Fluorite Deposits Research Articles

Genetic Relationship between Granite and Fluorite Mineralization in the Shuanghuajiang Fluorite Deposit, Northern Guangxi, South China: Evidence from Geochronology, REE, and Fluid Geochemistry

Hydrothermal vein-type fluorite deposits are the most important metallogenic type of fluorite deposits in South China, most of which are closely related to granitoid in space; however, the genetic relationship between granitoid and fluorite mineralization remains controversial. The Shuanghuajiang fluorite deposit in northern Guangxi of South China is a typical vein-type fluorite deposit hosted in a granite pluton, with the orebodies occurring within brittle faults. Zircon U-Pb dating of the hosting Xiangcaoping granite yields an emplacement age of 228.04 ± 0.76 Ma (MSWD = 0.072). Fluorite Sm-Nd dating yields an isochron age of 185 ± 18 Ma. The new age data indicate that the fluorite deposit was precipitated significantly later than the emplacement of the hosting Xiangcaoping granite pluton. The fluorite and granite exhibit similar rare earth element (REE) patterns with negative Eu anomalies, suggesting that fluorine (F) was derived from the granite. The fluorite fluid inclusions show a homogeneous temperature mainly ranging between 165 °C and 180 °C. Salinity is typically less than 1% NaCl eqv, while the δ18OV-SMOW and δDV-SMOW values are between −5.2‰–−6.1‰ and −17.35‰–−23.9‰, respectively. These indicate that the ore-forming fluids were a NaCl-H2O system with medium-low temperature and low salinity, which is typical for meteoric water. Given the combined evidence of geochronology, REE, and fluid geochemistry, the mineralization of the Shuanghuajiang fluorite deposit is unrelated to magmatic-hydrothermal activity but achieved via hydrothermal circulation and leaching mechanisms. Our study presents a genetic relationship between the fluorite deposit and granitoids based on an example of northern Guangxi, providing a better understanding of the genesis of hydrothermal vein-type fluorite deposits in granitoids outcropping areas.

Mineralization-tectonic Relationship in the JbelTirremi Fluorite Mine (Taourirt Region - Eastern Morocco): Contribution of Remote Sensing for Geological Exploration

The Tirremi fluorite deposit, located in the Taourirt region (Eastern Morocco), morphologically constitutes a mainly carbonate dome of the Jurassic age, crossed by numerous dykes of lamprophyric rocks of Eocene age. The tectonic study coupled with the study of lineaments extracted from band 2 of the sentinel-2 image shows that the main directions, in terms of frequency and size, are NE-SW and E-W to ENE-WSW. The other directions, N-S and NNW-SSE, are satellite faults with respect to the potential faults; but they are economically important since they give rise to fluorite-rich veins. Similarly, analysis of fracturing (faults, tension cracks, dykes, etc.) allows us to identify the Palaeostresses of stress responsible for the structuring of the Tirremi region. These phases, classified in chronological order based on field observations, are perfectly compatible and correlatable with previous work done in the area.

Textural features and in situ trace element analysis of fluorite from the Wujianfang fluorite deposit, Inner Mongolia (NE China): Insights into fluid metasomatism and ore-forming process

The Wujianfang fluorite deposit shows a four-stage mineralization history: (1) pre-ore stage of disseminated fluorites, (2) early-ore stage of fluorite-muscovite-pyrophyllite, (3) main-ore stage of fluorite-pyrophyllite, and (4) late-ore stage of fluorite-albite-quartz. Detailed cathodoluminescence imaging, fluid inclusion study, and in-situ LA-ICP-MS trace element analysis of fluorite in different stages or mineral assemblages were applied to reveal the fluorite mineralization and metasomatic history of this deposit. These data show that water-rock reaction between hydrothermal fluids and wall rocks not only provides the dominant ore-forming materials for fluorite mineralization, but also promotes the precipitation of fluorite by changing the pH of ore-forming fluids. Temperature change also plays an important role in fluorite precipitation. Fluorite grains from the pre-, early-, and main-ore stages have been variably metasomatized by a coupled dissolution-reprecipitation-recrystallization mechanism, which is characterized by complex petrographic and chemical zones. During this process, many trace elements were leached from the primary fluorite grains or other accompanied minerals, and parts of these elements were immediately reprecipitated into the new phases. Then, the recrystallized phases were formed from the leachate solutions of primary minerals. Our study highlights that fluorite generally has a complex growth history due to metasomatic alteration by hydrothermal fluids during the ore-forming process. Thus, in-situ microanalysis is essential and necessary to obtain effective and accurate constraints on hydrothermal evolution, and most of the interpretations based on bulk analysis of fluorites crystals should be cautioned.

Metallogenic Characteristics and Prediction of Fluorite Deposits in Shangkuli Area

Metallogenic Characteristics and Prediction of Fluorite Deposits in Shangkuli Area

Late-magmatic processes in the St. Lawrence Granite: Implications for fluorite mineralization

The St. Lawrence Granite (SLG), located in the Avalon Zone of the Appalachian Orogeny, is a peralkaline to metaluminous granite, best known for its association with extensive, and economically significant, fluorite deposits. Genetic models for the fluorite mineralization have been proposed, but major gaps and misconceptions still remain, such as the lack of fluorite in the country rocks, the source of Ca to form fluorite and the locally abundant calcite in the fluorite veins and the granite. Petrography, geochemistry and electron microprobe analysis revealed new details on the late-magmatic processes in the granite that played a significant role in fluorite mineralization.The SLG intruded at shallow levels and comprises several phases, each having different textures, mineralogy, and geochemistry. Most of the fluorite deposits are associated with the East lobe (E lobe), which is the only peralkaline and one of the most intensely altered phases of the granite. Alteration and fluorite mineralization are the results of devolatilization of the granite. The volatiles included F, Cl, CO2 and water. Early exsolution of a F-rich vapour, followed by a F-rich acidic fluid led to the fluorite mineralization. In the later stages, a F-poor and CO2-rich fluid was left and was unable to leave the granite, migrated along the upper contact of the granite and accumulated in the cupolas resulting in late carbonatization and extensive autometasomatism.Exsolution of a F-rich vapour, coupled with the shallow depth of intrusion of the SLG, allowed the F to leave the granite leading to fluorite mineralization in the country rocks, as demonstrated by the AGS fluorite deposit, which is partially hosted in sedimentary rocks overlying the granite; this encourages further exploration in the surrounding rocks. The source of the Ca is from the alteration of primary Ca-bearing feldspar and amphiboles in the granite, implying the lack of spatial correlation between fluorite mineralization and Ca-containing country rocks. This is significant for pursuing further exploration for fluorite in the St. Lawrence area, and elsewhere.

Vein-type fluorite mineralization of the Linxi district in the Great Xing'an Range, Northeast China: Insights from geochronology, mineral geochemistry, fluid inclusion and stable isotope systematics

The Linxi fluorite district is located in the southern Great Xing’an Range and tectonically belongs to the eastern segment of the Central Asian Orogenic Belt. Previous studies mainly focus on the metal deposits in this region, but relatively little attention has been paid to the fluorite mineralization. The Linxi district contains more than 60 fluorite deposits while the formation age, nature of mineralized fluids, and ore-forming processes are poorly understood. This study focuses on geology, geochronology and geochemistry of the fluorite deposits in the Linxi district which share similar and relatable geological features. Fluorite veins are strictly controlled by ∼S-N-, NNE-SSW- and NE-SW-striking fault zones. Ore mineral assemblages are quite simple and mainly include fluorite, quartz and calcite. Geochronological data indicate that the main-stage fluorite vein mineralization in the Linxi district occurred approximately at 137–132 Ma. Fluid inclusions hosted in fluorite, quartz and calcite mainly homogenize at 140–220 °C, corresponding to low salinities (mainly 0.3–1.2 wt% NaCl equivalent). Ore-forming fluids are characterized by low temperatures, low salinities and low densities of the H2O–NaCl system. The carbon, hydrogen and oxygen isotopic compositions of samples obtained from the Linxi fluorite district indicate an origin of meteoric water. Combined with trace element geochemistry, fluorite, quartz and calcite in this area share a common hydrothermal origin. The large-scale fluorite mineralization in this region may link to the Late Mesozoic metal metallogenic events in the southern Great Xing’an Range associated with the extensional tectonic setting.

Application of field-portable geophysical and geochemical methods for tracing the Mesozoic-Cenozoic vein-type fluorite deposits in shallow overburden areas: A case from the Wuliji’Oboo deposit, Inner Mongolia, NE China

Fluorite deposits are widespread throughout eastern China and commonly occur in vein systems. These vein-type fluorite deposits are the primary source of fluorine worldwide and were predominantly formed during the Mesozoic or Cenozoic periods. In the absence of ore outcrops, fluorite exploration is necessarily concentrated within the shallow overburden area. The Wuliji'Oboo fluorite deposit is an example of a medium–low temperature vein-type subsurface orebody in eastern Inner Mongolia. Five portable technology methods have been implemented within the study area, including multispectral remote sensing (RS) technology, very low-frequency electromagnetic measurement (VLF-EM), portable X-ray fluorescence analyses (PXRF), portable gamma-ray spectroscopy, and partial extraction geochemistry. This paper describes the application principles, influencing factors, and technical solutions for each method. By investigating various examples, the applications of portable technology methods and their associated limitations were evaluated. Combining geological research with multi-spectral RS techniques is essential for optimum fluorite ore body prediction, thus narrowing prospecting targets. First, the target area was scanned using VLF-EM to identify the distribution of potential anomalies. Second, PXRF was used to distinguish the mineralised anomaly. Finally, trenching and drilling were performed to verify the effectiveness of the combination of methods. This study establishes a geology-geophysics-geochemistry-remote sensing integrated exploration model that may provide theoretical and technical support for the prediction of fluorite ore bodies in large Quaternary shallow overburden areas.

Impact of freeze-thaw on the behaviour of flotation tailings from a rare earth deposit

The Ashram Rare Earth and Fluorspar Deposit, located in northern Quebec (Canada), contains a potential carbonatite-type rock source of rare earth elements (REE). A pilot scale pre-concentration of REE minerals produced flotation tailings. A kinetic leach column study was performed to evaluate the behaviour of these tailings in a northern context (i.e. freeze-thaw cycles). The tailings were exposed to 12 cycles (over 1 year) of leaching with deionized water under two different conditions. The first column, CW (water column), was stored at 5 °C for the duration of the experiment, while the second column, CFT (freeze-thaw column), was subjected to freeze-thaw cycling. A comparison with Quebec environmental guidelines showed that the tailings were not acid generating but deemed leachable for Cd, Pb, Zn and Mn. Leachate analysis for the CW (water column) showed that the behaviour of Ba, Ca, Sr and Mn appeared similar. These elements could originate from the dissolution of calcite [CaCO3], dolomite [CaMg(CO3)2], dolomite-Fe [Ca(Mg,Fe2+)(CO3)2] or ankerite [Ca(Fe2+,Mg,Mn)(CO3)2]. Mg, F and Si could originate from the dissolution of biotite [K2(Mg,Fe2+)6-4(Fe3+,Al,Ti)0-2(Si6-5Al2-3O20)(OH,F)2]. The release of these elements would, however, appear to come from separate minerals. The presence of fluorine in the leachate could come from the dissolution of fluorite [CaF2], apatite [Ca5(PO4)3(O,H,F,Cl)] or bastnaesite [(La,Ce)CO3F]. Mg could come from the dissolution of carbonate minerals such as magnesite [MgCO3]. Despite high Fe content (98,620 mg/kg) in the initial flotation tailings, Fe was not present in the leachate, probably because of potential precipitation in the form of iron oxides/hydroxides. Despite being only slightly soluble (<0.001% mobilized), some heavy REE (HREE), Er, Yb, Lu and Sc, have a distinct leaching behaviour compared to other REE. Overall, the freeze-thaw cycles only decreased the mobility of some elements (e.g. Ca, Ba, Sr and Mn) and, thus, the potential for environmental contamination from the tested REE tailings.

Investigation on the flotation separation of fluorite from celestite using a novel depressant: Sodium polynaphthalene formaldehyde sulfonate

Sulfate minerals have gradually become the main gangue minerals of fluorite deposits, and the flotation separation of fluorite and sulfate minerals is difficult with commonly used depressants. In this paper, the high selectivity of a novel depressant sodium polynaphthalene formaldehyde sulfonate (SPS) for the flotation separation of fluorite and celestite both in single mineral and artificial mixed ore experiments was studied, and the underlying separation mechanism was investigated by zeta potential measurement, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) analysis, and Atomic force microscopy (AFM) imaging analysis. Flotation results showed that, in the presence of sodium oleate (NaOL) and SPS, the flotation recovery difference between fluorite and celestite reached 76.26% and the grade of fluorite concentrates increased by 32.11% at pH 6.0. The analysis results showed that the adsorption of SPS on the fluorite surface was limited at pH 6.0, and the adsorption was most likely be through electrostatic interaction. For celestite, the adsorption of SPS on the surface significantly changed the chemical surrounding of celestite surface inhibiting the chemical adsorption of NaOL, and the chemical adsorption of SPS was more significant at pH 6.0.

Exploration of concealed fluorite deposit in shallow overburden areas: A case study in Elimutai, Inner Mongolia, China

Exploration of concealed fluorite deposit in shallow overburden areas: A case study in Elimutai, Inner Mongolia, China

Timing of fluorite mineralization and exhumation events in the east Central Alborz Mountains, northern Iran: constraints from fluorite (U–Th)/He thermochronometry

AbstractThe recently developed fluorite (U–Th)/He thermochronology (FHe) technique was applied to date fluorite mineralization and elucidate the exhumation history of the Mazandaran Fluorspar Mining District (MFMD) located in the east Central Alborz Mountains, Iran. A total of 32 fluorite single-crystal samples from four Middle Triassic carbonate-hosted fluorite deposits were dated. The presented FHe ages range between c. 85 Ma (age of fluorite mineralization) and c. 20 Ma (erosional cooling during the exhumation of the Alborz Mountains). The Late Cretaceous FHe ages (i.e. 84.5 ± 3.6, 78.8 ± 4.4 and 72.3 ± 3.5 Ma) are interpreted as the age of mineralization and confirm an epigenetic origin for ore mineralization in the MFMD, likely a result of prolonged hydrothermal circulation of basinal brines through potential source rocks. Most FHe ages scatter around the Eocene Epoch (55.4 ± 3.9 to 33.1 ± 1.7 Ma), recording an important cooling event after heating by regional magmatism in an extensional tectonic regime. Cooling of the heated fluorites, as a result of thermal relaxation in response to geothermal gradient re-equilibration after the end of magmatism, or exhumation cooling during extensional tectonics characterized by lower amount of erosion are most probably the causes of the recorded Eocene FHe cooling ages. Oligocene–Miocene FHe ages (i.e. 27.6 ± 1.4 to 19.5 ± 1.1 Ma) are related to the accelerated uplift of the whole Alborz Mountains, possibly as a result of the initial collision between the Afro-Arabian and Eurasian plates further to the south.

Integrated Exploration Model for Concealed Ore Deposit: A Case Study from Shuitou Fluorite Deposit, Inner Mongolia, North China

The demand for fluorite resource is increasing rapidly as most fluorite deposits on Earth’s surface have been exhausted. The newly discovered fluorite deposits in Inner Mongolia are hosted by Permian metamorphosed sandy slate, intermediate-acid intrusive rocks and Cretaceous volcanic sedimentary rocks. The ore bodies are strictly controlled by faults and buried by cover rocks. The feasibility and effectiveness of multi-techniques for prospecting concealed fluorite ore bodies are evaluated, and 10 anomalies are delineated. On the basis of geological features and effectiveness of different methods, the optimum combinations of ore prospecting techniques are proposed for the exploration of zonal type and burial type concealed fluorite ore bodies. Based on comprehensive researches, an integrated exploration model is proposed: (i) select key prospecting targets based on geological backgrounds, regional geochemical anomalies of F and Ca, and remote sensing images; (ii) identify the spatial distribution of low resistivity anomaly and ore-controlling structure from geophysical survey; (iii) evaluate the mineralization potential in fault zone based on F and Ca anomalies in key sections selected from low resistivity anomaly zones; and (iv) evaluate the mineralization potential and reveal the spatial distribution of fluorite ore bodies and ore-controlling faults based on integrated geophysical and geochemical anomalies. The integrated exploration model is verified to be a powerful tool for prospecting concealed fluorite ore bodies in coverage area.

Epithermal Fluorite Deposits in Transbaikalia (Geochemical Features, Sources of Matter and Fluids, and Genesis)

Abstract —We consider the isotope-geochemical features of epithermal fluorite deposits in Transbaikalia, including the REE compositions, Sr isotope ratios, Sm–Nd systems, and isotope compositions of oxygen, carbon, hydrogen, and sulfur. The 87Sr/86Sr ratios in fluorites are within 0.706–0.708, and the εNd values are negative. Oxygen in quartz, the main mineral of the deposits, has a light isotope composition (δ18O = –3.4 to +2.6‰), and the calculated isotope composition of oxygen in the fluid in equilibrium with quartz (δ18O = –9 to –16‰) indicates the presence of meteoric water. The latter is confirmed by analysis of the isotope compositions of oxygen and hydrogen in gas–liquid inclusions in fluorites from three deposits. These isotope compositions are due to recycling caused by the impact of shallow basic plutons. The isotope composition of sulfur indicates its deep source. During ascent, sulfur became enriched in its light isotope (δ34S = –1.8 to –7.7‰). We assess the association of fluorite ores with basaltoids widespread in the study area. The isotope and geochemical parameters suggest their spatial proximity. Probably, the basaltoids were responsible for the recycling of meteoric water. It is shown that the epithermal fluorite deposits formed by the same mechanism as fissure–vein thermal waters in western Transbaikalia.

Contribution of ERT on the Study of Ag-Pb-Zn, Fluorite, and Barite Deposits in Northeast Mexico

The results on the effectiveness of five 2D electrical resistivity tomography (ERT) survey profiles for Ag-Pb-Zn, fluorite, and barite exploration Mississippi Valley Type (MVT) and on the magmatic deposits of northeast Mexico, are presented. The profiles were made in areas with mining activities or mineralization outcrops. Schlumberger, dipole-dipole, and Wenner array configurations were used on the measurements. The results showed that electric resistivity can be used to distinguish between mineralized zones. In magmatic-type Pb-Zn and MVT Pb-Zn deposits, resistivity values are shown as low. In magmatic-type fluorite and MVT fluorite deposits, as well as the MVT barite deposit, low-resistivity values are related to Fe sulfides and clays. With these results it is possible to connect observed surface mineralization with underground mineralization. New mineralized zones are also found and their geometries, extensions, and dipping are reported. Therefore, lower resistivity values can be linked to mineral bodies with higher Ag-Pb-Zn contents, as well as bodies enriched in Fe sulfides, Fe oxides, and clays in the fluorite and barite mineralizations. In most ERT models, fractures and faults are identified, indicating a structural control on mineralization. From the geoelectric patterns we can infer the magmatic and MVT origin of these mineral deposits.

GOLD-SILVER MINERALIZATION IN THE VERKHNEKRUCHININSKOYE FLUORITE DEPOSIT IN TRANSBAIKALIA

The relevance lies in the establishment of mineral forms of gold and silver in a new mineral type of gold-silver deposits, where the leading minerals are fluorite and quartz. Hence, the aim of the study was to study the mineral composition of the sulfide-quartz association, on which the fluorite-quartz mineralization of the Verkhnekruchininskоyе fluorite deposit is superimposed. The object of the study is the vein material of the Verkhnekruchininskоyе fluorite deposit, and the subject is the mineral composition of mineral aggregates for the detection of thin inclusions of silver and gold minerals, their chemical composition and paragenesis. The methodology included the manufacture of polished sections, thin sections and their study, using optical and electron microscopic methods, as well as traditional methods for studying the chemical composition of a mineral substance. A preliminary study of polished sections was carried out using a polarizing microscope. An electron microscopic study was carried out by the author – candidate of technical sciences, S. V. Kanakin, the head of the laboratory of the Geological Institute of the SB RAS. Results. The study of the mineral and chemical composition of the fluorite-quartz vein samples containing pyrite was carried out. Sulfides are found mainly in fragments of ferromuscovite-kaolinite-carbonate-quartz composition, which are in fluorite-quartz material. It also contains apatite, represented mainly by fluorine-apatite. For the first time, the features of the chemical composition of pyrite have been identified and the associated acanthite (AgS), which is allocated along its periphery, has been identified. Some pyrite crystals are characterized by their arsenicity (up to 0,63 %), sometimes accompanied by the presence of cobalt (up to 0,59 %) and nickel (up to 0,34 %). The same elements are also present in iron hydroxides developing along pyrite in the oxidation zone. The content (wt %) of iron in pyrite varies from 47,31 to 48,74, and sulfur from 51,26 to 52,84. Formula coefficients, respectively, vary from 1,02 to 1,06 for iron and from 1,94 to 1,98 for sulfur. A significant part of the pyrite crystals is oxidized and surrounded by thin rims of iron hydroxides. Pyrite contains petcite (Ag3 AuTe2) and acanthite (Ag2S). Petzite is found in pyrite in the form of inclusions of the smallest crystals, while acanthite is found in the outer zone of pyrite crystals. It forms a fine dissemination of 1...2,5 microns in size. Its chemical composition is usual. It contains (wt%) 87.82 - 87.88 Ag and 12,12...12,18 S. According to its formula Ag2.05 S0.95, the mineral is characterized by an excess of silver and a lack of sulfur. The combination of petcite and acanthite in the early clastic material with pyrite cemented by a quartz-fluorite aggregate unambiguously indicates the possibility of sulfide-fluorite-quartz shallow gold-silver mineralization

Physicochemical Parameters of the Origin of Hydrothermal Mineral Deposits: Evidence from Fluid Inclusions. VI. Fluorite and Barite Deposits

Authors’ original continuously updated database, which currently comprises data from 22 300 publications on mineral-hosted fluid and melt inclusions, is used to generalize data on the physicochemical parameters of processes that produced fluorite and barite deposits. The paper presents data on the following parameters of the fluids: temperature, pressure, density, salinity, and gas composition. The average composition (Н2О, CO2, CH4, N2, H2S, and CnHm) of fluids at fluorite–barite deposits is calculated. The paper reports the average composition of major gas components (CO2, CH4, N2, and H2S) of natural fluids at these deposits on the basis of Raman spectroscopic analyses of individual inclusions. Average F, S, and Ba concentrations are calculated for silicate magmatic melts and natural mineral-forming fluids.

Geological and tectonic evolution characteristics of polymetallic metallogenic belt

According to the geological structure evolution characteristics of the polymetallic metallogenic belt, the key to solve the problem of mineral resources shortage is to analyze the dominant deposit types, metallogenic mechanism, and metallogenic process of the polymetallic metallogenic belt. On this basis, the analysis method of geological structure evolution characteristics of polymetallic metallogenic belt is put forward. Taking the Wuyishan polymetallic metallogenic belt as the research object, the comprehensive investigation methods of 2D seismic exploration, drilling, geophysical logging, and sampling test are used to control the structural morphology and polymetallic in Wuyishan area. Through drilling, logging, and laboratory tests, the occurrence range, buried depth, thickness, and structure of the polymetallic metallogenic belt are controlled. According to the evaluation results of mineral resources potential in China, it is proposed that the main mineral exploration directions of Wuyishan polymetallic metallogenic belt are rare earth, fluorite, copper-molybdenum, lead-zinc, tin, gold, and silver. The main types of ore deposits include weathering crust-type (ion adsorption type) rare earth deposit, porphyry copper-molybdenum gold deposit, and sedimentary reformed lead-zinc polymetallic deposit. Hydrothermal fluorite deposit and hydrothermal w-sn-bi-mo-ta deposit related to acid rocks are delineated, and eight key prospecting areas in the metallogenic belt are delineated.

Fluid composition and evolution of the Langxi Ba-F deposit, Yangtze Block, China: New insight from LA-ICP-MS study of individual fluid inclusion

The Langxi vein-type Ba-F deposit, located in the southeast of the Sichuan Basin in the central part of Yangtze Block, South China, is hosted by Ordovician limestone. The paragenesis of the deposit’s veins is subdivided into pre-, syn- and post-ore stages. The syn-ore stage includes two fluorite generations with the first (Fl-1) deposited at ~140° to 200° C and the second (Fl-2) at ~140° to 180 °C. The syn-ore barite mineralisation was deposited with the temperature range of 110°–160 °C, and the syn-ore calcite records a temperature range of 90° to 140 °C. These temperature ranges show that the mineralising fluids were low- to moderate in temperature and decreased with the initial deposition of fluorite followed by barite and then calcite. The types of fluid inclusions in the veins are classified as monophase liquid (L-type, type I), biphase liquid + vapour (L + V type, type II) and polyphase (L + V + S type, type III) brine inclusions. The salinity of the mineralising fluid for the three types of inclusions during the deposition of F-Ba-Ca is 0.35–21.7% NaCl eqv., indicating that the ore-forming fluid varied greatly during the mineralising process. There are no obvious differences in the fluid inclusion density in the different minerals with the average densities being 0.98 g/cm3 for Fl-1, 0.99 g/cm3 for Fl-2, 1.00 g/cm3 for barite, and 1.01 g/cm3 for calcite. This shows that the density of the F–Ba–Ca mineralising fluid belong to a moderate- low density. The deposition of the minerals took place with a change from a reducing to an oxidising environment. The liquid phase initially included Na+ and Cl−, and evolved containing Ca2+, SO42−, K+, and Mg2+. LA-ICP-MS analyses reveal that the L-V type fluid inclusions associated with Fl-1 assays 46,600 ppm Na, 3470 ppm K (with a mean Na/K ratio of ~24), ~28,200 ppm for Cl, and 1060 ppm Br (with a mean Cl/Br mass ratio of ~27). The second-generation fluorite L-V type fluid inclusions average around 47,000 ppm Na and 12,000 ppm K, corresponding to and a Na/K mass ratio of 7. The halogen content of Fl-2 averages 26,200 ppm Cl and 950 ppm Br, corresponding to a Cl/Br mass ratio of 28. These analyses indicate that the mineralising fluid was rich in NaCl, assuming the fluid inclusions represent samples of the mineralising fluid. It is proposed that Ba-F concentrated in the mineralising fluid were derived from basinal fluids mixed with meteoric water circulating through faults at increased temperature gradients. The driving force was Late Cretaceous tectonic activity related to the subduction of the Paleo-Pacific Oceanic Plate. This model is consistent with the geodynamic setting of other barite-fluorite-rich districts in the Yangtze Block of South China.

The role of the structures on the fluorite mineralization: Insight to fluid inclusion and alteration map of the Laal-kan fluorite deposit, NW Iran

The role of the structures on the fluorite mineralization: Insight to fluid inclusion and alteration map of the Laal-kan fluorite deposit, NW Iran

Rare earth element and Sr-Nd isotopic evidence for the origin of fluorite from the Silius vein deposit (southeastern Sardinia, Italy)

Rare earth element (REE) and Y contents along with Sr-Nd isotopic ratios have been determined in fluorite and calcite samples from the two main veins of the Silius deposit, hosted in Lower Paleozoic metavolcanic rocks, in southern Sardinia. Fluorite from the late San Giuseppe vein contains higher (107–336 mg/kg) (REE + Y) than fluorite from the early San Giorgio vein (29–94 mg/kg), whereas calcite exhibits a range (175–440 mg/kg) overlapping with that of San Giuseppe fluorite. Irrespective of either vein, the 87Sr/86Sr ratios of fluorite range from 0.71106 to 0.71566, overlapping with those of calcite (0.71257–0.71406), whereas the 143Nd/144Nd ratios are slightly higher for fluorite (0.51221–0.51236) than calcite (0.51211–0.5122). Moreover, the 147Sm/144Nd versus 143Nd/144Nd ratio relationship suggests that San Giuseppe fluorites were deposited by 294 ± 40 Ma, whereas it yields no information for San Giorgio fluorites. Assuming 270 Ma as the most probable age of emplacement, the initial Sr-Nd isotopic ratios and (REE + Y) contents in fluorite indicate the crustal origin of Silius mineralizing fluids, likely from mixing in different proportions of evaporated seawater brines with fluids from the Paleozoic siliciclastic basement and Late Variscan/post-Variscan magmatic rocks. Mineralizing fluids evolved their chemical and isotopic composition through interaction with wallrocks and/or dilution with meteoric waters circulating through the Paleozoic basement. As a whole, the chemical and isotopic composition of fluorite from the Silius deposit resembles that of other fluorite deposits from Variscan Europe.