重庆南川-武隆铝土矿含矿岩系稀土元素特征及其地质意义

重庆市南川武隆铝土矿是黔中渝南铝土矿成矿带的重要组成部分。为初步查明重庆地区铝土矿稀土元素的地质意义,弥补重庆铝土矿成因研究的不足,笔者以重庆南川武隆铝土矿含矿岩系为研究对象,分析稀土元素(REE)的地球化学特征。通过研究发现,稀土元素总量较高,多数样品轻稀土富集,重稀土不同程度亏损。由于含矿岩系中的REE含量在沉积后只有极微弱的变化,因此利用稀土元素的特征及有关参数对铝土矿含矿岩系的形成环境及其物质来源进行了初步判断:Eu中等负异常,含矿岩系以陆相沉积为主,部分为海相沉积;从含矿岩系样品稀土元素总和、Ce异常、Eu 异常情况来看,含矿岩系形成的古水介质呈弱酸性,含矿岩系主要形成于氧化环境中,氧化能力增强时有利于铝土矿的形成;含矿岩系物质来源具有多样性,志留系韩家店组粉砂质页岩与石炭系黄龙组灰岩均可能为物质来源。

REE Characteristics and Its Geological Significance of the Bauxite Deposits in Nanchuan Wulong Area,Chongqing

The composition of REE in ore bearing rocks of Nanchuan Wulong area indicates that the total amount of REE is high ,and the partition modes in the bauxite‐bearing horizons and in the underlying Silurian Hanjiadian Formation are quite consistent . This implies a genetic relationship between the bauxite source and Hanjiadian Formation .The values of LREE /HREE are great in the majority samples .It is obvious that the light rare earth elements are strongly enriched ;while the heavy rare earth elements are depleted to varied degrees with Eu middle negative anomaly .The content of REE in the ore bearing rocks changed only slightly after deposition .Based on the characteristics of rare earth elements and the related parameters , the environment of bauxite ore bearing rock series and their material sources are deduced as followings :ore bearing rocks were formed mainly in continental facies with some marine sediments ;based on Ce ,Eu anomalies ,acidity of paleo water media was weak ;ore bearing rock series were mainly formed in an oxidation environment , which was profitable for the formation of bauxite .Material sources of the ore bearing rock series are diversified ;both silty shale of Silurian Hanjiadian Formation and Carboniferous limestone of Huanglong Formation might be the source of material .