Abstract The Siilinjarvi phosphate deposit (Finland) is hosted by an Archean carbonatite complex. The main body is composed of glimmerite, carbonatite and combinations thereof. It is surrounded by a well-developed fenitization zone. Almost all the rocks pertaining to the glimmerite-carbonatite series are considered for exploitation of phosphate. New petrological and in-situ geochemical as well as spectroscopic data obtained by cathodoluminescence, Raman and laser-induced breakdown spectroscopy make it possible to constrain the genesis and evolution of apatite through time. Apatite in the glimmerite-carbonatite series formed by igneous processes. An increase in rare earth elements (REE) content during apatite deposition can be explained by re-equilibration of early apatite (via sub-solidus diffusion at the magmatic stage) with a fresh carbonatitic magma enriched in these elements. This late carbonatite emplacement has been known as a major contributor to the overall P and REE endowment of the system and is likely connected to fenitization and alkali-rich fluids. These fluids - enriched in REE - would have interacted with apatite in the fenite, resulting in an increase in REE content through coupled dissolution–reprecipitation processes. Finally, a marked decrease in LREE is observed in apatite hosted by fenite. It highlights the alteration of apatite by a REE-poor fluid during a late-magmatic/hydrothermal stage. Regarding the potential for REE exploitation, geochemical data combined with an estimation of the reserves indicate a sub-economic potential of REE to be exploited as by-products of phosphate mining. Spectroscopic analyses further provide helpful data for exploration, by determining the P and REE distribution and the enrichment in carbonatite and within apatite.

中文翻译：

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Siilinjärvi Carbonatite Complex 中磷灰石的地球化学和光谱研究：了解磷灰石形成过程和评估稀土元素潜力的关键

摘要 Siilinjarvi 磷酸盐矿床（芬兰）位于太古代碳酸盐岩复合体中。主体由闪锌矿、碳酸盐及其组合组成。它被一个发达的非尼化区所包围。几乎所有属于闪锌矿-碳酸岩系列的岩石都被考虑用于开发磷酸盐。新的岩石学和原位地球化学以及通过阴极发光、拉曼和激光诱导击穿光谱获得的光谱数据使得限制磷灰石随时间的发生和演化成为可能。通过火成岩过程形成的闪锌矿-碳酸盐系列中的磷灰石。磷灰石沉积过程中稀土元素 (REE) 含量的增加可以通过早期磷灰石（通过岩浆阶段的亚固相线扩散）与富含这些元素的新鲜碳酸岩岩浆重新平衡来解释。这种晚碳酸盐岩侵位被认为是该系统整体 P 和 REE 禀赋的主要贡献者，并且可能与非硝化和富碱流体有关。这些富含 REE 的流体会与磷灰石中的磷灰石相互作用，通过耦合溶解-再沉淀过程导致 REE 含量增加。最后，在由 fenite 承载的磷灰石中观察到 LREE 的显着减少。它强调了在晚岩浆/热液阶段，贫稀土流体对磷灰石的蚀变。关于 REE 开发的潜力，地球化学数据与储量估算相结合，表明 REE 作为磷矿开采的副产品具有次经济潜力。通过确定 P 和 REE 分布以及碳酸岩和磷灰石中的富集，光谱分析进一步为勘探提供了有用的数据。