老挝万象省爬立山铁矿成矿二长花岗岩锆石SHRIMP U-Pb定年及其地质意义

爬立山铁矿位于老挝．越南长山铜金铁多金属构造岩浆成矿带中段，为一大型矽卡岩型磁铁矿床。通过对矿床地质特征、岩体产出特征分析，认为该铁矿成矿作用受区内二长花岗岩岩浆活动制约。本文对含矿二长花岗岩进行了岩相学和锆石SHRIMPU-Pb定年研究。所测锆石内部结构、阴极发光图像特征及Th／u比值的研究表明，二长花浏岩中的锆石为岩浆锆石。U-Th-Pb同位素分析结果显示岩体形成年龄为280．3±2．9Ma（MSWD=0．70）。结合区域构造演化及构造岩浆岩带形成的动力学机制，认为爬立山铁矿系早二叠世洋板俯冲背景下弧岩浆作用主导的产物，与长山带海西晚期大规模铜金铁矿同属于一个活动陆缘成矿系统。

SHRIMP zircon U-Pb dating of the ore-forming monzogranite from the Phalek iron deposit, Vientiane, Laos and its geological implications

The Phalek iron deposit is a large-sized skarn-type magnetite deposit in the central part of the Cu-Au-Fe polymetallic structural-magmatic metallogenic belt in the Trung Son zone at the border area of Laos and Vietnam. Judged from the geology and occurrence of ore bodies, the mineralization of the iron deposit is dominantly controlled by the magmatism of the monzogranite in the study area. The present paper focuses on the petrography and SHRIMP zircon U-Pb dating of the ore-bearing monzogranite. The integration of internal structures, cathodoluminescence images and Th/U ratios of the measured zircons shows that the zircons from the monzogranite are of magmatic origin. As indicated by the U-Th-Pb isotopic analysis, the ages of the ore-bearing monzogranite masses are dated at 280.3 ± 2.9 Ma （ MSWD = 0.70）. The regional tectonic evolution and dynamic mechanisms for the formation of the structural-magmatic zone have also disclosed that the Phalek iron deposit resulted from the arc magmatism during the subduction of the Early Permian oceanic metallogenic system as the late Hercynian large-sized plate, and are assigned to the same active epicontinental Cu-Au-Fe deposits in the Trunk, Son metalloeenic halt