GENERAL31415

• Permit No: C1981038
• IBM Index Class Name: General Documents
• Doc Date: 9/3/1992
• Doc Name: PROPOSED DECISION & FINDINGS OF COMPLIANCE FOR FEDERAL COAL LEASES
• Permit Index Doc Type: Other Permits
• Media Type: D
• Archive: No

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Three coal horizons have been identified in the Upper Coal member; the "D"
(Oliver) Horizon, the "E" (Hawk's Nest) horizon, and the "F" horizon. The "D"
horizon occurs directly above the "massive" sandstone of the Lower
Coal-Bearing member and contains three seams. This horizon is currently being
mined in the Orchard Valley Mine, and is planned to be mined at the Hawk's
Nest Mine. This seam mdy also be mined in the future at the Mt. Gunnison
Mine, and by Bear Coal in the Bear No. 3 Mine. The "E" horizon occurs about
130 feet above the "D" horizon and contains two coal seams. This horizon is
currently being mined at the Hawk's Nest Mine and was mined at the Blue Ribbon
Mine. It mdy be mined at the Mt. Gunnison Mine and at the Bear No. 3 Mine in
the future. The "F" horizon contains two coal seams and presently is only
mined at the Mt. Gunnison Mine. Coal seams of the "F" horizon do not exist to
the north of the North Fork in thicknesses sufficient for mining.
The Barren (Undifferentiated) member of the Mesa Verde Formation consists of
up to 1,500 feet of terrestrial sedimentary rocks. This unit consists of
fine-grained, buff-colored, lenticular sandstones; gray shales and thin
lenticular coal beds. The sandstones predominate and are highly lenticular,
discontinuous and of limited lateral extent in outcrop (Johnson, 1948).
The Mesa Yerde Formation is unconformably overlain by the Tertiary Age Rudy or
Wasatch Formation. This formation consists of red to buff-colored shales, red
sandstones, and red to gray conglomerates. The sediments of this formation
are weathered volcanic rocks. The Ohio Creek conglomerate is the basal unit
within the formation and is 100 to 200 feet thick.
Tertiary igneous intrusive rocks exist within the North Fork Drainage Basin.
A diorite plug about 1,000 feet in diameter outcrops along Hubbard Creek in
the SE 1/4 of Section 7, T13S, R91W of the 6th P.M. This may represent the
erosional remnants of a volcanic flow feeder. Sills have injected the Lower
Coal-Bearing member, particularly the "B" and "C" seams. These sills consist
of diorite and appear to have their source to the northwest of Terror Creek.
The alluvium of the North Fork of the Gunnison River consists of Quaternary
Age deposits of mixed coarse sand, cobbles and boulders. These coarse
sediments are composed primarily of igneous and metamorphic rock types, and
have their source area in the headwaters and upper reaches of the North Fork.
This coarse alluvium is capped by finer sands and silts. The North Fork
alluvium in the area of the Hawk's Nest, Bear, Mt. Gunnison and Somerset Mines
is fairly narrow in width and between 50 to 70 feet thick. About a mile below
the town of Somerset, Colorado, the width of alluvium increases while the
thickness of alluvium decreases to about 35 feet.
DESCRIPTION OF THE GROUND WATER REGIME
Four categories of potential aquifers occur in the Somerset Coal Field. These
are: the alluvial and terrace deposits associated with the North Fork of the
Gunnison River; the localized, shallow alluvium along creeks tributary to the
North Fork; the discontinuous, lenticular and laminar sandstones of the Mesa
Verde Formation; and the Rollins sandstone. ~