Porphyry and epithermal deposits are important sources of base and precious metals. Most actively mined deposits have been exhumed such that ore bodies are relatively close to the surface and are therefore locatable and economic to extract. Identifying and characterizing concealed deposits, particularly more deeply buried porphyry deposits, represents a far greater challenge for mineral exploration, and will become progressively more important as near-surface resources are gradually exhausted over time. We report high-precision 40Ar/39Ar dates for coarsely crystalline alunite that precipitated from magmatic steam in open fractures in Oligocene dacitic volcanic rocks, and a SHRIMP 206Pb/238U zircon date for one of several rhyolite dikes present at Alunite Ridge and Deer Trail Mountain, Utah. Both the magmatic-steam alunite and rhyolite dikes are related to concealed intrusions. The rhyolite dike yielded an age of 30.72 ± 0.36 Ma, which is older than a commonly cited 27.1 Ma age estimate for the Three Creeks Tuff Member of the Bullion Canyon Volcanics that is cut by the dike. 40Ar/39Ar data for samples of magmatic-steam alunite and sericite from six mines and prospects provide evidence for at least two periods of episodic hydrothermal activity at ca. 15.7–15.1 Ma and ca. 14.7–13.8 Ma, with the older and younger pulses of activity recorded at the more eastern and western sites, respectively. These two periods of hydrothermal activity are consistent with previous interpretations that Alunite Ridge and Deer Trail Mountain are underlain by two concealed porphyry stocks. 40Ar/39Ar analyses of individual bands in a sample of massive, centimeter-scale banded vein alunite yield indistinguishable ages with a weighted mean of 13.98 ± 0.12 Ma, consistent with a short-lived (≲250 ka) magmatic event with episodic vapor discharge recurring on short timescales (≲36 ka). 40Ar/39Ar geochronology of magmatic-steam alunite is a valuable tool to constrain the timing and duration of magmatic hydrothermal activity associated with unexposed intrusions and potentially porphyry deposits, and therefore may be useful in exploration.

Oxygen, hydrogen, sulfur, and carbon isotopes have been analyzed in the Pea Ridge magnetite-apatite deposit, the largest historic producer among the known iron deposits in the southeast Missouri portion of the 1.5 to 1.3 Ga eastern granite-rhyolite province. The data were collected to investigate the sources of ore fluids, conditions of ore formation, and provenance of sulfur, and to improve the general understanding of the copper, gold, and rare earth element potential of iron deposits regionally. The δ 18 O values of Pea Ridge magnetite are 1.9 to 4.0‰, consistent with a model in which some magnetite crystallized from a melt and other magnetite—perhaps the majority—precipitated from an aqueous fluid of magmatic origin. The δ 18 O values of quartz, apatite, actinolite, K-feldspar, sulfates, and calcite are significantly higher, enough so as to indicate growth or equilibration under cooler conditions than magnetite and/or in the presence of a fluid that was not entirely magmatic. A variety of observations, including stable isotope observations, implicate a second fluid that may ultimately have been meteoric in origin and may have been modified by isotopic exchange with rocks or by evaporation during storage in lakes. Sulfur isotope analyses of sulfides from Pea Ridge and seven other mineral deposits in the region reveal two distinct populations that average 3 and 13‰. Two sulfur sources are implied. One was probably igneous melts or rocks belonging to the mafic- to intermediate-composition volcanic suite that is present at or near most of the iron deposits; the other was either melts or volcanic rocks that had degassed very extensively, or else volcanic lakes that had trapped rising magmatic gases. The higher δ 34 S values correspond to deposits or prospects where copper is noteworthy—the Central Dome portion of the Boss deposit, the Bourbon deposit, and the Vilander prospective area. The correspondence suggests that (1) sulfur either limited the deposition of copper or was cotransported with copper, and (2) sulfur isotope analysis may be useful in evaluating southeast Missouri iron deposits for copper and possibly for gold.

Supergene jarosite-group minerals are widespread in weathering profiles overlying Pb-Zn sulfide ores at Xitieshan, northern Tibetan Plateau, China. They consist predominantly of K-deficient natrojarosite, with lesser amounts of K-rich natrojarosite and plumbojarosite. Electron microprobe (EMP) analyses, scanning electron microcopy (SEM) investigation, and X-ray mapping reveal that the jarosite-group minerals are characterized by spectacular oscillatory zoning composed of alternating growth bands of K-deficient and K-bearing natrojarosite (K2O >1 wt.%). Plumbojarosite, whenever present, occurs as an overgrowth in the outermost bands, and its composition can be best represented by K0.29Na0.19Pb0.31Fe2.66Al0.22(SO4)1.65(PO4)0.31(AsO4)0.04(OH)7.37. The substitution of monovalent for divalent cations at the A site of plumbojarosite is charge balanced by the substitution of five-valent for six-valent anions in XO4 at the X site. Thermogravimetric analysis (TGA) of representative samples reveal mass losses of 11.46 wt.% at 446.6 °C and 21.42 wt.% at 683.4 °C due to dehydroxylation and desulfidation, respectively. TGA data also indicate that the natrojarosite structure collapses at 446.6 °C, resulting in the formation of NaFe(SO4)2 and minor hematite. The decomposition products of NaFe(SO4)2 are hematite and Na2SO4. Powder X-ray diffraction (XRD) analyses show that the jarosite-group minerals have mean unit-cell parameters of a = 7.315 Å and c = 016.598 Å. XRD and EMP data support the view that substitutions of Na for K in the A site and full Fe occupancy in the B site can considerably decrease the unit-cell parameter c, but only slightly increase a. The results from this study suggest that the observed oscillatory zoning of jarosite-group minerals at Xitieshan resulted mainly from substitutions of K for Na at the A site and P for S at the X site.

A synthesis of old and new paleoclimatic data from the Pyramid and Winnemucca lake basins indicates that, between 48.0 and 11.5.10(3) calibrated years BP (hereafter ka), the climate of the western Great Basin was, to a degree, linked with the climate of the North Atlantic. Paleomagnetic secular variation (PSV) records from Pyramid Lake core PLC08-1 were tied to the GISP2 ice-core record via PSV matches to North Atlantic sediment cores whose isotopic and(or) carbonate records could be linked to the GISP2 6180 record. Relatively dry intervals in the western Great Basin were associated with cold Heinrich events and relatively wet intervals were associated with warm Dansgaard-Oeschger (DO) oscillations. The association of western Great Basin dry events with North Atlantic cold events (and vice versa) switched sometime after the Laurentide Ice Sheet (LIS) reached its maximum extent. For example, the Lahontan highstand, which culminated at 15.5 ka, and a period of elevated lake level between 13.1 and 11.7 ka were associated with cold North Atlantic conditions, the latter period with the Youngest Dryas event. Relatively dry periods were associated with the Bolling and Allerod warm events. A large percentage of the LIS may have been lost to the North Atlantic during Heinrich events 1 and 2 and may have resulted in the repositioning of the Polar Jet Stream over North America. The Trego Hot Springs, Wono, Carson Sink, and Marble Bluff tephras found in core PLC08-1 have been assigned GISP2 calendar ages of respectively, 29.9, 33.7, 34.1, and 43.2 ka. Given its unique trace-element chemistry, the Carson Sink Bed is the same as Wilson Creek Ash 15 in the Mono Lake Basin. This implies that the Mono Lake magnetic excursion occurred at approximately 34 ka and it is not the Laschamp magnetic excursion.The entrance of the First Americans into the northern Great Basin is dated to approximately 14.4 ka, a time when the climate was relatively dry. Evidence for human occupation of the Great Basin is lacking for the next 1100 years (y); i.e., the oldest western stemmed point site in the Great Basin dates to 133 ka. Two hypotheses are suggested for this cultural hiatus: (1) the climate had deteriorated to the point that people vacated the Great Basin, or (2) people moved to basin-bottom wetlands that persisted during the dry period, and then the subsequent Younger Dryas wet event erased the archaeological evidence deposited around the low-elevation wetland sites. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.

Ore formation at the Spar Lake red bed-associated strata-bound Cu deposit took place across a mixing and reaction zone between a hot oxidized metals-transporting brine and a reservoir of "sour" (H2S-bearing) natural gas trapped in the host sandstones. Fluid inclusion volatile analyses have very high CH4 concentrations (>= 1 mol % in most samples), and a sample from the fringe of the deposit has between 18 and 36 mol % CH4. The ratio of CH4/CO2 in fluid inclusions appears to vary regularly across the deposit, with the lowest CH4/CO2 ratios from high-grade chalcocite-bearing ore, and the highest from the chalcopyrite-bearing fringe. The helium R/R-a isotope ratios (0.23-0.98) and concentrations define a mixture between crustal and atmospheric helium. The volatiles in fluid inclusions (CH4, CO2, H2S, SO2, H-2, H2O, and other organic gases) and values off fo(2) and temperature calculated from the volatiles data all show gradations across the deposit that are completely consistent with such a mixing and reaction zone. Other volatiles from the fluid inclusions (HCl, HF, He-3, He-4, N-2, Ar) characterize the brine and give evidence for only shallow crustal fluids with no magmatic influences. The brine entered the gas reservoir from below and along the axis of the deposit and migrated out along bedding to the southwest, northeast, and northwest. Metals-transporting brines may have been fed into the host sandstones from the East Fault, but that remains uncertain.Abundant ore-stage Fe and Mn calcite cements from the reduced fringe have delta C-13 values as low as -18.4 parts per thousand, and many values less than -1.0 parts per thousand, which indicate that significant carbonate was generated by oxidation of organic carbon from the natural gas. The zone of calcite cements with very low delta C-13 values approximately envelopes chalcocite-bearing ore.Sulfur isotope data of Cu, Pb, and Fe sulfides and barite indicate derivation of roughly half of the orebody sulfide directly from sour gas H2S. That sour gas H2S had developed in steps known from other sedimentary basins, starting with (1) bacterial sulfate reduction (BSR) of seawater sulfate having delta S-34 of about 20 parts per thousand and sequestering of the sulfide in organic matter in source rocks stratigraphically below the deposit host rocks, followed by (2) maturation of the sulfide-bearing organic matter into liquid petroleum with relatively homogeneous sulfide having delta S-34 of 5 +/- 5 parts per thousand, then by (3) thermal cracking of the oil to CH4 and H2S with relatively homogeneous sulfide having delta S-34 closely distributed, about 6 parts per thousand. The CH4 and H2S migrated and were trapped in sandstones of the upper member of the Revett Formation, where they were later met by the 200 degrees C metalstransporting brine. There was additional contribution of sulfide to ore from later thermochemical sulfate reduction (TSR) operating on sulfate delta S-34 of 20 to 29 parts per thousand in both formation waters and metals-transporting solutions. A large range of delta S-34 in sulfides resulted as the 6 parts per thousand sour gas sulfide was supplemented with varying proportions of 20 to 29 parts per thousand sulfide from TSR.

Evolutionary models of the hydrothermal systems that form porphyry Cu (Mo-Au) deposits are compromised because the aqueous fluids trapped in fluid inclusions within the ore zones of most deposits have changed from their original magmatic exsolution compositions during cooling, decompression, mineral precipitation, brine-vapor unmixing, and fluid-rock reactions. However, in quartz-rich, sulfide-poor veins, below numerous porphyry deposits, we have identified parental fluids trapped in fluid inclusions at near magmatic temperatures and pressures prior to unmixing and with minimal influence from the aforementioned processes. These inclusions were characterized using a variety of bulk and single inclusion analytical techniques. They contain 35-70 volume % bubble, 2-10 wt % NaCl, up to similar to 12 mol% CO2, and 100-10,000 ppm Cu. They have molar Na/Cl ratios greater than 1, which suggests that, in addition to chlorine, sulfur and/or carbonate must play a key role in Cu transport. Helium isotope ratios indicate that between similar to 15 and 100% of the helium in these fluids is mantle-derived. In contrast, the Ar isotopes have a dominantly atmospheric origin and fractionated Br/l/Cl signature that is similar to that observed in subducting oceanic lithosphere. The combined data are suggestive of mixing volatiles from the mantle wedge and recycled volatiles derived by slab dehydration.

A sediment core taken from the western edge of the Bonneville Basin has provided high-resolution proxy records of relative lake-size change for the period 45.1-10.5 calendar ka (hereafter ka). Age control was provided by a paleomagnetic secular variation (PSV)-based age model for Blue Lake core BL04-4. Continuous records of delta O-18 and total inorganic carbon (TIC) generally match an earlier lake-level envelope based on outcrops and geomorphic features, but with differences in the timing of some hydrologic events/states. The Stansbury Oscillation was found to consist of two oscillations centered on 25 and 24 ka. Lake Bonneville appears to have reached its geomorphic highstand and began spilling at 18.5 ka. The fall from the highstand to the Provo level occurred at 17.0 ka and the lake intermittently overflowed at the Provo level until 15.2 ka, at which time the lake fell again, bottoming out at similar to 14.7 ka. The lake also fell briefly below the Provo level at similar to 15.9 ka. Carbonate and delta O-18 data indicate that between 14.7 and 13.1 ka the lake slowly rose to the Gilbert shoreline and remained at about that elevation until 11.6 ka, when it fell again. Chemical and sedimentological data indicate that a marsh formed in the Blue Lake area at 10.5 ka.Relatively dry periods in the BL04-4 records are associated with Heinrich events H1-H4, suggesting that either the warming that closely followed a Heinrich event increased the evaporation rate in the Bonneville Basin and (or) that the core of the polar jet stream (PJS) shifted north of the Bonneville Basin in response to massive losses of ice from the Laurentide Ice Sheet (LIS) during the Heinrich event. The second Stansbury Oscillation occurred during Heinrich event H2, and the Gilbert wet event occurred during the Younger Dryas cold interval. Several relatively wet events in BL04-4 occur during Dansgaard-Oeschger (DO) warm events.The growth of the Bear River glacier between 32 and 17 ka paralleled changes in the values of proxy indicators of Bonneville Basin wetness and terminal moraines on the western side of the Wasatch Mountains have ages ranging from 16.9 to 15.2 ka. This suggests a near synchroneity of change in the hydrologic and cryologic balances occurring in the Bonneville drainage system and that glacial extent was linked to lake size. (C) 2010 Elsevier Ltd and INQUA. All rights reserved.

Wolves (Canis lupus) in North America are considered obligate predators of ungulates with other food resources playing little role in wolf population dynamics or wolf prey relations. However, spawning Pacific salmon (Oncorhyncus spp.) are common throughout wolf range in northwestern North America and may provide a marine subsidy affecting inland wolf-ungulate food webs far from the coast. We conducted stable-isotope analyses for nitrogen and carbon to evaluate the contribution of salmon to diets of wolves in Denali National Park and Preserve, 1200 river-km from tidewater in interior Alaska, USA. We analyzed bone collagen from 73 wolves equipped with radio collars during 1986-2002 and evaluated estimates of salmon in their diets relative to the availability of salmon and ungulates within their home ranges. We compared wolf densities and ungulate:wolf ratios among regions with differing salmon and ungulate availability to assess subsidizing effects of salmon on these wolf-ungulate systems. Wolves in the northwestern flats of the study area had access to spawning salmon but low ungulate availability and consumed more salmon (17% +/- 7% [mean +/- SD]) than in upland regions, where ungulates were sixfold more abundant and wolves did or did not have salmon spawning areas within their home ranges (8% +/- 6% and 3% +/- 3%, respectively). Wolves were only 17% less abundant on the northwestern flats compared to the remainder of the study area, even though ungulate densities were 78% lower. We estimated that biomass from fall runs of chum (O. keta) and coho (O. kisutch) salmon on the northwestern flats was comparable to the ungulate biomass there, and the contribution of salmon to wolf diets was similar to estimates reported for coastal wolves in southeast Alaska. Given the ubiquitous consumption of salmon by wolves on the northwestern flats and the abundance of salmon there, we conclude that wolf numbers in this region were enhanced by the allochthonous subsidy provided by salmon and discuss implications for wolf-ungulate relations.

Late Devonian porphyry Cu-Au deposits within the Oyu Tolgoi mineral district, Mongolia, occur in a north-northeast–trending zone 22 km long. They are related to quartz monzodiorite intrusions, and hosted by augite basalt lavas. The porphyry systems have been preserved beneath overturned and allochthonous stratigraphic sequences and geologic relationships suggest that fold-thrust belt deformation and tectonic burial occurred soon after their formation. Eight known separate porphyry centers currently contain a measured and indicated resource of 1,390 Mt at 1.33 wt percent Cu and 0.47 g/t Au, and an inferred resource of 2,200 Mt at 0.83 wt percent Cu and 0.37 g/t Au (at 0.6 wt % Cu equiv cutoff). Advanced argillic alteration is present for 6 km along a north-northeast trend and is characterized by minerals that include andalusite, corundum, diaspore, residual quartz, alunite plus aluminum-phosphate-sulfate minerals, zunyite, topaz, pyrophyllite, kaolinite, anhydrite, gypsum, and dickite but is dominated by pyrophyllite. This alteration is exposed at surface in the Central deposit and in the subsurface between 50 to 1,500 m depth at Hugo Dummett South and North deposits. The advanced argillic zone at the Hugo Dummett deposits closely envelopes high-grade porphyry Cu-Au mineralization, and overprints a deep zone of sericitic alteration. Mineralogical investigations show that pyrophyllite replaces fine-grained muscovite as coarse crystals (up to 25μm long), or replaces coarse muscovite crystals (50 μm long) along cleavage. Muscovite (δ18O = 6.7–10.4‰, δD = −116 to −92‰, n =13) and pyrophyllite (δ18O = 5.9–12.2‰, δD = −122 to −87‰, n = 28) have similar measured isotopic compositions. The calculated parent fluid compositions for all phyllosilicate minerals (muscovite, chlorite, pyrophyllite: δ18OH2O = 1–7.3‰, δDH2O = −102 to −67‰) suggest they were predominantly magmatic with a minor component of meteoric water. The composition of younger dickite (δ18O = −3.2 to +5.7‰, δD = −165 to −129‰, n = 13) shows evidence of magmatic fluid mixing with meteoric water, and provides an estimate of δD = −160 per mil for Late Devonian meteoric water. Sulfides (δ34S = −16 to −1.4‰) are isotopically light, whereas sulfates (δ34S = 4.2–17.9‰) are heavy, and the distribution suggest that initial fluids were SO2-dominant and ratios of reduced to oxidized sulfur species of fluids were buffered at near 1:1. Alunite is related to condensed magmatic vapor (δ18O(SO4) = 7.1–20.1‰ ( n = 14), δD = −92 to −37‰ ( n = 13), δ34S = 8–17.9‰ ( n = 18)) with a component of meteoric water, and contrasts in O and H isotope values from pyrophyllite, which is similar to muscovite. Pyrophyllite at shallow levels replaces earlier advanced argillic minerals, including alunite, whereas at deep levels it replaces muscovite in quartz monzodiorite, or chlorite-muscovite-illite (after biotite) in basaltic wall rocks. Field relationships, mineralogy, and stable isotopes suggest that pyrophyllite is derived from late magmatic-hydrothermal fluids during cooling.

The Boyongan and Bayugo porphyry copper-gold deposits are Part of an emerging belt of intrusion-centered gold-rich deposits in the Surigao district of northeast Mindanao, Philippines. Exhumation and weathering of these Late Pliocene-age deposits has led to the development of the world's deepest known porphyry oxidation profile at Boyongan (600 m), and yet only a modest (30-70 m) oxidation profile at adjacent Bayugo. Debris flows, volcanic rocks, and fluviolacustrine sediments accumulating in the actively extending Mainit graben subsequently covered the deposits and preserved the supergene profiles.At Boyongaii and Bayugo, there is a vertical transition from shallower supergene copper oxide minerals (malachite + azurite + cuprite) to deeper sulfide-stable assemblages (chalcocite +/- hypogene sulfides). This transition provides it time-integrated proxy for the position of the water table at the base of the saturated zone during supergene, oxidation, Contours of the elevation of the paleopotentiometric sill-face based oil this mineralogical transition show that the thickest portions of the unsaturated zone coincided with a silt-sand matrix diatreme breccia complex at Boyongan. Within the breccia complex, the thickness of the misaturated zone approached 600 m whereas outside the breccia complex (e.g., at Bayugo), the thickness averaged 50 m. Contours of the paleopotentiometric surface suggest that during weathering, groundwater flowed into the breccia complex from the north, south, and cast, and exited along it high permeability zone to the west. The high relief, (>550 m) on the elevation of the, paleopotentiometric surface is consistent with all environment of, high topographic relief, and the Outflow Zone to the west of, the breccia complex probably reflects proximity, to a steel) scarp intersecting the western breccia complex margin.Stable isotope paleoaltimetry has enabled estimation of the elevation of the land surface, which further constrains the physiographic setting during supergene oxidation Isotopic measurements of Oxygen ill supergene kaolinite from Boyongan suggest that local paleometeoric water involved ill weathering had a delta O-18 composition of approximately-5.7 per mil. At the latitude of the southern Philippines, this value corresponds to Pleistocene rain water condensing at elevations between 750 and 1,050 m above contemporary sea level, providing a maximum estimate for the surface elevation during weathering of the porphyry systems.Physiographic reconstructions suggest that the deep oxidation profile at Boyongan formed ill all environment of high topographic relief immediately east of a prominent (>550 m) escarpment. The high permeability contrast between the breccia Complex and the surrounding wall rocks, coupled with the proximity of the breccia complex to the escarpment, led to a depressed groundwater table and a vertically ex(extensive unsaturated zone in the immediate vicinity of Boyongan. This thick vadose zone and the low hypogene pyrite/copper sulfide ratios (0.6) at Boyongan promoted in situ oxidation of copper sulfides with only modest (<200 m) supergene remobilization of copper. In contrast, higher hypogene pyrite/chalcopyrite ratios (2.3) at Bayngo led to greater acid production during weathering and wore complete leaching of copper above the base, of oxidation. This process promoted significant (600 m) lateral dispersion of copper down the paleohydraulic gradient into the diatreme breccia comple, ultimately leading to the formation of an exotic copper deposit.

Sulfur- and oxygen-isotope analyses have been obtained for sediment-hosted stratiform barite deposits in Alaska, Nevada, Mexico, and China to examine the environment of formation of this deposit type. The barite is contained in sedimentary sequences as old as Late Neoproterozoic and as young as Mississippian. If previously published data for other localities are considered, sulfur- and oxygen-isotope data are now available for deposits spanning a host-rock age range of Late Neoproterozoic to Triassic. On a δ34S versus δ18O diagram, many deposits show linear or concave-upward trends that project down toward the isotopic composition of seawater sulfate. The trends suggest that barite formed from seawater sulfate that had been isotopically modified to varying degrees. The δ34S versus δ18O patterns resemble patterns that have been observed in the modern oceans in pore water sulfate and water column sulfate in some anoxic basins. However, the closest isotopic analog is barite mineralization that occurs at fluid seeps on modern continental margins. Thus the data favor genetic models for the deposits in which barium was delivered by seafloor seeps over models in which barium was delivered by sedimentation of pelagic organisms. The isotopic variations within the deposits appear to reflect bacterial sulfate reduction operating at different rates and possibly with different electron donors, oxygen isotope exchange between reduction intermediates and H2O, and sulfate availability. Because they are isotopically heterogeneous, sediment-hosted stratiform barite deposits are of limited value in reconstructing the isotopic composition of ancient seawater sulfate.

Stable isotope analyses have revolutionized the study of migratory connectivity. However, as with all tools, their limitations must, be understood in order to derive the maximum benefit of a particular application. The goal of this study was to evaluate the efficacy of stable isotopes of C, N, H, O and S for assigning known-origin feathers to the molting sites of migrant shorebird species wintering and breeding in Argentina. Specific objectives were to: 1) compare the efficacy of the technique for studying shorebird species with different migration patterns, life histories and habitat-use patterns; 2) evaluate the grouping of species with similar migration and habitat use patterns in a single analysis to potentially improve prediction accuracy; and 3) evaluate the potential gains in prediction accuracy that might be achieved front using multiple stable isotopes. The efficacy of stable isotope ratios to determine origin was found to vary with species. While one species (White-rumped Sandpiper, Calidris fuscicollis) had high levels of accuracy assigning samples to known origin (91% of samples correctly assigned), another (Collared Plover, Charadrius collaris) showed low levels of accuracy (52% of samples correctly assigned). Intra-individual variability may account for this difference: in efficacy. The prediction model for three species with similar migration and habitat-use patterns performed poorly compared with the model for just one of the species (71% versus 91% of samples correctly assigned). Thus, combining multiple sympatric species may not improve model prediction accuracy. Increasing the number of stable isotopes in the analyses increased the accuracy of assigning shorebirds to their molting origin, but the best combination - involving a subset of all the isotopes analyzed - varied among species.

Analyses have been made of 81 effluents from four gold leach operations in various stages of remediation to identify the most -persistent cyanide species. Total cyanide and weak acid-dissociable (WAD) cyanide were measured using improved methods, and metals known to form stable cyanocomplexes were also measured. Typically, total cyanide greatly exceeded WAD indicating that cyanide was predominantly in strong cyanometallic complexes. Iron was generally too low to accommodate the strongly complexed cyanide as Fe(CN)6s3- or Fe(CN)6(4-), but cobalt was abundant enough to implicate Co(CN)6(3-) or its dissociation products (Co(CN)(6-x)(H2O)x((3-x)-)). Supporting evidenceforcobalt-cyanide complexationwas found in tight correlations between cobalt and cyanide in some sample suites. Also, abundant free cyanide was produced upon UV illumination. Iron and cobalt cyanocomplexes both photodissociate; however, the iron concentration was insufficient to have carried the liberated cyanide, while the cobalt concentration was sufficient. Cobalt cyanocomplexes have not previously been recognized in cyanidation wastes. Their identification atfour separate operations, which had treated ores that were not especially rich in cobalt, suggests that cobalt complexation may be a common source of cyanide persistence. There is a need for more information on the importance and behavior of cobalt cyanocomplexes in ore-processing wastes at gold mines.

ARTICLE I NFO

This report documents water quality in Camp Far West Reservoir from October 2001 through August 2003. The reservoir, located at approximately 300 feet above sea level in the foothills of the northwestern Sierra Nevada, California, is a monomictic lake characterized by extreme drawdown in the late summer and fall. Thermal stratification in summer and fall is coupled with anoxic conditions in the hypolimnion. Water-quality sampling was done at approximately 3-month intervals on eight occasions at several stations in the reservoir, including a group of three stations along a flow path in the reservoir: an upstream station in the Bear River arm (principal tributary), a mid-reservoir station in the thalweg (prereservoir river channel), and a station in the deepest part of the reservoir, in the thalweg near Camp Far West Dam. Stations in other tributary arms of the reservoir included those in the Rock Creek arm of the reservoir, a relatively low-flow tributary, and the Dairy Farm arm, a small tributary that receives acidic, metal-rich drainage seasonally from the inactive Dairy Farm Mine, which produced copper, zinc, and gold from underground workings and a surface pit. Several water-quality constituents varied significantly by season at all sampling stations, including major cations and anions, total mercury (filtered and unfiltered samples), nitrogen (ammonia plus organic), and total phosphorus. A strong seasonal signal also was observed for the sulfurisotope composition of aqueous sulfate from filtered water. Although there were some spatial differences in water quality, the seasonal variations were more profound. Concentrations of total mercury (filtered and unfiltered water) were highest during fall and winter; these concentrations decreased at most stations during spring and summer. Anoxic conditions developed in deep parts of the reservoir during summer and fall in association with thermal stratification. The highest concentrations of methylmercury in unfiltered water were observed in samples collected during summer from deepwater stations in the anoxic hypolimnion. In the shallow (less than 14 meters depth) oxic epilimnion, concentrations of methylmercury in unfiltered water were highest during the spring and lowest during the fall. The ratio of methylmercury to total mercury (MeHg/HgT) increased systematically from winter to spring to summer, largely in response to the progressive seasonal decrease in total mercury concentrations, but also to some extent because of increases in MeHg concentrations during summer. Water-quality data for Camp Far West Reservoir are used in conjunction with data from linked studies of sediment and biota to develop and refine a conceptual model for mercury methylation and bioaccumulation in the reservoir and the lower Bear River watershed. It is hypothesized that MeHg is produced by sulfate-reducing bacteria in the anoxic parts of the water column and in shallow bed sediment. Conditions were optimal for this process during late summer and fall. Previous work has indicated that Camp Far West Reservoir is a phosphate-limited system - molar ratios of inorganic nitrogen to inorganic phosphorus in filtered water were consistently greater than 16 (the Redfield ratio), sometimes by orders of magnitude. Therefore, concentrations of orthophosphate were expectedly very low or below detection at all stations during all seasons. It is further hypothesized that iron-reducing bacteria facilitate release of phosphorus from iron-rich sediments during summer and early fall, stimulating phytoplankton growth in the fall and winter, and that the MeHg produced in the hypolimnion and metalimnion is released to the entire water column in the late fall during reservoir destratification (vertical mixing). Mercury bioaccumulation factors (BAF) were computed using data from linked studies of biota spanning a range of trophic position: zooplankton, midge larvae, mayfly nymphs, crayfish, threadfin shad, bluegill,

Knowledge of diet–tissue stable isotope discrimination is required to properly interpret stable isotope values and to identify possible diet shifts, such as might be expected from nursing through weaning. This study compared δ13C and δ15Ν οf paired serum and vibrissal roots with those of ingested milk (n = 52) from free-ranging Steller sea lion ( Eumetopias jubatus (Schreber, 1776)) pups (1–11 months) and juveniles (14–27 months) to estimate diet–tissue discrimination. Mean 15N enrichment from ingested milk to serum was 2.1‰ ± 0.6‰ and δ15Ν at the root of the vibrissae (representing current growth) were not significantly different from serum values. Milk was enriched for mean 13C by 5.0‰ ± 1.0‰ and 7.3‰ ± 1.2‰ relative to serum and vibrissal roots, respectively, which was due to the presence of 13C-depleted lipids in milk. This was confirmed by lipid extraction from a subset of milk and serum samples, resulting in a 5.8‰ ± 1.0‰ change only in milk. This study established that vibrissal roots and serum are reflective of a milk diet with approximately 2.0‰ 15N enrichment, and vibrissal roots reflect serum and lipid-extracted milk values with approximately 2.0‰ 13C enrichment. These discrimination factors are important to establish for stable isotope studies assessing diet shifts.