Isotopic U–Pb Age (LA-ICP-MS Method) of Zircon from Intrusive Rocks of the Large Vostok-2 Tungsten Skarn Deposit (Sikhote-Alin, Primorie, Russia)

This paper presents the new isotopic U–Pb data (LA-ICP-MS) for zircon from intrusive rocks of the large Vostok-2 tungsten–base-metal(–gold) deposit. This deposit, together with other tungsten, tin, and gold deposits, is part of the metallogenic belt which extends along the Central Sikhote-Alin Fault and corresponds to the occurrence of Early–Late Cretaceous magmatism and mineralization formed due to the development of a transform continental margin. The deposit comprises large bodies of pyroxene skarn altered during the development of the postskarn metasomatic rocks and related to intensive scheelite–gold–sulfide (with abundant pyrrhotite) mineralization and represents a “reduced” type of tungsten skarn deposits. The concordant isotope U–Pb dates were obtained for zircons from different granitoid rocks of the mineralized area: 109.7 ± 0.7 and 110.4 ± 0.6 Ma (MSWD = 0.047 and 0.003) (granodiorite and “plagiogranite” of the Central stock), 106.9 ± 1.6, 106.9 ± 0.7, 108.2 ± 0.8, and 108.0 ± 0.8 Ma (MSWD = 0.13, 0.0004, 0.27, and 0.54) (granodiorites of the Dalnensky massif), and 107.6 ± 1.7 Ma (MSWD = 0.45) (granite–porphyry). These data are indicative of a a generally low but persistent age decrease of rocks from the Dalnensky massif, as compared to those from the Central stock. These study results are consistent with distinguishing the latter as a distinct igneous complex earlier suggested based on their petro-geochemical signatures. Such complex of “small intrusions” could be the most productive for Au–W to W–Au mineralization in the region. The dates obtained for intrusive rocks from the Vostok-2 deposit are similar to those of the intrusive massifs accompanied by other tungsten–base-metal deposits in the belt as well as by some pluton-related (“reduced intrusion-related”) gold deposits. The rocks studied also contain “ancient” zircon xenocrysts inherited from various crustal protoliths and dated by a broad range of isotopic U–Pb ages.