Kimberly R. Beisner

Selenium and trace element mobility affected by periodic displacement of stratification in the Great Salt Lake, Utah

The Great Salt Lake (GSL) is a unique ecosystem in which trace element activity cannot be characterized by standard geochemical parameters due to the high salinity. Movement of selenium and other trace elements present in the lake bed sediments of GSL may occur due to periodic stratification displacement events or lake bed exposure. The water column of GSL is complicated by the presence of a chemocline persistent over annual to decadal time scales. The water below the chemocline is referred to as the deep brine layer (DBL), has a high salinity (16.5 to 22.9%) and is anoxic. The upper brine layer (UBL) resides above the chemocline, has lower salinity (12.6 to 14.7%) and is oxic. Displacement of the DBL may involve trace element movement within the water column due to changes in redox potential. Evidence of stratification displacement in the water column has been observed at two fixed stations on the lake by monitoring vertical water temperature profiles with horizontal and vertical velocity profiles. Stratification displacement events occur over periods of 12 to 24h and are associated with strong wind events that can produce seiches within the water column. In addition to displacement events, the DBL shrinks and expands in response to changes in the lake surface area over a period of months. Laboratory tests simulating the observed sediment re-suspension were conducted over daily, weekly and monthly time scales to understand the effect of placing anoxic bottom sediments in contact with oxic water, and the associated effect of trace element desorption and (or) dissolution. Results from the laboratory simulations indicate that a small percentage (1%) of selenium associated with anoxic bottom sediments is periodically solubilized into the UBL where it potentially can be incorporated into the biota utilizing the oxic part of GSL.

Assessment of geochemical and hydrologic conditions near Old Yuma Mine in Saguaro National Park, Arizona, 2014–17

The Old Yuma Mine is an abandoned copper, lead, zinc, silver, and gold mine located within the boundaries of Saguaro National Park, Tucson Mountain District, Arizona. This study analyzed the geochemistry of sediments associated with the Old Yuma mine and assessed hydrologic and geochemical conditions of groundwater to evaluate the area surrounding the Old Yuma Mine. The purpose of the study was to establish the geochemical signature of material associated with the Old Yuma Mine and to compare it with background material and groundwater in the area. Near the mine, groundwater generally flows to the northeast. A locally anomalous steep gradient in groundwater elevation is present beneath alluvial fan deposits in the center of the study area, near the projection of the Old Yuma Fault trend. Few groundwater samples exceeded the EPA drinking water standards. One sample exceeded the EPA primary drinking water standard for arsenic; one sample exceeded the EPA secondary drinking water standard for chloride, iron, and manganese and two other samples exceeded the total dissolved solids secondary drinking water standard. Analysis of groundwater age indicates groundwater with a component of modern water is present on the northwest side of the study area. Groundwater on the southeast side of the study area is primarily older, with a radiocarbon age ranging from approximately 600 to 6,700 years before present. Concentrations of several elements (As, Bi, Cd, Co, Cu, Fe, Hg, In, Li, Mn, Mo, Pb, Sb, U, V, W, and Zn) were elevated in the waste rock and mine tailings compared with concentrations in sediments collected in background areas. Concentrations of four elements (As, Mo, Pb, and V) in some sediment samples were greater than the EPA regional soil screening levels and (or) Arizona Department of Environmental Quality (AZDEQ) soil screening levels. A subset of 15 sediment samples was leached according to the EPA 1312 leachate method to simulate precipitation interacting with the solid material. The pH of the leachate samples increased following the leaching procedure. Several leachate samples had concentrations that exceeded the EPA drinking water standards for As, Mn, and Pb. Analysis of leachate samples compared to groundwater samples suggests that groundwater samples collected in this study are similar to each other and distinct from leachate samples associated with mining related material. Results suggest that at this time groundwater samples collected during this investigation are not influenced by elements leached from Old Yuma Mine materials. Introduction Saguaro National Park consists of two districts, the Rincon Mountain District and Tucson Mountain District on the far eastern and western sides, respectively, of the city of Tucson, Arizona (fig. 1). The Tucson Mountain District historically experienced gold and silver mining activity from 1880 to the 1970s and in 1994 Saguaro National Park acquired one of these mines, the Old Yuma Mine. The Old Yuma Mine was active from the dawn of the twentieth century through World War I, and produced steel-hardening minerals such as wulfenite, molybdenite, and vanadinite, and the base and precious metals lead, copper, zinc, silver, and gold (National Park Service, 2010). Mining History Located on a fault that trends east-northeast and dips steeply to the southeast, the Old Yuma Mine contains a relatively wide lenticular surface expression and a ~300-foot (ft) inclined shaft that dips at an angle of 43° and provides access to its underground workings (Wilson and Schlepp, 2008). Horizontal underground workings occur at the 65-, 100-, 200-, and 300-ft levels off the main incline. Between 1916 and 1947, this underground mine produced 5,700 tons of ore grading 4 percent lead, 1 percent copper, 0.6 percent zinc, 0.3 percent molybdenum, 1 ounce silver per ton, and 0.1 ounce gold per ton. This mine also produced high quality specimens of wulfenite (PbMoO4), a lead-molybdenum oxide, and vanadinite (Pb5(VO4)3Cl), a lead-vanadium mineral. Assessment of Geochemical and Hydrologic Conditions near Old Yuma Mine in Saguaro National Park, Arizona, 2014–17 By Kimberly R. Beisner and Floyd Gray 2 Geochemical and Hydrologic Conditions near Old Yuma Mine in Saguaro National Park The first claim to the Old Yuma Mine was filed in 1885, and a mill capable of handling 100 tons per day was constructed on site in 1916 for concentrating gold, molybdenum, and vanadium (Wilson and Schlepp, 2008). The mine changed ownership in 1930 and occasionally produced dump ore and surface material, but the mine was primarily used for acquiring mineral specimens. Around 1969, the ceiling of the main mine incline shaft caved in and large slabs of rock fell in single pieces. In addition to waste rock located around the property, approximately 7,000 cubic yards of tailings remain stockpiled at the Old Yuma Mine site, though this is only part of the original tailings pile. The remainder of the pile was used for road base in the surrounding area (Michael Baker Jr., Inc., 2005). The current mine site includes a large inclined excavation open to the surface, shafts (inclined and vertical), adits (nearly horizontal passageways into the mine), a headframe that was used to hoist the inclined main access shaft, a concrete mill foundation, a solid waste dumping area, and a small leach pad. The leach pad was constructed in 1984 for the purpose of reducing gold ore from the remnant mine tailings, but it was never operational (Michael Baker Jr., Inc., 2005). A local claimant, Richard A. Bideaux, received a patent on the valid claims from the Bureau of Land Management (BLM) near the time the land transferred from BLM to National Park Service management in 1994 (Comet 1 Lode, Old Yuma #1 Lode, and Old Yuma Placer Mining Claims, which were top-staked on one another and occupied a total of about 22 acres [9 hectares]). Saguaro National Park’s primary concern regarding this mine is potential injury owing to onsite hazards (National Park Service, 2010). Old Yuma Mine is currently under a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, or “Superfund”) investigation (National Park Service, 2010). Geologic Setting The Tucson Mountains, in which the Old Yuma Mine is located, are underlain by Late Cretaceous volcanic rocks interpreted as part of the fill of a large ash-flow caldera (Lipman, 1993). Volcanic rocks of the Old Yuma Mine area consist of compositionally diverse lava flows, intrusive dikes, and interleaved sedimentary rocks. Rock units around the Old Yuma Mine are described as aphanitic andesite [Kya] and aphanitic rhyolite and dacite flows [Kyr] (Lipman, 1993). Aphanitic andesite consists of dark-gray, fine-grained andesitic lava flows containing 20–40 percent small phenocrysts of plagioclase, augite, and serpentine pseudomorphs after olivine or orthopyroxene. Aphanitic rhyolite and dacite flows are described as tan to light-gray lava flows containing minor small phenocrysts of sanidine, plagioclase, and recrystallized biotite (Lipman, 1993). The ore deposit at the Old Yuma Mine consists of a porphyritic andesite or latite dike occupying a dip-slip fault dipping at about 43° through Cretaceous andesite (Wilson and Schlepp, 2008). The average width of the dike is 8–10 ft, but widens to 20 ft on the 65-ft level. The dike contains scattered pods of silver-rich galena altered to anglesite and cerussite, which released lead for the crystallization of vanadinite and wulfenite. Vanadinite and wulfenite occur in distinct zones and were reported to be milled in separate bins; wulfenite is found primarily on the western part of the fissure and vanadinite on the eastern part (Wilson and Schlepp, 2008). Hydrologic Setting No perennial surface water features exist in the study area, but ephemeral washes are present that flow episodically following precipitation events. Groundwater is present in the study area generally as part of fractured bedrock, alluvium, and alluvial fan deposits. Purpose and Scope Updated information on groundwater levels in the Old Yuma Mine area and chemistry of mining-related materials and groundwater are needed by Saguaro National Park for a better understanding of the presence and quality of groundwater near the Old Yuma Mine. This report (1) presents a groundwater surface elevation map to estimate the groundwater elevation below the Old Yuma Mine; (2) characterizes the chemistry of mining-related material, background sediment, and water leached from both of these materials; and (3) compares leachate chemistry to groundwater chemistry from the surrounding area. The study area includes groundwater wells located south of Ina Road, north of Camino del Cerro Road, west of Silverbell Road and east of Golden Gate Road (fig. 1).