Regional Geochemical Results from the Analyses of Rock, Water, Soil, Stream Sediment, and Vegetation Samples -- Fortymile River Watershed, East-Central Alaska, 1998 Sampling
Dates
Year
2000
Citation
Crock, J. G., Gough, L. P., Wanty, R. B., Day, W. C., Wang, B., Gamble, B. M., Henning, M., Brown, Z. A., and Meier, A. L., 2000, Regional Geochemical Results from the Analyses of Rock, Water, Soil, Stream Sediment, and Vegetation Samples -- Fortymile River Watershed, East-Central Alaska, 1998 Sampling: US Geological Survey, v. open file report 00-0511, 15 plus tables.
Summary
INTRODUCTION This report briefly describes and presents geochemical and biogeochemical data for a cooperative study in the Fortymile Mining District, east central Alaska. This study is being funded by the U.S. Geological Survey (USGS) Mineral Resources Program through Fiscal Year 2001. Cooperative funds are being provided from various State of Alaska sources through the Alaska Department of Natural Resources. Results for the first field season completed in June 1997 are presented in Crock and others (1999). The study's second field season was completed in June 1998 and the results of the sample analyses for this phase of the study are presented here. Primary objectives of this study are: * Determine the regional baseline geochemistry [...]
Summary
INTRODUCTION This report briefly describes and presents geochemical and biogeochemical data for a cooperative study in the Fortymile Mining District, east central Alaska. This study is being funded by the U.S. Geological Survey (USGS) Mineral Resources Program through Fiscal Year 2001. Cooperative funds are being provided from various State of Alaska sources through the Alaska Department of Natural Resources. Results for the first field season completed in June 1997 are presented in Crock and others (1999). The study's second field season was completed in June 1998 and the results of the sample analyses for this phase of the study are presented here. Primary objectives of this study are: * Determine the regional baseline geochemistry (waters, soils, rocks, sediments, and selected terrestrial vegetation) for a section of the Fortymile River watershed currently being mined for placer gold (suction dredge and "cat" or dozer operations). * Determine regional watershed geochemical fluxes. * Assess the influence of geology on water-rock signatures, and using these signatures, try to differentiate sources of surface and hyporheic water (shallow groundwater near a streambed). * Determine the movement of metals through ecosystems of specific interest, such as permafrost muskeg terrain, upland alluvial forests, and riverine floodplain shrub systems. * Using both a geologic and a hydrologic framework, define the relative contribution of the various natural sources of arsenic and cadmium and other environmentally important metals to the landscape. * Assist the State of Alaska and the U.S. Environmental Protection Agency (USEPA) in the arsenic risk-assessment process. Background The USGS and the Alaska Department of Natural Resources (AK-DNR) are currently investigating the environmental geochemistry of a portion of the Fortymile and Goodpaster River watersheds (fig. 1). The management of the region and its resources is complex due to diverse ownership and the many land-use options. In 1980, the Fortymile River and its major tributaries were designated a Wild and Scenic Corridor by the Alaska National Interest Lands Conservation Act (ANILCA). Jurisdiction of the land bordering the watershed continued to be the responsibility of the U.S. Bureau of Land Management (USBLM). The AK-DNR has jurisdiction over the management of the river's recreation (rafting, canoeing, and fishing) and mining. The USEPA is also involved because mining discharges require compliance with the National Pollutant Discharge Elimination System (NPDES) of the Clean Water Act. Finally, both sport and subsistence hunting are important in the region and are managed by several Federal and State agencies. Placer gold was first discovered in the Fortymile River Mining District in 1886 and has been mined there ever since. Yeend (1996) provides a summary of the gold mining history of the placers of the Fortymile River region. Historically from 1886 to 1995, the Fortymile Mining District has produced about 16,640 Kg (534,974 oz) of gold (Swainbank and others, 1998). Along the North Fork of the Fortymile River, and just above its confluence with the South Fork, mining is currently limited to a small number of suction dredges which when combined produce only a few hundred ounces of gold per year. A cooperative effort between the USGS and the AK-DNR was initiated in 1997 to provide data to address water quality concerns, as well as to establish regional baseline geochemical and biogeochemical data (Crock and others, 1999; Wanty and others, 2000). In June 1998, we continued our work of the previous year (Crock and others, 1999) with field measurements of pH, turbidity, electrical conductivity, and stream discharge for the Fortymile River and many of its tributaries. At the same time, samples of soils, rocks, stream sediments, water, and vegetation were collected for chemical analysis, and sent to the USGS laboratories in Denver, Colorado. This report lists the analytical results of the 1998 sampling. Figure 2 depicts the sampling locations for the 1998 sampling efforts i the Fortymile watershed. The analytical results of the 1997 sampling are listed in Crock and others (1999). In addition, similar studies were initiated at and near the new Teck-Pogo gold discovery located about forty miles northeast of Delta Junction, Alaska in the Big Delta quadrangle (fig. 1). Important to this study's assessment will be the evaluation of the flux and biogeochemical cycling of arsenic and cadmium between the terrestrial and aquatic phases. In addition to studying water-rock processes that mobilize arsenic and cadmium, this project is also examining other factors that affect their bioavailability to the environment (for example, in sites that are mined verses unmined; vegetated verses barren; saturated (permafrost) verses drained; forested verses muskeg) {Crock, Larison and Gough, 2000; Gough and Crock, 1999; Gough and others, 2001}.
