Geology topics

George L. Crenshaw

Publications and source records attributed to George L. Crenshaw.

3 recordsLinked to original sources

USGS1979

Petrographic and trace-element data on rocks from the Yemen Arab Republic

Petrographic descriptions are given for rocks in the Yemen Arab Republic (YAR), including mainly Precambrian igneous and metamorphic rocks from the southeastern part of the country, which previously was geologically undescribed. Also included are descriptions of Cretaceous and/or Tertiary lavas of the Yemen Volcanics, Miocene(?) alkali granite, Pliocene caprock of the Guma salt dome, and late Pleistocene and Holocene basalts of the Aden Volcanic Series (?). The petrographic studies permitted the selection of 11 samples of rock for future use in obtaining isotopic analyses for age determinations. Analyses of these rock specimens for trace amounts of gold, indium, mercury, selenium, and thallium completed the geochemical studies. Results of these analyses are interpreted to show that regional geochemical exploration should be undertaken for base and precious metals near Jibal Hufash, the Manakhah area, the region around Al Bayda, the Sa'dah-Majadh area, and the Wadi Jawf area. Additional studies of trace elements in commercial salt deposits of the YAR should be made to evaluate the amounts of mercury and selenium in this industrial raw material.

Open-File Report↗

USGS1975

Experimental results of atomic absorption analyses for indium and thallium in 803 nonmagnetic concentrates from Alaska

The development in the U.S. Geological Survey of rapid methods for the determination by atomic absorption spectrophotometry of indium and thallium at limits of detection as low as 0.2 ppm each in geologic materials affords great advantages over spectrographic methods in studies concerned with values at or near the crustal abundances of these elements. Experimental application of the technique to the analysis of 803 nonmagnetic concentrates from Alaska showed specific disadvantages owing to the insolubility of cassiterite--one of the major sources for indium in concentrates--under the conditions of dissolution used in the preparation of samples for analysis by atomic absorption. Where nonmagnetic concentrates are used as a geochemical sample medium, and an exploration program is based on the interpretation of multi-element data, little purpose is served by independent analyses for indium and thallium.

Alaska↗

USGS1974

A sensitive and rapid method for the determination of trace amounts of selenium in geologic materials

A sensitive method for the determination of less than crustal abundance amounts of selenium has been developed that can be useful in the geochemical investigation of selenium. The sample is roasted with a flux of sodium carbonate, chloride, and chlorate and then digested in a mixture of nitric and phosphoric acids. The resulting solution is stabilised; the selenium is reacted with 2,3-diaminonaphthalene to form 4,5-benzopiazselenol, extracted with cyclohexane, and measured fluorometrically. The lower limit of selenium content of a sample that can be determined by this method is 0.04 p/m using a 0.5-g sample.

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