云南省澜沧县离子吸附型稀土矿床地质特征分析与成矿过程探讨

云南省澜沧县地处临沧花岗岩的中南段,在其境内发现多地与花岗岩风化壳有关的离子吸附型稀土矿床。文章通过对该区晚三叠世黑云母二长花岗岩风化壳全风化层的剖面及钻孔样品分析,对赋存于花岗岩风化壳离子吸附型稀土矿床的成矿地质地球化学特征进行研究,探讨其关键成矿过程并总结地形地貌与风化壳和矿体露头的关系。研究表明,黑云母二长花岗岩风化壳分层特征明显,离子吸附型稀土矿体规模及形态严格受风化壳发育程度及微地貌控制;花岗岩风化壳全风化层稀土元素配分曲线呈右倾平滑的浅“W”型,轻稀土元素的分异程度强于重稀土元素;除Ce元素外,轻稀土元素的浸出率略高于重稀土元素;矿石类型为以轻稀土元素为主、中重稀土元素配分齐全的混合型稀土矿。通过厘定离子吸附型稀土矿床的关键成矿过程,文章发现内应力、渗透能力、风化程度、黏土矿物含量在风化壳剖面中由上至下变化特征综合决定了稀土矿体主要定位于风化壳全风化层。

Analysis on geological characteristics and discussion about metallogenic process for ion-adsorption type REE deposit in Lancang County, Yunnan Province

Many ion-adsorption type REE deposits were found in Lancang County, Yunnan Province, which is located in the Middle and South section of Lincang granite. Through analyzing the sample data of granite weathering crust section and typical boreholes in the weathering crust of biotite monzogranite about Late Triassic, this paper researches and analyzes metallogenic geology and geochemistry characteristics of ion-adsorption type REE deposits in weathering crust of granites, discusses the key metallogenic processes, summarizes the relationships between landform with weathering crust and ore outcrop. Researches show that the weathering crust of biotite monzogranite has obvious stratification, the size and morphology of ore body are strictly controlled by development degree of weathering crust and microtopography; REE partition curves are showen as "W" shape smoothly, the differentiation degree of LREE is stronger than HREE, and leaching rate of LREE is slightly higher than HREE except Ce; the ore type is a mixed type which is mainly LREE with MREE and HREE all have. Through deciphering the key metallogenic processes ion-adsorption type REE deposits, it is found that the changes of internal stress, permeability, weathering degree and clay mineral content in weathering crust profile from top to bottom determine that the ore body is mainly located in the full weathering layer of weathering crust.