江西某离子吸附型稀土矿床元素地球化学行为及成矿机理

Located in the east of Nanling W-Sn-Mo-Be-REE-Pb-Zn-Au metallogenic belt, An certain iron-absorbed type REE deposit is a LREE-type ore deposit of granite genesis, and the orebody occurs in the completely weathered layer of biotite moyite. The latest study shows that the weathered crust of HREE distribution type is developing in the plane and vertical of the deposit, attaining the industrial grade. However, the characteristics of spatial distribution,the formation process and the mechanism of REE redistribution and so forth concering LREE and HREE distribution-type weathered crust are yet to be clear. Taking the weathered crust of LREE and HREE and related granites of this iron-absorbed REE deposit as research subjects, this application is to identify the combination, content, ingredient, stability and evolutional characteristics of minerals of REE carrier(primary minerals,clay minerals after weathering and residual minerals containing REE in bedrock) in each layer of weathered crust profile, analyze the enrichment and impoverishment discipline of major element, trace element and rare element of the weathered-layer profile, and also discuss the metallogenic mechanism of ore-bearing LREE or HREE, for the purpose of providing the reference to mechanism of regional iron-absorbed type REE deposit of the same kind and guidance on the prospecting of iron-absorbed type REE deposit.

江西某离子吸附型稀土矿床位于南岭W-Sn-Mo-Be-REE-Pb-Zn-Au成矿带东段，为花岗岩成因的轻稀土型矿床，矿体赋存在黑云母钾长花岗岩全风化层中。最新的研究发现，该矿床平面上和垂向上均发育重稀土配分型风化壳，并已达到工业品位。但是轻、重稀土配分型风化壳的空间分布特征、形成过程以及稀土元素再分配的机理等科学问题尚未理清。本申请拟以该离子吸附型稀土矿床中的轻、重两类稀土配分型风化壳及基岩为研究对象，查明基岩和风化壳各层中稀土载体矿物组合、含量、成分、风化程度及演变特征；分析风化壳中主要元素、微量元素和稀土元素的富集与贫化规律；探讨轻、重稀土成矿机理，为区域上同类离子吸附型稀土矿成矿机制提供参考，也为离子吸附型重稀土矿床的勘查提供指导作用。

江西某离子吸附型稀土矿床较为特殊，不仅富集轻稀土（LREE）而且富集重稀土（HREE），不同于南岭典型的重稀土矿床（足洞）和轻稀土矿床（河岭），然而此类矿床的成矿机制并不清楚。本项目对寨背成矿花岗岩和风化壳进行了岩石学、稀土矿物学及地球化学特征研究，结果表明花岗岩由内部相的粗粒黑云母二长花岗岩、角闪黑云石英二长岩（少量），过渡相的中粒黑云母二长花岗岩和边缘相的细粒似斑状黑云母花岗岩、细粒白云母花岗岩组成，局部见花岗斑岩。从岩体的内部至边部，SiO2含量（62%~77%）逐渐升高，Al2O3、TiO2、MgO、FeO、CaO 含量逐渐降低，铕负异常增大，LREE/HREE比值降低（5~0.29），微量元素Zr、Hf、Sr、Ba含量降低，Rb、Cs、Nb含量增高，暗示岩浆演化经历了连续的分离结晶作用；稀土矿物组合分别为榍石-褐帘石-独居石-氟碳铈矿-钍石-水磷铈矿，褐帘石-独居石-磷钇矿-氟碳铈矿-钍石-水磷铈矿，磷钇矿-新奇钙钇矿-氟碳钇铈矿-富稀土钍石-水磷钇矿，其中榍石、褐帘石、独居石及磷钇矿等岩浆结晶的稀土矿物主导岩浆作用中稀土元素的地球化学行为，而稀土氟碳酸盐矿物的大量出现说明岩体遭受了富F、CO2、REE等成分的流体的强烈交代，交代作用使稀土元素发生了显著的富集。表生过程中，含榍石、褐帘石、氟碳铈矿等稀土矿物的内部相和部分过渡相花岗岩（LREE型）风化、解离为离子相LREE提供了物质来源，而含新奇钙钇矿、富稀土钍石、氟碳钇铈矿等矿物的边缘相花岗岩（HREE型）和花岗斑岩（富Y的LREE型）风化提供了丰富的离子相HREE。风化程度影响稀土元素的次生富集强度，当风化蚀变指数（CIA）介于75%~85%时，寨背花岗岩风化壳最有利于成矿。