A total of 25 named bituminous coal beds are present and have been mined in eastern Oklahoma. Most past production has been from the Hartshorne, Lower Hartshorne, McAlester, and Croweburg Coals, which were mined by underground methods. Coal rank, generalized for all coals at or near the surface, ranges from high-volatile bituminous in the northeast Oklahoma shelf and western Arkoma Basin to medium-volatile bituminous and low-volatile bituminous in the eastern Arkoma Basin in Oklahoma. Rank increases from west to east and with depth in the Arkoma Basin, attaining semi-anthracite in Arkansas.
At the southern edge of the coal region in Oklahoma, the Hartshorne Coal commonly is split into two beds by shale and sandstone that are 1 to 100 feet thick. The two beds are called the Upper and Lower Hartshorne Coals, and they have been extensively mined. North of the position of the long axis of the Arkoma Basin, the Hartshorne Coal is not split but is a single bed 1 to 7 feet thick containing, in most places, a persistent black shale or mudstone parting about 1 to 5 inches thick. Core drilling and successful efforts at underground mine development since 1969 have demonstrated significant underground coal resources in the Hartshorne Coal in areas in Haskell and LeFlore Counties, where it is 3 to 7 feet thick, of low- or medium-volatile bituminous rank, and an excellent coking coal. In 2014, two mining companies produced 601,380 tons of Hartshorne coal. 65% of Oklahoma’s coal production was from Hartshorne Coal.
LOWER HARTSHORNE COAL
Mined in the Arkoma Basin mostly for metallurgical coke manufacture for 115 years, the Lower Hartshorne Coal has been shipped to electric power plants since 1985. Hundreds of underground mines, many of them referred to as no more than “dog holes”, have been developed along the 120 miles of outcrop of the Lower Hartshorne Coal since 1872, at which time a railroad first connected McAlester, Pittsburg County, with Arkansas, and thus with the other states. The Lower Hartshorne Coal is 0.8 to 7.0 feet thick, averaging 4 feet in underground mines. The railroads used this premium-grade coal for steam, but historically the coal was shipped to blast furnaces in Colorado, Ohio, Pennsylvania, Texas and Japan. The Lower Hartshorne Coalbed contains at least 1,541,000 tons of remaining coal resources (Friedman, 1974), and it also contains coalbed methane resources.
UPPER HARTSHORNE COAL
The Upper Hartshorne Coal was once extensively mined at outcrops on the flanks of anticlines in LeFlore, Haskell, Latimer and Pittsburg Counties. It is 2 to 4 feet thick and is low- or medium-volatile bituminous in rank in the east end of the Arkoma Basin and high-volatile in the west end. The Upper Hartshorne Coalbed contains 663 million tons of remaining coal resources (Friedman, 1974), and it also contains coalbed methane resources.
The McAlester Coalbed has been extensively mined by underground methods at McAlester in central Pittsburg County and in southeastern Coal County. Throughout the Arkoma Basin, the McAlester Coalbed is 1.5 to 5.0 feet thick and mostly high-volatile bituminous in rank. The coal is thickest in Coal and Pittsburg Counties. It is suitable for use in electric power generation, for blending with higher rank coal for coke manufacture, in cement and lime manufacture, and it is suitable for gasification and liquefaction conversion processes. The McAlester Coal contains 1,012,000 tons of remaining resources (Friedman, 1974), and it contains significant coalbed methane resources in places where it is 3 to 5 feet thick.
Correlated with the McAlester Coal (Friedman, 1978), the Stigler Coal has been mined historically to depths of 30 to 45 feet by surface methods in Haskell, LeFlore, Muskogee and Sequoyah Counties. The Stigler Coal was mined to 100 feet in Sequoyah County and to 140 feet in Haskell County. Mostly of low- and medium-volatile bituminous rank, the low-sulfur (0.5 to 1.0%) Stigler Coal has been used in coke manufacture in U.S. and overseas markets. In 1978-1979, 11 companies operated surface mines in this high BTU (13,000 - 14,500) coal, where it is 1.0 to 2.7 feet thick. This premium grade coal is overlain by 15 to 110 feet of medium- and dark-gray mudstone, the Stigler Rider Coal (correlated with the Upper McAlester Coal of Latimer, Pittsburg and Coal Counties), one sandstone bed, and in places, Quaternary silt and sand. The Stigler Coalbed contains 533 million tons of remaining resources (Friedman, 1974). One mining company produced 72,381 tons of Stigler Coal, accounting for 8% of Oklahoma’s coal production in 2014.
The Cavanal Coal, moderate in ash and high in sulfur content, is of medium-volatile bituminous rank and crops out on the synclinal flanks of Cavanal Mountain in LeFlore County (Knechtel, 1949). Of high-volatile bituminous rank, it was mapped in Pittsburg County (Hendricks, 1937). In 1976, it was mined at a surface operation on the north side of Cavanal Mountain, where it is 2 feet thick and overlain by 35 feet of blue-gray shale that is overlain by sandstone. Total remaining resources in the Cavanal Coal in the Arkoma Basin are 159 million tons (Friedman, 1974). About 60 feet below the Cavanal, the Lower Cavanal Coal, 2.0 to 2.2 feet thick, was mined by surface and underground methods in LeFlore County in 1942-43 (Knechtel, 1949). This medium-volatile bituminous coal contains undetermined resources.
LOWER WITTEVILLE COAL
The Lower Witteville Coal is widely distributed in the Arkoma Basin. In the first half of the twentieth century, underground mines produced 522,000 tons of this coal from Cavanal Mountain, LeFlore County, where it is 3 to 4 feet thick and contains thin shale partings. The Lower Witteville may correlate with the Drywood Coal in the Savanna Formation of the Northeast Shelf area (Friedman, 1982), or with an unnamed coal that occurs in a shale interval within the Bluejacket sandstone member of the Boggy Formation (Hemish, 1994). It is medium-volatile bituminous in rank, and thus it probably contains coalbed methane resources. The Lower Witteville Coal contains 52 million tons of identified coal resources in LeFlore County (Friedman, 1974).
A high-sulfur, high-volatile bituminous coal, the Rowe is 0.8 to 3.0 feet thick in Craig, Mayes, Muskogee, Rogers and Wagoner Counties. The remaining resources in the Rowe Coal are 25 million tons (Hemish, 1986, 1989). The Rowe Coal may be suitable for gasification and liquefaction conversion processes.
The Secor Coal in the Boggy Formation contains a minimum of 446 million tons of identified coal resources (Friedman, 1974). Recent exploration and mining indicates that additional millions of tons of this coal are present in LeFlore County. The Secor Coalbed is 1.5 to 4.3 feet thick, moderately brightly banded and medium-to-high-volatile bituminous in rank. High in ash and sulfur content, it contains 12,000 to 14,000 BTU/lb. The coal has been considered of marginal economic value for most markets. Discovery of a rare occurrence of a low-sulfur (1% or less) deposit of the Secor Coal in McIntosh and Wagoner Counties (Friedman, 1978) resulted in 3.2 million tons of production of this rare coal from 10 strip mines from 1978-1990.
Correlated from outcrops and drilling data in southeastern Kansas (Friedman, 1974), the Weir-Pittsburg Coal contains 496 million tons of identified coal resources in the Northeastern Oklahoma Shelf. Mined by surface methods in Craig, Mayes, Rogers, and Wagoner Counties, the Weir-Pittsburg Coal is 1.1 to 3.0 feet thick and is overlain by 20 to 30 feet of gray shale that in some places contains marine invertebrate fossils. This coal is high in sulfur (more than 3%) and ash (more than 12%). No production has been reported from this coalbed since 1980 because its run-of-mine condition has been of marginal economic value.
MINERAL COAL & MORRIS COAL
The Mineral is a high-volatile bituminous coal, 1.2 to 2.7 feet thick, averaging 1.8 feet in Craig, Nowata, Rogers, Tulsa, and Wagoner Counties. The Mineral Coal is overlain by a hard, thin, impure limestone and gray shale in most places in Craig County. Dunham and Trumbull (1955) described the Morris Coal as 7 to 30 inches thick, averaging 16 inches in the Henryetta Mining District. About 30 million short tons of identified resources of Morris Coal have been determined (Friedman, 1974). Although adverse geologic and mining conditions are present in the faulted area north of Morris, additional resources and recoverable reserves of Morris Coal undoubtedly are present in other places in Okmulgee County. Physical, chemical, petrographic and stratigraphic characteristics of the Morris Coal strongly indicate its correlation with the Mineral Coal of the Northern Shelf area (and of Kansas and Missouri)(Friedman, 1974, 1982). The Eram Coal in Okmulgee County is also correlated with the Mineral Coal (Hemish, 1988). The Mineral Coal (and equivalent coalbeds) contains 198 million tons of identified coal resources in Craig, Nowata, Okmulgee, Rogers, Tulsa, and Wagoner Counties (Hemish, 1986, 1989, 1990, 1994).
The Croweburg has been one of three leading coals produced in Oklahoma, because it contains 1% or less sulfur and a Free Swelling Index (FSI) of 6 or more in most of the area of its distribution in the Northeastern Oklahoma Shelf. A total of 681 million tons of identified remaining resources of the Croweburg Coal has been reported (Hemish, 1986, 1989, 1990, 1994) as present in Oklahoma. The Croweburg has been known as the Henryetta Coal, the Broken Arrow Coal, and the “Sequoyah” Coal (Oakes, 1944). In 2014, two active mines sites in Northeastern Oklahoma produced 250,323 tons or 26% of Croweburg Coal.
IRON POST COAL
Fort Scott Coal is also known as Iron Post Coal. The Iron Post Coal is the uppermost commercial coal in the Senora Formation. It crops out across Craig, Nowata, and Rogers Counties in an irregular line roughly parallel to the outcrop line of the Croweburg Coal. The Iron Post Coal lies about 30 to 50 feet above the Verdigris Limestone and is overlain by a few inches to a few feet of black and gray shale. The shale is overlain in turn by a limestone known as Breezy Hill. It has a high BTU value that averages about 13,000. It averages about 12 inches in thickness, and has an average sulfur content of about 3.5%. In 2014, one company produced 11,061 tons of Iron Post Coal. Less than 1% of Oklahoma’s coal production was from Iron Post Coal.