A hydrothermal system in the Midcontinent region

Abstract

The Mississippi embayment syncline is proposed as a source of mineralizing solution for several mineral districts around the periphery of the embayment.Information developed by various forms of investigation in the Illinois-Kentucky fluorspar district has established certain requirements to form the mineral deposits of that district. The structural system of the fluorspar district is well known. Lateral migration of solutions is suggested in many of the deposits. The temperature range and chemical composition of the ore solution have been determined. Extensive solution of limestone in the area indicates that large volumes of solution were required to produce the deposits.Several features of the embayment suggest that it was the source of the ore solution for the fluorspar district. The structural system of the embayment appears to be related to the structure of the fluorspar district. The presence of evaporites and metal-rich brines in the embayment could account for the chemistry of the ore solutions. Evidence of extensive igneous activity in the embayment during Upper Cretaceous times suggests that this was the source of thermal energy for heating and propelling the solutions. The age and period of development of the embayment indicate that it may have been the source of large volumes of solution within the time period of formation of the deposits.Mineral zoning in three of the mineral districts indicates a common source of the base metal and barium minerals and a northerly direction of migration is indicated.