白云鄂博稀土白云岩电磁学特征与影响因素

白云鄂博是全球最大的稀土矿, 也是我国著名的铁矿区。稀土白云岩是白云鄂博稀土矿主要赋矿岩体, 大部分铁矿也赋存于其中。然而, 稀土白云岩的岩石电磁学特征至今没有清楚的认识, 影响了电磁法勘探资料解释及稀土白云岩发育规律的认识。本文测量了白云鄂博稀土白云岩、铁矿石样品和部分围岩的岩石复电阻率, 为分析岩矿石复电阻率的分布规律和影响因素, 还测量了样品的磁化率数据。利用手持XRF分析仪对样品进行成分粗分析, 部分样品进行了主微量分析和显微镜下分析。结果显示, 矿区岩石电阻率变化范围跨度大, 而且相同岩性岩石电阻率差异较大。矿区围岩与矿石(铁、稀土)之间有较为明显的磁化率差异、轻稀土元素含量(LREE: La、Ce、Pr、Nd)差异显著。岩石组分与岩石电磁属性的交汇结果显示, 岩石磁化率与岩石Fe₂O₃^T含量正相关。镜下分析发现, 磁铁矿的分布与联结程度影响白云鄂博铁矿石电阻率。白云鄂博稀土白云岩具有中高阻、甚至高阻特征, 岩石中大量发育的高阻矿物是影响其电磁学特征的重要影响因素。岩石电磁学分析为白云鄂博电磁法勘探数据解释和隐伏矿预测提供了重要的岩石物理依据。

Petro-electromagnetism of the ore-bearing carbonatite in Bayan Obo REE mining district,North China

Bayan Obo is the largest known rare element earth (REE) mine in the world and a famous iron mine in China. Carbonatite is the REE ore-bearing rock mass, in which most of the iron deposits develop. However, petro-electromagnetic property of the ore-bearing carbonatite and their origin remains unclear. Understanding and interpreting the electromagnetic exploration data prove difficult as well. We present a petro-electromagnetism study of the ore-bearing carbonatite in Bayan Obo and their adjacent areas in this paper. Complex impedance of some 190 samples is measured and their complex resistivity and phase are then calculated in frequency ranges from 0.002 to 10000 Hz. The magnetic susceptibility of samples is also measured. To analyze the distribution property and effect factors of rock and ore to the complex resistivity, the whole rock mineral compositions of 62 samples were measured with ME-XRF methods. Their element contents were analyzed by ways of ME-ICP or ME-MS. Most of other samples were analyzed using a portable XRF analyzer. Our result shows that the ore-bearing carbonatite features medium-high resistivity or even high resistivity ranges from 102Ω·m to 106Ω·m. Ore-bearing carbonatite with higher magnetite content has higher polarizability. The ore-bearing (magnetite, REE) rock has relatively high magnetic susceptibility. The content of the resistant minerals and the connectivity of conductive minerals affects the complex resistivity of ore-bearing carbonatite in Bayan Obo. The results provide important petrophysical basis for the interpretation of electromagnetic exploration data and the prediction of concealed orebody in Bayan Obo.