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• WHEXSIopeEvaluation AdrianBrown <br />1. INTRODUCTION <br />AngloGold, through its mining subsidiary Cripple Creek and Victor Mining (CC&V) is proposing to <br />develop the Wild Horse/Wild Horse Extension Mine (WHEX), located generally north of Cripple Creek <br />and Victor, Colorado (Plate 1). It is a surface gold mine. The mine is located in an historic mining <br />district, which has been mined since the 1890s, and is underlain by extensive underground workings that <br />have been drained to local streams by a series of drainage tunnels that were installed for this purpose. <br />The WHEX Mine is located on the contact between Tertiary Cripple Creek Brescia to the west and <br />Precambrian Pikes Peak Granite and Schist to the east. The mineralization is generally associated with <br />the contact. While CC&V has had extensive experience in designing slopes for and mining the volcanic <br />rock suite that comprises the Cripple Creek Diatreme, there is little design or mining experience in the <br />granitic rockmass that surrounds and in places remains as inliers to the diatreme. <br />The East Wall of the Cresson Mine was initially designed in 1994, using information obtained from <br />three geotechnical drill holes, material testing, and collection of information from a number of mines <br />developed in the area. Based on this study, an initial overall slope of 52° was selected, using a triple <br />bench approach (Call and Nicholas, 1994). <br />Since that time the mine has expanded to a depth of approximately 1,000 feet, and slopes up to 60° have <br />• been mined and have remained highly stable. Detailed geological evaluation, structural, and <br />mineralogical mapping, slope performance monitoring, and blasting technology evaluation have <br />provided extensive information on the geotechnics of mining in the volcanic deposit. <br />The WHEX Project has, for the first time, required evaluation of the stability of mine slopes in the <br />granitic materials at the periphery of the diatreme. To provide information for that re-evaluation, an <br />extensive drilling program involving twelve core holes (to date) has been performed. This program has <br />focused on the granitic rock materials that will form approximately half of the WHEX mine slope, and a <br />significant portion of the waste rock produced from this project. The materials obtained in this program <br />have been tested for strength, logged, and most of the holes have been visually logged using downhole <br />video technology. <br />This report presents a preliminary review of the available geotechnical information for the WHEX <br />project. Using this information a segmented slope design has been performed, using the Hoek and <br />Brown slope design method (Hoek and Brown, 1997; Hoek, 2001), together with wedge failure analysis. <br />The report presents the analysis and the proposed design of the slopes in the WHEX Mine. <br />• <br />Report 1385L.200309017 2 <br />