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Ali, Rinal Khaidar, Tri Winarno, and Muhammad Ainurrofiq Jamalulail. "Karakteristik Alterasi dan Mineralisasi Tipe Epitermal Daerah Gunung Budheg dan Sekitarnya, Tulungagung, Jawa Timur." EKSPLORIUM 41, no. 1 (May 30, 2020): 1. http://dx.doi.org/10.17146/eksplorium.2020.41.1.5676.
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ABSTRAK Penemuan bongkah-bongkah vuggy quartz di sekitar Desa Pojok, daerah Gunung Budheg, Tulungagung, Jawa Timur, mengindikasikan adanya proses endapan mineral di daerah tersebut. Tujuan penelitian ini adalah untuk membahas lebih detail karakteristik alterasi dan mineralisasi serta tipe endapan mineral di daerah penelitian. Metode penelitian berupa pengamatan lapangan dilengkapi dengan analisis laboratorium petrografi, X-ray Difraction (XRD) dan mineragrafi. Satuan batuan di daerah penelitian tersusun atas enam satuan litologi yaitu satuan intrusi dasit, satuan lava andesit, satuan breksi andesit, satuan breksi polimik, satuan batugamping terumbu dan aluvium. Tipe alterasi di daerah penelitian adalah alterasi profilitik, argilik, argilik lanjut, dan silisifikasi. Alterasi profilitik dicirikan oleh melimpahnya mineral klorit. Alterasi argilik dicirikan dengan melimpahnya mineral kaolin, sementara argilik lanjut dicirikan oleh hadirnya mineral kaolinit dan alunit. Alterasi silisifikasi yang dicirikan oleh melimpahnya mineral kuarsa. Mineral logam yang ditemukan di daerah penelitian didominasi oleh kelompok mineral sulfida seperti kovelit, kalkosit, enargit, kalkopirit, pirit, dan jarosit. Emas native ditemukan berasosiasi dengan enargit. Sistem endapan mineral pada daerah penelitian merupakan sistem epitermal sulfidasi tinggi dicirikan oleh kuarsa berongga (vuggy quartz) yang termineralisasi dan kehadiran mineral kaolin sebagai mineral hasil alterasi.ABSTRACT The discovery of vuggy quartz boulders around Pojok Village, Gunung Budheg area, Tulungagung, East Java, indicates the presence of mineral deposits process in this area. This study aims to discuss detailed characteristics of alteration and mineralization as well as mineral deposits type in the study area. The research methods are field observations completed with petrography, X-ray Diffraction (XRD), and mineragraphy laboratory analysis. The rock unit in the study area consists of six lithology units, a dacitic intrusion, andesitic lava, andesitic breccia, poly-mix breccia, reef limestone, and alluvium. The study area's alteration types are profilitic alteration, argillic alteration, advanced argillic, and silicification alteration. The profilitic alteration characterized by the abundance of chlorite minerals. The argillic alteration characterized by the abundance of kaolin minerals, while the advanced argillic alteration by the presence of kaolinite and alunite minerals. The silicification alteration characterized by abundance quartz minerals. The metallic minerals dominated in the area are sulfide minerals such as covellite, chalcocite, enargite, chalcopyrite, pyrite, and jarosite. The native gold found in an association with enargite. The study area's mineral deposit system is an epithermal high sulfidation system characterized by mineralized vuggy quartz and the presence of kaolinite mineral as an alteration mineral.
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Mavrogonatos, Constantinos, Panagiotis Voudouris, Paul G. Spry, Vasilios Melfos, Stephan Klemme, Jasper Berndt, Tim Baker, et al. "Mineralogical Study of the Advanced Argillic Alteration Zone at the Konos Hill Mo–Cu–Re–Au Porphyry Prospect, NE Greece." Minerals 8, no. 11 (October 24, 2018): 479. http://dx.doi.org/10.3390/min8110479.
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The Konos Hill prospect in NE Greece represents a telescoped Mo–Cu–Re–Au porphyry occurrence overprinted by deep-level high-sulfidation mineralization. Porphyry-style mineralization is exposed in the deeper parts of the system and comprises quartz stockwork veins hosted in subvolcanic intrusions of granodioritic composition. Ore minerals include pyrite, molybdenite, chalcopyrite, and rheniite. In the upper part of the system, intense hydrothermal alteration resulted in the formation of a silicified zone and the development of various advanced argillic alteration assemblages, which are spatially related to N–S, NNW–SSE, and E–W trending faults. More distal and downwards, advanced argillic alteration gradually evolves into phyllic assemblages dominated by quartz and sericite. Zunyite, along with various amounts of quartz, alunite, aluminum phosphate–sulfate minerals (APS), diaspore, kaolinite, and minor pyrophyllite, are the main minerals in the advanced argillic alteration. Mineral-chemical analyses reveal significant variance in the SiO2, F, and Cl content of zunyite. Alunite supergroup minerals display a wide compositional range corresponding to members of the alunite, beudantite, and plumbogummite subgroups. Diaspore displays an almost stoichiometric composition. Mineralization in the lithocap consists of pyrite, enargite, tetrahedrite/tennantite, and colusite. Bulk ore analyses of mineralized samples show a relative enrichment in elements such as Se, Mo, and Bi, which supports a genetic link between the studied lithocap and the underlying Konos Hill porphyry-style mineralization. The occurrence of advanced argillic alteration assemblages along the N–S, NNW–SSE, and E–W trending faults suggests that highly acidic hydrothermal fluids were ascending into the lithocap environment. Zunyite, along with diaspore, pyrophyllite, and Sr- and Rare Earth Elements-bearing APS minerals, mark the proximity of the hypogene advanced argillic alteration zone to the porphyry environment.
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Kilias, S. P., J. Naden, M. Paktsevanoglou, M. Giampouras, A. Stavropoulou, D. Apeiranthiti, I. Mitsis, Th Koutles, K. Michael, and C. Christidis. "Multistage alteration, mineralization and ore–forming fluid properties at the Viper (Sappes) Au–Cu–Ag–Te ore body, W. Thrace, Greece." Bulletin of the Geological Society of Greece 47, no. 4 (December 21, 2016): 1635. http://dx.doi.org/10.12681/bgsg.11007.
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The mineralogy of ore and hydrothermal alteration of the high-sulfidation enargite–Au–Ag–Te Viper (Thrace) orebody, and fluid inclusions, were studied in drillcore samples. The hydrothermal system has evolved through several stages from pre-ore advanced argillic I+vuggy silica alteration, ore-stage advanced argillic II+vuggy silica alteration and silicification that has developed to argillic alteration (sericite)+silicification through pH increase, and a return to acid conditions as crosscutting post-ore advanced argillic alteration III+silicification. Ore is characterized by early barren pyrite I corroded by: (i) enargite–Au± complex Pb–Bi–Cu sulfosalts, tellurides and selenides, coexisting with euhedral quartz, and (ii) zoned pyrite II distinguished by anomalous concentrations of Au, Cu, As, Te, Bi, Pb, Se, within vuggy quartz. High-grade gold ore is also intergrown with late brecciacementing and vein-type epithermal-like banded quartz+ pyrite. These alteration and mineralization observations are consistent with the changing composition, water fugacity, and density of an expanding column of metal-laden magmatic vapor, combined with changes in structural permeability. Part of the enargite─Au─ quartz assemblages have been probably quenched from sulfosalt melt at high─temperatures (>575°C). End product of the enargite–sulfhide–silica crystallization sequence is the formation of high-grade epithermal quartz-gold colloformbanded ore during cooling and/or dilution/mixing down to ~200°C.
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Faesal, Andi, Arifudin Idrus, and Djoko Wintolo. "PROMINE." PROMINE 5, no. 2 (January 3, 2017): 48–53. http://dx.doi.org/10.33019/promine.v5i2.918.
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The research sites are located in the village of Berambang, Sekotong District, West Lombok Regency,West Nusa Tenggara Province. This area was dominated by volcanic rocks composed of dasiticvolcanic rock, diatrema breccia, and diorite intrusion. Berambang area shows alteration in the form ofpotassic, propylitic, advanced argillic, and argillic alterations where in some places accompanied bypyritisation and stockwork structure, the type of mineralization in this area is a porphyry copper-goldtype. In the potasic alteration zone there are minerals that have a strong anomaly response to themagnetic due to the presence of oxide minerals magnetite (Fe2O3). Mineral sulfides such as pyrite(FeS2) and chalcopyrite (CuFeS2) will also provide significant anomalous responses that have anabundance of 2-5% in the potassic zone. In a propylitic alteration zone characterized by chlorite,calcite and epidote minerals that do not respond to magnetic anomalies, the presence of pyriteminerals, hematites and chalcopyrite with abundance of ≤1% will provide some magnetic anomaly inthe propylitic zone. As for advanceargillic alteration zones characterized by mineral andalusite, aluniteand quartz, there will not be any magnetic anomalies, the phenomena was due to the rarity ofmineralization in this zone gives an insignificant anomalous impact. Meanwhile, for the argillic zonecharacterized by mineral illite, kaolinite and smectite will not have anomalous magnetic impact, veryrare mineralization in the argillic zone so that the magnetic anomaly is not significant. From the floatingEuler 3D shows an anomalous source from a depth of 0 meters to a depth of more than 400 meters.
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WILLAN, ROBERT C. R., and DEBBIE C. ARMSTRONG. "Successive geothermal, volcanic-hydrothermal and contact-metasomatic events in Cenozoic volcanic-arc basalts, South Shetland Islands, Antarctica." Geological Magazine 139, no. 2 (March 2002): 209–31. http://dx.doi.org/10.1017/s0016756802006301.
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Hydrothermal alteration in volcanic arcs occurs in many settings and may involve magmatic, marine, lacustrine or groundwaters, driven by magmatic, tectonic or thermal events. King George Island, part of the South Shetland Island Cenozoic volcanic arc, contains an 80 km long zone of propylitized volcanic rocks, with numerous occurrences of quartz veining, silicic, sericitic, argillic and advanced-argillic alteration. On Barton Peninsula, a basaltic lava sequence (49–44 Ma) intruded by a small, high-level granodiorite pluton (∼42 Ma), contains these alteration types, previously interpreted as a single porphyry-copper system. In this study, we report three, possibly four, distinct fossil hydrothermal episodes. (1) Banded chalcedonic quartz, quartz-sericite and propylitic alteration occurs along ESE faults and as reworked clasts in nearby tuffs. Drusy quartz + calcite veins with silicic/sericitic, argillic and propylitic wallrocks may represent feeders to the near-surface silicification. These characteristics, and anomalous Ag + Pb + Sb + Au plus Te + Se + Zn + As, suggest a neutral-pH geothermal system that was active during volcanism. (2) The lavas and banded-quartz rocks were brecciated, veined and replaced by alunite+native sulphur+pyrite, and pyrophyllite + quartz + pyrite + zunyite + diaspore assemblages with anomalous Hg + Se + As + Bi + Au + Tl + Sb + Cu. Such advanced-argillic alteration is diagnostic of degassing of a felsic magma into shallow (<500 m) meteoric groundwaters. Rhyolite tuffs, previously not reported on King George Island, may represent leakage of this magma to the surface. (3) Subsequent burial to ∼3 km was followed by emplacement of a granodiorite pluton and formation of a silicic contact-metasomatic aureole containing muscovite, biotite, actinolite, magnetite, K-feldspar and tourmaline. Disseminated andalusite + corundum also formed in areas previously affected by the advanced-argillic alteration. Iron/copper-sulphide veinlets are locally abundant, but a porphyry-style geochemical signature is not present. Early Cretaceous Ar–Ar ages near the intrusive contact indicate flow of an excess Ar-bearing hydrothermal plume up the contact. Finally, isolated areas of propylitic alteration in the lavas nearby may be related either to quartz veins of episode 1 at depth or to (4) continued circulation of heated groundwaters around the cooling pluton.
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Armstrong, Debbie C. "Acid sulphate alteration in a magmatic hydrothermal environment, Barton Peninsula, King George Island, Antarctica." Mineralogical Magazine 59, no. 396 (September 1995): 429–41. http://dx.doi.org/10.1180/minmag.1995.059.396.05.
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AbstractVolcanic-hosted advanced argillic alteration on Barton Peninsula comprises an assemblage of chalcedonic silica, alunite family minerals, pyrophyllite, pyrite, native sulphur, zunyite and rutile, characteristic of an acid sulphate-type epithermal system. The minerals minamiite, (Na0.36Ca0.27K0.1□0.27)Al3(SO4)2(OH)6, and zunyite, Al13Si5O20(OH,F)18Cl, are reported at this locality, and in Antarctica, for the first time. The WNW-striking, 1 km-long zone of alteration is hosted by early Tertiary andesitic rocks and contained in a 1.5 km-wide depression, rimmed by an arcuate ridge, probably representing a volcanic crater or small caldera structure.Stability relations of minerals in the advanced argillic alteration zone indicate alteration took place under acidic conditions in the near-surface environment. Mineralogical and textural evidence also suggest alteration occurred in a magmatic hydrothermal system, possibly with a magmatic steam component, rather than in a supergene or steam-heated environment.
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Μιχαήλ, Κ., and Μ. Δημήτρουλα. "HYDROTHERMAL ALTERATION AND MINERALIZATION OF THE PETROTA EPITHERMAL SYSTEMS (W.THRACE, GREECE)." Bulletin of the Geological Society of Greece 36, no. 1 (January 1, 2004): 369. http://dx.doi.org/10.12681/bgsg.16687.
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At the Petrota graben important epithermal zones are developed. On the basis of the mineral assemblages of alteration zones and the type of the host rocks, the epithermal zones can be grouped into three epithermal systems: 1. Perama epithermal system 2. Mavrokoryfi epithermal system and 3. Othondoto epithermal system Hydrothermal alteration zones are developed within volcanoclastic rocks - epiclastic sandstones, andésite tuffs (Perama epithermal system), hyaloclastites (Mavrokoryfi) and rhyolitic rocks (Othondoto). Silicification (in various types) and advanced argillic alteration are the most important alteration zones and are established on the largest scale. Ore mineralisation occurs as veins, veinlets in silicification zones or secondary mineralisation in the supergene zone (Perama epithermal system). Disseminated ore mineralization is also found in the silicification zone at Othondoto and Mavrokoryfi epithermal systems. Based on the geological environment, the type of hydrothemal alteration zones (silicification and advanced argillic alteration) and the mineral compositon of the ore (enargite- luzonite), the hydrothermal systems of Petrota graben can be referred as high sulfidation systems.
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Noori, Lida, Amin Pour, Ghasem Askari, Nader Taghipour, Biswajeet Pradhan, Chang-Wook Lee, and Mehdi Honarmand. "Comparison of Different Algorithms to Map Hydrothermal Alteration Zones Using ASTER Remote Sensing Data for Polymetallic Vein-Type Ore Exploration: Toroud–Chahshirin Magmatic Belt (TCMB), North Iran." Remote Sensing 11, no. 5 (March 1, 2019): 495. http://dx.doi.org/10.3390/rs11050495.
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Polymetallic vein-type ores are important sources of precious metal and a principal type of orebody for various base-metals. In this research, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing data were used for mapping hydrothermal alteration zones associated with epithermal polymetallic vein-type mineralization in the Toroud–Chahshirin Magmatic Belt (TCMB), North of Iran. The TCMB is the largest known goldfield and base metals province in the central-north of Iran. Propylitic, phyllic, argillic, and advanced argillic alteration and silicification zones are typically associated with Au-Cu, Ag, and/or Pb-Zn mineralization in the TCMB. Specialized image processing techniques, namely Selective Principal Component Analysis (SPCA), Band Ratio Matrix Transformation (BRMT), Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) were implemented and compared to map hydrothermal alteration minerals at the pixel and sub-pixel levels. Subtle differences between altered and non-altered rocks and hydrothermal alteration mineral assemblages were detected and mapped in the study area. The SPCA and BRMT spectral transformation algorithms discriminated the propylitic, phyllic, argillic and advanced argillic alteration and silicification zones as well as lithological units. The SAM and MTMF spectral mapping algorithms detected spectrally dominated mineral groups such as muscovite/montmorillonite/illite, hematite/jarosite, and chlorite/epidote/calcite mineral assemblages, systematically. Comprehensive fieldwork and laboratory analysis, including X-ray diffraction (XRD), petrographic study, and spectroscopy were conducted in the study area for verifying the remote sensing outputs. Results indicate several high potential zones of epithermal polymetallic vein-type mineralization in the northeastern and southwestern parts of the study area, which can be considered for future systematic exploration programs. The approach used in this research has great implications for the exploration of epithermal polymetallic vein-type mineralization in other base metals provinces in Iran and semi-arid regions around the world.
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Swayze, G. A., R. N. Clark, A. F. H. Goetz, K. E. Livo, G. N. Breit, F. A. Kruse, S. J. Sutley, et al. "Mapping Advanced Argillic Alteration at Cuprite, Nevada, Using Imaging Spectroscopy." Economic Geology 109, no. 5 (May 15, 2014): 1179–221. http://dx.doi.org/10.2113/econgeo.109.5.1179.
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Idrus, Arifudin, Aji Syailendra Ubaidillah, I. Wayan Warmada, and Syafruddin Maula. "Geology, Rock Geochemistry and Ore Fluid Characteristics of the Brambang Copper-Gold Porphyry Prospect, Lombok Island, Indonesia." Journal of Geoscience, Engineering, Environment, and Technology 6, no. 1 (March 29, 2021): 67–73. http://dx.doi.org/10.25299/jgeet.2021.6.1.6145.
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Brambang is one of the porphyry copper-gold prospects/deposits situated along eastern Sunda arc. This study is aimed to understand geological framework, alteration geochemistry and ore fluid characteristics of the prospect. Fieldworks and various laboratory analyses were performed including petrography, ore microscopy, rock geochemistry, chlorite chemistry and fluid inclusion microthermometry. The prospect is composed of andesitic tuff and diorite which are intruded by tonalite porphyries. Tonalite porphyries are interpreted as ore mineralisation-bearing intrusion. Various hydrothermal alterations are identified including potassic, phyllic, propylitic, advanced argillic and argillic types. Ore mineralisation is characterized by magnetite and copper sulfides such as bornite and chalcopyrite. Potassic alteration is typified by secondary biotite, and associated with ore mineralisation. Mass balance calculation indicates SiO2, Fe2O3, K2O, Cu and Au are added during potassic alteration process. Ore forming fluid is dominated by magmatic fluid at high temperature (450-600ºC) and high salinity (60-70 wt. % NaCl eq.). Hydrothermal fluid was diluted by meteoric water incursion at low-moderate temperature of 150-400ºC and salinity of 0.5-7 wt. % NaCl eq.
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Dill, H. G., A. Fricke, K. H. Henning, and C. H. Theune. "Aluminium phosphate mineralization from the hypogene La Vanguardia kaolin deposit (Chile)." Clay Minerals 30, no. 3 (September 1995): 249–56. http://dx.doi.org/10.1180/claymin.1995.030.3.08.
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AbstractIn the region of Illapel, Chile, dioritic and andesitic rocks of Cretaceous to Paleocene age from the Unidad San Lorenzo Formation have suffered strong alteration resulting in the formation of a kaolin-rich zone, which is mined in the La Vanguardia open pit near Combarbalá. Detailed mineralogical and chemical investigations of channel samples from this mine, involving a combination of optical microscopy, XRD, SEM-EDX, XRF and TEM, permitted recognition of a zone of silicification and a zone of advanced argillic alteration, both of which contain alunite s.s. and aluminium-phosphate-sulphate (APS) minerals of the woodhouseite group with subordinate amounts of gorceixite, florencite and goyazite. These minerals are found to have originated from infiltration of meteoric waters. The passage from silicification into advanced argillic alteration was associated with an increase in sulphate activity as manifested by the increase of SO42— at the expense of PO43— in the alunite s.s. and by an increase of the Au content from 0.01 to 0.03 mg/kg Au. This high sulphidation type of wallrock alteration may be roughly compared with the Nansatu type of White (1991).
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Sillitoe, Richard H., Claudio Burgoa, and David R. Hopper. "Porphyry Copper Discovery Beneath the Valeriano Lithocap, Chile." SEG Discovery, no. 106 (July 1, 2016): 1–20. http://dx.doi.org/10.5382/segnews.2016-106.fea.
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ABSTRACT Exploration for porphyry copper deposits beneath barren or poorly mineralized, advanced argillic lithocaps is becoming commonplace; however, there have been few discoveries except in cases where the copper ± gold ± molybdenum mineralization has been partly exposed, typically as a result of partial lithocap erosion. At Valeriano, in the high Andes of northern Chile, completely concealed Miocene porphyry copper-gold mineralization was recently discovered beneath a lithocap. Here, the results of the staged drilling program that led to the discovery are summarized, with emphasis on the key geologic, alteration, and mineralization features that provided guidance. The final deep drill holes of the 16-hole program cut well-defined advanced argillic and sericitic alteration zones before entering chalcopyrite ± bornite–bearing, potassic-altered porphyry, with grades of 0.7 to 1.2% Cu equiv, at depths of ~1,000 to >1,800 m.
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Kelm, U., M. Pincheira, J. Oyarzún, and V. Sucha. "Combarbalá advanced argillic alteration zone, Chile: geology, geochemistry, mineralogy and mineralization potential." Applied Earth Science 110, no. 2 (August 2001): 91–102. http://dx.doi.org/10.1179/aes.2001.110.2.91.
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GLUKHOV, Anton, and Petr TIKHOMIROV. "Erguveem Ore Region in the eastern Chukotka Peninsula: An effect of the tectonics of the ore-bearing volcano-structures on composition of the gold-silver mineralization." Domestic geology, no. 3-4 (September 14, 2021): 52–59. http://dx.doi.org/10.47765/0869-7175-2021-10022.
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The geological and structural position of the Pepenveem and Korrida Au-Ag ore occurrences situated in the East-Chukotka segment of the Okhotsk-Chukotka Volcanogenic Belt (OCVB) was studied. The Pepenveem ore occurrence was characterized by one (volcanogenic) mineralization stage. It is localized within a graben-like monocline composed of Late Cretaceous volcanics. A relatively stable tectonic regime caused rather low temperature and pressure gradients during the ore formation and, consequently, simple mineral composition of the ores and absence of advanced argillic alteration. In contrast, the Korrida ore occurrence was characterized by two (volcanogenic and plutonogenic) mineralization stages. It is localized within a plutonogenic uplift complicated by a regional fault zone. Here, the basement of the volcano-structure, composed of island-arc volcano-sedimentary rocks, was uplifted to the surface by numerous high-angle faults. The here observed extensive development of zoned metasomatic haloes (including advanced argillic alterations), abundance of mineral species, and sharp temperature and pressure gradients could resulted from tectonic activity in a zone of interaction between the plutonic dome and deep-seated regional fault.
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Imura, Takumi, Yusuke Minami, Tsukasa Ohba, Akiko Matsumoto, Antonio Arribas, and Mitsuhiro Nakagawa. "Hydrothermal Aluminum-Phosphate-Sulfates in Ash from the 2014 Hydrothermal Eruption at Ontake Volcano, Central Honshu, Japan." Minerals 9, no. 8 (July 29, 2019): 462. http://dx.doi.org/10.3390/min9080462.
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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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Burrows, David R., Michael Rennison, David Burt, and Rod Davies. "The Onto Cu-Au Discovery, Eastern Sumbawa, Indonesia: A Large, Middle Pleistocene Lithocap-Hosted High-Sulfidation Covellite-Pyrite Porphyry Deposit." Economic Geology 115, no. 7 (November 1, 2020): 1385–412. http://dx.doi.org/10.5382/econgeo.4766.
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Abstract In 2013, a diamond drill program tested an extensive advanced argillic alteration lithocap within the Hu’u project on eastern Sumbawa Island, Indonesia. A very large and blind copper-gold deposit (Onto) was discovered, in which copper occurs largely as disseminated covellite with pyrite, and as pyrite-covellite veinlets in a tabular block measuring at least 1.5 × 1 km, with a vertical thickness of ≥1 km. Copper and gold are spatially related with a series of coalesced porphyry stocks that intrude a polymictic diatreme breccia capped by a sequence of intramaar laminated siltstones, volcaniclastic and pyroclastic rocks, and overlain by andesite flows and domes. The porphyry intrusions were emplaced at shallow depth (≤1.3 km), with A-B–type quartz veinlet stockworks developed over a vertical interval of 300 to 400 m between ~100 and 500 m below sea level (bsl), 600 to 1,000 m below the present surface, which is at 400 to 600 m above sea level. In the area drilled at Onto, the diatreme breccia, all porphyry intrusions and, to a lesser extent, the surrounding older andesite sequence have all been overprinted by intense subhorizontal advanced argillic alteration, zoned downward from illite-smectite, quartz-dickite to quartz-alunite and quartz-pyrophyllite ± diaspore alteration. The alteration package includes two particularly well-developed zones of residual quartz with vuggy texture in subhorizontal zones at shallow depth, the upper one is still porous but the lower horizon, ~100 m thick, is largely silicified and is located at or near the top of the quartz-alunite alteration. Mineralization starts below the lowermost silicic horizon with more than 90% of the current resource in quartz-pyrophyllite-alunite and quartz-alunite alteration. Mineralization is dominated by a high-sulfidation assemblage of covellite-pyrite ± native sulfur largely in open-space fillings and replacements, but also as discrete pyrite-covellite and covellite only veins down to at least 1 km. Although the greatest amount of copper occurs as paragenetically late covellite deposited during formation of the advanced argillic alteration, approximately 60% of resource at 0.3% Cu cutoff still occurs within the porphyry stocks, indicating the porphyry stocks are a fundamental control on mineralization. There is considerable remobilization and dispersion of copper and, to a lesser extent, gold into the surrounding pre-mineral breccia and the late intermineral intrusions from the two earliest porphyry phases, resulting in quite consistent copper and gold grades throughout the currently delineated mineral resource. The very high sulfidation state of the mineralization is thought to be a consequence of the metal-bearing ore fluids cooling in the advanced argillic-altered host rocks in the absence of a rock buffer. Early chalcopyrite-bornite ± pyrite mineralization with potassic ± chloritic and sericitic alteration is only preserved on the margins of the system and more rarely at depth in a few holes 600 m bsl (~1,100 m below surface) but makes up only a small proportion (~8%) of the current resource. The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 ± 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 ± 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 ± 0.02 and 0.35 ± 0.0011 Ma. 40Ar/39Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 ± 0.22 to 0.284 ± 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 ± 0.064 to 0.038 ± 0.018 Ma.
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Williams, Nicholas C., and Garry J. Davidson. "POSSIBLE SUBMARINE ADVANCED ARGILLIC ALTERATION AT THE BASIN LAKE PROSPECT, WESTERN TASMANIA, AUSTRALIA." Economic Geology 99, no. 5 (August 2004): 987–1002. http://dx.doi.org/10.2113/gsecongeo.99.5.987.
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Allibone, A. "Gold mineralisation and advanced argillic alteration at the Dobroyde prospect, central New South Wales." Australian Journal of Earth Sciences 44, no. 6 (December 1997): 727–42. http://dx.doi.org/10.1080/08120099708728350.
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Marquis, P., C. Hubert, A. C. Brown, and D. M. Rigg. "Overprinting of early, redistributed Fe and Pb–Zn mineralization by late-stage Au–Ag–Cu deposition at the Dumagami mine, Bousquet district, Abitibi, Quebec." Canadian Journal of Earth Sciences 27, no. 12 (December 1, 1990): 1651–71. http://dx.doi.org/10.1139/e90-174.
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The Dumagami Au–Ag–Cu deposits are hosted by strongly deformed and altered Archean felsic metavolcanites of the Blake River Group (BRG), southern Abitibi greenstone belt, Canada. Textural and structural features recorded within the lithologies of the BRG at Dumagami indicate that two stages of hydrothermal alteration, separated by a dynamometamorphic event, have affected the volcanic protoliths in the deposit area. Advanced argillic and sericitic alteration zones, massive pyrite bodies, and massive sphalerite–galena bodies resulted from the first stage of hydrothermal activity. Sericitic shells surround peraluminous cores, which host the massive pyrite bodies and massive sphalerite–galena bodies within the altered zones.This early-stage alteration was followed by a dynamometamorphic event that reached the greenschist–amphibolite grade and almost completely recrystallized both fresh and altered rocks and the enclosed massive sulphide bodies. White-mica schists and andalusite–kyanite schists represent the dynamometamorphic equivalents of the earlier sericitic and advanced argillic zones. Mesoscopic and microscopic structures and textures attest to the ductile behaviour of the massive pyrite bodies during this deformation and accompanying metamorphism.Portions of the deformed and metamorphosed altered zones are characterized by a late cataclastic deformation and by the development of fractures postdating the ductile deformation. The late hydrothermal alteration is concentrated within these cataclastic rocks and is characterized by the retrogression of the greenschist–amphibolite assemblages. Andalusite and kyanite are replaced by diaspore, kaolinite, and pyrophyllite assemblages, and pyrite is replaced by chalcopyrite–gold, chalcopyrite–bornite–gold, and bornite–stromeyerite assemblages. The concentration of the pre-dynamometamorphic alteration and sulphide mineralization within a narrow band along the southern BRG could indicate that this part of the BRG was the locus of a major Archean synvolcanic fault zone.
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Bolouki, Seyed Mohammad, Hamid Reza Ramazi, Abbas Maghsoudi, Amin Beiranvand Pour, and Ghahraman Sohrabi. "A Remote Sensing-Based Application of Bayesian Networks for Epithermal Gold Potential Mapping in Ahar-Arasbaran Area, NW Iran." Remote Sensing 12, no. 1 (December 27, 2019): 105. http://dx.doi.org/10.3390/rs12010105.
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Mapping hydrothermal alteration minerals using multispectral remote sensing satellite imagery provides vital information for the exploration of porphyry and epithermal ore mineralizations. The Ahar-Arasbaran region, NW Iran, contains a variety of porphyry, skarn and epithermal ore deposits. Gold mineralization occurs in the form of epithermal veins and veinlets, which is associated with hydrothermal alteration zones. Thus, the identification of hydrothermal alteration zones is one of the key indicators for targeting new prospective zones of epithermal gold mineralization in the Ahar-Arasbaran region. In this study, Landsat Enhanced Thematic Mapper+ (Landsat-7 ETM+), Landsat-8 and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) multispectral remote sensing datasets were processed to detect hydrothermal alteration zones associated with epithermal gold mineralization in the Ahar-Arasbaran region. Band ratio techniques and principal component analysis (PCA) were applied on Landsat-7 ETM+ and Landsat-8 data to map hydrothermal alteration zones. Advanced argillic, argillic-phyllic, propylitic and hydrous silica alteration zones were detected and discriminated by implementing band ratio, relative absorption band depth (RBD) and selective PCA to ASTER data. Subsequently, the Bayesian network classifier was used to synthesize the thematic layers of hydrothermal alteration zones. A mineral potential map was generated by the Bayesian network classifier, which shows several new prospective zones of epithermal gold mineralization in the Ahar-Arasbaran region. Besides, comprehensive field surveying and laboratory analysis were conducted to verify the remote sensing results and mineral potential map produced by the Bayesian network classifier. A good rate of agreement with field and laboratory data is achieved for remote sensing results and consequential mineral potential map. It is recommended that the Bayesian network classifier can be broadly used as a valuable model for fusing multi-sensor remote sensing results to generate mineral potential map for reconnaissance stages of epithermal gold exploration in the Ahar-Arasbaran region and other analogous metallogenic provinces around the world.
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Bottrill, R. S. "A corundum-quartz assemblage in altered volcanic rocks, Bond Range, Tasmania." Mineralogical Magazine 62, no. 3 (June 1998): 325–32. http://dx.doi.org/10.1180/002646198547710.
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AbstractUnusual corundum-bearing rocks occur in the Bond Range, northern Tasmania, in a hydrothermally altered Cambrian quartz porphyry. The assemblage exhibits quartz and corundum in mutual contact, a rare phenomenon, in association with andalusite, pyrophyllite, diaspore and other minerals. This metastable assemblage apparently resulted from advanced argillic alteration at moderate temperature and low pressure, followed by rapid depressurisation accompanying boiling of hydrothermal, granite-derived fluids. This corundum occurrence appears to be unrelated to the sapphires in placer deposits in Tasmania.
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Taghipour, Batoul, Mohammad Ali Mackizadeh, Mehdi Pourmoghani, Arthur Kasson, and Sedighe Taghipour. "Geology and mineralogy of advanced argillic alteration in the Keshe area (Mt. Karkas), Central Iran." Central European Geology 51, no. 1 (March 2008): 85–98. http://dx.doi.org/10.1556/ceugeol.51.2008.1.5.
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Patrier, Patricia, Sylvain Bruzac, Rebecca Pays, Daniel Beaufort, Vincent Bouchot, Chrystèle Verati, and Alain Gadalia. "Occurrence of K-feldspar-bearing hydrothermal breccias in the Bouillante geothermal field (Basse Terre – Guadeloupe)." Bulletin de la Société Géologique de France 184, no. 1-2 (January 1, 2013): 119–28. http://dx.doi.org/10.2113/gssgfbull.184.1-2.119.
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Abstract Surficial indicators of recent to present geothermal activity are present around Bouillante (Guadeloupe, French West Indies). Until lately, most mineralogical parageneses identified in this area were typical of low temperature alteration (< 100°C) with the occurrence of dioctahedral aluminous smectites accompanied by zeolites (heulandite-clinoptilolite) ± calcite ± silica ± kaolinite, as an evidence of the cap rock of the geothermal system. Recently, numerous boulders of highly silicified breccias containing high temperature minerals (> 200°C) have been identified in the Bouillante bay (Anse Marsolle). Their petrographic study revealed several hydrothermal parageneses typical of a multistage alteration process. Stage 1) An early potassic alteration facies typical of a high-temperature geothermal system characterized by K-feldspar/adularia + quartz + pyrite. K-feldspars have been shown to be present both in the clasts (replacement) and cement of these breccias. They are associated with quartz whose textural properties have revealed fracturing associated with boiling. Stage 2) An acid-sulphate advanced argillic alteration facies with the occurrence of jarosite, gypsum ± silica (≥ 150°C) as usually observed in the upper part of epithermal systems worldwide as marker of deeper boiling. Stage 3) An argillic alteration facies (illite/smectite mixed layers ± smectite ± calcite). With temperatures typically ranging from 100 to 200°C, this alteration facies is associated with near neutral fluids of mainly meteoric origin as known in the present geothermal reservoir (pH = 5.4). This alteration is the later one as evidenced by petrographic observations. These results highlight mineral assemblages and mineral textures characteristic of high temperature hydrothermal alteration in epithermal settings. The occurrence of these breccias involved the existence of eruptive events (magmatic/hydrothermal explosion) which ejected this material. Isotopic (oxygen, argon) and geochemical (trace elements) studies are now necessary to clarify the timing of these breccias and the nature and the connection of the original fluids with current geothermal fluids
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Deyell, C. L., J. FH Thompson, R. M. Friedman, and L. A. Groat. "Age and origin of advanced argillic alteration zones and related exotic limonite deposits in the Limonite Creek area, central British Columbia." Canadian Journal of Earth Sciences 37, no. 8 (August 1, 2000): 1093–107. http://dx.doi.org/10.1139/e00-019.
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The Limonite Creek property in north-central British Columbia contains several zones of silicic and acid-sulphate alteration. These zones grade through advanced argillic and aluminous mineral assemblages to sericitic and regional propylitic alteration. Alteration assemblages are characteristic of high-sulphidation systems, although the abundance of pyrophyllite and andalusite suggests formation at depths below typical epithermal environments. Alteration occurred between 212 and 52 Ma as determined from field relations and U-Pb dating of intrusions. The deformed nature of the alteration assemblages and a minimum age of alunite (144 ± 8 Ma) suggest formation in latest Triassic to Middle Jurassic time. Based on these age constraints, alteration zones at Limonite Creek are significantly older than the Eocene Equity Silver deposit (ca. 60 Ma), despite the latter's proximity and similar styles of alteration. Based on the new dates, host rocks at Limonite Creek are Late Triassic or older, and hence regional stratigraphy needs reassessment. Extensive exotic limonite deposits occur around the alteration zones and at lower elevations to the south. Radiocarbon dating indicates that the deposits have been accumulating for at least 8000 years. Iron released during weathering was transported in low-pH waters and precipitated initially as ferrihydrite, with subsequent conversion to goethite. Water chemistry confirms that the process is still active. In addition to iron, the limonite contains minor copper and zinc. The formation of low-pH waters and the transport of iron resulted from weathering of pyrite-rich alteration assemblages with negligible buffering capacity.
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Shebl, Ali, Mahmoud Abdellatif, Sayed O. Elkhateeb, and Árpád Csámer. "Multisource Data Analysis for Gold Potentiality Mapping of Atalla Area and Its Environs, Central Eastern Desert, Egypt." Minerals 11, no. 6 (June 16, 2021): 641. http://dx.doi.org/10.3390/min11060641.
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In this research, airborne geophysical and remote sensing datasets were integrated for gold potentiality mapping (GPM) over the Atalla area in Central Eastern Desert, Egypt. Utilizing aeromagnetic data, detailed structural complexity maps were constructed using the center for exploration targeting (CET) procedure. Then, spectrometric gamma-ray data primarily located hydrothermally altered tracts with discriminating various rock units. The latter are precisely outlined by implementing various techniques (false-color composite (FCC), band ratio (BR), relative absorption band depth (RBD), directed principal component analysis (DPCA), and constrained energy minimization (CEM)) to ASTER, Sentinel 2 and ALOS PRISM datasets, with reference to the geological maps. The study exhibits that gold mineralization is structurally controlled by NW-SE direction. The findings of structural complexity and hydrothermal alteration (argillic, advanced argillic, phyllic, and propylitic) were used as weighted inputs for contouring gold potentiality. The resultant GPM accentuated five gold-promising zones; two are confirmed via locations of ancient gold mines, while the remaining three zones are strongly recommended for their gold potentiality.
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Ramos, Yuddy, Kalifa Goïta, and Stéphane Péloquin. "Mapping advanced argillic alteration zones with ASTER and Hyperion data in the Andes Mountains of Peru." Journal of Applied Remote Sensing 10, no. 2 (June 7, 2016): 026031. http://dx.doi.org/10.1117/1.jrs.10.026031.
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Lerouge, C., A. Kunov, C. Fléhoc, S. Georgieva, A. Hikov, J. L. Lescuyer, R. Petrunov, and N. Velinova. "Constraints of stable isotopes on the origin of alunite from advanced argillic alteration systems in Bulgaria." Journal of Geochemical Exploration 90, no. 3 (September 2006): 166–82. http://dx.doi.org/10.1016/j.gexplo.2005.11.001.
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Feizi, F., and E. Mansouri. "Recognition of a porphyry system using ASTER data in Bideghan – Qom province (central of Iran)." Solid Earth Discussions 6, no. 2 (July 18, 2014): 1765–98. http://dx.doi.org/10.5194/sed-6-1765-2014.
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Abstract. The Bideghan area is located south of the Qom province (central of Iran). The most impressive geological features in the studied area are the Eocene sequences which are intruded by volcanic rocks with basic compositions. Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) image processing have been used for hydrothermal alteration mapping and lineaments identification in the investigated area. In this research false color composite, band ratio, Principal Component Analysis (PCA), Least Square Fit (LS-Fit) and Spectral Angel Mapping (SAM) techniques were applied on ASTER data and argillic, phyllic, Iron oxide and propylitic alteration zones were separated. Lineaments were identified by aid of false color composite, high pass filters and hill-shade DEM techniques. The results of this study demonstrate the usefulness of remote sensing method and ASTER multi-spectral data for alteration and lineament mapping. Finally, the results were confirmed by field investigation.
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Papoulis, D., P. Tsolis-Katagas, and C. Katagas. "NEW FIND OF ZUNYITE IN ADVANCED ARGILLIC ALTERATION OF RHYOLITES, KOS ISLAND, SOUTH AEGEAN VOLCANIC ARC , GREECE." Bulletin of the Geological Society of Greece 36, no. 1 (January 1, 2004): 474. http://dx.doi.org/10.12681/bgsg.16738.
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Zunyite [Ali3SÌ5C>2o(OH,F)i8CI], an extremely rare mineral, was found as an accessory mineral in highly altered rhyolitic rocks at Kefalos, southwestern Kos, and in a completely kaolinized rhyolitic dyke at Asfendiou, northeastern Kos. It is associated with dickite, kaolinite, quartz and minor pyrophyllite. Kos Island contains both Tertiary and Quaternary volcanic rocks. Zunyite has been identified by XRD and studied by SEM, EDS, Raman spectroscopy and FTIR spectroscopy. The presence of zunyite, in the highly altered samples is significant for the determination of the conditions of the hydrothermal alteration that took place. Zunyite crystals, are up to 90 pm in diameter but usually are less than 10 pm; the crystals are partly covered by kaolinite layers. EDX analyses on the surface of zunyite revealed AI2O3/S1O2 values raging from 2.6 to 2.7. The occurrence of zunyite suggests incorporation of hydrothermal fluids rich in F" and CI", thus indicating contamination by seawater
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Sahlström, Fredrik, Zhaoshan Chang, Antonio Arribas, Paul Dirks, Craig A. Johnson, Jan Marten Huizenga, and 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 (January 1, 2020): 129–52. http://dx.doi.org/10.5382/econgeo.4696.
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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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Camprubí, Antoni, Edith Fuentes-Guzmán, Pilar Ortega-Larrocea, María Colín-García, Janet Gabites, Luis F. Auqué, Vanessa Colás, and Eduardo González-Partida. "The Pliocene Ixtacamaxtitlán low sulfidation epithermal deposit (Puebla, Mexico): A case of fossil fungi consortia in a steam-heated environment." Boletín de la Sociedad Geológica Mexicana 72, no. 3 (November 28, 2020): A140420. http://dx.doi.org/10.18268/bsgm2020v72n3a140420.
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The Ixtacamaxtitlán area in northern Puebla (central Mexico) contains middle Miocene Cu-Mo-Au porphyry/skarn and Pliocene low-sulfidation Au-Ag epithermal deposits that are geologically associated with the evolution of the Trans-Mexican Volcanic Belt (TMVB). In this paper, a new 40Ar/39Ar age (2.87 ± 0.41 Ma) is provided for rhombohedral alunite from a kaolinite + alunite ± opal ± cristobalite ± smectite advanced argillic alteration assemblage. This age contributes to the definition of a metallogenic province that is confined to the TMVB, a relevant feature for regional exploration. A ~12 My gap is established between the formation of the Cu-Mo-Au porphyry/skarn and low-sulfidation Au-Ag epithermal deposits, which rules out the possibility that their overlapping was the result of telescoping. Advanced argillic alteration is conspicuous throughout the mineralized area. This alteration assemblage consists of a widespread kaolinite-rich blanket that underlies silica sinters, polymictic hydrothermal breccias, and an alunite-rich spongy layer that consists of vertical tubular structures that are interpreted as the result of gas venting in a subaerial environment. The above indicate a shallow hypogene origin for the advanced argillic alteration assemblage—that is, formation by the partial condensation within a phreatic paleoaquifer of acidic vapors that were boiled-off along fractures that host epithermal veins at depth. The formation of the spongy alunite layer and silica sinters is interpreted to have been synchronous. Within the alunite-rich spongy layer, tubular structures hosted microbial consortia dominated by fungi and possible prokaryote (Bacteria or Archaea) biofilms. Such consortia were developed on previously formed alunite and kaolinite and were preserved due to their replacement by opal, kaolinite, or alunite. This means that the proliferation of fungi and prokaryotes occurred during a lull in acidic gas venting during which other organisms (i.e., algae) might have also prospered. Periodic acidic gas venting is compatible with a multi-stage hydrothermal system with several boiling episodes, a feature typical of active geothermal systems and of low-sulfidation epithermal deposits. The microstructures, typical for fungi, are mycelia, hyphae with septa, anastomoses between branches, and cord-like groupings of hyphae. Possible evidence for skeletal remains of prokaryote biofilms is constituted by cobweb-like microstructures composed of <1 µm thick interwoven filaments in close association with hyphae (about 2.5 µm thick). Bioweathering of previously precipitated minerals is shown by penetrative biobrecciation due to extensive dissolution of kaolinite by mycelia and by dissolution grooves from hyphae on alunite surfaces. Such bioweathering was possibly predated by inorganically driven partial dissolution of alunite, which suggests a lull in acidic gas venting that allowed living organisms to thrive. This interpretation is sustained by the occurrence of geometrical dissolution pits in alunite covered by hyphae. Fungal bioweathering is particularly aggressive on kaolinite due to its relatively poor nutrient potential. Such delicate microstructures are not commonly preserved in the geological record. In addition, numerous chalcopyrite microcrystals or microaggregates are found within the alunite layer, which could be related to sulfate reduction due to bacterial activity from the sulfate previously released by fungal bioweathering of alunite. Hydrogeochemical modeling constrains pH to between ~3.2 and ~3.6 and temperature to between 53 and 75 °C during the stage in which fungi and other organisms thrived. These waters were cooler and more alkaline than in earlier and later stages, which were characterized dominantly by steam-heated waters. The most likely process to account for this interlude would be mixing with meteoric water or with upwelling mature water that did not undergo boiling.
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So, Chil-Sup, Seong-Taek Yun, and Maeng-Eon Park. "Geochemistry of a fossil hydrothermal system at Barton Peninsula, King George Island." Antarctic Science 7, no. 1 (March 1995): 63–72. http://dx.doi.org/10.1017/s0954102095000101.
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A fossil hydrothermal system on Barton Peninsula, King George Island, Antarctica, formed a series of lead-zinc- and pyrite + native sulphur-bearing epithermal quartz ± calcite veins, filling fault-related fractures in hydrothermally altered volcanic rocks of Eocene age. The lead-zinc veins occur within argillic hydrothermal alteration zones, whereas the pyrite + native sulphur veins are found within advanced argillic alteration zones. Fluid inclusion data indicate that the vein formation occurred at temperatures between about 125° and 370°C (sphalerite deposition formed at 123–211°C) from fluids with salinities of 0.5–4.6 wt.% eq. NaCl. Equilibrium thermodynamic interpretation of mineral assemblages indicates that the deposition of native sulphur in the upper and central portions of the hydrothermal system was a result of the mixing of condensates of ascending magmatic gases and meteoric water giving rise to fluids which had lower pH (<3.5) and higher fugacities of oxygen and sulphur than the lead-zinc-depositing fluids at depth. The δ34S values of sulphide minerals from the lead-zinc veins (δ34S = −4.6 to 0.7‰) are much higher than the values of pyrite and native sulphur from the pyrite + native sulphur veins (δ34S = −12.9 to −20.1‰). This indicates that the fluids depositing native sulphur had higher sulphate/H2S ratios under higher fo2 conditions. Sulphur isotope compositions indicate an igneous source of sulphur with a δ34SΣS value near 0‰, probably the Noel Hill Granodiorite. Measured and calculated δ18O and δD values of the epithermal fluids (δ18Owater = −6.0 to 2.7‰, δDwater = −87 to −75‰) indicate that local meteoric water played an important role for formation of lead-zinc and native sulphur-bearing quartz veins.
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Melfos, Vasilios, Panagiotis Voudouris, Todor Serafimovski, and Goran Tasev. "Fluid Inclusions at the Plavica Au-Ag-Cu Telescoped Porphyry–Epithermal System, Former Yugoslavian Republic of Macedonia (FYROM)." Geosciences 9, no. 2 (February 14, 2019): 88. http://dx.doi.org/10.3390/geosciences9020088.
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The Plavica Au-Ag-Cu porphyry and high sulfidation (HS) epithermal deposit is located at the Kratovo–Zlatovo volcanic field in Eastern Former Yugoslavian Republic of Macedonia. In this study, new fluid inclusions data provide additional evidence of the presence of a porphyry style mineralization which is associated with an overlain HS epithermal deposit. The Oligocene–Miocene magmatic rocks have a calc–alkaline to high-K calc–alkaline affinity and consist of sub-volcanic intrusions and volcanic rocks. Previous studies distinguished four alteration types: (a) Sericitic, (b) advanced argillic, (c) silicification, and (d) propylitic alteration. Fluid inclusions showed an early magmatic brine in porphyry style veins with high salinity (33–57 wt% NaCl equiv.), which coexists with a vapor rich fluid with lower salinity (14–20 wt% NaCl equiv.), at temperatures 380–500 °C, under boiling conditions. At shallower depths, the fluid inclusions demonstrate various HS–epithermal deposits which were formed by moderate to low salinity (3–14 wt% NaCl equiv.) hydrothermal fluids at lower temperatures from 200 to 300 °C.
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Bonnet, Anne-Laure, Louise Corriveau, and Marc R. La Flèche. "Chemical imprint of highly metamorphosed volcanic-hosted hydrothermal alterations in the La Romaine Supracrustal Belt, eastern Grenville Province, Quebec." Canadian Journal of Earth Sciences 42, no. 10 (October 1, 2005): 1783–814. http://dx.doi.org/10.1139/e05-098.
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The La Romaine Supracrustal Belt and the southeastern end of the Wakeham Group in the eastern Grenville Province, Canada, host a series of Pinwarian, 1.50 Ga felsic-dominated volcanic centres metamorphosed at amphibolite to granulite facies during the Grenville orogeny. The centres are interpreted as being related to the emergence of rhyolitic domes in shallow-marine intra-arc basins within the active Pinwarian continental magmatic arc. High-grade metamorphosed hydrothermal alteration zones are intimately associated with pyroclastic deposits composing these volcanic centres and an overlying composite amphibolite unit. They comprise layers of rhyolitic metatuff bearing networks of aluminous nodules and veins, migmatized garnetbiotitesillimanite gneiss with well-preserved volcanic fragments, and mottled quartzcordierite gneiss with textures similar to those of vuggy silica facies. Alteration zones of ironstone, carbonate and calc-silicate rocks, garnetite, diopsidite, epidosite, and sulphide mineralization collectively cut across the internal contacts of a composite amphibolite unit inferred to be a mafic lava and sill complex. Lithogeochemical analysis of inferred metamorphosed altered rocks and precursors highlights chemical changes typical of metamorphosed sericitic zones, advanced argillic and silicic zones, and discharge zones characterized by calcic alterations and copper mineralizations. Such zones involve the interaction of hot, very acidic to neutral fluids. Medium to heavy rare-earth elements (REE) and Zr behave as mobile elements in the hydrothermal system as a result of the presence of F-rich fluids. The chemical changes recorded by the various alteration zones share similarities with those observed in high-sulphidation, volcanic-hosted massive sulphide deposits occurring in proximal, shallow-marine, volcanic sequences.
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Sutarto, Sutarto, Arifudin Idrus, Agung Harijoko, Lucas Donny Setijadji, Franz Michael Meyer, Sven Sindern, and Sapto Putranto. "Hydrothermal Alteration and Mineralization of the Randu Kuning Porphyry Cu-Au and Intermediate Sulphidation Epithermal Au-Base Metals Deposits in Selogiri, Central Java, Indonesia." Journal of Applied Geology 1, no. 1 (July 26, 2016): 1. http://dx.doi.org/10.22146/jag.26951.
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The Randu Kuning Porphyry Cu-Au prospect area is situated in the Selogiri district, Wonogiri regency, Central Java, Indonesia, about 40 km to the South-East from Solo city, or approximately 70 km east of Yogyakarta city. The Randu Kuning area and its vicinity is a part of the East Java Southern Mountain Zone, mostly occupied by both plutonic and volcanic igneous rocks, volcaniclastic, silisiclastic and carbonate rocks. Magmatism-volcanism products were indicated by the abundant of igneous and volcaniclastic rocks of Mandalika and Semilir Formation. The Alteration zones distribution are generally controlled by the NE–SW and NW–SE trending structures. At least eight types of hydrothermal alteration at the Randu Kuning area and its vicinity had been identified, i.e. magnetite + biotite ± K-feldspar ± chlorite (potassic), chlorite + sericite + magnetite ± actinolite, chlorite + magnetite ± actinolite ± carbonate (inner propylitic), chlorite + epidote ± carbonate (outer propylitic), sericite + quartz + pyrite (phyllic), illite + kaolinite ± smectite (intermediate argillic), illite + kaolinite ± pyrophyllite ± alunite (advanced argillic) and quatz + chlorite (sillisic) zones. The Randu Kuning mineralization at Selogiri is co existing with the porphyry Cu-Au and intermediate sulphidation epithermal Au-base metals. Mineralization in the porphyry environment is mostly associated with the present of quartz-sulphides veins including AB, C, carbonate-sulphides veins (D vein) as well as disseminated sulphides. While in the epithermal prospect, mineralization is particularly associated with pyrite + sphalerite + chalcopyrite + carbonate ± galena veins as well as hydrothermal breccias. The Randu Kuning porphyry prospect has copper gold grade in range at about 0.66–5.7 gr/t Au and 0.04–1.24 % Cu, whereas in the intermediate sulphidation epithermal contain around 0.1–20.8 gr/t Au, 1.2–28.1 gr/t Ag, 0.05–0.9 % Zn, 0.14–0.59 % Pb and 0.01–0.65 % Cu.
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Michael, C. "EPITHERMAL SYSTEMS AND GOLD MINERALIZATION IN WESTERN THRACE (NORTHERN GREECE)." Bulletin of the Geological Society of Greece 36, no. 1 (January 1, 2004): 416. http://dx.doi.org/10.12681/bgsg.16727.
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Extensive epithermal systems occur within the Tertiary volcanosedimentary basins of western Thrace northern Greece. Gold deposits or perspective gold districts, related to the above epithermal systems have been recently found in the area. The gold mineralization is of the high – sulfidation type and is associated to a diversity in composition and style volcanic activity. Sappes epithermal system is the most important (Saint Demetrios and Viper deposits) and has developed in volcanic "ocks of intermediate composition accompanied by subvolcanic intrusives (dacite - andésites) and plutonio rocks (quartz - monzodiorites). Saint Demetrios and Viper gold deposits are flat lying and of high sulfidation type mineralizations hosted in hydrothermal breccia zones. Petrota epithermal system has developed in volcanoclastic and epiclastic rocks (Perama Hill gold deposit), in rhyolites (location Othontoto) and within hyaloclastites and crystal tuffs (location Mavrokoryfi). The mineralized epithermal zones have strong structural control. Perama gold deposit occurs at the intersection of NS and NW trending epithermal zones. These structures represent the higher grade "feeder" system. Pefka epithermal system is hosted in more acid volcanic vocks (dacites, rhyodacites) and at its southern part (Pasa lofos area) the system is associated with a more alkaline suit (shoshonitic rocks). The mineralized silicifid zones at Pefka mine would correspond to concentric fractures (sheeted fracturing) parallel to the margin of the breccia pipe. The gold mineralization occurs in veins. In general gold occurs in the form of native gold, gold tellurides or it is associated with enargite, luzonite, tetrahedhte. Advanced argillic alteration and intense silicification are very important for the epithermal systems in western Thrace. A unique low - sulfidation occurrence was found at the central and southern part of Sappes area. Adularla was found in veinlets overlapping argillic alteration zones of high - sulfidation system.
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Bijnaar, Ginny, Manfred J. van Bergen, and Theo E. Wong. "The kyanite quartzite of Bosland (Suriname): evidence for a Precambrian metamorphosed alteration system." Netherlands Journal of Geosciences - Geologie en Mijnbouw 95, no. 4 (November 3, 2016): 447–65. http://dx.doi.org/10.1017/njg.2016.38.
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AbstractThis article investigates the origin of a rare occurrence of kyanite quartzites in the Palaeoproterozoic greenstone belt of Suriname. The rocks form elongated hills in the Bosland area, Brokopondo district, where they are associated with meta-sedimentary, meta-volcanic and granitic lithologies. Their mineral content and unusual Si- and Al-rich chemical composition are inferred to be the result of advanced argillic alteration of felsic volcanic tuffs and a later overprint by regional metamorphism up to lower amphibolite facies during the Trans-Amazonian orogeny. Structurally, the Bosland area seems centred within a contractional strike-slip duplex of a major dextral fault system. The alteration was probably associated with a high-sulphidation environment and involved significant to almost complete removal of alkali and alkaline earth elements. Pseudosection modelling and textures suggest that the precipitation–temperature (P–T) history of the kyanite quartzites started with shallow (<2kbar) hydrothermal alteration of the acidic tuffaceous volcanics, possibly in the andalusite stability field (T>350°C), and ended in peak metamorphic conditions in the kyanite–staurolite stability field (P>4kbar andT=500–650°C). Alteration events that preceded the peak of Trans-Amazonian metamorphism may be more common in the rock record of Suriname's greenstone belt, which lends support to the hypothesis that gold mineralisations in the region can be pre-orogenic.
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Son, Young-Sun, Byoung-Woon You, Eun-Seok Bang, Seong-Jun Cho, Kwang-Eun Kim, Hyunseob Baik, and Hyeong-Tae Nam. "Mapping Alteration Mineralogy in Eastern Tsogttsetsii, Mongolia, Based on the WorldView-3 and Field Shortwave-Infrared Spectroscopy Analyses." Remote Sensing 13, no. 5 (March 1, 2021): 914. http://dx.doi.org/10.3390/rs13050914.
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This study produces alteration mineral maps based on WorldView-3 (WV-3) data and field shortwave-infrared (SWIR) spectroscopy. It is supported by conventional analytical methods such as X-ray diffraction, X-ray fluorescence, and electron probe X-ray micro analyzer as an initial step for mineral exploration in eastern Tsogttsetsii, Mongolia, where access is limited. Distributions of advanced argillic minerals (alunite, dickite, and kaolinite), illite/smectite (illite, smectite, and mixed-layered illite-smectite), and ammonium minerals (buddingtonite and NH4-illite) were mapped using the decorrelation stretch, band math, and mixture-tuned-matched filter (MTMF) techniques. The accuracy assessment of the WV-3 MTMF map using field SWIR data showed good WV-3 SWIR data accuracy for spectrally predominant alteration minerals such as alunite, kaolinite, buddingtonite, and NH4-illite. The combination of WV-3 SWIR mineral mapping and a drone photogrammetric-derived digital elevation model contributed to an understanding of the structural development of the hydrothermal system through visualization of the topographic and spatial distribution of surface alteration minerals. Field SWIR spectroscopy provided further detailed information regarding alteration minerals such as chemical variations of alunite, crystallinity of kaolinite, and aluminum abundance of illite that was unavailable in WV-3 SWIR data. Combining WV-3 SWIR data and field SWIR spectroscopy with conventional exploration methods can narrow the selection between deposit models and facilitate mineral exploration.
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Seewald, Jeffrey S., Eoghan P. Reeves, Wolfgang Bach, Peter J. Saccocia, Paul R. Craddock, Emily Walsh, Wayne C. Shanks, Sean P. Sylva, Thomas Pichler, and Martin Rosner. "Geochemistry of hot-springs at the SuSu Knolls hydrothermal field, Eastern Manus Basin: Advanced argillic alteration and vent fluid acidity." Geochimica et Cosmochimica Acta 255 (June 2019): 25–48. http://dx.doi.org/10.1016/j.gca.2019.03.034.
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Higueras, P., R. Oyarzun, R. Lunar, J. Sierra, and J. Parras. "The Las Cuevas deposit, Almaden district (Spain): An unusual case of deep-seated advanced argillic alteration related to mercury mineralization." Mineralium Deposita 34, no. 2 (January 1, 1999): 211–14. http://dx.doi.org/10.1007/s001260050197.
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Khashgerel, Bat-Erdene, Imants Kavalieris, and Ken-ichiro Hayashi. "Mineralogy, textures, and whole-rock geochemistry of advanced argillic alteration: Hugo Dummett porphyry Cu–Au deposit, Oyu Tolgoi mineral district, Mongolia." Mineralium Deposita 43, no. 8 (August 26, 2008): 913–32. http://dx.doi.org/10.1007/s00126-008-0205-3.
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Brathwaite, R., M. Simpson, K. Faure, and D. Skinner. "Telescoped porphyry Cu-Mo-Au mineralisation, advanced argillic alteration and quartz-sulphide-gold-anhydrite veins in the Thames District, New Zealand." Mineralium Deposita 36, no. 7 (October 2001): 623–40. http://dx.doi.org/10.1007/s001260100182.
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Flahaut, Jessica, Janice L. Bishop, Simone Silvestro, Dario Tedesco, Isabelle Daniel, and Damien Loizeau. "The Italian Solfatara as an analog for Mars fumarolic alteration." American Mineralogist 104, no. 11 (November 1, 2019): 1565–77. http://dx.doi.org/10.2138/am-2019-6899.
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Abstract The first definitive evidence for continental vents on Mars is the in situ detection of amorphous silica-rich outcrops by the Mars Exploration Rover Spirit. These outcrops have been tentatively interpreted as the result of either acid sulfate leaching in fumarolic environments or direct precipitation from hot springs. Such environments represent prime targets for upcoming astrobiology missions but remain difficult to identify with certainty, especially from orbit. To contribute to the identification of fumaroles and hot spring deposits on Mars, we surveyed their characteristics at the analog site of the Solfatara volcanic crater in central Italy. Several techniques of mineral identification (VNIR spectroscopy, Raman spectroscopy, XRD) were used both in the field and in the laboratory on selected samples. The faulted crater walls showed evidence of acid leaching and alteration into the advanced argillic-alunitic facies, with colorful deposits containing alunite, jarosite, and/or hematite. Sublimates containing various Al and Fe hydroxyl-sulfates were observed around the active fumarole vents at 90 °C. One vent at 160 °C was characterized by different sublimates enriched in As and Hb sulfide species. Amorphous silica and alunite assemblages that are diagnostic of silicic alteration were also observed at the Fangaia mud pots inside the crater. A wide range of minerals was identified at the 665 m diameter Solfatara crater that is diagnostic of acid-steam heated alteration of a trachytic, porous bedrock. Importantly, this mineral diversity was captured at each site investigated with at least one of the techniques used, which lends confidence for the recognition of similar environments with the next-generation Mars rovers.
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Bozkaya, Ömer, Ivan A. Baksheev, Nurullah Hanilçi, Gülcan Bozkaya, Vsevolod Y. Prokofiev, Yücel Öztaş, and David A. Banks. "Tourmaline Composition of the Kışladağ Porphyry Au Deposit, Western Turkey: Implication of Epithermal Overprint." Minerals 10, no. 9 (September 7, 2020): 789. http://dx.doi.org/10.3390/min10090789.
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The Kışladağ porphyry Au deposit occurs in a middle Miocene magmatic complex comprising three different intrusions and magmatic-hydrothermal brecciation related to the multiphase effects of the different intrusions. Tourmaline occurrences are common throughout the deposit, mostly as an outer alteration rim around the veins with lesser amounts disseminated in the intrusions, and are associated with every phase of mineralization. Tourmaline mineralization has developed as a tourmaline-rich matrix in brecciated zones and tourmaline-quartz and/or tourmaline-sulfide veinlets within the different intrusive rocks. Tourmaline was identified in the tourmaline-bearing breccia zone (TBZ) and intrusive rocks that had undergone potassic, phyllic, and advanced argillic alteration. The tourmaline is present as two morphological varieties, aggregates of fine crystals (rosettes, fan-shaped) and larger isolated crystals and their aggregates. Four tourmaline generations (tourmaline I to IV) have different compositions and substitutions. Tourmaline I in TBZ and INT#1 is distinguished by the highest Fetot and enriched in Fe3+. Tourmalines II and III occur as fine aggregates, accompanied by the formation of isolated crystals and are characterized by lower Fetot and Fe3+. Tourmaline IV is characterized by the lowest Fetot, enriched in Cl, and has the highest proportion of X-site vacancy among all the tourmalines. Tourmaline I may be attributed to the potassic stage in INT#1 and early tourmaline in TBZ. Tourmalines II and III from INT#1 and the TBZ could be referred to the phyllic stage. The low Fe content in tourmaline is caused by the simultaneous deposition of sulfide minerals. Tourmaline IV from the TBZ and tourmaline II from INT#3 are distinguished by the high X-site vacancy proportion up to the formation of X-site vacant species as well as enriched in Cl; they can be attributed to the argillic stage of the hydrothermal process. The textural and especially chemical data of the tourmaline from the Kışladağ Au deposit provide information on the physico-chemical conditions during the porphyry to epithermal transition and subsequent epithermal overprinting.
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Mars, John C., Gilpin R. Robinson, Jane M. Hammarstrom, Lukas Zürcher, Helen Whitney, Federico Solano, Mark Gettings, and Steve Ludington. "Porphyry Copper Potential of the United States Southern Basin and Range Using ASTER Data Integrated with Geochemical and Geologic Datasets to Assess Potential Near-Surface Deposits in Well-Explored Permissive Tracts." Economic Geology 114, no. 6 (September 1, 2019): 1095–121. http://dx.doi.org/10.5382/econgeo.4675.
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Abstract ArcGIS was used to spatially assess and rank potential porphyry copper deposits using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data together with geochemical and geologic datasets in order to estimate undiscovered deposits in the southern Basin and Range Province in the southwestern United States. The assessment was done using a traditional expert opinion three-part method and a prospectivity model developed using weights of evidence and logistic regression techniques to determine if ASTER data integrated with other geologic datasets can be used to find additional areas of prospectivity in well-explored permissive tracts. ASTER hydrothermal alteration data were expressed as 457 alteration polygons defined from a low-pass filtered alteration density map of combined argillic, phyllic, and propylitic rock units. Sediment stream samples were plotted as map grid data and used as spatial information in ASTER polygons. Gravity and magnetic data were also used to define basins greater than 1 km in depth. Each ASTER alteration polygon was ranked for porphyry copper potential using alteration types, spatial amounts of alteration, stream sediment geochemistry, lithology, polygon shape, proximity to other alteration polygons, and deposit and prospects data. Permissive tracts defined for the assessment in the southern Basin and Range Province include the Laramide Northwest, Laramide Southeast, Jurassic, and Tertiary tracts. Expert opinion estimates using the three-part assessment method resulted in a mean estimate of 17 undiscovered porphyry copper deposits, whereas the prospectivity modeling predicted a mean estimate of nine undiscovered deposits. In the well-explored Laramide Southeast tract, which contains the most deposits and has been explored for over 100 years, an average of 4.3 undiscovered deposits was estimated using ASTER alteration polygon data versus 2.8 undiscovered deposits without ASTER data. The Tertiary tract, which contains the largest number of ASTER alteration polygons not associated with known Tertiary deposits, was predicted to contain the most undiscovered resources in the southern Basin and Range Province.
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Dube, B., P. Mercier-Langevin, I. Kjarsgaard, M. Hannington, V. Becu, J. Cote, J. Moorhead, M. Legault, and N. Bedard. "The Bousquet 2-Dumagami World-Class Archean Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi, Quebec: Metamorphosed Submarine Advanced Argillic Alteration Footprint and Genesis." Economic Geology 109, no. 1 (November 19, 2013): 121–66. http://dx.doi.org/10.2113/econgeo.109.1.121.
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Voudouris, Panagiotis C. "Hydrothermal corundum, topaz, diaspore and alunite supergroup minerals in the advanced argillic alteration lithocap of the Kassiteres-Sapes porphyry-epithermal system, western Thrace, Greece." Neues Jahrbuch f??r Mineralogie - Abhandlungen: Journal of Mineralogy and Geoche 191, no. 2 (February 1, 2014): 117–36. http://dx.doi.org/10.1127/0077-7757/2014/0251.
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Shirmard, Hodjat, Ehsan Farahbakhsh, Amin Beiranvand Pour, Aidy M. Muslim, R. Dietmar Müller, and Rohitash Chandra. "Integration of Selective Dimensionality Reduction Techniques for Mineral Exploration Using ASTER Satellite Data." Remote Sensing 12, no. 8 (April 16, 2020): 1261. http://dx.doi.org/10.3390/rs12081261.
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There are a significant number of image processing methods that have been developed during the past decades for detecting anomalous areas, such as hydrothermal alteration zones, using satellite images. Among these methods, dimensionality reduction or transformation techniques are known to be a robust type of methods, which are helpful, as they reduce the extent of a study area at the initial stage of mineral exploration. Principal component analysis (PCA), independent component analysis (ICA), and minimum noise fraction (MNF) are the dimensionality reduction techniques known as multivariate statistical methods that convert a set of observed and correlated input variables into uncorrelated or independent components. In this study, these techniques were comprehensively compared and integrated, to show how they could be jointly applied in remote sensing data analysis for mapping hydrothermal alteration zones associated with epithermal Cu–Au deposits in the Toroud-Chahshirin range, Central Iran. These techniques were applied on specific subsets of the advanced spaceborne thermal emission and reflection radiometer (ASTER) spectral bands for mapping gossans and hydrothermal alteration zones, such as argillic, propylitic, and phyllic zones. The fuzzy logic model was used for integrating the most rational thematic layers derived from the transformation techniques, which led to an efficient remote sensing evidential layer for mineral prospectivity mapping. The results showed that ICA was a more robust technique for generating hydrothermal alteration thematic layers, compared to the other dimensionality reduction techniques. The capabilities of this technique in separating source signals from noise led to improved enhancement of geological features, such as specific alteration zones. In this investigation, several previously unmapped prospective zones were detected using the integrated hydrothermal alteration map and most of the known hydrothermal mineral occurrences showed a high prospectivity value. Fieldwork and laboratory analysis were conducted to validate the results and to verify new prospective zones in the study area, which indicated a good consistency with the remote sensing output. This study demonstrated that the integration of remote sensing-based alteration thematic layers derived from the transformation techniques is a reliable and low-cost approach for mineral prospectivity mapping in metallogenic provinces, at the reconnaissance stage of mineral exploration.
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Juliani, Caetano, Rafael Rodrigues de Assis, Lena Virgínia Soares Monteiro, Carlos Marcello Dias Fernandes, José Eduardo Zimmermann da Silva Martins, and Jhoseph Ricardo Costa e Costa. "Gold in Paleoproterozoic (2.1 to 1.77 Ga) Continental Magmatic Arcs at the Tapajós and Juruena Mineral Provinces (Amazonian Craton, Brazil): A New Frontier for the Exploration of Epithermal–Porphyry and Related Deposits." Minerals 11, no. 7 (July 1, 2021): 714. http://dx.doi.org/10.3390/min11070714.
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This review paper aims to integrate geological, tectonic and metallogenetic data, including new data, and propose a regional model for the gold (and base metal) mineralization in the south Amazonian Craton to support the mineral exploration concerning magmatic–hydrothermal deposits. The Proterozoic evolution of the Amazonian Craton comprises the accretion of terrains to the Archean Carajás Mineral Province. In the Tapajós and Juruena mineral provinces, located at the south part of the Amazonian craton, a long-lived ocean–continent subduction event produced ca. 2.0 to 1.77 Ga continental magmatic arcs. Extensive lava flows, volcaniclastic, sedimentary, and plutonic rocks were originated during at least four major orogenic magmatic events (ca. 2.1, 1.9, 1.88, and 1.80 Ga) and two post- to anorogenic events (ca. 1.87 and 1.77 Ga). Gold mineralization occurs in: (i) alluvial/colluvial occurrences, (ii) orogenic carbonate–sulfide-rich quartz veins in shear zones, (iii) stockworks, veins, and dissemination in granites, (iv) contact of basic dikes, (v) well-preserved high-, intermediate- and low-sulfidation epithermal mineralization, and (vi) porphyry-like and intrusion-related gold systems associated with late- to post-orogenic epizonal granites. The estimated historical gold production, mainly in secondary deposits, is over 27 Moz at the Tapajós and 6 Moz at the Juruena provinces. A total resource of over 5 Moz Au is currently defined in several small to large primary gold deposits. Andesite to rhyolite, volcaniclastic, and clastic sedimentary rocks (1.96–1.88 Ga) host epithermal (high-, intermediate-, and low-sulfidation) Au–(Ag–Pb–Zn) mineralization, whereas Au–Cu and Cu–M–Au mineralization is hosted in sub-volcanic tonalitic to granitic plutons. Advanced argillic alteration (alunite, pyrophyllite, enargite) associated with high-sulfidation mineralization occurs in ring volcanoes around nested volcanic calderas. This zone grades outward to propylitic or chlorite alteration, often covered by silica caps with vuggy silica. Lava flows and volcaniclastic rocks within faults or associated with volcanic edifices and rhyolitic domes host low- and intermediate-sulfidation mineralization. Low-sulfidation alteration zones typically have adularia and illite or sericite. Chalcopyrite, sphalerite, galena, pyrite, digenite, and manganiferous calcite are related to intermediate-sulfidation gold mineralization. Late- to post-orogenic evolved oxidized I-type granitoids host alkalic-type epithermal and porphyry-like gold mineralization. Porphyry-style hydrothermal alteration is analogous to those of modern systems, with inner sodic and potassic (potassic feldspar ± biotite or biotite) alterations grading to propylitic, muscovite-sericite, chlorite–sericite, and chlorite alterations. Potassic alteration zones are the locus of Cu–Mo mineralization, and gold-rich zones occur in muscovite/sericite–quartz–pyrite alteration. The Paleoproterozoic epithermal and porphyry-like mineralization in these large provinces defines a new frontier for the exploration of world-class gold deposits in the worldwide Proterozoic arc-related magmatic terrains.
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Allibone, Andrew H., Geoffrey R. Cordery, Gregg W. Morrison, Subhash Jaireth, and Jeffrey W. Lindhorst. "Synchronous advanced argillic alteration and deformation in a shear zone-hosted magmatic hydrothermal Au-Ag deposit at the Temora (Gidginburg) Mine, New South Wales, Australia." Economic Geology 90, no. 6 (October 1, 1995): 1570–603. http://dx.doi.org/10.2113/gsecongeo.90.6.1570.
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