EVALUATION OF GERMANIUM AND GALLIUM IN SPHALERITE COLLECTED FROM A MISSISSIPPI VALLEY TYPE DEPOSIT IN CENTRAL TENNESSEE, USA

Germanium and gallium are essential elements in the manufacturing of high-tech products, and the primary host for these elements is sphalerite. This study evaluates the spatial distribution of germanium and gallium at the Cumberland zinc mine in central Tennessee, USA. Mineralization at the Cumberland is classified as Mississippi Valley Type (MVT) and occurs along the flanks of the Nashville Dome, a part of the Cincinnati Arch situated between the Appalachian and Illinois basins. Mineralization consists of low iron sphalerite with minor galena, pyrite, fluorite, barite, and calcite hosted in Lower Ordovician, undeformed carbonate platform rocks. Mineralization occurs as replacement bodies in limestone units and as brecciated or fractured ore horizons in dolomite layers overlying limestone units. The latter style of mineralization occurs as open space fillings in collapse breccias that formed from the dissolution of the underlying limestone units. Fifteen samples of sphalerite and seven samples of calcite were collected from replacement ore bodies and brecciated ore zones at nine locations in the mine. Samples were crushed and hand-picked using a binocular microscope to isolate sphalerite and calcite. Samples were commercially analyzed via inductively coupled plasma mass spectrometry. Chemical data for calcite showed no detectable concentrations of germanium and gallium. Sphalerite samples contained elevated concentrations of germanium ranging from 221 to 453 ppm and gallium from 225 to >1000 ppm. These values are more elevated, in some case by an order of magnitude, than most MVT deposits worldwide. The data showed no detectable variation in concentrations spatially throughout the mine. Additionally, there were no notable variations in concentrations between the two styles of mineralization. This suggests the possibility that there was one pulse of mineralization or that the ore bearing fluids maintained a relatively consistent composition both spatially and temporally.