MINERALOGY AND GEOCHEMISTRY OF SHALE, SLATE AND PHYLLITE FROM THE OAK LEVEL, BORDEN SPRINGS, AND INDIAN MOUNTAIN 7.5 MINUTE QUADRANGLES: A COMPARISON WITH THE ROCKMART SLATE AND ATHENS SHALE IN GEORGIA

Geologic mapping of the Oak Level, Borden Springs, and Indian Mountain, Alabama-Georgia, 7.5' quadrangles by Kath and Crawford (2011, 2012) and Crawford and Kath (2016) reveals the complex relationship between shales and slates of the lower Cambrian Chilhowee Group, middle Ordovician Rockmart Slate, and several Blue Ridge phyllites (possibly Heflin Phyllite, Abel Gap Formation, and Lay Dam Formation) along the metamorphic front in the hanging wall of the Emerson-Talladega Fault. Lithologic similarities between the Chilhowee Group shales/slates and Rockmart Slate have led to many different and inconsistent interpretations by previous workers in this area. Using field criteria developed during mapping, which included identification based on mineralogy, weathering characteristics, structural style, and associated interlayered lithologies, Kath and Crawford (2011, 2012) were able to consistently separate these similar mappable units; to test these mapping criteria, a combined qualitative x-ray diffraction (XRD) and geochemical analysis was conducted on samples of the shales and slates of the Chilhowee Group, Rockmart Slate, and phyllites from the Blue Ridge south of the Emerson-Talladega Fault zone. This study was further extended to include the Athens Shale, Heflin Phyllite and other phyllites collected from the Oak Level, Alabama-Georgia, and Fruithurst, Alabama, 7.5' quadrangles. XRD analyses of the shales and slates allow for some discrimination: the Chilhowee Group shales/slates contain albite or orthoclase feldspar, the Rockmart Slate contains chlorite and a dolomitic carbonate phase, whereas the Athens Shale samples all contain calcite; the phyllites all contain chlorite. Interestingly, the XRD patterns of the Rockmart Slate are indistinguishable from Heflin Phyllites.

Geochemically, the Chilhowee Group slates and shales are indistinguishable from the Blue Ridge phyllites, whereas the Rockmart Slate has a higher CaO and MgO content. Even higher CaO concentrations were found in the Athens Shale samples. Based on these results, the Chilhowee Group shales and slates are a possible protolith for the Blue Ridge phyllites, and Rockmart Slate may be a possible protolith for the Heflin Phyllite. Furthermore, the results of this study support the field criteria established by Kath and Crawford.