Fluorite Veins Research Articles

Petrography, Mineral Chemistry, and Geochemistry of Calc‐Silicate Skarn Mineralization at Kuh‐e‐Gabri, Rafsanjan, Kerman, Southeastern Iran: A Possible Potential of Industrial Andradite–Wollastonite–Quartz Resource

ABSTRACTThe prograde calcic skarn mineralization at Kuh‐e‐Gabri area in Kerman province, Iran, is composed of andradite–grossularite, wollastonite, diopside, hematite, and vesuvianite formed by intrusion of Oligo‐Miocene highly differentiated I‐type granitic stocks into the Cretaceous limestone and conglomerate. The retrograde skarn includes epidote, calcite, hematite, and quartz overprinting on the prograde skarn mineralization. This was followed by impregnations of hydrothermal veins of hematite, quartz, fluorite, and calcite. Supergene oxidation processes led to the occurrence of chrysocolla, dioptase, malachite, and goethite. XRD, DTA, FTIRS, EDXS, XRF, and ICP‐OES data indicate that the garnets are enriched in andradite (22.97%–99.50%)–grossularite (62.50%–75.52%) compositions. The composition of wollastonite is highly depleted in iron, manganese, and hazardous elements and close to pure wollastonite (98.31%–99.79%). The mineral assemblages of quartz–calcite–wollastonite as well as hematite–quartz–calcite–andradite suggest that the prograde skarn formed at about 390°C–500°C under oxygen fugacity of 10−33—10−15 bar. The incompatible element patterns in andradite–grossularite and wollastonite display enrichment in Cs, U, Pb, LREE, and negative Eu anomaly. The occurrence of andradite–grossularite skarn at the Kuh‐e‐Gabri may be the most suitable mineral for abrasive without creating environmental hazards. Acicular wollastonite‐rich skarn may be used for production of ceramics and metallurgical applications. Development of colored andradite, transparent and colored quartz in the skarn and veins may be considered as the valuable resource for the semi‐gem cutting industry. The light‐colored marble is a suitable raw material for metallurgical and refractory applications.

Fluid inclusion and He-Ar-Pb isotope studies of the Dabie-type Leimengou giant porphyry Mo deposit, Qinling Orogen

The Leimengou deposit is a Dabie-type porphyry Mo system in the Leimengou-Qiyugou orefield of Qinling Orogen. Orebodies host within the porphyry and the metasedimentary Taihua Supergroup. However, the characteristics and sources of ore-forming fluid, metal precipitation mechanism, and the sources of mineralizing substances remain unclear. In this contribution, by a comprehensive study comprising an investigation of deposit geology, fluid inclusion microthermometry, and He-Ar-Pb isotope, we discuss the source and evolution of ore-forming fluids and the molybdenum precipitation mechanism of the Leimengou deposit. The mineralizing process is divided into the Stage I quartz ± K-feldspar vein in potassic altered zone, Stage IIa molybdenite ± quartz vein, and Stage IIb molybdenite + quartz + pyrite ± purple fluorite vein in silicification-phyllic altered zone, Stage III quartz + pyrite + sphalerite + galena ± chalcopyrite ± green fluorite ± pink calcite in prophylitic altered zone and Stage IV quartz ± calcite vein in carbonatization zone based on cross-relationship. The Stage IIa and IIb veins characterize the main molybdenum mineralization stages. By microthermometry, CO2-bearing (C-), Water (WV- and WL-), and daughter minerals-bearing (S-) types of inclusions were recognized. The Stage I quartz contains C-type fluid inclusion assemblages (FIAs) with a salinity of 6.3 ± 1.4 wt% NaCl equiv., and a total homogenization temperature (Th, total) of 473 ± 3 °C. This suggests that the early fluids show characteristics of high temperature, CO2-rich, and moderate salinity, distinguishing them from those of Endako-type and Climax-type deposits. C-type and coexisting W-type FIAs from Stage IIa show similar salinity, ranging from 1.9 to 13.0 wt% NaCl equiv. and 1.9 to 14.1 wt% NaCl equiv., with Th, total of 349–376 °C and 327–392 °C, respectively. Moreover, C-type FIAs homogenize to distinct phases and also show similar homogenization temperatures, indicating fluid immiscibility. The FIAs in Stage IIb show an average salinity of 8.3 ± 7.4 wt% NaCl equiv. and a Th, total of 302 ± 14 °C. WL-type and WV-type FIAs coexist, with similar temperatures varying from 308 to 310 °C during this stage, indicating significant fluid boiling. These observations indicate that the decrease in temperature, fluid immiscibility, and decompression boiling collectively led to the precipitation of molybdenite. Trapping pressures are estimated to be 82–231 MPa for Stage IIa and 43–115 MPa for Stage IIb, corresponding to ore-forming depths of approximately 8.4 km and 4.3 km, respectively. Additionally, the He-Ar isotopes obtained from pyrite indicate a clear mixing trend of crustal fluids with mantle fluids at Stage IIb, with mantle-derived fluid components increasing during Stage III. This coincides with the tectonic shift from regional compression to extension, leading to the formation of many Dabie-type Mo deposits, alongside crustal thinning and the upwelling of asthenospheric mantle materials. Futhermore, Pb isotopes from the ore, ore-hosted gneiss, and ore-causative granitoids demonstrate that the Taihua Supergroup gneiss supplied ore-forming materials, suggesting a crustal origin for the Leimengou Mo deposit.

The Spatial and Temporal Evolution of the Sadisdorf Li-Sn-(W-Cu) Magmatic-Hydrothermal Greisen and Vein System, Eastern Erzgebirge, Germany

Abstract The Sadisdorf Li-Sn-(W-Cu) prospect in eastern Germany is characterized by vein- and greisen-style mineralization hosted in and around a small granite stock that intruded into a shallow crustal environment. The nature and origin of this mineral system are evaluated in this contribution by a combination of petrography and fluid inclusion studies, complemented by Raman spectroscopy and whole-rock geochemical analyses. The early magmatic-hydrothermal evolution is characterized by a single-phase low-salinity (7.0 ± 4 wt % NaCl equiv), high-temperature (>340°C), CO2-CH4–bearing aqueous fluid, which caused greisen alteration and mineralization within the apical portions of the microgranite porphyry. The bimodal distribution of brine and vapor fluid inclusions, and the formation of a magmatic-hydrothermal breccia associated with the proximal vein mineralization are interpreted to mark the transition from lithostatic to hydrostatic pressure. The vein- and stockwork-style mineralization (main stage) displays lateral zonation, with quartz-cassiterite-wolframite-molybdenite mineral assemblages grading outward into base-metal sulfide-dominated assemblages with increasing distance from the intrusion. Late fluorite-bearing veinlets represent the waning stage in the evolution of the mineral system. The similarity in the homogenization temperature (250°–418°C) of fluid inclusions in quartz, cassiterite, and sphalerite across the Sadisdorf deposit suggests that cooling was not a significant factor in the mineral zonation. Instead, fluid-rock interaction along the fluid path is considered to have controlled this zonation. In contrast to quartz-, cassiterite- and sphalerite-hosted fluid inclusions, which have a salinity of 0.0 to 10.0 wt % NaCl equiv, the fluid inclusions in late fluorite veins that overprint all previous assemblages have a salinity of 0.0 to 3.0 wt % NaCl equiv and homogenize at temperatures of 120° to 270°C, thus indicating cooling with or without admixture of meteoric fluids during the waning stage of the mineral system. The Sadisdorf deposit shares similar characteristics with other deposits in the Erzgebirge region, including a shallow level of emplacement, similar mineralization/alteration styles, and a hydrothermal evolution that includes early-boiling, fluid-rock interaction, and late cooling. In contrast to most systems in the region, both proximal and distal mineralization are well preserved at Sadisdorf. The recognition of such spatial zoning may be a useful criterion for targeting greisen-related Li and Sn resources.

Geological features of the Zn-Pb prospect in the Bou-Izourane district (Morocco)

The Zn-Pb mineralization in the Bou-Izourane district, located in the High Atlas Mountains of Morocco, contains estimated reserves of 40 200 tons of ore with an average grade of 20% Zn and 3.5% Pb. It is developed on N–S to NNW–SSE-trending faults that cut Liassic carbonate marl deposits. The paragenetic mineral sequence consists of galena, sphalerite and late-stage calcite. Oxidation phases of galena into cerussite and sphalerite into smithsonite are common in the Bou-Izourane ore, linked to the infiltration of meteoric waters and the oxidation of these sulphides. The Zn-Pb mineralization runs parallel to the fluorite veins associated with the igneous rocks of Tamazeght, but no petrographic or field relationship has been demonstrated between these two mineralizations (i.e., Zn-Pb and fluorite). The distribution of rare earth elements and yttrium (REY) in the Zn-Pb mineralization of Bou-Izourane shows a notable similarity with the Mississippi Valley Type (MVT) mineralization of the Central High Atlas of Morocco, although the concentrations more closely resemble those of REY in fluorite linked to the magmatic-hydrothermal activity of Tamazeght. However, the analysis of their distribution in post-fluorite calcite and post-Zn-Pb calcite reveals a strong concordance, suggesting that these two calcites are associated with the same phase and have a common origin. The classification of the Zn-Pb prospect in Bou-Izourane remains controversial, fluctuating between an MVT-type mineralization, similar to most Zn-Pb mineralizations in the Central High Atlas of Morocco, and a mineralization linked to the magmatic-hydrothermal activity of Tamazeght, which could provide heat and metallogenic material. Characterizing the Zn-Pb ore of Bou-Izourane is crucial for the future exploration of zinc and lead deposits in the High Atlas of Morocco and could advance the development of Zn-Pb mining in the region, from artisanal exploitation to professional mining

Multistage fluorite mineralization in the southern Black Forest, Germany: evidence from rare earth element (REE) geochemistry

Abstract. The Black Forest hosts a wide range of hydrothermal mineralization, including fluorite–barite vein deposits. In a detailed investigation of the Finstergrund and Tannenboden deposits in the Wieden mining district (southern Black Forest), the diversity, geochemical evolution and relative chronology of multistage fluorite precipitation is tracked on the basis of rare earth element (REE) geochemistry, geologic field relationships and crystal zoning. Geochemical discrimination and mathematical λ coefficients suggest a total of seven fluorite REE groups, at least three distinguishable post-Variscan fluid mobilization events and independent formation histories for the deposits despite their spatial proximity. Fluorite vein mineralization at the Finstergrund deposit evolved over three fluid generations, was derived from gneissic source aquifers and comprises five distinct fluorite REE groups: the first fluid generation is characterized by fluorite precipitation above 200 ∘C (“group III”), below 200 ∘C (“group I”) and after fractional crystallization (“group IV”); the second generation comprises remobilized fluorite (“group II”); and the third generation revealed fluorite precipitation by meteoric water mixing (“group V”). Fluorite vein formation at the Tannenboden deposit is associated with two distinct fluorite REE patterns derived from the same fluid generation: fluorite precipitation above 200 ∘C (“group VII”) and after cooling below 200 ∘C (“group VI”). Its fluid source aquifer lithology best matches migmatites contrary to previous models that suggest either gneissic or granitic aquifer rocks for fluorite vein precipitation in the Black Forest. The decoupled formation history between the deposits is tectonically controlled as suggested by a new genetic model for the Wieden mining district. The model argues for a change in the local fluid percolation network and the termination of hydrothermal activity at the Tannenboden deposit after the first fluid mobilization event. The geochemical evolution of multistage fluorite mineralization, as exemplified by the Tannenboden and Finstergrund deposits in combination with other fluorite mineralizations in the Black Forest, provides unique insights into the lithospheric origin and precipitation behaviour of fluorite by various fluid–rock interaction processes occurring in large hydrothermal systems. The local diversity of REE patterns emphasizes the need for detailed investigations of individual hydrothermal vein deposits.

The genesis of hydrothermal veins in the Aukam valley SW Namibia– A far field consequence of Pangean rifting?

High purity fluorite veins (acid grade > 97 % CaF2) are generally rare in a global context. The fluorite-(±quartz-calcite) veins in the Aukam Valley mining district in SW Namibia have not previously been studied but due to their excellent exposure they are an ideal natural laboratory to study such mineralization. These veins cross-cut Mesoproterozoic high-grade gneisses and granites (Namaqua-Natal Metamorphic Province) close to the unconformity with the overlying late-Neoproterozoic Nama Group sedimentary rock cover. Based on the regional context, their genesis has been assumed to be related to nearby fluorite-bearing pegmatites. However, the present contribution provides new microthermometry data from vein fluorite (with 25.0–25.6 wt% NaCl and Th of 270–300 °C) that indicate precipitation from a mixed fluid with two chemically contrasting end-members for the early paragenetic fluorite stage. However, it was not possible to identify the chemical composition of the endmembers. Based on the chemical composition of the fluid mixture and the regional geological context, we propose that these end-members are F-rich brines sourced from the Namaqua basement and Ca-rich limestone-derived formation fluids of the Nama Group. A fluorite-overgrowing quartz precipitation is likely the effect of post-mixing fluid cooling as the fluid inclusions hosted in quartz show lower homogenization temperatures (Th 230–260 °C) with similar salinity. Locally, late-stage calcite is recognized with fluid inclusion compositions (0.2–2.7 wt% NaCl and Th of 60–92 °C) different from those observed in the fluorite and quartz. With significantly lower homogenization temperatures, they likely represent precipitates formed during the shutdown and collapse of the hydrothermal system. The fluorite veins are hosted in post-Cambrian N-trending brittle structures that probably formed during the opening of the South Atlantic in late Mesozoic times. Interestingly, similar massive fluorite mineralization on both sides of the Atlantic Ocean is also likely associated with Pangea rifting and known from numerous mining districts operating on unconformity-related hydrothermal veins in Central and North America, northern Africa and Europe.

Evolution and origin of the Bairendaba Ag–Pb–Zn deposit in Inner Mongolia, China: Constraints from infrared micro-thermometry, mineral composition, thermodynamic calculations, and in situ Pb isotope

The Bairendaba deposit is a typical large-scale Ag–Pb–Zn vein-type deposit in the Southern Great Hinggan Range, Inner Mongolia, China. Vein-type orebodies are hosted within biotite–plagioclase gneiss and quartz diorite and controlled by EW- and NE-trending faults with extensive hydrothermal alteration. Three primary mineralization/alteration stages have been recognised as the early ore stage, forming ore-barren quartz veins with arsenopyrite and pyrite, the primary ore stage, forming Zn-rich sulphide veins and Pb–Ag-rich sulphide–sulfosalt veins and the late barren stage, characterised by plenty of calcite, muscovite and fluorite veins. Infrared micro-thermometric data and mineral geothermometer show temperatures of ∼300 °C and ∼180 °C for Zn mineralization and Pb–Ag mineralization, respectively. A combination of mineralogical observations and thermodynamic calculations show that Zn mineralization is at pH 5.1 to 7.2 and logfO2 of −39.7 to −35.3, whereas Pb–Ag mineralization is at pH 5.6 to 7.4 and logfO2 of −48.2 to −40.3. The sulfidation state is estimated to be intermediate-low sulfidation. Conductive heat loss and extensive wall rock alteration are inferred to cause the Zn deposition, whereas an influx of meteoric water and wall rock alteration primarily trigger the large-scale Ag deposition. Laser ablation–inductively coupled plasma–mass spectrometry analysis shows that chalcopyrite is anomalously enriched in Sn (>1000 ppm). Sn is hosted in chalcopyrite of Zn mineralization in solid solution, whereas it exists as a stannite group phase in chalcopyrite of Pb–Ag mineralization. The occurrence of stannite group minerals in chalcopyrite of Pb–Ag mineralization might imply the decomposition of the Sn-bearing chalcopyrite at low temperature. In situ Pb isotope ratios of galena (206Pb/204Pb = 18.374–18.399, 207Pb/204Pb = 15.581–15.601 and 208Pb/204Pb = 38.332–38.416) indicate that the ore metals could be derived from the Mesozoic magma. Trace element compositions of sulphides in the Bairendaba deposit share the same characteristics with magma-related systems but differ considerably from non-magmatic and epithermal deposits. These results, combined with geological and isotopic evidence, suggest that the Bairendaba deposit is a magma-related hydrothermal vein-type deposit, indicating further exploration prospects for Sn mineralization near and/or under the Bairendaba mining area.

Hydrothermal fluorite solubility experiments and mobility of REE in acidic to alkaline solutions from 100 to 250 °C

Fluorite is a common vein mineral in critical mineral deposits that are overprinted by hydrothermal processes. Its chemistry potentially reflects the mobilization conditions of rare earth elements (REE) in these hydrothermal fluids. However, the controls of temperature and fluid chemistry (i.e., pH and salinity) on fluorite solubility and coupled REE mobilization is still uncertain. In this study, batch-type experiments were conducted to investigate REE mobility in aqueous fluids controlled by the solubility of fluorite at temperatures between 100 and 250 °C. Natural fluorite crystals from Cooke’s Peak (New Mexico) were equilibrated with aqueous solutions of variable starting pH (2–10), salinities (0 and 15 wt.% NaCl), and initial REE concentrations (0 and 0.5 ppm). Reacted fluorite crystals display dissolution-controlled reaction textures (i.e., etch pits and dissolution channels along fluorite cleavage planes), which are most pronounced in experiments conducted in acidic fluids and at elevated temperature. Addition of NaCl considerably enhances fluorite dissolution, in both acidic and alkaline solutions, which is also reflected by the compositions of the reacted solutions displaying an increase in Ca, F, and REE concentrations. The overall fluorite solubility is controlled by the association behavior of HF0 at acidic conditions, and by the formation of Ca chloride, Ca hydroxyl, and Na fluoride complexes, which become enhanced by addition of NaCl, including in mildly acidic and alkaline solutions. Mass balance calculations were used to compare the REE stoichiometry of unreacted fluorite crystals with measured REE concentrations in the reacted solutions, which reveal several possible controls on REE mobility: i) stoichiometric release of REE upon fluorite dissolution; ii) precipitation of secondary REE-depleted fluorite; and/or iii) precipitation of secondary light REE fluorides, which were observed to form on fluorite crystals surfaces in the REE-doped experiments. Fluorite solubility constants (Ksp) were regressed with available low temperature solubility data using the equation logKsp = A + BT + C/T + Dlog(T) (T, temperature in K) valid between 25–250 °C. Fitted coefficients yield: A = 171.180, B = 0.01477, C = −7794.10, D = −64.6634. The experimental results have important implications for geochemical modeling of natural systems, where fluorine controls the mobility of REE, and can be enhanced by addition of NaCl in both acidic and alkaline solutions. Therefore, the salinity of magmatic-hydrothermal fluids plays a crucial role in mobilizing REE during the formation of hydrothermal fluorite veins.

Age, fluid inclusion, and H–O–S–Pb isotope geochemistry of the Baiyinchagan Sn–Ag–polymetallic deposit in the southern Great Xing'an Range, NE China

The superlarge Baiyinchagan Sn–Ag–polymetallic deposit of Inner Mongolia is located in the west slope of the southern Great Xing'an Range, NE China. The vein orebodies of the deposit occur in the NEE-trending fault zones. The mineralization process at the deposit can be divided into four stages: quartz–fluorite–cassiterite–sphalerite stage (stage I), quartz–fluorite–cassiterite–sulfide stage (stage II), quartz–calcite–sulfide stage (stage III), and quartz–stibnite stage (stage IV). Cassiterite U–Pb dating indicates that the Baiyinchagan deposit formed approximately 140 Ma ago, and zircon U–Pb dating for granite porphyry in the Baiyinchagan deposit yielded an age of 140.8 Ma. Two types of fluid inclusions (FIs), including liquid-rich and gas-rich inclusions, have been distinguished in quartz and fluorite veins. The homogenization temperature of the FIs in the stage I ranges from 318 °C to 351 °C with salinities of 1.2–3.8 wt% NaCl eqv. The homogenization temperature of the FIs in the stage II is 262–276 °C with salinities of 1.8–3.4 wt% NaCl eqv. The homogenization temperature of the FIs in the stage III ranges from 174 °C to 233 °C with salinities of 1.8–3.0 wt% NaCl eqv. The homogenization temperature of the FIs in the stage IV is in the range of 136–168 °C, and the salinity is 0.8 wt% to 2.4 wt% NaCl eqv. The ore-forming fluid of the Baiyinchagan deposit is characterized by medium–high temperature and low salinity. The δ18Owater and δD values of ore-forming fluid range from −13.5 ‰ to 9.5 ‰ and −119 ‰ to −84 ‰, respectively, indicating that the ore-forming fluid was dominantly derived from magmatic fluid mixed with meteoric water. The calculated δ34SH2S values range from −12.3 ‰ to −6.2 ‰, implying that the sulfur mainly came from granitic magma, but magmatic degassing occurred during mineralization. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the sulfides are in the ranges of 18.180–18.339, 15.525–15.643, and 38.005–38.477, respectively. The Pb isotopic compositions of sulfides indicate that the Pb mainly derived from granitic magma that may be formed by partial melting of orogenic materials. Fluid immiscibility and mixing were the two primary mechanisms for mineral precipitation.

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

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

Highly evolved rare-metal bearing granite overprinted by alkali metasomatism in the Arabian Shield: A case study from the Jabal Tawlah granites

Jabal Tawlah granites represent a post-collisional composite stock of late Ediacaran age, exposed in the Midyan district of northwest Arabian Shield. The stock is extended in the northwest and tapers southeastward due to structural control by a NW-SE-striking fault, and a southern master fault exhibits dextral movement by an ENE-WSW fault trend. Two main phases of magmatic activity are recognized in the Jabal Tawlah stock. The early phase (rim) includes albite granite and quartz syenite, which was intruded by a late phase of microgranite. Most of the Tawlah granites are highly mineralized, which can be attributed to the Najd fault system and/or shear zones. The mineralization is represented by small fluorite veins and disseminated minerals such as columbite-tantalite, xenotime, thorite, cassiterite, fergusonite, pyrochlore, allanite, monazite, samarskite, zinnwaldite and bastnaesite. The Tawlah granites show some degree of alteration including silicification and albitization. Textural and geochemical data indicate that the Tawlah granites developed from a magmatic source, and were then overprinted by later sodic metasomatism. Ore minerals crystallized under both magmatic and hydrothermal conditions. The parent magma of Tawlah stock was generated through partial melting of a juvenile continental crust, followed by extensive fractional crystallization. The Tawlah granites should be considered as a potential resource to warrant exploration for REEs and other rare metals.

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

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

Genesis of a Ag-Pb-Zn-F system: Insights from in situ sulfur isotope and trace elements of pyrite, and rare earth elements of fluorite in the Baiyine'lebu deposit, Inner Mongolia, China

The recently discovered Baiyine’lebu Ag-Pb-Zn-F deposit in the southern Great Xing’an Range is hosted by NNE-trending transgressional fractures within Late Permian granodiorite. The fluorite ore veins in the periphery of the mining area show close spatial association with the Ag-Pb-Zn ore bodies. A total of four mineralization stages are recognized based on the cross-cutting relationships and mineral assemblages, among which three types of pyrite are identified, including: i) coarse-grained pyrite (Py1) from stage I quartz-pyrite vein, ii) fine-grained cubic pyrite (Py2) from stage II quartz sulfide-rich vein, showing association with metallic sulfide minerals, and iii) anhedral, irregular pyrite (Py3) disseminated in Ag-bearing sulfide ore vein from stage III. The stage IV is quartz-fluorite-calcite vein with very rare distribution of pyrite. Here we investigate the texture, trace element and sulfur isotopic composition of pyrite and rare earth elements (REEs) of fluorite to gain insights into the genesis and mineralization process of the Baiyine’lebu Ag-Pb-Zn-F deposit. Systematic trace element analyses indicate that the compatible and some other elements (Co, Ni, Cr and As) were incorporated in the pyrite structure via isomorphism in all pyrite types, whereas ore metals such as Cu, Pb, Zn, and Sn entered pyrite as structurally bound elements or micro/nanosized mineral inclusions. The Ag concentrations significantly increase from Py1 to Py3 in the form of invisible nanoparticles of sulfides or micro- to nano-sized mineral inclusions during the decrease of temperature. The narrow range of sulfur isotopic compositions from −0.80 to 3.88 ‰ (average in 1.17‰) indicates a relatively homogeneous sulfur source. In combination with REE patterns of fluorite, we propose that the ore-forming fluids originated mainly from post-magmatic hydrothermal fluid mixed with meteoric water in stage IV. The hydrothermal fluorite veins in the periphery of the Baiyine’lebu deposit could be genetically linked to the Ag-Pb-Zn veins. The purple fluorites with enriched REEs and positive Eu anomaly can be used as a proxy for prospecting Ag-Pb-Zn deposits. In addition, the high Sn content of pyrite in hydrothermal Ag-Pb-Zn deposit indicates the potential of Sn mineralization in the surrounding area or deeper level of the ore field in the South Great Xing’an Range.

Geology, mineralogy, and sulfur isotopes of the Mowana copper deposit, Matsitama Schist Belt, NE Botswana

AbstractThe Mowana hydrothermal Cu deposit is located within the Matsitama–Motloutse Complex in the southwestern part of the Zimbabwe Craton in the northeastern part of Botswana. This study aims to document the characteristics of the mineralization based on geology, quartz textures, ore mineralogy, chlorite geothermometry, and sulfur isotope analyses. The deposit is hosted by the NNE‐striking and nearly vertically dipping (70–80°) Bushman Lineament, within the graphitic schist lenses in the carbonaceous and argillaceous metasedimentary rocks of the Neoarchean to Paleoproterozoic Matsitama Sedimentary Group. The hydrothermal alteration of the host rocks is characterized by silicification, chloritization, epidotization, sericitization, hematite, and calcite alteration. Based on the alteration mineral assemblage, the main mineralization stage is attributed to near neutral pH fluids at temperatures between ~200 and ~340°C. The base metal mineralization of the Mowana deposit was evolved in at least two vein types. The first mineralization type, represented by the quartz+calcite±K‐feldspar veins and breccias is characterized by the precipitation of principal chalcopyrite with pyrite, minor bornite, and trace amounts of galena. The Type 2 veins represented by the quartz+calcite±fluorite veins, host appreciable amounts of galena. The supergene mineralization widely distributed in the shallow levels of the deposit is manifested by the significant presence of chalcocite, bornite, covellite, anglesite, malachite, and hematite. The temperature obtained from the chlorite geothermometry in the Type 1 veins indicate that the mineralization associated with chlorite alteration formed at a temperature ranging from 340 to 400°C. The ore mineral assemblage: pyrite, bornite, and chalcopyrite, paired with the chlorite geothermometry data indicate that the Type 1 veins formed at an intemediate to high sulfidation state. Sulfur isotopic ratios determined on the sulfides indicate the magmatic S and/or leaching of the host metasedimentary rocks and closed system reduction of seawater sulfate as the sources of S.

Epigenetic-Hydrothermal Fluorite Veins in a Phosphorite Deposit from Balaton Highland (Pannonian Basin, Hungary): Signatures of a Regional Fluid Flow System in an Alpine Triassic Platform

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.

The source, enrichment and precipitation of ore-forming elements for porphyry Mo deposit: Evidences from melt inclusions, biotite and fluorite in Dasuji deposit, China

The Dasuji ore deposit is a large-scale porphyry Mo deposit at the northern margin of the North China Craton, China. Four stages of hydrothermal veins were recognized in the deposit, from early to late: K-feldspar–quartz veins (stage 1), quartz–molybdenite veins (stage 2), quartz–carbonate–pyrite–galena–sphalerite veins and fluorite veins (stage 3), and carbonate–quartz ± fluorite veins (stage 4). The melt inclusions in the earliest K-feldspar–quartz veins retain information about the ore-forming magma. Melt inclusions in quartz were studied in detail to investigate the magmatic evolution. In chondrite- and primitive-mantle-normalized trace element diagrams, all the inclusions have negative Ba, Sr, and Eu, and positive Pb anomalies. The inclusions have uniform (La/Sm)N ratios, and Sr concentrations decrease with decreasing Ba content, indicating the magma experienced significant fractionation, particularly of plagioclase and biotite. With increasing SiO2, Mo concentrations gradually increased, whereas Cu concentrations first increased and then decreased, suggesting that magmatic evolution was beneficial for Mo, but not Cu, enrichment. This indicates that highly fractionated magmas are conducive to the formation of porphyry Mo ore deposits rather than Cu ore deposits. The high F contents in biotite (up to 4.03 wt%) and pervasive occurrence of fluorite are indicative of a high-F magmatic–hydrothermal system. The disappearance of magnetite means the decrease of oxygen fugacity during stage 2, which promotes molybdenite precipitation. The contents of trace elements in fluorite before the stage 4 changed little, indicating that the fluid system was closed prior to this stage. The highly fractionated granitic magmatic system with high oxygen fugacity and high fluorine content potentially contain new porphyry Mo deposit.

Genesis of the vein-type Gaocheng Ag-Pb-Zn deposit in the western Guangdong Province of China and its implication for regional exploration

Abstract The Daganshan region in the western part of the Guangdong Province is an important mineralised area containing W, Sn, and Ag–Pb–Zn occurrences. Although vein-type Ag-Pb-Zn deposits are usually spatially related to W-Sn and Sn deposits, the genetic links between them are still not understood. The newly discovered Gaocheng deposit is a typical vein-type Ag-Pb-Zn deposit in this region, which is hosted predominantly by a Silurian biotite monzogranite and to a lesser extent by a Late Cretaceous quartz porphyry . Here, we present new Rb-Sr dating of sphalerite, fluid inclusion microthermometry, and H-O-S isotopic geochemistry of the deposit, and whole-rock major and trace elements geochemistry of the mineralised quartz porphyry. The aim is to better understand the genesis of the Ag-Pb-Zn mineralisation and its link with W, and Sn deposits in the region. The sphalerite Rb-Sr age is 90 ± 6 Ma, indicating that mineralisation is Late Cretaceous similar to that of the quartz porphyry. Three vein sets have been recognised around the quartz porphyry comprising early arsenopyrite–pyrite–quartz veins crossed by sulphides–quartz–Ag veins and late (non-mineralised) calcite–quartz–fluorite veins. The fluid inclusions have homogenisation temperatures of 360–300 °C with salinities of 8.2–6.4% NaCl equivalent for the first vein set, 320–240 °C with salinities of 6.5–4% NaCl equivalent for the second vein set, and 220–160 °C with a corresponding salinity of 4.2–3.4% NaCl equivalent for the late vein set. This indicates a gradual decrease of temperature and salinity of the mineralising fluids. The composition of the vapour accompanying the saline fluid in the inclusions is H 2O with minor amounts of CO2 and CH4, which indicates that the mineralising fluid included H2O–NaCl(–CO2–CH4). The fluid inclusions in the early vein set assays +6.52 - +6.13‰ δ18OH2O and –91 - –85‰ δDH2O, and the fluid inclusions in the mineralised second vein set contains +5.72 to +2.41‰, δ18OH2O and −72 to −42‰ δDH2O. These data indicate that the mineralised fluids represented by the stage I and II vein sets included magmatic fluids that were gradually contaminated by meteoric fluids. The magmatic source of the mineralising fluid is also indicated by the narrow range of δ34 S values between −2.2 and −2.4‰. The whole-rock analyses show that the Late Cretaceous quartz porphyry is a highly fractional peraluminous granite , similar to the W- and Sn-related granites in the Daganshan region. The Gaocheng vein-type Ag-Pb-Zn deposit is therefore genetically related to the Late Cretaceous quartz porphyry and shares similar geochemical characteristics at Sn-bearing granites in the Daganshan region and is also prospective for Sn mineralisation.

Genesis of hydrothermal gold mineralization in the Qianhe deposit, central China: Constraints from in situ sulphur isotope and trace elements of pyrite

The Qianhe gold deposit, located at Xiong'ershan in Eastern Qinling, with estimated gold reserves of 22 tons, hosts six orebodies within auriferous quartz veins and hydrothermally‐altered rocks along E–W trending faults. Here we present results from an integrated study involving field investigation, ore petrology, in situ sulphur isotopes, and trace elements analysis of gold‐bearing pyrite with a view to understanding the genesis of the hydrothermal gold mineralization. Three generations of pyrite are identified in the Qianhe Au deposit: Py1 is composed of coarse‐grained, euhedral cubic grains occurring at the margin of stage I quartz + pyrite vein; Py2 is occurs as porous grains coexisting with other sulphide minerals in stage II quartz + polymetallic sulphide veins; and Py3 is mainly composed of anhedral grains in stage III quartz + calcite + fluorite vein. Among the three generations, Py2 has the highest contents of Au (mean = 3.5 ppm), Ag (mean = 46.0 ppm), Zn (mean = 303 ppm), and Cu (mean = 346 ppm). The distribution and concentration of these trace elements are likely to be controlled by micro/nano‐inclusions in pyrite. The Co/Ni ratios range from 0.010 to 296, with most values lying between 0.1 and 10. The δ34S values of the various pyrite generations show a wide range between −17.9‰ and 4.5‰ with obviously higher values in Py3 (2.0‰ to 4.5‰) than those in Py1 (−16.7‰ to −13.5‰) and Py2 (−17.9‰ to −9.0‰). The negative δ34S values in Py1 and Py2 possibly resulted from sulphur isotope fractionation between sulphide and sulphate minerals. As sulphate minerals are absent in stage III, the slightly positive δ34S values in Py3 suggest a mixed source from mantle‐derived material and wall rocks of the Xiong'er Group. We correlate the genesis of gold mineralization in the Qianhe deposit with the extension and lithospheric thinning during Early Cretaceous, when ore‐bearing fluids channelled along fault zones induced hydrothermal alteration and Au mineralization.

Genesis of the volcanic-related Be-U-Mo Baiyanghe deposit, West Junggar (NW China), constrained by mineralogical, trace element and U-Pb isotope signatures of the primary U mineralisation

The Volcanic-related Be-U-Mo Baiyanghe deposit is located in the Paleozoic Xuemisitan Volcanic Belt in West Junggar (NW China). It is the largest Be deposit in Asia which is dominantly hosted in late Devonian rhyolitic tuff and in the late Carboniferous Yangzhuang granite (313 ± 2 Ma) that were emplaced after the closure of the Junggar oceanic domain. The late Devonian rhyolitic tuff is a strongly fractionated peralkaline A1-type volcanic rock with a major magmatic enrichment in Nb, Y, Th, Be, Ta and U. Highly fractionated REE patterns and significant concentrations of Pb, Nb, Zr, Y, Th and Ta in the primary U mineralisation identified these tuffs as the dominant U and probably Be source for Be-U ore genesis in West Junggar. The primary high U concentrations (6.5 < Umean < 15.0 ppm) were released through volcanic glass devitrification and mobilised by oxidising fluids for the formation of hydrothermal mineralisation. The Yangzhuang granite is to the contrary a moderately fractionated moderate- to high-K calc-alkaline A2-type granite characterised by low magmatic U and Be enrichment (Umean = 2.9 ppm; Bemean = 4.7 ppm), and thus constituted a minor U source for the mineralisation as demonstrated by U release and remobilisation from metamict U-bearing accessory minerals.In the Baiyanghe deposit, structurally-controlled primary U mineralisation was temporally constrained by an in situ U-Pb isotopic minimum crystallisation age of 240 ± 7 Ma on pitchblende. This event represents the hydrothermal stage of U mineralisation that occurred during the early Permian–middle Triassic post-accretion event in West Junggar and paragenetically postdates the Be ore stage (ca. 303–265 Ma). The hydrothermal U mineralisation is mainly characterised by Pb-Nb-Ti-Zr-Mo-rich pitchblende veins associated with calcite and quartz, which crosscut Be-stage fluorite veins. During this episode of crustal extension, the Be-U-Mo ore therefore formed in a two-stage hydrothermal model within the same mineralising event: (i) oxidising meteoric and possibly basinal waters percolated downward into the basement through structures and mixed with CO2-bearing magmatic fluids derived from early generations of mafic dykes that intruded the host rocks in the Baiyanghe area. During the circulation of these thermal solutions along faults and fractured zones, Be was leached mainly from the Devonian rhyolitic tuff during hydrothermal alteration and dominantly transported as fluoride complexes in the fluids. These low-temperature (130–150 °C) ore solutions then reacted with Ca-rich minerals of the host rocks, which resulted in a pH increase that triggered fluorite precipitation in turn promoting Be deposition as bertrandite; and (ii) in a second stage, additional oxidising surface-derived fluids including meteoric waters and possibly basinal brines infiltrated the basement. U was also leached mainly from the late Devonian rhyolitic tuff and likely transported as chlorine and/or uranyl carbonate complexes in the fluids. U precipitated as pitchblende due to fO2 decrease when these low-temperature (120–125 °C) oxidising U-bearing solutions encountered favourable reducing environments mainly represented by dolerite and diabase dykes crosscutting the host rocks and/or carbonaceous shales at the contact with the Devonian rhyolitic tuff. Pitchblende then locally experienced dyke-emplacement related post-ore hydrothermal potassic alteration characterised by abundant illite crystallisation, significant Si gain and in situ relative enrichment of Nb, Ti, Th, and Ta due to strong U and Pb depletion. The primary U mineralisation was then largely oxidised into uranophane due to supergene alteration related to further meteoric water infiltration during late Mesozoic–Cenozoic crustal extension in West Junggar.The characteristics of the volcanic-related hydrothermal Be-U mineralisation in the Baiyanghe deposit show key similarities with Streltsovka (U-Mo-F) and Spor Mountain (Be-U) world-class districts, although Baiyanghe has much smaller resources than the ones in Streltsovka.

The Velardeña Zn–(Pb–Cu) skarn-epithermal deposits, central-northern Mexico: New physical-chemical constraints on ore-forming processes

The Velardeña mining district is economically the most important of Durango state. The ore deposits occur in different skarn zones developed within the intrusive contact between Mesozoic limestones and Eocene granitic stocks and dikes. The most important ore deposits are related to the Santa María dike and Reyna de Cobre porphyritic stock (separated from each other by 10 km). They occur as irregularly shaped replacement masses developed near the intrusive contact and have a skarn paragenesis dominated by calc-silicates and sulfides. The mineral assemblages show replacement textures and are dominated by calcic clinopyroxene (Di97-53Hd42-02Jh04-01) and garnet (Ad100-57Grs43-00) in the exoskarn, with wollastonite particularly abundant in the endoskarn. Hydrous silicates are actinolite, epidote, and chlorite, whereas sulfides include pyrite, sphalerite, pyrrhotite, galena, chalcopyrite, and sulfosalts. Scheelite, hematite, quartz, and calcite are also present. According to sphalerite geobarometry, the skarns formed at hypabyssal depths (~3–4 km). They developed by a succession of replacive mineralizing events, including (a) a prograde stage at temperatures from ≥470 to 335 °C in conditions of low f (CO2), followed by (b) a retrograde stage from 335 to 220 °C. There was a general increase in f (O2), accompanying the temperature decline during the formation of the system, which accounts for a process of mixing with cooler, oxidizing, and dilute water. During the retrograde stage, wollastonite, calcic garnet and clinopyroxene formed. On the other hand, hydrous silicates, sulfides, sulfosalts, scheelite, and hematite crystallized during the retrograde stage. Skarn mineralization is crosscut by veins of calcite, fluorite, adularia, and sphalerite. The vein mineralization formed at temperatures below 200 °C. The different ore deposits of Velardeña constitute a telescoped skarn–epithermal mineral system.