贵州平坝白云岩风化壳稀土超常富集层中稀土赋存状态的研究  

Occurrence of REE at REE extra-enric hed bed in Pingba dolomite weathering crust,Guizhou Province,China

作　　者：李艳丽[1] 孙承兴[2] 王世杰[1] 刘秀明[1] 

机构地区：[1]中国科学院地球化学研究所环境地球化学国家重点实验室 [2]华东师范大学河口海岸动力沉积和动力地貌综合国家重点实验室,上海200062

出　　处：《地球化学》2004年第6期627-633,共7页Geochimica

基　　金：中国科学院地球化学研究所知识创新工程领域前沿项目(IG0401);国家自然科学基金(4027301540371012);中国科学院"西部之光"资助项目

摘　　要：以平坝白云岩风化壳剖面为例,主要利用化学连续提取的方法,结合透射电镜的分析,对碳酸盐岩风化壳岩-土界面附近的稀土超常富集层中REE的赋存状态进行了研究,获得了REE在水溶态及可交换态(相态Ⅰ)、碳酸盐结合态及专性吸附态(相态Ⅱ)、非晶质氧化铁锰结合态(相态Ⅲ)、晶质氧化铁锰结合态(相态Ⅳ)、有机质及硫化物结合态(相态Ⅴ)和残渣态(相态Ⅵ)等6种相态的含量及变化规律。结果表明,REE在富集层中主要以专性吸附态、残渣态和有机态为主。风化前缘可溶态稀土所占比例较高,为稀土在风化壳中的迁移、转化提供可能;基岩中原生含磷稀土矿物的风化产生的稀土磷酸盐矿物的聚集导致了残渣态稀土大量存在于风化前缘;此外,由于风化淋溶的不断进行,可溶态的REE在高的pH值条件与剖面中的有机质、铁锰氧化物和粘土矿物共同作用下沉淀、富集,也导致了风化前缘稀土的超常富集。Behavior and fractionation of REE at a REE extra-enriched bed near the soil-rock boundary in Pingba weathering profile have been studie d by chemical sequential extraction experiment and TEM observation.REE in the profile was partitioned into six fractions including soluble and exchangeable(Ⅰ),carbonate and adsorbed(Ⅱ),amorphous Fe-Mn oxide(Ⅲ),crystalline Fe-Mn oxide(Ⅳ),organics and sulfide(Ⅴ),and residual(Ⅵ).The statesⅡ,ⅤandⅥprevail at the REE extra-enriched bed.Acid-soluble REEs are dominant in the weathering frontier,making REEs easy to migrate downwards and transfer into other s tates(for example,StateⅡ)during weathering process.The secondary mineral of rare earth phosphates form ed by weathering of primary phosphor-containing mineral in dolomite was f ound to be accumulated in the weathering frontier and was the major compon ents in the stateⅥ.With the progressive weathering an d leaching,the soluble REE leached f rom the upper profile can co-precipitate with organics,Fe-M n oxides and clay minerals under the h igh pH values near soil-rock boundary,leading to the formation of the REE extra-enriched bed at Pingba,Guizhou Province.

关 键 词：碳酸盐岩风化壳 稀土赋存状态 富集层 化学连续提取 贵州省 

分 类 号：P595[天文地球—地球化学]