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The surface properties of bastnaesite and parisite are similar to their associated gangue mineral, fluorite, which makes the flotation separation of these two rare earth minerals from fluorite one of the industry's most significant challenges. This study systematically investigates the inhibitory effects and mechanisms of sodium silicate (SS) on bastnaesite, parisite, and fluorite in an octyl hydroxamic acid (OHA) collector system through flotation experiments, various modern analytical methods, and DFT simulations. The flotation test results indicate that the inhibition effects of SS on the three minerals are in the order: fluorite > parisite > bastnaesite. Detection and analysis results indicate that SS forms hydrophilic complexes with Ca atoms on the surfaces of fluorite and parisite, enhancing surface hydrophilicity and inhibiting OHA adsorption, but its impact on bastnaesite is relatively minor. DFT simulation results show that OHA forms covalent bonds with metal ions on mineral surfaces, favoring five-membered hydroxamic-(O-O)-Ce/Ca complexes, and reacts more strongly with Ce atoms than Ca atoms. SS primarily forms covalent bonds with metal atoms on mineral surfaces via the SiO(OH)3− component, and OHA and SS compete for adsorption on the mineral surfaces. OHA has a stronger affinity for bastnaesite, whereas SS shows the highest affinity for fluorite, followed by parisite, and the weakest affinity for bastnaesite. [ABSTRACT FROM AUTHOR]

This study addresses the in situ mobility of fluoride and aluminum in two different ashfall deposits accumulated during the 2021 eruption of the Tajogaite volcano (La Palma, Canary Islands, Spain), which were exposed to contrasting conditions of ambient humidity and precipitation. We selected one site to the east of the volcanic emission center, located near the top of Cumbre Vieja Ridge and exposed to continuous humidity and rain, and another site to the west of the volcano situated in a lowland and characterized by much drier conditions. The mobility of fluoride and aluminum is markedly different at both sites, with the first sequence suggesting a downwards migration of Al and F, and the second sequence showing no sign of mobility. The migration of aluminum and fluorine results from the dissolution of different fluoride salts (mostly AlF3 and CaF2, as suggested by scanning electron microscopy) followed by vertical transport as ionic complexes (AlF3, AlF2+, AlF4−) during the percolation of rainwater through the ashfall deposits. Geochemical calculations suggest that the mobility of fluorine at neutral to alkaline conditions (pH 7.0–9.0) is likely limited by the solubility of fluorite (CaF2), whereas at slightly acidic conditions (pH < 6.5), the aqueous concentration of aluminum seems to be controlled by the solubility of gibbsite (Al(OH)3). This study demonstrates that aluminum and fluoride can be transported from volcanic ash to the underlying soil or groundwater, which is an environmental concern that should be followed in the future. [ABSTRACT FROM AUTHOR]

To overcome the difficulty of separating bastnaesite from fluorite through the flotation technique, the present study examined the suitability of sodium alginate (SA) as a depressant in the flotation process. The effect of SA on the flotation separation of bastnaesite and fluorite was evaluated using micro-flotation tests, zeta potential measurements, adsorption density measurements, Fourier infrared spectroscopy, and X-ray photoelectron spectroscopy. The micro-flotation results showed that SA exerted a strongly detrimental effect on fluorite flotation, while slightly affecting bastnaesite flotation. The surface chemistry results revealed that the -COO- and HO- functional groups in SA coordinated with Ca2+ on the fluorite surface, which induced hydrophilicity and hindered adsorption in the subsequent octylhydroxamic acid as a collector. However, the interaction of SA with the bastnaesite surface was marginal and did not affect the anchoring of the collector on the surface of bastnaesite. Based on these results, the present study proposes a possible model for the interaction of SA on the surfaces of the two minerals, laying a foundation for the flotation separation of bastnaesite from fluorite with SA as an environmentally benign depressant. [ABSTRACT FROM AUTHOR]

The Yama area is characterized by numerous large-scale fluorite–quartz veins that are located along faults within the widespread Late Devonian–Late Silurian syenogranites in the Tataleng granitic batholith, Qilian Orogen, Northwest China. These fluorite–quartz veins contribute to an important fluorite reserve, but their ore genesis remains unresolved so far. In this study, trace elements, rare earth elements (REEs), and hydrogen, oxygen, and strontium isotopic compositions of fluorites are analyzed. The studied fluorite samples have similar chondrite-normalized REEs, including Y patterns, with relatively strong enrichment in heavy REEs, negative Eu anomalies, strongly positive Y anomalies, and comparably invariable Y/Ho ratios of 41.43–73.79, suggesting a unique hydrothermal genesis. The relatively variable values of δD and δ18O are −77.4‰ to −102.4‰ and −12.7‰ to −4.3‰, respectively, close to the meteoric water line. These fluorites yield relatively invariable analytical 87Sr/86Sr ratios of 0.749089−0.756628 (except for an anomalously high ratio), and their calculated initial 87Sr/86Sr ratios, based on the ore-forming ages provided, are apparently higher than the calculated initial 87Sr/86Sr ratios of syenogranite wall rocks. Collectively, the geochemistry of trace elements, REEs, and stable isotopes (H, O, and Sr) suggests that the ore-forming fluids were of meteoric origin and that the Sr sources were directly derived from the ore-forming fluids themselves rather than syenogranite wall rocks. Finally, it was considered that the Yama fluorite deposit is a fault-controlled hydrothermal vein-type deposit which was possibly related to the evolution of the Paleo-Tethys Ocean in the Permian–Triassic. [ABSTRACT FROM AUTHOR]

In order to separate fluorite and calcite inhibited in tungsten tailings, the effect and mechanism of using ultrasonic external field activation to separate fluorite and calcite inhibited by sodium hexametaphosphate in a sodium oleate system were investigated. After pretreatment with an ultrasonic external field with a frequency of 40 kHz and sound intensity of 0.56, 0.50 and 0.40 W/cm2, the flotation recovery of calcite could be increased from 16.08% to about 80%, while the flotation recovery of fluorite was only increased from 7.5% to about 20%, with a difference of 60% between the two flotation recoveries, and the larger the sound intensity, the shorter the pretreatment time and the smaller the ultrasonic input energy. The contact angle of the calcite surface increased, sodium oleate adsorption increased, and zeta potential decreased after ultrasonic pretreatment, while the contact angle, sodium oleate adsorption, and zeta potential of fluorite surface were less changed. The results of heat of adsorption and XPS measurements showed that more heat was released from the interaction between sodium hexametaphosphate and fluorite, and the Ca2p peaks on the surface of fluorite were shifted to a greater extent after the interaction, which inferred that the adsorption of fluorite and sodium hexametaphosphate was relatively easier and stronger. It is presumed that the ultrasonic pretreatment can bring the mineral surface to different degrees of desorption according to the adsorption strength of sodium hexametaphosphate, exposing Ca2+ active sites for sodium oleate adsorption, while expanding the floatability difference between fluorite and calcite. [ABSTRACT FROM AUTHOR]

Uranium can be found in the Earth's crust in different reservoirs, with igneous rocks being the primary source of this element from which many types of secondary deposits are formed. Fluorspar deposits generally do not contain uranium, but in some cases, fluorite can carry both uranium in solid solutions and inclusions of uranium minerals. We studied the concentration (ICP-MS), composition (electronic microprobe), and spatial distribution (microscopy and auto-radiography) of elemental uranium and uranium minerals at different scales (microscopy and auto-radiography in fluorite from the La Azul fluorspar deposit (Taxco, Mexico) to assess the origin of uranium and its significance in this ore deposit. Auto-radiography images with the CR-39 detector were found to be impressive in their ability to elucidate uranium distribution at the millimeter scale. The limit between the solid solution of elemental uranium in natural fluorite and the appearance of uranium oxides as inclusions appeared to be between 20 μg g−1 and 40 μg g−1 bulk uranium concentration in this fluorspar ore. The maximum concentration of U in fluorite from the La Azul deposit was about 100 μg g−1. Using Raman spectroscopy and microprobe analysis, we identified the micro-inclusions of uranium minerals as uraninite (of the pitchblende variety); its composition suggested a hydrothermal origin for this fluorspar deposit. We also calculated a chemical age that can be compared with the previously published regional geology and isotopic (U-Th-Sm)/He ages in fluorite. Micro-thermometric studies of fluid inclusions were carried out in different samples of uranium-rich fluorite to identify the nature and origin of the mineralizing fluid and the precipitation mechanisms of uranium minerals. We concluded that the uranium-rich fluorite precipitated in the initial phases of mineralization from a reducing fluid, with low salinity (<8% NaCl eq.) and an intermediate temperature (110–230 °C), and that the presence of organic compounds and sulfides (mainly pyrite) favored the simultaneous precipitation of uraninite (pitchblende variety) and fluorite. [ABSTRACT FROM AUTHOR]

The mineral CaF2 is the archetype of the α fluorite structure and its high-pressure phase transition to γ cotunnite is an ideal test bed for exploring the effects of kinetics. The inter-disciplinary topic of the kinetics of dynamically driven phase transitions is at the forefront of condensed matter physics, both for its theoretical importance and its relevance to technological applications at extreme conditions of pressure and temperature. Here we probe the α → γ → α structural transformations taking place over the nanosecond timescale of a dynamic event, beginning-to-end: from the principal shock Hugoniot state, followed by a quasi-steady off-Hugoniot release state, and finally the unsteady return to near-ambient conditions. We present quantitative, atomic-scale data of the unfolding of the dynamically driven phase transition and its subsequent reversal close to the α/γ phase boundary. Dynamic loading with a two-stage gas gun is coupled with in situ time-resolved synchrotron X-ray diffraction and with continuum scale velocimetry at the Dynamic Compression Sector (DCS), Advanced Photon Source, Argonne National Laboratory. Our results demonstrate the time dependence of phase transitions and highlight the need for modeling of transition kinetics in dynamically driven processes. [ABSTRACT FROM AUTHOR]

Surface heterogeneity of minerals can significantly affect the adsorption of collectors. Petroleum sulfonate is widely used as a fluorite collector, but how the surface heterogeneity of fluorite influences the adsorption of alkyl sulfonates remains unknown. Herein, two kinds of surface heterogeneity situations, i.e., edge and (1 1 1) _vacancy, were modeled, and the adsorption of sodium dodecyl sulfonate on them was simulated. The results show that the stable adsorption configuration of sodium dodecyl sulfonate on the edge was in a bridged mode, and the stable interaction configuration with vacancy was in a tridentate mode. The 2p orbit of fluorine on the surface of the edge and the vacancy could hinder collector adsorption. After adsorption, the 3d orbit of calcium interacted with the collector orbit above Fermi level, and moved towards the lower energy level, benefiting the adsorption process. It was also found that the adsorption intensity/strength of alkyl sulfonate on fluorite was directly proportional to the interaction intensity of the collector with the 3d orbits of calcium ions on the surface and vacancy. Therefore, the rough fluorite surface had a stronger adsorption effect on the collector, and the existence of vacancy could improve the surface adsorption energy, and thus enhance the adsorption of the collector on the fluorite surface. The rough fluorite surface requires high collector concentration to achieve saturated monolayer adsorption, so increasing vacancy was the better choice to improve the adsorption capacity of alkyl sulfonate on the fluorite surface. This study provides novel insights into the flotation mechanism, in the context of surface heterogeneity, and could guide the design of high-performance collectors for fluorite ore flotation. [ABSTRACT FROM AUTHOR]

The Pinavand fluorite deposit is hosted by lower Cretaceous carbonate rocks in the structural-geological transitional zone of Central Iran. The purple and white fluorite occur, respectively, as early replacement masses and late cross-cutting veins. Both fluorites have different and distinct physicochemical characteristics. The purple fluorite has higher homogenization temperatures of fluid inclusions (170–260 °C) and lower ∑REE (1.6 ppm) and Y (1.3 ppm) than the white variety (90–150 °C, 11.12 ppm, and 21.3 ppm, respectively). All fluorite samples show positive Y anomalies (Y/Y*) in the range of 1.15–3.5. The average values of La/Ho in the purple and white fluorites are 23.1 and 3.4, respectively. The purple fluorite samples have lower Y/Ho values (an average of 63.45) than the white fluorite samples (an average of 87.64). The Tb/Ca ratio in the Pinavand fluorites ranges between 0.0000000348 and 0.00000105, and the Tb/La ratio varies between 0.01 and 0.4; these values suggest that both fluorite types are "hydrothermal" in origin. The purple fluorites have a lower Sr and a negative Eu anomaly. These differences in concentrations and ratios of various REE suggest that the physico–chemical conditions of mineralization changed during fluorite deposition at the Pinavand. These changes correspond to an increase in oxygen fugacity and pH, which occurred during white fluorite mineralization at lower temperatures. The δ34S values of the Pinavand barite samples (an average of 23.25‰) are similar to those of seawater sulfate in the upper Proterozoic. The δ34S values of galena range from −0.2‰ to −3.7‰, compatible with bacterial sulfate reduction (BSR). These features are similar to those in the hydrothermal and magmatic deposits. [ABSTRACT FROM AUTHOR]

Fluorite is a widespread mineral in porphyry and hydrothermal vein Mo-polymetallic deposits. Here, fluorite is utilised as a probe to trace the fluid source and reveal the fluid evolution process in the Chalukou giant Mo (Pb–Zn) deposit, Northeast China, which is characterised as early porphyry Mo and later vein-style Zn–Pb mineralisation. A detailed rare earth element (REE) and Sr–Nd isotope study of fluorite combined with Sr isotopes of sphalerite is conducted for the Chalukou deposit. The chondrite-normalised REE patterns of fluorites from molybdenite veins show light REE (LREE)-enriched patterns, with negative Eu anomalies (δEu = 0.60) and weakly negative Y anomalies (Y/Y* = 0.72). The fluorites associated with sphalerite veins exhibit rare earth element (REE)-flat patterns with negative Eu anomalies (δEu = 0.65 to 0.99) and positive Y anomalies (Y/Y* = 1.37 to 3.08). In addition, during the progression from Mo to Zn–Pb mineralisation, the total concentration of REEs decreases from 839 ppm to 53.7 ppm, and Y/Ho ratios increase from 22.1 to 92.5. These features may be explained by the different mobilities of REE complexes during fluid migration. The Eu anomalies are considered to be inherited from source fluids. All the initial 87Sr/86Sr ratios of fluorite and sphalerite are between those of ore-forming porphyries and wall rocks (rhyolite), with fluorite ratios ranging from 0.706942 to 0.707386 and sphalerite ratios varying from 0.705221 to 0.710417. The majority of εNd(t) values of fluorite varying from −6.4 to −3.6 are also located between the ratios exhibited by ore-forming porphyries and rhyolite, whereas three εNd(t) values of fluorites ranging from −0.26 to 0.36 are close to those of ore-forming porphyries. All the isotopic features indicate that the Sr-Nd isotope ratios of hydrothermal fluid are derived from porphyries and disturbed by fluid–rock reactions. Together with a two-stage Sr–Nd isotope mixing model, we suggest that different sources and fluid–rock interactions (syn-ore intrusions and strata) finally influence the Sr–Nd isotopes of the ore-forming fluids, which are recorded by the majority of fluorite and sphalerite. [ABSTRACT FROM AUTHOR]

During the flotation separation process of bastnaesite, it is difficult to separate bastnaesite from fluorite effectively. In this present study, sodium silicate (SS) can effectively improve the flotation separation effect of bastnaesite and fluorite in salicylhydroxamic acid (SHA) systemasa. Through relevant analyses, such as Zeta potential measurements, adsorption capacity tests, Fourier transform infrared (FTIR) spectroscopic analyses and X-ray photoelectron spectroscopy (XPS) tests, the selective suppressor of SS on fluorite was proven. At pH 10, the single mineral flotation results show that with the increase of SS dosage, the flotation recovery of fluorite rapidly decreases from 61.5% to 35.31%, while the flotation rate of bastnaesite is still high (recovery is 80.02%). Then, the experiment of artificial mixed ore proved that the flotation separation of fluorite and bastnaesite was effective under the appropriate dosage of inhibitor. The results of potentiodynamic measurement and an adsorption capacity test showed that the SiO OH 3 − structure of SS more easily reacted with fluorite, which further prevented the adsorption of SHA on the fluorite surface. FTIR test results and XPS analysis further showed that SS had a strong binding effect with the Ca site on the fluorite surface, but a weak binding effect with the Ce site on the bastnaesite surface. Consequently, SS can be used as an effective inhibitor in the flotation separation of fluorite and bastnaesite. [ABSTRACT FROM AUTHOR]

Nanlishu fluorite has had an annual output of nearly 10,000 tons since its discovery and mining in 1987. At present, few studies have been undertaken on the genesis of the Nanlishu fluorite deposit. Microscopy, Fourier transform infrared (FTIR) spectroscopy, Raman microprobe spectroscopy, and ultraviolet–visible (UV–Vis) spectroscopy were used to study the mineral composition, mineral structure, and spectral characteristics, and fluid inclusion and rare earth element (REE) geochemistry studies were conducted to discuss the characteristics and evolution of the ore-forming fluids and the mineralization process. The Nanlishu fluorite ore rock is composed mainly of fluorite, with minor amounts of quartz, pyrite, and apatite, and trace amounts of calcite. The purple in the fluorite is caused by the Ca colloids. The homogenization temperatures of fluid inclusions in Nanlishu fluorite vary from 116 to 179 °C, while the salinity ranges from 0.35 to 4.03 wt% NaCl equiv, and the density varies from 0.90 to 1.00 g/cm3. Ore-forming fluids were derived from heated meteoric water characterized by low temperature, low salinity, and low density. The total rare earth element (∑REE, excluding Y) content of the ore ranged from 8.072 to 27.230 ppm. The light/heavy REE ratio (LREE/HREE) varies from 0.971 to 1.513. The δEu value is 1.010–1.074 and the δCe value is 0.893–1.048. Compared with other deposits, the Nanlishu fluorite has lower ∑REE content, no obvious enrichment of LREEs or HREEs, and no anomalies in δEu and δCe. Water/rock reaction is the main mechanism for Nanlishu fluorite precipitation. The Nanlishu fluorite is a fault-controlled, low-temperature hydrothermal, fracture-filling deposit. [ABSTRACT FROM AUTHOR]

In the flotation of semi-soluble minerals such as calcite and fluorite, Ca2+ is one of the common dissolved components influencing the collector adsorption behaviors on the mineral surfaces. However, there is very limited research focusing on how the dissolved Ca2+ affects the separation of fluorite and calcite. In the study, with sodium oleate (NaOL) as a collector and tannic acid (TA) as a depressant, a flotation test, zeta potential measurement, and adsorption experiment in the presence of Ca2+ were conducted. Flotation tests indicated that in the presence of Ca2+, fluorite and calcite were both significantly depressed by TA, leading to difficulty in the separation of the two minerals. It was also found that the depression effect on fluorite flotation was minimized with a high concentration of NaOL. Zeta potential measurement and the adsorption experiment results are consistent with the flotation results, revealing that it is only in the low concentration of NaOL that the flotation of fluorite was depressed by TA in the presence of Ca2+. Specifically, in the low concentration of NaOL, TA adsorbed on the fluorite surface and depressed the flotation of fluorite due to the preferential interaction between NaOL and Ca2+ in the solution leading to a shortage in the effective NaOL in the solution. In the high concentration of NaOL, the adsorbed TA on the fluorite surface was displaced by the excessive NaOL in the solution; hence, the flotation of fluorite was recovered. In contrast, TA always hinders the interaction of NaOL with calcite regardless of the presence and absence of Ca2+ and NaOL, hence, depressing the flotation of calcite. The study presented that a high concentration of NaOL may mitigate the negative effect of Ca2+ on the fluorite surface and improve the separation of fluorite from calcite. [ABSTRACT FROM AUTHOR]

As an important strategic non-metallic mineral resource, fluorite has been widely used in various industrial fields, such as metallurgy, optics and semiconductor manufacturing, as well as fluorine-related chemical engineering. Since the major gangue minerals of fluorite ore are silicate and carbonate ones, flotation is the main beneficiation method for the concentration. Compared with the relatively easy operation for silicate-type fluorite ore, fluorite concentration from calcite has always been the most difficult challenge in the field of mineral processing. In this review, analyses of the fundamental reasons for the difficulties of flotation separation of fluorite from calcite are performed, from the similar surface properties of both calcium minerals to the deterioration by the interference of dissolved ions in the pulp during grinding and flotation. Recent achievements in the flotation separation of fluorite from calcite as the main contents are comprehensively summarized, covering all aspects of flotation reagents of collectors, depressants and modifiers. Finally, successful examples of industrial practices for fluorite and calcite flotation separation are introduced. This overview provides a detailed and comprehensive reference source for the current research status of fluorite and calcite flotation separation, and some suggestions for future research are provided. [ABSTRACT FROM AUTHOR]

Fluorite and scheelite, which are strategic calcium-bearing minerals, have similar active sites (Ca2+); as a result, the efficient separation of the two minerals is still one of the world's most difficult problems in the field of flotation. In this work, N-decanoylsarcosine sodium (SDAA), a non-toxic and low-cost amino acid surfactant, was applied in the flotation separation of fluorite from scheelite for the first time. In the test, single mineral, binary mixed minerals, and actual ore experiments showed that the pre-removal of fluorite from scheelite by reverse flotation can be achieved. The results of adsorption capacity detections, zeta potential tests, and FTIR analysis showed that the negatively charged SDAA prefers to adsorb onto the positively charged fluorite surface due to the electrostatic interaction. The results of crystal chemistry and DFT calculations showed that SDAA has a stronger chemical interaction and more electron transfer numbers to the Ca atom on the fluorite surface and forms a Ca-SDAA complex. Therefore, the significant difference in the adsorption behavior of SDAA on the surfaces of two minerals provided a new insight into the separation efficiency of amino acids and possesses a great potential for industrial application in scheelite flotation. [ABSTRACT FROM AUTHOR]

The recovery of scheelite from calcium-bearing carbonate ores by foam flotation is challenging due to its low separation efficiency. This study investigated the effect of pentasodium diethylenetriaminepentaacetate (PD) on the surface properties of scheelite and fluorite. For this purpose, we performed micro-flotation tests and carried out zeta potential measurements, as well as Fourier transform infrared (FT-IR) and X-ray photoelectron (XPS) spectroscopic measurements, in order to analyze the surface properties of these minerals. The addition of PD as a novel depressor significantly improved the effect of fluorite and sodium oleate (NaOl) on the flotation-based scheelite recovery and separation from fluorite. PD was spontaneously adsorbed onto fluorite through electrostatic and chemical adsorption. By contrast, PD did not appear on the scheelite because of the reaction conditions, surface site, and steric hindrance. X-ray photoelectron spectroscopy measurements and a solution chemistry analysis were used for the determination of the PD-selective adsorption mechanism and key factors derived from multi-layer adsorption onto fluorite, which completely hindered that of NaOl. [ABSTRACT FROM AUTHOR]

The Cuonadong deposit is the first large scale Sn-W-Be rare polymetallic deposit located in southern Tibet, China, where beryl is the main beryllium-bearing mineral. In this paper, the beryl crystals in the pegmatitic and hydrothermal vein orebody from the Xianglin area of the Cuonadong deposit are the research objects, marked as Beryl-I and Beryl-II, and they are investigated by EPMA, LA-ICP-MS and in situ micro-X-ray diffraction (XRD). Data by EPMA and LA-ICP-MS reveal that beryls from this area are alkaline beryls, among which Beryl-I is composed of Li-Cs beryl, and Beryl-II is composed of Na beryl and Na-Li beryl, indicating that beryls have undergone noticeable alkali metasomatism during formation. The Cs/Na ratio in Beryl-I ranges from 0.10 to 0.44, and the Mg/Fe ratio is almost 0, showing that Beryl-I is formed under high-differentiation evolution conditions and is rarely affected by hydrothermal transformation, whereas the Mg/Fe ratio in Beryl-II ranges from 2.73 to 17.31, and the Cs/Na ratio is nearly 0, indicating that Beryl-II has been obviously affected by late hydrothermal metasomatism. In situ XRD analysis shows that both Beryl-I and Beryl-II are t-beryl, and the c/a ratio of Beryl-I (1.0010–1.0012) is slightly higher than that of Beryl-II (1.0005–1.0008), which may also reflect the transition from magmatism to hydrothermal metasomatism in the late stage of pegmatitic magmatism. Based on comprehensive analysis, we believe that the precipitation of Beryl-I is mainly caused by the emplacement of highly fractionated magma containing Be to the top of the rock mass or surrounding rock, the melt-fluid undercooling, and the crystallization of volatile-bearing minerals (such as tourmaline and fluorite). Moreover, the Be-bearing ore-forming fluid has further migrated upward along the near north–south faults formed in the middle Miocene (16–15 Ma), during which Beryl-II precipitates owing to the hydrothermal water mixing, the ore-forming fluid cooling, and large amounts of crystallization of volatile-bearing minerals (mainly fluorite). Therefore, it can be concluded that beryl mineralization largely reflects the process of magmatic–hydrothermal mineralization. Because of a large number of mineralized areas with the similar metallogenic backgrounds to the Cuonadong deposit in the Himalayan region, it has great potential to be a new globally significant rare metal metallogenic belt. [ABSTRACT FROM AUTHOR]

The Weishan carbonatite-related rare earth element (REE) deposit in China contains both high- and low-grade REE mineralization and is an informative case study for the investigation of magmatic-hydrothermal REE enrichment processes in such deposits. The main REE-bearing mineral is bastnäsite, with lesser parisite and monazite. REE mineralization occurred at a late stage of hydrothermal evolution and was followed by a sulfide stage. Barite, calcite, and strontianite appear homogeneous in back-scattered electron images and have high REE contents of 103-217, 146-13,120, and 194-16,412 ppm in their mineral lattices, respectively. Two enrichment processes were necessary for the formation of the Weishan deposit: Production of mineralized carbonatite and subsequent enrichment by magmatic-hydrothermal processes. The geological setting and petrographic characteristics of the Weishan deposit indicate that two main factors facilitated REE enrichment: (1) fractures that facilitated circulation of ore-forming fluids and provided space for REE precipitation and (2) high ore fluorite and barite contents resulting in high F- and SO42- concentrations in the ore-forming fluids that promoted REE transport and deposition. [ABSTRACT FROM AUTHOR]

Fluorite (CaF2), as an important strategic mineral source, is usually separated from calcite by the common froth flotation method, but this separation is still not selective enough. The development of a selective collector and/or depressant is the key to achieving high selective separation. 1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP or H4L) is widely used as an environmentally friendly water treatment reagent due to its low cost and excellent anti-scaling performance in an aqueous solution. In this study, a novel reagent scheme was developed using HEDP as a fluorite depressant and sodium oleate (NaOL) as a calcite collector for the first time. When 3 x 10-5 mol/L of HEDP and 6 x 10-5 mol/L of NaOL were used at pH 6, the optimal selective separation for single minerals and mixed binary minerals was obtained. Zeta potential measurements indicated that HEDP possessed a stronger adsorption on fluorite than calcite, while NaOL did the opposite. This novel reagent scheme is of low cost, uses a small dosage, and is friendly to the environment, which makes it a promising reagent scheme for fluorite flotation in industrial application. [ABSTRACT FROM AUTHOR]

This investigation aims to demonstrate the effects of hydrophobic tails on the affinity and relevant flotation response of sulfonate-based collectors for fluorite. For this purpose, a series of alkyl sulfonates with different hydrophobic tails, namely sodium decanesulfonate (C10), sodium dodecylsulfate (C12), sodium hexadecanesulfonate (C16), and sodium dodecylbenzenesulfonate (C12B) were applied. The flotation tests showed that C12 and C12B had a better collecting performance than C10 and C16 at pH < 10, and the flotation recovery of fluorite was higher when adopting C12B as a collector compared with C12 with a strong base. The adsorption behaviors of collectors on the fluorite surface were studied through zeta potential, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. It was found that the affinity of alkyl sulfonates for fluorite was enhanced with the increase of the alkyl chain length from C10 to C16. The existence of phenyl in the hydrophobic tail of sulfonates could improve its activity for fluorite by reducing its surface tension. The abnormal phenomenon C16 with a high affinity for fluorite had a low collecting performance for fluorite mainly due to its overlong alkyl chain, resulting in low solubility in pulp, which restrained its interaction with fluorite. We concluded that C12B was the most applicable collector for fluorite among these reagents due to its high activity, high solubility, and low cost, which was further substantiated by calculating their molecular frontier orbital energy. [ABSTRACT FROM AUTHOR]

Fluorite (CaF2), a halogen elemental mineral, always co-exists with other minerals. The Ca element in fluorite is often replaced by rare earth elements (REEs), such as cerium (Ce) and yttrium (Y). In this work, the electronic structures of fluorite crystals containing REE (Ce, Th, U, and Y) impurities were studied by density functional theory (DFT). The calculated results showed that the presence of impurities increased the lattice parameter of fluorite. The impurities caused the Fermi level to shift towards the high energy direction, making the fluorite accept electrons more easily. The impurities except Y led to the occurrence of an impurities state in the valence band. The Mullinken population values of F-REE bonds were larger than that of F-Ca and F-F bonds, and F-Y bonds had the largest population value. Analysis of the frontier molecular orbital showed that the impurities contributed greatly to the lowest unoccupied molecular orbital (LUMO). The interaction between oleic acid and impurities-bearing fluorite were discussed. The results suggested that the incorporation of impurities would enhanced the reactivity of fluorite with oleic acid. [ABSTRACT FROM AUTHOR]

Fluorite is the principal mineral of fluorine and usually coexists with quartz in deposits. The removal of fine quartz in fluorite concentrate is the main problem in fluorite flotation. In this study, the flotation tests on fluorite, quartz and a weight equivalent mixture (all less than 10 μm) using water glass (with different modulus) as depressants and sodium oleate as collector were conducted. The mechanism of fine quartz entering the fluorite concentrate was investigated through optional observations and rheology measurements on the flotation pulp. The particle interactions between fine fluorite and quartz under flotation-related conditions were analyzed through zeta potential measurements and DLVO calculations. The results revealed that there existed strong hetero-coagulation between fluorite and quartz particles in the flotation pulp, which could be the main reason for the quartz entering the fluorite concentrate in the flotation process. Water glass with higher modulus could eliminate the hetero-coagulation more totally but inevitably influences the flotability of fluorite. [ABSTRACT FROM AUTHOR]

The depressing properties of sodium polyacrylate (PA-Na) for scheelite and fluorite were studied by micro-flotation tests, infrared spectroscopy (IR), zeta potentials, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). The flotation results reveal that the selective depression effect of PA-Na is better than that of sodium silicate, and PA-Na can depress fluorite more effectively than scheelite. The flotation recovery of scheelite and fluorite keeps at about 75% and 10%, respectively, at the pulp pH 9.3~9.6 and PA-Na concentration from 30 to 50 mg/L. IR spectra results suggest that PA-Na has a chemical effect on the surface of scheelite and fluorite. The zeta potential of fluorite becomes more negative than that of scheelite after PA-Na addition. XPS analysis deduces the occurrence of chemisorption between PA-Na and mineral surfaces, and the chemisorption of PA-Na on fluorite is stronger than on scheelite. DFT demonstrates that the absolute value of the adsorption energy in the presence of PA-Na is larger on the fluorite {111} surface than on the scheelite {111} surface. Thus, fluorite is more readily depressed than scheelite, which remarkably matches the micro-flotation test results. [ABSTRACT FROM AUTHOR]

Fluorite, barite and calcite are important industry minerals. However, they often co-exist, presenting difficulty in selectively separating them due to their similar surface properties. In this study, valonea extract and sodium fluosilicate were used as depressants to selectively separate them by flotation, with sodium oleate as the collector. The single mineral flotation results showed that valonea extract displayed the strongest depression on calcite, while sodium fluosilicate displayed the strongest depression on barite. These two depressants allowed selective separation of the three minerals through sequential flotation. The flotation of mixed minerals showed that 94% of the calcite was successfully depressed by the valonea extract, and 95% recovery of the fluorite was achieved in the subsequent flotation with sodium fluosilicate depressing barite. The different depressant-mineral interactions were investigated via electro-kinetic studies and molecular dynamics (MD) simulations using the Materials Studio 6.0 program. The valonea extract exhibited the strongest adsorption on the calcite surface, and sodium fluosilicate exhibited the strongest adsorption on the barite surface, which prevented oleate species from reacting with Ca2+ or Ba2+ surface sites. This study provides useful guidance for how to process fluorite, barite and calcite resources. [ABSTRACT FROM AUTHOR]

Fluorite is an important strategic mineral. In general, fluorite ores will contain a certain amount of calcite gangue mineral. Thus, they need to be separated from each other. For an economic separation, a reverse flotation process is used to float calcite gangue from fluorite. However, little information on the separation is available. In this study, a novel reagent schedule using citric acid (CA) as the depressant, sodium fluoride (NaF) as the regulator and sulfoleic acid (SOA) as the collector, was developed to separate calcite from fluorite. The results demonstrated a high selectivity for the flotation of calcite from fluorite using this new reagent schedule. The best selective separation for a single mineral and mixed binary minerals was obtained when 200 mg/L of NaF, 50 mg/L of CA, and 6 mg/L of SOA were used at pH 9. In addition, a batch flotation experiment was carried out using a run-of-mine feed material. Selective separation was achieved with 85.18% calcite removal while only 11.2% of fluorite was lost. An attempt was made to understand the effect of the new reagent schedule on the flotation of calcite. The results from both microflotation and bench scale flotation demonstrated a great potential for industrial application using this novel reagent schedule to upgrade fluorite ore. [ABSTRACT FROM AUTHOR]

As a common depressant, acidified water glass (AWG) has strong inhibitory effects on fluorite and calcite. The inhibited fluorite is difficult to be recovered, thus resulting in the waste of resources and low flotation efficiency. In this study, the interaction of fluoride ions with fluorite and calcite surfaces was investigated, and its effects of AWG adsorption on mineral surfaces were evaluated. Micro-flotation experiments indicated that the flotation recovery of fluorite is 88.72% after fluoride ion treatment, that is, approximately fourfold with respect to that without fluoride ion modification. The results of solution chemical calculations showed that SiO(OH)3− is the main component to inhibit fluorite, and Si(OH)4 is the main component to inhibit calcite in AWG solution. XPS and ICP-MS results showed that fluoride ions can improve the floatability of fluorite by converting CaSiO3 on the surface of fluorite into CaF2, but the conversion ability of Si(OH)4 on the surface of calcite is weak, which increases the difference in floatability between fluorite and calcite. The above results were further verified by the analysis of flotation foam image and contact angle measurement. After fluorine ion treatment, the contact angle of fluorite increased, and it was more easily adsorbed on the foam. Therefore, the interaction of the fluoride ion with the fluorite surfaces eliminated the adsorption of AWG on fluorite, thereby resulting in the enhanced hydrophobicity of fluorite. Different from the traditional metal ions modification, the idea of anion modification in this paper is expected to be further studied. [ABSTRACT FROM AUTHOR]

Fluorite mineralization associated with different types of magmatism is common in the Western Transbaikalia. This study deals with Arshan, Yuzhnoe, and Ulan-Ude fluorite occurrences, which are the most significant examples of carbonatite-related fluorite mineralization in the region. The present paper focused on new fluorite geochemistry and fluid inclusion data, is aimed at revealing conditions of the fluorite mineralization formation, highlighting its genetic relationship with magmatism, compared to other deposits of this type. All the three locations belong to the Late Mesozoic Central Asian carbonatite province. Fluorites here are characterized by high rare earth elements (REE), Sr, and elevated La/Yb values. Fluid inclusions data imply that the formation of fluorite mineralization is a long process extending from late magmatic to the hydrothermal stage. Early fluorite crystallized from sulfate-carbonate orthomagmatic fluids at temperatures up to 500 °C. True hydrothermal fluorite was formed from the same fluids that were probably mixed with meteoric waters, which caused the temperature to drop to below 420 °C and led to an increase in the chloride component. The REE compositions of fluorite from the studied locations are similar to compositions of REE-rich fluorites from carbonatite-related deposits around the world. [ABSTRACT FROM AUTHOR]

This article presents new isotope-geochronological results for the granites of the Voznesensky ore district (southeastern part of the Khanka massif). The granites are associated with extensive rare-metal–fluorite, tin and tantalum mineralization. Despite the numerous published results of Rb–Sr, Sm–Nd and U–Pb dating of ore-bearing granites and associated ores, the issues of age correlation and the genetic relationship of igneous rocks and mineralization remain unclear. U–Pb zircon SHRIMP dating reveals synchronous ages of 478 ± 4 Ma and 481 ± 7 Ma for two samples of biotite leucogranites as the age of magmatic crystallization of the Voznesensky granites. The composition of the studied zircon demonstrates the typical features of magmatic zircon and has the typical features of zircon exposed to fluids at the late/post-magmatic stage. Sm–Nd ID-TIMS dating of the fluorite of the Voznesenskoe deposit yields an age of 477 ± 9 Ma, and U–Pb ID-TIMS dating of cassiterite from the Yaroslavskoe and Chapaevskoe tin deposits yields an age of 480 ± 4 Ma, which confirms the direct genetic and age relationship of ore formation with granite magmatism. [ABSTRACT FROM AUTHOR]

The middle Anisian extensional tectonics of the Neotethyan realm developed a small, isolated carbonate platform in the middle part of the Balaton Highland (western Hungary), resulted in the deposition of uranium-bearing seamount phosphorite on the top of the drowned platform and produced some epigenetic fluorite veins in the Middle Triassic sequence. The stable C-O isotope data of carbonates are shifted from the typical Triassic carbonate ranges, confirming the epigenetic-hydrothermal origin of veining. Primary fluid inclusions in fluorite indicate that these veins were formed from low temperature (85–169 °C) and high salinity NaCl + CaCl2 + H2O type (apparent total salinity: 15.91–22.46 NaCl wt%) hydrothermal fluids, similar to parent fluids of the Alpine-type Pb-Zn deposits. These findings indicate that the Triassic regional fluid circulation systems in the Alpine platform carbonates also affected the area of the Balaton Highland. This is also in agreement with the previously established palinspatic tectonic reconstructions indicating that the Triassic carbonate and basement units in the Balaton Highland area were a part of the Southern Alpine. Similar fluorite veining in phosphorite deposits is also known in the Southern Alpine areas (e.g., Monte San Giorgi, Italy). Raman spectroscopic analyses detected H2 gas in the vapor phase of the fluid inclusions and a defect-rich fluorite structure in violet to black colored growth zones. This unique phenomenon is assumed to be the result of interaction between the uranium-rich phosphorite and the parent fluids of the epigenetic fluorite veins. [ABSTRACT FROM AUTHOR]

Fluorite is a nonrenewable mineral used to produce anhydrous hydrofluoric acid (AHF) and aluminum fluoride. The demand for low-grade fluorite powder (CaF2 < 97%) has fallen sharply owing to the current market conditions. Therefore, a large number of fluorite concentrates have been improved by acid leaching. While this approach can efficiently remove CaCO3 from fluorite concentrate, the SiO2 content, which significantly affects AHF consumption during the production of HF or aluminum fluoride, cannot be completely removed. To solve this problem, in this study, we used reverse flotation before leaching the fluorite concentrates. Subsequently, the feasibility of reverse flotation desilication was determined. The obtained results of the ZP (zeta potential) measurements, solution chemistry analysis, FTIR (Fourier transform infrared spectroscopy) analysis, and micro-flotation tests indicated that employing dodecylamine as the collector and citric acid as the depressor could effectively separate sericite from fluorite. The batch flotation experiment and the pilot test were conducted in Chenzhou (Hunan, China) followed by their operation in Xinyuan Mining Co. Ltd., which produces monolithic fluorite ore on the large scale in Asia. Notably, we found that the contents of both SiO2 and Al2O3 were from 2.82%, 1.17% reduced to 1.28%, 0.74% in the batch flotation experiment. The results of the pilot test showed that the new reverse flotation + leaching technology could dramatically reduce the potential environmental impact and costs, thereby significantly improving the economic benefits by satisfying the requirements of the market. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abundant fluorites occur in the Shihuiyao rare metal (Nb-Ta-Rb) deposit in Inner Mongolia of NE China, and they can be classified by their occurrence into three types. Type I occurs disseminated in greisen pockets of albitized granite. Type II occurs in the skarn zone between granite and carbonate host rocks, and it can be subdivided into different subtypes according to color, namely dark purple (II-D), magenta (II-M), green (II-G), light purple (II-P), and white (II-W). Type III are the fluorite-bearing veins in the silty mudstones. On the basis of petrography of the fluorites and their high contents of HFSEs (high field strength elements) and LILEs (large ion lithophile elements), strong negative Eu anomalies, and tetrad effects, we suggest that Type I fluorites crystallized in a late-magmatic stage with all the components derived from the granite. The high Y/Ho ratios suggest that the Type II fluorites crystallized in the early- or late-hydrothermal stage. The rare earth elements (REEs) characterized by various Eu anomalies of the Type II fluorites indicate a mixed origin for ore-forming metals from granite-related fluids and limestones, and the oxygen fugacity increased during fluid migration and cooling. Compared to the Type II fluorites, the similar trace element contents of the Type III suggest a similar origin, and remarkable positive Eu anomalies represent a more oxidizing environment. The Sr isotopic composition (87Sr/86Sr)i = 0.710861) of the Type I fluorites may represent that of the granite-derived fluids, whereas the (87Sr/86Sr)i ratios of the Type II (0.710168–0.710380) and Type III (0.709018) fluorites are lower than that of the Type I fluorites but higher than those of the Late Permian-Early Triassic seawater, suggesting a binary mixed Sr source, i.e., granite-derived fluids and marine limestones. Nevertheless, the proportion of limestone-derived Sr in the mixture forming the Type III fluorites is much higher than that of Type II. The rare metal Nb and Ta get into the granite-derived F-rich fluids by complexing with F and precipitate in the form of columbite-group minerals after the Type I fluorites crystallize. Most of Nb and Ta may have deposited as columbite-group minerals during the magmatic stage, resulting in no Nb-Ta mineralization in the hydrothermal stage when the Type II and III fluorites formed. Hence, the Type I fluorites in the Shihuiyao mining area can be used as an important exploration tool for the Nb-Ta mineralization. [ABSTRACT FROM AUTHOR]

The addition of ferrous sulfate as a depressant for Ca-bearing minerals such as calcite and fluorite during scheelite flotation was investigated to recover scheelite from tungsten mine tailings, using Hallimond-tube flotation tests, zeta-potential measurement and Fourier-transform infrared (FT-IR) analyses. The flotation tests indicate that the selectivity of scheelite recovery was the largest over calcite and fluorite under the following conditions: 0.5 g sample, 50 g/ton AF65, 1 × 10−3 M sodium oleate, 1200 g/ton SF2 (sodium silicate and ferrous sulfate) depressant with the 8:2 ratio of sodium silicate and ferrous sulfate, 50 mL/min air injection rate, 5 min flotation time, and pH 8. The selectivity of scheelite flotation increased when the amount of SF2 depressant addition increased to 1200 g/ton, but it decreased by adding 1400 g/ton SF2, which would result from the precipitation of iron components. In the zeta potential results, the zeta potentials of scheelite with the collector show similar results regardless of the addition of SF2, while the change of zeta potentials of calcite and fluorite by adding NaO collector diminished when SF2 was added. In FT-IR analyses, the spectrum of NaO in scheelite results was observed regardless of the addition of SF2, while the spectra of NaO in calcite and fluorite results disappeared when SF2 was added. These results suggest that the addition of SF2 prevents the adsorption of NaO on the surface of calcite and fluorite. Therefore, the addition of SF2 could enhance the selectivity of scheelite flotation over calcite and fluorite. [ABSTRACT FROM AUTHOR]

In this study, two new collectors for fluorite flotation DP-OMC-1033 (DP-I) and DP-OMC-1234 (DP-II) were tested and compared with oleic acid (OA), sodium oleate (SO) and potassium oleate (PO). According to fluorite grade and fluorite metallurgical recovery, the effect of each collector was determined, both in mechanical and pneumatic cell flotation. The effect of temperature on the collectors from 25 to 55 °C was studied. Flotation tests showed that the best results in terms of fluorite metallurgical recovery were 82.8% and 87.9% for new collectors DP-I and DP-II respectively, for a dosage of 100 g/t and using pneumatic cell. Additionally, in terms of fluorite grade, DP-I showed the best results, achieving 79.7% of CaF2 in roughing step for a dosage of 100 g/t. Fluorite metallurgical recovery and grade in concentrate increased for OA, SO and PO with increasing temperature. However temperature did not have a significant effect on both metallurgy recovery and CaF2 grade using DP-I and DP-II, so the process can be effective at 25 °C reducing operating costs. [ABSTRACT FROM AUTHOR]

Columbite-(Fe) is a post-magmatic accessory mineral occurring within syenogranites and greisens from the Desemborque Pluton. The petrographic (SEM) and geochemical (EPMA and LA-ICPMS) examination of this mineral shows two distinct textural types within both the rocks, named columbite-1 and columbite-2. The columbite-1 type is characterized by zoned crystals with two stages of crystallization: i) An early Nb-rich cores with low Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios (0.02–0.08 and 0.17 to 0.21 apfu, respectively), and ii) a later Ta-rich rims with higher Ta/(Ta + Nb) ratios (0.11–0.26) and similar Mn/(Mn + Fe) ratios (from 0.14 to 0.22) relative to the former cores. On the other hand, the columbite-2 type is defined by irregular crystals with patchy textures and very low Ta/(Ta + Nb) ratios (0.008–0.038) and moderate Mn/(Mn + Fe) ratios between 0.20 and 0.38. Trace element compositions of all columbite-(Fe) crystals are relatively enriched in HREEs and HFSEs; however, the columbite-2 presents higher abundances of REEs, Y, Th, U, Pb, Sc, and Sn relative to the columbite-1. This study highlights a unique hydrothermal origin for both the columbite types, but the textural relations of the columbite-2 crystals indicated that its formation is related to fluid-induced alterations of post-magmatic fluorite and/or cassiterite crystals at the final stage of the post-magmatic evolution. [ABSTRACT FROM AUTHOR]

Fluorite, CaF2, is considered a strategically important mineral as it is a raw material for many strategic industries. Froth flotation is reported to be the most efficient and economically viable process for the production of an acid-grade product with a CaF2 content of at least 97%. Selective flotation of fluorite from gangue minerals, e.g., calcite and barite, is challenging because these minerals have similar physicochemical properties. This study employed batch flotation tests coupled with mineralogical analysis to design suitable customised flowsheets and efficiently optimised reagent regimes for optimum production of acid-grade fluorite concentrate from two different fluorite ores by the froth flotation process. The effect of pulp temperature on fluorite flotation was investigated in this study with the objective of lowering pulp temperatures in fluorite flotation. The results showed that an acid-grade CaF2 concentrate could be obtained from the flotation of both ores at ambient pulp temperatures. This eliminates the requirement for high-temperature pulp treatment, which would result in a significant reduction in thermal energy costs. This study showed that an understanding of gangue mineralogy is key to process optimisation for acid-grade CaF2 production. Although an acid-grade CaF2 concentrate could be produced from both ores, the flowsheets and reagent regimes were markedly different. For instance, the production of an acid-grade CaF2 product from a high quartz and calcite ore was achieved by employing a simple rougher–multiple cleaner flotation circuit using tannin and sodium silicate as calcite and quartz depressants, respectively. On the other hand, the production of an acid-grade CaF2 product from the flotation of the pyritic ore required a pre-sulphide flotation stage for upfront sulphur removal and the use of a sulphide depressant. Multiple stages of cleaning were required for improved selectivity in the flotation of both ores. [ABSTRACT FROM AUTHOR]

The influences of long-term static interaction between flotation reagents and minerals on mineral surface properties and their flotation behaviors were investigated in this work. Single mineral results showed that when the static interaction time between flotation reagents and minerals increased from 0 to 8 days, there were no significant differences in the recovery of fluorite (ranging from 77.50% to 74.50%), while the recovery of calcite dramatically decreased from 97.17% to 41.13%. The collector adsorption results indicated that after the long-term static interaction between the collector and minerals, adsorption and desorption of collector on the minerals occurred, and the adsorption amount of collector on fluorite and calcite varied from 0.396 mg/g to 0.421 mg/g, and from 0.444 mg/g to 0.404 mg/g, respectively. The contact angles of fluorite and calcite decreased from 134.3° and 105.0° for 0 days to 109.7° and 52.5° for 8 days, respectively, which demonstrated that the fluorite had a higher hydrophobicity than that of calcite after 8 days of static interaction between the minerals and collector. The Fourier transform infrared spectroscopy (FTIR) analysis showed that there were chemisorptions between the collector and the surfaces of the fluorite and calcite. Meanwhile, the X-ray photoelectron spectroscopy (XPS) results further elucidated that the amount of C=O from the oleic acid (OA) molecule for calcite treated for 8 days was less than for that treated for 0 days. In addition, the flotation results of the tailings from Jiangxi containing fluorite and calcite, indicated that the grade and recovery of fluorite increased from 87.18% and 40.99% for 0 days to 93.00% and 46.01% for 8 days, respectively, indicating that the separation of fluorite from calcite could be achieved via increasing the long-term static interaction between the flotation reagents and minerals. [ABSTRACT FROM AUTHOR]

This study presents a highly selective reagent system that utilizes sodium hexametaphosphate (SHMP) to improve the separation of scheelite from calcite and fluorite using an anionic–nonionic collector. The recoveries of calcite and fluorite decreased to 20% as the SHMP dose exceeded 6 × 10−6 mol/L, whereas that of scheelite remained at 85%. The interaction mechanisms of minerals with SHMP were investigated through equilibrium speciation, Zeta potential, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy analyses. SHMP exists as hydrogen phosphate anion in the aqueous solution with a pH of 7–12. Moreover, it may be adsorbed intensively on the positively charged surfaces of calcite and fluorite via electrostatic force or chelation with calcium ion to impede further adsorption of the assembled collector. By comparison, the adsorption of SHMP is feeble on the scheelite surface because of its negative charge. The roughing grade of low-grade scheelite ore is substantially improved from 0.74% to 1.65% compared with that in the contrast test in the absence of SHMP. [ABSTRACT FROM AUTHOR]

F-containing wastewater does great harm to human health and the ecological environment and thus needs to be treated efficiently. In this paper, the new calcium-containing precipitant calcite and aided precipitant fluorite were adopted to purify F-containing wastewater. Relevant reaction conditions, such as reaction time, oscillation rate, dosage of hydrochloric acid, calcite dosage and the assisting sedimentation performance of fluorite, and action mechanism are analyzed. The experiment showed that the removal rate of fluoride in simulated wastewater reached 96.20%, when the reaction time, the dosage of calcite, the dosage of 5% dilute hydrochloric acid, and the oscillation rate was 30 min, 2 g/L, 21.76 g/L, and 160 r/min, respectively. Moreover, the removal rate of fluoride in the actual F-containing smelting wastewater reaches approximately 95% under the optimum condition of calcite dosage of 12 g/L, reaction time of 30 min, and oscillation rate of 160 r/min. The addition of fluorite significantly improves the sedimentation performance of the reactive precipitates. The experimental results showed that calcite and fluorite can effectively reduce the concentration of fluoride ions in F-containing wastewater and solve the problem of slow sedimentation of reactive precipitates. [ABSTRACT FROM AUTHOR]

The Shuiyindong Gold Mine hosts one of the largest and highest-grade, strata-bound Carlin-type gold deposits discovered to date in Southwestern China. The outcrop stratigraphy and drill core data of the deposit reveal Middle–Upper Permian and Lower Triassic formations. The ore is mainly hosted in Upper Permian bioclastic limestone near the axis of an anticline. The gold is mainly hosted in arsenian pyrite and arsenopyrite, mainly existing in the form of crystal lattice gold, submicroscopic particles and nanoparticles. Fluorite commonly occurs at the vicinity of an unconformity between the Middle–Upper Permian formations, which is proposed to be the structural conduit that fed the ore fluids. Calcite commonly fills fractures at the periphery of decarbonated rocks, which contain high grade orebodies. This study aimed to verify the occurrence of two distinct hydrothermal events at the Shuiyindong, based on Sm–Nd isotope dating of the fluorite and calcite. For this purpose, rare-earth element (REE) concentrations, Sm/Nd isotope ratios, and Sm–Nd isochron ages of the fluorite and calcite were determined. The fluorite and calcite contain relatively high total concentrations of REE (12.3–25.6 μg/g and 5.71–31.7 μg/g, respectively), exhibit variable Sm/Nd ratios (0.52–1.03 and 0.57–1.71, respectively), and yield Sm–Nd isochron ages of 200.1 ± 8.6 Ma and 150.2 ± 2.2 Ma, with slightly different initial ε Nd (t) values of −4.4 and −1.1, respectively. These two groups of Sm–Nd isochron ages suggest two episodes of hydrothermal events at the Shuiyindong gold deposit. The age of the calcite probably represents the late stage of the gold mineralization period. The initial ε Nd (t) values of the fluorite and calcite indicate that the Nd was probably derived from mixtures of basaltic volcanic tuff and bioclastic limestone from the Permian formations. [ABSTRACT FROM AUTHOR]

Fluorine is a species commonly present in many minerals in the Earth's interior, with a concentration ranging from a few ppm to more than 10 wt. %. Recent experimental studies on fluorine-bearing silicate minerals have proposed that fluorine might be an important charge carrier for electrical conduction of Earth materials at elevated conditions, but the results are somewhat ambiguous. In this investigation, the electrical conductivity of gem-quality natural single crystal fluorite, a simple bi-elemental (Ca and F) mineral, has been determined at 1 GPa and 200–650 °C in two replication runs, by a Solartron-1260 Impedance/Gain Phase analyzer in an end-loaded piston-cylinder apparatus. The sample composition remained unchanged after the runs. The conductivity data are reproducible between different runs and between heating-cooling cycles of each run. The conductivity (σ) increases with increasing temperature, and can be described by the Arrhenius law, σ = 10^(5.34 ± 0.07)·exp[−(130 ± 1, kJ/mol)/(RT)], where R is the gas constant and T is the temperature. According to the equation, the conductivity reaches ~0.01 S/m at 650 °C. This elevated conductivity is strong evidence that fluorine is important in charge transport. The simple construction of this mineral indicates that the electrical conduction is dominated by fluoride (F−). Therefore, fluorine is potentially an important charge carrier in influencing the electrical property of Fluorine-bearing Earth materials. [ABSTRACT FROM AUTHOR]

The origin of the mineralization at the world-class Las Cuevas (the largest single fluorite deposit in the world) has been historically disputed, essentially between skarn-related and Mississippi Valley Type (MVT) models. A systematic study of fluid inclusions in these deposits revealed that they were formed by low temperature (49 to 177 °C) and low salinity (0 to 1.9 wt % NaCl equiv) fluids. The obtained δ13C (between −2.39 and 0.20‰ VPDB) and δ18O (between −14.03 and −7.37‰ VPDB) data from local host limestones agreed with regionally representative values in the literature. The obtained δ13C (between −15.60 and −12.99‰ VPDB) and δ18O (between −5.56 and −1.84‰ VPDB) data from hydrothermal calcite associated with fluorite mineralization indicated that the isotopic composition of hydrothermal fluids initially reflected buffering by the host rocks, and then recorded the interaction between meteoric water and basinal brines. It is likely that such processes occurred with concurrent maturation of organic matter, and that the obtained compositions may also have recorded a thermal effect on the local limestones. Halogen geochemical studies in inclusion fluids showed a distribution that suggests that solutes in mineralizing fluids were due to scavenging of Na+ and Cl− through water–rock interaction or halite dissolution, and that secondary sources would have been the evaporation or infiltration of seawater. The basinal brines with which the formation of these deposits was associated were massively diluted by deeply evolved meteoric water, thus making a significant fluorine input by basinal brines unlikely. Fluorine would have been provided by local groundwater through its interaction with Oligocene topaz rhyolites and other F-rich volcanic and hypabyssal rocks. Such a possibility is supported by present-day groundwater, which presents a regional endemic case of fluorosis. The precipitation of fluorite is possible at low temperatures (at which the solubility of this mineral is very low) by means of chemical reactions and physical interactions among very diluted F-poor basinal brines, F-rich groundwater, and host carbonate rocks. The latter systematically experienced hydrothermal karstification, which would have provided Ca2+ for reaction with F− and resulted in the precipitation of fluorite. This scenario stands for a depositional model that recalls those proposed for MVT and associated industrial mineral deposits, but is distinct from common models with regard to the primal source for fluorine and the extremely low salinities of inclusion fluids. [ABSTRACT FROM AUTHOR]

The formation of most fluorite deposits in northern Coahuila (NE Mexico) is explained by MVT models, and is a part of the metallogenic province of northeastern Mexico. However, fluorite skarn deposits also occur in the same region, and there is evidence for late hydrothermal manifestations with no clear origin and evolution. The latter are the main focus of this study; in particular, F–Be–U–Mo–V–P stringers in the Aguachile-Cuatro Palmas area that overprint preexisting fluorite mantos. The region experienced the emplacement of several intrusives during the Eocene and the Oligocene that are collectively grouped into the East Mexico Alkaline Province (EMAP) and postdate MVT-like deposits. Some of these intrusives have associated skarn deposits; most of them are polymetallic, but the unusual El Pilote deposit contains fluorite mineralisation that was remobilised from MVT-like deposits. The formation of the Aguachile deposit (and, collectively, part of the Cuatro Palmas deposit) has been attributed to a shallow retrograde skarn model. The Cuatro Palmas and Las Alicias fluorite deposits consist of MVT-like deposits overprinted by late hydrothermal fluorite mineralisation rich in Be–U–Mo–V–P, and the Aguachile deposit consists entirely of the latter type. The systematic fluid inclusion study of MVT-like, skarn, and late hydrothermal fluorite deposits reveals a very different distribution of temperature and salinity data that allows the discrimination of mineralising fluids for the type of deposit. MVT-like deposits were formed by fluids with temperatures of homogenisation that range between 50 °C and 152 °C and salinities between 5 and 15.5 wt.% NaCl equivalent. The El Pilote fluorite skarn was formed by fluids with temperatures of homogenisation that range between 78 °C and 394 °C and salinities between 5 and 34 wt.% NaCl equivalent, and include CaCl2-rich brines with salinities that range between 24.5 and 29.1 wt.% CaCl2. Late shallow fluorite–Be–U–Mo–V–P hydrothermal deposits were formed by fluids with temperatures of homogenisation that range between 70 °C and 180 °C and salinities between 0.9 and 3.4 wt.% NaCl equivalent; the sole exception to the above is the La Fácil deposit, with salinities that range between 7.9 and 8.8 wt.% NaCl equivalent. While temperatures of homogenisation are similar between MVT-like and late hydrothermal deposits, and both even have hydrocarbon-rich fluid inclusion associations, the salinity of late deposits is similar to that of retrograde skarn fluids, although further diluted. However, homogenisation temperatures tend to be higher in late hydrothermal than in MVT-like deposits, thus making them more similar to retrograde skarn fluids. Although this characteristic cannot solely establish a genetic link between a retrograde skarn model and late hydrothermal deposits in the study area, the characteristics of fluids associated with the latter separate these deposits from those ascribed to an MVT-like model. Assuming that mineralising fluids for late fluorite–Be–U–Mo–V–P hydrothermal deposits may correspond to a retrograde skarn (or "epithermal") deposit, the source for fluorine may be either from (A) the dissolution of earlier formed MVT-like deposits, (B) the entrainment of remaining F-rich basinal brines, or (C) hydrothermal fluids exsolved from highly evolved magmas. Possibilities A and B are feasible due to a hypothetical situation similar to the El Pilote skarn, and due to the occurrence of hydrocarbon-rich fluid inclusions at the La Fácil deposit. Possibility C is feasible because intrusive bodies related to highly evolved magmas would have provided other highly lithophile elements like Be, U and Mo upon the exsolution of their hydrothermal fluids. Such intrusive bodies occur in both study areas, and are particularly conspicuous at the Aguachile collapse structure. [ABSTRACT FROM AUTHOR]