INITIAL ELECTRON MICROSCOPY INVESTIGATIONS OF HISTORICAL TALC ORE SAMPLES FROM THE YELLOWSTONE MINE, MONTANA

Talc is a hydrous phyllosilicate mineral that is commonly used in a wide range of industrial, commercial, and personal care applications. Talc is generally mined from either carbonate metasedimentary hosted deposits or altered mafic and ultramafic deposits. An example of the former is the Yellowstone mine in Montana where mining operations began in the 1950s and where annual average production of talc ore approximates 300,000 tons. Petrogenesis of the Yellowstone Mine talc is associated with hydrothermal alteration of dolomitic marble protoliths during the Proterozoic. This study aims to provide further insights into the nature of the Yellowstone Mine talc through a detailed scanning and transmission electron microscopy (SEM, TEM) investigation. Samples were collected during the 1970s by the Montana Bureau of Mines and Geology. An initial analysis of these samples was conducted with TEM and SEM utilizing grain mount sample preparation methods. Current TEM-Energy dispersive spectroscopy (EDS) analysis indicates that Fe is a common cationic substituent in talc particles. Minor F content is common but does not occur in all talc present. Fe-oxides are frequently observed, including a 300 nm Fe-oxide containing minor V and Ti. SEM-EDS analysis is ongoing. Electron microscopy findings are broadly consistent with existing literature on talc deposits in general. This work can provide constraints for future studies and work is ongoing to better refine the mineralogical nature and geologic history of the mine.