Noto, Masami; Kusakabe, Minoru; Uchida, Tetsuo.
Dehydration techniques were developed for the analysis of isotopic ratios of framework oxygen of wairakite, one of calcium zeolites often encountered in geothermal systems. Channel water in wairakite were separated from aluminosilicate framework by dehydration in vacuum at 300 deg, 400 deg, 450 deg, 500 deg, 550 deg, 650 deg, 750 deg, 850 deg, and 950 degC, and by stepwise heating at temperatures from 300 deg to 700 degC. The oxygen isotopic analyses of the separated channel water and the residual aluminosilicate framework of wairakite indicated that dehydration at temperatures higher than 400 degC is accompanied by isotopic exchang between the framework oxygen and dehydrating water vapor. The isotopic exchange during the high temperature dehydration makes the δ 18 O of framework oxygen lower and that of channel water higher than those obtained by dehydration at 300 degC. These results are consistent with dehydration behavior of wairakite under vacuum that the maximum rate of dehydration of channel water is attained at about 400 degC. Consequently it is recommended to dehydrate wairakite at a temperature as low as possible in order to avoid the effect of the isotopic exchange. Time required to attain complete dehydration becomes longer with lowering the temperature of dehydration. To compromise these conflicting effects, the optimum conditions of dehydration have been found that most of the channel water is dehydrated at 300 degC for 24 hours, followed by stepwise heating for additional 17 hours up to 700 degC. We obtained a better than ± 0.1 reproducibility for the framework oxygen isotopic determinations with this technique. (author)
Absar, A.; Blattner, P.
Fifteen drillholes at the Kawerau geothermal field penetrated a sequence of Quaternary volcanic rocks overlying Mesozoic greywackes and argillites in the depth range of 650 to 1220 m below sea level. Maximum temperature in the basement is 250 to 303 deg. C. Twelve greywacke cores were modally analysed in order to determine their intensity of alteration, which in turn was compared with their oxygen isotope composition. It is concluded that Kawerau geothermal field has experienced at least three hydrothermal regimes. The earliest was characterised by fluids with low m CO 2 and δ 18 O, as indicated by the wairakite-prehnite mineral assemblage in greywacke depleted by 5 ppm. This regime was followed by a period of hydraulic fracturing the formation of a mineral assemblage with abundant calcite indicative of fluids with high dissolved CO 2 . Precipitation of minerals during these two early successive hydrothermal regimes resulted in sealing of fractures in the southern part of the field. These two mineral assemblages are indicated to have formed prior to faulting. The latest mineral assemblage comprising quartz-calcite-adularia-calc silicates on the other hand, is related to a series of NE trending faults which enabled geothermal fluids to move northeastward after circulation was precluded in the southern part. This suggests that future exploration for production from the greywacke basement should be in the north where mineralogy and δ 18 O composition of calcite indicate that much better permeability occurs
Petrographic study and preliminary conceptual model of the Ixtlan de los Hervores geothermal zone, Michoacan, Mexico; Estudio petrografico y modelo conceptual preliminar de la zona geotermica de Ixtlan de los Hervores, Michoacan, Mexico
Viggiano-Guerra, Julio C; Gutierrez-Negrin, Luis C.A [Comision Federal de Electricidad (Mexico)
Petrographic studies of cuttings from the shallow well Ixtlan 2, drilled in the Ixtlan de los Hervores geothermal zone, State of Michoacan, Mexico, at a maximum depth of 159 meters, together with results of previous exploration studies, allow to delineate a preliminary conceptual model of the probable geothermal system. It is formed by a wide-fracture zone system, with low topographic relief and shallow water level. Its hydrothermal fluids are of sodium-chloride type, neutral pH, silica oversaturated in the discharge and with temperatures between 125 and 225 degrees Celsius, based on the geothermometry and the hydrothermal mineral assemblage encountered in the well. The assemblage of laumontite + quartz + calcite + chlorite/smectite + pyrite is typical for the zeolitic facies, beneath of which it is possible to encounter the epidote-wairakite facies, with higher temperatures. The favorable conditions of the zone allow to recommend continuation of exploration in the same. [Spanish] El estudio petrografico de muestras de canal de la perforacion del pozo somero Ixtlan 2, con una profundidad maxima de 159 metros y ubicado en la zona geotermica de Ixtlan de Los Hervores, Michoacan, Mexico, aunado a los resultados de estudios previos de exploracion superficial, han permitido la configuracion de un modelo conceptual preliminar del probable yacimiento geotermico. Se trata de un sistema zona de fractura ancha, bajo relieve y nivel freatico somero, con fluidos hidrotermales de tipo clorurado-sodico, pH neutro, sobresaturados de silice en la descarga, y con temperatura entre 125 y 225 grados Celsius, de acuerdo con la geotermometria + cuarzo + calcita + clorita/esmectita + pirita es tipica de la facies zeolitica, debajo de la cual podria hallarse la facies de epidota-wairakita, con temperaturas mas altas. Las condiciones favorables de la zona permiten recomendar la continuacion de la exploracion en la misma.
Tsukimura, K.; Matsuhisa, Y.; Kanai, Y.; Hirai, H.
In the long term of the high-level nuclear waste disposal, the dissolving rates of radionuclides from the waste will be controlled by crystalline phases secondarily formed in the borosilicate glass by reaction with ground water. We have determined the crystalline phases formed from borosilicate glass in a hydrothermal experiment. Borosilicate glass powder (50 mg, Si 40 B 20 Al 4 Li 12 Na 14 K 3 Ca 2 Fe 5 O 140 ) and 200 ml of water were reacted at 300degC and 300 bars for 2 weeks with a cold-seal type hydrothermal high pressure apparatus. After the reaction the liquid phase was analyzed with atomic absorption spectroscopy and the solid phases with x-ray powder diffraction and analytical electron microscopy. The liquid phase contains 58 % of Na, 14 % of Li and 11 % of K but less than 1 % of Ca and Fe. The solid phases were found to be zeolite and smectite. The zeolite is isostructural with analcime Na 2 Al 2 (SiO 3 ) 4 · 2H 2 O or wairakite CaAl 2 (SiO 3 ) 4 · 2H 2 O and contains Ca and Si as major constituents but does not contain Al. Although no direct analytical evidence is available, logical induction of the experimental results indicates that the chemical composition of the zeolite is CaB 2 (SiO 3 ) 4 . The remaining x-ray powder diffraction peaks are same as those of smectite Na 06.7 (Al 3.33 Mg 0.67 )Si 8 O 20 (OH) 4 . However, since our starting material was free of Mg, and Na was not detected by AEM, the smectite may contain Fe instead of Mg, and Li instead of Na. (author)
Chipera, Steve J.; Goff, Fraser; Goff, Cathy J.; Fittipaldo, Melissa
Quantitative X-ray diffraction analysis of about 80 rhyolite and associated lacustrine rocks has characterized previously unrecognized zeolitic alteration throughout the Valles caldera resurgent dome. The alteration assemblage consists primarily of smectite-clinoptilolite-mordenite-silica, which replaces groundmass and fills voids, especially in the tuffs and lacustrine rocks. Original rock textures are routinely preserved. Mineralization typically extends to depths of only a few tens of meters and resembles shallow "caldera-type zeolitization" as defined by Utada et al. [Utada, M., Shimizu, M., Ito, T., Inoue, A., 1999. Alteration of caldera-forming rocks related to the Sanzugawa volcanotectonic depression, northeast Honshu, Japan — with special reference to "caldera-type zeolitization." Resource Geol. Spec. Issue No. 20, 129-140]. Geology and 40Ar/ 39Ar dates limit the period of extensive zeolite growth to roughly the first 30 kyr after the current caldera formed (ca. 1.25 to 1.22 Ma). Zeolitic alteration was promoted by saturation of shallow rocks with alkaline lake water (a mixture of meteoric waters and degassed hydrothermal fluids) and by high thermal gradients caused by cooling of the underlying magma body and earliest post-caldera rhyolite eruptions. Zeolitic alteration of this type is not found in the later volcanic and lacustrine rocks of the caldera moat (≤ 0.8 Ma) suggesting that later lake waters were cooler and less alkaline. The shallow zeolitic alteration does not have characteristics resembling classic, alkaline lake zeolite deposits (no analcime, erionite, or chabazite) nor does it contain zeolites common in high-temperature hydrothermal systems (laumontite or wairakite). Although aerially extensive, the early zeolitic alteration does not form laterally continuous beds and are consequently, not of economic significance.
Engelsen, Christian J.; Sloot, Hans A. van der; Wibetoe, Grethe; Petkovic, Gordana; Stoltenberg-Hansson, Erik; Lund, Walter
The pH dependent leaching characteristics were assessed for different types of recycled concrete aggregates, including real construction debris and crushed fresh concrete samples prepared in laboratory. Carbonation effects were identified from the characteristic pH dependent leaching patterns for the major constituents Al, Ca, Fe, Mg, Si and SO 4 2- . The original particle size ranges were different for the samples investigated and this factor influenced the cement paste content in the samples which in turn controlled the leachable contents. Cement paste contents for concrete samples with fine particle size fractions (0-4 mm) were found to be higher than the originally present amount in the hardened concrete. Geochemical speciation modelling was applied over the entire pH range using the speciation and transport modelling framework ORCHESTRA, for which mineral saturation, solution speciation and sorption processes can be calculated based on equilibrium models and thermodynamic data. The simulated equilibrium concentrations by this model agreed well with the respective measured concentrations. The main differences between the fresh and aged materials were quantified, described and predicted by the ORCHESTRA. Solubility controlling mineral phase assemblages were calculated by the model as function of pH. Cement hydrate phases such as calcium silicate hydrate, calcium aluminate hydrate (AFm and AFt) and hydrogarnet were predominating at the material pH. The concentration of carboaluminates was found to be strongly dependent on the available carbonates in the samples. As the pH was decreased these phases decomposed to more soluble species or precipitates were formed including iron- and aluminium hydroxides, wairakite and amorphous silica. In the most acid region most phases dissolved, and the major elements were approaching maximum leachability, which was determined by the amount of cement paste.
Ambrosio, Michele; Doveri, Marco; Fagioli, Maria Teresa; Marini, Luigi; Principe, Claudia; Raco, Brunella
In this work, we investigated the water-rock interaction processes taking place in the hydrothermal reservoir of Nisyros through both: (1) a review of the hydrothermal mineralogy encountered in the deep geothermal borehole Nisyros-2; and (2) a comparison of the analytically-derived redox potentials and acidities of fumarolic-related liquids, with those controlled by redox buffers and pH buffers, involving hydrothermal mineral phases. The propylitic zone met in the deep geothermal borehole Nisyros-2, from 950 to 1547 m (total depth), is characterised by abundant, well crystallised epidote, adularia, albite, quartz, pyrite, chlorite, and sericite-muscovite, accompanied by less abundant anhydrite, stilpnomelane, wairakite, garnet, tremolite and pyroxene. These hydrothermal minerals were produced in a comparatively wide temperature range, from 230 to 300 °C, approximately. Hydrothermal assemblages are well developed from 950 to 1360 m, whereas they are less developed below this depth, probably due to low permeability. Based on the RH values calculated for fumarolic gases and for the deep geothermal fluids of Nisyros-1 and Nisyros-2 wells, redox equilibrium with the (FeO)/(FeO 1.5) rock buffer appears to be closely attained throughout the hydrothermal reservoir of Nisyros. This conclusion may be easily reconciled with the nearly ubiquitous occurrence of anhydrite and pyrite, since RH values controlled by coexistence of anhydrite and pyrite can be achieved by gas separation. The pH of the liquids feeding the fumarolic vents of Stephanos and Polybote Micros craters was computed, by means of the EQ3 code, based on the Cl- δD relationship which is constrained by the seawater-magmatic water mixing occurring at depth in the hydrothermal-magmatic system of Nisyros. The temperature dependence of analytically-derived pH values for the reservoir liquids feeding the fumarolic vents of Stephanos and Polybote Micros craters suggests that some unspecified pH buffer fixes the