Noble gases in the Xinjiang (Armanty) iron meteorite-A big object with a short cosmic-ray exposure age

We measured the concentrations and isotopic ratios of the cosmogenic noble gases He. Ne, and Ar in the very large iron meteorite Xinjiang (HIE). The He-3 and He-4 data indicate that a significant portion of the cosmogenic produced helium has been lost via diffusion or in a recent impact event. High Ne-22/Ne-21 ratios indicate that contributions to the cosmogenic Ne-21 from sulfur and/or phosphorous are significant. By combining the measured nuclide concentrations with model calculations for iron meteorites we were able to determine the preatmospheric diameter of Xinjiang to 260-320 cm, which corresponds to a total mass of about 70-135 tons. The cosmic-ray exposure age of Xinjiang is 62 +/- 16 Ma, i.e., relatively short compared to most of the other iron meteorites. With the current database we cannot firmly determine whether Xinjiang experienced a complex irradiation history. The finding of He-3 and He-4 losses might argue for a recent impact event and therefore for a complex exposure.