Salmon River Mountains Legacy Mining Studies Active

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Study Area Background

The Salmon River in central Idaho is a headwater tributary of the Columbia River watershed. The study area is in the U.S. Department of Agriculture (USDA) Payette and Boise National Forests. Mining records maintained by the Idaho Geological Survey include hundreds of legacy mines and prospects within this watershed, with commodities including gold (Au), silver (Ag), antimony (Sb), tungsten (W), mercury (Hg), cobalt (Co) and iron (Fe).  Historically mined areas on the South Fork Salmon River include Secesh River, Johnson Creek, with placer Au mining along the main branch of the South Fork Salmon River. Much of the Middle Fork Salmon River is within the Frank Church – River of No Return Wilderness Area (FC-RNR). Legacy mining areas on the Middle Fork Salmon River include the Golden Hand Mine in the Big Creek tributary, approximately three miles in from FC-RNR boundary, and Monumental Creek. While previous USGS studies (Holloway et al., 2017; Etheridge, 2015) have characterized impacts of legacy mining in the Stibnite and Cinnabar areas on the East Fork South Fork Salmon River, potential impact of legacy mining on surface and groundwater quality affecting fisheries in other areas within this region have not yet been addressed. Stakeholders for this area include the Nez Perce Tribe (NPT), the U.S. Fish and Wildlife Service (USFWS), the USEPA, Idaho Department of Environmental Quality (ID-DEQ), Payette National Forest, Boise National Forest, and Midas Gold, Ltd.

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Study Objective

This effort seeks to characterize the regional impact of legacy mining in the context of framework geology for the Salmon Mountains in central Idaho. The project structure has three interrelated tasks on framework geology, watershed biogeochemical processes, and trace metal characterization of sediment and tailings.

Framework Geology: Previous USGS studies of wilderness areas (e.g., Idaho Primitive Area, Sawtooth Primitive Area) produced unpublished data that are not readily available for general interpretations. These data often do not have accurately located samples, but can potentially provide information on the background and mining-impacted geochemistry in remote areas within the Middle Fork Salmon River watershed. Many of these legacy studies have stream sediment, rock and tailings samples archived on the Denver Federal Center. We are using original field notes and maps to accurately identify locations for these samples where possible. A subset of these samples will be selected for geochemical analyses based on geologic setting, presence or absence of mining, and watershed location. Samples will be selected to include sites above legacy mining sites and areas that directly downstream from legacy mining activity. Major mineral deposit types in the region include gold/antimony, copper/cobalt, and mercury.

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Watershed Biogeochemical Processes: This task will identify and evaluate the potential environmental degradation in low-order watersheds selected based on geologic setting (evaluated through the framework geology task), primary ore deposit type, and access to streams with and without legacy mining activity to determine background water chemistry. Aqueous geochemistry, sedimentation, and present or absence or key fish species identified in partnership with the Nez Perce Tribal Fisheries Program will be used as metrics. This task has two phases:

1. Geospatial data: Available geology, hydrology, and USMIN mineral deposit data supplemented with mining records from the Idaho Geological Survey are being used to select paired mined and unmined low-order watersheds within distinct geologic contexts. The geospatial approaches used are being developed in conjunction with the multi-scale screening techniques study.  Geochemical data acquired through this project will be integrated with this platform. We have established a base that includes hydrology coverages, geologic basemap, and mine/prospect locations and records acquired through the Idaho Geological Survey.
2. Field studies: Sites selected using geospatial data will be sampled for surface water and ground water at seeps and adits to determine redox chemistry for As, Sb and Hg, and to screen for other trace metals. This approach allows the identification of geologic background concentrations of constituents of environmental concern on a regional basis, placing legacy mine impacts in the context of natural background levels. The presence or absence of key fish species (bull trout, steelhead, Chinook salmon, and sculpin) will be determined using eDNA. 
   
   Further background studies on seasonality of mercury and arsenic loads on Cinnabar Creek are needed to inform the design of remediation activities conducted by the USEPA and potentially other stakeholders. This work is in cooperation with the USGS Idaho Water Science Center, who will be working with us to establish an autosampler station for collection of water during peak flow events.

Trace Metal Characterization of Sediments and Tailings: Task objective is to identify headwater streams within the Salmon River watershed that have potentially elevated input of geologic sources of trace metals and impacts linked to legacy mining activity. Many areas within the Wilderness Area are challenging to access within the scope of this study, thus archival materials will be relied upon for data in the Middle Fork Salmon River watershed. Geochemical stream sediment data collected during previous USGS studies in the area (Eppinger et al., 2003, Erickson et al., 2017) will be screened for association with selected geology types and presence or absence of mines, and commodity types associated with historical mining. The geospatial data analysis from the watershed biogeochemistry task will be used to select archived samples for reanalysis to characterize mercury, antimony, arsenic, rare earth elements, and other trace metals of interest. Archived samples identified through the framework geology task will be supplemented with stream sediment and tailings collected during the Biogeochemical Processes task field work.

Laboratory-based studies will be conducted on field material to characterize processes that affect colloid transport. Previous work (Holloway et al., 2017; Etheridge, 2014) has demonstrated that Hg in the East Fork South Fork Salmon River is transported downstream dominantly as colloids. A fraction of other trace metals, including arsenic and antimony, are also transported in surface water as colloids. We are developing laboratory approaches to constrain processes that affect colloid transport from waste rock into stream water.  The characterization of mercury in colloidal material will be done in collaboration with the USGS Wisconsin Water Science Center Mercury Laboratory.

References

Eppinger, R.G., Briggs, P.H., Rieffenberger, B., Van Dorn, C., Brown, Z., Crock, J.G., Hageman, P.H., Meier, A., Sutley, S.J., Theodorakos, P.M., and Wilson, S.A., 2003, Geochemical data for stream sediment and surface water samples from Panther Creek, the Middle Fork of the Salmon River, and the Main Salmon River, collected before and after the Clear Creek, Little Pistol, and Shellrock wildfires of 2000 in central Idaho: U.S. Geological Survey Open-File Report 2003-152, 32 p., https://doi.org/10.3133/ofr03152.

Erickson, T.M., Granitto, Matthew, Lund, Karen, and Smith, S.M., 2017, Geochemical Data Release for Gospel-Hump Wilderness Area, Magruder Corridor and Special Mining Management Zone Additions to the Frank Church River of No Return Wilderness Area, and adjacent areas Idaho and Montana: U.S. Geological Survey data release, https://doi.org/10.5066/F7N29V6N.

Etheridge, A.B., 2015, Occurrence and transport of selected constituents in streams near the Stibnite mining area, central Idaho, 2012–14: U.S. Geological Survey Scientific Investigations Report 2015–5166, 47 p., https://doi.org/10.3133/sir20155166.

Holloway, J.M., Pribil, M.J., McCleskey, R.B., Etheridge, A.B., Krabbenhoft, D.P., and Aiken, G.R., 2017, Mobilization of Mercury and Arsenic from a Carbonate-hosted Ore Deposit, Central Idaho, U.S.A.: Procedia Earth and Planetary Science, 17, p. 610-613, https://doi.org/10.1016/j.proeps.2016.12.163.

Lund, Karen, Mutschler, F.M., Pawlowski, M.R., Hall, B.S., Bruce, R.M., and Evans, K.V., 1992, Geologic maps of the Big Mallard, Middle Bargamin, and Magruder additions to the Frank Church-River-of-No-Return Wilderness, Lemhi, and Idaho counties, Idaho: U.S. Geological Survey Miscellaneous Field Studies Map 2204, https://doi.org/10.3133/mf2204.

Lund, Karen, Aleinikoff, J.N., and Evans, K.V., 2011, Chapter 39 The Edwardsburg Formation and related rocks, Windermere Supergroup, central Idaho, USA, in The Geological Record of Neoproterozoic: Geological Society, London, Memoirs, 36, 437-448, https://doi.org/10.1144/M36.39.

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