Hydrothermal Alteration Processes Research Articles

Hydrothermal alteration processes at midocean ridges: Experimental and theoretical constraints from Ca and Sr exchange reactions and Sr isotopic ratios

Diabase and basalt were reacted with Na‐Ca‐K‐Cl fluids of seawater chlorinity at 375–425°C, 375–400 bars, and fluid/rock mass ratios of 0.5–1.0 to assess the role of basalt chemistry and texture on Sr and Ca mobility during high‐temperature hydrothermal alteration. An additional experiment, utilizing an 84Sr spiked fluid, was performed to help quantify reaction rates of processes affecting Sr mobility. The experimental results help to constrain reaction processes responsible for the chemistry of hot spring fluids at midocean ridges. Alteration of basalt and diabase is characterized by formation of tremolite‐actinolite‐smectite‐chlorite and clinozoisitic epidote‐smectite‐chlorite, respectively. Diabase alteration produced dissolved Sr/Ca ratios similar to those observed for ridge crest hot spring fluids, whereas alteration of a mostly crystalline basalt produced significantly lower ratios. This observation supports the premise that the Sr/Ca ratios observed in vent fluids may be produced during deep‐seated reaction of the hydrothermal fluids with diabase dikes and/or gabbro at relatively low fluid/rock ratios and suggests that hydrothermal alteration of primary igneous minerals at relatively high temperatures (400°C) leads to formation of a mineral with low DSr/Ca, Possibly hydrothermal plagioclase. Results of the 84Sr spiked experiment indicated that only 4% of the Sr in basalt was mobilized after 800 hours of reaction despite the fact that B and Li were nearly quantitatively leached. It is thus suggested that B and Li are good indicators of the amount of fresh rock encountered by fluids, while Sr concentration and isotopic data can be used to estimate the degree of alteration that the Sr‐bearing primary minerals have undergone. The degree of alteration of subsurface reservoirs may be estimated by dividing the fluid/rock ratio obtained for highly mobile elements by the fluid/rock ratio obtained from path‐integrated Sr isotope and concentration data. Based on this method, for example, it can be estimated that only 5% of the primary Sr‐bearing minerals encountered by fluids in the subsurface at EPR 21°N are actually converted to secondary phases.

EVOLUÇÃO MINERALÓGICA DOS JACUPIRANGUITOS DE JACUPIRANGA (SP) DURANTE A ALTERAÇÃO INTEMPÉRICA

Samples were collected from a weathering profile developed above pyroxenites belonging to the alkaline massif of Jacupiranga. The primary minerals titanoaugite, magnetite, perovskite, phlogopite, and olivine - were first partially transformed by a hydrothermal alteration process and the completely altered by weathering. The earlier products of the supergene alteration of the pyroxenites -are smectites; these minerals change into kaolinite and goethite which are the principal components of the lateritic cover. This paper deals with micromorphological aspects of these transformations.

EVOLUÇÃO MINERALÓGICA DOS JACUPIRANGUITOS DE JACUPIRANGA (SP) DURANTE A ALTERAÇÃO INTEMPÉRICA

Samples were collected from a weathering profile developed above pyroxenites belonging to the alkaline massif of Jacupiranga. The primary minerals titanoaugite, magnetite, perovskite, phlogopite, and olivine - were first partially transformed by a hydrothermal alteration process and the completely altered by weathering. The earlier products of the supergene alteration of the pyroxenites -are smectites; these minerals change into kaolinite and goethite which are the principal components of the lateritic cover. This paper deals with micromorphological aspects of these transformations.

Mineralogía y Geotermometría de los diques ácidos con grafito asociados a rocas ultramáficas de la Serranía de Ronda. Málaga

A geological, mineralogical and geothermometrical study of a group of acidic graphitebearing dikes from the Ronda ultramafic massif (Malaga province) has been carried out. These dikes are hosted in serpentinized peridotites and they appear near the eastern and southern contacts of the massif. On the basis of their mineralogical features, two rock types have been distinguished, since they show or not hydrothermal alteration processes. Unaltered dikes present a mineral association composed by cordierite, garnet, quartz, biotite, graphite, Fe·Ti oxides, sulfides and minor amounts of plagioclase, sillimanite, hercynite and zircon. In the hydrothermally transformed dikes, this original mineral assemblage has been more or less erased, occuring pinitization of cordierite, chloritization of garnet and biotite, and ilmenite is transformed to Ieucoxene. Graphite is a main mineral in both the unaltered and transformed dikes, ranging their abundance about 15%. The geothermometrical study has been done using the biotite-garnet pair and the value of graphite c parameter. The estimated temperatures are clase to 800o C, that are in good agreement with the given temperature for the emplacement of the ultramafic body. From all these data, formation of the dikes by anateetic partial melting of the sedimentary wall rocks (belonging to the Blanca Unit), in presence of a CO 2 - and CH 4 rich fluid that migrated from the metamorphosed sediments towards low pressure fractures zones inside the peridotite massif, is proposed.

The characteristics and significance of secondary magnetite in a profile through the dike component of the Troodos, Cyprus, ophiolite

Secondary magnetite (SM) is the dominant Fe–Ti oxide over a 3–4 km thick vertical interval in a profile through the Troodos, Cyprus, ophiolite. SM is important in dikes and flows where dike density exceeds about 30% within the transition from extrusives to sheeted dikes and remains important until dike density falls below about 30% in the transition from sheeted dikes to plutonics. The association of SM with high dike density suggests that it is a product of the thermal metamorphism of hydrothermally metamorphosed dikes and flows. The most common occurrence of SM is at the site of primary titanomagnetites that had been altered earlier through deuteric, low-temperature, and regional hydrothermal alteration processes. SM often closely pseudomorphs the form of primary magnetite (PM) grains, but it can be distinguished from PM using a series of criteria. SM is low in TiO2 and other impurities. Estimated and observed Curie temperatures are undistinguishable, which, combined with optical evidence, indicates that SM is probably approximately stoichiometric.SM may also be present at depth in in situ oceanic crust, in other ophiolites, and in other hydrothermally altered volcanic sequences where the density of minor intrusions is sufficiently high.The formation of SM leads to the annealing of the features of altered PM that provide the ability to retain strong, stable remanent magnetization. In appropriate combinations of the timing of formation of SM and of geomagnetic field reversals, the different parts of a volcanic sequence may be magnetized with opposite polarities.

Experimental and Theoretical Constraints on Hydrothermal Alteration Processes at Mid-Ocean Ridges

Experimental and Theoretical Constraints on Hydrothermal Alteration Processes at Mid-Ocean Ridges

Characteristics of fluid inclusions in the porphyry copper deposit at La Granja, Peru

At La Granja, Northern Peru, a granodiorite porphyry of probably Mid-Tertiary age intruded into an Upper Triassic to Lower Tertiary volcano-sedimentary sequence. It was followed by intensive hydrothermal alteration and cogenetic mineralization processes which influenced the intrusive body as well as its sedimentary cover and host rocks, producting hydrothermal alteration assemblages typical of porphyry Cu deposits (potassic, propylitic, phyllic, advanced argillic, silicic). The investigation of fluid inclusions showed that: (1) generally three types of fluid inclusions can be distinguished. Apparently coexisting vapour- and liquid-rich inclusions are taken as evidence for boiling in the hydrothermal system; and (2) the overall abundance of different inclusion types correlates well with different alteration types. The microthermometric data obtained fit well into the published range for other Cu porphyry deposits. Together with the petrographic data the following model of fluid and alteration development is proposed: Highly saline fluids of probably magmatic origin developed - possibly by dilution - towards a boiling system of moderate salinity, producing potassic alteration centers surrounded by propylitic alteration and/or skarnification. A younger low-salinity fluid regime affected the centers by overprinting phyllic and/or advanced argillic alteration. Silicification partly occurred during the latest stage of hydrothermal activity. Possible practical aspects of the fluid inclusion investigations are discussed.

African anorogenic alkaline magmatism and mineralization — a discussion with reference to the Niger-Nigerian Province

The close of the Pan-African was characterized by a change from subduction and arc related magmatism to post tectonic alkaline magmatism in Saudi Arabia and West Africa. For the remainder of the Phanerozoic, folding and tectonism was more restricted in Africa than on any other continent and was limited to the Caledonian, Hercynian and Alpine orogenies in the extreme north, and the Cape fold belt at the southern tip of the continent, with an equivalent orogenic belt on the extreme east of the Arabian peninsula. Thus Phanerozoic magmatism was dominantly anorogenic in nature and alkaline in character throughout the African Plate. Such magmatism was initiated by reactivation of deep-seated lineaments with the peak of activity during the Mesozoic, which can be correlated with fragmentation of Gondwanaland. The Phanerozoic alkaline magmatism is characterised by small centres of subvolanic to plutonic nature often in the form of ring complexes. These can be subdivided into two separate associations consisting of Provinces dominated by centres of oversaturated magmatism such as Nigeria and Sudan. There are also provinces with undersaturated complexes and carbonatites with oversaturated magmatism such as in Namibia, Angola, and the East African rift system. Despite the contrasting nature of undersaturated and oversaturated magmatism many comparisons can be drawn between carbonatites and granitic complexes. Such comparisons include the source of the magmas, the mechanisms of emplacement, the cause and effect of alkali metasomatism and processes of hydrothermal alteration, the trace element geochemistry, the abundance of zircon, uranium, thorium and complex Ti-Zr silicates, the importance of columbite, pyrochlore, fluorine, and rare earth enrichment in mineralization, and in their current and future economic potential. The common feature is the development and reactivation of deep-seated lineaments which were not only controlled the emplacement of anorogenic complexes but also acted as channelways for hydrothermal mineralizing fluids. The development of a fluid phase during crystallisation occurred in both undersaturated and oversaturated alkaline rocks. Subsequent hydrothermal modifications, subsolidus reactions, geochemical variations and mineralization were dependent upon whether this fluid phase was retained or expelled.

Experimental And Theoretical Constraints On Hydrothermal Alteration Processes At Mid-Ocean Ridges

Experimental And Theoretical Constraints On Hydrothermal Alteration Processes At Mid-Ocean Ridges

Element mobility studies of two drill-cores from the Götemar Granite (Kråkemåla test site), southeast Sweden

A pilot study was carried out on two relatively deep drill-cores (∼ 600 m) from the Götemar Granite massif in S.E. Sweden. This granite is typical of the 1400-Ma anorogenic granites of the northern hemisphere. Samples from representative, unfractured parts of the cores, together with four samples taken along a profile tangential to a fracture plane at ∼ 280-m depth, were investigated chemically, mineralogically and isotopically. The results show that after crystallisation, subtle and pervasive open-system modifications of the trace-element chemistry of the granite took place. Whereas the major-element chemistry and minera-logical data emphasised the relative homogeneity of the Götemar Granite samples investigated, trace elements such as U, Rb, and Pb revealed irregular distributions which are probably the result of large-scale hydrothermal alteration processes. This conclusion is supported by isotopic studies which indicate that whole-rock samples were open to a gain or loss of Pb and possibly U at ∼ 420 ± 171 Ma ago. In addition, isotopic data for U-Pb and U-Ra are consistent with a recent minor loss of U. The pervasive alteration and the more recent mobilisation of U are evident to a depth of at least 600 m. The effects are most prevalent along major fracture zones and within the upper 250–300 m of one drill-hole where a high frequency of crush zones has been noted. Higher Fe oxidation ratios, higher Rb contents, lower U contents and correspondingly higher Th/U ratios, all characterise this zone.

Mass transfer in hydrothermal alteration systems—A conceptual approach

At very low fluid/rock mass ratios the hydrothermal alteration process corresponds to isochemical recrystallisation of the primary rock. The resulting full equilibrium assemblage with the composition of an average crustal rock contains the phases albite, K-feldspar, K-mica, biotite, quartz and (depending on temperature) epidote, prehnite or one of the Ca-zeolites. Relative Na +, K +, Mg 2+ and Ca 2+—solution activities in such a rock-dominated alteration system are uniquely fixed and provide useful reference points with regard to the degree of attainment of full fluid/rock equilibrium. With increasing fluid/rock mass ratios the composition of now increasingly fluid-dominated alteration assemblages is determined by the interplay of three major processes: hydrogen metasomatism as a function of CO 2 reactivity increasing with the horizontal distance from major fluid upflow zones and leading to the formation of Al-enriched alteration assemblages; potassium metasomatism accompanied by silicification in or close to major fluid upflow zones leading to potassic and phyllic alteration; sodium, magnesium, calcium metasomatism associated with descending and heating solutions leading to propylytic alteration of recharge zones. Two new parameters, reactivity and exchangeability, determining the effectiveness of fluid components with respect to hydrothermal alteration are introduced.

Europium redox equilibria in aqueous solution

Thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous Eu 2+ and Eu 3+ over a wide range of temperatures and pressures. At low temperatures, near earth surface conditions, the aqueous geochemistry of europium should be dominated by the trivalent state, except possibly in the most reducing, alkaline pore waters of anoxic marine sediments. However, at temperatures greater than about 250°C and elevated pressures, divalent europium should predominate. Even with significant amounts of complexing, trivalent europium is not stable at elevated temperatures and pressures. Consequently, under most hydrothermal and metamorphic conditions, europium in aqueous solution should be divalent. At intermediate temperatures, around 100°C, significant activities of both Eu 2+ and Eu 3+, and related complexes, can occur in aqueous solutions, depending on the oxidation state and the pH of the solutions, and the activities of potential ligands such as sulfate, carbonate and chloride. The predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high-temperature barites of hydrothermal and metamorphic origin reported by Guichard et al. [5] and with the observed depletion of europium as a result of high-temperature sericitization of feldspar-bearing assemblages discovered by Alderton et al. [1]. It is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high-temperature hydrothermal alteration processes, such as in the mid-oceanic ridge systems, because of the expected stability of divalent europium during these processes.

Mineralogy and stable isotope geochemistry of hydrothermally altered oceanic rocks

Mineralogical and isotopic variations observed in altered glassy and crystalline rocksfrom the East Pacific Rise and the Mid-Atlantic Ridge provide information about the temperatures of alteration and seawater/rock ratios for various hydrothermal regimes within the oceanic crust. A systematic increase in alteration temperature is evident for the glassy rocksin the sequence: (1) nontronite and celadonite vesicle fillings (35°C), (2) saponite-rich pillow breccias ( 130–170°C), (3) calcite-rich greenstone breccias and epidote-rich greenstone (200–350°C). Theseresults include the highest temperatures thus far reported for saponite formation. The “seawater-dominated” hydrothermal alteration process that formed the saponite-rich pillow breccias is characterized by high water/rock ratios (>0:1), low to moderate temperatures, a seawater origin of most of the carbon in vein calcites (δ 13 C≈0) and the predominance of Fe-rich saponite and calcite as secondary phases. Greenstones (chlorite-quartz-epidote) and greenstone breccias (chlorite-quartz-albite-calcite) are altered in a “rock-dominated” system with lower water/rock ratios (50:1 to 13 C≈−4). The crystalline rocks (diabase, gabbro, and metagabbro) are affected to varying degrees by pervasive high-temperature seawater interactions that commence soon after solidification, producing varying proportions of fine-grained secondary minerals including talc, smectite, chlorite, vermiculite, actinolite, and sodicplagioclase. Hydrothermal solutions, derived from alteration of the crystalline rocks, are of the appropriate temperature and isotopic composition to alter the overlying glassy rocks to the observed mineralogies as well as being the source of metal-rich deposits associated with the oceanic spreading centers.

A native nickel-heazlewoodite-ferroan trevorite assemblage from Mount Clifford, Western Australia

The Mount Clifford nickel sulfide deposit consists of several stratabound lenses of disseminated sulfides, averaging 1.5 to 2.0 percent Ni, in a serpentinized periodotite. The sulfide assemblage is Ni rich, represented by varying proportions of godlevskite, millerite, heazle-woodite, and Ni-rich pentlandite.In a single 50-cm section of core below the disseminated sulfide lenses, native nickel has been found as a significant component of irregular oxide-sulfide veins, stringers, and blebs in a serpentinized skeletal-textured periodotite. It is present as grains and granular aggregates ranging from 100 mu m to 3 mm in size, and averaging about 500 mu m. The chemical composition (average wt % from 24 electron microprobe analyses) is Ni, 96.41; Fe, 1.41; Co, 0.45; and Cu, 1.51; total, 99.78. Euhedral to subhedral spinels dominate the veins (approximate mode 75%) and are typically zoned from cores of nickeloan magnetite to rims of ferroan trevorite. The spinel both encloses and is included in an intergrowth of native nickel (15%) and heazlewoodite (10%). Minor phases include chalcocite, bornite, and maucherite, together with a rare unnamed mineral, close to Ni 4 S(Sn, Te, Sb) in composition.Secondary sulfides have developed in response to weathering and/or low-temperature hydrothermal alteration processes. Pentlandite is replaced by violarite-polydymite and millerite; godlevskite is replaced by millerite; heazlewoodite is replaced by godlevskite, which in turn is replaced by millerite. Carbonate-bearing solutions have caused alteration of coexisting native nickel and heazlewoodite to assemblages comprising native copper, nickel-iron carbonates, nickel and nickel-iron hydroxycarbonates, and nickel-rich silicates.The native nickel-heazlewoodite-ferroan trevorite assemblage is believed to have crystallized in a hydrothermal environment characterized by high nickel and low sulfur activities, and in which oxygen activity was sufficiently high to make nickel-iron sulfides and nickel-iron alloys unstable relative to nickel-iron oxides, nickel sulfides, and native nickel.

Mobility and fractionation of rare earth elements during weathering of a granodiorite

The rare earth elements (REE) have been mobilised and fractionated during supracrustal alteration of the Torrongo granodiorite. Compared with the parent granodiorite, incipiently and moderately altered rocks are particularly enriched in the heavy REE, while the extremely altered residual products are especially depleted in the heavy REE. Mobilisation of the REE probably results from pH changes of soil and ground waters as they encounter different chemical environments while fractionation may largely result from mineralogical controls. Submarine and subaerial weathering processes may affect REE similarly, producing intensively weathered materials appreciably depleted in the REE. Spilitisation and hydrothermal alteration processes may affect basaltic rocks in much the same way as do weathering processes.

Polytypes and expandability of sericite from the Itaya kaolin clay deposit, Northeast Japan.

Polytypes and expandability of sericite from the Itaya kaolin clay deposit were examined by X-ray powder diffraction method, with the hope of relating these structural features to the hydrothermal alteration processes which took place in two major periods, Late Miocene and Quaternary. 1M polytype is found to be predominant throughout the Miocene alteration area, while 2M1 polytype with rare occurrence of 2M2 polytype occurs mainly in the central parts of the deposit, where the hydrothermal argillization was most intense. Amount of 2M1 polytype tends to decrease outward, being accompanied by the increase of 1M polytype. lMd structure is found most frequently in sheared zones with intense pyrite dissemination (“black fault”), which are thought to be the latest stage product of the Miocene alteration. Expandability of the sericite is presented by “expandability index”, which is defined in this paper for the apparent contraction value (A) of the basal 10A reflection upon treatment with ethylene glycol. The sericite in the “black fault” and that in fragments of Miocene altered tuffs taken into the Quaternary silicified breccia dikes show much higher expandability than those in major Miocene altered rocks. The per cent expandable layers of each polytype estimated from the expandability index increases in the order of 2M1 (1-3%, in average), 1M (2-5%), 2M2 (5-9%) and 1Md (7-10%). A considerable difference of the expandability between two variations of 2M polytype is observed. The results indicate that the polytype occurrence was basically ruled by the intensity of hydrothermal argillization and that the expandability was mainly controlled by secondary degradation processes and polytype species. The enrichment of expandable layers and lMd structure in the sericite in the “black fault” may be ascribed to the hydrothermal fluid of the latest stage of the Miocene alteration which caused the pyrite dissemination. The Quaternary silicification may have been responsible for the increase of amounts of expandable layers in the sericite captured by the silicified dikes. However, no other degrading effect by the Quaternary alteration has been observed.

The geochemistry of altered volcanic rocks at Matagami, Quebec: a geothermal model for massive sulphide genesis

Volcanogenic exhalative massive sulphide deposits at Matagami are associated with a bimodal suite of tholeiitic basalt and rhyolite. However, these rocks now exhibit pseudo calc-alkaline alteration trends resulting from a hydrothermal alteration process in which footwall basalt was spilitized, and the host rhyolite was chloritized. These two alteration processes were contemporaneous events, which shared a common aqueous fluid, developed within cooling submarine volcanic rocks shortly after the extrusion of rhyolite, and terminated prior to extrusion of succeeding units.The geochemistry of the Garon Lake rhyolite and underlying basalt are examined in detail. Massive quantities of Fe, Mg and Ti, and over 10 ppm Zn and 5 ppm Cu were leached from basalt during spilitization, providing 30 000 t Zn and 15 000 t Cu, or approximately 1 Mt of ore grade material per km3 of basalt. Chlorite alteration zones and massive sulphide deposits in the overlying rhyolite were enriched in all those elements depleted from basalt. This evidence suggests a geothermal model for massive sulphide genesis, where Fe, Mg, Ti, Cu and Zn were leached from footwall rocks, flushed through a geothermal system, and then precipitated at the discharge point to form chlorite alteration zones in the overlying rhyolite and exhalite deposits at the sediment–seawater interface.

Notes on the Solfatara of Sousaki (Greece), a Recent Eruption at Methana (Greece), and Recent Maccalube at Vulcano

Previous articleNext article FreeThe Temperatures of Hot Springs and the Sources of Their Heat and Water Supply. IVNotes on the Solfatara of Sousaki (Greece), a Recent Eruption at Methana (Greece), and Recent Maccalube at VulcanoHenry S. WashingtonHenry S. Washington Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 32, Number 6Aug. - Sep., 1924 Article DOIhttps://doi.org/10.1086/623126 Views: 33Total views on this site Citations: 4Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:W. D'Alessandro, S. Calabrese, S. Bellomo, L. Brusca, K. Daskalopoulou, L. Li Vigni, L. Randazzo, K. Kyriakopoulos Impact of hydrothermal alteration processes on element mobility and potential environmental implications at the Sousaki solfataric field (Corinthia - Greece), Journal of Volcanology and Geothermal Research 407 (Dec 2020): 107121.https://doi.org/10.1016/j.jvolgeores.2020.107121W. D'Alessandro, L. Brusca, K. Kyriakopoulos, G. Michas, G. Papadakis Methana, the westernmost active volcanic system of the south Aegean arc (Greece): Insight from fluids geochemistry, Journal of Volcanology and Geothermal Research 178, no.44 (Dec 2008): 818–828.https://doi.org/10.1016/j.jvolgeores.2008.09.014Peter A. James, Christopher B. Mee, Gary J. Taylor Soil Erosion and the Archaeological Landscape of Methana, Greece, Journal of Field Archaeology 21, no.44 (Jul 2013): 395–416.https://doi.org/10.1179/009346994797175523G. G. Pe Volcanic rocks of methana, South Aegean arc, Greece, Bulletin Volcanologique 38, no.11 (Mar 1974): 270–290.https://doi.org/10.1007/BF02599408