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J.K. Böhlke

Publications and source records attributed to J.K. Böhlke.

68 records · Page 4Linked to original sources
USGS1997

Stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern Chile and southern California, U.S.A.

Natural surficial accumulations of nitrate-rich salts in the Atacama Desert, northern Chile, and in the Death Valley region of the Mojave Desert, southern California, are well known, but despite many geologic and geochemical studies, the origins of the nitrates have remained controversial. N and O isotopes in nitrate, and S isotopes in coexisting soluble sulfate, were measured to determine if some proposed N sources could be supported or rejected, and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters. High-grade calich-a-type nitrate deposits from both localities have δ 15 N values that range from −5 to +5‰, but are mostly near 0‰. Values of δ 15 N near 0‰ are consistent with either bulk atmospheric N deposition or microbial N fixation as major sources of the N in the deposits. δ 18 O values of those desert nitrates with δ 15 N near 0‰ range from about +31 to +50‰ (V-SMOW), significantly higher than that of atmospheric O 2 (+23.5‰). Such high values of δ 18 O are considered unlikely to result entirely from nitrification of reduced N, but rather resemble those of modern atmospheric nitrate in precipitation from some other localities. Assuming that limited modern atmospheric isotope data are applicable to the deposits, and allowing for nitrification of co-deposited ammonium, it is estimated that the fraction of the nitrate in the deposits that could be, accounted for isotopically by atmospheric N deposition may be at least 20% and possibly as much as 100%. δ 34 S values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits. The stable isotope data support the hypothesis that some high-grade caliche-type nitrate-rich salt deposits in some of the Earth's hyperarid deserts represent long-term accumulations of atmospheric deposition (possibly in the order of 104 yr for the Death Valley region, 10 7 yr for the Atacama Desert) in the relative absence of soil leaching or biologic cycling. The combined N and O isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate.

Chemical Geology↗
USGS1997

Hydrogeologic and water-quality data used to evaluate the effects of focused recharge on ground-water quality near Princeton, Minnesota, 1991-95

This study was part of the Management Systems Evaluation Area (MSEA) Program, a multi-scale, inter-agency initiative to evaluate the effects of agricultural systems on water quality in the midwest corn belt. The research was part of the U.S. Geological Survey Toxics Substances Hydrology Program. The research area was located in the Anoka Sand Plain about 5 kilometers southwest of Princeton, Minnesota. This report presents temperature, precipitation, soil-moisture, water-quality, and other data collected during 1991-95 to evaluate the effects of focused recharge on ground-water quality at the Princeton MSEA.

Minnesota↗
USGS1996

Denitrification and mixing in a stream-aquifer system: Effects on nitrate loading to surface water

Ground water in terrace deposits of the South Platte River alluvial aquifer near Greeley, Colorado, USA, had a median nitrate concentration of 1857 μmol l −1 . Median nitrate concentrations in ground water from adjacent floodplain deposits (468 μmol l −1 ) and riverbed sediments (461 μmol l −1 ), both of which are downgradient from the terrace deposits, were lower than the median concentration in the terrace deposits. The concentrations and δ 15 N values of nitrate and N 2 in ground water indicated that denitrifying activity in the floodplain deposits and riverbed sediments accounted for 15–30% of the difference in nitrate concentrations. Concentrations of Cl − and SiO 2 indicated that mixing between river water and ground water in the floodplain deposits and riverbed sediments accounted for the remainder of the difference in nitrate concentrations. River flux measurements indicated that ground-water discharge in a 7.5 km segment of river had a nitrate load of 1718 kg N day − and accounted for about 18% of the total nitrate load in the river at the downstream end of that segment. This nitrate load was 70% less than the load predicted on the basis of the median nitrate concentration in the terrace deposits and assuming no denitrification or mixing in the aquifer. Water exchange between the river and aquifer caused ground water that originally discharged to the river to reenter denitrifying sediments in the riverbed and floodplain, thereby further decreasing the nitrate load in this stream—aquifer system. Results from this study indicated that denitrification and mixing within akluvial aquifer sediments may substantially decrease the nitrate load added to rivers by discharging ground water.

Journal of Hydrology↗
USGS1995

Effect of ground-water/surface-water interactions on nitrate concentrations in discharge from the South Platte River alluvial aquifer, Colorado

Concentrations of dissolved nitrate in recharge-area water from a 200-km2 segment of the South Platte River alluvial aquifer near Greeley, Colorado, range from less than 0.1 to 58 mg/l as nitrogen, and the median concentration is 26 mg/l as nitrogen. Hydraulic-head data indicate that this nitrate-enriched ground water move toward the South Platte River. However, the median concentration of nitrate in ground water from the discharge area is only about 9 mg/l as nitrogen. Moreover, measurements of dissolved oxygen, nitrogen gas, nitrate, and nitrate-nitrogen isotope ratios are then taken, and comparison between chloride and silica concentrations in river and ground waters are also made.

Conference Paper↗
USGS1993

Chemical, isotopic, and microbiological evidence for denitrification during transport of domestic wastewater through a thick unsaturated zone in the Mojave Desert, San Bernardino County, California

Nitrogen in downward-infiltrating wastewater discharged from seepage pits (dry wells) at residences in the upper Mojave River Basin, California represents a significant potential source of nitrate contamination to the underlying ground water. However, increases in nitrate concentration in the ground water have not yet been observed. The low nitrate concentration in the ground water may be the result of lateral dispersion in the unsaturated zone, dilution below the water table, or denitrification of wastewater nitrate in the unsaturated zone. Measured vertical rates indicate that some wastewater has reached the water table beneath communities that are older than 5 to 10 years. As wastewater percolates from seepage pits into the unsaturated zone, reduced nitrogen is converted rapidly to nitrate at shallow depths and the nitrate concentrations commonly decrease with depth. The largest nitrate decreases seem to coincide with increased content of fine-grained sediments or with proximity to the water table. Between lysimeters at 160 and 199 feet at one residence, the decrease in nitrate concentration coincided with a large increase in sulfate, decrease in alkalinity, and increase in 815N in nitrate. Those data are consistent with denitrification by oxidation of iron sulfide to produce ferric oxides; but if such a reaction occurs, it must be in domains that are small in comparison with the sampled volumes because the waters also contain substantial quantities of dissolved oxygen. The predominantly low nitrate concentrations in the area's ground water are consistent with the operation of a nitrogen-removal mechanism, possibly denitrification; however, the reducing capacity of the sediments to maintain denitrification is not known.

Open-File Report↗
USGS1992

Brine history indicated by argon, krypton, chlorine, bromine, and iodine analyses of fluid inclusions from the Mississippi Valley type lead-fluorite-barite deposits at Hansonburg, New Mexico

Argon, krypton, chlorine, bromine, and iodine were measured in a homogeneous population of high-salinity hydrothermal fluid inclusions from the Tertiary-age Mississippi Valley-type (MVT) lead-fluorite-barite deposits at Hansonburg, New Mexico to establish new types of evidence for the history of both the fluid and the major dissolved salts. Noble gases and halogens in fluid inclusions containing 10 −10 –10 −9 L of brine ( Cl= 3 molal) were analyzed by laser microprobe noble-gas mass spectrometry ( lmngms ) on neutron-irradiated samples. The concentrations of 36 Ar ( 4.7 × 10 −8 molal) and 84 Kr 1.8 × 10 −9 molal) in the fluid inclusions are equal to those of fresh surface waters in equilibrium with air at approximately 20 ± 5 °. The mole ratios of Br/Cl ( 1.2 × 10 −4 ) and I/Cl ( 1–2 × 10 −6 ) are among the lowest measured in any natural waters, similar to those of modern brines formed by dissolution of Permian NaCl-bearing evaporites in southeast New Mexico. 40 Ar/ 36 Ar ratios (600) are twice that of air, and indicate that the fluid inclusions had excess radiogenic 40 Ar ( 1.4 × 10 −5 molal) when trapped. The amount of excess 40 Ar appears to be too large to have been acquired with Cl by congruent dissolution of halite-bearing evaporites, and possibly too small to have been acquired with Pb by congruent dissolution of granitic basement rocks with Proterozoic K Ar ages. From the lmngms data, combined with published Pb and S isotope data, we infer the following sequence of events in the history of the Hansonburg MVT hydrothermal brine: (1) the brine originated as relatively dilute meteoric water, and it did not gain or lose atmospheric Ar or Kr after recharge; (2) the originally dilute fluid acquired the bulk of its Cl and sulfate in the subsurface after recharge by dissolving halite-bearing Permian? marine evaporites; (3) the high salinity brine then acquired most of its Pb and excess radiogenic 40 Ar from interactions with aquifer rocks other than evaporites, possibly clastic sedimentary rocks or basement rocks with Phanerozoic K Ar “ages”; and (4) the brine deposited fluorite without having boiled or degassed.

Earth and Planetary Science Letters↗
USGS1992

Laser microprobe analyses of noble gas isotopes and halogens in fluid inclusions: Analyses of microstandards and synthetic inclusions in quartz

Ar, Kr, Xe, Cl, Br, I, and K abundances and isotopic compositions have been measured in microscopic fluid inclusions in minerals by noble gas mass spectrometry following neutron irradiation and laser extraction. The laser microprobe noble gas mass spectrometric (LMNGMS) technique was quantified by use of microstandards, including air-filled capillary tubes, synthetic basalt glass grains, standard hornblende grains, and synthetic fluid inclusions in quartz. Common natural concentrations of halogens (Cl, Br, and I) and noble gases (Ar and Kr) in trapped groundwaters and hydrothermal fluids can be analyzed simultaneously by LMNGMS in as little as 10 −11 L of inclusion fluid, with accuracy and precision to within 5–10% for element and isotope ratios. Multicomponent element and isotope correlations indicate contaminants or persistent reservoirs of excess Xe and/or unfractionated air in some synthetic and natural fluid inclusion samples. LMNGMS analyses of natural fluid inclusions using the methods and calibrations reported here may be used to obtain unique information on sources of fluids, sources of fluid salinity, mixing, boiling (or unmixing), and water-rock interactions in ancient fluid flow systems.

Geochimica et Cosmochimica Acta↗
USGS1992

Laser microprobe analyses of Cl, Br, I, and K in fluid inclusions: Implications for sources of salinity in some ancient hydrothermal fluids

The relative concentrations of Cl, Br, I, and K in fluid inclusions in hydrothermal minerals were measured by laser microprobe noble gas mass spectrometry on irradiated samples containing 10 −10 to 10 −8 L of fluid. Distinctive halogen signatures indicate contrasting sources of fluid salinity in fluid inclusions from representative “magmatic” (St. Austell), “metamorphic” (Alleghany), and “geothermal” (Creede, Salton Sea) aqueous systems. Br/Cl mol ratios are lowest at Salton Sea (0.27–0.33 × 10 −3 ), where high salinities are largely due to halite dissolution; intermediate at St. Austell (0.85 × 10 −3 ), possibly representative of magmatic volatiles; and highest (near that of seawater) at Creede (1.5–2.1 × 10 −3 ) and Alleghany (1.2–2.4 × 10 −3 ), where dissolved halogens probably were leached from volcanic and (or) nonevaporitic sedimentary rocks. I C1 "> IC1 mol ratios are lowest (near that of seawater) at Creede (1–14 × 10 −6 ), possibly because organisms scavenged I during low temperature recharge; intermediate at Salton Sea (24–26 × 10 −6 ) and St. Austell (81× 10 −6 ); and highest at Alleghany (320–940 × 10 −6 ), probably because the fluids interacted with organic-rich sediments at high temperatures before being trapped. K Cl "> KCl mol ratios indicate disequilibrium with respect to hypothetical feldspathic alkali-Al-silicate mineral buffers at fluid inclusion trapping temperatures at Creede, and large contributions of (Na, K)-bicarbonate to total fluid ionic strength at Alleghany. Significant variations in Cl/Br/I/K ratios among different fluid inclusion types are correlated with previously documented mineralization stages at Creede, and with the apparent oxidation state of dissolved carbon at Alleghany. The new data indicate that Cl/ Br/I ratios in hydrothermal fluid inclusions vary by several orders of magnitude, as they do in modern surface and ground waters. This study demonstrates that halogen signatures of fluid inclusions determined by microanalysis yield important information about sources of fluid salinity and provide excellent definition of fluid reservoirs and tracers of flow and interaction in ancient hydrothermal systems.

Geochimica et Cosmochimica Acta↗
USGS1990

Geochemistry of reduced gas related to serpentinization of the Zambales ophiolite, Philippines

Methane-hydrogen gas seeps with mantle-like C and noble gas isotopic characteristics issue from partially serpentinized ultramafic rocks in the Zambales ophiolite, Philippines. New measurements of noble gas and 14 C isotope abundances, rock/mixed-volatile equilibrium calculations, and previous chemical and isotopic data suggest that these reduced gases are products of periodotite hydration. The gas seeps are produced in rock-dominated zones of serpentinization, and similar gases may be ubiquitous in ultramafic terranes undergoing serpentinization.

Applied Geochemistry↗
USGS1989

Comparison of metasomatic reactions between a common CO2-rich vein fluid and diverse wall rocks: Intensive variables, mass transfers, and Au mineralization at Alleghany, California

The gold deposits at Alleghany, California, are typical of many epigenetic gold-bearing hydrothermal vein systems in metamorphic terranes worldwide. Detailed analyses of alteration halos in serpentinite, mafic amphibolite, and granite wall rocks at Alleghany indicate that widely contrasting deposit types, ranging from fuchsite-carbonate schists to pyrite-albitites, resulted when different wall rocks interacted with the same externally derived CO 2 -rich hydrothermal vein fluid. Patterns of element redistribution within halos and among lithologic units suggest a complex process involving fluid flow along vein fractures and diffusion (+ or - infiltration) normal to the veins. Wall rocks locally controlled both the directions and magnitudes of chemical fluxes across vein walls.Vein fluids at constant temperature and pressure, with relatively constant ratios of mobile species (Na (super +) /K (super +) /H (super +) and CO 2 /H 2 S/H 2 ), caused contrasting ("divergent") reactions in proximal alteration zones because the wall rocks controlled the ratios of relatively immobile species (Al/(Cr + Fe + Mg) and Fe/Mg), and the component activities, of hydrothermal mineral solid solutions. Thus, pyrite and albite were stable with respect to the relatively pure siderite and K mica that occur sparingly in proximal granite zones, but they were not stable with respect to the relatively impure siderite and K mica that characterize proximal serpentinite zones. Partly as a result of divergent reactions, altered rocks exhibit contrasting mobile element concentration gradients (e.g., Ca, Ba, Sr, Rb, Na/K, C/S) and imply local sources and sinks, and possibly short residence times, for some of these components along discordant fluid flow paths.Calculated reaction coefficients for H (super +) , H 2 , and H 2 S indicate that different wall rocks at different stages of alteration may have inhibited or promoted gold precipitation. The distribution of gold and its calculated solubility are consistent with its having been precipitated from Au(HS) 2 (super -) complexes in response to pyritization of granite (fluid desulfidation and reduction), and possibly in part, in response to dolomitization and sericitization of serpentinite (fluid acidification?). Strata-bound disseminated orebodies may be expected in a variety of other host rocks with higher than average Fe/Mg ratios, where pyrite was stable with respect to intermediate magnesite-siderite, as in the granite.It is proposed that the CO 2 -rich vein fluids approached partial equilibrium with alteration assemblages in the average, or dominant, rocks along their flow paths. Simpler, but radically different, proximal assemblages were then produced where the fluids encountered chemically extreme rock types. Fluid-rock interaction equilibria can account for much of the diversity in the mineralogy and chemistry of gold deposits in heterogeneous metamorphic terranes, while maintaining a simple genetic classification based on the distinctive chemistry of the hydrothermal fluids. Comparative studies of multicomponent phase equilibria and mass exchanges can provide both rationalizations and predictions of local wall-rock effects on geochemical anomalies and the locations of ore deposits in lithologically heterogeneous terranes. Simultaneous consideration of contrasting high-variance (phase-deficient) assemblages along discordant veins is suggested as a general method for quantifying fluid-intensive variables in metasomatic systems.

Economic Geology↗
USGS1981

Spectroscopic geochemical study of vanadiferous marine sediments of the Gibellini claims, southern Fish Creek Range, Eureka County, Nevada

Samples of cuttings from three drill holes in the Gibellini claims were analyzed by emission spectroscopic techniques for a large suite of major and trace elements. Unoxidized siliceous "black shale" from drill hole NGA 7 is strongly enriched in Cd, Mo, Sb, Se, V, and Zn, and also contains relatively high concentrations of As, Ba, Cu, Ni, and Tl compared with nonmetalliferous shales. Analyses of 103 samples plotted against depth in drill holes NGA, NG31, and NGA7, and selected XRD data, show the following: 1. Groups of elements with distinct distribution patterns define most of major mineralogic components of the rocks. The "normal shale" component, which includes several detrital and authigenic phases, is indicated by covariations among Ti, Al, Fe, Na, Mg, K, B, Be, Co, Cr, Ga, La, Sc, Sr, and Zr. The shale component is diluted by varying amounts of the following minerals (and associated elements): silica (Si); dolomite (Mg, Ca, Mn, Sr); apatite (Ca, Be, Cr, La, Sr, Y); barite (Ba, Sr); sphalerite (Zn, Cd, Fe?); smithsonite (Cd, Co, Mn, Ni, Zn); bianchite (Cd, Ni, Zn) ; and bokite (V). Pyrite, gypsum, and jarosite were also identified. 2. The highly siliceous kerogenous metalliferous Gibellini facies is underlain by argillaceous and (or) dolomitic rocks. The transition zone deduced from the chemical data is not well defined in all instances, but probably represents the bottom of the black shale deposit. 3. Oxidation has reached to variable depths up to at least 150 ft, and has caused profound changes in the distributions of the enriched metals. Molybdenum, Se, and V have been partially removed from the upper parts of the sections and are concentrated near or slightly above the base of the Gibellini facies. Cadmium, Ni, and Zn have been strongly leached and now occur at or below the base of the Gibellini facies. The variable depth of oxidation, the redistribution and separation of the metals, and the complex mineralogy of the deposit may make development of the claim complicated.

Open-File Report↗