Fluorite Mineralization Research Articles

Use of Mining Waste to Produce Ultra-High-Performance Fibre-Reinforced Concrete.

This research work analyses the influence of the use of by-products from a fluorite mine to replace the fine fraction of natural aggregates, on the properties of Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC). Replacing natural aggregates for different kinds of wastes is becoming common in concrete manufacturing and there are a number of studies into the use of waste from the construction sector in UHPFRC. However, there is very little work concerning the use of waste from the mining industry. Furthermore, most of the existing studies focus on granite wastes. So, using mining sand waste is an innovative alternative to replace natural aggregates in the manufacture of UHPFRC. The substitutions in this study are of 50%, 70% and 100% by volume of 0–0.5 mm natural silica sand. The results obtained show that the variations in the properties of consistency, compressive strength, modulus of elasticity and tensile strength, among others, are acceptable for substitutions of up to 70%. Therefore, fluorite mining sand waste is proved to be a viable alternative in the manufacturing of UHPFRC.

Hydrogeochemical signatures and suitability assessment of groundwater with elevated fluoride in unconfined aquifers Badin district, Sindh, Pakistan

The fluoride pollution in the groundwater is a significant human health risk around the world. However, many diseases including dental, crippling and skeletal fluorosis cause due to high fluoride contamination in the drinking water. The objectives of this study were to investigate the occurrence of higher F− in the groundwater, geochemical composition, water type mechanism for minerals enrichment and groundwater quality for drinking and irrigation purposes. Therefore, fifty-seven groundwater samples were collected for the appraisal. The mean concentrations of physical parameters like depth, Temperature, electrical conductivity, total dissolved solid, power of hydrogen ion (pH) and turbidity were observed as 28 m, 19.78 °C, 2283 uS/cm, 1456 mg/L, 7.4 and 21.80 NTU respectively. Whereas, the mean concentrations of chemical parameters such as cations (Ca+2, Mg+2, Na+ and K+) were observed to be (92.12, 83.63, 251 and 12.40) mg/L and anions (Cl−, SO42−, HCO3−, NO3− and F−) were (375, 300, 285, 4.9 and 1.9) mg/L respectively. While the mean concentration of total Fe in the drinking water samples of study are were reported as 0.28 mg/L respectively. The range concentration of F− were 0.23–6.8 mg/L shows that 47% of drinking water samples exceeded the WHO limit (1.5 mg/L). The piper plot resulted in the dominance of (NaCl), and Gibbs plot represents rock and precipitation dominance ratios; while SAR and Sodium percentage (Na %) validates the salinity and sodium risk to the use of groundwater for irrigation purposes. Saturation indices expressed; the saturation of the fluorite mineral found within the range of (− 2.3 to 1.24). PCA results reveals four significant factors with total percentage contribution were 70.73%. Whereas, the water quality index resulted with mean and standard deviation as (2502.62 ± 2164). The overall quality of the groundwater is unfit for human consumption and irrigation purposes to the local population of the study area.

Assessing atmospheric dry deposition via water-soluble ionic composition of roadside leaves

This study focuses on the water-soluble ion concentrations in the washing solution of leaves of different roadside tree species at three sites in Iran to estimate the ionic composition of the dry deposition of ambient air particulates. All considered water-soluble ion concentrations were significantly higher next to the roads with high traffic density compared to the reference site with low traffic density. The PCA results showed that Ca2+, Mg2+, and originated mainly from traffic activities and geological sources, and Na+, Cl−, K+ and F− from sea salts. In addition to sea salt, K+ and F− were also originated from anthropogenic sources i.e. industrial activities, biomass burning and fluorite mining. Moreover, the concentration of the water-soluble ions depended on species and site. C. lawsoniana had significantly higher ion concentrations in its leaf washing solution compared to L. japonicum and P. brutia which indicates C. lawsoniana is the most suitable species for accumulating of atmospheric dry deposition. From our results, it can be concluded that sites with similar traffic density can have different particle loads and water-soluble ion species, and that concentrations in leaf-washing solutions depend on site conditions and species-specific leaf surface characteristics.

Two distinct mechanisms of fluoride enrichment and associated health risk in springs' water near an inactive volcano, southeast Iran.

Groundwater fluoride contamination is a major issue of water pollution in the world with health hazards such as dental and skeletal fluorosis. This research focused on exposure to the high concentration of fluoride in the springs water in the Bazman volcanic area, southeast Iran. The combination of chemical/isotopic analysis, geochemical modeling, health risk assessment and multivariate statistical methods were applied to investigate the contamination and sources of fluoride in the samples. Groundwater samples were collected from cold and thermal springs. Major ions, fluoride, trace elements and stable isotopes δ18O and δD were measured in the samples using standard methods, ICP-MS and OA-ICOS, respectively. Fluoride content in springs varied from 0.5 to 3.75mg/L with an average value of 1.66mg/L. The highest fluoride concentrations were observed in the eastern cold springs while thermal springs showed the minimum fluoride contents. The majority of samples showed F contents higher than the calculated optimal concentration of fluoride (0.75mg/L). Reaction of fluorite mineral with HCO3 and replacement of F in clay minerals and metal oxy-hydroxides with OH- in water were likely cause fluoride enrichment in the eastern springs. Whereas, in the western springs and thermal springs, origin of fluoride was related to weathering of muscovite, cryolite, apatite and fluoroapatite minerals. The δ18O and δ2H of the water samples displayed the impact on evaporation on fluoride enrichment in all spring water samples. The average value of contamination index (Cd) in the water samples was 1.94 categorizing medium risk level while springs S7, S8, S9 and S4 were above the threshold value of Cd index. The fluoride hazard quotient (HQ) showed that 25%, 44%, 56% and 0% of springs' water resources had high risk level for age group of adults, teenager, children and infants, respectively. Therefore, health risk of fluoride in drinking water resources were in the following order: children>teenager>adults>infants.

Hydrochemistry of tropical springs using multivariate statistical analysis in Ithikkara and Kallada river basins, Kerala, India

Spring waters are the most important natural resource used for drinking by many people around the world, especially in arid and semi-arid areas. This resource cannot be optimally used and sustained, unless the quality of groundwater is assessed. The main objective of this study is to understand the quality and hydrochemistry of spring water sources of two important river basins of Southern Western Ghats—the Ithikkara and the Kallada river basins draining Kollam district of Southern Kerala as an example. Water Quality Index (WQI) values are used to assess the drinking suitability of spring water samples. Multivariate statistical approach (factor analysis and principal component analysis) allow driving hidden information from the data set about their possible influences of the environment on water quality. Multivariate analysis was performed on matrix of hydro-geochemical data. To study the influences of the environment on water quality, multivariate statistical approach is applied. A total of 57 samples were collected and analyzed for major cations and anions for pre-monsoon, monsoon and post-monsoon seasons of 2011–2012 periods from lowland and highland regions of the study area. The results of the WQI values show that majority of the samples fall in Excellent to Good category rendering these water samples suitable for drinking purposes. From the statistical analysis, it is inferred that in catchments rich with pyrite in rocks and clays, drainage of sulphuric acid may significantly contribute to acidity. The negative loading in pH and DO is due to anaerobic conditions in the spring source from the loading of high-dissolved organic matter, which results in the formation of ammonia and organic acids leading to a decrease in pH. The positive loading of SiO2 reflects the dissolution of silica minerals and high temperature. The evaluation of the saturation index of the water samples in highland regions indicted that water was oversaturated with respect to iron minerals and undersaturated with fluorite minerals. The chemistry of the spring waters favors kaolinization and subsequent leaching of mobile elements like alkali and alkaline earth elements. The study is helpful in understanding the relationship between individual ions and for the classification of groundwater types.

Virtues of fluorite-case of Bou-Izourane fluorite

Fluorite minerals are among the non-metallic natural substances that have played an important role in the industry for decades. The economic importance of each of the grades of fluorite marketed meets precise chemical specifications such as its melting quality and fluor content. They also provide specific and very diverse outlets: iron and steel industry, aluminum metallurgy, plastics manufacturing, solvents, refrigerants, welding, glassmaking, cement industry, etc. In Morocco, fluorite is a very important resource because of its multiple high-grade deposits, which currently make it the 8th largest producer of metallurgical fluorite concentrate in the world with 70 kt produced per year. In the Moroccan High Atlas, the fluorite district of Bou-Izourane, located 40 km south of the city of Midelt, is estimated to be one of the most important fluorite deposits in Morocco. There are at least four violet fluorite sites in this district, the two deposits of Bou-Izourane and Bou-kharouba in the eastern part of the study area. The western part of the Bou-Izourane region hosts the two other deposits (Tabja and Bou-Imtessene). Although the Bou-Izourane fluorite is more or less colored (Violet-Lilac) with remarkable quality and perfect transparency, its uranium content, especially at the Tabja and Bou-Imtessene sites, is quite high (97.4–188.5 ppm). This property of uranium richness is an axis of research in addition to the determination of its physico-chemical characteristics, which will define the virtues and the fields of use of this fluorite. This document has been written in the hope that it will be of some use in highlighting the potential of the fluorite of the Moroccan Bou-Izourane deposit.

Application of lanthanides tetrad effect as a geochemical indicator to identify fluorite generations: A case study from the Laal-Kan fluorite deposit, NW Iran

The Laal-Kan fluorite deposit situated in north margin of the Sanandaj-Sirjan metamorphic belt and Urmia-Dokhtar magmatic arc, NW Iran. The fluorite mineralization in the form of open-space filling, veins and veinlets have been deposited in the contact zone between highly metamorphosed schist, gneiss, amphibolite of the Paleozoic age and the Jangutaran limestone of the Precambrian age. The occurrence of convex tetrad effect and the calculated tetrad values indicate that early and late stage fluorite mineralization display various geochemical behavior, which are supported by the bivariate diagrams including T1, T3 and T4 versus each other and some geochemical parameters such as La/Ho, Y/Ho and Zr/Hf ratios. It can, therefore, deduced that fluorite have been probably formed during two stages from hydrothermal fluids with a relatively constant composition. The fluid-rock interaction during deposition of fluorite and REE-F complex were likely the main mechanisms for the occurrence of tetrad effect.

IMPROVING FLUORITE FLOTATION UNDER LOW TEMPERATURE AND NEUTRAL pH CONDITIONS

The authors provide insight into the problem of selective flotation of fluorite from quartz–fluorite ores. The flotation of fluorite mineral from ores by using acidized water glass as depressant has been studied for substitution of the commonly used depressant. It was found that the acidized water glass could achieve higher selectivity of fluorite minerals against gangue minerals in the fluorite flotation. The experimental results showed that YF collector has high selectivity in the flotation of fluoride for low-grade fluorite ores. The use of the YF collector also made it unnecessary to heat the pulp to a high temperature and achieved an acceptable reduction in the flotation temperature to [Formula: see text]C. The YF collector should be used in neutral pH to separate fluorite from gangue and it could also improve fluorite recovery and flotation rate.

Fluorite deposits in the Zhejiang Province, southeast China: The possible role of extension during the late stages in the subduction of the Paleo-Pacific oceanic plate, as indicated by the Gudongkeng fluorite deposit

Southeast China with its widespread occurrences of Mesozoic igneous rocks, is one of the largest magmatic provinces worldwide, containing a large variety of mineral types, including hypothermal W-Sn, porphyry Cu, epithermal Au deposits. The Gudongkeng deposit is an example consisting of fluorite mineralisation trending SE over a distance of about 6 km. The major minerals in the deposit include fluorite and calcite of a hydrothermal origin and interpreted as a vein-type deposit associated with the Linghou Granite that yields a zircon U–Pb date of 100 ± 1 Ma, but intriguingly the fluorite yields an Sm–Nd isochron age of 73 ± 3 Ma, placing the genesis of the fluorite as a post-magmatic event. Fluid inclusions in the fluorite have low homogenisation temperatures of 104–195° C, salinities of 0.5 to 2.24 wt% NaCl eqv., and densities of 0.67–0.94 g/cm3. The inclusions contain NaCl–H2O–CaF2 with δDV-SMOW values between −64.3 and-50.1‰ and δ18OV-SMOW values between −7.6 and −2‰. The initial 87Sr/86Sr ratios of the fluorite range from 0.709816 to 0.710165 are characteristic of a crustal contribution. The ore-forming fluids can be mainly attributed to a NaCl–H2O–CaF2 system of moderate to low temperature, low salinity, and low density. The ore-forming fluid has a meteoric water source, with the reaction between the fluid and wallrocks being the main mechanism for fluorite precipitation at relatively low temperatures. Gudongkeng is a low temperature epithermal deposit which was formed in an extensional setting within the Cathaysia Block during the Late Cretaceous.

Fault-controlled fluid evolution in the Xitian W–Sn–Pb–Zn–fluorite mineralization system (South China): Insights from fluorite texture, geochemistry and geochronology

Fluorite is one of the most common minerals in the granite-related hydrothermal systems, and widely distributed in the Xitan W–Sn polymetallic ore field (South China). It existed from the early W–Sn stage to the middle Pb–Zn stage and then to the late fluorite stage, thus responsible for the Xinggao and Guangming fluorite deposits in the region. In this research, textural, geochemical and geochronological analyses of fluorites were used to reconstruct the fluid evolutionary history and its bearings on fault activities in the ore field. The fluorites from the ore field yielded a Sm–Nd isochron age of 153.3 ± 8.0 Ma (initial 143Nd/144Nd = 0.511871 ± 0.000013, MSWD = 1.5) which is consistent to the timing of the W–Sn ore-forming stage within the error. This suggests that the fluorites were formed in the same time with the W–Sn ores. And the average value of εNd(t) is similar to those of the Jurassic granites (εNd(t) = −9.2 to −7.3) in the ore field. This indicates that fluorite mineralization is mainly related to the Jurassic granites, and the basement rocks could be the source for the ore-forming materials. From the early stage fluorites (coexisting with wolframite) to the late fluorite-only veins, the total amount of rare earth elements (∑REE) in the fluorites substantially decreases (average values vary from 174 to 37.2 ppm), especially the LREE (La/Lu values decrease from 80.0 to 16.6). In addition, the ore-forming elements (e.g., W, Sn, Mo) in the fluorites also decrease significantly with time. And the low δ18OH2O values (−4.30‰ to −3.90‰) and moderate δD values (−63.8‰ to −59.6‰) in the fluorites suggest that the late fluorite stage was contributed largely from meteoric water. Combined with previously reported fluid inclusion data in the ore field, we propose that the W–Sn mineralization was related to fluid boiling and mixing, the Pb–Zn ore was formed from the changing of the redox environment from oxidizing to reducing, and the fluorites were formed due to rapid cooling. The formation of the W–Sn, Pb–Zn, and fluorite ore-forming zones belong to a single magmatic-hydrothermal system but was controlled by the fault evolutionary processes from the early granite plutons intrusion to the large-scale crustal extension in the Xitian ore field.

A review of molybdenite, and fluorite mineralisation in Caledonian granite basement, western Ireland, incorporating new field and fluid inclusion studies, and Re-Os and U-Pb geochronology

The recent discovery of late-magmatic quartz vein hosted molybdenite, and exceptional gem quality vein fluorite, in the Caledonian Galway Granite Complex (GGC), has prompted a review of these contrasting styles of mineralisation in the late-Caledonian granite basement, Connemara, western Ireland. Existing published U-Pb and Re-Os chronometry and fluid inclusion microthermometry are combined with new: a) geological field observations, b) U-Pb zircon and Re-Os molybdenite geochronometry and c) fluid inclusion microthermometry to generate a new pressure-temperature-time model (P-T-t) of mineralisation for the GGC. Re-Os chronometry molybdenite indicates that granite related molybdenite mineralisation extended from 423 to 380Ma overlapping with the GGC emplacement history determined by U-Pb zircon chronometry. The P-T-t model reflects initial granite emplacement and Mo-mineralisation at ∼423Ma followed by lower P and T granite emplacement and related quartz vein hosted Mo-mineralisation at ∼410Ma (Carna pluton), ∼400Ma (Kilkieran pluton) and at ∼380Ma (Costelloe Murvey granite). The gem quality fluorite veins in the GGC represent late-Triassic hydrothermal mineralisation. These veins form part of a regional N Atlantic-European Triassic-Jurassic hydrothermal mineralisation province. Vein emplacement was triggered by the rifting of the N Atlantic facilitating crustal thinning and subsidence of continental crust and initiating hydrothermal activity at the margins of Mesozoic basins.

Contribution of fluorite mining waste to mercury contamination in coastal systems.

Samples from 13 beaches along the northern Spanish coast, a region with a history of heavy industries, were first screened to identify signs of pollution. High concentrations of Hg and Ba on Vega beach were found, both elements belong to the fluorite ore paragenesis, mined in the surroundings. Samples of beach and fluvial sediments, and nearby soils were collected in Vega beach area to address potential Hg pollution, fate and sources. Most samples showed a similar pollutants fingerprint to that of beach samples, especially those taken from white dunes, registering notable Hg concentrations. Hg was enriched in the finer fractions, and overall the main input was attributed to the mining waste discharged along the coast in the past. Although a specific risk assessment and study of the submerged sediments are advisable for this area, Hg bioavailability and methylation were low, thus indicating that this metal poses a reduced environmental risk.

New evidence from the Wuliji'Oboo fluorite deposit for the role of the paleo‐Pacific Plate and Mongol–Okhotsk suture in creating extensive fluorite mineralization in the Great Xing'an Range, NE China

The Wuliji'Oboo fluorite deposit is a newly discovered deposit hosted by volcanic rocks of the Early Cretaceous Baiyin'gaolao Formation, which are located in the Great Xing'an Range. Fluorite orebodies within this area are controlled by the NNE‐trending faults. The ΣREE of fluorite samples ranges from 19.18 to 361.22 ppm, with an average of 131.14 ppm. The homogenization temperatures are concentrated in the ranges of 100–150°C and 230–350°C, while the salinity is concentrated in 0.3–1.0 and 2.0–4.5 wt.% NaCl eqv., and the density has ranges of 0.92–0.96 and 0.75–0.8 g/cm3, respectively. The δDV‐SMOW values of fluid inclusions within the fluorite range between −122.3‰ and −105.6‰ with a mean of −115.36‰. The δ18OV‐SMOW of fluorite ranges from −12.0 to −8.5‰, average is −9.9‰. Sm–Nd isotopic data on the fluorite ore yield an isochron age of 122 ± 15 Ma and have ɛNd(t) values ranging from +3.15 to +4.16 and (87Sr/86Sr)i values ranging from 0.704907 to 0.705765. In this contribution, field, petrologic, and geochemical data lead us to the following salient findings: (a) The ore consists of fluorite, quartz, and calcite, with host rock alteration that includes silicification, calcitization, and sericitization. The major element data reveal that the host rocks are a series of highK calc‐alkaline rhyolite. The REEs suggest that F‐rich fluids in this region might have experienced a long‐distance migration. The Tb/Ca‐Tb/La diagram confirms a hydrothermal origin for the deposit. (b) Petrographic evidence and fluid inclusions in the fluorites indicate that this deposit might have two ore‐forming stages. The ore‐forming fluids can be attributed to a NaCl‐H2O‐F system with moderate‐low temperature, low salinity, and low density and have a meteoric water source, with water/rock reaction as the main mechanism for fluorite precipitation. (c) The deposit was formed in an anorogenic within‐plate extensional tectonic setting related to the lithospheric thinning occurring after the Mongolian–Okhotsk Ocean closure.

Evaluation of high fluoride contaminated fractured rock aquifer in South Africa – Geochemical and chemometric approaches

The first systematic study on high fluoride contaminated fractured rock aquifer in South Africa using geochemical and chemometric approach is presented. Groundwater samples were collected from 49 boreholes and analysed for EC, pH, major and minor ions. The groundwater with high fluoride is associated with NaCl water types. The groundwater chemistry is governed by mineral weathering, evaporation and wastewater infiltration. PHREEQC modelling indicates that carbonate mineral saturation is decreasing with increasing salinity due to evaporation whereas fluorite saturation increases with increasing F being one of the prime controlling factors. Silicate minerals namely chalcedony, quartz and talc express saturation and over-saturation while chrysotile and sepiolite are undersaturated in most of the samples. PCA provided four factors and justified the role of mineral weathering, evaporation, ion exchange, longer residence time and anthropogenic impacts on water chemistry. R-mode and Q-mode cluster analysis resulted in four clusters. In cluster 1, (29%) of groundwater is less mineralized due to recent recharge. In cluster 2 (45%), groundwater chemistry is governed by weathering of silicates and fluorite minerals. Cluster 3 (20%) reveals the impact of anthropogenic activities and induced mineral weathering. Cluster 4 shows high EC, TDS, major ions, F and low HCO3 implying that groundwater is affected by evaporation and longer residence time promoting mineral-water interaction and precipitation of carbonate minerals. More than 50% of the study area is degraded due to fluoride contamination which requires proper remedial actions and further investigations on human health risk due to impact of fluoride contamination in groundwater is recommended.

Influence of preparing conditions on the hot‐pressed sintering of transparent polycrystalline fluorite ceramics

AbstractTransparent polycrystalline fluorite ceramics were manufactured from naturally occurring fluorite mineral by a hot‐pressed sintering method. Naturally occurring fluorite minerals were ball milled by a planetary milling equipment. The phase structures of powders were single cubic fluorite phase, and diameters of fluorite powders were decreased from 100 to 20 μm with increasing ball milling duration. Influence of ball milling duration and sintering temperatures on optical properties of polycrystalline fluorite ceramics were studied systematically to obtain the optimum manufacturing process. For the mineral powders after 1 hours ball‐milling, the polycrystalline ceramic hot‐pressed at 1050°C exhibited the highest optical transmission. For a 2.5 mm thickness polycrystalline ceramic, the highest optical transmission at 500 and 1500 nm were about 60.1% and 75.7%, respectively.

Formation timing and genesis of Madiu fluorite deposit in East Qinling, China: Constraints from fluid inclusion, geochemistry, and H–O–Sr–Nd isotopes

The Heyu fluorite ore district is newly discovered in the East Qinling metallogenic belt (EQMB), central China. In this district, the large Madiu fluorite deposit contains five Mesozoic granite‐hosted orebodies. The deposit may have formed at shallow depth and occurred as continuous veins controlled by a series of N‐S‐ or NE‐trending, steeply dipping faults. The fluorite mineralization can be divided into two stages (I and II). Fluid inclusions in stage I fluorite homogenized at 132.2°C to 342.5°C (peak at 170°C–210°C) with salinities of 0.18 to 4.43 wt% NaCl equiv, whilst those in stage II fluorite homogenized at 122.2°C to 305.7°C (peak at 130°C–170°C) and salinities of 0.18 to 3.71 wt% NaCl equiv. Raman spectroscopic analysis of the fluid inclusions reveals that they comprise predominantly H2O. The rare earth element (REE) characteristics indicate that the deposit is of hydrothermal origin. The δ18OH2O (−8.8‰ to −0.5‰) and δDH2O (−69.0‰ to −61.9‰) values show a subhorizontal trend, suggesting that the oxygen isotopic compositions were modified by fluid–rock interactions. Fluid inclusion and stable isotopic data suggest that the ore‐forming fluids belong to a meteoric water‐sourced, medium–low temperature, and low salinity NaCl–H2O system. Initial fluorite 87Sr/86Sr ratios (0.708879–0.709682) resemble those of the Heyu batholith. The water–rock reaction, which leached Ca from the host rock and increased the fluid pH, was likely causative to the ore precipitation. Geochemical and mineralization features suggest that the Madiu fluorite deposit is best classified as a fault‐controlled hydrothermal vein‐type fluorite deposit. The Sm–Nd isochron age of 118.9 ± 7.8 Ma and its regional age correlation suggest that the fluorite mineralization occurred under regional extension or lithospheric thinning setting and that the fluorite mineralization was an important component of the Early Cretaceous mineralization event in the EQMB.

Fluid evolution and ore deposition in the Harz Mountains revisited: isotope and crush-leach analyses of fluid inclusions

Hydrothermal fluid flow along fault zones in the Harz Mountains led to widespread formation of economic vein-type Pb–Zn ore and Ba–F deposits during the Mesozoic. We reconstruct the fluid flow system responsible for the formation of these deposits using isotope ratios (δ2H and δ18O) and anion and cation contents of fluid inclusions in ore and gangue minerals. Building forward on extensive studies in the 1980s and 1990s, our new geochemical data reveal that seawater evaporation brines, which most likely originated from Zechstein evaporites, descended deeply into Paleozoic rocks to leach metals at depth. In Jurassic times, these metal-rich brines episodically recharged along fault zones and mixed with shallow crustal H2S-bearing brines. Primarily in the Upper Harz Mountains, this mixing system led to the formation of economic Pb–Zn–Cu mineralization, which locally shows banded textures with alternations of sulfide minerals and quartz or carbonate (mostly calcite). In the Middle and Lower Harz Mountains, Zechstein-derived brines interacted with K- and F-bearing basement rocks and/or magmatic rocks to deposit fluorite mineralization upon ascent in the Upper Cretaceous. The proposed model of mineralizing fluids originating as (evaporated) seawater has been shown to hold for numerous basin-hosted base-metal sulfide and fluoride deposits elsewhere in Europe.

Hydrogeochemical modeling of fluoride contents in groundwater in outcrop area of Guarani Aquifer System, southern Brazil

Groundwater quality problems with high fluoride contents were studied in an outcrop area on a portion of Guarani Aquifer System (GAS), in the state of Rio Grande do Sul, southern Brazil. The methodology was based on the evaluation of tectonic structures lineaments and geochemical modeling of 13 groundwater physical-chemical data with anomalies of fluoride from tube wells. The lineaments trace and speciation code PHREEQC 3.3.5 used suggest the occurrence of distinct mineralogical contributions, in which the precipitation of carbonate minerals from the mineral structure of the GAS sandstone and cation exchange play a fundamental role in the hydrogeochemistry of fluoride. The results were analyzed by the main transects, which allowed the definition of characteristics of mineral dissolution and precipitation in the environment. The halite and sylvite showed dissolution tendencies along the traced transects, towards the mineral equilibrium. The fluorite mineral presented undersaturation with tendencies to mineral equilibrium and, possibly, precipitation in the most salinized waters. The applied methodology allowed the extraction of information for a better understanding of the hydrogeochemical dynamics of salinized waters and their water/rock interactions in outcrop area of the GAS, constituting a material to support the research of anomalous fluoride concentrations in groundwater and the practices of management of this important aquifer system.

Regional variations in fluid formation and metal sources in MVT mineralization in the Pennine Orefield, UK: Implications from rare earth element and yttrium distribution, Sr-Nd isotopes and fluid inclusion compositions of hydrothermal vein fluorites

The Pennine Orefield is one of the most important ore fields for Pb-Zn-Ba-F mineralization in Great Britain. It is subdivided into the Northern Pennine Orefield (NPO), consisting of the Alston and Askrigg Blocks, and the Southern Pennine Orefield (SPO). The Alston Block is underlain by the early Devonian Weardale Granite and the Askrigg Block by the coeval Wensleydale Granite. The potential relationship between the batholiths and the mineralization is a matter of debate. We here studied the rare earth elements and Y (REY) geochemistry, Sr-Nd isotopes and fluid inclusion (FI) compositions of fluorites from the two structural blocks in the NPO and found that the fluorite mineralization in these blocks differ substantially. The REY in Askrigg fluorites show features that are characteristic for leaching of adjacent Lower Carboniferous limestones. In contrast, Alston fluorites have significantly higher REY concentrations, lack REYSN limestone signatures and show a decoupling of redox-sensitive Eu from its trivalent REY ‘neighbours’. Neodymium isotopes indicate a similar crustal source of REY in both blocks, but higher REY concentrations and lower Y/Ho ratios suggest Lower Carboniferous shales as potential REY source in the Alston Block. The fluids that precipitated the Alston fluorites experienced temperatures > 250 °C prior to mineral formation, as evidenced by Eu geothermometry. Fluorite formation, however, occurred at much lower temperatures, as suggested by homogenization temperatures in FI, that fall within ranges of 105–159 °C in Alston and 99–160 °C in Askrigg fluorites. Mineralization of the Mississippi-Valley Type usually lack association with igneous activity. We show that some of the fluids responsible for the NPO mineralization were influenced by magmatic sources. The REY systematics in Alston fluorites may be linked to an interaction of the Permian-age Whin Sill dolerite with the basement granite, which heated fluids and focussed fluid flow into the overlying sedimentary rocks. In the Askrigg Block, where such a dolerite intrusion was not described, fluorites lack any positive EuSN anomalies, indicating that these fluids had never been subjected to temperatures exceeding 200–250 °C.

Geology, mineralization, and fluid inclusion characteristics of the Koitash redox-intermediate W–Mo skarn and W–Au stockwork deposit, western Uzbekistan, Tien Shan

The Koitash W–Mo skarn deposit in the Tien Shan Gold Belt contained resources of 60 kt WO3 in altered skarn (averaging 0.56% WO3 and 0.029% Mo) and an additional 42 kt WO3 in separate zones of phyllic alteration (averaging 0.30% WO3, 0.97 g/t Au, 0.67% Cu, and 0.02% Bi). It is related to an Early Permian multiphase granodiorite–granite–leucogranite pluton that is composed of medium- to high-K, transitional metaluminous to peraluminous, weakly oxidized–weakly reduced, ilmenite–titanite series granitoids. The pluton was emplaced in a tectonic domain with inferred ancient continental crust; the latter, coupled with possible ascent of hot asthenospheric material, has likely defined a distinct W–Mo–Au metallogenic assemblage forming in a post-collisional environment. The deposit includes redox-intermediate prograde and retrograde pyroxene–garnet skarns, partially overprinted by propylitic and phyllic alteration assemblages, comprising scheelite, molybdenite, Cu–Bi–Ag–Te sulfides, and sulfosalts, as well as native Bi and Au. Compositional similarities between W–Mo deposits, containing Au–W–Cu–Bi mineralization in late alteration assemblages, and coeval intrusion-related Au-dominant (with minor W, Bi, etc.) deposits in the region support their possible genetic links. Fluid inclusion data indicate the involvement of carbonic-free moderately saline (10.5–15.0 to 8.0–11.7 wt% NaCl-eq.), high-pressure (2000 to 1500 bars), hot (> 550–600 °C) aqueous fluid, which was sourced from crystallizing magma and formed prograde calcic skarn. This fluid was followed by moderately saline, Ca-rich (14–16 wt% NaCl, 19–21 wt% CaCl2), lower pressure (800 bars) fluids toward the retrograde skarn stage, with the deposition of scheelite in association with pyrrhotite and molybdenite, locally with minor fluorite. Propylitic quartz–amphibole–chlorite–oligoclase–calcite, with scheelite, pyrrhotite, locally molybdenite, assemblages formed from boiling high-methane aqueous-carbonic fluids at temperatures of 370–400 °C and pressures of 950–1000 bars. Phyllic quartz–sericite–Fe–carbonate, locally with albite, fluorite, chlorite, scheelite, molybdenite, and other sulfides, also Bi and Au minerals, alteration assemblages initially formed from homogeneous and then from boiling aqueous-carbonic, low-salinity fluids at temperatures of 365–370 to 300–315 °C and pressures of ~ 2000 bars. δ34S increases from retrograde skarn (δ34S = + 2.0 to + 2.3‰) through propylitic (δ34S = + 3.0 to + 3.4‰) to phyllic alteration (δ34S = + 4.2 to + 4.7‰) stages.