COBALT AND NICKEL CONCENTRATIONS IN THE KOMATIITE COMPONENT OF APOLLO-16 POLYMICT SAMPLES

Some estimates for the concentrations of Co and Ni in the primitive mafic component of Apollo 16 breccias and soils are large, comparable to concentrations in terrestrial komatiites. These estimates may be erroneously high because the contribution from meteoritic contamination of the samples has been underestimated. However, even if the correction for meteoritic Co and Ni is valid and the calculated residual Ni is not of meteoritic origin, the Ni is presently carried by FeNi metal while the Fe and Mg are carried by mafic silicates. If any large-scale separation of metal and silicate phases has occurred, the concentration ratio of Ni to Fe + Mg in the mafic silicates of the ancient crust in the vicinity of the Apollo 16 site has not been preserved by Apollo 16 rocks. Apollo 16 polymict breccias and soils contain much higher concentrations of siderophile elements and FeNi metal than other nonmare samples from the Moon. Thus, it is likely that the Ni (Mg + Fe) ratio estimated for the komatiite component from Apollo 16 samples is high compared to the actual ratio for the lunar crust. © 1990.