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In phosphorites, the content and distribution of rare earth elements are linked to the environment of phosphogenesis. This paper focuses on the question of sources and processes controlling the rare earth element content of apatite from Belgian phosphorites formed during three major phosphogenic events in the Lower Palaeozoic, Late Cretaceous and Cenozoic. To constrain sources and processes, new data include petrological, mineralogical (including cathodoluminescence and Raman spectroscopy) and in situ trace element and Sr and O isotope analyses of apatite. Fluorapatite from Lower Palaeozoic P‐rich conglomerates has the greatest rare earth element enrichment. It is affected by metamorphism that led to deformation of apatite nodules and formation of garnet porphyroblast inclusions. The role of Fe‐oxyhydroxides in element scavenging is highlighted by some apatite nodules that maintain their primary middle rare earth element enrichment, while others are characterized by altered rare earth element patterns resulting from competition for these elements between co‐crystallizing minerals during deformation. A systematic shift towards lower δ18O and radiogenic Sr isotopic composition compared to contemporaneous seawater indicate interaction with 18O‐depleted meteoric fluids and a crustal component. By contrast, carbonate‐rich fluorapatite from the Late Cretaceous phosphatic chalk mostly keeps its primary trace element and isotopic signatures (close to seawater), although an external rare earth element addition is noted, as well as rare earth element redistribution induced by diagenetic alteration. Cenozoic carbonate fluorapatite nodules mostly present flat rare earth element patterns that are indicative of a detrital influence. Slight changes in rare earth element distribution are assigned to post‐depositional alteration, which also led to an increase in radiogenic Sr, with unchanged δ18O compared to seawater. The methodology followed here efficiently helps in deciphering the processes that modified the chemistry of apatite in the frame of major phosphogenic events. [ABSTRACT FROM AUTHOR]

The Phalaborwa world-class phosphate deposit (South Africa) is hosted by a Paleoproterozoic alkaline complex mainly composed of phoscorite, carbonatite, pyroxenitic rocks, and subordinate fenite. In addition, syenite and trachyte occur in numerous satellite bodies. New petrological and in-situ geochemical data along with O and Sr isotope data obtained on apatite demonstrate that apatite is in the principal host rocks (pyroxenitic rocks, phoscorite and carbonatite) formed primarily by igneous processes from mantle-derived carbonatitic magmas. Early-formed magmatic apatite is particularly enriched in light rare earth elements (LREE), with a decrease in the REE content ascribed to magma differentiation and early apatite fractionation in isolated interstitial melt pockets. Rayleigh fractionation favored a slight increase in δ18O (below 1%) at a constant Sr isotopic composition. Intrusion of fresh carbonatitic magma into earlier-formed carbonatite bodies locally induced re-equilibration of early apatite with REE enrichment but at constant O and Sr isotopic compositions. In fenite, syenite and trachyte, apatite displays alteration textures and LREE depletion, reflecting interaction with fluids. A marked decrease in δ18O in apatite from syenite and trachyte indicates a contribution from δ18O-depleted meteoric fluids. This is consistent with the epizonal emplacement of the satellite bodies. The general increase of the Sr isotope ratios in apatite in these rocks reflects progressive interaction with the country rocks over time. This study made it possible to decipher, with unmatched precision, the succession of geological processes that led to one of the most important phosphate deposits worldwide. [ABSTRACT FROM AUTHOR]

[Display omitted] • This study focuses on apatite in the Niutitang formation. • Petrological and geochemical in-situ study helps deciphering its genesis. • A hydrothermal contribution is evidenced. • Element sources are better constrained. The Early Cambrian Mo-Ni-PGE sulphidic black shale in the Niutitang Formation on the margin of the Yangtze Craton (Southern China) is known for its extremely high metal concentrations. It is also very rich in phosphate that formed contemporaneously with the sulphides. Detailed petrological as well as in-situ trace element and Sr isotope analyses of authigenic apatite revealed new information on the metallogenesis of this enigmatic rock unit. In the ore bed, apatite forms nodules or is found in phosphatic (phoslithoclasts) and sulphide clasts. In the latter, the replacement of organic matter and sulphides by apatite microspherules suggests a microbially mediated phosphogenesis. Enrichment in middle rare earth elements emphasizes the role played by Fe-oxyhydroxides and organic matter in element scavenging. Moderately reducing conditions are supported by a lack of Ce and Eu anomalies. The trace element signature of apatite and its initial 87Sr/86Sr (0.7032–0.7190), which is - for a group of analyses - well below the signature of Lower Cambrian seawater, points to some contribution from mafic rock-sourced hydrothermal brines. This effectively explains the exceptional enrichment of Ni and PGE in the sulphides. Seawater remains, however, the preferred source for other elements such as P and Mo. [ABSTRACT FROM AUTHOR]

The Siilinjärvi 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. • This study focuses on apatite and its REE content at Siilinjärvi (Finland). • Petrological and geochemical study helps deciphering its genesis. • Igneous processes and metasomatic alteration are evidenced. • A sub-economic potential of REE to be exploited as by-products is considered. [ABSTRACT FROM AUTHOR]