Osmium, ruthenium, iridium, and uranium in silicates and chromite from the eastern Bushveld Complex, South Africa

Journal Article · Fri Feb 01 04:00:00 EDT 1974 · Geochim. Cosmochim. Acta, v. 38, no. 2, pp. 319-337

DOI:https://doi.org/10.1016/0016-7037(74)90113-6· OSTI ID:4347488

Gijbels, R H; Millard, Jr, H T; Desborough, G A; Bartel, A J

Osmium, ruthenium, iridium, and uranium contents were determined in eight orthopyroxene, seven plagioclase, and three chromite mineral separates from the eastern Bushveld Complex. Neutron activation analysis was used to measure the platinum metals, and uranium was determined by a fission track technique. The platinum metals were found to be present within each mineral in the proportions Os: Ru: Ir = 1:7: 1, while the concentrations of these metals in the minerals are in the ratios orthopyroxene: plagioclase: chromite = 1: 16: 700. The concentration of uranium was found to range from 11 to 66 ppB (parts per billion) and not to vary significantly from mineral to mineral. Data for the platinum metals are consistent with a model in which the eastern Bushveld Complex was formed by the fractional crystallization of two separately injected magmas. The existence of two types of chromite was hypothesized; one type with a large distribution coefficient, presumably formed as a cumulus phase at high temperature, and another, more prevalent type with a smaller distribution coefficient, which may have been formed by postcumulus growth at a lower temperature. This hypothesis is supported by data for coexisting chromite- silicate pairs, which indicate that the chromite grains expelled these platinum metals as they cooled. (auth)

• Research Organization: Geological Survey, Denver
• NSA Number: NSA-29-018038
• OSTI ID: 4347488
• Journal Information: Geochim. Cosmochim. Acta, v. 38, no. 2, pp. 319-337, Journal Name: Geochim. Cosmochim. Acta, v. 38, no. 2, pp. 319-337; ISSN GCACA
• Country of Publication: United Kingdom
• Language: English

Related Subjects

*IRIDIUM-- ACTIVATION ANALYSIS
*OSMIUM-- ACTIVATION ANALYSIS
*RUTHENIUM-- ACTIVATION ANALYSIS
*URANIUM-- NUCLEAR REACTION ANALYSIS
CHEMICAL COMPOSITION
DISTRIBUTION
FISSION TRACKS
GEOCHEMISTRY
MINERALS
N40110* --Chemistry--Analytical & Separations Chemistry-- Activation & Nuclear Reaction Procedures
QUANTITATIVE CHEMICAL ANALYSIS
QUANTITY RATIO
SILICATES
SOUTH AFRICA