FORMATION OF ASBESTIFORM TALC FROM NON-ASBESTIFORM CHAIN-SILICATES IN THE GOUVERNEUR, NEW YORK TALC MINING DISTRICT

We characterized the chemical composition and morphology of minerals in rock samples and processed products from two former talc mines owned by the R. T. Vanderbilt Co. in the Gouverneur Mining District, New York. The main mineral phases within these samples are tremolite, anthophyllite, and talc with serpentine, quartz, calcite, and diopside. Bulk analyses of the samples were performed by powder X-ray diffraction (XRD) for structural phases and by X-ray fluorescence (XRF) for bulk chemical composition. Precise compositional data of individual grains were collected by wavelength dispersive spectroscopy (WDS) using an electron microprobe. Mineral formulas were calculated from the resulting weight percent oxides. The morphology of the different mineral phases was observed with backscatter electron (BSE) images and polarized light microscopy (PLM).

All of the mineral phases analyzed have near end-member compositions. The compositions and morphology of the minerals do not vary significantly between the two mines. Tremolite occurs in the samples mainly as unaltered, blocky crystals. Anthophyllite occurs in blocky and acicular textures often with a series of fractures perpendicular to the long axis of the crystal; we saw no asbestifrom anthophyllite in the 10's of samples we studied. Talc occurs both as platy crystals and as fine-grained asbestiform particles as alteration products of primarily anthophyllite, but also of manganocummingtonite and diopside. (Partial support for this project was provided by R. T. Vanderbilt Co.)