Quartz Inclusions Research Articles

About the assessment of sampling error and representative sample in X-ray fluorescence analysis of mineral powders

The assessment of laboratory sampling errors in X-ray fluorescence analysis (XRF) of mineral powders ground to a particle size less than 75 μm is important when analyzing specimen portions less than 100–300 mg. The sampling error can be found from Poisson statistics, which allows one to estimate the variations in the number of mineral grains containing an analyte in a powder sample of a fixed mass. However, the absorption of X-ray radiation in the sample imposes a limitation on the analyzed mass due to the low penetration depth of X-rays, especially in the energy region below 4 keV.In this paper, we propose the sampling error estimation based on Poisson statistics taking into account the size of powder particles in comparison with the penetration depth of X-rays. Two limiting cases are considered, when the penetration depth is greater or less than the size of the grains containing the analyte. Zircon, ilmenite, and quartz were considered as grains containing the analyte, and boric acid and clay were taken as matrices. Measurements were carried out with wavelength dispersive XRF spectrometer. It was shown that the sampling errors obtained experimentally for different model mixtures are close to the sampling errors calculated using Poisson statistics. The described model of quartz inclusions in clay matrix was used to explain the relatively low sampling error in determining the main components Al2O3, SiO2, K2O in course-grain Neolithic ceramics.

Fluid evolution and metallogenesis of the Zhangjiapingzi gold deposit in mianning, Sichuan province: constraints from fluid inclusion studies

Introduction: The Zhangjiapingzi gold deposit, located at the western margin of the Yangtze Craton and controlled by the Jinhe-Chenghai deep fault, is a newly discovered super-large gold deposit in the Danba-Mianning metallogenic belt. The gold ore bodies are hosted in the Middle Triassic (T2) altered dolomite (Dm), and have two types of mineralization: altered rock type and quartz vein type. Previous studies on this deposit are rare, especially on the ore-fluid characteristics, which limit the understanding on the ore genesis.Methods: This study focused on fluid inclusions in quartz from altered rocks, and used microthermometry and laser Raman spectroscopy to investigate the properties and sources of ore-forming fluids, and to determine the ore genetic type.Results and discussion: The results show that the fluid inclusions are mainly CO2-H2O-NaCl inclusions, with medium temperature (220–300°C), low salinity (<10%), medium-low density (0.79–1.01 g/cm3) and high contents of CO2 and CH4, resembling typical orogenic gold ore fluids. We suggest that the Zhangjiapingzi is best classified as orogenic type, and our findings provide new insights into the fluid origin and metallogenesis of orogenic gold deposits in the Danba-Mianning metallogenic belt.

Sb-As LOJAN DEPOSIT (REPUBLIC OF NORTH MACEDONIA): ORE TYPES, CONDITIONS OF ORE TYPES LOCALIZATION AND GEOCHEMICAL FEATURES

This article discusses the results of comprehensive studies of Sb-As ores of the Lojan deposit, located in the north-east of the Republic of North Macedonia (RSM), near the border with Serbia. 5 types of Sb-As ores have been identified: breccated realgar-auripigment ores, realgar breccias, breccated antimonite ores, massive, almost monomineral realgar ores, as well as realgar-antimonite nest-shaped ores. The ores are characterized not only by an unusual paragenesis of nickel, arsenic and antimony minerals, but also by a very close fusion of antimonite, realgar and collomorphic quartz. A wide range of elements in ores (As, Sb, Cr, Ti, Mn, Ni, Mo, Co, Ag, Tl, U, etc.) is apparently due to the combination of mineralization in ores of several different-time parageneses. As a result of thermometric studies of fluid inclusions in quartz, Thom vary from 180 OC to 220 OC (the average value is 201 OC). Studies of the isotopic composition of sulfur in antimonite and realgar have shown rather narrow ranges of δ34S values from -5.19 to -0.26 and from -4.80 to 1.92, respectively, which indicates an endogenous source of sulfur. The results obtained allow us to attribute the Lojan deposit to the epithermal class

Quartz-in-garnet (QuiG) under pressure: insights from in situ Raman spectroscopy

Elastic geothermobarometry relies on the contrast between the thermal expansion and compressibility of a mineral inclusion and its surrounding host, leading to a residual pressure in the inclusion (Pinc) that may differ significantly from the external pressure. Quartz-in-garnet (QuiG) inclusion-host systems are widely used in elastic geothermobarometry to estimate the inclusion entrapment conditions and thus the rock petrogenesis. To elucidate the behaviour of QuiG at elevated pressures, we have applied in situ high-pressure Raman spectroscopy on three QuiG samples having Pinc close to 0 GPa at room temperature. We demonstrate that upon pressure increase, the garnet host acts as a shield to the softer quartz inclusion. Consequently, the Pinc increases with a smaller rate compared to that of the external pressure. Up to 2.5 GPa, the evolution of Pinc calculated from the Raman data agrees very well with prediction from the equations of state. Furthermore, the behaviour of a quartz inclusion in a relatively thin host specimen was explored up to external pressures of 7 GPa. Our results indicate that the shielding effect of the host (even if only partial because of the insufficient distance between the inclusion and the host surface) can keep the quartz inclusions thermodynamically stable up to about 2 GPa above the equilibrium quartz–coesite phase boundary. In addition, the partial shielding leads to the development of anisotropic symmetry-breaking stresses and quartz inclusions undergo a reversible crossover to a lower symmetry state. Given that the presence of non-hydrostatic stress may influence the quartz-to-coesite phase boundary, especially at elevated temperatures relevant for entrapment conditions, our results emphasize the importance of elastic anisotropy of QuiG systems, especially when quartz inclusion entrapment occurs under conditions close to the coesite stability field.

Fluid inclusions in minerals: from geosciences to the physics of water and back

Natural mineral samples often contain small volumes of trapped fluid material. They carry information about the history of the host mineral and its environment, and for this reason are used by geoscientists. Physicists and physico-chemists have successfully harnessed water inclusions in quartz to bring liquid water to a metastable state, at a pressure well below its equilibrium pressure with vapor. The pressure can reach negative values as large as -140 MPa, which exceeds by far the limits of other techniques, and approaches the theoretical threshold for spontaneous nucleation of a vapor bubble. This has enabled a deeper understanding of nucleation and of the anomalies of water. In turn, the optical techniques developed to study water’s properties have recently found a new application in the reconstruction of palaeotemperatures in surface processes. I review here some aspects of fluid inclusions, these fascinating objects at the crossroads between disciplines.

Quartz under stress: Raman calibration and applications of metamorphic inclusions to geobarometry

Abstract. An experimental calibration of the shifts of three major Raman peaks of quartz with hydrostatic pressure and uniaxial differential stress is presented, and implications for their use in geobarometry based on Raman spectroscopy of quartz inclusions are discussed. The position of the 206 cm−1 peak depends only on hydrostatic pressure P, and its pressure dependence is recalibrated with a peak-fitting procedure that is more adequate for Raman barometry than previous calibrations. The position of the 128 and 464 cm−1 peaks depends on P and also on differential stress σ, which can be determined from the position of these two peaks knowing hydrostatic pressure from the position of the 206 cm−1 peak. The results obtained here are different from those inferred previously from first-principles calculations. The present calibration provides direct relationships between Raman shifts and stress, with a simple formulation of residual pressure and differential stress assuming uniaxial stress along the c axis of quartz inclusions. It is tested on data from experimental and natural inclusions. Residual pressures from the present calibration are similar within uncertainties to those obtained with previous experimental calibrations. Residual differential stresses obtained from the 128 and 464 cm−1 peaks are very sensitive to the precision of Raman measurements. Experimental inclusions yield residual pressures consistent with synthesis pressure. Differential stresses obtained on some experimental inclusions are sometimes incompatible, providing a criterion for identifying inclusions under complex stress conditions that are not appropriate for geobarometry. Recent data on natural inclusions show self-consistent differential stress, consistent with the assumption of major stress along the symmetry axis of the inclusion crystals. The average pressure values from the 128 and 464 cm−1 peaks are similar to the residual pressure from the 206 cm−1 peak that depends only on hydrostatic pressure. It can be used to obtain pressure when the 206 cm−1 peak position cannot be used due to interference with host mineral peaks. Using the 128 and 464 cm−1 peaks alone, or averaging either 128 and 206 or 206 and 464 cm−1 peaks, can induce systematic bias in the residual pressure determination. Applications of the present results to natural inclusions suggest that combined determination of residual pressure and differential stress may be used for both barometry and thermometry pending further calibration.

Условия образования кварцевожильной минерализации Кыввожского золотороссыпного поля на Среднем Тимане (по данным изучения флюидных включений)

We present a novel study of fluid inclusions in the vein quartz of the Kyvvozh gold placer field and in the quartz of gold-quartz intergrowths from the placer (methods of homogenization, cryometry, and Raman spectroscopy were used). We determined that in vein quartz the homogenization temperature of fluid inclusions fluctuated in the range of 220–425 °C, the liquid phase was represented by aqueous solutions, predominantly sodium and magnesium chloride. The homogenization temperature of fluid inclusions in quartz of gold–quartz intergrowths is 220–330 °C, and an aqueous solution of sodium chloride predominates in the liquid phase. Mineral formation proceeded in two stages: at the first stage, the fluid was enriched with nitrogen, at the second stage — with carbon dioxide.

Fluid evolution and genesis of the Sankuanggou Fe[sbnd]Cu skarn deposit, Duobaoshan ore field, Northeast China: Evidence from fluid inclusions and H-O-S-Pb isotopes

The Sankuanggou FeCu skarn deposit is located in the Duobaoshan ore field in the northern Great Xing'an Range, Notheast China. The ore bodies occurred in the skarn of the contact zone between the Yanshanian granodiorite and the middle Ordovician Duobaoshan Formation marble. According to the field investigations and mineral crosscutting relationships, five paragenetic stages were identified: the anhydrous skarn (Stage I); hydrous skarn (Stage II); chalcopyrite-pyrite-quartz-molybdenite (Stage III); sphalerite-quartz stage (Stage IV) and quartz-calcite (Stage V). In the Stage I and II, the assemblage of fluid inclusions (FIs) in quartz is characterized by the development of daughter mineral-bearing three-phase FIs (S-type), vapor-rich two-phase aqueous FIs (LV-type) and liquid-rich two-phase aqueous FIs (VL-type). VL- and LV-type FIs were found in the Stage III quartz, whereas only VL-type FIs were present in the Stage IV quartz and Stage V calcite. The homogeneous temperatures of the FIs in Stages I to V were 364–495, 295–405, 243–360 and 135–207 °C, respectively, with salinities of 4.16–58.42, 4.17–47.99, 3.37–14.2, 1.03–11.11 and 3.53–8.4 wt% NaCl eqv., respectively. In general, the ore-forming fluids changed from high-temperature NaCl-H2O system fluids, that contained negligible amounts of CO2 and CH4 and exhibited obvious boiling, to a medium- to low-temperature and low-salinity NaCl–H2O system with fluid mixing. According to the HO isotopic analysis of Stages I and II (δ18OH2O = 0.3–6.3 ‰, δ18D = −112.6 to −79.9 ‰), the ore-forming fluid was identified as magmatic fluid. In contrast, the δ18OH2O and δ18D values in Stages III and IV gradually decreased (δ18OH2O = −9.6 to −2.3 ‰, δ18D = −133.1 to −118.9 ‰), implying a gradual meteoric water input into the fluid. The S isotopic analysis (δ34S range from −4 to −0.8 ‰) revealed that S mainly originates from the magma during the mineralization process. Further, the Pb isotopic (208Pb/204Pb = 37.64–38.725, 207Pb/204Pb = 15.45–15.606 and 206Pb/204Pb = 18.115 to 19.786) investigations indicated that the ore-forming materials of this deposit are derived from the crust-mantle mixing. Based on the previously reported geochronologic and geodynamic data, we can conclude that the Sankuanggou deposit is a typical FeCu skarn deposit and formed during the Early Jurassic Paleo-Pacific Plate subduction.

Molecular mechanism of metamorphic alteration on traces of early life in banded iron formations

It is well-known that multi-stage metamorphism can result in the alteration of indigenous biological molecules, limiting our understanding of early life on Earth. However, the physiochemical mechanisms involved in these processes are still poorly understood. In this study, we present petrographic observations and micro- to nano-geochemical investigations on the carbonaceous matter (CM) in representative Neoarchean banded iron formations (BIFs) from North China, which have undergone significant alteration during lower amphibolite-facies prograde metamorphism, and subsequent retrograde alteration. The CM is in paragenetic equilibrium with prograde mineral phases, and is often associated with apatite that occurs in Fe-rich bands parallel to layering. This implies that the CM is most likely inherited from syn-depositional biomass, as confirmed by the nanoscale infrared spectroscopy, which shows the presence of CC, CH, and CN/NH bonds. Raman spectroscopic analyses reveal that the maximum metamorphic temperature of CM is 479 ± 50°C, which is consistent with the metamorphic peak conditions of the host BIFs from petrographic constraints (i.e., garnet-bearing amphibolite-face metamorphism). The BIFs possess average bulk δ13Corg values of −20.0 ± 0.9‰ (1σ) and δ13Ccarb values of −12.9 ± 1.8‰ (1σ), further indicating syngenetic biomass graphitization during prograde metamorphism. This thermal cracking process may have released gaseous hydrocarbons, as shown by secondary CH4 fluid inclusions in quartz. We further use quantum mechanical simulations to constrain dissociative tendencies for functional groups (CC, CH, CO, and CN) of original organic molecules to assess the stability of organic chemical bonds during prograde metamorphism (0–600°C, 0–15 kbar). The relatively high thermal durability of CH and the armoring effects of primary organic-phyllosilicate complexes may account for CH preservation in BIFs. Furthermore, the electron microscopy combined with elemental analysis reveals widespread nano-chlorite infiltration into CM during retrograde metamorphism (i.e., partial replacement of garnet by chlorite). The pervasive CM alteration is likely responsible for the absence of CO bonds, where nanopore-scale reactions might have played a key role. Altogether, we suggest that multi-stage metamorphic processes, involving mineral-organic reactions and nanoscale interface interactions, may have governed the preservation of ancient biosignatures in BIFs. Our findings highlight the importance of evaluating metamorphic effects when using molecular signals to reconstruct early life behaviors, and shed new light on the study of primordial microorganisms, particularly those found in iron-rich sediments on early Earth.

Melt Inclusions in Arclogitic Xenoliths Constrain the Genesis of the Lower Continental Arc Crust beneath the Northern Volcanic Zone, Colombia

ABSTRACT Volcanic arcs above subduction zones are thought to be the principal locations where juvenile magmatic crust forms and is refined to become continental crust with an andesitic composition. During this refinement mechanism, the formation of dense garnet pyroxenites (arclogites), represented by high-pressure cumulates and restites after partial melting, leads to the delamination of the lower arc crust. The Mercaderes-Río Mayo area in southern Colombia is the only known locality in an active volcanic arc where arclogitic xenoliths have been recovered. These xenoliths are entrained in the Granatifera Tuff, a late Cenozoic volcanic vent, and they mainly consist of garnet, clinopyroxene, amphibole, plagioclase, rarely scapolite, and accessory mineral inclusions of rutile, apatite, zircons, and quartz. Moreover, the arclogites are also characterized by the presence of melt inclusions (MI), which are mainly found within garnet, but can be also observed in amphibole, plagioclase, clinopyroxene, and scapolite. The glasses measured for the MI in garnet and scapolite typically have SiO2 contents >57 wt.%, ranging from andesite to rhyolite in composition. Petrographic and geochemical investigations allowed to discriminate between cumulitic and restitic arclogites, with the latter showing the concomitant presence of primary MI and quartz inclusions within the peritectic garnets. Therefore, our study provides for the first time a strong evidence, at the microscale, for the anatectic origin of some arclogitic xenoliths. Pressure and temperature conditions for the studied arclogites were estimated by intracrystalline geothermometry, elastic geothermobarometry, phase equilibria modelling and classical Fe–Mg exchange between garnet and clinopyroxene. Results fall within the range of 960°C to 1150°C and 1.6 to 1.9 GPa for most samples. We suggest that the investigated arclogites derive from the root of the active Colombian volcanic arc, where differentiation processes from mantle-derived melts and lower crust anatexis occur in close association.

Magma Composition and Formation Conditions of Alkaline-Salic Rocks of the Early Mesozoic Adaatsag Bimodal Association of the Kharkhorin Rift Zone, Central Asia: Data from the Study of Melt Inclusions in Minerals

The composition and formation conditions of magmas of comendites of the Early Mesozoic Adaatsag volcanic association are determined using electron and ion microprobe analysis of melt inclusions, and mechanisms favorable for the accumulation of trace and rare earth elements are identified. The melt and fluid inclusions are found in quartz of comendites sampled in various parts of the section of a volcanic sequence. The melt inclusions consist of glass, a gas bubble, and daughter minerals (fluorite, polylithionite, and K-feldspar). The composition of a gas phase in melt inclusions was studied using Raman spectroscopy. The dominant gas phase components include water and hydrogen. The fluid inclusions are aqueous fluids probably corresponding to KF. The thermometric studies of melt inclusions and the analysis of glasses of homogenized melt inclusions in quartz phenocrysts of comendites showed that magmas crystallized from water-saturated rare metal melts with high Li, Zr, F, Rb, Nb, Y, and Th contents at a temperature of 880–930°C and a pressure of 1000 bar at a depth of ~3.5 km accompanied by degassing. The comparison of our data of the study of melt inclusions in phenocrysts of alkaline salic rocks of the coeval Adaatsag, Dzarta-Khuduk, and Sant volcanic associations, which occur within the Kharkhorin Rift Zone, revealed common principles of magma evolution. This allowed us to propose a similar mechanism of their formation, involving the accumulation of many rare and rare-earth elements, as well as volatile components (F, H2O) in the process of crystallization differentiation. Subsequently, a salt melt rich in Li, F and water could be separated from such comendite magmas. The detection of fluoride aqueous inclusions in quartz allows us to suppose the further evolution of the salt melt leading to the appearance of a concentrated aqueous fluid and the possible participation of the latter in metasomatic processes.

When rainfall trapped in fluid inclusion restores the relief of an orogen: Insights from the Cenozoic Himalayas

The involvement of meteoric water in orogens dynamics through surface processes is well known as for example in the Himalayas where erosion, resulting of the interplay between climate and tectonics shapes the most spectacular landscapes on the planet. But what about more internal and deepest surface fluid infiltration? Here we report analysis of the δ18O(water) and δD(water) of extracted water from fluid inclusions hosted into Cenozoic quartz veins sampled in the core of the Himalayan range, near the Main Central Thrust and the South Tibetan Detachment. Isotopic and microthermometric values suggest a meteoric origin for the fluids trapped in the quartz of syn- to post-kinematic veins formed between 10 to 20 km depth. Moreover, the isotopic compositions obtained in this study on quartz fluid inclusions water collected along a transect across the Himalayan range evolved with the topography in a similar manner than the modern meteoric water. Considering the age of formation of the quartz veins between 18 and 12 Ma, we deduce that the morphology of the Himalayan topographic front was already shaped during the Miocene but located further north.

Hetero- and Homogeneous States of Hydrocarbon Fluids in the Earth’s Interior: Evidence from the Study of Synthetic Fluid Inclusions

Based on experiments including in situ studies of the phase composition and states of aqueous–hydrocarbon fluids in synthetic inclusions in quartz, the thermometric data indicating a heterogeneous state of fluids at shallow, medium, and great depths of oil- and gas-bearing layers were obtained. It was shown that aqueous–hydrocarbon fluids with an oil content of ≥10 vol % remain heterogeneous even at depths of up to 10–12 km at temperatures of 250–290°С. As is evident from experiments, homogenization in such fluids was achieved at temperatures above 380–400°C. However, such temperatures have not yet been recorded in any of the real oil and gas basins of the world. The results of our studies allow us to hope for the discovery of homogeneous deep deposits of oil and other hydrocarbons in the future.

Geology, morphology and mineralogy of sulfide-carbonate hydrothermal-bacterial structures on the surface of Tessel paleovolcano lava (south coast of Crimea)

Research subject. Sulfide-carbonate hydrothermal-bacterial structures on the surface of Tessel paleovolcano lava. Materials and methods. The structures under study were found during detailed geological works. Petrographic thin sections were studied using an Olympus Bx5 microscope. Carbonate and sulfide samples were examined using an RZMMA-202M scanning electron microscope. Results. For the first time, the contacts of the studied structures with their enclosing siltstones and mudstones were described. The structures are of tubular and flat shapes. In terms of mineral composition, the structures exhibit three zones: central, lateral and that of bacterial overgrowth. The middle part of the central zone features a fluid channel with inclusions of quartz, barite, nakrite, galena, chalcopyrite, pyrrhotite, sphalerite, pyrite, shells of largefauna, ash and tuff material. Spherulites and microtubular carbonate formations testify to the participation of bacterial and archaean communities in the construction process. The study of carbonates and sulfides confirmed the use of deep fluids by prokaryotes. Conclusion. The main role in the formation of the sulfide-carbonate hydrothermal-bacterial structures under study belonged to the community of prokaryotes and fluids from the depths. The external morphology of the studied structures along with the presence of mineralogical zonality, a fluid channel, oil products, and oases of life with a large fauna indicate the similarity of their formation conditions to those of sulfide-carbonate smokers of the Piip volcano. Some differences in the mineral composition are associated with different depths and fluids of their formation.

Almandine jewelry garnet from the Kitelya deposit (Karelia): composition and spectroscopic properties

Research subject. The chemical composition and spectroscopic properties of almandine jewelry garnets from the Kite-lya deposit in the Northern Ladoga region (Karelia). Materials and methods. The chemical composition, impurity elements, mineral inclusions and spectroscopic properties of almandine jewelry crystals were studied using IR and Mössbauer spectroscopy. Results. Garnet crystals were found to exhibit a weakly pronounced zonal composition, varying from Alm75Pir15Sps7Grs3 in the center to Alm80Pir14Sps4Grs2 at their edges. Therefore, the Ca and Mn contents decrease towards the grain edges. This zonality of garnets is characteristic of the processes of progressive metamorphism of their host rocks. The garnet crystals feature small inclusions of quartz, chlorite, mica FACI (biotite), ilmenite, rutile, monazite, zircon and pyrrhotite. The composition of chlorite, biotite and zircon was established. The parameter of the cube unit cell ao = 11.522 ± 0.003 Å was calculated. The IR absorption spectra of 995, 966, 901, 878, 638, 568, 528, 476 and 455 cm–1 are characteristic of the pyrope-almandine difference. Mössbauer spectroscopy revealed an insignificant admixture of trivalent iron (Fe3+) in the structure of Kitelya garnets (≈1 % of the amount of isomorphic iron). The obtained optical absorption spectra of garnet plates in the visible light spectrum indicate that Fe2+ ions in dodecahedral positions, to a lesser extent dodecahedral Mn2+ ions, as well as possibly octahedral Fe3+ ions are responsible for the bright red-crimson color of pyrop-almandine from the Kitelya deposit. Conclusions. A “portrait” of typomorphic features (composition and properties) of the pyrope-almandine jewelry garnet from the Kitelya deposit was obtained. This portrait can be used when analyzing the historical finds of faceted or cabochonized differences of almandine in jewelry, church utensils in both Russia and Europe (where this jewelry material was exported during the 17th century). The preservation of garnet jewelry differences in the host rock is due to the presence of thin amorphous kelefite shells or soft minerals (sericite, chlorite, kaolinite etc.).

Metasediments from the lower crust reveal the history of the Picuris orogeny, southwest USA

Petrologic and geochronologic data for metapelitic lower crustal xenoliths from New Mexico (USA) and Chihuahua (Mexico) states provide evidence for both a magmatic and collisional component to the enigmatic Mesoproterozoic Picuris orogeny. These garnet-sillimanite-bearing metapelites are found within the southern Rio Grande rift at Kilbourne Hole and Potrillo Maar in southern New Mexico and northern Chihuahua. Geothermobarometry and rutile with Quaternary U-Pb dates indicate equilibration in the local lower crust, which is actively undergoing ultra-high temperature (UHT) metamorphism (Cipar et al., 2020). The samples contain older detrital zircons dating back to the Paleoproterozoic, marking their deposition at the surface. Coupled zircon U-Pb dates and trace-element ratios (e.g., Gd/Yb) show a clear transition from oscillatory-zoned, low-Gd/Yb detrital magmatic zircon to featureless, high-Gd/Yb metamorphic zircon between 1500 and 1400 Ma, marking the transition from subduction to collision during this period. Metamorphic zircon and monazite grew in two major intervals. The first, between ca. 1450 and 1350 Ma, documents the journey of the sediments to depth within the orogen and provides evidence of extended Mesoproterozoic metamorphism in the region. The second corresponds with UHT metamorphism that commenced at ca. 32 Ma and is associated with the Rio Grande rift. Whereas nearly all garnets are homogeneous in both major and trace elements, a single garnet from one sample has a core defined by abundant quartz and acicular sillimanite inclusions. The core and rim of this garnet is homogeneous in major and most trace elements, but the rim is enriched in the slowest diffusing elements, Zr and Hf, which likely indicates rim growth at higher temperatures. We interpret the garnet core to have grown at the time of emplacement of the sediments into the lower crust. Because this occurred in the sillimanite stability field and because the metamorphic zircon and monazite all have negative Eu anomalies, indicating their equilibration with feldspar (stable at depths of <45 km), we conclude that the sediments were not emplaced via subduction and/or relamination of forearc sediments, but were instead metamorphosed under warmer, shallower conditions in an orogenic setting. Collectively, the data point to a collisional orogen during the inferred timing of the Picuris orogeny. These samples may therefore define the location of the Picuris suture zone, a key feature of this orogenic event.

Metal budget and origin of aqueous brines depositing deep-seated Zn-Pb mineralization linked to hydrocarbon reservoirs, North German Basin

The origin, evolution, and interplay of brine and hydrocarbon fluid systems play a crucial role in the formation of deep sediment-hosted base metal ore deposits. Here we investigate ratios of halogens, noble gases, stable C and S isotopes, and metal budgets of aqueous brines, which deposited deep-seated and near-surface hydrothermal Zn-Pb mineralization hosted by Zechstein carbonates in the Lower Saxony Basin (North German Basin), by studies of fluid inclusions in sphalerite and quartz. Major and trace element geochemistry and noble gas isotopic signatures of brine inclusions revealed that the ore-forming fluids were highly reactive and experienced prolonged interactions with host rocks in the constricted, over-pressured metal source regions and consequently evolved from near-neutral, oxidized brines towards more reduced, acidic high-salinity brines. Quartz-hosted halite-saturated fluid inclusions with Th <200°C contain Zn and Pb concentrations up to ca. 9400 μg g-1 and 5200 μg g-1, respectively, and indicate the efficiency of metal scavenging processes. The interactions with Westphalian coals and Corg-rich shales influenced the redox state as well as the trace and critical element budget of the sphalerite-hosted fluid inclusions, with enrichment in Ge, Pd, Sb, Tl, Bi, and Ag. The salinities of metalliferous fluids originated primarily from seawater evaporation, however in addition a significant halite-dissolution component is present in the southern part of the Lower Saxony Basin. High concentrations of radiogenic noble gases and potassium in the sphalerite-hosted fluid inclusions are ascribed to strong interactions with the Paleozoic siliciclastic sedimentary pile and crystalline basement rocks. Reflux of the strongly modified, sulfur-poor, Zn-Pb-bearing acidic brines, proceeded via re-activated structurally controlled pathways into sour gas or gas-saturated brine pools in the Zechstein Ca2 carbonate unit. Here, mixing of the ascending metal-rich brines with H2S derived from thermochemical sulfate reduction (TSR), resulted in the deposition of deep-seated Zn-Pb ores in the Lower Saxony Basin. The overall timing of the Zn-Pb ore formation can be constrained to the Upper Cretaceous basin inversion.

Formation of High-Silica Leucocratic Granitoids on the Late Devonian Peraluminous Series of the Russian Altai: Mineralogical, Geochemical, and Isotope Reconstructions

This paper presents data on the geological position, geochemical features, main mineral composition (micas, feldspars), and melt and fluid inclusions in quartz from Aba high-silica leucocratic granitoids in the western part of the Talitsa batholith, Russian Altai. According to these new geochemical data, the granitoids are classified as S-type, meaning they are formed via the partial melting of metasedimentary source rocks. Geological data and oxygen isotope composition analysis indicate that major-phase granitoid magma evolution took place at the level of intrusion formation, whereas the parent melt of late-phase leucogranite evolved in a deeper chamber. The geochemical features (HFSE and REE, and REE spectra) of the granitoids indicate significantly higher differentiation in the late leucocratic phase. The presence of coexisting syngenetic melt and fluid inclusions shows that leucogranite magma was already saturated with volatiles in the early crystallization stages. Based on the new data presented in this work, the Aba rock formation is associated with the volatile saturation of magmatic melts, the exsolution of a fluid phase, and magma degassing.

Tellurium mineralization of the Priozernoe gold-quartz deposit (Northern Urals, Russia)

Primary and supergene Te minerals are identifed in quartz veins of the Priozernoe deposit (Sverdlovsk oblast, Northern Urals, Russia) and studied by optical methods, electron microprobe analysis, X-ray diffraction and Raman spectroscopy. Tellurides include altaite, hessite, melonite, petzite, and sylvanite. Their individual grains and intergrowths occur as small inclusions in quartz. Supergene minerals include telluroperite, northstarite, adanite, burckhardtite, kuranakhite, and schieffelinite. They replace galena, hessite and cerussite or form monomineral grains and veinlets in quartz. Northstarite, adanite, and schieffelinite are found for the frst time in Russian Federation, while the fndings of telluroperite and burckhardtite are second. Kuranakhite is found for the frst time in the Northern Urals. The fndings of supergene Te minerals in Russia are reviewed. Keywords: Priozernoe deposit, Northern Urals, tellurium mineralization, tellurides, tellurates, north-starite, adanite, schieffelinite, burckhardtite, frst fnds of minerals in Russia, supergene minerals.

Calibrating a Handheld LIBS for Li Exploration in the Barroso–Alvão Aplite-Pegmatite Field, Northern Portugal: Textural Precautions and Procedures When Analyzing Spodumene and Petalite

In pegmatites containing abundant petalite and spodumene, such as those from the Barroso–Alvão (BA) aplite-pegmatite field, calibrating a portable laser-induced breakdown spectroscopy (pLIBS) equipment to identify and analyze these minerals may be challenging. Forty-nine samples of spodumene, petalite and spodumene + quartz were collected from 22 aplite-pegmatites from the BA field and sent for inductively coupled plasma-mass spectroscopy analysis. One calibration for both spodumene and petalite has been proven to be impossible since almost all the LIBS intensity ratios, including for Li, overlapped on both minerals. Thus, three calibrations were developed: one qualitative to distinguish both minerals and two more quantitative, specifically made for each mineral. The first LIBS calibration only has Fe since it is the sole element with intensity ratios different enough to distinguish both minerals. Eleven calibration lines were created: Li, Al, Si, Be, Na, P, K, Mn, Fe, Rb and Cs; however, only the Li, Al, and Si have consistent errors below 20%. Thin sections were produced and observed with optical microscopy and cathodoluminescence (CL) to control the purity and mineral paragenesis of the samples. The petalite pellets were also controlled with cold CL since petalite crystals often present fine spodumene and quartz inclusions.