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USGS1976

Chromium in rocks and minerals from the southern California batholith

Chromium, determined by neutron-activation analysis in a suite of rocks and minerals from the southern California batholith, shows Cr concentrated in the mafic differentiates, decreasing as the more felsic rocks are approached. This trend is evident for samples of the Woodson Mountain Granodiorite from a single differentiated stock. The distribution of Cr in the minerals from the rocks of the southern California batholith shows that Cr was depleted in the magma during the course of crystallization. The data indicate that the minerals were in equilibrium with the magma during crystallization, and the distribution coefficient (Cr in biotite/Cr in hornblende) is correlated with differentiation indices, indicating either temperature or compositional dependence. The average distribution coefficient (Cr in biotite/Cr in hornblende) is 1.18, which compares favorably with the average values found by other investigators for other suites. ?? 1976.

Chemical Geology↗

USGS1975

Determination of tungsten in geologic materials by neutron activation analysis

A method is described for the determination of tungsten in geologic materials. After fusion with sodium peroxide, tungsten is isolated by extraction into chloroform with a-benzoinoxime, back extraction into aqueous potassium hydroxide, and precipitation with a-benzoinoxime. The activities of the 0.13 and 0.48 MeV gamma rays are measured. The activity of the 0.155 MeV gamma ray of 188 Re ( 188 W), added prior to the fusion, is measured to determine the yield; yields normally range from 40 to 90 percent. The coefficients of variation for less than part-per-million concentrations of tungsten are normally <20 percent; the limit of detection is 0.005 ppm for a 100-mg sample.

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