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At least 271 records · Page 15Linked to original sources
USGS1977

An improved ion-selective electrode method for the rapid determination of fluorine in rocks and soil

An improved method based on an ion-selective electrode technique for the analysis of fluorine in rocks and soils is presented. Analyses are made by using a sodium carbonate-potassium carbonate fusion and a citric acid dissolution of the fuseate. Prior to determining the fluorine concentration by a standard-addition procedure, sodium citrate buffer is added to the solution. The proposed method yields fluorine values in agreement with known values for standard rocks. Values of this method are also presented for six geochemical exploration rock-and-soil reference samples and compared to those from other ion-selective electrode techniques. Fifty samples can be analyzed in 1 person-day. The sensitivity of the method is 100 parts per million, and samples containing up to 45 percent fluorine have been successfully analyzed.

Journal of Research of the U.S. Geological Survey↗
USGS1977

Preparation of pyrite-coated sand grains for research on roll-type uranium deposits

Ordinary quartz sand grains can be coated with pyrite for use in laboratory experiments on the genetic geochemistry of roll-type uranium deposits. The sand is first added to a ferric chloride solution. The slow addition of sodium hydroxide to the mixture gives the sand grains an iron oxide coating. This coating is then converted to pyrite by reaction with hydrogen sulfide, thus yielding a product suitable for experimental use.

Journal of Research of the U.S. Geological Survey↗
USGS1977

Pressure corrections for fluid-inclusion homogenization temperatures based on the volumetric properties of the system NaCl-H 2 O

A series of pressure correction diagrams for 1-, 5-, 10-, 15-, 20-, and 25-percent NaCl solutions has been generated from the volumetric data for NaCl by R. W. Potter II and D. L. Brown in 1975. The diagrams cover the temperature range from 20° to 400° C at pressures up to 200 megapascals (2000 bars). These data can be used to correct fluid-inclusion homogenization temperatures for pressures greater than the liquid-vapor pressure-temperature curve.

Journal of Research of the U.S. Geological Survey↗
USGS1977

Exploration geochemical studies of some sandstone copper-uranium deposits, Bradford, Columbia, and Lycoming Counties, Pa

Semi-quantitative spectrographic analyses of mineralized and unmineralized sandstone, siltstone, and claystone from the Catskill Formation of Devonian age in Bradford, Columbia, and Lycoming Counties, Pa., suggest that copper, silver, and uranium are the principal metallic elements concentrated in the mineralized rock. Lead, mercury, and molybdenum may be concentrated slightly in mineralized rock but values are too low to be of use in exploration. The deposits are too small to make large anomalies in stream sediments except in drainage basins of less than a few acres. However, if a large deposit were exposed to weathering, it would probably be detectable by stream sediment sampling. Analyses of oxalic acid leachates of the minus 80-mesh fraction of the stream-sediment samples gave more useful values than analyses of the minus 80-mesh samples in separating drainage basins that have copper deposits from those that have no known copper deposits.

Pennsylvania↗
USGS1977

Rare earths, thorium, and other minor elements in sphene from some plutonic rocks in west-central Alaska

Sphene is an abundant accessory mineral in some abnormally radioactive plutonic rocks in west-central Alaska. Seven samples of sphene from four different areas in west-central Alaska contained from 20350 to 39180 parts per million total rare earths and 390 to 2000 ppm thorium. The lanthanide content in six of the seven sphenes is chiefly the light rare earths and is similar to that of crustal abundance; a seventh sphene from the Darby Mountains, however, contains above average amounts of the heavy rare earths. A comparison of the lanthanide distribution in sphene from several areas indicates that the structure of sphene will accommodate whatever lanthanides are available when the mineral crystallizes. The amount of thorium and rare earths in sphene is also affected by the presence of other accessory minerals. Sphene in rocks containing either allanite or zircon has a lower thorium content than in rocks that do not contain allanite or zircon. Sphene, because of its abundance, may contain the greater part of the rare earths and thorium in some of the plutonic rocks of west-central Alaska.

Alaska↗
USGS1977

Platinum, palladium, and rhodium in volcanic and plutonic rocks from the Gravina-Nutzotin belt, Alaska

The Gravina-Nutzotin belt of Middle (?) Jurassic to middle Cretaceous sedimentary and volcanic rocks in south and southeastern Alaska includes concentrically zoned ultramafic complexes known to contain platinum-group metals. Previous isotopic, petrologic, and geologic studies suggested a close relation in time and space between the volcanic rocks and the ultramafic complexes. Interpretation of 40 analyses for platinum, palladium, and rhodium in volcanic and plutonic rocks of the belt indicates a strong geochemical correlation between the two groups of rocks and is in support of their being cogenetic either from directly connected magma chambers and flows or indirectly by selective concentration processes from similar mantle material.

Alaska↗
USGS1977

Occurrence of bloedite and related minerals in marine shale of Diablo and Temblor Ranges, California

Bloedite, epsomite, and related minerals occur in small amounts throughout the arid eastern foothills of the Diablo and Temblor Ranges, as efflorescences on siliceous shale and as deposits around small springs and a brine pond. These minerals ultimately are products of weathering of underlying organic shale, and they are reminders that the chemistry of weathering of reduced organic shale is largely a reversal of the chemistry of its early diagenesis.

California↗
USGS1977

Comparison of granitic intrusions in the Pelona and Orocopia Schists, southern California

Dating of some small plutons in the San Gabriel and Chocolate Mountains, southern California, yields Miocene K-Ar ages. A single granodiorite pluton that has been segmented by branches of the San Jacinto fault intrudes the Pelona Schist and yields ages of 14.0 to 18.6 million years. Several quartz monzonite plutons in the Chocolate Mountains, 235 kilometers to the southeast and on the opposite side of the San Andreas fault, yield ages ranging from 20.0 to 23.4 m.y. At least one pluton in the Chocolate Mountains intrudes the Orocopia Schist, a probable equivalent of the Pelona Schist. Chemical, modal, textural, mineralogical, and apparent K-Ar age differences suggest that the two groups of plutons are not offset parts of a single body, but the differences do not preclude the two groups from being related in a general way.

California↗
USGS1975

Information through color imagery

The color-sensing capability of the human eye is a powerful tool. In remote sensing we should use color to display data more meaningfully, not to re-create the scene. Color disappears with distance, and features change color with viewing angle. Color infrared film lets us apply color with additional meaning even though we introduce a false color response. Although the marginal gray scale on an ERTS (Earth Resources Technology Satellite) image may indicate balance between the green, red, and infrared bands, and although each band may be printed in a primary color, tests show that we are not fully applying the three primary colors. Therefore, contrast in the green band should be raised. For true three-color remote sensing of the Earth, we must find two generally meaningful signatures in the visible spectrum, or perhaps extend our spectral range. Before turning to costly digital processing we should explore analog processing. Most ERTS users deal with relative spectral radiance; the few concerned with absolute radiance could use the computer-compatible tapes or special annotations. NASA (National Aeronautics and Space Administration), which assigns the range and contrast to the ERTS image, controls processing and could adjust the density range for maximum contrast in any ERTS scene. NASA cannot alter processing for local changes in reflective characteristics of the Earth but could adjust for Sun elevation and optimize the contrast in a given band.

Journal of Research of the U.S. Geological Survey↗
USGS1975

Estimates of temperature and precipitation for northeastern Utah

Estimates of temperature and precipitation were made for northeastern Utah from information that was collected at 67 locations. The variable-length records were converted to the common-time base of 1941-70; then general relations were developed to extend the converted point values to unsampled sites. Regression techniques were used to fill voids in the temperature-data base. Incomplete precipitation records were adjusted to the 1941-70 average on the assumption that the ratio of concurrent data is directly proportional to the ratio of the respective 1941-70 average annual values at nearby sites. Equations were then developed through a computer program to express the relationship of temperature and precipitation with altitude and location and to extend the information to unsampled sites. Two-thirds of the observed and estimated average annual temperature and precipitation values are within ±1.5°F (1.0°C) and 2.08 in (53 mm), respectively, of the calculated averages. Schematic diagrams, plotted by computer, were prepared to show variations of altitude, temperature, and precipitation; and maps, also plotted by computer, show lines of equal altitude, precipitation, and temperature.

Utah↗
USGS1975

Delineation of buried glacial drift aquifers

Locating and delineating buried glacial-drift aquifers poses one of the major problems to hydrogeologists working in glacial terrain. To show the vertical and horizontal boundaries of aquifers, most techniques require a multiple set of maps, a fence diagram, or a combination of maps and sections. Calculations of the first two moments, mean and standard deviation, of a discontinuous distribution result in values that represent the center of gravity (mean position) and spread (standard deviation) of all the sand units in a drill hole. Data for the moment method consist of depth to center point and thickness of each sand unit. A 2.600 mi 2 (6,730 km 2 ) area in northwestern Minnesota that, contained 71 test holes drilled to bedrock was used to test the usefulness of the moment method in glacial terrain. Plots of relative position of center of gravity and relative spread (calculated as percentage of total drift thickness) showed three groupings for relative center of gravity (shallow, 0-26 percent, medium, 30-55. and deep 58-72) and three for spread of sand units (narrow, 1-5 percent, medium, 8-19, and wide, 22-38). The resulting vertical-variability pattern map shows the areas of each of the nine combinations of these two factors. Because the vertical-variability map does not show quantity of sand, the map is most informative if the total thickness of sand, 01- percent sand of total drift thickness, is recorded by each hole location on the map. The center of gravity is useful for describing the vertical position of the principal sand in a drill hole because it lies within the principal sand unit in 34 of the 63 holes that contained sand, and it is within 15 percent (based on total drift, thickness) of the principal sand unit in 22 of the remaining 29 holes.

Michigan, Minnesota↗
USGS1975

Relative efficiencies of square and triangular grids in the search for elliptically shaped resource target

The relative efficiencies of equivalent-density, square and equilateral triangular (hexagonal) grids used in the search for elliptical targets are determined for ellipses having relative semi-major axes ranging from 0.50 to 1.00 of the square grid spacing and having shapes (minor axes/major axes) ranging from 0.2 to 1.0. Using the probability of one or more hits, the grid types are equally efficient for targets having semi-major axes less than or equal to one-half of the grid spacing. The triangular grid is as much as 6 percent more efficient for targets having relative sizes greater than 0.50. The square grid is less than 1 percent more efficient in a small region centered on a relative size of 0.80 and a shape of 0.45. Both grids are equally efficient for targets that are hit with certainty and tend toward equal efficiency as the ellipses become more needlelike in shape. A random search is more efficient than both grid types when the relative size is less than 0.50 and the probability of two or more hits is used to define relative efficiency. For two or more hits and targets having relative sizes larger than 0.50, the triangular grid is as much as 91 percent less efficient than the square grid; however, the probabilities are small. In a region centered on a relative size of 0.80, the triangular grid is slightly more efficient if the criterion is two or more hits. The probability of two or more hits is inversely related to the probability of one or more hits for many target sizes and shapes.

Journal of Research of the U.S. Geological Survey↗
USGS1975

Linkage effects between deposit discovery and postdiscovery exploratory drilling

For the 1950-71 period of petroleum exploration in the Powder River Basin, northeastern Wyoming and southeastern Montana, three specific topics were investigated. First, the wildcat wells drilled during the ambient phases of exploration are estimated to have discovered 2.80 times as much petroleum per well as the wildcat wells drilled during the cyclical phases of exploration, periods when exploration plays were active. Second, the hypothesis was tested and verified that during ambient phases of exploration the discovery of deposits could be anticipated by a small but statistically significant rise in the ambient drilling rate during the year prior to the year of discovery. Closer examination of the data suggests that this anticipation effect decreases through time. Third, a regression model utilizing the two independent variables of (1) the volume of petroleum contained in each deposit discovered in a cell and the directly adjacent cells and (2) the respective depths of these deposits was constructed to predict the expected yearly cyclical wildcat drilling rate in four 30 by 30 min (approximately 860 mi 2 ) sized cells. In two of these cells relatively large volumes of petroleum were discovered, whereas in the other two cells smaller volumes were discovered. The predicted and actual rates of wildcat drilling which occurred in each cell agreed rather closely.

Montana, Wyoming↗
USGS1975

An integrated-intensity method for emission spectrographic computer analysis

An integrated-intensity method has been devised to improve the computer analysis of data by emission spectrography. The area of the intensity profile of a spectral line is approximated by a rectangle whose height is related to the intensity difference between the peak and background of the line and whose width is measured at a fixed transmittance below the apex of the line. The method is illustrated by the determination of strontium in the presence of greater than 10 percent calcium. The Sr 3380.711-A line, which is unaffected by calcium and which has a linear analytical curve extending from 100-3,000 ppm, has been used to determine strontium in 18 standard reference rocks covering a wide range of geologic materials. Both the accuracy and the precision of the determinations were well within the accepted range for a semiquantitative procedure.

Journal of Research of the U.S. Geological Survey↗
USGS1975

Spectrophotometric-isotope dilution determination of arsenic in soils and rock

Arsenic in soil and rock samples may be determined in part-per-million concentrations using a radiochemical-isotope dilution method. Arsenic in the sample plus added As 76 tracer is separated as arsine and determined spectrophotometrically as a molybdenum blue complex. The As 76 activity in the absorbing solution allows corrections for chemical losses. A lower limit of 1 ppm is determinate in a 0.5-g sample.

Journal of Research of the U.S. Geological Survey↗
USGS1975

Analysis for tellurium in rocks to 5 parts per billion

In the proposed method, a 12.5-g sample is digested with nitric acid and evaporated to dryness; the excess nitric acid is removed by reaction with formic acid. Tellurium is extracted from the dried residue into hydrobromic acid and is then coprecipitated with arsenic, using hypophosphorous acid as the reducing agent. The precipitate is dissolved in a solution of hydrobromic acid and bromine, from which the tellurium is extracted into 0.6 ml of methyl isobutyl ketone. Tellurium content is estimated by atomic absorption spectrophotometry. Recovery of tellurium from nitric acid solutions carried through the procedure approached 100 percent through the analytical range 5-200 ppb. The relative standard deviation of five consecutive analyses of USGS standard rock GSP-1 was 5.26 percent at a mean concentration of 20.8 ppb. Under optimum conditions an average of 20 samples may be analyzed per man-day.

Colorado↗
USGS1975

Perched silica minerals on mordenite fiber

Ellipsoidal quartz grains and spherulitic chalcedony are perched on mordenite fibers in geodes from Chihuahua, Mexico. Examination of samples of fibrous mordenite from six additional localities indicated that most mordenites have perched quartz crystals. A linear relationship exists between the Si:Al ratios and the refractive indices of the mordenites. The pH of the mineralizing solutions appears to be the primary factor controlling the presence of perched silica minerals (the lower the pH, the higher the Si:Al ratios and the lower the probability of precipitating quartz). Other factors that may affect the presence of lurched silica minerals are (1) the compactness of the mordenite fibers, (2) the morphology of the fibers, and (3) the concentration of Al, Ca, Na, and K in the mineralizing solutions.

Journal of Research of the U.S. Geological Survey↗
USGS1975

Experimental abrasion of detrital gold

The physical breakdown and abrasion rates of gold were studied using a tumbler to simulate natural high-energy environments. The gold fragments were tumbled for periods ranging from 30 to 240 h with different combinations of sand, cobbles, and water at velocities of 0.5 and 2.0 mi/h (0.85 and 3.22 km/h). With sand and gravel, the common bedload of the rivers that deposited the gold-bearing Tertiary sedimentary rocks of the Sierra Nevada, gold is abraded at rates of 0.015 to 0.007 percent (by weight) per hour of travel (at 0.5 mi/h or 0.845 km/h). Cobbles, rather than sand, are responsible for most of the physical changes and abrasion of the gold. Ten gold fragments tumbled for 120 h with cobbles and water (no sand) were broken down to 68 recoverable fragments and lost about 25 percent of their weight to particles smaller than could be recovered using conventional panning techniques. Gold tumbled for 120 h with sand and water lost less than 1 percent of its weight. Gold was abraded faster by wet sand than by dry sand. Velocity appears to be more important as a factor in abrasion of gold than travel distance a fourfold increase in velocity produced a tenfold increase in hourly abrasion rates of gold. Scanning electron microscope examination of the gold fragments after the tumbling experiments revealed differences in surface texture between fragments tumbled with (1) sand, (2) sand and cobbles, and (3) cobbles only.

Journal of Research of the U.S. Geological Survey↗