ERIONITE IN TUFFS OF NORTH DAKOTA: THE NEED FOR ERIONITE HAZARD MAPS

Erionite occurs in altered tuffs within the late Oligocene to early Miocene Arikaree Formation in the Killdeer Mountains of North Dakota. Erionite there formed through diagenesis involving increasing alkalinity of pore water as revealed by the petrographic sequence of glass grain dissolution--montmorillonite--erionite--calcite. In the early 1980's a mining and rock crushing operation took place within the Killdeer Mountains involving these erionite-containing sediments. That mined material appears to have been used in asphalt. The mine site is no longer active and has been partially reburied. Erionite is listed as a Group 1 carcinogen by the IARC and as a known human carcinogen by the NIH. Some studies suggest erionite to be more toxic than asbestos. Today, a 90-day advance notice must be provided the EPA before putting erionite to any use. Today, mining should abandon sites found to contain erionite. Two years ago, a consulting laboratory was engaged to determine the mineralogy of material to be mined from the Cretaceous Linton Ash of North Dakota. Erionite had not been previously found in that ash, but the consulting laboratory reported erionite in the material they tested apparently by XRD. That finding has not been able to be duplicated and is thus questioned. An effort is underway to map erionite hazard zones in North Dakota, as a precaution against future inadvertent mining. There are numerous tuffs in North Dakota. Being the product of diagenesis, erionite is not expected to occur along all portions of an altered tuff, thus careful petrography is being used to determine factors of predictive value for mapping of hazard zones.