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The New Horizon Mine is located near the axis of the Nucla Syncline (San Miguel Syncline), a <br />shallow, broad synclinal fold running northwesterly for a length of 65 miles. No evidence of <br />faulting was observed in drill holes at New Horizon Mine 2 area. The Nucla Syncline is 10 to 15 <br />miles southwest of the major regional geologic feature of the area, the Uncompahgre uplift. The <br />region lies in the Dolores River basin. The mine is located between two and three miles <br />northeast of the San Miguel River. Gently rolling terrain traverses the area and the mine <br />occupies a predominantly southwestern exposure. <br />The mine is located in the Nucla-Naturita coal field. The coal is found in late Cretaceous <br />sediments. The youngest Cretaceous rocks in the area are Mancos shale, a dark gray marine <br />shale, comprising the isolated hilltops south of the town of Nucla. The Mancos shale overlies the <br />Dakota sandstone. Two hundred feet of Dakota sandstone outcrops extensively along the axis of <br />the Nucla syncline. This formation consists of a yellowish-gray, fissile sandstone and <br />conglomeratic sandstone interbedded xxith dark b ay shale and coal There are t:x'o Coal seams <br />within 100 feet of the base of the Dakota. The lower Cretaceous unit in the area, the Burro <br />Canyon Formation, is separated from the Dakota by an unconformity. The Burro Canyon is <br />comprised of white, gray and light brown sandstones and conglomerates interbedded with green <br />and purplish shales, siltstones, mudstones and thin beds of limestone. This formation has a <br />maximum thickness of 200 feet and outcrops on rims of canyons west and northwest of the mine. <br />The Burro Canyon formation is difficult to differentiate from the Dakota in this area and is <br />commonly considered hydrogeologically similar. The Jurassic Morrison Formation below is <br />composed of 250 feet to 600 feet of varicolored siltstones and mudstones with beds of limestone <br />and sandstone. <br />The New Horizon Mine 1 produced coal from both the upper and lower Dakota coal seams. The <br />upper Dakota coal seam ranged in thickness from 1.6 feet to 3.3 feet and was separated from the <br />lower Dakota seam by 7 to 11 feet of interbedded sandstone and shale. The lower Dakota seam <br />varies in thickness from 5.9 feet to 7.9 feet. The base of the lower Dakota coal is 83 feet above <br />the top of the Burro Canyon Formation. The coal dips V to 2° southwest and strikes N 25°W to <br />N 45° W. <br />The New Horizon Mine 2 primarily produces coal from the Lower Dakota coal seam and utilizes <br />the Upper Dakota coal seam when the seam is thick enough and of sufficient quality. The lower <br />Dakota coal seam at New Horizon Mine 2 ranges in thickness from 4.2 feet to 6.9 feet and is 99 <br />feet above the top of the Burro Canyon Formation. The coal dips 4.5° SW along a strike of N <br />45° W. <br />C. Surface Water <br />The San Miguel River has its source in the San Juan Mountains. These mountains are primarily <br />composed of Tertiary volcanic rocks. Ioms et. al. (1965a) has shown these waters to be of a <br />calcium bicarbonate-sulfate type during high flow periods. These waters contain less <br />bicarbonate during low flows while the calcium and sulfate concentrations increase due to less <br />dilution from snowmelt runoff. The San Miguel River traverses the interior portions of a basin <br />that is chiefly underlain by Dakota Sandstones, the Morrison Formation and Mancos Shales. The <br />Morrison Formation and Mancos Shale have the greatest potential for influencing the river water <br />10