GENERAL43121

• Permit No: C1981038
• IBM Index Class Name: General Documents
• Doc Date: 8/1/1984
• Doc Name: ADDENDUM TO FINDINGS OF COMPLIANCE
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

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Three coal horizons have been identified in the Upper Coal member; the
"U" (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 may 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 at the Blue Ribbon Mine. It may 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 Mesaverde Formation consists
of up to 1,600 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 Mesaverde 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.
Igneous intrusive rocks exist within the North Fork Drainage Basin. H
diorite plug about 1,000 feet in diameter outcrops along Hubbard Creek in
the SE 1/4 of Section 7. 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 Mesaverde Formation; and the Rollins sandstone.