长江中下游地区首例低温独立铊矿床的Sm-Nd同位素定年及其意义

Samarium—Neodymium Isotope Dating of Fluorites from the Xiangquan Deposit——the First Independent Thalliumy Deposit Discovered in the Middle—Lower Reach of Yangtze River

为了确定长江中下游地区首例独立铊矿床—安徽和县香泉铊矿床的热液改造期成矿时代,对矿床中早晚两阶段10件萤石样品进行了Sm-Nd同位素测定,得出早、晚两阶段萤石的等时线年龄分别为131.6±3.0Ma和79±11Ma。结合矿床地质地球化学特征,认为该独立铊矿床低温热液成矿作用发生在晚燕山期,并在燕山期末发生过一期热(泉)活动的叠加。该矿床的发现指示在长江中下游地区存在晚燕山期低温成矿事件和可能的低温成矿域。长江中下游地区燕山期以铊为代表的低温热液成矿作用和以铜(铁)金为代表的中高温热液成矿作用之间可能存在着密切的成因关系,为同一热液流体系统的产物。

The Xiangquan thallium deposit is located in Anhui province, China, which is the first example of a thallium-only deposit discovered in the Middle-Lower Reach of Yangtze River, east China and in the world. Sm-Nd isotopic compositions of early- and late-stage fluorites in the deposit fall on two well-defined lines in the isochron plot with isochrons corresponding to 131.7±2.7 and 79±11Ma. The isochron ages suggest that epithermal thallium mineralization took place in the Early Cretaceous period （Yanshanian period）, which experienced an alteration of hot spring in Late Cretaceous period. The epithermal thallium mineralization maybe has close relationship with the copper （iron）-gold hydrothermal mineralization. The ore-forming solution, which formed the T1 deposit and the Cu （Fe）-Au deposits maybe belong to the same ore-forming fluid system.