广西崇左地区火山岩风化壳离子吸附型稀土矿床地质特征及成因

Characteristics and genesis of ion-adsorbed rare-earth deposits in volcanic weathering crust in Chongzuo area of Guangxi

广西的中酸性火山岩风化壳离子吸附型稀土矿床主要分布在桂西南崇左至凭祥一带,是一种非常具有找矿前景的矿床类型。文章从成矿母岩地球化学特征、风化壳结构特征、矿床地质特征及稀土元素配分等方面,对广西崇左地区火山岩风化壳离子吸附型稀土矿床的成因进行探讨。本区广泛分布的早三叠世中酸性火山岩稀土元素丰度高,在亚热带季风气候条件以及地表水和地下水的综合作用下发生分解,使原岩中的稀土元素在风化壳中发生迁移,并在全风化层的中下部至半风化层的顶部富集成矿,矿石稀土元素配分类型呈轻稀土富集的右倾型分布且Eu呈明显负异常。

The ion-adsorbed rare-earth deposits in the weathering crust of intermediate-acid volcanic rocks in Guangxi are mainly distributed in the Chongzuo-Pingxiang area of southwestern Guangxi,which is a very prospecting type.In this paper,the genesis of ion-adsorbed rare-earth deposits in volcanic weathering crust in Chongzuo area of Guangxi is discussed in terms of geochemical characteristics of ore-forming parent rocks,structural characteristics of weathering crust,geological characteristics of ore deposits and distribution of rare-earth elements.The Early Triassic intermediate-acid volcanic rocks widely distributed in this area are rich in rare-earth elements,which are decomposed under the combined action of subtropical monsoon climate conditions and surface water and groundwater,and made a migration of rare-earth elements of the original rocks in the weathering crust.In consequence,the rare-earth elements enrich and mineralize from the middle and lower part of the whole weathering layer to the top of the semi-weathering layer.The chondrite-normalized REE distribution curves of ores belong to the right-leaning type of light rare-earth enrichment and Eu show obvious negative anomaly.