Sources and Age of the Gold Mineralization of the Irokinda Deposit, Northern Transbaikalia: Evidence from Pb, S, Sr, and Nd Isotope-Geochemical and 39Ar–40Ar Geochronological Data

Numerous orogenic gold deposits of different age, scale, and mineralization type are located within Northern Transbaikalia. Among them, there is a large group of Early Permian deposits, whose sources and relationships with Late Paleozoic magmatism remain debatable. These issues were solved by the example of the middle-scale (~24 t, Au) Irokinda deposit, localized within the Precambrian rocks of the Baikal–Muya Terrane. 39Ar–40Ar geochronological dating of the ore-hosting altered rocks indicates that hydrothermal–metasomatic process took place about 270 myr ago. Gold mineralization has heterogeneous Pb-, S-, Sr-, and Nd-isotopic characteristics. Variations in the Pb, S, Sr, and Nd isotopic composition of ore and gangue minerals suggest that the mineral-forming components were involved in the hydrothermal system from different sources. Among them, the leading role belonged to the rocks of the Precambrian crust of the Baikal–Muya Terrane. Pb isotopic composition of the second identified source is close to that of the Early Permian alkaline and subalkaline rocks of the Baikal–Muya Terrane. This fact may indicate a genetic relationship between the Irokinda gold mineralization and intraplate alkaline magmatism, which developed in the region simultaneously with ore-forming processes.