Abstract:
The previously published and newly obtained geological and geochronological (Rb-Sr and Ar-Ar) data show that the igneous rocks and products of hydrothermal alteration in the Dukat ore field pertain to two ore-forming magmatic-hydrothermal systems (OMHSs). The igneous rocks of the Early Cretaceous rift-related OMHS are represented by potassium rhyolites of the Askol'd Formation with Rb-Sr ages of 124 ± 3 and 119.3 ± 3.4 Ma and intercalating amygdaloidal basalts. The products of the hydrothermal activity of this OMHS are the metasomatic anatase-chlorite assemblage of the root zone, which replaces potassium rhyolites, and shallow-seated quartz-adularia and quartz-carbonate-feldspar veinlets retained in rhyolite fragments in Late Cretaceous conglomerate and breccia. The Late Cretaceous OMHS was related to the origination of the Okhotsk-Chukotka volcanic belt and consists of calc-alkaline basaltic andesites of the Tavvatum Formation and moderately silicic K-Na rhyolites of the Nayakhan Formation with a Rb-Sr age of 84 ± 4 Ma. The Late Cretaceous postmagmatic hydrothermal activity in the Dukat ore field resulted in the formation of preore metasomatic rocks and orebodies of the unique Dukat Au-Ag deposit. The first stage of the Late Cretaceous hydrothermal activity gave birth to preore propylites with a Rb-Sr isochron age of adularia samples estimated at 85 ± 1 Ma and quartz-chlorite-sulfide and Ag-bearing quartz-chlorite-adularia orebodies with Rb-Sr isochron ages of adularia estimated at 84 ± 1 and 86.1 ± 4 Ma. The second stage was marked by the formation of garnet-bearing propylites and quartz-rhodonite orebodies with a Rb-Sr age of 73 ± 3 Ma. Further hydrothermal activity occurred after a break related to structural rearrangement of the ore field and was expressed in the replacement of propylites by products of argillin alteration and Ag-bearing Mn hydroxides. Paleogene basaltic dikes and related subeconomic mineralization concluded magmatic and hydrothermal processes in the Dukat ore field. © Pleiades Publishing, Inc. 2006.
