1986-12-11_PERMIT FILE - C1981017

Home Browse Search

-12- Very little additional surface disturbance will be necessary in the Coal Basin mine plan area over the planned life of the mine. Cultural resource surveys will be performed before any further surface disturbance is approved. Pursuant to Rule 2.07.6(2)(e) , the Division finds that the proposed mining operation will not adversely affect any publicly owned park or place listed on the National Register of Historic Places. The proposed operation is in compliance with the requirements of this section. IV. Geology - Rules 2.04.5 and 2.04.6 The Coal Basin mines are located on the southeast edge of the Piceance Basin within the Coal Basin. The Coal Basin is an eroded anticline superimposed on the Grand Hogback Monocline. The strata of Coal Basin consist principally of the Cretaceous Mancos shale and Mesaverde Group, although rocks varying in age from Pennsylvanian to Tertiary are present. The Mancos shale, which consists of silty shale to shaley siltstone, makes up the vast majority of the floor of Coal Basin. Below the Mancos shale, bedrock units are the Cretaceous Dakota, Jurrasic Morrison and Jurrasic Entrada sandstones, Permian Weber sandstone, and Permo-Pennsylvania Maroon formations. These bedrock units outcrop on the Grand Hogback, then dip steeply beneath the overlying Coal Basin strata. They occur far beneath, and are unaffected by, mining activity. The overlying Mesaverde Group consists mainly of shale beds interspersed with sandstone units. The Mesaverde Group is customarily described in terms of a lower formation, called the Iles, and an upper formation, called the Williams Fork. The Iles Formation overlies the Mancos shale and, as noted, the Williams Fork Formation overlies the Iles. The Iles Formation consists of two sandstone members divided by a 1 ,000 foot "tongue" of shale. The lower member, the Cozzette, is a 6 foot layer of very fine grained silty sandstone, which overlies a 40 foot thick layer of silty to sandy shale. The upper sandstone member of the Iles Formation, known as the Rollins, is 120 feet to 140 feet thick. A shale tongue of 5 feet to 30 feet thickness, and identical to the underlying shale, occurs within the Rollins member 25 feet to 75 feet above the base. The Rollins sandstone varies in grain from very fine to coarse, but medium texture predominates. Within the overlying Williams Fork Formation, two sandstone members, known as the Middle and Upper sandstone members, separate thick shale formations. Above the sandstone members lie coal seams.