Appendix 3.0-D Pre-Feasibility Geotech Pit Slope Design

129 Pages·2012·8.31 MB·English

KITSAULT MINE PROJECT
ENVIRONMENTAL ASSESSMENT
APPENDICES

APPENDIX 3.0-D
Pre-Feasibility Geotech Pit Slope Design
Kitsault Molybdenum Project

VE51988 – Appendices

Avanti Mining Inc.
Pre-feasibility
Geotechnical Pit Slope Design
Kitsault Molybdenum Project
British Columbia, Canada

Prepared for:
Avanti Mining Inc.
5251 DTC Parkway
Suite 405
Greenwood Village, CO 80111

Prepared by:

7175 W. Jefferson Ave.
Suite 3000
Lakewood, CO 80235

Project Reference No:
179702

June 2009
Avanti Mining Inc. i
Kitsault Molybdenum Project Pre-feasibility Geotechnical Pit Slope Design
Table of Contents
1  INTRODUCTION AND BACKGROUND .......................................................................... 1-1 
1.1  Objectives .................................................................................................................. 1-1 
1.2  Scope of Work and Terms of Reference .................................................................... 1-1 
2  GEOLOGIC SETTING ......................................................................................................... 2-1 
2.1  Local Geology ............................................................................................................ 2-1 
2.2  Major Geologic Structures ......................................................................................... 2-1 
3  GEOTECHNICAL FIELD DATA COLLECTION .............................................................. 3-1 
3.1  Geotechnical Core Logging ....................................................................................... 3-1 
3.2  Core Drilling Method ................................................................................................. 3-1 
3.3  Geotechnical Logging Procedures ............................................................................. 3-2 
3.3.1  Core Orientation .......................................................................................... 3-2 
3.4  Geotechnical Observations of Existing Pit ................................................................ 3-3 
4  LABORATORY TESTING................................................................................................... 4-1 
4.1  Unconfined Compressive Strength Testing and Elastic Property Measurements ..... 4-1 
4.2  Triaxial Compressive Strength Testing ..................................................................... 4-2 
4.3  Direct Shear Testing .................................................................................................. 4-3 
4.4  Unit Weight Measurements ....................................................................................... 4-4 
5  GEOTECHNICAL MODEL ................................................................................................. 5-1 
5.1  Data Analysis ............................................................................................................. 5-1 
5.1.1  Intact Rock Properties ................................................................................. 5-1 
5.1.2  Discontinuity Shear Strength ....................................................................... 5-2 
5.1.3  Discontinuity Orientation ............................................................................ 5-2 
5.1.4  Rock Quality Designation (RQD) ............................................................... 5-3 
5.1.5  Discontinuity Frequency ............................................................................. 5-3 
5.2  Rock Mass Quality ..................................................................................................... 5-3 
5.2.1  Intrusives ..................................................................................................... 5-4 
5.2.2  Hornfels ....................................................................................................... 5-4 
5.3  Groundwater .............................................................................................................. 5-4 
5.4  Model Methodology................................................................................................... 5-5 
5.5  Pit Slope Design Sectors ............................................................................................ 5-6 
6  SLOPE STABILITY ANALYSES ........................................................................................ 6-1 
6.1  Interramp/Overall Stability Analyses ........................................................................ 6-1 
6.1.1  Static Analysis ............................................................................................. 6-3 
6.1.2  Pseudostatic Analysis .................................................................................. 6-3 
6.2  Bench Stability Considerations .................................................................................. 6-3 
7  SLOPE DESIGN RECOMMENDATIONS .......................................................................... 7-1 
8  REFERENCES ...................................................................................................................... 8-2 

SRK Consulting (US), Inc. June 2009
179702_Kitsault_PFS_Geotechnical_Pit_Slope_Design _Report_FINAL_03JUN2009.docx
Avanti Mining Inc. ii
Kitsault Molybdenum Project Pre-feasibility Geotechnical Pit Slope Design

List of Tables
Table 3.1.1: Summary of Drillholes Oriented and Logged for Geotechnical Data .......................... 3-1 
Table 3.3.1.1: Summary of Core Orientation ................................................................................... 3-3 
Table 4.1.1: Summary of Uniaxial Compressive Strength Testing .................................................. 4-2 
Table 4.2.1: Summary of Triaxial Compressive Strength Testing ................................................... 4-3 
Table 4.3.1: Summary of Direct Shear Testing ................................................................................ 4-4 
Table 5.1.1.1: Summary of Laboratory UCS Values by Geotechnical Domain ............................... 5-2 
Table 5.1.1.2: Summary of Total Unit Weights by Geetechnical Domain ....................................... 5-2 
Table 5.1.4.1: Summary of RQD Data by Geotechnical Domain .................................................... 5-3 
Table 5.3.1: Primary Hoek-Brown Parameters Stochastic Input ...................................................... 5-5 
Table 5.3.2: Secondary Hoek-Brown Parameters Stochastic Input .................................................. 5-6 

List of Figures
Figure 1-1: Site Location Map .......................................................................................................... 1-2 
Figure 3-1: Location of Geotechnical Coreholes .............................................................................. 3-4 
Figure 5-1: Contour Plots of Oriented Core Discontinuities ............................................................ 5-7 
Figure 5-2: Shear Strength/Normal Stress Envelope: Intrusives ...................................................... 5-8 
Figure 5-3: Shear Strength/Normal Stress Envelope: Hornfels ........................................................ 5-9 
Figure 6-1: Explanation of Pit Slope Terminology ........................................................................... 6-5 
Figure 6-2: Location of Slope Stability Profiles ............................................................................... 6-6 

List of Appendices
Appendix A – Geotechnical Field Data
Appendix A-1: Geotechnical Core Logging Data
Appendix A-2: Discontinuity Orientation Data
Appendix B – Laboratory Test Data
Appendix B-1: Uniaxial Compressive Strength Test Results
Appendix B-2: Triaxial Compressive Strength Test Results
Appendix B-3: Direct Shear Test Results

SRK Consulting (US), Inc. June 2009
179702_Kitsault_PFS_Geotechnical_Pit_Slope_Design _Report_FINAL_03JUN2009.docx
Avanti Mining Inc. iii
Kitsault Molybdenum Project Pre-feasibility Geotechnical Pit Slope Design
Appendix C – Data Analysis
Appendix C-1: Geotechnical Core Logs
Appendix D – Slope Stability Output Files
Appendix D-1: Limit Equilibrium Analyses
Appendix D-2: Finite Element Analyses
SRK Consulting (US), Inc. June 2009
179702_Kitsault_PFS_Geotechnical_Pit_Slope_Design _Report_FINAL_03JUN2009.docx
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Kitsault Molybdenum Project Pre-feasibility Geotechnical Pit Slope Design
1 Introduction and Background
SRK Consulting (US), Inc. (SRK) has prepared this geotechnical pit slope evaluation of the
Avanti Mining Inc. (Avanti), Kitsault project open pit. As commissioned, the work reported
herein is performed at a pre-feasibility design level. The Kitsault property is located in
northwestern British Columbia, Canada (Figure 1-1). The preliminary assessment (SRK, 2008)
ultimate pit and geologic surfaces provided by Avanti were used as the basis for the evaluation.
1.1 Objectives
The primary objectives of this evaluation were to evaluate rock mass conditions in the area of the
anticipated Kitsault pit and to consequentially recommend pit slope design criteria, including
interramp slope and bench configuration, to be used for further mine planning and pit design.
1.2 Scope of Work and Terms of Reference
This Scope of Work consisted of five primary tasks:
• Geotechnical core logging and discontinuity orientation;
• Laboratory strength testing and geologic material characterization;
• Development of a geotechnical model to provide a basis for slope stability analyses;
• Performance of slope stability analyses; and,
• Preparation of a final report to include pre-feasibility pit slope design recommendations
for interramp slope angles and bench configurations.
SRK Consulting (US), Inc. June 2009
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Avanti Mining Inc. 2-1
Kitsault Molybdenum Project Pre-feasibility Geotechnical Pit Slope Design
2 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.
2.1 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 is within the Lime Creek Intrusive Complex, hosted by the sedimentary
units of Bowser Lake Group. The intrusive 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, occuring 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 ore body.
2.2 Major Geologic Structures
Major geologic structures are those features, such as faults, shear zones, and contacts that have
dimensions on the same order of magnitude as the proposed pit. 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 effect pit
stability.
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Kitsault Molybdenum Project Pre-feasibility Geotechnical Pit Slope Design
3 Geotechnical 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 as well as largely
subjective observations of existing pit wall conditions.
3.1 Geotechnical Core Logging
Logging and discontinuity orientation of the core recovered from six drillholes were conducted
for this investigation. Five of the holes, 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 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, an additional hole (K-08-06) was
drilled specifically to examine rock expected to comprise that wall segment. Geotechnical
logging of the six holes was conducted between September 18, and October 17, 2008.
The geotechnical core logging program was intended to maximize the collection of slope design
relevant geotechinical information during the resource drilling program, thereby reducing the
amount of further geotechnical drilling necessary for future pit slope design. Information such as
geologic contacts, profiles of rock strength and characterization of discontinuities was recorded
during the program. Details of the orientation and geotechnical logging programs follow.
Corehole inclinations of approximately 60 degrees from the horizontal were selected since they
were judged to be more likely to intersect geologic structures such as joints and fracture systems
which, if present, will influence slope stability than would vertical coreholes. Depth to
groundwater could not be determined at the time of hole advancement due to 24 hour per day
drilling schedule, with its resulting continuous fluid injection and circulation.
Collar locations and the drillhole azimuths of the six geotechnical holes are summarized in Table
3.1.1 and presented on Figure 3-1, while hole inclinations are summarized in Table 3.1.
Geotechnical corehole logs are presented in Appendix A.
Table 3.1.1: Summary of Drillholes Oriented and Logged for Geotechnical Data
Collar Location (m) Casing Total
Azimuth Inclination
Hole ID Length Length
Northing Easting Elevation (deg) (deg)
(m) (m)
K-08-04 6141730.0 473100.3 560.2 185 -58 2.7 300.5
K-08-06 6141850.0 473000.0 579.0 275 -60 3.1 401.4
K-08-09 6141934.7 473743.9 672.5 277 -53 9.1 433.4
K-08-12 6141980.0 473300.0 594.2 002 -43 6.1 315.8
K-08-14 6141850.0 473570.0 594.2 089 -43 3.5 349.6
K-08-16 6141600.0 473580.0 593.6 086 -46 4.6 286.8
3.2 Core Drilling Method
The coreholes were drilled by Driftwood Diamond Drilling, Ltd., from Smithers, British
Columbia, using a skid mounted drill rig with 10 feet, approximately 3 meter, long HQ and NQ
standard sampling barrels. All coreholes were initiated with HQ diameter equipment and
SRK Consulting (US), Inc. June 2009
179702_Kitsault_PFS_Geotechnical_Pit_Slope_Design _Report_FINAL_03JUN2009.docx