中文摘要：

选取新模向斜的一个钻孔剖面，对铝土矿的矿物组成及稀土元素地球化学特征进行了研究。铝土矿矿石矿物以一水硬铝石为主，另有少量一水软铝石。其次为高岭石、绿泥石等黏土矿物，以及少量重矿物。此外，在含矿岩系近底部还发现有富集Ce元素的矿物氟菱钙铈矿[Ce2Ca（CO3）3F2]。从剖面顶部至底部，铝土矿中稀土元素含量呈逐渐增加的趋势，且稀土元素参数La_N／Yb_N、La_N／Sm_N和Gd_N／Yb_N。的数值均随深度逐渐增大。说明从剖面顶部至底部，稀土元素的淋滤迁出逐渐减弱，且稀土元素间存在一定的分异。稀土元素间的分异可能由不同的含稀土元素矿物抗风化淋滤差异所致。铝土矿稀土元素配分模式表现为LREE明显富集、MREE中等一弱富集、HREE相对平坦的特征，且具有明显的正Ce异常。犯e异常值随深度增加逐渐减小，接近含矿岩系底部，δCe异常值再次增大。含矿岩系上部的Ce异常是由氧化条件下Ce3＋向Ce4＋转变并形成方铈矿（CeO2）所致。随着深度的增加，含矿岩系的氧化性逐渐减弱，从而δCe异常值逐渐减小。接近含矿岩系底部，由于氟菱钙铈矿[Ce2Ca（CO3）3F2]的形成，导致δCe异常值再次增大。氟菱钙铈矿的沉淀可通过氟化物络合物（CeF2＋或CeCO3F^0）与Ca2＋和HCO_3^-发生反应来完成。

英文摘要：

The mineralogical composition and rare earth geochemistry （REE） of one drilling profile in Xin- mo syncline have been studied. The main ore mineral is diaspore, with certain boehmite. Clay mineral in- cluding kaolinite and chlorite is a minor mineral constituent. Furthermore, the authors found a significant Ce-bearing mineral that is parisite （Ce2Ca（CO3）3F2） near the bottom of the ore-bearing strata. The sam- ples collected along a vertical profile show a downward enrichment for the REE concentration. A similar enrichment trend is also observed in the value of La_N/Yb_N, La_N/Sm_N and GdN/Yb_N. The above character- istics showed that the REE losses are caused by leaching decreased gradually from the top to the bottom of the profile, and REE exhibited interelemental fractionation during weathering processes. The interelemen- tal fractionation of REE may be attributed to differences of combination between REE and anion complexs. The analyzed samples show similar chondrite-normalized REE patterns, with distinct enrichments of the LREE （La-Nd）, moderate to weak enrichments of MREE （Sin-Ho）, and flat distribution of HREE （Er -Lu）. Meanwhile, remarkable positive Ce-anomalies are also noticeable. The value of δCe decreased downward, and increased again near the bottom of the ore-bearing strata. The positive Ce-anomaly in the uppermost part of the ore-bearing strata has been attributed to the redox change of Ce3＋ to Ce4＋ and the consequent precipitation of cerianite （CeO2）. A decrease of the oxidation downward causes the decrease of the value of δCe. The formation of parisite near the bottom of the ore-bearing strata leads up to the in- crease of the value of 3Ce again. And the precipitation of parisite may occur by the reaction between the fluoride complexs （CeF2＋ or CeCO3F^0） and Ca2＋ and HCO_3^-.