Laserfiche WebLink
<br />• Main CressonSlopeEvaluation AdrianBrown <br />7. INTRODUCTION <br />The Main Cresson Mine is located between Cripple Creek and Victor, Colorado. It is a surface gold <br />mine, which is currently designed to extend to a depth of approximately 700 feet below the highest point <br />of excavation. The mine is located in an historic mining district, which has been mined since the 1890s. <br />The Main Cresson Mine area is underlain by extensive underground workings from that prior mining <br />activity, and has been drained to local streams by a series of drainage tunnels which were installed for <br />this purpose during the prior mining activities. <br />The East Wall of the Main Cresson Mine was initially designed in 1994, using information obtained <br />from three geotechnical drill holes, material testing, and collection of information from a number of <br />mines developed in the area. Based on this study, an initial overall slope of 52° was selected, using a <br />triple bench approach (Call and Nicholas, 1994). <br />Since that time the mine has been developed, and at the current time (Spring, 1998) the maximum wall <br />height is approximately 350 feet, which is half the currently proposed maximum wall height. The current <br />mine development is presented in Plate 1. During the development of the mine, detailed geological, <br />structural, and mineralogical mapping of the exposed slopes and benches has been performed by the <br />Cresson Geological Division, resulting in an extensive and increasing database which provides <br />• information about the nature and condition of the slopes. In addition, information on the groundwater <br />conditions within the slope has been collected. Slope performance has been monitored by inspection, <br />supported by Electronic Distance Measurement (EDM) surveying of slope movement monitoring <br />stations. Finally blasting and excavation technology have been varied to provide information on impact <br />of different mining methods on slope stability. <br />Amendment 7 of the mine plan proposes an expansion of the Main Cresson Mine, which has lead to a re- <br />evaluation of the stability of the mine slopes. Using the information collected before and during the <br />operation of the current mine, the proposed design for the principal slope (the East Wall) provides an <br />overall slope of 60°, with triple or quadruple benches of 25 feet height. The slopes of the other walls of <br />the mine are determined in general by ore considerations, rather than geotechnical considerations; their <br />slopes have not been re-designed in this evaluation. <br />This report presents a review of the existing information which relates to the slope stability and mine <br />slope performance, and presents the analysis of that information which is the basis of the proposed <br />design of the slopes in the mine. <br />U <br />1385D.98067 2 ~ <br />