The distribution of some trace elements in iron meteorites,as determined by neutron activation

The ten trace elements germanium, arsenic, antimony, copper, chromium molybdenum, silver, indium, zinc and palladium have been determined in sixty-seven different meteorites, using neutron activation and radiochemical separations. In addition the meteorites have been analysed for gallium using either neutron activation or colorimetric methods. The sulphur content of twenty-five of the meteorites has also been measured, using an evolution and colorimetric method. The meteorites analysed consist of a reasonably representative selection of all the structural types of irons.The distribution of the determined trace elements is discussed, in relation to the structural classifications of the iron meteorites. It is shown that a number of meteorites belonging to specific structural classes have the same or closely similar trace element composition. Thus, the following five groups can be specified: seven hexahedrites, three coarsest octahedrites, seven coarse octahedrites, twelve medium octahedrites and six fine octahedrites. Particular attention is paid to the behaviour of germanium and gallium following the widely accepted division of iron meteorites into four distinct GaGe “quantized” groups.It is also shown that arsenic, antimony, silver, indium and zinc are generally concentrated in the coarse and coarsest octahedrite groups, compared with the remaining structural groups. In the case of indium this behaviour is observed even at the 0·0005–0·01 ppm levels. It is also seen that the distribution of zinc does not appear to be related to that of sulphur.Finally, the five structural groups are discussed in relation to the evolution of iron meteorites, and to possible correlations with cosmic-ray exposure ages.