Session 3: Petrology and Mineralogy

Tuesday, 19 May 2020
8:00 AM - 12:05 PM

PRELIMINARY MINERALOGICAL INVESTIGATION OF BREATHITT GROUP SANDSTONES FROM BREATHITT COUNTY, KENTUCKY REVEALS UNEXPECTED MINERALOGICAL COMPLEXITY

Program: Virtual Meeting
Time: 8:00 AM – 12:05 PM

Authors

Abstract

Breathitt County, Kentucky is located in the western foothills of the Appalachian Mountains within Kentucky’s eastern coal field; roughly 30 miles north of Hazard, Kentucky and 85 miles southeast of Lexington, Kentucky. Surficial rocks in Breathitt County are defined by six types of major Pennsylvanian fluvial deposits: offshore siltstone, interbedded mouthbars, fine-grained floodplains, minor channel fills, major distributary channel fills, and major stacked-channel fills (Aitken et al. 1995). Previous work has identified silver and a lone occurrence of silt-sized gold, both associated with Breathitt Group Sandstones in Breathitt County. This project investigates possible sources or mechanisms of these metals by examining the mineralogy of thin sections of coarse channel lags of some Breathitt Group sandstones. Thin sections from were analyzed using Polarized Light Microscopy (PLM) and Scanning Electron Microscopy (SEM) paired with Electron Dispersive Spectroscopy (EDS). PLM defined each thin section as one the following: sandstone, conglomerate, laminated sandstone, and a micaceous sandstone. Most grains were rounded-subrounded varying from medium silt to coarse sand sized with heavily altered areas showing clay-fine silt sizes and well rounded-rounded grains. Each sandstone was defined as a subarkose wacke based on mineralogy, percent matrix, and lithology while the conglomerate was more represented as a sublithic-lithic wacke. Quartz, feldspars, and other aluminosilicates were present in all thin sections. Sericitic alteration was also present in all thin sections. Muscovite, biotite, chlorite, illite, ilmenite, siderite, and pyrite as well as other Fe, Ti, and Mg oxides and clays were common. Ilmenite had shown exsolution textures both in PLM and SEM between Fe and Ti as well as some other clays and oxides showing similar exsolution textures. SEM paired with EDS identified zircons, a beam sensitive Hg-S phase, and a Zn-S phase. Spherules of aluminosilicates with trace oxides were also found in SEM. Results indicate previously unrecognized mineralogical complexity in the Breathitt Sandstones of Breathitt County, Kentucky. Mineral composition is consistent with some contribution from a metamorphic source. Mercury and zinc phases may have some environmental and human health implications.

Geological Society of America Abstracts with Programs. Vol. 52, No. 5

doi: 10.1130/abs/2020NC-347812

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