2013-04-10_PERMIT FILE - C1981019A (10)

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RULE 2 PERMITS 2.04.6 Geology Description The coal to be mined in the Collom permit expansion area is located in the northern extent of the Danforth Hills coal field of the Uinta Region. The Danforth Hills coal field comprises the coal deposits on the northeast flank of the Piceance Creek basin and is bordered on the northeast by the Axial Basin Anticline. Map 7A presents a regional geologic map showing bedrock outcrops and structural features in the general area. The Cretaceous Williams Fork Formation contains the mineable coals in the Collom permit expansion area. The coal deposit is contained within approximately 77 seams or seam splits with up to 27 seams planned for mining. The general stratigraphy within the Collom permit expansion area is shown in Exhibit 6, Item 7 (Collom Area Geology Pre - Feasibility Report), Figure 3.1, and Exhibit 6, Item 8 (Addendum to the Pre - Feasibility Report). The stratigraphy is also represented on eight cross sections presented as Figures 2.04.6 -5A through 2.04.6 -5H. A key to the location of the geologic cross sections are shown on Map l OB. Coal seams Y25 and X34 will be mined in the relatively shallow Little Collom X pit. Coal seams Y25 through Gab will be mined in the Collom Lite pit. The thicknesses of the seams vary in the Collom permit expansion area with seam thickness of 5 feet to 11 feet common. The coal to be mined has a high BTU value of 10,000 to 11,000 BTU per pound, low sulfur, and low ash content. There exists a market for this coal, in part because of its ideal qualities. The analyses of the coal seams to be mined are considered confidential and are provided in the original permit application and will be provided to the Colorado Division of Reclamation, Mining, and Safety (CDRMS) under separate cover. Stratigraphy The Collom permit expansion area is underlain by as much as 13,500 feet of sedimentary rock consisting of approximately 4,500 feet of Paleozoic quartzite, limestone, shale, sandstone, and gypsum; and 9,000 feet of Mesozoic limestone, shale, mudstone, sandstone, and conglomerate (Hallgarth, 1959). The coal seams mined at the Colowyo operation are of Upper Cretaceous Age. The generalized geological setting is shown on Map 7A. The stratigraphic positions of the coals mined by Colowyo are illustrated in Figures 2.04.6 -5A through 2.04.6 -5H. The surficial geologic formations within the area are the Upper Cretaceous Mancos Shale, which is overlain by the upper Cretaceous Mesaverde Group. The Mesaverde Group is comprised of the Iles Formation and Williams Fork Formation. Details of each formation are described below. Mancos Shale — This thick marine formation is the oldest exposed unit in the area and is located north of the active Colowyo mine area in the Axial Basin. The formation is approximately 5,000 feet thick, consisting predominantly of a calcareous lower phase and an upper phase that contains a few thin bedded, tan, silty fine- grained sandstone layers within massive sandy shale. The deposition of the Mancos Shale occurred in quiet offshore conditions when the western interior of the North American continent was inundated by an epeiric seaway during the late Cretaceous. The Mancos Shale is generally more than 3,000 feet below ground surface in the Collom permit expansion area and is about 1,700 feet below the base of projected mining. Mesaverde Group - The Mesaverde Group generally consists of interbedded sandstones, mudstoncs and siltstones of varying thicknesses. These beds were deposited in predo ninantly a near -shore terrestrial Collom — Rule 2, Page 27 Revision Date: 9/28/11 Revision No.: PR -03