内蒙古白云鄂博矿床碳酸岩侵位方式与三维形态及稀土潜在资源

稀土元素是关键金属的重要成员, 我国稀土资源禀赋优越, 并主要来自白云鄂博矿床, 但其巨量金属富集机理、矿体空间形态以及潜在资源等, 一直存在不同认识, 制约了稀土资源评价以及有效利用。在地质、地球化学和地球物理多学科联合攻关基础上, 本文对白云鄂博碳酸岩就位机制、演化过程和三维形态, 以及稀土超常富集机理与潜在资源等进行了探讨。白云鄂博早-中元古代沉积岩经历了区域性的挤压构造变形, 原水平地层褶皱后又被置换成陡立、近E-W走向的构造片理, 这为碳酸岩浆的上涌提供了有利通道。白云鄂博H8白云岩为火成碳酸岩, 它侵位于~13亿年, 经历了铁质-镁质-钙质的演化, 碳酸岩既为稀土成矿母岩, 也是稀土矿体; 古生代两次改造作用导致了稀土活化及新生矿物生成, 但没有外来稀土的明显加入。高磁与低阻地球物理异常体揭示出了碳酸岩体的三维形态, 碳酸岩的侵位中心位于主、东矿之间, 侵位后沿构造置换陡立面理, 往东西两侧推进。利用获得的碳酸岩体积、(最小)密度以及稀土含量, 推算出白云鄂博矿区500~1000m以浅稀土潜在资源为3.33亿t, 这远超目前公认的矿山及全球稀土资源量。建议开展新一轮以稀土为主的勘探与验证工作, 以获取白云鄂博战略矿产资源的准确家底。

Intrusive style,three-dimensional morphology of carbonatite and REE potential resources in the Bayan Obo giant deposit,Inner Mongolia

Rare earth elements (REE) have been considered as critical metals in modern society. China is dominated in world REE resources, with most of the REE concentrated in the Bayan Obo deposit. Despite its economic importance, the mechanism of REE mineralization, the spatial distribution of orebodies, and REE potential resources have long been contentious in the Bayan Obo deposit, which hinders further exploration and utilization of REE. Combining geological, geochemical and geophysical investigations, this paper studies the intrusive style, evolution process and three-dimensional morphology of ore-related carbonatite, and the enrichment mechanism of REE. In addition, the REE potential resources are estimated. In the Bayan Obo district, the Paleo- to Mesoproterozoic sedimentary rocks experienced compression. As a result, the primary horizontal rocks have been changed to E-W trending, steeply inclined strata, which provides suitable channels for ore-related carbonatitic melts. The ore-related carbonatite was intruded at ca. 1.3Ga, and evolved from ferric carbonatite, to magnesian carbonatite, and further to calcic carbonatite. The ore-related carbonatite contains high contents of REE, and thus it can be taken as REE orebody. The deposit experienced hydrothermal overprint in the Paleozoic time, during which the REE were mobilized but the REE resources were not enhanced. According to high magnetic and low resistance anomaly, the shape of the ore-related carbonatite is defined, i.e., the intruding center is located between the East Pit and Main Pit, and the melts moved toward west and east along the tectonic foliation. According to the volume, density and REE contents of ore-related carbonatite, the RE2O3 potential resources is estimated to reach 333 million tons. This number is much larger than previously thought. It is proposed that further exploration is highly required to accurately determine the real REE reserve of the Bayan Obo deposit.