Year: 1936
Type: report
Abstract: The thickest beds of coal, which are also those of highest rank, are in the northern area.The principal beds there are in the highest zone and in two exposures show 34 and 24 feet of clean coal, but this is considerably shattered.To the east and west this coal zone thins rapidly.The middle zone lies about 120 feet deeper and locally shows coal and bone as much as 10 feet in thickness.Westward this zone thins rapidly, but eastward.itthickens and contains several beds of coal.This zone seems to be 600 or 700 feet above the base of the Chickaloon formation, which overlies marine deposits of Upper Cretaceous age.The lowest coal zone is-not present in this area.These coals are sernianthracite to anthracite, having been altered from coals of lower rank.Probably this change was produced chiefly by heat from the intruding masses of igneous rock, which drove off some of the volatile matter from the coal.The heat resulting from the later compression and folding of the beds may also in some places have been an agent in their alteration.The coal beds of the eastern area belong mainly to the middle zone and consist of four or five beds with a total .-.of about 10 feet of coal in a zone 50 feet thick.Although these coals have been in places closely folded, they have not been appreciably altered and are of bituminous rank.On middle Muddy Creek the lowest coal zone is exposed and consists of a 6-foot bed of bituminous coal 140 feet below the middle zone.; In the southwest area there are about six.coal beds, distributed through a thickness of nearly 400 feet of sediments.The uppermost bed seems to be about equivalent to the upper coals of the northern area, .and the others accord approximately with the middle and lower coal zones.These southwestern coals are bituminous to semibituminous in rank.Although the studies indicated that the outcropping beds of coal are not of great economic importance at present because of their irregular character and broken condition, evidence was obtained which indicated that the highrank coals might be present, less broken and of great potential value, beneath the synclinal area south of the pi'incipal outcrqps.This area was,tested, in 1932 by eight diamond-drill holes, a total of 8,000 feet being core drilled.Observations on the dip of the strata indicated that the horizon of the anthracite would be found at a depth of 1,500 or 1,600 feet.The deepest hole reached 1,820 feet.It penetrated numerous beds of black shale containing plant remains, and between the depths of 1,300 and 1,550 feet there were several layers of carbonaceous shale and small amounts of coal gas, but no.coal other than veinlets 1/32 to 1/8 inch in thickness was found.None of the other drill holes encountered coal beds, though coal veinlets in the shale, and fragments of coal in the sandstone and conglomerate were found at many horizons.During the period or periods of coal deposition the present synclinal area apparently was not an area in which coal was formed.Except for a few locally altered lenses, all the known coal of anthracite rank in the district is confined to an area half a mile long and a quarter of a mile wide, on the south flank of the ridge.This area is folded and faulted, and the coal beds are much shattered, with inclusions of bone and shale and intrusions of igneous rock.The amount of coal in the most promising 20 acres of this area has been estimated at'750,000 tons.The tract lies high on the side of the ridge, 2,500 to 3,000 feet above : the river and nearly 20 miles from the former railroad terminus at Chickaloon.All the other beds of workable thickness in the district are of semibituminous and bituminous coals.Their, outcrops are of small extent, and the beds are so irregular in.thickness that.. estimates of available tonnage cannot be made on the basis of present information.Much detailed prospecting supplemented by trenching and core drilling would be necessary for this purpose.Chemical analyses show that none of these coals have appreciable fuel advantage over the more accessible deposits being mined in the western part of the Matanuska Valley.Although the district probably contains several million tons of bituminous Coal, in addition to the 750,000 tons of anthracite and semianthracite, the beds are broken and irregular in thickness, and much dead work would be involved in mining.Local demand is so small and other markets are so remote that attempts to produce coal from the district in competition with more accessible areas is not warranted at the present time.
DOI: 10.3133/b861
Author: Gerald Ashley Waring
Language: English
Subfield: Geology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W9284847