花岗岩风化壳中Ce地球化学特征及其找矿意义——以滇西岔河离子吸附型稀土矿床为例

近年来,临沧花岗岩体风化壳内离子吸附型稀土(IREE)矿床的找矿勘查取得重要进展,岔河IREE矿床是该区新发现的中大型矿床之一,为IREE矿床成矿预测提供了研究实例.文章对岔河IREE矿床11个探矿工程风化剖面样品和1370件土壤地球化学样品的稀土元素,以及Ce异常分布、迁移及富集等表生地球化学特征和规律进行研究,结合前人研究成果总结出该区找矿模型,实施工程验证并取得了找矿发现.研究表明,风化花岗岩稀土元素配分模式与母岩相似,风化过程中REE发生淋滤、富集作用(全风化层富集程度最高),LREE和HREE发生了分异作用(LREE分异程度相对较高).在风化过程中,Ce异常与稀土元素氧化物总量(ΣREO)呈负相关,且Ce异常存在明显的分异作用,如风化剖面中黏土层Ce正异常(1.69)与全风化层上部Ce负异常(0.75)数值具有明显差异,为Ce异常用于IREE矿床成矿预测成为可能(见矿率达90％).该研究不仅能定位、定量的圈定IREE矿床成矿预测区,而且完善了IREE矿床找矿模型,具有重要的推广和应用价值.

Ce geochemical characteristics of granite weathering crust and its prospecting significance: A case study of Chahe ion adsorption rare earth deposit in western Yunnan

In recent years, great progresses have been achieved in the prospecting and exploration of ion-adsorbed rare earth (IREE) deposits in the weathering crust of Lincang granite. Chahe IREE deposit is one of the newly discovered medium and large deposits in this area, which provides a research example for metallogenic prediction of IREE deposits. This paper studies the epigenetic geochemical characteristics and regular pattern of the distribution, migration and enrichment of rare earth elements and Ce anomalies through 11 weathering profiles sample and 1370 soil geochemical samples of the Chahe IREE deposit. Combined with previous research results, the exploration model for IREE in this area is summarized, target testing has been carried out, and new orebodies are delineated. The results show that the REE distribution pattern of weathered granite is similar to that of its mother rock. REEs are leached and enriched during weathering (the completely weathered layer has the highest enrichment level), and LREE and HREE are differentiated (differentiation of LREE is relatively higher). During the weathering process, the Ce anomaly is negatively correlated with the total amount of rare earth elements, and the Ce anomaly has obvious differentiation. For example, there is significant difference between the positive Ce anomaly (1.69) in the clay layer and the negative Ce anomaly (0.75) in the upper part of the completely weathered layer, which makes it possible for Ce anomaly to be used in the mineralization prediction of IREE deposits (the success rate is up to 90%). This study can not only locate and quantitatively define the high prospective areas of IREE deposit, but also improve the exploration model of IREE deposit, which could be demonstrated and applied to other exploration projects.