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<br />MLESIoaeDesian <br />Surface mining has been conducted at the Cresson Project for the last 15 years to depths in excess of <br />1,500 feet and at slope angles up to 60° without any observable slope failure other than occasional <br />bench-scale raveling. <br />In the slope design and development of these mines, a great deal of data has been obtained and extensive <br />experience has been gained with respect to the strength parameters, geologic setting, and the- <br />geotechnical behavior of the rock types that are found in the District. This information and experience is <br />used in this design report. <br />3. SLOPE DESIGN <br />3.1 Stability Zones <br />Slope stability in the District is controlled by material type, structure, and water occurrence. <br />Five stability zones have been identified in the District: <br />• Dry Volcanic Rock : ..........................Volcanic rock of the Cripple Creek diatreme <br />• Drv Granitic Rock :............................Granitic rock within the Cripple Creek diatreme. <br />• <br />• Adverse Granitic Rock : .............. <br />• Drv Pipe Rock :............................ <br />...Granitic rock in Grassy Valley. <br />• Colluvium : ................................... <br />.Cresson, Globe Hill, and Ironclad Pipes. <br />Unconsolidated material in the District. <br />The locations of each of the rock zones are shown on Figure 2. <br />3.2 Dry Volcanic Rock <br />Dry Volcanic Rock in the Cripple Creek diatreme is strong, dry, and moderately fractured with <br />predominant vertical structure. Slope analysis (ABC, 19971) and experience has shown that this rock <br />will stand at any height at the maximum minable slope of 60°. <br />The slope design for this rock is presented in Table 1 and Figure 3. <br />3.3 Dry Granitic Rock <br />Dry Granitic Rock occurs on most of the periphery of the Cripple Creek diatreme, and in inliers of <br />granite, particularly Granite Island and Schist Island. Dry Granitic Rock is moderately strong, dry, and <br />moderately fractured with predominant vertical structure. Slope analysis (ABC, 2003a2) and limited <br />mining experience indicates that this rock will stand at 50°. <br />The slope design for this rock is presented in Table 1 and Figure 4. <br />• 1 A copy of this report is presented in Attachment 1. <br />z A copy of this report is presented in Attachment 3. <br />Report 1385E.20080411 2 <br />