The Geochemical Characteristics of Ore-Forming Fluids in the Jebel Stah Fluorite Deposit in Northeast Tunisia: Insights from LA-ICP-MS and Sr Isotope Analyses

Abstract

The Zaghouan Fluorite Province (ZFP) encloses F-Ba(Pb-Zn) ores hosted within Jurassic carbonate series, in northeastern Tunisia. Critical breakthroughs on the Jebel Stah fluorite deposits, an MVT-style F-mineralization, have been made within the Lower Jurassic limestones along the Zaghouan Fault, which is a major target for mineralization. This study presents the first REE-Y analyses conducted by LA-ICP-MS on fluorites in Tunisia, and specifically on the fluorites of Jebel Stah deposit. This analytical technique provides highly accurate insights into the geochemical regime of mineralizing fluids and the related scavenging sources. Distinct geochemical characteristics between two fluorite generations (G1 and G2) were revealed. Fluorites (Fl2) from the early generation (G1) showed low ΣREE + Y (36.3 and 39.73 ppm, respectively). When normalized to chondrites, early fluorite G1 displayed a bell-shaped REE + Y pattern with a depletion in LREE relative to HREE and a slight MREE hump. Late fluorite (Fl3) generation (G2) displayed higher ΣREE + Y concentrations (77.43 ppm), but an almost similar REE pattern. Ce/Ce* ratios demonstrated strong negative Ce anomalies in all fluorites, while Eu/Eu* ratios indicated weak negative Eu anomalies. The positive Y anomaly observed in the REE + Y patterns of fluorites G1 and G2 suggests Y-Ho fractionation in the fluid system. Moreover, significant degrees of differentiation between terbium (Tb) and lanthanum (La) have been observed in all fluorite samples. The plot of fluorites from both fluorite generations on the Tb/La–Tb/Ca diagram gives evidence of the sedimentary hydrothermal origin of the ore-forming fluids in the Jebel Stah F-deposit. Sr isotopes show that the mineralizing fluids are radiogenic and deeply sourced basinal brines, whereas the small variation in ⁸⁷Sr/⁸⁶Sr ratios suggests a similar source for Sr in fluorites G1 and G2. These results allow us to conclude that the economic fluorite (G1) ore of Jebel Stah was deposited due to the interaction of the deeply sourced hydrothermal fluid with the carbonated host rocks (dolomitization, an increase in pH, and Ca activity), whereas the late fluorite (G2) is an accessory and could have resulted from the mixing of the hydrothermal fluid with shallow meteoric waters.

1. Introduction

Rare earth elements and yttrium (REE + Y) and fluorite have been designated as critical materials by the European Commission [1] due to their high economic importance and potential supply risks. Fluorite acts as a reliable geochemical archive that can preserve the REE + Y signature of the hydrothermal fluid from which they were formed. The assessment of REE + Y in Ca-rich minerals provides crucial data on mineral sources, fluid migration, temperature conditions, chemical fluid composition, and host–rock interactions [2,3,4,5]. The distribution of trace elements in fluorite has been the subject of numerous studies (e.g., [3,4,6,7,8,9,10,11]).

REE-bearing deposits are derived from various sources, including hydrothermal, magmatic, or even supergene sources. Economic F deposits can form in diverse host lithologies, although they are typically formed through hydrothermal processes associated with sedimentary origins, primarily carbonates with similarities to MVT mineralization [12,13,14]. However, vein and replacement F deposits in sedimentary host rocks have more variable origins, as they could have originated directly from sedimentary rocks, deep metamorphic fluids, or magmatic sources [5,15,16].

The Zaghouan Fluorite Province (ZFP) is located in northern Tunisia in the Zaghouan region and hosts abundant Pb-Zn-Ba-Sr-F ore deposits (Figure 1). The lithostratigraphic section consists mainly of carbonates, shales, and siliciclastic rocks ranging from the Triassic to Miocene periods (Figure 1 and Figure 2). These deposits have been extensively studied (e.g., [17,18,19,20,21,22,23,24,25,26,27,28]). The ZFP spans over 1000 km² and is structurally controlled by the NE-trending Zaghouan Fault (ZF), a deep-seated structure [29] that separated Jurassic limestone massifs (e.g., Jebel Ressas and Jebel Zaghouan), and has been intruded by Triassic salt layers and diapirs. This fault system has been active since the Early Jurassic period and controls a NE-SW series of paleohigh structures.

The F-(Ba–Pb–Zn) deposits in the Zaghouan district (Figure 2) occur as stratabound or stratiform bodies, located either within or above the Jurassic reef limestones, along unconformity surfaces separating the Oust Formation (Stah, Kohol) or the Ressas Formation (Zriba–Guebli, Mecella) from the overlying sequences. Fracture-controlled mineralization is also observed in uplifted limestone blocks and their overburden (Hammam Jedidi, Oust, and Sidi Taya). Despite a consistent Liassic stratigraphy across the district (Stah, Kohol, Oust, Zaress, Bent Saidane, Fkirine; Figure 2), significant epigenetic dolomitization associated with stratabound fluorite mineralization is primarily restricted to Jebel Stah and the adjacent Jebel Kohol deposit. Fluid inclusion studies, including microthermometry and crush–leach bulk chemistry, conducted on minerals from various deposits in the Zaghouan district [25,26,27], revealed highly saline (12–34 wt% NaCl equivalent) Na- and Ca-chloride-rich hydrothermal fluids with moderate temperatures (100 to 250 °C). Mean homogenization temperatures (Th) and salinities (S) of fluid inclusions in fluorites from ore deposits in northeastern Tunisia are summarized in Table 1. Geothermometric analysis suggests an average reservoir temperature of approximately 275 ± 25 °C.

Table 1. Mean homogenization temperatures (Th) and salinities (S) of the fluid inclusions in fluorites from ore deposits in northeastern Tunisia.

Locality	Fluorite Generation	Mean Th ± 5 (°C)	Mean Salinity ± 1 (wt% eq. NaCl)	Reference
Jebel Stah	1	130	19.5	[25,27]
	2	175	10
Hammam Zriba	1	125	13	[24]
	2	135	15
	3	170	17
Sidi Taya	-	130	19.5	[25]
Jebel Mecella	-	138	18.75	[30]
Jebel Oust	-	202	32	[25]
Oued M’tak	-	120–140	14–17	[30]

Table 1. Mean homogenization temperatures (Th) and salinities (S) of the fluid inclusions in fluorites from ore deposits in northeastern Tunisia.

Locality	Fluorite Generation	Mean Th ± 5 (°C)	Mean Salinity ± 1 (wt% eq. NaCl)	Reference
Jebel Stah	1	130	19.5	[25,27]
	2	175	10
Hammam Zriba	1	125	13	[24]
	2	135	15
	3	170	17
Sidi Taya	-	130	19.5	[25]
Jebel Mecella	-	138	18.75	[30]
Jebel Oust	-	202	32	[25]
Oued M’tak	-	120–140	14–17	[30]

This paper reviews the REE + Y distribution at the Jebel Stah F deposit and aims to determine whether there are shared factors with the neighboring deposits, controlling their formation. The present contribution involved the following essential elements: (1) the identification of major elements by SEM-EDS analysis; (2) the characterization of REE + Y compositions in two generations of fluorite (G1 and G2) using the LA-ICP-MS technique; (3) constraining the geochemical regime of fluorites; and (4) using the Sr isotope analysis to discuss fluid sources and fluid–rock interactions. These findings aimed to gain new data on the mineralization system, which could be correlated with several F deposits commonly found in MVT F-Ba-(Pb-Zn) stratabounds and veins (e.g., [31,32,33,34]).

Figure 1. (A) Geological and geodynamic setting of the study area at the southern margin of the Mediterranean Sea [35]. (B) General tectonic and metallogenic map of northern Tunisia [36,37,38,39,40,41,42].

Figure 1. (A) Geological and geodynamic setting of the study area at the southern margin of the Mediterranean Sea [35]. (B) General tectonic and metallogenic map of northern Tunisia [36,37,38,39,40,41,42].

Figure 2. The stratigraphic positions and types of mineralizations of the northeastern Tunisian ore deposits (after [20,25]). 1 Gypsum and clays; 2 Reef limestones; 3 Phosphatic limestones or limestones; 4 Limestone–marl alternation; 5 Conglomeratic limestone; 6 Limestone–marl alternation; 7 reef limestones or limestone–marl alternation; 8 Limestone–marl alternation with interbedded limestone layers; 9 Limestones; 10 Limestone–marl alternation; 11 Limestones; 12 Marls; 13 Limestones; 14 Sandstones; 15 Clays, sandstones and sandy limestones; 16 Conglomerate–sand unit.

Figure 2. The stratigraphic positions and types of mineralizations of the northeastern Tunisian ore deposits (after [20,25]). 1 Gypsum and clays; 2 Reef limestones; 3 Phosphatic limestones or limestones; 4 Limestone–marl alternation; 5 Conglomeratic limestone; 6 Limestone–marl alternation; 7 reef limestones or limestone–marl alternation; 8 Limestone–marl alternation with interbedded limestone layers; 9 Limestones; 10 Limestone–marl alternation; 11 Limestones; 12 Marls; 13 Limestones; 14 Sandstones; 15 Clays, sandstones and sandy limestones; 16 Conglomerate–sand unit.

This study presents the first in situ LA-ICP-MS analysis of REE-Y geochemistry in Tunisian fluorite deposits, providing a microscale perspective that was previously unattainable with conventional bulk ICP-MS. Unlike bulk methods, which yield averaged compositions and obscure spatial variations, LA-ICP-MS preserves mineral integrity and reveals fine-scale heterogeneities in REE-Y distribution within individual fluorite crystals. This approach enables a refined interpretation of fluid chemistry and mineralizing processes. Additionally, our study introduces the first yttrium (Y) measurements in these fluorites, along with Y/Ho vs. La/Ho and Tb/La–Tb/Ca diagrams, offering new insights into REE fractionation trends. The high spatial resolution of LA-ICP-MS enhances our understanding of fluorite precipitation mechanisms in the Jebel Stah deposit, marking a significant advancement in the geochemical characterization of the Zaghouan Fluorite Province.

2. Lithostratigraphy and Main Syngenetic/Epigenetic Events

The oldest exposed rocks in northern Tunisia, particularly within the study area, are of Triassic age (Figure 1 and Figure 3). These rocks consist of chaotic assemblages of gypsum, clay, sandstone, and carbonates (dolomites or dolomitic limestones) (Figure 2). They may also be host to various authigenic minerals, including quartz, dolomite, magnesite, albite, K-feldspars, phlogopite, phengite and chlorite. In comparison to the surrounding areas, the Triassic series in the Zaghouan area is estimated to exceed 1000 m in thickness [43]. The overlying stratigraphic sequence mainly consists of alternating marls and limestones. Additionally, the subsidence rate is particularly significant to the west of the Zaghouan Fault. The Jurassic, Cretaceous, and Tertiary series reach their maximum thickness near the Jebel Oust, estimated at approximately 1200 m, 4500 m, and 3500 m, respectively [29]. In contrast, significant uplifts and emergence are observed eastward across the province. At Hammam Zriba, the Campanian to Miocene formations reach a maximum thickness of only 2100 m [24].

At Jebel Stah, mineralization occurs along the Hettangian–Lower Sinemurian gray limestones of the uppermost Oust Formation, which composes an uplifted block and remains within the overlying Carixian phosphatic limestone layer (Figure 4 and Figure 5). The uppermost limestones of the Oust Formation contain abundant authigenic bipyramidal quartz crystals (0.2 to 2 mm) and 1 to 2 cm long gypsum molds, which are entirely filled with calcite and are invaded by an extended epigenetic dolomitization [23,27]. The well-defined crystalline structure of the authigenic quartz, along with the presence of carbonate inclusions, indicates its formation during an early diagenetic phase within a pre-evaporitic setting. This environment also facilitated gypsum precipitation, as evidenced by sulfate molds found in both limestones and dolostones.

An emergence surface, marked by a hard-ground and small karstic cavities, lies at the top of the Oust Formation (Figure 5). Overlying the Oust Formation is the Carixian condensed layer, which is between 0.2 and 1.2 m thick (Figure 4 and Figure 5). This layer is composed of thin lenticular limestones enriched with phosphatic nodules, gastropods, ammonites, glauconite grains, and authigenic quartz. A few-millimeter-thick pyritic crust covers the limestone beds [23,44]. Finely laminated detrital silico-carbonated deposits, accumulated in the karstic cavities at the top of the Oust Formation, provide evidence for a second emergence phase during the Lower Domerian [45]. The overlying Middle–Upper Domerian is made of a condensed layer (0.1–1.5 m) consisting of lenticular dark gray limestone rich in belemnites with thin intercalated dark green clays. The subsequent Toarcian to Neocomian interval is characterized by a sequence of alternating marls and limestones (Figure 3 and Figure 4).

The epigenetic dolomitization process resulted in (i) a reddish, homogeneous dolosparite (Figure 6) that affects (i) the top of the Oust Formation, giving rise to a reddish, homogeneous dolosparite “D1”, frequently showing extensive recrystallization, giving rise to a banded texture (Figure 6a) or a vuggy solution breccia (Figure 6b), in which a second generation of dolomite (D2) occurs as pure light-colored large rhombohedra crystallizing after the dolosparite (D1); (ii) dolomitization extends beyond the emergence surface and partially impacts both the Carixian phosphatic limestones and the finely laminated karst deposits (Figure 6e).

The dolomite crystals exhibit wavy extinction, indicating a calcium to magnesium ratio exceeding one [46] This dolomite can contain up to 60 mole% CaCO₃. These dolomites crystallized at temperatures exceeding those typically found at the seawater–sediment interface. Their crystallization subsequent to quartz and the emergence surface indicates a late diagenetic to epigenetic origin [46,47,48,49]. The uppermost section of the dolomitic layer features dissolution breccias and rhythmic structures, formed by homogeneous dolosparite crystallization. Similar dolomites are commonly associated with Mississippi Valley-Type ore deposits [47,48,50]. The observed rhythmic structures are comparable to the diagenetic crystallization rhythmites (DCRs) documented by Fontbote et al. [51]. The formation of DCRs is widely attributed to the interaction of hot brines with the surrounding rock in an open system, occurring long after lithification [52,53,54].

3. Ore Deposit Morphology and Petrography

Mineralization at Jebel Stah occurs in three types of orebodies: stratiform, cavity fillings, and veins [19,25,27,28] (

Table A1. Samples selected for the REE + Y geochemistry in the different fluorite orebodies of the Jebel Stah deposit.

Sample	Orebody	Host Rocks	Ore Description	Petrographic Type of Fluorite	Fluorite Gene- Ration
FlCI1	Vein	Topmost HLS * (Oust) Formation-Carixian series	Fluorite, colorless to purple, in coarse crystals	2	I
JSCIV			Fluorite, massive, colorless to white		I
JSFv	Cavity fillings	Topmost HLS * (Oust) Formation	Fluorire, colorless to purple fluorite in coarse crystals (2 m below the Carixian phosphatic condensed layer).	3	II

*: Hettangian–Lower Sinemurian.

,

Table A2. Samples selected for the REE geochemistry in the different petrographic facies of the wallrocks and the fluorite ore of Jebel Stah [20,28].

Petrographic Group	Lithology/Ore Facies/Orebody	Age of Layer/Ore- Bearing Layer(s)	Sample	Petrographic Description	Petrographic Type of Fluorite	Mineralogy
I: Limestone and authigenic quartz	Backreef limestones	Lower Sinemurian	L6-5	Gray limestones	-	Calcite
			L6-30	Gray limestones with authigenic quartz	-	Calcite, Quartz
			L6-30Q	Authigenic quartz	-	Quartz
II: Dolostones and associated fluorite	Dolostones (Upper part of the Oust Formation)		L5-3	Massive yellow dolosparite	-	Dolomite
			DZ6-G	Gray dolosparite of the pseudo-brecciated facies	-
			DZ6-J	White sparry dolosparite of antipolar growth of the pseudo-brecciated facies	-
			DZ6-F	Colorless fluorite filling voids in the pseudo-brecciated dolostone facies	Fl3	Fluorite
III: Phosphatic limestone and associated fluorite	Phosphatic limestone	Carixian	JS1-6P	Nodular gray phosphate	-	Apatite, calcite
	Macrocrystalline fluorite associated with the phosphatic limestone		CC3-3	Macrogranular purple fluorite	Fl1b	Fluorite
			CC3-2
			JS1-6F	Macrogranular white fluorite
IV: Finely laminated dolostones and associated fluorite	Finely laminated karst deposits		L3-21D	Dolomicrite	-	Dolomite, quartz s
			L3-21F	Microgranular fluorite replacing the carbonated matrix	Fl1a	Fluorite, dolomite s quartz m
			L5-16	Microgranular black fluorite with remains of matrix
			L5-15F	Microgranular fluorite rich in matrix remains		Fluorite, quartz s, dolomite s, calcite s, apatite m
			L5-15G	Mesogranular-purple fluorite layers alternating with sample L5-15F	Fl1b
V: Banded ore			FZ-5N	Microgranular fluorite with matrix remains	Fl1a
			FZ-5B	Macrogranular-white fluorite	Fl1b	Fluorite, quartz s
VI: Megacrystalline fluorite and calcite in lodes		Sinemurian to Lower Toarcian	JS5-F	Cm-sized fluorite crystals	Fl2	Fluorite
			JS6-F
			JS5-C	Cm- to dm-sized rhombohedral calcite crystals	-	Calcite
			JS6-C
VII: Fluorite in cavities	Intradolomitic pockets filled with residual clays	Lower Sinemurian	L4-2	Cm- to dm-sized, cubic blue and purple fluorite	Fl3	Fluorite
	Geode	Carixian	JS3-5	Cm-sized cubic fluorite

^s: secondary mineral phase; ^m: minor mineral phase.

and

Table A3. Samples selected for the REE geochemistry of the wallrock carbonates and the associated ores in the Zaghouan Fluorite District [20,28].

Petrographic Group	Lithology/Ore Facies/Orebody	Layer/Ore Bearing Layer(s) Age	Sample	Petrographic Description (Petrographic Type of Fluorite)	Mineralogy
Limestone	Backreef limestones	Uppermost Jurassic	ST9	Gray limestones	Calcite
Fluorite in lodes	Veins cutting the Ressas Formation		ST42-5	White to smoky massive fluorite	Fluorite
			STIII-5
			ST50-2
Fluorite in lodes with calcite	Lodes cutting the Oust Formation	Lowermost Jurassic	HJ-2F	Colorless to white megacrystalline fluorite
Celestite in lodes			HJ-1Sr	Colorless megacrystalline celestite	Celestite
Fluorite with calcite in lodes trending N 90–110° E, N 160–180° E or N 30–60° E	Lodes cutting the Oust Formation and its Upper Jurassic (marl-limestone) cover	Lowermost Jurassic–Upper Jurassic	JOIII-10	White massive fluorite	Fluorite
			JO2-1
			JO-F	White megacrystalline fluorite
			JO-FC	Onyx-like calcite associated with fluorite (JO-F)	Calcite
	Veins cutting the Lower Miocene sandstone layer	Burdigalian	OM1	Colorless megacrystalline fluorite	Fluorite
			OM-FC	White megacrystalline calcite associated with fluorite (OM1)	Calcite

Abbreviations: ST: Sidi Taya; HJ: Hammam Jedidi; JO: Jebel Oust; OM: Oued M’tak.

; Figure 5). The stratiform Carixian orebody, measuring more than 700 m long and 0.2 to 1.5 m in thickness, bears the petrographic type 1 fluorite “Fl1”, with its two sub-types (Fl1a, Fl1b). These fluorite ore bodies demonstrate both banded (Figure 6f and Figure 7) and solution breccia (Figure 6c and Figure 7) textures, where the dark zones are made of a microgranular fluorite “Fl1a” replacing the carbonated/phosphatic matrix, and the clear zones consist of a coarse crystalline white to purple pure fluorite “Fl1b”, stemming from the recrystallization of the fluorite “Fl1a”. Colorless to white coarse-grained fluorite along with megacrystalline calcite fills large dissolution cavities associated with veins (N 90–130° E and N 30–70° E), extending from the Hettangian to Toarcian sequences (Figure 5), making the second petrographic type “Fl2”. Fluorite occurring on the wall of dm-sized cavities (geodes), as colorless, white, or purple cubic crystals, 1–4 cm in size, is referred to as the third petrographic type “Fl3” (Figure 5).

Based on microthermometric and geochemical analysis of fluid inclusions, Souissi et al. [25,27] have demonstrated that the petrographic types Fl1a, Fl1b, and Fl2 are cogenetic and belong to the first generation, whereas the petrographic type Fl3 occurs subsequently as a second generation.

4. Sampling and Analytical Techniques

Three fluorite samples (FlCI1, JSFv, JSC_IV) were collected from the ZFP in the Jebel Stah deposit (Table A1). Three polished, thick sections were prepared from selected representative samples: two vein fluorites (FlCI1 and JSC_IV) from the first generation and one cavity-filling fluorite sample (JSFv) from the second generation. These samples were subjected to detailed mineralogical and geochemical analyses.

4.1. SEM-EDS Analysis

The major element contents of the fluorites were measured by SEM–EDS at CeSAR laboratories (University of Cagliari, Italy). Preliminary observations were made using a polarization microscope, followed by BSE imaging using an FEI Quanta 200 SEM, equipped with a Thermo Scientific TM Ultra Dry EDS Detector for qualitative mineral chemistry. SEM imaging was conducted on polished, C-coated, thin and thick sections. The data were collected and processed using Pathfinder 3.1 software to determine qualitative information on the mineral species.

4.2. LA-ICP-MS for REE Analysis

The trace-element composition of fluorite was analyzed by Inductively Coupled Plasma-quadrupole Mass Spectrometry (ICP-MS, PE-ElanDRC) after laser ablation (LA, New Wave Research UP213 deep-UV YAG). The LA-ICP-MS analysis was performed at pulse rates of 5 Hz, 65% energy (arbitrary scale of the instrument), and spot sizes of 50–65 μm. Isotopes of 58 elements ranging from Li to U were measured, but only a few of these were detected at concentrations above the instrumental detection limit. These elements included Ca, Sr, Rb, and fourteen light and heavy REEs. The isotope ⁴³Ca was used as an internal standard to control variations in signal intensity due to time-differential ablation efficiencies. NIST612 standard glasses were measured before and after each sample batch to monitor instrument stability and calculate sample concentrations. The detection limits for LA-ICP-MS analyses are presented in Table S1.

4.3. TIMS for Sr Isotope Analysis

The geochemical compositions of the samples, including their Rb and Sr contents and Rb/Sr ratios, were determined using wavelength-dispersive X-ray fluorescence (XRF) and ICP-MS with an Agilent Technologies 7700 series spectrometer, at the geochemistry labs of the Department of Geosciences of the UA. For these analyses, bulk fluorite samples were initially powdered under clean conditions to prevent contamination. For Sr isotope analysis, a carefully selected small fraction (0.02 g) of the powdered fluorite was used. Sample selection was based on mineralogical purity and textural homogeneity to minimize potential contamination from surrounding phases. While fluorite can contain fluid inclusions, their potential influence on the measured ⁸⁷Sr/⁸⁶Sr ratios is considered negligible due to the high-temperature acid dissolution process, which ensures a complete breakdown of the mineral lattice and efficient Sr release from the fluorite structure itself.

At the laboratory of isotope geology of the UA, the selected powder samples were chemically dissolved in Teflon Parr acid-digestion bombs containing an HCl/HNO₃ solution and heated to approximately 120 °C. After the evaporation of the remaining solution, the samples were dissolved in HCl (6.2 N) and dried again. The separation of purified Sr was performed through ion chromatography using ion-exchange columns filled with Sr-Resin (TrisKem International). All reagents used in sample preparation were distilled under sub-boiling conditions, and pure water was obtained by a Milli-Q Element equipment. Phosphoric acid (H₃PO₄) was used to load Sr onto a single Ta filament. The ⁸⁷Sr/⁸⁶Sr isotope ratios were measured using a VG Sector 54 multi-collector Thermal Ionization Mass Spectrometer (TIMS).

Measurements were made in dynamic mode at 1–2 V for ⁸⁸Sr. Mass fractionation affecting measurements of Sr isotopic ratios was corrected by normalizing to a value of ⁸⁸Sr/⁸⁶Sr = 0.1194. The standard NIST SRM-987 served as a reference during the study, with an average value of ⁸⁷Sr/⁸⁶Sr = 0.710259 (+/−24) (N = 10; confidence limit = 95%).

5. Results

5.1. Ore Mineralogy

Ore minerals at Jebel Stah show similar mineral assemblages, mainly composed of fluorite (CaF₂). Macroscopic, microscopic and SEM-EDS analyses (Figure 8 and Figure 9) reveal a mineral association where calcite (CaCO₃) serves as the primary gangue mineral, accompanied by hematite (Fe₂O₃), traces of galena (PbS), and accessory sulfides (pyrite: FeS₂; sphalerite (Zn,Fe)S), accessory sulfates (barite BaSO₄, celestine SrSO₄), and apatite (Ca₅(PO₄)₃F).

5.2. REE + Y Geochemistry of Fluorites

Mineral chemical analyses were conducted on two fluorite generations (G1 and G2) using LA-ICP-MS. These analyses were performed on two thin, double-polished sections of G1 (samples FlCI1 and JSC_IV; Table A1), and on one thin, double-polished section of G2 (sample JSFv; Table A1). The REE + Y concentration patterns were normalized to chondrite values from Taylor and McLennan [55] and are presented in Figure 10 and

Table A9. Initial ΣREE + Y values and individual REE + Y values calculated after chondrite normalization, and ${(\mathrm{R}\mathrm{E}\mathrm{E}+\mathrm{Y})}_{\mathrm{C}\mathrm{N}}$ ratios for fluorite vein (G1) samples (FICI1 and JSCIV) and fluorite cavity-filling (G2) sample (JSFv).

Fluorite Type	Laser Spots	ΣREE + Y	ΣLREE	ΣHREE	ΣMREE	${(\mathbf{R}\mathbf{E}\mathbf{E}+\mathbf{Y})}_{\mathbf{C}\mathbf{N}}$	${\mathbf{L}\mathbf{R}\mathbf{E}\mathbf{E}}_{\mathbf{C}\mathbf{N}}$	${\mathbf{M}\mathbf{R}\mathbf{E}\mathbf{E}}_{\mathbf{C}\mathbf{N}}$	${\mathbf{H}\mathbf{R}\mathbf{E}\mathbf{E}}_{\mathbf{C}\mathbf{N}}$
Fluorite vein G1	04-FIlCI1-01	2.5082	0.8175	0.125	1.6907	2.801	0.796	0.897	2.005
	05-FlCI1-02	2.0149	0.8237	0.1302	1.1912	1.7187	0.6607	0	1.058
	06-FlCI1-03	2.1522	0.8686	0.1585	1.2836	1.83	0.694	0.376	1.136
	07-FlCI1-04	2.4342	1.684	0.1084	0.7502	3.43	2.887	0.51	0.543
	08-FlCI1-05	2.2643	1.1532	0.2183	1.1111	2.191	0.749	0.573	1.442
	09-FlCI1-06	2.6486	1.6325	0.2153	1.0161	2.232	1.134	0.735	1.098
	10-FlCI1-07	1.9981	0.9653	0.2183	1.0328	0.7855	0.1685	0	0.617
	11-FlCI1-08	1.0829	0.7624	0.0783	0.3205	0.383	0.137	0	0.246
	12-FlCI1-09	1.6257	1.1017	0.149	0.524	1.334	0.969	0	0.365
	13-FlCI1-10	3.982	2.5842	0.4825	1.3978	8.386	6.013	2.136	2.373
	14-FlCI1-11	2.5758	1.0265	0.2167	1.5493	2.247	0.646	0.739	1.601
	15-FlCI1-12	2.9467	2.045	0.2895	0.9017	3.47	2.659	0.876	0.811
	16-FlCI1-13	2.324	1.4276	0.2049	0.8964	2.497	0.468	0.35	2.029
	17-FlCI1-14	1.4222	0.8141	0.2073	0.6081	0.922	0.38	0.38	0.542
	18-FlCI1-15	4.3519	3.279	0.2097	1.0729	7.417	5.974	0.982	1.443
		Σ = 36.3317	Σ = 20.9853	Σ = 3.0119	Σ = 15.3464	Σ = 41.6442	Σ = 24.335	Σ = 8.554	Σ = 17.309
	17-JSCIV-01	1.768	0.861	0.1861	0.907	0.872	0.57	0	0.302
	18-JSCIV-02	2.195	0.852	0.261	1.343	4.805	0.36	1.32	4.445
	19-JSCIV-03	1.839	0.729	0.128	1.11	1.2464	0.512	0.34	0.734
	20-JSCIV-04	1.923	0.659	0.2082	1.263	1.172	0.37	0.65	0.802
	21-JSCIV-05	2.155	0.692	0.2421	1.463	1.505	0.226	0.448	1.279
	22-JSCIV-06	2.503	1.044	0.392	1.458	3.512	1.502	1.32	2.01
	23-JSCIV-07	2.543	1.059	0.3499	1.484	5.793	2.703	2.05	3.09
	24-JSCIV-08	2.313	0.819	0.2325	1.495	8.166	0.679	0.89	7.487
	25-JSCIV-09	2.738	0.842	0.296	1.896	3.563	1.135	0.68	2.428
	26-JSCIV-10	1.541	0.415	0.109	1.125	0.703	0.16	0.16	0.543
	27-JSCIV-11	1.377	0.443	0.133	0.934	1.427	0.317	0.569	1.11
	28-JSCIV-12	2.005	0.682	0.227	1.323	1.897	0.83	0.837	1.067
	29-JSCIV-13	2.545	1.132	0.439	1.413	3.413	2.407	1.295	1.006
	30-JSCIV-14	1.949	0.762	0.301	1.187	2.087	1.117	0.78	0.97
	31-JSCIV-15	2.130	0.629	0.169	1.501	1.835	0.701	0.998	1.134
	32-JSCIV-16	2.315	0.846	0.253	1.469	2.825	1.03	0.85	1.795
	33-JSCIV-17	2.319	0.880	0.279	1.439	1.584	0.632	0.95	0.952
	34-JSCIV-18	3.574	1.496	0.555	2.077	5.883	4.36	2.4	1.523
		Σ = 39.733	Σ = 14.842	Σ = 4.762	Σ = 24.891	Σ = 52.289	Σ = 19.612	Σ = 16.537	Σ = 32.677
Fluorite Cavity fillings G2	04-JSFv-01	4.3152	1.353	0.3721	2.9622	4.765	2.058	1.2	2.707
	05-JSFv-02	5.6921	1.703	0.46	3.9891	6.675	1.901	2.03	4.774
	06-JSFv-03	4.672	1.271	0.316	3.401	3.984	1.137	1.07	2.847
	07-JSFv-04	5.343	1.645	0.552	3.697	7.561	2.83	2.26	4.731
	08-JSFv-05	4.337	1.167	0.387	3.17	3.289	1.182	0.96	2.107
	09-JSFv-06	4.961	1.215	0.371	3.746	3.165	0.557	0.51	2.608
	10-JSFv-07	4.691	1.682	0.368	3.009	4.128	2.188	0.93	1.94
	11-JSFv-08	4.642	1.405	0.187	3.237	5.058	2.107	0	2.951
	12-JSFv-09	4.055	1.076	0.197	2.979	3.505	0.416	0.218	3.089
	13-JSFv-10	4.5241	1.073	0.317	3.451	4.016	0.605	1.11	3.411
	14-JSFv-11	4.556	1	0.196	3.556	6.231	1.971	0.802	4.26
	15-JSFv-12	4.522	1.01	0.398	3.512	4.724	1.075	1.6	3.649
	16-JSFv-13	5.044	1.327	0.346	3.717	3.504	1.046	1.19	2.458
	17-JSFv-14	5.676	1.788	0.526	3.888	5.603	2.059	1.39	3.544
	18-JSFv-15	4.651	1.414	0.323	3.2374	5.017	2.289	1.39	2.728
	19-JSFv-16	5.744	1.762	0.48	3.982	7.153	2.407	1.7	4.746
		Σ = 77.4267	Σ = 21.8922	Σ = 5.801	Σ = 55.534	Σ = 78.378	Σ = 25.828	Σ = 18.36	Σ = 52.55

. Our results will be compared, in Section 6.5, to those obtained by Souissi et al. [20,28] on fluorite samples from Jebel Stah (Table A2) and the Zaghouan Fluorite Province (Table A3).

The studied fluorites (G1 and G2) show low contents of most measured trace elements (

Table A4. Initial individual REE and Y contents (mg·kg⁻¹) obtained in fluorite vein (G1) sample (FICI1).

Laser Spots                                                              Fluorite Vein (G1)
Element	01_NIST612_01	02_NIST612_02	03_NIST612_03	04_FlCI1_01	05_FlCI1_02	06_FlCI1_03	07_FlCI1_04	08_FlCI1_05	09_FlCI1_06	10_FlCI1_07	11_FlCI1_08	12_FlCI1_09	13_FlCI1_10	14_FlCI1_11	15_FlCI1_12	16_FlCI1_13	17_FlCI1_14	18_FlCI1_15	19_NIST612_04	20_NIST612_05	21_NIST612_06
Sc	41.66	42.33	40.93	0.54	0.5	0.49	0.4	0.85	1.18	0.57	0.5	0.68	0.44	0.61	0.61	1.02	0.47	0.52	39.34	41.30	39.80
Y	39.42	39.38	37.19	1.5	0.953	1.054	0.642	0.844	0.827	0.847	0.238	0.354	0.984	1.34	0.657	0.633	0.409	0.89	38.53	39.42	35.89
La	36.42	35.75	35.08	0.034	0.018	0.045	0.066	0.012	0.023	0.019	0.029	0.0482	0.546	0.007	0.087	0.023	0.022	0.11	36.06	36.55	35.31
Ce	39.26	38.11	37.65	0.018	0.010	0.029	0.234	0.02	0.09	0.011	0.016	0.066	0.471	0.03	0.31	0.020	0.022	0.492	38.05	39.71	37.92
Pr	37.94	36.99	36.76	0.016	0.015	0.018	0.065	0.010	0.021	0.02	0.013	0.015	0.196	0.022	0.069	0.013	0.013	0.163	37.10	37.59	36.66
Nd	35.91	35.18	34.27	0.063	0.071	0.136	0.739	0.043	0.066	0.074	0.049	0.098	0.513	0.136	0.609	0.08	0.076	1.69	34.23	37.53	35.40
Sm	35.13	37.48	35.67	0.081	0.126	0.06	0.103	0.15	0.088	0.107	0.077	0.103	0.206	0.117	0.125	0.125	0.069	0.189	39.05	38.82	36.93
Eu	35.85	34.56	33.46	0.037	0.018	0.023	0.032	0.015	0.023	0.036	0.017	0.0151	0.029	0.024	0.034	0.04	0.027	0.048	34.39	35.16	33.56
Gd	38.75	36.85	35.41	0.027	0.065	0.067	0.045	0.053	0.141	0.128	0.061	0.076	0.183	0.08	0.201	0.106	0.115	0.067	37.42	37.88	36.34
Tb	37.05	36.37	34.78	0.015	0.009	0.008	0.006	0.012	0.016	0.010	0	0.013	0.033	0.012	0.012	0.017	0.009	0.0137	36.20	36.57	35.14
Dy	38.09	36.18	34.26	0.046	0.038	0.06	0.0254	0.138	0.035	0.044	0	0.045	0.237	0.101	0.042	0.042	0.056	0.081	35.78	37.29	35.09
Ho	39.17	38.00	37.02	0.044	0.009	0.009	0.0219	0.011	0.012	0.01	0.006	0.008	0.024	0.032	0.004	0.016	0	0.0051	38.54	38.16	36.65
Er	39.77	37.39	35.77	0.036	0.1	0.064	0.039	0.038	0.054	0.068	0	0.035	0.054	0	0.046	0.046	0.043	0.022	38.94	37.82	35.88
Tm	39.08	37.89	36.53	0.011	0.013	0.017	0.006	0.008	0.008	0.011	0.005	0.011	0.007	0.012	0.009	0.025	0.014	0.020	37.31	38.63	36.17
Yb	39.30	39.15	40.37	0.025	0.058	0.062	0	0.055	0.054	0.031	0.071	0.05	0.058	0.04	0.115	0.1	0.063	0.032	41.56	40.01	40.03
Lu	39.20	38.95	35.79	0.013	0.010	0.009	0.009	0.004	0.009	0.012	0	0.008	0	0.013	0.016	0.02	0.014	0.011	38.65	38.59	36.28

,

Table A5. Initial individual REE and Y contents (mg·kg⁻¹) obtained in fluorite vein (G1) sample (JSCIV).

Laser Spots                                                                                   Fluorite Vein (G1)
Element	15_NIST612_04	16_NIST612_05	17-JSCIV-01	18-JSCIV-02	19-JSCIV-03	20-JSCIV-04	21-JSCIV-05	22-JSCIV-06	23-JSCIV-07	24-JSCIV-08	25-JSCIV-09	26-JSCIV-10	27-JSCIV-11	28-JSCIV-12	29-JSCIV-13	30-JSCIV-14	31-JSCIV-15	32-JSCIV-16	33-JSCIV-17	34-JSCIV-18	35_NIST612_06	36_NIST612_07	37_NIST612_08
Sc	4.81	5.02	0.44	0.41	0.37	0.32	0.3	0.43	0.4	0.37	0.4	0.21	0.21	0.33	0.28	0.25	0.32	0.41	0.45	0.39	4.64	4.83	4.63
Y	17.68	17.25	0.679	0.91	0.887	1.18	1.22	1.06	1.17	1.12	1.41	1.02	0.806	1.1	1.24	1.09	1.3	1.29	1.22	1.79	17.34	16.88	17.01
La	97.91	99.34	0.028	0.02	0.017	0.011	0.011	0.021	0.022	0.019	0.02	0.020	0.012	0.011	0.012	0.011	0.018	0.031	0.034	0.03	91.95	99.43	98.42
Ce	39.45	40.79	0.019	0.019	0.0119	0.018	0.021	0.06	0.025	0.046	0.043	0.012	0.008	0.018	0.012	0.011	0.018	0.022	0.02	0.019	37.10	42.25	40.62
Pr	270.77	278.09	0.019	0.011	0.022	0.015	0.017	0.024	0.031	0.023	0.057	0.013	0.025	0.011	0.014	0.014	0.02	0.01	0.016	0.011	258.92	276.01	276.61
Nd	48.98	52.18	0.1	0.12	0.151	0.075	0.124	0.132	0.143	0.094	0	0.051	0.053	0.08	0.219	0.135	0.071	0.064	0.159	0.135	48.01	50.74	50.64
Sm	158.58	161.70	0.133	0.156	0.114	0.07	0.107	0.131	0.149	0.099	0.091	0.047	0.069	0.074	0.22	0.08	0.07	0.177	0	0.47	148.06	155.76	165.10
Eu	387.09	399.85	0.035	0.031	0.043	0.037	0.029	0.037	0.108	0.026	0.024	0.0126	0.024	0.02	0.021	0.021	0.052	0.05	0.035	0.081	379.55	416.47	392.90
Gd	120.34	120.30	0.086	0.085	0	0.115	0.082	0.209	0.181	0.141	0.207	0.049	0.041	0.137	0.353	0.239	0.063	0.082	0.166	0.36	118.47	118.06	122.77
Tb	632.27	643.30	0.012	0.04	0.02	0.016	0.007	0.017	0.0129	0.025	0.011	0.009	0.0176	0.01	0.010	0.007	0.017	0.018	0.0238	0.012	592.06	627.26	616.36
Dy	98.57	98.42	0.053	0.105	0.065	0.04	0.124	0.129	0.048	0.04	0.053	0.039	0.051	0.06	0.055	0.033	0.037	0.103	0.054	0.102	89.04	94.75	96.36
Ho	439.36	468.51	0.018	0.035	0	0	0	0.014	0.055	0	0.031	0.007	0.012	0.015	0.011	0	0.013	0.025	0.022	0.0125	418.75	451.81	445.05
Er	150.86	161.12	0	0.078	0.05	0	0.038	0.225	0.059	0.061	0.203	0.041	0	0.063	0.077	0.032	0.04	0	0	0.054	139.73	154.27	150.80
Tm	1067.3	1084.7	0.012	0.079	0.02	0.009	0.010	0.013	0.011	0.020	0.012	0.009	0.005	0	0.011	0.013	0.009	0.02	0.018	0.017	1027.2	1048.4	1042.9
Yb	161.00	168.08	0.113	0.079	0.07	0	0.055	0	0.085	0	0.151	0	0.035	0.065	0	0	0.084	0	0.081	0.077	155.30	163.06	156.52
Lu	986.53	1026.9	0.019	0.017	0	0.017	0.009	0	0.043	0.228	0.0233	0	0.006	0.011	0.008	0.012	0	0.0131	0.019	0.013	941.89	1006.1	978.18

and

Table A6. Initial individual REE and Y contents (mg·kg⁻¹) obtained in fluorite cavity-filling (G2) sample (JSFv).

Laser Spots											Cavity-Filling Fluorite (G2)
Element	01_NIST612_01	02_NIST612_02	03_NIST612_03	04-JSFv-01	05-JSFv-02	06-JSFv-03	07-JSFv-04	08-JSFv-05	09-JSFv-06	10-JSFv-07	11-JSFv-08	12-JSFv-09	13-JSFv-10	14-JSFv-11	15-JSFv-12	16-JSFv-13	17-JSFv-14	18-JSFv-15	19-JSFv-16	20_NIST612_04	21_NIST612_05	22_NIST612_06
Sc	41.36	40.51	41.32	0.52	0.68	0.51	0.65	0.53	0.48	0.85	0.45	0.46	0.52	0.35	0.43	0.54	0.5	0.51	0.52	40.94	41.70	40.70
Y	38.24	38.08	38.48	2.54	3.34	3.04	3.09	2.76	3.46	2.61	2.96	2.78	2.97	3.09	3.04	3.33	3.43	2.82	3.34	38.46	37.98	38.24
La	36.04	35.14	36.23	0.076	0.129	0.046	0.094	0.056	0.044	0.054	0.257	0.089	0.068	0.066	0.094	0.031	0.107	0.183	0.144	35.63	36.61	35.31
Ce	39.24	37.80	37.85	0.124	0.309	0.165	0.085	0.048	0.073	0.089	0.198	0.167	0.077	0.081	0.093	0.088	0.209	0.167	0.309	38.77	38.55	37.97
Pr	37.31	36.71	37.59	0.068	0.035	0.051	0.0227	0.052	0.05	0.021	0.03	0.025	0.024	0.021	0.022	0.026	0.027	0.068	0.056	36.13	37.92	37.58
Nd	34.72	35.28	35.96	0.281	0.191	0.085	0.366	0.189	0.122	0.22	0.128	0.107	0.085	0.118	0.102	0.287	0.425	0.126	0.34	35.04	35.28	35.28
Sm	36.88	35.65	37.97	0.06	0.155	0.218	0.201	0.16	0.193	0.21	0.226	0.098	0.155	0.278	0.132	0.119	0.188	0.163	0.111	36.22	38.12	36.15
Eu	34.37	34.33	34.67	0.05	0.027	0.051	0.036	0.0304	0.042	0.045	0.026	0.037	0.041	0.008	0.049	0.041	0.041	0.059	0.051	34.46	34.86	34.11
Gd	35.74	37.31	38.41	0.174	0.177	0.145	0.191	0.102	0.211	0.193	0.09	0.093	0.103	0.078	0.088	0.195	0.291	0.138	0.231	35.77	36.29	38.34
Tb	35.86	35.59	36.43	0.0161	0.032	0.034	0.0264	0.0148	0.03	0.0155	0.018	0.013	0.0215	0.011	0.024	0.042	0.025	0.0215	0.03	35.94	36.74	35.31
Dy	35.99	35.71	36.31	0.132	0.224	0.086	0.299	0.24	0.088	0.115	0.054	0.055	0.152	0.099	0.237	0.068	0.169	0.105	0.168	35.92	35.38	36.43
Ho	37.82	37.16	38.93	0.042	0.049	0.0073	0.025	0.0215	0.048	0.0165	0.056	0.02	0.022	0.020	0.046	0.029	0.045	0.027	0.039	37.50	38.74	37.52
Er	37.34	37.06	37.95	0.063	0.205	0.063	0.08	0.095	0	0.1	0.034	0.029	0.066	0.143	0.056	0.066	0.083	0.089	0.239	38.89	37.88	35.90
Tm	37.47	36.98	38.42	0.020	0.027	0.015	0.046	0.015	0.022	0.016	0.008	0.02	0.037	0.038	0.006	0.0165	0.025	0.016	0.013	37.73	37.94	37.06
Yb	40.52	38.74	40.80	0.131	0.096	0.139	0.111	0	0.1	0.119	0.099	0.042	0.166	0.135	0.082	0.148	0.095	0.129	0.129	40.43	39.37	39.95
Lu	37.93	36.76	38.72	0.017	0.016	0.016	0.0197	0.023	0	0.0173	0.008	0.021	0.016	0.019	0.0205	0.017	0.016	0.029	0.0231	37.15	39.28	37.12

), whereas the contents of the major elements are high in Na with maximum values of 501.45 ppm in fluorite G1 and 1787.36 ppm in fluorite G2. Similarly, Si ranges from 826.48 ppm in G1 to 1142.71 ppm in G2, and Mg varies between 826.48 and 1142.71 ppm in G2 (

Table A10. Initial individual major elements contents (mg·kg⁻¹) obtained in fluorite vein (G1) samples (FICI1 and JSCIV) and cavity-filling (G2) sample (JSFv).

Fluorite Type	Laser Spots	Major Elements
		Ca	Na	Mg	Al	Si	Rb	Sr
Fluorite vein G1	01_NIST612_01	85,262.52	104,750.09	73.46	11,469.85	342,876.16	32.86	77.16
	02_NIST612_02	85,262.52	103,792.62	79.28	11,263.92	338,900.53	31.82	75.97
	03_NIST612_03	85,262.52	102,096.27	71.71	10,886.57	334,418.59	30.87	76.16
	04-FlCI1-01	513,369.75	12.57	1.64	24.45	364.27	0.058	46.75
	05-FlCI1-02	513,369.72	2.72	0.81	1.28	1601.92	0.054	42.72
	06-FlCI1-03	513,369.72	67.25	0.88	7.76	2484.1	0.067	44.59
	07-FlCI1-04	513,369.72	64.62	0.7	8.15	1631.22	0.063	43.62
	08-FlCI1-05	513,369.72	19.42	1.03	3.46	1980.85	0.122	38.58
	09-FlCI1-06	513,369.72	21.5	1	3.33	2160.93	0.057	41.32
	10-FlCI1-07	513,369.72	1.3	1.14	1.36	1982.41	0.089	38.91
	11-FlCI1-08	513,369.75	90.95	9.97	15.06	3434.06	0.045	22.52
	12-FlCI1-09	513,369.72	501.45	1.31	2.94	2606.88	0.065	3.1
	13-FlCI1-10	513,369.72	25.86	239.33	412.4	4112.35	0.409	19.53
	14-FlCI1-11	513,369.72	164.46	1.13	1.37	1622.99	0.074	43.23
	15-FlCI1-12	513,369.72	21.3	1	18.82	2623.79	0.073	44.74
	16-FlCI1-13	513,369.69	16.58	0.63	1.3	2399.2	0.092	39.25
	17-FlCI1-14	513,369.69	0.79	0.6	1.13	1924.19	0.062	40.61
	18-FlCI1-15	513,369.69	1.18	0.62	1.29	2313.33	0.077	44.16
	19_NIST612_04	85,262.51	104,032.79	81.74	11,140.96	330,369.06	31.87	76.64
	20_NIST612_05	85,262.51	107,011.46	92.34	11,474.85	337,018.63	31.49	76.66
	21_NIST612_06	85,262.51	102,465.41	80.10	10,895.44	328,093.16	30.90	73.86
	15_NIST612_04	6.32	14.14	0.00053	0.868	2.09	9.55	6.51
	16_NIST612_05	6.32	14.74	0.00055	0.893	2.11	8.98	6.62
	17-JSCIV-01	38.03	81.31	2.28	1.01	2953.16	0.084	15.61
	18-JSCIV-02	38.03	13.84	4.17	1.85	2985.04	0.052	13.81
	19-JSCIV-03	38.03	2.78	0.53	0.82	2624.46	0.057	14.71
	20-JSCIV-04	38.03	6.64	2.38	2.24	1959.84	0.045	14.54
	21-JSCIV-05	38.03	76.31	19.77	12.37	3734.2	0.105	20.25
	22-JSCIV-06	38.03	4.48	13.63	0.97	2776.13	0.088	12.15
	23-JSCIV-07	38.03	17.65	14.03	4.2	2620.21	0.068	22.2
	24-JSCIV-08	38.03	3.84	2.2	1.06	2492.42	0.085	18.47
	25-JSCIV-09	38.03	3.75	2.43	0.9	1753.37	0.054	13.26
	26-JSCIV-10	38.03	3.41	1.74	0.5	2075.22	0.042	12.8
	27-JSCIV-11	38.03	332.94	826.48	34.32	2316.11	0.115	24.57
	28-JSCIV-12	38.03	2230.76	308.41	12.72	2509.5	0.4	39.88
	29-JSCIV-13	38.03	138.08	2.96	2.54	2390.01	0.053	22.34
	30-JSCIV-14	38.03	10.3	2.78	2.7	2707.83	0.088	25.09
	31-JSCIV-15	38.03	293.3	9.49	1.49	2465.02	0.085	23.61
	32-JSCIV-16	38.03	186.1	5.62	0.96	2141.51	0.086	24.04
	33-JSCIV-17	38.03	4.53	1.35	0.94	3209.87	0.058	25.37
		38.03
	35_NIST612_06	6.32	13.30	0.00051	0.836	1.97	8.66	6.44
	36_NIST612_07	6.32	14.62	0.00057	0.873	2.18	9.14	6.50
	37_NIST612_08	6.32	14.58	0.00060	0.871	2.13	9.25	6.30
	38_NIST612_09	6.32	14.61	0.00051	0.866	2.11	9.47	6.26
Fluorite cavity fillings G2	01_NIST612_01	85,262.52	104,124.49	82.81	11,239.08	338,817.94	31.97	77.25
	02_NIST612_02	85,262.41	102,799.94	72.30	10,966.10	335,126.28	31.92	74.87
	03_NIST612_03	85,262.53	104,387.88	77.67	11,329.59	333,216.16	30.87	76.33
	04_JSFv_01	513,369.78	1431.75	550.56	136.85	4031.50	0.136	164.22
		513,369.78
	06-JSFv-03	513,369.81	1467.01	506.31	157.15	6992.34	0.086	43.35
	07-JSFv-04	513,369.78	1422.21	407.51	121.53	7374.52	0.264	43.23
	08-JSFv-05	513,369.78	978.93	252.55	69.60	5002.42	<0.109	46.65
	09-JSFv-06	513,369.78	844.21	213.26	59.27	4722.07	<0.102	121.39
	10-JSFv-07	513,369.81	815.84	324.68	78.54	5324.23	<0.120	40.63
	11-JSFv-08	513,369.78	1609.93	535.54	184.21	6992.11	<0.109	4582.06
	12-JSFv-09	513,369.72	1000.24	326.62	101.94	6377.11	0.154	34.41
	13-JSFv-10	513,369.72	832.31	262.78	69.29	5139.72	<0.112	45.21
	14-JSFv-11	513,369.75	693.34	185.77	54.77	4226.74	<0.071	37.99
	15-JSFv-12	513,369.75	1256.30	442.28	127.45	6428.53	<0.082	43.31
	16-JSFv-13	513,369.75	1545.58	517.89	127.98	7057.51	0.171	37.85
	17-JSFv-14	513,369.72	1664.82	554.88	176.50	8261.05	<0.096	44.66
	18-JSFv-15	513,369.72	1787.36	615.04	183.03	8200.88	0.209	37.95
		513,369.72
	20_NIST612_04	85,262.52	104,124.49	73.39	11,149.42	330,768.38	30.75	75.25
	21_NIST612_05	85,262.52	102,799.94	83.81	11,239.94	341,675.63	31.45	78.46
	22_NIST612_06	85,262.52	104,387.88	77.56	11,119.97	337,126.47	32.71	75.49

). While laser ablation was carefully applied to the pure fluorite portions (G1 and G2) of the samples, the SEM-EDS analysis revealed the presence of calcite as the primary gangue mineral, along with minor accessory minerals such as barite, hematite, quartz, and dolomite within the fluorite (See Section 5.1; Figure 8 and Figure 9). This mineral association can introduce trace elements, such as (Na), (Si), and (Mg), into the LA-ICP-MS data, even though these secondary minerals were not directly targeted during the analysis. Consequently, the elevated concentrations of Na, Si, and Mg may originate from these adjacent minerals. On the other hand, fluorite from the studied deposit is notably rich in fluid inclusions, which are typical of hydrothermal brine systems [7] and can significantly influence the measured elemental concentrations. During LA-ICP-MS analysis, these inclusions may contribute to elevated Na values. If Na were primarily incorporated into the fluorite crystal lattice, its concentration would be expected to remain relatively stable across different analytical spots. However, the presence of fluid inclusions can lead to localized Na enrichment, resulting in considerable variability in measured Na content (Table A10). This is particularly relevant in the context of the Jebel Stah deposit, where the fluorite formation resulted from highly saline (18 ± 34 wt% NaCl equivalents: Table 1) and Na-rich fluids [19]. Petrographic observations confirm the abundance of fluid inclusions within the analyzed fluorite samples, further supporting the hypothesis that a significant portion of the detected Na originates from these trapped hydrothermal fluids rather than structural substitution within the fluorite lattice. However, distinguishing between lattice-bound and inclusion-hosted Na requires additional techniques such as an electron microprobe.

The individual REE + Y content was recorded in laser-spot ranges between 1.08 and 5.74 ppm (Table A4, Table A5 and Table A6 ). The overall values of the individual ${(\mathrm{R}\mathrm{E}\mathrm{E}+\mathrm{Y})}_{\mathrm{C}\mathrm{N}}$ concentrations are low, ranging from 0.383 and 8.386 ppm (Table A9). The variable colors of fluorite do not significantly correlate with various compositions. Despite their different macroscopic appearances, the ${(\mathrm{R}\mathrm{E}\mathrm{E}+\mathrm{Y})}_{\mathrm{C}\mathrm{N}}$ patterns of white to colorless and purple fluorite (G1) are almost identical (Table A9). The ${(\mathrm{R}\mathrm{E}\mathrm{E}+\mathrm{Y})}_{\mathrm{C}\mathrm{N}}$ patterns of both G1 and G2 fluorite samples are distinguished by graphically detectable strong negative ${\mathrm{C}\mathrm{e}}_{\mathrm{C}\mathrm{N}}$ anomalies. While the average data indicate weak negative Eu_CN anomalies (Figure 10c), individual LA-ICP-MS analyses exhibit some variability, with certain ablation spots showing near-neutral or slightly positive Eu_CN values (Figure 10a–c); however, both G1 and G2 samples show predominantly negative Eu anomalies. Fluorite G1 displays moderate positive ${\mathrm{Y}}_{\mathrm{C}\mathrm{N}}$ anomalies (Figure 10a,b), while the fluorite G2 (sample JSFV) shows a strong positive ${\mathrm{Y}}_{\mathrm{C}\mathrm{N}}$ anomaly (Figure 10c).

The fractionation of ${\mathrm{Y}}_{\mathrm{C}\mathrm{N}}$ relative to ${\mathrm{H}\mathrm{o}}_{\mathrm{C}\mathrm{N}}$ is observed in all the analyzed fluorite samples, with almost consistent ${(\mathrm{Y}/\mathrm{H}\mathrm{o})}_{\mathrm{C}\mathrm{N}}$ fractionation ratios in G1 ranging from 0.48 to 3.99. The ${\mathrm{Y}}_{\mathrm{C}\mathrm{N}}$ concentrations in Fl3 of G2 are greater than those recorded in Fl2 of G1. The ${(\mathrm{Y}/\mathrm{H}\mathrm{o})}_{\mathrm{C}\mathrm{N}}$ ratios in G2 are higher, ranging from 1.99 to 15.70 (

Table A11. Calculated REE to REE and Y to REE ratios: ${(\mathrm{T}\mathrm{b}/\mathrm{L}\mathrm{a})}_{\mathrm{C}\mathrm{N}}$ and ${(\mathrm{L}\mathrm{a}/\mathrm{L}\mathrm{u})}_{\mathrm{C}\mathrm{N}}$ ratios, Y/Ho and La/Ho initial ratios, Y/Ho and La/Ho normalized ratios, Tb/La and Tb/Ca atomic ratios, Eu/Eu* and Ce/Ce* anomalies of fluorite vein (G1) samples (FlCI1 and JSC_IV) and fluorite cavity-filling (G2) sample (JSFv).

			REEs Ratios
Fluorite Type	Laser Spots	${(\mathbf{T}\mathbf{b}/\mathbf{L}\mathbf{a})}_{\mathbf{C}\mathbf{N}}$	${(\mathbf{L}\mathbf{a}/\mathbf{L}\mathbf{u})}_{\mathbf{C}\mathbf{N}}$	Y/Ho	La/Ho	${(\mathbf{Y}/\mathbf{H}\mathbf{o})}_{\mathbf{C}\mathbf{N}}$	${(\mathbf{L}\mathbf{a}/\mathbf{H}\mathbf{o})}_{\mathbf{C}\mathbf{N}}$	Tb/Caatom ratio	Tb/Laatom ratio	Eu/Eu*	Ce/Ce*
Fluorite vein G1		3.19	0.23	2.10	0.77	0.78	0.15	7.50 × 10−9	0.38	0	0
		3.58	0.16	6.15	1.91	2.28	0.37	4.50 × 10−9	0.43	0	0
		1.33	0.42	7.43	5.11	2.75	0.99	4.10 × 10−9	0.16	0	0.24
		0.66	0.60	1.82	3.01	0.67	0.58	3.00 × 10−9	0.08	1.40	0.83
		7.27	0.23	4.63	1.09	1.72	0.21	6.15 × 10−9	0.87	0	0
	FlCI1	4.95	0.23	4.14	1.90	1.53	0.37	8.00 × 10−9	0.60	0	0
		3.84	0.15	5.30	1.97	1.96	0.38	5.15 × 10−9	0.46	0	0
		0	0	2.27	4.46	0.84	0.86	0	0	0	0
		1.95	0.53	2.74	6.03	1.02	1.17	6.45 × 10−9	0.23	0	0.57
		0.44	0	2.49	22.29	0.92	4.32	1.67 × 10−8	0.05	0.47	0.34
		12.26	0.05	2.60	0.22	0.96	0.04	5.90 × 10−9	1.47	0	0
		1.04	0.48	9.05	19.33	3.35	3.75	6.25 × 10−9	0.13	0	0.93
		5.34	0.12	2.45	1.44	0.91	0.28	8.45 × 10−9	0.64	0	0
		3.07	0.14	0	0	0	0	4.65 × 10−9	0.37	0	0
		0.91	0.88	10.80	21.57	4.00	4.18	6.85 × 10−9	0.11	1.29	0.86
		3.14	0.13	37.31	1.54	0.86	0.30	6.05 × 10−9	0.38	0	0
		14.55	0.10	26.00	0.57	0.60	0.11	2.00 × 10−8	1.75	0	0
		8.56	0	0	0	0	0	1.00 × 10−8	1.03	0	0
		11.01	0.05	0	0	0	0	8.10 × 10−9	1.32	0	0
		4.49	0.11	0	0	0	0	3.55 × 10−9	0.54	0	0
		5.89	0	76.26	1.51	1.75	0.29	8.50 × 10−9	0.71	0	0
		4.26	0.04	21.27	0.40	0.49	0.08	6.45 × 10−9	0.51	2.00	0
		9.67	0.01	0	0	0	0	1.25 × 10−8	1.16	0	0
	JSCIV	4.40	0.08	45.48	0.65	1.04	0.13	6.05 × 10−9	0.53	0	0
		3.14	0	136.00	2.75	3.12	0.53	4.45 × 10−9	0.38	0	0
		10.41	0.17	64.48	0.98	1.48	0.19	8.80 × 10−9	1.25	0	0
		6.26	0.09	74.83	0.78	1.72	0.15	4.95 × 10−9	0.75	0	0
		6.28	0.13	108.77	1.09	2.50	0.21	5.35 × 10−9	0.75	0	0
		4.87	0.08	0	0	0	0	3.75 × 10−9	0.59	0	0.20
		6.87	0	95.59	1.34	2.19	0.26	8.60 × 10−9	0.83	0	0
		4.22	0.21	51.60	1.24	1.18	0.24	9.00 × 10−9	0.51	0	0
		5.09	0.15	53.74	1.50	1.23	0.29	1.19 × 10−8	0.61	0	0
		2.86	0.20	143.20	2.40	3.29	0.47	5.90 × 10−9	0.34	0.60	0
		1.54	0.38	60.48	1.81	2.30	0.42	8.05 × 10−9	1.33 × 10−3	0	0.41
Fluorite cavity fillings G2		1.80	0.70	68.16	2.63	2.56	0.61	1.60 × 10−8	1.56 × 10−3	0	1.07
		5.47	0.25	-	6.30	15.71	1.45	1.73 × 10−8	4.73 × 10−3	0	0.80
		2.04	0.42	123.60	3.76	0	0	1.32 × 10−8	1.77 × 10−3	0.56	0
		1.92	0.21	128.37	2.60	4.91	0.61	7.40 × 10−9	1.66 × 10−3	0	0.21
		4.96	0	72.08	0.92	2.75	0.22	1.50 × 10−8	4.29 × 10−3	0	0.36
	JSFv	2.09	0.27	158.18	3.27	0	0	7.50 × 10−9	0.38	0	0
		0.50	2.71	52.86	4.59	1.99	1.06	4.50 × 10−9	0.43	0	0
		1.04	0.37	141.12	4.52	5.37	1.05	4.10 × 10−9	0.16	0	0.24
		2.30	0.37	135.00	3.09	5.08	0.71	3.0 0× 10−9	0.08	1.40	0.83
		1.20	0.30	152.97	3.27	5.78	0.75	6.15 × 10−9	0.87	0	0
		1.90	0.40	66.09	2.04	2.50	0.47	8.00 × 10−9	0.60	0	0
		9.85	0.16	114.83	1.07	0	0	5.15 × 10−9	0.46	0	0
		1.70	0.59	76.22	2.38	2.88	0.55	0	0	0	0
		0.85	0.54	102.55	6.65	3.87	1.54	6.45 × 10−9	0.23	0	0.57

). Very low ${(\mathrm{L}\mathrm{a}/\mathrm{L}\mathrm{u})}_{\mathrm{C}\mathrm{N}}$ ratios ranging between 0.007 and 0.87 (Table A11) are observed in Fl2 of G1. G2 exhibited slightly higher ${(\mathrm{L}\mathrm{a}/\mathrm{L}\mathrm{u})}_{\mathrm{C}\mathrm{N}}$ ratios (between 0.15 and 2.70) recorded in the fluorite sample JSFv (FI3) (Table A11).

Fluorite samples of Generation 1 (FlCI1 and JSC_IV) reveal a bell-shaped pattern with REE + Y pattern characterized by depletion in LREE relative to HREE and a slight hump for MREE (Figure 10). In contrast, the fluorite of Generation 2 (JSFv) has a distinct REE + Y pattern with moderate LREE depletion, a nearly flat MREE–HREE pattern (Figure 10).

The plot of Y/Ho vs. La/Ho (Figure 11) shows that the three samples are almost separated in three clusters, characterized by the almost similar La/Ho ratios, but differing Y/Ho ratios. The sample JSC_IV (G1) occurs almost in between. This suggests that the fluorite JSC_IV may have been deposited from a fluid that evolved subsequently to the deposition of the fluorite FlCI1 (G1). The discriminative (Tb/La)_{atom ratio} versus (Tb/Ca)_{atom ratio} diagram shows a clear grouping of two endmember fluids (Figure 12). G1 fluorites plot in the sedimentary field, while the G2 fluorites plot in the hydrothermal field.

5.3. Rb and Sr Elemental and Isotopic Data

All the samples have ⁸⁷Sr/⁸⁶Sr ratios, within a relatively small range between 0.708102 and 0.708812, which corresponds to more radiogenic values than the ratios typical of seawater during all the Mesozoic. The data are consistent with the earlier results of Souissi et al. [19]. ⁸⁷Rb/⁸⁶Sr ratios range between 0.0087 and 0.39. Most fluorite samples have Rb concentrations less than 4 ppm, while their Sr concentrations most commonly vary between 19 and 100 ppm. The corresponding initial ⁸⁷Sr/⁸⁶Sr ratios range from 0.7079 to 0.7086 ± 0.000045, which are higher than those observed in the upper mantle.

6. Discussion

6.1. Physicochemical Regime of REE + Y-Bearing Fluids

The fluorite compositions serve as reliable markers for the systematic behavior of REE + Y. At Jebel Stah, the analyzed fluorite samples from Generation 1 (FlCI1 and JSC_IV) show ΣREE concentrations of 36.33 and 39.73 ppm (Table A9), respectively, with a REE pattern characterized by a depletion in LREE relative to HREE and a slight hump for MREE (Figure 10). These patterns, coupled with low LREE contents and negative Ce anomalies, are similar to those observed in fluorites from Mississippi Valley-Type (MVT) Pb-Zn deposits [14]. In contrast, the fluorite of Generation 2 (JSFv) has a higher ΣREE concentration of 77.43 ppm (Table A9) and an REE pattern depleted in LREE but nearly flat in its MREE–HREE side (Figure 10). These differences highlight the geochemical variations between fluorite generations within the study area.

The (REE + Y) patterns of the Jebel Stah fluorites (Figure 10) show a bell-shaped distribution and share similarities in anomalies reported in previous studies [8,19,20]. ICP-MS data [20,28] (

Table A7. The results of the REE (mg·kg⁻¹) analysis conducted on the different petrographic types of the fluorite ore of Jebel Stah [26].

		I				II				III				IV			V				VI		VII
	L6-5	L6-30	L6-30Q	L5-3	DZ6-G	DZ6-J	DZ6-F	JS1-6P	CC3-3	CC3-2	JS1-6F	L3-21D	L3-21F	L5-16	L5-15F	L5-15G	FZ-5N	FZ-5B	JS5-F	JS6-HF	JS5-C	JS6-HC	L4-2	JS3-5
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ΣREE	0.384 0.47 0.09 0.444 0.107 0.05 0.129 0.016 0.094 0.018 0.054 0.007 0.037 0.006 1.91	0.35 0.42 0.08 0.39 0.1 0.05 0.13 0.02 0.11 0.02 0.06 0.01 0.05 0.01 1.8	0.068 0.109 0.019 0.075 0.019 0.006 0.019 0.002 0.013 0.003 0.007 0.001 0.006 0.001 0.35	0.17 0.24 0.034 0.146 0.024 0.011 0.025 0.003 0.018 0.004 0.013 0.001 0 0.001 0.69	0.56 0.73 0.11 0.38 0.037 0.007 0.034 0.006 0.034 0.009 0.031 0.005 0.04 0.007 1.99	0.21 0.3 0.06 0.28 0.061 0.015 0.075 0.011 0.066 0.015 0.047 0.007 0.055 0.01 1.212	0.01 0.01 0.0027 0.02 0.011 0.003 0.023 0.003 0.022 0.005 0.01 0.001 0.002 0.0002 0.12	4.354 4.717 1.313 6.618 1.506 0.609 1.752 0.23 1.394 0.284 0.744 0.085 0.262 0.064 23.9	0.12 0.2 0.05 0.31 0.104 0.03 0.229 0.038 0.253 0.056 0.154 0.017 0.091 0.012 1.66	0.068 0.122 0.036 0.224 0.088 0.051 0.232 0.037 0.244 0.054 0.146 0.016 0 0.012 1.33	0.076 0.144 0.04 0.237 0.08 0.042 0.197 0.03 0.197 0.043 0.114 0.012 0 0.009 1.221	0.15 0.22 0.03 0.13 0.028 0.008 0.044 0.007 0.045 0.011 0.033 0.004 0.022 0.003 0.74	0.149 0.256 0.048 0.237 0.057 0.016 0.106 0.015 0.1 0.022 0.06 0.006 0.031 0.004 1.107	1.792 2.32 0.372 1.562 0.249 0.099 0.302 0.043 0.272 0.059 0.157 0.018 0 0.015 7.26	11.5 14.8 3.32 16.9 4.79 1.06 5.18 0.67 3.47 0.643 1.629 0.19 1.08 0.163 65.4	3.36 4.23 0.856 3.89 0.946 0.217 1.09 0.146 0.766 0.145 0.377 0.043 0.251 0.035 16.4	1.41 1.95 0.27 0.95 0.15 0.043 0.202 0.032 0.218 0.049 0.134 0.016 0.093 0.013 5.53	0.03 0.07 0.02 0.13 0.051 0.017 0.129 0.022 0.153 0.032 0.091 0.009 0.05 0.006 0.81	0.007 0.02 0.004 0.022 0.014 0.006 0.029 0.004 0.024 0.005 0.01 0.001 0.004 0.001 0.151	0.004 0.012 0.004 0.023 0.012 0.004 0.032 0.004 0.019 0.004 0.008 0.001 0.006 0.001 0.13	0.154 0.73 0.218 1.37 0.54 0.138 0.62 0.091 0.491 0.09 0.23 0.028 0.17 0.022 4.892	0.458 1.83 0.61 4.06 2.14 0.64 2.92 0.486 2.59 0.46 1.13 0.129 0.789 0.109 18.4	0.008 0.017 0.003 0.024 0.01 0.005 0.021 0.003 0.014 0.003 0.006 0.0004 0.003 0.0005 0.12	0.01 0.01 0.0032 0.02 0.015 0.005 0.035 0.004 0.024 0.005 0.01 0.001 0.006 0.001 0.15

and

Table A8. REE data (mg·kg⁻¹) conducted on the fluorite ores in the Zaghouan Fluorite District [28].

Sidi Taya					Hammam Jedidi		Jebel Oust				Oued M’Tek
	ST9	STIII-5	ST42-5	ST50-2F	HJ-2F	HJ-1Sr	JO2-1	JOIII-10	JO-F	JO-FC	OM1	OM-FC
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ΣREE	0.544 0.627 0.107 0.47 0.092 0.039 0.099 0.014 0.085 0.018 0.057 0.008 0 0.006 2.166	0.024 0.039 0.009 0.063 0.034 0.011 0.084 0.014 0.084 0.017 0.048 0.005 0.025 0.003 0.46	0.021 0.037 0.011 0.086 0.049 0.018 0.124 0.019 0.122 0.025 0.066 0.007 0.038 0.005 0.628	0.042 0.095 0.015 0.094 0.055 0.378 0.21 0.023 0.189 0.04 0.102 0.011 0 0 1.254	0.274 0.464 0.063 0.281 0.085 0.022 0.114 0.016 0.107 0.017 0.053 0.006 0.037 0.005 1.55	0.033 0.067 0.005 0.015 0 0.025 0.0003 0.00004 0.0003 0 0.0006 0.0002 0.0005 0.0001 0.15	0.68 0.75 0.09 0.35 0.051 0.018 0.09 0.011 0.06 0.013 0.031 0.003 0.011 0.001 2.159	8.23 11.63 1.77 7.35 0.83 0.16 0.69 0.053 0.19 0.021 0.041 0.002 0.006 0.001 30.974	0.077 0.079 0.013 0.082 0.038 0.032 0.135 0.018 0.11 0.023 0.056 0.005 0 0.003 0.671	0.076 0.164 0.045 0.276 0.099 0.063 0.289 0.044 0.305 0.068 0.184 0.02 0.11 0.015 1.76	0.093 0.475 0.110 0.919 1.21 0.439 4.38 0.85 4.61 0.776 1.64 0.145 0.637 0.066 16.36	0.050 0.251 0.072 0.736 1.274 0.542 5.10 1.03 5.75 0.96 2.01 0.178 0.751 0.074 18.795

) from Jebel Stah and neighboring ore deposits of the ZFP reveal variable ΣREE contents: at Sidi Taya, from 0.46 ppm to 2166 ppm; at Hammam Jedidi, from 0.15 ppm to 1.55 ppm; at Jebel Oust, from 0.67 ppm to 30.97 ppm; and at Oued M’Tek, from 16.36 ppm to 18.795 ppm. These REE + Y concentrations are similar to those documented by [11,56,57,58]. Despite these consistencies, the ΣREE concentrations in the fluorite samples from the study area (Table A4, Table A5 and Table A6) and the overall ZFP are relatively low (Table A8 and Table A9). Such low ΣREE values are typically associated with a sedimentary origin for fluorite [59,60], which aligns with the sedimentary host rocks of the fluorites from Jebel Stah and the broader ZFP area.

Taking into consideration that fluorites formed during the early mineralization stages display REE patterns with enriched LREE [28], whereas those crystallizing in the later stages show a depletion in LREE and enrichment in HREE [60,61,62,63], it can be stated that the studied fluorites Fl2 (FlCI1, JSC_IV) and Fl3 (JSFv) from Jebel Stah result from late-stage crystallization.

Figure 12. LA-ICP-MS data of Jebel Stah fluorites plotted into Tb/Ca versus Tb/La diagram. The composition of fluorite is examined and analyzed in this study in terms of the trends and fields defined by Möller et al. [63], using a constant, stoichiometric abundance of calcium in pure and ideal fluorite.

Figure 12. LA-ICP-MS data of Jebel Stah fluorites plotted into Tb/Ca versus Tb/La diagram. The composition of fluorite is examined and analyzed in this study in terms of the trends and fields defined by Möller et al. [63], using a constant, stoichiometric abundance of calcium in pure and ideal fluorite.

Moreover, an examination of major element compositions provides additional evidence supporting the geochemical similarity between the two G1 fluorite samples and their distinction from G2. The contents of Na, Si, Sr, Rb, and REE + Y do not significantly differ between the two samples of vein fluorites G1 (Na: FICI1 0.79–501.45 ppm, JSC_IV 2.78–332.94 ppm; Si: FICI1 364.27–4112.35 ppm, JSC_IV 1753.37–3734.2 ppm; Rb: FlCI1 0.045–0.409 ppm, JSC_IV 0.042–0.4 ppm; Sr: FlCI1 3.1–46.75 ppm, JSC_IV 12.15–76.63 ppm) (Table A10). This indicates that fluorite veins G1 were deposited by paleofluids of a similar composition. However, the cavity-filling fluorite G2 (sample JSFv) is significantly enriched in Na (693.34–3226.90 ppm), Si (4226.74–8261.05 ppm) and to a lesser extent in Mg and Al, while also exhibiting lower Rb contents (0.071–0.264 ppm) (Table A9). Sr appears to be the only element with similar concentrations between G1 and G2 (JSFv 34.41–121.39 ppm). These differences strongly suggest the involvement of two distinct paleofluids during mineralization. The enrichment of these major elements in G2 could explain its significantly higher ΣREE + Y concentrations (Table A10). This observation has been documented in numerous studies (e.g., [64]), which indicate that REE + Y concentrations in fluorite are positively correlated with Al, Mg, and Si concentrations, suggesting that these elements may play a role in the incorporation of REEs and Y into fluorite.

The obtained (REE + Y) patterns (Figure 10) are usually consistent with the general REE + Y distribution in hydrothermal fluorites. Both fluorite generations G1 and G2 have very low (La/Lu) ratios < 1 (between 0.007 and 0.875 in G1, and between 0.155 and 2.709 in G2: Table A11). In alkaline fluids containing carbonate species and/or halogens as complexing agents, HREE are preferentially enriched in the solution, resulting in REE patterns with a (La/Lu) ratio of less than 1 [7]. An increase in the concentrations of MREEs and HREEs relative to LREEs can result in the stable chemical complexing of the former (MREEs and HREEs) when they react with CO₃²⁻ and OH⁻ in alkaline fluids [65]. These alkaline fluids are typically rich in complex ligands such as mono- and bicarbonate ions [6,7].

Furthermore, the (REE + Y) patterns of Jebel Stah fluorites could be correlated with those observed in marine evaporites or evaporated seawater, which are characterized by low (La/Lu) ratios [66]. In addition, REE complexation in alkaline fluids promotes the dissolution of REEs, while the buffering of pH or the introduction of fluorine, phosphates, and carbonates from the surrounding rocks facilitates the precipitation of REEs [65]. However, when the pH of the fluid is buffered or when fluorine, phosphates, and carbonates are added from host rocks, the REEs are more likely to precipitate out of solution and form minerals. In this context, REE + Y-bearing fluids, particularly those involved in the formation of fluorites in Neogene host rocks, revealed a high pH value [8].

The origin of REEs in fluorite has previously been attributed to structurally controlled reservoirs pierced by Triassic salt [8]. Based on the (REE + Y) patterns observed in the present data, it is suggested that most fluorites precipitated from a prevailing fluid, consisting of a NaCl ± CaCl₂-rich brine arising mainly from the underlying salts. The significant dissolution of the carbonate host rock indicates that the hydrothermal fluid was initially acidic. The reaction of such an acidic hydrothermal fluid with carbonate host rock led to the dolomitization of the limestones and released Ca from carbonate minerals, while simultaneously neutralizing the hydrothermal fluid. Fluorite subsequently crystallized, replacing dolomite, as evidenced by the paragenetic sequence. As aqueous fluids dissolved the carbonate host rock, the pH increased rapidly. This process may promote the release of Ca ions into the fluid and facilitate the deposition of fluorite [67], including some of the REE + Y dissolved in these fluids. During fluorite mineralization, the fluoride ion serves as a binding ligand that facilitates the deposition of REE + Y rather than functioning as a complex ligand [68]. Tsay et al. [69] further reported that LREE/HREE fractionation can occur at high temperatures in the presence of chloride ligands. The enrichment of HREE concentrations in the Jebel Stah F deposits at moderate to high temperatures may be attributed to the predominance of Cl as the primary ligand in the hydrothermal fluids, leading to the preferential remobilization of HREEs. In contrast, MREEs and LREEs could have been transported predominantly as fluoride complexes. As crystallization proceeded, the fluids became enriched in HREE due to the decomposition of the LREE–fluorite complex. This early fluorite (G1) episode was defined by high Tb/La atomic ratios (Figure 13 and Figure 14; Table A11).

6.2. Potential Factors for Ce, Eu, and Y Anomalies

The anomalies observed in the elements Eu and Ce have served as crucial indicators to unravel the properties of the fluids responsible for ore formation, such as their temperature and redox state [70].

6.2.1. Ce Anomaly

All fluorite samples had significant negative Ce anomalies, with Ce/Ce* ratios ranging from 0.20 and 1.07 (Table A11) indicating oxic seawater-derived REE + Y patterns. This anomaly is characteristic of fluorite formed under conditions of extreme oxygen fugacity (fO₂), which indicates prevailing physicochemical conditions during the deposition period. The occurrence of negative Ce anomalies in hydrothermal fluorite can be attributed to the synergistic effects of Ce³⁺ oxidation and Ce⁴⁺ inactivity [61]. Ce³⁺ is readily oxidized to Ce⁴⁺, which can precipitate rapidly as insoluble Ce(IV) through oxidative scavenging [71]. This process reduces Ce concentration in the fluid, creating a Ce-deficient environment and resulting in a negative Ce anomaly in the crystallized material.

The influence of water-related parameters on the mobility and migration of REEs is a significant concern. Numerous studies have investigated water–rock interactions and water-cycle mechanisms, such as the mixing of water from various sources [72,73]. In general, a negative Ce anomaly and Ce depletion are typically observed in seawater [74], confirming that the ore-forming fluids in the Jebel Stah fluorite were derived from a mixture of basinal brine and shallow water. This suggests the presence of a high fluid fO₂, as found in surface waters [6]. Consequently, the negative Ce anomaly inherent in the brine persists during the ore-formation process and can be mainly attributed to the oxidizing environment. This finding aligns with previous studies [8,19], which reported negative Ce anomalies in Jebel Stah fluorites that formed under high fO₂ conditions. The Ce anomaly may also result from leaching activities involving the host rocks, since Souissi et al. [19] reported a negative Ce anomaly in the wallrock limestones.

6.2.2. Eu Anomaly

Eu anomalies are a useful tool to study the sources of REEs and the transport of redox-sensitive elements. All fluorite samples show negative Eu/Eu* values (Table A11). Usually, the Eu³⁺/Eu²⁺ redox potential of hydrothermal and aqueous fluids is strongly controlled by thermal and chemical factors, typically redox conditions during sedimentation [75]. Three possible explanations for the presence of a moderate negative Eu anomaly have been suggested: (a) precipitation from reducing fluids at high temperatures (>250 °C), leading to the dominance of Eu²⁺ over Eu³⁺ [76,77,78]; (b) the presence of organic matter as a contributor to the negative Eu anomaly during fluorite deposition; and (c) inheritance through redox condition during interaction with the host rock or the leaching of external rocks by evolving fluids (e.g., [5,7,76,79,80]).

(a)

At high temperatures (>250 °C), Eu²⁺ tends to dominate in hydrothermal fluids, even under acidic and weakly reducing conditions [81]. Under reducing conditions, Eu²⁺ can be preferentially mobilized over other trivalent REEs, leading to the separation of Eu from the rest of the lanthanide series [82]. When Eu³⁺ is reduced to Eu²⁺, the resulting Eu²⁺ ion is too large to be incorporated into the fluorite lattice. This leads to a crystallographically controlled fractionation process during fluorite deposition that ultimately results in the observed negative Eu anomaly [75].

(b)

Taking into consideration that at Jebel Stah, the fluorite ore has occurred at temperatures below 200 °C [19,27,28], only organic matter could have been involved as a reducing agent of Eu, as long as the accumulation of organic matter in carbonate sediments requires a high oxygen deficiency and reflects anoxic conditions [83]. This may explain the observed negative Eu anomaly due to the crystallographically controlled fractionation process during fluorite deposition at Jebel Stah under the experienced low temperature (130–175 °C) conditions. The decomposition of organic matter can produce organic acids, creating an acidic environment favorable for fluorite precipitation with low REE content and negative Eu anomalies. Therefore, it can be deduced that the lack of Eu in the fluorite-forming fluid is the primary factor of the Eu depletion in fluorites G1 and G2.

(c)

The negative Eu anomaly in fluorite REE + Y patterns can occur if Eu²⁺ was stable during fluid migration [80]. This anomaly reflects the presence of Eu²⁺ rather than Eu³⁺ in the hydrothermal fluid during fluorite crystallization [84,85]. At temperatures above 200 °C, Eu²⁺ does not replace Ca²⁺ in the fluorite structure due to the difference in ionic radius, leading to Eu depletion in the fluorite [5,7,61]. Such fluids precipitate fluorite as temperatures decreases or fO₂ increases. When acidic, fluorine-rich fluids interact with carbonate host rocks, they dissolve CaCO₃ and form fluorite with low total REE concentrations and a negative Eu anomaly.

6.3. Y Anomaly and Y/Ho vs. La/Ho Diagram

The positive Y_CN anomaly recorded in fluorites G1 (sample FICI1) and G2 (sample JSF_V) (Figure 10), is a characteristic commonly observed in several fluorite occurrences worldwide, such as those of the Schwarzwald Harz Mountains in Germany [86], as well as the Pennine Ore Field in the UK [56,87,88], High Atlas in Morocco [89], Eastern Ladakh in India [90], Estern Qinling Mo Belt in North China Craton [91], etc. The average Y in fluorite samples is 0.81 and 3.03 ppm, respectively. Both fluorites G1 and G2 show positive Y anomalies in the range of 0.25 to 1.28. Yttrium enrichment in fluorites is primarily influenced by the presence of fluoride complexes [6,86] and can be attributed to the increased stability of YF⁺² compared to HoF²⁺ fluoride complex structures in hydrothermal solutions [56,92,93]. Hence, the Y/Ho ratio is expected to increase in fluorine-rich solutions (Figure 11).

The positive values of Y anomalies in fluorite samples suggest the strong fractionation of Y relative to its geochemical analog Ho, as evidenced by Y/Ho ratios ranging from 1.82 to 158.2 (Table A11). These Y/Ho ratios are consistent with those observed in numerous fluorite occurrences worldwide [56,91,94]. The observed variations in Y/Ho and La/Ho ratios (Table A11; Figure 11) indicate fractionation from different REE + Y sources, which support the concept that fluorite formation involved multiple precipitation events [4]. Notably, fluorite G2 has a greater Y/Ho ratio than fluorite G1 (Table A11; Figure 11). In this context, [56] suggested that Y/Ho ratios tend to increase during the migration of F-rich aqueous fluids. Loges et al. [93] proposed that Y/Ho ratios would increase at relatively higher depositional temperatures. The lower Y/Ho ratios observed in G1 fluorite veins (sample FlCI1: Table A11) suggest precipitation at lower temperatures [4,93], which is in accordance with the microthermometric results given in Table 1.

Hydrothermal fluorites are characterized by high Y/Ho ratios, typically ranging between 35 and 250 [56]. The range of Y/Ho ratio in the studied fluorites (Table A11) significantly exceeds the chondritic Y/Ho ratio [95] but aligns with the Y/Ho values observed in hydrothermal fluorites (Figure 11). The overlap of Y/Ho ratios with those of typical hydrothermal fluorite occurrences (e.g., [56,87,96,97]) further supports a hydrothermal source for the Jebel Stah F deposit. The analyzed samples also show seawater-like REE + Y patterns with superchondritic Y_CN contents that are consistent with the measurements reported for seawater by Tostevin et al. [66]. Given that the solubility rate of HoF₃(s) is higher than that of YF₃(s) at lower temperatures, Ho is extracted from the water column much more efficiently than Y, resulting in a marine superchondritic Y/Ho ratio. Consequently, both G1 and G2 are likely to preserve the geochemical features of coeval seawater [93]. This may suggest that the Jebel Stah fluorite has a mixed seawater–hydrothermal source.

6.4. The Tb/Ca vs. Tb/La Diagram

The Tb/Ca and Tb/La ratios are used to distinguish fluorite deposits based on their sedimentary, hydrothermal, or pegmatitic origins [63]. During fluorite crystallization, terbium (Tb) and lanthanum (La) exhibit significant levels of differentiation across all fluorite types [98]. The Tb/La ratio reflects the extent of REE remobilization and differentiation during crystallization [63,98]. On the other hand, the Tb/Ca ratio is indicative of the geochemical conditions prevailing during fluorite crystallization [14].

The Tb/Ca vs. Tb/La diagram (Figure 12) shows that all fluorite samples of Jebel Stah display Tb/Ca ratios varying in a very narrow interval, but Tb/La ratios of Fl2 samples from G1 (FlCl1, JSC_IV) are higher than that of the fluorite Fl3 (JSF_V) from G2; as a result, the former plot in the sedimentary field, but the second plot in the hydrothermal field. According to Yuan et al. [99], Makin et al. [100], and Khorshidi and Etemadi [101], such a pattern provides evidence of the sedimentary–hydrothermal origin of fluorites at Jebel Stah.

The plot of the G1 fluorite samples within the sedimentary field should result from the partial interaction of the hydrothermal fluids with calcium-rich sedimentary brines (cf. [102]) and/or sedimentary host rocks [63,103], and suggests that ore-forming solutions (130 °C, 19.5 wt% NaCl eq.; Table 1) dissolved and incorporated calcium-rich carbonate rocks as known in many Mississippi Valley-Type (MVT) deposits [5,63]. G2 samples plot within the hydrothermal field and display lower Tb/La ratios, suggesting the formation of fluorites from ƩREE-enriched and warmer (175 °C) but less saline (10 wt% NaCl eq.) fluid (Table 1).

Souissi et al. [20,28] have analyzed fluorites from ore deposits of the ZFP (Jebel Stah, Sidi Taya, Jebel Oust, Hammam Jedidi, and Oued M’Tak: Table A2 and Table A3) for REE by ICP-MS (Table A7 and Table A8). When plotted in the Tb/Ca vs. Tb/La diagram (Figure 13), these deposits are distributed across both hydrothermal and sedimentary fields, confirming the sedimentary–hydrothermal origin of the fluorites in the ZFP.

It is worth noting, however, that the REE patterns of the fluorites Fl2 and Fl3 from G1 and G2 generations are consistent with those drawn from ICP-MS data from Souissi et al. [20,28]. The similarity of the results from these two techniques shows that LA-ICP-MS analysis can be a reliable substitute for the ICP-MS method for the analysis of rare-earth elements in fluorites from mineral deposits [104].

6.5. Strontium Isotope Tracing

Strontium isotopes are valuable tracers of various geological processes and events. In general, hydrothermal minerals such as fluorite, barite, calcite, and gypsum are enriched in Sr but depleted in Rb [105]. As a result, these minerals typically exhibit low Rb/Sr ratios [106,107]. The ⁸⁷Rb/⁸⁶Sr ratios range from 0.0087 to 0.39, a variation primarily resulting from the low Rb concentrations in fluorite. This sensitivity can result in a broad range of ratios, even with slight fluctuations in Rb levels. For instance, studies have reported fluorite samples with Rb contents as low as 13 ppm and Sr contents up to 1420 ppm, leading to variable ⁸⁷Rb/⁸⁶Sr ratios (e.g., [108,109]).

Due to the minimal Rb content, the contribution of in situ radiogenic ingrowth of ⁸⁷Sr over time is negligible. Therefore, the ⁸⁷Sr/⁸⁶Sr ratios provide an accurate measurement of the Sr isotopic composition of mineralizing fluids [80,107]. These methods can serve as sensitive tools for determining the origin of ore-forming fluids and the reservoirs from which Sr has been extracted [106,107].

The ⁸⁷Sr/⁸⁶Sr ratios determined for fluorite may reflect the initial values of the paleoluids during deposition. The small range in ⁸⁷Sr/⁸⁶Sr ratios (0.708102–0.708812) suggests the involvement of one similar Sr source for both fluorite generations G1 and G2, which is supported by the REE + Y pattern distribution. These achievements are in accordance with the previously published data of Dill et al. [8] and Souissi et al. [19] (Figure 14).

It is worth noting that the aforementioned Sr-isotope ratios are higher than the Mesozoic (Triassic, Jurassic, Cretaceous) seawater [110,111]. The exact timing of ore deposition at Jebel Stah, where F-mineralization is hosted along the Lower–Middle Liassic unconformity [25], is not yet known. However, it has been suggested that the ores in the ZFP, including those of Jebel Stah, were formed during the Upper Miocene compressional phase [20,40,112,113]. As a result, it can be stated that the mineralizing fluids at Jebel Stah are related to more radiogenic basinal brines derived from the even more deeply buried siliciclastic megasequences (>10 km-thick) of the Paleozoic.

Based on these findings, it is suggested that the deposition of the fluorite ore (G1) at Jebel Stah involved basinal brines (connate waters) coming from the underlying Paleozoic basin along deep-seated NE-SW-oriented faults. These fluids were in equilibrium with the siliciclastic sediments and their circulation were triggered in response to hydraulic fracturing in a high geothermal gradient setting [20,28]. Their high salinity (≈20 wt% eq. NaCl) was acquired during their ascent, by the interaction with the Triassic salt layers.

Figure 14. A comparative diagram of the ⁸⁷Sr/⁸⁶Sr ratio of fluorite samples from the Zaghouan Fluorite Province with the literature results of Dill et al. [8] and Souissi et al. [19]. The isotopic strontium intervals of Mesozoic seawater are based on Burke et al. [110] and Koepnick et al. [111], while the Paleozoic data are from Burke et al. [110].

Figure 14. A comparative diagram of the ⁸⁷Sr/⁸⁶Sr ratio of fluorite samples from the Zaghouan Fluorite Province with the literature results of Dill et al. [8] and Souissi et al. [19]. The isotopic strontium intervals of Mesozoic seawater are based on Burke et al. [110] and Koepnick et al. [111], while the Paleozoic data are from Burke et al. [110].

7. Conclusions

This work represents the first application of REE-Y geochemistry by LA-ICP-MS analysis on fluorite mineralization in Tunisia, providing new evidence in support to the genetic model for fluorite mineralization at Jebel Stah documented in previous studies [20,25,27,28].

The classification of Jebel Stah fluorites is determined exclusively by analyzing their REE + Y compositions and their plotted position within the Tb/La–Tb/Ca and Y/Ho–La/Ho diagrams. The observed variations in overall REE + Y content and Y/Ho fractionation confirm that the hydrothermal fluorites originated from paleofluids exposed to different physicochemical conditions, particularly in terms of temperature and REE + Y sources. The two REE + Y pattern types of fluorites, along with their locations on the Tb/Ca–Tb/La diagram, reveal distinguishing features and confirm their suitability as proxies for determining the origin of the fluids involved in Jebel Stah fluorite mineralization. The Tb/Ca ratios in the fluorite samples prove their hydrothermal–sedimentary origin.

The REE concentrations in the studied fluorites are generally low, with the highest contents observed in late-stage fluorites from the second generation G2. The chondrite-normalized REE-Y patterns fall into two groups: (i) REE-Y patterns characteristic of early-stage fluorites (G1) exhibit LREE depletion, a slight hump for MREE, and pronounced negative Ce anomalies with small negative Eu anomalies and moderate positive Y anomalies; (ii) REE + Y patterns, associated with late-stage fluorites (G2), displaying slight LREE depletion, and a nearly flat MREE-HREE segment, along with a strong positive Y anomaly, reflecting the influence of residual fluids during later stages of mineralization.

The Eu/Eu* ratios show small negative anomalies in both early and late fluorites, which indicates formation temperatures below 200 °C. Similarly, the Ce/Ce* ratios reveal strong negative anomalies in both fluorite generations, which implies oxidative conditions in the mineralizing fluids. The LREE depletion, combined with negative Ce anomalies in the studied fluorites, are similar to the REE + Y patterns typically observed in fluorites from Mississippi Valley-Type Pb-Zn deposits.

Combining microthermometric data and REE + Y geochemistry, it is suggested that the Jebel Stah fluorite deposit has experienced two main fluid-circulation events. During the first event, a radiogenic REE + Y-depleted fluid was responsible for the precipitation of the early fluorite G1, making the economic ore. This fluid, similar to hydrothermal basinal brines rich in fluorine with low temperature and high salinity, could be attributed to the upward migration of deep-seated fluids trapped in the siliciclastic sedimentary column of the Paleozoic basin, along deep NE-SW trending faults. The fluorite ore would have been deposited as a result of fluid–rock interaction, causing the dolomitization of the host-rock carbonates and the subsequent increase in pH and calcium activity in solution. During the second event, a radiogenic REE + Y-rich fluid with lower salinity and higher temperature was responsible for the formation of the accessory fluorite G2. The decrease in salinity could be due to the mixing of the hydrothermal basinal brine with meteoric water, which is considered as a triggering process for fluorite crystallization.

Sr isotope ratios show that the mineralizing fluids at Jebel Stah are more radiogenic than the Mesozoic sea water, giving evidence that these fluids are sourced from the deeply buried siliciclastic megasequences of the Paleozoic basin.