# Solubility of monazite-cheralite and xenotime in granitic melts, and experimental evidence of liquid-liquid immiscibility in concentrating ree

Marieke van Lichtervelde, Philippe Goncalves, Aurélien Eglinger, Aurélia Colin, Jean-Marc Montel, Nicolas Dacheux

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## To cite this version:

Marieke van Lichtervelde, Philippe Goncalves, Aurélien Eglinger, Aurélia Colin, Jean-Marc Montel, et al. Solubility of monazite-cheralite and xenotime in granitic melts, and experimental evidence of liquid-liquid immiscibility in concentrating ree. Journal of Petrology, 2021, 62 (8), egab020 [20 p.]. 10.1093/petrology/egab020. hal-04704225

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Submitted on 6 Mar 2025

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# Solubility of Monazite-Cheralite and Xenotime in Granitic Melts, and Experimental Evidence of Liquid-Liquid Immiscibility in Concentrating REE

Running title: Monazite-Cheralite Solubility

Marieke Van Lichtervelde¹, Philippe Goncalves², Aurélien Eglinger³, Aurélia Colin¹, Jean-Marc Montel³, Nicolas Dacheux⁴

¹Géosciences Environnement Toulouse, Université de Toulouse, CNES, CNRS, IRD, UPS, 31400 Toulouse, France

²Chrono-environnement, Université de Bourgogne-Franche-Comté, 16 route de Gray, 25030 Besançon, France

³GeoRessources, CNRS, Université de Lorraine, CREGU, 54506 Vandœuvre-lès-Nancy, France

⁴ICSM, Univ Montpellier, CEA, CNRS, ENSCM, Site de Marcoule, Bagnols sur Ceze, France

## ABSTRACT

We provide new experimental data of monazite, xenotime and U-Th-bearing cheralite solubility in slightly peralkaline to peraluminous granitic melts using dissolution and reverse (i.e., recrystallisation after dissolution) experiments in water-saturated and flux-bearing (P+F+Li) granitic melts, at 800°C and 200 MPa. Although a positive correlation between REE solubility and melt peralkalinity is confirmed, monazite solubilities reported here are much lower than the values previously published. We suggest that the presence of elevated phosphorus concentrations in our melts depresses monazite solubility, principally because phosphorus complexes with Al and alkali which normally depolymerise the melt through the formation of non-bridging oxygens. The new solubility data provide an explanation for the very low REE concentrations generally encountered in phosphorus-bearing peraluminous
granites and pegmatites. This accounts for the compatibility of REE in peraluminous systems,
as the early crystallisation of REE-bearing minerals (mainly monazite and zircon) leads to
progressive REE depletion during liquid differentiation.

In addition, dissolution and reverse experiments of U-Th-bearing cheralite-monazite
display liquid-liquid immiscibility processes in our slightly peralkaline glass. The immiscible
liquid forms droplets up to 10 µm in diameter and hosts in average 35 wt.% P₂O₅, 25-30 wt.%
F, 22 wt.% Al₂O₃, 4 wt.% CaO, 5 wt.% Na₂O, 2 wt.% La₂O₃, and 12 wt.% ThO₂+UO₂. We
believe that the droplets formed during the runs and may have coalesced to larger droplets
during quenching. We suggest that liquid-liquid immiscibility is a possible mechanism of
REE concentration in highly-fluxed melts and should be considered in natural systems where
REE are extremely concentrated (up to thousands of µg/g) in magmatic rocks.

**Key Words:** dissolution experiments; granitic melts; liquid-liquid immiscibility; monazite-cheralite solubility; pegmatites

INTRODUCTION

Rare metal concentrations and enrichment processes in crustal melts are mainly controlled by accessory minerals that include, for the most common, zircon (Zr, Hf and the rare-earth elements REE), monazite (U, Th and the light rare-earth elements LREE), allanite (REE), xenotime (Y and the heavy rare-earth elements HREE) and Ti-Nb-Ta-oxides (Poitrasson et al., 2002; Linnen et al., 2015). These accessories, most of which constitute strategic mineral resources, are mainly hosted by igneous rocks such as carbonatites, peralkaline silicate rocks, peraluminous granites and pegmatites (Chakhmouradian & Zaitsev, 2012; Linnen et al., 2015). In order to better constrain rare metal fractionation processes by accessory minerals in magmatic systems, extensive experimental data are needed to document mineral solubilities in
magmas, crystallisation kinetics and mineral-melt partition coefficients.

The rare-earth element phosphates monazite and xenotime are the main controllers of REE evolution in Ca-poor granitic melts, through monazite fractionation, which is LREE (La to Eu) selective, and xenotime fractionation, which is HREE (Gd to Lu) selective (Duc-Tin & Keppler, 2015). Moreover, magmatic monazite contains elevated ThO₂ concentrations (commonly up to 10 wt.%, but occasionally much more, e.g., Montel et al., 2018) and a small amount of UO₂ (commonly thousands of µg/g, and occasionally above 1 wt.%, e.g., Xing et al., 2013) so it also controls U/Th fractionation in granitic melts (Stepanov et al., 2012). Monazite and xenotime are ubiquitous in most granite compositions ranging from peralkaline to peraluminous, with allanite being present only in Ca-rich granites.

A number of experimental studies have investigated monazite solubility and mineral-
melt partitioning in granitic melts (Montel, 1986; 1993; Rapp & Watson, 1986; Rapp et al.,
1987; Keppler, 1993; Wolf & London, 1995; Skora & Blundy, 2012; Stepanov et al., 2012;
Xing et al., 2013; Duc-Tin & Keppler, 2015; Rusiecka & Baker, 2019; see compilation of
experimental conditions in Table 1). In contrast, xenotime (YPO₄) solubility has been
investigated only recently (Duc-Tin & Keppler, 2015; Rusiecka & Baker, 2019). These
experimental datasets showed that the main controlling parameters of REE-phosphate
solubility are temperature and liquid composition. The alumina over alkali ratio
(ASI=Al/[Na+K+Ca]) is the most important compositional parameter. At 800°C and 200
MPa, peralkaline (ASI<1) melts can dissolve up to thousands µg/g REE (Montel, 1993),
whereas peraluminous melts (ASI>1) dissolve only a hundred µg/g REE (Montel, 1993;
Stepanov et al., 2012; Duc-Tin & Keppler, 2015). The experimental solubility data are in
agreement with natural granite compositions, which display thousands µg/g REE in
peralkaline granites, and a few tens of µg/g REE in peraluminous granites (Fig. 1; Linnen &
Cuney, 2005).
Peraluminous granites are generally associated with intermediate to high phosphorus concentrations, ranging from 0.1 to 1.7 wt.% P₂O₅ (Linnen & Cuney, 2005). A compilation of the literature data (Fig. 1 and Annex Table) reveals a negative correlation between REE and P₂O₅ concentrations in bulk rock granites. The highest REE concentrations in peraluminous granite (~100 µg/g) are associated with the lowest P₂O₅ concentrations (<0.1 wt.%), and peralkaline granites, which are strongly enriched in REE (>1000 µg/g), are depleted in P. Despite their low REE concentrations in whole-rock, high-P peraluminous granites contain monazite and xenotime (Breiter *et al.*, 2007), which means that their parental melts were saturated in these minerals. Therefore, high phosphorus concentrations seem to have a strong negative impact on monazite and xenotime solubilities. However, solubility data in P-rich melts are missing. This study aims at filling this gap.

Our study brings new experimental data for monazite and xenotime solubility in slightly peralkaline to peraluminous systems using dissolution experiments in water-saturated and both flux-poor and flux-rich (P+F+Li) granitic melts. High F+Li flux contents were used in addition to phosphorus to increase crystallisation kinetics and cation diffusivity, and to avoid analytical problems associated with diffusion profiles caused by the slow REE diffusivity in melts. The experiments were designed first to feed a global monazite and xenotime solubility database for a variety of starting glasses and crystals, and second, to investigate the effect of elevated phosphorus contents on monazite solubility. The high F+Li compositions also allow interpreting monazite solubility results in evolved granitic and pegmatitic environments. A major observation in some experiments is the occurrence of liquid-liquid immiscibility, which allows questioning the role of liquid-liquid immiscibility processes in concentrating the REE in evolved granitic and pegmatite-forming melts.

## PREVIOUS WORK
Major studies that present monazite solubility data are compiled in Table 1 and all the data at 800°C and 200 MPa are summarized in Figure 2. Montel (1986) first showed the effect of melt composition on synthetic Ce-monazite solubility using both dissolution and crystallisation experiments. He defined monazite solubility as the REE concentration in the melt based on the monazite dissolution reaction

$$REEPO_{4(\text{monazite})} \rightarrow REE^{3+}_{\text{melt}} + PO_{4}^{3-}_{\text{melt}} \quad (1)$$

which has an equilibrium constant $K_{REEPO4} = a_{REE}^{\text{melt}} \cdot a_{PO4}^{\text{melt}} / a_{REEPO4}^{\text{monazite}}$

Since $a_{REEPO4} = 1$ for pure minerals, $K_{REEPO4} = \gamma_{REE}^{\text{melt}} \cdot \gamma_{PO4}^{\text{melt}} \cdot [REE] \cdot [PO_4]$ where $\gamma$ are the respective activity coefficients. If REE and PO₄ melt concentrations are low (i.e., at trace level), Henry's law applies and $\gamma_{REE}^{\text{melt}} \cdot \gamma_{PO4}^{\text{melt}}$ is constant and close to 1. So the equilibrium constant can be approximated by $[REE] \cdot [PO_4]$, and monazite solubility can be approximated by $K_{REEPO4} = [REE] \cdot [PO_4]^{\gamma_{REE}^{\text{melt}} \cdot \gamma_{PO4}^{\text{melt}}}$ conditioned to the constant concentration of PO₄³⁻ in the melt.

Montel (1986) measured compositions at 800°C and 200 MPa and found as low as 300 µg/g Ce for ASI=1.1 (EMPA measurements with detection limit of 130 µg/g). Rapp & Watson (1986) reported solubility data for natural monazite at higher P (800 MPa) and T (1000-1400°C) using diffusion profiles. Their results extrapolated at 800°C gave $\Sigma LREE$ values of ~200 µg/g for a melt composition of ASI=1.16. A subsequent study by Rapp *et al.* (1987) further investigated the role of melt composition on REE solubility between ASI 0.7 and 1.1, and obtained constant REE saturation values of several hundreds µg/g between metaluminous and peraluminous compositions at 800 MPa and 850°C. Montel (1993) compiled the existing experimental data and proposed an equation describing the solubility of monazite in Ca-Fe-Mg-poor felsic melts depending on T, H₂O concentration and a compositional parameter D defined as $(Na+K+Li+2Ca)/Al \cdot (Al+Si)$ (elements in at%). This equation predicts a continuous evolution of solubility with ASI both in the peralkaline and the peraluminous fields. He also showed that all LREE-phosphates (La to Sm) have similar
solubilities, which was latter contradicted by Duc-Tin & Keppler (2015). Skora & Blundy (2012) investigated monazite solubility at high pressure (3 GPa) relevant to subduction zone conditions. They showed that monazite at these conditions dissolves predominantly as its dissociated constituent ions (LREE³⁺ and PO₄³⁻) in contrast to low pressure conditions relevant to granitic systems, where it dissolves as molecular LREEPO₄ species, independently of the amount of P dissolved in the melt. Stepanov *et al.* (2012) conducted crystallisation experiments of monazite from doped synthetic melts with the goal to determine mineral-melt partition coefficients for a large number of trace elements. They showed a decrease of monazite solubility with increasing pressure and proposed an equation that relates the solubility to H₂O contents, *P* and *T* for pressures above 1 GPa and peraluminous compositions. Duc-Tin & Keppler (2015) investigated the solubility of monazite- to xenotime-structured phosphates for individual rare-earth elements in water-saturated melts at 800-1100°C and 200 MPa. They showed that the solubility of monazite and xenotime does not change significantly in peraluminous melts, and fluorine has no major effect on solubility. They point out the relevance of taking phosphorus into account as solubility decreases with increasing P concentration in the melt, due to the dissolution of monazite as ionic species LREE³⁺ and PO₄³⁻ at low P₂O₅ concentrations, and as GdPO₄ molecules at high P₂O₅ concentrations (1.5 wt.%). Finally, Rusiecka & Baker (2019) conducted monazite and xenotime dissolution experiments in hydrous, boron-bearing metaluminous rhyolite melts at 1000–1400 °C and 800 MPa. They showed that xenotime and monazite solubilities are similar, and concluded that the equilibrium crystallisation of one or the other mineral only depends on the availability of LREE and Y+HREE.

Among all these experimental studies, Duc-Tin & Keppler (2015) more precisely investigated the influence of phosphorus on monazite and xenotime solubility. However, their P-rich experiments were run with peralkaline to metaluminous starting glasses (ASI ~1, or *D*
~1.2). Consequently, solubility data at high P concentrations in peraluminous glasses are still needed. This is particularly important since phosphorus is known to polymerise the melt by complexing with Al in peraluminous melt compositions (Mysen et al., 1999).

## EXPERIMENTAL TECHNIQUES AND ANALYTICAL METHODS

For dissolution experiments three types of materials were used : i) pure synthetic monazite and xenotime ($LaPO_4$, $CePO_4$, $NdPO_4$, $SmPO_4$, $YPO_4$) previously used by Montel (1986; 1993), ii) natural Manangotry monazite with the composition

$Ce_{0.4}La_{0.2}Nd_{0.15}Pr_{0.05}Ca_{0.05}Th_{0.15}PO_4$ (Montel *et al.*, 2018) and iii) synthetic crystals of the monazite-cheralite solid solution containing 0.5 apfu La(+Eu), 0.25 apfu Ca and various proportions of Th and U ($[La,Eu]_{0.5}Ca_{0.25}[U,Th]_{0.25}PO_4$) (see Annex for synthesis procedure). The later material is made of very small (<1 µm) sintered crystals of anhedral shape. The U-Th-bearing monazite-cheralite solid solutions were used to measure saturation values for REE in the presence of other mineral constituents that are not Essential Structural Constituents (ESC) of monazite (e.g., Ca, U and Th). In some experiments, newly-formed, euhedral monazite-cheralite crystals form at the expense of the starting sintered crystals; in that case, we refer to reverse experiments.

Four types of starting glasses were used (Table 2): one natural obsidian and three synthetic glasses. The obsidian is metaluminous in composition, and the synthetic glasses are peraluminous and slightly peralkaline, and correspond to the peraluminous glass B ($ASI_{Li} = 1.16$) and the peralkaline glasses C and D ($ASI_{Li} = 0.8$, with different Na/K ratios) of Van Lichtervelde *et al.* (2010). Those glasses were synthesised from reagent grade oxides and carbonates (high purity $SiO_2$, $Al_2O_3$, $Na_2CO_3$, $K_2CO_3$, $Li_2CO_3$, $AlF_3$, $[NH_4]H_2PO_4$), then finely ground in agate mortars, and melted for 2h at 1600°C and atmospheric pressure. Such high temperature inevitably provoked the loss of some lithium and fluorine but it permitted to
obtain relatively homogeneous glasses without a second melting process.

Approximately 0.4 mg of powdered (<50 µm) fragments of sintered crystals were loaded in gold capsules (15 mm long, 2.8 mm i.d., 3.0 mm o.d.) with ~40 mg of powdered (<50 µm) glass and ~3 mg of distilled water (corresponding to a H₂O concentration of ~7 wt.%, which is close to saturation in those melts, Van Lichtervelde *et al.*, 2010). In one experiment (Gu17), a large (~500 µm in size) fragment of sintered monazite-cheralite was loaded at the capsule bottom; that run aimed at measuring diffusion profiles for REE-U-Th in the melt in order to estimate the attainment of equilibrium in our experiments (see discussion). Capsules were sealed using a precision welder under argon and their weight was checked at all stages of preparation. Experiments were conducted for 14 days at 800°C and 200 MPa in cold-seal pressure vessels (CSPV) at the GET laboratory, Université de Toulouse. In CSPVs, fO₂ conditions are close to Nickel-Nickel Oxide buffer (Matthews *et al.*, 2003). The CSPV setup did not allow rapid isobaric quenching, but the quenching in a stream of air was fast enough (4-5 min) to prevent the formation of quench phases. This quench rate is referred to normal quenching in the following. Temperature was measured with a NiCr-Ni (type K) thermocouple inserted in a hole at the bottom of the vessel, which allows temperature measurement during quenching. Quenching was non-isobaric, but this should have had no significant effect on the experimental charges because the pressure only dropped to 170 MPa by the time the temperature dropped below 500°C, which is the glass transition for our glasses.

In order to test the influence of quenching on immiscible droplet formation, two experiments (Gu13 and Gu14) were duplicated with isobaric quenching at a higher quench rate (<1 min, referred to as rapid quench in the following) at the Mineralogy Institute of Hannover, and the differences in the final products are discussed below (only Gu14b was analysed for major and trace elements). Finally, in order to bring evidence of equilibrium
attainment during dissolution and reverse experiments, one crystallisation experiment
(Gu14X) of monazite-cheralite was run from a homogeneous La-Ca-U-Th-doped glass.

Peralkaline glass was remelted for 1h at 1400°C and atmospheric pressure in the presence of small amounts of powdered monazite-cheralite (La<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.125</sub>U<sub>0.125</sub>PO<sub>4</sub>). The doped glass major element composition is close to that of the starting glass and its trace element composition is 750 µg/g Ca, 1500 µg/g La, 700 µg/g U and 700 µg/g Th (glass homogeneity was checked under SEM). The experiment is hence equivalent to run Gu14. It was conducted during 3 weeks at the same conditions (800°C and 200 MPa) as the dissolution experiments.
The different crystal-glass combinations are presented graphically in Figure 3.

Before mounting them for polished sections, the capsules were cut perpendicular to their long axis (that was horizontal in the furnace) because the low viscosity of our melts allows the largest crystals to fall down at the capsule bottom (see Fig. 4b).

Experimental products were imaged by backscattered electron imaging with a JSM 6360
Scanning Electron Microscope (SEM). Glass major element composition was analysed by
electron probe microanalyses (EPMA), using 15 keV, 10 nA, 20 µm defocused beam, 10–20 s
counting times, PAP matrix correction, and standardisation on albite, wollastonite, Al₂O₃,
orthoclase, SrF₂ and apatite. Trace element (REE, Ca, U, Th) concentrations were measured
by LA-ICPMS at the laboratoire Magmas et Volcans Clermont-Ferrand (France). The
analyses involved the ablation of glass with a Resonetics Resolution M-50 powered by an
ultra short pulse ATL Atlex Excimer laser system operating at a wavelength of 193 nm and
2.8 J/cm² fluence. Spot diameters of 25 µm and repetition rates of 2 to 3 Hz were used. The
ablated material was carried in helium, and then mixed with nitrogen and argon, before
injection into the plasma source of an Agilent 7500 cs ICP-MS. Data are corrected for
fractionation occurring during laser sampling and for instrumental mass discrimination (mass
bias) by standard bracketing with repeated measurements of NIST SRM 610 and NIST SRM
612 standards. The internal standard was 27Al measured by EPMA. Data reduction was
carried out with the software package GLITTER® (van Achterbergh et al., 2001). Crystal
relics were spaced large enough to ensure large (>50 µm) glass pools to be properly analysed
with a 25 µm spot size. One-sigma analytical error is < 1 µg/g, and standard deviation on a
minimum of 8 analytical points is < 5 µg/g. Li2O and Na2O concentrations were also
measured by LA-ICPMS using NIST 610 and 612 standards. For Na2O, EPMA results are
systematically lower than the LA-ICPMS results, which is explained by Na loss under the
electron beam, which cannot be fully corrected. Therefore, Na2O concentrations by LA-
ICPMS were used for the calculation of ASI or D parameter (Na+K+Li+2Ca) / Al·(Al+Si).
The composition of the monazite-cheralite crystals in the experimental products was checked
by Field Emission Gun EPMA (Cameca SXFive-FE, Université de Toulouse) using
instrumental conditions of 10 keV and 20 nA (excitation volume of 900x600 nm). Standards
are wollastonite (Ca, Si), LaPO4, EuPO4, ThO2 and UO2. The immiscible droplets were
imaged under Field Emission Gun SEM using a JSM 6700F instrument, and analysed using
the glass setting of the EPMA (15 kV, 10 nA, 5 µm beam) to which we added the elements of
the monazite setting.

RESULTS

Experimental products

The experimental products consist of REE-phosphate crystals disseminated in bubble-rich
glass (Fig. 4, Table 3). Bubbles are thought to form by aqueous fluid exsolution during
normal quenching; they are absent in the duplicated experiments with rapid quench. Glass
chemical compositions are shown in Table 4 (major elements) and Table 5 (trace elements),
whereas Table 6 shows the chemical compositions of the monazite-cheralite crystal products.

*Experiments with powdered crystals*
Sixteen experiments were run with powdered crystals: Gu1 to Gu14, Gu18 and Gu19. In most of these experiments, the crystals are disseminated through the glass (Fig. 4a), but in some runs, crystals sank down the capsule (Fig. 4b). In peraluminous glass and metaluminous natural obsidian, crystals are angular, showing no evidence of extensive dissolution, except in the experiments with monazite-cheralite (runs Gu18 and 19), where the crystal fragments are rounded with extensive dissolution along grain boundaries (Fig. 4c and close-up). In experiments with the peralkaline glass and pure monazite, the crystals are angular, whereas the experiment with natural monazite (Gu9) displays rare, rounded monazite grains that accumulated at the capsule bottom. The experiments with the peralkaline glass and monazite-cheralite (Gu13 and 14) show rounded aggregates of euhedral monazite-cheralite crystals. These are interpreted as newly-formed monazite-cheralite that replaces the starting material (Fig. 4d-e).

All experiments with natural Manangotry monazite (and also expectedly with pure REEPO₄) display crystal compositions similar to the starting materials (Table 3). In dissolution experiments of monazite-cheralite in peraluminous glass, the crystals are partly dissolved and their chemical composition remains close to the starting material (e.g., Gu19; Fig. 5 and Table 6). In peralkaline glass (Gu13 and 14), monazite-cheralite is fully re-crystallized, with a Th(+U)+Ca loss and a REE gain (only for La, interestingly, and not for Eu, see Table 6). For the two starting monazite-cheralite compositions, either (La,Eu)₀.₅Ca₀.₂₅Th₀.₂₅PO₄ or La₀.₅Ca₀.₂₅Th₀.₁₂₅U₀.₁₂₅PO₄, the new composition is (La,Eu)₀.₇Ca₀.₁₅Th₀.₁₅PO₄ and tends toward a pure Th-bearing and U-free monazite composition (Fig. 5).

Experimental glass compositions are homogeneous, and their major element contents are close to those of the starting glasses (compare Tables 2 and 4). Trace element concentrations measured by LA-ICPMS are homogeneous through the experimental glasses
and they are not higher next to the crystals, which excludes the development of diffusion profiles in these experiments, even in the experiments where the crystals accumulated at the capsule bottom wall.

## Experiment with a large fragment of monazite-cheralite (Gu17)

One experiment (Gu17) with a large fragment of sintered crystals aimed at estimating the diffusion-controlled distribution of REE in peralkaline glass away from the fragment rims, as shown in Figure 4f. The large fragment of sintered material is replaced by an aggregate of small (<10 µm) euhedral monazite-cheralite crystals with rare uraninite grains (Fig. 4f). The close-up of Figure 4f shows that uraninite encloses anhedral monazite-cheralite grains that probably belong to the initial sintered material, whereas the euhedral shape of the other grains is evidence of their neoformed nature. The sintered monazite-cheralite is partially re-equilibrated and its composition slightly deviates from the starting product composition (Table 6). Five concentration profiles were completed in the glass, at different angles from the main fragment elongation. They follow three distinct exponentially fitted equations, with contrasting intercept values for U (1700 to 2500 µg/g), Th (440 to 600 µg/g) and La (40 to 50 µg/g) (Fig. 6).

## Crystallisation experiment (Gu14X)

In order to show that the newly-formed monazite-cheralite crystals of our reverse experiments are in equilibrium with the glass (runs Gu13 and Gu14), one crystallisation experiment of monazite-cheralite (Gu14X) was run from a homogeneous La-Ca-U-Th-doped glass. The experimental product consists of abundant small (~1 µm) crystals in bubble-rich glass (Fig. 7g). The crystal density does not allow proper analysis of the glass by LA-ICPMS, and the EPMA detection limit for La (200 µg/g) is too high to estimate solubility values. However, the crystals can be analysed by FEG-EPMA. The composition of the crystals is very homogeneous and corresponds to a monazite-cheralite composition of La<sub>0.7</sub>Ca<sub>0.15</sub>Th<sub>0.15</sub>PO<sub>4</sub>
similar to the crystal products of Gu14 (Table 6).

*Evidence of liquid-phase separation*

In the experiments with peralkaline glass and monazite-cheralite (Gu13 and Gu14), perfectly rounded droplets, 3-6 µm in diameter and lighter in BSE images, are disseminated in the glass (Fig. 7a-d). The droplets are also present in the duplicated experiments (Gu13b and Gu14b) with rapid quench, although they are much smaller (<1 µm, Fig. 7e-f). In Gu13 and Gu14, they reveal extremely high contents of P₂O₅ (~36 wt.% in average), F (~24 and 28 wt.%), ThO₂ (~7 and 11 wt.%), UO₂ (~5 wt.% in Gu14), La₂O₃ (~2 wt.% in average) and Eu₂O₃ (~1.6 wt.% in Gu13), high contents of Al₂O₃ (22 wt.% in average) and Na₂O (4.2 and 5.1 wt.%, probably underestimated by EPMA due to Na loss under the electron beam) and low contents of SiO₂ (<1 wt.%) and K₂O (<1.3 wt.%) (Table 6). The totals are close to 100 wt.% which indicates that water is not a significant component of this glass.

**REE-phosphate solubility data**

Our synthetic glass compositions are phosphorus-rich with P₂O₅ contents around 3 wt.%, so we can estimate monazite solubility as K<sub>monazite</sub> = [REE], as shown by Duc-Tin & Keppler (2015). In monazite-cheralite solid solution, the incorporation of Th, U and Ca lowers the activity of REEPO₄ (Montel, 1993) and one can estimate monazite solubility by normalizing REE concentrations to the proportion of pure monazite in the solid solution, therefore K<sub>monazite</sub> = [REE]/X<sub>REEPO4</sub>, where X<sub>REEPO4</sub> is the sum of the mole fractions of REE-phosphates in monazite-cheralite, assuming ideality for REEPO₄ – cheralite solid-solution. Monazite solubilities are shown in Table 5. In order to have a full dataset with different ASI compositions, eight experiments from Montel (S18-V2, S18-V3, S19-V4 and S19-V7 with Sm: Montel, 1986; S04-V1, S04-V2, S07-V7 and S07-V8 with Ce: Montel, 1993) were re-analysed for REE by LA-ICPMS and incorporated in our experimental dataset (Table 5).
Lanthanum concentrations are comparable between the electron microprobe data of Montel (1993) and LA-ICPMS data, but the author did not measure other REE which should not be neglected in the experimental products (up to 121 µg/g Gd, 80 µg/g La and 53 µg/g Nd in the Sm-bearing experiments) and should be inserted in the total REE dissolved in glass. Similarly, our dissolution experiments of pure monazite display slight concentrations of REE other than the main REE present in the starting material. This is explained by the presence of impurities in the reagent grade powders. Consequently, the solubility data were taken as the sum of all REE³⁺ including Y dissolved in the glass. It excludes Eu as a divalent REE because its incorporation mechanisms in the melt are different (see discussion).

Montel's experiments were run with a felsic melt (synthetic) of *D* ranging from 1.08 to 1.9. Their total REE concentrations (ΣREE) range from 145 µg/g in the peraluminous glass (*D* ~ 1) to 4620 µg/g in the peralkaline glass (*D* ~ 1.9). In our synthetic peraluminous glass, K<sub>REEPO4</sub> ranges from 12 µg/g to 20 µg/g for La, 16 µg/g for Nd and 15 µg/g for Y. The sum of all REE (ΣREE) dissolved from natural monazite equals 19 µg/g. In the peralkaline glass, K<sub>REEPO4</sub> ranges from 50 µg/g to 70 µg/g, except with xenotime where it reaches 266 µg/g Y. With natural monazite, ΣREE equals 93 µg/g. The rapidly-quenched experiment (Gu14b) shows a higher monazite solubility compared to the normally-quenched experiment (Gu14) (89 µg/g in Gu14b instead of 50 µg/g in Gu14). This is explained by the abundance of very small immiscible glass droplets, which contain ~2wt.% La<sub>2</sub>O<sub>3</sub> and that could not be avoided during LA-ICPMS analysis. In Gu14, the droplets are large enough to be avoided. That value of 89 µg/g is close to the solubility observed at the contact with the large sintered monazite-cheralite of Gu17 (91 µg/g), which also shows very small immiscible glass droplets (Fig. 7h). Consequently, that value can be considered as a maximum solubility value for REE in the peralkaline glass, but it is certainly impacted by the high REE concentrations of the immiscible droplets. In natural obsidian, the initial REE concentrations of the glass must be
taken into account (30 µg/g Y, 16 µg/g La, 26 µg/g Ce, 13 µg/g Nd and approximately 4 µg/g of each of the other REE). REE-phosphate saturation is reached between 194 and 233 µg/g ΣREE with monazite-cheralite, and up to 248 µg/g Y with xenotime.

Total REE concentrations (ΣREE including Y and excluding Eu) are shown in Figure 8 as a function of melt composition expressed as $D = (Na+K+Li) / Al \cdot (Al+Si)$. Figure 8 shows in dashed line the original correlation determined by Montel (1993):

$$ \Sigma_{REE} = 9.5 + 2.34 D + 0.3879 \sqrt{H_2O} - \frac{13318}{T} $$
with H₂O = 6 wt.% and T = 800°C in Kelvin. This correlation was modified to fit the new solubility data from Montel's experiments, together with our solubility data in natural obsidian (plain line). The new

equation is calculated as
$$ \Sigma_{REE} = 8.3 + 3.34 D + 0.3879 \sqrt{H_2O} - \frac{13318}{T} $$
with an R² of 0.93.

The solubility data for the flux-rich glasses, at the exception of Y in peralkaline glass, follow a parallel trend almost an order of magnitude below the original Montel's trend, with an

equation:
$$ \Sigma_{REE} = 7 + 2.34 D + 0.3879 \sqrt{H_2O} - \frac{13318}{T} $$
and an R² of 0.95.

# DISCUSSION

## Attainment of equilibrium

An important requirement in solubility experiments is that the melt attained equilibrium, i.e., all cations were homogeneously distributed through the melt over the experiment duration. If this is not the case, saturation values must be measured in the vicinity of the dissolving minerals. A classical method is to measure diffusion profiles, in order to unravel the problem of slow diffusion kinetics in viscous silicate melts (Rapp & Watson, 1986). Concentrations are measured with distance *d* away from a grain boundary, and the saturation value is taken as the intersect at *d*=0. In our experiments with powdered monazite crystals (i.e., all experiments at the exception of Gu17), glass compositions (major and trace elements) are homogeneous,
even in the runs where the crystals accumulated at the capsule bottom, which is evidence of
the high cation diffusivity (accompanied by low viscosity) in these highly hydrated and flux-
rich melts. We conclude that, in the runs with powdered crystals, the distance between the
crystals is small enough to allow full homogeneisation by cation diffusion in the glass.

Experiment Gu17 with a large fragment of sintered monazite-cheralite allows comparing the diffusion-profile method with random glass analysis. The intersect values for La are similar between the five profiles (41 to 50 µg/g), and these concentrations are comparable to the average concentration measured in the glass of Gu14 (36 µg/g). The slopes of the exponentially-fitted correlation lines indicate the speed at which La diffused back to the glass. Profiles 1, 2 and 5 have steeper slopes than profiles 3 and 4. An explanation could be that cation equilibration was more efficient near the capsule walls (profiles 3 and 4). Diffusion profiles also show that La concentrations at a distance of 200 µm are only 10% lower than their intersect value. For comparison, in the experiments of Rapp & Watson (1986) in natural obsidian, REE concentrations fell to zero over that distance. The higher REE diffusivity in our experiments is most probably due to the presence of flux elements (Li, F and P).

Equilibration is also observed between melt and crystals. In reverse (i.e.,
crystallisation after dissolution) experiments, equilibration occurs either by partial to complete
dissolution-reprecipitation of crystals, or by solid-state diffusion. The former process is
certainly dominant in re-equilibrating minerals in our experiments because diffusion
coefficients in monazite are extremely low (Cherniak, 2010; Cherniak & Pyle, 2008).
Evidence of dissolution-reprecipitation is also brought by the euhedral-angular faces of
newly-formed crystals (Fig. 4d-e-f and close-ups) whereas the partly-dissolved, non-
equilibrated crystals are more rounded (see Fig. 4c and close-up). The two reverse
experiments of finely powdered monazite-cheralite in peralkaline glass (Gu13 and Gu14)
show another clear evidence of complete dissolution-reprecipitation of the starting material
because the new composition is radically different from the starting composition (Table 6, Fig. 5). In run Gu17, the composition of the large sintered fragment tends toward that of the fully re-equilibrated Gu14 monazite-cheralite. It suggests that the melt had time to migrate along the grain boundaries and to partly dissolve the crystals, but cation diffusivity was not sufficient to allow complete melt homogenisation and full crystal re-equilibration. Evidence of crystal-melt equilibrium in reverse experiments is also brought by run Gu14X. In that run, the crystals directly crystallised from the melt, in equilibrium with it. In crystallisation experiments, crystal saturation (i.e., crystal nucleation and growth) occurs from an initially homogeneous glass, and the crystals grow only if cations diffuse fast enough to reach the crystal-melt interface. Consequently, getting crystals in crystallisation experiments implies that equilibrium is attained in the melt. In Gu14X, the crystals display the same composition as the crystals in Gu14, which formed by dissolution-recrystallisation of the starting monazite-cheralite. Consequently, we can infer with good confidence the equilibrated state of the recrystallised minerals in our reverse experiments.

## Controls on monazite-cheralite solubilities, and implication for REE contents in granitic rocks

Solubility data from literature (Montel, 1993; Duc-Tin & Keppler, 2015) predict ΣREE concentrations at saturation at 800°C and 200 MPa in the order of 100 to 1000 µg/g in peraluminous glasses (D~1) (Fig. 2). These solubilities are confirmed by our experiments with the natural obsidian, which is slightly peraluminous with a low flux content. Our experiments with the flux-rich synthetic glasses also confirm the strong compositional effect on solubilities from peraluminous to peralkaline compositions. However, in our P+F-bearing experiments, solubility data are much lower, in the order of 10 µg/g for the peraluminous glass, and below 100 µg/g for the peralkaline glass, which is an order of magnitude lower than
the solubilities reported in the literature (Fig. 8). We conclude that the fluxing components
have a strong impact on monazite solubilities in both peralkaline and peraluminous melts.
Although the total flux content (around 6 wt.%) of our synthetic glasses attain levels that
cannot be compared to standard natural granitic compositions, they reflect highly
differentiated rare-element granites and pegmatites, where flux concentrations may attain
more than 1 wt.% Li₂O, 4 wt.% P₂O₅ and 2 wt.% F (Linnen & Cuney, 2005). Consequently,
our solubility data can be used to understand REE enrichment in strongly differentiated melts.

The influence of fluorine and phosphorus on accessory mineral solubilities has been
documented by Keppler (1993) and Fiege et al. (2011; 2018). Keppler (1993) and Fiege et al.
(2011) showed that fluorine has no effect on monazite and columbite-group mineral
solubilities in haplogranitic melts. Duc-Tin (2007) investigated in more detail the role of
fluorine on monazite solubility and showed a slight decrease in REE solubility (all elements)
with F contents up to 4 wt.%, but he did not explain that observation. Fiege et al. (2018)
showed that the addition of P decreases the solubility of columbite-group minerals in
peralkaline granitic melts. This effect is explained by the polymerising character of P that
forms alkali-phosphate complexes in the melt. In peraluminous melts, the polymerising
character of P is even more pronounced because of its tendency to form alumina-phosphate
complexes (Mysen et al., 1999). This means that the melt structure does not offer enough
non-bridging oxygens to accommodate highly-charged cations as the REE. Additionally, Duc-
Tin (2007) explained the decrease in monazite solubility with P concentration in the melt
(concentrations below 1.5 wt.% P₂O₅) because of the partial dissolution of monazite as ionic
(PO₄³⁻ and REE³⁺) species. In that case, monazite solubility is expressed as the solubility
product of these two species, and an increase in PO₄³⁻ causes a decrease in REE³⁺. Therefore,
monazite solubilities as expressed as LREE concentrations, can only be directly compared at
constant P₂O₅ contents in the melt. At high P₂O₅ concentrations (1.5 wt.% in Duc-Tin's
experiments), more than 90 mol% of the Gd is dissolved as GdPO₄ molecules. In that case, monazite solubility is poorly dependent on P concentration and LREE concentration should not decrease with increasing phosphorus concentration. Consequently, the drastic monazite solubility drop in our flux-bearing melts is most probably due to the combined effects of the alumina- or alkali-phosphate complexing together with the ionic competition between PO₄³⁻ and REE³⁺ species.

It is interesting to note that no distinction in solubility appears between the various REE in our experiments, contrary to the results of Duc-Tin & Keppler (2015). The variation in solubility from La to Gd observed by Duc-Tin & Keppler (2015) decreases with increasing ASI, so it can be inferred that this variability disappears at the most peraluminous compositions, or at least decreases below the experimental variability (i.e., the experimentally-determined solubilities do not perfectly plot along a linear correlation and this variability is inherent to experimental conditions).

The data show that the REE compete for each other during dissolution of monazite-cheralite, i.e., the sum of all REE dissolved from natural monazite is comparable to the REE concentration dissolved from pure REEPO₄. However, Eu behaves differently: in our synthetic glasses, Eu and La concentrations are similar. Moreover, La concentrations are similar where La is dissolved alone in the glasses and where it is dissolved together with Eu (Table 5). This means that Eu does not compete with La and occupies distinct melt structural sites. This could be explained by the divalent state of Eu in experiments at NNO conditions (Burnham *et al.*, 2015), whereas other REE are trivalent. A similar observation is made for xenotime dissolved in peralkaline glass. The Y concentration is higher (262 µg/g) than the sum of all REE dissolved from natural monazite (93 µg/g normalized), consequently Y does not compete with other REE in peralkaline glass, although they certainly have the same valence. However, in peraluminous glass, the sum of all REE dissolved from natural monazite
equals the Y concentration, so it can be suggested that Y and REE compete for each other in peraluminous glass. This is certainly linked to the glass structure. In peralkaline glass, rare metals can be accommodated by a variety of structural sites associated with excess alkali that make non-bridging oxygens (NBO) available, whereas in peraluminous systems, NBO associated with excess Al are less frequent (Linnen & Keppler, 1997; Van Lichtervelde et al., 2010). The constant decrease of REE solubility from peralkaline to peraluminous glass is an indirect evidence that REE are associated with NBO liberated by excess alkali.

The behavior of REE can be compared to that of high-field strength elements in the same magmas. Van Lichtervelde et al. (2010) showed that tantalite-Mn solubility increases with both peralkalinity and peraluminosity away from ASI=1, although that increase is faster in peralkaline compositions compared to peraluminous compositions. This is explained by different bounding for the different rare metals. For example, Van Lichtervelde et al. (2010) showed that tantalum preferentially bounds to Al, which explains the increase of tantalite solubility with peraluminosity and the global affinity of tantalum for peraluminous granites and pegmatites. In the case of the REE, Al-bounding is evidently not significant compared to alkali-bounding.

Our solubility data are consistent with the compatible behaviour of REE during differentiation in peraluminous granitic suites (Emmermann et al., 1975; Miller & Mittlefehldt, 1982; Ward et al., 1992; Siebel et al., 1995; Boulvais et al., 2007). In peraluminous rocks, very low monazite and xenotime solubilities lead to the early crystallisation of these minerals, together with REE-rich zircon which is also poorly soluble in peraluminous melts (Watson & Harrison, 1983). REE concentrations in peraluminous granites are very low, generally below 200 µg/g (Table in Annex), and they decrease with monazite fractional crystallisation. In intermediate to high-P peraluminous granites, they are even lower than the average upper crustal abundance (148 µg/g ΣREE, Rudnick & Gao, 2003). Our new
solubility results imply that these concentrations are very low in flux-rich melts where F and P
may decrease monazite solubilities even more. In peralkaline systems, the effect of flux
enrichment associated with granitic differentiation remains to be investigated. Our results
with P-rich peralkaline melts are less applicable to natural systems because peralkaline
granites are generally poor in phosphorus (Fig. 1).

**The role of liquid-liquid immiscibility in concentrating REE (and U+Th)**

*Evidence of liquid-liquid immiscibility during the runs*

Our three experiments with peralkaline glass and monazite-cheralite show perfectly-rounded
droplets of a F- and P-rich material. The droplets consist of vitreous and water-poor
quenchable glass that can be analysed with EPMA. Compared to the global glass, the droplets
are strongly enriched in P and F, slightly enriched in Al and Na, strongly peraluminous, and
strongly depleted in Si and K (Table 6). Lithium is probably not abundant given that most of
the analytical totals are close to 100 wt.%. They are also highly concentrated in the monazite-
cheralite mineral constituents Ca, La(+Eu) and Th(+U).

The droplets could represent a phase equivalent to the hydrosaline liquid of Webster
(2004). However, their depletion in H₂O compared to the global melt eliminates this
possibility, and rather suggests that the immiscible droplets represent a distinct fluoro-
phosphate liquid. They could also represent seeds of a cotectic fluoro-phosphate mineral. In
all cases, the key question about these droplets is to know whether they are really present
during the runs at high temperature, even as very small (sub-micron size) droplets.

The role of quenching in the droplet formation can be questioned as the duplicate runs
of Gu13 and Gu14 with rapid-quench do not display large droplets like in the normally-
quenched runs. However, the normally-quenched runs Gu14 and Gu17 also display small
droplets. In particular, Gu14 displays both large and small droplets (Fig. 7c). Constraining the
precise nature of quench rate on the droplet formation is not possible with our experimental
setup, as quench rates of one versus four minutes are not much different.

In Gu13b, some newly-formed monazite-cheralite crystals are surrounded by a
droplet-free moat zone (Fig. 7e). This is also visible around the sintered crystals of Gu17 (Fig.
7h). If the droplets were entirely formed during quenching, we believe that their distribution
would have been homogeneous. Instead, the moat zone could be a « feeding zone » around
the crystals. However, it is still possible that these crystals formed during quenching,
overgrown on the original crystals, and that the droplets represent seeds of monazite-cheralite.

The backscattered electron images under FEG-SEM of the droplets show a porous
texture. In Gu13 and Gu14, the dissolving monazite-cheralite crystals form aggregates of
newly-formed euhedral monazite-cheralite grains that are embedded in a porous material with
a similar texture (see close-ups in Fig. 4d-e and Fig. 7a). This material, interstitial to the
grains, has a composition intermediate between the monazite-cheralite crystals and the
droplets. This interstitial material seems to be the direct product of the monazite-cheralite
dissolution, with the porosity being evidence of the change in volume associated with the
melting reaction. Given the compositional similarity between the interstitial porous material
and the droplets, we suggest that the droplets are collect products of an intermediary liquid
produced by monazite-cheralite dissolution, before its full assimilation by the global melt.

Finally, in Gu13, we observe examples of droplets that contain newly-formed
monazite crystals (Fig. 7a), which are unlikely to form during quenching. The material inside
the crystal-bearing droplet is porous and its composition is similar to the glassy material of the
crystal-free droplets. We conclude that the droplets are made of an immiscible liquid that
appears during monazite dissolution and that feeds the newly-formed monazite crystals.
Figure 9 is a schematic representation of that process. Dissolution of the starting monazite-
cheralite generates an immiscible liquid that first wraps the dissolving crystals, and that ends
up forming spherical droplets. Newly-formed crystals precipitate from this immiscible liquid, either as overgrowths on the dissolving aggregates, or as new disseminated crystals. Around some of these crystals, the droplets disappear, while in rare occurrences, crystals precipitate directly inside the largest droplets. During the normal quench stage of 4-5 minutes, the droplets may have coalesced and grown larger because of the slight pressure drop that occurred during the non-isobaric quenching.

In their recent study of monazite and xenotime solubility in hydrous, boron-bearing rhyolitic melts at 1000–1400 °C and 800 MPa, Rusiecka & Baker (2019) observed a “nanoparticle moat zone” around dissolving monazite crystals. In these moats, Rusiecka & Baker (2019) described spherical droplets rich in P and REE that quenched to crystalline monazite-like phosphates, but they could not analyse them because of their small size. The authors argued that they are unlikely to form during quenching, as particles of these sizes would take longer times than the quenching duration to form. They concluded that their droplets may reflect the absence of equilibrium during the dissolution-recrystallisation processes, i.e., monazite did not have time to fully recrystallise in an equilibrated composition. This does not occur in our experiments because the flux-rich nature of the melt allows high cation diffusivity through the glass, which is evidenced by the formation of relatively large (1-2 µm) monazite crystals. However, the droplet formation process observed by Rusiecka & Baker (2019) is probably the same at work in our experiments: it is the result of the monazite dissolution, and in our experiments, the cation diffusivity is fast enough to allow the formation of large droplets and new crystals, whereas in the experiments of Rusiecka & Baker (2019), the droplets remained as very small glass droplets that quenched as monazite-like crystals.

It can be concluded that the droplets formed during the experiment and the non-isobaric quenching enabled them to coalesce and grow larger (Fig. 9). Therefore, we interpret
these droplets as the result of a liquid-liquid immiscibility process. In any case, the
appearance of these droplets, be it during the experiments or at lower temperatures, is
evidence that liquid-liquid immiscibility can occur in these types of melts. The presence of the
immiscible droplets do not affect monazite-cheralite solubility in the melt, suggesting that
liquid-liquid immiscibility is a way for the melt to accommodate excess REE produced by
monazite-cheralite dissolution.

Processes controlling liquid-liquid immiscibility

Why does immiscibility occur in the peralkaline glass and not in the peraluminous glass,
although their F and P concentrations are similar? In P-rich peraluminous melts, phosphorus
easily complexes with excess Al (Mysen et al., 1999) which may prevent liquid-liquid
immiscibility. In P-rich metaluminous and slightly peralkaline melts, phosphorus is free in the
melt structure and the addition of P by the dissolution of monazite-cheralite may destabilise
the melt and trigger liquid-liquid immiscibility between a flux (P, F)-rich melt and the global
melt. However, liquid-liquid immiscibility occurs with monazite-cheralite dissolution and not
with pure monazite dissolution, so P alone cannot trigger melt destabilisation. Calcium
certainly plays a major role in stabilising an immiscible liquid, since immiscibility does not
occur with pure REE-phosphates. One hypothesis is that calcium, as an alkali, moves the D
composition of the melt toward more peralkaline compositions where P can no longer be
accommodated. The Ca excess triggers the formation of a liquid whose structure can
accommodate large amounts of high-field strength cations such as P, REE, and U-Th.
Consequently in our experiments, immiscibility may be triggered by the diffusion of Ca into
the global melt. Calcium concentrations are, however, too low to form apatite (Pichavant et
al., 1992).

The atomic scale mechanism behind liquid-liquid immiscibility in silicate melts has
been established by Hess (1996) and Hudon & Baker (2002). They showed that liquid phase
separation is due to coulombic repulsion between network-modifying cations. Repulsions
occur when modifier cations are not coordinated by a sufficient number of non-bridging
oxygen (i.e., the melt is too strongly polymerized). Consequently, the addition of one
particular network-modifying cation in the melt may trigger phase separation. In our case, this
cation seems to be Ca, provided to the melt by the monazite-cheralite dissolution.

Role of liquid-liquid immiscibility in concentrating REE

With a total of approximately 60 wt.% F + P₂O₅ in the fluorophosphate immiscible liquid, our silicate-fluorophosphate system is very close in composition to the silicate-phosphate and silicate-fluoride systems studied by Veksler *et al.* (2012). We find remarkable similarities with the experiments of these authors, such as the strong partitioning of Si into the silicate melt, the strong partitioning of Ca into the fluoride and phosphate melts, and the moderate partitioning of Al into the fluoride melt. As these authors notice, making a fluoride-silicate mixture that will produce two liquids is not easy, because of the high mutual solubility of the melts. Their immiscible liquids have good capacities to extract and concentrate a large number of elements, in particular their fluoride and phosphate melts which strongly partition the REE. We conclude that high concentrations of rare metals and other ore-forming elements should be expected in immiscible fluoride and phosphate melts.

Other experimental studies investigated liquid-liquid immiscibility in granitic systems under geologically relevant conditions (Veksler, 2004; Dolejs & Baker, 2007; Alferyeva et al., 2011). Our experiments are different in composition from all these studies, but similarities can be highlighted. In his review of liquid immiscibility, Veksler (2004) notes that “liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions”, e.g., fluorine. In their fluoride glass, Vasyukova & Williams-Jones (2014) observe considerable Ca concentrations and their ΣREE contents are comparable to the REE+Th+U contents of our immiscible droplets. Rusiecka & Baker (2019) also conclude to a process of
liquid-liquid phase separation at high phosphorus concentrations, and they highlight that "liquid-liquid immiscibility would become a significant fractionation mechanism in magmatic systems only when the P concentration exceeds 0.4 wt.%".

In nature, liquid-liquid immiscibility commonly occurs in a number of undersaturated magmatic environments, such as mafic and ultramafic systems, but it is less common in silica-rich systems. It may be the cause of REE mineralisation in carbonatites (Chakhmouradian & Zaitsev, 2012). In evolved granitic environments, it occurs in either peraluminous (Borisova et al., 2012; Thomas et al., 2006; Thomas & Davidson, 2016; Kaeter et al., 2018; Stern et al., 2018), metaluminous (Muller et al., 2018) or peralkaline systems (Suk, 2012; Vasyukova & Williams-Jones, 2014; 2016). Veksler et al. (2005), Vasyukova & Williams-Jones (2014; 2016) and Stern et al. (2018) all showed that the primary concentration of the REE is caused by the separation and physical accumulation of an immiscible fluoride or fluoride-phosphate melt into which the REE partitioned preferentially. Muller et al. (2018) showed that the albite zones in NYF pegmatites of Norway result from the extreme internal chemical differentiation of the pegmatite-forming melt, resulting in melt/melt and additional melt/fluid immiscibility. Dolejs & Zajacz (2018) showed that high F concentrations in peraluminous silica-saturated and Ca-poor systems may lead to fluoride-silicate liquid immiscibility. The immiscible multicomponent fluoride melts (brines) preferentially concentrate high-field strength elements and REE. Therefore, our observations are in good agreement with previous studies on natural systems that show that liquid-liquid immiscibility is an important mechanism in concentrating fluxes and high-field strength cations such as REE and U+Th. Moreover, our immiscible droplets primarily show that liquid-liquid immiscibility is a potential mechanism of REE and U+Th concentration in melts where REE- and U+Th-bearing minerals have low solubilities.

ACKNOWLEDGMENTS
We are grateful to Jean-Luc Devidal, Stephane Le Blond Du Plouy, Sophie Gouy and Philippe de Parseval for their contribution to SEM imaging and LA-ICPMS and EPMA analysis. We also thank François Holtz and the Mineralogy Institute of Hannover for running some rapidly-quenched experiments. In-depth reviews and constructive comments by Alexander Stepanov, Olga Vasyukova, Andreas Audôtat and an anonymous reviewer were greatly appreciated, and special gratitude goes to Andreas Audôtat for his patient editorial work, despite the divergence of some of our views. This project was funded by the French National Research Agency (ANR – VARPEG project 2015-2019) and the French National Institute of Universe Sciences (INSU – NEEDS project 2014). The post-doctoral fellowship of AE was funded by the University of Franche-Comté - Accueil de jeunes chercheurs 2015.

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FIGURE CAPTIONS

Figure 1. Literature data compiled from Linnen and Cuney (2005) (1), unpublished data from the first author (2), Boulvais *et al.* (2007) (3), Neiva *et al.* (1987) (4), René (2018) (5), Chen *et al.* (2018) (6), and Li *et al.* (2017) (7), showing the negative correlation between the concentrations of rare-earth elements and phosphorus dissolved in peralkaline to peraluminous granites and pegmatites. See Annex Table for data compilation and their details.

Figure 2. Compilation of solubility data as a function of glass composition expressed as D = (Na+K+Li+2Ca) / Al·(Al+Si) (in at%). All data were obtained at 800°C and 200 MPa. The arrows represent the range from La to Gd of Duc-Tin & Keppler (2015). The linear correlation is that of Montel (1993).

Figure 3. Graphical visualisation of the different types of experiments performed. Grey color marks reverse experiments, the others are dissolution experiments.

Figure 4. BSE images of experimental charges with close-ups on crystals. (a) disseminated angular crystals of YPO₄ in peraluminous glass. (b) angular crystals of NdPO₄ in metaluminous glass. (c) rounded monazite-cheralite in peraluminous glass. (d,e) newly-formed monazite-cheralite in peralkaline glass. The close-ups also show light-grey immiscible glass droplets and the porous material interstitial to the dissolving grains. (f) fragment of sintered monazite-cheralite crystals in peralkaline glass. The close-up shows euhedral newly-formed crystals and uraninite grains.

Figure 5. Chemical composition of experimental monazite- cheralite, element concentrations expressed as atoms per formula units. The U+Th+Si+Ca versus REE+P diagram shows the re-equilibration of the starting cheralite toward pure monazite in peralkaline glass.
Figure 6. Diffusion profiles in experiment Gu17 (large fragment of sintered monazite-cheralite in peralkaline glass) for U, Th and La. See Fig. 4f for profile locations. Calcium shows no diffusion profile. Errors are given as 2σ.

Figure 7. Detailed backscattered-electron images of the runs with peralkaline glass and monazite-cheralite. (a), (c), (d) and (f) are taken with FEG-SEM. The immiscible droplets are visible in (b), (c), (e), (f) and (h). Contrast was maximised in the pictures to highlight the light-grey droplets. The brightest particles are monazite-cheralite crystals, pointed by arrows in (g). In (a), newly-formed monazite-cheralite crystals occur in a large spherical droplet of composition similar to the smaller droplets. (d) is a close view of a crystal-free droplet. In (e), the monazite-cheralite crystals are surrounded by a moat zone devoid of immiscible droplets.

Figure 8. REE solubilities versus glass composition expressed as D=(Na+K+Li+2Ca)/Al·(Al+Si) in at%. Total REE (excluding Eu) are normalized to the pure monazite component in non-pure natural monazite and synthetic cheralite. The solid line is the linear correlation modified from Montel (1993) to fit Montel's new solubility data and ours in natural obsidian. The dashed line is the original linear correlation determined by Montel (1993). The dotted line is the linear correlation for our P and F-rich synthetic glasses.

Figure 9. Schematic representation of the successive steps of immiscible droplet formation during reverse (recrystallisation after dissolution) experiments.
<figure><img src="image_3.png" /></figure>

Figure 1. Literature data compiled from Linnen and Cuney (2005) (1), unpublished data from the first author (2), Boulvais et al. (2007) (3), Neiva et al. (1987) (4), René (2018) (5), Chen et al. (2018) (6), and Li et al. (2017) (7), showing the negative correlation between the rare-earths and phosphorus in peralkaline to peraluminous granites and pegmatites. See Annex Table for data compilation and their details.
<figure><img src="image_4.png" /><figcaption>Figure 2. Compilation of solubility data as a function of glass composition expressed as D = (Na+K+Li+2Ca)/Al.(Al+Si) (in at%) from the literature at 800°C and 200 MPa. The arrows represent the range from La to Gd of Duc-Tin & Keppler (2015). The linear correlation is that of Montel (1993).</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Figure 3. Flowchart of the different experiments. In grey are reverse experiments, the others are dissolution experiments.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Figure 4. BSE images of experimental charges with close-ups on crystals. A. disseminated tabular crystals of YPO4 in peraluminous glass. B. tabular crystals of NdPO4 in metaluminous glass. C. rounded monazite-cheralite in peraluminous glass. D and E. newly-formed monazite-cheralite in peralkaline glass. The close-ups also show light-grey immiscible glass droplets and the porous material interstitial to the dissolving grains. F. sintered crystal of monazite-cheralite in paralkaline glass. The close-up shows euhedral newly-formed crystals and uraninite grains.</figcaption></figure>

Figure 4. BSE images of experimental charges with close-ups on crystals. (a) disseminated tabular crystals of YPO4 in peraluminous glass. (b) tabular crystals of NdPO4 in metaluminous glass. (c) rounded monazite-cheralite in peraluminous glass. (d&e) newly-formed monazite-cheralite in peralkaline glass. The close-ups also show light-grey immiscible glass droplets and the porous material interstitial to the dissolving grains. (f) sintered crystal of monazite-cheralite in peralkaline glass. The close-up shows euhedral newly-formed crystals and uraninite grains.
<figure><img src="image_7.png" /><figcaption>Figure 5. Chemical composition of experimental monazite- cheralite, element concentrations expressed as atoms per formula units. The U+Th+Si+Ca versus REE+P diagram shows the re-equilibration of the starting cheralite toward pure monazite in peralkaline glass.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Figure 6. Diffusion profiles in experiment Gu17 (large fragment of sintered monazite-cheralite in peralkaline glass) for U, Th and La. See Fig. 4f for profile locations. Calcium shows no diffusion profile. Errors are given as 2σ.</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>Figure 7. Detailed backscattered-electron images of the runs with peralkaline glass and monazite-cheralite. (a), (c), (d) and (f) are taken with FEG-SEM. The immiscible droplets are visible in (b), (c), (e), (f) and (h).</figcaption></figure>

Contrast was maximised in the pictures to highlight the light-grey droplets. The brightest particles are monazite-cheralite crystals, pointed by arrows in (g). In (a), newly-formed monazite-cheralite crystals occur in a large spherical droplet of composition similar to the smaller droplets. (d) is a close view of a crystal-free droplet. In (e), the monazite-cheralite crystals are surrounded by a moat zone devoid of immiscible droplets.
<figure><img src="image_10.png" /><figcaption>Figure 8. REE solubilities versus glass composition expressed as D=(Na+K+Li+2Ca) / Al.(Al+Si) in at%. Total REE (excluding Eu) are normalized to the pure monazite component in non-pure natural monazite and synthetic cheralite. The solid line is the linear correlation modified from Montel (1993) to fit Montel's new solubility data and ours in natural obsidian. The dashed line is the original linear correlation determined by Montel (1993). The dotted line is the linear correlation for our P and F-rich synthetic glasses.</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>Figure 9. Schematic representation of the successive steps of immiscible droplet formation during reverse (recrystallisation after dissolution) experiments.</figcaption></figure>
<table><caption>Table 1: Experimental conditions of previous studies of monazite solubility</caption><thead><tr><th>Study</th><th>Investigated REE</th><th>Starting mineral</th><th>Starting glass</th><th>Type of experiment</th><th>T°C</th><th>P (MPa)</th><th>ASI</th><th>Specific conditions</th></tr></thead><tbody><tr><td>Present study</td><td>La-Ce-Nd-Sm-Y</td><td>Synthetic and natural monazite, synthetic U-Th cheralite</td><td>Synthetic and natural obsidian</td><td>Dissolution and crystallisation</td><td>800</td><td>200</td><td>0.9 to 1.4</td><td>H₂O-saturated + F, Li and P</td></tr><tr><td>Montel (1986)</td><td>Ce</td><td>Synthetic monazite</td><td>Synthetic</td><td>Dissolution and crystallisation</td><td>800</td><td>200</td><td>0.5 to 1.1</td><td>H₂O-saturated</td></tr><tr><td>Rapp and Watson (1986)</td><td>La-Ce-Nd-Sm</td><td>Natural</td><td>Natural obsidian</td><td>Dissolution</td><td>1000-1400</td><td>800</td><td>1.16</td><td>1-6 wt% H₂O</td></tr><tr><td>Rapp et al. (1987)</td><td>La-Ce-Nd-Sm-Gd</td><td>Natural</td><td>Natural</td><td>Dissolution</td><td>850-1000</td><td>800</td><td>0.7 to 1.1</td><td>H₂O-saturated</td></tr><tr><td>Montel (1993)</td><td>Sm</td><td>Synthetic monazite</td><td>Synthetic</td><td>Dissolution</td><td>800</td><td>200</td><td>0.6 to 1.1</td><td></td></tr><tr><td>Stepanov et al. (2012)</td><td>All</td><td>-</td><td>Synthetic</td><td>Crystallisation</td><td>750-1200</td><td>1000-5000</td><td>0.85 to 1.1</td><td>6-17 wt% H₂O</td></tr><tr><td>Xing et al. (2013)</td><td>Ce</td><td>-</td><td>Synthetic</td><td>Crystallisation</td><td>900-1100</td><td>1000</td><td>0.4 to 2</td><td>Th+U</td></tr><tr><td>Duc-Tin and Keppler (2015)</td><td>All</td><td>Synthetic monazite</td><td>Synthetic</td><td>Dissolution</td><td>800-1100</td><td>200</td><td>0.7 to 1.3</td><td>6 wt% H₂O</td></tr><tr><td>Rusiecka and Baker (2019)</td><td>All</td><td>Natural</td><td>Natural obsidian</td><td>Dissolution</td><td>1000-1400</td><td>800</td><td>1</td><td>3 wt% H₂O + B and Li</td></tr></tbody></table>
<table><caption>Table 2: EPMA starting glass compositions (in wt.%)</caption><thead><tr><th></th><th>SiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>Na<sub>2</sub>O</th><th>K<sub>2</sub>O</th><th>Li<sub>2</sub>O</th><th>P<sub>2</sub>O<sub>5</sub></th><th>F</th><th>FeO</th><th>CaO</th><th>ASI</th><th>ASI(Li)</th></tr></thead><tbody><tr><td>Peraluminous</td><td>66.92<br>1.52</td><td>16.58<br>0.78</td><td>3.07<br>0.13</td><td>5.71<br>0.20</td><td>0.9</td><td>3.59<br>0.43</td><td>2.96<br>0.60</td><td>-</td><td>-</td><td>1.48</td><td>1.16</td></tr><tr><td>Peralkaline (K&gt;Na)</td><td>62.84<br>0.54</td><td>16.20<br>0.22</td><td>3.72<br>0.14</td><td>7.40<br>0.12</td><td>1.6</td><td>3.65<br>0.23</td><td>3.10<br>0.22</td><td>-</td><td>-</td><td>1.15</td><td>0.83</td></tr><tr><td>Peralkaline (Na&gt;K)</td><td>62.50<br>0.50</td><td>18.87<br>0.25</td><td>8.41<br>0.21</td><td>3.75<br>0.07</td><td>1.6</td><td>3.53<br>0.28</td><td>2.41<br>0.28</td><td>-</td><td>-</td><td>1.05</td><td>0.81</td></tr><tr><td>Natural obsidian</td><td>76.5</td><td>12.6</td><td>4.5</td><td>4.2</td><td>n.a.</td><td>n.a.</td><td>n.a.</td><td>0.7</td><td>0.3</td><td>1</td><td>-</td></tr></tbody></table>

Li₂O is calculated from the theoretical composition of the starting powder

In italics are 2-sigma standard deviation on minimum 10 analyses

The natural obsidian, a rhyolite from Güney Dağı, Turkey, is described in Mourtada-Bonnefoi & Laporte (2002)

n.a.: non analysed
<table><caption>Table 3: Experimental products</caption><thead><tr><th>Glass</th><th>Run</th><th>Starting material</th><th>Final products</th><th>Immiscible droplets</th></tr></thead><tbody><tr><td rowspan="6">Peraluminous</td><td>Gu1</td><td>YPO<sub>4</sub></td><td>Angular YPO<sub>4</sub></td><td>No</td></tr><tr><td>Gu2</td><td>NdPO<sub>4</sub></td><td>Angular NdPO<sub>4</sub></td><td>No</td></tr><tr><td>Gu3</td><td>LaPO<sub>4</sub></td><td>Angular LaPO<sub>4</sub></td><td>No</td></tr><tr><td>Gu8</td><td>Manangotry monazite</td><td>Angular Manangotry monazite</td><td>No</td></tr><tr><td>Gu18</td><td>(La,Eu)<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.25</sub>PO<sub>4</sub></td><td>Rounded (La,Eu)<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.25</sub>PO<sub>4</sub></td><td>No</td></tr><tr><td>Gu19</td><td>La<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.125</sub>U<sub>0.125</sub>PO<sub>4</sub></td><td>Rounded La<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.125</sub>U<sub>0.125</sub>PO<sub>4</sub></td><td>No</td></tr><tr><td rowspan="5">Natural</td><td>Gu4</td><td>YPO<sub>4</sub></td><td>Angular YPO<sub>4</sub></td><td>No</td></tr><tr><td>Gu5</td><td>NdPO<sub>4</sub></td><td>Angular NdPO<sub>4</sub></td><td>No</td></tr><tr><td>Gu6</td><td>LaPO<sub>4</sub></td><td>Angular LaPO<sub>4</sub></td><td>No</td></tr><tr><td>Gu7</td><td>Manangotry monazite</td><td>Angular Manangotry monazite</td><td>No</td></tr><tr><td>Gu10</td><td>YPO<sub>4</sub></td><td>Angular to rounded YPO<sub>4</sub></td><td>No</td></tr><tr><td rowspan="6">Peral alkaline</td><td>Gu11</td><td>NdPO<sub>4</sub></td><td>Angular to rounded NdPO<sub>4</sub></td><td>No</td></tr><tr><td>Gu12</td><td>LaPO<sub>4</sub></td><td>Angular to rounded LaPO<sub>4</sub></td><td>No</td></tr><tr><td>Gu9</td><td>Manangotry monazite</td><td>Rounded Manangotry monazite (rare)</td><td>No</td></tr><tr><td>Gu13</td><td>(La,Eu)<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.25</sub>PO<sub>4</sub></td><td>Newly-formed angular cheralite</td><td>Yes</td></tr><tr><td>Gu14</td><td>La<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.125</sub>U<sub>0.125</sub>PO<sub>4</sub></td><td>Newly-formed angular cheralite</td><td>Yes</td></tr><tr><td rowspan="5">Peralkaline (extra runs)</td><td>Gu13b*</td><td>(La,Eu)<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.25</sub>PO<sub>4</sub></td><td>Newly-formed angular cheralite</td><td>Yes</td></tr><tr><td>Gu14b*</td><td>La<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.125</sub>U<sub>0.125</sub>PO<sub>4</sub></td><td>Newly-formed angular cheralite</td><td>Yes</td></tr><tr><td>Gu14X</td><td>La<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.125</sub>U<sub>0.125</sub>PO<sub>4</sub></td><td>Newly-formed angular cheralite</td><td>No</td></tr><tr><td>Gu17</td><td>La<sub>0.5</sub>Ca<sub>0.25</sub>Th<sub>0.15</sub>U<sub>0.1</sub>PO<sub>4</sub></td><td>Newly-formed angular cheralite + uraninite inclusions</td><td>Yes</td></tr><tr><td>Gu17</td><td>Large fragment</td><td></td><td></td></tr></tbody></table>

<footnote>* runs duplicated with rapid, isobaric quenching</footnote>
<table><caption>Table 4: major element composition (in wt.%) of experimental glasses</caption><thead><tr><th rowspan="2"></th><th rowspan="2"></th><th colspan="7">EPMA</th><th colspan="3">LA-ICPMS</th></tr><tr><th>ASI*</th><th>F</th><th>SiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>K<sub>2</sub>O</th><th>P<sub>2</sub>O<sub>5</sub></th><th>Na<sub>2</sub>O</th><th>Li<sub>2</sub>O</th><th>Na<sub>2</sub>O</th><th>D**</th></tr></thead><tbody><tr><td rowspan="12">Peraluminous</td><td>Gu1</td><td>1.24</td><td>4.33</td><td>62.81</td><td>15.72</td><td>5.30</td><td>3.08</td><td>n.a.</td><td>0.80</td><td>2.5</td><td>0.92</td></tr><tr><td>N=10</td><td></td><td>0.47</td><td>0.55</td><td>0.21</td><td>0.06</td><td>0.24</td><td></td><td>0.03</td><td>0.1</td><td></td></tr><tr><td>Gu2</td><td>1.24</td><td>4.49</td><td>63.71</td><td>16.08</td><td>5.52</td><td>3.11</td><td>n.a.</td><td>0.81</td><td>2.6</td><td>0.92</td></tr><tr><td>N=10</td><td></td><td>0.42</td><td>0.37</td><td>0.14</td><td>0.10</td><td>0.19</td><td></td><td>0.04</td><td>0.0</td><td></td></tr><tr><td>Gu3</td><td>1.19</td><td>4.66</td><td>62.16</td><td>15.54</td><td>5.37</td><td>2.87</td><td>2.41</td><td>0.88</td><td>2.6</td><td>0.93</td></tr><tr><td>N=14</td><td></td><td>0.35</td><td>0.69</td><td>0.38</td><td>0.15</td><td>0.35</td><td>0.21</td><td>0.08</td><td>0.1</td><td></td></tr><tr><td>Gu8</td><td>1.14</td><td>4.71</td><td>61.26</td><td>15.36</td><td>5.25</td><td>2.75</td><td>2.47</td><td>0.95</td><td>2.8</td><td>0.98</td></tr><tr><td>N=16</td><td></td><td>0.19</td><td>0.54</td><td>0.30</td><td>0.15</td><td>0.12</td><td>0.10</td><td>0.04</td><td>0.1</td><td></td></tr><tr><td>Gu18</td><td>1.14</td><td>n.a</td><td>62.38</td><td>15.32</td><td>5.37</td><td>3.31</td><td>2.55</td><td>n.a.</td><td>2.8</td><td>1.01</td></tr><tr><td>N=16</td><td></td><td></td><td>0.38</td><td>0.18</td><td>0.12</td><td>0.23</td><td>0.08</td><td></td><td>0.1</td><td></td></tr><tr><td>Gu19</td><td>1.15</td><td>n.a</td><td>63.60</td><td>15.80</td><td>5.49</td><td>3.40</td><td>2.74</td><td>0.92</td><td>2.8</td><td>1.00</td></tr><tr><td>N=8</td><td></td><td></td><td>0.24</td><td>0.17</td><td>0.09</td><td>0.13</td><td>0.14</td><td>0.10</td><td>0.0</td><td></td></tr><tr><td rowspan="12">Natural obsidian</td><td>Gu4</td><td>0.96</td><td>0.10</td><td>72.17</td><td>11.73</td><td>4.06</td><td>0.01</td><td>3.42</td><td>0.02</td><td>4.7</td><td>1.23</td></tr><tr><td>N=15</td><td></td><td>0.09</td><td>0.40</td><td>0.13</td><td>0.12</td><td>0.01</td><td>0.09</td><td>0.00</td><td>0.1</td><td></td></tr><tr><td>Gu5</td><td>1.07</td><td>0.10</td><td>72.17</td><td>11.73</td><td>4.01</td><td>0.01</td><td>3.39</td><td>0.02</td><td>4.0</td><td>1.04</td></tr><tr><td>N=14</td><td></td><td>0.10</td><td>0.34</td><td>0.14</td><td>0.14</td><td>0.01</td><td>0.10</td><td>0.00</td><td>0.1</td><td></td></tr><tr><td>Gu6</td><td>1.06</td><td>0.15</td><td>72.02</td><td>11.79</td><td>4.03</td><td>0.01</td><td>3.39</td><td>0.02</td><td>4.1</td><td>1.06</td></tr><tr><td>N=12</td><td></td><td>0.14</td><td>0.47</td><td>0.06</td><td>0.11</td><td>0.01</td><td>0.10</td><td>0.00</td><td>0.3</td><td></td></tr><tr><td>Gu7</td><td>1.06</td><td>0.13</td><td>72.27</td><td>11.72</td><td>4.04</td><td>0.01</td><td>3.35</td><td>0.02</td><td>4.0</td><td>1.05</td></tr><tr><td>N=11</td><td></td><td>0.13</td><td>0.37</td><td>0.11</td><td>0.10</td><td>0.01</td><td>0.12</td><td>0.00</td><td>0.1</td><td></td></tr><tr><td>Gu9</td><td>0.83</td><td>5.50</td><td>57.31</td><td>17.37</td><td>3.24</td><td>2.70</td><td>6.41</td><td>1.69</td><td>7.1</td><td>1.45</td></tr><tr><td>N=19</td><td></td><td>0.48</td><td>0.43</td><td>0.34</td><td>0.06</td><td>0.12</td><td>0.20</td><td>0.15</td><td>0.1</td><td></td></tr><tr><td>Gu10</td><td>0.82</td><td>6.10</td><td>60.03</td><td>15.43</td><td>6.62</td><td>3.06</td><td>n.a.</td><td>n.a.</td><td>3.5</td><td>1.45</td></tr><tr><td>N=8</td><td></td><td>0.59</td><td>1.12</td><td>0.35</td><td>0.24</td><td>0.18</td><td></td><td></td><td>0.1</td><td></td></tr><tr><td rowspan="12">Peralkaline</td><td>Gu11</td><td>0.82</td><td>n.a</td><td>60.57</td><td>15.59</td><td>6.82</td><td>3.08</td><td>3.44</td><td>1.56</td><td>3.4</td><td>1.41</td></tr><tr><td>N=11</td><td></td><td></td><td>0.44</td><td>0.24</td><td>0.18</td><td>0.25</td><td>0.17</td><td>0.08</td><td>0.1</td><td></td></tr><tr><td>Gu12</td><td>0.84</td><td>5.15</td><td>60.27</td><td>15.57</td><td>6.45</td><td>2.78</td><td>n.a.</td><td>n.a.</td><td>3.5</td><td>1.42</td></tr><tr><td>N=7</td><td></td><td>0.60</td><td>0.72</td><td>0.07</td><td>0.15</td><td>0.25</td><td></td><td></td><td>0.0</td><td></td></tr><tr><td>Gu13</td><td>0.79</td><td>n.a</td><td>60.99</td><td>15.64</td><td>6.96</td><td>3.03</td><td>3.46</td><td>n.a.</td><td>3.9</td><td>1.51</td></tr><tr><td>N=10</td><td></td><td></td><td>0.37</td><td>0.21</td><td>0.10</td><td>0.23</td><td>0.15</td><td></td><td>0.1</td><td></td></tr><tr><td>Gu14</td><td>0.82</td><td>5.22</td><td>60.11</td><td>15.39</td><td>6.75</td><td>2.89</td><td>n.a.</td><td>1.71</td><td>3.5</td><td>1.47</td></tr><tr><td>N=11</td><td></td><td>0.71</td><td>0.79</td><td>0.15</td><td>0.25</td><td>0.30</td><td></td><td>0.19</td><td>0.0</td><td></td></tr><tr><td>Gu14b</td><td>0.77</td><td>5.68</td><td>58.90</td><td>15.10</td><td>6.89</td><td>2.81</td><td>3.37</td><td>n.a.</td><td>3.8</td><td>1.52</td></tr><tr><td>N=14</td><td></td><td>0.44</td><td>0.26</td><td>0.14</td><td>0.08</td><td>0.12</td><td>0.08</td><td></td><td>0.0</td><td></td></tr><tr><td>Gu17</td><td>0.79</td><td>5.49</td><td>59.98</td><td>15.42</td><td>6.68</td><td>3.21</td><td>n.a.</td><td>1.65</td><td>3.9</td><td>1.52</td></tr><tr><td>N=12</td><td></td><td>0.54</td><td>0.74</td><td>0.19</td><td>0.15</td><td>0.21</td><td></td><td>0.08</td><td>0.1</td><td></td></tr></tbody></table>

In italics are 2-sigma standard deviation on N analyses

* ASI = Al/(Na+K+Li) atomic ratio with Na measured by LA-ICPMS. Where not measured, Li₂O is taken as 0.9 wt.% in peraluminous glass and 1.7 wt.% in peralkaline glass

**D=(Na+K+Li+2Ca) / Al·(Al+Si) in at.%
<table><caption>Table 5: Trace element composition (in µg/g) of experimental glasses and solubility data</caption><thead><tr><th>Element</th><th>Ca44</th><th>Y89</th><th>La139</th><th>Ce140</th><th>Pr141</th><th>Nd146</th><th>Sm147</th><th>Eu153</th><th>Gd157</th><th>Tb159</th><th>Dy163</th><th>Ho165</th><th>Er166</th><th>Yb172</th><th>Th232</th><th>U238</th><th>ΣREE+Y-Eu*</th><th>XREEPO<sub>4</sub></th><th>K(REEPO<sub>4</sub>)</th></tr></thead><tbody><tr><td>Gu1</td><td></td><td><strong>14.4</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>14.4</td><td>1</td><td>14.4</td></tr><tr><td>N=11</td><td></td><td>0.3</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Gu2</td><td></td><td>2.8</td><td>1.2</td><td></td><td></td><td><strong>11.9</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>15.9</td><td>1</td><td>15.9</td></tr><tr><td>N=9</td><td></td><td>0.8</td><td>0.2</td><td></td><td></td><td>2.2</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Gu3</td><td></td><td>0.3</td><td><strong>12.1</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>12.4</td><td>1</td><td>12.4</td></tr><tr><td>N=10</td><td></td><td>0.1</td><td>0.3</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Gu8</td><td></td><td>1.0</td><td><strong>3.2</strong></td><td><strong>7.1</strong></td><td><strong>0.7</strong></td><td><strong>2.8</strong></td><td>0.5</td><td></td><td>0.5</td><td>0.1</td><td>0.3</td><td></td><td></td><td></td><td></td><td>29.1</td><td>1.1</td><td>16.0</td><td>0.84</td><td>19.1</td></tr><tr><td>N=7</td><td></td><td>0.3</td><td>0.1</td><td>0.2</td><td>0.0</td><td>0.3</td><td>0.1</td><td></td><td>0.1</td><td>0.0</td><td>0.0</td><td></td><td></td><td></td><td></td><td>7.7</td><td>0.6</td><td></td><td></td><td></td></tr><tr><td>Gu18</td><td>380</td><td>0.1</td><td><strong>8.9</strong></td><td></td><td></td><td></td><td></td><td><strong>9.7</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>100.6</td><td>0.2</td><td>9.0</td><td>0.44</td><td>20.5</td></tr><tr><td>N=16</td><td>106</td><td>0.0</td><td>3.2</td><td></td><td></td><td></td><td>0.6</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>4.0</td><td>0.1</td><td></td><td></td><td></td></tr><tr><td>Gu19</td><td>448</td><td></td><td><strong>9.2</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>52.1</td><td>303.5</td><td>9.2</td><td>0.5</td><td>18.4</td></tr><tr><td>N=7</td><td>121</td><td></td><td>1.7</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1.3</td><td>12.4</td><td></td><td></td><td></td></tr><tr><td>Gu4</td><td>3166</td><td><strong>158.2</strong></td><td>16.9</td><td>31.6</td><td>3.5</td><td>15.4</td><td>3.8</td><td></td><td>3.9</td><td>0.7</td><td>4.8</td><td>1.0</td><td>3.2</td><td>3.8</td><td>33.8</td><td>13.2</td><td>248.0</td><td>1</td><td>248.0</td></tr><tr><td>N=10</td><td>87</td><td>2.6</td><td>0.5</td><td>0.6</td><td>0.1</td><td>0.5</td><td>0.2</td><td></td><td>0.1</td><td>0.0</td><td>0.2</td><td>0.0</td><td>0.2</td><td>0.2</td><td>1.4</td><td>0.5</td><td></td><td></td><td></td></tr><tr><td>Gu5</td><td>2629</td><td>30.3</td><td>15.6</td><td>24.1</td><td>2.7</td><td><strong>139.4</strong></td><td>3.0</td><td></td><td>3.5</td><td>0.7</td><td>4.5</td><td>1.0</td><td>3.0</td><td>3.6</td><td>27.6</td><td>11.1</td><td>232.6</td><td>1</td><td>232.6</td></tr><tr><td>N=9</td><td>85</td><td>0.3</td><td>0.6</td><td>0.4</td><td>0.0</td><td>3.6</td><td>0.7</td><td></td><td>0.1</td><td>0.0</td><td>0.1</td><td>0.0</td><td>0.1</td><td>0.2</td><td>0.8</td><td>0.3</td><td></td><td></td><td></td></tr><tr><td>Gu6</td><td>2567</td><td>30.3</td><td><strong>139.6</strong></td><td>21.7</td><td>2.5</td><td>10.9</td><td>3.2</td><td></td><td>3.3</td><td>0.6</td><td>4.3</td><td>1.0</td><td>3.0</td><td>3.5</td><td>26.5</td><td>11.1</td><td>224.9</td><td>1</td><td>224.9</td></tr><tr><td>N=7</td><td>106</td><td>0.4</td><td>1.6</td><td>0.2</td><td>0.1</td><td>0.2</td><td>0.4</td><td></td><td>0.4</td><td>0.1</td><td>0.2</td><td>0.0</td><td>0.1</td><td>0.2</td><td>0.9</td><td>0.5</td><td></td><td></td><td></td></tr><tr><td>Gu7</td><td>2687</td><td>30.1</td><td><strong>31.3</strong></td><td><strong>50.8</strong></td><td><strong>5.5</strong></td><td><strong>22.7</strong></td><td>4.5</td><td></td><td>4.0</td><td>0.7</td><td>4.7</td><td>1.0</td><td>2.9</td><td>3.6</td><td>40.9</td><td>11.9</td><td>162.8</td><td>0.84</td><td>193.8</td></tr><tr><td>N=7</td><td>56</td><td>0.4</td><td>0.5</td><td>1.3</td><td>0.2</td><td>0.4</td><td>0.1</td><td></td><td>0.2</td><td>0.0</td><td>0.1</td><td>0.0</td><td>0.1</td><td>0.1</td><td>2.2</td><td>0.4</td><td></td><td></td><td></td></tr><tr><td>Gu9</td><td>477</td><td>1.3</td><td><strong>14.6</strong></td><td><strong>36.1</strong></td><td><strong>4.2</strong></td><td><strong>16.3</strong></td><td>3.3</td><td></td><td>1.7</td><td>0.1</td><td>0.4</td><td></td><td></td><td></td><td></td><td>49.5</td><td>0.8</td><td>78.0</td><td>0.84</td><td>92.9</td></tr><tr><td>N=7</td><td>44</td><td>0.1</td><td>0.4</td><td>0.9</td><td>0.1</td><td>0.4</td><td>0.2</td><td></td><td>0.2</td><td>0.0</td><td>0.1</td><td></td><td></td><td></td><td></td><td>5.8</td><td>0.1</td><td></td><td></td><td></td></tr><tr><td>Gu10</td><td></td><td><strong>261.7</strong></td><td>1.5</td><td>2.4</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1.5</td><td></td><td></td><td></td><td></td></tr><tr><td>N=8</td><td></td><td>5.5</td><td>0.5</td><td>1.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1.0</td><td></td><td></td><td></td><td></td></tr><tr><td>Gu11</td><td></td><td></td><td>3.1</td><td></td><td></td><td><strong>67.0</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>N=18</td><td></td><td></td><td>0.3</td><td></td><td></td><td>4.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Gu12</td><td></td><td></td><td><strong>57.7</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>N=8</td><td></td><td></td><td>0.7</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Gu13</td><td>306</td><td></td><td><strong>46.2</strong></td><td></td><td></td><td></td><td></td><td><strong>49.6</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>633.3</td><td>0.3</td><td>46.2</td><td>0.66</td><td>70.0</td></tr><tr><td>N=17</td><td>56</td><td></td><td>2.7</td><td></td><td></td><td></td><td>2.6</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>31.0</td><td>0.0</td><td></td><td></td><td></td></tr><tr><td>Gu14</td><td>320</td><td>0.2</td><td><strong>35.9</strong></td><td></td><td></td><td></td><td>0.2</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>324.9</td><td>1156.4</td><td>36.3</td><td>0.73</td><td>49.7</td></tr><tr><td>N=6</td><td>49</td><td>0.0</td><td>0.4</td><td></td><td></td><td></td><td>0.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>5.6</td><td>30.9</td><td></td><td></td><td></td></tr><tr><td>Gu14b</td><td>377</td><td>0.2</td><td><strong>64.5</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>406.4</td><td>642.3</td><td>64.7</td><td>0.73</td><td>88.6</td></tr><tr><td>N=20</td><td>85</td><td>0.0</td><td>1.4</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>8.4</td><td>13.2</td><td></td><td></td><td></td></tr><tr><td>Gu17-max**</td><td>694</td><td></td><td>50.2</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>583.8</td><td>2443.7</td><td>50.2</td><td>0.55</td><td>91.3</td></tr><tr><td>Gu17-aver</td><td>473</td><td></td><td><strong>41.5</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>485.8</td><td>1940.4</td><td>41.5</td><td>0.55</td><td>75.4</td></tr><tr><td>N=25</td><td>130</td><td></td><td>5.4</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>61.1</td><td>266.9</td><td></td><td></td><td></td></tr><tr><td>S19-V4</td><td>504</td><td></td><td>11.2</td><td>5.4</td><td>0.6</td><td>2.9</td><td><strong>123.9</strong></td><td></td><td>1.8</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.3</td><td>145.8</td><td>1</td><td>145.8</td></tr><tr><td>N=5</td><td>90</td><td></td><td>1.3</td><td>1.4</td><td>0.3</td><td>0.6</td><td>2.9</td><td></td><td>0.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.1</td><td></td><td></td><td></td><td></td></tr><tr><td>S19-V7</td><td>432</td><td>0.3</td><td>80.2</td><td>7.3</td><td>2.3</td><td>53.4</td><td><strong>3312.0</strong></td><td>0.2</td><td>70.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.8</td><td>3526.2</td><td>1</td><td>3526.2</td></tr><tr><td>N=5</td><td>55</td><td>0.0</td><td>0.8</td><td>0.6</td><td>0.1</td><td>1.1</td><td>36.2</td><td>0.0</td><td>3.7</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.0</td><td></td><td></td><td></td><td></td></tr><tr><td>S18-V2</td><td>508</td><td>0.2</td><td>28.0</td><td>30.9</td><td>0.5</td><td>7.1</td><td><strong>837.2</strong></td><td></td><td>40.7</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.9</td><td>944.6</td><td>1</td><td>944.6</td></tr><tr><td>N=5</td><td>123</td><td>0.0</td><td>1.3</td><td>3.0</td><td>0.1</td><td>0.8</td><td>13.7</td><td></td><td>8.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.1</td><td></td><td></td><td></td><td></td></tr><tr><td>S18-V3</td><td>687</td><td>0.3</td><td>60.9</td><td>26.4</td><td>3.0</td><td>23.0</td><td><strong>2252.7</strong></td><td>0.2</td><td>121.3</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.8</td><td>8.5</td><td>2487.7</td><td>1</td><td>2487.7</td></tr><tr><td>N=5</td><td>62</td><td>0.0</td><td>4.0</td><td>4.0</td><td>0.0</td><td>0.8</td><td>8.2</td><td>0.0</td><td>14.9</td><td></td><td></td><td></td><td></td><td></td><td>0.1</td><td>0.7</td><td></td><td></td><td></td><td></td></tr><tr><td>S4V2</td><td>562</td><td>0.1</td><td>6.7</td><td><strong>4611.7</strong></td><td></td><td></td><td></td><td></td><td>2.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.6</td><td>0.4</td><td>4621.0</td><td>1</td><td>4621.0</td></tr><tr><td>N=5</td><td>30</td><td>0.0</td><td>0.1</td><td>11.5</td><td></td><td></td><td></td><td></td><td>0.2</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.0</td><td>0.0</td><td></td><td></td><td></td></tr><tr><td>S4V1</td><td>924</td><td>0.1</td><td>2.9</td><td><strong>715.5</strong></td><td>0.1</td><td></td><td></td><td></td><td>0.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.9</td><td>1.9</td><td>719.0</td><td>1</td><td>719.0</td></tr><tr><td>N=5</td><td>127</td><td>0.0</td><td>1.0</td><td>49.0</td><td>0.1</td><td></td><td></td><td></td><td>0.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.2</td><td></td><td></td><td></td><td></td></tr><tr><td>S7V7</td><td>486</td><td></td><td>0.1</td><td><strong>795.1</strong></td><td></td><td></td><td></td><td></td><td>0.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td>1.0</td><td>795.7</td><td>1</td><td>795.7</td><td></td></tr><tr><td>N=5</td><td>112</td><td></td><td>0.0</td><td>6.6</td><td></td><td></td><td></td><td></td><td>0.2</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.2</td><td></td><td></td><td></td><td></td></tr><tr><td>V7V8</td><td>526</td><td></td><td>0.4</td><td><strong>2161.9</strong></td><td></td><td></td><td></td><td></td><td>1.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td>2.4</td><td>2163.5</td><td>1</td><td>2163.5</td><td></td></tr><tr><td>N=5</td><td>133</td><td></td><td>0.0</td><td>91.9</td><td></td><td></td><td></td><td></td><td>0.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.1</td><td></td><td></td><td></td><td></td></tr></tbody></table>

XREEPO₄ is the molar proportion of monazite in cheralite (newly-formed cheralite where different from starting cheralite)

Highlighted in bold is the concentration of the most important REE in each experiment

In italics are 2-sigma standard deviation on N analyses

Tm and Lu were measured <1 µg/g

* Eu is excluded from the ΣREE because of its divalent valence

** Maximum value is given as the closest point to the fragment
<table><caption>Table 6. Electron microprobe analyses (in wt.%) of experimental products (crystals and immiscible droplets). Start cheralite compositions are given as theoretical values and were checked by EPMA.</caption><thead><tr><th></th><th></th><th>SiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>Na<sub>2</sub>O</th><th>K<sub>2</sub>O</th><th>P<sub>2</sub>O<sub>5</sub></th><th>F</th><th>CaO</th><th>La<sub>2</sub>O<sub>3</sub></th><th>Eu<sub>2</sub>O<sub>3</sub></th><th>UO<sub>2</sub></th><th>ThO<sub>2</sub></th><th>Total</th></tr></thead><tbody><tr><td rowspan="5">Immiscible droplets</td><td>Gu13</td><td>1.00</td><td>22.00</td><td>5.13</td><td>1.26</td><td>35.26</td><td>24.44</td><td>2.80</td><td>2.15</td><td>1.64</td><td></td><td>10.91</td><td>96.32*</td></tr><tr><td>N=9</td><td>0.50</td><td>2.40</td><td>1.07</td><td>0.17</td><td>1.70</td><td>2.74</td><td>0.30</td><td>0.33</td><td>0.28</td><td></td><td>1.07</td><td>4.09</td></tr><tr><td>Gu14</td><td>0.73</td><td>21.77</td><td>4.25</td><td>0.86</td><td>36.26</td><td>28.61</td><td>4.98</td><td>1.93</td><td></td><td>5.36</td><td>6.50</td><td>99.35*</td></tr><tr><td>N=6</td><td>0.42</td><td>1.49</td><td>1.21</td><td>0.31</td><td>0.93</td><td>1.73</td><td>0.54</td><td>0.12</td><td></td><td>0.59</td><td>0.95</td><td>1.63</td></tr><tr><td>Start cheralite</td><td>0.00</td><td></td><td></td><td></td><td>30.36</td><td></td><td>6.00</td><td>27.88</td><td>7.53</td><td></td><td>28.24</td><td>100.00</td></tr><tr><td rowspan="5">Monazite-cheralite crystals</td><td>Gu 13</td><td>0.99</td><td></td><td></td><td>0.16</td><td>30.13</td><td></td><td>2.94</td><td>41.92</td><td>7.85</td><td></td><td>15.14</td><td>99.36</td></tr><tr><td>N=11</td><td>0.21</td><td></td><td></td><td>0.10</td><td>0.43</td><td></td><td>0.74</td><td>4.63</td><td>0.83</td><td></td><td>4.04</td><td>1.10</td></tr><tr><td>Gu18</td><td>1.75</td><td></td><td></td><td>0.11</td><td>30.22</td><td></td><td>5.19</td><td>27.83</td><td>8.30</td><td></td><td>27.26</td><td>101.06</td></tr><tr><td>N=13</td><td>1.54</td><td></td><td></td><td>0.11</td><td>0.69</td><td></td><td>0.71</td><td>3.10</td><td>2.35</td><td></td><td>4.39</td><td>1.55</td></tr><tr><td>Start cheralite</td><td>0.00</td><td></td><td></td><td></td><td>30.45</td><td></td><td>6.02</td><td>34.95</td><td></td><td>11.59</td><td>16.99</td><td>100.00</td></tr><tr><td rowspan="5"></td><td>Gu17</td><td>1.15</td><td></td><td></td><td></td><td>28.94</td><td></td><td>5.31</td><td>38.70</td><td></td><td>8.40</td><td>17.59</td><td>100.09</td></tr><tr><td>N=27</td><td>0.53</td><td></td><td></td><td></td><td>0.38</td><td></td><td>0.65</td><td>3.73</td><td></td><td>3.07</td><td>1.07</td><td>0.57</td></tr><tr><td>Start cheralite</td><td>0.00</td><td></td><td></td><td></td><td>30.43</td><td></td><td>6.01</td><td>34.93</td><td></td><td>14.47</td><td>14.15</td><td>100.00</td></tr><tr><td>Gu14</td><td>0.18</td><td></td><td></td><td>0.07</td><td>28.85</td><td></td><td>3.25</td><td>49.74</td><td></td><td>2.46</td><td>13.62</td><td>98.18</td></tr><tr><td>N=12</td><td>0.06</td><td></td><td></td><td>0.04</td><td>0.45</td><td></td><td>0.14</td><td>1.36</td><td></td><td>0.57</td><td>0.45</td><td>1.09</td></tr><tr><td rowspan="5"></td><td>Gu14b</td><td>1.30</td><td></td><td></td><td>0.13</td><td>29.99</td><td></td><td>1.99</td><td>56.20</td><td></td><td>1.14</td><td>8.71</td><td>99.47</td></tr><tr><td>N=15</td><td>0.68</td><td></td><td></td><td>0.06</td><td>0.48</td><td></td><td>0.33</td><td>2.50</td><td></td><td>0.71</td><td>1.61</td><td>0.82</td></tr><tr><td>Gu14X</td><td>0.65</td><td></td><td></td><td></td><td>30.20</td><td></td><td>2.27</td><td>55.31</td><td></td><td>0.73</td><td>10.74</td><td>99.25</td></tr><tr><td>N=16</td><td>0.35</td><td></td><td></td><td></td><td>0.55</td><td></td><td>0.14</td><td>1.38</td><td></td><td>0.14</td><td>0.74</td><td>1.12</td></tr><tr><td>Gu19</td><td>0.11</td><td></td><td></td><td>0.11</td><td>30.20</td><td></td><td>6.12</td><td>35.06</td><td></td><td>14.21</td><td>14.27</td><td>100.08</td></tr><tr><td rowspan="5"></td><td>N=10</td><td>0.08</td><td></td><td></td><td>0.03</td><td>0.21</td><td></td><td>0.13</td><td>0.87</td><td></td><td>0.62</td><td>0.67</td><td>0.66</td></tr></tbody></table>

In italics are 2-sigma standard deviation on *N* analyses

* Totals are corrected for oxygens equivalent to F