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Scientific Investigations Report 2007-5246

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## Uranium in Surface Waters and Sediments Affected by Historical Mining in the Denver West 1:100,000 Quadrangle, Colorado

#### By Robert A. Zielinski, James K. Otton, R. Randall Schumann, and Laurie Wirt

| *Scientific Investigations Report*2007-5246 PDF (9.91 MB)*Scientific Investigations Report*2007-5246 PDF (9.91 MB)**Abstract**
Geochemical sampling of 82 stream waters and 87 streamsediments within mountainous areas immediately west ofDenver, Colorado, was conducted by the U.S. GeologicalSurvey in October 1994. The primary purpose was to evaluateregionally the effects of geology and past mining on the concentrationand distribution of uranium. The study area containsuranium- and thorium-rich bedrock, numerous noneconomicoccurrences of uranium minerals, and several uranium depositsof variable size and production history. During the samplingperiod, local streams had low discharge and were moresusceptible to uranium-bearing acid drainage originating fromhistorical mines of base- and precious-metal sulfides.

Results indicated that the spatial distribution of Precambrian          granites and metamorphic rocks strongly influences the          concentration of uranium in stream sediments. Within-stream          transport increases the dispersion of uranium- and thorium rich          mineral grains derived primarily from granitic source          rocks. Dissolved uranium occurs predominantly as uranyl          carbonate complexes, and concentrations ranged from less          than 1 to 65 micrograms per liter. Most values were less than          5 micrograms per liter, which is less than the current drinking water          standard of 30 micrograms per liter and much less than          locally applied aquatic-life toxicity standards of several hundred          micrograms per liter.          

In local streams that are affected by uranium-bearing acid          mine drainage, dissolved uranium is moderated by dilution          and sorptive uptake by stream sediments. Sorbents include          mineral alteration products and chemical precipitates of          iron- and aluminum-oxyhydroxides, which form where acid          drainage enters streams and is neutralized. Suspended uranium          is relatively abundant in some stream segments affected by          nearby acid drainage, which likely represents mobilization of          these chemical precipitates. The 234U/238U activity ratio of acid          drainage (0.95–1.0) is distinct from that of local surface waters          (more than 1.05), and this distinctive isotopic composition          may be preserved in iron-oxyhydroxide precipitates of acid          drainage origin.          

The study area includes a particularly large vein-type          uranium deposit (Schwartzwalder mine) with past uranium          production. Stream water and sediment collected downstream          from the mine’s surface operations have locally anomalous          concentrations of uranium. Fine-grained sediments downstream          from the mine contain rare minute particles (10–20          micrometers) of uraninite, which is unstable in a stream          environment and thus probably of recent origin related to mining.          Additional rare particles of very fine grained (less than          5 micrometer) barite likely entered the stream as discharge          from settling ponds in which barite precipitation was formerly          used to scavenge dissolved radium from mine effluent.       | Version 1.0

Posted May 2008
-  **Report** PDF (9.91 MB) 
- **Data Files for Table 4, 5, and 6** |
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**Suggested citation:**

 Zielinski, R.A.,  Otton, J.K., Schumann, R.R., and  Wirt, Laurie, 2008, Uranium in surface waters and sediments affected by historical mining in the Denver West 1:100,000 quadrangle, Colorado:  U.S. Geological Survey Scientific Investigations Report 2007–5246, 54 p.

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### Contents

Abstract

Introduction

Description of the Study Area

Uranium Mines and Mining History

Sampling

Analytical Methods

Waters

Sediments

Surface Water

General Chemical Character of Filtered Surface Water

Stream Discharge and Uranium Load

Aqueous Geochemistry of Uranium

Dissolved or Particulate Uranium

Spatial Distribution of Dissolved Uranium

Uranium Isotopes

Comparison of Stream-Water Concentrations with Water-Quality Standards

Stream Sediments

General Summary

Sediment Composition Variations Within the Main Stem of Clear Creek

Spatial Distribution of Uranium in Sediment

Sediment Concentrations and Sediment Quality Guidelines for Ecotoxicity

Fission-Track Radiography of Stream Sediments

Scanning Electron Microscope Observations

The Schwartzwalder Uranium Deposit

Description and Mining History

Previous Studies of Mining Effects

Mining Effects Determined in this Study

Conclusions

Acknowledgments

References Cited

Supplemental Files

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U.S. Department of the Interior | U.S. Geological Survey	URL: *http://pubsdata.usgs.gov/pubs/sir/2007/5246/index.html*	Questions or Assistance: Contact USGS	Last modified: Thursday, 01-Dec-2016 20:02:05 EST