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U.S. Geological Survey Scientific Investigations Report 2009-5115

Stream-Sediment Geochemistry in Mining-Impacted Drainages of the Yankee Fork of the Salmon River, Custer County, Idaho

By Thomas P. Frost and Stephen E. Box

ABSTRACT

Thumbnail of and link to report PDF (16.5 MB)

This reconnaissance study was undertaken at the request of the USDA Forest Service, Region 4, to assess the geochemistry, in particular the mercury and selenium contents, of mining-impacted sediments in the Yankee Fork of the Salmon River in Custer County Idaho. The Yankee Fork has been the site of hard-rock and placer mining, primarily for gold and silver, starting in the 1880s. Major dredge placer mining from the 1930s to 1950s in the Yankee Fork disturbed about a 10-kilometer reach. Mercury was commonly used in early hard-rock mining and placer operations for amalgamation and recovery of gold. During the late 1970s, feasibility studies were done on cyanide-heap leach recovery of gold from low-grade ores of the Sunbeam and related deposits. In the mid-1990s a major open-pit bulk-vat leach operation was started at the Grouse Creek Mine. This operation shut down when gold values proved to be lower than expected.

Mercury in stream sediments in the Yankee Fork ranges from below 0.02 ppm to 7 ppm, with the highest values associated with old mill locations and lode and placer mines. Selenium ranges from below the detection limit for this study of 0.2 ppm to 4 ppm in Yankee Fork sediment samples. The generally elevated selenium content in the sediment samples reflect the generally high selenium contents in the volcanic rocks that underlie the Yankee Fork and the presence of gold and silver selenides in some of the veins that were exploited in the early phases of mining.

  • Report PDF (16.5 MB)
  • Data folder. The four tables in this report are provided here as data files in .xls, .txt, and .csv formats (352 kB total).
  • This report is available only on the Web.

For additional information:
Contact Information, Western Mineral Resources Science Center, Spokane Office
U.S. Geological Survey
904 W. Riverside Ave., Room 202
Spokane, WA 99201
http://minerals.usgs.gov/west/

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Suggested citation:

Frost, T.P., and Box, S.E., 2009, Streams-sediment geochemistry in mining-impacted drainages of the Yankee Fork of the Salmon River, Custer County, Idaho: U.S. Geological Survey Scientific Investigations Report 2009-5115, 49 p. and data files.



Contents

Abstract

Introduction

Regional Setting

Mineral Deposits

Sampling and Geochemistry

Results

Discussion

Suggestions for Additional Sampling

References Cited

four data tables

two Appendixes


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