Paper No. 5
Presentation Time: 2:25 PM
THE SEARCH FOR ASBESTOS WITHIN THE PETER MITCHELL TACONITE IRON ORE MINE, BABBITT, MINNESOTA
Asbestos crystallizes within rock formations undergoing intense deformation characterized by folding, faulting, shearing, and dilation. Such conditions prevailed during formation of the taconite iron ore deposits in the eastern Mesabi Iron Range of Minnesota, which includes the Peter Mitchell taconite mine at Babbitt, Minnesota. The mine pit is over 8 miles long, up to 1 mile wide. We collected 53 samples from 30 areas within the pit where fibrous minerals might occur, that is those areas showing deformation. Samples from seven stops contain significant amounts of ferroactinolite amphibole that is partially to completely altered to fibrous actinolite. Two samples contain ferroactinolite degraded to ropy masses of fibers consisting mostly of ferrian sepiolite. Eight samples contain unaltered ferroactinolite as well as ferroactinolite partially to completely altered to fiber bundles defined by X-ray diffraction and chemical analysis as ferrian sepiolite and/or fibrous grunerite. The fibrous amphiboles and ferrian sepiolite collected at the Peter Mitchell mine composes a tiny fraction of one percent of the total rock mass of the taconite deposit; an even a smaller amount gets into the ambient air during mining. The fibrous minerals thus do not present a significant health hazard to the miners or to those non-occupationally exposed.