Long Evolution of a Magmatic–Ore System of the Muruntau Gold Deposit, Western Uzbekistan, Tien Shan: Evidence from the LA–ICP–MS U–Pb Isotopic Age of Zircon from Granitoids of the Sardara (Sarykty) Pluton

Abstract

The LA–ICP–MS U–Pb age was determined for the first time for zircon from granodiorites–granites of the Sardara (Sarykty) intrusive in area of the giant Muruntau gold deposit in Western Tien Shan (Uzbekistan). Three crystal groups were identified in a combined sample: their concordant U–Pb age is 322.0 ± 3.7 (four grains), 301.6 ± 2.1 (11 grains), and 289.5 ± 4.9 Ma (two grains) (MSWD = 3.1, 0.17, and 0.98, respectively). The dispersion of the isotopic age can be explained using a model of a successive crystallization of different zircon generations in magmatic chambers at various depths and their further entrapment upon differentiation/crystallization of new magma portions. The similarity of two (youngest) age intervals with concordant U–Pb ages previously published for zircons of granitoid rocks directly at the Muruntau deposit is noteworthy. The latter ages could thus represent dike branching at the corresponding stages of evolution (progressive differentiation) of deeper sources of granitoid magma, the larger intrusions of which include Sardara (Sarykty) and other plutons exposed at some distance from the deposit. The older U–Pb isotopic ages of zircons from granitoids of the Sardara (Sarykty) pluton (~322 and 302 Ma) generally correspond to the subduction stage, whereas the youngest zircons (~289.5 Ma) correspond to the postcollision stage of the region. The origination and initial evolution of the magmatic sources in area of the Muruntau deposit could thus occur under subduction conditions; however, the final differentiation and crystallization of granitoid magma has finished at the postcollision stage.