Postcollision Porphyry Mo Mineralization of Central Tien Shan: First Data on U–Pb Isotopic (LA-ICP-MS) Dating of Zircon from Rocks of the Molo-Sarychat Productive Pluton, East Kazakhstan

Abstract

First data on the U–Pb isotopic (LA-ICP-MS) age of zircon from intrusive rocks of the Molo-Sarychat pluton, which is confined to a system of deep faults of the “V.A. Nikolaev line” in East Kyrgyzstan, are presented. The rocks of this pluton belong to high-K calc-alkaline and shoshonite series with spatially and genetically related intense Mo(‒W‒Cu‒Au) (mainly, porphyry Mo) mineralization. In addition to other Au, W, and Cu deposits and occurrences, this mineralization is part of an extended metallogenic belt of Tien Shan; however, the occurrences of porphyry Mo mineralization are few in number in this belt. The concordant U–Pb isotopic age of zircon autocrysts indicates the crystallization of quartz monzonites and monzogranites in the Early Permian: 293.3 ± 4.2 and 286.6 ± 2.4 Ma, respectively. The age of zircon antecrysts is 306‒320 Ma. The age of crystallization corresponds to the postcollision evolutionary stage of this territory, whereas the presence of antecrysts expands the period of the origination of the pluton in the Late Carboniferous–Early Permian, thus spanning the tectonic settings first of subduction and then of postcollision regimes. We therefore identified the postcollision nature of Mo(‒W‒Cu‒Au) (porphyry Mo) mineralization, which is related to the studied pluton and formed after the intrusion of quartz monzonites and monzonites (early and late-stage mineralization, respectively). A significant enrichment in Mo can be related to its progressive accumulation during magmatic differentiation, which led to the intrusion of quartz monzonites and, especially, monzogranites. These processes occurred under a more mature postcollision tectonic regime with the possible formation of intermediate magmatic sources in the Early Proterozoic substrate of metamorphic rocks and ancient granitoids. The age values of rocks of the Molo-Sarychat pluton are similar to those identified for metasomatic and igneous rocks of the large Kumtor Au deposit also confined to the “V.A. Nikolaev line.”