The distribution of trace elements in chondritic meteorites. 1. Gallium, germanium and indium

Abstract

A rapid neutron activation technique, using the nuclides 70Ga + 72Ga, 75Ge and 116mIn, was developed for the simultaneous determination of gallium, germanium and indium in geological materials. This method was employed to examine the fractionation of gallium, germanium and indium between ordinary, enstatite and carbonaceous chondrites and to investigate the distribution of gallium and germanium between the magnetic and non-magnetic fractions of ordinary and enstatite chondrites. A comparison of the gallium and germanium contents of the metal phases of different chondrite groups was also made. Some indium determinations on separated ordinary chondrite phases show that indium is concentrated mainly in the non-magnetic phases. Germanium is strongly siderophile in both ordinary and enstatite chondrites; gallium is strongly siderophile in enstatite chondrites, but less strongly in ordinary chondrites. Germanium results for metal phases belonging to the same chondrite groups are very similar, but there exist distinct differences between the germanium values found in the metal phases of enstatite, bronzite and hypersthene chondrites. The gallium and germanium contents of chondritic metal phases are not so variable as gallium and germanium results for iron meteorites. All three elements are shown to be fractionated among the different chondrite classes with depletion ratios in the order Ga< Ge⪡ In. Germanium, but not gallium, is enriched in bronzite relative to hypersthene chondrites. The results obtained here are in support of previous suggestions that enstatite chondrites should be subdivided into two groups. The fractionation patterns of gallium and germanium between types I, II and III carbonaceous chondrites are similar, but indium is more strongly fractionated.