2016-12-23_PERMIT FILE - C1982056A (8)

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which form the Twentymile Park basin. They cause the strata to dip in excess of 15 percent near the periphery of the basin and form the outer boundaries of the mine area. The coal measures are also disturbed by northwest striking normal faults. Detailed structure and Wadge Seam outcrop are shown on Map 6, Wadge Seam Structure. Additional structural information, as well as lithologic information for both the Wadge and Wolf Creek seams are shown on Maps 7, 8, 9, 9A, Figure IA Geologic Cross-Sections A-A', B-B', C-C', D-D', and E-E', and in Exhibit 53, Wolf Creek Geologic and Mine Plan Information. Overburden depths in the planned permit area range from "outcrop" near the portal area, to approximately 1,700 feet (Wadge Seam) and 1,850 feet (Wolf Creek Seam) in the central portion of the basin. This information is presented on Map 10, Wadge Seam Overburden, and in Exhibit 53. Stratigraphy&Physical Characteristics of the Coal Seam and Other Strata in the Area to be Mined Generalized stratigraphy of the area is shown on Figure 2, General Stratigraphic column. Detailed site-specific stratigraphy is shown on Map 6, Map 7, Geologic Cross-Sections A-A', Map 8, Geologic Cross-Sections B-B', Map 9, Geologic Cross-Sections C-C', Map 9A, Geologic Cross-Sections E-E', Figure IA, Geologic Cross- Sections D-D', and in Exhibit 53. It should be noted that the faults shown on the maps are of a regional character and are outside of the PR 99-05 mine plan area. Map 23, Mine Plan, presents the faults that have been encountered in the mine. The coal to be mined by the planned underground operations includes the Wadge and Wolf Creek Seams. Both seams occur within a sequence of sedimentary rocks characterized by shales, claystones, mudstones, siltstones, sandstones, and minor coal stringers in the Upper Cretaceous Mesaverde Group. This sedimentary sequence is about 75 million years old and is composed of terrigenous clastics deposited in offshore, shallow, and near-marine environments at the western edge of the epieric seaway. This seaway was located in interior western North America during the latter part of the Early Cretaceous, and most of the Late Cretaceous,time. The sandstones were formed in beach environments and are generally fine to fine-grained, of low porosity, and are well-cemented. The very thick shale formations, such as the 650-foot shale member below the Twentymile Sandstone, are offshore marine deposits and are characterized by their lateral continuity, extremely fine-grained nature, and extremely low horizontal and vertical permeability. The youngest rocks exposed in the planned mine area belong to the massive marine-deposited Lewis Shale Formation, which varies from zero to 700 feet in thickness. Near the base of the Lewis Shale is the Fish Creek Seam, approximately four feet thick. Approximately 200 feet of interbedded shale, siltstone, and fine-grained sandstone separate the Fish Creek Seam from the underlying massive Twentymile Sandstone. This interval is locally referred to as the Holderness Member. The Twentymile Sandstone is a key mapping unit and can be identified and traced throughout most of the Yampa Coal Field. The rock immediately below the Twentymile Sandstone is another massive marine shale member: a "tongue"of the Lewis Shale (Fig. 2). The thickness averages approximately 650 feet. The Fish Creek Seam, Holderness Member, the Twentymile Sandstone, and the thick marine shale member make up the majority of the upper Williams Fork Formation. The lower portion of the Williams Fork Formation consists of the coal-bearing sequence. This sequence is the "Middle Coal Group" of the Mesaverde Group. The "Middle Coal Group" contains the Lennox Seam, Wadge Seam,and the Wolf Creek Seams. The Lennox Seam is located 10 to 15 feet below the marine shale member, and ranges in thickness from zero to four feet. The low seam height, poor quality, and poor lateral continuity of the Lennox seam render it un-minable. In the proposed mine area, the strata below the Lennox Seam consists mainly of stacked deltaic sequences. Four distinct sequences have been mapped through the mine area. They are characterized by a coarsening of mean grain size upwards within each sequence. The lithologies consist of mudstones and claystones, siltstones, and very fine-grained interbedded sandstones. The combined thickness of these sequences range from sixty to ninety feet. These rocks directly overlie the Wadge Seam,which is the primary target of the planned underground operations. PR14-10 2.04-14 12/18/14