This session aims to explore magma-mush systems feeding volcanism and magmatic ore deposits, with a focus on magma dynamics and volatile budgets driving eruptions and mineralisation in critical metals for the green energy transition. We welcome contributions that use field observations, petrography and textural data, bulk and microchemical analyses from volcanic/plutonic rocks, and/or combine natural data with experimental petrology and with thermodynamic, kinetic, and thermomechanical models to better understand pre-eruptive magma storage and volatiles, and the mush switches that drive volcanic eruptions or economic-grade ore mineralisation.
Orals: Tue, 5 May, 14:00–15:45 | Room 0.51
Recent experimental and theoretical studies show that although deep sulfide-rich cumulates may sequester metals at depth, subsequent sulfide resorption during decompression and oxidation, together with physical flotation and transport of sulfide droplets, can strongly influence Cu–Au mobility in evolving magmatic systems and ultimately their ore potential. Despite its importance for metal redistribution between deep magmatic reservoirs, transient storage during ascent, and shallow ore-forming environments, the physical behaviour of magmatic sulfides during magma ascent and degassing remains poorly constrained.
Here we present new petrographic and geochemical observations from the active Brothers submarine volcano, focusing on sulfide- and vesicle-rich enclaves that provide direct evidence for sulfide–volatile interaction during shallow magma evolution. Optical microscopy, EPMA sulfide chemistry, and quantitative mineral mapping (QEMSCAN) indicate that most Brothers samples host compositionally similar arc-type magmatic sulfides (dominantly pyrrhotite ± minor chalcopyrite). However, cone lavas are markedly more sulfide-rich (0.004–0.02 area %, with groundmass sulfides 500 μm to 1.5 mm in size) than caldera lavas (≤0.003 area %, with sulfide inclusions <50 μm). Rare and diverse, previously undocumented sulfide-rich enclaves (10–30 area %) occur within highly vitrophyric (>90% glass) host lavas at hydrothermally active (NWC) and extinct (EC) Caldera sites, as well as within the Cone lavas. The latter, Cone-hosted enclaves represent earlier, more evolved (rhyolitic) melts relative to their dacitic hosts and locally preserve comparatively intact sulfide textures. In contrast, most Caldera-hosted enclaves display pervasive sulfide dissolution, resorption embayments, and replacement by Fe–Ti oxides, indicating efficient sulfide destabilisation and enhanced metal release during shallow degassing. These sulfide–vesicle–oxide textures closely resemble compound sulfide–vapour droplets described from Nea Kameni and Kolumbo in the Hellenic arc, suggesting a broader relevance of such phases in submarine magmatic–hydrothermal systems. An exception is a single cumulate enclave from the NWC containing exclusively Cu-rich magmatic sulfides (chalcopyrite + bornite; ~0.003 area %), confirming the presence of deep, cryptic sulfide-rich cumulates capable of scavenging significant metal contents at depth. Ongoing in situ LA-ICP-MS mapping of sulfides and their replacement products will further constrain the behaviour of Au, PGE, Se, and Te during these processes.
Taken together, these results provide the first direct petrographic evidence linking deep Cu-rich cumulates and transient sulfide-rich enclaves to volatile exsolution and late-stage degassing at Brothers submarine volcano. In a system dominated by late, shallow degassing, as independently constrained by melt inclusions and apatite, sulfide resorption and physical transport can dominate metal redistribution during magma ascent, with sulfide–vesicle compound phases acting as efficient transient carriers linking deep magmatic processes to shallow SMS mineralisation and offering insights relevant to porphyry-type systems.
How to cite: Georgatou, A. A., de Ronde, C., and Li, Z.: Beyond vapours and brines: physical sulfide transport as a missing link in metal transfer at Brothers submarine volcano, with comparison to the Hellenic arc, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16983, https://doi.org/10.5194/egusphere-egu26-16983, 2026.
A variety of mechanisms have been cited for priming a magmatic system for eruption, from injection of mafic magma to primary and secondary boiling. Volatile saturation and the presence of fluids are often invoked as a prerequisite for priming a magma system for large explosive eruptions. The presence of an exsolved volatile phase increases the compressibility of the system, allowing continued growth of the magma reservoir without generating significant overpressures that could trigger an eruption, and helping to sustain eruptions. However, recent work unlocking volatile budgets using apatite suggests that water saturation is not a systematic prerequisite for caldera forming eruption.
We present results on the apatite volatile record from a series of eruptions from two caldera systems, Santorini (Greece) and Mt Mazama (USA). Both have undergone multiple large explosive eruptions and smaller sub-Plinian eruptions. At Santorini (Greece), each eruption exhibits an extended? range of apatite volatile chemistry with a distinct volatile signature, indicating extensive fractionation. The inferred volatile saturation state remains constant throughout the evolution of each magma, regardless of the scale of the eruption. Water-saturated magmas usually feed Plinian to caldera-forming eruptions, whilst water-undersaturated magmas feed both sub-Plinian and caldera-forming eruptions. In contrast, apatite from the caldera-forming dacitic eruption of Mt. Mazama and its two-preceding explosive eruptions display a very restricted compositional range for each eruption. Apatite from co-erupted mafic scoria in the deposits of the caldera-forming eruption are consistent with water-undersaturated conditions. This suggests that melt volatile evolution in the dacite was initially affected by efficient hybridisation within the magma reservoir, maintaining the quantity of volatiles in the melt at a near-consistent concentration, but the eruption was triggered by interaction with water-undersaturated mafic magma, immediately prior to eruption.
These case studies highlight the complex role of water saturation in priming a magma reservoir for eruption and the multiple pathways by which a system is conditioned for eruption. There is no evidence that magmas reached H2O saturation immediately prior to eruption. We therefore infer that, for most magmas, an external trigger such as mafic magma injection or fluid migration within the storage system is typically required to initiate an eruption. This work demonstrates that whilst the presence of exsolved fluid is critical to syn-eruption processes, a magma body is not necessarily required to be saturated with volatiles to trigger the wholesale mobilisation and eruption of a magmatic mush.
How to cite: Colby, D., Humphreys, M., Lormand, C., Smith, V., De Hoog, C.-J., and Vougioukalakis, G.: The influence of magmatic volatiles in priming a magma system for eruption., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18845, https://doi.org/10.5194/egusphere-egu26-18845, 2026.
The formation of porphyry copper deposits (PCDs) has been proposed to be incompatible with the occurrence of coeval explosive volcanism. In fact, these deposits need a substantial volume of magma in the upper crust that degasses large quantities of metal-bearing hydrothermal fluids, which would be lost in the case of a volcanic eruption. We examine the Jurassic batholith in Yerington, NV, where a tilted crustal section has exposed a sequence of cogenetic volcanic rocks, mineralising porphyry dikes, and an underlying composite batholith.
We study the petrochronology of zircon from the Yerington volcanics by pairing in-situ LA-ICP-MS and high-precision CA-ID-TIMS U-Pb methods. Geochronological data show that eruptions occurred both pre- and post-mineralisation, and reveal a <1 Myr gap in volcanism that corresponds to the emplacement of porphyry dikes associated with the copper mineralisation. Whole-rock and zircon trace element compositions show that the pre-porphyry volcanic rocks are compositionally distinct (e.g. higher Ti, lower Yb/Dy, Eu/Eu* in zircon) from later units, and are more closely related to older (i.e. precursor) intrusive phases of the composite Yerington batholith. Conversely, the porphyry dikes and post-porphyry volcanic rocks show similar whole-rock and zircon trace element compositions, indicating a similar, more evolved magma source.
To investigate potential mechanisms behind the renewed volcanic activity in the latter stages of the Yerington system, we characterized the volatile content (Cl, F, OH) of apatite inclusions in zircon from the porphyry dikes and post-porphyry volcanics using EMPA, applying numerical modelling to those results to reconstruct melt volatile contents. Results indicate a sharp increase in apatite Cl and OH between porphyry dikes and immediately post-porphyry volcanic units that indicates a reinjection of volatiles into the system prior to eruption. We conclude that recharge by a deeper, volatile-loaded melt into the existing magmatic system, or fluid recharge from a more deeply emplaced magma likely triggered explosive volcanism late in the lifespan of the Yerington magmatic system, terminating copper mineralisation potential, and thus limiting the total copper endowment at Yerington.
How to cite: Freudenstein, A., Szymanowski, D., Tavazzani, L., Nathwani, C., Dilles, J., and Chelle-Michou, C.: A volatile situation: zircon and apatite insights into the plutonic-volcanic transitions in Yerington, NV, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22008, https://doi.org/10.5194/egusphere-egu26-22008, 2026.
The Bushveld Complex is commonly interpreted as an open-system magma chamber that grew incrementally through several major and numerous minor replenishment events, with magma sourced from deep magma reservoirs. A central point of debate is whether these replenishing magmas were crystal-rich (i.e., crystal slurries) or effectively crystal-free (ranging from normal to superheated melts). We address this question using the chemistry of cumulus orthopyroxene throughout the Bushveld Complex. Recent seismic and gravity imaging has identified a deep staging chamber at depths of ~40–45 km, corresponding to pressures of ~1.0 GPa, thereby defining the pressure conditions under which any deep-sourced crystal slurries must have formed. Experimental crystallization of Bushveld-type magmas at ~1.0 GPa produces orthopyroxene enriched in Al₂O₃ (~3.5–7.0 wt%) and Cr₂O₃ (~1.7–2.2 wt%), providing a quantitative benchmark for high-pressure orthopyroxene. In contrast, cumulus orthopyroxene across the Bushveld Complex is systematically low in Al₂O₃ (<1.5 wt%) and Cr₂O₃ (<0.5 wt%), irrespective of stratigraphic position or the presence of chromite. Reduction of Al₂O₃ in high-pressure orthopyroxene during decompression can occur by solid-state plagioclase exsolution, a process documented in massif anorthosites, but no such exsolution textures are observed in Bushveld orthopyroxene. Post-emplacement re-equilibration by interaction with co-existing melt is likewise ineffective: diffusion kinetics and thermal constraints show that melt–crystal exchange cannot reset bulk orthopyroxene compositions and would be restricted to thin crystal rims. Extensive dissolution–reprecipitation is also unsupported by preserved zoning patterns and the absence of diagnostic reaction textures. Mass-balance considerations further demonstrate that even complete equilibration between high-pressure orthopyroxene and basaltic melt would yield Cr contents substantially higher than those observed. We therefore conclude that orthopyroxene—and by inference, all other co-crystallizing minerals—formed at low pressure within the Bushveld magma chamber itself. These results impose a fundamental mineral-chemical constraint on petrogenetic interpretations and effectively rule out models invoking deep-sourced crystal-rich slurries. They further imply that the chromite, platinum, and magnetite reefs formed from crystal-free melts within a shallow, melt-dominated Bushveld magma chamber.
How to cite: Latypov, R. and Chistyakova, S.: Orthopyroxene chemistry excludes deep-sourced crystal slurries in the Bushveld Complex, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2338, https://doi.org/10.5194/egusphere-egu26-2338, 2026.
The classic A-type Pikes Peak batholith (PPB) hosts multiple alkaline intrusions, traditionally interpreted as late-stage features, and divided into a ‘sodic’ and a ‘potassic’ series (Smith et al., 1999). A-type granites are known for their gemstones (e.g., amazonite, topaz, aquamarine) and rare-earth element (REE) deposits, which crystallize from late magmatic fluids, for example, in pegmatites. Here, we investigate the concentrically zoned Lake George Ring Complex (LGRC) at the western PPB margin to constrain its temporal relationship to the main granite of the batholith (i.e., the Pikes Peak granite; PPG) and to evaluate the role of late magmatic fluids in its formation.
Mineral textures and compositions were characterized using backscatter electron images and quantitative electron microprobe mapping. Zircon trace-element analysis and U/Pb dating using LA-ICP-MS provide insight into the evolution of these lithologies. Concordant zircons from the LGRC were selected for high-precision CA-ID-TIMS dating. Our CA-ID-TIMS ages show that the LGRC postdates the local PPG by ca. 5 Myr, overturning previous results (Guitreau et al., 2016) that placed the LGRC early in the magmatic sequence. The PPG yields Th-corrected 206Pb/238U ages between 1082.61 ± 0.68 Ma and 1086.29 ± 0.66 Ma. The syenomonzonite core yields ages of 1078.25 ± 0.70 Ma to 1079.45 ± 0.85 Ma; the inner syenogranite ring, 1078.5 ± 1.4 Ma to 1079.05 ± 0.93 Ma; and the second, syenitic ring, 1079.08 ± 0.53 Ma to 1083.9 ± 1.0 Ma. These data fill a temporal gap in existing datasets (Fonseca Teixeira et al., 2025) and reveal continuous magmatism in the Pikes Peak batholith lasting up to 15 Myr.
Zircons from all LGRC lithologies typically exhibit high U (>1000 μg/g) and low Ti (<20 μg/g), indicating crystallization below the granite solidus (Fonseca Teixeira et al., 2023) and at a highly evolved stage. This contrasts with higher-Ti, lower-U zircon from the main PPG. Zircon from other alkaline complexes of the PPB, such as the Redskin granite (Fonseca Teixeira et al., 2025) and the Mount Rosa complex, shows U and Ti signals similar to those in the LGRC, suggesting a shared influence of late magmatic fluids. In contrast, PPG zircon preserves a predominantly magmatic signature.
All ‘rings’ of the LGRC contain large volumes of near end-member orthoclase and albite (ca. An5), more evolved than feldspars in the PPG (ca. An25). These feldspars occur as perthite exsolution, albite overgrowths, and ‘patch perthite’ (Norberg et al., 2013), indicating extensive (re)crystallization from a cool (< 500°C), fluid-saturated environment, rich in flux elements such as F. Albitization of Ca-rich plagioclase by Na-rich fluids generated abundant fluorite, which is coeval with the crystallization of REE-rich minerals in associated pegmatites (Hendrickx et al., 2024).
We interpret the LGRC as a late-stage intrusion with extensive crystallization from and alteration by late magmatic fluids. These results highlight the potential for prolonged (>10 Myr) magmatism in large A-type systems, driven by late magmatic fluids and persisting well beyond the traditionally inferred granite solidus (~700 °C).
How to cite: Hendrickx, T. J., Allaz, J. M., Freudenstein, A. E., Wickland, T., and Bachmann, O.: Granites simmering in their own juices: alkalic centers and the longevity of the Pikes Peak batholith, Colorado, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21122, https://doi.org/10.5194/egusphere-egu26-21122, 2026.
We use a one-dimensional numerical model to investigate how the presence of a volatile phase (e.g., H₂O) impacts the formation and dynamics of crustal magma reservoirs. The system is driven by the repeated intrusion of mantle-derived basalt sills containing several weight percent volatiles. The model solves for conductive and advective heat transfer within a three-phase framework. The solid matrix and silicate melt are coupled as a two-phase porous/particulate flow system, capturing compaction at low melt fractions and hindered settling at high melt fractions. In contrast, the transport of the volatile component is simplified and modeled via one-directional (upward) diffusion, which facilitates flux melting of the crust. The chemical model incorporates three components (high/low SiO₂ and volatile), with solidus and liquidus temperatures dependent on bulk SiO₂ and melt volatile content. Volatile exchange between solid and melt phases is described by a partition coefficient, and a free volatile phase exsolves when melt saturation is exceeded. Our results show that magma can accumulate at the top of a reservoir and we also capture rapid upwards transport of this magma via dykes if a critical buoyancy threshold is exceeded.
We find that the nonlinear coupling between volatile content, phase equilibria, two-phase melt-solid dynamics, latent heat, and dike transport, generates complex system behavior. A general conclusion is that reservoir growth is strongly controlled by crustal fertility and strength; if the crust can melt in response to added heat and volatiles, and dike initiation is inhibited by tectonic compression or high crust strength, the top of the reservoir migrates upward via partial melting to create a vertically extensive, mush dominated system. However, if the crust is infertile and magma frequently evacuates via dykes, then magmatism is primarily observed at distinct depth intervals separated by solid rock.
In systems where rapid vertical dike transport is inhibited and sill intrusion rates are high (>~2 mm/year, parameter-dependent), upwards migration halts at mid-crustal depths. The reservoir develops as a thick mush column hosting numerous transient, thin, high melt-fraction layers that are evolved and volatile-rich, interspersed with refractory material. These layers propagate, merge, and split, but remain confined to the mid-to-lower crust.
In systems where dyke transport is efficient, the system evolves differently. Reservoir supplied by high parental magma intrusion rates converge toward a behavior similar to those with slow intrusion rates (≤1 mm/year). High melt-fraction material is continuously extracted upward leading to the formation of a shallow silicic system, culminating in a single, dominant silicic melt layer near the top of the reservoir at approximately 5–7 km depth which cools for form a silicic pluton.
Overall, our model predicts that crustal magmatic systems are highly dynamic, with melt fraction varying significantly in time and space. The presence of volatiles and the efficiency of vertical transport are first-order controls on how and where magma is stored and transported through the crust.
How to cite: Hu, H., Jackson, M., and Booth, C.: Effects of a Volatile Phase and Dike Transport on the Creation and Dynamics of Crustal Magma Reservoirs: A Three-Phase Numerical Model Study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7166, https://doi.org/10.5194/egusphere-egu26-7166, 2026.
Subduction zones are home to Earth’s most dangerous volcanoes and the largest deposits of porphyry copper, which supply about three-quarters of the global copper. However, it is still unclear why some magma erupts, while other magma stalls and contributes to crustal growth, or why certain magma formations lead to the creation of economically valuable minerals.
In this study, we examine the plagioclase record within both the volcanic and plutonic formations of the Andean arc, focusing on key components: porphyry Cu-Mo deposits (El Teniente), barren intrusions (within the El Teniente district, Central Chile, and global datasets), and a diverse suite of Central Andean volcanoes (stratovolcanoes, cones, and volcanic fields).
We analyse magmatic plagioclase using high-resolution in-situ microanalytical techniques within a rigorous textural and chemical framework that isolates primary magmatic signals from hydrothermal overprinting in porphyry intrusions coeval with mineralisation. Major and trace elements, together with Sr isotopes, were quantified by electron microprobe and LA-ICP-MS (quadrupole and multicollector), while crystal textures were characterised using petrographic microscopy and X-ray fluorescence microscopy. We found that the anorthite content in plagioclase is an excellent proxy for magmatic copper fertility, defining a narrow range of An30±4 in magmas that host mineralisation from El Teniente, but also in global Cu-Mo deposits. The low An content indicates growth from cold, evolved magma, which sharply contrasts with plagioclase from barren intrusions and volcanic rocks. Interestingly, our results reveal chemical and textural similarities between plagioclase from mineralised porphyries and specific volcanoes located in tectonically anomalous segments of the arc that exhibit petrographic signs of mush development.
Porphyry-related plagioclase also displays significant sharp increases in Sr with minor variations in Fe, along with increasing Sr/Y ratios, indicative of amphibole/garnet fractionation. In contrast, plagioclase from barren intrusions and volcanoes along the main arc show Sr–Fe trends indicative of mafic magma recharge and low Sr/Y ratios, pointing to a lack of deep fractionation. Isotopically, fertile and barren magmas indicate distinctive magmatic pulses, with fertile magmas showing limited isotopic variation.
Thermodynamic modelling of El Teniente magmas indicates that our An30±4 range crystallised at temperatures below 850°C and immediately after the point of volatile exsolution at low pressure (< 300 MPa). The crystallisation of mineral phases other than plagioclase, such as garnet, orthopyroxene, clinopyroxene, biotite, and alkali feldspar, demonstrates a progression from a more anhydrous magma to a water-rich environment.
These findings indicate a shift in magma dynamics from a barren stage to a fertile stage. During the fertile stage, cold, evolved, calm and hydrous magmatic environments create the conditions necessary to generate porphyry copper deposits. Volcanoes that exhibit similarities to fertile magmas in their plagioclase characteristics may represent systems currently developing the perfect environment to become porphyry deposits.
How to cite: Parra-Encalada, D., Ubide, T., Cajal, Y., Rosenbaum, G., Wang, C., Tomkins, A., Campbell, I., and Paterson, D.: Plagioclase records metal fertility in Andean magmatic systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2251, https://doi.org/10.5194/egusphere-egu26-2251, 2026.
Granitic pegmatites are renowned as significant sources of rare metals (e.g., Li, Ta, Nb, Be, Cs). However, the origins and mechanisms underlying the enrichment of rare metals in granitic pegmatites remain debatable. This study provides comprehensive petrography, major and trace element analyses of muscovite and tourmaline, and isotopic data from pegmatite dikes associated with the Early Cretaceous Mufushan composite batholith, South China to elucidate geochemical fractionation processes and the mechanisms responsible for rare metals mineralization.
Rare-metal pegmatites and barren pegmatites are found within the metasedimentary strata and the granitoid batholith, respectively. Both types of pegmatite dikes exhibit internal zoning, featuring three distinct structural zones with varied mineral assemblages, where muscovite and tourmaline are ubiquitously present. Both rare-metal pegmatites and barren pegmatites show a limited monazite εNd(t) range between -9.0 and -7.6, which is aligned with the apatite εNd(t) values of -9.8 to -7.8 from distinct monzogranites, indicating that they were derived from a similar magmatic source. The most primitive units of both pegmatites show differentiation degrees of muscovite and tourmaline both lower than the muscovite monzogranite, implying that the pegmatites and monzogranites might represent independent evolutionary products.
For rare metal pegmatites, buffered Be and Nb contents, and continuously increasing Li and Ta contents in early-stage muscovites and tourmalines indicate that early-stage fractional crystallization promoted the precipitation of beryl and columbite group minerals, and the enrichment of rare metals (e.g. Li and Ta) in the residual pegmatitic liquids. Meanwhile, highly evolved melts become saturated in magmatic volatile phases (e.g., H2O, F, and B) corresponding to incremental differentiation. Whereas the late-stage evolved melt and coexisting aqueous fluid phases drive further enrichment of both fluid-mobile elements (e.g., Li, Na, Sn, Pb, Bi) and fluid-immobile elements (e.g., Be, Al, Mn, Nb, and Ta), and subsequent saturation and crystallization of lepidolite, Cs-rich lepidolite, manganotantalite, and microlite.
Melt compositions (Li, Rb, and Cs) in equilibrium with muscovites for pegmatites are quantitatively calculated, evaluated, and aligned with a Rayleigh fractional crystallization model. Our modeling indicates that the formation of barren pegmatite requires merely 50% Rayleigh fractional crystallization degree, whereas the intermediate zone, marking the initial conspicuous occurrence of rare metal minerals in rare metal pegmatites, necessitates ∼90% Rayleigh fractional crystallization degree.
The δ11B values of tourmalines show narrow ranges in biotite monzogranites (-14.6‰ ~ -14.1‰), muscovite monzogranites (-16.7‰ ~ -14.0‰), and barren pegmatites (-14.7‰ ~ -14.5‰), but relatively larger variations in rare-metal pegmatites (-17.1‰ ~ -11.9‰). The calculated δ11B values (-17.5‰ ~ -16.0‰) of primary magmatic melts for four host-rock units are indistinguishable due to co-crystallization of tourmaline and mica, while the relatively heavier and more variable boron isotopic compositions in rare-metal pegmatites reflect Rayleigh degassing and intense fluid activities. Compared with the slight change in boron isotopes of tourmalines, trace elements in both muscovites and tourmalines are much more sensitive to magmatic-hydrothermal evolution and the associated mineralization processes, which can distinguish rare-metal mineralization in pegmatite systems.
How to cite: Zheng, S. and Zhao, X.-F.: Using muscovite and tourmaline to trace the origin and evolution of rare metal pegmatites in the Mufushan batholith, South China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2316, https://doi.org/10.5194/egusphere-egu26-2316, 2026.
Within the last 20 years, exploration for critical metals has shifted from pattern matching towards a mineral systems approach that focuses on the physical processes driving ore formation. The Scottish Highlands host long-recognised mineralisation in critical chalcophile elements (e.g. Pb, Cu, Ag, Au), which continue to be mined today. Recent sulfur isotope work (Graham et al., 2017) indicates that at least part of this mineralisation is magmatic in origin, implying a direct contribution from mantle-derived magmas rather than solely crustal or hydrothermal sources. Our study focuses on the Grampian and the Northwest Highlands. These tectonostratigraphic terranes are separated by the late Caledonian (Scandian) Great Glen Fault, interpreted to record large sinistral displacement on the order of hundreds of kilometres (Prave et al., 2024). Most known mineralisation occurs in the Grampian terrane, whereas the Northwest Highlands remain comparatively barren, presenting a key exploration and geodynamic question.
In this study, we use the geochemistry of appinites to investigate the origin of the disparity in mineralisation between the Grampian and Northwest Highlands terranes. Appinites are hydrous, mantle-derived, largely mafic intrusions dominated by amphibole phenocrysts, and are widely developed across the Caledonian orogen. Appinite emplacement in both terranes occurred during the Scandian event c.430 Ma (e.g. Rogers and Dunning, 1991), when collision between Baltica and Laurentia closed the Iapetus Ocean and led to slab failure beneath the orogen. We have analysed major and trace elements in 30 appinite samples from the Grampian terrane and 21 from the Northwest Highlands terrane. We combine these data with amphibole-only thermobarometry to constrain magma evolution, storage and ascent pathways on either side of the Great Glen Fault. We aim to constrain mantle melting conditions and to clarify how metasomatised mantle sources, magmatic sulfur, and evolving crustal structures controlled the transport and deposition of chalcophile elements. Our goal is to refine regional models for critical metal fertility in the Scottish Highlands, and to link these processes via a mineral systems framework to provide transferable criteria for assessing critical metal potential in other ancient convergent margins worldwide, where similar metasomatised mantle sources and slab failure tectonics may localise globally significant metal resources.
Graham, S.D., Holwell, D.A., McDonald, I., Jenkin, G.R.T., Hill, N.J., Boyce, A.J., Smith, J., and Sangster, C., 2017, Magmatic Cu-Ni-PGE-Au sulfide mineralisation in alkaline igneous systems: An example from the Sron Garbh intrusion, Tyndrum, Scotland: Ore Geology Reviews, v. 80, p. 961–984, doi:10.1016/j.oregeorev.2016.08.031.
Prave, A.R., Stephens, W.E., Fallick, A.E., Williams, I.S., and Kirsimäe, K., 2024, How great is the Great Glen Fault? Journal of the Geological Society, v. 181, p. jgs2024- 085, doi:10.1144/jgs2024-085.
Rogers, G., and Dunning, G., 1991, Geochronology of appinitic and related granitic magmatism in the W Highlands of Scotland: constraints on the timing of transcurrent fault movement: Journal of the Geological Society, v. 148, p. 17–27, doi:10.1144/gsjgs.148.1.0017.
How to cite: Bronziet, J., Hartley, M., Neave, D., and Covey-Crump, S.: Using Appinite Geochemistry to Understand Critical Metal Mineralisation in the Scottish Highlands: A Mineral Systems Approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1218, https://doi.org/10.5194/egusphere-egu26-1218, 2026.
Apatite is a common accessory mineral that incorporates major magmatic volatiles and can therefore record the volatile evolution of magmas. Constraining the timing of volatile saturation and fluid exsolution is crucial for understanding porphyry and epithermal deposit formation, as exsolved hydrothermal fluids control the transport and concentration of metals such as Cu, Au, Ag and Mo. Therefore, the composition of apatite can provide important insights into the ore-forming potential of magmas.
Numerous porphyry and epithermal systems related to subduction zone magmatism occur throughout the eastern Aegean region. Ongoing subduction of the African plate beneath the Eurasian plate since ~30 Ma with associated slab rollback has caused a southward migration of the subduction zone. This migration allows spatial and temporal variations in the volatile evolution of arc magmatism to be traced over a distance of ~300 km, from the early magmatism in Western Thrace (NE Greece) to the currently active South Aegean Volcanic Arc. Apatite chemistry from volcanic and plutonic rocks across several Aegean localities (Western Thrace, Limnos, Chalkidiki, Samos, Aegina and Milos) reveals substantial variations in halogen contents (Cl = 0.06–3.07 wt%, F = 0.22–3.67 wt%), reflecting differences in the volatile evolution of these magmas.
In Western Thrace, strong negative Eu anomalies in apatites from the most primitive samples (whole-rock SiO2 < 53 wt%) indicate early plagioclase fractionation, consistent with relatively dry initial magma compositions. During differentiation, increasing Sr/Y ratios likely reflect amphibole fractionation, implying an increase in melt H2O contents. Variations in apatite halogen and S contents further indicate that early fluid saturation, shallow magma intrusion depths and sustained degassing appear to favour the formation of porphyry mineralized systems (e.g., at Maronia). In contrast, later fluid saturation and more explosive eruption mechanisms may inhibit extensive mineralisation, as observed, for example, in nearby shoshonitic volcanic rocks of the Petrota graben. Despite similar whole-rock geochemical signatures at these nearby sites, apatite chemistry records differences in the timing of volatile saturation and fluid exsolution, reflecting distinct conditions of magma storage and ascent.
How to cite: Hars, E., Keith, M., Wolf, J., Haase, K. M., and Voudouris, P.: Volatile evolution of ore-forming magmas in the Aegean constrained by apatite major and trace element geochemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8990, https://doi.org/10.5194/egusphere-egu26-8990, 2026.
The effect of magmatic volatiles on the metal budget of hydrothermal mineralization often remains unclear and requires novel tools to be developed for a more comprehensive understanding. Here, we present coupled Se and S isotope data combined with trace element micro-analysis of hydrothermal sulfides from the PACMANUS hydrothermal system in the Eastern Manus back-arc basin. PACMANUS includes several dacite-hosted vent fields that occur at a water depth of 1640 to 1740 m, and which discharge fluids of distinct temperatures (6 to 360°C). The sample set includes hydrothermal sulfides from chimneys and talus material sampled by ROV, as well as from the sub-seafloor upflow zone recovered by rock-drill and during ODP Leg 193. The sample set therefore features a vertical geochemical record through a hydrothermal system with variable magmatic volatile input that allows to study the Se isotope fractionation processes and its potential application to trace magmatic volatile influx. The mineralization of the chimneys is characterized by an inner chalcopyrite-dominated lining along the central fluid conduits, which transitions into zones of pyrite, marcasite, chalcopyrite, barite, and anhydrite, and finally into a sphalerite, pyrite, and marcasite assemblage in the outermost chimney wall. High-precision δ82/76Se and δ34S data coupled with Te/Sb, and Te/As ratios in hydrothermal sulfides - a novel proxy for constraining magmatic volatile influx in subduction-related submarine hydrothermal systems [1] - revealed a positive correlation, implying that magmatic volatile influx is recorded by the Se isotope system. In addition, seawater mixing has little effect on the δ82/76Se composition of hydrothermal sulfides, which makes it superior for tracing metal sources compared to the S isotope system that often yields ambiguous source signatures due to seawater overprinting [2]. We suggest that Se isotopes can trace the variable input of magmatic volatiles and define two endmembers: (1) a seawater-rock dominated endmember with low Te/Sb, positive δ34S, and strongly negative δ82/76Se values, and (2) a magmatic volatile dominated endmember with high Te/Sb, negative δ34S, and δ82/76Se values of ~0 ‰. Our integrated approach introduces Se isotopes as a novel tool to elucidate the geochemical evolution of seafloor hydrothermal systems and the processes controlling the mobilization and transport of elements in these environments.
[1] Falkenberg, J. J. et al. (2024), Geochimica et Cosmochimica Acta, 373, 52-67. [2] Grosche, A. et al. (2024), Geochimica et Cosmochimica Acta, 372, 13-27.
How to cite: Hampel, F., Keith, M., Grosche, A., Haase, K. M., Klemd, R., Petersen, S., Bach, W., Strauss, H., Rosca, C., and König, S.: Coupled Se and S isotope systematics of sulfides: a novel tool to trace magmatic volatile input into submarine hydrothermal systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17980, https://doi.org/10.5194/egusphere-egu26-17980, 2026.
Understanding the magma storage and differentiation processes that lead to the formation of small, highly differentiated granites is essential for constraining how evolved silicic magma reservoirs are assembled and differentiated, as well as how associated mineral ores form. Once saturated in rare-metals (e.g., Sn, Nb, Ta), these magmas start to crystallise metal-bearing minerals such as cassiterite (SnO2) or columbo-tantalite (Mn,Fe)(Nb,Ta)2O6. Since the stoichiometry of columbo-tantalite (CT) allows two major substitutions, the CT composition will vary with melt composition. Therefore, the detailed study of these minerals can provide strong insights into the mechanisms related to emplacement, differentiation, and mineralisation processes in highly differentiated magma reservoirs.
To better understand how evolved, upper crustal, mineralised granites form, we investigated the internal texture and chemical composition of CT from the Beauvoir rare-metal granite (Massif Central, France). By combining chemical mapping and electron probe microanalysis of CT from various samples throughout the 900 m deep borehole that intersect the Beauvoir granite, we demonstrate that the CT composition can be used as a proxy of magma differentiation. More specifically, systematic variations in CT Mn* (Mn/Mn+Fe in atomic prop.) throughout the granite indicate that several compositionally distinct magma batches were involved during the construction of the Beauvoir granite. As these results are consistent with those obtained with lepidolite1, we show for the first time that the CT composition can be used to identify several episodes of magma sheet stacking during the construction of a rare-metal granite body.
Once emplaced, the differentiation of these magma sheets is recorded by an increase in CT Ta* (Ta/Ta+Nb in atomic prop.), which mimics the progressive increase of Ta content in residual melts. The differentiation trends recorded by CT are also sensitive to the nature of the crystallising phases, and especially minerals competing for Fe. Notably, we show that when Fe-rich lepidolite crystallises, the CT’s Mn* remains stable, while it decreases with magma differentiation when CT is controlling the melt Fe budget. It reflects the lower solubility of the Mn-CT compared to Fe-CT in peraluminous magmas.
Overall, this study demonstrates that CT effectively records magma compositional evolution (differentiation and recharges) during rare-metal granite emplacement. These results highlight the potential of CT as tracers of magma plumbing processes and metal enrichment, with broader applicability to cogenetic granite–pegmatite systems.
- Esteves, N. (2025). From melt to pluton: Magmatic emplacement, differentiation & duration of the Beauvoir rare-metal granite(Doctoral dissertation, Université de Lorraine).
How to cite: Copie, S., Esteves, N., France, L., and Bouilhol, P.: Assessing the emplacement and differentiation processes in highly differentiated magmas through the study of Nb-Ta oxides (CT). Insights from the Beauvoir rare-metal granite (Massif Central, France), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18170, https://doi.org/10.5194/egusphere-egu26-18170, 2026.
Dozens of uranium deposits and mineralization sites are distributed within the Mesozoic–Cenozoic volcanic rock - red bed belt of northeastern Jiangxi, mainly hosted by volcanic rocks, granite, metamorphic rocks and sandstone, and their uranium sources are subject to crustal mantle disputes. Iron isotope analysis, combined with previous geochronological and geochemical data, show that: (1) Four geological events were observed, which probably genetic related to uranium enrichment, namely, the development of uranium ore shoots were related to faults, the mineralization age span was large (148-47 Ma), the hydrothermal fluids were a mixture of atmospheric precipitation, magmatic water, and mantle fluid, and the uranium deposit surrounding rock is not selective. It is noteworthy that different stable isotope data often suggest a different origin mineralier, including meteoric water, magmatic fluids, and mantle-derived components, even within a single deposit. (2) Despite differing host rocks, the Zoujiashan and Yunji uranium deposits and the Yingtan-113, 364, and Tongboshan mineralization sites exhibit consistently positive δ⁵⁶Fe values ranging from 0 to +0.92‰. Collectively, the evidence disfavors a mantle-derived uranium source, instead pointing to the red beds as the more plausible origin. Mineralization model of "crustal source (red bed uranium source) - structural control - multi-stage hydrothermal superposition" was proposed: in arid and oxidizing environments, uranium containing minerals in the red layer were leached, and hydrothermal uranium deposits are formed by long-term coupling with mantle-derived reducing fluids through fault structures.
Funding: National Natural Science Foundation of China (42472130) and ECUT Research Development Fund (K20240017, K20240018).
Keywords: uranium deposit, iron isotopes, uranium source, northeastern Jiangxi, red beds
How to cite: Li, G., Zhu, S., Ni, F., Guo, F., Liu, J., and Wu, Z.: On the uranium source of North-eastern Jiangxi, South China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9009, https://doi.org/10.5194/egusphere-egu26-9009, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 3
EGU26-2162 | ECS | Posters virtual | VPS25
Magmatic controls on skarn-type Cu–Fe–Au mineralization in the Tonglushan ore field, Middle–Lower Yangtze River Metallogenic BeltThu, 07 May, 14:39–14:42 (CEST) vPoster spot 3
Skarn-type Cu–Fe–Au mineralization in the Middle–Lower Yangtze River Metallogenic Belt (MLYRB) is closely associated with Early Cretaceous intermediate to felsic magmatism; however, the links between magmatic evolution and ore-forming efficiency remain poorly constrained. In the Tonglushan ore field, one of the largest Cu–Fe–Au skarn systems in eastern China, multiple intrusive phases are spatially distributed, providing an ideal opportunity to investigate how magmatic processes control metallogenic potential. Here we present new geochronological and geochemical constraints on quartz monzodiorite porphyry, quartz monzodiorite, quartz diorite, and their mafic microgranular enclaves (MMEs) from different sectors of the Tonglushan ore field.
Zircon U–Pb ages indicate synchronous emplacement of all intrusive phases and MMEs at ca. 142–140 Ma. Whole-rock geochemistry and Sr–Nd–Hf isotopes indicate that these intrusive rocks belong to a high-K calc-alkaline to weakly adakitic series and were derived from an enriched lithospheric mantle source modified by slab-derived components, followed by extensive fractional crystallization. The MMEs record efficient mixing between mafic and felsic magmas, highlighting the role of mafic recharge in supplying heat and metal components to the evolving system. Estimates of magmatic water contents and oxygen fugacity from zircon compositions reveal systematic variations among different intrusions. The Jiguanzui and Tonglushan quartz monzodiorite porphyries are characterized by high water contents and elevated oxidation states, consistent with intense Cu–Au and Cu–Fe–Au mineralization, whereas the weakly mineralized Zhengjiawan quartz diorite exhibits lower values. These observations suggest that, beyond structural controls, the metallogenic fertility of intrusions in the Tonglushan ore field was primarily governed by fractional crystallization, mafic magma input, and the development of highly hydrous and oxidized magmatic systems.
Our study demonstrates that integrated whole-rock and zircon geochemical indicators provide effective tools for evaluating the ore-forming potential of skarn-type Cu–Fe–Au mineralization related intrusions in the MLYRB.
How to cite: Zhang, M. and Tan, J.: Magmatic controls on skarn-type Cu–Fe–Au mineralization in the Tonglushan ore field, Middle–Lower Yangtze River Metallogenic Belt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2162, https://doi.org/10.5194/egusphere-egu26-2162, 2026.
EGU26-4396 | ECS | Posters virtual | VPS25
Magmatic and geodynamic processes control on the formation of porphyry molybdenum deposits: Insights from the Yanshan-Liaoning metallogenic belt, northern margin of North China CratonThu, 07 May, 14:42–14:45 (CEST) vPoster spot 3
The Yanshan-Liaoning metallogenic belt (YLMB), the second-largest molybdenum deposit cluster in China, hosts over twenty porphyry molybdenum deposits, including the large-scale Caosiyao, Sadaigoumen, and Dasuji deposits, as well as the newly discovered medium- to large-scale Qiandongdamiao, Zhujiawa, and Taipingcun deposits. Geochronological data indicate that the duration of molybdenum mineralization spanned ca. 100 Myrs, from the Triassic to Early Cretaceous (240–140 Ma). However, the reasons for such a prolonged or multi-period metallogenic event, and the magmatic and geodynamic processes controlling the spatial–temporal distribution of these deposits, remain poorly understood.
Here we summarize the geological, chronological and geochemical data from selected molybdenum deposit to reconstruct the temporal–spatial distribution and tectonic setting of ore- metallogenic history in the YLMB. The formation of molybdenum deposit in the YLMB can be divided into three periods of 240–220 Ma, 185–180 Ma and 160–140 Ma. The ore-forming intrusions among these three periods illustrate an overall characteristic that metaluminous to peraluminous, high-K calc-alkalic to shoshonite series acidic rocks, and the source of intrusions is the Archaean–Paleoproterozoic lower crust. Through in-depth analysis of Sr-Nd-Hf isotopic data, we find that the magma source that during the 185-180 Ma stage is relatively younger, mainly reflecting the partial melting of Paleoproterozoic crust, whereas the magma source that during the 240–220 Ma and 160–140 Ma stages likely are contained both from the Paleoproterozoic and Neoarchean crust. Further calculations using trace element content ratios reveal a shallower magma source along the magma evolution during the 240–220 Ma period, which supported by the gradual decrease trend in crustal thickness. In contrast, the calculation of crustal thickness during the 185–180 Ma and 160–140 Ma stages show an increase trend, suggested an thicken process in the depth of the magma source.
Spatially, the porphyry molybdenum deposits formed during these three periods exhibit distinct geographic distributions. Deposits formed at 240–220 Ma are mainly located in the northern part of the YLMB, including the Chengde-Zhangbei-Fengning district. Those formed at 185–180 Ma are primarily located in the Liaoxi district, eastern part of the YLMB while deposits formed at 160–140 Ma are located in the southern part of the YLMB, particularly in the Xinghe-Zhangjiakou-Xinglong district. We propose that the variations of the spatial–temporal distribution and geochemical characteristics of the molybdenum deposit formed during different periods in the YLMB are controlled by variations of their geodynamic settings. The porphyry molybdenum deposits formed in 240–220 Ma are under the post-collision or post-orogenic extension environment between the North China Plate and the Siberian Plate in the Middle Triassic. Deposits formed in 185–180 Ma are under the extension environment in the early stage of the Yanshanian movement, and porphyry molybdenum deposits formed in 160–140 Ma are in the strong extrusion environment in the main stage of the Yanshanian movement.
Our findings demonstrate the multi-period metallogenic history of the YLMB, highlighting the critical role of magma source, storage depth, and geodynamic setting in controlling the formation of porphyry molybdenum deposits.
How to cite: Jiang, C., Liu, Q., Cao, L., Li, A., and Fu, L.: Magmatic and geodynamic processes control on the formation of porphyry molybdenum deposits: Insights from the Yanshan-Liaoning metallogenic belt, northern margin of North China Craton, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4396, https://doi.org/10.5194/egusphere-egu26-4396, 2026.
EGU26-22040 | Posters virtual | VPS25
Magmatic sulfate‑melt exsolution as a mechanism for excess sulfur in porphyry systemsThu, 07 May, 14:45–14:48 (CEST) vPoster spot 3
Sulfur released by magmatic activity strongly impacts the climate and is essential for ore mineralisation. Many porphyry systems contain up to billions of tons of sulfur, far exceeding the sulfur capacity of silicate melt and therefore requiring an additional, efficient S‑transfer mechanism.
We present a unique mafic rock (SiO₂ = 53–59 wt.%, MgO = 5.3–7.3 wt.%) containing ~15–20 vol.% anhydrite, ~30–40 vol.% biotite and ~40–50 vol.% plagioclase from the largest porphyry–epithermal system in China. Magmatic anhydrite, indicated by textural relations and LREE‑rich compositions, yields bulk‑rock S contents of ~2–3 wt.%, far above experimental S solubilities.
Plagioclase shows sharp core–rim decreases from An₅₀–₇₀ to An₂₅–₄₅, recording strong CaO depletion caused by sulfate saturation. Extensive sulfate saturation also suppressed amphibole/orthopyroxene and removed a large proportion of LREEs from the melt, producing flat REE patterns in co-crystallised apatite. Biotite exhibits pronounced Ba depletion from core to rim. Because Ba partitions strongly into sulfate melt, not into anhydrite, this Ba zoning is best explained by the formation of a sulfate melt, rather than by crystallisation of anhydrite from a silicate melt.
Nd isotopic compositions (ԑNd(t) ≈ -1.0) indicate that the magma was derived from partial melting of the mantle wedge. We suggest that ascent of this oxidised, sulfur‑rich mafic magma led to decompression-driven oxidation of S²⁻ to S⁶⁺, sulfate saturation, and exsolution of an immiscible sulfate melt. This discrete sulfate‑melt migrated upward and provided an efficient pathway for long‑distance transfer of large amounts of sulfur to porphyry systems. This sulfate‑melt exsolution process is a previously unrecognised mechanism that relaxes the constraint imposed by the sulfur capacity of silicate melt, and LREE‑depleted apatite associated with abundant magmatic sulfate phases may serve as an indicator of sulfate‑melt exsolution and a proxy for porphyry mineralisation potential in the upper crust.
How to cite: Huang, W., Humphreys, M., and Liang, H.: Magmatic sulfate‑melt exsolution as a mechanism for excess sulfur in porphyry systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22040, https://doi.org/10.5194/egusphere-egu26-22040, 2026.
EGU26-938 | ECS | Posters virtual | VPS25
Insights into the copper accumulation potential of magmas along the Sunda-Banda arc, Indonesia from apatite and its mineral hostsThu, 07 May, 15:09–15:12 (CEST) vPoster spot 3
Current demand for critical metals including Cu is outstripping current supply and will further escalate in the future. A significant source of Cu comes from porphyry deposits, which contribute to >60% of global Cu ore production. Many of these porphyry Cu deposits are found along convergent margins such as the Andes and the Sunda-Banda arc in Indonesia and these same arcs also host highly active volcanoes. Understanding the magmatic and geodynamic factors that contribute towards priming magmas for Cu fertility as opposed to volcanic eruptions can aid in identification of prospective targets for exploration.
Here we present analyses of apatite populations from known porphyry Cu deposits and active volcanoes along the Sunda-Banda arc in Indonesia. To gain a complete overview of the mineral associations and their information, we incorporate textural information to analyze both apatite inclusions and their mineral hosts, such as pyroxenes and amphiboles, as well as groundmass apatite. These mineral compositions will serve as input for thermodynamic models to constrain the volatile chemistry and budget, as well as the volatile saturation depths. The information gathered will be combined to test our working hypotheses that the magmas with high Cu fertility store at distinct depths, have geochemical signatures that suggest deep fractionation of garnet and amphibole, and are associated with anomalous geodynamic features such as slab tears.
Our ongoing work advances current understanding on magma storage and transfer along and across fertile magmatic arcs, aiming to better understand magmatic pre-conditioning for porphyry copper deposit formation to complement exploration efforts to find copper deposits in the geological records.
How to cite: Utami, S. B., Ubide, T., Rosenbaum, G., Li, W., Handini, E., Wood, S., Handley, H., and Goode, L.: Insights into the copper accumulation potential of magmas along the Sunda-Banda arc, Indonesia from apatite and its mineral hosts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-938, https://doi.org/10.5194/egusphere-egu26-938, 2026.
