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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
<br />the basin and form the outer boundaries of the mine area. The coal measures are also disturbed by northwest
<br />striking normal faults. Detailed structure and Wadge Seam outcrop are shown on Map 6, Wadge Seam Structure.
<br />Additional structural information, as well as lithologic information for both the Wadge and Wolf Creek seams are
<br />shown on Maps 7, 8, 9, 9A; Figure I Geologic Cross - Sections A -A', B -B', C -C', D -D', and E -E'; and in Exhibit
<br />35 (Wolf Creek Geologic and Mine Plan Information).
<br />Overburden depths above the Wadge Seam in the Mine Permit Area range from "outcrop" near the portal area, to
<br />approximately 1,700 feet in the central portion of the basin. This information is presented on Map 10, Wadge Seam
<br />Overburden and in Exhibit 53.
<br />Stratiffraahv & Phvsical Characteristics of the Coal Seam and Other Strata in the Area to be Mined
<br />Generalized stratigraphy of the area is shown on Figure 2, General Stratigraphic column. Detailed site - specific
<br />stratigraphy is shown on Map 6, Map 7, Geologic Cross - Sections A -A', Map 8, Geologic Cross - Sections B -B',
<br />Map 9, Geologic Cross - Sections C -C', Map 9A, Geologic Cross - Sections E -E', and Figure IA, Geologic Cross -
<br />Sections D -D' respectively. It should be noted that the faults shown on the maps are of a regional character and are
<br />outside of the PR 99 -05 mine plan area. Map 23, Mine Plan, presents the faults that have been encountered in the
<br />mine. The coal to be mined by the planned underground operations includes the Wadge and Wolf Creek Seams.
<br />Both seams occur within a sequence of sedimentary rocks characterized by shales, claystones, mudstones,
<br />siltstones, sandstones, and minor coal stringers in the Upper Cretaceous Mesaverde Group. This sedimentary
<br />sequence is about 75 million years old and is composed of terrigenous clastics deposited in offshore, shallow, and
<br />near - marine environments at the western edge of the epieric seaway. This seaway was located in interior western
<br />North America during the latter part of the Early Cretaceous, and most of the Late Cretaceous, time.
<br />The sandstones were formed in beach environments and are generally fine to fine - grained, of low porosity, and are
<br />well- cemented. The very thick shale formations, such as the 650 -foot shale member below the Twentymile
<br />Sandstone, are offshore marine deposits and are characterized by their lateral continuity, extremely fine- grained
<br />nature, and extremely low horizontal and vertical permeability.
<br />The youngest rocks exposed in the planned mine area belong to the massive marine- deposited Lewis Shale
<br />Formation, which varies from zero to 700 feet in thickness. Near the base of the Lewis Shale is the Fish Creek
<br />Seam, approximately four feet thick. Approximately 200 feet of interbedded shale, siltstone, and fine - grained
<br />sandstone separate the Fish Creek Seam from the underlying massive Twentymile Sandstone. This interval is
<br />locally referred to as the Holderness Member.
<br />The Twentymile Sandstone is a key mapping unit and can be identified and traced throughout most of the Yampa
<br />Coal Field. The rock immediately below the Twentymile Sandstone is another massive marine shale member: a
<br />"tongue" of the Lewis Shale (Fig. 2). The thickness averages approximately 650 feet.
<br />The Fish Creek Seam, Holderness Member, the Twentymile Sandstone, and the thick marine shale member make
<br />up the majority of the Williams Fork Formation. The lower portion of the Williams Fork Formation consists of the
<br />coal- bearing sequence. This sequence is the "Middle Coal Group" of the Mesaverde Group. The "Middle Coal
<br />Group" contains 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 thickness from zero to four
<br />feet. The low seam height, poor quality, and poor lateral continuity of the Lennox seam render it unminable. In the
<br />proposed mine area, the strata below the Lennox Seam consists mainly of stacked deltaic sequences. Four distinct
<br />sequences have been mapped through the mine area. They are characterized by a coarsening of mean grain size
<br />upwards within each sequence. The lithologies consist of mudstones and claystones, siltstones, and very fine- grained
<br />interbedded sandstones. The combined thickness of these sequences range from sixty to ninety feet. These rocks
<br />directly overlie the Wadge Seam, which is the primary target of the current underground operations.
<br />TR13 -83 2.04 -14 11/03/14
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