Late Paleozoic Stages of Ore Formation in the Middle Tian Shan: Isotopic U–Pb Zircon Dating (LA-ICP-MS Method) of Intrusive Rocks from the Sonkul and Kokturpak Plutons (Eastern Kyrgyzstan)

Abstract

The paper presents the isotopic U–Pb study data (LA-ICP-MS method) of zircon from intrusive rocks of the Sonkul and Kokturpak plutons situated along the deep-seated fault system of the “Nikolaev Line” in the eastern Kyrgyzstan. These plutons of high-potassic rocks are spatially and genetically associated with the Kumbel and Kashkasu W–Mo–Cu–Au deposits, respectively, as well as other occurrences of W and W–Au mineralization. Together with other Au, W and Cu deposits, they are parts of the extended metallogenic belt of Tien Shan. The concordant isotopic U–Pb ages of zircon autocrysts for the consecutive intrusive phases span over the interval of approximately 303 to 283 Ma. This interval included the crystallization of olivine gabbro (299 ± 2 Ma) in the Sonkul pluton, monzonite (300 ± 3 Ma) in the Kokturpak pluton, granodiorite of the main intrusive phase (299 ± 3 Ma in the Sonkul pluton and 297 ± 4 Ma in the Kokturpak pluton), and monzogranite (289 ± 4 Ma in the Sonkul pluton and 285 ± 2 Ma in the Kokturpak pluton). Zircon antecrysts dated at 306–311 (to 323?) Ma have also been distinguished. The age data obtained correspond to the pluton emplacement in the Late Carboniferous-Early Permian initially in subduction-related and then post-collisional tectonic settings. Besides, in the Middle Tien Shan, this age interval corresponds to one of the regional pulses of high-potassic calc-alkaline and shoshonitic magmatism. A distinct metallogenic evolution corresponds to these pulses that is expressed in the change from porphyry Cu–Au–Mo deposits related to the early pulse to essentially tungsten (W–Mo–Cu–Au) and then essentially gold deposits related to younger pulses. The rocks also contain zircon xenocrysts with ancient age (in the order of 1.5–2.5 Ga) that probably represent the age of the Tarim craton basement.