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1 <br />• Main CressonSlopeEvaluation AdrianBrown <br />2. GEOLOGY <br />The overall geology of the mine area is presented in Plate 2. For the most part, the materials in the mine <br />vicinity are volcanics: porphyry, breccia, dikes, and pipes. <br />1. Porphryitic Phonolite. This material is frequently columnar, and the intact rock is durable and strong <br />2. Cripple Creek Breccia. This breccia comprises a volcanic matrix, in which are fragments of <br />volcanics. The intact material has similar strength to the porphryitic phonoiite. <br />3. Dikes. The Cresson Mine area is interlaced with intruded phonoiite and lamprophyre dikes. While <br />these dikes comprise a relatively small proportion of the rockmass, particularly the lamprophyre <br />dikes are subject to weathering, which can result in the dikes forming low strength zones in the rock. <br />Most of the dikes are vertical. <br />4. Cresson Pipe. In addition to the above main types, in the middle of the mine area there is a breccia <br />pipe known as the Cresson Pipe. The material within the pipe is weak compared to the other rock <br />types. <br />From a geomechanical point of view, the two principal materials which occur in the Main Cresson Mine <br />are not significantly different. The phonoiite tends to be more columnar, with the breccia being more <br />• vertically jointed. Neither of these two materials appear to host many intermediate angle (30° to 60° dip) <br />joints or other features. All of the rocks in the mine have been altered by potassic metasomatism. <br />However, alteration to clay or other geotechnically weak materials is limited within the mine, with a <br />very limited amount of clayey material evident in the mine walls, or in corehoies drilled in the mine <br />walls. <br />• <br />1385D.980612 2 <br />