RAPID X-RAY FLUORESCENCE ANALYSIS OF PYRITIFEROUS BLACK SHALE: A CASE STUDY OF THE MIDDLE-LATE DEVONIAN MILLBORO SHALE FROM SW-VIRGINIA

Recent advancements in portable analytical technologies offer promise for a more rapid, yet dependable, investigation of mineralogy of many lithologies including black shales. X-ray Fluorescence (XRF) is one form that is quickly evolving into the development of cost-effective and reliable field-use models. However, field versus lab-based studies are needed to evaluate the application-potential of such technology before its use in environmental assessment and mitigation projects. In this paper, we present results of our evaluation of a portable, XRF instrument used to analyze elemental profiles of various mineral phases in the Millboro Shale.

The Millboro Shale is a Middle-Late Devonian unit that extends through West Virginia, Virginia, Tennessee, Maryland, and Pennsylvania. This shale is abundant in organic-carbon rich sediment typical of a shallow-marine depositional setting. Consisting of highly-pyritized intervals, this shale oxidizes to produce sulfuric acid presenting a hazard to local groundwater.

This research proposes that using Low-Sulfur Polypropylene Thin Film, as opposed to Mylar Thin Film, reveals a strong correlation with sample extraction and laboratory analysis. Polypropylene thin film is more receptive to light elements, allowing for more accurate field analyses. This shale is ideal for such a study due to its variability of bioturbation and mineralogy including clay minerals, quartz, gypsum, calcite, and abundant pyrite. The degree of bioturbation for samples was noted using the Droser-Bottjer ichnofabric index.

By rappelling down a ten-meter outcrop of Millboro Shale in Radford, Virginia, researchers analyzed samples using the portable XRF at regular intervals which were then extracted for laboratory analysis. Tests are also being done to show variations in data gathered at high moisture levels. Comparing the field and lab data will reveal the validity of the portable XRF, making near-instant field analyses more convenient than laboratory analyses.