白云鄂博主、东矿三个剖面地球化学特征及其研究意义

近年来关于白云鄂博Nb-REE-Fe矿床H8岩体火成水成归属的争论已渐息，而矿床成矿过程以及REE富集机制仍是学术界关注的热点。文章对白云鄂博矿床白云石碳酸岩体、霓长岩化蚀变带、尖山组板岩3个典型剖面开展系统的岩石地球化学工作，发现赋矿碳酸岩、霓长岩、铁矿石微量与稀土元素配分模式具有相似性，靠近H8岩体的尖山组板岩往往有着更高的稀土元素含量，以及与成矿碳酸岩相近的微量元素配分模式。区内各类岩石单元稀土元素分馏明显，全岩La_N/Nd_N比值的变化规律显示，H8岩体内部比边缘更富La，边缘比岩体内部更富Nd。通过岩（矿）石薄片BSE图像结合矿物电子探针分析显示，H8岩体内的稀土元素矿物（主要是独居石、氟碳铈矿等）可分为2组，一组相对富La，呈半自形-他形，星点状分布；另一组相对富Nd，呈他形细粒，脉状分布。两组矿物中不同元素的富集特征可能代表了结晶过程中流体环境的改变。上述实验结合地质勘查结果表明，白云鄂博矿床初始成矿物质的起源与H8碳酸岩一致，均来源于中元古代碳酸岩岩浆活动，而不同类型的稀土元素矿物对应了白云岩成岩阶段与萤石矿化阶段两个不同的稀土矿化阶段。

Geochemical characteristics of three profiles of main and east ore bodies of Bayan Obo deposit and its geological significance

In recent years, the debate on the genesis of the H8 rock mass in the Bayan Obo Nb-REE-Fe deposit has gradually subsided, but the mineralization process of the deposit and the mechanism of REE enrichment are still the focus of academic circles. In this paper, systematic rock geochemical work is carried out on three typical profiles of carbonatite, aegirine alteration zone and slate of Jianshan Fm in Bayan Obo deposit. We found that the trace elements and REE distribution curves of ore-bearing carbonatite, fenite and iron ore are basically consistent. Slate of Jianshan Fm near H8 rock often has higher REE content and similar trace element distribution mode to the carbonatite. The fractionation of REE in various rock is obvious. The variation of La_N/Nd_N ratio in the whole rock shows that La is more enriched in the interior of H8 rock mass, and Nd is more abundant in the edge. BSE images and electron microprobe analysis show that the REE minerals (mainly monazite, bastnaesite, etc.) in the H8 rock mass can be divided into two groups. One group is relatively rich in La, showing a hypidiomorphic to xenomorphic-granular, star-shaped distribution; the other group is relatively rich in Nd, showing a xenomorphic-granular and distributing as veins. The enrichment characteristics of different elements in the two groups of minerals may represent the change of fluid environment during crystallization. The results of the above experiments combined with geological exploration show that the origin of the initial metallogenic materials of the Bayan Obo deposit is consistent with that of the H8 carbonatite, both of which are derived from Mesoproterozoic carbonatite magmatic activity. Different types of REE minerals correspond to two different REE mineralization stages:dolomite carbonatite stage and fluorite mineralization stage.