东坪金矿床成矿过程中稀土元素活动性

尽管稀土元素常被认为是惰性元素，但在热液交代蚀变和化学风化作用过程中具有一定程度的活动性，河北省东坪与碱性岩有关的改进改造型热液金矿床成矿过程中，热液蚀变作用使近矿围岩ＬＲＥＥ／ＨＲＥＥ比值增大，并出现现铈正常异常；石英脉型金矿石的稀土元素分布模式呈出现明显的继承性，脉石矿物石英，钾长石的稀土元素组成相对富ＨＲＥＥ，且在脉石石英出现明显的铕正异常，研究结果表明在中，高温，近中性，较高氧逸度成矿流体

RARE-EARTH ELEMENT MOBILITY DURING ORE-FORMING PROCESS OF DONGPING GOLD DEPOSIT

Although the rare-earth elements are often considered to be relatively immobile,they are significantly mobile during hydrothermal alteration, metasomatism and chemical weathering. The investigation on the REE compositions of the source rocks,altered wall rocks, ores and the gangue minerals of Dengping gold deposit suggests that the REE are mobilized and differentiated during hydrothermal alteration. Because of the severe hydrothermal alteration, the altered wall rocks show positive Ce anomaly and higher LREE / HREE ratios comparing to unaltered rocks. The Chondrite-normalized REE patterns of the quartz vein-type gold ores are similar to those of the wall rocks;the gangue quartz and K-feldspar show relative lower LREE / HREE ratios. The most interesting phenomia is that the gangue quartz show significant positive Eu anomalies,while the secondary K-feldspars show less or no positive Eu anomalies. The data derived from this inveshgation and other workers' indicate that the REE are mobile during hydrothermal alteration in the ore-forming process of the Dongping gold deposit under conditions of mid-high temperature, mildly acidic to mildl basic,and high f_o. The REE fluoride complexes and REE fluorocarbonate complexes might be important during the rock-flind interaction, which results in the preferentialy HREE transporting into the fluid phase. Due to the oxidation of part of the Ce~(3+) to Ce~(4+) and Eu~(2+) to Eu~(3+) under high f_o, some of the Ce~(4+) precipitated, whereas Eu~(3+) retains in the fluid rather than into the secondary K-feldspar. Thus the altered wall rocks show HREE depleted patterns and the gangue quartz (hydrothermal fluid) shows HREE enriched patterns.