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Technical Memorandum ®■ <br /> Cripple Creek&Victor Gold Mine ■ <br /> SGVLF Stability Evaluation—Nonagglomerated Tailings <br /> NewFields Job No.475.0106.009 <br /> 1June 2017 <br /> Based on laboratory strength testing, tailings have an effective friction angle of 36.4 degrees <br /> (Table 3). Results from previous slope stability analyses presented that a minimum friction <br /> angle of 38 degrees is required to maintain stability for the most critical section. <br /> Qualitatively it does not appear that concentrated pockets, or seams, of tailings within the VLF <br /> will have an impact on global stability. Nonetheless, we have evaluated the influence of <br /> concentrated zones of tailings with a modified stability evaluation of Section B, which required <br /> the greatest minimum friction angle of ore/tailings under pseudostatic conditions. For each lift, <br /> a 2-foot thick zone of pure tailings was modeled at a setback of 25 feet from the final VLF slope. <br /> Additional 1 to 2-foot thick seams were included further from the slope face. The minimum <br /> required friction angle of 38 degrees, as shown in Table 3, was used for the ore/tailings mixture <br /> and the friction angle of the pure tailings seams were conservatively reduced by 20 percent to <br /> 29 degrees, to model softening caused by pseudostatic conditions. The model was also <br /> evaluated under static conditions with the same parameters. The stability models are shown in <br /> Attachment D. <br /> Results of the evaluation indicate that seams of tailings will not affect the global stability of the <br /> heap leach pad. <br /> 4.0 DISCUSSION <br /> Based on the recent laboratory testing and subsequent stability evaluation for the SGVLF, we <br /> have the following comments: <br /> Results from the shear strength tests do not indicate that the introduction of small amounts <br /> of nonagglomerated tailings (10% maximum) into the ore significantly alters the mobilized <br /> shear strength. Laboratory strength tests results indicate a friction angle between 38.2 and <br /> 40.2 degrees for the ore/tailings mixture, which is greater than the 38-degree friction angle <br /> needed to achieve the minimum required factors of safety. <br /> In the unlikely case that significant seams of pure tailings develop within the heap due to <br /> poor mixing of the tailings and ore during end dumping, the global stability of the heap <br /> leach pad will remain unaffected. <br /> The stability evaluation indicates that placement of ore mixed with nonagglomerated <br /> tailings does not have an adverse effect on the stability of the SGVLF. The SGVLF will <br /> remain stable provided the ore and tailings are mixed and placed in a similar manner as <br /> currently utilized by CC&V operations. Existing placement criteria requires that tailings not <br /> be placed within 25 feet of the crest of any ore lift, to minimize the potential for localized <br /> ore sloughing by blending tailings close to the ore face, and those recommendations are still <br /> valid and warranted. <br /> Page 7 <br />