新疆富蕴县蒙库铁矿床赋矿浅粒岩锆石U-Pb年代学研究

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

蒙库铁矿床位于阿尔泰山南缘成矿带的麦兹火山-沉积盆地内,矿床主矿体成因类型为与火山作用有关的热水喷流沉积矿床.矿体主要赋存于泥盆系康布铁堡组地层中,主要岩性有浅粒岩、变粒岩及斜长角闪岩,原岩恢复显示为海相火山岩,主要为细碧岩-角斑岩-石英角斑岩,次为流纹岩-凝灰岩,沉积岩为钙质凝灰质砂岩夹结晶灰岩.通过对蒙库铁矿床浅粒岩锆石LA-ICP-MS U-Pb定年,确定了矿床的形成时代及康布铁堡组地层的形成时代.锆石中Th含量分别为29.5×10^-6-82.7×10^-6和32.1×10^-6-109.3×10^-6,U含量分别为35.7×10^-6-132.1×10^-6和47.6×10^-6-140.6×10^-6,Th/U比值为0.41-1.19和0.51-0.85,为典型岩浆锆石特征.蒙库铁矿浅粒岩的U-Pb年龄分别为397.5±2.5 Ma和389.0±4.7 Ma.结合区域年代学资料,确定康布铁堡组形成于早泥盆世,康布铁堡组下亚组上限为389±4.7 Ma,而蒙库铁矿床主矿体形成时代为397.5±2.5 Ma.

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^-6to 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.