冀东马城沉积变质型铁矿床流体包裹体研究

Fluid Inclusions of the Macheng Sedimentary Metamorphic Iron Deposit in Eastern Hebei Province

马城沉积变质型铁矿床是在近几年铁矿勘查中新发现超大型矿床,其矿体赋存于新太古界滦县群,铁矿形成后遭受了多期变质变形作用及后期热液蚀变。本文在野外工作的基础上,对马城沉积变质型铁矿床中不同类型磁铁石英岩中的石英开展了详细的流体包裹体研究,马城铁矿遭受绿帘-角闪岩相变质作用的峰期阶段主要形成IIb类气体包裹体和IV类含液态CO2三相包裹体,流体包裹体均一温度为314℃~580℃,盐度主要位于2wt%~10 wt%Na Cl区间,表现为低盐度特征;绿帘-角闪岩相变质作用峰后形成IIa类液体包裹体和III类含子矿物包裹体,流体包裹体主体均一温度为120~447℃,盐度0.88wt%~35.32wt%Na Cl,均一温度和盐度变化范围较大,可能代表了区域变质峰后阶段变质流体具有多期性的特点;后期热液蚀变阶段形成I类次生包裹体,包裹体均一温度为131~239℃,盐度为1.4wt%~21.6wt%Na Cl,表现为中低盐度特征。

The Macheng sedimentary metamorphic iron deposit is a super- large one which was discovered in recent years. Its ore bodies are hosted in the Neo- Archean Luanxian Group and had been reformed by multiperiod metamorphism and post- hydrothermal alteration. Based on field work,we have studied the fluid inclusions in quartz from this iron deposit. The results show that two kinds of fluid inclusions formed in the peak stage of epidote-amphibolite facies metamorphism: IIb- type vapor- rich inclusion and IV- type three- phase inclusion containing liquid CO2. The homogenization temperatures of these inclusions range from 314℃ ~ 580℃ and salinity values vary in the range of 2wt % ~ 10 wt % Na Cl,indicating that the metamorphic fluid is characterized by low salinity. Two kinds of fluid inclusions formed after the peak stage of epidote- amphibolite facies metamorphism: IIa- type liquid inclusion and III- type daughter mineral- bearing inclusion. The homogenization temperatures of these inclusions range from 120 ~ 447℃ and salinity values vary in the range of 0. 88 wt % ~ 35. 32 wt % Na Cl,which show that the metamorphic fluid has the characteristics of multi- stages after the regional metamorphic peak. I- type inclusions formed in the stage of post- hydrothermal alteration. The homogenization temperatures range from 131 ~239℃ and salinity values vary in the range of 1. 4wt% ~ 21. 6wt % Na Cl,which means that the metamorphic fluid is of middle- low salinity.