GENERAL56423 - Laserfiche WebLink

Home Browse Search

approximately ten miles each way. Baseline environmental information collected for the Seneca II-W Mine can be located in Tabs 4 through 11 in the permit application. Geologv and To o rayhy Elevation of the general mine site varies from approximately 6400 to 8350 feet. Slopes range from about 2 percent to nearly 100 percent. Prominent ledges are formed by the Twentymile sandstone in the western permit area and the Trout Creek sandstone ledge in the eastern permit boundary. Many of the drainages are deeply incised. The Seneca II-W Mine is situated in the southeastern synclinal portion of the Sand Wash Structural Basin of northwestern Colorado and south central Wyoming. Exposed strata near the mine site vary in age from Late Cretaceous to Quaternary. Most units in the area are sedimentary. However, some Miocene extrusives are locally present. Many faults and folds modify the regional synclinal structure, however, no faults have been identified at the site. The most significant local fold is the Sage Creek Anticline, located just east of the mine. Rock units dip 8 to. 14 degrees to the west. The Seneca II-W Mine lies on the western flank of this anticline. The largest local structure is the Tow Creek Anticline, located about 10 miles northeast of the permit area. The local stratigraphic sequence, in ascending order, is the Mancos Shale; the Mesaverde Group, which is subdivided into the Iles and Williams Fork Formations; and the Lewis Shale. The Iles Formation is divided into three members. The basal Tow Creek Sandstone is a massive, fine grained, well sorted sand. The Tow Creek varies from 35 to 125 feet thick. Overlying the Tow Creek are 1200 feet of interbedded shales, sandstones, and coals. The coals, while mined in the vicinity, are too deep to be considered economically recoverable at the Seneca II-W Mine. The massive, fine grained, 100 feet thick Trout Creek Sandstone is the uppermost unit of the Iles Formation. Conformably overlying the Iles is the Williams Fork Formation. The lower unit of the Williams Fork Formation is a series of interbedded shales, sandstones, sandy shales and coal. The middle coal group contains the seams of economic importance. Four coal seams of economic importance are found in the Williams Fork Formation. These seams are, in ascending order, the Wolf Creek, Sage Creek, Wadge, and Lennox coals. Due to discontinuous occurrence of the Sage Creek seam, and excessive overburden cover relative to seam thickness over much of the permit area, the operator proposes to extract Wolf Creek and Sage Creek coals within only selected areas of the South Extension Area. The Wadge coal will continue to be mined as part of this operation. The Lennox seam is locally present in the Wadge overburden. It is usually two to five feet thick, but has been eroded away in some areas, and is not recovered by mining operations. Seneca II-W Findings Document 8 November 17, 2004 Permit Revision No. 4