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1
Eichelberger, John, Alexey Kiryukhin, Silvio Mollo, Noriyoshi Tsuchiya et Marlène Villeneuve. « Exploring and Modeling the Magma–Hydrothermal Regime ». Geosciences 10, no 6 (18 juin 2020) : 234. http://dx.doi.org/10.3390/geosciences10060234.
Texte intégralRésumé :
This special issue comprises 12 papers from authors in 10 countries with new insights on the close coupling between magma as an energy and fluid source with hydrothermal systems as a primary control of magmatic behavior. Data and interpretation are provided on the rise of magma through a hydrothermal system, the relative timing of magmatic and hydrothermal events, the temporal evolution of supercritical aqueous fluids associated with ore formation, the magmatic and meteoric contributions of water to the systems, the big picture for the highly active Krafla Caldera, Iceland, as well as the implications of results from drilling at Krafla concerning the magma–hydrothermal boundary. Some of the more provocative concepts are that magma can intrude a hydrothermal system silently, that coplanar and coeval seismic events signal “magma fracking” beneath active volcanoes, that intrusive accumulations may far outlast volcanism, that arid climate favors formation of large magma chambers, and that even relatively dry rhyolite magma can convect rapidly and so lack a crystallizing mush roof. A shared theme is that hydrothermal and magmatic reservoirs need to be treated as a single system.
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Mohammadi, Nadia, Christopher R. M. McFarlane, David R. Lentz et Kathleen G. Thorne. « Timing of magmatic crystallization and Sn–W–Mo greisen vein formation within the Mount Douglas Granite, New Brunswick, Canada ». Canadian Journal of Earth Sciences 57, no 7 (juillet 2020) : 814–39. http://dx.doi.org/10.1139/cjes-2019-0043.
Texte intégralRésumé :
U–Pb geochronology was applied to a combination of magmatic and hydrothermal minerals to help constrain the timing of emplacement of three units in the Mount Douglas Granite (MDG) and reveal their association with a complex mineralized hydrothermal system containing endogranitic Sn–W–Mo–Zn–Bi–U-bearing greisen/sheeted veins within the pluton. Magmatic monazite and zircon U–Pb ages obtained by LA–ICP–MS overlap at 368 Ma, recording a Late Devonian crystallization age for the MDG. Although discrimination, outside analytical error, of sequential pulses of magmatism is beyond the resolution of LA–ICP–MS U–Pb geochronology, geochemical variations of monazite accompanied by previous whole-rock geochemical analyses support a progressive fractional crystallization process starting from a parental magma (Dmd1), leading to the generation of Dmd2, and finally Dmd3 as the most fractionated unit. Hydrothermal uraninite, cassiterite, and monazite, collected from endogranitic greisen/sheeted veins, reveal evidence for syn-magmatic-related mineralization and a longer-lived post-magmatic hydrothermal system. The first stage is recorded by concordant uraninite dates at 367 ± 3 Ma and by an inverse isochron lower intercept of 362 ± 8 Ma for cassiterite. In contrast, hydrothermal monazite crystallized over a wider range of ages from 368 to 344 Ma, demonstrating post-magmatic hydrothermal activity within the MDG. These magmatic and hydrothermal ages combined with the geochemical signature of the MDG are similar to those documented for the nearby Mount Pleasant Sn–W–Mo–Bi–In granite-related deposit, which suggests that the two mineralizing systems occur at different levels of the same magmatic system.
3
Tajima, Yasuhisa, Setsuya Nakada, Fukashi Maeno, Toshio Huruzono, Masaaki Takahashi, Akihiko Inamura, Takeshi Matsushima, Masashi Nagai et Jun Funasaki. « Shallow Magmatic Hydrothermal Eruption in April 2018 on Ebinokogen Ioyama Volcano in Kirishima Volcano Group, Kyushu, Japan ». Geosciences 10, no 5 (14 mai 2020) : 183. http://dx.doi.org/10.3390/geosciences10050183.
Texte intégralRésumé :
The Kirishima Volcano Group is a volcanic field ideal for studying the mechanism of steam-driven eruptions because many eruptions of this type occurred in the historical era and geophysical observation networks have been installed in this volcano. We made regular geothermal observations to understand the hydrothermal activity in Ebinokogen Ioyama Volcano. Geothermal activity resumed around the Ioyama from December 2015. A steam blowout occurred in April 2017, and a hydrothermal eruption occurred in April 2018. Geothermal activity had gradually increased before these events, suggesting intrusion of the magmatic component fluids in the hydrothermal system under the volcano. The April 2018 eruption was a magmatic hydrothermal eruption caused by the injection of magmatic fluids into a very-shallow hydrothermal system as a bottom–up fluid pressurization, although juvenile materials were not identifiable. Additionally, the upwelling of mixed magma–meteoric fluids to the surface as a kick was observed just before the eruption to cause the top–down flashing of April 2018. A series of events was generated in the shallower hydrothermal regime consisting of multiple systems divided by conductive caprock layers.
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Fulignati, Paolo. « Hydrothermal fluid evolution in the ‘Botro ai Marmi’ quartz-monzonitic intrusion, Campiglia Marittima, Tuscany, Italy. Evidence from a fluid-inclusion investigation ». Mineralogical Magazine 82, no 5 (29 mai 2018) : 1169–85. http://dx.doi.org/10.1180/mgm.2018.116.
Texte intégralRésumé :
ABSTRACTThe quartz-monzonitic intrusion of ‘Botro ai Marmi’ in Tuscany, Italy, can be considered to be a typical example of an intrusion-centred magmatic hydrothermal system. The evolution of hydrothermal fluids in the ‘Botro ai Marmi’ intrusion was investigated using fluid-inclusion analyses to provide suitable physico-chemical constraints on the fluids involved in the late- to post-magmatic hydrothermal activity that affected the intrusion, providing inferences on their origin and variations of temperature and pressure with time.This work demonstrates that the earliest fluids circulating in the ‘Botro ai Marmi’ intrusion were high-temperature brines exsolved directly from the crystallizing magma. This fluid circulated in the intrusion under lithostatic conditions (P > 90 MPa, T > 540°C). A second evolutionary stage of the magmatic hydrothermal system is marked by the transition from lithostatic (>90 MPa) to hydrostatic dominated conditions (50 to 10 MPa). In this stage the fluids are also interpreted to be mainly orthomagmatic in origin but unmixed in a high-salinity brine and in a low-salinity vapour aqueous phase, at a temperature ranging from ~500 to 300°C. These fluids were responsible for the potassic alteration facies. At a later stage of hydrothermal evolution, abundant meteoric dominated fluids entered the system and are associated with propylitic alteration. This event marks the transition from a magmatic-hydrothermal system to a typical hydrothermal (‘geothermal’) system, which can be assumed to be similar to some extent to the nearby active high-enthalpy geothermal system of Larderello. Low-temperature and low-salinity meteoric water-dominated fluids characterize the latest stage of the ‘Botro ai Marmi’ hydrothermal system.
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Mathieu, Lucie, Taylor D. Wasuita, Ross Sherlock, Fred Speidel, Jeffrey H. Marsh, Benoît Dubé et Olivier Côté-Mantha. « Zircon from Altered Monzonite Rocks Provides Insights into Magmatic and Mineralizing Processes at the Douay Au Project, Abitibi Greenstone Belt ». Geosciences 12, no 3 (2 mars 2022) : 114. http://dx.doi.org/10.3390/geosciences12030114.
Texte intégralRésumé :
Zircon provides essential information on the age and oxidation state of magmatic systems and can be used to characterize magmatic-hydrothermal Au mineralizing systems. Using the Douay intrusion-related gold system (IRGS) as a type example of Neoarchean syenite-associated mineralization (Abitibi greenstone belt), we demonstrate that zircon from altered quartz-monzonite rocks can also be used to infer the age of a magmatic-hydrothermal event. Here, zircon chemistry is used to identify the following sequence of events at the Douay exploration project: (1) the crystallization of zircon at ~2690 Ma in evolved residual melts with distinct U-contents (quartz-monzonite magma); (2) the extensive radiation damage for the U-rich grains over a period of ~10–15 My; and (3) the alteration of zircon grains at ~2676 Ma by interaction with magmatic-hydrothermal mineralizing fluids derived from syenite and carbonatite intrusive phases. This study also distinguishes extensively altered zircon grains from pristine to least-altered zircon formed in distinct magmatic environments using a Th/U vs. U discrimination diagram.
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Stearns, Michael A., John M. Bartley, John R. Bowman, Clayton W. Forster, Carl J. Beno, Daniel D. Riddle, Samuel J. Callis et Nicholas D. Udy. « Simultaneous Magmatic and Hydrothermal Regimes in Alta–Little Cottonwood Stocks, Utah, USA, Recorded Using Multiphase U-Pb Petrochronology ». Geosciences 10, no 4 (2 avril 2020) : 129. http://dx.doi.org/10.3390/geosciences10040129.
Texte intégralRésumé :
Magmatic and hydrothermal systems are intimately linked, significantly overlapping through time but persisting in different parts of a system. New preliminary U-Pb and trace element petrochronology from zircon and titanite demonstrate the protracted and episodic record of magmatic and hydrothermal processes in the Alta stock–Little Cottonwood stock plutonic and volcanic system. This system spans the upper ~11.5 km of the crust and includes a large composite pluton (e.g., Little Cottonwood stock), dike-like conduit (e.g., Alta stock), and surficial volcanic edifices (East Traverse and Park City volcanic units). A temperature–time path for the system was constructed using U-Pb and tetravalent cation thermometry to establish a record of >10 Myr of pluton emplacement, magma transport, volcanic eruption, and coeval hydrothermal circulation. Zircons from the Alta and Little Cottonwood stocks recorded a single population of apparent temperatures of ~625 ± 35 °C, while titanite apparent temperatures formed two distinct populations interpreted as magmatic (~725 ± 50 °C) and hydrothermal (~575 ± 50 °C). The spatial and temporal variations required episodic magma input, which overlapped in time with hydrothermal fluid flow in the structurally higher portions of the system. The hydrothermal system was itself episodic and migrated within the margin of the Alta stock and its aureole through time, and eventually focused at the contact of the Alta stock. First-order estimates of magma flux in this system suggest that the volcanic flux was 2–5× higher than the intrusive magma accumulation rate throughout its lifespan, consistent with intrusive volcanic systems around the world.
7
Yu, Ming-Zhen, Xue-Gang Chen, Dieter Garbe-Schönberg, Ying Ye et Chen-Tung Arthur Chen. « Volatile Chalcophile Elements in Native Sulfur from a Submarine Hydrothermal System at Kueishantao, Offshore NE Taiwan ». Minerals 9, no 4 (21 avril 2019) : 245. http://dx.doi.org/10.3390/min9040245.
Texte intégralRésumé :
We analyzed sulfur isotopes, trace elements and chalcophile elements (Se, Te, As, Sb, and Hg) in the native sulfur matrix from the Kueishantao hydrothermal system and conducted a systematic micro-analytical investigation. The sulfur matrix lacked all measured metals (e.g., Fe, Cu) and rare earth elements (REEs) while being significantly enriched in Te, As, Se (750–1500 ppm), Sb (around 100 ppm) and some Hg. The δ34S data (0.2–2.4‰) suggest a magmatic source leached from igneous rocks and a small contribution of seawater sulfates to the sulfur in hydrothermal deposits. Correlations between Te, As, Sb, and S (r2 = 0.30–0.61) indicate that these elements behave coherently in magmatic-hydrothermal processes. The enrichment factors and content ratios of these elements demonstrate their abundance in the sulfur matrix and minor fractionation after being partitioned into the metallic melt and forming a separate vapor phase to transport. Our study focuses on the native sulfur matrix in a shallow-water volcanic hydrothermal system, to which relatively little attention has previously been paid. This will expand our understanding of hydrothermal precipitates. The study of volatile chalcophile elements in the matrix will provide significant information about their sources, distributions and other geochemical behaviors in magmatic-hydrothermal processes and help to understand the Kueishantao hydrothermal circulation better.
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Cangelosi, Delia, Sam Broom-Fendley, David Banks, Daniel Morgan et Bruce Yardley. « Light rare earth element redistribution during hydrothermal alteration at the Okorusu carbonatite complex, Namibia ». Mineralogical Magazine 84, no 1 (15 août 2019) : 49–64. http://dx.doi.org/10.1180/mgm.2019.54.
Texte intégralRésumé :
AbstractThe Cretaceous Okorusu carbonatite, Namibia, includes diopside-bearing and pegmatitic calcite carbonatites, both exhibiting hydrothermally altered mineral assemblages. In unaltered carbonatite, Sr, Ba and rare earth elements (REE) are hosted principally by calcite and fluorapatite. However, in hydrothermally altered carbonatites, small (<50 µm) parisite-(Ce) grains are the dominant REE host, while Ba and Sr are hosted in baryte, celestine, strontianite and witherite. Hydrothermal calcite has a much lower trace-element content than the original, magmatic calcite. Regardless of the low REE contents of the hydrothermal calcite, the REE patterns are similar to those of parisite-(Ce), magmatic minerals and mafic rocks associated with the carbonatites. These similarities suggest that hydrothermal alteration remobilised REE from magmatic minerals, predominantly calcite, without significant fractionation or addition from an external source. Barium and Sr released during alteration were mainly reprecipitated as sulfates. The breakdown of magmatic pyrite into iron hydroxide is inferred to be the main source of sulfate. The behaviour of sulfur suggests that the hydrothermal fluid was somewhat oxidising and it may have been part of a geothermal circulation system. Late hydrothermal massive fluorite replaced the calcite carbonatites at Okorusu and resulted in extensive chemical change, suggesting continued magmatic contributions to the fluid system.
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Launay, Gaëtan, Stanislas Sizaret, Philippe Lach, Jérémie Melleton, Eric Gloaguen et Marc Poujol. « Genetic relationship between greisenization and Sn–W mineralization in vein and greisen deposits : Insights from the Panasqueira deposit (Portugal) ». BSGF - Earth Sciences Bulletin 192 (2021) : 2. http://dx.doi.org/10.1051/bsgf/2020046.
Texte intégralRésumé :
The W–Sn Panasqueira ore deposit is a magmatic-hydrothermal system, which includes a high-grade quartz-vein type mineralization and a disseminated greisen-type mineralization occurring in the upper part of the Panasqueira two-mica granite. We investigated the genetic and chronological relationships between the greisenization of the Panasqueira granite and the formation of ore-bearing quartz veins by monitoring major and trace elements variations in quartz-white mica assemblages composing the two-mica granite, greisen and W–Sn-bearing quartz veins. The greisen is characterized by an overall depletion in Mg, Ti, Ca, Na, Ba, Sr, REE and enrichment in Fe, Li, Rb, Cs, Sn, W which reflect the breakdown of feldspars and fluid-rock interactions with W–Sn-bearing fluids. White-mica from greisen and mineralized quartz veins are enriched in granophile elements (F, Rb, Cs, Li, Sn, W and Zn) compared to magmatic muscovite from the two-mica granite. Trace elements contents in quartz depict trends which show the progressive enrichment in Ge and B and depletion in Al, Ti and Li from magmatic to hydrothermal quartz that emphasize the progressive evolution and cooling of the magmatic-hydrothermal system of Panasqueira. Geochemical similarities between quartz-white mica assemblages from greisen and wolframite-bearing veins suggest that greisenization and the formation of mineralized veins result from the same hydrothermal event and derived from the same source of hydrothermal fluids. Apatite from greisen and quartz vein yielded U–Pb ages of 292 ± 10 Ma and 295 ± 5 Ma respectively confirming that greisenization and the formation of mineralized veins occurred roughly at the same time. These ages also overlap with the emplacement age of the Panasqueira granite (296 ± 4 Ma), indicating a temporal link between greisenization, W–Sn mineralization and granite crystallization. Temperatures of the magmatic-hydrothermal system constrained by Ti-in quartz thermometry depicts a cooling trend from magmatic quartz of granite (700–600 °C) to hydrothermal quartz of greisen (500–400 °C) and veins (450–350 °C). These results suggest that greisenization and the formation of W–Sn bearing quartz veins occurred at the magmatic-hydrothermal transition, during which orthomagmatic fluids rich in volatils, incompatible elements and W–Sn were exsolved during the final solidification stage of the Panasqueira two-mica granite.
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Hanson, R. Brooks. « Hydrodynamics of magmatic and meteoric fluids in the vicinity of granitic intrusions ». Earth and Environmental Science Transactions of the Royal Society of Edinburgh 87, no 1-2 (1996) : 251–59. http://dx.doi.org/10.1017/s0263593300006660.
Texte intégralRésumé :
ABSTRACT:Numerical models that account for fluid flow, magmatic and metamorphic fluid production, topography and thermal expansion of the fluid following emplacement of a granitic magma in the upper crust reveal controls on the distribution of magmatic fluids during the evolution of a hydrothermal system. Initially, fluid pressures are close to lithostatic in and near an intrusion, and internally generated magmatic and metamorphic fluids are expelled. Later, fluid pressures drop to hydrostatic values and meteoric fluids circulate throughout the system. High permeabilities and low rates of fluid production accelerate this transition. Fluid production in the magma and wallrocks is the dominant mechanism elevating fluid pressures to lithostatic values. For granitic intrusions, about three to five times as much magmatic fluid is produced as metamorphic fluid. Continuous fluid release from a granitic magma with a vertical dimensions of 10 km produces a dynamic permeability of up to several tens of microdarcies.Near the surface, topography associated with a typical volcano acts to maintain a shallow meteoric flow system and drive fluids laterally. The exponential decay with depth of the influence of topography on fluid pressures results in a persistent zone of mixing at a depth of 1-2 km between these meteoric fluids and magmatic fluids despite variations in the strength of the magmatic hydrothermal system. However, in shallow systems where fluid release is episodic, dramatic changes in the region of mixing are still possible because fluid pressure is sensitive to variations in the rates of fluid production. At depth, high rates of metamorphic fluid production in the wallrocks and low permeabilities (< 1 μD) produce elevated fluid pressures, which hinder the lateral flow of magmatic fluids. Together, these patterns are consistent with the distribution and evolution of skarns and hydrothermal ore deposits around granitic magmas.
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Zhao, He-Dong, Kui-Dong Zhao, Martin R. Palmer, Shao-Yong Jiang et Wei Chen. « Magmatic-Hydrothermal Mineralization Processes at the Yidong Tin Deposit, South China : Insights from In Situ Chemical and Boron Isotope Changes of Tourmaline ». Economic Geology 116, no 7 (1 novembre 2021) : 1625–47. http://dx.doi.org/10.5382/econgeo.4868.
Texte intégralRésumé :
Abstract Owing to the superimposition of water-rock interaction and external fluids, magmatic source signatures of ore-forming fluids for vein-type tin deposits are commonly overprinted. Hence, there is uncertainty regarding the involvement of magmatic fluids in mineralization processes within these deposits. Tourmaline is a common gangue mineral in Sn deposits and can crystallize from both the magmas and the hydrothermal fluids. We have therefore undertaken an in situ major, trace element, and B isotope study of tourmaline from the Yidong Sn deposit in South China to study the transition from late magmatic to hydrothermal mineralization. Six tourmaline types were identified: (1) early tourmaline (Tur-OE) and (2) late tourmaline (Tur-OL) in tourmaline-quartz orbicules from the Pingying granite, (3) early tourmaline (Tur-DE) and (4) late tourmaline (Tur-DL) in tourmaline-quartz dikelets in the granite, and (5 and 6) core (Tur-OC) and rim (Tur-OR), respectively of hydrothermal tourmaline from the Sn ores. Most of the tourmaline types belong to the alkali group and the schorl-dravite solid-solution series, but the different generations of magmatic and hydrothermal tourmaline are geochemically distinct. Key differences include the hundredfold enrichment of Sn in hydrothermal tourmaline compared to magmatic tourmaline, which indicates that hydrothermal fluids exsolving from the magma were highly enriched in Sn. Tourmaline from the Sn ores is enriched in Fe3+ compared to the hydrothermal tourmaline from the granite and displays trends of decreasing Al and increasing Fe content from core to rim, relating to the exchange vector Fe3+Al–1. This reflects oxidation of fluids during the interaction between hydrothermal fluids and the mafic-ultramafic wall rocks, which led to precipitation of cassiterite. The hydrothermal tourmaline has slightly higher δ11B values than the magmatic tourmaline (which reflects the metasedimentary source for the granite), but overall, the tourmaline from the ores has δ11B values similar to those from the granite, implying a magmatic origin for the ore-forming fluids. We identify five stages in the magmatic-hydrothermal evolution of the system that led to formation of the Sn ores in the Yidong deposit based on chemical and boron isotope changes of tourmaline: (1) emplacement of a B-rich, S-type granitic magma, (2) separation of an immiscible B-rich melt, (3) exsolution of an Sn-rich, reduced hydrothermal fluid, (4) migration of fluid into the country rocks, and (5) acid-consuming reactions with the surrounding mafic-ultramafic rocks and oxidation of the fluid, leading to cassiterite precipitation.
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Milenkov, Georgi, Rossitsa Vassileva, Sylvina Georgieva, Valentin Grozdev et Irena Peytcheva. « Trace-element signatures and U-Pb geochronology of magmatic and hydrothermal titanites from the Petrovitsa Pb-Zn deposit, Madan region, Central Rhodopes (Bulgaria) ». Geologica Balcanica 51, no 2 (30 août 2022) : 79–91. http://dx.doi.org/10.52321/geolbalc.51.2.79.
Texte intégralRésumé :
The current study presents new geochronological and geochemical data for the Petrovitsa Pb-Zn deposit, Central Rhodopes, South Bulgaria. Based on in-situ U-Pb dating of titanites from pegmatites and skarnified mineralized marbles, it aims to provide new insights into the pegmatite formation and their relation to the hydrothermal system in the region. Titanite is an abundant accessory mineral in pegmatites and skarns within the Madan ore district. Commonly, it associates with feldspars, epidote, clinopyroxene, chlorite, hematite, zircon, apatite, allanite and monazite in both lithologies. Crystal size varies from 5 μm to 600 μm. The combined analytical approach revealed compositional and age variations of the studied titanites divided into: (i) early formed magmatic; and (ii) later hydrothermal. The magmatic crystals are characterized by mean Th/U of 1.91, Lu/Hf averaging at 0.59, and Dy/Yb of 2.03. The chondrite-normalized REE patterns show LREE dominance over HREE. The average ƩREE is 6548 ppm. The hydrothermal titanites have a mean Th/U of 0.22, Lu/Hf of 1.20, and average Dy/Yb of 1.50. HREE content slightly prevails over LREE. ƩREE is two times lower compared to magmatic titanites – 3388 ppm. Negative Eu-anomaly is common for both types. The LA-ICP-MS U-Pb geochronology shows a well-defined age distinction of magmatic and hydrothermal titanites. The calculated U-Pb weighted average age for the magmatic titanites is 48.9±2.3 Ма, while the pegmatite-hosted hydrothermal titanites are dated at 39.2±1.5 Ma. The hydrothermal titanites from skarns yield a weighted average age of 37.7±1.3 Ma. Data suggest pegmatite emplacement in the Rhodope metamorphic complex during the late Ypresian. Later hydrothermal fluids precipitated younger titanites with different signature.
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Pokrovski, Gleb S., Jacques Roux et Jean-Claude Harrichoury. « Fluid density control on vapor-liquid partitioning of metals in hydrothermal systems ». Geology 33, no 8 (1 août 2005) : 657–60. http://dx.doi.org/10.1130/g21475ar.1.
Texte intégralRésumé :
Abstract Hot aqueous fluids, both vapor and saline liquid, are primary transporting media for metals in hydrothermal-magmatic systems. Despite the growing geological evidence that the vapor phase, formed through boiling of magmatic ore-bearing fluids, can selectively concentrate and transport metals, the physical-chemical mechanisms that control the metal vapor-liquid fractionation remain poorly understood. We performed systematic experiments to investigate the metal vapor-liquid partitioning in model water-salt-gas systems H2O-NaCl-KCl-HCl at hydrothermal conditions. Measurements show that equilibrium vapor-liquid fractionation patterns of many metals are directly related to the densities of the coexisting vapor and liquid phases. Despite differences in the vapor-phase chemistry of various metals that form hydroxide, chloride, or sulfide gaseous molecules of contrasting volatile properties, water-solute interaction is a key factor that controls the metal transfer by vapor-like fluids in Earth's crust. These findings allow quantitative prediction of the vapor-liquid distribution patterns and vapor-phase metal transport in a wide range of conditions. Our density model accounts well for the vapor-brine distribution patterns of Na, Si, Fe, Zn, As, Sb, and Ag observed in fluid inclusions from magmatic-hydrothermal deposits. For Au and Cu, the partitioning in favor of the liquid phase, predicted in a sulfur-free system, contrasts with the copper and gold enrichment observed in natural vapor-like inclusions. The formation of stable complexes of Cu and Au with reduced sulfur may allow for their enhanced transport by sulfur-enriched magmatic-hydrothermal vapors.
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Lotfi, Mohammad, Mansoureh Shirnavard Shirazi, Nima Nezafati et Arash Gourabjeripour. « MINERALOGY AND GEOCHEMISTRY STUDY OF REE MINERALS IN HOST ROCKS IN IIC IRON DEPOSIT, BAFGH MINERAL AREA, CENTRAL IRAN ». Geosaberes 11 (8 janvier 2020) : 51. http://dx.doi.org/10.26895/geosaberes.v11i0.909.
Texte intégralRésumé :
The IIC deposit area to the east of the Bafq region exposes rocks that comprise the part of the Central Iran continental terrane. The IIC deposit iron orebodies are magmatic-related hydrothermal deposits that, when considered collectively display a vertical zonation from high-temperature, magmatic ± hydrothermal deposits emplaced at moderate depths (~1–2 km) to magnetite-dominant IOCG deposits emplaced at an even shallower subvolcanic level. The shallowest parts of these systems include near-surface, iron oxide-only replacement deposits, surficial epithermal sediment-hosted replacement deposits, and synsedimentary (exhalative) ironstone deposits. Alteration associated with the IOCG mineralizing system within the host volcanic, plutonic, and sedimentary rocks dominantly produced potassic with lesser amounts of calcic- and sodic-rich mineral assemblages. Our data suggest that hydrothermal magmatic fluids contributed to formation of the primary sodic and calcic alterations. The aim of this study is to delineate and recognize the different iron mineralized zones, based on surface and subsurface study. However, the data do not discriminate between a magmatic-hydrothermal source fluids resolved from Fe-rich immiscible liquid or Fe-rich silicate magma. Iron ores, occurring as massive-type and vein-type bodies are chemically different. Minor pyrite occurs as a late phase in the iron ores. The REE patterns of the mineralized metasomatites show LREE enrichment and strong Eu negative anomalies. The strong negative Eu anomaly probably indicates near-surface fractionation of alkali rhyolites involving feldspars. Field observations, ore mineral and alteration assemblages, coupled with lithogeochemical data suggest that an evolving fluid from magmatic dominated to surficial brine-rich fluid has contributed to the formation of the IIC deposit.
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Elliott, Brent. « Petrogenesis of Heavy Rare Earth Element Enriched Rhyolite : Source and Magmatic Evolution of the Round Top Laccolith, Trans-Pecos, Texas ». Minerals 8, no 10 (22 septembre 2018) : 423. http://dx.doi.org/10.3390/min8100423.
Texte intégralRésumé :
The Round Top rhyolite located in Trans-Pecos Texas is enriched in Be, F, Li, Nb, Rb, Sn, Th, U, Y, Zr, and rare earth elements (REEs). REE-bearing minerals are mainly ubiquitous nano-scale accessory phases throughout the groundmass, incorporated in synchysite-group minerals, xenotime-(Y), Y- and Ce-rich fluorite, and zircon. The rhyolite is peraluminous, high-silica, alkaline (not peralkaline), with elevated heavy rare earth element concentrations and anonymously negative Eu values. Pervasive spongy groundmass and recrystallization textures are consistent with the elevated and remobilized Zr, Th, and Y + HREE (heavy rare earth element) concentrations and a high field strength element (HFSE) soluble, sub-alkalic, F-rich, magmatic system. REE-bearing minerals are present as late-magmatic, interstitial phases and attributed with closed-system, post-magmatic, hydrothermal alteration. Petrogenetic modeling provides scenarios that explain the geochemical evolution and REE complexing behavior in evolved rhyolite magmas, and determines possible source compositions and evolution. Trace element models suggest a system typical of having extensive magmatic differentiation. The resulting rhyolite magma is indicative of a silica-rich magmatic system enriched in H2O, Li, and/or F that could be considered transitional between pure silicate melt and hydrothermal fluid, where fluorine-ligand complexing was prevalent through late magmatic cooling and crystallization processes. Thorough differentiation and high fluorine activity contributed to the late stage crystallization of REE-bearing minerals in the Round Top rhyolite.
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Wang, Zhen-Yu, Hong-Rui Fan, Lingli Zhou, Kui-Feng Yang et Hai-Dong She. « Carbonatite-Related REE Deposits : An Overview ». Minerals 10, no 11 (28 octobre 2020) : 965. http://dx.doi.org/10.3390/min10110965.
Texte intégralRésumé :
The rare earth elements (REEs) have unique and diverse properties that make them function as an “industrial vitamin” and thus, many countries consider them as strategically important resources. China, responsible for more than 60% of the world’s REE production, is one of the REE-rich countries in the world. Most REE (especially light rare earth elements (LREE)) deposits are closely related to carbonatite in China. Such a type of deposit may also contain appreciable amounts of industrially critical metals, such as Nb, Th and Sc. According to the genesis, the carbonatite-related REE deposits can be divided into three types: primary magmatic type, hydrothermal type and carbonatite weathering-crust type. This paper provides an overview of the carbonatite-related endogenetic REE deposits, i.e., primary magmatic type and hydrothermal type. The carbonatite-related endogenetic REE deposits are mainly distributed in continental margin depression or rift belts, e.g., Bayan Obo REE-Nb-Fe deposit, and orogenic belts on the margin of craton such as the Miaoya Nb-REE deposit. The genesis of carbonatite-related endogenetic REE deposits is still debated. It is generally believed that the carbonatite magma is originated from the low-degree partial melting of the mantle. During the evolution process, the carbonatite rocks or dykes rich in REE were formed through the immiscibility of carbonate-silicate magma and fractional crystallization of carbonate minerals from carbonatite magma. The ore-forming elements are mainly sourced from primitive mantle, with possible contribution of crustal materials that carry a large amount of REE. In the magmatic-hydrothermal system, REEs migrate in the form of complexes, and precipitate corresponding to changes of temperature, pressure, pH and composition of the fluids. A simple magmatic evolution process cannot ensure massive enrichment of REE to economic values. Fractional crystallization of carbonate minerals and immiscibility of melts and hydrothermal fluids in the hydrothermal evolution stage play an important role in upgrading the REE mineralization. Future work of experimental petrology will be fundamental to understand the partitioning behaviors of REE in magmatic-hydrothermal system through simulation of the metallogenic geological environment. Applying “comparative metallogeny” methods to investigate both REE fertile and barren carbonatites will enhance the understanding of factors controlling the fertility.
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Fulignati, P., A. Gioncada, S. Costa, D. Di Genova, F. Di Traglia et M. Pistolesi. « Magmatic sulfide immiscibility at an active magmatic-hydrothermal system : The case of La Fossa (Vulcano, Italy) ». Journal of Volcanology and Geothermal Research 358 (juin 2018) : 45–57. http://dx.doi.org/10.1016/j.jvolgeores.2018.06.009.
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Moore, Joseph N., et Richard P. Gunderson. « Fluid inclusion and isotopic systematics of an evolving magmatic-hydrothermal system ». Geochimica et Cosmochimica Acta 59, no 19 (octobre 1995) : 3887–907. http://dx.doi.org/10.1016/0016-7037(95)00289-c.
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Stimac, James A., Fraser Goff et Ken Wohletz. « Thermal modeling of the Clear Lake magmatic-hydrothermal system, California, USA ». Geothermics 30, no 2-3 (avril 2001) : 349–90. http://dx.doi.org/10.1016/s0375-6505(00)00062-6.
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Imura, Takumi, Yusuke Minami, Tsukasa Ohba, Akiko Matsumoto, Antonio Arribas et Mitsuhiro Nakagawa. « Hydrothermal Aluminum-Phosphate-Sulfates in Ash from the 2014 Hydrothermal Eruption at Ontake Volcano, Central Honshu, Japan ». Minerals 9, no 8 (29 juillet 2019) : 462. http://dx.doi.org/10.3390/min9080462.
Texte intégralRésumé :
Aluminum-phosphate-sulfates (APS) of the alunite supergroup occur in igneous rocks within zones of advanced argillic and silicic alteration in porphyry and epithermal ore environments. In this study we report on the presence of woodhouseite-rich APS in ash from the 27 September 2014 hydrothermal eruption of Ontake volcano. Scanning electron microscope coupled with energy dispersive X-ray spectrometer (SEM-EDS) and field emission (FE)-SEM-EDS observations show two types of occurrence of woodhouseite: (a) as cores within chemically zoned alunite-APS crystals (Zoned-alunite-woodhouseite-APS), and (b) as a coherent single-phase mineral in micro-veinlets intergrown with similar micro-veinlets of silica minerals (Micro-wormy-vein woodhouseite-APS). The genetic environment of APS minerals at Ontake volcano is that of a highly acidic hydrothermal system existing beneath the volcano summit, formed by condensation in magmatic steam and/or ground waters of sulfur-rich magmatic volatiles exsolved from the magma chamber beneath Mt. Ontake. Under these conditions, an advanced argillic alteration assemblage forms, which is composed of silica, pyrophyllite, alunite and kaolinite/dickite, plus APS, among other minerals. The discovery of woodhouseite in the volcanic ash of the Ontake 2014 hydrothermal eruption represents the first reported presence of APS within an active volcano. Other volcanoes in Japan and elsewhere with similar phreatic eruptions ejecting altered ash fragments will likely contain APS minerals derived from magmatic-hydrothermal systems within the subvolcanic environment. The presence of APS minerals within the advanced argillic zone below the summit vent of Ontake volcano, together with the prior documentation of phyllic and potassically altered ash fragments, provides evidence for the existence within an active volcano in Japan of an alteration column comparable to that of porphyry copper systems globally.
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Gilmer, Amy, R. Sparks, Dan Barfod, Emily Brugge et Ian Parkinson. « Duration of Hydrothermal Alteration and Mineralization of the Don Manuel Porphyry Copper System, Central Chile ». Minerals 11, no 2 (8 février 2021) : 174. http://dx.doi.org/10.3390/min11020174.
Texte intégralRésumé :
The Don Manuel porphyry copper system, located in the Miocene–Pliocene metallogenic belt of central Chile, contains spatially zoned alteration styles common to other porphyry copper deposits including extensive potassic alteration, propylitic alteration, localized sericite-chlorite alteration and argillic alteration but lacks pervasive hydrolytic alteration typical of some deposits. It is one of the youngest porphyry copper deposits in the Andes. Timing of mineralization and the hydrothermal system at Don Manuel are consistent with emplacement of the associated intrusions (ca. 4 and 3.6 Ma). Two molybdenite samples yielded consistent ages of 3.412 ± 0.037 and 3.425 ± 0.037 Ma. 40Ar/39Ar ages on hydrothermal biotites (3.57 ± 0.02, 3.51 ± 0.02, 3.41 ± 0.01, and 3.37 ± 0.01 Ma) are associated with potassic alteration. These ages are younger than the youngest intrusion by ~300 k.y. recording the cooling of the system below 350 °C. Such a time gap can be explained by fluxing of hot magmatic fluids from deeper magmatic sources.
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Harlaux, Matthieu, Julien Mercadier, Wilédio Marc-Emile Bonzi, Valentin Kremer, Christian Marignac et Michel Cuney. « Geochemical Signature of Magmatic-Hydrothermal Fluids Exsolved from the Beauvoir Rare-Metal Granite (Massif Central, France) : Insights from LA-ICPMS Analysis of Primary Fluid Inclusions ». Geofluids 2017 (2017) : 1–25. http://dx.doi.org/10.1155/2017/1925817.
Texte intégralRésumé :
The Beauvoir granite (Massif Central, France) represents an exceptional case in the European Variscan belt of a peraluminous rare-metal granite crosscutting an early W stockwork. The latter was strongly overprinted by rare-metal magmatic-hydrothermal fluids derived from the Beauvoir granite, resulting in a massive topazification of the quartz-ferberite vein system. This work presents a complete study of primary fluid inclusions hosted in quartz and topaz from the Beauvoir granite and the metasomatized stockwork, in order to characterize the geochemical composition of the magmatic fluids exsolved during the crystallization of this evolved rare-metal peraluminous granite. Microthermometric and Raman spectrometry data show that the earliest fluid (L1) is of high temperature (500 to >600°C), high salinity (17–28 wt.% NaCl eq), and Li-rich (Te<−70°C) with Na/Li ratios ~5. LA-ICPMS analyses of L1-type fluid inclusions reveal that the chemical composition of this magmatic-hydrothermal fluid is dominated by Na, K, Cs, and Rb, with significant concentrations (101–104 ppm) in rare-metals (W, Nb, Ta, Sn, and Li). This study demonstrates that primary fluid inclusions preserved the pristine signature of the magmatic-hydrothermal fluids in the Beauvoir granite but also in the metasomatized W stockwork, despite the distance from the granitic cupola (>100 m) and interaction with external fluids.
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Holley, Elizabeth A., Thomas Monecke, Thomas Bissig et T. James Reynolds. « Evolution of High-Level Magmatic-Hydrothermal Systems : New Insights from Ore Paragenesis of the Veladero High-Sulfidation Epithermal Au-Ag Deposit, El Indio-Pascua Belt, Argentina ». Economic Geology 112, no 7 (1 novembre 2017) : 1747–71. http://dx.doi.org/10.5382/econgeo.2017.4528.
Texte intégralRésumé :
Abstract The world-class Veladero high-sulfidation epithermal Au-Ag deposit is located in the Andean cordillera of Argentina near the northern end of the El Indio-Pascua metallogenic belt. The deposit comprises two nearly coalescing subhorizontal orebodies that are centered on an extensive zone of intense hydrothermal alteration. Intensely altered volcanic rocks are composed of fine-grained groundmass quartz that formed as a result of extreme acid leaching. These quartz grains contain ubiquitous rutile inclusions as well as healed microfractures of vapor-filled inclusions that record magmatic vapor streaming through the Miocene volcanic host succession. Condensation of the magmatic vapor into ambient groundwater generated the highly acidic waters responsible for the alteration. Alunite is present in the fine-grained groundmass quartz and fills vugs in the altered rocks. Stable isotope data indicate that the alunite formed through the disproportionation of SO2 in the condensed magmatic vapor. The fine-grained groundmass quartz is crosscut by later fracture-controlled euhedral quartz that is texturally associated with ore minerals. The euhedral quartz crystals show oscillatory growth zoning and contain rare primary fluid inclusions suggesting that quartz formation occurred at ~200°C from a moderately saline (<5 wt % NaCl equiv) liquid-phase hydrothermal fluid. High-fineness native Au grains are hosted in euhedral quartzlined void spaces and along fractures. In addition to native Au, vugs and fractures in the silicified volcanic rocks host Fe oxide/hydroxide and jarosite that are interpreted to represent the oxidation products of hypogene sulfide minerals that formed during and after the late stages of quartz formation. Results of previous jarosite dating suggest that pervasive oxidation of the orebody commenced during the waning stages of the hydrothermal activity or immediately thereafter. Oxidation of the orebody continued in the supergene environment for at least 3 m.y. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) showed that jarosite, which formed as a result of the oxidation of the orebody, is the principal host for Ag in Veladero ore, explaining the low (ca. 10%) Ag recovery from the oxide ore. The Veladero high-sulfidation epithermal deposit is interpreted to have formed in the shallow part of a magmatic-hydrothermal system. Early alteration related to magmatic vapor discharge was followed by later mineralization from liquid-phase hydrothermal fluids under reduced and slightly acidic to near-neutral conditions. This change from early vapor-dominated to later liquid-dominated magmatic-hydrothermal fluid flow was key in formation of the deposit.
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Harlaux, Matthieu, Kalin Kouzmanov, Stefano Gialli, Oscar Laurent, Andrea Rielli, Andrea Dini, Alain Chauvet, Andrew Menzies, Miroslav Kalinaj et Lluís Fontboté. « Tourmaline as a Tracer of Late-Magmatic to Hydrothermal Fluid Evolution : The World-Class San Rafael Tin (-Copper) Deposit, Peru ». Economic Geology 115, no 8 (18 août 2020) : 1665–97. http://dx.doi.org/10.5382/econgeo.4762.
Texte intégralRésumé :
Abstract The world-class San Rafael tin (-copper) deposit (central Andean tin belt, southeast Peru) is an exceptionally large and rich (>1 million metric tons Sn; grades typically >2% Sn) cassiterite-bearing hydrothermal vein system hosted by a late Oligocene (ca. 24 Ma) peraluminous K-feldspar-megacrystic granitic complex and surrounding Ordovician shales affected by deformation and low-grade metamorphism. The mineralization consists of NW-trending, quartz-cassiterite-sulfide veins and fault-controlled breccia bodies (>1.4 km in vertical and horizontal extension). They show volumetrically important tourmaline alteration that principally formed prior to the main ore stage, similar to other granite-related Sn deposits worldwide. We present here a detailed textural and geochemical study of tourmaline, aiming to trace fluid evolution of the San Rafael magmatic-hydrothermal system that led to the deposition of tin mineralization. Based on previous works and new petrographic observations, three main generations of tourmaline of both magmatic and hydrothermal origin were distinguished and were analyzed in situ for their major, minor, and trace element composition by electron microprobe analyzer and laser ablation-inductively coupled plasma-mass spectrometry, as well as for their bulk Sr, Nd, and Pb isotope compositions by multicollector-inductively coupled plasma-mass spectrometry. A first late-magmatic tourmaline generation (Tur 1) occurs in peraluminous granitic rocks as nodules and disseminations, which do not show evidence of alteration. This early Tur 1 is texturally and compositionally homogeneous; it has a dravitic composition, with Fe/(Fe + Mg) = 0.36 to 0.52, close to the schorl-dravite limit, and relatively high contents (10s to 100s ppm) of Li, K, Mn, light rare earth elements, and Zn. The second generation (Tur 2)—the most important volumetrically—is pre-ore, high-temperature (>500°C), hydrothermal tourmaline occurring as phenocryst replacement (Tur 2a) and open-space fillings in veins and breccias (Tur 2b) and microbreccias (Tur 2c) emplaced in the host granites and shales. Pre-ore Tur 2 typically shows oscillatory zoning, possibly reflecting rapid changes in the hydrothermal system, and has a large compositional range that spans the schorl to dravite fields, with Fe/(Fe + Mg) = 0.02 to 0.83. Trace element contents of Tur 2 are similar to those of Tur 1. Compositional variations within Tur 2 may be explained by the different degree of interaction of the magmatic-hydrothermal fluid with the host rocks (granites and shales), in part because of the effect of replacement versus open-space filling. The third generation is syn-ore hydrothermal tourmaline (Tur 3). It forms microscopic veinlets and overgrowths, partly cutting previous tourmaline generations, and is locally intergrown with cassiterite, chlorite, quartz, and minor pyrrhotite and arsenopyrite from the main ore assemblage. Syn-ore Tur 3 has schorl-foititic compositions, with Fe/(Fe + Mg) = 0.48 to 0.94, that partly differ from those of late-magmatic Tur 1 and pre-ore hydrothermal Tur 2. Relative to Tur 1 and Tur 2, syn-ore Tur 3 has higher contents of Sr and heavy rare earth elements (10s to 100s ppm) and unusually high contents of Sn (up to >1,000 ppm). Existence of these three main tourmaline generations, each having specific textural and compositional characteristics, reflects a boron-rich protracted magmatic-hydrothermal system with repeated episodes of hydrofracturing and fluid-assisted reopening, generating veins and breccias. Most trace elements in the San Rafael tourmaline do not correlate with Fe/(Fe + Mg) ratios, suggesting that their incorporation was likely controlled by the melt/fluid composition and local fluid-rock interactions. The initial radiogenic Sr and Nd isotope compositions of the three aforementioned tourmaline generations (0.7160–0.7276 for 87Sr/86Sr(i) and 0.5119–0.5124 for 143Nd/144Nd(i)) mostly overlap those of the San Rafael granites (87Sr/86Sr(i) = 0.7131–0.7202 and 143Nd/144Nd(i) = 0.5121–0.5122) and support a dominantly magmatic origin of the hydrothermal fluids. These compositions also overlap the initial Nd isotope values of Bolivian tin porphyries. The initial Pb isotope compositions of tourmaline show larger variations, with 206Pb/204Pb(i), 207Pb/204Pb(i), and 208Pb/204Pb(i) ratios mostly falling in the range of 18.6 to 19.3, 15.6 to 16.0, and 38.6 to 39.7, respectively. These compositions partly overlap the initial Pb isotope values of the San Rafael granites (206Pb/204Pb(i) = 18.6–18.8, 207Pb/204Pb(i) = 15.6–15.7, and 208Pb/204Pb(i) = 38.9–39.0) and are also similar to those of other Oligocene to Miocene Sn-W ± Cu-Zn-Pb-Ag deposits in southeast Peru. Rare earth element patterns of tourmaline are characterized, from Tur 1 to Tur 3, by decreasing (Eu/Eu*)N ratios (from 20 to 2) that correlate with increasing Sn contents (from 10s to >1,000 ppm). These variations are interpreted to reflect evolution of the hydrothermal system from reducing toward relatively more oxidizing conditions, still in a low-sulfidation environment, as indicated by the pyrrhotite-arsenopyrite assemblage. The changing textural and compositional features of Tur 1 to Tur 3 reflect the evolution of the San Rafael magmatic-hydrothermal system and support the model of fluid mixing between reduced, Sn-rich magmatic fluids and cooler, oxidizing meteoric waters as the main process that caused cassiterite precipitation.
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Sahlström, Fredrik, Zhaoshan Chang, Antonio Arribas, Paul Dirks, Craig A. Johnson, Jan Marten Huizenga et Isaac Corral. « Reconstruction of an Early Permian, Sublacustrine Magmatic-Hydrothermal System : Mount Carlton Epithermal Au-Ag-Cu Deposit, Northeastern Australia ». Economic Geology 115, no 1 (1 janvier 2020) : 129–52. http://dx.doi.org/10.5382/econgeo.4696.
Texte intégralRésumé :
Abstract The Mt. Carlton Au-Ag-Cu deposit, northern Bowen basin, northeastern Australia, is an uncommon example of a sublacustrine hydrothermal system containing economic high-sulfidation epithermal mineralization. The deposit formed in the early Permian and comprises vein- and hydrothermal breccia-hosted Au-Cu mineralization within a massive rhyodacite porphyry (V2 open pit) and stratabound Ag-barite mineralization within volcano-lacustrine sedimentary rocks (A39 open pit). These orebodies are all associated with extensive advanced argillic alteration of the volcanic host rocks. Stable isotope data for disseminated alunite (δ34S = 6.3–29.2‰; δ18OSO4 = –0.1 to 9.8‰; δ18OOH = –15.3 to –3.4‰; δD = –102 to –79‰) and pyrite (δ34S = –8.8 to –2.7‰), and void-filling anhydrite (δ34S = 17.2–19.2‰; δ18OSO4 = 1.8–5.7‰), suggest that early advanced argillic alteration formed within a magmatic-hydrothermal system. The ascending magmatic vapor (δ34SΣS ≈ –1.3‰) was absorbed by meteoric water (~50–60% meteoric component), producing an acidic (pH ≈ 1) condensate that formed a silicic → quartz-alunite → quartz-dickite-kaolinite zoned alteration halo with increasing distance from feeder structures. The oxygen and hydrogen isotope compositions of alunite-forming fluids at Mt. Carlton are lighter than those documented at similar deposits elsewhere, probably due to the high paleolatitude (~S60°) of northeastern Australia in the early Permian. Veins of coarse-grained, banded plumose alunite (δ34S = 0.4– 7.0‰; δ18OSO4 = 2.3–6.0‰; δ18OOH = –10.3 to –2.9‰; δD = –106 to –93‰) formed within feeder structures during the final stages of advanced argillic alteration. Epithermal mineralization was deposited subsequently, initially as fracture- and fissure-filling, Au-Cu–rich assemblages within feeder structures at depth. As the mineralizing fluids discharged into lakes, they produced syngenetic Ag-barite ore. Isotope data for ore-related sulfides and sulfosalts (δ34S = –15.0 to –3.0‰) and barite (δ34S = 22.3–23.8‰; δ18OSO4 = –0.2 to 1.3‰), and microthermometric data for primary fluid inclusions in barite (Th = 116°– 233°C; 0.0–1.7 wt % NaCl), are consistent with metal deposition at temperatures of ~200 ± 40°C (for Au-Cu mineralization in V2 pit) and ~150 ± 30°C (Ag mineralization in A39 pit) from a low-salinity, sulfur- and metal-rich magmatic-hydrothermal liquid that mixed with vapor-heated meteoric water. The mineralizing fluids initially had a high-sulfidation state, producing enargite-dominated ore with associated silicification of the early-altered wall rock. With time, the fluids evolved to an intermediate-sulfidation state, depositing sphalerite- and tennantite-dominated ore mineral assemblages. Void-filling massive dickite (δ18O = –1.1 to 2.1‰; δD = –121 to –103‰) with pyrite was deposited from an increasingly diluted magmatic-hydrothermal liquid (≥70% meteoric component) exsolved from a progressively degassed magma. Gypsum (δ34S = 11.4–19.2‰; δ18OSO4 = 0.5–3.4‰) occurs in veins within postmineralization faults and fracture networks, likely derived from early anhydrite that was dissolved by circulating meteoric water during extensional deformation. This process may explain the apparent scarcity of hypogene anhydrite in lithocaps elsewhere. While the Mt. Carlton system is similar to those that form subaerial high-sulfidation epithermal deposits, it also shares several key characteristics with magmatic-hydrothermal systems that form base and precious metal mineralization in shallow-submarine volcanic arc and back-arc settings. The lacustrine paleosurface features documented at Mt. Carlton may be useful as exploration indicators for concealed epithermal mineralization in similar extensional terranes elsewhere.
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Escolme, Angela, David R. Cooke, Julie Hunt, Ron F. Berry, Roland Maas et Robert A. Creaser. « The Productora Cu-Au-Mo Deposit, Chile : A Mesozoic Magmatic-Hydrothermal Breccia Complex with Both Porphyry and Iron Oxide Cu-Au Affinities ». Economic Geology 115, no 3 (1 mai 2020) : 543–80. http://dx.doi.org/10.5382/econgeo.4718.
Texte intégralRésumé :
Abstract The Productora Cu-Au-Mo deposit is hosted by a Cretaceous hydrothermal breccia complex in the Coastal Cordillera of northern Chile. The current resource, which includes the neighboring Alice Cu-Mo porphyry deposit, is estimated at 236.6 Mt grading 0.48% Cu, 0.10 g/t Au, and 135 ppm Mo. Local wall rocks consist of a thick sequence of broadly coeval rhyolite to rhyodacite lapilli tuffs (128.7 ± 1.3 Ma; U-Pbzircon) and two major intrusions: the Cachiyuyito tonalite and Ruta Cinco granodiorite batholith (92.0 ± 1.0 Ma; U-Pbzircon). Previous studies at Productora concluded the deposit had strong affinities with the iron oxide copper-gold (IOCG) clan and likened the deposit to Candelaria. Based on new information, we document the deposit geology in detail and propose a new genetic model and alternative classification as a magmatic-hydrothermal breccia complex with closer affinities to porphyry systems. Hydrothermal and tectonic breccias, veins, and alteration assemblages at Productora define five paragenetic stages: stage 1 quartz-pyrite–cemented breccias associated with muscovite alteration, stage 2 chaotic matrix-supported tectonic-hydrothermal breccia with kaolinite-muscovite-pyrite alteration, stage 3 tourmaline-pyrite-chalcopyrite ± magnetite ± biotite-cemented breccias and associated K-feldspar ± albite alteration, stage 4 chalcopyrite ± pyrite ± muscovite, illite, epidote, and chlorite veins, and stage 5 calcite veins. The Productora hydrothermal system crosscuts earlier-formed sodic-calcic alteration and magnetite-apatite mineralization associated with the Cachiyuyito stock. Main-stage mineralization at Productora was associated with formation of the stage 3 hydrothermal breccia. Chalcopyrite is the dominant hypogene Cu mineral and occurs predominantly as breccia cement and synbreccia veins with pyrite. The Alice Cu-Mo porphyry deposit is characterized by disseminated chalcopyrite and quartz-pyrite-chalcopyrite ± molybdenite vein stockworks hosted by a granodiorite porphyry stock. Alice is spatially associated with the Silica Ridge lithocap, which is characterized by massive, fine-grained, quartz-altered rock above domains of alunite, pyrophyllite, and dickite. Rhenium-Os dating of molybdenite indicates that main-stage mineralization at Productora occurred at 130.1 ± 0.6 Ma, and at 124.1 ± 0.6 Ma in the Alice porphyry. Chalcopyrite and pyrite from Productora have δ34Ssulfide values from –8.5 to +2.2‰, consistent with a magmatic sulfur source and fluids evolving under oxidizing conditions. No significant input from evaporite- or seawater-sourced fluids was detected. Stage 3 tourmalines have average initial Sr of 0.70397, consistent with an igneous-derived Sr source. The Productora magmatic-hydrothermal breccia complex formed as a result of explosive volatile fluid release from a hydrous intrusive complex. Metal-bearing fluids were of magmatic affinity and evolved under oxidizing conditions. Despite sharing many similarities with the Andean IOCG clan (strong structural control, regional sodic-calcic alteration, locally anomalous U), fluid evolution at the Productora Cu-Au-Mo deposit is more consistent with that of a porphyry-related magmatic hydrothermal breccia (sulfur-rich, acid alteration assemblages and relatively low magnetite contents, <5 vol %). The Productora camp is an excellent example of the close spatial association of Mesozoic magnetite-apatite, porphyry, and magmatic-hydrothermal breccia mineralization styles, a relationship seen throughout the Coastal Cordillera of northern Chile.
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Matsunaga, Yasuo, et Wataru Kanda. « Numerical Modeling of a Volcanic Hydrothermal System Based on Resistivity Structure ». Journal of Disaster Research 17, no 5 (1 août 2022) : 654–62. http://dx.doi.org/10.20965/jdr.2022.p0654.
Texte intégralRésumé :
Numerical simulation is a useful method for studying the magmatic-hydrothermal systems of volcanoes. However, no comprehensive scheme has been established for constructing subsurface permeability structures that have a significant impact on fluid flow within the volcano. In this study, as a first step to establishing such a scheme, numerical simulations of hydrothermal fluid flow incorporating the heterogeneous properties of the permeability structure were performed utilizing the resistivity structure observed at Kusatsu-Shirane Volcano, central Japan. Although the constructed permeability structure was relatively simple, the simulation results closely reproduced some observations, such as the broad resistivity structure and the distribution and discharge patterns of hot springs around the volcano. These results suggest that the uncertainty in generating permeability structures in hydrothermal fluid flow simulations can be greatly reduced by using resistivity structures.
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Geilert, Sonja, Christian Hensen, Mark Schmidt, Volker Liebetrau, Florian Scholz, Mechthild Doll, Longhui Deng et al. « On the formation of hydrothermal vents and cold seeps in the Guaymas Basin, Gulf of California ». Biogeosciences 15, no 18 (27 septembre 2018) : 5715–31. http://dx.doi.org/10.5194/bg-15-5715-2018.
Texte intégralRésumé :
Abstract. Magmatic sill intrusions into organic-rich sediments cause the release of thermogenic CH4 and CO2. Pore fluids from the Guaymas Basin (Gulf of California), a sedimentary basin with recent magmatic activity, were investigated to constrain the link between sill intrusions and fluid seepage as well as the timing of sill-induced hydrothermal activity. Sampling sites were close to a hydrothermal vent field at the northern rift axis and at cold seeps located up to 30 km away from the rift. Pore fluids close to the active hydrothermal vent field showed a slight imprint by hydrothermal fluids and indicated a shallow circulation system transporting seawater to the hydrothermal catchment area. Geochemical data of pore fluids at cold seeps showed a mainly ambient diagenetic fluid composition without any imprint related to high temperature processes at greater depth. Seep communities at the seafloor were mainly sustained by microbial methane, which rose along pathways formed earlier by hydrothermal activity, driving the anaerobic oxidation of methane (AOM) and the formation of authigenic carbonates. Overall, our data from the cold seep sites suggest that at present, sill-induced hydrothermalism is not active away from the ridge axis, and the vigorous venting of hydrothermal fluids is restricted to the ridge axis. Using the sediment thickness above extinct conduits and carbonate dating, we calculated that deep fluid and thermogenic gas flow ceased 28 to 7 kyr ago. These findings imply a short lifetime of hydrothermal systems, limiting the time of unhindered carbon release as suggested in previous modeling studies. Consequently, activation and deactivation mechanisms of these systems need to be better constrained for the use in climate modeling approaches.
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Yuan, Feng, Shao-Yong Jiang, Jiajun Liu, Shuai Zhang, Zhibin Xiao, Gang Liu et Xiaojia Hu. « Geochronology and Geochemistry of Uraninite and Coffinite : Insights into Ore-Forming Process in the Pegmatite-Hosted Uraniferous Province, North Qinling, Central China ». Minerals 9, no 9 (13 septembre 2019) : 552. http://dx.doi.org/10.3390/min9090552.
Texte intégralRésumé :
The biotite pegmatites in the Shangdan domain of the North Qinling orogenic belt contain economic concentrations of U, constituting a low-grade, large-tonnage pegmatite-hosted uraniferous province. Uraninite is predominant and ubiquitous ore mineral and coffinite is common alteration mineral after initial deposit formation. A comprehensive survey of the uraninite and coffinite assemblage of the Chenjiazhuang, Xiaohuacha, and Guangshigou biotite pegmatites in this uraniferous province reveal the primary magmatic U mineralization and its response during subsequent hydrothermal events. Integrating the ID-TIMS (Isotope Dilution Thermal Ionization Mass Spectrometry) 206Pb/238U ages and U-Th-Pb chemical ages for the uraninites with those reported from previous studies suggests that the timing of U mineralization in the uraniferous province was constrained at 407–415 Ma, confirming an Early Devonian magmatic ore-forming event. Based on microtextural relationships and compositional variation, three generations of uranium minerals can be identified: uaninite-A (high Th-low U-variable Y group), uranite-B (low Th-high U, Y group), and coffinite (high Si, Ca-low U, Pb group). Petrographic and microanalytical observations support a three-stage evolution model of uranium minerals from primary to subsequent generations as follows: (1) during the Early Devonian (stage 1), U derived from the hydrous silicate melt was mainly concentrated in primary magmatic uaninite-A by high-T (450–607 °C) precipitation; (2) during the Late Devonian (stage 2), U was mobilized and dissolved from pre-existing uraninite-A by U-bearing fluids and in situ reprecipitated as uraninite-B under reduced conditions. The in situ transformation of primary uraninite-A to second uraninite-B represent a local medium-T (250–450 °C) hydrothermal U-event; and (3) during the later low-T (100–140 °C) hydrothermal alteration (stage 3), U was remobilized and derived from the dissolution of pre-existing uraninite by CO2- and SiO2-rich fluids and interacted with reducing agent (e.g., pyrite) leading to reprecipitation of coffinite. This process represents a regional and extensive low-T hydrothermal U-event. In view of this, U minerals evolved from magmatic uraninite-A though fluid-induced recrystallized uraninite-B to coffinite, revealing three episodes of U circulation in the magmatic-hydrothermal system.
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Reed, M., B. Rusk et J. Palandri. « The Butte Magmatic-Hydrothermal System : One Fluid Yields All Alteration and Veins ». Economic Geology 108, no 6 (13 août 2013) : 1379–96. http://dx.doi.org/10.2113/econgeo.108.6.1379.
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Matsunaga, Yasuo, Wataru Kanda, Shinichi Takakura, Takao Koyama, Zenshiro Saito, Kaori Seki, Atsushi Suzuki, Takahiro Kishita, Yusuke Kinoshita et Yasuo Ogawa. « Magmatic hydrothermal system inferred from the resistivity structure of Kusatsu-Shirane Volcano ». Journal of Volcanology and Geothermal Research 390 (janvier 2020) : 106742. http://dx.doi.org/10.1016/j.jvolgeores.2019.106742.
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Ambrosio, Michele, Marco Doveri, Maria Teresa Fagioli, Luigi Marini, Claudia Principe et Brunella Raco. « Water–rock interaction in the magmatic-hydrothermal system of Nisyros Island (Greece) ». Journal of Volcanology and Geothermal Research 192, no 1-2 (avril 2010) : 57–68. http://dx.doi.org/10.1016/j.jvolgeores.2010.02.005.
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Monecke, Thomas, Ulf Kempe, Michael Trinkler, Rainer Thomas, Peter Dulski et Thomas Wagner. « Unusual rare earth element fractionation in a tin-bearing magmatic-hydrothermal system ». Geology 39, no 4 (avril 2011) : 295–98. http://dx.doi.org/10.1130/g31659.1.
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Birski, Słaby, Chatzitheodoridis, Wirth, Majzner, Kozub-Budzyń, Sláma, Liszewska, Kocjan et Zagórska. « Apatite from NWA 10153 and NWA 10645—The Key to Deciphering Magmatic and Fluid Evolution History in Nakhlites ». Minerals 9, no 11 (10 novembre 2019) : 695. http://dx.doi.org/10.3390/min9110695.
Texte intégralRésumé :
Apatites from Martian nakhlites NWA 10153 and NWA 10645 were used to obtain insight into their crystallization environment and the subsequent postcrystallization evolution path. The research results acquired using multi-tool analyses show distinctive transformation processes that were not fully completed. The crystallization history of three apatite generations (OH-bearing, Cl-rich fluorapatite as well as OH-poor, F-rich chlorapatite and fluorapatite) were reconstructed using transmission electron microscopy and geochemical analyses. Magmatic OH-bearing, Cl-rich fluorapatite changed its primary composition and evolved toward OH-poor, F-rich chlorapatite because of its interaction with fluids. Degassing of restitic magma causes fluorapatite crystallization, which shows a strong structural affinity for the last episode of system evolution. In addition to the three apatite generations, a fourth amorphous phase of calcium phosphate has been identified with Raman spectroscopy. This amorphous phase may be considered a transition phase between magmatic and hydrothermal phases. It may give insight into the dissolution process of magmatic phosphates, help in processing reconstruction, and allow to decipher mineral interactions with hydrothermal fluids.
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Fox, David C. M., Samuel C. Spinks, Milo Barham, Christopher L. Kirkland, Mark A. Pearce, Mehrooz Aspandiar, Renee Birchall et Ed Mead. « Working up an Apatite : Enigmatic Mesoarchean Hydrothermal Cu-Co-Au Mineralization in the Pilbara Craton ». Economic Geology 116, no 7 (1 novembre 2021) : 1561–73. http://dx.doi.org/10.5382/econgeo.4842.
Texte intégralRésumé :
Abstract Globally, significant examples of hydrothermal Cu-Co mineralization are rare within Archean greenstone belts, especially relative to the endowment of these terranes with other world-class hydrothermal ore deposits, particularly Au deposits. Using U-Pb geochronology of hydrothermal apatite, this study provides the first absolute age constraints on the timing of mineralization for the Carlow Castle Cu-Co-Au deposit. Carlow Castle is a complex, shear zone-hosted, veined Cu-Co-Au mineral system situated within the Paleo-Mesoarchean Roebourne greenstone belt of the Pilbara craton of northwestern Western Australia. Although U-Pb geochronology of this deposit is challenging due to low levels of radiogenic Pb in synmineralization apatite, mineralization is best estimated at 2957 ± 67 Ma (n = 61). Additionally, analysis of alteration phases associated with Carlow Castle mineralization suggests that it is dominated by a propylitic assemblage that is characteristic of alkaline fluid chemistry and peak temperatures >300°C. Within proximal portions of the northwest Pilbara craton, the period of Carlow Castle’s formation constrained here is associated with significant base-metal volcanogenic massive sulfide mineralization and magmatic activity related to back-arc rifting. This rifting and associated magmatic activity are the most likely source of Carlow Castle’s unique Cu-Co-Au mineralization. Carlow Castle’s Mesoarchean mineralization age makes it among the oldest discovered Cu-Co-Au deposits globally, and unique in the broader context of hydrothermal Cu-Co-Au deposits. Globally, hydrothermal Cu-Co mineralization occurs almost exclusively as Proterozoic and Phanerozoic stratiform sediment-hosted Cu-Co deposits due to the necessity of meteorically derived oxidized ore fluids in their formation. This research therefore has implications for exploration for atypical Cu-Co deposits and Cu-Co metallogenesis through recognition of comparably uncommon magmatic-hydrothermal Cu-Co-Au ore-forming processes and, consequently, the potential for analogous Cu-Co-Au mineralization in other Archean greenstone belts.
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Yang, Guang Shu, Yong Feng Yan et Peng Yu Feng. « Ore-Forming Fluid System of the Anqing Cu-Fe Deposit, Anhui Province, China ». Advanced Materials Research 734-737 (août 2013) : 135–38. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.135.
Texte intégralRésumé :
Fluid inclusions, carbon and oxygen isotopic compositions were discussed to understanding the ore-forming fluid system of Anqing Cu-Fe deposit. Homogeneous temperatures of fluid inclusions ranged from 124°C to 570°C, δ13CPDBvalues of the gangue minerals ranged from-3.3 to-0.9, and δ18O values ranged from 9.4 to 10.7, respectively. The results reveal that the primary ore-forming fluid was magmatic hydrothermal fluid characterized by high temperature, the boiling and mixing of fluids occurred in the main mineralization stage, the magmatic water was dominant in the ore-forming process, the physicochemical condition changes of the fluid system led to the formation of skarn and the deposition of the ore minerals. The ore-forming materials were mainly derived from magma, partly provided by sedimentary strata.
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Hussain, Zahid, Chunhui Tao, Chun-Feng Li, Shili Liao, Masroor Alam, Muhammad Farhan, Huichao Zhang et Amjad Hussain. « Mineralogy, Fluid Inclusions, and Isotopic Study of the Kargah Cu-Pb Polymetallic Vein-Type Deposit, Kohistan Island Arc, Northern Pakistan : Implication for Ore Genesis ». Minerals 11, no 11 (14 novembre 2021) : 1266. http://dx.doi.org/10.3390/min11111266.
Texte intégralRésumé :
The Kargah Cu-Pb polymetallic deposit is a newly discovered ore deposit from the Gilgit-Baltistan region, located in the Kohistan Island Arc, northern Pakistan. However, this area is poorly researched on the ore genesis, and its origin and the evolution of its magmatic-hydrothermal system remain unclear. Three stages of mineralization were identified, including quartz-pyrite, quartz-sulfide, and carbonate representing early, middle, and late stages, respectively. The major ore minerals are pyrite, chalcopyrite, galena, and zincian tetrahedrite with minor native silver, and native gold mainly distributed in pyrite. Here, we present a systematic study on ore geology, hydrothermal alterations, trace element composition of pyrite, fluid inclusions, and isotopes (S and Pb) characteristics to gain insights into the nature of the ore-forming fluids, types of unknown deposits, and hydrothermal fluid evolution. The high Co/Ni ratio (1.3–16.4) and Co content (average 1201 ppm), the low Mo/Ni ratio (0.43–0.94) and Mo contents (average 108 ppm) of both Py-I and Py-II suggest a mafic source for the mineralization. The Au-Ni plots, Co-As-Ni correlation, and the δ34S values range from −2.8 to 6.4‰ (average of 3.4‰) indicating the affiliation of the mineralization with a mantle-derived magmatic-hydrothermal provenance. The Pb isotope data showing the narrow variations in 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values suggest a single lead source from crustal-derived materials. The microthermometry data suggest that the dominant mechanisms are fluid boiling and mixing for mineral precipitation at temperatures ranging between 155 and 555 °C, and represent an intrusion-related magmatic-hydrothermal environment for the Kargah Cu-Pb polymetallic deposit.
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Murzintsev, N. G., I. Yu Annikova, A. V. Travin, A. G. Vladimirov, B. A. Dyachkov, V. I. Maslov, T. A. Oitseva et O. A. Gavryushkina. « THERMOCHRONOLOGY AND MATHEMATICAL MODELING OF THE FORMATION DYNAMICS OF RARE‐METAL‐GRANITE DEPOSITS OF THE ALTAI COLLISION SYSTEM ». Geodynamics & ; Tectonophysics 10, no 2 (24 juin 2019) : 375–404. http://dx.doi.org/10.5800/gt-2019-10-2-0419.
Texte intégralRésumé :
The article presents an event correlation of the Permian‐Triassic granites of the Altai collision system, which are associated with industrial ore deposits and occurrences (Mo‐W, Sn‐W, Li‐Ta‐Be). The multi‐system and multi‐mineral isotope datings of igneous rocks and ore bodies (U/Pb, Re/Os, Rb/Sr, Ar/Ar‐methods) suggest the postcollisional (intraplate) formation of ore‐magmatic systems (OMS), the duration of which depended on the crustmantle interaction and the rates of tectonic exposure of geoblocks to the upper crustal levels.Two cases of the OMS thermal history are described: (1) Kalguty Mo‐W deposit associated with rare‐metal granite‐leucogranites and ongonite‐ elvan dykes, and (2) Novo‐Akhmirov Li‐Ta deposit represented by topaz‐zinnwaldite granites and the contemporary lamprophyre and ongonit‐elvan dykes. For these geological objects, numerical modeling was carried out. The proposed models show thermal cooling of the deep magmatic chambers of granite composition, resulting in the residual foci of rare‐metal‐granite melts, which are known as the petrological indicators of industrial ore deposits (Mo‐W, Sn‐W, Li‐Ta‐Be). According to the simulation results concerning the framework of a closed magmatic system with a complex multistage development history, the magmatic chamber has a lower underlying observable massif and a reservoir associated with it. A long‐term magmatic differentiation of the parental melt (a source of rare‐metal‐granite melts and ore hydrothermal fluids) takes place in this reservoir.
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Alizadeh Sevari, B., et A. Hezarkhani. « Fluid Evolution of the Magmatic Hydrothermal Porphyry Copper Deposit Based on Fluid Inclusion and Stable Isotope Studies at Darrehzar, Iran ». ISRN Geology 2014 (8 janvier 2014) : 1–10. http://dx.doi.org/10.1155/2014/865941.
Texte intégralRésumé :
The Darrehzar porphyry Cu-Mo deposit is located in southwestern Iran (~70 km southwest of Kerman City). The porphyries occur as Tertiary quartz-monzonite stocks and dikes, ranging in composition from microdiorite to diorite and granodiorite. Hydrothermal alteration and mineralization at Darrehzar are centered on the stock and were broadly synchronous with its emplacement. Early hydrothermal alteration was dominantly potassic and propylitic and was followed by later phyllic and argillic alteration. The hydrothermal system involved both magmatic and meteoric water which were boiled extensively. Copper mineralization was accompanied by both potassic and phyllic alterations. Based on number, nature, and phases number which are available in room temperature, three types of fluid inclusions are typically observed in these veins: (1) vapor rich, (2) liquid rich and (3) multi phase. The primary multiphase inclusions within the quartz crystals were chosen for microthermometric analyses. Early hydrothermal alteration was caused by high-temperature, high-salinity orthomagmatic fluid and produced a potassic assemblage. Phyllic alteration was caused by high-salinity and lower-temperature orthomagmatic fluid. Magmatic and meteoric water mixtures were developed in the peripheral part of the stock and caused propylitic alteration which is attributed to a liquid-rich, lower temperature.
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Taran, Yuri, et Elena Kalacheva. « Seawater-rock interaction at Ushishir volcano-hydrothermal system, Kuril Islands ». E3S Web of Conferences 98 (2019) : 01049. http://dx.doi.org/10.1051/e3sconf/20199801049.
Texte intégralRésumé :
Ushishir volcano is located in the middle of the Kuril Arc. The Ushishir crater, a closed bay connected with the ocean by a narrow and shallow strait is characterized by a strong hydrothermal activity. Boiling springs, hot pools, fumaroles and shallow submarine vents are manifestations of a magmatic-seawater hydrothermal system with the discharging solution similar in chemical and isotopic composition to the seafloor hydrothermal fluids. The main features of the Ushishir fluids are: (1) water has close to zero δD and a large oxygen isotopic shift (6 7‰); (2) high boron concentration (~70 ppm); (3) a significant uptake of Ca and Sr from the rock and Ca/Sr higher than that for seawater with 87Sr/86Sr ~0.7037, a bit higher than the rock value (0.7032). The measured onshore discharge of boiling water is ~ 5 kg/s; however, a large plume of the discoloured seawater releasing from the outer submarine slope of the volcano indicates a much higher total mass and heat output.
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Pandit, Dinesh, Sourabh Bhattacharya et Mruganka K. Panigrahi. « Dissecting through the metallogenic potentials of Precambrian granitoids : case studies from the Bastar and Eastern Dharwar Cratons, India ». Geological Society, London, Special Publications 489, no 1 (8 janvier 2019) : 157–88. http://dx.doi.org/10.1144/sp489-2019-342.
Texte intégralRésumé :
AbstractThe Malanjkhand granodiorite in the Bastar Craton hosts a major copper (+ molybdenum) deposit. It represents a Precambrian granite–ore system lacking in key morphological features of porphyry-type deposits but is comparable as a chemical package with a distinct mode of evolution of the magmatic-hydrothermal system. Mineral chemistry of biotite and apatite along with bulk geochemical data constrain critical parameters such as initial water and halogen contents of the magma. Evolution of the magmatic-hydrothermal fluid has been envisaged with available thermobarometric data. A quantitative ore genetic model in terms of efficiency of removal of metals and resultant mineralization in terms of quantity of metals has been attempted for the Malanjkhand deposit. The Eastern Dharwar Craton witnessed prolific granitic activities in multiple phases during the Late Archean and are spatially close to auriferous schist belts. Against a widely held view of a single metamorphogenic origin of metal and ore fluid, a granite–gold connection can be visualized for the auriferous schist belts of the Eastern Dharwar Craton through comparison of fluid characteristics in the granitoid and ore regimes and mineral chemical constraints. Although a quantitative genetic link between the granitoid and gold would need more data, a magmatic component of the ore fluid could be established based on the available information.
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Lima, A., R. J. Bodnar, B. De Vivo, F. J. Spera et H. E. Belkin. « Interpretation of Recent Unrest Events (Bradyseism) at Campi Flegrei, Napoli (Italy) : Comparison of Models Based on Cyclical Hydrothermal Events versus Shallow Magmatic Intrusive Events ». Geofluids 2021 (14 octobre 2021) : 1–16. http://dx.doi.org/10.1155/2021/2000255.
Texte intégralRésumé :
Several recent models that have been put forth to explain bradyseism at Campi Flegrei (CF), Italy, are discussed. Data obtained during long-term monitoring of the CF volcanic district has led to the development of a model based on lithological-structural and stratigraphic features that produce anisotropic and heterogeneous permeability features showing large variations both horizontally and vertically; these data are inconsistent with a model in which bradyseism is driven exclusively by shallow magmatic intrusions. CF bradyseism events are driven by cyclical magmatic-hydrothermal activity. Bradyseism events are characterized by cyclical, constant invariant signals repeating over time, such as area deformation along with a spatially well-defined seismogenic volume. These similarities have been defined as “bradyseism signatures” that allow us to relate the bradyseism with impending eruption precursors. Bradyseism is governed by an impermeable shallow layer (B-layer), which is the cap of an anticlinal geological structure culminating at Pozzuoli, where maximum uplift is recorded. This B-layer acts as a throttling valve between the upper aquifer and the deeper hydrothermal system that experiences short (1-102 yr) timescale fluctuations between lithostatic/hydrostatic pressure. The hydrothermal system also communicates episodically with a cooling and quasi-steady-state long timescale (103-104 yr) magmatic system enclosed by an impermeable carapace (A layer). Connectivity between hydrostatic and lithostatic reservoirs is episodically turned on and off causing alternatively subsidence (when the systems are connected) or uplift (when the systems are disconnected), depending on whether permeability by fractures is established or not. Earthquake swarms are the manifestation of hydrofracturing which allows fluid expansion; this same process promotes silica precipitation that seals cracks and serves to isolate the two reservoirs. Faults and fractures promote outgassing and reduce the vertical uplift rate depending on fluid pressure gradients and spatial and temporal variations in the permeability field. The miniuplift episodes also show “bradyseism signatures” and are well explained in the context of the short timescale process.
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Lima, A., R. J. Bodnar, B. De Vivo, F. J. Spera et H. E. Belkin. « Interpretation of Recent Unrest Events (Bradyseism) at Campi Flegrei, Napoli (Italy) : Comparison of Models Based on Cyclical Hydrothermal Events versus Shallow Magmatic Intrusive Events ». Geofluids 2021 (14 octobre 2021) : 1–16. http://dx.doi.org/10.1155/2021/2000255.
Texte intégralRésumé :
Several recent models that have been put forth to explain bradyseism at Campi Flegrei (CF), Italy, are discussed. Data obtained during long-term monitoring of the CF volcanic district has led to the development of a model based on lithological-structural and stratigraphic features that produce anisotropic and heterogeneous permeability features showing large variations both horizontally and vertically; these data are inconsistent with a model in which bradyseism is driven exclusively by shallow magmatic intrusions. CF bradyseism events are driven by cyclical magmatic-hydrothermal activity. Bradyseism events are characterized by cyclical, constant invariant signals repeating over time, such as area deformation along with a spatially well-defined seismogenic volume. These similarities have been defined as “bradyseism signatures” that allow us to relate the bradyseism with impending eruption precursors. Bradyseism is governed by an impermeable shallow layer (B-layer), which is the cap of an anticlinal geological structure culminating at Pozzuoli, where maximum uplift is recorded. This B-layer acts as a throttling valve between the upper aquifer and the deeper hydrothermal system that experiences short (1-102 yr) timescale fluctuations between lithostatic/hydrostatic pressure. The hydrothermal system also communicates episodically with a cooling and quasi-steady-state long timescale (103-104 yr) magmatic system enclosed by an impermeable carapace (A layer). Connectivity between hydrostatic and lithostatic reservoirs is episodically turned on and off causing alternatively subsidence (when the systems are connected) or uplift (when the systems are disconnected), depending on whether permeability by fractures is established or not. Earthquake swarms are the manifestation of hydrofracturing which allows fluid expansion; this same process promotes silica precipitation that seals cracks and serves to isolate the two reservoirs. Faults and fractures promote outgassing and reduce the vertical uplift rate depending on fluid pressure gradients and spatial and temporal variations in the permeability field. The miniuplift episodes also show “bradyseism signatures” and are well explained in the context of the short timescale process.
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Druschel, Gregory K., et Philip E. Rosenberg. « Non-magmatic fracture-controlled hydrothermal systems in the Idaho Batholith : South Fork Payette geothermal system ». Chemical Geology 173, no 4 (mars 2001) : 271–91. http://dx.doi.org/10.1016/s0009-2541(00)00280-1.
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Bortnikov, N. S., L. Ya Aranovich, S. G. Kryazhev, S. Z. Smirnov, V. G. Gonevchuk, B. I. Semanyak, E. O. Dubinina, N. V. Gorelikova et E. N. Sokolova. « Badzhal tin magmatic-fluid system (Far east, Russia) : the transition from the granite crystallization to the hydrothermal ore deposition ». Геология рудных месторождений 61, no 3 (19 juin 2019) : 3–30. http://dx.doi.org/10.31857/s0016-77706133-30.
Texte intégralRésumé :
With a view to reveal special characteristics of the transition stage from granite crystallization to rare-metal ore deposition it is studied Badzhal tin-bearing magmatic-fluid system of eponymously-named volcano-plutonic zone of the Middle Priamyrie. For that end the detail research of melt, fluid-melt and fluid inclusions and oxygen isotopes from minerals of granitoids from Verkne-Urmi massif from Badzhal volcano-plutonic zone and also minerals of Sn-W deposits Pravo-Urmi and Blizhnee have been carried out. The formation of greisens and hydrothermal veins were caused by the development of the integrated system associating with establishing of Verkne-Urmi granite massif which is one of a dome fold of Badzhal cryptobatholith. For the first time for tin deposits it has been followed up the transition from the magmatic phase of granite crystallization to the hydrothermal ore formation stage and the evolution of magmatic fluid from its separation from magmatic melt to Sn-W ore deposition. The direct evidence of tin-bearing fluid separation under melt crystallization is combined fluid-melt inclusions. Glass composition in inclusions shows that granites and granite-porphyry were crystallizing from acid and from limited to high-aluminous melts, that is value ASI changes from 0.95 to 1.33 and a content of alkalies varies from 6.02 up to 9.02 mass.%. Cl and F concentrations in glasses are according 0.03–0.14 and 0.14–0.44 mass.% and turned out to be higher of same in the total composition of rocks (0.02 and 0.05–0.13 mass.% in accordance). These differences indicate that Cl and F could be separated from granite melt under its crystallization and degasation. H2O content made from total deficiency electron microprobe analysis is 8–11 mass.%. This evaluation was made inclusive of a probable effect of “Na loss” (Nielsen, Sigurdson, 1981) under aqueous glass crystallization. Considering a high error of a such estimation (Devine et al., 1995), it should take to obtained values as a very approximate evaluation and consider that examined melts contained about 9,5–10,0 mass.% of H2O.
The results of melt inclusion examination show that at any rate a part of melt forming magmatic rocks of Badzhal Ore Magmatic System are crystallizing at about T = 650 °C. These melts were acid, limited fluoride and meta- and high aluminous. The reason of low temperatures of its crystallization are likely a high pressure of aqua and also a increased content of F. Most likely that examined inclusions characterize the final stage of establishing of the massif, herewith at the system crystals, residual liquor and magmatic fluid phase coexist.
The fluid from which greisens of Pravo-Urmi deposit formed is similar in properties to the supercritical fluid absorbing by magmatic minerals. The salinity of this fluid varying from ~9 to 12 mass.% equiv. NaCl, maximal T = 550 °C (with consideration for the temperature correction of T gom on a pressure ~1 кbar) are similar to such of magmatic fluid, which permit to connect its origin with pluton cooling. The formation of greisens and quartz-topaz veins of Pravo-Urmi deposit is related to fall of temperature of magmatic fluid from 550–450 up to 480–380 °C. The evolution of fluid deposited quartz-cassiterite veins of Blizhnee deposit, which based upon oxygen isotope composition (d18ОН2О ≈ 8.5‰) also separated from magma, was going at more subsurface conditions under much lesser pressure. That led to the gas separation of a fluid with salinity ~13 mass.% equa. NaCl under T = 420–340 °C on thin low salinity vapour and brine with concentration 33.5–37.4 mass.% equiv. NaCl. The research of oxygen isotope system testifies that oxygen isotope composition of ore-forming fluid controlled by equilibrium with granites at wide interval temperatures (from ~700 °С up to the beginning of greisen crystallization). Correspondence of measured and calculation data of the offered model indicates that the considerable volume of external fluid with other isotope characteristics which did not reach the isotope equilibrium with Verkhne-Urmi massif did not come into the magmatic isotope system. The discovered differences of physico-chemical conditions for two studied deposits are not “critical” and support an idea about their formation as the single magmatic-fluid system.
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Yergeau, D., P. Mercier-Langevin, B. Dubé, V. McNicoll, S. E. Jackson, M. Malo et A. Savoie. « The Westwood Deposit, Southern Abitibi Greenstone Belt, Canada : An Archean Au-Rich Polymetallic Magmatic-Hydrothermal System—Part II. Hydrothermal Alteration, Mineralization, and Geologic Model ». Economic Geology 117, no 3 (1 mai 2022) : 577–608. http://dx.doi.org/10.5382/econgeo.4879.
Texte intégralRésumé :
Abstract The Westwood deposit, located in the Archean Doyon-Bousquet-LaRonde mining camp in the southern Archean Abitibi greenstone belt, contains 4.5 Moz (140 metric t) of gold. The deposit is hosted in the 2699–2695 Ma submarine, tholeiitic to calc-alkaline volcanic, volcaniclastic, and intrusive rocks of the Bousquet Formation. The deposit is located near the synvolcanic (ca. 2699–2696 Ma) Mooshla Intrusive Complex that hosts the Doyon epizonal intrusion-related Au ± Cu deposit, whereas several Au-rich volcanogenic massive sulfide (VMS) deposits are present east of the Westwood deposit. The Westwood deposit consists of stratigraphically stacked, contrasting, and overprinting mineralization styles that share analogies with both the intrusion-related and VMS deposits of the camp. The ore zones form three distinct, slightly discordant to stratabound corridors that are, from north (base) to south (top), the Zone 2 Extension, the North Corridor, and the Westwood Corridor. Syn- to late-main regional deformation and upper greenschist to lower amphibolite facies regional metamorphism affect the ore zones, alteration assemblages, and host rocks. The Zone 2 Extension consists of Au ± Cu sulfide (pyrite-chalcopyrite)-quartz veins and zones of disseminated to semimassive sulfides. The ore zones are spatially associated with a series of calc-alkaline felsic sills and dikes that crosscut the mafic to intermediate, tholeiitic to transitional, lower Bousquet Formation volcanic rocks. The metamorphosed proximal alteration consists of muscovite-quartz-pyrite ± gypsum-andalusite-kyanite-pyrophyllite argillic to advanced argillic-style tabular envelope that is up to a few tens of meters thick. The North Corridor consists of auriferous semimassive to massive sulfide veins, zones of sulfide stringers, and disseminated sulfides that are hosted in intermediate volcaniclastic rocks at the base of the upper Bousquet Formation. The Westwood Corridor consists of semimassive to massive sulfide lenses, veins, zones of sulfide stringers, and disseminated sulfides that are located higher in the stratigraphic sequence, at or near the contact between calc-alkaline dacite domes and overlying calc-alkaline rhyodacite of the upper Bousquet Formation. A large, semiconformable distal alteration zone that encompasses the North Corridor is present in the footwall and vicinity of the Westwood Corridor. This metamorphosed alteration zone consists of an assemblage of biotite-Mn garnet-chlorite-carbonate ± muscovite-albite. A proximal muscovite-quartz-chlorite-pyrite argillic-style alteration assemblage is associated with both corridors. The Zone 2 Extension ore zones and associated alteration are considered synvolcanic based on crosscutting relationships and U-Pb geochronology and are interpreted as being the distal expression of an epizonal magmatic-hydrothermal system that is centered on the upper part of the synvolcanic Mooshla Intrusive Complex. The North and Westwood corridors consist of bimodal-felsic Au-rich VMS-type mineralization and alteration produced by the convective circulation of modified seawater that included a magmatic contribution from the coeval epizonal Zone 2 Extension magmatic-hydrothermal system. The Westwood Au deposit represents one of the very few documented examples of an Archean magmatic-hydrothermal system—or at least of such systems formed in a subaqueous environment. The study of the Westwood deposit resulted in a better understanding of the critical role of magmatic fluid input toward the formation of Archean epizonal intrusion-related Au ± Cu and seafloor/subseafloor Au-rich VMS-type mineralization.
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Choi, Woohyun, Changyun Park, Yungoo Song, Chaewon Park, Ha Kim et Chulgyoo Lee. « Sequential Scheelite Mineralization of Quartz–Scheelite Veins at the Sangdong W-Deposit : Microtextural and Geochemical Approach ». Minerals 10, no 8 (30 juillet 2020) : 678. http://dx.doi.org/10.3390/min10080678.
Texte intégralRésumé :
The Sangdong W (tungsten)-deposit is known as one of the world’s largest W-deposits, a magmatic–hydrothermal ore deposit including both skarn and hydrothermal alteration zones. The strata-bound characteristic of the deposit resulted in three major orebodies (hanging wall, main, footwall). The main ore mineral is a scheelite (CaWO4)–powellite (CaMoO4) solid solution. We examined the fluid evolution and scheelite formation process of the quartz–scheelite veins of the ore deposit, based on the microtextures and geochemical characteristics of the scheelite. After the initial magmatic–hydrothermal fluid release from the granitic body, prograde skarn is formed. In the later prograde stage, secondary fluid rises and precipitates stage I scheelite. Well-developed oscillatory zoning with the highest Mo content indicates continuous fluid infiltration under an open system. Pressure rises as mineralization occurs, generating the pressure release of the retrograde fluid. Fluid migrates downward by the gravitational backflow mechanism, forming stage II to IV scheelites. Dented oscillatory zoning of stage II scheelite is strong evidence of this pressure release. Stage III and IV scheelite do not show specific internal structures with pure scheelite composition. Retrograde scheelites are formed by fractional crystallization under a closed system. The observation of systematical fractional crystallization in the quartz–scheelite vein system is a meaningful result of our research. The geochemical characteristics and microtextural evidence imprinted in scheelites from each stage provide crucial evidence for the understanding of sequential scheelite mineralization of the quartz–scheelite vein system of the Sangdong W-deposit.
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Delmelle, P., A. Bernard, M. Kusakabe, T. P. Fischer et B. Takano. « Geochemistry of the magmatic–hydrothermal system of Kawah Ijen volcano, East Java, Indonesia ». Journal of Volcanology and Geothermal Research 97, no 1-4 (avril 2000) : 31–53. http://dx.doi.org/10.1016/s0377-0273(99)00158-4.
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Principe, Claudia, et Luigi Marini. « Evolution of the Vesuvius magmatic-hydrothermal system before the 16 December 1631 eruption ». Journal of Volcanology and Geothermal Research 171, no 3-4 (avril 2008) : 301–6. http://dx.doi.org/10.1016/j.jvolgeores.2007.12.004.
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Brombach, Tatjana, Stefano Caliro, Giovanni Chiodini, Jens Fiebig, Johannes C. Hunziker et Brunella Raco. « Geochemical evidence for mixing of magmatic fluids with seawater, Nisyros hydrothermal system, Greece ». Bulletin of Volcanology 65, no 7 (1 octobre 2003) : 505–16. http://dx.doi.org/10.1007/s00445-003-0278-x.
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