GENERAL STRATIGRAPHY OF THE USIBELLI COAL MINE
“Mining Coal is Easy. Getting to it is the Hard Part.”
The Nenana Coal Field is currently the only active coal producing field in Alaska and has produced a record 50 mil- lion tons of coal. At the Usibelli Coal Mine in Healy, up to 100 feet of unconsolidated sandstone or overburden must be moved to uncover the top seam (seam 6) of coal. Another 120 feet of interburden must be moved to uncover the second seam (seam 4), and roughly 80 feet of interburden must be removed to uncover the third seam of coal (seam 3) reaching nearly 400 feet at its deepest point. The overburden is removed by four different methods: 1) The dragline removes the bulk of the overburden; 2) Blasting utilizing explosives loosens and casts the overburden; 3) Bulldozers move overburden short distances prior to drag line operations; and, 4) Shovels strip and load overburden and coal into the haul trucks.
The following information is excerpted from the USGS publication: “Alaska Coal Geology, Resources, and Coalbed Methane Potential,” Romeo M. Flores, Gary D. Stricker, and Scott A. Kinney (2004), DDS–77 USGS, and was edited for TPG by Jean M. Neubeck. The complete report with cited references can be found at:
https://catalog.data.gov/dataset/alaska- coal-geology-resources-and-coalbed-methane-potential.
Clyde Wahrhaftig(USGS) deserves special recognition for his geologic work and mapping that the USGS references throughout their report. Interested readers can use the follow- ing link to download the local Healy D-4 Quad Geologic Map that covers the area that AIPG members toured during the field trip. The map contains the type section of the coal-bearing for- mations at Suntrana Creek:
http://ngmdb.usgs.gov/Prodesc/
Coal mining has been intermittent in the Central Alaskan- Nenana and Southern Alaska-Cook Inlet coal provinces, with only a small fraction of the identified coal resource having been produced from some dozen underground and strip mines. Alaskan coals have a lower sulfur content (averaging 0.3 per- cent) than most coals in the conterminous United States and are within or below minimum sulfur value mandated by the 1990 Clean Air Act amendments.
The identified resources are near existing and planned infrastructure to promote development, transportation, and marketing of this low-sulfur coal. The relatively short dis- tances to countries in the west Pacific Rim make them more exportable to these countries than to the lower 48 States of the United States.
Central Alaska-Nenana Coal Province and Mining History
The Central Alaska Nenana coal province is in the north- ern foothills of the Alaska Range, extending from about 50 mi (80 km) west to 50 mi (80 km) east of the Parks Highway and Alaska Railroad corridor. It consists of several east-west trending synclinal basins partly or wholly detached from each other by erosion of coal-bearing rocks from intervening structural highs. These coal-bearing synclinal basins are recognized as coalfields that include the Jarvis Creek, East Delta, West Delta, Wood River, Mystic Creek, Tatlanika Creek, Lignite Creek, Healy Creek, Rex Creek, and Western Nenana coalfields. The Healy Creek (aka Suntrana) and Lignite Creek (aka Hoseanna) deposits are currently mined and account for the majority of coal historically mined in Alaska.
The construction of the Alaska Railroad provided the initial transportation to market. In 1918, underground coal mining by the Healy River Coal Corporation began at Suntrana, 4 mi (6.4 km) east of the confluence of Healy Creek and the Nenana River. Horse-drawn sleds to the railroad camp in Healy origi- nally transported coal until a railroad spur was built to the mine in 1922. The Healy River coal mine accounted for one- half of Alaska’s production from 1920 to 1940. The rest of the production was from the Evan Jones mine in the Matanuska coalfield in the Southern Alaska-Cook Inlet coal province.
proddesc_2108.htm
Estimated Alaska coal resources are largely in Cretaceous and Tertiary rocks that are distributed within three major provinces; NorthernAlaska-Slope, Central Alaska-Nenana, and Southern Alaska-Cook Inlet. Most of the Tertiary resourc- es, mainly lignite to subbituminous coal with minor amounts of bituminous and semianthracite coals, are in the provinces of Southern Alaska-Cook Inlet, and also the Central Alaska- Nenana province, which is sumamrized herein.
The combined measured, indicated, inferred, and hypotheti- cal coal resources in the three areas are estimated to be 5,526 billion short tons (5,012 billion metric tons), which constitutes about 87 percent of Alaska’s coal and surpasses the total coal resources of the conterminous United States by 40 percent.
The military buildup in Alaska in the 1940s and after World War II provided a new market for coal that resulted in open- ing more mines to meet the demand. UCM opened the first surface mine in the coal province east of Suntrana in 1943. In 1961, UCM purchased the Healy River Coal Corporation and continued mining underground. The Arctic Coal Company opened a small mine on Lignite Creek and operated it until 1963. The Vitro Mineral Mine was opened in 1963 east of Suntrana and was purchased by UCM in 1970. UCM remains the only active coal mine in Alaska today.
(UCM reports that it delivers coal directly to Golden Valley Electric Association’s Healy #1 and #2 mine-mouth power plants by truck and also supplies coal northward by rail to five additional Interior Alaska power plants. UCM has also sup- plied coal to the south by rail and onto ocean-going vessels out of the Seward Coal Terminal for international export since 1985.)
Tertiary Usibelli Group
The Usibelli Group (Wahrhaftig, 1987), a nonmarine sedi- mentary sequence of Tertiary age, consists, from bottom to top, of the coal-bearing Healy Creek Formation, Sanctuary Shale Formation, coal-bearing Suntrana Formation, Lignite Creek
www.aipg.org
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