PRELIMINARY INVESTIGATION OF RADIOGENIC ISOTOPES OF MISSISSIPPI VALLEY-TYPE MINERALIZATION ACROSS CENTRAL TENNESSEE AND KENTUCKY

In the past, Mississippi Valley-type (MVT) deposits in central North America were primarily exploited for lead and zinc. Critical metals are gaining increasing importance in various industries. Notably, sphalerite, a key mineral found in MVT deposits is an important source of zinc and is also a significant source of gallium and germanium. In this study, we are investigating radiogenic isotopes in minerals from multiple occurrences of MVT mineralization in central Tennessee, south-central Kentucky, and central Kentucky to gain a deeper understanding of the mineralizing systems responsible for the deposition of sphalerite, galena, and fluorite in these occurrences. Our main objective is to elucidate the genetic relationship between the various mineral occurrences in the region. Furthermore, results of this study may also help to inform exploration efforts in the future.

Preliminary lead isotope data of galena from across central Tennessee show a range in ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios (19.58-19.73, 15.72-15.751, and 39.12-39.34, respectively). These ratios fit in a continuum of increasingly radiogenic ratios from deposits in the east (Appalachian region) westward through the Illinois-Kentucky Fluorspar District (IKFD) and into Missouri. Lead isotopes of galena samples from central Kentucky will help to verify this trend. Fluorite rare earth element (REE) concentrations from samples across central Tennessee show similar chondrite-normalized REE distribution patterns, mostly with positive europium anomalies. Light- to medium-REEs (atomic numbers 57-67) show only minor enrichment or depletion, whereas these fluorites are depleted in the heavy-REEs (68-71). This suggests that fluorite from across the region precipitated from a similar fluid system. This is in direct contrast to the IKFD where highly variable fluorite REE distribution patterns are observed across various occurrences. A fluorite Sm-Nd isochron did not produce a reliable age estimate of fluorite mineralization. Nevertheless, these data suggest a less radiogenic fluid source unique from those previously documented in the IKFD. Sphalerite samples from central Tennessee are being analyzed for Rb-Sr isotopes to date the mineralization, to characterize the mineralizing fluids, and to identify fluid and metal sources.