Environmental effects of hydrothermal alteration and historical mining on water and sediment quality in Central Colorado

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Abstract

The U.S. Geological Survey conducted an environmental assessment of 198 catchments in a 54,000-km2 area of central Colorado, much of which is on Federal land. The Colorado Mineral Belt, a northeast-trending zone of historical base- and precious-metal mining, cuts diagonally across the study area. The investigation was intended to test the hypothesis that degraded water and sediment quality are restricted to catchments in which historical mining has occurred. Water, streambed sediment, and aquatic insects were collected from (1) catchments underlain by single lithogeochemical units, some of which were hydrothermally altered, that had not been prospected or mined; (2) catchments that contained evidence of prospecting, most of which contain hydrothermally altered rock, but no historical mining; and (3) catchments, all of which contain hydrothermally altered rock, where historical but now inactive mines occur. Geochemical data determined from catchments that did not contain hydrothermal alteration or historical mines met water quality criteria and sediment quality guidelines. Base-metal concentrations from these types of catchments showed small geochemical variations that reflect host lithology. Hydrothermal alteration and mineralization typically are associated with igneous rocks that have intruded older bedrock in a catchment. This alteration was regionally mapped and characterized primarily through the analysis of remote sensing data acquired by the ASTER satellite sensor. Base-metal concentrations among unaltered rock types showed small geochemical variations that reflect host lithology. Base-metal concentrations were elevated in sediment from catchments underlain by hydrothermally altered rock. Classification of catchments on the basis of mineral deposit types proved to be an efficient and accurate method for discriminating catchments that have degraded water and sediment quality. Only about 4.5 percent of the study area has been affected by historical mining, whereas a larger part of the study area is underlain by hydrothermally altered rock that has weathered to produce water and sediment with naturally elevated geochemical baselines. 

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Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Environmental effects of hydrothermal alteration and historical mining on water and sediment quality in Central Colorado
Year Published 2009
Language English
Publisher U.S Geological Survey
Publisher location Reston, VA
Description 11 p.
Larger Work Type Report
Larger Work Subtype USGS Numbered Series
Larger Work Title Planning for an uncertain future - Monitoring, integration, and adaptation (SIR 2009-5049)
First page 85
Last page 95
Conference Title Third interagency conference on research in the watersheds
Conference Location Estes Park, CO
Conference Date September 8-11, 2008
Country United States
State Colorado
Online Only (Y/N) N
Additional Online Files (Y/N) N