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At least 271 records · Page 15Linked to original sources
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

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↗
USGS1975

Cylindrical jointing in mafic dikes, central Beartooth Mountains, Montana

Cylindrical joints are well displayed in two Precambrian mafic dikes that cut granitic gneiss in the central Beartooth Mountains, Mont. The dikes are vertical and about 23 m (75 ft) and 23 to 46 m (75-150 ft) thick, respectively. The cylindrical joints are perpendicular to the dike walls, and the cylinders defined by the joints are as much as 5 m (16 ft) in diameter. No petrographic, textural, or other features related to or possibly responsible for the joints are recognized. The dikes are chemically and petrographically similar to quartz dolerite dikes found throughout the Beartooth Mountains. Some of these dikes show typical polygonal columnar joints; a few others have cylindrical jointing, but in most dikes neither kind of jointing was observed. The orientation of the cylindrical joints normal to the walls of the dikes indicates that they probably formed by thermal contraction during post-crystallization cooling of the dikes and are thus genetically related to the much more common polygonal jointing. However, the model proposed to explain the cylindrical joints suggests that their origin is partly dependent on the geometric relation between the orientation of the dikes and that of the predike fracture pattern in the host rock.

Montana, Wyoming↗
USGS1975

Preliminary results of a gravity survey of the Henrys Lake quadrangle, Idaho and Montana

A gravity survey of the Henrys Lake quadrangle shows that a gravity low with about 10 milligals of closure coincides with the Henrys Lake basin. The low is interpreted to reflect a basin fill of 1,100 m or more of Cenozoic sediments and volcanic rock. The data indicate that on the east and probably on the west the basin is bounded by northwest- and north-trending faults, and near its waist by the east-trending Centennial fault. A model constructed across the Henrys Lake basin suggests a northwest-trending fault, located near the southeast corner of Henrys Lake and concealed beneath the basin fill. The sparse gravity data east of the Centennial Mountains are not sufficient to provide any evidence on the extension of the Centennial fault across the Henrys Lake basin.

Idaho, Montana, Wyoming↗
USGS1975

Comparison of fission-track, K-Ar, and Rb-Sr radiometric age determinations from some granite plutons in Maine

Fission-track ages have been determined on eight apatite and four sphene concentrates separated from plutonic rocks in Maine. K-Ar and Rb-Sr ages for some of these rocks were previously published. In northeastern Maine the whole-rock Rb-Sr, biotite K-Ar, and apatite fission-track ages are concordant at 400-420 million years, whereas in south-central Maine the apatite fission-track age is 150 m.y. and the biotite K-Ar age is about 250 m.y. At intermediate positions along the traverse the whole-rock Rb-Sr, biotite K-Ar, and sphene fission-track ages agree fairly well in the range 390-325 m.y., but the apatite fission-track ages are all about 100 m.y. younger. This pattern is consistent with the hypothesis of burial metamorphism and uplift as proposed in 1970 by Zartman, Hurley, Krueger, and Giletti to explain the abundance of Permian K-Ar ages in central New England.

Maine↗
USGS1975

K-Ar ages of plutonic rocks in the Lassiter Coast area, Antarctica

Numerous middle Cretaceous stocks and small batholiths intruded Middle and Upper Jurassic sedimentary and volcanic rocks in the Lassiter Coast area of the southern Antarctic Peninsula. To establish the age of the quartz diorite and granodiorite plutonic events, five plutons were dated by the K-Ar method. The results indicate a timespan of about 20 m.y. for the emplacement of the plutons and a minimum age of 120 m.y. for the deformation of the sedimentary (Latady Formation) and volcanic rocks. Three of the more silicic plutons have concordant biotite and hornblende ages of 100 and 106 m.y.; two discordant ages of about 118 m.y. were obtained on the more mafic plutons. Petrographically, chemically, and geochronologically, the plutons of the southern to central Lassiter Coast are similar to the calc-alkaline suite of igneous rocks of the Andes of Patagonia, the Antarctic Peninsula, and eastern Ellsworth Land.

Journal of Research of the U.S. Geological Survey↗
USGS1976

Hydrogeology of a drift-filled bedrock valley near Lino Lakes, Anoka County, Minnesota

The bedrock surface of east-central Minnesota is dissected by an intricate network of valleys. Outside the bedrock valley at site B, 3 mi (4. 8 km) from site A, 100 ft (30 m) of drift overlies the bedrock surface. Observation wells were installed at the two sites to determine the vertical ground-water movement between the various aquifer units and the lateral movement between the two sites. An aquifer test of the lowest valley-fill aquifer at site A showed that the observation well completed in the same aquifer as the pumping well responded immediately; whereas a lag of about 100 min occurred between the lower valley fill and uppermost body of sand and gravel. This indicates that the hydraulic connection between these two layers is poor at the immediate site. Test results show that the lower sand-and-gravel aquifer has a transmissivity between 14,000 and 27,000 ft 2 /d (1,300 and 2,500 m 2 /d). Although the hydraulic gradient is vertically downward in the valley, much of the drift fill is poorly permeable. This suggests that the quantity of downward-percolating water reaching the lowest valley-fill aquifer is relatively small at the test site. Because valley cut through a number of bedrock aquifers in the region, they could potentially be an important avenue of contamination from land-surface waste. In addition, the vast network of bedrock valleys in the Twin Cities area might cause contaminants to disseminate rather rapidly throughout a large area.

Minnesota↗
USGS1978

Three-dimensional finite-difference model of ground-water system underlying the Muskegon County wastewater disposal system, Michigan

The spray irrigation system used by Muskegon County for wastewater treatment is the largest of its kind in the United States. It has 2200 hectares of irrigated farm land, 688 hectares of treatment lagoons, and 105 kilometers of drainage tile. The system has a design capacity of 1.8 cubic meters of wastewater per second. A three-dimensional finite-difference model was developed to study the effect of the disposal operation on ground-water conditions. Model calculations show that the water table at and adjacent to most of the wastewater site is lower as a result of the operation of the system to date. However, along the northwest boundary of the site, where irrigated land was not undertiled, the water table is 1 to 2 meters higher than it would be under natural conditions. Predictive simulations indicate that, even if the drainage tiles lost 75 percent of their effectiveness, the impact of disposal operations on ground-water levels would be negligible outside of the wastewater site.

Michigan↗