Petrologic and Chemical Characteristics of Deep-Subsurface Wilcox (Eocene) Lignites from East and East-Central Texas: ABSTRACT

A recent drilling program has provided new petrographic and chemical data on deep-subsurface Wilcox Group lignites in east and east-central Texas. The seams occur in major lignite-bearing horizons of the Wilcox Group at depths of 240-1,040 ft (70-315 m). The petrologic examination has been performed using white and blue light reflectance microscopy. The seams contain limited well-preserved plant material. Humodetrinite is the dominant maceral, and many of the huminites have undergone partial or complete gelification. The liptinite content is high and may exceed 30%, much of it occurring as a fine-grained matrix. Seams with less liptinite tend to contain more inertinite. Some of the huminites contain granular material which has a low reflectance and weak orange fluorescence. It is believed to represent an early stage in the formation of micrinite, with which it may be found in close association. Chemical characterization includes proximate and ultimate analyses, forms of sulfur, ash oxides, plus minor and trace element concentrations. Most seams are low in sulfur, except for a seam underlying a marine unit at the top of the Wilcox, in which the dry sulfur content exceeds 5%. Ash contents are variable and largely determine calorific value. Sodium content increases from shallow to deeper seams, coincident with the evolution of ground-water chemistry from Ca-HCO3 to Na-HCO3 with increased depth. Comparison between petrographic and chemical data show that lignites with larger amounts of liptinite have higher hydrogen contents and calorific values. End_of_Article - Last_Page 493------------