2012-06-20_PERMIT FILE - C2010089A (10)

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split to the north. This is due to a parting in the lower portion of the seam. The LDx Seam is characterized by two thin (0.2 to 0.3 ft.) tonstiens (altered volcanic ash) located in the upper half of the seam. Map 2.04.6 -6 is an isopach map of the LDx Seam in the NHN permit area. The UD1 Seam lies above the LDx and is separated from it by 7 to 12 feet of interburden. The interburden consists of carbonaceous shale and lenticular (channel) sandstone that is very hard in areas where it is thickest. The UD1 Seam varies in thickness from over two feet to a feather edge within the permit area. As the seam thins to the north, it facies to a dark brown to black carbonaceous shale. The UD1 has higher ash and sulfur than does the LDx Seam but will be recovered to a minimum thickness of about 0.75 ft. Map 2.04.6 -7 is an isopach map of the UD1 Seam thickness and shows the thinning to the north as does Cross Section A -A' (Map 2.04.6 -4). The predominant lithologies in overburden material within the NHN permit area are shales, siltstones, and sandstones of the Upper Member of the Dakota Formation. The sandstones are generally fine to medium grained, of low porosity, well cemented, lenticular, discordant, and crossbedded. Both cross sections A -A' and B -B' show a persistent sandstone located from less than 20 ft to near 30 ft. above the top of the LDx Seam. Two thin, white clay (bentonitic) tonstien beds (altered volcanic ash) exists in the permit area where the overburden is thickest. These two beds of clays range from 0.5 to 2.5 feet in thickness and are found approximately 55 to 65 feet above the top of the LDx coal seam as shown on Cross Section A -A' (Map 2.04.6 -4). A major component of the overburden is the zone of weathered bedrock. While weathering does not affect the ltihology or stratigraphy of the overburden, it affects both the physical character and mineralogy of the overburden. The "weathered zone" (oxidized zone) in the NHN permit area extends from the base of the soil profile to depths of more than 30 ft. The most obvious character differences between weathered bedrock and unweathered bedrock are color and rock strength. Weathered sandstones, siltstone, and shales vary in color from light brown or tan to rusty brown or orange. Where as, the parent strata (unweathered bedrock) are typically shades of gray, dark brown or black. Only the color of relatively pure white sandstone appears unaffected by weathering in the NHN permit area. The strength of the weathered strata is greatly reduced by open joints and fractures and open bedding planes. Very tight siltstones with clay or carbonaceous laminations are reduced by weathering to plate like shards that can be plucked from outcrop or high -wall by hand because of clay hydration and oxidation of carbonaceous materials. Calcareous sandstones are more porous and also separate easily along bedding planes. Weathered argillaceous shale and mudstone are reduced to the strength of stiff bread dough. Both Cross Sections, A -A' and B -B', (Maps 2.04.6 -5 and 2.04.6 -6) demonstrate the depth of weathering at NHN. Weathered strata is easily identifiable from drill hole cuttings in the NHN permit area. WFC has taken advantage of the reduction in strength that the effects of weathering afford. Weathered rock at the New Horizon Mine is mined separately, (from a single overburden bench), from unweathered bedrock primarily because it is less expensive to do so. The weathered rock is mined and loaded into trucks by the hydraulic excavator without the expense of blasting. The weathered rock is referred to as the "free dig zone" and is hauled around the ends of the pit where it is placed on top of the unweathered bedrock that has been blast casted and dozer pushed across the pit from the high -wall to the backfill. This results in minimal mixing of the weathered Section 2.04.6 Page 5 April 2011