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Open-File Report 2010-1056

Examination of Libby, Montana, Fill Material for Background Levels of Amphibole from the Rainy Creek Complex Using Scanning Electron Microscopy and X-Ray Microanalysis

By David T. Adams, William H. Langer, Todd M. Hoefen, Bradley S. Van Gosen, and Gregory P. Meeker

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Natural background levels of Libby-type amphibole in the sediment of the Libby valley in Montana have not, up to this point, been determined. The purpose of this report is to provide the preliminary findings of a study designed by both the U.S. Geological Survey and the U.S. Environmental Protection Agency and performed by the U.S. Geological Survey. The study worked to constrain the natural background levels of fibrous amphiboles potentially derived from the nearby Rainy Creek Complex. The material selected for this study was sampled from three localities, two of which are active open-pit sand and gravel mines. Seventy samples were collected in total and examined using a scanning electron microscope equipped with an energy dispersive x-ray spectrometer. All samples contained varying amounts of feldspars, ilmenite, magnetite, quartz, clay minerals, pyroxene minerals, and non-fibrous amphiboles such as tremolite, actinolite, and magnesiohornblende. Of the 70 samples collected, only three had detectable levels of fibrous amphiboles compatible with those found in the rainy creek complex. The maximum concentration, identified here, of the amphiboles potentially from the Rainy Creek Complex is 0.083 percent by weight.

First posted March 30, 2010

For additional information contact:

USGS Central Mineral and Environmental Resources Science Center
Box 25046, MS-973
Denver Federal Center
Denver, CO 80225

http://minerals.cr.usgs.gov/

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Suggested citation:

Adams, D.T., Langer, W.H., Hoefen, T.M., Van Gosen, B.F., and Meeker, G.P., 2010, Examination of Libby, Montana, fill material for background levels of amphibole from the Rainy Creek complex using scanning electron microscopy and X-ray microanalysis: U.S. Geological Survey Open-File Report 2010-1056, 10 p.



Contents

Abstract

Introduction

Background

Sampling

Sample Preparation

Results

Conclusions

References Cited


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