Abstract The Keivy alkali granite complex, Kola Peninsula, NW Russia, contains numerous Zr-REE-Y-Nb occurrences and deposits, formed by a complex sequence of pegmatitic, hydrothermal and metasomatic processes. The rare-metal rich lithologies have abundant fergusonite-(Y) mineralization. >90 EPMA analyses of fergusonite-(Y) from different occurrences are used to document REE behavior during crystallization and alteration of the mineral. Variations in Y/HREE ratio during growth of fergusonite-(Y) in a pegmatite are explained by a change of the fluorine content in the fluid. Loss of Y and HREE and addition of Ce during alteration are governed by two major processes: Ce accumulation in late derivatives and high F contents in the crystallization environment. The decreases of Ce and other REE in some occurrences resulted from a low F content. The extent of alteration possibly depends on the actinide content in fergusonite-(Y) and the resulting radiation damage. Positive Eu/Eu* anomalies in fergusonite-(Y) from a number of occurrences were due to external contributions of Eu into the fluid from country rocks after the breakdown of plagioclase. The specific REE distribution in fergusonite-(Y) indicates crystallization at low CO2/H2O and changing F activity. A F-rich fluid is suggested during fergusonite-(Y) formation in alkali granite pegmatite and quartzolite, and a low-F fluid is characteristic of minerals from a metasomatite and amazonite pegmatite located in country rocks of alkali granite massifs.

中文翻译：

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俄罗斯西北部 Keivy 碱性花岗岩复合体的富含 Zr-REE-Nb 的晚期岩浆产物到后期岩浆产物中的铁格石-(Y)结晶和蚀变过程中的稀土分馏

摘要 俄罗斯西北部科拉半岛的 Keivy 碱性花岗岩杂岩体包含大量 Zr-REE-Y-Nb 矿点和矿床，由伟晶岩、热液和交代过程的复杂序列形成。富含稀有金属的岩性具有丰富的镁铝榴石-(Y)矿化。来自不同矿点的铁镁铝榴石 (Y) 的 >90 EPMA 分析用于记录矿物结晶和蚀变过程中的 REE 行为。伟晶岩中镁铝榴石-(Y) 生长过程中Y/HREE 比率的变化可以通过流体中氟含量的变化来解释。蚀变过程中 Y 和 HREE 的损失以及 Ce 的添加受两个主要过程的控制：晚期衍生物中的 Ce 积累和结晶环境中的高 F 含量。在某些情况下，Ce 和其他 REE 的减少是由于 F 含量低造成的。改变的程度可能取决于镁铝石-(Y) 中锕系元素的含量以及由此产生的辐射损伤。铁格石-(Y) 中的正 Eu/Eu* 异常是由于斜长石分解后 Eu 进入围岩流体的外部贡献。镁铝榴石-(Y) 中特定的 REE 分布表明在低 CO2/H2O 和变化的 F 活性下结晶。碱性花岗岩伟晶岩和石英岩中的辉格长石-(Y)形成过程中显示出富F流体，低F流体是碱性花岗岩地块围岩中交代岩和天河伟晶岩矿物的特征。铁格石-(Y) 中的正 Eu/Eu* 异常是由于斜长石分解后 Eu 进入围岩流体的外部贡献。镁铝榴石-(Y) 中特定的 REE 分布表明在低 CO2/H2O 和变化的 F 活性下结晶。碱性花岗岩伟晶岩和石英岩中的辉格长石-(Y)形成过程中显示出富F流体，低F流体是碱性花岗岩地块围岩中交代岩和天河伟晶岩矿物的特征。铁格石-(Y) 中的正 Eu/Eu* 异常是由于斜长石分解后 Eu 进入围岩流体的外部贡献。镁铝榴石-(Y) 中特定的 REE 分布表明在低 CO2/H2O 和变化的 F 活性下结晶。碱性花岗岩伟晶岩和石英岩中的辉格长石-(Y)形成过程中显示出富F流体，低F流体是碱性花岗岩地块围岩中交代岩和天河伟晶岩矿物的特征。