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 δ 18 O (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 δ 18 O in apatite from syenite and trachyte indicates a contribution from δ 18 O-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.

中文翻译：

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基于阴极发光、LA-ICPMS 和原位 O 和 Sr 同位素分析，揭示控制 Phalaborwa Complex（南非）磷灰石形成的过程

Phalaborwa 世界级磷酸盐矿床（南非）由古元古代碱性杂岩体组成，主要由亚磷铁矿、碳酸岩、辉石岩和次生粉铁矿组成。此外，正长岩和粗面岩出现在许多卫星天体中。新的岩石学和原位地球化学数据以及在磷灰石上获得的 O 和 Sr 同位素数据表明，磷灰石存在于主要由来自地幔的碳酸岩岩浆的火成岩过程形成的主要寄主岩（辉石岩、亚磷铁矿和碳酸岩）中。早期形成的岩浆磷灰石特别富含轻稀土元素 (LREE)，稀土含量下降归因于岩浆分异和孤立的间隙熔袋中的早期磷灰石分馏。在恒定 Sr 同位素组成下，瑞利分馏有利于 δ 18 O（低于 1%）略有增加。新鲜碳酸岩岩浆侵入早期形成的碳酸岩体，局部诱导早期磷灰石重新平衡，稀土元素富集，但 O 和 Sr 同位素组成不变。在铁粉岩、正长岩和粗面岩中，磷灰石显示出蚀变纹理和轻稀土元素消耗，反映了与流体的相互作用。来自正长岩和粗面岩的磷灰石中 δ 18 O 的显着减少表明来自 δ 18 O 耗尽的陨石流体的贡献。这与卫星天体的表带位置是一致的。这些岩石中磷灰石中 Sr 同位素比率的普遍增加反映了随着时间的推移与围岩的逐渐相互作用。这项研究使破译成为可能，具有无与伦比的精度，