Littérature scientifique sur le sujet « Altered volcanic rock »
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Articles de revues sur le sujet "Altered volcanic rock"
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Friele, Pierre A., et John J. Clague. « Large Holocene landslides from Pylon Peak, southwestern British Columbia ». Canadian Journal of Earth Sciences 41, no 2 (1 février 2004) : 165–82. http://dx.doi.org/10.1139/e03-089.
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Mount Meager massif, the northernmost volcano of the Cascade volcanic belt, has been the site of very large (>107 m3) landslides in the Holocene Epoch. We document two complex landslides at Pylon Peak, one of the peaks of the Mount Meager massif, about 7900 14C and 3900 14C years ago (about 8700 and 4400 calendar years ago). Together, the two landslides displaced ~ 6 × 108 m3 of volcanic rock from the south flank of Pylon Peak into nearby Meager Creek valley. Each landslide consisted of at least two phases, an early debris flow resulting from failure of hydrothermally altered pyroclastic rock at mid levels on the mountain and a later rock avalanche from a higher source. Both debris flows likely traveled down Meager Creek, and preliminary evidence from drilling indicates the 4400-year-old event traveled down Lillooet River into areas that are now settled and where population density is increasing rapidly. The mobility of the debris flows was due to the high content of fine, weathered volcanic sediment and the availability of sufficient water. The causes of the landslides are a wet climate and the presence of weak, hydrothermally altered volcanic rock containing abundant phreatic water on glacially oversteepened slopes. The landslides may have been triggered by earthquakes or by upwelling of magma to shallow depths within the volcano. However, they may also have occurred without specific triggers following extended periods of progressive weakening of the volcanic rocks.
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REYES, AGNES G., WILLIAM J. TROMPETTER et IAN J. GRAHAM. « PROPENSITY FOR MINERALIZATION IN VOLCANOES — EVIDENCE FROM MELT INCLUSIONS ». International Journal of PIXE 22, no 01n02 (janvier 2012) : 157–64. http://dx.doi.org/10.1142/s0129083512400074.
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Rocks and melt inclusions (MI) from 11 volcanic centers of the Kermadec-Tofua arc, in the South West Pacific, were petrographically studied prior to chemical analysis under the ion beam. The abundance of MI with daughter minerals are volcano-specific with the most abundant found in "U", Putoto, and Hinepuia volcanoes where >50% of MI contain daughter minerals. The B , Li , Cl and S contents in MI generally increase with the silica content of the rock. Fe , Ni , Mn , Cu and Zn are common in MI of all rock types but Mo , Hg and Cu have the highest concentrations in dacite-rhyodacites. The highest concentrations of B , Ti , V , Fe , Co and Mo occur in plagioclase MI; S , Ni , Ge and Hg in pyroxene MI; Cl and Li in quartz MI; and Cu , Zn and M in hornblende MI. Different ore-forming components in volcanic rocks can be correlated with rock composition, Cl/S and B/S of the melts, the presence and abundance of mineral sinks for various elements and the occurrence of hydrothermally altered rock at depth and on the seafloor.
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Pe-Piper, Georgia, et David J. W. Piper. « Volcanic ash in the Lower Cretaceous Chaswood Formation of Nova Scotia : source and implicationsGeological Survey of Canada Contribution 20100082. » Canadian Journal of Earth Sciences 47, no 11 (novembre 2010) : 1427–43. http://dx.doi.org/10.1139/e10-078.
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Lignites and coals, because of their low sedimentation rates of terrigenous detritus, may preserve a record of volcanic ash fall. Lignite from the Lower Cretaceous Chaswood Formation in central Nova Scotia was studied to identify whether any volcanic ash is present and can be correlated to known Early Cretaceous volcanism in southeastern Canada and adjacent New England. The bulk mineralogy and geochemistry of lignite and lignitic mudstones was determined by X-ray diffraction and whole-rock geochemical analysis of ashed samples; selected samples were examined by electron microprobe and scanning electron microscope. Much of the terrigenous component of some lignites consists of detrital sediments. In some lignites, distinctive rare earth element patterns are due to leaching from monazite and concentration in organic matter. Some lignites, however, lack illite and (or) quartz indicative of detrital sources, but show unusual abundance of stable high-field-strength elements such as Nb, Ta, and Hf, suggesting a volcanic source. Wood or charcoal fragments appear mineralized and diagenetic talc is present. Most of any ash component has been altered to kaolinite. Bulk composition of original ash ranges from basaltic to rhyolitic and matches chemically with subalkaline volcanic rocks on the SW Grand Banks and Orpheus graben. Coeval volcanic rocks on the U.S. continental margin and the New England–Quebec igneous province are more alkaline. Altered ash in lignite in the lower member of the Chaswood Formation correlates with Neocomian volcanism on the SW Grand Banks; and in the middle and upper members with Aptian–Albian volcanism in Orpheus graben.
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Carrillo-Rosúa, Javier, Iñaki Esteban-Arispe et Salvador Morales-Ruano. « Anion Composition of Apatite in the Au-Cu Epithermal Deposit of Palai-Islica (Almería, SE Spain) as an Indicator of Hydrothermal Alteration ». Minerals 11, no 12 (30 novembre 2021) : 1358. http://dx.doi.org/10.3390/min11121358.
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The Palai-Islica deposit (Almería, SE Spain) is an Au-Cu epithermal deposit hosted in Neogene calc-alkaline andesites and dacites from the Cabo de Gata-Cartagena volcanic belt in the Betic Cordillera. Major element compositions of apatite from Palai-Islica orebody and related hydrothermally altered and unaltered volcanic rock from the region hosting the deposit were obtained to clarify the processes involved in their formation. Apatite in the host volcanic rocks is rich in chlorapatite and hydroxylapatite components (50–57% and 24–36%) and poor in fluorapatite components (12–21%), indicating assimilation processes of cortical Cl-rich material in the magmatic evolution. Apatite in the orebody sometimes has corrosion textures and is mostly fluorapatite (94–100%). Apatite from the hydrothermally altered host rock of the orebody systematically bears signs of corrosion and has variable and intermediate fluorapatite (19–100%), chlorapatite (1–50%), and hydroxylapatite (0–47%) components. The style of zonation and the composition are related to the proximity to the orebody. These features can be interpreted as the result of hydrothermal modification of high Cl, OH-rich volcanic apatites into F-rich apatites. The enrichment of F is related to the intensity of hydrothermal alteration and could therefore constitute a geochemical index of alteration and of mineralization processes.
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Whalen, Joseph B., Neil Rogers, Cees R. van Staal, Frederick J. Longstaffe, George A. Jenner et John A. Winchester. « Geochemical and isotopic (Nd, O) data from Ordovician felsic plutonic and volcanic rocks of the Miramichi Highlands : petrogenetic and metallogenic implications for the Bathurst Mining Camp ». Canadian Journal of Earth Sciences 35, no 3 (1 mars 1998) : 237–52. http://dx.doi.org/10.1139/e97-102.
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Middle Ordovician felsic magmatism contemporaneous with Bathurst Camp Pb-Zn volcanogenic massive sulphide(VMS) deposits consists of strongly altered volcanic to subvolcanic rocks, belonging to the Tetagouche Group, and relativelyunaltered granitoid plutons, which are divided into northern, central, and southern groups within the Miramichi Highlands.Calc-alkalic felsic volcanic rocks and northern plus central plutons have EpsilonNd(T) values ranging from -8.2 to -1.9 and -4.0 to +0.3, respectively. They exhibit within-plate-type volcanic and transitional I- to A-type granite geochemical characteristics.Granitoid rock Delta18O values range from +8.0 to +10.1. Published granitoid rock Pb isotopic compositions overlapunpublished galena data from Bathurst VMS deposits. Field, geochemical, and isotopic evidence indicate that these volcanicand granitoids rocks are consanguineous and mainly derived from Proterozoic orolder infracrustal sources. Alkalic felsic volcanic rocks, and associated alkaline basaltic rocks, are more juvenile (EpsilonNd(T) = +3.2 to +4.2) and were possibly derivedfrom slightly enriched mantle sources. Southern plutons exhibit continental arc-type features. The felsic magmatism and VMS deposits likely formed in an Okinawa-type back-arc basin developed from rifting the Early Ordovician Popelogan continentalarc, of which the southern plutons are remnants. Correlations between pluton groups and volcanic formations indicate that felsic magmatism was erupted through and onto the Miramichi Group. As most felsic volcanic formations lack plutonicequivalents, the Tetagouche Group probably does not represent disrupted slices of an originally conformable stratigraphic section. This supports a model in which thrust slices juxtapose remnants of volcanic centres erupted at different locationswithin a back-arc basin.
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Marantos, I., Th Markopoulos, G. E. Christidis et V. Perdikatsis. « Geochemical characteristics of the alteration of volcanic and volcaniclastic rocks in the Feres Basin, Thrace, NE Greece ». Clay Minerals 43, no 4 (décembre 2008) : 575–95. http://dx.doi.org/10.1180/claymin.2008.043.4.05.
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AbstractThe Tertiary basin of Feres consists of sedimentary rocks, andesitic-rhyolitic volcanic rocks of K-rich calc-alkaline affinities, rocks with calc-alkaline and shoshonitic affinities and volcaniclastic fall and flow deposits. Volcanic and volcaniclastic rocks have variable concentrations of LIL elements (Ba, Sr, Rb, Th) and HFS elements (Zr, V) due to their mode of origin. The pyroclastic flows frequently show more or less intense devitrification, vapour-phase crystallization and, in some cases, evidence of fumarolic activity, as is indicated by the presence of scapolite. The volcanic and volcaniclastic rocks display various types of alteration including formation of zeolites (clinoptilolite, heulandite, mordenite, and laumontite) and smectite, as well as hydrothermal alteration (development of silicic, argillic, sericitic and propylitic zones) associated with polymetallic mineralization. The behaviour of chemical elements during alteration varies. Some are immobile and their distribution is controlled by the conditions prevailing during parent-rock formation and emplacement, but others, such as Ba and Sr, are mobile and selectively fractionate in zeolite extra-framework sites. The formation of zeolite from alteration of volcanic glass is accompanied by an increase in Mg and Al content, and a decrease in Si and Na content, whereas Ca is not affected by alteration. In certain pyroclastic flows, there is a significant difference in K-content between incipient glass and altered rock, due to K-feldspar formation during devitrification and vapour-phase crystallization.
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Chaves, Alexandre, et Luiz Knauer. « Vulcânicas potássicas intemperizadas como protólitos dos filitos hematíticos da Serra do Espinhaço Meridional (Minas Gerais) ». Geochimica Brasiliensis 34, no 2 (21 décembre 2020) : 183–94. http://dx.doi.org/10.21715/gb2358-2812.2020342183.
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The hematitic phyllite is a rock that occurs in the São João da Chapada and Sopa-Brumadinho formations of the southern Espinhaço range. Its origin is widely discussed in papers on Espinhaço, but there is no consensus on its protolith due to certain characteristics of the lithotype, such as its chemical composition and textural features. The pattern of rare earth elements strongly enriched [(La/Yb)N 6.80-17.68], with light rare earth elements [(La/Sm)N 2.54-4.83] richer than heavy ones [(Gd/Yb)N 1.28-3,32], suggests that the protolith was an alkaline volcanic rock formed during the rift that generated the Espinhaço basin. The major elements indicate that the alkaline rock met weathering processes, becoming a regolith. During the Brasiliano metamorphism, it finally became hematitic phyllite. Other characteristics of the lithotype, such as the presence of sericite-bearing rounded parts (possibly formed by alteration and deformation of leucite crystals) and the preservation of igneous layering, suggest a potassic volcanic origin for hematitic phyllite. In diagram that allows identifying altered and metamorphic volcanic rocks, the investigated samples have composition similar to a feldspathoid-rich alkali-basalt, probably a leucite tephrite, a leucitite or even a lamproite, rocks from mantle source.
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Papoulis, D., et P. Tsolis-Katagas. « Formation of alteration zones and kaolin genesis, Limnos Island, northeast Aegean Sea, Greece ». Clay Minerals 43, no 4 (décembre 2008) : 631–46. http://dx.doi.org/10.1180/claymin.2008.043.4.08.
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AbstractKaolin deposits extending over an area of ~10 km2in the western and southern parts of Limnos Island, northeast Aegean Sea, Greece, were studied. The kaolin deposits are alteration products of volcanic rocks, mainly trachytes, trachyandesites, andesites and dacites. Study of the collected samples was carried out using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive scanning electron microscopy (SEM-EDS), Fourier transform Raman spectroscopy (FT-Raman), Fourier transform infrared (FTIR) techniques and inductively-coupled plasma (ICP) bulk rock chemical analyses for major, trace and rare earth elements. The extensive alteration of the parent rocks resulted from the circulation of hydrothermal fluids through faults and fractures. The development of the various assemblages depends not only on the temperature and composition of the hydrothermal fluids but also on the distance of the rock from the fault or the channel of the ascending hydrothermal fluids.Kaolinite, dickite, halloysite, illite, smectite and mixed-layer illite-smectite and jarosite were detected in the altered volcanic rocks forming locally various alteration zones. Smectite-rich zones and illite-rich zones are relatively infrequent. In the halloysite-rich zones, the kaolinization of feldspars is accomplished in four stages. The kaolinizaton of feldspars in the kaolinite-dickite-rich zones follows five discrete stages. In the less altered rocks, thin layers of kaolinite are formed on the surface of feldspars. With increasing kaolinization, kaolinite is developed on the surface of feldspars forming extended parallel booklets of newly formed kaolinite. In the third stage, feldspar crystals are partially altered to kaolinite booklets. As kaolinization advances, kaolinite becomes well formed and, in the most altered rocks, feldspars are partially or completely altered to dickite books, depending on the temperature of the hydrothermal fluids.
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PETCH, C. A. « The Geology and Mineralization of the High Lake Volcanic-hosted Massive Sulfide Deposit, Nunavut ». Exploration and Mining Geology 13, no 1-4 (1 janvier 2004) : 37–47. http://dx.doi.org/10.2113/gsemg.13.1-4.37.
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Abstract The High Lake polymetallic deposit is located in the northern Slave province, 40 km south of Coronation Gulf, Nunavut. The main zone, the AB zone, hosts an estimated resource of 3.56 Mt grading 5.0% copper, 1.1% zinc, 0.06% lead, 1.7 g/t gold, and 18.2 g/t silver. Archean felsic metavolcanic and metavolcaniclastic rocks are the dominant rock type and are associated with lesser mafic metavolcanic and carbonate-rich metasedimentary rocks. The sequence strikes north-northeast, dips steeply to the west, and is truncated to the west by a large granodioritic intrusion. The mineralization at the AB zone is comprised of massive and stringer chalcopyrite-sphalerite-pyrrhotite-pyrite±galena. At the core of the mineralized zone, intensely chlorite-altered rocks are locally metamorphosed to form distinctive zones of anthophyllite-magnetite-cordierite-altered rock. Peripheral to the mineralized core, alteration consists of sericitization, silicification, and weaker chloritization. Primary morphology and facing direction of the zone are difficult to interpret in part due to poor primary metal zonation of the deposit. However, the irregular shape of the mineralized zone and the erratic zones of zinc enrichment at the fringes are consistent with the interpretation that the zone was formed by the replacement of a porous volcaniclastic pile.
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Sell, Bryan Keith, et Scott Douglas Samson. « A tephrochronologic method based on apatite trace-element chemistry ». Quaternary Research 76, no 1 (juillet 2011) : 157–66. http://dx.doi.org/10.1016/j.yqres.2011.03.007.
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AbstractGeochemical correlation of ash-fall beds with conventional tephrochronologic methods is not feasible when original glass composition is altered. Thus, alternative correlation methods may be required. Initial studies of heavily altered Paleozoic tephra (K-bentonites) have suggested the potential for employing trace-element concentrations in apatite as ash-fall bed discriminators. To further test the utility of apatite trace-element tephrochronology, we analyzed apatite phenocrysts from unaltered volcanic rocks with an electron microprobe: nine samples from rocks erupted during the Quaternary and one sample from a rock erupted during the Paleogene. The resulting apatite trace-element data provide unique bed discriminators despite within-crystal variability. Each of the volcanic rocks studied possesses unique trends in Mg, Cl, Mn, Fe, Ce and Y concentrations in apatite. The results from this study establish an important tephrochronologic method that can be applied to nearly all portions of the Phanerozoic stratigraphic record and greatly assist development of an advanced timescale. In addition to establishing a fingerprint for a particular eruption, apatite chemistry provides useful information about the source magma.
Thèses sur le sujet "Altered volcanic rock"
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POLA, VILLASENOR ANTONIO. « Physical and Mechanical characterization of altered volcanic rocks for the stability of volcanic edifices ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2011. http://hdl.handle.net/10281/18917.
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Geomechanical characterisation of altered volcanic rocks and their role in flank volcanoes stability are evaluated in this study. Physical and mechanical properties and their variation with the degree of alteration are described in detailed. A series of multidisciplinary tests were performed to identify and quantify the progressive degradation of the properties. They are as follow: 1) petrographycal and chemical studies (thin-sections, x-ray diffractions and x-ray fluorescence); 2) effective and total porosity (standard test procedure, mercury intrusion porosimetry, pycnometer tests, two-dimensional and x-ray CT image analysis); 3) Ultrasonic pulse velocity measurements; 4) uniaxial compressive tests (with p-wave measurements, cyclic loading); tensile tests (with strain gauge measurements); and 5) triaxial tests (single-stage and multi-stage). Preliminary numerical modelling was mainly focus on the effect of altered rocks content and gravity effects, even if different perturbations such as pore water pressure (e.g. rainfall, vapour and gas), and regional or local tectonics (e.g. faults, earthquakes and dynamic loading) are presented in volcanoes nature.
Collected samples are representative of four different classes of volcanic deposits: i) trachytic lava with abundant crystals; ii) pyroclastic deposits, with lava clasts and pumice elements with different sizes; iii) Green tuff, constructed prevalently by pumice clasts; and iv) ignimbrite deposits characterized by low density. Petrographical and chemical characteristics, in particular weathering indexes reveal large differences not only between lithotypes, but also between samples. These differences are well quantified by physical properties, in particular porosity and shear wave velocity values. Decay of the properties, well represented by regression analysis with significant correlation parameter (R2>85), is observed when average values of the compressive strength, tensile strength and Young’s modulus are compared with the average porosity value, fractal dimension and grade of alteration. Failure of rocks were well documented by the evolution of elastic properties, differences between each lithotype are discussed. Post-failure reconstruction of samples reveals that the nature of deformation is controlled by textural properties (e.g. grains, pores, and cement) and the behaviour strongly influences the response of the specimen. Anisotropy of rocks is clear represented by triaxial tests post-failure reconstruction, abrupt differences between fresh and altered samples are observed. Finally, a simplified 2-D numerical stress‐strain modelling was carried out in order to visualize the effects of rock properties degradation in volcanic flank failure. Modelling was aimed at clarifying the role of the altered volcanic rocks in the evolution of volcano stability. The results, in terms of maximum computed values of shear strain and displacements, show that degradation of rock properties is capable of defining and controlling large zones of instability.
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Chandler, Matthew R. « The Provenance of Eocene Tuff Beds in the Fossil Butte Member of the Green River Formation of Wyoming : Relation to the Absaroka and Challis Volcanic Fields ». Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1517.pdf.
Texte intégralLivres sur le sujet "Altered volcanic rock"
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Keith, Terry E. C. Geochemical data of fumarolically altered rocks, Valley of Ten Thousand Smokes, Alaska. [Reston, Va.] : U.S. Dept. of the Interior, U.S. Geological Survey, 1995.
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Keith, Terry E. C. Geochemical data of fumarolically altered rocks, Valley of Ten Thousand Smokes, Alaska. [Menlo Park, CA] : U.S. Geological Survey, 1995.
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Geological Survey (U.S.), dir. Geochemical data of fumarolically altered rocks, Valley of Ten Thousand Smokes, Alaska. [Reston, Va.] : U.S. Dept. of the Interior, U.S. Geological Survey, 1995.
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Byron, Michael J. Geochemistry and stratigraphic correlation of highly altered volcanic rocks Holloway township, Ontario. [s.l : s.n.], 1990.
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Gifkins, Cathryn. Altered Volcanic Rocks : A Guide to Description and Interpretation. Centre for Ore Deposit Research, 2005.
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Mumin, Abdul-Hamid *. Tectonic and structural controls on massive sulfide deposition in the South Sturgeon Lake volcanic pile, Northwestern Ontario and hydrothermally altered rocks associated with the Lyon Lake archean volcanogenic massive sulfide ore deposits, Sturgeon Lake, Northwestern Ontario. 1988.
Trouver le texte intégralChapitres de livres sur le sujet "Altered volcanic rock"
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Ohta, Takehiro, Shuichi Hattori, Yoshihiro Kikuchi et Dai Shimofusa. « Experimental and Numerical Study of the Groundwater Quality in Altered Volcanic Rock Area ». Dans IAEG/AEG Annual Meeting Proceedings, San Francisco, California, 2018 - Volume 4, 89–95. Cham : Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-93133-3_12.
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Pelleter, Ewan, Alain Cheilletz, Abdellah Mouttaqi, Abdelkhalek El Hakour et Gasquet Dominique. « Volcanic sequences, lithostratigraphy and geochemistry of altered rocks at the Jbel Malek deposit : Clues for the origins of a Neoproterozoic gold deposit, High-Atlas, Morocco ». Dans Mineral Deposit Research : Meeting the Global Challenge, 675–78. Berlin, Heidelberg : Springer Berlin Heidelberg, 2005. http://dx.doi.org/10.1007/3-540-27946-6_172.
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Kumar, Naveen, et Naresh Kumar. « Petro-Mineralogical and Geochemical Study of the Acid Magmatic Rocks of Tusham Ring Complex, NW Peninsular India ». Dans Petrology [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.95836.
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The present contribution reports about the field and petrographical observations which are very important to explain the magmatic evolution and geodynamic setting of Tusham Ring Complex (TRC). TRC is associated with A-type acid volcano-plutonic rock-association which is very common characteristics of Neoproterozoic Malani Igneous Suite (MIS). Based on the geological field information, the investigated rock-types are classified as volcanic phase, plutonic phase and dyke phase. Petrographically, rhyolites show porphyritic, granophyric, glomeroporphyritic, aphyritic, spherulitic and perlitic textures whereas granites show hypidomorphic, granophyric and microgranophyric textures. Based on mineral chemistry and whole-rock geochemistry, the petro-mineralogical results are justified and proposed that the rocks under study belong to A-type affinity, within-plate and anorogenic magmatism. Physiochemical features i.e. F and Cl-rich biotite, pegmatite rim, high mineralized veins, micro-granular enclaves and altered mineralogy indicate rock-fluid interactions which are caused by magmatic origin or secondary metasomatic alteration superimposed on the host rock.
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Martí, Joan. « Volcano Geology Applications to Ancient Volcanism-Influenced Terrains : Paleovolcanism ». Dans Updates in Volcanology - Linking Active Volcanism and the Geological Record [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.108770.
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This chapter discusses how to apply the most significant aspects and concepts of modern volcanology to the study the ancient volcanic terrains, where volcanic successions appear exposed in discontinuous outcrops, with various degrees of deformation, which are often manifested in the presence of metamorphosed and hydrothermally altered volcanic rock assemblages. The way to understand paleovolcanism is through the identification and interpretation of the products of past volcanic activity in terms that is equivalent to what is done in modern terrains, despite the difficulty of having to characterize and recompose all those subsequent geological processes that have been superimposed upon them. This chapter summarizes the most fundamental aspects of the study of ancient volcanic terrains, paying special attention to the definition of facies associations, the characterization of their spatial and genetic relationships, and their paleoenvironmental and paleogeographic significance, as well as to the possible causes of the original facies modification. The implications for the presence of volcanism in the dynamics of sedimentary basins and its relationship with different geodynamic environments are also analyzed.
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Juo, Anthony S. R., et Kathrin Franzluebbers. « Mineralogy ». Dans Tropical Soils. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195115987.003.0005.
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Soils are weathering products of rocks and minerals. The rocks in Earth’s outer surface can be classified as igneous, sedimentary, or metamorphic rocks. Igneous rocks are formed from molten magma. They are composed of primary minerals, which are minerals that have not been altered chemically since they formed as molten lava solidified. Examples of primary minerals are the light-colored minerals quartz, muscovite, feldspars, and orthoclase, and the dark-colored minerals biotite, augite, and hornblende. In general, dark-colored minerals contain iron (Fe) and magnesium (Mg) and are more easily weathered than light-colored minerals. Coarse-grained igneous rocks, such as granite and diorite, contain mainly lightcolored minerals, while medium-grained igneous rocks such as gabbro, peridotite, and hornblendite are composed of dark-colored primary minerals. Rhyolite and andesite are medium-grained igneous rocks containing light-colored primary minerals. Basalt is dark-colored with an intermediate to fine rock texture, and basaltic volcanic glass has a fine texture. Examples of light-colored igneous rocks with a fine texture are felsite and obsidian. Sedimentary rocks are the most common type of rock, covering about 75% of Earth’s land surface. They are mainly composed of secondary minerals, which are minerals that are recrystallized products of the chemical breakdown and/or alteration of primary minerals. Sedimentary rocks form when weathering products from rocks are cemented or compacted. For example, quartz (SiO2) sand, a weathering product of granite, may become cemented into sandstone. Another common sedimentary rock is limestone. There are two types of limestone, namely, calcite (CaCO3), and dolomite (CaCO3.MgCO3). Clays may become cemented into a sedimentary rock, which is known as shale. A sedimentary rock with several dominant minerals is called a conglomerate, in which small stones with different mineralogy are cemented together. Metamorphic rocks are formed by the metamorphism of igneous or sedimentary rocks. Great pressure and high temperatures, caused by the shifting of continental plates, can compress, distort, and/or partially re-melt the original rocks. Igneous rocks are commonly modified to form schist and gneiss, in which light and dark minerals have been reoriented into bands. Sedimentary rocks, such as limestone and shale, may be metamorphosed to form marble and slate, respectively.
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Gvozdeva, I. P., et O. V. Zerkal. « Hydrothermally altered rocks as a field of dangerous slope processes (the Geysers Valley, Kamchatka peninsula, Russia) ». Dans Volcanic Rocks and Soils, 101–2. CRC Press, 2015. http://dx.doi.org/10.1201/b18897-9.
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Simmons, Stuart F., Benjamin M. Tutolo, Shaun L. L. Barker, Richard J. Goldfarb et François Robert. « Chapter 38 : Hydrothermal Gold Deposition in Epithermal, Carlin, and Orogenic Deposits ». Dans Geology of the World’s Major Gold Deposits and Provinces, 823–45. Society of Economic Geologists, 2020. http://dx.doi.org/10.5382/sp.23.38.
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Abstract Epithermal, Carlin, and orogenic Au deposits form in diverse geologic settings and over a wide range of depths, where Au precipitates from hydrothermal fluids in response to various physical and chemical processes. The compositions of Au-bearing sulfidic hydrothermal solutions across all three deposit types, however, are broadly similar. In most cases, they comprise low-salinity waters, which are reduced, have a near-neutral pH, and CO2 concentrations that range from <4 to >10 wt %. Experimental studies show that the main factor controlling the concentration of Au in hydrothermal solutions is the concentration of reduced S, and in the absence of Fe-bearing minerals, Au solubility is insensitive to temperature. In a solution containing ~300 ppm H2S, the maximum concentration of Au is ~1 ppm, representing a reasonable upper limit for many ore-forming solutions. Where Fe-bearing minerals are being converted to pyrite, Au solubility decreases as temperature cools due to the decreasing concentration of reduced S. High Au concentrations (~500 ppb) can also be achieved in strongly oxidizing and strongly acidic chloride solutions, reflecting chemical conditions that only develop during intense hydrolytic leaching in magmatic-hydrothermal high-sulfidation epithermal environments. Gold is also soluble at low to moderate levels (10–100 ppb) over a relatively wide range of pH values and redox states. The chemical mechanisms which induce Au deposition are divided into two broad groups. One involves achieving states of Au supersaturation through perturbations in solution equilibria caused by physical and chemical processes, involving phase separation (boiling), fluid mixing, and pyrite deposition via sulfidation of Fe-bearing minerals. The second involves the sorption of ionic Au on to the surfaces of growing sulfide crystals, mainly arsenian pyrite. Both groups of mechanisms have capability to produce ore, with distinct mineralogical and geochemical characteristics. Gold transport and deposition processes in the Taupo Volcanic Zone, New Zealand, show how ore-grade concentrations of Au can accumulate by two different mechanisms of precipitation, phase separation and sorption, in three separate hydrothermal environments. Phase separation caused by flashing, induced by depressurization and associated with energetic fluid flow in geothermal wells, produces sulfide precipitates containing up to 6 wt.% Au from a hydrothermal solution containing a few ppb Au. Sorption on to As-Sb-S colloids produces precipitates containing tens to hundreds of ppm Au in the Champagne Pool hot spring. Sorption on to As-rich pyrite also leads to anomalous endowments of Au of up to 1 ppm in hydrothermally altered volcanic rocks occurring in the subsurface. In all of these environments, Au-undersaturated solutions produce anomalous concentrations of Au that match and surpass typical ore-grade concentrations, indicating that near-saturated concentrations of dissolved metal are not a prerequisite for generating economic deposits of Au. The causes of Au deposition in epithermal deposits are related to sharp temperature-pressure gradients that induce phase separation (boiling) and mixing. In Carlin deposits, Au deposition is controlled by surface chemistry and sorption processes on to rims of As-rich pyrite. In orogenic deposits, at least two Au-depositing mechanisms appear to produce ore; one involves phase separation and the other involves sulfidation reactions during water-rock interaction that produces pyrite; a third mechanism involving codeposition of Au-As in sulfides might also be important. Differences in the regimes of hydrothermal fluid flow combined with mechanisms of Au precipitation play an important role in shaping the dimensions and geometries of ore zones. There is also a strong link between Au-depositing mechanisms and metallurgical characteristics of ores.
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Sa\'ad ZA Kader, Al-Mashaikie. « Abnormal Ophiolite (Olivine/Pyroxene Rich) Sandstone NE Iraq : An Approach to the Origin and Tectonosedimentary Evolution of Zagros Foreland Basin ». Dans New Insights in Sedimentary Rocks [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.108333.
Texte intégralRésumé :
Unusual Paleocene ophiolite sandstone rich in olivine/pyroxene identified in Zagros Thrust Belt (NZTB) in NE Iraq. NZTB is regionally extended from Iran to Alpen Belt. Kolosh sandstones are controlled by progressive thrusting during late Cretaceous-Paleocene. Zagros thrust sheets composed of ophiolites, oceanic crust, basaltic flows, and ash sequences. Kolosh sandstones reveal high percentages of fresh olivine-pyroxene grains accompanied by igneous intrusive and volcanic ultrabasic-basic fragments, which are reported for the first time in NE Iraq and along ZTB. Olivine, pyroxene, ultrabasic igneous altered, serpentine and chlorite fragments, heavy minerals (includes chrome spinal), anorthite, and labradorite all together composed about 70% of the mineralogical composition. Sanidine, anorthoclase, quartz and cristobalite, argillaceous, carbonate and chert fragments all together composed (12.25%), supported by argillaceous matrix (16.53%), which are derived from mantle and oceanic crust/ophiolite sequences from NE Iraq, emplaced during late Cretaceous with arc volcanism, which subjected to rapid submarine erosion and deposition. Intense wave action accelerated the erosion of beach rocks, and concentrate the heavy minerals insitue that slumped to deeper margins. Identified lithofacies types, grouped in four associations, slope/submarine channel, inner, outer fan, and hemipelagic/pelagic, respectively, represented progressive upward transgression from slope to basin plain systems controlled by progressive thrusting.
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Baker, T., S. Mckinley, S. Juras, Y. Oztas, J. Hunt, L. Paolillo, S. Pontual, M. Chiaradia, A. Ulianov et D. Selby. « Chapter 23 : Alteration, Mineralization, and Age Relationships at the Kışladağ Porphyry Gold Deposit, Turkey ». Dans Geology of the World’s Major Gold Deposits and Provinces, 467–95. Society of Economic Geologists, 2020. http://dx.doi.org/10.5382/sp.23.23.
Texte intégralRésumé :
Abstract The Miocene Kışladağ deposit (~17 Moz), located in western Anatolia, Turkey, is one of the few global examples of Au-only porphyry deposits. It occurs within the West Tethyan magmatic belt that can be divided into Cretaceous, Cu-dominant, subduction-related magmatic arc systems and the more widespread Au-rich Cenozoic magmatic belts. In western Anatolia, Miocene magmatism was postcollisional and was focused in extension-related volcanosedimentary basins that formed in response to slab roll back and a major north-south slab tear. Kışladağ formed within multiple monzonite porphyry stocks and dikes at the contact between Menderes massif metamorphic basement and volcanic rocks of the Beydağı stratovolcano in the Uşak-Güre basin. The mineralized magmatic-hydrothermal system formed rapidly (<400 kyr) between ~14.75 and 14.36 Ma in a shallow (<1 km) volcanic environment. Volcanism continued to at least 14.26 ± 0.09 Ma based on new age data from a latite lava flow at nearby Emiril Tepe. Intrusions 1 and 2 were the earliest (14.73 ± 0.05 and 14.76 ± 0.01 Ma, respectively) and best mineralized phases (average median grades of 0.64 and 0.51 g/t Au, respectively), whereas younger intrusions host progressively less Au (Intrusion 2A: 14.60 ± 0.06 Ma and 0.41 g/t Au; Intrusion 2 NW: 14.45 ± 0.08 Ma and 0.41 g/t Au; Intrusion 3: 14.39 ± 0.06 and 14.36 ± 0.13 Ma and 0.19 g/t Au). A new molybdenite age of 14.60 ± 0.07 Ma is within uncertainty of the previously published molybdenite age (14.49 ± 0.06 Ma), and supports field observations that the bulk of the mineralization formed prior to the emplacement of Intrusion 3. Intrusions 1 and 2 are altered to potassic (biotite-K-feldspar-quartz ± magnetite) and younger but deeper sodic-calcic (feldspar-amphibole-magnetite ± quartz ± carbonate) assemblages, both typically pervasive with disseminated to veinlet-hosted pyrite ± chalcopyrite ± molybdenite and localized quartz-feldspar stockwork veinlets and sodic-calcic breccias. Tourmaline-white mica-quartz-pyrite alteration surrounds the potassic core both within the intrusions and outboard in the volcanic rocks. Tourmaline was most strongly developed on the inner margins of the tourmaline-white mica zone, particularly along the Intrusion 1 volcanic contact where it formed breccias and veins, including Maricunga-style veinlets. Field relationships show that the early magmatic-hydrothermal events were cut by Intrusion 2A, which was then overprinted by Au-bearing argillic (kaolinite-pyrite ± quartz) alteration, followed by Intrusion 3 and late-stage, low-grade to barren argillic and advanced argillic alteration (quartz-pyrite ± alunite ± dickite ± pyrophyllite). Gold deportment changes with each successive hydrothermal event. The early potassic and sodic-calcic alteration controls much of the original Au distribution, with the Au dominantly deposited with feldspar and lesser quartz and pyrite. Tourmaline-white mica and argillic alteration events overprinted and altered the early Au-bearing feldspathic alteration and introduced additional Au that was dominantly associated with pyrite. Analogous Au-only deposits such as Maricunga, Chile, La Colosa, Colombia, and Biely Vrch, Slovakia, are characterized by similar alteration styles and Au deportment. The deportment of Au in these Au-only porphyry deposits differs markedly from that in Au-rich porphyry Cu deposits where Au is typically associated with Cu sulfides.
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Adam, L., et C. Massiot. « Data report : in situ elastic properties of hydrothermally altered volcanic rocks, IODP Expedition 376, Brothers volcano, Kermadec arc ». Dans Volume 376 : Brothers Arc Flux. International Ocean Discovery Program, 2022. http://dx.doi.org/10.14379/iodp.proc.376.201.2022.
Texte intégralActes de conférences sur le sujet "Altered volcanic rock"
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Catalina, Sanchez Roa, Mahzari Pedram, Mitchell Tom, Snaebjornsdottir Sandra Osk, Sigfusson Bergur, Meredith Phil, Oelkers Eric, Jones Adrian et Striolo Alberto. « Understanding Fluid-Rock Interactions in Hydrothermally Altered Rocks of the Hengill Volcano, Iceland : Implications for Geothermal Energy and CO2 Storage ». Dans Goldschmidt2020. Geochemical Society, 2020. http://dx.doi.org/10.46427/gold2020.338.
Texte intégralRapports d'organisations sur le sujet "Altered volcanic rock"
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Schetselaar, E. M., G. Bellefleur et P. Hunt. Integrated analyses of density, P-wave velocity, lithogeochemistry, and mineralogy to investigate effects of hydrothermal alteration and metamorphism on seismic reflectivity : a summary of results from the Lalor volcanogenic massive-sulfide deposit, Snow Lake, Manitoba. Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/327999.
Texte intégralRésumé :
We present herein a summary of integrated data analyses aimed at investigating the effects of hydrothermal alteration on seismic reflectivity in the footwall of the Lalor volcanogenic massive-sulfide (VMS) deposit, Manitoba. Multivariate analyses of seismic rock properties, lithofacies, and hydrothermal alteration indices show an increase in P-wave velocity for altered volcanic and volcaniclastic lithofacies with respect to their least-altered equivalents. Scanning electron microscopy-energy dispersive X-ray spectrometry analyses of drill-core samples suggest that this P-wave velocity increase is due to the high abundance of high P-wave velocity aluminous minerals, including cordierite, Fe-Mg amphibole, and garnet, which in volcanic rocks are characteristic of VMS-associated hydrothermal alteration metamorphosed in the amphibolite facies. A seismic synthetic profile computed from a simple amphibolite-facies mineral assemblage model, consisting of mafic-felsic host rock contacts, a sulfide ore lens, and a discordant hydrothermal conduit, show enhanced seismic reflections at conduit-host rock contacts in comparison to the equivalent greenschist facies mineral assemblage model. Collectively our results suggest that VMS footwall hydrothermal alteration zones metamorphosed under middle- to upper-amphibolite facies conditions have enhanced potential for seismic detection.
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Boily-Auclair, É., P. Mercier-Langevin, P. S. Ross et D. Pitre. Alteration and ore assemblages of the LaRonde Zone 5 (LZ5) deposit and Ellison mineralized zones, Doyon-Bousquet-LaRonde mining camp, Abitibi, Quebec. Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/329637.
Texte intégralRésumé :
The LaRonde Zone 5 (LZ5) mine is part of the Doyon-Bousquet-LaRonde mining camp and is located in the southern part of the Abitibi greenstone belt in northwestern Quebec. The LZ5 deposit consists of three stacked mineralized corridors: Zone 4, Zone 4.1, and Zone 5. Zones 4 and 4.1 are discontinuous satellite mineralized corridors, whereas Zone 5 represents the main mineralized body. The mineralized zones of the LZ5 deposit and adjacent Ellison property (Ellison A and B zones) are hosted in the strongly-deformed, 2699-2695 Ma transitional to calcalkaline, intermediate to felsic, volcanic and volcaniclastic rocks of the Bousquet Formation upper member, which is part of the Blake River Group (2704-2695 Ma). Zones 4, 4.1, and 5 at the LZ5 mine are hosted in intermediate volcanic and volcaniclastic rocks of the Westwood andesitic to rhyodacitic unit (unit 5.1a), which forms the base of the upper member of the Bousquet Formation. The Ellison Zone A is hosted higher up in the stratigraphic sequence within a newly described intermediate volcanic unit. The Ellison Zone B is hosted in felsic volcanic and volcaniclastic rocks of the Westwood feldsparphyric rhyolite dome (subunit 5.3a-(b)). Mineralization in all three zones of the LZ5 deposit consists of discordant networks of millimeter- to centimeter-thick pyrite ±chalcopyrite ±sphalerite ±pyrrhotite veins and veinlets (10-20 % of the volume of the rock) and, to a lesser extent, very finely disseminated pyrite and boudinaged veins (less than or equal to 5 vol. % each) in strongly altered host rocks. Gold commonly occurs as microscopic inclusions in granoblastic pyrite and at the triple junction between recrystallized grains. The veins, stockworks, and disseminations were intensely folded and transposed in the steeply south-dipping, east-west trending S2 foliation. The vein network is at least partly discordant to the stratigraphy. A distal alteration halo envelops the LZ5 mineralized corridors and consists of a sericite-carbonate-chlorite- feldspar ±biotite assemblage. A proximal sericite-carbonate-chlorite-pyrite-quartz- feldspar-biotite ±epidote alteration assemblage is present within the LZ5 mineralized zones. A local proximal alteration assemblage of sericite-quartz-pyrite is also locally developed within Zone 4 and Zone 5 of the LZ5 deposit. Mass gains in Fe2O3 (t) and K2O, and mass losses in CaO, MgO, Na2O, and locally SiO2, are characteristic of the LZ5 alteration zones. The Ellison zone A and B are similar to LZ5 in terms of style of mineralization, but thin (10-20 cm) veins or bands of semi-massive to massive, finely recrystallized disseminated pyrite (0.1-1 mm) are distinctive. Chalcopyrite and sphalerite are also slightly more abundant in the mineralized corridors of the Ellison property and are usually associated with elevated gold grades. The zones are also slightly richer than at LZ5 in terms of gold and silver content, but narrower and less continuous in general. The Ellison Zone A is characterized by gains in Fe2O3 (t) and K2O and losses in CaO, MgO, Na2O, and SiO2. Gains in Fe2O3 (t) and local gains in K2O, MgO, and MnO, and losses in CO2, Na2O, P2O5, and SiO2, characterize the felsic host rocks of the Zone B corridor. The style of mineralization at LZ5 (pyrite ±chalcopyrite veins and veinlets, ±disseminated pyrite with low base metal content), its setting (i.e. in rocks of intermediate composition at the base of the upper member of the Bousquet Formation), and the geometry of its ore zones (stacked lenses of sulfide veins and veinlets, without massive sulfide lenses) differ from the other major deposits of the Doyon-Bousquet-LaRonde mining camp. Despite these differences, this study indicates that the LZ5 and Ellison mineralized corridors are of synvolcanic hydrothermal origin and have most likely been formed by convective circulation of seawater below the seafloor. An influx of magmatic fluids from the Mooshla synvolcanic intrusive complex or its parent magma chamber could explain the Au enrichment at LZ5, as has been suggested for other deposits of the camp. Evidence for a pre-deformation synvolcanic mineralization at LZ5 includes ductile deformation and recrystallization of the sulfides, the stacked nature of its ore zones, subconcordant alteration halos that envelop the mineralized corridors, evidence that the mineralized system was already active when the LZ5 lenses were deposited and control on mineralization by primary volcanic features such as the permeability and porosity of the volcanic rocks.
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Lentz, D. R., et W. D. Goodfellow. Petrology and geochemistry of altered volcanic and sedimentary rocks associated with the FAB stringer sulphide zone, Bathurst, New Brunswick. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1994. http://dx.doi.org/10.4095/193861.
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