New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/32 Upper Cretaceous (Campanian) coal resources of western Colorado D. Keith Murray, 1981, pp. 233-240 in: Western Slope (Western Colorado), Epis, R. C.; Callender, J. F.; [eds.], New Mexico Geological Society 32nd Annual Fall Field Conference Guidebook, 337 p. This is one of many related papers that were included in the 1981 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. 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KEITH MURRAY Colorado School of Mines Research Institute Golden, Colorado 80401 INTRODUCTION source is believed to consist of coals of Cretaceous age, no data Colorado encompasses parts or all of eight distinct coal-bearing presently are available regarding the breakdown of coal resources regions, which cover nearly 30 percent of the total area of the in Colorado by geologic age or formation. However, based on the State (fig. 1). These eight regions, within which are located 21 known distribution and thicknesses of the widespread, multiple designated coal fields, contain more than 10 percent of the total (often numbering 20 to 30 or more) coal beds encountered in the coal reserves of the United States above a depth of 1,830 m (6,000 Mesaverde Group and equivalents (essentially, Campanian in age), ft), or at least 434 billion short (394 billion metric) tons of in-place there is little doubt that the bulk of the coal resources of Colorado coal. Of this resource, more than 273 billion short (248 billion lies within this sequence. In the southeast part of the Uinta region, metric) tons, or 63 percent of the total, have been estimated for for example, total net thickness of Mesaverde coals in places ex- the Green River, San Juan River, and Uinta coal regions of western ceeds 24 m, based on an evaluation of oil and gas well geophysical Colorado (see Murray, 1980a, 1980b). Although most of this re logs in the area (see Murray and others, 1977, p. 389). In the Dan- 234 MURRAY forth Hills coal field, Rio Blanco and Moffat Counties (fig. 1), total The Cretaceous-age coal-bearing sequences (fig. 2) and coal coal thicknesses in the 30-47 m range have been noted, based ranks present in the western Colorado regions can be generalized upon subsurface information. To date, western Colorado coal as follows (units presently being mined are in bold-face type) (Mur- fields have produced more than 224 million short (203 million ray, 1980a): metric) tons of coal, which amounts to nearly 33.5 percent of the GREEN RIVER REGION: State's cumulative production, from 1864 through 1980, of nearly Lance Formation (Upper Cretaceous)-probably mostly subbi- 670 million short (608 million metric) tons. During 1980, the three tuminous B and C. western Colorado coal regions produced more than 17 million short (15.4 million metric) tons of coal, or 90 percent of the State's Mesaverde Group (Upper Cretaceous)-mostly high-volatile C total. Virtually all of the historic coal production from western Col- bituminous, some high-volatile B bituminous and subbitumi- orado has come from Cretaceous-age sequences; and all of the nous A. present production consists of coals of this age. Based on prelimi- SAN JUAN RIVER REGION: nary data from the Colorado Division of Mines, nearly 12 million Fruitland Formation (Upper Cretaceous)-high-volatile B and short (10.9 million metric) tons of coal was surface-mined in west- C bituminous. ern Colorado during 1980, which comprises 70 percent of all coal Menefee Formation of Mesaverde Group (Upper Creta- mined in that region and nearly 93 percent of all surface-mined ceous)-high-volatile A and B bituminous (locally of coking coal in Colorado. quality). COAL-BEARING ROCKS Dakota Group (Upper Cretaceous)-high-volatile B and C Colorado coals range in age from early Late Cretaceous to Eo- bituminous (currently mined only in Nucla-Naturita field; may cene. The higher rank bituminous coals, which comprise the larg- locally be of coking quality). est reserves, generally are found in the Upper Cretaceous Dakota and Mesaverde Groups in western Colorado, especially in the re- UINTA REGION: gion extending from Garfield County south to the New Mexico Mesaverde Group (Upper Cretaceous)-anthracite and semi- state line. The oldest coals in Colorado occur in the Dakota Group anthracite (restricted to areas of igneous activity in southeast- in the southwestern part of the State (northern San Juan River re- ern part of area, especially in Crested Butte field); medium- gion, Durango to Nucla-Naturita field areas). Successively younger volatile bituminous (high-grade coking coal, chiefly in Coal coals were laid down as the Late Cretaceous Western Interior sea Basin area of Carbondale field); high-volatile A, B, and C bitu- retreated eastward and northeastward from the region (Murray, minous (of coking quality in parts of Carbondale and Somer- set fields); subbituminous A and B(?) (only in local areas near 1980a). The youngest coals, generally of lower rank (subbituminous A to outcrops). lignite), are found in latest Cretaceous and early Tertiary rocks in the Green River, North and South Park, Raton Mesa and Denver STRUCTURE OF COAL-BEARING REGIONS coal regions. Subbituminous coals occur in the Cretaceous Lance, The San Juan River, Uinta and Green River coal regions, for the Laramie, and Vermejo formations; in the Paleocene Fort Union and most part, are located within Laramide-age structural basins. The Raton formations; and in the Paleocene-Eocene Wasatch and interior areas of these basins appear to be relatively free from Coalmont formations. Lignite is restricted to the Paleocene-age structural complications; here the coal beds probably are not upper part of the Denver Formation in the central Denver coal re- highly folded, faulted or otherwise disturbed. However, some gion (Murray, 1980a). margins of these structural basins are moderately to severely UPPER CRETACEOUS COAL RESOURCES 235 folded and faulted. In places, Tertiary igneous activity has chemical characteristics of coals from the Green River region, in metamorphosed the coal to anthracite, and even to coke. The northwest Colorado, with coals from the entire Rocky Mountain Uinta region, which is located partially within the Piceance Creek coal province (of which Colorado is a part), Interior province (Illi- basin, and the Green River region, the Colorado portion of which nois, Iowa, Kansas, etc.), and Northern Great Plains province (Mon- includes the Sand Wash basin, each contains significant coal tana, North and South Dakota, and northeastern Wyoming). resources to depths exceeding 3000 m. The Piceance Creek and None of the Colorado coals sampled to date, which include Sand Wash basins are the deepest structural depressions in the coals from all of the larger producing mines in the State, appears State (Murray, 1980a). to contain significant quantities of toxic or radioactive elements Only a small part, possibly 5 to 10 percent, of the coal resources (such as arsenic, mercury, selenium, strontium, thorium, and ura- of Colorado today are considered to be surface-minable due to nium). In fact, most appear to contain smaller amounts of these the limited areas within the coal-bearing regions in which the coal substances than do coals from other regions of the United States beds are both of gentle dip and under "shallow" cover (Murray, (Murray, 1980b). 1980a). Moisture, volatile matter, and fixed carbon contents of Colorado coals vary considerably with rank from region to region. Moisture CHARACTERISTICS OF UPPER CRETACEOUS COALS content is generally in the 1- to 20-percent range, as-received. An Coal Rank overall average of about 12 percent moisture is a general value for Statewide, Colorado coals range in rank from lignite to anthra- Colorado coals. Statewide, volatile matter content varies from 6.9 cite; however, western Colorado coals vary from subbituminous percent (in anthracite in Crested Butte field) to approximately 45 to anthracite in rank, but are predominantly bituminous. More percent, with most coals being in the 31-40 percent range.