Interramp/Overall Stability Analysis Bench Design Description of Models Used Methodology Likelihood of Occurrence Likelihood of Exceeding Shear Resistance Likelihood of Kinematic Admissibility MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

7 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page ii 8.3 Results Pit Slope Design Recommendations Assessment of Future Geotechnical Work References MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

8 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page iii List of Tables Table 1: Drillholes Oriented and Logged for Geotechnical Data... 7 Table 2: Summary of Discontinuity Orientation... 8 Table 3: Uniaxial Compressive Strength Testing Table 4: Triaxial Compressive Strength Testing Table 5: Summary of Residual Shear Strengths Table 6: Direct Tensile Strength Testing Table 7: Discontinuity Sets Delineated for Analysis Table 8: In-situ Rock Mass Rating (IRMR) Distributions Table 9: Secondary Hoek-Brown Parameters Stochastic Input Table : Results of Overall Slope Stability Modeling Table 11: Summary of Potential Failure Forming Sets Table 12: Summary of Discontinuity Set Spacings Table 13: Composited Results of Backbreak Analysis Table 14: Summary of Pit Slope Design Recommendations and Expectations List of Figures Figure 1: Site Location Map... 2 Figure 2: Location of Geotechnical Drillholes... Figure 3: Point Load Index UCS Correlation Factor Figure 4: Rock Mass Parameters Figure 5: Distribution of Friction Angles (Zero Cohesion) Figure 6: Discontinuity Pole Plots Figure 7: Drillhole RQD Cross-Sections Figure 8: Geologic Model and Geotechnical Cross Sections Figure 9: Rock Mass Shear Strength: Hornfels Figure : Rock Mass Shear Strength: Intrusives Figure 11: Summary of vibrating wire piezometer data from K09-07 (El=595.71) Figure 12: Summary of vibrating wire piezometer data from K09-12 (El=548.49) Figure 13: Groundwater Pressures Measured in K Figure 14: Groundwater Pressures Measured in K Figure 15: Pit Slope Design Sectors Figure 16: Explanation of Pit Slope Terminology Figure 17: Preliminary Interramp Slope Design Curves: Hornfels Figure 18: Discontinuity Contour Plot for Backbreak Analysis Figure 19: Explanation of Backbreak Terminology Figure 20: Maximum Interramp Slope Angle Recommendations List of Appendices Appendix A: Geotechnical Core Logs Appendix B: Laboratory Testing Uniaxial Compressive Strength Testing Triaxial Compressive Strength Testing Direct Shear Testing Brazilian Disk Tension Testing Appendix C: Slope Stability Modeling MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

9 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page iv Limit Equilibrium Modeling Finite Element Modeling MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

10 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 1 1 Introduction and Background SRK Consulting (US), Inc. (SRK) was requested by Avanti Mining Inc. (Avanti) to carry out a feasibility level geotechnical evaluation for the Kitsault Project Open Pit in the British Columbia, Canada (Figure 1). This report presents a complete description of the methods used to collect pertinent information, the information so gathered, the analytical tools employed to produce assessments of the anticipated response of the geologic environments to the development of the open pit and the recommendations based upon those assessments. The feasibility study (AMEC, 20) ultimate pit and current geologic solids provided by Avanti were used as the basis for the evaluation. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

11 KITSAULT PROJECT SITE PIT SLOPE EVALUATION SITE LOCATION MAP SRK PROJECT NO.:1CA FILE NAME: KITSAULT PROJECT DATE: FEB. 20 APPROVED: MEL FIGURE NO.: 1 REVISION NO. A

12 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 3 2 Program Objectives and Work Program 2.1 Program Objectives The primary objectives of the feasibility-level geotechnical evaluation for the Kitsault project were: To collect additional and to assimilate existing geotechnical information pertaining to the insitu materials; To geotechnically characterize the in-situ materials; To undertake laboratory testing of geomechanical properties of samples of the in-situ materials; To develop a geotechnical model to serve as the basis for geomechanical analyses; To conduct geomechanical analyses; and, To make recommendations pertaining to optimal slope angles and pit architecture for mine design purposes. 2.2 Work Program The principle stages of the geotechnical evaluation work program were comprised of the following: Recommendation of the number, location and orientation of core holes sufficient to characterize in-situ materials in the open pit area; Geotechnical core logging and discontinuity orientation of core recovered from the drill holes; Selection of representative drill core samples from the respective lithological units encountered in the geotechnical drill holes; Submission of the representative samples to the University of Arizona Rock Mechanics Laboratory in Tucson, Arizona, for geomechanical testing; Analyses and interpretation of the geotechnical data and laboratory test results to produce a comprehensive analytical model of in-situ properties; Examination of the anticipated behavior of the geotechnical model to expected mininginduced stresses, using various analytical methods; and, Compilation of a feasibility-level geotechnical pit slope evaluation report incorporating recommendations pertaining to optimal pit slope angles and pit architecture for mine design purposes. As commissioned, the work reported herein was performed at a feasibility design level. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

13 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 4 3 Geologic Setting The following description of the Kitsault geologic setting was extracted from previous work by Steininger (1981). The Kitsault Molybdenum ore deposit is located within the Intermountain tectonic belt of the large Canadian geologic province know as the Cordillera. Rock types present within this belt range in age from Devonian to early Cenozoic, typically consisting of sedimentary, granitic, volcanic island and continental arc formations, and marine and non-marine clastics eroded mainly from uplifting of the Omineca Belt. Significant deformation has occurred in this region of the province, primarily caused by compression and extension transtensional forces. 3.1 Local Geology The Kitsault project site is located approximately 2 km east of the Coast Plutonic Complex, consisting of a northwest trending belt of metamorphic and intrusive rocks. Hornfels is the predominant metamorphic lithology, while intrusive lithologies are typically granodiorite to quartz monzonite, with minor granite, as plutons. Intense intrusive activity within this region, including recent plateau lava flows, can be attributed to the Coast Plutonic Complex. Extensive glaciation has occurred in this area, deeply eroding valleys. Glacial remains are only present as thin alluvium veneers and swamplands covering outcrops. The Kitsault deposit lies within the Lime Creek Intrusive Complex, hosted by the sedimentary units of Bowser Lake Group. The intrusives at the site consist of quartz diorite, granodiorite, and decreased amounts of quartz monzonite. Mineralization within the deposit is related to the last two phases of the Lime Creek Complex, i.e., the Central Stock (granodiorite) and the Northeast Porphyry (porphyritic granodiorite). The Bowser Lake Group is primarily comprised of interbedded greywacke and argillite with bed thicknesses ranging from inches to tens of feet. The formation is primarily greywacke with all members being metamorphosed to greenschist facies. Hornfels within the Bowser Lake Formation were likely produced in reaction to intrusions along the eastern border of the Coast Plutonic Complex. Lamprophyre dikes, occurring as numerous northeast trending swarms, are present throughout the deposit. These swarms, which are likely related to the Alice Arm Intrusives, consist of several to hundreds of dikes per mile and range in thickness from inches to 50 feet. Typically northeast trending faults, although common, appear to have had little effect on the units within the ore body. 3.2 Major Geologic Structures Major geologic structures are those features, such as faults, dikes, shear zones, and contacts that have dimensions on the same order of magnitude as the area being characterized. These structures are treated as individual elements for design purposes, as opposed to joints, which are handled statistically. To date, there are no known major structural features within the immediate area of the anticipated Kitsault pit. Smaller scale, high angle faulting is, however, evident in the exposed north pit wall, but it is generally oriented such that it is not expected to adversely affect pit stability. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

14 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 5 Several smaller scale faults or shear zones have also been identified in resource and geotechnical drilling. Most of these structures are not anticipated to significantly impact pit slope stability due to their apparent lack of persistence and associated limited degree of rock degradation. Lamprophyre dikes are exposed in existing pit walls and have been encountered in drillholes. The dikes are generally of good rock quality and are not expected to significantly impact pit slope stability. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

15 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 6 4 Field Data Collection The field data collection program was developed with the primary objective of rock mass characterization to support development of a geotechnical model suitable for pit slope stability evaluation. Field data collection consisted of geotechnical core logging and largely subjective observations of existing pit wall conditions. 4.1 Geotechnical Core Logging Geotechnical logging, field point load testing and discontinuity orientation of core recovered from two drill holes were conducted for this investigation. The two drill holes were designed to supplement the 2008 pre-feasibility geotechnical core logging program. In addition to the two geotechnical coreholes drilled in 2009 for this investigation, data from the six geotechnical coreholes drilled in 2008 for the previous SRK (2009) Kitsault Pre-feasibility Geotechnical Pit Slope Evaluation were also considered in the analyses. Based on the current understanding of the deposit and mine plan, drillhole locations and orientations were selected to provide the best coverage possible of rock likely to form pit walls. The geotechnical drillhole locations were initially chosen based on preliminary and historic pit shells and, in some instances, drillhole intersections with the final pre-feasibility pit slopes were not optimal relative to the latest pit designs. It is believed, however, that this factor does not adversely impact the analyses conducted to a significant degree. Five of the previous six geotechnical drillholes, i.e., K-08-04, K-08-09, K-08-12, K-08-14, and K-08-16, were drilled to coincide with holes planned for the Avanti 2008 resource drilling program. Based on the current understanding of the deposit, those particular five holes were selected to provide the best coverage possible of rock likely to form the Kitsault pit walls. Since no further resource drilling was planned in the area of the anticipated western pit wall, an additional hole (K-08-06) was drilled specifically to examine rock expected to comprise that wall segment. Drillhole inclinations of approximately 60 degrees below the horizontal were selected over vertical holes since they were judged more likely to intersect geologic structures such as joints and fracture systems which, if present, will influence slope stability. Collar locations and the drillhole azimuths of the two supplemental geotechnical holes drilled for this investigation as well as the six holes considered in the previous (SRK, 2009) investigation are summarized in Table 1 and presented on Figure 2. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

16 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 7 Table 1: Drillholes Oriented and Logged for Geotechnical Data Collar Coordinates Hole ID Azimuth Inclination Length Northing Easting Elevation (deg) (deg) (m) K K K K K K K K Geotechnical Logging Procedures Core retrieved from the two geotechnical coreholes were logged on a 24 hour per day basis, at the rig, in the liners, or splits, prior to boxing and transporting. The geotechnical core logging program was developed to yield information pertinent to modeling of pit slope stability, such as geologic contacts, profiles of rock strength, and characterization and frequency of discontinuities. Specific parameters that were logged included: General lithology and structures; Total core recovery; Rock Quality Designation (RQD); Rock weathering and intact strength indices; Frequency of discontinuities; Discontinuity characteristics (type, roughness, infillings and wall condition); and, Discontinuity orientation (when possible). Care was taken to exclude handling or mechanically induced fracturing of the core as the inclusion of such would produce lower rock quality classifications, potentially contributing to an unnecessarily conservative slope design. Geotechnical corehole logs are presented in Appendix A. During core logging, redundant samples of the core were collected to provide specimens for laboratory strength testing. Samples were collected at approximately 30 meter intervals, or when significant rock type or strength changes were apparent. Each sample was sealed and safely stored at the time of collection. Upon completion of the drilling, samples were shipped to SRK s office in Denver, Colorado, for test sample selection. Select samples were then repackaged and shipped to the University of Arizona Rock Mechanics Laboratory in Tucson, Arizona, for testing Core Drilling Method The coreholes were drilled by Driftwood Diamond Drilling, Ltd., from Smithers, British Columbia, using a skid mounted Hydracore 2000 drill rig with a 61.1mm I.D.(HQ3), 1.5m and 3.0m long triple-tube sampling barrels. The coreholes were advanced with a face discharge bit MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

17 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 8 system using a polymer mixture to facilitate core recovery. This coring method facilitated the recovery of continuous core samples as the holes advanced. Downhole surveys were conducted by Driftwood upon completion of drilling; subsequently, the surface casing was pulled and the hole allowed to collapse. Depth to groundwater could not be determined at the time of hole advancement due to the 24 hour per day drilling schedule, with its continuous fluid injection and circulation. 4.2 Discontinuity Orientation Orientation of discontinuities in each run was accomplished using an A.C.T. core orientation system manufactured by Reflex Instruments. The depth, alpha angle and beta angle were measured for each discontinuity on all core runs that were successfully oriented. The beta angle, i.e., the angle from the lowest part of the ellipse formed by the intersection of each discontinuity with the core, was measured from the bottom of the core in a clockwise direction when looking down hole. The alpha angle was measured as the maximum angle made by the discontinuity with respect to the core axis. It was possible to orient a total of 1,847 discontinuities out of the total 3,360 discontinuities logged (55%) in the two supplemental geotechnical coreholes drilled for this evaluation. A summary of oriented core information by hole, including the six previous 2008 holes, is presented in Table 2. Table 2: Summary of Discontinuity Orientation Hole ID Drillhole Length (m) Core Length Oriented (m) Total Discontinuities Logged Total Discontinuities Oriented Percentage of Discontinuitie s Oriented K % K % K % K % K , % K % K , % K , % 4.3 Point Load Testing Point Load Tests (PLT) were performed during core logging at a frequency of approximately one test per every 2 to 3m using a Roctest Pil-7 test machine to provide detailed and nearly continuous profiles of relative rock strength. PLTs were conducted according to International Society for Rock Mechanics (ISRM, 1985) procedures. Both axial (parallel to the long axis of the core) and diametral (perpendicular to the long axis of the core) loading tests were conducted. Axial point load testing was performed as samples suitable for testing in an axial orientation were obtained from coring or were produced by breaking especially long sticks of core in diametral tests. A combined total of 2 point load tests were conducted on core from the two 2009 geotechnical coreholes; of those, 42 met test criteria for passing test results. Point load indices (Is (50) ) were MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

18 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 9 calculated from the field PLT data using the ISRM (1985) suggested method. Calculated point load index strengths (Is (50) ) ranged between 0.3 and.5 MPa, with an average of 5.0 MPa. In addition to the tests routinely conducted at 2 to 3 meter intervals, at least one PLT was also performed adjacent to each UCS sample obtained for laboratory testing. The reason for the paired PLT and UCS samples was to permit estimation of a correlation factor for conversion of the field PLT tests to laboratory UCS values. 4.4 Geotechnical Observations of Existing Pit During a site visit by SRK between September 8 and September 11, 2008, geotechnical observations of the existing pit wall conditions and performance were made and noted. The outer walls of the currently exposed pit consist primarily of a hornfels unit cut by relatively small intrusive bodies and lamprophyre dikes. The existing outer pit walls are comprised of up to approximately six meter high benches separated by catch benches, resulting in interramp slope angles of approximately 43 degrees to 45 degrees over a total vertical height of 60 meters. A relatively low slope comprised of one to two benches is exposed in the interior, intrusive portion of the pit. Based on the field observations, both the outer, hornfels slopes and the inner, intrusive slopes are in good condition, showing only minor raveling and very few observable rock displacements. The displacements observed included relatively limited plane shear and bench scale wedge failures which were noted particularly in the outer, north to northeast pit walls, and which most likely occurred during excavation when the pit was last active 26 years ago. No major fault structures were observed in the pit walls during the SRK site visit; however, some small scale, high angle faulting, as described in Section 3.2, was evident in the north pit wall. In August, 2009, a preliminary survey of the current pit did not identify significant seeping of groundwater in the current pit walls. Observations of significant seepage from pit walls during quarterly seepage surveys during mine reclamation studies were reported (SRK, 2004); however, no flow rates were measured. It is likely that localized inflows will vary seasonally, and be influenced by surface water flows. Current pit inflows may be recharged by surface water runoff. 4.5 Packer Testing Hydraulic packer testing was carried out at intervals covering the full depths of the two 2009 supplemental geotechnical drill holes. This provided profiles of hydraulic conductivity necessary to evaluate hydrogeologic characteristics of the rock mass. Details of the packer testing procedures and results are presented in the (SRK, 2009) Kitsault Pre-feasibility Study Pit Hydrogeology report. Conclusions are summarized herein in Section 6.5. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 7:09 PM November 20

19 T:\Kitsault British Columbia\!040_AutoCAD\Feasibility Pit Slopes Figures\Novemeber.20.Updates\1CA Rev.A.Fig,2.Location.of.Geotech.Drillholes dwg N N K08-12 K09-07 K08-09 K08-06 K08-14 K08-04 K09-12 K N N E E E LEGEND NOTE EXISTING GROUND CONTOURS (MAJOR/MINOR) 5 METER INTERVAL GEOTECHNICAL DRILLHOLE COLLAR LOCATION AND HORIZONTAL BOREHOLE PROJECTION 1. PIT TOPOGRAPHY SHOWN IS WARDROP (2009) PRE-FEASIBILITY STUDY. PIT SLOPE EVALUATION 7175 West Jefferson Ave. Suite 3000 Denver, Colorado LOCATION OF GEOTECHNICAL DRILLHOLES SRK JOB NO.: 1CA FILE NAME: 1CA Rev.A.Fig,2.Location.of.Geotech.Drillholes dwg KITSAULT BRITISH COLUMBIA, CANADA DATE: APPROVED: FIGURE: NOV. 20 ML 2 REVISION NO. A

20 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 11 5 Laboratory Testing Geomechanical testing was conducted at the University of Arizona Rock Mechanics Laboratory in Tucson, Arizona, to determine strength characteristics for the in-situ materials. The overall laboratory program consisted of direct shear, uniaxial and triaxial compressive strength, and direct tensile strength testing as well as measurements of unit weight and elastic properties. A total of 75 laboratory tests were conducted on samples selected to represent the range of the rock conditions observed in the eight geotechnical borings. After completion of the laboratory testing program, the tested samples were returned to SRK for forensic review. Raw laboratory test data is included in Appendix B. 5.1 Unconfined Compressive Strength and Elastic Properties The uniaxial compressive strength (UCS) test involves the application of a steadily increasing axial load upon a core sample with a length-to-diameter (L/D) ratio of, ideally, between 2.0 and 2.5. The uniaxial compressive strength (in terms of stress) of the sample is the applied load that produces failure divided by the cross-sectional area of the core. For selected UCS tests, strain gauges were applied to the samples to monitor longitudinal and lateral strains which are produced in response to the axial loading. The elastic properties are derived from the strain gauge output; specifically, Young s Modulus ( ) is the ratio of the vertical stress to the longitudinal strain, while Poisson s Ratio ( ) describes the relationship between the lateral strain and the longitudinal strain. Uniaxial compressive strength (UCS) testing was conducted on 32 samples according to ASTM Method D7012. Elastic properties (Young s Modulus and Poisson s Ratio) were measured for eight of the 32 UCS samples. Upon post-testing examination of the samples, it was noted that samples K08-6 at 35.8m, K08-14 at meters and K08-12 at meters had unusually low strengths (11.31 to MPa) and appeared to have fractured on pre-existing discontinuities and not through the actual intact rock as should occur in a valid UCS test. Valid tests produced UCS values ranging from 41.9 to MPa, with a mean of 5.3 MPa; Young s Moduli ranging from 13.7 to 69.4 GPa, with a mean value of 46.3 GPa; and, Poisson s Ratios ranging from to 0.302, with a mean value of Results of the UCS and elastic properties testing from the 2008 and 2009 programs are summarized in Table 3. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

21 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 12 Table 3: Uniaxial Compressive Strength Testing SRK Hole ID Sample Depth (m) UCS (MPa) Young s Modulus (GPa) Poisson s Ratio Unit Wt. (kn/m 3 ) Rock Type K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K ** 26.9 Quartz Monzonite K * 30.5 Diorite K * Hornfels K Hornfels K Quartz Monzonite K * 28.2 Hornfels K Lamprophyr K Hornfels K * Hornfels K Hornfels K ** 26.0 Hornfels K ** 30.4 Hornfels K * 25.6 Hornfels K * 26.2 Hornfels K Hornfels K Quartz Monzonite K Quartz Monzonite K HF Hornfels K HF Hornfels K Lamprophyr K Hornfels K Hornfels K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite * Correction factor applied to account sample L/D ratio of less than 2.0. ** UCS test results considered invalid and excluded from further analysis. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 7:06 PM November 20

22 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 13 The intact Young s Moduli determined from laboratory testing were used for empirical calculations of a rock mass deformation modulus for each domain by methods presented by Hoek and Diederichs (2006). 5.2 Triaxial Compressive Strength Testing The triaxial compressive strength (TCS) test involves encasing a core sample in an impervious membrane and subjecting it to a selected confining pressure ( 3 ) while the sample is loaded axially ( 1 ) until failure occurs. The applied load that results in failure divided by the crosssectional area of the core is the triaxial compressive strength given the confining pressure. For this project, triaxial compressive strength (TCS) tests were conducted on 11 samples using ASTM Method D7012. The samples were tested at confining pressures selected to range from zero to approximately one-half of the UCS values as suggested by Hoek and Brown (1997). TCS testing yielded compressive strengths ( 1 ) ranging between and MPa with a mean value of MPa under confining pressures ( 3 ) ranging between 6.9 and 20.7 MPa, with a mean of 13.8 MPa. The results of the TCS testing are summarized in Table 4. Table 4: Triaxial Compressive Strength Testing Sample Unit Wt. Hole ID Depth (m) 3 (MPa) 1 (MPa) (kn/m 3 Rock Type ) K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Hornfels K Hornfels K Hornfels K Hornfels K Hornfels K Quartz Monzonite K Hornfels K Quartz Monzonite Intact rock shear strength envelopes were derived by combining tests from the respective rock types. Quartz monzonite samples yielded a peak intact friction angle of 50 and 27.7MPa cohesion. Hornfels samples yielded a combined peak intact friction angle of 50 and 20.9MPa. 5.3 Direct Shear Testing The direct shear test involves applying a load perpendicular (normal) to a discontinuity separating two blocks of rock and continuously monitoring the shear stress necessary to displace the blocks relative to each other. To define the overall shear strength envelope, three or more normal stresses are applied to the sample and continuous displacement/shear stress data is obtained at each of the normal loads. For each normal load, the peak (maximum) and residual (steady state relative to displacement) shear stresses are recorded, thereby defining the peak and residual shear strengths given each normal stress. The relationship between an applied normal stress and the resulting shear strength defines a point on the shear strength envelope. Peak and residual shear strength envelopes can then be determined from the shear strength/normal stress points using statistical regression methods. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

23 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 14 Direct shear testing is commonly used for estimating the expected shear strength along natural rock discontinuities such as joints, fractures and faults. Since the stress levels developed within open pits are usually much lower than the rock substance or intact strength, displacement frequently occurs along pre-existing geologic discontinuities, making the determination of discontinuity shear strength a necessity. For open pit design, direct shear testing is preferred over other methods of estimating discontinuity shear strength, such as triaxial compression testing, because direct shear testing permits a higher degree of control over the selection of the actual surface tested. For this project, 11 core samples were selected for four point, small scale direct shear (SSDS) tests (ASTM Method D5607) to obtain discontinuity shear strength data. Natural core discontinuities preserved in the field were used for of the direct shear tests. To facilitate the estimation of lower bound residual discontinuity shear strengths, a saw-cut discontinuity was created in one sample prior to testing. The range of normal stresses applied during testing was selected to span estimated ranges of insitu stresses that are expected to develop within the slopes and to reasonably define the characteristics of the shear strength envelopes. The selected normal loads ranged from approximately 170 to 2,070 kpa. In order to fit a shear strength envelope to the laboratory data points, a linear or curvilinear regression analysis is typically conducted. For a linear fit, the envelope is presented according to the Mohr-Coulomb criterion, i.e., in the form of a friction angle (Φ), which corresponds to the inverse tangent of the slope of the least-squares regression line, and apparent cohesion (c), which corresponds to the shear strength intercept at zero normal stress. When conducting a linear regression with discontinuity shear strength data, the line is commonly forced through the origin simulating zero cohesion. A curvilinear strength envelope can be presented in terms of a power curve with k and m values as described by Jeager (1971) or other nonlinear relationships such as the Hoek-Brown (Hoek, et al, 2002) criterion. For sufficiently strong rock, the curvilinear fit is considered a more realistic representation of the shear strength/normal stress relationship, particularly at relatively low normal stresses, which typify conditions in a majority of open pit mine slopes. Although results of direct shear testing of discontinuities on some of the Kitsault samples tested demonstrated curvilinear shear strength/normal stress envelopes, most analytical stability models, including those used by SRK for backbreak analyses, utilize linear, Mohr-Coulomb parameters. Shear strengths were typified using the Mohr-Coulomb and power curve shear strength/normal stress relationships. The results are summarized in Table 5. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

24 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 15 Table 5: Summary of Residual Shear Strengths Hole ID Sample Depth (m) Linear Regression Power Regression Discontinuity Type Φ* ( ) C (kpa) Φ**( ) k m K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Hornfels K Hornfels K Hornfels K Hornfels K HF Hornfels K Hornfels K Quartz Monzonite K Quartz Monzonite * Best linear fit friction angle given the apparent cohesion calculated and noted ** Best linear fit friction angle assuming a zero apparent cohesion. 5.4 Direct Tensile Strength Testing Brazilian disk tension testing according to ASTM method D3967 was conducted on 13 samples indicating intact tensile strengths ranging from 4.21 to MPa, with a mean value of.48 MPa. Results of the direct tensile strength testing are summarized in Table 6. Table 6: Direct Tensile Strength Testing Hole ID Sample Depth (m) Tensile Strength (MPa) Unit Wt. (kn/m 3 ) Rock Type K Quartz Monzonite K HF Hornfels K HF Hornfels K Hornfels K Hornfels K Hornfels K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite K Quartz Monzonite 5.5 Unit Weight Measurements Prior to actual testing of core samples, sample dimensions and weights were measured and used to calculate total unit weights for each sample. The combined data set included 54 unit weight measurements ranging from 24.7 to 30.7 kn/m 3 with a mean value of 26.4 kn/m 3. Unit weights are summarized along with the various strength measurements in the preceding Tables 3, 4 and 6. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

25 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 16 6 Geotechnical Model Rock mass models were developed for Kitsault to provide a framework for interramp/overall slope stability modeling by mathematically simulating site geotechnical conditions. The term rock mass refers to the entire body of rock, including discontinuities. In contrast, intact rock or substance strength refers to the rock between discontinuities in a rock mass. Primary inputs to the rock mass models included intact rock strength, degree of fracturing and strength of fractures. 6.1 Data Analysis Evaluation of the field and laboratory data collection programs indicates a high degree of variability in rock strength and geologic structure at Kitsault. This natural variation in rock strength and structure suggests that a probability-based method of analysis is most appropriate, yielding less conservative slope angles than would the selection of a unique, potentially overconservative value as is typical in strictly deterministic analyses. Probabilistic methods differ from deterministic methods in that each model parameter is characterized by a statistical distribution of values having a central tendency and some variation around that central tendency, rather than by a single, unique value. Further details of the probabilistic method used in this evaluation follow. Details of the data analysis methods are discussed in subsequent sections Intact Rock Strength Intact rock strengths were assessed in the field qualitatively using ISRM (1978) methods and by conducting point load tests (PLT) as discussed in Section 4.3. Several samples of core were also selected for laboratory uniaxial compressive strength (UCS) and triaxial compressive strength (TCS) testing as described in Sections 5.1 and 5.2, respectively. UCS and Is (50) values, as well as the field estimates of intact rock strength, are plotted with depth on the geotechnical logs presented in Appendix A. Each laboratory UCS test was paired with an adjacent field PLT Is (50) value for estimation of a correlation factor for conversion of the field PLT tests to laboratory UCS values. Overall, a relatively linear relationship was apparent between the two variables, yielding a correlation factor of 24 (UCS:Is (50) ). The correlation between the laboratory UCS tests and the PLTs is demonstrated on Figure 3. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

26 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 17 Figure 3: Point Load Index UCS Correlation Factor The conversion of the field PLTs to laboratory UCS values allowed nearly continuous profiles of rock strength for each corehole and provided a large population for defining UCS statistical distributions for the probabilistic analyses. As demonstrated in the plots contained on Figure 4, both the hornfels and intrusive domains have similar ranges in UCS, however, the intrusives posses a higher mode or peak concentration (116MPa) than does the hornfels domain (61MPa). TCS test results, as described in Section 5.2, were used for direct determination of the Hoek- Brown (Hoek, et al, 2002) material coefficient m i. As described by Hoek (1983), the Hoek- Brown constant m i is very approximately analogous to the angle of friction of the conventional Mohr-Coulomb failure criterion. Higher m i values are characteristic of brittle igneous and metamorphic rocks producing relatively steeply inclined strength envelopes and high instantaneous friction angles at lower normal stress levels. Material coefficient m i values of 28.8 and 30.2 were calculated for the hornfels and intrusive, respectively Discontinuity Frequency The fracture (discontinuity) frequency or its inverse, fracture spacing, is a critical parameter influencing rock mass behavior. Fracture frequency is expressed as the number of fractures per unit length and fracture spacing is defined as the distance between fractures. Fracture frequency per meter was recorded during drilling for each run, thereby enabling calculation of mean fracture spacings for use in rock mass characterization and bench scale analyses, both of which are discussed in more detail in the following sections. For expedience, it was assumed that each measurement began and ended with a fracture, thereby resulting in a maximum possible spacing of about 1.5 meters, the length of the core barrel. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

27 Intrusives Lithologic Domain Hornfels Lithologic Domain Mean IRMR = 48 (516) Mean IRMR = 47 (904) Mean UCS = 128 MPa (43) Mean UCS = 92 MPa (28) Mean ff/m = 6.1 (285) Mean ff/m = 4.8 (195) Note: Number in parenthesis represents the number of samples for the respective data set. PIT SLOPE EVALUATION ROCK MASS PARAMETERS SRK PROJECT NO.:1CA FILE NAME: KITSAULT PROJECT DATE: OCT. 20 APPROVED: MEL FIGURE NO.: 4 REVISION NO. A

28 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 19 As demonstrated in the plots contained on Figure 4, both the hornfels and intrusive domains display similar distributions of fracture frequency. Discontinuity spacings are discussed further in Section Discontinuity Shear Strength Discontinuity shear strengths are a function of geologic history as well as rock mass weathering, alteration and/or infilling. Direct shear testing was conducted on a number of rock samples as previously discussed in Section 5.3 to provide information on the distribution of discontinuity shear strengths. Although results of direct shear testing of discontinuities on some of the samples tested demonstrated curvilinear shear strength/normal stress envelopes, most analytical stability models, including those used by SRK for backbreak analyses, utilize linear, Mohr-Coulomb parameters. Tests results indicate similar shear strengths between the different domains and, consequently, discontinuity shear strengths were grouped together into one distribution. For the combined dataset of direct shear results, calculated friction angles (assuming zero apparent cohesion as discussed in Section 5.3) ranged from 26 to 49, while apparent cohesion values ranged from 0 to 8kPa. The mean friction angle was 35 and the mean apparent cohesion was 25 kpa. The combined distribution of friction angles obtained from direct shear testing is shown on Figure 5. Figure 5: Distribution of Friction Angles (Zero Cohesion) Discontinuity Orientation Geologic discontinuity influenced failure mechanisms were analyzed at both the pit wall and bench scales. The term discontinuity refers to any significant mechanical break or fracture having negligible tensile strength in the rock. Discontinuities are formed by a wide range of geological processes and can collectively include most types of joints, faults, fissures, fractures, veins, bedding planes, foliation, shear zones, dikes and contacts. Minor discontinuities such as joints, foliation and bedding planes, represent an infinite population for practical purposes and, due to sampling limitations, are best modeled with stochastic (probabilistic) techniques. A discontinuity set denotes a grouping of discontinuities that are expected to have similar impact upon the proposed design. In open pit design, this criterion is usually modified so that all discontinuities in a similar range of orientations, i.e., dip direction and dip, are designated as a single discontinuity set. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

29 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 20 To enable the calculation of the true dip direction and dip, the depth of intercept and the angles of the discontinuities relative to the core axis and perpendicular to the core axis, (alpha and beta angles, respectively) were measured during logging. Accounting for the plunge and azimuth of each drillhole, discontinuity alpha and beta angles were converted to dip and dip direction using the commercially available software package, Dips developed by Rocscience, Inc. (2003). Discontinuity data from each of the geotechnical coreholes was contoured on an equal area percent plot for analysis of structural stability. In most cases, visual inspection of these plots revealed preferred discontinuity orientations. The contour plots are presented on Figure 6. A summary of discontinuity sets delineated and incorporated in the analysis of bench stability is presented in Table 7. Table 7: Discontinuity Sets Delineated for Analysis Set ID No. Dip Dip Direction Mean Std. dev. Mean Std. dev. A B C D E F G H Rock Mass Classification Rock mass characterization is a largely empirical process of classification based on information obtained primarily from field data and enhanced with further data analysis and laboratory testing. The basic geotechnical parameters recorded for each core run were applied to the Laubscher (1990) In-situ Rock Mass Rating (IRMR) system, thereby creating a profile of IRMR with depth for each of the eight geotechnical holes drilled for this investigation. The Laubscher IRMR system consists of three primary parameters; intact rock strength (IRS), fracture frequency per meter (FF/m) and joint conditions (Jc). The individual parameters as well as the IRMR value out of a total of 0 for each run are displayed on the two 2009 geotechnical core logs presented in Appendix A. A large scale joint expression of slight undulation and dry conditions were assumed. It is appropriate to assign the groundwater parameter the full value when using rock mass rating systems as input to the Hoek-Brown (2002) shear strength criterion. Groundwater pressures are accounted for by using effective stress stability analyses. The IRMR is typically adjusted to account for the expected mining environment, namely the influence of weathering, structural orientations, induced or changes to stresses and blasting to produce the Mining Rock Mass Rating (MRMR). The adjustments to the IRMR are introduced in recognition of the type of excavation proposed and the time dependant behavior of the rock mass. The potential for these adjustments were considered independently for this analysis and were not incorporated into the rock mass rating. A summary of IRMR values per domain is presented in Table 8. MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

30 SRK Consulting Feasibility Geotechnical Pit Slope Evaluation, Kitsault Project Page 21 Table 8: In-situ Rock Mass Rating (IRMR) Distributions Domain Distribution Sample No. Mean Std. Dev. Min Max Hornfels Beta Intrusives Weibull MEL/lb 1CA _Kitsault_FS_Geotechnical_Evaluation_FINAL.doc, Nov. 15,, 5:25 PM November 20

31 K09-07 K08-12 K08-09 X X X N 828 POLES MAXIMUM CONCENTRATION 4.8% 351 POLES MAXIMUM CONCENTRATION 4.7% 383 POLES MAXIMUM CONCENTRATION 3.9% K08-06 K N X K08-12 K09-07 K08-09 X K08-06 K08-14 K POLES MAXIMUM CONCENTRATION 5.1% 649 POLES MAXIMUM CONCENTRATION 6.3% K09-12 K N K08-16 K08-04 K09-12 X N X 298 POLES MAXIMUM CONCENTRATION 4.3% LEGEND E E E E 11 POLES MAXIMUM CONCENTRATION 5.4% X E E 722 POLES MAXIMUM CONCENTRATION 4.7% E E X INDICATES MEAN DRILLHOLE TREND AND PLUNGE NOTE EXISTING GROUND CONTOURS (MAJOR/MINOR) 5 METER INTERVAL VARIOUS IGNEOUS INTRUSIONS COLLECTIVELY REFERRED TO HEREIN AS THE INTRUSIVES UNIT. HORNFELS UNIT PIT SLOPE EVALUATION PLOTS ARE LOWER HEMISPHERE, EQUAL AREA CONTOURED AS FISHER CONCENTRATIONS (PERCENT OF TOTAL PER 1 PERCENT AREA) PIT TOPOGRAPHY SHOWN IS WARDROP (2009) PRE-FEASIBILITY STUDY GEOLOGY INTERCEPTS WITH PIT TOPOGRAPHY WERE ESTIMATED BASED ON GEOLOGICAL MODEL PROVIDED AVANTI CONTOUR PLOTS OF ORIENTED CORE DISCONTINUITIES 7175 West Jefferson Ave. Suite 3000 Denver, Colorado SRK JOB NO.: 1CA FILE NAME: 1CA Rev.A.Fig.6.Contour.Plots dwg KITSAULT BRITISH COLUMBIA, CANADA DATE: NOV. 20 APPROVED: ML FIGURE: REVISION NO. 6 A