Chemical and mineralogical compositions of more than 100 samples of Illinois basin coals have been examined from an existing data base. Multi-variate statistical analysis of the data shows that variation of many trace elements is related to mineral impurities in coal, including pyrite, clay minerals, calcite, sphalerite, and quartz. Organic sulfur, germanium, and boron are associated primarily with organic matter. The high sulfur content in most Illinois basin coal results from seawater permeation immediately following peat deposition. Low-sulfur coal (< 2.5% total sulfur) occurs in restricted areas where the coal is overlain by a thick fluvial gray shale (such as the Energy Shale Member that overlies the Herrin Coal Member). The gray shale, which predates marine trans ression, acted as an impermeable barrier that effectively reduced infiltration of seawater into the peat. The interpretation is consistent with sulfur-isotopic data indicating that bacterially reduced sulfate is a principal source of sulfur enrichment. High-sulfur coal is significantly enriched in molybdenum, boron, mercury, uranium, iron, and thallium relative to low-sulfur coal. Seawater is a possible source of the high molybdenum, boron, mercury, and uranium contents in high-sulfur coal. Concentrations of iron and thallium in seawater are very low, suggesting that these two elements were probably derived from a terrigenous source and transported to the swamp by rivers. Positive correlation between sulfur and all these trace elements in Illinois basin coal indicates that their variatio s are also related to the postdepositional sedimentary environment.

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