A Mantle–Plume Model for the Formation of the Zun-Kholba Orogenic Gold Deposit (Eastern Sayan, Russia): Mineralogical Results, Rb–Sr and 40Ar–39Ar Geochronological and Pb–Pb Isotope Studies

Abstract

The large Zun-Kholba deposit, relating to a numerous group of orogenic-type gold deposits, is in the Eastern Sayan (Russia)—a segment of the Altai-Sayan fold system of the Central Asian Orogenic Belt. The paper discusses the results of mineralogical, geochemical, geochronological, and Pb-isotopic studies of gold mineralization; the purpose was to verify the genetic model of the deposit. Mineralogical and geochemical data obtained for ore bodies located between hypsometric levels from 1290 to 2090 m indicate a complex distribution of mineral associations at the deposit. There is no vertical and horizontal zonation in the distribution of mineral associations, in the chemical composition of the main ore minerals, as well as in the content of impurity elements in them. In dating ore-forming processes at the Zun-Kholba deposit, a comprehensive approach based on the study of K–Ar and Rb–Sr isotope systems of metasomatites was applied. The combination of Rb–Sr and ⁴⁰Ar–³⁹Ar methods allowed us to determine that the age of gold mineralization is 411 ± 2 Ma, while the age of the superimposed event, which is associated with redistribution of ore, as well as disturbance of the Rb–Sr and K–Ar isotopic systems of metasomatites, is about 380 Ma. Pb–Pb isotopic study of ore mineralization at the deposit and host Precambrian rocks allowed to prove the leading contribution of the latter in ore lead supply to the mineral-forming system. The model of formation of the Zun-Kholba orogenic gold deposit assumes a genetic relationship between ore-forming processes and intraplate alkaline mafic magmatism due to the impact of the plume in the Early Devonian time on the lithosphere of the Tuva-Mongolian terrane.