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C. M. Bunker

Publications and source records attributed to C. M. Bunker.

At least 19 recordsLinked to original sources
USGS1983

Preliminary assessment of the geochemistry and mineral favorability of the postorogenic granites of the southeastern Arabian Shield, Kingdom of Saudi Arabia

Chemical analyses of samples for 19 postorogenic plutons from the southeastern Arabian Shield show that these rocks have average potassium/rubidium ratios (162) and average rubidium/strontium ratios (11.8) characteristic of highly evolved granites. Most of the analyzed samples are peraluminous. Three plutons are physically similar in terms of shape and megascopic textural zonation to peralkaline complexes in the northeastern part of the Shield, but none of the samples from these plutons is peralkaline. However, these plutons do contain the least-evolved samples. Zinc, yttrium, uranium, thorium, and possibly copper, each occur in anomalously high concentrations in at least one pluton relative to contents typically cited for granite. The average regional concentrations of copper and zinc are anomalously high. These facts suggest at least a moderate potential for mineralization in the southeastern part of the Shield. Good correlations (r of 0.5 to 0.8) between uranium, thorium, yttrium, and rubidium and an excellent correlation (r=0.98) between uranium and radium-equivalent uranium suggest that secondary deposits of these elements are unlikely and that magmatic deposits, especially of a pegmatitic nature, are more likely. Concentrations of some major elements and several trace elements covary with sample location as measured by latitude and longitude. This fact is interpreted to reflect regional variations in the protolith that have been proposed on the basis of lead isotopic data. The chemical variations suggest a largely oceanic crustal component for granites in the southwestern part of the southeastern Shield and a largely continental crustal component to the northeast. Further quantitative analysis is recommended to verify and accurately delineate anomalous concentrations of trace elements. Trend surface analysis of all available data for postorogenic granites from the eastern Arabian Shield is suggested as a method for testing regional variations in the protolith that might control locations of highly favorable areas of ore deposition.

Open-File Report↗
USGS1977

Geochemical and petrological studies of a uraniferous granite from the Granite Mountains, Wyoming

Granite rocks from the Granite Mountains, Wyo. have been proposed as the source of uranium deposits in the Crooks Gap, Gas Hills and Shirley Basin uranium districts, Wyoming. We have divided these granitic rocks into four units: (1) a biotitic phase which forms the dominant unit at the western end of the Granite Mountains, (2) a leucocratic phase which was found from 215 to 405 metres in drill hole GM-1, (3) silicified zones which crosscut the granitic rocks and form topographic highs, and (4) fractured zones, in drill hole GM-1, which seem to have been hydrothermally altered. The biotitic phase is hypidiomorphic-granular to xenomorphic-granular alkali granite with anomalously high contents of U (10 parts per million), Th (50 ppm), and Pb (50 ppm). Fission-track studies show that uranium is located in zircon, sphene, apatite, monzite, xenotime, biotite, chlorite, epidote, and magnetite; no intergranular uranium was found. The leucocratic phase is mineralogically similar to the biotitic phase, but contains less than half as much iron. It is xenomorphic granular and commonly contains rounded and retrograded garnets, which suggests that this phase is either metamorphic or contaminated with metamorphic materials. The leucocratic phase has anomalously high contents of U (8 ppm) and Pb (55 ppm), but has a low Th content (10 ppm). The silicified phase and fracture zones exhibit cataclastic and crystalloblastic textures and are highly variable in mineralogy. Potassium-bearing minerals are generally absent. Microcline is replaced by albite and (or) quartz, and biotite is replaced by clinozoisite. Uranium values may be anomalously high in the fracture zones. One sample contains 1100 ppm radium-equivalent uranium. In this and other uranium-rich samples from the fracture zones, the uranium is associated with iron oxides which commonly fill microfractures. According to our model and currently available data, an alkali granite is the best crystalline source rock for uranium, especially if it is unmetamorphosed and rapidly exposed to near-surface conditions for the first time when a favorable basin existed nearby.

Wyoming↗
USGS1973

Radioelement and radiogenic heat distribution in Drill Hole UCe-1, Belmont Stock, Central Nevada

Uranium, thorium, and potassium concentrations were measured in 60 samples collected from an exploratory hole drilled in the Belmont stock about 40 miles north-northeast of Tonopah, Nev. The results indicate that, at least within 2,000 feet of the surface, the granitic pluton contains radioelement concentrations similar to those in average granodiorites and that local variations in concentrations may reflect the effects of argillic alteration.

Nevada↗
USGS1973

Radioelement distribution in the basement complex of the Yukon-Tanana upland, Eielson deep test hole, Alaska

Uranium, thorium, and potassium contents were determined in 94 samples of drill cuttings from a 9,774-foot-deep exploratory hole drilled entirely in crystalline schists of the basement complex of the Yukon-Tanana Upland. The data indicate two distinctively different rock types and reflect differences in the calcite content of the rock. Zones of anomalously high concentrations of the radioelements probably reflect the effects of the emplacement of the nearby Eielson pluton.

Alaska↗
USGS1971

Correlation of uranium, thorium, and potassium with aeroradioaetivity in the Berea Area, Virginia

In the Berea area, a small quartz monzonite pluton intrudes chlorite-actinolite schist and is overlapped by Coastal Plain sand and gravel deposits. A detailed aeroradioactivity survey of the area shows unusually high radioactivity (1,150 counts per second) over the quartz monzonite. A total of 22 auger samples was taken across all formations to a depth of 2 to 3 feet, and radioelement concentrations were determined by gamma-ray spectrometry. There is a general direct correlation of high radioactivity with increase in radioelement concentrations. Abundances of uranium and particularly thorium in the quartz monzonite are two and three times the average for rocks of this type; a comparison is made with other granitic rocks high in uranium and thorium. © 1971 Society of Economic Geologists, Inc.

Virginia↗
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↗