山东大张矽卡岩型铁矿床中铁的富集机制 ——来自流体包裹体和氢、氧同位素的证据

大张铁矿是鲁西地区近年来新发现的一个重要的矽卡岩型矿床.矿体主要赋存于石英二长闪长岩与奥陶系马家沟组灰岩接触带及其附近.根据脉体穿插关系和交代蚀变特征,将大张矽卡岩型铁矿床成矿过程划分为矽卡岩阶段、氧化物阶段、硫化物阶段和碳酸盐阶段.通过对透辉石、绿帘石、石英和方解石等透明矿物显微观察发现,大张铁矿中流体包裹体类型主要...

Enrichment mechanism of iron in Dazhang skarn iron deposit, Shandong Province: Evidence from fluid inclusions and hydrogen-oxygen isotopes

The Dazhang iron deposit is an important skarn deposit newly discovered in the Luxi district in recent years.Orebodies mainly occur in the contact zone between quartz monzodiorite and Ordovician Majiagou Formation limestone and its vicinity.Based on the crosscutting relationship of veins and metasomatic alteration characteris‐tics,the mineralization process of the Dazhang skarn iron deposit can be divided into skarn,oxide,sulfide and carbonate stages.Microscopic observation of transparent minerals such as diopside,epidote,quartz and calcite in‐dicates that the fluid inclusions in the Dazhang deposit are mainly three-phase inclusions containing daughter minerals,gas-rich two-phase inclusions and liquid-rich two-phase inclusions.The microthermal measurement re‐sults show that the ore-forming fluid has undergone a continuous evolution process from high temperature(494.1℃to 550℃)and high salinity(w(Na Cl_eq)=18.07%~56.42%)to low temperature(156.4℃to 225.1℃)and low salinity(w(Na Cl_eq)=1.23%~6.16%)from skarn stage to carbonate stage.Fluid inclusions and hydrogen and oxygen isotopes(δ¹⁸O_fluid=-1.8‰~11.4‰,δD_fluid=-101.1‰~-93.40‰)show that the fluids were mainly magmatic water in the early ore-forming stage and mixed with meteoric water in the late ore-forming stage.Fluid boiling,fluid-carbonate interaction and fluid mixing occurred during fluid evolution.Comprehensive analysis shows that the decrease in temperature and the mixing of meteoric water and magmatic fluid are the main mechanism lead‐ing to the iron precipitation and formation of high grade ores in the Dazhang deposit.