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Results for “Geochimica et Cosmochimica Acta”

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At least 91 records · Page 5Linked to original sources
USGS1963

The precipitation of aluminum, iron and manganese at the junction of Deer Creek with the Snake River in Summit County, Colorado

The oxidation of disseminated pyrite in relatively acid schists and gneisses of the Snake River drainage basin provides abundant iron sulfate and sulfuric acid to ground and surface water. This acid water dissolves large quantities of many elements, particularly aluminum and surprisingly large quantities of elements, such as magnesium and zinc, not expected to be abundant in the drainage basin. The adjoining drainage to the west, Deer Creek, is underlain by basic rocks, from which the water inherits a high pH. Despite the presence of base- and precious- metal veins in the drainage basin of Deer Creek, it carries less metal than the Snake River. The principal precipitate on the bed of the Snake River is hydrated iron oxide with small quantities of the other metals. In Deer Creek manganese oxide is precipitated with iron oxide and large quantities of other metals are carried down with this precipitate. Below the junction of these streams the pH stabilizes at a near-neutral value. Iron is removed from the Snake River water at the junction, and aluminum is precipitated for some distance downstream. The aluminum precipitate carries down other metals in concentrations slightly less than that in the manganese precipitate on Deer Creek. The natural processes observed in this junction if carried to a larger scale could provide the mechanism described by Ansheles (1927) for the formation of bauxite. In the environment described, geochemical exploration by either water or stream sediment techniques is difficult because of (1) the extreme pH differential between the streams above their junction and (2) the difference in the precipitates formed on the streambeds.

Colorado↗
USGS1963

Implications of the minor element content of some major streams of the world

Of 15 or more minor elements in the world's principal river waters only aluminum, iron, manganese, barium and strontium range much over 100 μg l "> 100 μgl . (parts per billion). Most minor elements range at or below 100 μg 1 "> 100 μg1 . and have median (or middle) values of 10 micrograms per liter or less. Significant areal differences in minor element content are found in the river waters. For example, Atlantic Coastal river waters in the aggregate are slightly more enriched in concentrations of silver, chromium, manganese, molybdenum, nickel, strontium and titanium, and slightly deficient in barium and lithium when compared with median values for North America. Median values of ratios Ba Sr "> BaSr , Ni Cr "> NiCr and Ni Cu "> NiCu are reasonably consistent (within a factor of two) in principal drainage from North America. Noteworthy are consistent median ratios of Ni Cu "> NiCu for large rivers of United States, but the ratio tends to be slightly greater in global northern latitudes than in southern latitudes. Median values for aluminum, barium, copper, lead, molybdenum and silver in North American runoff are of the same order as published world averages for ocean water. Hydrologic and geochemical aspects of continental runoff are strongly implied in observations of minor element content of large rivers. Evidence to date is that median values of Ba Sr ratios "> BaSr ratios are relatively uniform in global river waters. There is real danger in oversimplifying chemical systems in broad assessments of lower reaches of large drainage basins because individual hydrologic and chemical events upstream are largely obscured.

Geochimica et Cosmochimica Acta↗
USGS1963

Releasing-addition method for the flame-photometric determination of calcium in thermal waters

Study of the interferences of silica and sulfate in the flame-photometric determination of calcium in thermal waters has led to the development of a method requiring no prior chemical separations. The interference effects of silica, sulfate, potassium, sodium, aluminum, and phosphate are overcome by an addition technique coupled with the use of magnesium as a releasing agent.

Geochimica et Cosmochimica Acta↗
USGS1964

Minor-element composition and organic carbon content of marine and nonmarine shales of Late Cretaceous age in the western interior of the United States

The composition of nonmarine shales of Cretaceous age that contain less than 1 per cent organic carbon is assumed to represent the inherited minor-element composition of clayey sediments delivered to the Cretaceous sea that occupied the western interior region of North America. Differences in minor-element content between these samples and samples of 1. (a) nonmarine carbonaceous shales (1 to 17 per cent organic carbon), 2. (b) nearshore marine shales (less than 1 per cent organic carbon), and 3. (c) offshore marine shales (as much as 8 per cent organic carbon), all of the same age, reveal certain aspects of the role played by clay minerals and organic materials in affecting the minor-element composition of the rocks. The organic carbon in the nonmarine rocks occurs in disseminated coaly plant remains. The organic carbon in the marine rocks occurs predominantly in humic material derived from terrestrial plants. The close similarity in composition between the organic isolates from the marine samples and low-rank coal suggests that the amount of marine organic material in these rocks is small. The minor-element content of the two kinds of nonmarine shales is the same despite the relatively large amount of organic carbon in the carbonaceous shales. The nearshore marine shales, however, contain larger median amounts of arsenic, boron, chromium, vanadium and zinc than do the nonmarine rocks; and the offshore marine shales contain even larger amounts of these elements. Cobalt, molybdenum, lead and zirconium show insignificant differences in median content between the nonmarine and marine rocks, although as much as 25 ppm molybdenum is present in some offshore marine samples. The gallium content is lower in the marine than in the nonmarine samples. Copper and selenium contents of the two kinds of nonmarine rocks and the nearshore marine samples are the same, but those of the offshore samples are larger. In general, arsenic, chromium, copper, molybdenum, selenium, vanadium and zinc are concentrated in those offshore marine samples having the largest amounts of organic carbon, but samples with equal amounts of vanadium, for instance, may differ by a factor of 3 in their amount of organic carbon. Arsenic and molybdenum occur in some samples chiefly in syngenetic pyrite but also are present in relatively large amounts in samples that contain little pyrite. The data on nonmarine carbonaceous shales indicate that organic matter of terrestrial origin in marine shales contributes little to the minor-element content of such rocks. It is possible that marine organic matter, even though seemingly small in amount in marine shales, contributes to the minor-element composition of the shales. In addition to any such contribution, however, the great effectiveness in sorption processes of humic materials in conjunction with clay minerals suggests that such processes must have played an important role as these materials moved from the relatively dilute solutions of the nonmarine environment to the relatively concentrated solution of sea water. The volumes of sea water sufficient to supply for sorption the amounts of most minor elements in the offshore marine samples are insignificant compared to the volumes of water with which the clay and organic matter were in contact during their transportation and sedimentation. Consequently, the chemical characteristics of the environment in which the clay minerals and organic matter accumulated and underwent diagenesis probably were the most important factors in controlling the degree to which sorption processes and the formation of syngenetic minerals affected the final composition of the rocks.

Geochimica et Cosmochimica Acta↗
USGS1964

Vapor pressure and vapor fractionation of silicate melts of tektite composition

The total vapor pressure of Philippine tektite melts of approximately 70 per cent silica has been determined at temperatures ranging from 1500 to 2100°C. This pressure is 190 ± 40 mm Hg at 1500°C, 450 ± 50 mm at 1800°C and 850 ± 70 mm at 2100° C. Determinations were made by visually observing the temperature at which bubbles began to form at a constant low ambient pressure. By varying the ambient pressure, a boiling point curve was constructed. This curve differs from the equilibrium vapor pressure curve due to surface tension effects. This difference was evaluated by determining the equilibrium bubble size in the melt and calculating the pressure due to surface tension, assuming the latter to be 380 dyn/cm. The relative volatility from tektite melts of the oxides of Na, K, Fe, Al and Si has been determined as a function of temperature, total pressure arid roughly, of oxygen fugacity. The volatility of SiO 2 is decreased and that of Na 2 O and K 2 O is increased in an oxygen-poor environment. Preliminary results indicate that volatilization at 2100°C under atmospheric pressure caused little or no change in the percentage Na 2 O and K 2 O. The ratio Fe 3 Fe 2 "> Fe 3 Fe 2 of the tektite is increased in ambient air at a pressure of 9 × 10 −4 mm Hg (= 10 6.5 atm O 2 , partial pressure) at 2000°C. This suggests that tektites were formed either at lower oxygen pressures or that they are a product of incomplete oxidation of parent material with a still lower ferricferrous ratio.

Geochimica et Cosmochimica Acta↗
USGS1964

Submicroscopic spherules and color of tektites

Magnetic susceptibility measurements of 18 tektites from various strewn fields have been made as a function of temperature from 77°K to room temperature. A relatively large temperature-independent component of the magnetic susceptibility was observed in all cases, and an analysis of the data shows that this component is the result of submicroscopic iron spherules in the tektites. An analysis of the color of tektites in terms of the magnetic measurements and also of the optical absorption spectra suggests that the basic color of all tektites is green or greenish-blue, and that the brown to black coloration in some tektites is due to finely dispersed Fe 2 O 3 and/or many metallic spherules, both probably of colloidal size.

Geochimica et Cosmochimica Acta↗
USGS1964

The electrum-tarnish method for the determination of the fugacity of sulfur in laboratory sulfide systems

A new method for the determination of the fugacity of sulfur in laboratory systems consists of visual observation of the development and decomposition of a sulfide tarnish phase on silver-gold alloy (electrum) of precisely known composition. The alloy system is calibrated against pure sulfur. The method has the following advantages: simple apparatus; ability to cover a large range of fugacity of S 2 ; ability to cover a large temperature range by permitting runs of long duration; ability to tolerate other components in the gas phase; and ease of recovery of the quenched charges for determinations of phases and compositions. Results obtained by the electrum-tarnish method are in satisfactory agreement with those obtained by other workers for the f s2 vs. T curves for the assemblage Ni (1– x ) S + NiS 2 . The electrum-tarnish method shows promise for investigating many other reactions. Univariant reactions studied by this method can be represented as lines forming a genetic grid in terms of the environmental parameters f s2 and T , The slopes of such lines can yield valuable thermodynamic data for the phases involved, but activity coefficients must be known for phases of variable composition.

Geochimica et Cosmochimica Acta↗
USGS1964

A thermodynamic study of pyrite and pyrrhotite

Through the use of the electrum-tarnish method the following equation has been found to interrelate the composition of pyrrhotite, fugacity of sulfur, and temperature: In this equation f s2 is the fugacity of sulfur relative to the ideal diatomic gas at 1 atm, N is the mol fraction of FeS in pyrrhotite (in the system FeS-S 2 ), and T the absolute temperature. The experimental uncertainty in the equation is 0–003 in N . The activity of FeS ( a FeS ) in pyrrhotite relative to the pure substance at the temperature of consideration follows from the above equation by virtue of the Gibbs-Duhem relation; it is given by: The electrum-tarnish method has permitted us to determine the f s2 vs. T curve for the univariant assemblage pyrrhotite-pyrite-vapor from 743 to 325°C. Our determinations of the composition of pyrrhotite are in excellent agreement with the results of Arnold. The activity of FeS in pyrite-saturated pyrrhotite is very different from unity, a fact that greatly influences the interpretation of some other phase equilibrium studies involving pyrrhotite and their application to sulfide mineral assemblages, but has little effect on the more general calculations of composition of hydrothermal or magmatic fluids. Pressure effects calculated from available volumetric data on the phases are small.

Geochimica et Cosmochimica Acta↗
USGS1965

Some aspects of the geochemistry of yttrium and the lanthanides

Recent data on the relative abundances of the lanthanides and yttrium in meteorites, basaltic rocks, granitic rocks and sedimentary rocks are reviewed. It is shown that the data are inadequate to substantiate or to disprove Taylor's derivation from these data of a 1:1 abundance ratio of basaltic to granitic rocks in the continental crust. Graphs are given to illustrate the variation of lanthanides in minerals with paragenesis. Both the paragenesis and the crystal chemistry of minerals affect the composition of the lanthanides.

Geochimica et Cosmochimica Acta↗
USGS1965

Alkali content of alpine ultramafic rocks

The lower limit of abundance of sodium and potassium in ultramafic rocks is less than the threshold amount detectable by conventional analytical methods. By a dilutionaddition modification of the flame-spectrophotometric method, sodium and potassium have been determined in 40 specimens of alpine ultramafic rocks. Samples represent six regions in the United States and one in Australia, and include dunite, peridotite, pyroxenite, and their variably serpentinized and metamorphosed derivatives. The median value found for Na 2 O is 0.004 per cent, and the range of Na 2 O is 0.001–0.19. The median value for K 2 O is 0.0034 per cent and the range is 0.001–0.031 per cent. Alkali concentrations are below 0.01 per cent Na 2 O in 28 samples and below 0.01 per cent K 2 O in 35. Derivation of basalt magma from upper-mantle material similar to such ultramafic rocks, as has been postulated, is precluded by the relative amounts of sodium and potassium, which are from 200 to 600 times more abundant in basalt than in the ultramafic rocks. Similar factors apply to a number of other elements. No reasonable process could produce such concentrations in, for example, tens of thousands of cubic miles of uniform tholeiitic basalt. The ultramafic rocks might have originated either as magmatic crystal precipitates or as mantle residues left after fusion and removal of basaltic magma. Injection of ultramafic rocks to exposed positions is tectonic rather than magmatic.

Geochimica et Cosmochimica Acta↗
USGS1965

Age and metamorphism of some massive sulfide deposits in Virginia, North Carolina and Tennessee

Isotopic ages of vein and wall-rock samples have been determined on five massive sulflde deposits of the southern Appalachians. Vein mineral ages of about 1100 m.y. indicate that some ore bodies formed at least as early as the Grenville metamorphism, and probably soon after the formation of the enclosing gneiss and schist. Present textures of the ore were formed during subsequent metamorphic periods at about 450 m.y. and 300 to 330 m.y. ago.

North Carolina, Tennessee, Virginia↗
USGS1965

Glass electrode determination of sodium in closed basin waters

Because of its direct relation to total dissolved solids content, sodium concentration is the most useful single hydrochemical parameter of closed basin waters in the western United States. Therefore, it is advantageous to have a rapid method for sodium determination which could be readily adapted to field use. Accordingly, thirty waters of highly variable concentration and anionic composition from the western Great Basin have been analyzed with a sodium-sensitive glass electrode. Na + values ranged from 10 to 130,000 ppm in waters containing from 102 to 401,000 ppm total dissolved solids. The electrode values were compared with conventional sodium determinations; results differed by as much as 11 per cent, although over two-thirds were within 5 per cent. No significant relation was found between the glass electrode and conventional method differences and the total dissolved solids or sodium concentration. The comparative accuracy of electrode and conventional procedures was checked, employing solutions of known sodium concentration. It was concluded that for the analysis of sodium in natural waters the glass electrode method offers results comparable in accuracy to those obtained by conventional methods, but with increased simplicity, and therefore the possibility of rapid, accurate field measurements.

Geochimica et Cosmochimica Acta↗
USGS1965

Geochemistry of Birch Creek, Inyo County, California a travertine depositing creek in an arid climate

A small stream in eastern California was studied in detail to determine the causes of travertine deposition from the stream. Although the ground water feeding the stream is slightly supersaturated to just saturated with calcite, the ground water is supersaturated with CO 2 with respect to the overlying air. The water becomes increasingly supersaturated with calcite in a downstream direction as CO 2 loss to the air and by photosynthesis exceeds the rate of precipitation of calcite. Water loss by evaporation was below detection and does not play an important role in calcite deposition in this case. The water loss is by seepage through the stream bed. Observations showed variations in HCO − 3 , pH, discharge, Ca +2 , relative humidity, water and air temperatures, and dissolved CO 2 . Comparisons of observed and equilibrium states are given for five sampling stations along the stream.

California↗
USGS1966

Hot brines and recent iron deposits in deeps of the Red Sea

Sedimentary iron and heavy-metal deposits of undetermined size have been found in the middle of the Red Sea some 2000 meters below the surface of the sea (Fig. 1). This discovery has been made from the Research Vessel Atlantis II , which is still at sea engaged in a series of oceanographic investigations which ultimately will end in November 1965, after the ship has circumnavigated the globe. The discovery is significant because the environment and the processes controlling deposition of heavy metals are observable and appear to be still active.

Geochimica et Cosmochimica Acta↗
USGS1966

Some alkali and titania analyses of tektites before and after G-1 precision monitoring

A comparison of 55 older analyses of Australasian tektites with 110 modern precisely monitored analyses suggests that more than half of the older alkali and titania determinations are decidedly inaccurate and misleading. Deviations of the older analyses from the restricted values of the modern analyses are comparable to the imprecisions shown by early analyses of G-1 granite and W-1 diabase. This suggests that a high percentage of older alkali and titania analyses, such as those of Washington's tables, are of questionable quality.

Geochimica et Cosmochimica Acta↗
USGS1966

Chemical composition of phosphorites of the Phosphoria Formation

The chemical composition, both major and minor constituents, of 60 samples of phosphorite from the Phosphoria Formation was determined. Major constituents of the average phosphorite are, by weight per cent: SiO 2 , 11·9; Al 2 O 3 , 1·7; Fe 2 O 3 ,1·1; MgO, 0·3; CaO, 44·0; Na 2 O, 0·6; K 2 O, 0·5; total H 2 O, 2·2; H 2 O − , 0·6; TiO 2 , 0·1; P 2 O 5 , 30·5; CO 2 , 2·2; SO 3 , 1·8; F, 3·1; organic matter, 2·1; and oil, 0·2. Uranium averages 0·009 per cent. The phosphate mineral is basically apatite, Ca 5 (PO 4 ) 3 F, with small but significant and variable substitutions—Na, Sr, U and Th for Ca, and CO 3 and SO 4 for PO 4 . Rare metals not associated with apatite are associated principally with the organic-matter component of the rocks. This group includes As, Ag, Cd, Cr, Cu, Mo, Ni, Sb, Se, V and Zn. Chromium is the most abundant, having a modal abundance of 0·1 per cent and a maximum concentration of 0·3 per cent. The average phosphorite is composed of approximately 80 per cent apatite, 10 per cent quartz, 5 per cent muscovite-illite, 2 per cent organic matter, 1 per cent dolomite—calcite, 1 per cent iron oxide, and 1 per cent other components. It is texturally a medium-grained pellet phosphorite.

Geochimica et Cosmochimica Acta↗
USGS1967

U.S. Geological Survey silicate rock standards

The U.S. Geological Survey has processed six silicate rocks to provide new reference samples to supplement G-1 and W-1. Complete conventional, rapid rock, and spectrochemical analyses by the U.S. Geological Survey are reported for a granite (replacement for G-1), a granodiorite, an andesite, a peridotite, a dunite, and a basalt. Analyses of variance for nickel, chromium, copper, and zirconium in each rock sample showed that for these elements, the rocks can be considered homogeneous. Spectrochemical estimates are given for the nickel, chromium, copper, and zirconium contents of the samples. The petrography of five of the six rocks is described and CIPW norms are presented.

Geochimica et Cosmochimica Acta↗