Chemical analyses of lignite from the Wilcox Group, Texas region, central and eastern Texas

Abstract

As part of a continuing program by the U.S. Geological Survey to collect and chemically analyze representative sales of U.S. coal, 45 samples of lignite and lignite-associated rocks were collected strip mines and drill holes in Freestone and Milam counties in central Texas, and in Harrison, Rains, Titus, Van Zandt, and Wood Counties in eastern Texas. The sampled areas are in the Texas region of the Gulf province (Trumbull, 1960). Figure 1 shows the counties from which the samples were collected. Brief descriptions of the 45 samples are given in table 1. Thirty-one samples (twenty-six lignite and five lignite-associated rock) were collected from four active strip mines in Freestone, Harrison, Milam, and Titus Counties by the Texas Bureau of Economic Geology; 14 samples (13 lignite and 1 carbonaceous shale) were collected from nine drill holes in connection with the U.S. Bureau of Mines evaluation of coal resources in the proposed Carl L. Estes Lake site, Rains, Van Zandt, and Wood Counties (Ward, 1977). All samples included in this report are from the Wilcox Group of Eocene age. The Wilcox Group is undifferentiated in Harrison, Rains, Titus, Van Zandt, and Wood Counties. Lignite in this area is in the upper two-thirds of the Wilcox. In Freestone and Milam Counties, the Wilcox Group is subdivided into the Hooper, Simsboro, and Calvert Bluff Formations. Lignite in this area is predominantly in the Calvert Bluff Formation, with minor amounts in the Hooper Formation. A generalized stratigraphic column of the Wilcox Group and associated Tertiary strata is given in figure 2. The Calvert Bluff Formation and undifferentiated Wilcox Group consist of clastic debris deposited in a fluvial environment, in which major channel complexes characterized by sand deposition divide interchannel areas composed of mud. Lignite was deposited as a blanket peat in freshwater swamps and marshes within interchannel areas. Individual lignite beds are lenticular bodies extending 3 to 20 km laterally; thicknesses are generally 1 to 3 m, rarely as much as 6 m. Descriptions of geology and lignite occurrences are in Fisher (1963), Kaiser (1974, 1978), and Kaiser and others (1978).