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t1AR-17-66 15:12 From:CCBV GOLD ~ 17196693254 • T-317 P. D7/ID Joh-647 <br />Proposed slope design <br />CC&V's examination of the highwalls9 [hey have been exposed have provided the basis to <br />steepen the highwall. In particular, che'~imonstration of excellent fracture orientation, good <br />rock quality, and the absence of ground-water pressure in the highwalls allow a steeper <br />inte;bench and overall highwall angle (catch bench-[o-catch bench). 'the revised highwall design <br />incorporates the following: <br />1. Bench height. It has been found to be more efficient to utilize 25-foot high benches, <br />based on equipment selection as well as the nature of the ore with depth. This increase <br />in bench height results in three (3) mine benches between catch benches, which is a <br />spacing between cauh benches of 75 feet, or five feet less than the original design. <br />2: Interbench angle. The interbench angle has been steepened to about 79°. This slope <br />has been found to best utilize the natural joint inclination for the north-south aligned <br />highwalls. <br />3. Interbench offset. The 2-foot offset has been eliminated because it is not needed for <br />blas[ing or for stability. <br />4. Catch benches. The catch benches now range from 28 to 80 feet in width, depending <br />on the orientation of the bench relative [o fractures and joints as well as the overall <br />stability of the rock mass. These catch bench widths are, then, the same as the total <br />offset. <br />5. Overall slopes. The resulting overall slopes range from 40 to 60 degrees, with the <br />walls being presently cut at the lower angle, because they are not the final push-back <br />~ highwalls. However, several azeas well within the Mine boundary have been mined at <br />the 60° slope as a test of the stability of this configuration. These areas are standing <br />well. <br />Evaluation of Stability <br />The stability of the maximum overall interramp slope (60°) has been evaluated using [he most <br />conservative method available: circular slope failurc. Four different assumptions about the <br />amount of intact rock within the curved failure pathway: <br />1. No intact rock in path of circular failure. <br />2. 1 percent intact rock in path. <br />3. 10 percen[ intact rock in path. <br />4. 100 percent intac[ rock in path. <br />6 <br />