GENERAL50201

• Permit No: C1991078
• IBM Index Class Name: General Documents
• Doc Date: 12/14/1992
• Doc Name: PROPOSED DECISION & FINDINGS OF COMPLIANCE FOR PR1
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

geologic feature of the area, the Uncompahgre Uplift. The region lies in the
Dolores River Basin. The mine is located one and one half miles south of the
San Miguel River.
The mine is located in the Nucla-Naturita Coal Field. The coal is found in
Late Cretaceous sediments. The youngest Cretaceous rocks in the area consist
of Mancos Shale, a dark gray marine shale, present only on isolated hilltops
south of the town of Nucla. Two hundred feet of Dakota sandstone outcrops
extensively along the axis of the Nucla Syncline. This formation consists of
a yellowish-gray, fissile sandstone and conglomeratic sandstone interbedded
with dark gray shale and coal. There are nine coal seams within 100 feet of
the base of the Dakota (Figure 2). The Lower Cretaceous unit in the area, the
Burro Canyon Formation, is separated from the Dakota by an unconformity. The
Burro Canyon is comprised of white, gray and light brown sandstones and
conglomerates interbedded with green and purplish shales, siltstones,
mudstones and thin beds of limestone. This formation has a maximum thickness
of 200 feet and outcrops on rims of canyons northwest of the mine. This
formation is difficult to differentiate from the Dakota in this area, and is
commonly considered hydrogeologically similar.
Five coal seams have been identified in the horizon to be mined in the permit
area (Figure 2). They are identified, in descending order, as the Upper
Dakota-l, (UD-1), Lower Dakota-1, (LD-1>, Lower Dakota-2, (LD-2), Lower
Dakota-3 (LD-3), and Lower Dakota-4, (LD-4>. The LD-2 and LD-3 seams are of a
mineable thickness throughout the permit area. In the southern portion of the
permit area the LD-4 seam is of a mineable thickness. The thickness of the
LD-2 seam ranges from 1.6 to 3.5 feet thick with an average thickness
throughout the permit area of 2.5 feet with depths form the surface to the top
of the seam ranging from 7.2 to 28.7 feet. The LD-3 seam averages l.6 feet
thick and ranges from 0.8 to 2.9 feet thick. The LD-4 seam ranges from 1.2 to
3.1 feet in thickness with an average of 2.1 feet.
The splits between coal consist primarily of thin, lenticular, dark,
carbonaceous shales. The split between the LD-2 and LD-3 seam ranges in
thickness from 0.3 to 1.0 feet with an average of 0.6 feet thick throughout
the permit area. The split between the LD-3 and LD-4 seam averages a
thickness of 1.1 feet and ranges from 0.7 to 1.7 feet in thickness. Any
splits within the seams of thickness less than 0.3 feet will be taken with the
coal during the mining operation.
There are two rider coal seams identified in the permit area, referred to as
the UD-1 and LD-1 seams. Neither rider seam is consistent in extent within
the permit area and therefore not considered mineable. Where identifiable,
the UD-1 and LD-1 rider seams are as much as 1.2 and 2.0 feet in thickness,
respectfuily. Rider seam LD-1 overlies an average .08 feet thick dark shale
layer. The stratum which overlies the LD-1 rider seam and underlies the UD-1
rider seam consists of an average 7.0 feet thick gray shale. The stratum
overlying the UD-1 rider seam consists of a soft, yellowish, fine-grained
sandstone that varies in thickness from 2.8 to 19.0 feet thick from the top
of UD-1 to the ground surface.
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