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At least 73 records · Page 4Linked to original sources
USGS1961

Niobium content of soils from West Africa

Analysis of twenty lateritic soil samples from West Africa has shown them to contain an average 24 p.p.m. of niobium; four similar samples taken from within a few miles from a niobium deposit contain from 79 to 87 p.p.m. niobium. It has been shown that as the aluminum content of the soils increases, the following depletion sequence is obtained: Si > Nb > Al = Fe The data indicate that, in general, high enrichments of niobium are not to be expected in lateritic soils.

Geochimica et Cosmochimica Acta↗
USGS1961

Aqua de Ney, California, a spring of unique chemical character

The chemistry of water of Aqua de Ney, a cold spring of unusual character located in Siskiyou County, Calif., has been re-examined as part of a study of the relation of water chemistry to rock environment. The water has a pH of 11·6 and a silica content of 4000 parts per million (p.p.m.), the highest values known to occur in natural ground waters. The rocks exposed nearby consist of two volcanic sequences, one predominantly basaltic in composition, the other highly siliceous. Neither these rocks nor the sedimentary and igneous rocks presumed to underlie the area at depth seem to offer explanation of the unusual mineralization which includes 240 p.p.m. of boron, 1000 p.p.m. of sulphide (as H 2 S), and 148 p.p.m. of ammonia nitrogen (as NH 4 ) in a water that is predominantly sodium chloride and sodium carbonate in character. By analogy, it is assumed that water from Aqua de Ney is the product of an initial mixture of connate sea water with a calcium magnesium sulphate water. It is postulated that ion exchange has increased the content of sodium and reduced that of calcium and magnesium, and that sulphate reduction has brought about the high alkalinity, high pH, and high content of sulphide. The large silica value is explained as the result of solution of silica by water having the high pH observed.

California↗
USGS1961

Graphic and algebraic solutions of the discordant lead-uranium age problem

Uranium-bearing minerals that give lead-uranium and lead—lead ages that are essentially in agreement, i.e. concordant, generally are considered to have had a relatively simple geologic history and to have been unaltered since their deposition. The concordant ages obtained on such materials are, therefore, assumed to approach closely the actual age of the minerals. Many uranium-bearing samples, particularly uranium ores, give the following discordant age sequences; Pb 206 U 238 &lt; Pb 207 U 235 &#x2AA1; Pb 207 Pb 206 "> Pb 206 U 238 <Pb 207 U 235 ⪡Pb 207 Pb 206 or, less frequently, Pb 207 Pb 206 &#x2AA1; Pb 207 U 235 &lt; Pb 206 U 238 "> Pb 207 Pb 206 ⪡Pb 207 U 235 <Pb 206 U 238 . These discordant age sequences have been attributed most often to uncertainties in the common lead correction, selective loss of radio-active daughter products, loss or gain of lead or uranium, or contamination by an older generation of radiogenic lead. The evaluation of discordant lead isotope age data may be separated into two operations. The first operation, with which this paper is concerned, is mechanical in nature and involves the calculation of the different possible concordant ages corresponding to the various processes assumed to have produced the discordant ages. The second operation is more difficult to define and requires, in part, some personal judgement. It includes a synthesis of the possible concordant age solutions with other independent geologic and isotopic evidence. The concordant age ultimately chosen as most acceptable should be consistent not only with the known events in the geologic history of the area, the age relations of the enclosing rocks, and the mineralogic and paragenetic evidence, but also with other independent age measurements and the isotopic data obtained on the lead in related or associated non-radioactive minerals. The calculation of the possible concordant ages from discordant age data has been greatly simplified by Wetherill's graphical method of plotting the mole ratios of radiogenic Pb 206 U 238 "> Pb 206 U 238 ( N 206 N 238 "> N 206 N 238 ) vs. radiogenic Pb 207 U 235 "> Pb 207 U 235 ( N 207 N 235 "> N 207 N 235 ) after correcting for the contaminating common Pb 206 and Pb 207 . The linear relationships noted in this graphical procedure have been extended to plots of the mole ratios of total Pb 206 U 238 "> Pb 206 U 238 ( t N 206 N 238 "> t N 206 N 238 ) vs. total Pb 207 U 235 "> Pb 207 U 235 ( t N 207 N 235 "> t N 207 N 235 ). This modification permits the calculation of concordant ages for unaltered samples using only the Pb 207 Pb 206 "> Pb 207 Pb 206 ratio of the contaminating common lead. If isotopic data are available for two samples of the same age, x and y , from the same or related deposits or outcrops, graphs of the normalized difference ratios [ ( N 206 N 204 )x &#x2212; ( N 206 N 204 )y ( N 238 N 204 )x &#x2212;( N 238 N 204 )y ] vs. [ ( N 207 N 204 )x &#x2212; ( N 207 N 204 )y ( N 235 N 204 )x &#x2212;( N 235 N 204 )y ] "> [(N 206 N 204 )x − (N 206 N 204 )y(N 238 N 204 )x −(N 238 N 204 )y] vs. [(N 207 N 204 )x − (N 207 N 204 )y(N 235 N 204 )x −(N 235 N 204 )y] can give concordant ages corrected for unknown amounts of a common lead with an unknown Pb 207 / Pb 206 ratio. (If thorium is absent the difference ratios may be normalized with the more abundant index isotope, Pb 208 .) Similar plots of tho normalized, difference ratios for three genetically related samples ( x − y ) and( x − z ), will give concordant ages corrected, in addition, for either one unknown period of past alteration or initial contamination by an older generation of radiogenic lead of unknown Pb 207 /Pb 206 ratio. Practical numerical solutions for many of tho concordant age calculations are not currently available. However, the algebraic equivalents of these new graphical methods give equations which may be programmed for computing machines. For geologically probable parameters the equations of higher order have two positive real roots that rapidly converge on the exact concordant ages corrected for original radiogenic lead and for loss or gain of lead or uranium. Modifications of these general age equations expanded only to the second degree have been derived for use with desk calculators. These graphical and algebraic methods clearly suggest both the type and minimum number of samples necessary for adequate mathematical analysis of discordant lead isotope age data. This mathematical treatment also makes it clear that discordant lead isotope data alone cannot provide the basis for the choice of one of the possible concordant age solutions. The new equations, in particular, provide an incentive to improve our physical constants, analytical techniques and sampling methods in order that we may derive all of the useful geologic information that is available in a comprehensive lead isotope age study.

Geochimica et Cosmochimica Acta↗
USGS1962

K/Na ratio of Cenozoic igneous rocks of the western United States

The potassium and sodium content of chemically analysed Cenozoic igneous rocks from about 150 areas of the western United States has been examined. For each area a plot of the molecular proportion K 2 O (K 2 O + Na 2 O) "> K 2 O(K 2 O + Na 2 O) [Niggli's k -value] is shown, and the projected k -value determined at 50 and 60 weight per cent SiO 2 . The k -values are plotted and contoured on maps of the western United States. These maps show that potassium is least abundant relative to total alkali (when rocks of the same SiO 2 content are compared) in a zone along the Pacific Coast, becomes more abundant eastward, and is highest in the Colorado Plateau and Northern Rocky Mountains. These k -value variations can be related to regional variations in the abundance of certain trace elements and of different types of older granitic rocks, and to Bouguer gravity maps. This correspondence indicates that the alkali ratio of Cenozoic igneous rocks is closely related to the character of the crust where the rocks are formed.

Arizona, California, Colorado, Idaho, Montana, Nev↗
USGS1962

The solubility of quartz in water in the temperature interval from 25° to 300° C

The solubility of quartz in water was investigated by three sets of experiments at 1000 atm P H 2 O and temperatures ranging from 45&deg; to 300&deg;C at water pressures appropriate for the coexistence of three phases, gaseous water, liquid, and quartz, at temperatures ranging from 69&deg; to 240&deg;C a long term study of the dissolution of quartz grains which were continuously tumbled in water at room temperature. Saturated silica solutions in equilibrium with quartz were obtained in a few days at temperatures above 100&deg;C. Equilibrium is shown by reproducible results for runs of different durations and by the precipitation of quartz from initially supersaturated solutions. The differential heat of solution derived from the data obtained at 1000 atm pressure is 5.38 kcal/mole. At room temperature and pressure, highly supersaturated silica solutions were obtained by continuously rotating quartz grains and water in plastic bottles at 75 rev/min. In one run the amount of silica in solution increased to a maximum value of 395 p.p.m. after 370 days. Another run reached 80 p.p.m. silica after 386 days and then dropped to 6 p.p.m. silica. It is concluded that quartz was precipitated at room temperature from this supersaturated solution and that 6 p.p.m. is essentially the true solubility of quartz at 25&deg;C. In contrast to the runs rotated at 75 rev/min, quartz grains, and also silica glass grains, continuously rotated in water at rev/min, each contributed less than 1 p.p.m. colorimetric silica into solution after 1 year. Thus, vigorous agitation of the liquid is necessary to remove dissolved silica from the vicinity of surfaces of both quartz and glass. Two significant factors that may have contributed to the formation of supersaturated silica solutions in the runs rotated at 75 rev/min at room temperature are stresses and structural irregularities at the surfaces of the crushed quartz grains, which contributed silica into solution more readily than well crystallized quartz the very slow rate at which dissolved silica polymerizes to species appropriate to act as nuclei for quartz growth. At the termination of the runs rotated at 75 rev/min, spikelike projections were present on many of the quartz grains. These are interpreted as indicating that abrasion was not the dominant cause for the great supersaturations which were obtained.

Geochimica et Cosmochimica Acta↗
USGS1962

Problem of the thermodynamic status of the mixed-layer minerals

Minerals that show mixed layering, particularly with the component layers in random sequence, pose problems because they may behave thermodynamically as single phases or as polyphase aggregates. Two operational criteria are proposed for their distinction. The first scheme requires two samples of mixed-layer material which differ only in the proportions of the layers. If each of these two samples are allowed to equilibrate with the same suitably chosen monitoring solution, then the intensive parameters of the solution will be invariant if the mixed-layer sample is a polyphase aggregate, but not otherwise. The second scheme makes use of the fact that portions of many titration curves of clay minerals show constancy of the chemical activities of the components in the equilibrating solutions, suggesting phase separation. If such phase separation occurs for a mixed-layer material, then, knowing the number of independent components in the system, it should be possible to decide on the number of phases the mixed-layer material represents. Knowledge of the phase status of mixed-layer material is essential to the study of the equilibrium relations of mineral assemblages involving such material, because a given mixed-layer mineral will be plotted and treated differently on a phase diagram, depending on whether it is a single phase or a polyphase aggregate. Extension of the titration technique to minerals other than the mixed-layer type is possible. In particular, this method may be used to determine if cryptoperthites and peristerites are polyphase aggregates. In general, for any high-order phase separation, the method may be used to decide just at what point in this continuous process the system must be regarded operationally as a polyphase aggregate.

Geochimica et Cosmochimica Acta↗
USGS1962

The effect of CO2 at low temperature and pressure on solutions supersaturated with silica in the presence of limestone and dolomite

The effect of 1 atm of CO 2 over initially neutral solutions supersaturated with silica, at room temperature, as contrasted with 1 atm of air was determined over a period of 5 months, together with changes brought about by the introduction of calcite and dolomite to these solutions in the form of either chips or finely ground powder. In the absence of CO 2 all solutions quickly reached equilibrium and no silica precipitated. In the presence of CO 2 approximately two-thirds of the silica precipitated as silica gel within the first 2 months; the amount of silica precipitated was not affected by the presence of limestone or dolomite. Silica gel precipitated as a fine powder in the presence of finely ground calcite and dolomite, but as a cloudy gelatinous mass in the presence of coarse chips of dolomite and calcite, and in the absence of either calcite or dolomite. Preferential leaching of calcium from dolomite took place, both in the presence of air and in the presence of CO 2 , but was more pronounced in the presence of air. There was no evidence of physical replacement of either limestone or dolomite by precipitated silica.

Geochimica et Cosmochimica Acta↗
USGS1962

Summary of new data on rock samples G-1 and W-1

Published and unpublished analyses for major and minor constituents that have become available since April, 1960, are collected for the granite G-1 and diabase W-1. “Best values” are suggested for some of the elements.

Geochimica et Cosmochimica Acta↗
USGS1962

Behaviour of calcium carbonate in sea water

Anomalies in the behaviour of calcium carbonate in natural solutions diminish when considered in context. Best values found by traditional oceanographie methods for the apparent solubility product constant K ' CaCO 3 in sea water at atmospheric pressure are consistent mineralogically—at 36 parts per thousand salinity and T-25°C, K ' aragonlte is estimated as 1.12 × 10 −6 and K ' calcite as 0.61 × 10 −6 . At 30°C the corresponding values are 0.98 × 10 −6 for aragonite and 0.53 × 10 −6 for calcite. Because the K ' computations do not compensate for ionic activity, however, they cannot give thermodynamically satisfactory results. It is of interest, therefore, that approximate methods and information now available permit the estimation from the same basic data of an activity product constant K CaCO 3 close to that found in solutions to which Debye-Hückel theory applies. Such methods indicate approximate K aragonite 7.8 × 10 −9 for surface sea water at 29°C; K calcite would be proportionately lower. Field data and experimental results indicate that the mineralogy of precipitated CaCO 3 depends primarily on degree of supersaturation, thus also on kinetic or biologic factors that facilitate or inhibit a high degree of supersaturation. The shallow, generally hypersaline bank waters west of Andros Island yield aragonitic sediments with O 18 O 16 "> O18O16 ratios that imply precipitation mainly during the warmer months, when the combination of a high rate of evaporation, increasing salinity (and ionic strength), maximal temperatures and photosynthetic removal of CO 2 result in high apparent supersaturation. The usual precipitate from solutions of low ionic strength is calcite, except where the aragonite level of supersaturation is reached as a result of diffusion phenomena ( e.g. dripstones), gradual and marked evaporation, or biologic intervention. Published data also suggest the possibility of distinct chemical milieus for crystallographic variations in skeletal calcium carbonate. It appears that in nature aragonite precipitates from solutions that are supersaturated with respect to both calcite and aragonite and calcite between saturation levels for the two species. Such a relation is consistent with Ostwald's rule of successive reactions. Aragonitc of marine origin persists in contact with supersaturated interstitial solutions at ordinary temperature and pressure. Conversion to calcite follows transfer to solutions undersaturated with respect to aragonite or upon exposure to the moist atmosphere.

Geochimica et Cosmochimica Acta↗
USGS1963

Deuterium in Iceland waters

From the deuterium analysis of 159 samples of water collected in Iceland from hot-water boreholes, cold and hot springs, rivers and rain, the geographical distribution of deuterium in surface waters is plotted. On the basis of the deuterium analysis, the water from boreholes near Reykjavik does not originate from local precipitation. The variation of deuterium content of these water wells with time suggests that these data can be used to determine the time of travel of recharge water to the various boreholes, as well as the surface recharge area.

Geochimica et Cosmochimica Acta↗
USGS1963

The abundance of scandium in volcanic rocks, a preliminary estimate

Using Rittman's classification to determine the clan, we suggest the following abundance figures: basalts (99), 38 p.p.m. Sc; andesites (72), 34 p.p.m. Sc; dacites (68), 21 p.p.m. Sc; rhyodacites (32), 14 p.p.m. Sc; quartz latites (14), 11 p.p.m; rhyolites (24), 5 p.p.m. The scandium was determined spectrographically on samples for which there were complete rock analyses. In addition we suggest that extrusive equivalents of peridotites should contain about 9 p.p.m. Sc; extrusive equivalents of perknites should contain about 30 p.p.m. Sc. We see no reason why these figures should not apply to the intrusive equivalents. We tentatively suggest a figure of 30 p.p.m. for Sc for the crust, using Poldervaart's suggested ratio of rock types.

Geochimica et Cosmochimica Acta↗
USGS1963

New chemical determinations of zinc in basalts, and rocks of similar composition

New determinations of zinc in 124 basalts by the chemical method described ( Huff-Man et al. 1963) are reported. Average zinc values, in per cent, for basalts from diverse regions are as follows: Idaho, 28 samples, 0.013; Hawaii, 33 samples, 0.010; Connecticut, 27 samples, 0.0090; Oregon, 17 samples, 0.0081; California, 8 samples, 0.0071; and New Mexico, 11 samples, 0.0086; average, all samples, 0.0099 per cent zinc. A plot of differentiation indicator ratios calculated from the conventional rock analyses, CaO/(Na 2 O + K 2 O) as the ordinate and SiO 2 /MgO as the abscissa, was used to select, from different localities, samples essentially the same in chemical composition that were to be used for comparisons of zinc and other minor elements. Zinc correlates with MnO and with total iron as FeO. An inverse relationship found for zinc and manganese is related to the total iron content of the basalts. Thus for a given iron concentration as zinc increases, manganese decreases and vice versa. Ratios of zinc, the common denominator, to 11 other minor elements determined spectro-graphically show correlations with cobalt, gallium, scandium, yttrium, and zirconium.

Geochimica et Cosmochimica Acta↗
USGS1963

Spectrophotometric determination of micro quantities of zinc in rocks

A chemical method is presented for the determination of microgram amounts of zinc in rocks. Zinc is absorbed on anion-exchange resin from 1.2 M hydrochloric acid and eluted with 0.01 M hydrochloric acid. A diethyldithiocarbamate separation removes traces of interfering elements from the eluate. The zinc-diethyldithiocarbamate complex is extracted into chloroform at pH 8.5 and reextracted from other elements in the chloroform solution with 0.16 M hydrochloric acid and finally determined spectrophotometrically as the zincon complex at 621 mμ. The coefficient of variation of the method determined from replicate determinations of zinc on 75 selected samples of basalt, ranging in zinc content from 0.004 to 0.018 per cent, was found to be 6.3 per cent and essentially constant in the range of zinc content studied. This method of analysis has been used extensively for a study of zinc in basalts reported by Rader, Swadley, Huffman and Lipp (companion paper, 1963).

Geochimica et Cosmochimica Acta↗
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 &#x3BC;g l "> 100 μgl . (parts per billion). Most minor elements range at or below 100 &#x3BC;g 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↗