滇西临沧花岗岩中段离子吸附型稀土矿成矿特征研究

滇西临沧花岗岩中段岩性主体为黑云母二长花岗岩,是离子吸附型稀土矿的天然成矿母岩。研究区湿热的气候使得在地势相对平缓的中山地区形成巨厚的花岗岩风化带,依据风化程度由地表至基岩依次分为腐殖土层、亚黏土层、全风化层、半风化层、弱风化层和新鲜基岩。全风化层是本区离子吸附型稀土矿的主要赋矿层位,该层位元素地球化学特征显示,经过风化后稀土元素发生了富集和分馏,稀土矿化是以轻稀土为主。轻稀土又以La和Ce这两种元素为主。依据本区不同地貌类型建立了倾缓的山脊、平缓的山顶和低缓的山丘3种离子吸附型稀土矿成矿模式。

Mineralization of the ion adsorption-type REE deposits in the central part of the Lincang granites in western Yunnan

The Late Triassic biotite monzogranites in the central part of the Lincang granites in western Yunnan are considered as the naturally mineralized parent rocks of the ion adsorption-type REE deposits. The hot and humid climatic conditions in this area are responsible for the formation of the tremendous granite weathering crust, and the preservation in the flat terrains, moderate mountains, moderate mountains-hills and intermontane basins in the moderate mountains. The granite weathering crust may be divided, according to the intensity of weathering from the surface to the bedrock, into the humus layer, loam layer, completely weathering layer, locally weathering layer, slightly weathering layer and fresh bedrock. The completely weathering layers occur as the main pay streaks of the ion adsorption-type REE deposits. Geochemically, the weathering processes gave rise to the fractionation and concentration of the rare earth elements, with the stress on the mineralization of light rare earth elements such as La and Ce. Three types of mineralization model for the ion adsorption-type REE deposits are presented here according to the geomorphological types. The majority of the REE ore bodies reside in the gently moderate mountains and moderate mountains-hills in the study area.