U-Pb ZIRCON GEOCHRONOLOGY OF THE LEUCOGRANULITE IN MENGKU IRON DEPOSIT, FUYUN COUNTY, XINJIANG

The Mengku iron deposit in Fuyun County, Xinjiang is located in the Maizi volcanic-sedimentary basin along the southern margin of Altai metallogenic belt. Its main ore bodies are genetically of volcanism-related hydrothermal spout sedimentation type. The ore bodies occur mainly in Kangbutiebao Formation with leucogranulite, granulitite and amphibolite. The protolith recovery displays marine volcanic rocks of mainly spilite-keratophyre and quartz keratophyre, with minus rhyolite-tuff. The sedimentary rocks involve calcareous tuffaceous sandstone intercalated with crystalline limestone. By zircon LA-ICP-MS U-Pb dating of the leucogranulite in Mengku iron deposit, the age of Kangbutiebao Formation and the deposit is defined. The contents of Th range from 29.5×10^-6-82.7×10^-6 to 32.1×10^-6-109.3×10^-6; while of U, from 35.7×10^-6-132.1×10^-6 to 47.6×10^-6-140.6×10^-6, with Th/U ratio between 0.41-1.19 and 0.51-0.85, showing typical features of magmatic zircons. The zircon ages of the leucogranulite in Mengku deposit are 397.5±2.5 Ma and 389.0±4.7 Ma. Combined with regional geochronological data, it is concluded that the Kangbutiebao Formation was formed in the Early Devonian, with a ceiling age of 389±4.7 Ma. The main ore bodies of the deposit are dated at 397.5±2.5 Ma.