Native iron in Quaternary deposits of the Darhad Basin (northern Mongolia)

Quaternary sediments from the borehole DBC-1 drilled in the Darhad Basin, northern Mongolia, have been studied by thermomagnetic analysis (248 samples) and probe microanalysis (9 samples) to determine the origin (cosmic or terrestrial) of native iron. Most of the samples showed extremely low contents of native iron. Only 26 samples have iron in contents sufficient for its reliable identification (10^–5–10^–3%). The negligible content of native iron in the Darhad Basin sediments distinguishes them from the earlier studied sediments of different geologic associations of Eurasia and the Atlantic, which we explain by the high sedimentation rate in this basin. However, the bimodal distribution of native-iron contents in the samples with a distinct “zero” mode, similar to that in the objects of Eurasia and the Atlantic, testifies to the predominantly cosmic origin of the native iron.