MINERALOGY AND RADIOGENIC ISOTOPES OF THE BELL-ORREN PROSPECT: A MISSISSIPPI VALLEY-TYPE SURFACE VEIN IN CENTRAL TENNESSEE

Mississippi Valley-type (MVT) deposits are found globally with a range of mineralogic characteristics, formed in part from fluids driven out of foreland basins during orogenic events. These deposits are a source of lead, zinc, fluorspar, and barite, and some deposits including those in the Central Tennessee district have known byproducts of gallium and germanium. In the past, MVT deposits may have been overlooked as a source of critical metals of recently-growing economic importance such as indium, rhenium, and platinum group elements. Investigation of regional occurrences and trends can help to answer questions on the genesis of these deposits, such as the source of metals and timing of the large ore-forming systems.

Located ~3 miles west of Lascassas, Tennessee within outcrops of Ordovician Ridley limestone, the Bell-Orren prospect consists of two small shafts about 25-35 ft deep. The shafts were excavated around the year 1900 and have remained relatively untouched since. Historic reports indicate a mineralized MVT vein at the site that strikes northeast with near vertical dip. In this study, samples were obtained from waste piles surrounding one of the shafts. The mineralogy was determined to be predominantly barite (BaSO₄) with cross-cutting colorless fluorite (CaF₂) veins that contain abundant galena (PbS). Less abundant phases include red-brown fluorite, coarse-grained calcite (CaCO₃), and an Fe-poor sphalerite (ZnS). A yellow-white fluorescing strontianite (SrCO₃) has been observed in-filling radial growth barite and along red-brown fluorite fractures and grain boundaries. Fluorescence petrography of doubly polished thick sections has identified two-phase (oil and gas) and three-phase (oil, gas, and water) petroleum-bearing fluid inclusion assemblages along secondary trails in the red-brown fluorite.

Fluorite Sm-Nd will be used to determine an age of fluorite mineralization to compare with other MVT deposit ages in the Central Tennessee, East Tennessee, and Kentucky-Fluorspar districts. Trace element and REE analysis of whole rock and fluorite samples will help to identify the potential for overlooked critical metals and uniqueness of fluorite phases. Lead isotope analysis of barite, fluorite, galena, and calcite may further identify source and timing of unique mineralizing events.