Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Geochimica et Cosmochimica Acta”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
USGS1968

Activity product constant of cryolite at 25°C and one atmosphere using selective-ion electrodes to estimate sodium and fluoride activities

The activity product constant of cryolite (Na 3 AlF 6 ) at 25°C and 1 atm total pressure was calculated from data for solutions from which synthetic cryolite or mixtures of cryolite and a solid apparently related to ralstonite had precipitated. The activities of fluoride and of sodium were estimated using specific ion electrodes. The activity of Al 3+ was calculated from aluminum concentrations using equations which involve aluminum species existing in water solutions containing fluoride and hydroxide ions. For the reaction Na 3 AlF 6 ( c ) = 3 Na ( aq ) + + Al 3+ ( aq ) + 6 E - ( aq ) the activity product constant K so is 10 −33.84 , and the standard free energy of formation at 25°C is -745.4±1.0 kcal mole −1 . This latter is identical to a value from the literature which is based on calorimetric data. Although cryolite and related minerals are easily precipitated in the laboratory, their relative scarcity in nature suggests that the effect of influences, perhaps solutes other than those occurring in the structure, may inhibit or prevent the formation of cryolite.

Geochimica et Cosmochimica Acta↗
USGS1968

Studies in the system MgO-SiO2-CO2-H2O(I): The activity-product constant of chrysotile

Chrysotile dissolves congruently in water according to the reaction: Mg 3 Si 2 O 6 ( OH ) 4 c + 5 H 2 O l = 3 Mg aq 2+ + 6 OH aq − + 2 H 4 SiO 4 aq . Experimental determination of the activity-product constant of chrysotile, K chr = [ Mg 2+ ] 3 [ OH − ] 6 [ H 4 SiO 4 aq ] 2 , at 90°C, yields the value of K chr = 10 −49.2 ± 10 0.5 . A synthetic sample and a natural sample from New Idria, California, were used in the determination. Values of K chr were calculated for temperatures ranging from 0°C to 200°C, using the thermochemical data of King et al . (1967) for chrysotile and antigorite, various solubility data for silica, and ionic partial molal heat capacities estimated by the method of criss and Cobble (1964a). K chr is 10 −54.1 at 0°C, rises to a maximum value of 10 −48.5 at approximately 135°C, and is 10 −49.1 at 200°C (all values for the three-phase system, chrysotile plus solution plus vapor). The calculated 90°C value is 10 −49.1 , in excellent agreement with the experimental value; for 25°C, the calculated value is 10 −50.8 .

Geochimica et Cosmochimica Acta↗
USGS1968

Variation of Nb-Ta, Zr-Hf, Th-U and K-Cs in two diabase-granophyre suites

Concentrations of Nb, Ta, Zr, Hf, Th, U and Cs have been determined in samples of igneous rocks representing the diabase-granophyre suites from Dillsburg, Pennsylvania, and Great Lake, Tasmania. Niobium and tantalum have a three to fourfold increase with differentiation in each of the suites. The chilled margin of the Great Lake intrusion contains half the niobium and tantalum content (5.3 ppm and 0.4 ppm, respectively) of the chilled basalt from Dillsburg (10 ppm and 0.9 ppm, respectively). The twofold difference between the suites is correlated with differences in their titanium content. The average Nb Ta "> NbTa ratios for each suite are similar: 13.5 for the Great Lake suite, and 14.4 for the Dillsburg suite. The zirconium content of the two suites is essentially the same and increases from 50 to 60 ppm in the chilled margins to 240–300 ppm in the granophyres. Hafnium is low in the early formed rocks (0.5 –1.5 ppm and achieves a maximum in the granophyres (5–8 ppm). The Zr Hf "> ZrHf ratio decreases from 68 to 33 with progressive differentiation. In the Dillsburg suite thorium and uranium increase from 2.6 ppm and 0.6 ppm, respectively, in the chilled samples to 11.8 ppm and 3.1 ppm in the granophyres. The chilled margin of the Great Lake suite contains 3.2 ppm thorium and 9.8 ppm uranium; the granophyre contains 11.2 ppm thorium and 2.8 ppm uranium. The average Th U "> ThU ratios of the Dillsburg and Great Lake suites are nearly the same—4.1 and 4.4, respectively. Within each suite the Th U "> ThU ratio remains quite constant. Cesium and the K Cs "> KCs ratio do not vary systematically in the Dillsburg suite possibly because of redistribution or loss of cesium by complex geologic processes. Except for the chilled margin of the Great Lake suite, the variation of Cs and the K Cs "> KCs ratio are in accord with theoretical considerations. Cesium increases from about 0.6 ppm in the lower zone to 3.5 ppm in the granophyre; the K Cs "> KCs ratio varies from 10 × 10 3 in the lower zone to 6 × 10 3 in the granophyre. A comparison of the abundance of some of these elements is made with those reported on oceanic tholeiites from the Atlantic and Pacific oceans. Trace elements with large ionic radii (Th, U, Cs) are present in significantly greater concentrations in the two continental tholeiitic series than in the oceanic tholeiites. However, this does not seem to be true for lithophilic elements of smaller ionic radii (Zr and Nb). These trace element distribution patterns, when considered with other minor element and isotopic studies, indicate that 1. crustal contamination does not entirely account for differences between continental and oceanic tholeiites, and 2. the oceanic tholeiites do not necessarily delimit the geochemical characteristics of the mantle.

Geochimica et Cosmochimica Acta↗
USGS1968

Dissociation constants of KSO 4 - from 10°-50°C

A cell without liquid junction was used to obtain dissociation constants for the reaction: KSO 4 − = K + + SO 4 2− . At 10°, 25°, 38° and 50°C, values for K diss KSO 4 − are, respectively, 0.19 5 , 0.14 2 , 0.11 7 , and 0.09 5 . At 25°C, , and values for the KSO 4 − ion are −245.96 and −274.02 kcal mole −1 , and S ° is +42.3 cal mole −1 deg −1 .

Geochimica et Cosmochimica Acta↗
USGS1968

Isotope studies of dolomite formation under sedimentary conditions

Measurements of stable isotope abundances of the carbonate portion of the sediment in Deep Springs Lake, California, indicate the presence of at least three phases: a magnesian calcite, a primary sedimentary dolomite, and a detrital dolomite. The former two have isotopic compositions consistent with precipitation at isotopic equilibrium from waters of the lake area. The measured isotopic fractionation factor between sedimentary dolomite and its interstitial water is 1.0351, which is outside the range possible for calcite-water. This indicates that the dolomite has formed by direct crystallization from solution and not from a caloite precursor without further isotope exchange. Isotopic and X-ray evidence does not support the contention of Peterson et al . (1966) that Deep Springs Lake dolomite crystals grow by means of a calcite-like surface layer.

Geochimica et Cosmochimica Acta↗
USGS1968

Spectrographic date on cores from the Pacific Ocean and the Gulf of Mexico

Average quantitative spectrographic data are presented for V, Ti, Zr, Ni, Co, Sc, Cr and La in the following Pacific deep-sea cores: siliceous ooze (3), red clay (6), volcanic mud (3), calcareous ooze (3) and one manganese nodule, and in 23 near-shore cores, mostly from the Gulf of Mexico.

Geochimica et Cosmochimica Acta↗
USGS1969

Thermochemical study of the system Fe-As-S

The results of Toulmin and Barton (1964) for the Fe-S system have been combined with a series of new measurements on As-bearing assemblages in the 500°–850°C temperature range to derive data on the free energies, enthalpies, and entropies of formation for arsenopyrite, loellingite, orpiment, realgar, FeAs, and Fe 2 As. The enthalpies and free energies of formation of orpiment and realgar are only approximately one-half as large as indicated in recent compilations of thermochemical data ( Wagman et al ., 1965). Data are also presented for the covariation of activity of S 2 (g) with temperature and composition of the sulfur-arsenic liquid.

Geochimica et Cosmochimica Acta↗
USGS1969

U.S. Geological Survey standards-II. First compilation of data for the new U.S.G.S. rocks

Rock analyses, determinations of major and minor constituents, and determinations of 57 trace elements reported by analysts throughout the world are presented for the new series of U.S. Geological Survey rock samples. Averages for both the constituents generally reported in a rock analysis and the trace elements are given. Variances of the distributions of data by rock analysts for several oxides in G-2 are compared with similar variances for G-l.

Geochimica et Cosmochimica Acta↗
USGS1969

The isotopic composition of lead in potassium feldspars from some 1.0-b.y. old North American igneous rocks

The isotopic composition of lead and the uranium, thorium and lead concentrations in potassium feldspars are determined for more than 30 1.0-b.y. old North American igneous rocks. Samples representing a broad spectrum in petrographic type and mode of occurrence were chosen; an effort was made to include only rocks having well-documented ages from 950 to 1140 m.y. and showing minimal evidence of subsequent metamorphism. Most samples, including those from extensive terranes of contemporaneous age, have limited lead isotope variations ( Pb 206 Pb 204 = 16.74–17.38 "> Pb206Pb204= 16.74–17.38 ; Pb 207 Pb 204 = 15.39–15.59 "> Pb207Pb204= 15.39–15.59 ; Pb 208 Pb 204 = 36.38–37.10 "> Pb208Pb204= 36.38–37.10 ), which yield model ages close to the radiometric ages. Granite, pegmatite, and rhyolite from within the Grenville province of Canada and age-equivalent rocks of New York, Virginia, Texas, and Colorado and granophyric units associated with the Duluth Gabbro Complex of Minnesota are among the materials yielding this main isotopic spectrum. Several samples were encountered which had isotopic compositions very different from the above group. Lead showing a marked deficiency in radiogenic isotopes was found in two granitic bodies associated with older Labrador Trough rocks from Quebec, in a rapakivi granite from southern Nevada, and in a small granite stock from Mellen, Wisconsin. These occurrences all involve small intrusions of granite which lie near considerably older areas of basement rock. Model ages calculated from the Pb 206 Pb 204 "> Pb206Pb204 ratio are older than the age of the intrusions and approach the age of the host basement rock. Several possible interpretations are offered to explain the isotopic behavior encountered in this study. In particular, a “vertically differentiated crust” model is proposed which will account for both the main spectrum and the anomalous lead. The significance of lead isotopic studies in understanding crustal structure in continental regions is discussed.

Geochimica et Cosmochimica Acta↗
USGS1969

The relationship of the rare-earth composition of minerals to geological environment

It has been known for a long time that the composition of the lanthanides in minerals is controlled to a large degree by crystallo-chemical factors, but is also greatly influenced by changes in geological environment. In general, igneous rocks rich in silica are favourable for the concentration of the heavy lanthanides and yttrium; those low in silica and high in carbonate are favourable for the concentration of the light lanthanides. These generalizations are illustrated by summaries of the available data on monazite, sphene, and apatite from different geological environments. Apatite of marine sedimentary origin (a large potential source of rare earths) shows marked depletion of cerium, as has been noted previously for sea water.

Geochimica et Cosmochimica Acta↗
USGS1969

Pyrolysis of humic and fulvic acids

Pyrolysis of humic and fulvic acids isolated from a North Carolina soil yields a variety of aromatic, heterocyclic and straight chain organ compounds. The pyrolysis products identified by gas chromatography and mass spectrometry indicate that humic and fulvic acids have aromatic and polysaccharide structures in their molecules.

Geochimica et Cosmochimica Acta↗
USGS1969

Geochemistry and origin of formation waters in the western Canada sedimentary basin-I. Stable isotopes of hydrogen and oxygen

Stable isotopes of hydrogen and oxygen, together with chemical analyses, were determined for 20 surface waters, 8 shallow potable formation waters, and 79 formation waters from oil fields and gas fields. The observed isotope ratios can be explained by mixing of surface water and diagenetically modified sea water, accompanied by a process which enriches the heavy oxygen isotope. Mass balances for deuterium and total dissolved solids in the western Canada sedimentary basin demonstrate that the present distribution of deuterium in formation waters of the basin can be derived through mixing of the diagenetically modified sea water with not more than 2.9 times as much fresh water at the same latitude, and that the movement of fresh water through the basin has redistributed the dissolved solids of the modified sea water into the observed salinity variations. Statistical analysis of the isotope data indicates that although exchange of deuterium between water and hydrogen sulphide takes place within the basin, the effect is minimized because of an insignificant mass of hydrogen sulphide compared to the mass of formation water. Conversely, exchange of oxygen isotopes between water and carbonate minerals causes a major oxygen-18 enrichment of formation waters, depending on the relative masses of water and carbonate. Qualitative evidence confirms the isotopic fractionation of deuterium on passage of water through micropores in shales.

Alberta↗
USGS1970

Phase relations of a simulated lunar basalt as a function of oxygen fugacity, and their bearing on the petrogenesis of the Apollo 11 basalts

A glass of Apollo 11 basalt composition crystallizing at 1 atm at low ƒ 0 2 ">ƒ ƒ02 showed the following crystallization sequence; ferropseudobrookite at 1210°C, olivine at 1200°C, ilmenite and plagioclase at 1140°C, clinopyroxene at 1113°C. Ferropseudobrookite and olivine have a reaction relation to the melt. This sequence agrees with that assumed on textural grounds for some Apollo 11 basalts. It also indicates that the Apollo 11 basalts cannot have been modified by low-pressure fractionation.

Geochimica et Cosmochimica Acta↗
USGS1970

Some investigations of the deposition of travertine from Hot Springs-I. The isotopic chemistry of a travertine-depositing spring

The isotopic compositions of the travertine and of the hot spring solutions were studied at Main Springs and New Highland Terrace in the Mammoth Hot Springs area of Yellowstone Park. The springs issue at 74°C and a pH of 6.65 and the carbon isotopic composition of the travertine depositing at the orifice is +2%.δC 13 (PDB). As the water travels out from the orifice, it cools and loses CO 2 . The travertine depositing at lower temperature is enriched in C 13 , reaching values of +4.8%. and the solution has a pH of 8.2 at 27°C. The δC 13 of the carbon species in solution is about −2.3%. at 74° and about +4.3 at 27°C. Therefore, the difference in δC 13 between the solid and solution is approximately 4%. at 74° and decreases to zero at about 20°C. These differences are shown to be due to kinetic (non-equilibrium) factors. The δO 18 contents of the travertine and water show that in most samples the carbonate oxygen is in equilibrium with the water O 18 at the temperatures of deposition. This is especially true for travertine depositing slowly and at temperatures above about 50°C. Calculations based on pH and alkalinity titrations of the hot spring waters in situ show that at the spring orifice the water is very high in free CO 2 , which is quickly lost in transit. The springs are supersaturated with respect to both aragonite and calcite during most of their travel in the open air. The carbon isotopic composition of the travertine is similar to that in the marine carbonates that are adjacent to the springs and that are the probable source of the calcium carbonate. The travertine from inactive prehistoric springs near Mammoth has similar δC 13 and O 18 to that from the active springs. Soda Butte, an inactive center 25 miles east of Mammoth, contains heavier carbon and oxygen than the springs near Mammoth.

Geochimica et Cosmochimica Acta↗
USGS1970

Effect of sample inhomogeneity in K Ar dating

Error in K-Ar ages is often due more to deficiencies in the splitting process, whereby portions of the sample are taken for potassium and for argon determination, than to imprecision in the analytical methods. The effect of the grain size of a sample and of the composition of a contaminating mineral can be evaluated, and this provides a useful guide in attempts to minimize error. Rocks and minerals should be prepared for age determination with the effects of contaminants and grain size in mind. The magnitude of such effects can be much larger than intuitive estimates might indicate.

Geochimica et Cosmochimica Acta↗
USGS1970

Fugacity of H2O from 0° to 350°C at the liquid-vapor equilibrium and at 1 atmosphere

The fugacity and fugacity coefficient of H 2 O at the liquid-vapor equilibrium, the fugacity and the Gibbs free energy of formation of H 2 O at 1 atm (1.01325 bars) total pressure have been calculated from published data on the physical and thermodynamic properties of H 2 O and are presented at ten-degree intervals from 0° to 350°C.

Geochimica et Cosmochimica Acta↗
USGS1970

Isotopic composition of strontium in sea water throughout Phanerozoic time

Isotopic analyses of strontium in primary fossil carbonate reveal significant variations in Sr 87 Sr 86 "> Sr87Sr86 of sea water during the Phanerozoic. The strontium isotopic composition may have been uniform from the Ordovician through the Mississippian, with an average Sr 87 Sr 86 "> Sr87Sr86 of 0.7078. A subsequent decrease in this value into the Mesozoic is interrupted by two provisionally documented positive pulses in Sr 87 Sr 86 "> Sr87Sr86 —one in the Early Pennsylvanian and one in the Early Triassic. The lowest observed value (0.7068) occurred in Late Jurassic time, and this was followed by a gradual increase to 0.7075 in the Late Cretaceous and a more rapid increase through the Tertiary to 0.7090 for modern sea water. These variations are thought to be the result of a complex interplay of periods of intense volcanism and epeirogenic movements of the continents on a worldwide scale.

Geochimica et Cosmochimica Acta↗
USGS1970

A new technique for pumping hydrogen gas

A system for pumping hydrogen gas without isotopic fractionation has been developed. The pump contains uranium metal, which when heated to about 80°C reacts with hydrogen to form UH 3 . The UH 3 is heated to above 500°C to decompose the hydride and regenerate the hydrogen.

Geochimica et Cosmochimica Acta↗