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Twentymile Coal, LLC (TC) <br />Narrative <br />Lease by Modification Application Wolf Creek Reserve — April 2014 <br />Creek, and Fish Creek anticlines, are the most prominent structural features which define the <br />Twentymile Park Basin. They cause the strata to dip in excess of 15 percent near the periphery <br />of the basin and form the outer boundaries of TC's Foidel Creek Mine. The Wolf Creek <br />Reserve lease modification tract is located on the southeast flank of the Twentymile Park <br />Syncline. <br />Detailed site-specific lithology of the area is shown on Figures 1 and 2. The coal to be mined <br />by the planned underground operations is in the Wolf Creek Seam. The Wolf Creek Seam <br />lies within a sequence of sedimentary rocks characterized by shales, claystones, mudstones, <br />siltstones, sandstones and minor coal stringers in the Upper Cretaceous MesaVerde Group. <br />This sedimentary sequence is about 75 million years old, and is composed of terrigenous <br />clastics deposited in offshore, shallow, and near -marine environments at the western edge of <br />an epeiric seaway. This seaway was located in interior western North America during the <br />later part of the Early Cretaceous and most of Late Cretaceous time. <br />The sandstones were formed in beach environments, and are generally very fine to fine- <br />grained, of low porosity, and are well -cemented. The very thick shale formations, such as <br />the 590 -foot shale member below the Twentymile Sandstone, are offshore marine deposits <br />and are characterized by their lateral continuity, fine-grained texture, and extremely low <br />horizontal and vertical permeability. The youngest rocks exposed in the planned area belong <br />to the massive, marine -deposited Lewis Shale. Near the base of the Lewis Shale is the Fish <br />Creek Seam, which is only approximately four feet thick. Approximately 165 feet of <br />interbedded shale, siltstone, and fine-grained sandstone separate the Fish Creek Seam from <br />the underlying massive Twentymile Sandstone. <br />The Twentymile Sandstone is a key mapping unit and can be identified and traced throughout <br />most of the Yampa Coal Field. The rock immediately below the Twentymile Sandstone is <br />another massive marine shale member, a "tongue" of the Lewis Shale which averages <br />approximately 590 feet in thickness. The Fish Creek Seam, the Twentymile Sandstone, and <br />the thick marine shale make up the majority of the Williams Fork Formation. The lower <br />portion of the Williams Fork Formation consists of the coal -bearing sequence. This sequence <br />is the "Middle Coal Group" of the MesaVerde Group. The "Middle Coal Group" contains <br />the Lennox Seam, Wadge Seam, and the Wolf Creek Seams. <br />The Lennox Seam is located 10 to 15 feet below the marine shale member and ranges in <br />thickness from zero to four feet. The low seam height, poor quality, and poor lateral <br />continuity of the seam render it impractical to mine. In the proposed mine area, the strata <br />below the Lennox Seam consist mainly of stacked deltaic sequences. Four distinct sequences <br />have been mapped throughout the mine area. They are characterized by a coarsening of <br />mean grain size upwards within each sequence. The lithology consists of mudstones and <br />claystones, siltstones, and very fine-grained interbedded sandstones. The combined <br />thickness of these sequences range from sixty to ninety feet. These rocks directly overlie the <br />Wadge Seam, which has previously been mined within the mine plan area. The Wadge Seam <br />thickness averages 8.0 to 11.0 feet in this area, and overburden depths to the Wadge seam <br />WCR BLM Lease App Narrative 0414.docx Page 5 <br />