ERIONITE, A NATURALLY OCCURRING FIBROUS MINERAL HAZARD IN THE TRI-STATE AREA OF NORTH DAKOTA, SOUTH DAKOTA, AND MONTANA

Erionite, a naturally occurring fibrous zeolite mineral, was previously identified in the Killdeer Mountains of North Dakota and in several areas of the western U.S. associated with low temperature diagenesis of tertiary volcanics by alkaline groundwater. Recent sampling and analysis has expanded the detection of erionite south across the Tri-State region of North Dakota, Montana, and South Dakota associated with butte capping outcrops and eroded sediments derived from the Late Oligocene-Miocene Arikaree Formation as mapped in Montana and the Arikaree, Brule, and Chadron Formations as mapped in South Dakota. Disturbance of the erionite-bearing outcrop and sediments has occurred in some locales through fire suppression actions, aggregate mining, road construction, timber harvesting, recreational uses, agricultural and ranching activities.

Malignant mesothelioma disease clusters associated with erionite exposure have been recognized in Turkey since the late 1970s and recently in Mexico. Disease clusters have not been identified in the U.S. and the mineral remains largely unregulated here; however, animal studies indicate that some forms of erionite have the potential to be more carcinogenic than asbestiform minerals. Data collection and analysis efforts are underway at the state and federal level to identify the extent of naturally occurring erionite-bearing geologic materials and evaluate the exposure and potential human health hazard resulting from past management activities. Data from these studies should be incorporated into land use management decision-making and overall environmental management.