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i, <br />' 1.0 INTRODUCTION <br />Battle Mountain Gold Company (BMG) is in the process of developing the San Luis Project in <br />~' Colorado. Steffen Robertson and Kirsten (SRK) were requested by BMG to investigate the stability <br />of the ultimate slope walls for the San Luis Open Pit and to recommend design angles. <br />i' The San Luis deposit is comprised of two pits, the West and East Ore Zone. Materials encountered <br />in the open pit are primarily conglomerates and gneisses at various stages of alteration. In <br />i ' addition, a major thrust fault (Green Clay) forms the contact between the altered material above <br />and the strong gneissic materials below. Zones of high alteration would significantly reduce the <br />wall stability and therefore require a flatter slope angle. The objective of the study was to <br />~, recommend ultimate slope angles for the final feasibility study and for mine design to bring the San <br />Luis Project into production. This required the identification of the following parameters: <br />- The potential for joint controlled instability within the unaltered gneisses (Biotite Gneiss) <br />- The strengths of weak rock mass zones formed by the highly altered Pink Gneiss and <br />' Santa Fe Conglomerates that occur above the Green Clay Fault. <br />- The influence of the Green Clay on the stability of the overlying material. <br />2.0 PROJECT AND STUDY DESCRIPTION <br />' 2.1 Location and Topography <br />' The San Luis Project is located in Costilla County, Southern Colorado, approximately seven miles <br />northeast of the town of San Luis, Figure 1. The deposit occurs along the Rito Seca River in the <br />ioothills of the Sangre de Cristo mountian range. Topography ranges from gentle to moderate <br />sloping terrain at elevations ranging between 8,200 feet to 9,000 feet above sea level. <br />' 2.2 Project Description <br />The San Luis Project Is a heap leach open pit gold operation consisting of two pits as shown in <br />', Figure 2. The East Ore Zone will be mined first Approximately 5000 tpd of ore are expected to be <br />mined over a seven to ten year mine life. The West Pit will be approximately 2400 fee? x 2500 feet. <br />The pit depth will vary from a maximum of 345 feet for the north wall to a minimum depth of 180 <br />' feet for the south wall. The East Pit is approximately 1200 feet x 700 feet x 210 feet in oepth. <br />:~ Present exposures of bedrock on the property is limfted to road cuts and metallurgical pits. The <br />only outcrop is located in the East Pit where old mine workings and a road cut have exposed a <br />slope that is approximately 1000 feet long x 80 feet in vertical height. The material is comprised of <br />' unaltered 8iotfte Gneiss <br /> <br /> <br />