Special Issue "Magmatic–Hydrothermal Alteration and Mineralizing Processes"

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: closed (20 May 2020).

Special Issue Editor

Prof. Dr. David Lentz
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Guest Editor
Research Chair in Economic Geology, Department of Earth Sciences, University of New Brunswick, Fredericton, NB, Canada
Interests: magmatic hydrothermal; devolatilization; fluid exsolution; saturation textures; high temperature alteration; mineralization

Special Issue Information

Dear Colleagues,

This Special Issue focused on mineralized hypabyssal felsic intrusions welcomes specific contributions related to: 1) detailed deposit system studies of magmatic hydrothermal processes; 2) felsic intrusion emplacement and the hydrogeologic analysis of structure related to fluid flow; 3) detailed mineral–chemical research; 4) analysis of textures; 5) crystallized melt and fluid inclusions; 6) examinations of geochronologic, stable and radiogenic isotopic, and petrogeochemical constraints on deposit formation; and 7) physiochemical analysis of the mobilization of the depositional mechanisms responsible for contributing to various types of magmatic hydrothermal mineralization systems. 

Prof. Dr. David Lentz
Guest Editor

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Published Papers (11 papers)

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Open AccessArticle
Mineralization Age and Hydrothermal Evolution of the Fukeshan Cu (Mo) Deposit in the Northern Great Xing’an Range, Northeast China: Evidence from Fluid Inclusions, H–O–S–Pb Isotopes, and Re–Os Geochronology
Minerals 2020, 10(7), 591; https://doi.org/10.3390/min10070591 - 30 Jun 2020
Abstract
The Fukeshan Cu (Mo) deposit is a newfound porphyry deposit in the northern Great Xing’an Range (GXR), northeast China. In this paper, we present results of chalcopyrite Re–Os geochronology, microthermometry of the fluid inclusions (FIs), and isotopic (H–O–S–Pb) compositions of the Fukeshan Cu [...] Read more.
The Fukeshan Cu (Mo) deposit is a newfound porphyry deposit in the northern Great Xing’an Range (GXR), northeast China. In this paper, we present results of chalcopyrite Re–Os geochronology, microthermometry of the fluid inclusions (FIs), and isotopic (H–O–S–Pb) compositions of the Fukeshan Cu (Mo) deposit. Its ore-forming process can be divided into sulfide-barren quartz veins (A vein; stage I), quartz + chalcopyrite + pyrite veins (B vein; stage II), quartz + polymetallic sulfide veins (D vein; stage III), and barren quartz + carbonate ± pyrite veins (E vein; stage IV), with Cu mineralization mainly occurred in stage II. Three types of FIs are identified in this deposit: liquid-rich two-phase (L-type) FIs, vapor-rich two-phase (V-type) FIs, daughter mineral-bearing three-phase (S-type) FIs. The homogenization temperatures of primary FIs hosted in quartz of stages I–IV are 381–494 °C, 282–398 °C, 233–340 °C, and 144–239 °C, with salinities of 7.2–58.6, 4.8–9.9, 1.4–7.9, and 0.9–3.9 wt. % NaCl equivalent, respectively. FIs microthermometry and H–O isotope data suggest that the ore-forming fluids were magmatic in origin and were gradually mixed with meteoric water from stages II to IV. Sulfur and lead isotope results indicate that the ore-forming materials of the Fukeshan Cu (Mo) deposit were likely to have originated from Late Jurassic intrusive rocks. The available data suggest that fluid cooling and incursions of meteoric water into the magmatic fluids were two important factors for Cu precipitation in the Fukeshan Cu (Mo) deposit. Chalcopyrite Re–Os dating yielded an isochron age of 144.7 ± 5.4 Ma, which is similar to the zircon U–Pb age of the quartz diorite porphyry, indicating that Late Jurassic quartz diorite porphyry and Cu mineralization occurred contemporaneously. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessArticle
Using Whole Rock and Zircon Geochemistry to Assess Porphyry Copper Potential of the Tonggou Copper Deposit, Eastern Tianshan
Minerals 2020, 10(7), 584; https://doi.org/10.3390/min10070584 - 28 Jun 2020
Abstract
Eastern Tianshan hosts a number of porphyry Cu deposits. However, these mainly formed in the Jueluotage Belt, in the middle part of Eastern Tianshan. The Tonggou porphyry Cu mineralization is an exception to this, since it is located in the Bogda Orogenic Belt, [...] Read more.
Eastern Tianshan hosts a number of porphyry Cu deposits. However, these mainly formed in the Jueluotage Belt, in the middle part of Eastern Tianshan. The Tonggou porphyry Cu mineralization is an exception to this, since it is located in the Bogda Orogenic Belt, north of Eastern Tianshan. We obtained new zircon U–Pb ages, whole-rock geochemical data, zircon Hf isotope data, and zircon trace element compositions. LA-ICP-MS zircon U–Pb dating indicates a crystallization age of 302.2–303.0 Ma for the Tonggou mineralized granodiorite (TMG), which suggests that the Tonggou porphyry Cu mineralization formed in the Late Carboniferous period. εHf (t) data (1.8–14.1) for TMG suggests it was sourced from juvenile crustal melts, mixed with some mantle materials. TMG displays low ΣREE, compatible elements (Ba, Sr, Zr, and Hf), Zr/Hf and Nb/Ta ratios, as well as clearly negative Eu anomalies in whole rocks analyses. In addition, TMG is enriched in P, Hf and Th/U ratios in zircon, and has lower crystallization temperatures (734 to 735 °C) than the Daheyan barren granodiorite (DBG) (753 to 802 °C). Whole rock and zircon geochemical analyses show that the TMG was formed by fractional crystallization to a greater extent than the DBG in the Bogda Orogenic Belt. Moreover, zircon grains of the TMG show high Ce4+/Ce3+ ratios (159–286), which are consistent with related values from large porphyry deposits of the Central Asian Orogenic Belt (CAOB). High Ce4+/Ce3+ ratios reflect oxidizing magmas as a result of fractional crystallization, which indicates that the Tonggou deposit has potential to host a large porphyry Cu deposit. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
Open AccessArticle
U-Pb, Ar-Ar, and Re-Os Geochronological Constraints on Multiple Magmatic–Hydrothermal Episodes at the Lake George Mine, Central New Brunswick
Minerals 2020, 10(6), 566; https://doi.org/10.3390/min10060566 - 23 Jun 2020
Abstract
The Lake George antimony mine was at one time North America’s largest producer of antimony. Despite being widely known for the antimony mineralization, the deposit also hosts a range of styles of mineralization such as multiple generations of W-Mo bearing quartz veins as [...] Read more.
The Lake George antimony mine was at one time North America’s largest producer of antimony. Despite being widely known for the antimony mineralization, the deposit also hosts a range of styles of mineralization such as multiple generations of W-Mo bearing quartz veins as well as a system of As-Au bearing quartz–carbonate veins. In situ U-Pb zircon geochronology, using LA ICP-MS, of the Lake George granodiorite yielded a weighted mean 206Pb/238U age of 419.6 ± 3.0 Ma. Step heating of phlogopite separated from the lamprophyre dykes produced a 40Ar/39Ar plateau segment date of 419.4 ± 1.4 Ma. Single molybdenite crystal analysis for Re-Os geochronology was conducted on two W-Mo-bearing quartz veins, which cross-cut altered granodiorite and altered metasedimentary rocks and yielded two dates of 415.7 ± 1.7 Ma and 416.1 ± 1.7 Ma respectively. 40Ar/39Ar geochronology of muscovite from alteration associated with Au-bearing quartz–carbonate veins yielded one representative plateau segment date of 414.1 ± 1.3 Ma. The dates produced in this study revealed that the different magmatic–hydrothermal events at the Lake George mine occurred over approximately a 10-million-year period at the end of the Silurian and the start of the Devonian following the termination of the Acadian orogeny. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessArticle
Composition of Garnet from the Xianghualing Skarn Sn Deposit, South China: Its Petrogenetic Significance and Exploration Potential
Minerals 2020, 10(5), 456; https://doi.org/10.3390/min10050456 - 18 May 2020
Abstract
The Xianghualing skarn Sn deposit in the southwestern part of the southern Hunan Metallogenic Belt is a large Sn deposit in the Nanling area. In this paper, the garnet has been analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to obtain the concentrations [...] Read more.
The Xianghualing skarn Sn deposit in the southwestern part of the southern Hunan Metallogenic Belt is a large Sn deposit in the Nanling area. In this paper, the garnet has been analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to obtain the concentrations of the major and trace elements. The results reveal that the garnets from the Xianghualing deposit mainly belong to andradite-grossular (grandite) solid solution and are typically richer in Al than in Fe. They show enrichment in heavy rare earth elements (HREEs) and notably lower light rare earth elements (LREEs), and commonly negative Eu anomalies, indicative of a relatively reduced formation environment. The garnets have high Sn concentrations between 2313 ppm and 5766 ppm. It is also evident that there is a positive correlation between Sn and Fe, suggesting that Sn4+ substitutes into the garnets through substituting for Fe3+ in the octahedral position. Combined with previous studies, it can be recognized that the Sn concentrations of garnet in skarn Sn deposits are generally high, whereas the W concentrations are relatively low. This is just the opposite in garnets from skarn W deposits that typically have high W, but low Sn concentrations. In polymetallic skarn deposits with both economic Sn and W, the concentrations of both metals in garnets are relatively high, although varying greatly. Therefore, the Sn and W concentrations in garnets can be used to evaluate a skarn deposit’s potential to produce Sn and (or) W mineralization, which is helpful in exploration. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessArticle
Re-Os Geochronology, Whole-Rock and Radiogenic Isotope Geochemistry of the Wulandele Porphyry Molybdenum Deposit in Inner Mongolia, China, and Their Geological Significance
Minerals 2020, 10(4), 374; https://doi.org/10.3390/min10040374 - 21 Apr 2020
Abstract
The Wulandele molybdenum deposit is a porphyry-type Mo deposit in the Dalaimiao area of northern Inner Mongolia, China. Molybdenite Re-Os dating yields a model age of 134.8 ± 1.9 Ma, with the fine-grained monzogranite most closely related to the mineralization. The lithogeochemical data [...] Read more.
The Wulandele molybdenum deposit is a porphyry-type Mo deposit in the Dalaimiao area of northern Inner Mongolia, China. Molybdenite Re-Os dating yields a model age of 134.8 ± 1.9 Ma, with the fine-grained monzogranite most closely related to the mineralization. The lithogeochemical data show that the monzogranite is weakly peraluminous, high-K calc-alkaline series, with reduced to slightly oxidized, highly fractionated I-type granite characteristics. The relatively low initial 87Sr/86Sr (range from 0.705347 to 0.705771), weakly negative εNd(t) (range from −2.0 to −1.3), and crust-mantle mixing of Pb isotopes suggest that the monzogranite originated from the partial melting of mafic juvenile lower continental crust derived from the depleted mantle, with a minor component of ancient continental crust. Combined with the regional tectonic evolution, we argue that the partial melting, then injection, of the monzogranite melt was probably triggered by collapse or delamination of the thickened lithosphere, which was mainly in response to the post-orogenic extensional setting of the Mongol–Okhotsk belt; this is possibly coupled with a back-arc extension related to Paleo-Pacific plate subduction. The extensively fractional crystallization of the monzogranite melt is the crucial enrichment process, resulting in magmatic hydrothermal Mo mineralization in the Wulandele deposit, and the Cretaceous granitoids are generally favorable to form Mo mineralization in the Dalaimiao area. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessArticle
Ore Geology, Fluid Inclusions, and (H-O-S-Pb) Isotope Geochemistry of the Sediment-Hosted Antimony Mineralization, Lyhamyar Sb Deposit, Southern Shan Plateau, Eastern Myanmar: Implications for Ore Genesis
Minerals 2020, 10(4), 296; https://doi.org/10.3390/min10040296 - 26 Mar 2020
Abstract
The Lyhamyar deposit is a large Sb deposit in the Southern Shan Plateau, Eastern Myanmar. The deposit is located in the Early Silurian Linwe Formation, occurring as syntectonic quartz-stibnite veins. The ore body forms an irregular staircase shape, probably related to steep faulting. [...] Read more.
The Lyhamyar deposit is a large Sb deposit in the Southern Shan Plateau, Eastern Myanmar. The deposit is located in the Early Silurian Linwe Formation, occurring as syntectonic quartz-stibnite veins. The ore body forms an irregular staircase shape, probably related to steep faulting. Based on the mineral assemblages and cross-cutting relationships, the deposit shows two mineralization stages: (1) the pre-ore sedimentary and diagenetic stage, and (2) the main-ore hydrothermal ore-forming stage (including stages I, II, and III), i.e., (i) early-ore stage (stage I) Quartz-Stibnite, (ii) late-ore stage (stage II) Quartz-calcite-Stibnite ± Pyrite, and (iii) post-ore stage (stage III) carbonate. The ore-forming fluid homogenization temperatures from the study of primary fluid inclusions in quartz and calcite indicate that the ore-forming fluid was of a low temperature (143.8–260.4 °C) and moderate to high-salinity (2.9–20.9 wt. % NaCl equivalent). Hydrogen and oxygen isotopes suggest that the ore-forming fluids of the Lyhamyar deposit were derived from circulating meteoric water mixed with magmatic fluids that underwent isotopic exchange with the surrounding rocks. Sulfur in Lyhamyar was dominated by thermochemical sulfate reduction (TSR) with dominant magmatic source sulfur. The lead isotope compositions of the stibnite indicate that the lead from the ore-forming metals was from the upper crustal lead reservoir and orogenic lead reservoir. On the basis of the integrated geological setting, ore geology, fluid inclusions, (H-O-S-Pb) isotope data, and previous literature, we propose a new ore-deposit model for the Lyhamyar Sb deposit: It was involved in an early deposition of pyrite in sedimentary and diagenetic stages and later Sb mineralization by mixing of circulating meteoric water with ascending magmatic fluids during the hydrothermal mineralization stage. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessArticle
Tonalite-Dominated Magmatism in the Abitibi Subprovince, Canada, and Significance for Cu-Au Magmatic-Hydrothermal Systems
Minerals 2020, 10(3), 242; https://doi.org/10.3390/min10030242 - 07 Mar 2020
Abstract
In Archean greenstone belts, magmatism is dominated by intrusive and volcanic rocks with tholeiitic affinities, as well as tonalite- and granodiorite-dominated large-volume batholiths, i.e., tonalite–trondhjemite–granodiorite (TTG) suites. These intrusions are associated with poorly documented mineralization (Cu-Au porphyries) that, in the Neoarchean Abitibi Subprovince [...] Read more.
In Archean greenstone belts, magmatism is dominated by intrusive and volcanic rocks with tholeiitic affinities, as well as tonalite- and granodiorite-dominated large-volume batholiths, i.e., tonalite–trondhjemite–granodiorite (TTG) suites. These intrusions are associated with poorly documented mineralization (Cu-Au porphyries) that, in the Neoarchean Abitibi Subprovince (>2.79 to ~2.65 Ga), Superior Province, Canada, are associated with diorite bearing plutons, i.e., tonalite–trondhjemite–diorite (TTD) suites. The importance of TTG versus TTD suites in the evolution of greenstone belts and of their magmatic-hydrothermal systems and related mineralization is unconstrained. The aim of this study was to portray the chemistry and distribution of these suites in the Abitibi Subprovince. The study used data compiled by the geological surveys of Québec and Ontario to evaluate the chemistry of TTG and TTD suites and uncovered two coeval magmas that significantly differentiated (fractional crystallization mostly): 1) a heavy rare earth elements (HREE)-depleted tonalitic magma from high pressure melting of an hydrated basalt source; and 2) a hybrid HREE-undepleted magma that may be a mixture of mantle-derived (tholeiite) and tonalitic melts. The HREE-depleted rocks (mostly tonalite and granodiorite) display chemical characteristics of TTG suites (HREE, Ti, Nb, Ta, Y, and Sr depletion, lack of mafic unit, Na-rich), while the other rocks (tonalite and diorite) formed TTD suites. Tonalite-dominated magmatism, in the Abitibi Subprovince, comprises crustal melts as well as a significant proportion of mantle-derived magmas and this may be essential for Cu-Au magmatic-hydrothermal mineralizing systems. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessArticle
Fluid Inclusion Study of the Penjom, Tersang, and Selinsing Orogenic Gold Deposits, Peninsular Malaysia
Minerals 2020, 10(2), 111; https://doi.org/10.3390/min10020111 - 28 Jan 2020
Abstract
Ore-forming fluids in the auriferous district of the Central gold belt in Peninsular Malaysia were studied for their temperature, salinity, and relationship to the surrounding geology. Microthermometric analysis carried out showed homogenisation temperatures range from 210 to 348 °C (Tersang), between 194 and [...] Read more.
Ore-forming fluids in the auriferous district of the Central gold belt in Peninsular Malaysia were studied for their temperature, salinity, and relationship to the surrounding geology. Microthermometric analysis carried out showed homogenisation temperatures range from 210 to 348 °C (Tersang), between 194 and 348 °C (Selinsing), and from 221 to 346 °C (Penjom). Salinities range from 2.41 to 8.95 wt % NaCl equiv (Tersang), between 1.23 and 9.98 wt % NaCl equiv (Selinsing), and from 4.34 to 9.34 wt % NaCl equiv (Penjom). Laser Raman studies indicated that at the Tersang gold deposit, most inclusions are either pure or nearly pure CO2-rich (87–100 mol %), except for one inclusion, which contains CH4 gas (13 mol %). In addition, at Selinsing, most inclusions are CO2-rich (100 mol %). However, an inclusion was found containing CO2 (90 mol %), with minor N2 and CH4. Additionally, at the Penjom gold deposit, most fluid inclusions are CO2-rich (91–100 mol %), whereas one fluid inclusion is N2-rich (100 mol %) and another one has minor N2 and CH4. At a basin scale, homogenisation temperatures against salinity suggests an isothermal mixing of fluids. Most fluids are CO2-rich and are interpreted to be of metamorphic origin. The evidence further indicates involvement of magmatic fluids that is supported by the association of sandstone and carbonaceous black shales with magmatic rocks, such as rhyolite, rhyolite-dacite, and trachyte-andesite at the Tersang and Penjom orogenic gold deposits. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessArticle
Petrogenesis, Ore Mineralogy, and Fluid Inclusion Studies of the Tagu Sn–W Deposit, Myeik, Southern Myanmar
Minerals 2019, 9(11), 654; https://doi.org/10.3390/min9110654 - 24 Oct 2019
Abstract
Most of the granite-related Sn–W deposits in Myanmar are located in the Western Granitoid Province (WGP) of Southeast Asia. The Tagu deposit in the southern part of the WGP is a granite related Sn–W deposit. The biotite granite is composed of quartz, feldspars [...] Read more.
Most of the granite-related Sn–W deposits in Myanmar are located in the Western Granitoid Province (WGP) of Southeast Asia. The Tagu deposit in the southern part of the WGP is a granite related Sn–W deposit. The biotite granite is composed of quartz, feldspars (plagioclase, orthoclase, and microcline), and micas (muscovite and biotite) and belongs to S-type peraluminous granite. Abundances of large-ion lithophile elements (LILEs), such as Rb, K, and Pb, coupled with the deficiency of high-field-strength elements (HFSEs), such as Nb, P, and Ti, indicate that the parental magma for the Tagu granite was derived from the lower continental crust at syn-collisional setting. Mineralized veins consist of early-formed oxide ore minerals, such as cassiterite and wolframite, which were followed by the formation of sulfide minerals. Three main types of fluid inclusions were distinguished from the mineralized quartz veins hosted by granite and metasedimentary rocks: Type-A—two phases, liquid (L) + vapor (V) aqueous inclusions; Type-B—two phases, vapor (V) + liquid (L) vapor-rich inclusions; And type-C—three phases, liquid + CO2-liquid + CO2-vapor inclusions. Quartz in the veins hosted in granite corresponding with earlier deposition contains type-A, type-B, and type-C fluid inclusions, whereas that in the veins hosted in metasedimentary rocks corresponding with later deposition contains only type-A fluid inclusions. The homogenization temperatures of type-A inclusions range from 140 °C to 330 °C (mode at 230 °C), with corresponding salinities from 1.1 wt.% to 8.9 wt.% NaCl equivalent for quartz veins hosted in metasedimentary rocks, and from 230 °C to 370 °C (mode at 280 °C), with corresponding salinities from 2.9 wt.% to 10.6 wt.% NaCl equivalents for quartz veins hosted in granite. The homogenization temperatures of type-B vapor-rich inclusions in quartz veins in granite range from 310 °C to 390 °C (mode at 350 °C), with corresponding salinities from 6.7 wt.% to 12.2 wt.% NaCl equivalent. The homogenization temperatures of type-C H2O–CO2–NaCl inclusions vary from 270 °C to 405 °C (mode at 330 °C), with corresponding salinities from 1.8 wt.% to 5.6 wt.% NaCl equivalent. The original ascending ore fluid was probably CO2-bearing fluid which evolved into two phase fluid by immiscibility due to pressure drop in the mineralization channels. Furthermore, the temperature and salinities of two-phase aqueous fluids were later most likely decreased by the mixing with meteoric water. The salinities of the type-B vapor-rich inclusions are higher than those of the type-C CO2-rich inclusions, which may have resulted from CO2 separation from the fluids. The escape of gases can lead to an increase in the salinity of the residual fluids. Therefore, the main ore-forming mechanisms of the Tagu Sn–W deposit are characterized by fluid immiscibility during an early stage, and fluid mixing with meteoric water in the late stage at a lower temperature. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessTechnical Note
Silver-Rich Chalcopyrite from the Active Cerro Pabellón Geothermal System, Northern Chile
Minerals 2020, 10(2), 113; https://doi.org/10.3390/min10020113 - 28 Jan 2020
Abstract
Active subaerial geothermal systems are regarded as modern analogues of low- to intermediate-sulfidation epithermal Au–Ag deposits, where minor amounts of Cu are mostly present as chalcopyrite. Although trace element data concerning sulfides are scarce in active geothermal systems at convergent settings, studies in [...] Read more.
Active subaerial geothermal systems are regarded as modern analogues of low- to intermediate-sulfidation epithermal Au–Ag deposits, where minor amounts of Cu are mostly present as chalcopyrite. Although trace element data concerning sulfides are scarce in active geothermal systems at convergent settings, studies in several other environments have demonstrated that chalcopyrite is a relevant host of Ag and other trace elements. Here, we focus on the active Cerro Pabellón geothermal system in the Altiplano of northern Chile, where chalcopyrite-bearing samples were retrieved from a 561 m drill core that crosscuts the high-enthalpy geothermal reservoir at depth. A combination of EMPA and LA-ICP-MS data shows that chalcopyrite from Cerro Pabellón is silver-rich (Ag > 1000 ppm) and hosts a wide range of trace elements, most notably Se, Te, Zn, Sb, As, and Ni, which can reach 100 s of ppm. Other elements detected include Co, Pb, Cr, Ga, Ge, Sn, Cd, and Hg but are often present in low concentrations (<100 ppm), whereas Au, Bi, Tl, and In are generally below 1 ppm. Chalcopyrite shows a distinct geochemical signature with depth, with significantly higher Ag concentrations in the shallow sample (494 m) and increasing Cd and In contents towards the bottom of the studied drill core (549 m). These differences in the trace element contents of chalcopyrite are interpreted as related to temperature gradients during the waning stages of boiling at Cerro Pabellón, although further studies are still needed to assess the precise partitioning controls. Our data provide evidence that chalcopyrite may play a relevant role as a scavenger of certain metals and a monitor of fluid changes in hydrothermal systems. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessFeature PaperLetter
Hydrothermal Aluminum-Phosphate-Sulfates in Ash from the 2014 Hydrothermal Eruption at Ontake Volcano, Central Honshu, Japan
Minerals 2019, 9(8), 462; https://doi.org/10.3390/min9080462 - 29 Jul 2019
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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