The First Data on the U-Pb Ages and Compositions of Zircons from Ore-Bearing Syenites of Gora Rudnaya (South Yakutia)

摘要

This paper presents the first isotope-geochemical study (SHRIMP-II, SIMS) of zircons from syenites of Gora Rudnaya (South Yakutia), which host the recently discovered Morozkinsky gold deposit. Gora Rudnaya is a laccolith located in the Central Aldan ore district. Vein and vein-disseminated gold mineralization occur in low-temperature acid metasomatites, beresites (Qz-Ser-Ank-Py), restricted to steeply dipping submeridional brecciation zones. According to zircon dating, the age of the ore-bearing syenite is approximately 130 Ma. The obtained age corresponds to the main magmatic stage and associated hydrothermal-metasomatic activity within the Central Aldan ore district. Two groups of zircons have been distinguished in syenites. The first group shows features of magmatic genesis. The second group reveals evidence of fluid reworking, in particular, elevated contents of U, Th, and some nonformula elements (LREE, Ca, Ti, and Sr). The presence of two zircon varieties that differ in composition and appearance but have the same age indicates that the magmatic crystallization of syenites from Gora Rudnaya and their fluid reworking occurred practically simultaneously.