Sector Zoning Research Articles

MINERALOGICAL, PETROGRAPHIC AND GEOCHEMICAL EVIDENCE FOR ZIRCON FORMATION CONDITIONS WITHIN THE BURPALA MASSIF, NORTHERN BAIKAL REGION

This paper reports investigation on zircons from quartz syenite, alkaline and foid syenite, as well as metasomatic rock from the fenitization zone hosted by the Burpala massif. It is performed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), cathodoluminescence (CL), laser ablation inductively coupled plasma mass spectrometry (LA ICP MS), and Raman spectroscopy. Generally, all zircons from igneous rocks show rhythmic, crystal growth zoning or sector zoning (type I) except for some zircons from alkaline syenites (type II) showing patchy zoning. They systematically contain pores or cavities. The REE patterns of magmatic zircons share similar features: e.g. depletion of LREE ((Yb/La)N up to 35000), large positive Ce (Ce/Ce* 6–427) and small negative Eu (Eu/Eu* 0.37–0.93) anomalies. Zircons crystallized from quartz syenites at 830±30 °C at the early stage of rock formation, while zircons from alkaline and foid syenites crystallized at the later stage of rock formation (680–750 °C). Meanwhile, crystallization of zircons with rhythmic zoning (type I) occurs at later magmatic stage, while the formation zircons of type II is probably related to the separation of the highly fluorinated aqueous fluid from the residual melt.Zircons from fenites have a bipyramidal habit holding a heterogeneous mosaic core and a homogeneous (or rhythmic zoning) rim. The cores of zircon show flat REE patterns without significant anomalies, while the rims are characterized by noticeable fractionation of REE ((Yb/La)N 85–615) and show a positive Ce anomaly (Ce/Ce* 4–18). The Raman spectra of the cores show a higher degree of crystallinity than the rims, and their flat REE spectra are probably related to the contamination by micro inclusions. The discordant U-Pb age of 295±3 Ma was obtained for zircon rims, which is consistent with the age of formation of igneous rocks of the Burpala massif (298–291 Ma). The latter supports the syngenetic origin of metasomatic ore mineralization with the main stage of massif formation.

Exploring intrusive processes through the crystal cargo of volcanic rocks: The case of lava flows from Taranaki volcano, New Zealand

The present-day edifice of Taranaki volcano, New Zealand, is largely made up of lava flows extruded over approximately the last 8 kyr. The crystal cargo of plagioclase, pyroxene and amphibole in these lavas displays varied major, minor, and trace element zoning patterns, pointing to long and complex crystal growth histories. Crystal zoning patterns do not vary systematically between stratigraphic units, and multiple patterns are seen within the same sample over very short length scales. Intracrystalline elemental variations reveal mineral-melt interactions, which result in repeated resorption and recrystallisation in varied environments. Variable degrees of undercooling are evidenced by clinopyroxenes, with most crystals displaying sector zoning (ΔT < 50 K), while others only show concentric zoning, which suggests very low ΔT. The common occurrence of resorbed cores within the crystals and the prevalence of glomerocrysts indicate antecrystic and/or xenocrystic origins and crystal aggregation processes. We hypothesise that the repeated intrusion of melts into the crustal basement of Taranaki volcano has resulted in the formation of a heterogeneous subsolidus plutonic to supersolidus mushy (∼15–55 vol% crystals) system that interacts with intruding melts from the mantle. These interactions result in disaggregation of crystal clots from the plutonic intrusives and remobilization of the crystals through various sub-environments of small ephemeral mush pockets. Eruption-triggering injections of melt then pick up these crystals with varied growth histories to be extruded.

Extent and survival of zoned pyroxene within intrusions hosting magmatic sulfides: Implications for zoned pyroxene as a prospectivity indicator

AbstractChromium-zoning patterns in pyroxene from the economically significant Ni-Cu sulfide deposits at Nova-Bollinger (Western Australia) and Kevitsa (Northern Finland) were investigated using XRF mapping, automated mineralogy, and EPMA analyses. At Nova-Bollinger, complex Cr-zoning patterns are found widely throughout the cumulus orthopyroxene and clinopyroxene within the Lower Intrusion, a small chonolith that hosts the vast extent of the sulfide mineralisation. Cumulus pyroxenes with visible sector and abrupt zonation patterns have been found up to 150 m vertically away from the massive sulfide ore. Complex zoning patterns are observed throughout the Kevitsa intrusion, in the form of strong oscillatory zoning in cumulus clinopyroxene and sector zoning in idiomorphic orthopyroxene oikocrysts. Kevitsa pyroxenes show varying degrees of hydration, leading to epitaxial replacement by amphibole. Cr zonation is visible through the early stages of this alteration, with preservation enabled by the presence of Cr-rich epitaxial amphibole; however, the remnant zoning is lost as the amphibole alteration progresses. Results suggest that Cr zonation in pyroxene may be an effective indicator of dynamic recharged conduits and therefore an indicator of favourable conditions for metal enriched magmatic sulfide ore formation. Such indicators have significant vertical extent from the ore body and can survive partial alteration, which makes them a useful tool for prospectivity assessment of drilled intrusions. Furthermore, our data show that there is potential for complexly zoned pyroxene to be used as an ex-situ prospectivity indicator in glacial till.

Provenance Analysis and Diagenesis Using Integrated SEM-Cathodoluminescence and Optical Microscopy for the Sandstones of the Pirispiki Formation, Kurdistan Region, Northern Iraq

The paragenetic history and provenance of framework grains in marginal marine and deltaic sandstones of the Pirispiki Formation in two sections, (Ora and Kaista), northern Iraq were examined. This was achieved using an integrated approach employing scanning electron microscopy-cathodoluminescence (SEM-CL), and optical microscopy. The Pirispiki Formation is lithologically characterized by alternating layers of thin- and thick-bedded sandstones. These were intercalated with thin laminae of grey-black shale. Petrographic analysis revealed that the dominant detrital grains in the mature quartz arenite sandstone were monocrystalline quartz grains with undulose extinction. The diagenetic analysis of the sandstones documented several processes that occur in three distinct stages. The SEM-CL technique enabled the identification of two distinct quartz overgrowth phases. Quartz cementations are of two types, the earliest phase and the most significant by volume is the Q1 cement characterized by dark non-luminescence which led to the destruction of most of the primary pores and the healing of mechanically induced cracks. Q2 cement is formed after major compaction and is characterized by bright luminescence with sector zoning, revealing an intricate SEM-CL zonation. CL revealed five special textures within detrital quartz grains including healed fractures and zoning. The provenance of the detrital quartz grains indicated the dominance of plutonic and metamorphic sources, with trace amounts originating from volcanic sources. These were mostly derived from the Bitlis Massif Zone in Turkey.

Recognition of Neogene tin mineralization in the Southeast Asian tin belt

The Southeast (SE) Asian tin belt is a major tin producer globally, with a prolonged mineralization history from the Permian to Paleogene (ca. 285−45 Ma). Tin deposits in this region are typically associated with tectonic settings that involve subduction and collision of the Paleo-, Meso-, and Neo-Tethys slabs. Ca. 40 Ma, a notable transition occurred in the tectonic regime of SE Tibet, with the Neo-Tethys subduction giving way to lateral extrusion of the Indochina block along major strike-slip faults. Previously, it was believed that this shift had brought tin mineralization to a halt. In this study, we present in situ laser ablation−inductively coupled plasma−mass spectrometry U-Pb cassiterite ages of 21−19 Ma from the Yunling tin deposit located in western Yunnan, China. Yunling produces gem-quality cassiterite that is transparent but contains low U contents, which renders usual U-Pb dating techniques unusable. To address this, a customized dating protocol involving cathodoluminescence (CL) imaging and testing of U distribution on crystallographically well-defined cassiterite crystals was applied. The study revealed two types of primary microstructures in cassiterite: volumetrically dominant concentric oscillatory growth zones and subordinate CL-dark sector zones. The U content shows a preferential enrichment in the CL-dark sector zones, typically tens of parts per million (ppm), which is two orders of magnitude greater than the U content in the concentric zone. This is significant, as the dating results (21−19 Ma) obtained through the targeted selection of CL-dark sector zones represent the youngest tin mineralization event in the SE Asian tin belt. Additionally, these results challenge the established belief that the ore-hosting Indosinian granite, dated to ca. 215 Ma, was related to Sn mineralization in the Yunling area. We suggest that emplacement of the early Neogene Sn mineralization at Yunling may be genetically connected to extensive delamination of the lithosphere in southeastern Tibet. The lithospheric delamination led to the upwelling and decompression partial melting of the asthenosphere, which provides a plausible explanation for the high temperature required for the release of Sn from biotite-dehydration melting of sedimentary protolith. The study also highlights the potential of Oligocene−Miocene-aged granites situated in the Sanjiang Tethys and adjacent areas of western Yunnan as prospective exploration targets for tin mineralization.

Trace element concentrations and chemical zoning of spodumene from magmatic and hydrothermal origins

Spodumene is a major lithium ore mineral mined from granitic pegmatites and can crystallize (1) from magma, (2) from hydrothermal fluid in miarolitic cavities or fracture-filling units, or (3) as a product of petalite breakdown. Although spodumene’s purity influences the economic value of lithium ore, its trace-element geochemistry is not entirely understood. This study investigated 24 unaltered spodumene samples from 21 localities formed through each of these three modes of origin. The chemical zoning of each spodumene sample was characterized using cathodoluminescence (CL), micro-X-Ray fluorescence mapping (µXRF), and/or qualitative laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) line scans, whereas the concentrations of trace elements were quantified using LA-ICP-MS point analyses. Intra-crystalline chemical zoning was present in all three spodumene types as either oscillatory growth bands and/or sector zoning. For the four most abundant transition and post-transition metals analyzed (Fe, Mn, Ga, Sn), the concentrations ranged from below detection to 10510 ppm (Fe), 1850 ppm (Mn), 300 ppm (Ga), 320 ppm (Sn), whereas Rb and Cs were below detection. Magmatic spodumene had the highest mean concentrations of Fe (2345 ppm) and Sn (94 ppm), hydrothermal spodumene had the highest mean concentrations of Mn (641 ppm) and Ga (94 ppm), and spodumene formed from the breakdown of petalite consistently had the lowest mean concentrations, though there was significant overlap in the datasets. In addition, texturally similar spodumene-quartz intergrowths of primary and secondary origins were distinguished via trace-element geochemistry. Principle component analysis of Fe, Mn, Ga, Sn, Ti, and Zn values from all 325 LA-ICP-MS measurements showed discrimination by CL color, as well as color in handsample for gem-varieties of hydrothermal spodumene.

Geochemistry of hydrothermal and stream sedimentary rutile in the Tiegelongnan porphyry-epithermal Cu (Au) deposit, Tibet: A tool for exploration

Rutile is a common and stable mineral in porphyry Cu deposits, and morphology and geochemistry of rutile are recognized as a potential indicator mineral for exploration. In this study, we investigate physical features and chemical composition of hydrothermal rutile in the Tiegelongnan porphyry-epithermal system, as well as rutile in stream sediments nearby to establish a method to apply rutile as an exploration proxy. Four stages of hydrothermal rutile have been identified. Potassic alteration stage rutile (Rt1) is associated with biotite, with elongated and acicular shape and small grain size (20–50 μm). Rutile from lower temperature phyllic alteration (Rt2), quartz veins (Rt3), and advanced argillic alteration (Rt4), has characteristic sector zoning and larger grain size (50–150 μm). The sector zoning is more commonly present in Rt2, Rt3, Rt4, that are associated with high-grade Cu mineralization, and is associated with incorporation of W, Fe, V, Sn, and Zr. The earlier rutile (Rt1) also has a geochemical signature different from the other three types of rutile, characterized by significantly lower Al, Cu, Zr, Nb, Sn, Hf, and higher Sc and Fe contents. Low-temperature hydrothermal alteration stage rutile (Rt2, 3, 4) share many geochemical similarities, but Rt3 has higher Nb and Ta contents (median = 3371.0 and 176.0 ppm, respectively), whereas Rt4 has higher Sb content (median = 24.3 ppm).Rutile trace element data from this study and literature are integrated to develop a Partial Least Square-Discriminant Analysis (PLS-DA) multivariate statistics plots that can discriminate porphyry Cu deposit rutile from orogenic gold and VHMS deposits, as well as rutile from different alteration stages. The PLS-DA plots predict that stream sedimentary gold-bearing rutile (RtSAu) adjacent to the Tiegelongnan deposit are derived from the deposit, and mainly from low-temperature phyllic and advanced argillic alteration stages. This is consistent with geochemical similarity between the RtSAu and the Tiegelongnan low-temperature hydrothermal rutile (Rt2 + Rt4). This is further confirmed by a U-Pb age of 125.3 ± 4.7 Ma (n = 24, 2σ) for RtSAu, which is consistent with the main porphyry mineralization age of ∼ 120 Ma in the Tiegelongnan deposit. We infer that the RtSAu may have formed during the ∼120 Ma epithermal system at Tiegelongnan, which has already largely eroded. In general, our findings prove the capability of using rutile, by combing the texture, geochemical compositions, geochronology, PLS-DA tools, and their spatial distribution, as a proxy mineral for the exploration of porphyry Cu deposits.

Zircon and cassiterite U-Pb dating identifies the first Early Cretaceous Sn deposit in Fujian: Implication for tin mineralization potential in the southeastern coastal belt of South China

The Xiayi Sn deposit, located in the Sanming city, southeast China, is the largest Sn deposit in Fujian province. The mineralization mainly consists of cassiterite-bearing veinlets and stockworks, and it is spatially associated with the granodiorite porphyry. Despite its economic significance, few studies have been carried out, and the mineralization age remains unknown. In this paper, we present the first geochronological data on the cassiterite and the associated granodiorite porphyry, Hf isotope of the zircon, and trace element compositions of cassiterite from the Xiayi Sn deposit. These data give precise age of the Sn mineralization and constrain its relationship with the granitic intrusion. Zircon U-Pb dating of the ore-related granodiorite porphyry yielded the age of 138.3 ± 1.8 Ma, which agreed well with the cassiterite U-Pb age of 136.5 ± 1.4 Ma, documenting the genetic link between the Sn mineralization and granitic magmatism. Zircon εHf(t) ranged from −4.5 to −1.8 with a weighted mean of −3.4 and the Hf model ages (TDM2) vary from 1.31 to 1.47 Ga with a mean value of 1.40 Ga. These data indicate that the granodiorite porphyry originates from the partial melting of the crustal materials of Mesoproterozoic basement and show the addition of mantle-derived materials, similar to typical Sn mineralized granite in the southeastern coastal tin belt and Nanling tungsten-tin belt. Besides, cassiterite from Xiayi deposit show clear CL-bright and CL-dark sector zonation in the cathodoluminescence images. LA-ICP-MS trace element analyses of cassiterites indicate a high Ti and Fe but low Nb and Ta contents in both CL-bright and CL-dark sector zones, while the W content is significantly high in the CL-dark zone and low in the CL-bright zone. Cassiterite trace element compositions together with the mineralization pattern and alteration assemblages indicate that Xiayi is a porphyry tin deposit. These results provide proof of the extension of the southeastern coastal Sn metallogenic belt and offer potential breakthroughs in tin deposit exploration in southwestern Fujian Province.

Trace element partitioning in basaltic systems as a function of oxygen fugacity

Along with temperature, pressure and melt chemistry, magmatic oxygen fugacity (fO2) has an important influence on liquid and solid differentiation trends and melt structure. To explore the effect of redox conditions on mineral stability and mineral-melt partitioning in basaltic systems we performed equilibrium, one-atmosphere experiments on a picrite at 1200–1110 °C with fO2 ranging from NNO-4 log units to air. Clinopyroxene crystallizes from 1180 °C to near-solidus, along with plagioclase, olivine and spinel. Olivine Mg# increases with increasing fO2, eventually reacting to pigeonite. Spinel is absent under strongly reducing conditions. Mineral-melt partition coefficients (D) of redox-sensitive elements (Cr, Eu, V, Fe) vary systematically with fO2 and, in some cases, temperature (e.g. DCr in clinopyroxene). Clinopyroxene sector zoning is common; sectors along a- and b-axes have higher AlIV, AlVI, Cr and Ti and lower Mg than c-axis sectors. In terms of coupled substitutions, clinopyroxene CaTs (MgSi = AlVIAlIV) prevails under oxidized conditions (≥ NNO), where Fe3+ balances the charge, but is limited under reduced conditions. Overall, AlIV is maximised under high temperature, oxidizing conditions and in slowly grown (a–b) sectors. High AlIV facilitates incorporation of REE (REEAlIV = CaSi), but DREE (except DEu) show no systematic dependence on fO2 across the experimental suite. In sector zoned clinopyroxenes enrichment in REE3+ in Al-rich sectors is quantitatively consistent with the greater availability of suitably-charged M2 lattice sites and the electrostatic energy penalty required to insert REE3+ onto unsuitably-charged M2 sites. By combining our experimental results with published data, we explore the potential for trace element oxybarometry. We show that olivine-melt DV, clinopyroxene-melt DV/DSc and plagioclase-melt DEu/DSr all have potential as oxybarometers and we present expressions for these as a function of fO2 relative to NNO. The crystal chemical sensitivity of heterovalent cation incorporation into clinopyroxene and the melt compositional sensitivity of the Eu2+–Eu3+ redox potential limit the use of clinopyroxene-melt and plagioclase-melt, however, olivine-melt DV affords considerable precision and accuracy as an oxybarometer that is independent of temperature, and crystal and melt composition. Variation of DV and DV/DSc with fO2 for olivine and clinopyroxene contains information on redox speciation of V in coexisting melt. By comparing the redox speciation constraints from partitioning to data from Fe-free synthetic systems and XANES spectroscopy of quenched glasses, we show that homogenous equilibria involving Fe and V species modify V speciation on quench, leading to a net overall reduction in the average vanadium valence. Mineral-melt partitioning of polyvalent species can be a useful probe of redox speciation in Fe-bearing systems that is unaffected by quench effects.

Kinetic partitioning of trace cations between zoned clinopyroxene and a variably cooled-decompressed alkali basalt: Thermodynamic considerations on lattice strain and electrostatic energies of substitution

We present kinetic partitioning data for trace cations measured in zoned clinopyroxene crystals obtained from a variably cooled and decompressed olivine basalt erupted at Mt. Etna volcano in Italy. Supersaturation effects and compositional heterogeneities at the interface melt lead to the development of sector zoning, concentric zoning, and patchy zoning in clinopyroxene crystals. Apparent partition coefficients between compositionally different growth layers and adjacent melts (Di) for isovalent groups of trace elements are tested for internal consistency on the thermodynamic basis of lattice strain (ΔGstrain) and electrostatic (ΔGelec) energies of substitutions. The excess energy of partitioning (ΔGpartitioning) for trace cations in zoned crystals accounts for a kinetic incorporation control leading to large enthalpic effects through distortion of the lattice and changes in the electrostatic forces. ΔGpartitioning depends upon the complementary relationship between ΔGstrain and ΔGelec, which is the most appropriate thermodynamic description for the accommodation of rare earth elements and high field strength elements in the lattice site of zoned crystals. Polyhedral sectors, skeletal forms, and overgrowth zones have Di values settled by the number of charge-balanced and -imbalanced configurations taking place in the lattice site as a function of aluminium in tetrahedral coordination, and crystal structural changes produced by heterovalent cation substitutions. In an energetically unstable macroscopic system ruled by cooling and decompression, thermodynamic requirements for the crystallochemical control of Di encompass the attainment of local equilibrium at the crystal-melt interface via the establishment of small-volume reaction kinetics. The requisite of local interface equilibrium is however susceptible to the anisotropic growth velocity of each specific clinopyroxene surface, thereby giving reason to different energetic properties of the crystallographic site. This axiomatic control requires that transition metal cations partition also in consideration of electronic effects related to the crystal field stabilization energy. The overriding implication is that Di values for trace cations having different size, charge, and electronic configuration serve as sensitive probes of the different crystal growth mechanisms, surface incorporation sites, and arrangements of atoms at the lattice-scale. In this perspective, fractional crystallization modeling of 2011–2013 bulk rock data from lava fountains indicates that the compositional evolution of magmas erupted at Mt. Etna cannot be described by a unique equilibrium value of Di for a given clinopyroxene-melt interface. The leverage of interface kinetics is distinctively dominant along the subvolcanic plumbing system, thereby requiring that values of Di differ for structurally and compositionally distinct zones in clinopyroxene phenocrysts. To successfully interpret the trace element signature of Etnean magmas, the archetypal constancy of partition coefficient at bulk thermodynamic equilibrium must be in some measure reappraised in favor of the establishment of a local interface equilibrium upon highly dynamic crystallization and growth conditions.

The Influence of Undercooling and Sector Zoning on Clinopyroxene–Melt Equilibrium and Thermobarometry

Abstract Thermobarometry provides a critical means of assessing locations of magma storage and dynamics in the lead-up to volcanic eruptions and crustal growth. A common approach is to utilise minerals that have compositions sensitive to changes in pressure and/or temperature, such as clinopyroxene, which is ubiquitous in mafic to intermediate magmas. However, clinopyroxene thermobarometry may carry significant uncertainty and require an appropriate equilibrium melt composition. In addition, the degree of magma undercooling (ΔT) affects clinopyroxene composition and zoning, with common sector zoning potentially obfuscating thermobarometry results. Here, we use a set of crystallisation experiments on a primitive trachybasalt from Mt. Etna (Italy) at ΔT = 25–233 °C, P = 400–800 MPa, H2O = 0–4 wt % and fO2 = NNO + 2, with clinopyroxene crystals defined by Al-rich zones (prisms and skeletons) and Al-poor zones (hourglass and overgrowths) to assess common equilibrium models and thermobarometric approaches. Under the studied conditions, our data suggest that the commonly applied Fe–Mg exchange (cpx-meltKdFe–Mg) is insensitive to increasing ΔT and may not be a reliable indicator of equilibrium. The combined use of DiHd (CaMgSi2O6 + CaFeSi2O6) and EnFs (Mg2Si2O6 + Fe2Si2O6) models indicate the attainment of equilibrium in both Al-rich and Al-poor zones for almost all investigated ΔT. In contrast, CaTs (CaAl2SiO6) and CaTi (CaTiAl2O6) models reveal substantial deviations from equilibrium with increasing ΔT, particularly in Al-rich zones. We postulate that this reflects slower diffusion of Al and Ti in the melt compared with Ca and Mg and recommend the concurrent application of these four models to evaluate equilibrium between clinopyroxene and melt, particularly for sector-zoned crystals. Thermobarometers calibrated with only isothermal–isobaric experiments closely reproduce experimental P–T at low ΔT, equivalent to natural phenocrysts cores and sector-zoned mantles. Models that also consider decompression experiments are most accurate at high ΔT and are therefore suitable for outermost phenocryst rims and groundmass microlites. Recent machine learning approaches reproduce P–T conditions across all ΔT conditions. Applying our experimental constraints to sector-zoned microphenocrysts and groundmass microlites erupted during the 1974 eccentric eruption at Mt. Etna, we highlight that both hourglass and prism sectors are suitable for thermobarometry, given that equilibrium is sufficiently tested for. The combination of DiHd, EnFs, CaTs and CaTi models identifies compositions closest to equilibrium with the bulk melt composition, and results in smaller differences in P–T calculated for hourglass and prism sectors compared with applying only DiHd and EnFs equilibrium models. This provides a framework to assess crystallisation conditions recorded by sector-zoned clinopyroxene crystals in mafic alkaline settings.

Relationship between cathodoluminescence response and trace element characterization of cassiterite from the Yunling tin deposit in western Yunnan, China: Implications for substitution mechanism and ore genesis

Cathodoluminescent (CL) imaging, combined quantitative geochemical analyses using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), was employed to study the cassiterite crystals from the Yunling tin deposit in western Yunnan Province, China. This investigation aimed to establish a connection between CL response with trace element compositions. The CL imaging of a well-formed centimeter-scale euhedral single crystal of cassiterite revealed two types of primary growth domains, namely oscillatory and sector zoning. High spatial resolution LA-ICP-MS spot analysis along three centimeter-scale profiles revealed that the oscillatory zoning patterns were primarily defined by the concentrations of Nb and Ta. The CL response associated with the oscillatory zoning was attributed to the interplay between activators such as Ti, Nb, Ta, and V, and quenchers like Fe. On the other hand, sector zoning exhibited significantly high W content, reaching three orders of magnitude greater than that in the oscillatory zoning. Consequently, the sectors displayed a dark CL response. Furthermore, U showed a sectoral preference, with contents within the sector zoning examined in this study reaching up to 10 ppm. The systematic variations in geochemical compositions suggest that the incorporation of trace elements in Yunling cassiterite involves a coupled substitutional mechanism of pentavalent and trivalent elements (e.g., Sc3+ + V5+ ↔ 2Sn4+) with H+ potentially serving as a compensating ion for the Fe3+ excess.It is worth noting that the trace element enrichment and potential substitution in the sector and non-sector regions of the single crystal may differ significantly. Therefore, the use of cassiterite trace elements as indicators of the mineralization environment requires careful consideration, particularly when analyzing randomly selected particles obtained from crushing. In such instances, it is recommended to utilize cassiterite samples that exhibit a preserved crystal texture extending from the core to the rim, such as cassiterite in thin sections or morphology-integral cassiterite separates. Moreover, the contrasting W contents observed between the sector and non-sector zones may provide an explanation for two trends in the Fe–W diagram of cassiterite associated with granite that were previously-unspecified.

Tracking timescales of magma reservoir recharge through caldera cycles at Santorini (Greece). Emphasis on an explosive eruption of Kameni Volcano

Pre-eruptive processes and their timescales are critical information for risk management at explosive volcanoes, and Santorini caldera (Greece) provides an excellent context in which to approach this subject. We ask two questions. First, are pre-eruptive processes the same for small and big eruptions? To investigate, we performed a multi-mineral diffusion timescale study of a small explosive eruption of Kameni Volcano and compared the results with those published for larger caldera-forming eruptions at Santorini. The Kameni dacite resembles products of larger eruptions in being crystal-poor, containing plagioclase with antecrystic cores and autocrystic rims, bearing orthopyroxene with sector zoning and phantom skeletal morphologies, and showing evidence for mixing of different silicic magmas prior to eruption. Diffusion timescales from Mg-Fe profiles in orthopyroxene and clinopyroxene phenocrysts are &amp;lt;1–23 years, and Mg diffusion modelling in plagioclase gives &amp;lt;10 years. Our physical model for the Kameni eruption is similar to those proposed for larger eruptions, where silicic melt produced in gabbroic to dioritic lower to middle crustal mush bodies is transferred (along with entrained mafic magma) to an upper crustal reservoir. Crystals grow in the hydrous silicic melts due to decompression, cooling, and magma mixing during ascent and injection into upper crust. We propose that large eruptions are preceded by similar processes as small ones, but on a larger scale. Our second question: do diffusion timescales relate to eruptive volume or position in a caldera cycle? For this, we obtained orthopyroxene Mg-Fe diffusion timescales for three additional eruptions, growing our orthopyroxene timescale database to seven eruptions of different sizes and cycle timings. No clear relationship exists between diffusion timescale and volume; however, timescales are systematically shorter (&amp;lt;0.01–10 years) early in a cycle and longer (1–5,000 years) late in a cycle. Thermal maturation and H2O-flushing of the crustal magma reservoir through the caldera cycle could explain this, as the reservoir would change from a rigid to more mushy state as the cycle progresses. This would change the mechanical response to melt input and allow accumulation of progressively larger melt layers in the upper crust, resulting in increasing crystal residence times.

IN SITU U-Pb DATING OF GARNET AND CASSITERITE FROM THE KANBAUK W-Sn(-F) SKARN DEPOSIT, DAWEI REGION, SOUTHERN MYANMAR: NEW INSIGHTS ON THE REGIONAL Sn-W METALLOGENY IN THE SOUTHEAST ASIAN TIN BELT

Abstract Skarn ores have recently been identified beneath the historically mined placer Sn deposit at Kanbauk of the Dawei region, southern Myanmar. A large-tonnage skarn ore reserve at Kanbauk is estimated to be over 100 million tonnes, with reported ore grades of 0.17% WO3, 0.26% Sn, and 15.4% CaF2, potentially making it one of the largest W-Sn skarn deposits in the Southeast Asian tin belt. The mineralized skarns lie between marbles to the east and metasediments of the Mergui Group to the west. The timing of the mineralization is unclear, and thus the genetic relationship with regional magmatic events is not known. We report laser ablation-inductively coupled plasma-mass spectrometry U-Pb ages of garnet and cassiterite from the mineralized skarns. Garnet grains from the massive prograde skarns are typically subhedral to euhedral and show both sector and oscillatory zoning. They have 15 to 23% andradite (Ad), 55 to 67% grossularite (Gr), and 16 to 30% pyralspite (Py) (Ad15-23Gr55-67Py16-30) and contain 0.08 to 306 ppm U with a lower intercept 206Pb/238U age of 56.0 ± 1.5 Ma. Cassiterite grains from retrograde veinlets are subhedral to anhedral and have U contents from 110 to 12,000 ppm with a lower intercept 206Pb/238U age of 54.2 ± 1.7 Ma. Garnet and cassiterite have ages consistent within error and can be taken to indicate the formation of the Kanbauk W-Sn(-F) skarn deposit at around 55 Ma. Together with published ages of primary Sn-W deposits in the Dawei region, our study confirms a westwardly younging trend of mineralization toward the coast and provides support for rollback of the Neo-Tethyan subducting slab since the Late Cretaceous, which is considered as the main mechanism for the regional, extensive Sn-W mineralization.

The effect of variations in cooling rates on mineral compositions in mid-ocean ridge basalts

We present textural and chemical analyses of minerals from a 150 m thick sequence of submarine mid-ocean ridge basalts from the South China Sea in order to showcase the effect of variations in magma cooling rates on mineral texture and mineral composition. Groundmass plagioclase and clinopyroxene show gradual changes in texture and composition as flows grade from slowly cooled, meter-thick massive flows to more rapidly cooled dm-thick pillow lobes with quenched glassy margins. The corresponding change in cooling-rate is estimated to vary from <1 to ≥100 °C/h. With increasing cooling rate, plagioclase forms elongated, sector-zoned swallow-tail crystals. Sector zoning is associated with increasing FeO (up to 1.5 wt%) and MgO (up to 0.6 wt%) abundances at near-constant anorthite (An), related to a two orders of magnitude increase in growth rate. Sr, Ba, Li and Ti abundances remain constant and appear unaffected by kinetic factors at such growth rates. With increasing cooling rate clinopyroxene becomes dendritic, and its composition is sensitive to changes in crystallization conditions. Increasing cooling rate (<1 to ≥100 °C/h) leads to increasing Al2O3 (average of 3.2 to 4.3 wt%), TiO2 (1.3 to 2.8 wt%) and Na2O (0.37 to 0.44 wt%) and a decrease in SiO2 (50.1 to 46.4 wt%) and Mg#Fetot, i.e., molar MgO/(MgO + FeOtot), from 71.3 to 53.1. Trace element abundances (Y, Zr, Ce, V, Sr) in clinopyroxene increase by up to an order of magnitude at cooling rates ≥100 °C/h and become more heterogeneous spatially. These results support experimental evidence that rapid crystal growth leads to significant departure of mineral compositions from equilibrium, in particular for clinopyroxene. Although plagioclase composition remains relatively insensitive to changes in growth conditions at the studied cooling rates, the sensitivity of clinopyroxene composition to growth rates imply that it should be used with caution as a tool to infer magmatic crystallization conditions.

Crystallization and Solidification of Poikilitic and Granular Rocks in the Ultramafic Sequence of the Xinjie Layered Intrusion (SW China): Constraints from Complex Growth Zoning of Clinopyroxene and Spatial Variation of Dihedral Angles

AbstractCrystallization and solidification pathways in crustal magma chambers control the chemical and textural evolution of igneous rocks. However, deciphering these codes from completely solidified cumulates is challenging and requires a full understanding of growth processes of minerals and textures of rocks. In this study, we collected samples from a ca. 380-m-thick drill core intersecting the ultramafic sequence of the Xinjie layered intrusion in SW China, which is composed of wehrlite with poikilitic clinopyroxene (Cpx), and clinopyroxenite and olivine clinopyroxenite with euhedral to subhedral Cpx grains. Using micro-X-ray fluorescence and electron probe micro-analyzer mapping techniques, we found that the Cpx grains in clinopyroxenite and olivine clinopyroxenite are characterized by sector-zoned, Cr-rich cores, whereas the Cpx oikocrysts in wehrlite only show Cr-rich cores without sector zoning. The sector-zoned cores of the Cpx grains are widespread in clinopyroxenite and olivine clinopyroxenite and consist of Si–Mg-rich hourglass sectors and Cr–Al–Ti-rich prism sectors, indicating rapid growth of the Cpx grains due to moderate degrees of undercooling, which may be induced by fast cooling during initial emplacement of Cpx-saturated magma into cold country rocks. The sector-zoned Cpx grains thus likely constructed the initial crystal framework in the magma chamber. In contrast, the absence of sector zoning in Cr-rich cores of the Cpx oikocrysts indicates that an olivine-saturated magma may have intruded a high-temperature, Cpx-laden crystal mush so that magma undercooling was significantly reduced or eliminated and no sector zoning developed in the Cpx oikocrysts. Such a process may also result in the spatial variation of the medians of Cpx–Cpx–plagioclase dihedral angles (Θccp) in clinopyroxenite, which shows a significant reduction from an original impingement angle of ~60° in the middle and upper parts to ~40° in the basal part of the sequence. The reduction of Θccp could be attributed to melt-present textural equilibration in the Cpx-laden mush that was sustained by additional heat supplied by massive olivine-saturated melt input in the ~40-m-thick basal part. Here, we propose that the ultramafic sequence of the Xinjie layered intrusion may have formed by the intrusion of primitive, olivine-saturated magma into an early-formed Cpx-laden mush in a manner of sill-like sheets. This study provides new perspectives on the early history of a magma chamber and emphasizes the role of sill intrusion of primitive magmas into crystal mush in the formation of ultramafic sequences in layered intrusions, which has been relatively overlooked in previous studies.

The Sukari Gold Deposit, Egypt: Geochemical and Geochronological Constraints on the Ore Genesis and Implications for Regional Exploration

AbstractThe Sukari gold deposit (&amp;gt;15 Moz Au) in the Eastern Desert of Egypt is hosted by a deformed granitoid stock (Sukari tonalite-trondhjemite intrusion) and mainly occurs as a network of crosscutting sulfide-bearing quartz (± carbonate) veins and intensely sulfidized-silicified-sericitized wall rock. Emplacement of the Sukari intrusion into a tectonized Neoproterozoic accretionary complex was controlled by a system of NE- to NNE-trending oblique faults that are related to a deep-seated positive flower structure. A robust genetic model has been hampered by the poorly understood relationships between gold mineralization and host rocks. In this study, zircon U-Pb ages of three samples from the Sukari intrusion define a crystallization age of ~695 ± 2 Ma. In contrast, hydrothermal sericite from the ore zone yields an 40Ar/39Ar age of ~625 ± 3 Ma, which coincides with the onset of major sinistral transpression in the region.Features including sigmoidal morphology of gold quartz veins and abundant subhorizontal tension gashes alongside widespread brecciation and recrystallization suggest that quartz veining occurred during renewed shortening and exhumation through the brittle-ductile transition. Petrographic and micro-X-ray fluorescence (µXRF) studies indicate that disseminated gold and sulfides, commonly associated with sericite and carbonate alteration, are mostly confined to stylolitic bands in the quartz veins. Oscillatory and sector zoning patterns, irregular As-rich bands, and truncations between early- and late-genetic pyrites reflect variations in temperature and mechanism of ore deposition, demonstrated by variable As/S and Co/Ni ratios in the different pyrite generations. Laser ablation-inductively coupled plasma-mass spectrometry analysis pinpoints the covariance of gold and arsenic contents in pyrite, but free milling gold inclusions in microfractures consistently have a mercury-bearing electrum composition, depicting different ore formation stages.Ore fluids with δ34SH2s values of –1.9 to –3.0‰, modeled from gold-associated pyrite and arsenopyrite assemblages with nearly identical δ34S values, suggest a likely single source of sulfur. Alternatively, multisourced sulfur could have extensively mixed and equilibrated by fluid reaction with carbonaceous wall rock. Gold deposition was triggered by abrupt changes in fluid pH and fO2. As an implication for future exploration, sites of maximized strain gradients adjacent to granitoid bodies along extensive transpression zones in the district could be highly prospective targets, particularly where imprinted by sericite-carbonate ± graphite alteration.

Concurrent magma mixing and crystallization processes revealed by clinopyroxene macrocrysts from Lamont guyot lavas in NW Pacific

Minerals in volcanic rocks have been commonly used to reconstruct the physicochemical conditions of crystallization and magma chamber processes (magma mixing and recharge) prior to eruption which are fundamental to deduce the petrogenesis of volcanic rocks. Here we present mineral chemistry including in situ major-trace element and Sr isotopic data for clinopyroxene (Cpx) and plagioclase macrocrysts from lavas collected from Lamont guyot in the Wake seamount group, NW Pacific. The Cpx macrocrysts display normal and reverse zoning or complex zoning (e.g., combination of reverse, normal, sector and/or patchy zoning). The normally-zoned Cpx macrocrysts are euhedral and in Fe Mg equilibrium with the host rock compositions. In contrast, the cores of reversely- and complexly-zoned Cpx macrocrysts are in textural (e.g., resorption texture) and chemical (very low Mg#) disequilibrium with their host rock compositions. These reversed cores, however, form coherent compositional trends with and display parallel trace element patterns to the normally zoned Cpx crystals, suggesting that these resorbed cores are most likely antecrysts which crystallized from progenitor melts. The continuously changing major-trace element contents with Cpx Mg# values can be explained by crystallization of these Cpx crystals from melts that progressively fractionate Cpx, plagioclase and Fe Ti oxides. Together with those of the complexly-zoned plagioclase, the complex zoning patterns and large ranges of La/Yb and Sm/Yb ratios at a restricted Cpx Mg# range record magmatic processes of fractional crystallization and mixing in the magma plumbing system. The Cpx crystals from a single lava sample have various 87 Sr/ 86 Sr ratios (0.7025–0.7042) extending from HIMU (high μ = 238 U/ 204 Pb) to FOZO (focal zone) mantle components suggesting that the large 87 Sr/ 86 Sr variation in Cpx could be explained by mixing between HIMU and FOZO components. Our data suggest that frequent recharging of melts derived from different mantle sources and concurrent mixing and crystallization are important processes that shape the currently observed compositional variation of Lamont guyot lavas. • Textural and compositional zoning of Cpx from Lamont seamount lavas, NW Pacific • Cpx shows large trace element and 87 Sr/ 86 Sr variations at a restricted Mg# range. • Reverse and complex zoning textures of Cpx record magma recharge and mixing. • Mixing of multiple batches of HIMU- and FOZO-derived melts. • Concurrent mixing and crystallization played a key role in forming the Cpx crystals.

Genesis and mineralogical studies of zircons in the Alamas, Yurungkash and Karakash Rivers nephrite deposits, Western Kunlun, Xinjiang, China

Nephrite, an aggregate of fine-grained tremolite or actinolite, is mainly found in Mg-skarn at the contact zone between granitoids and dolomitic marble. The nephrite belt in the southern Western Kunlun Mountains in China is the largest in the world, and includes 11 major skarn deposits and >20 orebodies including the Alamas deposit. In addition, economic placer nephrite deposits occur along the Yurungkash & Karakash Rivers. The nephrite in these deposits contains numerous zircons and some grains have high δ18O values, but the genesis of these zircons is not clear. In this study, we investigated the formation mechanism of the nephrite and origin of zircons in nephrite based on the geochemical and δ18O characteristics of zircons in nephrite from the deposits at Alamas and along the Yurungkash & Karakash Rivers, as well as the CO isotopes of the dolomitic marble at Alamas. We found that zircons in nephrite often occur with tremolite and apatite and the major elements of these zircons are close to those of common magmatic zircon. Zircon grains in the Alamas nephrite are mainly subhedral, 80–130 μm long, 50–90 μm wide, and have clear oscillatory zoning. These zircons have similar REE patterns with Alamas granodiorite, including heavy REE (HREE) enrichment and large positive Ce anomalies (Ce/Ce* = 5.30–368). Such petrographic and geochemical characteristics suggest most zircons are magmatic zircons, with some experienced hydrothermal alteration. Zircon δ18O values in Alamas nephrite are 5.69 ‰–8.85 ‰ (n = 25; an exception of 13.35 ‰), close to those zircons in Alamas granodiorite (6.4 ‰–9.0 ‰) but higher than mantle magmatic zircon (5.3 ± 0.3 ‰). The δ13C (0.79 ‰–1.02 ‰) and δ18O (18.7 ‰–20.6 ‰) values of the Alamas dolomitic marble indicate formation by the partial dissolution of marine carbonate rocks. Zircons in nephrite from Yurungkash & Karakash Rivers deposits are mainly subhedral, 100–160 μm long, 80–30 μm wide, and show clear or obscure irregular zoning. They show HREE enrichment and relatively weak positive Ce anomalies (2.58–35.8), suggesting most zircons have magmatic origin, with some experienced hydrothermal alteration. Zircons from Yurungkash & Karakash Rivers have δ18O values range from 14.6 ‰ to 21.37 ‰ (n = 31; an exception of 9.03 ‰). Irregular baddeleyite grains occur in the nephrite, and fragmented or granular grains occur locally within the nephrite zircons or fissures of zircon. These baddeleyite may have formed via the following reaction between zircon and dolomite: 2Zr[SiO4] + CaMg[CO3]2 → 2ZrO2 + CaMg[SiO3]2 + 2CO2 at 660–710 ℃ and 3 kbar. In Yurungkash & Karakash Rivers nephrite deposits, considering these placer nephrite come from Mg-skarn, these high δ18O zircons probably have initially formed within endoskarn, close to the margin of the granitoid where marble with high δ18O was assimilated into the melt, and retain nice oscillatory and/or sector zoning.

Method of multidimensional scaling for evaluating the effectiveness of interaction between investment and construction sector enterprises and special economic zones in the aspect of improving the financial and innovative potential of construction industry

Introduction. The article is devoted to the study and application of method of multidimensional scaling to assess the process of interaction between enterprises of the investment and construction sector (ICS) and special economic zones (SEZ) to increase the financial, economic, and innovative potential of construction industry. The relevance of the study is due to the growing importance of using territorial development tools (SEZ) to solve the tasks of implementing technological changes aimed at increasing the emergence of a variety of innovative projects that will allow us to form completely different approaches to ensure continuous development in various construction sectors and transform existing methods of assessing and analyzing the financial and economic condition of ICS enterprises in terms of interaction with SEZ.&#x0D; &#x0D; Materials and methods. Proposed evaluation method in the article has a strict scientific consistency and an appropriate theoretical basis, which served as the basis for its development. Developed method of multidimensional scaling for evaluating the process described in the article has universal applicability for various enterprises of construction industry, since it is structured in accordance with the purpose and objectives of the study. The key approaches that used in framework of scientific research were methods of qualimetric assessment and the construction of infographic models of interaction which illustrating the dynamics of indicators of financial and economic analysis of the ICS enterprise&#x0D; &#x0D; Results. The results of using multidimensional scaling provide an effective way to obtain visual information about prospects of interaction between enterprises of the ICS and SEZ in dynamics, characterized by the availability of managerial application for management of enterprises and persons responsible for interaction. The peculiarity of multidimensional scaling is possibility of considering properties of phenomenon under study arising from both the external and internal environment, which allows for a comprehensive assessment reflecting data from various information sources.&#x0D; &#x0D; Conclusions. Construction scales of importance and influence organizes the evaluation procedure based on specialized systems of representation of quantitative results that demonstrate positive and negative trends in the deviation of values of indicators in the form of a qualitative characteristic that can be supplemented for further research, depending on the purpose of scientific research.