Abstract Minerals have been extracted from the Illinois-Kentucky Fluorite District for over 170 years. Theories concerning the inter-relationship between the fluorite mineralization, tectonism, and igneous activity will be discussed by several geologists during this field trip. The Columbia mine (vein deposit) will be visited in Kentucky, and the only mine currently producing fluorite in this district, the Hastie Limestone Quarry (strata-bound deposit), will be visited in Illinois. The mining history of this region will be explained at the American Fluorite Museum, where numerous mineral specimens can be examined. The Hicks Dome, a Permian crypto-volcanic feature (?) in Illinois, will also be discussed. The trip will conclude with a walking tour at the Garden of the Gods Recreational Area to view the Eagle Valley Syncline and Lower Pennsylvanian units.

Abstract The Okorusu deposit, located in north-central Namibia about 200 km north of Windhoek, is the largest fluorite deposit in Namibia. Its annual production of 40,000 tons fluorspar concentrate per year rivals recent annual concentrate production from the Southern Illinois-Kentucky Fluorspar District. The Okorusu ores consist of massive replacement fluorite and large fluorite crystals deposited in vugs. Purple and green replacement fluorite contains abundant finely crystallized inclusions of quartz, apatite, goethite, and calcite, together with minor strontianite, barite, rutile, pyrite, galena, and synchysite. The fluorite deposits at Okorusu are spatially related to an alkaline igneous-carbonatite ring dike complex. The presence of apatite, synchysite, and elevated rare earth element (REE) concentrations in the Okorusu fluorite ores indicate that those ores are also genetically related to that alkaline complex. Poorly studied deep fluorite ores in the Hicks Dome area of the Southern Illinois-Kentucky Fluorite District share some similarities with the Okorusu fluorite ores.

Abstract This guidebook complements the field trips offered during the 42nd Annual Meeting of the GSA North-Central Section, held in Evansville, Indiana. Topics include analysis and correlation of Silurian depositional sequences across the Cincinnati Arch in Ohio, Kentucky, and Indiana; conodonts and Pennsylvanian stratigraphy in southwestern Indiana; relationships between tectonism, igneous activity, and fluorite mineralization within the Illinois-Kentucky Fluorite District; characteristics and origin of the highly eroded Pennsylvanian sandstones at the Garden of the Gods in Illinois; use of filled-fracture features as indicators of seismicity within the lower Wabash and Ohio River valleys; and hydrogeology of an abandoned mine site in Indiana, with applications to planning for disposal of coal-combustion products. Two chapters focus on the history of New Harmony, Indiana, which served as headquarters for the pioneering naturalists who worked to characterize and map this country's interior. Another chapter relates the history of Evansville to the availability and use of geologic materials, with discussions on the characteristics and origins of building stones, building techniques, and architectural styles. References to mining history, with respect to building stone, coal, and fluorite, are made throughout.

Abstract Many strata-bound Zn-Pb ± Ag mineral occurrence in carbonate rocks of Alaska have characteristics of Mississippi Valley-type deposits as well as similarities to Irish Carboniferous Zn-Pb deposits. Common characteristics are a simple mineralogy low Fe sulfide content, no apparent igneous association, partial dolomitization or silicification of wall-rock limestone, variable barite and fluorite content, and structural preparation, often brecciation, of host rocks. Zinc-rich, smithsonite-dominant prospects in the Reef Ridge district, central Alaska, and the Charley River and Livengood areas of east-central Alaska contain solution, karst, and shatter breccias indicating structural preparation of host rocks; they are the closest Alaskan analogues to Mississippi Valley-type deposits. Epigenetic prospects of various forms, with variable amounts of Zn, Pb, Ag, fluorite, and barite, in southeastern, northern, and east-central Alaska and on the Seward Peninsula, may also have formed by Mississippi Valley-type mechanisms and are similar to areas such as the Illinois-Kentucky fluorspar district. Several prospects on the Seward Peninsula and in central and eastern interior Alaska with lensoid and disseminated Pb-Zn-Ag mineralization may have a diagenetic origin similar to that of Irish stratabound Zn deposits. Lead- and Ag-enriched occurrences on the Seward Peninsula and in southeastern Alaska may be higher temperalute carbonate-replacement deposits distal to, and genetically derived from, felsic intrusions. The age of formation of carbonate-hosted Zn-Pb ± Ag mineral occurrences in Alaska ranges from no earlier than latest Proterozoic (Three Castle Mountain) to Tettiaay(?) (Mo-Udall). The fluids that formed them were apparently derived from latest Proterozoic(?). Paleozoic, and Mesozoic mixed carbonate and siliciclastic basins. The sedimentologic, diagenetic, and tectonic history of these basins, and the chemistry and migration pathways of mineralizing fluids, are poorly known. Strata-bound Cu ± Co ± Zn sulfide stockworks in Alaska are unusual epigenetic deposits in Late Proterozoic to Devonian carbonate rocks. The larger Alaskan occurrences (Ruby Creek, Omar) are similar to Irish Cu deposits related to basin dewatering and to Australian Cu deposits interpreted as proximal vent sites for shalehosted Zn-Pb-Ag massive sulfide deposits ("sedex"). These Cu ± Co ± Zn stockworks have stratigraphic and tectonic settings similar to many of the carbonate-hosted Zn-Pb ± Ag deposits. Their different metal contents may result from fluids derived from different sources passing through aquifers of different composition and/or may indicate a mafic rock source for elements such as Co. Small noneconomic Cu occunences on the Seward Peninsula have been interpreted as a tectonogenic mineralization related to thrust fault formation. Extensive, locally thick Late Proterozoic and Paleozoic platform carbonate rocks, and some mixed carbonateclastic slope or basinal facies in Alaska, are prospective for additional Zn-Pb ± Ag strata-bound and stockwork Cu ± Co ± Zn deposits. Thinner, Pennil to Jurassic carbonate sequences outboard of the displaced North American continental margin are less likely hosts for these deposits.

Abstract On the first day, we travel from St. Louis to Lebanon, Tennessee, via Rosiclare, Illinois. The purpose of the detour is to take a brief look at one example of the fluorite mineralization in the Illinois-Kentucky fluorspar district. We will arrive at Lebanon fairly late in the evening.