ERIONITE, AN ELUSIVE MINERAL: NEWLY IDENTIFIED ERIONITE BEARING STRATA IN CENTRAL AND NORTHWESTERN WYOMING

The U. S. Department of Interior Bureau of Land Management (BLM) is required to perform a National Environmental Policy Act (NEPA) analysis for most proposed actions on federal lands. These analyses include potential impacts to public health and safety. Erionite is a mineral that has potential to affect both public health and safety. Erionite is a naturally occurring zeolite mineral known to cause mesothelioma when respired. No regulatory, consensus standards or occupational exposure limits (OEL) exist for airborne erionite fibers. Erionite is known to occur in volcanic ash-falls and tuffs that are hydrothermally altered. Recommendations to limit exposure to erionite require that formations known to contain erionite be better identified. The BLM Washington Office Solid Minerals program decided to conduct an outcrop inspection of Eocene aged ash falls through the National Minerals Testing Laboratory (NMTL) located in Wyoming. The project is to see if erionite is present. Ash-fall tuffs on federally managed lands that had the potential to contain erionite were identified using geologic maps and aerial photography. BLM Direct Hire Authority Program interns working through the BLM’s NMTL conducted field studies of potential erionite bearing outcrops to test for erionite. Wagon Bed formation rocks were identified on Hawks Butte in Hot Springs County, WY. Eocene aged tuffs were identified on Jim Mountain in Park County, Wyoming. Miocene Split Rock formation ash containing erionite was identified in lacustrine sediments near Beulah Belle Lake in Natrona County, Wyoming. Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy (SEM-EDS) was used to identify erionite, along with X-Ray Diffraction (XRD) and polarized microscopy. Erionite is present at all three locations identified. Identification of erionite bearing strata provides a tool for best practice management decisions for the BLM and its sister agencies.