Geologic Controls on Mineral-Matter Content of Coal in Central Appalachian Basin: ABSTRACT

Abstract

Mineral-matter content of coal in the central Appalachian basin was primarily controlled by chemical conditions in a peat-forming paleoenvironment. Coal that is low in mineral matter was derived from peat that accumulated under highly acidic conditions (pH<4.5), whereas coal having high mineral-matter content was derived from peat that accumulated under pH conditions ranging from 4.5 to 7.5. Highly acid conditions during the peat-forming stage of coal formation favored leaching of mineral matter and inhibited bacterial degradation. Increasing pH resulting from buffering by dissolved calcium carbonate species could have (1) reduced the degree of leaching of mineral matter and (2) concentrated mineral matter, including sulfur compounds, because of increased bacterial deg adation of peat and concomitant sulfate reduction. Coal that has a low mineral-matter content (1) is associated with noncalcareous sedimentary sequences; (2) has a high kaolinite to illite ratio; and (3) has a relatively low calcium carbonate content. The converse is true for coal having high mineral-matter content. Mineral matter other than calcium, iron, and sulfur in Appalachian basin coal is dominated by inherent ash derived from plants. Calcium, iron, and sulfur contents are thought to have been fixed primarily by chemical reactions indirectly resulting from bacterial degradation during the early stages of coal formation. End_of_Article - Last_Page 689------------