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• WHEXSIopeEvaluation AdrianBrown <br />planes aze not extensive over large azeas (which seems unlikely), the slope angle could be increased to <br />60 degrees. <br />6.4.2 Southeast <br />The southeast wall of the mine has been investigated with three drill holes: GT03-04, GT03-O5, and (in <br />the Wild Horse Mine area) WHC02-32. The findings can be summarized as follows: <br />1. Mine Wall Material. Altered gneiss, schist, and granite. Weathering is limited, with the oxidized <br />zone extending down to about 400 feet, below the proposed depth of the mine in this azea. Intact <br />rock strength is good, averaging approximately 11,000 psi. The southern edge of the mine is <br />contiguous with the Wild Horse Mine area, and will expose both volcanic and grantic rock in the <br />wall. <br />2. Rock Quality. Good, reducing with depth and to the south due to reducing intact rock strength <br />and increasing fracture frequency. Some fractures and faults aze infilled with clayey materials, <br />and some display slickensides. <br />3. Structure. Generally adverse. Foliation of gneiss and schist rocks in the slope dips into the mine <br />at angles ranging from 30 to 70 degrees. Some foliation planes aze not intact. Fracturing in the <br />• rock also generally dips adversely into the mine, although it is not expected that these features are <br />extensive. Extensive fractures and faults are expected to be sub-vertical, and not a stability issue. <br />4. Water. Water has not been observed in drill holes. Based on this finding, water pressure will be <br />less than 10% of hydrostatic. Any water in the mine is expected to drain, and water pressure is <br />not expected to affect slope performance. <br />Based on the evaluation presented in the Attachments for the holes in this azea, the recommended slope <br />angle for this portion of the wall is 50 degrees, controlled by the potential for large-scale sliding (wedge) <br />failure along foliation or in-dipping extensive fracture planes. If it transpires that the foliation planes are <br />not extensive over large areas (which seems unlikely), the slope angle could be increased to 60 degrees. <br />6.4.3 West <br />The west wall of the mine has been investigated (to date) with three drill holes: GT03-06, GR-443, and <br />GT03-08. The findings can be summarized as follows: <br />1. Mine Wall Material. Tertiary volcanic phonolite and breccia. Weathering is limited. Intact rock <br />strength is excellent, averaging approximately 13,200 psi. <br />2. Rock Quality. Good. Fracturing is modest, with very few fractures showing evidence of <br />movement, or of clayey coating or infill. <br />3. Structure. Generally neutral. There is some evidence of a general jointset that dips to the east or <br />northeast at between 25° and 65°, which may create some opportunity for local failure. However, <br />there is little evidence from drilling that these joints are sufficiently extensive to impact overall <br />• slope performance. While it is expected that there will be major sub-vertical faults and joints, the <br />drilling has provided little evidence that these features exist in this portion of the district. <br />Report 1385L.200309017 15 <br />