First Data on the U-Pb Isotopic Age for Zircon

The first data of a U-Pb isotopic study (LA-ICP-MS method) of zircon from leucocratic granites of the giant Tyrnyauz Mo-W deposit (North Caucasus) are presented. The emplacement of this granite separated the formation stages of Mo-W skarns and younger large stockworks with Mo-mineralization. Two types of zircons are distinguished among the grains identified. The first type is represented by rare tabular and short-prismatic crystals (xenocrysts) of an ancient zircon, with large variations of the U-Pb isotopic age (from about 300 Ma to almost 1500 Ma). The second type includes more abundant long-prismatic crystals of a young zircon; its weighted average U-Pb isotopic age (2.67 ± 0.04 Ma) corresponds to the time of leucocratic granite crystallization.