Date of this Version
The Journal of Geology, 1994, volume 102, p. 111-116
The microdistribution of Mn (786 to 9480 ppm), Sr (<5 to 461 ppm), and Fe (52 to 16,700 ppm) was determined for cleat-filling calcites in the Herrin, Springfield, and Colchester Coals, using focussed synchrotron radiation. Compositional zonation in the calcites reflects a multistage history of precipitation from fluids with differing trace-element characteristics. In nearly all of the samples, a high Fe (≥~5000 ppm) calcite is the latest composition to form, replacing earlier stages with varying, but generally lower Fe contents. Partitioning data for Sr suggest that a typical calcite with 200 ppm Sr formed from a fluid with a Sr/Ca of about 0.005. This Sr/Ca is ~4 times lower than seawater, and ~12 times lower than the average for present day Illinois Basin saline formation waters. Formation of cleat-filling calcite is best explained by precipitation from fluids similar to present day dilute (shallow) formation waters having a meteoric source.