SECONDARY MINERALIZATION IN NODULAR SIDERITE LAYERS FOUND IN INTERBEDDED SHALES FROM BREATHITT COUNTY, KENTUCKY

Siderite beds in outcrops of the Grundy Formation / Breathitt sandstone group in northern Breathitt County, Kentucky are poorly understood. Siderite occurs as isolated concretions, stringers of concretions and coherent beds 3-5 cm thick. The most common mode of occurrence is the continuous 3-5 cm thick beds that are interbedded with black shales. Siderite samples were collected to investigate the spatial relationship and chemical gradients with relation to neighboring shale. The nodular siderite samples collected were broken to investigate the internal mineralogy. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) indicate veins found in the siderite are composed of multiple secondary mineral phases. EDS shows concentrations of Fe, Cr, S, Zn, and Ag which suggest mineral phases such as pyrite, crocoite, sphalerite and silver. The mechanisms for secondary mineralization are currently unclear but suggest complex oxidation-reduction chemistry. Secondary mineral phases were observed primarily in siderite nodules and to a lesser extent in surrounding massive siderite beds or shale. Siderite nodules containing secondary mineralization were found in localized areas at the base of outcrops where there is evidence of deformation. Future work will focus on the distribution of the secondary mineral phases within the surrounding sedimentary units (i.e. shale and sandstone). The identification of metals of environmental concern have implications for local water resources. The complexity of the siderite points to the need for more detailed work