辽东砖庙硼矿含硼岩系富镁大理岩地球化学特征及其成因

Geochemical Characteristics and Genesis of Mg-rich Marbles of the Zhuanmiao Borate Ore District in Eastern Liaoning

富镁大理岩是辽东砖庙硼矿的主要容矿岩石。对该区富镁大理岩的岩石特征、全岩化学、稀土元素、微量元素和C、O同位素地球化学进行了测试分析。结果表明本区富镁大理岩具有岩浆碳酸岩的特征:主量元素具富镁高硅的特点;微量元素中B、F、Rb、Cs、Th和U含量较高,V、Cr、Co、Ni等相对较低,高场强元素相关比值与岩浆碳酸岩相似;稀土元素含量偏低,分配型式略显右倾,与后仙峪镁橄榄岩的稀土配分型式一致;C、O同位素含量较世界各地岩浆碳酸岩偏高。分析认为,辽东砖庙硼矿富镁大理岩的形成可能与地壳物质混染有关,δ18O-δ13C相关图解显示其为海相原生碳酸岩。

Mg-rich marble is the mainly host rock of borate deposit in Zhuanmiao borate ore district in Eastern Liaoning.The petrologic features,chemistry of the whole rock,REE and trace elements,and C,O isotope geochemistries of Mg-rich marble are studied in this paper.The results show that Mg-rich marble has the characteristics of magmatic carbonatite： the major elements indicate that the rock is rich in Mg and Si.With relatively high trace elements contents of B,F,Rb,Cs,Th,U and comparatively low contents of V,Cr,Co,Ni,HFSE,the related ratios are similar to those of magmatic carbonatite.The contents of REE are relatively low,showing a LREE-rich pattern in the figure of chondrite-normalized REE-pattern,and in concordance with ultra-mafic peridotite in Houxianyu.Carbon and oxygen isotopic compositions of whole-rock samples lie within ranges of-2.6‰ to ＋5.59‰ for δ^13C and 12.91‰ to 20.95‰ for δ^18O.The δ^13C and δ^18O values of Mg-rich marble fall on the zone of primary and marine carbonatite in the diagram of δ^18O-δ^13C.The contents of carbon and oxygen isotope are higher than those of magmatic carbonatite all over the world,which may be concerned with the contamination of crustal materials.