The critical metal lithium (Li) is increasingly sourced from spodumene and petalite pegmatite deposits due to their relatively high grades, lower mining environmental impacts and widespread global distribution. However, there are numerous gaps in our understanding of their genesis and the formation of unzoned or poorly zoned Li pegmatites is particularly difficult to explain. To investigate this, both spodumene-bearing and non-mineralized pegmatites and aplites are studied in the Moylisha segment of the Leinster pegmatite belt of SE Ireland, which were emplaced within the East Carlow Deformation Zone (ECDZ). Trace element modeling suggests that granite melts can achieve Li concentrations high enough (similar to 5000 ppm) to crystallize spodumene. However, once crystallization begins, Li levels will drop rapidly below this threshold. While Li could be replenished by incoming melts, there is no supporting textural evidence for this, such as internal magmatic contacts, crosscutting relationships, or mingling. We test the hypothesis that low viscosity, Li-rich fluids from underlying reservoirs, most likely almost fully crystallized granite magmas or mush, continuously migrate through the heterogeneously crystallizing pegmatite-forming melts by percolative reactive flow, refertilizing interstitial melt by diffusion under favorable geochemical gradients. The flow of fluids is likely maintained due to their low relative density and periodic shearing within the ECDZ. Fluids with >10,000 ppm Li, derived by >95% crystallization (Rayleigh fractionation) of a granite magma, are shown to be capable of refertilizing a pegmatitic crystal mush after its emplacement. Supporting evidence includes macro- and micro-textures indicative of paragenetically late spodumene crystallization along apparent fluid flow pathways in mineralized pegmatites and aplites. Similar features are common in spodumene pegmatites worldwide and suggest that Li upgrading by fluid flow through crystallizing spodumene pegmatites may be a key process in enhancing Li grades and in some cases in producing economically favored low-Fe spodumene.

We investigate the origin and evolution of quartz populations in tourmaline‑bearing rocks of the Cornubian Batholith, SW England, to constrain fluid sources and Sn‑mineralization processes. Our study focuses on massive quartz–tourmaline rocks (MQT) because of their spatial and genetic association with Sn mineralization. MQT occur as small stock‑ to dyke‑like bodies (typically < 300 m) exemplified by Roche Rock and Porth Ledden. Fifteen quartz samples from MQT and comparative quartz from biotite granite, tourmaline granite, pegmatite, tourmaline breccia and veins (Porth Ledden, Porthmeor Cove, Roche Rock, Tresayes, Wheal Remfry) were subject to SEM‑cathodoluminescence and oxygen‑isotope (δ18O) analysis. SEM‑CL reveals multiple quartz generations: primary magmatic quartz (granites, aplites, MQT), pegmatitic quartz, secondary fracture‑fill quartz, oscillatory hydrothermal overgrowths on magmatic cores (typical in MQT), and complexly zoned vein quartz. All δ18O values are relatively high (+ 11.5 to + 27.7‰), mostly clustering between + 12 and + 15‰. Magmatic quartz (granites, aplites) range from + 11.5 to + 14.8‰, overlapping pegmatite quartz, implying incorporation into the granitic melts of high‑δ18O metasedimentary material, consistent with local Devonian metasediments. Hydrothermal quartz spans + 12.7 to + 27.7‰; two anomalously high values (+ 25.6, + 27.7‰) in crystal rims suggest late addition of formation waters. We infer that MQT at Porth Ledden and Roche Rock formed by partial metasomatic replacement of tourmaline granite due to infiltration and entrapment of pneumatolytic, B‑rich fluids in the roof zone. Metasomatism dissolved K‑feldspar, mobilizing K, Rb, Ba, Sr, Cs, Pb and notably Sn, producing cavities later infilled by hydrothermal quartz and tourmaline. A progressive increase in δ18O from magmatic to late hydrothermal quartz suggests fluid cooling and possible mixing with oxidizing formation waters, rather than a component of meteoric-derived waters that contributed to the precipitation of cassiterite.

This contribution is a new multimethod toolset to explore for buried, small-scale (0.01-5 million m3) rare metal and high-purity quartz pegmatites, which was developed as part of the four-and-a-half-year European Union H2020 GREENPEG project. It is underpinned by a complementary suite of existing, revised, and new methodologies, the use of three GREENPEG-developed geophysical exploration devices (EASA-certified, helicoptercompatible nose stinger magnetometer, piezoelectric seismograph, and drone-borne hyperspectral system), and two new databases (spectral library and petrophysical database for pegmatite ores). The toolset is based on the latest understanding of how pegmatites form and become enriched in ore minerals. In this regard, the theoretical component of the toolset resembles that of a comprehensive review article. The toolset has been tested in four active pegmatite exploration areas in a representative range of European surface environments-from coastal Arctic to temperate forest, alpine, and Mediterranean settings. Individual tools or tool combinations can be used to vector toward buried pegmatite-related mineralization, such as for Li, high-purity quartz for silica and metallic Si, ceramic feldspar, rare earth elements, Ta, Be, and Cs, to maximize the success of subsequent more costly exploration such as drilling in ways that optimize environmental, social, and governance outcomes. The tools are optimized for the small size, variable surface environment, depth, geologic setting, mineralogy, chemistry, and often highly variable physicochemical properties of pegmatite ore deposits. They can be used at province, district, and/or prospect scale. This guide is for those who have exploration knowledge and/or experience but who may be new or need updating in the state of the art of pegmatite exploration.

Group 2/NYF pegmatites may be economically enriched in rare minerals. In this study we report testing of two exploration methods, gamma ray surveying and soil geochemical mapping, undertaken within the GREENPEG project. Palaeoproterozoic metapegmatites in the Tysfjord area, Nordland, Norway, include some which have been mined for pure quartz. Geologically, the ore zones are the quartz cores of metapegmatites whose other zones and metasomatic halos are enriched in U, Th, REE, Nb and other rare elements. The Jennyhaugen metapegmatite was the main test site because its subcrop beneath 0.1-1.0 m soil can be traced from an open pit mine, and aerial surveying is unobstructed by trees. Helicopter-borne radiometry at 60 m altitude and droneborne radiometry at 25-35 m altitude detect the metapegmatite, while walking (1.0 or 1.6 m height) and 15 m altitude drone-borne radiometry resolve the metapegmatite and metasomatic halo subcrop in detail. Total gamma ray count measurements provide as good an exploration tool as Th or U radiation; K radiation does not show useful anomalies. Both A- and C-horizon soil geochemical mapping also reveal U, Th, Nb and other geochemical anomalies above metapegmatite and halo subcrop. A-horizon soil samples appear to more accurately locate these targets, perhaps because they effectively sample larger surface areas of subcropping rock, whose grain size is very coarse (typically metre scale) within the metapegmatite. C-horizon samples collected from the soil-rock interface are less likely to be representative of the metapegmatite. Gamma ray surveying is recommended rather than soil chemical mapping for exploration, by helicopter at district scale and by drone or walking at prospect scale. It is quicker, requires less field workers, has higher resolution and is less expensive than soil geochemical mapping. Soil chemistry may be preferred for prospect-scale exploration, however, where the commodity sought does not spatially correlate with U and/or Th concentrations.

The timescales of extraction and focussing of sufficient volumes of mineralising fluids to form porphyry Cu(-Au-Mo) deposits remains unclear. Here, we provide fundamental constraints from detailed field, mineralogical, geochemical and geochronological studies of the classic Yerington porphyry-district of Nevada. Porphyry-type deposits are exposed in an exceptionally well preserved, ca. 8 km palaeodepth section which is now near horizonal due to Cenozoic extension and tilting. From high precision zircon U-Pb age determinations, the Luhr Hill granite cupola of the Yerington batholith and multiple generations of aplitic- and porphyry dykes, on which the porphyry-type deposits are centred, were emplaced within only a few 100 kyrs. Cu mineralisation within miarolitic cavities and USTs in the dykes, and associated quartz veins, was paragenetically late, not occurring until the fluids responsible had cooled below similar to 600 degrees C. From molybdenite Re-Os age determinations, hydrothermal mineralisation in the Bear and Ann Mason deposits was coeval with and much longer lived (>1 Myrs) than magma emplacement. We suggest that the early, high temperature fluids probably travelled up into the epithermal environment and possibly out of the system, and it was fluids from deeper, which had cooled over time, which moved up through highly permeable, partially crystallised 'mush' dykes which caused the hypogene mineralisation.

Porphyry Cu(-Au-Mo) deposits form in the upper (similar to 2-8 km) regions of large, long-lived magmatic-hydrothermal systems. Although extensively studied, the timescales over which sufficient volumes of mineralizing fluids are extracted from magma source regions and focused into narrow, shallow zones of mineralization remain poorly understood. Here, we provide constraints on the onset and duration of porphyry-style mineralization from detailed field, mineralogical, geochemical and geochronological studies of the classic Yerington porphyry district of Nevada, where Cenozoic extension and tilting has exposed an exceptional similar to 8-km top-to-bottom cross section through the porphyry system. From high-precision zircon U-Pb dating, the exposed Luhr Hill granite cupola of the Yerington batholith, and multiple generations of aplitic- and porphyry dikes, on which the porphyry-type deposits are centered, were emplaced within only similar to 100 k.y. Cu mineralization of miarolitic cavities and unidirectional solidification textures within the dikes, and in associated quartz veins, was late in the transition from magmatic to hydrothermal conditions, only occurring once fluids cooled below similar to 600 degrees C. From Re-Os age determinations for vein molybdenite in the Bear and Ann Mason deposits, mineralization was coeval with, and much longer lived (>1 m.y.) than pluton and dike emplacement. We propose that magmatic-hydrothermal fluids exsolving early and deep (at porphyry-forming depths) were initially too hot to precipitate ore minerals. However, as these fluids ascended and cooled, mineralization could occur at shallower (epithermal) levels. At the depth of porphyry deposit formation, it was only as magmatism waned that the fluids could cool adequately to precipitate hypogene ore minerals. We suggest that future studies integrate microtextural studies with multi-faceted geochronology to further characterize and model these processes in porphyry and similar types of magmatic-hydrothermal systems

Porphyry-type Cu ± Au ± Mo deposits form in the upper (ca. 2–5 km deep) parts of large, long-lived magmatic-hydrothermal systems in which mineralising fluids are thought to be derived from mid-to shallow-crustal magma chambers. Increasingly, however, magmatic systems are viewed as consisting of mush with minor and transient lenses of magma, with mush being a variably packed framework of crystals with interstitial melt and magmatic volatile phase (MVP). In this context, questions remain as to the source (mainly depth) and mechanisms of transport and focussing of the vast volumes of fluids required for shallow level porphyry-type mineralisation. Even more problematic is a paucity of first-order textural evidence for the presence of mush in magmatic-hydrothermal systems, including those which host porphyry-type deposits. To address this, we have studied the aplitic porphyry cupola of the Saginaw Hill magmatic system, Tuscon, Arizona, United States, where magmatic-hydrothermal features are exceptionally well exposed, including a massive silica cap, quartz unidirectional solidification textures (USTs), stockworks of multiple generations of variably mineralised quartz veins and mineralised miarolitic cavities. From field-to micro-scale textural and geochemical studies, particularly observations of vermiform quartz between earlier generations of magmatic quartz and feldspar, we evidence the development of fluid pathways through mush at the magmatic-hydrothermal transition. These are shown to connect and provide fluids and ore constituents to the mineralised miarolitic cavities and early quartz vein stockworks. We suggest that this process should be considered in all new genetic, exploration and numerical models for porphyry and similar types of magmatic-hydrothermal ore-deposits.

The composition of 'indicator' minerals is thought to provide a guide to the potential of magmatic arc systems to form porphyry Cu deposits, but whether this is also the case for endoskarn- and exoskarn-dominated systems remains unclear, despite their importance as a source of Cu, Fe and Au. In a first step to address this, we compare the texture, cathodoluminescence (CL) colour and composition of apatite between relatively fresh quartz monzodiorite (QMD) and porphyry-type-, endoskarn- and Fe-(Cu)-mineralised exoskarn components of the Tonglushan porphyry-skarn system of the Daye ore district, China. In the relatively fresh QMD, apatite luminesces yellow-green due to elevated Mn contents. However, where affected by potassic-sodic alteration, it shows green-blue CL thought to reflect partial removal of Mn and an associated increase in REE. Apatite in the endoskarn is more pervasively replaced and veined, and shows mid-blue luminescence due to relatively low Mn, Mg and Cl. The exoskarns contain apatite with variable grain shapes and navy blue-violet or bright to dark blue CL colours, caused by low Mn and elevated Ce, and with only small patches of pale yellow-green CL. Apatite is near absent in the limestone wall rocks and xenoliths and, therefore, where present in the exoskarns is interpreted to have precipitated from the same fluids as the Fe-(Cu) mineralization. Apatite CL colour and chemistry is indicative of the different styles of alteration and mineralisation in the Tonglushan system and provides insights into the composition of skarn-forming fluids. Our results offer a potentially effective method for utilising apatite as a porphyry and skarn deposit indicator mineral in a range of exploration materials including regolith and stream sediments.

The formation of ore-barren endoskarns in association with exoskarn Cu-Fe deposits, rather than extensive porphyry-style alteration and mineralization, is investigated in the Tonglushan quartz monzodiorite porphyry system of eastern China. The Tonglushan endoskarn underwent: 1) muscovite-dominated alteration; 2) prograde and 3) retrograde skarnification; 4) potassic and 5) sodic alteration; and 6) carbonatization, and the quartz monzodiorites distal to the endoskarn minor potassic alteration and weak Fe-Cu sulphide mineralization, and then sodic alteration. The stage 1 muscovite-dominated alteration was caused by hot and saline magmatic aqueous fluids which then mixed with Ca-(+/- CO2)-bearing fluids from exoskarnification of surrounding car-bonates, to cause prograde (stage 2) and then retrograde (stage 3) endoskarnification of the variously altered quartz monzodiorite. A second pulse of moderately hot, weakly acidic to neutral magmatic fluids produced potassic alteration in the endoskarn (stage 4), and similar fluids caused porphyry-style potassic alteration and weak Cu-Fe mineralization in the quartz monzodiorite distal to the endoskarn and extensive sulphide precipi-tation in the exoskarns. Subsequent sodic alteration (stage 5) in both environments was due to ingress of Na-(CO2)-rich fluids from surrounding carbonate rocks. Primary Cu mineralization is absent in the endoskarns and instead concentrated in the exoskarns which had a more reducing and alkaline environment and into which fluid flow was focused. The latter was due to decar-bonation of wall rock marbles and related upwards migration of CO2 to produce a self-sustaining chimney effect which further drew in fluids towards the marbles to form, alter and mineralize the exoskarns. Porphyry-style mineralization in the quartz monzodiorites was limited as magmatic-hydrothermal fluids ascending within the magmatic system were CO2-rich, due to magmatic assimilation of carbonate, and therefore incapable of carrying elevated concentrations of Cu. This contribution offers new insights into why certain porphyry systems host 'barren' endoskarns and mineralized exoskarns rather than porphyry-style Cu deposits.

Understanding the mechanical evolution of magmatic systems requires careful assessment of their rheological characteristics, particularly in light of the growing evidence that magma reservoirs are dominated by magma‐mush surrounded by thermally‐altered host‐rock. To address this complexity, we develop models for volcano deformation based on a poroviscoelastic source within a thermo‐viscoelastic host. We use Finite Element modeling to investigate the rheological and mechanical response to melt injection in a Maxwell poroviscoelastic reservoir hosted in a temperature‐dependent standard linear solid viscoelastic (“thermo‐viscoelastic”) crust. Our models consider the competing roles of poroelastic diffusion, and viscoelastic creep and relaxation. All cause time‐dependent post‐injection deformation. Post‐injection deformation of a poroviscoelastic reservoir in an elastic crust is dominated by poroelastic diffusion, a consequence of the short relaxation timescale of a hot and relatively low viscosity mush. For cooler, more viscous mush, the magnitude of viscoelastic deformation increases, supplementing the deformation caused by post‐injection poroelastic diffusion. Thermo‐viscoelasticity of the crust amplifies the poroelastic deformation response of the magma‐mush, leading to increased time‐dependent deformation both during and after melt injection. The rate of post‐injection surface deformation decreases at a rate proportional to the reservoir temperature. Crucially, our model sensitivity analysis demonstrates that the wall rock thermo‐viscoelastic response contributes more to surface deformation than the viscous effect of the magma‐mush. For this reason, neglecting the viscoelastic properties of the host rock and the poroelastic properties of the reservoir in interpretations of surface deformation data could produce errors in inferred processes (e.g., injection duration) and subsurface characteristics (e.g., reservoir compressibility, shape and depth).

We modelled ground deformation at Soufrière Hills Volcano (SHV), using data collected by the Montserrat Volcano Observatory from 2010–2019. We investigate the combined use of Electronic Distance Measuring (EDM) and Global Positioning System (GPS) to distinguish shallow from mid-crustal magmatic processes and their surface deformation profiles. Our results suggest that the EDM network responds predominantly to changes in the shallow magmatic system, whereas GPS records variation at mid-crustal levels. In addition, we show that the behaviour of the EDM network, and of the GPS site HERM, can be explained by underpressurisation in a shallow dyke conduit orientated NNW–SSE, while the mid-crustal system was still undergoing pressurisation. The modelled dyke may be responding to magma cooling and contraction associated with a previous intrusion. We find that geodetic monitoring coverage of multiple flanks within 1 km of the vent can improve our understanding of shallow magmatic system processes with asymmetric deformation fields.

Element mobility and chemical mass transfer are evaluated in the formation of Cu-Fe exoskarn deposits and endoskarn and minor porphyry-style alteration in the Tonglushan quartz monzodiorite (QMD) system, eastern China. Endoskarn formation involved the migration of Ca into the QMD from the exoskarnification of carbonates (now marble) xenoliths and wall rocks, addition of Fe and Mn by magmatic-hydrothermal fluids emanating from the interior of the QMD, and removal of alkali elements due to the replacement of feldspars and mica by prograde skarn minerals. Zirconium, Hf, U, and rare earth elements (REE) were added by hydrothermal fluids which were able to carry these often poorly mobile high field strength elements (HFSE) due to elevated F activity. Additions of Al were likely from Na-rich fluids that also caused sodic alteration. Several factors favored mineralization within the exoskarns rather than endoskarns and QMD. The endoskarns were relatively oxidizing, as evidenced by a significant addition of Fe3+, which caused Cu to remain in magmatic-hydrothermal fluids until they entered and precipitated sulphides in the more reducing environment of the exoskarns. Fluid migration from the QMD through the endoskarns and into the exoskarns was favored due to decarbonation of wall rock carbonates and related upwards migration of CO2 to produce a self-sustaining chimney effect, which drew further fluids towards the carbonates to form, alter and mineralize the exoskarns. The higher porosity and permeability of the endoskarns compared with the QMD further promoted the lateral flow of Cu-bearing fluids towards the exoskarns and limited porphyry-style alteration and mineralization within the QMD. This proposed mechanism is only likely to be relevant for porphyry-type systems developed predominantly within carbonate host rocks. Its significance for exploration models is that relatively poorly mineralized porphyry stocks in this setting may be associated with more substantive exoskarn deposits on their margins.

Understanding the mechanical behaviour of melt reservoirs is vital for advancing geophysical models that aim to constrain the evolution of subvolcanic systems and inform hazard monitoring and mitigation. From geophysical and petrological studies, large melt-dominated (magma) reservoirs are difficult to sustain over long periods of time. Melt is more likely to reside within reservoirs which consist of variably packed frameworks of crystals, so-called crystal mush, as well as in pockets of magma, in changing proportions over time. The behaviour of crystal mush, in particular, is emerging as a vital consideration in understanding how magmatic systems evolve. In addition, current models for volcano deformation often consider static magma sources and thus provide little insight into the internal dynamics of melt reservoirs; and these models ignore the presence of crystals and therefore the likely poroelastic mechanical response to melt intrusion or withdrawal. Our study considers the melt reservoir to be partly crystalline (> 50% crystal fraction), with melt residing between crystals. We examine the influence of poroelastic mechanical behaviour on the evolution of reservoir pressure and the resultant surface deformation. From our results, the modelling of a crystal mush rather than a 100% melt magma reservoir can significantly modify the resulting spatial and temporal mechanical evolution of the system. Specifically, the poroelastic behaviour of a mush reservoir will continue to develop following the end of a melt injection period, generating further time-dependent surface displacements. Post-injection and post-eruption inflation can occur, which are linked to a poroelastic response associated with continuous melt diffusion. Following an injection/eruption, a steady-state point is eventually achieved when the fluid pressure reaches a uniform value throughout the reservoir. This process is controlled by the poroelastic diffusivity. Increasing the reservoir crystal fraction from 50% to 90% reduces the mobility of melts, decreases permeability, and leads to a slow rate of melt diffusion. Our study confirms that volcanic surface deformation can occur without continued intrusion or withdrawal of melt.

The GREENPEG project, which is funded by the European Commission Horizon 2020 ‘Climate action, environment, resource efficiency and raw materials’ programme, aims to develop multi-method exploration toolsets for the identification of European, buried, small-scale (0.01-5 million m3) pegmatite ore deposits of the Nb-Y-F (NYF) and Li-Cs-Ta (LCT) chemical types. The project is being coordinated by the Natural History Museum of the University of Oslo and involves three exploration services/mining operators, one geological survey, three consulting companies and five academic institutions from eight European countries.  The target raw materials are Li, high-purity quartz for silica and metallic Si, ceramic feldspar, REE, Ta, Be and Cs, which are naturally concentrated in granitic pegmatites. Silicon and Li are two of the most sought-after green technology metals as they are essential for photovoltaics and Li-ion batteries for electric cars, respectively. GREENPEG will change the focus of exploration strategies from large-volume towards small-volume, high quality ores and overcome the lack of exploration technologies for pegmatite ore deposits by developing toolsets tailored to these ore types. This contribution focuses on the methods applied in the GREENPEG project and as such provides a potential pathway towards the ’Green Stone Age’ from the perspective of pegmatite-sourced minerals.

Porphyry-type deposits are a vital source of green technology metals such as copper and molybdenum. They typically form in subduction-related settings from large, long-lived magmatic systems. The most widely accepted model for their formation requires that mantle-derived magmas undergo an increase in volatiles and ore-forming constituents in mid- to lower crustal reservoirs over millions of years, however, this is mostly based on observations from shallow, sporadically exposed parts of porphyry systems. To examine this paradigm, we have evaluated the timeframe and geochemical signatures of magmatism in a ~ 8 km palaeodepth cross-section through plutonic and volcanic rocks of the classic Yerington magmatic system, Nevada. We show that the magmas in the upper parts of the system (< 8 km) underwent a major and rapid change in chemistry over a period of < 200 kyrs that is coincident with the initiation of ore formation. We attribute this change to a shift from extraction of quartz monzodiorite and quartz monzonite magmas evolving in mid-crustal reservoirs, and that had relatively poor ore-forming potential, to extraction of volatile-rich granitic magmas from greater (~ 30 km) depths. As the granites crystallised, late stage melts were intruded through the carapace as aplite dykes which contain traceable expressions of the porphyry deposit-forming fluids. The rapid nature of the shift in ore-forming potential narrows the temporal-geochemical footprint of magmas associated with porphyry mineralisation and provides new constraints for exploration models.

Despite international efforts to limit worker exposure to coal dust, it continues to impact the health of thousands of miners across Europe. Airborne coal dust has been studied to improve risk models and its control to protect workers. Particle size distribution analyses shows that using spraying systems to suppress airborne dusts can reduce particulate matter concentrations and that coals with higher ash yields produce finer dust. There are marked chemical differences between parent coals and relatively coarse deposited dusts (up to 500 µm, DD500). Enrichments in Ca, K, Ba, Se, Pb, Cr, Mo, Ni and especially As, Sn, Cu, Zn and Sb in the finest respirable dust fractions could originate from: (i) mechanical machinery wear; (ii) variations in coal mineralogy; (iii) coal fly ash used in shotcrete, and carbonates used to reduce the risk of explosions. Unusual enrichments in Ca in mine dusts are attributed to the use of such concrete, and elevated K to raised levels of phyllosilicate mineral matter. Sulphur concentrations are higher in the parent coal than in the DD500, probably due to relatively lower levels of organic matter. Mass concentrations of all elements observed in this study remained below occupational exposure limits.

Characterizing the physical properties and mechanical behavior of melt reservoirs is essential for enhancing geophysical models that aim to understand the evolution of subvolcanic systems and support hazard forecasting. Increasing evidence suggests that shallow magmatic reservoirs consist of variably packed crystal frameworks with small volumes of interstitial melt, commonly referred to as “mushes.” Current volcano deformation models often implement static magma sources with a cavity and thus provide little insight into dynamic internal reservoir processes; they also ignore the presence of crystals, melt and other fluids, and therefore the likely poroelastic mechanical response to melt addition or withdrawal. Here we investigate the influence of poroelastic mechanical behavior on reservoir pressure evolution and resultant spatio‐temporal surface deformation. We consider the melt reservoir to be largely crystalline (10%–50% melt fraction) with melt distributed between crystals; we show that the presence of crystals affects the spatial and temporal mechanics of magma reservoir behavior. In contrast to classical models for volcanic surface deformation, our results suggest that a poroelastic surface deformation response continues to develop after withdrawal/upward emplacement of melt has terminated, and importantly that the withdrawal/injection point can affect the evolution of the relative magnitudes of vertical and radial deformation over time. These protracted displacements are caused by melt diffusion, which depends principally on mush hydraulic properties and melt characteristics. Following an intrusion/withdrawal event, a steady state is eventually reached when the fluid pressure is uniform in the mush reservoir.

Investigating the temporal development of magma reservoir pressure and associated surface displacements can reveal fundamental aspects of subsurface magmatic processes and aid in eruption forecasting. The limitation with existing volcano deformation models is that they typically ignore magma intrusion dynamics and focus on the response of surrounding rocks to source boundary pressure. Magma fluid dynamics should be incorporated into magmatic modelling to track the temporal development of a system, instead of the widely used kinematic techniques. Here, we compare analytical and numerical solutions for magma intrusion into a shallow reservoir, using two schemes of intrusion boundary condition, inlet pressure and inlet mass flow. Model sensitivity tests are conducted to explore key factors controlling the two-way coupling between solid and fluid components, assuming an incompressible magma for a first-order approach. For intrusions of viscous magma (?10(8) Pa s) or a narrow feeder conduit (5-20 m), applying an inlet pressure causes the resultant pressure and surface deformation to develop at a very slow rate; lower viscosity magmas produce faster deformation rates. The mass flow boundary condition reduces the number of model parameters as it is independent of poorly constrained parameters such as conduit and magma characteristics. For both boundary conditions, reservoir pressurization, and hence spatio-temporal surface deformation, are strongly influenced by reservoir geometry due to geometric compressibility. Our results provide fundamental knowledge to advance to more complex coupled fluid-solid mechanics models in volcano geodesy.

The skarns at Gryll’s Bunny are dominated by garnet and magnetite with small amounts of hornblende, epidote, apatite and tourmaline. They formed discordantly within a succession of metabasalts and metapelites (the Mylor Slate formation) within the metamorphic aureole of the Land’s End granite. The skarns subdivide into discrete mineralogical types that include garnet-skarn with medium-coarse grained garnet, epidote, tourmaline, amphibole and biotite; hornblende-skarn with coarse-grained tabular hornblende, medium grained garnet, epidote, titanite, apatite and tourmaline; the foliated metapelite contains fine-grained hornblende and garnet with alkali feldspar, sericite, muscovite, titanite, quartz, epidote, apatite and tourmaline; cassiterite-rich “tin floors” are overlain by (variably metasomatized) metabasite that include horizontal bodies of tourmalinite with cassiterite, titanite, chlorite and apatite. The lithologies contain variable amounts of magnetite that can be classified into 5 types. Magnetite in the metapelite (type 1) is very fine grained. Magnetite in hornblende-skarn associated with the metapelite (type 2) is fine grained with ilmenite lamellae and is associated with maghemite. Magnetite in the hornblende skarn adjacent to garnet skarn (type 3) contains abundant ulvöspinel lamellae. Magnetite in the garnet skarn is medium to coarse-grained with a granular recrystallized texture and spinel exsolutions (type 4). All of these types have been partially replaced by hematite along edges and cracks. Magnetite related with the tourmaline zone (type 5) is generally euhedral and free of exsolution lamellae. In addition, the tourmaline-cassiterite zone has abundant titanite with ilmenite laths. Fluid inclusions in garnet, amphibole and epidote of the metasomatized rocks, garnet related with type-3 magnetite has higher homogenization temperature (291- >600 oC) and almost similar low-moderate salinity (2.4-13.7 wt. % NaCl equiv.) than that of type-2 magnetite (222-428 oC and 3.9-14.8 wt. % NaCl equiv). EPMA and LA-ICP-MS analysis demonstrate that garnets are of grossular (60-76)-andradite (13-32) composition and rich in TiO2; amphiboles are sadanagaite-pargasite, tourmalines are shorl-feruvite and apatites are fluor- and hydroxyl-apatite composition. V/Ti and Ga/Ti in magnetite decrease progressively from type 1 to 5, indicating that type 1 and 2 retain characteristics of their mafic host rock as well as metamorphic process, development towards type 5 is interpreted by the increasing significance of granitic fluids. All of the magnetite types have elevated Sn and Zn whilst Zr, Mg and Al are low. The homogeneity of type 5 magnetite supports a purely metasomatic origin at the final stage of skarn development. Key words: SW England, Gryll’s Bunny skarns, Botallack, Magnetite, Mineralogy, Geochemistry, Fluid inclusions

Porphyry-type deposits are spatially and temporally associated with the relatively shallow and texturally complex parts of magmatic systems. Whilst certain textures offer snapshots into the physical processes which result in fluid exsolution and hydrothermal mineralisation, their documentation and interpretation remains disjointed. To address this, we describe a suite of magmatic and magmatic-hydrothermal textures from the classic Yerington Cu (-Mo-Au) porphyry district, Nevada, where Cenozoic extension and tilting has exposed a unique, similar to 8 km palaeodepth, cross-section through the magmatic system. Within the granite cupolas that underlie the Ann Mason and Yerington porphyry deposits, these textures include pegmatitic pods and massive silica bodies. Emplaced through the cupolas, and genetically associated with ore formation, are aplite dykes that host min-eralised unidirectional solidification textures (USTs), pegmatitic segregations, miarolitic cavities and early A type quartz veins. Based on field relations, including associations with hypogene mineralisation, petrography and Ti-in-quartz crystallisation temperatures, we highlight how these textures may record the timing and location of the magmatic-hydrothermal transition and ore-formation. By doing so we provide a textural framework for exploration geologists to assess the likely 3D spatial and temporal architecture of porphyry mineralisation at the district-prospect scale before employing more invasive and expensive techniques.