津巴布韦大岩墙层状铬铁矿地球化学特征及地质意义

津巴布韦大岩墙中的层状铬铁矿储量丰富,易于开采且矿石质量较高。本文通过对产自不同次岩浆房的铬铁矿样品进行电子探针分析,表明铬铁矿的地球化学数据较为集中,TiO_2含量较低,Mg#变化不大,Cr#逐渐升高,表现出随着温度和压力的降低,铬铁矿化学成分向着富Cr和富Fe的方向演变。综合分析表明该层状铬铁矿是在拉张环境背景下,由于深大断裂诱发深部地幔发生部分熔融,形成的基性-超基性岩浆快速上涌,随着温度和压力的逐渐降低,由分离结晶作用导致铬铁矿矿物的堆晶沉淀形成层状矿体。

Geochemistry and geological significance of the layered chromite in the Great Dyke of Zimbabwe

The layered chromite in the Great Dyke of Zimbabwe contains abundant reserves, with high quality ores, being easy to exploit. Electron microprobe analysis on four chromite samples from different magma subchambers shows concentrated geochemical data of this ore with low TiO2 content, little change of Mg#, while Cr# increasing gradually with the decrease of temperature and pressure, as well as an evolution of chemical composition of chromite ore towards Cr-rich and Fe-rich. In combinination with other data, we suggest that this larered chromite formed in an extensional environment, where the partial mantle melt was induced by deep faults, leading to rapid rise of basic-ultrabasic magma. With the decrease of temperature and pressure, the crystallization differentiation caused chromite mineral to accumulate forming layered ore body.