Introduction

Daisy Creek is a headwater tributary of the Stillwater River near Cooke City in south-central Montana (fig. 1) near the northeast corner of Yellowstone National Park. Water quality and aquatic habitat in Daisy Creek have been affected by acid rock drainage from the New World Mining District (Gurrieri, 1998), where mining started in 1869. The metals and acid in Daisy Creek are derived from waste rock and adit discharge at the McLaren Mine as well as from natural weathering of pyrite-rich mineralized rock that forms and surrounds the ore zones in the district.

 

Figure 1.  Location of New World Mining District and study area, Montana. (click here for pdf file)

Although the metals and acid in Daisy Creek are derived generally from the McLaren Mine area, the specific source areas and transport pathways are not well understood. In addition, the relative contributions of acid rock drainage from disturbed rock in mined areas and from mineralized rock that was not mined have not been quantified. Similarly, the relative importance of surface runoff and ground water (either shallow subsurface flow or deeper flow) as pathways for transporting metals to Daisy Creek is not well understood. Remediation activities are being planned for the McLaren Mine area by the U.S. Department of Agriculture-Forest Service (USDA-Forest Service) (Maxim Technologies, Inc., 1999) to improve water quality in Daisy Creek and the Stillwater River. Knowledge of the main sources and transport pathways of metals and acid can aid resource managers in planning and conducting effective and cost-efficient remediation activities.

Metal-loading studies have been useful in characterizing water quality in historical mining areas and identifying metal sources and pathways (Kimball, 1997; Kimball, Runkel, and others, 1999). In these studies, detailed profiles of metal loads along a stream are developed from streamflow data (obtained by tracer injection) and metal-concentration data (obtained by synoptic water-quality sampling) collected at many closely spaced sites. Downstream changes in metal loads in the stream then can be attributed to sources along the stream as well as to instream geochemical reactions. These sources can include visible surface inflows, such as discharge from mine adits or drainage from waste-rock and tailing piles, and ground water that enters the stream as subsurface inflow. Similarly, the relative contribution of metals from natural rock weathering in unmined areas can be investigated. Examples of this type of study are reported by Kimball and others (1994, 1998) for streams affected by acid rock drainage in Colorado and by Kimball, Nimick, and others (1999) for Fisher Creek (fig. 1), another stream draining the New World Mining District. The methods described in these reports were used during this study to quantify metal loads in Daisy Creek and a short reach of the Stillwater River.

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