Chemical analysis and evaluation of 40 samples from Upper Cretaceous coal beds from the Wind River basin, Wyoming

Abstract

Detailed chemical analysis of 40 drill-core samples (reported on whole-coal and laboratory-ash basis) from the Wind River Basin r Wyoming, indicate that 29 of the coals are subbituminous A, B, and C in rank. Eleven samples are bituminous C in rank, probably the results of intense deformation in the northwestern corner of the basin and depth of burial in the central part of the basin. The quality of the Wind River Basin coal is similar to other sampled western subbituminous coals. Chemical elements which are of environmental concern are found in the Wind River Basin coal beds in approximately the same concentrations as they are found in other sampled western subbituminous coals. The major coal-bearing sequences in the western Wind River Basin are in the Mesaverde and Meeteetse Formations and a minor occurrence is in the Frontier Formation, all of Cretaceous age. Organic matter accumulated in an extensive coastal swamp environment on a prograding delta system during deposition of the Frontier and Mesaverde Formations. In contrast, peat in the Meeteetse Formation developed in a more restricted intermontane basin which was subjected to tectonic deformation accompanied by considerable amount of air laden with volcanic ash. These contrasting depositional environments have resulted in differences in the coal chemistry and quality. Coals in the Mesaverde Formation generally contain more iron and sulfur,whereas those in the Meeteetse Formation contain more ash, calcium, and silica. Coals in the Wind River Basin have a higher ash-fusion temperature than other sampled western coals and should be highly competitive in the marketplace for combustion processes. Introduction The Wind River Basin (fig. 1) includes approximately 8,500 square miles in west central Wyoming, largely in Fremont, Natrona, and Hot Springs Counties. The basin is bounded on the north by the southern Bighorn Mountains, the Owl Creek Mountains, and the Washakie range; on the southwest by the Wind River Mountains; on the south by the Granite Mountains (Sweetwater Arch); and on the east by the Casper Arch. Except for the Casper Arch (fig. 1), the surrounding uplifts have exposed cores of Precambrian crystalline rock. The deepest part of the basin contains sedimentary rocks whose aggregated thickness may be more than 26,000 ft. The Mesaverde and Meeteetse Formations of Late Cretaceous age are the major coal-bearing strata in the western Wind River Basin, and underlie approximately 5,500 square miles. Several coal beds in the Mesaverde and Meeteetse Formations are as much as 240 in. thick. These formations are limited to isolated outcrops of low dip angle in the south and southwest parts of the basin and steeply dipping to overturned, folded, and faulted strata in the north and northwest part of the basin (fig. 2). A minor deposit of coal in the Frontier Formation, near the town of Wilderness, locally is as much as 42 in. thick. A near-surface channel sample (W210031) is the only source of data on this coal bed. Previous investigations The Wind River Basin was included in the early geologic investigations of F.V. Hayden in 1869. The geology in the northern part of Fremont County, Wyoming, was investigated by T.B. Comstock (1874) and by G.H. Eldridge (1894). W.C. Knight (1895) summarized the coal fields in Wyoming and E.G. Woodruff (1907) prepared a detailed report on the Lander coal field. In 1906, N.H. Barton made a stratigraphic study of the Paleozoic and Mesozoic rocks of central Wyoming. In 1912, Woodruff and Winchester completed an investigation of the coal resources of Cretaceous and Tertiary strata in the Wind River Basin. H.L. Berryhill and others (1950) estimated the coal resources of Wyoming. Thompson and White (1952) described the geology and coal resources of the Alkali Butte, Big Sand Draw, and Beaver Creek coal fields. W.R. Reefer and others (1957, 1961, 1964, 1970, 1972) prepared numerous detailed geologic reports on the stratigraphy and structure of the Wind River Basin, as well as geologic maps and oil and gas investigations. D.A. Seeland and E.F. Branch (1975) compiled a mineral-resource investigation for the Bureau of Indian Affairs in 1975, and a coal-resource report on the Wind River Basin was updated by Glass and Roberts in 1978. Present investigations This report evaluates the chemical analyses of coal samples collected during a geologic study of the western Wind River Basin. These data describe the quality of the coal collected from 39 drill-core samples and one outcrop sample (figs. 3, 4, 5, and 6). Stratigraphic distribution and sample numbers are shown in figure 6. Chemical data indicate that the rank of the coal ranges from subbituminous C to high-volatile bituminous C (table 1). 2