_GENERAL DOCUMENTS - C1981017 ‎(279)‎

• Permit No: C1981017
• IBM Index Class Name: GENERAL DOCUMENTS
• Doc Name: Bid Documents ‎(IMP)‎
• Media Type: D
• Archive: No

DEPARTMENT OF NATURAL RESOURCES
9O D Monte Pascoe,Executive Director
MINED LAND RECLAMATION DIVISION
DAVID C.SHELTON Director
1876.�`:
Richard D Lamm
Governor
March 2, 1982
TO: Jim Herron
t
FROM: David Craig !
SUBJECT: Geologic Description for the Coal Basin Mine Findings Document
Geology
Description of Existing Environment
The Mid-Continent coal mining operation is located in Coal Basin, a structural
and topographic feature on the southern edge of the Piceance Basin in west
central Colorado. The strata of Coal Basin consists, principally, of the
Mancos Shale and the Mesa Verde Group. Stratigraphically, the Mesa Verde
Group conformably overlies the Mancos shale (see Plate III - C-2 of the permit
application) . The coal being mined by the applicant is located in the Williams
Fork Formation of the Mesa Verde Group. For a detailed description of the
geology of Coal Basin, see Section III-D of the permit application.
The Mancos Shale generally consists of drab gray, sparsely fossiliferous silty
shale to shaley siltstone. It floors the vast majority of the basin and is
about 3,000 feet thick.
The overlying Mesa Verde Group generally consists of shale beds interbedded with
sandstones and coals. The Mesa Verde Group is further subdivided into a lower
formation, called the Iles, and an upper formation, called the Williams Fork
(see Figure III-D-1 of the permit application) . The Williams Fork Formation
contains the economically - mineable coal-bearing strata. The coal seams
being mined by the applicant occur within the Bowie Shale Member of the Williams
Fork Formation.
For a more detailed understanding of stratigraphic relationships in Coal Basin,
see Plate III-C-2 of the permit application.
The structure of Coal Basin generally consists of sedimentary strata domed over an
igneous intrusion, probably a laccolith (see the geologic cross-section drawing on
Plate II of the permit application) . The folding of the strata is thought to
be the result of upward pressure from the underlying intruding igneous body.
The resultant anticline has been breached by erosion. The exposure and resultant
erosion of the Mancos Shale has left the basin - like topographic expression
observed today. The mineable coal, exposed on the outer wall of the basin,
dips to the west at about 100-150. Being on the western limb of the anticline,
the coal strata maintain a relatively constant dip for several miles. Many
igneous dikes and sills have intruded the coal strata. Faulting is common
with displacements ranging from 20 feet to more than 450 feet. Faulting is a
significant determinant of the drainage pattern of coal basin.
423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. [phone]