The dispersion of fibrous amphiboles by glacial processes in the area surrounding Libby,Montana, USA |
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| Authors: | William H Langer Bradley S Van Gosen Gregory P Meeker David T Adams Todd M Hoefen |
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| Institution: | (1) U.S. Geological Survey, Denver, CO, USA |
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| Abstract: | Mining operations began at a world-class vermiculite deposit at Vermiculite Mountain near Libby, Montana, circa 1920 and ended
in 1990. Fibrous and asbestiform amphiboles intergrown with vermiculite ore are suspected to be a causative factor in an abnormally
high number of cases of respiratory diseases in former mine and mill workers, and in residents of Libby. The question addressed
in this report is whether some of the amphibole from Vermiculite Mountain could have been dispersed by Pleistocene glacial
processes rather than by human activity after vermiculite mining began. The history of Pinedale glaciation in the Libby area
provides a framework for estimating the presence and distribution of asbestiform amphiboles derived from Vermiculite Mountain
and found in naturally occurring sediments of Glacial Lake Kootenai that underlie the Libby Valley area. There were two situations
where sediments derived from Vermiculite Mountain were deposited into Glacial Lake Kootenai: (1) as lake-bottom sediments
derived from meltwater flowing down Rainy Creek when the valley south of Vermiculite Mountain was free of ice but active ice
still covered Vermiculite Mountain; and (2) as lake-bottom sediments eroded from the Rainy Creek outwash and re-deposited
during a re-advance of the Purcell Trench Glacier lobe near Moyie Springs, Idaho. |
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