Dale Counce

Passive infrared remote sensing evidence for large, intermittent CO2 emissions at Popocatépetl volcano, Mexico

Abstract Passive infrared (FTIR) and correlation spectrometer (COSPEC) measurements were conducted at Popocatepetl volcano during February 10 to 26, 1998 from sites 4 to 17 km distant from the summit. Volcano behavior was relatively quiet and SO 2 flux averaged 1670±1420 t/day (51 measurements), relatively small for Popocatepetl. Concurrent HCl/SO 2 and HF/SO 2 ratios were 0.17±0.01 and 0.031±0.003, respectively, about the same as ratios measured from 1994 to 1997. The amount of CO 2 in the volcanic plume was quantified using FASCODE in which atmospheric CO 2 is numerically subtracted from the total infrared spectrum to obtain the residual magmatic CO 2 . Surprisingly, CO 2 /SO 2 mass ratios rose dramatically to values as high as 140, about 30 times higher than typical values of 2 to 8 measured from 1994 to 1996. These excursions in high CO 2 /SO 2 ratios were short-lived, lasting no longer than about 0.5 to 3.0 h but CO 2 flux occasionally exceeded 100,000 t/day. We estimate that the average CO 2 /SO 2 ratio for the period was about 23, yielding an average CO 2 flux of roughly 38,000 t/day. Chemical and petrographic analyses of lava and pumice erupted during explosions on June 30, 1997 and January 1, 1998 show conclusively that Popocatepetl produces mixed products formed by injection of mafic magma into a more silicic chamber at temperatures and pressures of roughly 1040°C and 5 kbar. In addition, Popocatepetl eruptive products include xenoliths of metamorphosed carbonate rocks containing wollastonite and other calc-silicate minerals indicating reaction of magma with Cretaceous limestone underlying the volcano. Using a normal CO 2 /SO 2 ratio of 4 for reference, we calculate an average excess CO 2 production of 32,000 t/day for 17 days. This would require assimilation of only 5×10 −4 km 3 of limestone, an amount easily accessible in the 3-km-thick Cretaceous section beneath the volcano. We also examine two scenarios in which excess CO 2 is produced by degassing of subjacent basalt magma, but these explanations seem less plausible to us. Because many other volcanoes are underlain by carbonate sequences, short-duration bursts of CO 2 flux, and increased CO 2 /SO 2 ratio, might be observed at other sites, if simultaneous, real-time measurements of major gas species are made.

The chemical and isotopic composition of fumarolic gases and spring discharges from Galeras Volcano, Colombia

Abstract Galeras fumarole discharges have been collected since its reactivation, in 1988, through December 1995. The gases are dominated by H2O, CO2, S (as SO2 and H2S) and HCl. The relative proportions of these gases classify them as ‘magmatic’. Thermodynamic equilibrium temperatures of the gases range from 260 to > 600 °C. The relative abundance of inert gases, N2, Ar and He, can be used as ‘tracers’ to identify the source of the fumarole discharges. At Galeras the majority of the samples have a composition characteristic of gases originating from arc-related magmas, with relatively high N2 contents and minor He and Ar. During 1993, the year of frequent eruptions, the gas composition changed to basaltic or ‘mantle-derived’ gases, with significantly higher He contents. This is interpreted to be the result of injection of volatiles from a basaltic magma body at depth prior to and during the increased eruptive activity of 1993. The δ13C values for CO2 in fumarole discharges are typical of andesitic volcanoes and may indicate addition of MORB-derived CO2. The δ15N values for N2 may indicate significant contribution of N2 from marine sediments and only minor contribution of MORB-derived N2. The δ D and δ18O values of the discharging steam lie on a mixing trend between the isotopic composition of ‘arc-related’ magmatic water and18O-shifted meteoric water. The most magmatic discharges have δ D values of −30 to −35‰; while the most meteoric discharges have values of −70 to −75‰, similar to Galeras thermal spring waters. Galeras thermal water discharges consist of acid sulfate and bicarbonate waters.S/Cl ratios in the acid sulfate waters are similar to fumarole ratios, suggesting direct absorption of magmatic gases into shallow ground waters. This is supported by the essentially meteoric δD and δ18O values of the discharges and by elevated3He/4He ratios of thermal spring waters. The absorption of acid S- and Cl-rich gases yield acid waters which are capable of dissolving rocks. The thermal waters, however, are far from equilibrium with Galeras lavas and pyroclastic rocks, providing evidence of the immaturity of the Galeras hydrothermal system. The SO4 and Cl content, as well as the O and H isotopic composition of Galeras thermal springs vary with the activity of the volcano. The 7-year sampling program at Galeras revealed intriguing results concerning the activity of Galeras, its magmatic-hydrothermal system and the origin of the volatiles. Despite decreasing outlet temperatures since 1992, deep temperatures remain high, implying continued unrest in the Galeras magmatic system.

Geochemical surveillance of magmatic volatiles at Popocatépetl volcano, Mexico

Surveillance of Popocatepetl volcanic plume geochemistry and SO 2 flux began in early 1994 after fumarolic and seismic activity increased significantly during 1993. Volatile traps placed around the summit were collected at near-monthly intervals until the volcano erupted on December 21, 1994. Additional trap samples were obtained in early 1996 before the volcano erupted again, emplacing a small dacite dome in the summit crater. Abundances of volatile constituents (ppm/day of Cl, S total , F, CO 2 , Hg, and As) varied, but most constituents were relatively high in early and late 1994. However, ratios of these constituents to Cl were highest in mid-1994. δ 34 S-S total in trap solutions ranged from 1.5‰ to 6.4‰; lowest values generally occurred during late 1994. δ 13 C-CO 2 of trap solutions were greatly contaminated with atmospheric CO 2 and affected by absorption kinetics. When trap data are combined with SO 2 flux measurements made through November 1996, Popocatepetl released about 3.9 Mt SO 2 , 16 Mt CO 2 , 0.75 Mt HCl, 0.075 Mt HF, 260 t As, 2.6 t Hg, and roughly 200 Mt H 2 O. Near-vent gas concentrations in the volcanic plume measured by correlation spectrometer (COSPEC) and Fourier transform infrared (FTIR) commonly exceed human recommended exposure limits and may constitute a potential health hazard. Volatile geochemistry combined with petrologic observations and melt-inclusion studies show that mafic magma injection into a preexisting silicic chamber has accompanied renewed volcanism at Popocatepetl. Minor assimilation of Cretaceous wall rocks probably occurred in mid-1994.

Hot dry rock geothermal reservoir testing: 1978 to 1980

Experimental results and re-evaluation of the Phase I Hot Dry Rock Geothermal Energy reservoirs at the Fenton Hill field site are summarized. Reservoir growth is traced. Reservoir growth was caused not only by pressurization and hydraulic fracturing, but also by heat extraction and thermal contraction effects. Reservoir heat-transfer area grew from 8000 to 50,000 m/sup 2/ and reservoir fracture volume grew from 11 to 266/sup 3/m. Despite this reservoir growth, the water loss rate increased only 30%, under similar pressure environments. For comparable temperature and pressure conditions, the flow impedance (a measure of the resistance to circulation of water through the reservoir) remained essentially unchanged, and if reproduced in the Phase II reservoir under development, could result in self pumping. Geochemical and seismic hazards have been nonexistent in the Phase I reservoirs. The produced water is relatively low in total dissolved solids and shows little tendency for corrosion or scaling. The largest microearthquake associated with heat extraction measures less than -1 on the extrapolated Richter scale.

Testing and parameterizing a conceptual solute transport model in saturated fractured tuff using sorbing and nonsorbing tracers in cross-hole tracer tests

Two cross-hole tracer tests involving the simultaneous injection of two nonsorbing solute tracers with different diffusion coefficients (bromide and pentafluorobenzoate) and one weakly sorbing solute tracer (lithium ion) were conducted in two different intervals at the C-wells complex near the site of a potential high-level nuclear waste repository at Yucca Mountain, NV. The tests were conducted to (1) test a conceptual radionuclide transport model for saturated, fractured tuffs near Yucca Mountain and (2) obtain transport parameter estimates for predictive modeling of radionuclide transport. The differences between the responses of the two nonsorbing tracers and the sorbing tracer (when normalized to injection masses) were consistent with a dual-porosity transport system in which matrix diffusion was occurring. The concentration attenuation of the sorbing tracer relative to the nonsorbing tracers suggested that diffusion occurred primarily into matrix pores, not simply into stagnant water within the fractures. The K(d) values deduced from the lithium responses were generally larger than K(d) values measured in laboratory batch sorption tests using crushed C-wells cores. This result supports the use of laboratory-derived K(d) values for predicting sorbing species transport at the site, as the laboratory K(d) values would result in underprediction of sorption and hence conservative transport predictions. The tracer tests also provided estimates of effective flow porosity and longitudinal dispersivity at the site. The tests clearly demonstrated the advantages of using multiple tracers of different physical and chemical characteristics to distinguish between alternative conceptual transport models and to obtain transport parameter estimates that are better constrained than can be obtained using only a single tracer or using multiple nonsorbing tracers without a sorbing tracer.

Evaluation of ultramafic deposits in the Eastern United States and Puerto Rico as sources of magnesium for carbon dioxide sequestration

In this report, the authors evaluate the resource potential of extractable magnesium from ultramafic bodies located in Vermont, the Pennsylvania-Maryland-District-of-Columbia (PA-MD-DC) region, western North Carolina, and southwestern Puerto Rico. The first three regions occur in the Appalachian Mountains and contain the most attractive deposits in the eastern United States. They were formed during prograde metamorphism of serpentinized peridotite fragments originating from an ophiolite protolith. The ultramafic rocks consist of variably serpentinized dunite, harzburgite, and minor iherzolite generally containing antigorite and/or lizardite as the major serpentine minor phases. Chrysotile contents vary from minor to major, depending on occurrence. Most bodies contain an outer sheath of chlorite-talc-tremolite rock. Larger deposits in Vermont and most deposits in North Carolina contain a core of dunite. Magnesite and other carbonates are common accessories. In these deposits, MgO ranges from 36 to 48 wt % with relatively pure dunite having the highest MgO and lowest H{sub 2}O contents. Ultramafic deposits in southwestern Puerto Rico consist of serpentinized dunite and harzburgite thought to be emplaced as large diapirs or as fragments in tectonic melanges. They consist of nearly pure, low-grade serpentinite in which lizardite and chrysotile are the primary serpentine minerals. Chlorite is ubiquitous in trace amounts. Magnesite is a common accessory. Contents of MgO and H{sub 2}O are rather uniform at roughly 36 and 13 wt %. Dissolution experiments show that all serpentinites and dunite-rich rocks are soluble in 1:1 mixtures of 35% HCl and water by volume. The experiments suggest that low-grade serpentinites from Puerto Rico are slightly more reactive than the higher grade, antigorite-bearing serpentinites of the Appalachian Mountains. The experiments also show that the low-grade serpentinites and relatively pure dunites contain the least amounts of undesirable insoluble silicates. Individual ultramafic bodies in the Appalachian Mountains are as great as 7 km{sup 3} although typically they are {le}1 km{sup 3}. In contrast, ultramafic deposits in southwestern Puerto Rico have an estimated volume of roughly 150 km{sup 3}. Based on the few detailed geophysical studies in North Carolina and Puerto Rico, it is evident that volume estimates of any ultramafic deposit would benefit greatly from gravity and magnetic investigations, and from corehole drilling. Nevertheless, the data show that the ultramafic deposits of the eastern United States and southwestern Puerto Rico could potentially sequester many years of annual CO{sub 2} emissions if favorable geotechnical, engineering, and environmental conditions prevail.

Geology, water geochemistry and geothermal potential of the jemez springs area, Canon de San Diego, new Mexico

Abstract Studies of the geology, geochemistry of thermal waters, and of one exploratory geothermal well show that two related hot spring systems discharge in Canon de San Diego at Soda Dam (48°C) and Jemez Springs (72°C). The hot springs discharge from separate strands of the Jemez fault zone which trends northeastward towards the center of Valles Caldera. Exploration drilling to Precambrian basement beneath Jemez Springs encountered a hot aquifer (68°C) at the top of Paleozoic limestone of appropriate temperature and composition to be the local source of the fluids in the surface hot springs at Jemez Springs. Comparisons of the soluble elements Na, Li, Cl, and B, arguments based on isotopic evidence, and chemical geothermometry indicate that the hot spring fluids are derivatives of the deep geothermal fluid within Valles Caldera. No hot aquifer was discovered in or on top of Precambrian basement. It appears that low- to moderate-temperature geothermal reservoirs (

Rock-water interactions in hot dry rock geothermal systems: field investigations of in situ geochemical behavior

Abstract Two hot dry rock (HDR) geothermal energy reservoirs have been created by hydraulic fracturing of Precambrian granitic rock between two wells on the west flank of the Valles Caldera in the Jemez Mountains of northern New Mexico. Heat is extracted by injecting water into one well, flowing it through the fractured region and recovering the heated water from the second well. The produced fluid is cooled on the surface and reinjected into the system. The first reservoir was formed by fracturing the injection well at a depth of 2.75 km where the initial rock temperature was 185° C. A heat-extraction experiment conducted in this reservoir was run from January 27 to April 13, 1978. A second, larger reservoir was created after cementing the fracture-to-wellbore connections at 2.75 km in the injection well and refracturing 180 m deeper. This second reservoir was tested from October 23 to November 16, 1979. During each of these experiments, samples of the geothermal fluids and gases were collected at regular intervals from the injection wellhead, the production wellhead, and at the make-up pump which provided the water from storage ponds to replace the water lost downhole by permeation into the reservoir walls. Changes in the composition of the produced fluid provide a means for studying the reservoir behaviour under normal (recirculating) operating conditions. Certain of the dissolved species appear to be derived by displacement of an indigenous pore-fluid, while others appear to be derived by dissolving minerals known to be present in the reservoir rock. In this paper we describe the results of the chemical analysis of the geothermal fluids and relate the fluid and gas chemistry to geochemical processes that result from the heat- extraction experiments. In particular, the implications of the silica and NaKCa geothermometers and the pore-fluid displacement theory are examined for insight about the long-term effects of fluid geochemistry on heat extraction from HDR reservoirs.

Hydrogeochemical exploration of geothermal prospects in the Tecuamburro Volcano region, Guatemala

Abstract Chemical and isotopic analyses of thermal and nonthermal waters and of gases from springs and fumaroles are used to evaluate the geothermal potential of the Tecuamburro Volcano region, Guatemala. Chemically distinct geothermal surface manifestations generally occur in separate hydrogeologic areas within this 400 km 2 region: low-pressure fumaroles with temperatures near local boiling occur at 1470 m elevation in a sulfur mine near the summit of Tecuamburro Volcano; non-boiling acid-sulfate hot springs and mud pots are restricted to the Laguna Ixpaco area, about 5 km NNW of the sulfur mine and 350–400 m lower in elevation; steam-heated and thermal-meteoric waters are found on the flanks of Tecuamburro Volcano and several kilometers to the north in the andesitic highland, where the Infernitos fumarole (97°C at 1180 m) is the primary feature; neutral-chloride hot springs discharge along Rio Los Esclavos, principally near Colmenares at 490 m elevation, about 8–10 km SE of Infernitos. Maximum geothermometer temperatures calculated from Colmenares neutral-chloride spring compositions are ∼180° C , whereas maximum subsurface temperatures based on Laguna Ixpaco gas compositions are ∼310° C . An exploration core hole drilled to a depth of 808 m about 0.3 km south of Laguna Ixpaco had a bottom-hole temperature of 238°C but did not produce sufficient fluids to confirm or chemically characterize a geothermal reservoir. Hydrogeochemical data combined with regional geologic interpretations indicate that there are probably two hydrothermal-convection systems, which are separated by a major NW-trending structural boundary, the Ixpaco fault. One system with reservoir temperatures near 300°C lies beneath Tecuamburro Volcano and consists of a large vapor zone that feeds steam to the Laguna Ixpaco area, with underlying hot water that flows laterally to feed a small group of warm, chloriderich springs SE of Tecuamburro Volcano. The other system is located beneath the Infernitos area in the andesitic highland and consists of a lower-temperature (150–190°C) reservoir with a large natural discharge that feeds the Colmenares hot springs.

EFFECTS OF MINERALOGY, EXCHANGE CAPACITY, SURFACE AREA AND GRAIN SIZE ON LITHIUM SORPTION TO ZEOLITIC ALLUVIUM NEAR YUCCA MOUNTAIN, NEVADA

The resistance to acidic and sulfate attack of Portland-pozzolan cement containing 35 wt.% of zeolite was compared with that of unamended Portland cement. Mortar specimens kept in 0.5% and 1.0% HCl solution, 5% Na2SO4 solution, and in reference water for 365 and 720 days were tested using a set of physical-mechanical and chemical techniques. The ability of mortars containing zeolitic cements with 15 to 50 wt.% of zeolite to protect steel against corrosion was verified by a potentiodynamic method. Mortar with zeolitic cement performs better when exposed to 1% HCl solution due to the presence of a finer pore matrix, a hydrate phase poorer in CaO-containing hydration products with lower leachability, and the high resistance of zeolite material itself to acidic attack, compared with Portland cement and siliceous sand. The improved sulfate resistance of the mortar with zeolitic cement is caused by the decreased C3A in the cement blend in comparison with that in Portland cement, a reduction in SO3 binding into the cement paste and decreased amount of CaO-containing hydration products capable of reacting with a sulfate solution forming voluminous reaction products, and consequent crack propagation, large expansion and structural disintegration. Passivation of steel in mortars with blends of Portland cement to zeolite percentage ratios of 85/15, 75/25 and 65/35 by weight is comparable to that of Portland cement mortar. This is particularly important because the mortar with zeolitic cement exhibits late strengths similar to that of Portland cement mortar. This confirms that zeolitic cement can replace Portland cement in many applications with the advantage of higher resistance to acidic and sulfate attack.The Li + ion is used frequently as an environmentally acceptable surrogate for sorbing radionuclides in field tracer tests, and experiments using Li are an important part of assessing the potential transport of radionuclides in saturated alluvium south of Yucca Mountain, Nevada, the site of a proposed nuclear waste repository. Equilibrium partition constants (Li + K d s) were measured using batch studies incorporating a wide range of Li + concentrations and two different grain-size fractions of alluvium samples from multiple depth intervals in two wells. Cation exchange capacity, surface area, bulk mineralogy from quantitative X-ray powder diffraction, and trace Mn- and Fe-oxyhydroxide mineralogy from extractive studies were evaluated as predictors for linearized Li + K d values (K lin ) in the alluvium. Many of the predictor variables are correlated with each other and this was considered in the analysis. Linearized K d values were consistently higher for fine particle-size fractions than for coarse fractions. Single and multivariate linear regression analyses indicated that the clinoptilolite + smectite content, taken together as a combined variable, was the best predictor for Li + sorption in the alluvium, although clinoptilolite content was clearly a better predictor when the two variables were considered separately in simple linear regressions. Even so, Li + K lin predictions based on clinoptilolite and smectite abundance were accurate only to within about ±100%. This uncertainty suggests that there is either a high inherent variability in Li + K lin values or that additional alluvium characteristics not measured or evaluated here may play an important role in simple Li + cation exchange in the alluvium.