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At least 739 records · Page 41Linked to original sources
USGS2004

Chemistry & migration mysteries: Fur holds clues to previous journeys

The bat was not only pregnant but downright angry as I snipped a bit of fur from her back. Within a few seconds, however, she flapped her powerful wings, took off from my hand and disappeared into the night, rejoining thousands of female hoary bats ( Lasiurus cinereus ) on their migration through the mountains of New Mexico. Every spring, hundreds of these expectant mothers pass through this small stream drainage on their way to birthing grounds farther east. Their annual passage was first reported here more than 30 years ago, and it is still one of the few known migration corridors in the area. My task that night was simple: catch hoary bats and snip tiny samples of fur from their thick coats, then let them continue on their way. The explanation, however, is a bit more complicated.

BATS Magazine↗
USGS1982

Evolution of geothermal fluids deduced from chemistry plots: Yellowstone National Park (U.S.A.)

Large amounts of chemical data, obtained in geothermal fields, may readily be sorted-out by the aid of a simple set of graphs that provide a clear over-all picture and facilitate the understanding of geochemical processes taking place. As a case study, data from several hundred samples of the thermal springs at the well-known Yellowstone National Park are discussed. The pattern obtained seems to indicate: (1) geochemical similarity between the spring groups of Heart Lake, Shoshone, Upper, Midway, Lower and Norris Geyser Basins, i.e., a geochemical uniformity of major spring groups located over 40 km apart; (2) these groups may be described as originating from a common fluid, most resembling the composition of Norris waters, accompanied by CO2, and other volatiles, that react with igneous rocks, forming local variations; (3) the secondary reactions occur at (medium) depth, before the ascent to the surface; (4) extensive concentration-dilution processes occur during the ascent to the surface. The water of the Mammoth group may be described as originating from the same Norris-like fluid that has been diluted (low Na and Cl contents) and intensively reacted with carbonaceous rocks, thus gaining in Ca, Mg, SO4, and HCO3. ?? 1982.

Journal of Volcanology and Geothermal Research↗
USGS1985

Chemistry of thermal and nonthermal springs in the vicinity of Lassen Volcanic National Park

Meaningful applications of water geothermometry to thermal springs in and around Lassen Volcanic National Park (LVNP) are limited to Growler Hot Spring and Morgan Hot Springs. Most hot springs located within LVNP are low-chloride, acid-sulfate waters associated with nearby steam vents. This type of hot-spring activity is characteristically found above vapor-dominated hydrothermal systems. These acid-sulfate waters are not generally useful for liquid chemical geothermometry, however, because their chemical compositions result from water-rock interaction at relatively shallow depths. Thermal waters at Drakesbad and in Little Hot Springs Valley have neutral-pH, low-Cl concentrations and have estimated Na-K-Ca and Na-Li geothermometer temperatures close to measured spring temperatures of 65 to 95??C. Hot-spring waters located south of LVNP at Growler Hot Spring, Morgan Hot Springs, and in the south-central part of LVNP in the Walker "O" No. 1 well at Terminal Geyser are rich in chloride and yield calculated geothermometer temperatures between 220 and 230??C. These thermal waters probably originate within a zone of upflow of high-enthalpy fluid inside LVNP and cool conductively during lateral flow to the south and southeast. ?? 1985.

Journal of Volcanology and Geothermal Research↗
USGS1991

Role of sediment-trace element chemistry in water-quality monitoring and the need for standard analytical methods

Multiple linear regression models calculated from readily obtainable chemical and physical parameters can explain a high percentage (70% or greater) of observed sediment trace-element variance for Cu, Zn, Pb, Cr, Ni, Co, As, Sb, Se, and Hg. Almost all the factors used in the various models fall into the category of operational definitions (e.g., grain size, surface area, and geochemical substrates such as amorphous iron and manganese oxides). Thus, the concentrations and distributions used in the various models are operationally defined, and are subject to substantial change depending on the method used to determine them. Without standardized procedures, data from different sources are not comparable, and the utility and applicability of the various models would be questionable.

Conference Paper↗
USGS1989

Pb-Bi-Ag-Cu-(Hg) chemistry of galena and some associated sulfosalts. A review and some new data from Colorado California and Pennsylvania

Galena, associated with Pb-Bi-Ag sulfosalts and simple sulfides, contains varied amounts of Ag and Bi in the Dandy vein system, Idarado mine, Ouray, Colorado; the Jackass mine, Darwin District, California; and the Leadville district, Colorado. Silver- and bismuth-bearing galena associated with minor amounts of pyrite, chalcopyrite and sphalerite occur at the Pequea mine, Lancaster County, Pennsylvania. Ag and Bi contents in the Dandy suite of galena range from about 1.4 to 3.4 and 2.5 to 6.5 wt.% respectively, and are comparable or lower in galena from the other localities. Exsolved matildite is present in galena from the Dandy, Jackass and Leadville localities. The presence in significant amounts of both Ag and Bi in a Pb-rich sulfide system is necessary for formation of PbSss (galena solid-solution). If Ag (especially) and Bi (to a lesser extent) are absent, the galena formed will be essentially pure PbS. Some minor Sb may substitute for Bi. Compositional data for all of the galena samples are in agreement with a previously proposed linear relationship between a and Ag-Bi(Sb) content. Matildite and seven additional Pb-Bi-Ag-Cu sulfosalts have been identified from the Dandy vein system, based on electron-microprobe analyses and some X-ray powder-diffraction data.

Canadian Mineralogist↗
USGS1991

Spatial variability and collector requirements for sampling throughfall volume and chemistry under a mixed-hardwood canopy

Ion concentrations were generally less variable within storms compared with net ion input data. Concentrations and net inputs of some ions were consistently less variable than others; for example, Ca2+, NO3-, and SO42- were less variable than NH4 + and K+. These patterns of variability were consistent in comparisons both within and among storms. The relatively low variability of NO3- and SO42- is probably due to dry deposition of these ions as anthropogenic pollutants, while the low variability of Ca2+ is the result of deposition in windblown soil particles. The high variability of NH4+ and K+ is probably the result of biological processes. Ammonium is strongly retained by the canopy, and K+ is readily leached from it. Retention by, and leaching from, the canopy can induce spatial variability as a result of spatial heterogeneity in the biota. Throughfall volume also displayed low variability within and among events, requiring an average of 11 collectors to estimate the mean within 10% at the 95% confidence level. -from Author

Canadian Journal of Forest Research↗
USGS1994

Geochemistry of the 1989-1990 eruption of redoubt volcano: Part II. Evidence from mineral and glass chemistry

Early stages (December 1989) of the 1989-1990 eruption of Redoubt Volcano produced two distinct lavas. Both lavas are high-silica andesites with a narrow range of bulk composition (58-64 wt.%) and similar mineralogies (phenocrysts of plagioclase, hornblende, augite, hypersthene and FeTi oxides in a groundmass of the same phases plus glass). The two lavas are distinguished by groundmass glass compositions, one is dacitic and the other rhyolitic. Sharp boundaries between the two glasses in compositionally banded pumices, lack of extensive coronas on hornblende phenocrysts, and seismic data suggest that a magma-mixing event immediately preceeded the eruption in December 1989. Textural disequilibrium in the phenocrysts suggests both magmas (dacitic and rhyolitic glasses) had a mixing history prior to their interaction and eruption in 1989. Sievey plagioclase and overgrowths of magnetite on ilmenite are textures that are at least consistent with magma mixing. The presence of two hornblende compositions (one a high-Al pargasitic hornblende and one a low-Al magnesiohornblende) in both the dacitic and rhyolitic groundmasses indicates a mixing event to yield these two amphibole populations prior to the magma mixing in December 1989. The pargasitic hornblende and the presence of Ca-rich overgrowths in the sievey zones of the plagioclase together indicate at least one component of this earlier mixing event was a mafic magma, either a basalt or a basaltic andesite. Eruptions in 1990 produced only andesite with a rhyolitic groundmass glass. Glass compositions in the 1990 andesite are identical to the rhyolitic glass in the 1989 andesite. Cognate xenoliths from the magma chamber (or conduit) are also found in the 1990 lavas. Magma mixing probably triggered the eruption in 1989. The eruption ended when this rather viscous (rhyolitic groundmass glass, magma capable of entraining sidewall xenoliths) magma stabalized within the conduit. ?? 1994.

Journal of Volcanology and Geothermal Research↗
USGS1994

Geochemistry of the 1989-1990 eruption of redoubt volcano: Part I. Whole-rock major- and trace-element chemistry

The 1989-1990 eruption of Redoubt Volcano produced medium-K calc-alkaline andesite and dacite of limited compositional range (58.2-63.4% SiO2) and entrained quenched andesitic inclusions (55% SiO2) which bear chemical similarities to the rest of the ejecta. The earliest (December 15) magmas are pumiceous, often compositionally banded, and the majority is relatively mafic (< 59% SiO2). The most silicic magmas of the eruption are the late December to early January domes (up to 63.4% SiO2). Subsequent magmas formed domes and rare pumices which converge on 60% SiO2. Chemical variations among ejecta comprise tight, linear, two-component arrays for all elements for which the analytical uncertainty is much less than the compositional range. The two-component arrays are interpreted as mixing arrays between unrelated magmas because several of the arrays are at steep angles to the normal liquid line of descent. Additionally, the felsic endmember cannot be easily related to the mafic endmember by normal high-temperature igneous processes (e.g., the silicic endmember has higher Zr yet lower Hf than the mafic endmember). Also relative enrichments of highly incompatible elements are dramatically different across the arrays. The mixing event must have preceded eruption by a significant, yet unspecified amount of time because groundmass glass compositions are homogeneous for all post-December samples (Swanson et al., 1994-this volume), in spite of the whole-rock chemical diversity. This implies time for additional crystallization after the mixing event. Swanson et al. (1994-this volume) discuss evidence for a potentially different mixing event recorded only in December 15 magmas. Cognate cumulate xenoliths composed of pl+cpx+opx+hb+mt+melt were recovered from January and April deposits. These blocks differ from local batholithic country rock in their low concentrations of incompatible elements (e.g., Rb < 5 ppm vs 20-90 ppm, Ba < 150 ppm vs 300-2000 ppm) and low SiO2 (< 50 wt.% vs > 60 wt.%). They have Mg, Cr, Ni, Sc, and V contents higher than the andesites, but lower than Redoubt basalts and basaltic andesites. Thus, they may be crystallization products of andesites, but do not represent the cumulate residue of basalt fractionation. The xenoliths were probably derived from a shallow or intermediate crustal chamber. ?? 1994.

Journal of Volcanology and Geothermal Research↗
USGS1993

Sampling and major element chemistry of the recent (A.D. 1631-1944) Vesuvius activity

Detailed sampling of the Vesuvius lavas erupted in the period A.D. 1631-1944 provides a suite of samples for comprehensive chemical analyses and related studies. Major elements (Si, Ti, Al, Fetotal, Mn, Mg, Ca, Na, K and P), volatile species (Cl, F, S, H2O+, H2O- and CO2), and ferrous iron (Fe2+) were determined for one hundred and forty-nine lavas and five tephra from the A.D. 1631-1944 Vesuvius activity. The lavas represent a relatively homogeneous suite with respect to SiO2, TiO2, FeOtotal, MnO and P2O5, but show systematic variations among MgO, K2O, Na2O, Al2O3 and CaO. The average SiO2 content is 48.0 wt.% and the rocks are classified as tephriphonolites according to their content of alkalis. All of the lavas are silica-undersaturated and are nepheline, leucite, and olivine normative. There is no systematic variation in major-element composition with time, over the period A.D. 1631-1944. The inter-eruption and intra-eruption compositional differences are the same magnitude. The lavas are highly porphyritic with clinopyroxene and leucite as the major phases. Fractionation effects are not reflected in the silica content of the lavas. The variability of MgO, K2O, Na2O, and CaO can be modelled as a relative depletion or accumulation of clinopyroxene. ?? 1993.

Journal of Volcanology and Geothermal Research↗
USGS1998

Paragenesis and chemistry of multistage tourmaline formation in the sullivan Pb-Zn-Ag deposit, British Columbia

Detailed petrographic study, scanning electron microscope imaging, and electron microprobe analyses of tourmalines from the Sullivan Pb-Zn-Ag massive sulfide deposit (British Columbia, Canada) document multiple paragenetic stages and large compositional variations. The tourmalines mainly belong to two common solid-solution series: dravite-schorl and dravite-uvite. Ca- and Fe-rich feruvite and alkali-deficient tourmalines are present locally. Products of tourmaline-forming stages include (from oldest to youngest): (1) rare Fe-rich dravite-schorl within black tourmalinite clasts in footwall fragmental rocks; (2) widespread Mg-rich, very fine grained, felted dravite in the footwall (the main type of tourmaline in the footwall tourmalinite pipe); (3) recrystallized, Fe-rich dravite-schorl (locally Ca-Fe feruvite) in the tourmalinite pipe, which preferentially occurs near postore gabbroic intrusions; (4) Mg-rich dravite or uvite associated with chlorite-pyrrhotite and chlorite-albite-pyrite-altered rocks in the shallow footwall and hanging wall; (5) discrete Mg-rich tourmaline grains associated with chlorite and discordant Mg-rich tourmaline rims which occur on disseminated Fe-rich schorl in the bedded Pb-Zn-Ag ores. The timing of rare Fe-rich schorl in the bedded ores is uncertain, but it most likely occurred during or between stages 2 and 3. The different paragenetic stages and their respective tourmaline compositions are interpreted in terms of a multistage evolution involving contributions from: (1) variable mixtures of synsedimentary, Fe-rich hydrothermal fluids and entrained seawater; (2) postore, Fe-rich, gabbro-related hydrothermal fluids; and (3) postore metamorphic reactions. Early synsedimentary, Fe-rich hydrothermal fluids which contained little or no entrained seawater formed Fe-rich black tourmalinite clasts locally in the footwall. The major type of tourmaline in the footwall tourmalinite pipe is Mg rich, recording seawater entrainment under high water/rock conditions, rather than control by the chemical composition of the original host sediments. Rare Fe-rich schorl within the bedded Pb-Zn-Ag ores is believed to have formed on the sea floor by reaction of an Fe-rich brine pool with detrital aluminous sediments. Postore emplacement of gabbro sills and local dikes in the footwall produced Fe-rich hydrothermal fluids, which were responsible for formation of minor Fe-rich dravite-schorl which overprinted earlier dravite. Postore, but synsedimentary, hydrothermal alteration involving entrained seawater was responsible for deposition of dravite and uvite in the hanging wall and for dravite in the brown tourmalinites of the shallow footwall. Mg-rich dravite-uvite associated with chlorite and in discordant rims on schorl in the bedded ores formed by sulfide-silicate reactions during greenschist facies regional metamorphism.

Economic Geology↗
USGS1999

Chlorine-bearing amphiboles from the Fraser mine, Sudbury, Ontario, Canada: Description and crystal chemistry

Three chemically distinct populations of Cl-bearing amphibole have been recognized in association with contact Ni-Cu ore deposits in Footwall Breccia at the Fraser mine, Sudbury, Ontario. The first population, defined as halogen-poor (<0.5 wt.% Cl) actinolite and magnesiohornblende, occurs predominantly as pale green grains and cores. These are generally overgrown by amphibole of the other two populations: a) Fe-rich, halogen-poor deep green rim of ferro-actinolite to ferrohornblende, and b) Fe-rich, Cl-rich (up to 4 wt.% Cl) ferrotschermakite to hastingsite to potassic-chlorohastingsite, which exhibits a characteristic deep blue-green pleochroism. Rare F-rich (up to 1.1 wt.% F) magnesiohornblende also is observed in the same environment. Major-element data for the Cl-rich amphiboles indicate linear, positive relationships for both Mg and K versus Cl, and a logarithmic, positive one for ([4])Al versus Cl. These data, along with selected X-ray maps, indicate that Cl is homogeneously distributed and likely structurally bound. Calculated Fe3+/Fe2+ values suggest crystallization under conditions of relatively low f(O2). At least two chemically distinct fluids seem to have been responsible for crystallization of the amphiboles. The first, which resulted in the crystallization of halogen-poor, pale green actinolite and magnesiohornblende, was likely relatively hot (???650??C) and contemporaneous with sulfide emplacement. This was followed by a lower-T (???350??C), Cl-rich fluid from which the Cl-rich amphiboles crystallized. This latter fluid may have been a modified product of the initial fluid or possibly a second discrete fluid. A subsequent F-rich fluid led to development of F-rich magnesiohornblende. The source of both Cl and F is not clear; whole-rock analyses of Footwall rocks of the Levack Gneiss Complex, however, reveal anomalous enrichments in both Cl (>700 ppm) and F (2500 ppm). These rocks thus may have been a significant contributor to the fluids.

Canadian Mineralogist↗
USGS2001

Water chemistry at Snowshoe Mountain, Colorado: mixed processes in a common bedrock

At Snowshoe Mountain the primary bedrock is quite homogeneous, but weathering processes vary as waters moves through the soils, vadose zone and phreatic zone of the subsurface. In the thin soil, physical degradation of tuff facilitates preferential dissolution of potassium ion from glass within the rock matrix, while other silicate minerals remain unaltered. In the vadose zone, in the upper few meters of fractured bedrock, dilute water infiltrates during spring snowmelt and summer storms, leading to preferential dissolution of augite exposed on fracture surfaces. Deeper yet, in the phreatic zone of the fractured bedrock, Pleistocene calcite fracture fillings dissolve, and dioctahedral and trioctahedral clays form as penetrative weathering alters feldspar and pyroxene. Alkalinity is generated and silica concentrations are buffered by mineral alteration reactions.

Colorado↗