云南红河州超大规模离子吸附型稀土矿的发现及其意义

Finding and Implication of an Undiscovered Giant Deposit of Ion-adsorption Rare Earth Elements in Honghe, South Yunnan, China

围绕国家战略性产业发展对稀土资源的需求,特别是紧缺的重稀土资源,如何快速有效地发现富含重稀土矿床找矿靶区是勘查地球化学急需解决的问题。“化学地球”大科学计划获得全国地球化学基准数据,圈定稀土异常超常富集区9处,其中新发现的滇南红河州蒙自—中越边境地区稀土富集区轻重稀土比值(LREE/HREE)为3.5,与华南富含重稀土的离子吸附型稀土矿异常LREE/HREE比值一致。结合地质背景、成矿母岩、气候和地形地貌特点等初步判断具有寻找类似华南富含重稀土的离子吸附型稀土矿资源潜力。因此,对这一异常的核心区,开展了1:25万、1:5万地球化学调查和风化剖面测量,并经29个钻孔验证,初步发现马鞍底潜在超大型富含重稀土离子吸附型稀土矿。富矿区分布于坡度较缓的坡脚处,风化母岩为印支期和燕山期花岗岩、元古界斜长片麻岩和变粒岩。风化剖面厚度最深可达25 m左右,富矿层位位于全风化层,一般在2~13m深度,矿体平均厚度6~13m,最厚可达21m,平均品位0.14%。根据29个钻孔和84个风化壳剖面测量,初步估算稀土潜在矿石量约9.46亿吨、稀土氧化物潜在资源约100万吨。这是我国首次在滇南地区发现潜在超大型离子吸附型稀土矿。该离子吸附型稀土矿同时富含轻稀土(镧、铈、镨、钕)和重稀土(钆、铽、镝、钇),具有重大经济价值和科学意义。这一发现表明开展从极低密度、低密度到高密度地球化学调查,获得全部16个稀土元素高质量数据是发现离子吸附型稀土矿的快速有效方法。

Rare earth elements(REEs), particularly heavy rare earth elements(HREE), are critically needed by high-tech industries and modern society. Geochemical methods are used in the exploration and delineation of the targets of HREE-enriched deposits. A total of 9 REE-enriched geochemical provinces were delineated throughout China by Mapping Chemical Earth Program-China Geochemical Baselines project. The targets with 3.5 of LREE/HREE, similar to the ion-adsorption HREE-enriched deposits discovered in Huanan, located in Honghe,Yunnan province, southwestern China, were selected for follow-up geochemical surveys at scales of 1:250 000and 1:50 000. A giant ion-adsorbed REE deposit with an ore reserve of 946 million tones and TRE;O;reserve of approximately 1.0 million tones at an average REE grade of 0.14% has been discovered by a drilling program at Maandi, Honghe. The ore bodies hosted in regolith range in depth from 2 m to 13 m, which developed from the parent rocks of Indosinian and Yanshanian granites and Proterozoic gneiss and leptynite, and are distributed at gentle slope areas. This is the first discovery of ion-adsorption REE deposits containing LREE(La, Ce, Pr and Nd)and HREE(Gd, Tb, Dy and Y) with both economic and scientific value in south Yunan, China. This finding shows that global-, regional-to local-scale geochemical surveys by using wide-spaced, low-density and high-density sampling to provide high-quality data of 16 rare earth elements is a cost-effective method to delineate targets for regolith-hosted ion-adsorption HREE deposits.