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In the literature, little information is found about the crystal structure of epidote; however, there is limited knowledge about the thermoluminescent properties of this mineral. The mineral epidote has the chemical formula Ca 2 Al 2 Fe 3 + [Si 2 O 7 ][SiO 4 ]O(OH) and exhibits a dark green coloration. A sample of the mineral epidote, collected in Peru, was investigated. As these are naturally occurring samples, the crystallography of each mineral may vary due to damage caused by natural radiation and the climatic conditions of pressure and temperature to which this mineral has been exposed. Therefore, to determine if the thermoluminescent behavior of different epidote samples would be similar, a mineral collected in Brazil was investigated. The samples were pulverized, and grain sizes ranging from 80 to 180 μ m in dimension were utilized. The experiments were conducted employing different thermal treatments and gamma radiation doses aiming identifying the best thermal treatment that allows the obtention of an intense and distinct TL signal. Preliminary TL results demonstrated a clear response of samples irradiated with high doses, exceeding 10 kGy, and thermally treated at 900 °C for 1 h, indicating its potential as a dosimeter for industrial applications. The results of the Thermoluminescence (TL) analysis conducted on the epidote sample from Brazil revealed similarities when compared to the TL analyses of the epidote sample from Peru. [ABSTRACT FROM AUTHOR]

Epidote group minerals, including allanite, clinozoisite and epidote are common in a range of metamorphic, igneous and hydrothermal systems, and are stable across a wide range of pressure–temperature (P–T) conditions. These minerals can incorporate substantial amounts of rare earth elements (REEs) during their crystallisation, making them potential candidates for Lu–Hf geochronology to provide age constraints on various geological processes. Here we report on a first exploration into the feasibility of in situ Lu–Hf geochronology for epidote group minerals from various geological settings and compare the results with age constraints from other geochronometers. Magmatic allanite samples from pegmatites and monzogranites in the Greenland anorthosite complex, Coompana Province and Qingling Orogen provided dates consistent with magmatic events spanning from c. 2660 to 1171 Ma. In the Qingling pegmatites, a younger phase of hydrothermal allanite was dated at c. 215 Ma, consistent with the timing of regional REE mineralisation. Allanite from the Yambah Shear Zone, Strangways Metamorphic Complex, yielded Lu–Hf age of c. 430 Ma. It predates the garnet and apatite growth at c. 380 Ma, suggesting the Lu–Hf system can be preserved in allanite during prograde amphibolite-facies metamorphism. Additionally, Lu–Hf dates for hydrothermal clinozoisite and epidote are consistent with the timing of hydrothermal alteration and mineralisation in a range of settings, demonstrating the utility of the technique for mineral exploration. Despite the current lack of matrix-matched reference materials, the successful application of laser ablation Lu–Hf geochronology to epidote group minerals offers valuable geochronological insights into various geological processes that can be difficult to access through other geochronometers. [ABSTRACT FROM AUTHOR]

We use U–Pb dating of allanite and REE-rich epidote in three polymetamorphosed units from the Eastern Alps to constrain the timing of prograde metamorphism. All three units (Ennstal, Wölz and Rappold Complex) record several metamorphic cycles (Variscan, Permian and Eoalpine) and presently define an Eoalpine (Cretaceous) metamorphic field gradient from lower greenschist to amphibolite facies. For U–Pb data, a method is introduced to test the magnitude of 230Th disequilibrium and potentially approximate the Th/U ratio of the reservoir out of which allanite and REE-rich epidote grew. We also show that the modelled stability of epidote-group minerals in the REE-free MnNCKFMASH and MnNCKFMASHTO systems and REE-bearing systems is nearly identical. By combining the stability fields of (clino-)zoisite and epidote modelled in REE-free systems with known geothermal gradients for the region, REE-rich epidote growth is constrained to 200–450 °C and 0.2–0.8 GPa during prograde metamorphism. In the Rappold Complex, allanite cores yield a Variscan age of ca. 327 Ma. In the Ennstal and Wölz Complex, allanite growth during the Permian event occurred at ca. 279–286 Ma. Importantly, recrystallized allanite laths and REE-rich epidote overgrowths in samples from all three units yield prograde Eoalpine ages of ca. 100 Ma, even though these units subsequently reached different peak conditions, most likely at different times. This suggests that all units were buried roughly at the same time during the onset of Eoalpine continental subduction. This interpretation leaves room for the model proposing that diachronous peak metamorphic conditions reported for the field gradient may be related to the inertia of thermal equilibration rather than tectonic processes. [ABSTRACT FROM AUTHOR]

Tectonic slices of greenschist – epidote blueschist – epidote amphibole schist – garnet epidote amphibole schist are exposed in the northern part of the NOC. Metamorphic P-T conditions and P-T paths of the garnet epidote amphibole schist and epidote blueschist were determined with the help of pseudosection calculations in the MnNCKFMASHTO system using the software Perple_X. The garnet epidote amphibole schist records a pre-peak metamorphic stage at ~12 kbar and ~360°C in the lawsonite blueschist facies field. Lawsonite and glaucophane are not preserved in the rock and are attributed to progressive metamorphic reactions during prograde metamorphism. The peak metamorphic stage is constrained at ~14 kbar and ~570°C in the hornblende eclogite facies field. Post-peak metamorphism shows slight cooling and decompression from ~550°C and ~13 kbar, possibly down to ~350°C and ~7 kbar in the greenschist facies field. These three metamorphic stages reveal a clockwise metamorphic P-T path of evolution for the garnet epidote amphibole schist. The geotherm at metamorphic peak P-T condition is ~12.5°C/km, which is hotter by ~350°C compared to thermal models of mature subduction zones but shows good agreement with models of warm subduction zones. Therefore, the low geothermal gradient of ~8°C/km during the prograde metamorphism possibly reflects the subduction of cold Neo-Tethyan ocean crust when the temperature conditions of the subduction zone were still warm. The epidote blueschist shows peak metamorphism at ~10 kbar and 380°C with a clockwise P-T path. It indicates metamorphism at a more mature stage of subduction. Buoyancy-driven exhumation along the subduction channel due to the serpentinization of the upper mantle wedge played a vital role in the detachment and exhumation of the tectonic slivers of metamorphic rocks from different depth sections in the northern margin of the NOC. [ABSTRACT FROM AUTHOR]

Titanites can be excellent markers of element transfer in medium-temperature retrograde metamorphism. Euhedral titanites from several alpine fissures from Mont Blanc, particularly those of Périades and Courtes, crystallised at the end of the main quartz stage and are synchronous with the formation of green biotites and albite before chlorite formation. Micro-XRF, SEM, electron probe, and LA-ICP-MS analyses show that these titanites have a wide range of Al2O3 content from 1 to 8%, are dominated by -OH versus F, and have a wide range of Nb (up to 4500 ppm), Y (up to 3000 ppm), Zr (up to 1800 ppm), and Sn (up to 1400 ppm) concentrations. The allanite from the granite, partly destabilised into epidote, is the most likely source of Nb, Y, Zr, Sn, and REE. Titanites are enriched in HREE and show variations in LREE depending on the studied sites. Like quartz, they formed at around 400 ± 20 °C, which is compatible with the formation of green biotites after the destabilisation of granite Fe-Mg silicates. This early stage of fluid circulation, synchronous with the Mont Blanc massif uplift, is therefore marked by the titanite formation at the transition between the biotite and chlorite stability fields. [ABSTRACT FROM AUTHOR]

The Koyna-Warna Seismogenic Region of western India has been recognized as one of the hotspots for reservoir-triggered seismicity (RTS) since 1967. The current study investigates the fluid's interaction with the severely fractured granitoid basement of this area and its potential contribution to the recurring seismicity. The presence of several secondary minerals, such as chlorite, epidote, calcite, illite, etc., along the pre-existing faults and fractures, is revealed by detailed petrologic investigation at mesoscopic and microscopic scales along with XRD analysis. This indicates the fluid-rock interaction along these mechanically weak planes and subsequent propylitic grade of hydrothermal alteration under acidic to neutral conditions (pH 5.5–7) and the temperature of above 200–220 °C up to about 350 °C. Additionally, the transformation of biotite into chlorite due to fluid interaction has been inferred from the microscopic appearance of biotitic remnant within neoformed chlorite which is further supported by the mass loss of K2O and concurrent gain of MgO and FeO, demonstrating the replacement of potassium (K) interlayer sheet by brucite-like [Mg (OH)2] layer during biotite chloritization. However, this released K2O further assists in the formation of illite resulting in the mass gain of K2O at a few certain depths, whereas the dissolution of plagioclase justifies the formation of albite and calcite as evidenced by the gain of Na2O and CaO. The present study also highlights that the recurring nature of the seismicity in this area may be related to clay mineralization along the faults and fractures due to fluid-rock interaction, such as chlorite, illite, etc., in addition to the existing fault geometry and stress build-up due to reservoir impoundment. At increasing stress condition, the anisotropic and weakly bonded, layered crystal structure of chlorite forming ripplocations may develop kink bands and increases the yield strength proportionally with rising pressure up to dehydration temperature. Such visco-elastic behaviour of chlorite may promote aseismic creep in the faults. On the other hand, epidote noticed at certain depths has a contrasting behaviour; it tends to wear at the micron or submicron‐scale asperity contacts and produce fine particles which generate unstable sliding. However, the relatively higher abundance of chlorite in the faults and fractures disrupts the epidote‐epidote contact asperities and prevents such wearing of epidote grains into fine particles. Thus, biotite chloritization in conjunction with relatively less production of epidote along pre-existing faults and fractures helps to release the accumulated stress through a series of small-scale earthquakes and results in the steady fault creep observed in this region during the past 50 years. In this context, fluid-rock interaction along the pre-existing faults and fractures at shallow depth has acted as a blessing for the Koyna-Warna Seismogenic region shielding it from relatively large magnitude earthquakes – a boon for the region. [ABSTRACT FROM AUTHOR]

A new occurrence of epidote-(Sr) CaSr(Al2Fe3+)[Si2O7][SiO4]O(OH), Sr-REE-rich epidote and Sr-rich allanite-(Ce) is located in Lower Cretaceous, Sr-rich hydrothermally altered leucocratic dykes penetrating alkaline igneous rocks (teschenites) near the Nový Jičín town (the Silesian Unit, Outer Western Carpathians). The dykes contain phenocrysts of pyroxene, amphibole, biotite, fluorapatite and dominant felsic groundmass consisting mostly of alkali feldspars and zeolites (analcime, natrolite and thomsonite-Ca). Accessory minerals include Ti-rich magnetite, prehnite, chamosite, pyrite, calcite, (OH, F)-rich grossular, epidote-group minerals, HFSE-, REE-rich minerals, Sr-rich baryte and slawsonite. The Sr-rich epidote forms columnar crystals or irregular aggregates, which are mostly spatially related to chamosite-titanite pseudomorphs; it contains 0.15–0.81 apfu Sr, ≤ 0.55 apfu REE; Fe3+/(Fe3+ + Al) = 0.16–0.48. The Sr2+ substitutes Ca2+ in the A2 site by a coupled substitution involving other A2 (REE3+, Th4+) or M (Al3+, Fe3+, Fe2+) cations. The Sr-rich epidote crystallized from hydrothermal solutions, probably at temperatures between ~ 250–430 °C, during cooling of the host rock. The dykes show higher Sr contents (5680–7830 ppm) and 87Sr/86Sri(120 Ma) ratios (~ 0.7046–0.7047) compared to host mesocratic teschenites (1310–1470 ppm Sr and ~ 0.7038–0.7045, respectively). The Sr isotopes indicate origin of most Sr from primary magmatic plagioclase in parent teschenite. Nevertheless, there also participated external fluids, derived from the Lower Cretaceous seawater or diagenetic waters related to associated siliciclastic sediments with 87Sr/86Sri(120 Ma) = ~ 0.7073–0.7083. These more radiogenic sources contributed at least 6–21% of the bulk Sr budget of the studied Sr-rich epidote-bearing leucocratic dykes. [ABSTRACT FROM AUTHOR]

We investigated the mineral assemblage, mineral and bulk-rock chemistry, and zircon U–Pb age of a manganiferous quartzite layer in the Lanterman Range, northern Victoria Land, Antarctica. The mineral assemblage consists primarily of phengite and quartz, along with spessartine-rich garnet, Mn 3+ and rare earth element–yttrium (REY)-zoned epidote-group minerals, and titanohematite. Mineral inclusions such as tephroite, rutile and pyrophanite are hosted in porphyroblasts of the latter three minerals and suggest prograde blueschist-facies to low- T eclogite-facies metamorphism (M 1). Epidote-group minerals commonly exhibit multiple growth zones of piemontite and/or epidote (M 1), REY-rich piemontite (M 2), REY-rich epidote (M 3), and epidote (M 4) from core to rim. Pseudobinary f O 2 – X diagrams at constant P – T support the stability of an epidote-group mineral-bearing assemblage under highly oxidized conditions during prograde M 2 to peak M 3 metamorphism. In marked contrast, tephroite-bearing assemblages (M 1) are limited to relatively reduced environments and Mn-rich, silica-deficient bulk-rock compositions. Mn nodules have such characteristics, and the contribution of this hydrogenous component is inferred from bulk-rock chemical features such as a strong positive Ce anomaly. The major-element composition of the manganiferous quartzite suggests a protolith primarily consisting of a mixture of chert and pelagic clay. The presence of rare detrital zircons supports terrigenous input from a craton and constrains the maximum time of deposition to be ca. 546 Ma. The lack of arc-derived detrital zircons in the quartzite and the predominance of siliciclastic metasedimentary rocks among the surrounding rocks suggest that the deep-sea protolith was most likely deposited in an arc/back-arc setting at a continental margin. High- P metamorphism associated with terrane accretion during the Ross orogeny took place in the middle Cambrian (ca. 506 Ma), broadly coeval with the metamorphic peak recorded in the associated high- P rocks such as mafic eclogites. Finally, it is noteworthy that the high- P manganiferous quartzite was amenable to exhumation because the paleo-position of the protolith was likely distal from the leading edge of the downgoing slab. [ABSTRACT FROM AUTHOR]

The study of terrigenous rocks of the Shatak Complex, which includes rocks of the Kuz"elga and Karan subformations (Mashak Formation, Upper Riphean) revealed numerous rare-earth minerals: allanite-(Ce), monazite-(Se), monazite-(Nd), xenotime-(Y), REE-bearing epidote, and unidentified compounds. It has been established that the detrital zircon plays the role of a selective concentrator of Y, HREE, and Th during the terrigenous rock metamorphism. The comparative analysis showed that rare-earth minerals, such as monazite-(Ce) and xenotime-(Y), in the Shatak Complex differ significantly (in terms of chemical composition) from counterparts in other complexes located on the western slope of the Southern Urals by the presence of Gd in monazite, and LREE (Ce, Nd, Sm) in xenotime. In the case of similar thermobaric parameters of rock metamorphism characterizing the alteration degree of lithostructural complexes in the Southern Urals, the chemistry of mineral formation environment is among the main factors governing the compositional features of rare-earth minerals. [ABSTRACT FROM AUTHOR]

In natural lower crustal rocks, we observe that plagioclase breakdown is often partial as evidenced by the presence of epidote‐group minerals and the absence of the remaining reaction products for example, kyanite and quartz. Due to the lack of experimental data on epidote deformation, it is unclear if this partial reaction would affect the strength of the plagioclase‐rich lower continental crust. We experimentally investigated the relative strength of pure epidote and pure plagioclase aggregates at a confining pressure of 1 GPa, two different temperatures (550 and 650°C) and two different strain rates (5 × 10−5 and 5 × 10−6 s−1) using a Griggs apparatus. Furthermore, we investigated potential strength differences due to differences in grain size by deforming aggregates with grain‐size ranges of either ≈90–135 μm or <25 μm. Under identical conditions, epidote aggregates are either as strong as their plagioclase counterparts or moderately stronger, suggesting that the partial replacement of plagioclase by epidote‐group minerals would not have a permanent weakening effect on the strength of the lower continental crust. Plain Language Summary: At depths of the lower continental crust, fluids trigger the breakdown of plagioclase, resulting in the growth of epidote‐group minerals, kyanite, quartz, and albite or jadeite. This reaction has been experimentally shown to significantly weaken the rock. In nature, lower crustal rocks regularly exhibit the growth of epidote‐group minerals only, indicating that reaction is partial. By quantifying the relative strength between pure epidote and pure plagioclase aggregates, we aim to investigate the potential impact of partial plagioclase breakdown on the strength of the lower continental crust. Using a Griggs‐deformation apparatus, we deformed pure epidote and plagioclase aggregates at a confining pressure of 1 GPa, two different temperatures (550 and 650°C) and two different strain rates (5 × 10−5 and 5 × 10−6 s−1). To investigate the influence of grain size on strength, we deformed aggregates with two different grain sizes, that is, with 90–135 μm or <25 μm. Under identical conditions, epidote aggregates are either as strong as their plagioclase counterparts or moderately stronger. We assume that partial reaction has no long‐lasting effect on the strength of the lower continental crust. Key Points: At identical experimental conditions, epidote aggregates are at least as strong as plagioclase aggregates or show a higher strengthPartial reaction in the plagioclase‐rich lower crust has little to no influence on its long‐term strength [ABSTRACT FROM AUTHOR]

A new member of the epidote supergroup, ferriandrosite-(Ce), ideally MnCeFe3+AlMn2+(Si2O7)(SiO4)O(OH), was found at the Július manganese ore occurrence near Betliar, Rožňava Co., Košice Region, Slovakia. It occurs as subhedral grains and polycrystalline aggregates, up to 0.3 mm in size, enclosed in pyroxmangite. Other associated minerals are spessartine, rhodochrosite, quartz, baryte and pyrosmalite-(Mn). Ferriandrosite-(Ce) is dark brown, with a light brown streak and vitreous lustre. The Mohs hardness is ~6½ to 7 and tenacity is brittle with no observable cleavage or fracture. The calculated density is 4.321 g⋅cm–3. Ferriandrosite-(Ce) is optically biaxial (+), with weak pleochroism, high surface relief and the mean calculated refractive index is 1.832. The empirical structural formula of ferriandrosite-(Ce), based on 13 anions per formula unit, is A1(Mn2+0.63Ca0.35Ce0.02)Σ1.00A2(Ce0.53La0.27Nd0.14Pr0.05REE*0.01)Σ1.00M1(Fe3+0.41Al0.12V3+0.01Mg0.40Ti0.05)Σ0.99M2Al1.00M3(Mn2+0.75Fe2+0.22Mg0.03)Σ1.00T1–3Si3.00O11O4(O0.67F0.33)(OH), where REE* are minor rare earth elements. Ferriandrosite-(Ce) is monoclinic, space group P 21/ m , a = 8.8483(4) Å, b = 5.7307(3) Å c = 10.0314(5) Å, β = 113.3659(15)°, V = 466.95(4) Å3 and Z = 2. The crystal structure of ferriandrosite-(Ce) was refined to a final R 1 = 0.0210 for 1910 reflections with F o > 4σ(F o) and 127 refined parameters. Structural features of ferriandrosite-(Ce) are discussed and compared with other members of the androsite-series. [ABSTRACT FROM AUTHOR]

The skarn alteration is poorly preserved at the Elatsite, restricted to the hornfelses from the East, Southeast and Southern part of the deposit. The rocks are defined as exoskarns, with a mineral composition including garnets, epidote, pyroxene, amphiboles, carbonates, prehnite, quartz, sulphides. The newly formed minerals occur in poorly preserved layers. The garnet grains are subhedral with inclusions of epidote and quartz, while some of them are corrode with carbonate and zeolites formed in the fractures. The garnets are grossular-andradite type, with higher values for HREE over LREE, and low values for Rb, Sr, Ba, Pb and U. The skarn formation is related with the intrusion of the magma which causes the heating of the metamorphic rocks (rich in carbonate material -- chlorite-sericite-carbonite, sericite-carbonate schists, etc.) from the low-grade metamorphic rocks. The Fe+3--Al+3 exchanges in the cores of the garnets indicate their formation from fluids with high oxygen fugacity. [ABSTRACT FROM AUTHOR]

Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks, pervasively altered by a propylitic mineralogical assemblage with epidote, chlorite, and quartz with minor titanite, illite and prehnite. These propylitically altered rocks host significant gold mineralization in veins, deeply exploited in the last decades. Porphyry Au-Cu deposits also occur in the area. This work focuses on the study of this propylitic alteration to assess the genetic conditions and the relation with the distance from the porphyry system, through the chemical composition of the secondary minerals (particularly trace elements in epidote and chlorite) and fluid inclusion data. The aim is to improve knowledge of the trace element geochemistry of secondary minerals in propylitic alteration and their relationship to the causative porphyry systems. The results of this work indicate that alteration affecting the rocks of the Pallatanga Fm. can be related to the propylitic hydrothermal alteration halo of porphyry copper deposits. Fluid inclusion investigation in quartz veins associated with epidote and chlorite evidenced at least two pulses of hydrothermal fluids characterized by temperature around 345°C for the first one and around 305°C for the second one. The salinity of the fluids is always low (around 1.5 wt% NaClequiv.) suggesting a dominantly meteoric component. Evidence of boiling processes have not been observed. We hypothesize that the hydrothermally altered “green rocks” of the Ponce Enriquez Mining District could be envisaged as the propylitic halo of the Miocene hornblende-bearing Au-Cu porphyry deposits of Gaby-Papa Grande, and discuss the epidote and chlorite trace element composition in this scenario. The results help improving the general knowledge of the propylitically altered rocks in southern Ecuador and add new data for the use of trace element chemistry of epidote and chlorite in mineral exploration elsewhere.

Metamorphic transformations in felsic and mafic rocks in a zone of intense tectonic movements were compared. The object of study is the exhumed part of damage zone of Primorsky fault—main collision suture, which connects the Siberian Craton and the Olkhon Terrane. The studied area is located near the Khorga River. Collected metamorphic rock samples are represented by both "felsic" (plagiogranite-gneiss) and more "mafic" (amphibole–biotite plagiogneiss) rocks. The samples present two different parent rocks contacting each other but differ in chemical composition. The formation of identical metamorphic minerals of the garnet and epidote groups, associated with the processes of high-pressure regional metamorphism and, possibly, later collisional events, is detected in both rock types. The study of the chemical composition of rock-forming minerals provided estimates of the P–T conditions of metamorphism of these rocks by the method of multimineral thermobarometry. It was established that conditions of early metamorphism retain in amphibole-biotite plagiogneiss. Early metamorphism is characterized by high-pressure amphibolite facies of medium temperature next to eclogite facies. The parameters of later metamorphism are recorded in plagiogranite-gneiss, which occurred at higher pressure, but at a lower temperature, within the paragonite–kyanite–zoisite subfacies of the eclogitic facies, bordering on the greenschist facies. Associations of early metamorphism are poorly preserved in plagiogneiss. [ABSTRACT FROM AUTHOR]

Greisenization is typically linked with highly fractionated granites and is often associated with hydrothermal vein systems. Late to postmagmatic metasomatic processes involve the enrichment of volatile components such as boron and halogens as well as several metallic elements. The purpose of this study is to reveal the main metasomatic effects and paragenetic sequences of the related mineralizations in Highiş granitoids, Romania. In a natural outcrop, more than 30 samples were collected from granitoids, felsic veins, and country rocks. We carried out a detailed mineralogical and petrological characterization of carefully selected samples using X-ray powder diffractometry, electron microprobe analysis, and microscopic methods together with K–Ar ages of whole rocks and K-bearing minerals. Several characteristic features of albitization, sericitization, tourmalinization, epidotization, and hematitization were recognized in the studied samples. Crystallization of quartz, K-feldspar, and magnetite represents the first stage during the magmatic-hydrothermal transition. The mineral assemblage of albite, sericite, schorl, and quartz originates from the early and main stages of greisenization. While the subsequent mineral assemblages, which predominantly include dravite, specular hematite, and epidote, are closely related to the late vein-depositing stage. We propose that the study area could belong to a boron-rich open greisen system in the apical portion of Guadalupian A-type granite. Based on a new hypothesis, the previously published Permian crystallization ages (between ~272 Ma and ~259 Ma) could be homogenized and/or partially rejuvenated during the hydrothermal mineralization processes due to uraniferous vein minerals. Additionally, the Highiș granite-related system suffered a Cretaceous thermal overprint (between ~100 Ma and ~96 Ma). The results may help to understand the evolution of highly evolved granite intrusions worldwide and improve our knowledge of the effect of hydrothermal mineralization processes on the emplacement ages. [ABSTRACT FROM AUTHOR]

A new natural epidote reference material, PSV, sourced from Alchuri village, Shigar valley, Haramosh mountains, Gilgit, Pakistan, is characterized in this study for O and Sr isotope composition analysis by micro-beam analytical techniques. Comprehensive studies including thermal ionization mass spectrometry (TIMS), solution nebulization multi-collector inductively coupled plasma-mass spectrometry (SN-MC-ICP-MS), laser ablation multi-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS), secondary ion mass spectrometry (SIMS), and laser fluorination have been performed on PSV epidote to assess the homogeneity of O and Sr isotope compositions and provide recommended values for δ18O and the 87Sr/86Sr ratio. The mean δ18O value measured by the laser fluorination method is 12.58 ± 0.07‰ (2s, n = 12), recommended as the reference value for micro-beam analysis. Seventy SIMS analyses were performed on PSV epidote, resulting in a mean δ18O value of 19.67 ± 0.03‰ (2s, n = 70) obtained without external calibration utilizing matrix-matched reference materials. This finding emphasizes the necessity of employing external calibration with matrix-matched reference materials for accurate determination of oxygen isotope ratios in epidote utilizing the SIMS method. The mean 87Sr/86Sr ratio derived by TIMS and SN-MC-ICP-MS is 0.707672 ± 0.000013 (2s, n = 2) and 0.707679 ± 0.000007 (2s, n = 10), respectively. The in situ Sr isotopic analysis utilizing LA-MC-ICP-MS revealed homogeneous Sr isotopic compositions at a micro-scale of 40 to 85 μm. The weighted mean 87Sr/86Sr ratio was determined to be 0.70768 ± 0.00001 (2s, n = 336; MSWD = 2.0), which is in agreement with the solution value within the analytical uncertainty. In conclusion, despite the chemical composition variability, the PSV epidote exhibits reproducible O and Sr isotope compositions, making it a suitable reference material for in situ O–Sr isotope ratio analysis utilizing micro-beam methods. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effect of the Hilla River sediments on the heterogeneity of the distribution of heavy sand minerals for the fine and very fine sand classes as well as for the surface and subsurface layers. The results showed that the heavy sand minerals that were determined according to the specific gravity of each mineral and the specific gravity of the particles of minerals identified in the soils under study ranged between (2.5-4.5) and were divided into four groups in terms of the specific gravity. The first group included each of the minerals (Mica and Chlorite) of low specific gravity, while the second group contains (Pyroxene, Amphibole, Epidote Group). The third group includes minerals (Tourmaline and Garnet, Staurolite and Kyanite) and the two groups are classified as minerals of medium-specific gravity; in turn, the fourth group contains minerals of high specific gravity, namely (Zircon, Rutile and Opaques). As a result, the most important factors affecting the sedimentation, sorting and sedimentation processes are the conveyor's speed, load capacity, the size of the separation particles and their specific gravity. The complete mismatch of the horizontal distribution of the minerals of one group is due to the varying ranges of the specific gravity of the minerals within the general range of specific gravity. [ABSTRACT FROM AUTHOR]

It is a general tendency that epidote, which is a typical greenschist facies mineral, is scarce in the lower oceanic crust, in spite of the widespread occurrence of the other minerals indicative of similar temperature conditions such as chlorite, actinolite, prehnite and serpentine. To find the cause of this, we carried out petrological analyses of lower crustal rocks of the Oman ophiolite sampled by the Oman Drilling Project of the International Continental Scientific Drilling Program (ICDP). Petrographic observations revealed the tendency, as expected, that the amount of epidote formed by static alteration of plagioclase decreases with depth. Because mineral assemblages indicative of a wide range of temperature conditions from amphibolite to subgreenschist facies occur throughout the cores without systematic variations of abundance, the decrease of epidote amount cannot be explained by the difference of temperature condition of alteration. Petrographic observations also revealed that epidote is absent or rare in rocks containing serpentinized olivine in contrast to prehnite showing a close association with serpentinization of olivine. In an exceptional sample containing both epidote and serpentinized olivine, epidote occurs with chlorite that cuts or replaces plagioclase, mantles adjacent olivine and is connected with chlorite + lizardite veins cutting mesh‐forming serpentine veins. The distribution and mode of occurrence of epidote suggest decoupling of its formation with the main stage of serpentinization. Serpentine veins cutting olivine to form mesh texture are typically lizardite with magnetite ribbons at vein centres and have compositions of lizardite–cronstedtite solid solution at vein margins or in magnetite‐free veins, suggesting a chemical condition with low silica and low oxygen potentials at an early stage of serpentinization. Thermodynamic modelling for olivine and plagioclase alteration at greenschist facies conditions indicates that silica potential for plagioclase alteration to form prehnite + chlorite and epidote + chlorite could be higher than for olivine serpentinization. On the other hand, oxygen potential for the prehnite + chlorite formation is lower than for the epidote + chlorite formation and is comparable with that for olivine serpentinization. From the observations and analyses, it is concluded that epidote formation is inhibited by olivine serpentinization, which maintains a reducing condition for alteration in the lower oceanic crust. [ABSTRACT FROM AUTHOR]

In the Republic of North Macedonia, the northern marginal part of the Pelagonian Unit comprises several isolated slivers of low-grade blueschist-facies rocks. These rocks were metamorphosed at conditions of the epidote-blueschist facies with rare transitions to the lawsonite-epidote blueschist facies. If present, lawsonite occurs as relic inclusions in albite, suggesting a local metasomatic enrichment of Na. No aragonite or fibrous calcite was detected, suggesting that the rocks were equilibrated at pressures below the aragonite-calcite boundary. When present, calcite + quartz coexist with glaucophane, epidote, and titanite suggesting the presence of a metamorphic H2O-rich fluid phase with very low X CO2 values (< 0.002). Most samples contain chlorite and only some have garnet, which is nearly free of Mg, but contains an andradite component. Albite only occurs in garnet-free rocks. A core-to-rim decrease of Fe3+/(Fe3++Al3++Cr + Mn3+) in epidote, VIFe3+/VI(Fe3++Al) in blue Na-rich amphibole, and Fe3+/(Fe2++Fe3+) in garnet grains suggest a decrease of ƒO2 during metamorphism. The general absence of magnetite and the presence of very small amounts of hematite in some samples suggest that the hematite–magnetite buffer curve was probably not crossed. It is thought that the investigated blueschist-facies rocks were part of the once highly oxidized sedimentary cover of the subducting oceanic plate. The underlying basaltic crust and oceanic mantle, however, were probably relatively reduced. Aqueous fluids which left this part of the lithosphere during subduction (dehydration) partially reduced the overlying oxidized metasediments. Concerning metamorphic P – T conditions, a pressure range of 0.7–0.9 GPa is defined by the presence of glaucophane + epidote + quartz at the lower boundary and the absence of aragonite at the higher boundary. The temperature range of 320–420°C is defined by the absence of Fe-Mg-pumpellyite at the lower side and the presence of lawsonite + albite at the higher side. These conditions can be narrowed down by using calculated equilibrium mineral assemblage diagrams (pseudosections) for three different bulk-rock compositions, resulting in P  = 0.74–0.85 GPa and T  = 340–370°C. It must, however, be emphasized that many phases (garnet, glaucophane, epidote, and phengite) show significant chemical zonation, which makes the use of pseudosections problematic. [ABSTRACT FROM AUTHOR]

Diopside-rich rocks (diopsidites) are interlaminated with nephrite in boulders derived from metasomatic contacts developed between Pounamu Ultramafic meta-serpentinite and country rock Alpine Schist, Westland, New Zealand. Petrographic textures indicate that parental tremolite rock, formed by metasomatic diffusion during metamorphism, has been intensely deformed and recrystallised to alternating semi-nephrite and nephrite domains during development of a secondary crenulation cleavage. Nephrites are subsequently sequentially overprinted by porphyroblastic tremolite, diopside, then further tremolite. Crystallisation is controlled by fluctuating activities of SiO2, CaO and H2O in associated fluids. Pervasive dissolution of nephritic tremolite and crystallisation of diopside generates diopsidites containing accessory epidote, uvarovite and zincian chromite formed in equilibrium with H2O-rich fluids. Diopsidites are in turn overgrown by coarse grained (in places > 50 cm long) diopside crystals, interpreted to have infilled an extension fracture that formed during ongoing uplift of the Southern Alps. [ABSTRACT FROM AUTHOR]

To provide a tool for fast estimation of the Fe 3+ content in Ca 2 (Al, Fe 3+)3 Si 3 O 12 (OH) epidote grains, including in thin sections and crude-rock samples, we applied Raman spectroscopy to 33 areas from 15 natural samples with Fe 3+ ranging from 0.22 to 1.13 atoms per formula unit (apfu), the chemistry of which was independently determined by wavelength-dispersive electron microprobe analysis (WD-EPMA). The Raman spectra were collected from the very areas subjected to WD-EPMA. We have analysed both the OH-stretching region (3215–3615 cm -1) and the spectral range generated by the framework vibrations (15–1215 cm -1). Similarly to the IR spectra, the Raman peaks in the OH-stretching region shift toward higher wavenumbers with increasing Fe. However, the quantification of Fe 3+ based on OH-stretching Raman peaks can be hindered by the multicomponent overlapping and significant intensity variations with the crystal orientation. Among the Raman signals generated by framework vibrations, the position of four peaks (near 250, 570, 600, and 1090 cm -1) exhibit a steady linear regression with the increase in Fe content (in apfu). However, the peak near 250 cm -1 attributed to MO 6 vibrations also depends on the crystal orientation and therefore is not always well resolved, which worsens the accuracy in Fe-content determination based on its position. The peaks near 570, 600, and 1090 cm -1 arise from Si 2 O 7 vibrational modes, and although their intensities also vary with the crystal orientation, all three signals are well resolved in a random orientation. However, among the three Si 2 O 7 -related signals, the 570 cm -1 peak is the sharpest (peak width <10 cm -1) and is easily recognized as a separate peak. Hence, we propose to use the position of this peak as a highly reliable parameter to estimate the Fe content, via the linear trend given as ω570=577.1(3)-12.7(4)x , where ω is the wavenumber (cm -1) and x is Fe content (apfu), with accuracy ± 0.04 Fe 3+ apfu. The peaks near 600 and 1090 cm -1 may be complementarily used for the Fe estimate, based on the following relations: ω600=611.6(2)-13.8(4)x and ω1090=1098.8(3)-13.5(5)x. Analyses of the effect of Sr as a substitution for Ca and Cr at the octahedral sites indicate that contents of Sr <0.12 apfu do not interfere with the quantification of Fe via the ω570 (x) relation, whereas Cr >0.16 apfu leads to overestimation of Fe; Cr presence can be recognized however by the broadening of the peaks near 95 and 250 cm -1. [ABSTRACT FROM AUTHOR]

The formation of titanite coronae after rutile is common in retrograde high‐ to ultrahigh‐pressure meta‐mafic rocks, which provides a good opportunity to address the geochemical behavior of HFSE in crustal environments. In the Sumdo eclogite, titanite occurs either as a corona around rutile grains or as semi‐continuous veins cross‐cutting the major foliation, whereas rutile grains occur either as inclusions in garnet or omphacite or as a relict core surrounded by titanite. Textural relationships and trace elements characteristics of rutile and titanite with different occurrences indicate that both minerals preferentially incorporate Nb and Hf over Ta and Zr in aqueous fluid. Moreover, the breakdown of omphacite and epidote could release substantial amounts of aqueous fluids enriched in Ca, Si, Fe and REE, which would react with rutile to form titanite coronae and veins. During this process, water‐insoluble elements, like HFSE and HREE, behave like mobile elements, but they do not migrate substantially out of the system, instead, tending to react in situ. This suggests that the aqueous fluids released during the retrograde metamorphic reactions in mafic rocks could not substantially transfer fluid‐immobile elements into the overlying mantle wedge in subduction environments. [ABSTRACT FROM AUTHOR]

In this study, it is aimed to determine the geology, petrography, ore microscopy properties and mineral chemistry content of Fe-Cu skarn mineralization in Köprüyanı locality within the borders of Trabzon province in the Northern Zone of the Eastern Pontides. Actinolite, tremolite, pyrite, chalcopyrite, magnetite and malachite minerals; and limonitization, hematitization, chloritization and epidotization type alterations developed along the fractured crack zones are observed in the Köprüyanı mineralization area. Magnetite minerals are generally found together with chalcopyrite, pyrite and garnet, TiO2 contents are very low (0.02-1.02%), whereas FeOt contents vary between 83.13-92.00%. It has been determined that the Cu content of the chalcopyrite minerals found together with magnetite and located in the exoskarn zone varies between 33.50-43.27% and the Fe content varies between 29.84-39.11%. It was determined that Al contents of epidote minerals were high (2.06-2.46), Mn contents were low (0.01-0.03) and Fe+3 contents were relatively high (0.59- 0.96). It has been determined that the type of epidotes rich in Al is clinozoisite. Garnet species are predominantly andradite and grossular-andradite. Based on the data compiled within the scope of ore microscopy and mineral chemistry studies, it was concluded that Köprüyanı mineralization is of Fe-Cu type and shows similar features in paragenesis, succession and mineral chemistry data when compared to that of the existing skarn mineralizations in the region. [ABSTRACT FROM AUTHOR]

Epidote is a major hydrous mineral in subducted mafic oceanic crust. Understanding its stability in the subduction zone environment is important for evaluating its role as a conveyor of water into the deep Earth. Here we report experimental results on epidote by simulating the high-pressure-temperature (P-T) conditions of the plate subduction environment. We used a diamond-anvil cell with an external resistance heating system, combined with in situ X-ray diffraction (XRD) and Raman spectroscopy techniques. Experiments at ambient pressure and high temperatures indicate that epidote starts to decompose at 1223 K and breaks down completely at 1373 K. In situ XRD analyses show no phase transition at temperatures up to 1272 K and pressures up to 14.0 GPa. Raman spectra indicate that epidote is stable at 1272 K and 14.0 GPa, but the energies of two Si-O bonds (v2,v5) and one M-O bond (v3) increase with increasing temperature. The cation H+ moves for a distance when the P-T is increased to 13.0 GPa and 1123 K. Based on the thermal structure of subducted slabs in typical hot and cold subduction zones, we infer that epidote can convey water downward into the mantle transition zone through subducted mafic oceanic crust. [ABSTRACT FROM AUTHOR]

Quartz, calcite, feldspars, kaolinite, mica (biotite or sericite), and chlorite were determined as predominant minerals. Dolomite, amphibole, and johansenite are presented in smaller quantities. Epidote, hypogene hematite, rarely silver nugget, garnet, rhodonite, and wollastonite are also observed. Pyrite and chalcopyrite, less often sphalerite and galena are the main ore minerals. The distribution of minerals is relatively homogeneous in the samples taken from the main area, although stratification is observed in depth, with alternating layers rich in sulfides and those composed mainly of quartz. All cases of enrichment with heavy mineral fractions are associated with washing with seasonal processes and no permanent mineral distribution can be established. The results suggested that only quartz and feldspar minerals could be of interest for practical use. [ABSTRACT FROM AUTHOR]

Authigenic epidote supergroups are an abundant accessory mineral in the calcium–aluminum silicate and thermometamorphic hydrothermal zones of the Campi Flegrei (Phlegraean Fields) geothermal field located west of Naples, Italy. Geothermal exploration for high-enthalpy fluid produced drill core and cuttings to ∼ 3 km depth in the Mofete (MF1, MF2, MF5) and San Vito (SV1, SV3) wells, where measured down-hole temperatures of epidote-bearing samples range from 270–350 ∘ C and from 285–390 ∘ C for the Mofete and San Vito areas, respectively. Two epidote group (epidote, clinozoisite), some rare earth element (REE)-bearing, and two allanite group (allanite-(Ce), ferriallanite-(Ce)) minerals were identified by electron microprobe. The allanite group is light rare earth element (LREE, La–Gd) enriched, Ce dominant, with REE + Y that varies from 30.59 wt %–14.32 wt %. Complex compositional variation such as oscillatory, sector, and complex (mixed) zoning is a ubiquitous feature observed in the epidote group, which occurs as veins, in vugs, as various size masses, and as isolated single crystals. Compositional zoning is caused by variable Fe ↔ Al 3+ substitution and X Fe [(Fe 3+) / (Fe 3++ Al)] ranges from 0.06–0.33 (Fe 3+=0.185 –0.967 apfu). X Fe tends to decrease with increasing temperature in the Mofete wells, but its distribution is more complex in the San Vito wells, which records recent fault displacement. The variety and complexity of the epidote supergroup zoning suggest rapid fluid composition and/or intensive parameter fluctuations in the local hydrothermal system. [ABSTRACT FROM AUTHOR]

Upper amphibolite-facies metamorphism in subduction zone rocks may occur under exceptional tectonic settings. Differentiating competing mechanisms for its occurrence requires carefully integrated, high-resolution thermobarometric and geochronologic studies of mélange rocks with well-defined field relationships. We present new pressure, temperature, and age data from the classic Cretaceous Catalina Schist in southern California (USA) that allow us to establish a plausible model for its high-temperature metamorphic history. Our results indicate that garnet-amphibolite blocks in the structurally highest amphibolite-facies mélange preserve evidence of three stages of tectonic evolution: (1) prograde lawsonite eclogite-facies metamorphism that peaked at 2.4-2.7 GPa with temperatures >580 °C during fixed-trench subduction (120-115 Ma); (2) post-peak epidote eclogite-facies metamorphism followed by amphibolite-facies metamorphism at 1.4-1.3 GPa with temperatures of 740-790 °C during trench retreat (115-105 Ma); and (3) isothermal decompression (1.3 GPa to <1.0 GPa at temperatures of 780 °C) and cooling during trench advance and slab-flattening subduction (ca. 105-100 Ma). Our model implies the presence of a continuous Cordilleran subduction system in the Cretaceous, which had varying tectonic regimes through episodes of trench retreat/advance and slab shallowing/steepening that, in turn, dictated the development of the Cordilleran arc system. [ABSTRACT FROM AUTHOR]

Deformation of polymineralic aggregates can be accommodated by viscous granular flow, a process mediated by the interplay among intracrystalline plasticity and dissolution–precipitation, each active in specific minerals under given P – T conditions. Some rock-forming minerals like quartz and feldspars have been intensively studied in terms of deformation processes. Instead, the deformation behavior of epidote and its role during viscous granular flow is not well investigated, although this mineral is ubiquitous in granitic rocks deforming under greenschist-facies conditions. In this contribution, we provide microstructural and geochemical evidence for the occurrence of dissolution–precipitation of epidote during deformation of an epidote–quartz vein. The main part of the vein is deformed, producing a fold, which is visible due to relicts of primary-growth layering inside the vein. The deformation mechanisms active during deformation include dynamic recrystallization of quartz by subgrain rotation recrystallization, producing grain size reduction in the primary vein quartz. Recrystallization occurs contemporaneously with dissolution and (re)precipitation of epidote and quartz grain boundary sliding, leading to a combined process described as viscous granular flow. The combination of grain boundary sliding and dissolution locally and repeatedly produces creep cavities. These represent not only loci for nucleation of new epidote grains at the expense of dissolved ones, but they also allow fluid-mediated transport of elements. The same trace element patterns between old epidote relicts and newly formed grains, with much narrower variability in the latter, indicate a process of chemical homogenization. The nature of the fluid that mediates deformation is investigated using Pb–Sr isotope data of epidote, which suggest that deformation is assisted by internally recycled fluids with the addition of a syn-kinematic external fluid component. [ABSTRACT FROM AUTHOR]

Albite granite from Mt. Medvednica in northern Croatia is the only known surface appearance of granite in the complex Zagorje-Mid-Transdanubian zone. This granite contains almost pure albite (An01,-50-55 vol. %), quartz (-20-25 vol. %), epidote (-1 vol. %), phengite (5-12 vol. %), and secondary chlorite (-10-15 vol. %) and calcite -5 vol. %). Accessories are zircon, apatite, and ilmenite. The granite has a calc-alkaline geochemical signature with a metaluminous and high-Na character. CaO, MgO, and FeO contents are relatively low. Normalised contents of rareearth elements (REE) show a relatively flat distribution of those that are heavy, suggesting a magma source in the lower continental crust. The modelled empirical relationship for average crustal thickness based on Sr/Y ratio and contents of REE indicates a 34 km thick continental crust. Zircon typology is characterised by the predominance of {100} prisms and {101} bipyramids. This typology, zircon chemistry, zircon saturation temperature (775 °C), and Ti-in-zircon temperature (mean 785 °C) also suggest a deep-seated magma source. Epidote and perhaps phengite crystallised at a pressure around 1.0 GPa from the melt according to thermodynamic modelling. Temperatures were 650 °C or more at this stage. A U--Pb concordia age of 242.9±4.0 Ma (2σ) was determined on zircon coinciding with the Middle Triassic peak of magmatic activity in the Dinarides, but also in the Southern Alps and Western Carpathians. The age is interpreted as marking the beginning of the fragmentation of continental lithosphere and the onset of rifting processes, which was followed by the broadening of the newly-formed Neotethys Ocean. [ABSTRACT FROM AUTHOR]

Albite granite from Mt. Medvednica in northern Croatia is the only known surface appearance of granite in the complex Zagorje-Mid-Transdanubian zone. This granite contains almost pure albite (An01, -50-55 vol. %), quartz (-20-25 vol. %), epidote (-1 vol. %), phengite (5-12 vol. %), and secondary chlorite (-10-15 vol. %) and calcite (-5 vol. %). Accessories are zircon, apatite, and ilmenite. The granite has a calc-alkaline geochemical signature with a metaluminous and high-Na character. CaO, MgO, and FeO contents are relatively low. Normalised contents of rareearth elements (REE) show a relatively flat distribution of those that are heavy, suggesting a magma source in the lower continental crust. The modelled empirical relationship for average crustal thickness based on Sr/Y ratio and contents of REE indicates a 34 km thick continental crust. Zircon typology is characterised by the predominance of {100} prisms and {101} bipyramids. This typology, zircon chemistry, zircon saturation temperature (775 °C), and Ti-in-zircon temperature (mean 785 °C) also suggest a deep-seated magma source. Epidote and perhaps phengite crystallised at a pressure around 1.0 GPa from the melt according to thermodynamic modelling. Temperatures were 650 °C or more at this stage. A U--Pb concordia age of 242.9±4.0 Ma (2σ) was determined on zircon coinciding with the Middle Triassic peak of magmatic activity in the Dinarides, but also in the Southern Alps and Western Carpathians. The age is interpreted as marking the beginning of the fragmentation of continental lithosphere and the onset of rifting processes, which was followed by the broadening of the newly-formed Neotethys Ocean. [ABSTRACT FROM AUTHOR]

Greisenization is typically linked with highly fractionated granites and is often associated with hydrothermal vein systems. Late to postmagmatic metasomatic processes involve the enrichment of volatile components such as boron and halogens as well as several metallic elements. The purpose of this study is to reveal the main metasomatic effects and paragenetic sequences of the related mineralizations in Highiş granitoids, Romania. In a natural outcrop, more than 30 samples were collected from granitoids, felsic veins, and country rocks. We carried out a detailed mineralogical and petrological characterization of carefully selected samples using X-ray powder diffractometry, electron microprobe analysis, and microscopic methods together with K–Ar ages of whole rocks and K-bearing minerals. Several characteristic features of albitization, sericitization, tourmalinization, epidotization, and hematitization were recognized in the studied samples. Crystallization of quartz, K-feldspar, and magnetite represents the first stage during the magmatic-hydrothermal transition. The mineral assemblage of albite, sericite, schorl, and quartz originates from the early and main stages of greisenization. While the subsequent mineral assemblages, which predominantly include dravite, specular hematite, and epidote, are closely related to the late vein-depositing stage. We propose that the study area could belong to a boron-rich open greisen system in the apical portion of Guadalupian A-type granite. Based on a new hypothesis, the previously published Permian crystallization ages (between ~272 Ma and ~259 Ma) could be homogenized and/or partially rejuvenated during the hydrothermal mineralization processes due to uraniferous vein minerals. Additionally, the Highiș granite-related system suffered a Cretaceous thermal overprint (between ~100 Ma and ~96 Ma). The results may help to understand the evolution of highly evolved granite intrusions worldwide and improve our knowledge of the effect of hydrothermal mineralization processes on the emplacement ages.

The article focuses on the discovery of pink to red epidote clusters in transparent cabochons of rock crystal quartz, including their origin from Chenzhou in China; gemological testing indicating piemontite initially; and Raman microanalysis revealing epidote with manganese causing the color.

The article focuses on the iridescent healed fissures in a 4.18 carat yellowish brown cushion-cut epidote, include the appearance of the fissures under fiber-optic illumination; the commonality of healed fissures in gemstones; and the secondary fluid believed to facilitate the healing process.

The geochemical behaviour of major, rare, and trace elements in members of epidote-group minerals formed at different stages of magmatic and hydrothermal activity in pegmatites from the Madan ore district was studied. Accessory allanite-(Ce) and two generations of hydrothermal clinozoisite–epidote occur in hydrothermally-altered pegmatite bodies at the 820 mine level in the Petrovitsa Pb–Zn deposit. Abundant large concordant and crosscutting pegmatites (age 49.63±0.94 Ma) with a thickness of more than 2 m are embedded in a high-grade metamorphic complex composed of various gneisses, amphibolites, and marbles in the area of the Petrovitsa deposit. The pegmatites consist mainly of feldspars and quartz, with plagioclases (albite–oligoclase, oligoclase–andesine, anorthite) predominating over K-feldspars. The main accessory minerals are allanite-(Ce), zircon, apatite, and an abundance of titanite. The overprinted hydrothermal mineral association is characterised by the formation of clinozoisite–epidote, adularia, chlorite, Ca-garnet, titanite, leucoxene, carbonates, hematite, and quartz. Based on petrographic observations, mineral relationships, and chemical properties, two generations of epidotes (sensu lato) were recognised: early epidote (Ep1) and late epidote (Ep2). Chemically, allanite-(Ce) contains high amounts of La and Th. The mineral suffered alteration due to several multiphase hydrothermal events and is partly or entirely transformed into REE-rich clinozoisite, causing depletion in REE and Th as well as enrichment of Si, Al, and Ca. The epidote 1 generation is defined chemically as clinozoisite to clinozoisite– epidote, whereas the late epidote 2 generation is clinozoisite–epidote, reaching epidote members. The REE contents in the studied epidotes from both generations are equally low with minor exceptions. The influx of later fluids percolated through and probably extracted REE from allanite and thereafter concentrated them in late-generation epidotes. This is also evidenced by some high REE contents in epidotes from both generations, formed in close proximity to allanite or titanite and/or overgrowing them, which is a sign of restricted REE transport. [ABSTRACT FROM AUTHOR]

Igneous epidote occurring in tonalite–trondhjemite–granodiorite (TTG) rocks provides valuable insight into the physiochemical parameters of their magmatic system. Epidote has been identified within a newly discovered, rare, Ediacaran, high‐Al TTG‐suite at the Fannani Igneous Complex (FIC), Nubian Shield. The objective is to assess P–T conditions of magma emplacement using petrographic‐, mineral chemical data, and thermobarometry methods. The TTG‐suite is made up of ubiquitous oligoclase, variable contents of quartz, K‐feldspar, amphibole, biotite, epidote, accessory titanite, zircon, apatite and magnetite. Feldspars vary from An14 to An26 in plagioclase, with K‐feldspar having near‐end‐member compositions (Or91–Or95). Amphiboles are Al‐rich (AlT = 1.65–2.04 atoms per formula unit [apfu]), calcic (Ca = 1.83–1.93, apfu), with average Mg/(Fe + Mg) of 0.44, and are ferroedenite–edenite–ferropargasite. Biotites are moderately Fe‐rich (Fe/(Fe + Mg) = 0.50–0.58) characteristic of type 'C'–biotite of calc–alkaline orogenic rocks. Epidote exhibits pistacite components [Ps = Fe3+/(Fe3++Al)] of Ps24–Ps33, typical of magmatic epidote. The average crystallization pressure of 5.41 kbar (calculated using the Al‐in‐Hb barometer) is consistent with the presence of magmatic epidote and reflects the mesozonal crustal levels of emplacement. The Hb–Plag–geothermometer produced an average crystallization temperature of 721°C. These values fall within experimentally‐determined P–T ranges of stability of magmatic epidote with fO2 buffered from nickel‐nickel‐oxide (NNO) to hematite (HM). The FIC rocks were developed from a wet, subsolvus, orogenic, Al‐rich magmatic system. Findings reported here could have implications for conditions of magma emplacement and mineralogical characterization of TTGs occurring within various continental masses. [ABSTRACT FROM AUTHOR]

The Southern Alps are the retro-vergent belt of the European Alps that developed from Late Cretaceous subduction to Neogene times. The most prominent Alpine thrusts and folds, nowadays sealed off by the Adamello intrusion, were already developed before the continental collision and clasts derived from the eroded pre-collisional wedge can be found in the Cretaceous foredeep sequences. In contrast, the thermal state attained by the Southern Alps during the long-lasting Alpine evolution is still unknown. This contribution provides evidence for Alpine metamorphism in the northern part of the central Southern Alps. Metamorphic conditions are determined for the alkaline Edolo diabase dykes that emplaced in the exhumed Variscan basement rocks before being deformed during the Alpine convergence (D3). The Alpine foliation in the Edolo diabase dykes is marked by actinolite, biotite, chlorite, epidote, albite, and titanite and it developed under greenschist facies conditions at temperature of 350–420 °C and pressure ≤0.2 GPa. The T/depth ratio indicates a minimum of 50–60 °C/km that is compatible with thermal gradients characteristic of arc settings. Based on radiometric ages from the literature, these conditions were attained during the Alpine subduction. [ABSTRACT FROM AUTHOR]

Fission tracks are used for geologic age-dating and for the reconstruction of thermal histories of Earth’s upper crust. However, there remains a gap in the understanding between the atomic-scale annealing mechanism of latent (unetched) fission tracks and the observations of etched tracks at the micrometer scale. This is because the structure of latent fission tracks is lost during the leaching process. We have conducted the first comparison of the thermal-annealing behavior of latent and etched tracks in epidote, using transmission electron microscopy (TEM) and optical microscopy, respectively. For high-resolution TEM observations, we used ion tracks instead of fission tracks to control the density of tracks, and we demonstrated that latent ion tracks are amorphous in epidote. The reduction in diameters of latent tracks is insignificant after thermal annealing at 800 °C for 24 h, indicating that the track diameter does not appear to change substantially until the final stage of annealing. The optical observations show that the parallel etched ion-induced tracks have a lower track density reduction rate at or below 500 °C and an accelerated reduction rate above 500 °C as compared with randomly oriented fission tracks. However, the two types of tracks display a comparable thermal-annealing behavior as evidenced by the fit of the two curves for the normalized density of ion and fission tracks as a function of temperature with the same equation but with different fitting parameters. Thus, ion-induced tracks can be used to simulate fission tracks in epidote and provide a basis for understanding the annealing of latent and etched tracks. [ABSTRACT FROM AUTHOR]

The most common beneficiation method for feldspar is flotation with a cationic (amine) collector under acidic conditions. However, there are several disadvantages to this, such as environmental pollution and equipment corrosion. In order to resolve such problems, it is important to study the flotation of feldspar using anionic collectors under natural pH conditions. The purpose of this paper is to study the effects and mechanism of Fe3+ on flotation separation of feldspar and epidote using sodium oleate (NaOL) at a natural pH. Through flotation experiments, adsorption measurements, zeta potential testing, FTIR analysis and X-ray photoelectron spectroscopy (XPS), the mechanism of Fe3+ on the surface of feldspar and epidote is revealed, and the reason behind the difference in flotation of the two minerals is discussed. The flotation test results show that Fe3+ can significantly improve the flotation behavior of minerals when NaOL is used as a collector under natural pH, and the highest recovery rates of feldspar and epidote are 90% and 43%, respectively. Analysis of the solution and adsorption measurement results show that Fe3+ is adsorbed on the minerals′ surface in the form of Fe(OH)3, which promotes the adsorption of NaOL on the minerals' surface through Fe(OH)3, activating the flotation of feldspar and epidote. The difference in adsorption of Fe3+ between feldspar and epidote is the reason for this difference in flotation behavior. The results of the zeta potentials show that after being treated with Fe3+, the electrostatic adsorption of NaOL displays a significant negative shift on the surface of feldspar, while there is almost no electrostatic adsorption of NaOL on the surface of Fe3+-treated epidote. FTIR analysis confirmed that the difference in the adsorption of Fe3+ and NaOL on the surface of feldspar and epidote is due to the fact that there are more active particles (metal bonds) on the surface of feldspar than on the surface of epidote, and the properties of these metal bonds can be changed by Fe3+, which allows NaOL to be more easily adsorbed on the mineral surface through –COO−. The possible adsorption form is "mineral-Fe3+–COO−". Compared with the infrared spectrum of epidote, there is a new absorption peak at 1713.68 cm−1, which can be attributed to the C=O characteristic peak of NaOL in the infrared spectrum of Fe3+–NaOL-treated feldspar, which is why the floatability of feldspar is better than epidote. XPS confirmed that the Fe on the surface of feldspar is Fe3+ in the form of Fe(OH)3, while Fe on the surface of epidote is mainly Fe2O3 (Fe–O) contained in mineral crystals. Furthermore, there is less adsorption of Fe3+ on the surface of epidote, and this discrepancy leads to the difference in the adsorption of NaOL on the minerals' surface, which itself leads to the difference in flotation behavior between feldspar and epidote. These findings indicate that the flotation separation of feldspar and epidote can be achieved using Fe3+ and NaOL under natural pH. This study may provide a reference for the flotation mechanism of feldspar and epidote under natural pH. [ABSTRACT FROM AUTHOR]

Much work has been done on hydrothermal alteration and serpentinization of high-magnesian bulks like dunite or peridotite. In contrast, serpentinization of dolomite has received scant attention. In this study we focus on a system of nearly monomineralic intersecting veins comprising serpentine or epidote or calcite developed within Vempalle dolomite of unmetamorphosed Cuddapah Supergroup of rocks, Eastern Dharwar Craton, India. Our studies show that hydrothermal alteration under moderately low temperature, low pressure and moderate silica activity can lead to extensive serpentinization of the dolomitic host. Development of talc can occur under increased silica activity at similar P-T conditions. We also explore the mechanism of formation of chrysotile veins, epidote veins and calcite veins that transect the lizardite which replaces dolomite. [ABSTRACT FROM AUTHOR]

The presence of metamorphic epidote on faults has been implicated in the transition from stable to unstable slip and the nucleation of earthquakes. We present structured laboratory observations of mixed epidote and simulated Pohang granodiorite (analogous to the EGS‐enhanced geothermal system site) gouges to evaluate the impact of heterogeneity and contiguity of epidote‐patch structure on frictional instability. Experiments are at a confining pressure of 110 MPa, pore fluid pressures of 42–63 MPa, temperatures 100–250°C and epidote percentages of 0–100 vol.%. The simulated Pohang granodiorite gouge is frictionally strong (friction coefficient ∼0.71) but transits from velocity‐strengthening to velocity‐weakening at temperatures >150°C. This velocity‐weakening effect is amplified in approximate proportion to increasing epidote content. Modes of epidote precipitation likely control the size and contiguity of the epidote‐only patches and this in turn changes the response of 50:50 epidote‐granodiorite mixed gouges for different geometric configurations. However, 50:50 epidote‐granodiorite mixtures that are variously homogeneously mixed, encapsulated and checkerboarded in their structures are insensitive to their geometries – all reflect the high frictional strength and strong velocity‐weakening response of 100:0 pure epidote. This suggests that the epidote present as thin coatings on fractures/faults can enhance velocity‐weakening behavior, independent of individual patch size and can thereby support the potential seismic reactivation of faults. Considering the frictional and stability properties of epidote at conditions typical of shallow depths, the presence of low‐grade metamorphism exerts a potentially important control on fault stability in granitoids with relevance as a marker mineral for susceptibility to injection‐induced seismicity. Plain Language Summary: Epidote is a common mineral on fractures/faults in granites that results from both the natural and forced circulation of hot fluids – for example, in geothermal reservoirs. Its presence, even in trace quantities and as a film on fractures can impact the ability of faults to slip either stably or unstably – the latter generating earthquakes. We conduct shear experiments on simulated faults of powdered granodiorite gouge containing varying percentages and structures of epidote through pure epidote and at varying temperatures and pressures representative of geothermal reservoirs. The powdered granodiorite and epidote gouges show similar and high frictional strengths but the addition of epidote results in unstable slip and the potential for seismicity. Increasing epidote proportion amplifies the weakening until 50:50 mixtures that behave as unstably as pure epidote – regardless of the epidote‐granite structure. This suggests that even trace amounts of epidote in thin films may be effective in destabilizing faults – with implications for the control of fault instability and earthquake triggering in geothermal reservoirs. Key Points: Epidote gouge is more v‐weakening than simulated gouge derived from the Pohang granite host above a transition T of ∼150°CHomogeneous and structured 50:50 mixtures of epidote:granodiorite show v‐weakening similar to epidote and are insensitive to structureTrace percentages of epidote present as thin coatings and even at small patch sizes are a potential factor controlling fault instability [ABSTRACT FROM AUTHOR]

The pressure–temperature (P‐T) path of blueschist is usually applied to understanding the evolution of the subducted oceanic crust. Garnet plays a key role in calculating the metamorphic conditions, but sometimes it is absent in the blueschists. Nevertheless, the high‐P experimental simulation may serve as a useful tool to constrain the P‐T conditions. In the middle of the Longmu Co‐Shuanghu Suture, North Tibet, blueschist blocks embedded in the marble were discovered, where garnet is abundant in the core but absent in the marble‐contacting margin. These two kinds of blueschist contain similar mineral assemblage (glaucophane, epidote, and phengite) and show comparable basaltic character. Pseudosection modelling was applied to the garnet‐bearing blueschist that calculated the peak metamorphic condition of ca. 1.9 GPa and 530°C. As for the garnet‐absent blueschist, experiments (1.2–2.3 GPa and 500–800°C) were performed on the designed mixture of 93 wt% basalt and 7 wt% calcite. The results show that the total Fe content in the glaucophane and barroisite is positively correlated with the pressure but not with temperature, which could be regarded as a geobarometer. Accordingly, the peak condition was constrained at 2.3 GPa and 500–600°C. Therefore, the equivalent metamorphic conditions of the blueschists indicate that the Palaeo‐Tethys oceanic crust subducted into at least 70 km. Furthermore, both the experiments and the T‐X (CaCO3) pseudosection, constructed based on basaltic lithology, support that the absence of garnet in the blueschist is predominantly caused by the mixing of calcite. In summary, this study provides a valid attempt in exploring metamorphic conditions by experiment simulation, and evaluates the profound influence of the interaction between the basaltic crust and overlying carbonate‐bearing sediments in the subduction zone. [ABSTRACT FROM AUTHOR]

In this study, we made a review of the published metamorphic and geochronological data of an array of high‐pressure metamorphic rocks from the Nagaland Ophiolite Complex, North‐east India, and present them in the tectonic framework of two temporally separate subduction systems within the eastern arm of the Neo‐Tethys. The metamorphic rocks are studied in terms of three structural units. The structurally lowermost Mokie–Satuza–Thewati (MST) unit shows a metamorphic zonation from greenschist through pumpellyite–diopside (TMax ~ 335°C at ~6 kbar) to lawsonite blueschist (TMax ~ 340°C at ~11.5 kbar) to epidote eclogite (TMax ~ 550–660°C at ~24 kbar in Mokie to TMax ~ 630°C at ~26–28 kbar in Thewati localities) facies structurally upward. Both the blueschists and eclogites record a clockwise (CW) P–T path of evolution. We relate the low apparent thermal gradient at the metamorphic peak (7–9°C/km), the steep dP/dT slope of the metamorphic field gradient, the general CW metamorphic P–T paths, and the published U–Pb zircon dates in the eclogites (between ca. 205 and ca. 172 Ma) and radiolarian biostratigraphy data in the MST metamorphic sequence with the development of a Late Triassic to Middle Jurassic‐aged cold mature stage of an intra‐oceanic subduction system within the Neo‐Tethys. This is considered to be one of the oldest in the Yarlung–Tsangpo Suture Zone. The metamorphosed uppermost part of the structurally intermediate unit, named the Moya–Salumi (MS) sequence, consists of a structurally upper hornblende‐eclogite (Hbl‐EC) to epidote amphibolite facies subunit and a lower epidote blueschist (EBS) facies subunit. The eclogite subunit is polyphase metamorphosed (Hbl‐EC facies M1 with TMax ~ 625°C at ~13.8 kbar and garnetiferous EBS facies M2 with TMax ~ 540°C at ~14.4 kbar) with both the events recording counterclockwise P–T paths. The monocyclic EBS facies subunit, on the other hand, has a memory of the M2 cycle of metamorphism only. We relate this combined M1–M2 cycles of metamorphism in the MS sequence to a second oceanic subduction beneath the continental Naga Metamorphics, the latter constituting the structurally uppermost unit. The metamorphic pulses together reflect progressive cooling of the second subduction channel from an initially warm stage during subduction infancy to a later cold mature stage of subduction. The different metamorphic rocks in the MST and MS units reveal architectures of two temporally separate accretionary complexes. Their present occurrence as a tectonic collage is likely to be the product of the Eocene collision of the Indian and the Myanmar plates. [ABSTRACT FROM AUTHOR]

The Sin Quyen deposit is characterized by a high accumulation of rare earth elements (REE). This deposit belongs to the IOCG type copper deposits (Iron Oxide Copper-Gold Deposits). In the deposit, the REE carrier minerals have been identified as follow: allanite, titanite, uraninite, monazite, apatite, chevkinite, aeschynite, bastnäsite, and epidote. In the skarn zone, contents of allanite range from single percentages to 10% in hand-size specimens. Locally, minerals of epidote subgroup which occur in large amounts in the host rocks are important. The studied allanites have concentrations of: REE (14-27 wt%), Ca (9-16 wt%), Al (8-19 wt%), Si (26-34 wt%) and Fe (12-21 wt%). Two populations of allanite are documented, the first is texturally older and probably related to the Ca-K alteration (second stage of crystallization). This population has higher REE concentration ranging from 20 to 27 wt%. The second population is texturally younger and has a lower total REE concentration ranging from 14 to 19.9 wt%, which occur mostly as a rim surrounding the older and likely arose during the K alteration with Cu-Au mineralization (third crystallization). The chemical composition indicates that the studied allanites belong to the Ce-La-ferriallanite family, with low SHREE and an average of 0.21 wt.%. A temperature of 355°C which was calculated using a value of d34S isotopes is interpreted as a temperature of the second crystallization stage of allanite. In the studied deposit, excluding allanite and titanite, the other bearing REE minerals have an insignificant role in the REE balance, since they either have the total content of REE, which is often close to the WDS detection limit (rf. the epidote subgroup), or their only occur at the single points. The content of total REE in accessory uraninites is high and range from 1.311% up to 7.959% with an average value of 4.852%. [ABSTRACT FROM AUTHOR]

The dominant rocks in the area between the village of Kovda and township of Zelenoborskii in northern Karelia, Russia, are amphibole–biotite and biotite plagiomigmatites, which develop after amphibolites. These plagiomigmatites contain epidote that replaces the amphibole and biotite and is found in reaction relations with these minerals. The epidote occurs as thin rims around mineral grains it replaced and in large euhedral crystals. The rocks contain 5–15% epidote. The epidote contains relatively little FeO (no more than 10.57 wt %) but elevated concentrations of CaО (up to 27.53 wt %) and Al2O3 (up to 31.28 wt %), i.e., the mole fraction of the pistacite end member is 0.14–0.22. The mineral crystallized at 400–600°C and 5 kbar. It was formed by metasomatic processes, when components of the replaced minerals interacted with components of the fluid. The amphibole–biotite and biotite rocks in which the epidote crystallized resemble amphibole–biotite and biotite gneisses. Geological, petrographic, and geochemical characteristics of the rocks indicate that they are plagiomigmatites that developed after amphibolites. The paper reports features that enable distinguishing between the plagiomigmatites and similar gneisses. The transformations of the amphibolite at its migmatization starts with the replacement of the hornblende by biotite, up to the complete replacement of the former at a certain progress of this process. Chemically, the original rocks in their migmatization sequence are gradually depleted in Fe, Ti, Mg, and Ca and enriched in Si, Na, and K. The normalized REE patterns of the plagiomigmatites are strongly fractionated: (La/Yb)n = 18.3 for the biotite plagiomigmatite and 30.9 for the biotite–hornblende plagiomigmatite. The rocks of the area occur in a tectonized zone, which is the boundary between two domains in the Belomorian Belt exhumed at 1.8 Ga according to the mechanism of metamorphic cores. This was favorable for the intense inflow of fluids, created a certain pressure (both total and that of H2O + CO2), temperature, and elevated oxidation potential, i.e., conditions required for epidote crystallization. [ABSTRACT FROM AUTHOR]

The article "Opal with Epidote Inclusions from Madagascar" discusses the discovery of opal with epidote inclusions in the Antsirabe region of Madagascar. The stones were mined from an open-pit quarry in the Vangaindrano area and subsequently cut into faceted stones and cabochons. Gemmological properties, such as color, pleochroism, polish lustre, and diaphaneity, were examined and found to be consistent with opal for the white matrix and epidote for the dark greenish brown inclusions. The article concludes that the combination of opal and epidote in this gemstone makes it an interesting addition to the gem market. [Extracted from the article]

In November of 2020, an exciting occurrence of epidote pseudomorphs after orthoclase was rediscovered in the Orogrande district in southern New Mexico (fig. 1). A specimen showing very little alteration to epidote but exhibiting the surficial intergrowth with late-stage albite alteration; 3.0 × 1.6 cm. Enchanted Minerals specimen, Erin Delventhal and Philip Simmons photo. The pair of pseudomorphs in Ray DeMark's collection that inspired the search; left crystal is 4.3 cm. Ray DeMark specimens, Philip Simmons and Erin Delventhal photo. A cross-section of rock showing an epidote "blob" overprinting two defined feldspar crystals; 9.4 × 6.3 cm. Note that although the gradation of the epidote tapers off, some crystals well within its halo of influence remain largely unaffected. [Extracted from the article]