冀东水厂沉积变质型铁矿床流体包裹体特征

Characteristics of the Fluid Inclusions from the Shuichang Sedimentary Metamorphic Iron Deposit in Eastern Hebei Province

水厂铁矿是冀东地区一大型铁矿床,属于典型的BIF型铁矿床,矿体赋存于晚太古代变质岩系中。本文选取不同类型的磁铁石英岩样品,对其中石英流体包裹体进行系统的岩相学特征分析及显微测温测试,探讨变质流体的物化性质。流体包裹体岩相学结果显示,水厂铁矿主要发育五类包裹体,分为Ⅰ型次生包裹体、Ⅱ型富液的两相包裹体、Ⅲ型富气的两相包裹体、Ⅳ型含子晶的三相包裹体和Ⅴ型富CO_2的三相包裹体。流体包裹体显微测温结果显示,水厂铁矿变质作用峰期发育Ⅲ型和Ⅴ型包裹体,峰期变质流体均一温度为377~>580℃,盐度(0.35wt%~9.73wt%)NaCleqv,显示高温低盐度特征;而变质作用峰期期后发育Ⅰ型、Ⅱ型和Ⅳ型包裹体,均一温度介于101~537℃之间,盐度范围为(0.88wt%~20.07wt%)NaCleqv,均一温度及盐度范围较宽。水厂铁矿以上流体包裹体特征结合其它地质证据,共同验证了水厂铁矿形成后遭受到变质作用的改造,并且可能存在多期次的特征。

The Shuichang deposit is a typical sedimentary metamorphic iron deposit with a large scale in eastern Hebei Province. The orebodies are hosted in metamorphic rock series of Late Archaean. The fluid inclusions in quartz from different types of iron ores were analyzed by systematical petrography characteristics and tested by microscopic temperature measurement for investigating the physical properties of metamorphic fluids. The results show that there are five types of fluid inclusions in the Shuichang iron ores： type-I secondary fluid inclusion, type-Ⅱ fluid-rich two-phase inclusion, type-Ⅲ gas-rich two-phase inclusion, type-Ⅳ daughter mineral-bearing three-phase fluid inclusion, and type-Ⅴ CO2-rich three-phase fluid inclusion. Among them, type-Ⅲ and type-Ⅴ-type ones were formed during the metamorphic culminating period, when the homogenization temperature of the metamorphic fluids was 377~〉580℃, with salinity of 0.35wt%~9.73wt%NaCleqv, indicating that the metamorphic fluid is characterized by high temperature and low salinity. Type I, Ⅱ and Ⅳ inclusions were formed after the metamorphic peak stage, during which the fluid homogenization temperature and salinity were 101~537℃ and 0.88wt%~20.07wt%NaCleqv, respectively, showing broad ranges. The characteristics of fluid inclusions combined with other geologic evidence reveal that the Shuichang iron ores were reformed by metamorphism after their formation and probably have a feature of multiple periods.