Unravelling the processes controlling apatite formation in the Phalaborwa Complex (South Africa) based on combined cathodoluminescence, LA-ICPMS and in-situ O and Sr isotope analyses

Rare earth element mobility in and around carbonatites controlled by sodium, potassium, and silica

“…Fenites often have lower LREE/HREE ratios (i.e., higher HREE proportions), than their associated carbonatites (10,21,22,24). Given our experimental results, we interpret these field observations as follows.…”

Geochemical and spectroscopic investigation of apatite in the Siilinjärvi carbonatite complex: Keys to understanding apatite forming processes and assessing potential for rare earth elements

“…The magmatic origin of apatite in the glimmerite-carbonatite series is confirmed by the blue cathodoluminescence of this mineral (e.g., Broom-Fendley et al, 2016;Decrée et al, 2016Decrée et al, , 2020Waychunas, 2002), the enrichment in LREE and the lack of complex textures such as turbid or conversion textures under CL (e.g., Broom-Fendley et al, 2017;Zirner et al, 2015). LIBS images of the investigated apatite ore (an apatite-rich carbonatite exploited for its very high P content; Fig.…”

“…These studies constitute important steps towards the understanding of apatite genesis in the Siilinjärvi Carbonatite Complex. However, apatite is typically characterized by small-scale heterogeneities that reveal the complexity of the processes involved in its formation (e.g., Chakhmouradian et al, 2017;Broom-Fendley et al, 2016Decrée et al, 2016Decrée et al, , 2020. Thus, a careful petrographic study and in-situ geochemical analyses are needed to document these textural and chemical variations and to better constrain the sequence of processes in the apatite's genesis explaining the variability of P and REE contents observed within the deposit.…”

“…In amphibole-and pyroxene-rich fenites, apatite displays a complex zonation (alteration and conversion textures), which can be regarded as the product of apatite re-equilibration with highly evolved melts and/or fluids (e.g., Zirner et al, 2015;Broom-Fendley et al, 2017;Chakhmouradian et al, 2017;Decrée et al, 2020). Late-stage interactions with water-rich fluids were already assumed at Siilinjärvi, based on the general tendency of decreasing Sr concentrations with increasing δ 18 O ratios (Tichomirowa et al, 2006).…”

“…With a theoretical maximal content of 3.73 wt% F in apatite, phosphate rocks can contain up to 3-4% F (Notholt et al, 1979). Phosphate formation and accumulation in these rocks can result from various processes that range from magmatic to hydrothermal (metasomatic) to supergene alteration (e.g., Walter et al, 1995;Broom-Fendley et al, 2016Chakhmouradian et al, 2017;Decrée et al, 2015Decrée et al, , 2016Decrée et al, , 2020. These processes also affect the content of other elements (such as F and REE) in apatite, leading locally to significant enrichment and economic potential of these resources as by-product of phosphate production (Ihlen et al, 2014;Decrée et al, 2016).…”