ONGOING ELECTRON MICROSCOPY INVESTIGATIONS OF TALC AND ASSOCIATED MINERALS FROM THE YELLOWSTONE MINE, MONTANA

Talc is a hydrous phyllosilicate mineral that has wide applications within the context of industrial, commercial, and consumer products. Talc is typically mined from altered mafic to ultramafic deposits or carbonate metasedimentary deposits. Due to the complex geologic histories of these deposits, the potential exists for numerous impurities to occur. A review of available United States Geological Survey, and previous United States Bureau of Mines data, indicates that Montana has been a major producer of talc since the 1940s and has generally sustained an increasing production trend. One of the major sources of talc in Montana is the Yellowstone mine. Detailed textural, mineralogical, and geochemical investigations of talc materials from the Yellowstone mine are sparse. The work presented here details results of continuing scanning electron microscopy (SEM) and transmission electron microscopy (TEM) efforts on some historical ore samples from the Yellowstone Mine obtained from the Montana Bureau of Mines and Geology. TEM-Energy dispersive spectroscopy (EDS) analysis indicates that Fe is a common cationic substituent in talc. Fluorine is observed in some talc particles but is not ubiquitous. Several Fe-oxides are present in addition to V-bearing Fe-oxide and zircons. A variety of minerals containing the following metals occur: V, Ti, Au, Ag, Cr, Ni, Al, and Pb, but not all minerals have been identified. The observed minerals, and the F content of some talc particles, is consistent with hydrothermal origins of the talc deposits. The diversity of minerals observed has not been previously recognized within this deposit and indicates the geochemistry and mineralogy of the Yellowstone Mine talc deposits is complex. Although these are initial findings, results warrant further investigation of talc ore samples and talc materials derived from ores over the life of the mine. Results open questions regarding potential human exposure, and the variability of the talc ores’ environmental properties from the Yellowstone Mine over its operational period. Detailed investigations of talc ores and derived materials using TEM, SEM, and bulk chemistry may potentially provide geochemical fingerprinting for talc sources and provide some constraints for medical professionals conducting health investigations.