新疆伊吾县宝山铁矿床矽卡岩成因研究

Genesis of skarn from Baoshan iron deposit in Yiwu County,Xinjiang

宝山铁矿床位于东准噶尔库兰卡孜干-北塔山-纸房-琼河坝岛弧带东段。宝山铁矿中矽卡岩与铁矿体密切共生,是重要的找矿标志。研究区矽卡岩中石榴子石、透辉石单矿物电子探针分析结果显示,石榴子石属于钙铁榴石-钙铝榴石系列,透辉石属于透辉石-钙铁辉石系列。矽卡岩中高场强元素(如Nb、Ta、Zr、Hf)相对亏损,稀土元素表现出LREE富集,HREE亏损的特点。∑REE为39.90×10^(-6)~178.43×10^(-6),∑LREE/∑HREE比值1.64~7.53,(La/Yb)N比值为1.32~10.10,轻、重稀土元素分异程度较弱,与玄武质凝灰岩具有相似的地球化学特征,这说明矽卡岩是玄武质凝灰岩受后期岩浆热液改造形成,随着温度和压力降低,磁铁矿沉淀形成铁矿体。

The Baoshan iron deposit is located in the east part of the Kulankazigan-Beitashan-Zhifang-Qiongheba island arc belt,East Junggar.The skarn,as an important indicator,occurs along with iron orebodies in the Baoshan deposit.Electron microprobe analysis of garnet and diopside from the skarn in the study area was carried out for the first time,and the results show that the garnet belongs to the calcium garnet-calcium aluminum garnet series and the diopside belongs to the diopside-calc pyroxene series.This kind of garnet and diopside assemblages has similar characteristics to the other large skarn magnetite deposits in the world.The skarn shows the characteristics of deficiency of high field strength elements（HFSE）,enrichment of light rare earth elements（LREE） and depletion of heavy rare earth elements（HREE）.The values of the total rare earth elements（∑ REE） are 39.90×10^（-6）~178.43×10^（-6）,the ratios of ∑LREE/∑HREE are 1.64~7.53,and the values of（La/Yb）Nare 1.32~10.10.The degree of differentiation between LREE and HREE is weak,which is similar to the characteristics of the basaltic tuff from the Beitashan Formation.These data indicate that the skarn was formed by alteration of basaltic tuff with a large amount of high-temperature hydrothermal fluid.During this process,with the decrease of temperature and pressure of the hydrothermal fluid,the magnetite was deposited and the ore deposit was formed.