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Geology topics

R.M. Moxham

Publications and source records attributed to R.M. Moxham.

At least 19 recordsLinked to original sources
USGS1977

Importance of neutron energy distribution in borehole activation analysis in relatively dry, low-porosity rocks

To evaluate the importance of variations in the neutron energy distribution in borehole activation analysis, capture gamma-ray measurements were made in relatively dry, low-porosity gabbro of the Duluth Complex. Although sections of over a meter of solid rock were encountered in the borehole, there was significant fracturing with interstitial water leading to a substantial variation of water with depth in the borehole. The linear-correlation coefficients calculated for the peak intensities of several elements compared to the chemical core analyses were generally poor throughout the depth investigated. The data suggest and arguments are given which indicate that the variation of the thermal-to-intermediate-to-fast neutron flux density as a function of borehole depth is a serious source of error and is a major cause of the changes observed in the capture gamma-ray peak intensities. These variations in neutron energy may also cause a shift in the observed capture gamma-ray energy.

Geoexploration↗
USGS1976

Intrinsic germanium detector used in borehole sonde for uranium exploration

A borehole sonde (~1.7 m long; 7.3 cm diameter) using a 200 mm 2 planar intrinsic germanium detector, mounted in a cryostat cooled by removable canisters of frozen propane, has been constructed and tested. The sonde is especially useful in measuring X- and low-energy gamma-ray spectra (40–400 keV). Laboratory tests in an artificial borehole facility indicate its potential for in-situ uranium analyses in boreholes irrespective of the state of equilibrium in the uranium series. Both natural gamma-ray and neutron-activation gamma-ray spectra have been measured with the sonde. Although the neutron-activation technique yields greater sensitivity, improvements being made in the resolution and efficiency of intrinsic germanium detectors suggest that it will soon be possible to use a similar sonde in the passive mode for measurement of uranium in a borehole down to about 0.1% with acceptable accuracy. Using a similar detector and neutron activation, the sonde can be used to measure uranium down to 0.01%.

Nuclear Instruments and Methods↗
USGS1972

Borehole activation analysis by delayed and capture gamma rays using a 252Cf neutron source

Theoretical analysis and experimental comparison of the radiative capture and delayed gamma-ray activation techniques indicate the latter to be more efficient for the detection of copper, whereas the radiative capture method is preferable for nickel. A conservative lower detection limit for both copper and nickel is '-0.5%. Borehole spectra by both techniques were made in a copper- and nickel-bearing gabbro, utilizing a Ge(Li) propane-cooled detector. Al, Mn, Na, Mg, Cu, and V were readily activated and detected by the delayed method. H, Fe, Si, and Ni were not usually present in the delayed spectra but they responded well in the capture mode. It is shown that the borehole sonde can be configured to permit simultaneous delayed and capture spectra, permitting detection of all of these elements. Simulated borehole experiments indicate that, in the delayed gamma-ray mode, an infinite sample is achieved when the ore layer has a vertical thickness of ∼20 cm and a horizontal distance of '10 cm into the wallrock. The depth resolution is thus relatively good but horizontal penetration through the wallrock is limited. © 1972 Society of Economic Geologists, Inc.

Economic Geology↗
USGS1972

A probe for neutron activation analysis in a drill hole using 252Cf, and a Ge(Li) detector cooled by a melting cryogen

A sonde has been built for high-resolution measurement of natural or neutron-induced gamma rays in boreholes. The sonde is 7.3 cm in diameter and about 2.2 m in length and weighs about 16 kg. The lithium-compensated germanium semiconductor detector is stabilized at −185 to −188°C for as much as ten hours by a cryostatic reservoir containing melting propane. During periods when the sonde is not in use the propane is kept frozen by a gravity-fed trickle of liquid nitrogen from a reservoir temporarily attached to the cryostat section. A 252 Cf source, shielded from the detector, may be placed in the bottom section of the sonde for anlysis by measurement of neutron-activation or neutron-capture gamma rays. Stability of the cryostat with changing hydrostatic pressure, absence of vibration, lack of need for power to the cryostat during operation, and freedom of orientation make the method desirable for borehole, undersea, space, and some laboratory applications.

Nuclear Instruments and Methods↗
USGS1970

Thermal features at Volcanoes in the cascade range, as observed by aerial infrared surveys

There have been no substantial changes in the thermal patterns at the summit of Mount Rainier in the period September 1964–September 1966, within the detection limits of the infrared instrumentation. Some differences in radiance are attributed to differences in snow cover. The highest apparent temperature is at a snow-free area on the west flank of the summit cone, several hundred feet below the west crater rim. An anomaly at this site was recorded on both infrared surveys, but no prior reports of thermal activity here have been made by ground parties. Other anomalous thermal zones at the summit are on the northern quadrants of both crater rims. A very small, low-temperature fumarole reported on Mount Adams was not detected, nor were any other thermal manifestations recorded. One anomaly consisting of a close-spaced cluster of thermal spots was detected at The Boot on Mount St. Helens and corresponds to a known fumarole area. The only thermal feature seen on Mount Shasta is near the summit at a thermal spring that has been observed by many climbers. Two anomalies were found on the north flank of Lassen Peak. Thermal activity had not been previously reported at either site, though one is in a known solfatarized area. No ground investigation has been made at the other location. Much of the other thermal activity in the Lassen Peak area is in the northeast quadrant of Brokeoff Caldera. Most of these features are well documented in the literature; others not previously described are in fairly accessible areas and doubtless result from springs and fumaroles related to Brokeoff Caldera.

California, Washington↗
USGS1967

Changes in surface temperature at Taal Volcano, Philippines 1965-1966

Taal Volcano erupted in September 1965 ending a dormant period of 54 years. A quiescent interval of 9 months followed, terminated by new eruptions in July 1966 at the same site. Aerial surveys with a scanning infrared radiometer were made at three periods during the quiescent interval and twice following the July 1966 eruption. The survey technique yields a quasiphotographic image of the radiant temperature of the volcanic terrain. Results indicate that the principal changes in surface temperature stemmed from changes in convective heat transfer by hydrothermal fluids. New hot springs developed along the structurally-controlled northwest and southeast flanks of the 1965 explosion crater. The northwest spring grew in size prior to the 1966 eruption, persisted through that eruption and has since maintained its discharge. The 1965 cinder cone meanwhile showed a persistent rim of hydrothermal activity with some shift in position of maximum discharge. The July 1966 eruptions took place on the rim about midway between two positions of maximum discharge.

Bulletin Volcanologique↗
USGS1965

Gamma-ray spectrometer studies of hydro-thermally altered rocks

The uranium, thorium, and potassium content of hydrothermally altered rocks in the vicinity of several copper and copper-lead-zinc deposits in Arizona was determined by chemical analysis. Potassium in the more intensely altered zones is about twice that in unaltered areas. There is no corresponding increase in thorium, so a higher potassium/thorium ratio also results from alteration; abnormally high uranium, locally in secular disequilibrium, was observed at the Bagdad porphyry copper deposit. A truck-mounted gammarray spectrometer was used to obtain a spectrum of gamma emission at each sample location. Equating the spectrometric with the chemical data gave standard errors of 0.6 percent potassium, 3 ppm thorium, and 10 ppm uranium for the outcrop analyses with the spectrometer . The amount of potassium introduced by hydrothermal alteration is thought sufficient in quantity to be detected by either surface or aerial spectrometry; spectrometric detection of anomalous uranium is probably marginal, owing to the disequilibrium. The potassium/thorium ratio may provide a means of distinguishing, in such surveys, between hydrothermally altered high-potassium zones and unaltered extrinsically high-potassium intrusives.

Economic Geology↗
USGS1964

Radioelement dispersion in a sedimentary environment and its effect on uranium exploration

The radioelement content of the major part of the southeast Texas Coastal Plain sedimentary sequence falls within a range common for sandstones and shales. Exceptions to the normal limit are mainly in small, widely scattered areas. One anomalous area, however, covers several tens of square miles and contains most of the important uranium deposits. Both mechanical and chemical dispersion of radioelements takes place in the immediate vicinity of the ore deposits, though no attempt is made to extend this local dispersion model to the large, regional gamma radiation anomaly. It is suggested that the point-source concept for sedimentary uranium deposits is unrealistic and that conventional aeroradiometric survey grid spacing can be substantially enlarged without seriously reducing efficiency in uranium exploration .

Texas↗
USGS1964

Infrared surveys of Hawaiian volcanoes

Aerial infrared-sensor surveys of Kilauea volcano have depicted the areal extent and the relative intensity of abnormal thermal features in the caldera area of the volcano and along its associated rift zones. Many of these anomalies show correlation with visible steaming and reflect convective transfer of heat to the surface from subterranean sources. Structural details of the volcano, some not evident from surface observation, are also delineated by their thermal abnormalities. Several changes were observed in the patterns of infrared emission during the period of study; two such changes show correlation in location with subsequent eruptions, but the cause-and-effect relationship is uncertain. Thermal anomalies were also observed on the southwest flank of Mauna Loa; images of other volcanoes on the island of Hawaii, and of Haleakala on the island of Maui, revealed no thermal abnormalities. Approximately 25 large springs issuing into the ocean around the periphery of Hawaii have been detected. Infrared emission varies widely with surface texture and composition, suggesting that similar observations may have value for estimating surface conditions on the moon or planets.

Hawai'i↗
USGS1963

Natural radioactivity in Washington County, Maryland

Natural gamma- radioactivity patterns in Washington County , Maryland , reflect the principal variations in lithology. The highest radioactivity is associated with the more argillaceous parts of the geologic section and with soils derived from high-potassium carbonate rocks. Surface radiation intensity ranges from about 5 to 30 microroentgens per hour, of which the rocks contribute 30 to 90 percent. From the aerial survey data, the surface radiation intensity from extended sources can be estimated to within about three microroentgens per hour and the equivalent uranium content can be estimated to within approximately 5 ppm.

Maryland↗
USGS1958

Airborne radioactivity surveys in geologic exploration

The value of airborne radioactivity surveys in guiding uranium exploration has been well established. Recent improvements in circuitry and development of semiquantitative analytical techniques permit a more comprehensive evaluation of the geologic distribution of radioactive materials that may prove useful in exploration for other minerals and in regional geologic studies. It is shown that placer deposits of heavy minerals can be detected from the air, and that the geometric configuration and average grade of the surficial part of the deposit can be approximated. Uranium-bearing phosphorite deposits may be similarly evaluated. Airborne surveys over the Coastal Plain area, Texas, show that the radioactivity profiles in some instances reflect the lithologic character of the underlying rocks. The sandstones are generally low in radioactivity (≈ 10 ppm equivalent uranium), the clays and tuffaceous rocks relatively higher. The intrinsic radioactivity of some lithologic units is sufficiently uniform and distinctive in character to permit their identification and lateral correlation on the airborne survey records. The results suggest that airborne surveys may thereby provide useful guidance in delineating lithologic continuity where the geology is poorly known or obscured.

Trace Elements Investigations↗
USGS1953

Geology and cement raw materials of the Windy Creek area, Alaska

The Windy Creek area, on the south flank of the Alaska Range in the Alaska Railroad belt, contains deposits of raw materials which could be utilized in the manufacture of portland cement. Bedrock in this region includes limestone, argillaceous rocks, chert, and a wide variety of other lithologic types ranging in age from Devonian to Cretaceous. The major geologic structures of the area are oriented parallel to the regional northeast trend of the Alaska Range. Devonian rocks crop out on the south flank of the range, with generally north-dipping strata of Mesozoic age occurring in the area to the southeast. A northeast-trending fault separates the rocks of the two eras. Two limestone deposits of the Devonian system are of adequate size and quality for cement manufacturing purposes. They are located 7 and 11 miles west of the Alaska Railroad; argillaceous rocks occur in both the Devonian and Jurassic(?) systems and are found in many parts of the area. Chert, of Triassic age, possibly of some value as a high-silica component, was found adjacent to the Alaska Railroad near Windy Station.

Alaska↗
USGS1953

Airborne radioactivity survey of the Devils Tower area, Crook county, Wyoming

The accompanying map shows the results of an airborne radioactivity survey covering 45 square miles northwest of Devils Tower, Crook County, Wyoming. The survey was made by the U.S. Geological Survey on September 4, 1952, as part of a cooperative program with the U.S. Atomic Energy Commission. The survey was made with scintillation-detection equipment mounted in a Douglas DC-3 aircraft. Parallel traverse lines, spaced at quarter-mile intervals, were flown approximately 500 feet above the ground. Aerial photographs were used for pilot guidance, and the flight path of the aircraft was recorded by a gyro-stabilized, continuous-strip-film camera. The distance of the aircraft from the ground was measured with a continuously recording radio altimeter. At 500 feet above the ground, the width of the zone from which anomalous radioactivity is measured varies with the intensity of radiation of the source and, for strong sources, the width would be as much as 1,400 feet. Quarter-mile spacing of the flight paths of the aircraft should be adequate to detect anomalies from strong sources of radioactivity. However, small areas of considerable radioactivity midway between flight paths may not be noted. The approximate location of each radioactivity anomaly is shown on the accompanying map. The plotted position of an anomaly may be in error by as much as a quarter of a mile owing to errors in the available base maps up to several square miles in which it is impossible to find and plot recognizable landmarks. The radioactivity that is recorded by airborne measurements at 500 feet above the ground can be caused by: 1. A moderately large area in which the rocks and soils are slightly more radioactive than the rocks and soils of the surrounding area. 2. A smaller area in which the rocks and soils are considerably more radioactive than rocks and soils in the surrounding area. 3. A very small area in which to rocks and soils are much more radioactive than the rocks and soils of the surrounding area. Any particular anomaly, therefore, may represent either slightly greater-than-average radioactivity over an area of a few thousand square feet, or high radioactivity over an area of a few hundred square feet. The radioactivity anomalies shown on the accompanying map indicate localities of more-than-average radioactivity, and therefore, suggest areas in which uranium or thorium deposits are more likely to occur.

Wyoming↗
USGS1953

Airborne radioactivity survey of the Miller Hill area, Carbon county, Wyoming

The accompanying map shows the results of an airborne radioactivity survey covering 65 square miles northwest of Miller Hill, Carbon county, Wyoming. The survey was made by the U.S. Geological Survey as part of a cooperative program with the U.S. Atomic Energy Commission. At 500 feet above the ground, the width of the zone from which anomalous radioactivity is measured varies with the intensity of radiation of the source and, for strong sources, the width would be as much as 1,400 feet. Quarter-mile spacing of the flight paths of the aircraft should be adequate to detect anomalies from strong sources of radioactivity. However, small areas of considerable radioactivity midway between flight paths may not be noted. The approximate location of each radioactivity anomaly is shown on the accompanying map. The plotted position of an anomaly may be in error by as much as a quarter of a mile owing to errors in the available base maps up to several square miles in which it is impossible to find and plot recognizable landmarks. The radioactivity anomalies shown on the accompanying map cannot be interpreted in terms of either the radioactive content or the extent of the source materials. The present technique of airborne radioactivity measurement does not permit distinguishing between activity due to thorium and that due to uranium. An anomaly, therefore, may represent radioactivity due entirely to uranium, or to thorium, or to a combination of uranium and thorium. The radioactivity that is recorded by airborne measurements at 500 feet above the ground can be caused by: 1. A moderately large area in which the rocks and soils are slightly more radioactive than the rocks and soils of the surrounding area. 2. A smaller area in which the rocks and soils are considerably more radioactive than rocks and soils in the surrounding area. 3. A very small area in which to rocks and soils are much more radioactive than the rocks and soils of the surrounding area. Any particular anomaly, therefore, may represent either slightly greater-than-average radioactivity over an area of a few thousand square feet, or high radioactivity over an area of a few hundred square feet. The radioactivity anomalies shown on the accompanying map indicate localities of more-than-average radioactivity, and therefore, suggest areas in which uranium or thorium deposits are more likely to occur.

Wyoming↗
USGS1953

Airborne radioactivity of portions of the Defiance Uplift and Carrizo Mountains, Apache county, Arizona

The accompanying map shows the results of an airborne radioactivity survey covering 940 square miles in Apache county, Arizona. The survey was made by the U.S. Geological Survey from September 8 to October 3, 1952, as part of a cooperative program with the U.S. Atomic Energy Commission. The survey was made with scintillation-detection equipment mounted in a Douglas DC-3 aircraft. Parallel traverse lines, spaced at quarter-mile intervals, were flown approximately 500 feet above the ground. Aerial photographs were used for pilot guidance, and the flight path of the aircraft was recorded by a gyro-stabilized, continuous-strip-film camera. The distance of the aircraft from the ground was measured with a continuously recording radio altimeter. At 500 feet above the ground, the width of the zone from which anomalous radioactivity is measured varies with the intensity of radiation of the source and, for strong sources, the width would be as much as 1,400 feet. Quarter-mile spacing of the flight paths of the aircraft should be adequate to detect anomalies from strong sources of radioactivity. However, small areas of considerable radioactivity midway between flight paths may not be noted. The approximate location of each radioactivity anomaly is shown on the accompanying map. The plotted position of an anomaly may be in error by as much as a quarter of a mile owing to errors in the available base maps up to several square miles in which it is impossible to find and plot recognizable landmarks. The radioactivity anomaly that is recorded by airborne measurements at 500 feet above the ground can be caused by: 1. A moderately large area in which the rocks and soils are slightly more radioactive than the rocks and soils of the surrounding area. 2. A smaller area in which the rocks and soils are considerably more radioactive than rocks and soils in the surrounding area. 3. A very small area in which to rocks and soils are much more radioactive than the rocks and soils of the surrounding area. Any particular anomaly, therefore, may represent either slightly greater-than-average radioactivity over an area of a few thousand square feet, or high radioactivity over an area of a few hundred square feet. The radioactivity anomalies shown on the accompanying map indicate localities of more-than-average radioactivity, and therefore, suggest areas in which uranium or thorium deposits are more likely to occur.

Arizona↗