Fortunately significant sulfate evaporites occur in the older and deeper Mississippian and Devonian rock systems in central, south-central, and southeast Iowa. Mississippian evaporites occur in the St. Louis and Spergen Formations and were first discovered near Centerville in Appanoose County during exploratory drilling for coal by the Scandinavian Coal Company in 1910. The Centerville Gypsum Company eventually opened an underground mine to develop this deposit, but the mine closed in the early 1930s because of a slump in demand and because of high percentages of the contaminant anhydrite. Interest in the Mississippian gypsum was renewed after World War II, and exploration efforts at Albia in Monroe County, and Bussey and Harvey in Marion County proved the existence of significant subsurface gypsum deposits. Currently, Mississippian gypsum is extracted at the Durham Mine in Marion County by Kaser Corporation.
Devonian evaporites are present in the subsurface over a broad area of the state.
These deposits occur at several horizons in the Wapsipinicon and Cedar Valley Formations, and their existence was first noted in the early 1900s during the drilling of deep water wells. Geological Survey Bureau well records show that gypsum-anhydrite occurs in zones ranging in thickness from five to greater than 100 feet, and at depths between 400 and 2,000 feet. In 1960, the U.S. Gypsum Company opened the Sperry Mine in Des Moines County to become the first company to mine gypsum from the Wapsipinicon Formation. The potential for economic deposits of Devonian gypsum appears to be good, especially along the northern and northeastern margins of evaporite occurrence, where thick horizons of evaporite have been encountered in drilling at depths of between 400 and 700 feet. The future of the gypsum industry in Iowa seems bright, and it appears certain that Iowa will remain a major gypsum producing state well into the twenty-first century.