240 Coal Geology (Posters): New Developments in Environmental and Geochemical Coal Research

Wednesday, 12 October 2011
9:00 AM - 6:00 PM
Hall C

GEOCHEMISTRY OF THERMALLY ALTERED COALS: A CASE STUDY OF THE SPRINGFIELD (NO. 5) COAL, ILLINOIS BASIN

Paper number: 240-7
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Igneous intrusion of coal seams (in the form of dikes or sills) have been documented in various parts of the world including the USA, Europe, Africa, Australia, and Antarctica. Igneous intrusions change the coal geochemically and leave both an organic and inorganic alteration signature. Understanding the geochemistry of thermally altered coals is important due to interest in the CO2-sequestration potential of intruded coals that have high adsorption properties (Saghafi et al., 2007), the role of intrusions into coals and other organic-rich rocks in the geologic past that may have resulted in the release of greenhouse gases (such as CH4 and CO2) leading to global warming and mass extinction events (e.g., McElwain et al., 2005; Svenson et al., 2007), or the potential role of coal fly ashes released from intruded coals that may be linked to mass extinction events (Grasby et al., 2011). The current study reports on geochemical and mineralogical changes associated with igneous intrusion of the Springfield (No. 5) Coal in the Illinois Basin.

From background levels around 0.5%, vitrinite reflectance increases towards the dike up to 4.8%; a coal block entrained within the dike reaches vitrinite reflectance levels of ~7%. Accompanying this increase in reflectance is a loss of liptinite macerals and the formation of volatilization vacuoles, isotropic coke, and, ultimately, fine mosaic texture closest to the intrusion. Based on established vitrinite reflectance–temperature relationships, the maximum temperature at the coal/intrusion contact is calculated to have been at least 355°C; ambient temperatures for the unmetamorphosed coal are ~78°C. Approaching the dike, sulfur and moisture decrease whereas ash content increases; X-ray diffraction shows an increase in carbonates within the mineral matter, especially ankerite, close to the intrusion. Geochemical and mineralogical trends seen in this transect will be discussed and compared to other examples of intruded coals.