Robert O. Fournier

An empirical NaKCa geothermometer for natural waters

Abstract An empirical method of estimating the last temperature of water-rock interaction has been devised. It is based upon molar Na, K and Ca concentrations in natural waters from temperature environments ranging from 4 to 340°C. The data for most geothermal waters cluster near a straight line when plotted as the function log ( Na K ) + β log [ √ (Ca) Na ] vs reciprocal of absolute temperature, where β is either 1 3 or 4 3 depending upon whether the water equilibrated above or below 100°C. For most waters tested, the method gives better results than the Na K methods suggested by other workers. The ratio Na K should not be used to estimate temperature if √ ( M Ca ) M Na is greater than 1. The Na K values of such waters generally yield calculated temperatures much higher than the actual temperature at which water interacted with the rock. A comparison of the composition of boiling hot-spring water with that obtained from a nearby well (170°C) in Yellowstone Park shows that continued water-rock reactions may occur during ascent of water even though that ascent is so rapid that little or no heat is lost to the country rock, i.e. the water cools adiabatically. As a result of such continued reaction, waters which dissolve additional Ca as they ascend from the aquifer to the surface will yield estimated aquifer temperatures that are too low. On the other hand, waters initially having enough Ca to deposit calcium carbonate during ascent may yield estimated aquifer temperatures that are too high if aqueous Na and K are prevented from further reaction with country rock owing to armoring by calcite or silica minerals. The Na-K-Ca geothermometer is of particular interest to those prospecting for geothermal energy. The method also may be of use in interpreting compositions of fluid inclusions.

Chemical geothermometers and mixing models for geothermal systems

Abstract Qualitative chemical geothermometers utilize anomalous concentrations of various “indicator” elements in groundwaters, streams, soils, and soil gases to outline favorable places to explore for geothermal energy. Some of the qualitative methods, such as the delineation of mercury and helium anomalies in soil gases, do not require the presence of hot springs or fumaroles. However, these techniques may also outline fossil thermal areas that are now cold. Quantitative chemical geothermometers and mixing models can provide information about present probable minimum subsurface temperatures. Interpretation is easiest where several hot or warm springs are present in a given area. At this time the most widely used quantitative chemical geothermometers are silica, Na/K, and Na-K-Ca.

An equation correlating the solubility of quartz in water from 25° to 900°C at pressures up to 10,000 bars

The solubility of quartz in water from 25° to 900°C at specific volume of the solvent ranging from about 1 to 10 and from 300° to 600°C at specific volume of the solvent ranging from about 10 to 100 is given by an empirically derived equation of the form: log m = A + B(log V) + C(log V)2 where m is the molal silica concentration, V is the specific volume of pure water, and A = −4.66206 + 0.0034063T + 2179.7T−1 − 1.1292 × 106T−2 + 1.3543 × 108T−3B = −0.0014180T— 806.97T−1C = 3.9465 × 10−4T T is temperature in kelvins. The experimental data used in formulating the empirical relation ranged in pressure from 1 bar at 25°C to about 10,000 bars at 900°C, and the lowest pressure in the low-density steam region was about 30 bars. According to the above equation, the average difference in molality between 518 measured and calculated solubilities is −0.016 m with a standard deviation of 0.089.

Magnesium correction to the NaKCa chemical geothermometer

Abstract Equations and graphs have been devised to correct for the adverse effects of magnesium upon the Na-K-Ca chemical geothermometer. Either the equations or graphs can be used to determine appropriate temperature corrections for given waters with calculated NaKCa temperatures > 70°C and R R = { Mg (Mg + Ca + K) } × 100 with cation concentrations expressed in equivalents. Waters with R > 50 are probably derived from relatively cool aquifers with temperatures approximately equal to the measured spring temperature, irrespective of much higher calculated Na-K-Ca temperatures.

The solubility of quartz in water in the temperature interval from 25° to 300° C☆

Abstract The solubility of quartz in water was investigated by three sets of experiments 1. (1) at 1000 atm PH2O and temperatures ranging from 45° to 300°C 2. (2) at water pressures appropriate for the coexistence of three phases, gaseous water, liquid, and quartz, at temperatures ranging from 69° to 240°C 3. (3) a long term study of the dissolution of quartz grains which were continuously tumbled in water at room temperature. Saturated silica solutions in equilibrium with quartz were obtained in a few days at temperatures above 100°C. Equilibrium is shown by reproducible results for runs of different durations and by the precipitation of quartz from initially supersaturated solutions. The differential heat of solution derived from the data obtained at 1000 atm pressure is 5.38 kcal/mole. At room temperature and pressure, highly supersaturated silica solutions were obtained by continuously rotating quartz grains and water in plastic bottles at 75 rev/min. In one run the amount of silica in solution increased to a maximum value of 395 p.p.m. after 370 days. Another run reached 80 p.p.m. silica after 386 days and then dropped to 6 p.p.m. silica. It is concluded that quartz was precipitated at room temperature from this supersaturated solution and that 6 p.p.m. is essentially the true solubility of quartz at 25°C. In contrast to the runs rotated at 75 rev/min, quartz grains, and also silica glass grains, continuously rotated in water at 1 2 rev/min, each contributed less than 1 p.p.m. colorimetric silica into solution after 1 year. Thus, vigorous agitation of the liquid is necessary to remove dissolved silica from the vicinity of surfaces of both quartz and glass. Two significant factors that may have contributed to the formation of supersaturated silica solutions in the runs rotated at 75 rev/min at room temperature are 1. (1) stresses and structural irregularities at the surfaces of the crushed quartz grains, which contributed silica into solution more readily than well crystallized quartz 2. (2) the very slow rate at which dissolved silica polymerizes to species appropriate to act as nuclei for quartz growth. At the termination of the runs rotated at 75 rev/min, spikelike projections were present on many of the quartz grains. These are interpreted as indicating that abrasion was not the dominant cause for the great supersaturations which were obtained.

A method of calculating quartz solubilities in aqueous sodium chloride solutions

Abstract The aqueous silica species that form when quartz dissolves in water or saline solutions are hydrated. Therefore, the amount of quartz that will dissolve at a given temperature is influenced by the prevailing activity of water. Using a standard state in which there are 1,000 g of water (55.51 moles) per 1,000 cm 3 of solution allows activity of water in a NaCl solution at high temperature to be closely approximated by the effective density of water, p e , in that solution, i.e. the product of the density of the NaCl solution times the weight fraction of water in the solution, corrected for the amount of water strongly bound to aqueous silica and Na + as water of hydration. Generally, the hydration of water correction is negligible. The solubility of quartz in pure water is well known over a large temperature-pressure range. An empirical formula expresses that solubility in terms of temperature and density of water and thus takes care of activity coefficient and pressure-effect terms. Solubilities of quartz in NaCl solutions can be calculated by using that equation and substituting p e , for the density of pure water. Calculated and experimentally determined quartz solubilities in NaCl solutions show excellent agreement when the experiments were carried out in non-reactive platinum, gold, or gold plus titanium containers. Reactive metal containers generally yield dissolved silica concentrations higher than calculated, probably because of the formation of metal chlorides plus NaOH and H 2 . In the absence of NaOH there appears to be no detectable silica complexing in NaCl solutions, and the variation in quartz solubility with NaCl concentration at constant temperature can be accounted for entirely by variations in the activity of water. The average hydration number per molecule of dissolved SiO 2 in liquid water and NaCl solutions decreases from about 2.4 at 200°C to about 2.1 at 350°C. This suggests that H 4 SiO 4 may be the dominant aqueous silica species at 350°C, but other polymeric forms become important at lower temperatures.

Geochemical and hydrologic considerations and the use of enthalpy-chloride diagrams in the prediction of underground conditions in hot-spring systems

Abstract Thermal water ascending in a hot-spring system may cool by conduction of heat to the surrounding rock, by boiling, by mixing with cooler water, or by a combination of these processes. Complete or partial chemical reequilibration may occur as a result of this cooling. In spite of these complexities, in many places chemical compositions of hot-spring waters may be used to estimate underground conditions. A plot of enthalpy versus chloride is particularly useful for determining underground temperatures, salinities, and boiling and mixing relations. The utility of this approach is illustrated using hot-spring composition data from Cerro Prieto, Mexico, Orakeikorako, New Zealand, and Yellowstone National Park, Wyoming.

Recent crustal subsidence at Yellowstone Caldera, Wyoming

AbstractFollowing a period of net uplift at an average rate of 15±1 mm/year from 1923 to 1984, the east-central floor of Yellowstone Caldera stopped rising during 1984–1985 and then subsided 25±7 mm during 1985–1986 and an additional 35±7 mm during 1986–1987. The average horizontal strain rates in the northeast part of the caldera for the period from 1984 to 1987 were:

The generation of HCl in the system CaCl2-H2O: Vapor-liquid relations from 380–500 °C

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