Mining geology in the Rosiclare fluorspar district

"The Illinois-Kentucky Fluorspar district is the largest of its kind in the United States and is one of the most important in the world. It lies on either side or the Ohio River in the extreme southeastern part of Illinois and the western part of Kentucky. The mineralized area is relatively small, embracing about 1500 square miles in all. On the Illinois side, the village of Rosiclare is the center of activity. With the exception of Cave-in-Rock, practically the entire production of Illinois comes from the immediate vicinity of Rosiclare and is produced by two companies, the Rosiclare Lead and Fluorspar Mining Co. and the Hillside Fluor Spar Mines.Fluorspar is of considerable economic importance. In the steel industry and in foundry practice it is extensively used as a flux. It is of especial advantage in the basic open hearth process where it not only lessens the viscosity of the slag but materially assists in the passage or impurities into the slag. It is used in the ceramic industry in the making of certain kinds of opalescent glass. It is also the principal source for the manufacture of hydrofluoric acid and is used to some extent in the aluminum industry.From a geological standpoint the district as a whole has always attracted considerable attention. The various phases of the historical, structural, and economic geology have been abundantly discussed at different times by the most capable of authorities. In general the country is composed of nearly flat-lying sedimentaries such as limestone, shale, and sandstone, which have been extensively faulted. Some of these faults have been subsequently filled with calcite, fluorite and associated minerals to form typical fissure veins. This injection from deep-seated magmas was probably in the order as named. It is probable that mineralization and faulting were contemporaneous to some extent and that the various minerals intruded overlapped each other in the several stages of vein filling"--Introduction, pages 1-2.