The First Data on the U-Pb Age and Composition of Zircons From Ore-Bearing Syenites of Gora Rudnaya (South Yakutia)

Abstract

The isotope-geochemical study (SHRIMP-II, SIMS) of zircons from syenites of Gora Rudnaya (South Yakutia) was carried out. Gora Rudnaya is a syenite massif in the form of a laccolith. It is located within the Central Aldan ore district and includes the recently discovered Morozkinskoye gold deposit. Vein and vein-disseminated gold mineralization occurs in low-temperature acid metasomatites – beresites (Qz-Ser-Ank-Py). Mineralization is restricted to steeply dipping submeridional crush zones within the intrusion. According to the zircon dating data, the age of ore-bearing syenites is about 130 Ma. The obtained age corresponds to the main stage of magmatism and the associated hydrothermal-metasomatic activity within the Central Aldan ore district. Two groups of zircons have been distinguished in syenites. The first group is characterized by features of magmatic genesis. For the second group of zircons, there is evidence of the influence of fluids on zircons: increased content of U, Th, and some non-formula elements (LREE, Ca, Ti, Sr). The presence of two varieties of zircons that are contrasting in composition and appearance, but of the same age, indicates that the magmatic crystallization of syenites from Gora Rudnaya and their fluid processing occurred simultaneously.