SCANNING ELECTRON MICROSCOPY (SEM) OF NON-CLAY MINERAL COMPONENTS OF THE KOPE FORMATION AND THE MARTINSBURG FORMATION: INSIGHT INTO ENVIRONMENTAL PROPERTIES OF SHALES

A comparative analysis of non-clay mineral components of two Ordovician shales, the Martinsburg Formation in Pennsylvania and the Kope Formation in Northern Kentucky was done using scanning electron microscopy (SEM) to determine the nature and variability of the mineralogy and their environmental properties. Rare earth element (REE) phosphates are common in both lithologies however these minerals were far more abundant in the Martinsburg Formation. REE phosphates are commonly subhedral to euhedral and often have micrometer to nanoscale fractures. REE phosphates are known to contain minor to trace amounts of U and Th and fractures observed may serve as pathways for potential fluid interactions. Apatite was also observed in the Kope Formation samples by transmission electron microscopy and aggregates consisted of euhedral nanoscale crystals suggesting an authigenic origin. Like REE phosphates, apatite is known to have trace and minor amounts of U and Th. Fe-oxides are found to be common within the Martinsburg Formation whereas a variety of pyrite is common in the Kope Formation. Kope Formation pyrite occurs as both large multi-micrometer scale crystals as well as near nanoscale crystals. Pyrite in the Kope Formation has complex textures and very small particle size suggesting geomicrobiological processes occurred in a patchy spatial distribution. Discrete subhedral to euhedral biotite crystals approximately 20 to 30 micrometers in diameter were observed in some Kope material and appears likely to be volcanogenic. Rarely, cassiterite has been observed in Kope material as well. The results of this study provide constraints on the phases that control U series radionuclides which are a major environmental concern in hydraulic fracturing practices. Trace and minor mineralogy may also be controls on environmental background and a thorough understanding of these minerals may be important for understanding environmental or geologic background in the context of pollution.