Thèses sur le sujet « Magmatic-hydrothermal system »

This PhD was made possible by funding from the Natural Environment Research Council and the British Geological Survey. Additional funds came from the Society of Economic Geologists, Robert’s Skills Fund, Whitaker Fund, the Mineralogical Society and the Geochemical Society.

Hydrothermal systems at oceanic spreading centers play an important role in the composition of seawater, the formation of ore deposits, the support of microbial and macrofaunal ecosystems, and even for the development of life on early earth. These circulation systems are driven by heat transport from the underlying magma chamber, where latent heat of crystallization and sensible heat from cooling are transferred by vigorous, high Rayleigh number convection through a thin conductive boundary layer. The traditional study of magmatic-hydrothermal systems is primarily based on the time-series observation, which takes the form of repeat visits, continuous offline monitoring by autonomous instruments, or continuous online monitoring by instruments with satellite or cable links to shore. Although a number of studies have deployed autonomous monitoring instruments at vents and around mid-ocean ridges to investigate geophysical and hydrothermal processes, the data are still rather limited and a comprehensive understanding of magma-hydrothermal processes at oceanic spreading centers is lacking. Numerical modeling needs to be employed to elucidate the dynamic behavior of magmatic hydrothermal systems and for testing completing hypotheses in these complex, data-poor environments. In this dissertation, I develop a mathematical framework for investigating heat transport from a vigorously convecting, crystallizing, cooling, and replenished magma chamber to an overlying hydrothermal system at an oceanic spreading center. The resulting equations are solved numerically using MATLAB. The simulations proceed step-by-step to investigate several different aspects of the system. First, I consider a hydrothermal system driven by convection, cooling and crystallization in a ~ 100 m thick basaltic magma sill representing an axial magma chamber (AMC) at an oceanic spreading center. I investigate two different crystallization scenarios, crystal-suspended and crystal-settling, and consider both un-replenished and replenished AMCs. In cases without magma replenishment, the simulation results for crystals-suspended models show that heat output and the hydrothermal temperature decrease rapidly and crystallinity reaches 60% in less than ten years. In crystals-settling models, magma convection may last for decades, but decreasing heat output and hydrothermal temperatures still occur on decadal timescales. When magma replenishment is included, the magmatic heat flux approaches steady state on decadal timescales, while the magma body grows to double its original size. The rate of magma replenishment needed ranges between 5 x 10⁵ and 5 x 10⁶ m³/yr, which is somewhat faster than required for seafloor spreading, but less than fluxes to some terrestrial and subseafloor volcanoes on similar timescales. The heat output from a convecting, crystallizing, replenished magma body that is needed to drive observed high-temperature hydrothermal systems is consistent, with gabbro glacier models of crustal production at mid-ocean ridges. Secondly, I study the heat transfer model from a parametric perspective and examine the effects of both initial magma chamber thickness and magma replenishment rate on the hydrothermal heat output. The initial rate of convective heat transfer is independent of the initial sill thickness; but without magma replenishment, the rate of decay of the heat output varies linearly with thickness, resulting in short convective lifetimes and decaying hydrothermal temperatures for sills up to ~ 100m thick. When magma replenishment is included in crystals settling scenarios at constant or exponentially decreasing rates of ~ 10⁻⁸ m/s to the base of the sill, growth of the sill results in stabilized heat output and hydrothermal temperature on decadal timescales and a relatively constant to increasing thickness of the liquid layer. Sills initially ~ 10 m thick can grow, in principal, to ~ 10 times their initial size with stable heat output and a final melt thickness less than 100m. Seismic data provides evidence of AMC thickness, but it can not discriminate whether it denotes initial magma thickness or is a result of replenishment. These results suggest that magma replenishment might not be seismically detectable on decadal time scales. Periodic replenishment may also result in quasi-stable heat output, but the magnitude of the heat output may vary considerably in crystals suspended models at low frequencies; compared to crystals settling models. In these models the direct coupling between magmatic and hydrothermal heat output suggests that heat output fluctuations might be recorded in hydrothermal vents; but if damping effects of the basal conductive boundary layer and the upflow zone are taken into account, it seems unlikely that heat output fluctuations on a time scale of years would be recorded in hydrothermal vent temperatures or heat output. Thirdly, I extend the work to the binary system motivated by the fact that the real magmas are multi-component fluids. I focus on the extensively studied binary system, diopside-anorthite (Di-An), and investigate the effects of convection of a two-component magma system on the hydrothermal circulation system through the dynamic modeling of both temperature and heat output. I model the melt temperature and viscosity as a function of Di concentration, and incorporate these relations in the modeling of the heat flux. Simulations comparing the effects of different initial Di concentrations indicate that magmas with higher initial Di concentrations convect more vigorously, which results in faster heat transfer, more rapid removal of Di from the melt and growth of crystals on the floor. With magma replenishment, I assume that the magma chamber grows either horizontally or vertically. In either case magma replenishment at a constant rate of ~ 10⁻⁸ m³/a can maintain relatively stable heat output of 10⁷-10⁹ Watts and reasonable hydrothermal vent temperatures for decades. The final stabilized heat flux increases with increasing Di content of the added magma. Periodic replenishment with a 10 year period results in temperature perturbations within the magma that also increase as a function of increasing Di. With the simple magma model used here, one can not discern conclusively whether the decrease in magma temperature between the 1991/1992 and the 2005/2006 eruptions at EPR 9°50'N involved replenishment with more or less evolved magmas. Fourthly, I investigate a high-silica magma chamber as the hydrothermal circulation driver. I construct viscosity models for andesite and dacite melts as a function of temperature and water content and incorporate these expressions into a numerical model of thermal convective heat transport from a high Rayleigh number, well-mixed, crystallizing and replenished magma sill beneath a hydrothermal circulation system. Simulations comparing the time dependent heat flux from basalt, 0.1wt.% andesite, 3wt.% andesite, and 4wt.% dacite, indicate that higher viscosity magmas convect less vigorously, which results not only in lower heat transport and hydrothermal vent temperatures, but also in a lower decay rate of the vent temperature. Though somewhat colder, hydrothermal systems driven by unreplenished high-silica melts tend to have a longer lifetime than those driven by basalts, assuming a heat output cutoff of 10⁷ Watts. As in the basaltic case, magma replenishment at a rate of ~ 3 x 10⁵ - 3 x 10⁶ m³/a can maintain relatively stable heat output of 10⁷-10⁹ Watts and hydrothermal vent temperatures for decades. Idealized models of porous flow through the lower crust suggest such replenishment rates are not likely to occur, especially for high-viscosity magmas such as andesite and dacite. Long term stability of hydrothermal systems driven by these magmas requires an alternate means of magma replenishment. Finally, the dissertation concludes by discussing some avenues for future work. Most important of these are to: (1) couple magma convection with more realistic hydrothermal models and (2) link magma chamber processes to better physical models of replenishment and eruption.

Hydrothermal processes at oceanic spreading centers are largely influenced by changing magmatic heat input. I use the FISHES code to investigate the evolution of surface temperature and salinity as a function of time-varying heat flux at the base of a two-phase, vapor-brine hydrothermal system. I consider a two-dimensional rectangular box that is 1.5 km deep and 4 km long with homogeneous permeability. Impermeable, insulated conditions are imposed on the left and right hand boundaries. To simulate time-varying heat flux from a sub-axial magma chamber of 500 m long half-width, I consider a variety of basal boundary conditions: (1) a constant heat flux with an value of 130 W/m2; (2) a sinusoidal heat flux with a period of 6 years and an amplitude ranging between 100 and 50 W/m2; (3) step, random, and exponential heat fluxes ranging between 200 and 15 W/m2; and (4) an analytical function of temporally decaying heat flux resulting from a simulated cooling, crystallizing magmatic sill. As a result of the investigation I find: (1) changes in bottom temperature and salinity closely follow the temporal variations in magmatic heat inputs; (2) the surface temperature response is severely damped and high frequency variations in heat flow are not detected; (3) in regions where phase separation of vapor and brine occurs, surface salinity variations may be recorded in response to changing conditions at depth, but these are smaller in amplitude.
Master of Science

[Truncated abstract. Formulae and special characters can only be approximated here. Please see the pdf version of this abstract for an accurate representation.] The 3.24 Ga Panorama VMS District, located in the Pilbara Craton of Western Australia, is exposed as a cross-section through subvolcanic granite intrusions and a coeval submarine volcanic sequence that hosts Zn-Cu mineralization. The near-complete exposure across the district, the very low metamorphic grade, and the remarkable preservation of primary igneous and volcanic textures provides an unparalleled opportunity to examine the P-T-X-source evolution of a VMS ore-forming system and to assess the role of the subvolcanic intrusions as heat sources and/or metal contributors to the overlying VMS hydrothermal system. Detailed mapping of the Panorama VMS District has revealed seven major vein types related to the VMS hydrothermal system or to the subvolcanic intrusions. (1) Quartz-chalcopyrite veins, hosted in granophyric granite immediately beneath the granite-volcanic contact, formed prior to main stage VMS hydrothermal convection, and were precipitated from mixed H2OCO 2-NaCl-KCl fluids with variable salinities (2.5 to 8.5 wt% NaCl equiv). (2) Quartz-sericite veins, ubiquitous across the top 50m of the volcanic sequence, were formed from an Archean seawater with a salinity of 9.7 to 11.2 wt% NaCl equiv at temperatures of 90° to 135°C. These veins formed synchronous with the regional feldspar-sericite-quartz-ankerite alteration during seawater recharge into the main stage VMS hydrothermal convection cells. (3) Quartz-pyrite veins hosted in granophyric granite, and (4) quartz-carbonate-pyrite veins hosted in andesitebasalt, also formed from relatively unevolved Archean seawater (5.5 to 10.1 wt% NaCl equiv; 150° to 225°C), but during the collapse of the VMS hydrothermal system when cool, unmodified seawater invaded the top of the subvolcanic intrusions. (5) Quartz-topaz-muscovite greisen, (6) quartz-chlorite-chalcopyrite vein greisen, and (7) hydrothermal Cu-Zn-Sn veins are hosted in the subvolcanic intrusions. Primary H2O-NaCl-CaCl2 fluid inclusions in the vein greisens were complex high temperature hypersaline inclusions (up to 590°C and up to 56 wt% NaCl equiv). The H2O-CO2-NaCl fluid inclusions in the Cu-Zn-Sn veins have variable salinities, ranging from 4.9 to 14.1 wt% NaCl equiv, and homogenization temperatures ranging from 160° to 325°C. The hydrothermal quartz veins and magmatic metasomatic phases in the subvolcanic intrusions were formed from a magmatic-hydrothermal fluid that had evolved through wallrock reactions, cooling, and finally mixing with seawater-derived VMS hydrothermal fluids.

Twangiza mine is a gold deposit situated in the eastern Democratic Republic of Congo. The rock types at the Twangiza Mine consist of black shale, including carbonaceous mudstone and thin intercalated layers of siltstone, and feldspar-rich granitoid intrusive sills, referred to as albitite, folded into a major antiformal structure. The gold mineralization at the mine is commonly found associated with sulphides. The sulphide textures and compositions of mineralized and unmineralized samples of black shales, albitite sills and hydrothermal veins in the mine are considered for the understanding of the spatial association of gold with sulphides and gold mineralization history of the mine. The sulphides within the Twangiza mine consist of pyrite, arsenopyrite, pyrrhotite, chalcopyrite and rare cobaltite. The primary pyrite texture occurs in unmineralized black shale and is interpreted to be diagenetic. It consists of fine-grained anhedral pyrite crystals aggregating into spherical nodules and formed in replacement of organic material during the diagenesis process. The secondary pyrite textures resulted from the hydrothermal fluids activity and include (i) aggregates of annealed anhedral crystals into sulphide-rich lenses; (ii) elongated anhedral pyrite in the form of short stringers; (iii) fine-grained subhedral to euhedral pyrite randomly distributed within the rock matrix; (iv) euhedral zoned pyrite crystals occurring within veins; (v) aggregations of fine-grained anhedral pyrite, locally distributed in the matrix; (vi) abundant dissemination of fine-grained subhedral to anhedral pyrite crystals within the vein selvedge in the host rock; (vii) and coarse-grained massive pyrite bodies. The pyrite major elemental composition does not vary significantly in the different textures and sample types. The Fe content ranges from 44.57 to 46.40 wt. %, and the S content ranges from 53.75 to 55.25 wt. %. Pyrite from mineralized black shale and hydrothermal veins contains relatively higher concentrations of As (~ 1 wt. %) than pyrite from other sample types. The arsenopyrite commonly occurs as fine-grained anhedral crystals as inclusions within pyrite, medium-grained crystal intergrowing with pyrite and/or as coarse-grained massive arsenopyrite bodies in the massive sulphide veins. The arsenopyrite composition is uniform in all textural and sample type with Fe content ranging from 33.44 to 35.20 wt. %, S content ranging from 21.13 to 22.55 wt. % and As content ranging from 42.20 to 43.97 wt. %. In mineralized black shale and unmineralized black shale, the arsenopyrite shows, however, minor concentrations of Ni with 0.39 and 0.70 wt. % respectively. The pyrrhotite occurs as fine-grained anhedral patchy crystals randomly distributed within the rock matrix of unmineralized black shale and unmineralized granitoid, and / or as inclusions within pyrite in mineralized granitoid. The pyrrhotite shows a uniform composition in all samples and textural types, though minor concentrations of Ni (2.06 wt. %) content are reported in unmineralized granitoid. Chalcopyrite occurs as fine-grained crystals in inclusions within pyrite; and cobaltite occurs as rare fine-grained anhedral crystals occasionally disseminated in the albitite sill matrix. The chalcopyrite composition does not vary considerably in all sample and textural types, and cobaltite shows minor concentrations of Ni (4.55 wt. %) and Fe (3.45 wt. %). Native gold grains are commonly found associated with the secondary pyrite texture especially within the sulphide-rich lenses and in the massive sulphide veins, and are almost pure with ~97 wt. %. A Na-rich hydrothermal fluid from low-grade metamorphism associated with the E-W compressive tectonic event, which caused formation of the antiform structure which control the mineralization in the deposit area, led to the albitization of the deposit rocks and specially the alteration of the granitic assemblage to form albitite, and the deposition of aggregates of fine-grained anhedral crystals and growth and annealing of pyrite in sulphide-rich lenses. Afterward, the CO2-rich hydrothermal fluids influx circulated through reactivated structures, including quartz veins, and led to the precipitation of dolomite, ankerite, siderite and magnesite. They also led to the precipitation of pyrite of secondary textures as well as arsenopyrite, chalcopyrite and formation of pyrrhotite from the desulphurization of early pyrite. The CO2-rich hydrothermal fluids probably leached gold and other trace elements such as As, Co, etc. from the sedimentary host rocks and deposited them into suitable traps, such as the sulphide-rich lenses and massive sulphide bodies, preferably within the hinge zone of anticline axis constituting a hydrothermal fluid pathway.

The Whistler Corridor is located in the Alaskan Range 150 km northwest of Anchorage. Hosted by the regionally extensive Kahiltna flysch terrane, the Whistler Igneous Suite (WIS) volcano-magmatic sequence is calc-alkalic, metaluminous, and exhibits an arc related trace element signature. Extrusive rocks comprise andesite flows, volcaniclastic rocks, and hypabyssal dykes and sills. Intrusive rocks are dioritic with two major phases. An initial phase associated with porphyry mineralisation was dated by zircon U-Pb (CA-TIMS) at 76.4 ± 0.3 Ma. A later unmineralised phase had previously been determined by hornblende Ar-Ar at 75.5 ± 0.3 Ma. Mineralised diorite exhibits Nb/Y ratios >1.1 distinct from unmineralised diorite (Nb/Y<1.1). Of several porphyry occurrences the largest is the Whistler deposit hosting an indicated and inferred resource of 3.13 Moz Au and 769 Mlbs Cu. The main Au-Cu zone is characterised by feldspar-stable albite-magnetite (sodic-ferric) and K-feldspar-magnetite (potassic) alteration associated with magnetite (M-) and quartz (A-, B-) veins. High-temperature albitic alteration was characterised using energy dispersive spectroscopic (EDS) analyses of previously unidentified alteration. A peripheral zone of quartz-sericite-pyrite (phyllic) alteration is associated with quartz (D1-3) and pyrite (D4-5) veins. Sphalerite and galena in D3-veins define an overprinting Zn-Pb zone. An intermineral intrusive phase in the core of the deposit is associated with a magmatic-hydrothermal breccia hosting the highest-grade Cu-Au zone. Locally, shallow-level equivalent of D3-veins comprise colloform and crustiform textured intermediate-sulphidation Pb-Zn-Ag-Au veins. Sulphide δ³⁴S isotopes range from 0.4-7.7‰ (xˉ=3.8‰; σ=1.3‰). δ³⁴S in M/A-veins is 1.7‰; B-veins 3.4‰; D1-3 veins 3.7‰; D4-5 veins 4.9‰; and E-veins 6.5‰. δ³⁴S values increase temporally due to the preferential fractionation of ³⁴S into increasingly acidic, reduced fluids. Chlorite and sericite overprint feldspar-stable alteration. Short-wave infrared spectroscopy and X-Ray diffraction demonstrate higher temperature, more crystalline sericite in phyllic than chlorite-sericite alteration. A lack of a negative Nb-Ta anomaly, consistently positive sulphide δ³⁴S isotopes, and oxidised magnetite-series igneous rocks suggest a lack of crustal contamination. Thus, at ca. 76 Ma Whistler represents the earliest, least crustally contaminated, porphyry occurrences of the Late Cretaceous magmatic epoch in SW Alaska.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

In this dissertation, I use seismic imaging and waveform modeling methods to investigate melt migration processes and the structure of the magma plumbing system beneath the East Pacific Rise (EPR) and Endeavour segment of the Juan de Fuca Ridge, respectively. This work begins by studying shallow mantle reflections beneath the EPR. I find the amplitude versus offset and waveform characteristics of the reflections to be consistent with a sub-horizontal dunite channels located up to 20 km off-axis. The depth of the dunite channels correlate with patterns of mantle melt delivery and the predicted base of the thermal lithosphere, suggesting the channels are thermally controlled and may have formed in situ via dissolution by focused flow at the base of the lithosphere. This interpretation is consistent with field observations in ophiolites and numerical modeling of melt-focusing channels. The three-dimensional velocity structure of the Endeavour segment is then investigated to identify how patterns of mantle melt delivery influence the segment-scale distribution of crustal melt and crustal accretion. The results from this study indicate that the mantle magmatic system is skewed relative to the ridge-tracking crustal magmatic system and that this skew exerts primary control on magmatic, tectonic, and hydrothermal activity at the Endeavour segment. In regions where mantle melt delivery is axis-centered, mantle-derived melts are efficiently transported from the mantle to the crust, resulting in frequent crustal melt replenishment, associated seismogenic cracking, and enhanced crustal melt content that drives vigorous hydrothermal activity. Conversely, sites of off-axis melt delivery are characterized by less efficient vertical melt transport, resulting in infrequent crustal melt injection and hence, reduced crustal melt content and hydrothermal activity. Next, I focus on how along-axis variations in magma replenishment modulate crustal permeability and the intensity of hydrothermal circulation. Using full-waveform inversion, I show that sites of localized magma replenishment to the axial magma lens, along with induced seismogenic cracking, coincide with enhanced permeability. I conclude that the frequency of magma injection governs hydrothermal circulation patterns and heat flux at mid-ocean ridges. This dissertation includes previously published and unpublished coauthored material.

The Cripple Creek district, Colorado is renowned for its epithermal gold telluride veins which have produced over 21 million ounces of gold from an intensely altered alkaline diatreme complex (total production + economic resources of >900 tons Au, geologic resource >>1000 tons). Gold mineralization principally occurs as telluride minerals hosted by swarms of narrow veins composed of quartz ± fluorite, carbonate, adularia, pyrite > barite/celestite and accessory base metal sulfides. Mineralized hydrothermal breccias are also found in the district, along with low-grade, bulk tonnage resources that are targets of current mining activities. Newly recognized is a complex history of hydrothermal alteration and magmatism that led up to, and continued past the development of gold mineralization. These include the development of large volumes of low-temperature, alkali feldspar-rich styles of alteration, and more restricted volumes of high temperature, pyroxene and biotite-rich types. Gold mineralization is associated with voluminous K-feldspar + pyrite ± carbonate alteration that largely postdates igneous activity, and these are widely developed in the upper ∼1000 m of the volcanic complex. These follow a complex magmatic history characterized by at least three cycles of recharge. Although voluminous sulfate (anhydrite) and sulfide-rich styles of mineralization were also developed in the latest stages of hydrothermal activity, a remarkable aspect of Cripple Creek is the distinct underdevelopment of acid styles of alteration; feldspar and carbonate-rich styles of alteration predominate at all levels of exposure. The link between alkaline magmatism and gold deposits has been long recognized, but relatively recent discoveries of large, high grade deposits (Ladolam, Philippines, Porgera, Papua New Guinea), along with continued production from districts like Cripple Creek, encourages continued exploration. Salient characteristics shared by these deposits include telluride-rich mineralization accompanied by extensive carbonation, and voluminous K-metasomatism. Likewise, hydrolytic (acid) alteration tends to be poorly developed in many alkaline systems. This has important environmental implications, as the high acid buffering potential makes these deposits environmentally favorable to mine. The potential in alkaline systems for large and high grade deposits, coupled with the common lack of recognition of their distinctive styles of alteration and mineralization, makes these a compelling exploration target.

The Hub, Charlie and Northwest Copper are spatially related mineral showings (Cu ± Mo) located in the Tchaikazan River area of southwest British Columbia. The Tchaikazan River area is located on the boundary between the Intermontane Belt and southeast Coast Belt (SECB). Evidence of magmatic-hydrothermal alteration is preserved throughout the study area. Multiple episodes of magmatic-hydrothermal activity are associated with these three centres of porphyry-style mineralization. The Hub diorite is the oldest dated pluton in the area, with a U-Pb zircon emplacement age of 81.19 ± 0.78 Ma. ZFT/AFT data suggests an emplacement depth of> 4km for the Hub diorite. The Hub diorite is crosscut by a biotite ± magnetite (± quartz) matrix/cemented hydrothermal breccia. A feldspar hornblende dyke crosscuts both the diorite and hydrothermal breccia and gives a U-Pb zircon age of 79.9 ± 1.5 Ma. Copper, molybdenite ± galena occurs in quartz veining and cement to the hydrothermal breccia. ZFT/U-Pb and Ar-Ar ages for the Hub diorite are within error of each other. AFT data suggests an average erosion rate of 40 m/myr for intrusive rocks in the Taseko Lakes area. Field relationships, geophysical anomalies, geochronology, and stable isotope data suggest that there are three centres for magmatic-hydrothermal activity in the Tchaikazan River area: The Hub, Northwest Copper pluton, and Ravioli Ridge. The area displays evidence for multiple, temporally-distinct intrusive, alteration and mineralizing events.

Magnetite-apatite-actinolite deposits occur as pervasive replacement, veins, pods and breccias within wall rocks to the plutons of the Mystery Island intrusive suite at Echo Bay, Northwest Territories. The plutons and their altered wall rocks host previously-mined pitchblende, native Ag, Ni-Co arsenide veins. Although numerous studies were carried out on the pitchblende, native Ag, Ni-Co arsenide veins, the origin of the altered rocks which host them remains uncertain. Overall, this study reveals that the formation of magnetite-apatite-actinolite veins, pervasive replacement of rocks by albite and magnetite-apatite-actinolite, and hydrothermal brecciation by magmatic fluids is consistent with geologic and isotopic data. Thus, it is inferred that these deposits formed by replacement in a hydrothermal system dominated by magmatic fluids exsolved by cooling epizonal plutons of the Mystery Island intrusive suite. (Abstract shortened by UMI.)

This dissertation investigates the possible role of hydrothermally driven groundwater outflow in the formation of fluvial valleys on Mars. Although these landforms have often been cited as evidence for a past wanner climate and denser atmosphere, recent theoretical modeling precludes such climatic conditions on early Mars when most fluvial valleys formed. Because fluvial valleys continued to form throughout Mars' geological history and the most earth-like stream valleys on Mars formed well after the decline of the early putative earth-like climate, it may be unnecessary to invoke drastically different climatic conditions for the formation of the earliest stream valleys. The morphology of most Martian fluvial valleys indicates formation by ground-water sapping which is consistent with a subsurface origin. Additionally, many Martian fluvial valleys formed on volcanoes, impact craters, near fractures, or adjacent to terrains interpreted as igneous intrusions; all are possible locales of vigorous, geologically long-lived hydrothermal circulation. Comparison of Martian valley morphology to similar features on Earth constrains valley genesis scenarios. Volumes of measured Martian fluvial valleys range from 10¹⁰ to 10¹³ m³. Based on terrestrial analogs, total water volumes required to erode these valleys range from -10¹⁰ to 10¹⁵ m³. The clustered distribution of Martian valleys within a given terrain type, the sapping dominated morphology, and the general lack of associated runoff valleys all indicate the importance of localized ground-water outflow in the formation of these fluvial systems. An analytic model of a conductively cooling cylindrical intrusion is coupled with the U.S. Geological Survey's numerical ground-water computer code SUTRA to evaluate the magnitude of ground-water outflow expected from magmatically-driven hydrothermal systems on Mars. Results indicate that magmatic intrusions of several 10² km³ or larger can provide sufficient ground-water outflow over periods (several 10⁵ years) required to form Martian fluvial Valleys. Therefore, a vastly different climate on early Mars may not be necessary to explain the formation of the observed Valleys. Martian hydrothermal systems would have also produced long-lived sources of near-surface water; these localized regions may have provided oases for any microbial life that may have evolved on the planet.

Le Granite Passa Três est situé à l'Est de l'Etat du Paraná, au Sud du Brésil, et est allongé selon une direction NNE-SSW. Sa mise en place se fait au cœur des metapélites mesoprotérozoïques du Groupe Açungui (Province Mantiqueira). La minéralisation d’or du Granite Passa Três est composée par des veines de quartz contenant des quantités variables de fluorite, sulfures et carbonates. Les objectifs principaux de ce travail de thèse sont : de comprendre le modèle de formation du système de veines minéralisées en prenant en compte les relations entre magmatisme, hydrothermalisme, déformation et minéralogie à la fois dans l’espace et dans le temps ; la caractérisation de la nature, de la source et des conditions de dépôt des fluides ; et la caractérisation du modèle métallogénique de ce gisement singulier. Pour arriver à ces objectifs, les méthodes utilisées seront, en sus de la géologie structurale et de terrain : la pétrographie, la géochronologie U-Pb (LA-ICP-MS) sur zircon et 40Ar-39Ar sur muscovite, la microscopie électronique à balayage (MEB), la microsonde électronique, la fluorescence X (XFR), l’analyse isotopique du soufre (δ34S) et l’analyse microthermométrique et RAMAN des inclusions fluides. Les données structurales ont montré la coexistence de deux systèmes principaux de filons minéralisés, l’un N-S et l’autre E-W, avec des pendages de 60-75°W et 45-70°S, respectivement. Les deux systèmes sont interprétés comme contemporains et conjugués. Les corps minéralisés forment des géométries sigmoïdales qui résultent de l’ouverture en pull-aparts résultant de mouvements en faille normale le long de plans de glissement à faible pendage. Le fort pendage des structures minéralisées s’explique par l’enveloppe globale formée par la succession des pull-aparts. Quatre étapes minéralogiques sont à l’origine de la formation du système minéralisé : phase 1 [qtz 1 + fl], phase 2a [qtz 2 + py 2a ± or ± cpy ± aik ± fl ± sph ± musc], phase 2b [qtz 2 + py 2b + or + cpy + aik + ank ± sph ± fl ± musc] et phase 3 [qtz 3 + ank + calc + molyb ± aik ± musc ± fl]. L’or se trouve dans la forme d’or invisible et d’or natif dans des fractures qui affectent les pyrites des phases 2a et b, systématiquement associé avec la chalcopyrite et l’aikinite. L’altération associée à la minéralisation inclue des assemblages composés par muscovite/quartz/pyrite (altération du type greisen) et séricite/carbonate/clinochlore (altération phyllique). Les valeurs δ34S des pyrites (de -0.1‰ à 1.1‰) indiquant que le soufre du dépôt peut être d’origine magmatique. Cette hypothèse est en accord avec l’observation systématique, dans les parties supérieures du granite (sondage et niveaux supérieurs de la mine), de structures caractéristiques de transition magmatique-hydrothermale comme des systèmes aplo-pegmatitiques, des veines de quartz à bordure de K-feldspath, des concentrations de quartz de type stockscheider et des textures de solidification unilatérales (UST). Les résultats de géochronologie confirment cette hypothèse avec des âges U-Pb sur zircon (611.9±4.7 et 611.9±5.6 Ma pour le granite à grain moyen (GEM) et le microgranite (GEF) et 40Ar-39Ar sur muscovite (veines à bordure de K-feldspath : 612.9±2 à 608.8±2 Ma ; veines minéralisées : 611.7±2 à 608.8±2 Ma ; veines de quartz précoces : 608.4±2 Ma) très proches. Ces âges obtenus indiquent que la mise-en-place du granite, l’exsolution du fluide magmatique-hydrothermal et la formation des veines de quartz aurifères ont été réalisées pendant un écart de temps de 5 Ma, entre 613 et 608 Ma. La minéralisation (611 à 608 Ma) contemporaine de la cristallisation du granite (612 à 610 Ma), l’association de l’or avec des minéraux de bismuth (aikinite), la démonstration du contrôle structural sur la formation des veines et les évidences de transition magmatique-hydrothermale en domaine de coupole granitique montrent que le dépôt d’or du Granite Passa Três partage plusieurs similitudes avec les dépôts du type intrusion-related
The Passa Três Granite is situated in southern Brazil (Paraná State) and presents a NNE-SSW elongated shape. This intrusion is emplaced within metapelites of the Mesoproterozoic Açungui Group (Ribeira Belt, Mantiqueira Province), between the N40E trending Morro Agudo and Lancinha faults. Gold mineralisation is composed of centimetric to metric quartz veins with fluorite, sulphides and carbonates. The main objectives of this work are i) to understand the model of formation of the mineralised veins systems taking into account the relationships between magmatism, hydrothermalism, deformation and mineralogy in space and time; ii) the characterization of the nature, source and emplacement conditions of the ore fluids; and iii) the characterization of a metallogenic model for this singular deposit. In order to reach these purposes, the methods to be applied include, beyond the structural geology and field works: petrography, U-Pb zircon (LA-ICP-MS) and 40Ar-39Ar muscovite geochronology, scanning electron microscopy (SEM), electron-microprobe analyses (EPMA), X-ray fluorescence (XRF), isotopic analysis of sulphur (δ34S), and microthermometric and Raman analysis of fluid inclusions. Structural data showed the coexistence of two major normal mineralised vein systems, one N-S and the other one E-W, with dips of 60-75ºW and 45-70ºS, respectively. Both systems are interpreted to be contemporaneous and conjugated. Orebodies form sigmoidal geometries that resulted of the opening of pull-aparts as a consequence of the normal movements along low-angle fault planes. High-angle dip of the global mineralised structures is explained by the succession of the pull-aparts. Four mineralogical stages resulted in the formation of the mineralised system: phase 1 [quartz 1 + fluorite], phase 2a [quartz 2 + pyrite 2a ± gold ± chalcopyrite ± aikinite ± fluorite ± sphalerite ± muscovite], phase 2b [quartz 2 + pyrite 2b + gold + chalcopyrite + aikinite + ankerite ± sphalerite ± fluorite ± muscovite] and phase 3 [quartz 3 + ankerite + calcite + molybdenite ± aikinite ± muscovite ± fluorite]. Gold occurs as invisible gold and as native grains within fractures that affect pyrite 2a and 2b, commonly associated with chalcopyrite and aikinite. Alteration related to the mineralisation includes muscovite/quartz/pyrite (greisen type alteration) and sericite/carbonato/clinochlore (phyllic alteration) assemblages. The δ34S values of pyrite crystals (from -0.1‰ to 1.1‰) indicate that the sulphur in this deposit may have a magmatic origin. This hypothesis agrees with the systematic observation, within the upper part of the granite (drill holes and superior levels of the mine), of structures typical of magmatic-hydrothermal transition such as aplite-pegmatite systems, quartz veins with K-feldspar border, quartz concentration of stockscheider type and unilateral solidification textures (UST). Geochronological data confirm this hypothesis with U-Pb zircon ages (611.9±4.7 and 611.9±5.6 Ma for medium grained granite facies (GEM) and microgranite (GEF), respectively) and 40Ar-39Ar muscovite dating (veins with K-feldspar border: 612.9±2 to 608.8±2 Ma; mineralised veins: 611.7±2 to 608.8±2 Ma; barren vein: 608.4±2 Ma), that are very close. These ages indicate that the granite emplacement, the magmatic-hydrothermal fluid release and the formation of gold-bearing quartz veins occur during a time lapse of approximately 5 Ma, between 613 and 608 Ma. The mineralisation (611 to 608 Ma) coeval to granite crystallization (612 to 610 Ma), the association of gold with Bi minerals (aikinite), the strong structural control for veins and magmatic-hydrothermal transition features at the roof of a small granitic intrusion suggest that the Passa Três gold deposit shares several similarities with intrusion-related gold deposits

The biotite bearing Schultze Granite (Globe-Miami district) and the biotite-hornblende bearing Ruby Star Granodiorite (Pima district) compose two intrusive centers that produced multiple porphyry copper deposits during the Laramide orogeny. Both magmatic-hydrothermal systems were dismembered and tilted by Tertiary extension, as indicated by tilted Tertiary sedimentary rocks, paleomagnetic data, and geobarometry, thereby producing extraordinary exposures of these magmatic-hydrothermal systems: ~ 1 to ~10 km (Globe-Miami district) and <1 to>12 km (Pima district). Ages of emplacement range from 68 to 61 Ma for the Schultze Granite and 64 to 58 Ma for the Ruby Star Granodiorite. The plutons were formed by rapid accumulation of magma within short periods of time (~1 m.y.). The Schultze Granite is a high-silica granite and did not evolve chemically with time, except during formation of late porphyry and aplite dikes. Phases of the Ruby Star pluton range from granodiorite to granite, but appear to be distinct intrusive events separated in time by several million years. Each pluton is chemically homogenous with depth, probably due to convection. The low iron contents of biotites suggest that magmas related to porphyry copper deposits have higher oxidation states than typical granitic bodies. Hydrothermal alteration was associated with most phases of each pluton, with multiple alteration types overlapping to create complex centers. Veins persist to >10 km beneath porphyry copper deposits. Deep styles of alteration differ in the two plutons. The Schultze Granite contains biotite veins and greisen veins (coarse-grained muscovite) (~10 km). The Ruby Star Granodiorite contains sodic-calcic alteration (4-8 km) and greisen veins (4-12 km). The sodic-calcic alteration is asymmetrically distributed on the eastern side of the Sierrita deposit and is interpreted to have been created by influx of external sedimentary brines from Paleozoic sedimentary rocks that only are present on the eastern side of the pluton. Greisen alteration occurs late in the hydrothermal history and may be the last fluids that were exsolved from the magma as the magma chamber completely crystallized. These deep alteration styles can be used to predict where porphyry copper deposition may have occurred, which can lead to discoveries in extended terranes.

This thesis investigates the tectonic and magmatic setting of a Copper-rich seafloor massive sulfide deposit. Integrated multi-scale data analysis produced a regional to deposit-scale framework to constrain how, why and where these types of mineral deposits form. Outcomes from this research advance our understanding of 1) regional tectonic evolution of the East Manus Basin, and 2) volcanic and magmatic processes conducive to seafloor massive sulfide deposit formation.

Porphyry and high sulfidation epithermal ore-forming systems are genetically associated with calc-alkaline volcanism in subduction zones, and where erosion has not been too deep, the volcanic rocks are still commonly exposed in close proximity to the deposits. Most models for porphyry copper and high sulfidation epithermal gold systems include a shallow magmatic reservoir (the porphyry stock), an overlying hydrothermal cell, its alteration paragenesis and a stratovolcano. Some investigations also discuss the importance of underlying granitoid batholiths as feeders for porphyry stocks and their hydrothermal systems. Although it is commonly believed that the ores deposit during the waning stages of volcanism, given the time span over which these deposits form (tens of thousands to several million years) and the undeniable existence of hydrothermal systems beneath volcanoes, it is quite probable that their formation is initiated at times when volcanoes are still active. Although currently mined ore deposits are excellent places to focus research, subduction zone stratovolcanoes provide important windows on the magmatic-hydrothermal processes at play.This thesis describes an investigation of the magmatic-hydrothermal environment that resides beneath Merapi volcano, Indonesia. The research involved sampling and chemical analysis of minuscule aliquots of evolving silicate and sulfide melts trapped as inclusions at different times and in different locations in growing crystals subsequently ejected during eruptions. The research also involved sampling and analysis of fumarolic gases (and their precipitates) emitted at Merapi volcano during times of quiescence and eruptive activity, as well as compilation of published compositional data for fumarolic gases from other arc volcanoes. These gases are the surface equivalents of ore-forming magmatic-hydrothermal fluids. Finally the research involved compilation from the literature of compositional data for fluid inclusions (micron-scale droplets of magmatic volatile phases) trapped in gangue minerals in porphyry copper deposits. The focus of the research was the behaviour of copper, nickel, cobalt, zinc, lead and molybdenum in magmatic hydrothermal systems.The research reported in Chapter 1 showed that injections of sulfide melt-saturated mafic magma into shallower, more evolved and more oxidized resident magma at Merapi volcano induced exsolution of a magmatic volatile phase from the mafic magma. This hydrothermal fluid dissolved the sulfide melt and became enriched in chalcophile (notably copper) and siderophile metals. An argument is presented that the overpressure generated by the exsolution of a fluid originating in this manner triggered an explosive eruption at Merapi volcano in 2006. This is supported by the observation that the metal content, particularly of copper, was higher in the volcanic gas sampled immediately after this eruption than during periods of quiescence and that metal ratios of the gas are remarkably similar to those of sulfide melt inclusions. In Chapter 2, it is shown that the mafic magma mixed poorly with the more felsic magma, that both magmas evolved via assimilation and fractional crystallization and, most importantly, that the magmatic volatile phase transferred base metals to the more felsic magma. In Chapter 3, the fluid inclusion and volcanic gas data are used to make inferences about the evolution of porphyry ore-forming systems and link mechanisms of ore-formation to those operative during the eruptive cycles of volcanoes. Finally, the thesis integrates the findings of this study into a model that provides new insights into the formation of porphyry copper deposits below stratovolcanoes.
Les gîtes de types porphyriques et épithermaux sont génétiquement associés au volcanisme des zones de subduction et les roches volcaniques cogénétiques à ces gisements sont souvent encore présentes. Tous les modèles actuels de mise en place de ces gîtes définissent un réservoir magmatique peu profond, lequel est coiffé d'une cellule hydrothermale et de sa séquence complexe d'altération, ainsi que d'un stratovolcan. Certains auteurs discutent aussi de l'importance de batholites sous-jacents ayant généré le porphyre et ses fluides hydrothermaux. Quoiqu'il soit généralement accepté que ces gîtes se forment durant le déclin du volcanisme, étant donné la longévité des périodes proposées pour la formation de ceux-ci (de dizaines de milliers à plusieurs millions d'années) et l'existence indéniable de systèmes hydrothermaux associés, il est fort probable que la formation de ces gîtes soit initiée alors que le volcanisme est encore actif. Les volcans situés en zones de subduction représentent d'importants points d'observation des processus magmatiques-hydrothermaux actuels.La présente recherche porte sur l'environnement magmatique-hydrothermal qui existe sous le volcan Mérapi, situé en Indonésie. Des échantillons de liquides silicatés et sulfurés piégés à l'intérieur de cristaux durant leur croissance à différents moments et endroits dans le magma et avant d'être éjectés hors des réservoirs magmatiques lors d'éruptions volcaniques ont été prélevés et dosés. Des gaz fumerolliens de haute température et leurs sublimats émis au volcan Mérapi durant des phases de dégazage passif et d'éruption explosive ont été échantillonnés et analysés. Des résultats similaires pour les gaz d'autres volcans, ainsi que des analyses d'inclusions fluides de systèmes hydrothermaux de porphyres cuprifères ont été compilés à partir de la littérature. Les gaz volcaniques analysés sont les équivalents superficiels des fluides magmatiques-hydrothermaux qui génèrent les gisements métallifères.Dans le premier chapitre, il a été démontré que des magmas mafiques d'origine profonde et saturés en liquide sulfuré ont été injectés dans le réservoir magmatique peu profond de Mérapi, celui-ci contenant un magma plus évolué et plus oxydé. La décompression qu'a subie le magma mafique a provoqué l'exsolution d'une phase magmatique volatile (un fluide hydrothermal) qui a dissous le liquide sulfuré et ses métaux chalcophiles et sidérophiles (notamment le cuivre). La surpression générée par l'exsolution de ce fluide hydrothermal a provoqué l'éruption explosive du volcan Mérapi de mars à août 2006. Ceci est corroboré par l'observation que certains métaux, particulièrement le cuivre, étaient enrichis dans les gaz volcaniques émis après l'explosion par rapport aux niveaux mesurés durant la phase de dégazage passif, et par le fait que les rapports des métaux dans ces gaz post-explosion étaient soudainement semblables à ceux mesurés dans les inclusions sulfurées, alors qu'ils étaient bien différents durant les phases de dégazage passif du volcan. Dans le second chapitre, je démontre que le magma plus mafique et le magma plus felsique ne se sont pas bien mélangés, que les deux magmas ont évolué via l'assimilation de roches encaissantes et la cristallisation fractionnée, et que la phase magmatique volatile qui s'est séparée du magma mafique et qui a dissous le liquide sulfuré a transféré ses métaux au magma plus felsique. Dans le troisième et dernier chapitre, les inclusions fluides et les gaz volcaniques ont été utilisés en conjonction avec les connaissances acquises et décrites dans les deux premiers chapitres afin de proposer un modèle pour l'évolution du système porphyrique et d'établir les liens qui existent entre les mécanismes de formation des gîtes porphyriques et épithermaux acides, et ceux qui opèrent durant les cycles éruptifs des volcans. Un modèle pour la formation des porphyres cuprifères sous les stratovolcans actifs des zones de subduction est finalement proposé.

Geological and mineralogical investigations of four moderately peraluminous monzogranitic plutons (Preissac, Moly Hill, Lamotte, Lacorne) in the Archean Preissac-Lacorne batholith (northwestern Quebec) indicate that each consists of biotite, two-mica and muscovite monzogranite facies, and that these facies are zonally distributed in this order from margin to core or the larger Lamotte and Lacorne plutons. Rare-element-enriched granitic pegmatites are associated with the Lamotte and Lacorne plutons and are also regionally zoned, in this case, with respect to their respective plutons, from beryl-bearing in the plutons to spodumene-bearing in the country rocks. Molybdenite mineralized albitites and stockworks occur beyond the spodumene pegmatites and in the Preissac and Moly Hill plutons. The monzogranites display systematic mineralogical and major- and trace-element trends from biotite to muscovite monzogranite in the four plutons that are best explained by fractional crystallization of a biotite monzogranite-forming liquid. These petrochemical trends in the Lamotte and Lacorne plutons extend to the rare-element pegmatites, indicating that the latter are comagmatic with the monzogranite. A model is proposed in which the liquids of the Lamotte and Lacorne plutons underwent an initial side-wall crystallization to produce the observed zonation of the monzogranite types, followed by extreme differentiation inside the magma chamber, from where batches of pegmatite-forming liquid were sequentially injected into the overlying rocks. Pegmatites are rare and barren from the smaller Preissac and Moly Hill plutons due to early saturation of the residual liquid with aqueous fluid, from which quartz vein molybdenite precipitate to form quartz vein stockworks adjacent to the muscovite-bearing monzogranite.
The fractionation of the pegmatite-forming liquid is recorded partly in the crystal-chemistry of columbite-tantalite solid-solutions, by progressively higher Ta/(Ta + Nb) and Mn/(Mn + Fe) values with evolution from beryl- to spodumene-bearing pegmatite. These trends correlate to the greater solubility of Mn- relative to Fe- and of Ta- relative to Nb-columbite-tantalite end-members in the magma. In the Lacorne pagmatites, these trends were modified by contemporaneous crystallization of spessartine garnet, which buffered the Mn and Fe activities of the columbite-tantalite.
The pegmatite-forming liquid became saturated with an aqueous fluid at the onset of crystallization as shown by the entrapment of primary fluid inclusions in the paragenetically early beryl and spodumene. The orthomagmatic fluid was NaCl-dominated, had low salinity, contained appreciable dissolved CO$ sb2$, and evolved from Fe-bearing in beryl to Mn-, Li- and Cs-bearing in spodumene pegmatite in concert with the petrochemical evolution of the magma. Subsequent fluid evolution was marked by influx of externally derived Ca-brines of metamorphic origin and eventual unmixing of the orthomagmatic fluid into aqueous and carbonic phases.
The study represents the first comprehensive reconstruction of the petrological and fluid evolution in a comagmatic suite of monzogranites and rare-element granitic pegmatites.

Processes of post-magmatic element mobilisation have been reported for a number of magmatic-hydrothermal systems occurring in diverse geodynamic contexts. To constrain the processes that control these types of systems is a challenging task because the effects of hydrothermal/metasomatic processes on element distribution are poorly known, also the relationships of alteration types to mineralisation stages have not been well documented. This study presents the results of a detailed petrogeochemical and geochronological investigation, involving mineral and bulk-rock analysis as well as a precise CA-ID-TIMS U-Pb zircon dating. Based on these data, a model has been developed to explain the role of metasomatic processes in mobilising elements in a granitic system and to define the timing of igneous events controlling the mobility of fluids observed at Campiglia Marittima magmatic-hydrothermal system. At Campiglia the occurrence of multiple magmatic events over about 1 Ma generated an intense metasomatic fluid circulation. These magmatic processes began with the emplacement of the Botro ai Marmi monzogranitic pluton (~5.4 Ma), that was followed by mafic and later felsic porphyritic bodies (from 4.9 to 4.5 Ma) crosscutting the contact aureole generated by the monzogranite intrusion in the carbonate host rock. The closing event is represented by the early Pliocene (~4.4 Ma) rhyolitic extrusive complex of San Vincenzo. The hydrothermal metasomatic activity related to the whole igneous cycle generated proximal endo- and exoskarn as well as distal mineralised skarn bodies, exploited for Cu-Pb-Zn-Ag for over twenty-seven centuries and which are considered as a classic example of contact exoskarn generated by the interaction between a magmatic body and a marble host rock. This study focuses on (i) the characterisation of the different metasomatic lithofacies occurring at the pluton-host carbonate contact, resulting from prolonged fluids-rock interaction, (ii) the identification of the metasomatic processes that generated chemical transformation and a consequent replacement of the original granite and host carbonate, (iii) the identification of the geochemical processes responsible for the significant element mobilisation, regarding also the local mobilisation of usually poorly mobile elements, such as HFSE and REE. Thus, this study carried out detailed textural and geochemical investigations of the monzogranite, the host carbonate, and the products of their hydrothermal- metasomatic alteration, in the field, under the optical and electron microscope, and by QEMSCAN, EPMA and (LA)- ICP-MS. The obtained results allowed to discriminate between metasomatic processes occurred at variable temperature, fluid composition and pH, as well as to recognise preferential pathways for fluid circulation. Moreover, the reconstruction of the mineral paragenetic sequence coupled with chemical analysis allows to reconstruct the sequence of these metasomatic events. To define the chronological framework of the multiple igneous episodes occurring in the Campiglia Marittima area and to constrain the multiple hydrothermal episodes, a precise CA-ID-TIMS U-Pb dating has been carried out at the University of Geneva, on carefully selected zircon grains from the Botro ai Marmi monzogranite, the San Vincenzo rhyolite and the Temperino mafic porphyry crosscutting the metasomatic aureole. The Campiglia system offers exposures of the full range of emplacement types for magmas and related fluids, thus represents a prime case study to investigate the timescales of mechanism of magma deep storage, extraction, transfer, and shallow emplacement/eruption. New U-Pb CA-ID-TIMS geochronology from the Campiglia igneous system allows to reconstruct the evolution of crustal-derived and mantle-derived magmas that fed plutonic, subvolcanic and volcanic units over 1000 ka. Distribution of zircon ages is at odds with what can be expected for the crystallization interval of an igneous body. Indeed, that interval is short for the Botro ai Marmi pluton (100 ka), intermediate for the subvolcanic mafic Temperino porphyry (450 ka), and long for the volcanic San Vincenzo rhyolite (700 ka). The youngest zircons from the Botro ai Marmi granite have ages identical to 40Ar-39Ar ages of biotite from the granite and metasomatic phlogopite from skarn crosscutting the granite. The Temperino mafic porphyry and the San Vincenzo rhyolite show younger sanidine ages (emplacement/eruption age). The youngest zircon age from the pluton is therefore assumed to approximate the age of emplacement and final crystallization of the melt, whereas the zircons from the Temperino mafic porphyry and the San Vincenzo rhyolite are considered antecrystic, derived from re-mobilised earlier magma extracted from a deeper reservoir at the emplacement age. The new documentation of an extended period of crystallization for the Campiglia igneous system (about 1000 ka) matches with observations for the long-lived magmatic systems of Larderello and Elba Island. These data support the existence of multiple crustal reservoirs far larger than the outcropping igneous products. The observed mantle signature of metasomatic fluids suggests the presence of hidden mantle-derived reservoir able to activate episodically crustal melting and magma transfer to shallow levels. This sequential magmatic activity (both from mantle and crust) could be controlled by multiple, small batches of mafic magma, that did not lead to the formation of a single, homogeneous, hybrid pluton at the emplacement level.

La Fossa is the active volcanic center of Vulcano Island, the southernmost of Aeolian Islands (Italy). Although the volcano has been the site of many volcanological, petrological and geochemical studies since decades, some questions are still debated. Examples are the genetic relationships between the mafic and rhyolitic magmas, often involved in the same eruptions, and the depth of their storage. An additional limitation to the present knowledge comes from the fact that much of the deposits of La Fossa are ash-sized and, therefore, explosive phases of La Fossa volcanic history are less studied by a petrological point of view with respect to lava and coarse pyroclastic material, exception made for the famous AD 1888–90 last eruption. Further interest in this volcano comes from the fact that La Fossa hosts an acid-sulfate hydrothermal system which has been involved in phreatic eruptions, whose fine ashes are enriched in metals carried by hydrothermal fluids, and metal-bearing sulfide accessories have been found in some recent products. Thus, the plumbing system of this volcano may be an ideal site where studying the evolution of chalcophile metal concentration in magmas. In this PhD thesis, a study integrating petrography, whole-rock geochemistry, compositional analyses of mineral phases, melt inclusions and high pressure high temperature experimental petrology has been carried out on the products representative of the whole magmatic differentiation path (from basalt to rhyolite) of Vulcano, mostly focusing on the explosive products of the last 1000 years erupted at La Fossa. The main aim was to improve the knowledge of the plumbing system of La Fossa by defining the genetic relationships between the mafic and felsic magmas and their crystallization conditions, modeling their geochemical evolution including the concentration of chalcophile metals, and identifying an appropriate approach for reconstructing magma dynamics along the ash-dominated pyroclastic sequences. Whole-rock major and trace element analyses, major and trace element compositions of mineral and glass phases of natural and experimental products (temperature gradients experiments that simulate differentiation in a thermal-zoned reservoir), together with thermobarometric calculations and geochemical modelling allowed to depict the plumbing system of La Fossa as a complex polybaric system where rhyolitic magmas can be generated by extraction from crystal mush regions. The partial melting of the crystal mush by mafic magma inputs is accountable for the chemical and textural variability of the erupted intermediate and evolved products including the genesis of K- and Ba-rich trachytic magma. The stratigraphic record of La Fossa is mostly characterized by ash-sized deposits, originated by long-lasting low-intensity eruptive phases, that have not been fully employed to gain insights into La Fossa plumbing system dynamics. In this thesis, clinopyroxene phenocrysts were analyzed along the complex explosive sequence of the Palizzi Eruptive Unit (12th-13th century) that represents one of the most important eruptive period of the last 1000 years activity at La Fossa. Major element core to rim chemical profiles of clinopyroxene phenocrysts have been employed to perform a hierarchical cluster analysis that allows to recognize four chemical clusters. The compositional differences between the clusters have been reconciled with variations in the degree of undercooling and in the silicate melt composition towards both a mafic and an evolved end-members. The clusters distribution in the different portions of the crystals (cores, mantles and rims) and thermobarometric calculations, allowed to recognize several cycles of mafic magma input followed by ascent and eruption. The polybaric nature of the plumbing system together with the evidence of sulfide-silicate melt immiscibility in intermediate and evolved products erupted at La Fossa allowed to investigate the evolution of chalcophile metal concentration in crustal magma reservoirs, thus shedding light on mechanisms at the base of mineralization processes beneath arc volcanoes. Indeed, the mineralization potential of arc magmas depends, among other factors, on the timing of sulfide melt saturation relative to magma differentiation and to exsolution of a magmatic fluid phase. In this thesis, the major and trace element analyses of silicate melt and sulfide inclusions, for the basalt to rhyolite compositional spectrum, have been carried out to understand the evolution of chalcophile metals in the plumbing system and to give insights into magma fertility potential. The obtained results suggest that in case of sulfide-undersaturated arc basalts, metals reach the highest abundances in intermediate lati-trachytic magmas. At the point of sulfide saturation the chalcophile metal contents in the silicate melt dramatic decrease after fractionation of only 0.2-0.3 wt.% of sulfide in the solid assemblage. In this thesis the whole-rock Platinum-group elements (PGE) concentrations of the Vulcano magmatic suite have been measured with a Ni-sulfide fire assay method. The PGE are sensitive indicators of sulfide saturation because of their very high partition coefficients into a sulfide phase. The decrease in PGE constrained the onset of the sulfide saturation during magma differentiation at ~ 4 wt.% MgO; by this point magma evolution takes place under sulfide-saturated conditions. The obtained results, together with the high content of Pd comparable to other arc- related igneous suites associated with mineralized deposits, suggest that magmatic evolution in crustal magma reservoirs at an arc-related magmatic system similar to La Fossa, fed by sulfide-undersaturated shoshonitic basalts, has the potential to produce fertile magmas.

The Río Blanco–Los Bronces (Chile) is one of the richest endowed porphyry copper-molybdenum districts worldwide, where about 20% of the known mineralization is hosted by tourmaline-cemented hydrothermal breccia. This work seeks: (1) to find a relationship between tourmaline chemical and/or isotopic composition and the degree of mineralization in the breccia, (2) to constrain the source of the mineralizing fluid in the breccia, and (3) to determine of the composition and age of intrusive units in three new exploration projects and correlate them with the known intrusive rocks of the mine areas. Tourmaline from mineralized and barren breccias has similar boron isotopic compositions but differences in Mg/(Mg+Fe) ratios, Al-contents and Al-Fe correlation, which may have exploration value. Boron and sulfur isotopes results are consistent with a magmatic source of hydrothermal fluids. Results of whole rock geochemistry and U-Pb and 40Ar/39Ar geochronology of intrusive units, breccia and late-stage veins are combined with previous U-Pb, Ar/Ar and Re-Os ages to elucidate the magmatic and hydrothermal history of the district.:1 Introduction 1.1 Motivation of the study and statement of research questions 1.2 Scope of the study 2 Porphyry copper deposits (PCDs) 2.1 Introduction 2.1.1 Global copper inventory 2.1.2 Definition and classification of PCDs 2.2 Regional scale characteristics of PCDs 2.2.1 Tectonic setting 2.2.2 Space and time distribution 2.2.3 Porphyry stocks and their pluton and volcanic connections 2.2.4 Wall-rock Influence 2.3 Deposit-scale characteristics 2.3.1 Porphyry stocks and dikes 2.3.2 Hydrothermal breccia 2.3.3 Alteration-mineralization zoning 2.4 Processes of PCD formation 2.4.1 Arc magmatism 2.4.2 Magmatic volatiles 2.4.3 Genetic models 3 Regional setting of the study area 3.1 Tectono-magmatic setting 3.2 Metallogenic belts 4 Río Blanco – Los Bronces mining district 4.1 Mining history 4.2 District geology 4.2.1 Stratified rocks 4.2.2 Plutonic and hypabyssal intrusions 4.2.3 Structures 4.2.4 Alteration and mineralization 4.2.1 Geochronology database 5 Results 5.1 Plutonic units 5.1.1 Petrography 5.1.2 Whole rock (WR) geochemistry 5.1.3 Geochronology 5.2 Mineralization 5.2.1 Petrography 5.2.2 Tourmaline occurrence and composition 5.2.3 Sulfides and sulfates 6 Discussion 6.1 Time-space relationships of intrusion, brecciation and hydrothermal alteration 6.2 Stable isotope constraints on fluid source and evolution 6.2.1 Oxygen, hydrogen and sulfur isotopes 6.2.2 Boron isotopes 6.3 Tourmaline as a redox indicator and significance for exploration 7 Summary and conclusions 8 References Digital supplement Appendix (Methods) 9 Appendix Methods 9.1 Optical microscopy (OM) 9.2 Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) 9.3 Whole rock chemical analysis 9.4 Electron microprobe analyses (EMPA) 9.5 Boron isotopes 9.6 Sulfur isotopes 9.7 40Ar/39Ar dating 9.8 Zircon separation and characterization 9.9 U-Pb zircon LA-ICP-MS dating 9.10 U-Pb zircon CA-ID-TIMS dating 9.11 Single zircon evaporation as screening method

Metals with high demand and a supply risk are called critical metals. One solution to the criticality problem is source diversification. We do not fully understand critical metal enrichment in ore deposits. I focus on two groups: the rare earth elements (REE) and the platinum group elements (PGE). At Nolans, NT, REE are hosted in fluorapatite veins up to several metres thick. I show experiments testing two formation hypotheses. First, I tested whether REE are hydrothermally mobile. I ran layers of rock-like compositions, REE-free apatite, REE, and a saline solution in piston cylinder experiments at 2-5 kbar and 550-700 C. The results show that the REE layer bonded with the more soluble elements (Si, Al, Mg, Fe) to produce insoluble REE minerals such as allanite or britholite. Formation of REE-bearing apatite was limited to a thin zone between the REE and apatite. In a P-F dominated fluid, the solubility of REE is negligible. Second, I tested the reaction between a REE-P-F-bearing carbonatite layer and a silicate layer, at 6 kbar and 650-900 C. The experiments resulted in a reaction zone consisting of diopside and REE-rich apatite. This indicates that carbonatites can carry P and REE, and form REE-rich apatite in reaction with silicate rocks. These textures closely reproduce the Nolans ore. The Nolans REE are now hosted in alteration products consisting of carbonates, phosphates and silicates. This study documents the alteration mineralogy. I show a decoupling between Ce and La, caused by oxidation of Ce(III) to Ce(IV), leading to its incorporation in Th-bearing minerals. La, Nd and Pr are concentrated in Ce-free phases. This has implications for mineral processing. Thorium is an unwanted by-product of REE production, and Ce is a lower-value product. The concentration of Ce and Th in a single mineral may allow its separation before processing, increasing the monetary value and reducing the environmental hazard. Analysis methods for fluorapatite compositions typical for carbonatite (LREE-enriched, carbonate bearing) are discussed. Rhenium is another critical metal that commonly occurs in molybdenite. Carbonatite-hosted molybdenites commonly host 100s ppm of Re. Carbonatites are usually considered as deposits for REE or Nb, and the occurrence of Re-rich molybdenite is perplexing. I performed experiments which tested whether (1) carbonatites can recrystallise molybdenite powder, and (2) whether rheniite can crystallise in carbonatites. The powder was recrystallised to coarse crystals, and similarly sized rheniite crystals formed by reaction of perrhenate and sulfate. Thus, carbonatites flux molybdenite and rheniite growth. It is a first step in understanding the reason for the occurrence of molybdenite in carbonatites. These experiments also tested the behaviour of other PGE in peralkaline melts. It is uncertain whether PGE must be concentrated from silicate melts by sulfide saturation, or can they be transported as nanonuggets in silicate melts independently of any presence of a sulfide phase. Nanonuggets are well known from PGE solubility experiments in which they are treated as experimental artefacts. I exploited the tendency of these metals to form nanonuggets to further explore their behaviour. These experiments were conducted in Ag-Pd, Au, or Pt capsules at 5 kbar and 1050-1100 C. Textural evidence indicates that the nanonuggets formed by reduction of an initially oxidised melt. They preferentially stick to magnetite and coarsen by consumption of existing nanonuggets. PGE can be transported as nanonuggets in silicate melts regardless of the presence of sulfide, and their concentration can be greater than that allowed by equilibrium solubility. Re-bearing sodalite that formed in those experiments was in equilibrium with Re metal, suggesting the role of the peralkaline melt for stabilising the higher oxidation state.

Three models have been proposed for cassiterite (SnO2) mineralisation in magmatic–hydrothermal environments: (1) magmatic crystallisation from a granitic melt, (2) late-stage magmatic partition of Sn into a fluid or vapour phase and subsequent cassiterite deposition, and (3) hydrothermal leaching of Sn from granite and/or country rocks and subsequent deposition. The complex chemistry of the ‘tin’ granites, and the large and pervasive hydrothermal systems which can overprint and destroy primary features make understanding the processes responsible for Sn enrichment difficult. Two new analytical methods were developed. Firstly, a method for the determination of Rb–Sr and Sm–Nd isotopic compositions of magmatic and hydrothermal tourmalines, which can record the compositional evolution of magmas and their hydrothermal fluids. Secondly, cassiterite U–Pb geochronology to constrain the absolute age and duration of magmatic–hydrothermal Sn systems. These data, together with major and trace element compositions of tourmaline, whole-rock geochemistry, quartz δ18O values and zircon U–Pb geochronology are applied to two Sn deposits associated with the Ardlethan and Mole granites of eastern Australia. The geochemical and isotope data of tourmaline show large compositional changes across the magmatic–hydrothermal transition. In the Ardlethan Granite, tourmaline 87Rb–86Sr isotope compositions, which provide robust estimates of 87Sr/86Sr(i) because of their low 87Rb/86Sr, are used to model the assimilation and fractional crystallisation processes that lead to a 30-times enrichment of Sn in residual melts relative to the source rocks. However, caution must be taken with interpreting 87Sr/86Sr(i) tourmaline data as high 87Rb/86Sr of parental melts and fluids can lead to significant in-situ decay of 87Rb prior to tourmaline precipitation. This phenomon is hypothesised for the parental melts of the Mole Granite which due toextreme fractional crystallisation have extreme 87Rb/86Sr of ~900. Subsequently 87Sr/86Sr(i) tourmaline compositions are more evolved the the whole rock composition. The Sn concentration of tourmaline increases from magmatic to hydrothermal settings within the Ardlethan and Mole granites, recording the exsolution of a fluid from a silicate melt. The enrichment of Sn during fluid fractionation, recorded by tourmaline, agrees with experimentally determined melt–fluid partitioning coefficients. Fluid fractionation is the dominant enrichment process for greisen deposits of the Ardlethan Granite, and all deposits of the Mole Granite. Fluid leaching of host rocks is evidenced by convergence of Fe/(Fe+Mg), Sr, 87Sr/86Sr(i) and εNd(i) in hydrothermal tourmaline from the original source rock composition to the host rock composition. At Ardlethan, the host rock of mineralised breccia pipes is enriched in Sn (~50 ppm) and fluid leaching results in an increase of Sn in the mineralising fluids. Although fluid leaching occurs around the Mole Granite, the low Sn concentrations in the host rocks limits Sn enrichment. Melt/fluid-mineral partitioning is a major uncertainty in the interpretation of tourmaline trace element geochemistry. Natural studies performed here provide some constraints, however, more targeted experimental work is required. A new method for U–Pb characterisation of cassiterite by ID-TIMS has provided a matrix-matched reference material for in-situ techniques. However, common-Pb corrections of in-situ techniques remain a large uncertainty in cassiterite geochronology. At Ardlethan, the common-Pb compositions are appropriately estimated by terrestrial Earth models and are more precise than isochron ages. Conversely, the common-Pb associated with the Mole Granite appears variable between a terrestrial Earth composition and a highly evolved composition. Cassiterite U–Pb geochronology of both the Ardlethan and Mole granite mineralisation systems indicate precipitation synchronous with emplacement. The method does not have sufficient precision (~4 % absolute) to distinguish the age of cassiterite precipitation from that of zircon, however, the magmatic–hydrothermal systems of the Ardlethan and Mole granites persisted for a maximum of 4.2 Ma.

This study aims to develop a robust research methodology to examine the evolution of magmatic volatile phases during the cooling of felsic magmas via detailed melt- and fluid-inclusion studies, in particular the investigation of inclusions originally containing both melt and aqueous fluid. Then, using these techniques I will examine fluid immiscibility processes in two felsic magmatic systems, one mineralised, the other barren. In particular, I address the constraints on the exsolution of magmatic vapour and aqueous liquids, and how it is manifested in quartz-hosted inclusions, as well as the nature and composition of the exsolved phases. In developing a research philosophy two factors need to be paramount, it needs to be as widely applicable as possible, and the limitations need to be recognised and explored. Thus, the results deriving from these techniques may provide a test of the methodology. The thesis is based on two case studies, Rio Blanco (Chile) and Okataina (New Zealand). The first case study involves sub-volcanic intrusives and associated extrusives from the La Copa Rhyolite, and intrusives from the Don Luis Porphyry, two post-ore rhyolitic suites from the Los Bronces-Rio Blanco Porphyry Cu-Mo deposit. The second case study involves rhyolitic lavas (< 65 Ka) from the Okataina Volcanic Centre in the Taupo Volcanic Zone in New Zealand. This study is not intended to examine the geology of these systems, but rather to use them as examples of felsic systems, in diverse tectonic settings. Both as test cases for developing robust research techniques and for any information that they can provide regarding late-stage magmatic processes, particularly volatile phase exsolution, and the role of melt/fluid and liquid/vapour immiscibility. At Rio Blanco, the melt inclusion populations consist predominantly of glass inclusions and coexisting dark, inhomogeneous crystalline silicate melt inclusions (CSMI's). An important discovery from this study is the recognition that CSMI's trap volatile-rich melt, probably identical to the melt trapped as glass inclusions, and are crystallised, not "devitrified" or the product of post-magmatic alteration. Heating experiments demonstrate that both the glass and CSMI's from Rio Blanco have decrepitated and degassed post-trapping, notwithstanding the apparent lack of petrographic indicators of degassing in the glass inclusions. This coexistence appears to be a common occurrence; however, its significance seems to have been overlooked in a number of previous studies. From an initial volatile-rich melt, aqueous volatile phases (dominantly vapour) exsolved, forming bubbly magmatic emulsions. Inherently, magmatic emulsions are metastable, and disrupt into discrete melt and vapour phases. The vapour-rich phases separated from the melt and escaped, cooling, condensing, and mixing as they did so. Rio Blanco melt inclusions and fluid inclusions trapped all of these phases, in various combinations, both demonstrating the process in fine detail, and sampling the phase compositions. Analysis of the phases demonstrates partitioning of metals (Cu, Zn, and possibly Pb) into the vapour phase, its transport out of some of the magma bodies, and implies concentration by mixing and condensing to form metal-rich hypersaline fluid inclusions in the carapace of the Don Luis Porphyry. The Okataina case study provided an invaluable counterpoint to Rio Blanco. Phenocryst crystallisation pressures were supercritical, although the evidence suggests that volatile phase exsolution (VPE) occurred post- rather than pre-trapping, so that trapped magmatic emulsions are not observed. Okataina also contains coexisting CSMI's and glass inclusions, although many of the samples contains a complex array of partly crystalline silicate melt inclusions. Importantly for this study, many of the inclusions do homogenise during experimental heating, indicating that decrepitation and degassing were not as pronounced as at Rio Blanco. Heating experiments showed that despite coexisting CSMI's and glass inclusions, there was only a single melt trapped. This provides evidence of the post-trapping behaviour of melt inclusions, lacking at Rio Blanco. Although pre-trapping VPE did not occur to a large degree, post-trapping VPE did. Inclusions in which exsolution of an aqueous volatile phase has occurred provide a measure and sample of the amounts of fluids that were exsolved from a known quantity of melt, and may provide a method of determining the actual amounts of hydrothermal fluids that a magma body may exsolve. In evaluating these results some inevitable limitations of the techniques have been uncovered, particularly those relating to the vagaries of melt inclusion formation and preservation, and these have been evaluated. However, qualitative, and to some extent quantitative results have been produced, some of which have been published in research journals. Together, the case studies demonstrate and sample the fine detail of the exsolution of volatile-rich phases from silicate melts, their escape from those melts, and eventual cooling and condensing to form the kinds of hypersaline hydrothermal fluids found as fluid inclusions in ore-bodies. Further, they provide insights into common post-trapping behaviours of melt inclusions, some aspects of which appear to have been misinterpreted in some published melt inclusion studies.

Brothers submarine caldera volcano is one of 30 large volcanic centres that comprise the Kermadec arc, which stretches for ~1300 km NE of New Zealand. The NW Caldera vent field at Brothers straddles the caldera wall and hosts numerous, active, high-temperature (up to 302°C) black smoker chimneys and a greater number of inactive, sulfide-rich spires. The addition of magmatic fluids to the hydrothermal system is indicated by high \(^3He\), `CO_(2(g))`, and `H_2S_((g))` concentrations, low pH, and negative `δ^(15)N` and `δD_(H2O)` values for the vent fluids, in concert with local advanced argillic alteration assemblages in the host rocks. This study examines the mineralogy, trace element composition and Cu isotopes of the sulphide chimneys to test the hypothesis that magmatic fluids significantly affect the composition of mineralization at Brothers NW Caldera vent field. Petrographic analysis was undertaken to describe chimney mineralogy and formation. Chimney types were identified based on the composition and relative proportion of mineralogical layers. Two are Zn-rich, i.e., sphalerite-chalcopyrite and sphalerite-barite chimneys, and two are Cu-rich, i.e., chalcopyrite-sulfate and chalcopyrite-bornite chimneys. Discovery of small Bi-Au telluride inclusions explains previously enigmatic whole rock Au contents up to 91 ppm. Enriched Bi contents are commensurate with large amounts of sediment being subducted at the Kermadec trench, whereas the Bi-Au association suggests liquid Bi scavenged Au. Both findings are consistent with magmatic contributions to the NW Caldera vent site. Synchrotron radiation X-ray fluorescence microscopy (XFM) was used to produce high-resolution trace element maps (2 μm beam, covering `84 – 136 mm^2`) of Fe, Cu, Zn, As, Se, Sr, Pb ± Ga, Au, Bi and U distribution across the inner chimney walls. In addition, lower resolution (47 μm beam) maps generated by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) imaged those same elements, plus Ca, Co, Ni, Mo, Ag, Cd, In, Sn, Sb, Ba, Tl ± V and Te. Elemental zonation and textural features of sphalerite in the two Znrich chimneys show a progression of sphalerite replacement by chalcopyrite. The two Cu-rich chimneys show contrasting formation styles based on their massive chalcopyrite linings. The first displays elongate chalcopyrite grains radiating into and infilling the conduit, which merge together some millimetres from the centre. The second style shows deposition of successive laminations (0.25 - 1 mm) of chalcopyrite inside the conduit that progressively narrowed the orifice. Additionally, fine (15 - 40 μm) rings of concentrated trace elements occur within, and between, the laminations of Co, Ni, Zn, As, Se, Mo, Ag, Cd, Sn, Te, Au, Tl, Pb, Bi and U. The presence of U specifically indicates repeated, brief incursions of seawater into the chimney interior, during which perturbation of the resultant chemical gradients induced abrupt precipitation of these elements. Thus, the rings are a proxy for secular variations in vent fluid composition. Calculated enrichment factors, used to differentiate magmatically-derived elements, are generally consistent between the chimney trace element rings, fumarole condensates from subaerial volcanoes, and a ‘pond’ of molten (condensed) sulfur atop a submarine volcano. These indicate that Au, Te, Bi, Se, Ag and Cu in Brothers chimneys have a magmatic source. Isotopic analysis of primary chalcopyrite was utilized to investigate high-temperature hydrothermal Cu isotope fractionation at Brothers. The majority of the samples range between `δ^(65)Cu` = ~0.00 and 0.50‰, which is representative of a mantle source for the Cu. A few higher `δ^(65)Cu` values (>0.90‰) occur randomly distributed through chalcopyrite of the same age (<1 yr) in two chimneys. This suggests the higher `δ^(65)Cu` values are not related to seawater oxidation, which would decrease `δ^(65)Cu values in residual chalcopyrite, but rather could indicate isotopic variation within the vent fluids. Theoretical studies show significant isotopic fractionation can occur between aqueous and vaporous complexing species. Thus, given the evidence for magmatic volatiles at Brothers, vapour transport of Cu could account for the observed isotopic fractionation, again consistent with a magmatic origin. In summary, the application of techniques ranging from petrography to element mapping to Cu isotopes, shows that Au, Te, Bi, Se, Ag and Cu in this high-temperature, seafloor hydrothermal system are derived by magmatic fluids, where Bimelts concentrated Au effectively and Cu may be transported by vapour.

Volatiles are a fundamental component of the Magmatic-Hydrothermal model of platinum group element (PGE) ore deposition for PGE deposits in layered mafic intrusions such as Bushveld and Stillwater. Volatiles have the potential to complex with PGEs in silicate melts and hydrothermal fluids, increasing PGE solubility; in order to assess the models of PGE ore deposition reliable estimates on the solubilities in the various magmatic phases must be known. However, experimental studies on the solubility and partitioning behaviour of PGEs in mafic magmatic-hydrothermal systems under relevant conditions are sparse, and the data that do exist produce conflicting results and new or adapted experimental methods must be applied to investigate these systems. Experimental results are presented here, investigating the effect of volatiles (i.e. H2O, Cl and CO2) on Pt and Ir solubility in a haplobasaltic melt and fluid-melt partitioning of Pt between an aqueous fluid and a haplobasaltic melt under magmatic conditions using a sealed-capsule technique. Also included are the details of the development of a novel experimental technique to observe fluid-melt partitioning in mafic systems and application of the method to the fluid-melt partition of Pt. Solubility experiments were conducted to assess the effect of volatiles on Pt and Ir solubility in a haplobasaltic melt of dry diopside-anorthite eutectic composition at 1523K and 0.2GPa. Synthetic glass powder of an anhydrous, 1-atm eutectic, diopside-anorthite (An42-Di58) haplobasalt composition was sealed in a platinum or platinum-iridium alloy capsule and was allowed to equilibrate with the noble metal capsule and a source of volatiles (i.e. H2O, H2O-Cl or H2O-CO2) at experimental conditions. All experiments were run in an internally-heated pressure vessel equipped with a rapid quench device, with oxygen fugacity controlled by the water activity and intrinsic hydrogen fugacity of the autoclave (MnO-Mn3O4). The resultant crystal- and bubble-free run product glasses were analyzed using a combination of laser ablation ICP-MS and bulk solution isotope-dilution ICP-MS to determine equilibrium solubilities of Pt and Ir and investigate the formation and contribution of micronuggets to overall bulk determined concentrations. In water-bearing experiments, it was determined that water content did not have an intrinsic effect on Pt or Ir solubility for water contents between 0.9 wt. % and 4.4 wt. % (saturation). Water content controlled the oxygen fugacity of the experiment and the resulting variations in oxygen fugacity, and the corresponding solubilities of Pt and Ir, indicate that over geologically relevant conditions both Pt and Ir are dissolved primarily in the 2+ valence state. Pt data suggest minor influence of Pt4+ at higher oxygen fugacities; however, there is no evidence of higher valence states for Ir. The ability of the sealed capsule technique to produce micronugget-free run product glasses in water-only experiments, allowed the solubility of Pt to be determined in hydrous haplobasalt at lower oxygen fugacities (and concentrations) then was previously observed. Pt and Ir solubility can be represented as a function of oxygen fugacity (bars) by the following equations: [Pt](ppb)= 1389(fO-sub-2)+7531(fO-sub-2)^(1/2) [Ir](ppb)=17140(fO-sub-2)^(1/2) In Cl-bearing experiments, experimental products from short run duration (<96hrs) experiments contained numerous micronuggets, preventing accurate determination of platinum and iridium solubility. Longer run duration experiments showed decreasing amounts of micronuggets, allowing accurate determination of solubility; results indicate that under the conditions studied chlorine has no discernable effect on Pt solubility in the silicate melt from 0.6 to 2.75 wt. % Cl (saturation). Over the same conditions, a systematic increase in Ir solubility is found with increasing Cl content; however, the observed increase is within the analytical variation/error and is therefore not conclusive. If there is an effect of Cl on PGE solubility the effect is minor resulting in increased Ir solubilities of 60% at chlorine saturation. However, the abundance of micronuggets in short run duration experiments, which decreases in abundance with time and increases with Cl-content, offers compelling evidence that Cl-bearing fluids have the capacity to transport significant amounts of Pt and Ir under magmatic conditions. It is suggested that platinum and iridium dissolved within the Cl-bearing fluid are left behind as the fluid dissolves into the melt during the heating stages of the experiment, leaving small amounts of Pt and Ir along the former particle boundaries. With increasing run duration, the metal migrates back to the capsule walls decreasing the amount of micronuggets contained within the glass. Estimates based on this model, using mass-balance calculations on the excess amount of Pt and Ir in the run product glasses (i.e. above equilibrium solubility) in short duration experiments, indicate estimated Pt and Ir concentrations in the Cl-bearing fluid ranging from tens to a few hundred ppm, versus ppb levels in the melt. Respective apparent (equilibrium has not been established) partition coefficients (D,fluid-melt) of 1x10^3 to 4x10^3 and 300-1100 were determined for Pt and Ir in Cl-bearing fluids; suggesting that Cl-bearing fluids can be highly efficient at enriching and transporting PGE in mafic magmatic-hydrothermal ore-forming systems. Platinum solubility was also determined as a function of CO2 content in a hydrous haplobasalt at controlled oxygen fugacity. Using the same sealed capsule techniques and melt composition as for H2O and Cl, a hydrous haplobasaltic melt was allowed to equilibrate with the platinum capsule and a CO2-source (CaCO3 or silver oxalate) at 1523 K and 0.2 GPa. Experiments were conducted with a water content of approximately 1 wt. %, fixing the log oxygen fugacity (bars) between -5.3 and -6.1 (log NNO = -6.95 @ 1573 K and 0.2 GPa). Carbon dioxide contents in the run product glasses ranged from 800-2500 ppm; and over these conditions, CO2 was found to have a negligible effect on Pt solubility in the silicate melt. Analogous to the Cl-bearing experiments, bulk concentrations of Pt in CO2-bearing experiments increased with increasing CO2 content due to micronugget formation. Apparent Pt concentrations in the H2O-CO2 fluid phase, prior to fluid dissolution, were calculated to be 1.6 to 42 ppm, resulting in apparent partition coefficients(D,fluid-melt) of 1.5 x 10^2 to 4.2 x 10^3, increasing with increasing mol CO2:H2O up to approximately 0.15, after which increasing CO2 content does not further increase partitioning. As well, a novel technique was developed and applied to assess the partitioning of Pt between an aqueous fluid and a hydrous diopside-anorthite melt under magmatic conditions. Building upon the sealed-capsule technique utilized for solubility studies, a method was developed by adding a seed crystal to the capsule along with a silicate melt and fluid. By generating conditions favourable to crystal growth, and growing the crystal from the fluid, it is possible to entrap fluid inclusions in the growing crystal, allowing direct sampling of the fluid phase at the conditions of the experiment. Using a diopside seed crystal with the diopside-anorthite eutectic melt, it was possible to control diopside crystallization by controlling the temperature, thus allowing control of the crystallization and fluid inclusion entrapment conditions. Subsequent laser ablation ICP-MS analysis of the fluid inclusions allowed fluid–melt partition coefficients of Pt to be determined. Synthetic glass powder of an anhydrous, 1-atm eutectic, diopside-anorthite (An42¬Di58) haplobasalt composition (with ppm levels of Ba, Cs, Sr and Rb added as internal standards), water and a diopside seed crystal were sealed in a platinum capsule and were allowed to equilibrate at experimental conditions. Water was added in amounts to maintain a free fluid phase throughout the experiment, and the diopside crystal was separated from the melt. All experiments were run in an internally heated pressure vessel equipped with a rapid-quench device, with oxygen fugacity controlled by the water activity and intrinsic hydrogen fugacity of the autoclave (MnO-Mn3O4). Experiments were allowed to equilibrate (6-48 hrs) at experimental conditions (i.e. 1498K, 0.2 GPa, fluid+melt+diopside stable) before temperature was dropped (i.e. to 1483K) to induce crystallization. Crystals were allowed to grow for a period of 18-61 hours, prior to rapid isobaric quenching to 293K at the conclusion of the experiment. Experimental run products were a crystal- and bubble-free glass and the diopside seed crystal with a fluid-inclusion-bearing overgrowth. Analysis of fluid inclusions provides initial solubility estimates of Pt in a H2O fluid phase at 1488 K and 0.2 GPa at or near ppm levels and fluid melt partition coefficients ranging from 2 – 48. This indicates substantial metal enrichment in the fluid phase in the absence of major ligands such as carbonate or chlorine. The results of this study indicate that the volatiles studied (i.e. H2O, CO2, and Cl) do not have a significant effect on Pt and Ir solubility in a haplobasaltic melt at magmatic conditions. These results suggest that complexing of Pt and Ir by OH, Cl, and carbonate species in a haplobasaltic melt is insignificant and the presence of these volatiles will not result in significantly increased PGE contents over their dry counterparts, as has been suggested. Preliminary evidence of minor Cl-complexing of Ir is presented; however, resulting in only a slight increase (<100%) in Ir solubility at Cl-saturation. Significant partitioning of Pt and Ir into a fluid phase at magmatic conditions has been demonstrated; with estimates of fluid-haplobasaltic melt partition coefficients increasing from 1x10^1 for pure water to up to an apparent 4x10^3 with the addition of Cl or CO2 to the system. This result indicates complexing of Pt and Ir with OH< HxCOy≤ Cl. Using these estimates, Cl- or CO2-bearing magmatic fluids can be highly efficient at enriching and transporting platinum group elements (PGEs) in mafic magmatic-hydrothermal ore-forming systems.