EARLY PERMIAN AGE OF INTRUSIONS AT THE INGICHKE AND MELIKSU TUNGSTEN-POLYMETALLIC DEPOSITS IN THE SOUTHERN TIEN SHAN: FIRST ISOTOPIC U-Pb DATA ON ZIRCON (LA-ICP-MS METHOD) FROM THE INTRUSIVE ROCKS OF THE ZIRABULAK PLUTON (UZBEKISTAN) AND MELIKSU STOCK (KYRGYZSTAN)

The paper presents the first data on the isotopic U-Pb dating of zircon (LA-ICP-MS method) form the intrusive rocks of the large Zirabulak granitoid pluton (Uzbekistan), which the Ingichke, the largest one in the Central Asia (about 100 Kt WO₃), and the Meliksu tungsten-polymetallic skarn deposits are associated with. These deposits, together with other deposits of tungsten, gold and other metals are part of the largest gold-tungsten metallogenic belt of Tien Shan. They are represented by bodies of hydrothermally-altered skarn with scheelite and sulfides (pyrrhotite, chalcopyrite), and subsequent within- and near-intrusion stockworks of late post-skarn metasomatites (propylitic and phyllic alteration) with polymetallic-scheelite mineralization. The concordant isotopic U-Pb zircon age dates of zircon from rocks of the Zirabulak pluton (289 ± 3.8 Ma for granodiorite of the main intrusive phase and 288 ± 3.3 Ma for granite) and the Meliksu stock (285.8 ± 2.5 Ma and 283 ± 2 Ma for granodiorite of the main intrusive phase) were obtained; they indicate the intrusion emplacement in the Early Permian. This is significantly younger than the known dates (some 300-310 Ma) of granodiorites but is coincident with the dates of granites in the other monzodiorite-granodiorite-granite intrusive massifs of the region, which the significantly smaller tungsten but locally large gold (with subordinate tungsten) deposits (Jilau, Yakhton, Kabuty) are associated with. Such age and metallogenic peculiarities of the productive intrusions can be correlated to the specific features of the geodynamic evolution of the region in the Late Carboniferous-Early Permian.