Multiple episodes of Late Paleozoic Cu-Au mineralization in the Chatkal-Kurama terrane: New constraints from the Kuru-Tegerek and Bozymchak skarn deposits, Kyrgyzstan

Abstract

The Chatkal-Kurama terrane is the most fertile region for porphyry-skarn Cu-Au mineralization (~31 Mt Cu and 2300 t Au) in the West Tianshan, even though in the Chatkal range of Kyrgyzstan only limited studies have been conducted. We present the first robust geochronological and geochemical data for the important Kuru-Tegerek and Bozymchak skarn Cu-Au mineralization and related magmatism in the Chatkal region. Consistent zircon SHRIMP U-Pb and molybdenite Re-Os ages reveal that the Kuru-Tegerek skarn Cu-Au deposit formed at about 325 Ma (zircon U-Pb, 326 ± 3 Ma; molybdenite Re-Os, 323 ± 2 Ma), and the Bozymchak skarn Cu-Au deposit formed at about 305 Ma (zircon U-Pb, 304 ± 2 Ma; molybdenite Re-Os, 305 ± 3 Ma). The new ages, in combination with previous data, suggest four pulses of Cu-Au mineralization and related magmatic events in response to changing dynamic settings. The ca. 325 Ma Kuru-Tegerek in the NE Chatkal is associated with low- to medium-K calc-alkaline tonalite porphyry derived from Precambrian continental crust (εNdt = −16.3 to −20.0, T2DM = 2.4–2.7 Ga) in an early subduction stage. The ca. 315 Ma time slice records the peak of tremendous porphyry Cu-Au mineralization (Kal’makyr and Sarycheku) and voluminous magmatism with high-K calc-alkaline to shoshonite series rocks of mixed origin of continental crust and metasomatized mantle-derived that denote a compressive regime due to flat subduction. The ca. 305 Ma Bozymchak Cu-Au skarn deposit is also associated with a high-K calc-alkaline intrusion (granodiorite porphyry) and supposedly marks the cessation of supra-subduction magmatism. The Early Permian Kochbulak high sulfidation epithermal Au deposit is related to a stratovolcano setting that is closely associated with post-collisional shoshonitic rocks related to slab breakoff. Collectively, the Cu-Au mineralization in the Chatkal-Kurama terrane formed during a 30 My period related to multiple magmatic pulses in a geodynamic setting evolving from early over peak to late subduction to post-collisional slab breakoff.