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Mass spectrometer measurements in the thermal areas of New Zealand
Qeochimica et Cosmochimica Acta, 1962, Vol. 26, pp. 383 to 397. Pergamon Press Ltd. Printed in Northern Ireland
Mass spectrometer measurements in the thermal areas of New Zealand Part 1. C arbon dioxide and residualgas analyses* J. R. HULSTON and W. J. MCCABE Institute of Nuclear Sciences, Department of Scientifk and Industrial Reseatoh, Lower Hutt, New Zealand (Received 7 November
1960)
Abstract-Mass spectrometer measurements have been made on carbon dioxide and residual gases in some thirty geothermal bores, fumaroles and pools in New Zealand. With one exception, the A’O/A*e ratio in the discharges show the argon to be of atmospheric origin. Consideration of argon to water ratios appears to confkn the hypothesis that loss of gas occurs underground in some areas. The argon to nitrogen ratios which were lower than the 2.7/100 value expected from heated ground water, suggest an alternative source of nitrogen. The excess nitrogen appears to be related to the total hydrogen content by a square law. The underground temperatures calculated assuming chemical equilibrium between carbon dioxide itnd methane are given in some cases and are in reasonable agreement with boremeasure-
ments. MUCH of the published work on analysis of thermal gases has been directed towards explaining the composition in terms of an original simple gas mixture, which has been variously modified by temperature and pressure variations and reactions with country rock before being discharged. While this approach seems to be the correct one the possibility of significant quantities of gases of surface origin entering the system should not be overlooked. For example, nitrogen, oxygen and argon from the atmosphere and ammonia and methane from decayed organic matter are likely to appear in geothermal gases in amounts which may represent the major part of these gases present. ELLIS (1957)has concluded that magmatic gases approach a state of chemical equilibrium. If this is true for the reaction (ELLIS, 1957; CRAIG, 1953) CO2 + 4H, % CH, + 2H,O it would be possible to calculate the temperature of the mixture when equilibrium was obtained, if the relative quantities of the constituents were known. While a survey of the thermal areas of New Zealand (Fig. 1) was being made to study the carbon isotopes, advantage was taken of the available samples to analyse them with a view to obtaining further information on the processes that produce the discharges. The mass spectrometer provides a convenient method of analysing gas mixtures, some components of which are difficult to determine by conventional gas analysis, e.g. inert gases. The sampling methods used, while being designed particularly to produce isotopically uncontaminated carbon samples, are still quite suitable for general gas collection. The collection of hydrogen sulphide which was not required here would, however, necessitate all metal apparatus being made of stainless steel. * Contribution No. 68 from Institute of Nuclear Sciences, New Zealand. 383
The methods described below are developments of methods ~~sctl previously )JJ workers in the geothermal areas of New Zealand. The gas bubbling from pools was collected in 000 ml bottles by \vater displacement. These bottles described by WILSOS (I!).%). are fit~ted with a :3-in.
NORTH ISLAND mrapiti
i
length of butyl rubber tubing on the inlet, a Hofiman clip and a glass plug, and are evacuated to a few microns pressure before use. Prior to collecting the sample this plug \vas removed and t’he short stem of a shallow but, broad funnel inserted into the tubing. The funnel, the size of which depended on the gas flow from t,he pool. w-as weighted around the edge to reduce buoyancy. Air was removed from the funnel once it was in t’hr pool by inverting it. ‘l’h~ clip was removed and the bott.le filled with water. The’ bottle and funnel nere tIllen winvcrted and placed
Mass spectrometer
measurements
in the thermal areas of New Zealand
385
over the source of gas. The total gas output from the pool was estimated from the time taken to fill the sample bottle, together with an estimate of the proportion of the pool gas output being collected by the funnel. The water outflow was measured by observing the time taken to fill a container of known volume at the outflow, or if this was not possible, the cross-sectional area of the outflow channel and the velocity of the water in it were estimated. Samples of the total discharge of fumaroles were collected in an evacuated flask of several litres capacity containing 8N NaOH. One end of a long length of copper tubing was pushed well down into the vent and the tube flushed with steam before connecting it to the flask. Collection continued until cooling of the flask indicated that no more steam was being condensed. The gas to water ratios were obtained from the relative quantities of carbon dioxide, residual gases and condensate, determined during sample preparation. The apparatus shown in Fig. 2 for collecting gas samples from bores is a development of that described by FERCUSSON and KNOX (1959). The apparatus used by the authors completely separates gas from water and so is not limited by the quantity of water condensed. Because of more efficient cooling and preliminary separation the sample is collected more quickly. The first steam and water cyclone separator operating at as high a pressure as possible removes most of the water, which if not removed would increase the load on the first cooler and dissolve appreciable quantities of gas. The steam from S, at 150-200°C is cooled by the boiling water condenser to 130-170°C. The valve V3 controls the pressure at Pg and consequently the temperature of the steam in the condenser. The second separator, operating at low pressure, removes condensed water, the volume of which is measured, and the steam and gas pass into the air-cooled condenser. The water condensed in the top of this section tends to dissolve some gas on cooling, but this gas is largely removed by the incoming steam containing gas at a much lower partial pressure. The tlow of dry gas from the top of the condenser is observed in the glass gas bubbler containing water and the pressure maintained at approximately one atmosphere by means of the screw clip on the lead into the evacuated flask containing 500 ml of 1ON sodium hydroxide. An average of 35 litres of carbon dioxide and 400 ml of residual gases were obtained from a collection lasting an hour. The collection of bore water and condensate samples was made according to the methods used by ELLIS and WILSON (pers. comm.) by utilizing the lagged stainless steel separator S, shown in Fig. 2. For the water collection the finned tubing was transferred to V, and the outlet led into a 29 litre bottle. The valves were adjusted so that some surplus water was present in the steam discharged. For the collection of condensate the finned tubing was removed from the separator and the valves readjusted so that dry steam was being discharged through V,. Some of this dry steam was led into a 5 litre glass bulb with connections at both ends. When this flask had been thoroughly heated and swept with steam, the outlet was closed off and the flask cooled. Cooling was continued until no further steam was drawn into the flask and the inlet was closed off. The relative quantities of water and steam were calculated from enthalpy values obtained from the Ministry of Works. These values, together with the quantity of carbon dioxide, residual gases and
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Mass spectrometer measurements in the thermal areas of New Zealand
387
condensate obtained from the apparatus shown in Fig. 2, were used to calculate the ratios of carbon dioxide and residual gases to water. SAMPLE PREPARATION The preparation of gases for mass spectrometer analysis was carried out in a laboratory vacuum system in which were incorporated a trap cooled in dry ice to remove water, a liquid oxygen cooled trap to condense carbon dioxide and a toepler pump to handle non-condensable (residual) gases. The quantities of carbon dioxide and residual gases were determined in calibrated volumes by pressure measurements, and samples for analysis taken in breakseal tubes. Some residual gases were processed further as described in Part II of this paper. To each of the flasks containing the bore condensates was added 100 ml of carbonate free, 10N sodium hydroxide solution to absorb the carbon dioxide. To recover the carbon dioxide gas from this solution from fumarole condensates, and from water samples containing free carbon dioxide and bicarbonate ions, the liquid was acidified, swept with nitrogen and the mixed gases dried and the carbon dioxide condensed as before. A few water samples were swept with nitrogen to remove the free carbon dioxide before acidification and removal of the bicarbonate ion. MASS SPECTROMETERANALYSIS The mass spectrometer used is a 60” Nier type using magnetic ion selection and manual peak height measurement. A calibration of this instrument for the gas mixtures N, and O,, N, and H,, N, and A, A and CH,, and for the argon isotopes was carried out before the analyses were started. As greater accuracy was needed for the argon-nitrogen ratios this calibration was repeated several times during the period in which the measurements were carried out. It is estimated that the accuracy of these A/N ratios is approximately 1-123 per cent of the values given. The accuracy of the other components is approximately 10 per cent of the values given. The measurement of A40/A36 ratios was complicated by the fact that apparatus to remove the nitrogen from the sample was not available at the time when the majority of the samples were analyzed, and it was necessary to measure the A40/A36 ratios by introducing the sample to the mass spectrometer at higher pressures than usual. This is reasonably satisfactory for samples containing more than 1 part of argon per 100 parts of nitrogen, provided there is no mass 36 hydrocarbon contamination present in the sample. Samples which gave A40/A36 ratios less than 240 were rejected, and where possible were held until they could be processed in a system containing both a Calcium furnace (to remove the nitrogen), and a Cu-CuO furnace and a cold trap (to remove the hydrocarbons and hydrogen). The standard deviation of the A4°/A36 ratios given in Table 1 is 5 per cent. RESULTS The analytical parts of nitrogen.
results for individual gases given in Table I are referred to 100 The relative values given for carbon dioxide were estimated
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and
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from the relative quantities of carbon dioxide and total residual gases obt,ained iii the chemical separation process. The ratios of argon and carbon dioxide in the gas phase to total water discharge (H,O,) were calculated from the gas to water ratios measured as described above. The tot’al quantity of carbon dioxide in the water expressed in ,umoles per mole of total wat’er. the pH and t’he surface temperature of the water are given where these are available. The output and temperatures of the JVairakei bores are found to vary- w-ith time. The results in ‘Table 1 refer to collections made in April, 1!)5~.
Argon4O/urgons6 ratios Potassium bearing rocks of great age build up quantities of argon 40 due to the K-capture decay of potassium 40. If these rocks are later heated to sufficient temperature to release A 4o then this may appear in the gas discharge and thus upset the calculations which are based on the assumption that’ all the argon in the discharge is of atmospheric origin. Since radiogenic argon is pure AJO but atmospheric argon contains I part of As6 per 295 parts of A40, the presence of radiogenic argon can be determined by measuring the A40/A3’j ratio of the samples as described previously. BOATO et al. (1952) have reported A40/L436ratios up to 100 per cent above the atmospheric value in particular cases, and in the Larderello thermal area the variations range from 10 to 25 per cent, above atmospheric. ZARTMAK> WASSERBERG and REYNOLDS (1961) have reported values ranging from approximately .i per cent above to one hundred times atmospheric for natural gas wells in America. It will be seen in Table I that all ratios, with the exception of that from Hammer Springs, are not significantly different from atmospheric. In the following discussions it has been assumed that virtually all argon is of atmospheric origin. Some radiogenic argon may be present, but it cannot, be detect,ed owing t,o the relativeI) large amount of argon of atmospheric origin which occurs.
A small number of samples were checked at high sensitivity for helium, as the presence of this gas would indicate that uranium bearing rocks occurred underground. These measurements showed that there is approximately 041 parts of helium present per 100 parts of nitrogen. This is of the same order as that present in samples collected from non-thermal gas flows in New Zealand (FARE and ROGERS, 1929) and is approximately 200 times that present in air. Argon-watw
ratios
The ratios of argon to water have been recorded in Table I, where it has been possible to obtain the necessary information. From solubility tables one would expect pure water at 10” C in equilibrium with air to contain 12 ,umoles of nitrogen and 0.32 pmoles of argon per mole of water (,uM/M), i.e. an argon to nitrogen ratio of 2.7 to 100, as dissolved gases together with oxygen and carbon dioxide. The results for the Waikato River between !l’aupo and Wairakei at 11” C’ showed
Mass spectrometer measurements in the thermal areas of New Zealand
391
the presence of 12 ,uM/M of nitrogen and 0.30 ,uM/M of argon which is in good agreement with the above. Thus, if water in equilibrium with air passed underground, was heated, and there was no separation of gas and steam from the water, or addition of gas or water from another source, it would be expected that this ratio of argon and nitrogen would be maintained in a bore discharge. From Table I it will be seen that in all the gas samples measured, the argon to water ratios are less than 0.32 ,uM/M. However, in pools which have a low carbon dioxide content in the gas phase, the partial pressure of argon is sufficiently h.igh for it to be lost to the water phase as dissolved gas. For example, if the total argon output of Awakeri Springs is measured it is found that 0*42 & O-1 PM/M of argon is discharged which is in the range expected. For the other samples measured the correction is very small and the results still give much less argon than expected. One reason for this may be that only part of the water is ground water. However, WILSON (1955) estimates from chloride contents that the magmatic water contribution at Wairakei is about 8 per cent. Thus a more likely explanation for this area is that there has been a separation of gas and water at some point between the water intake and the thermal discharge and that this gas has been lost. For example, an argon to water ratio of 0.03 PM/M would indicate that approximately 10 per cent of the gas remained. This agrees with a gas loss estimate of 90 per cent given by RAFTER, WILSON and SHILTON (1958) based on hydrogen sulphide content of bore discharges. If this was the reason for the low ratios, it would seem that between 80 and 95 per cent of the gas had been lost. The very high carbon dioxide to water ratio and temperature of the Big Donald fumaroles on White Island could be explained by a large proportion of the gas .discharge being of magmatic origin. This could also explain the low argon to water ratio found for these fumaroles without the necessity of postulating a loss of gas mechanism. The high argon content of the gas from the Seven Dwarfs fumarole, however, suggests a large dilution with argon containing water. Argon-nitrogen
ratios
It will be seen from Table I that the measured argon to nitrogen ratios are lower than the 2.7/100 value calculated above from solubility data. Two possible explanations of this will be considered. (i) Fractionation of the gases when argon and nitrogen are lost to the water phase. (ii) The addition of nitrogen from magmatic gases and from ammonia of organic origin. (i) When the discharge is from a pool where argon and nitrogen are lost in the water phase, there is fractionation of these gases. Under equilibrium conditions in the temperature range O-90” C the ratio (A/N) water phase (A/N) gas phase
+ 2.2.
Fig. 3 illustrates the calculated effect of different temperature and carbon dioxide contents on the argon to nitrogen ratio of the gas phase in a pool discharging a
total of 0.31 ,uM/M of argon and 12 PM/M of nitrogen. in the following manner:
These curves are obtained
(‘1
N,- is then calculated from the solubility tables and the percentage of nitrogen in the gas phase. Laboratory experiments on air saturated water at room temperature show that when a portion of the dissolved gas was removed by suddenly decreasing the pressure, the initial argon to nitrogen ratio of the gas and water phases is the same, but after the remaining mixture had been shaken for a few minutes equilibrium conditions were found to exist. Thus the fractionation shown in Fig. 3 will apply only to pools where the gas and liquid phases are in contact for sufficient time for equilibrium to be established. Although the relative solubilities of argon and nitrogen are not known above about 00” C it is probable that the argon still favours the water phase at these temperatures. Thus if the loss of gas underground occurs under equilibrium conditions the argon to nitrogen ratio in the water phase will rise above the 2*7/100 value. However, if equilibrium conditions are not attained, there would be little change in the argon to nitrogen ratio in the \vater remaining. It is possible in some of the pools where the gas discharge is rather slog that equilibrium conditions are reached in the surface discharge and that fractionation occurs. It is also possible that there is much less than 0.32 ,LM/M of argon (due to prior loss of gas) and hence t,hc fractionation is greater than t’hat shown in Fig. 3. Pool lS6 in Geyser Valley may be at1 example of this. The gas to water ratio of this pool was not measured, but’ calculations using equation (4) in the form 4: __ 0-32X where S is the proportion of gas remaining, indicate that it N,: 12x + l.dN,, would be necessary for t’here to be Z/3 loss of gas in the underground water supplying the pool. .In a few pools, A/N values have been measured for both t,ho gas and water phases, and these results are given in Table I. In Rotoma Soda Hprings the ratios are similar and probably indicat,c that equilibrium is not reached. 111 Awakeri Springs the A/N ratio is lower in the gas thaii in the water. This indicates that equilibrium conditions could exist. but, it’ is also possible that cold water of A/S ratio 2*7/100 and hot gas and steal11 of about I .3/100 ratio coultl bo mising just below the surface wit,hont, equilibrium being re-estJabIishetl. ‘I’he latt(xr j)ossibilit> is suggested by t’he work of Felts: I-YSOS (pers. comm.) who tlctc~ctctl considerably more carbon-14 in the \\,ater l)has~~than in t)he gas phase, although i[I a rcpcnt collection to confirm this result insufficient carbon dioxide could be obtained from the gas phase to make a carbon-14 cleterminat,ion.
Mass spectrometer
meesuromonts
in t.he thermal
areas
of New Zealand
393
(ii) The majority of the samples in Table 1 have argon to nitrogen ratios which are lower than can be explained by the system above, as is illustrated by the results plotted in Fig. 3. These results are possibly due to nitrogen being added from both magmatic gases and ammonia of organic origin. ‘NH,
-+ 3H, + N,
If the latter were the main contribution, then t.here should be a linear correlation between the additional nitrogen and the hydrogen content. This is complicated by some of the hydrogen reacting to form other molecules such as methane: 4H, + CO, L+ eH,O
+ CH,
-
1.4
3 \i + !3‘2%
‘I-*
30 Pool
50
60
lem3ermure.
OC
90
Fig. 3. Argon-Nitrogen ration of B pool discharging water which has originally been in equilibrium (at 10’ C) with air, together with some natural pool results.
Jn Fig. 4 a function of the total hydrogen content, obtained by adding to the measured hydrogen an amount of hydrogen equal to four t.imes the measured methane, has been plotted against a function of the surplus nitrogen, which is defined as all the nitrogen above the quantity needed to give an argon to nitrogen ratio of 2*7/100. These functions, which are respectively the ratio of total hydrogen to argon and surplus nitrogen to argon, were used as being equivalent to total hydrogen t.o water and surplus nitrogen to water ratios, assuming that there had been no gas loss. It will be seen, in Fig. 4, that with the exception of two Big Donald samples, the concentration of tot.al hydrogen is very approximately proportional to the square of the surplus nitrogen concentration. As the relationship is not a first order one, the ammonia decomposition does not appear to be the major contributor to the surplus N,. Furthermore, since a
394
and TV.
J. R. HCLSTOW
J.
MCCABE
relationship does appear to exist, there may be some other equilibrium in existence. It has not been possible, however, t,o identify a particular reaction which might be responsible for this relationship.
Since conditions underground are reducing, it would be expect,ed that very little oxygen should be present in the samples collected from t,he discharges. The difference in oxygen content between surface and underground is shown in the I
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of “Surplus
Xtrogon”
r,$
hydrogen/argon
to “Total
Hytlrogcn“
in geot~hormal tlisrhargrs.
oxygen to nitrogen ratios for the Hutt River at Silverstream of 59/100, and the same water after having passed through the Hutt’ Valley artesian system with a ratio of 3/100. It will be seen from Table 1 that the samples from most of the bores and fumaroles contain about 0.3 parts of oxygen per 100 parts of nitrogen. This may be due to air contamination of the sample. If this were so, it would represent l-5 per cent air in the residual gas. Although samples from some pools, namely, Whale Island (R477/1 and 6), Onepu (R473/1), Waiotapu and h’gawha, are of the same order, the tendency is for pool samples to contain more oxygen. In the Geyser Valley (Wairakei) samples for example the lowest oxygen content is 5-2 parts per 100 parts of nitrogen. It is worthwhile considering whether this is due to air contamination of the sample. If this occurred, then in the worst case, pool 186, the collection would need to be one third air. As however the gas pressures in the bottles were
Mass spectrometer
measurements
in the thermal areas of New Zealand
398
measured in the first step of the chemical separation and were found to vary by only &5 per cent at 65 cm of mercury, it is improbable that this is due to leakage into the bottles after collection. It thus appears likely that the oxygen content of these samples is at least partially real. ALLEN and DAY (1935) found the oxygen contents in pool samples from Yellowstone Park, U.S.A., to be larger than normal for air contamination and suggested that this might be due to dissolved oxygen carried down by locally descending surface water. This appears to be the most likely explanation for the oxygen present in these Geyser Valley pools, particularly as they are all below the level of the surrounding country. Chemical equilibrium
between CO, and CH,
Previous workers (CRAIG 1953, ELLIS 1957) in this field have considered the chemical and isotopic equilibrium of methane and carbon dioxide in geothermal discharges. The overall mechanism usually suggested is the reaction: CH, + 2H,O<,, + CO, + 4H, It is probable that carbon monoxide is an intermediary in the reaction, but the chemical equilibrium constants are such that the concentration is normally very low, and was not detected by the authors. In Table 2 values of K, calculated by Ellis for the above reaction are given where
Table
2.
Values of equilibrium constant for methane-carbon dioxide reaction T” K 1000 700 600
-
K, (atmospheres0) 2.78 x 1O-2 4.21 x 102 7.40 x 104 8.73 x 10’ 2.75 x 10la
It will be seen that there is considerable variation of K, with temperature. In Table 1 the equilibrium temperatures have been calculated for chemical equilibrium of the gases analysed. In making this calculation the partial pressure of water vapour has been taken to be that of saturated water vapour at that temperature. On the assumption that there is only a small gas phase, the partial pressures have been calculated using the molar concentrations derived from Table 1 together with gas solubility data obtained from Ellis and Fyfe (1957) and from the Handbook of Physics and Chemistry. Some extrapolation was necessary -for the methane data. It will be seen from Table 1 that in general there is reasonable agreement between temperatures based on chemical equilibrium and on geothermograph measurements, especially considering the possible errors in the chemical measurements.
396
J. K. HULSTOS
and \is. 5. McCxaz
(1957) concluded that the agreement between field results and those calculated was an indication that magmatic gases approach a state of chemical equilibri~~ni. It will also be seen from Table 1 that, the llydrogen contents of two samples collected from Big Donald Mound on White Island are widely different,. The difference in the calculated equilibrium temperatures is, however, in the same direction as that estimated when the samples were collected. Bs the reaction given above is normally thought to be rather dew at the temperatures involved here it was decided to conduct a laboratory experiment. Carbon dioxide, hydrogen and water were heated in a steel bomb at al)proximately 250” f ’ for a period of t-we months. 1Jhe contents of the bomb were then analysed on the mass spectrometer and the methane found to be just above the mass spectrometer background. From this it was estimated that the reaction has a half time of at’ least five years in a typical bore. Because catalysts or poisons could easily change the rate in the ~~x~(~ergroundsit~~atioI~s,these e~perimel~ts were not ~ursued~ ELLIS
The use of argon as a tracer of atmospheric gases indicates that there has been a considerable loss of gas in many areas, particularly at Wairakei. This would tend to support the hypothesis that in the latter area the water has travelled some distance horizontally before reaching the bores sampled here. The argon to nitrogen ratios are in most cases much lower t~han expected for gas collected from heated ground water. The square of tSlic concentration of nit’rogen in excess of that expected from ground water appears to be proportional to the t’otal hydrogen concentration. The I~resence of appreciable oxygen perceIltages in pool samyies is ~,ho~~gl~tt,o be due to contamination with shallow groundwater containing dissolved oxygen. The AJ0/A36 ratios of the samples measured were not significantly different from t’hat obtained from argon of atmospheric origin, except in the case of Hnnmer Springs. Comparison of temperatures calculated assuming t,ho existence of chemical equilibrium between CO, and CH, with t)emperatures measured, show reasonably good agreement and thus tend to indicate that these gases at least approach a state of chemical equilibrium.
REBEREXCES ALLJXN E. T. and DAY A. L. (1935) Hot, Springs of the Yellowstone Nat,ional l%rk.
Carnegie Inst., Washington, P&l. A-0. 466, 525 pp. BOAT0 G. C&I%ERI G, and SAWI!ANGELO RiI.(1952) !qpn Isotopt~s in ~8,txard i&~% ~~zmw Cimento 9, 44-49. c&wckitn. et C’owwchim. A&l, CRAIG H. (1953) The Geochemistry of the Stable Carbon Isotopes. 3, 53-92. ELLIS A. J. (1957) Chemical ~~~lilibriunl in ~~~~at~c Gases. Bm,er. J. Sri. 255, 4tii-431. ELLIS A. J. Pomona1 Communication. ELLIS A. J. and FYFIZ I%',S. (1957) Hydrothermal Chemistry. Rev. .Vwr. dppI. C'kern.7, 261416. FARR C. C. and ROGERS M. N. (1929) Helium in Sew Zealand. ,V.%. J. Sri. Tech. 10, 300408. FERGUSSOW f:. J. and K~:ox P. B. (1959) The Possibilities of Nat,iond Radio-carbon as a Ground Water Tracer in Thermal Areas. X.Z. J. Sci. 2, 431-441.
Mass spectrometer
measurements
in the thermal areas of New Zealand
397
Handbook of Chemistry and Physics. 38th Edition. p. 1608. Chemical Rubber Publishing Co., Ohio. RAFTER T. A. WITSON S. H. and SHILTON B. W. (1958) Sulphur Isotopic Variations in Nature. Pt 5-Sulphur Isotopic Variations in New Zealand Geothermal Bore Waters. N.Z. J. ii’& 1, 103-126. WILSON S. H. (1953) The Chemical Investigation of the Hot Springs of the New Zealand Thermal Region. Proo. Seventh Pacific Science Congress 2, 449-469. WILSON S. H. (1955) Geothermal Steam for Power in New Zealand-Chemical Investigations. N.Z.D.S.I.R. Bull. 177, pages 27-42. WILSON S. H. Personal Communication. ZARTMAN R. E., WASSERBURG G. J., and REYNOLDS J. H. (1961) Helium, Argon, and Carbon in Some Natural Gases. J. Geo~~~,~s.Res. 61,277-306.
Mass spectrometer measurements in the thermal areas of New Zealand Part 1. C arbon dioxide and residualgas analyses* J. R. HULSTON and W. J. MCCABE Institute of Nuclear Sciences, Department of Scientifk and Industrial Reseatoh, Lower Hutt, New Zealand (Received 7 November
1960)
Abstract-Mass spectrometer measurements have been made on carbon dioxide and residual gases in some thirty geothermal bores, fumaroles and pools in New Zealand. With one exception, the A’O/A*e ratio in the discharges show the argon to be of atmospheric origin. Consideration of argon to water ratios appears to confkn the hypothesis that loss of gas occurs underground in some areas. The argon to nitrogen ratios which were lower than the 2.7/100 value expected from heated ground water, suggest an alternative source of nitrogen. The excess nitrogen appears to be related to the total hydrogen content by a square law. The underground temperatures calculated assuming chemical equilibrium between carbon dioxide itnd methane are given in some cases and are in reasonable agreement with boremeasure-
ments. MUCH of the published work on analysis of thermal gases has been directed towards explaining the composition in terms of an original simple gas mixture, which has been variously modified by temperature and pressure variations and reactions with country rock before being discharged. While this approach seems to be the correct one the possibility of significant quantities of gases of surface origin entering the system should not be overlooked. For example, nitrogen, oxygen and argon from the atmosphere and ammonia and methane from decayed organic matter are likely to appear in geothermal gases in amounts which may represent the major part of these gases present. ELLIS (1957)has concluded that magmatic gases approach a state of chemical equilibrium. If this is true for the reaction (ELLIS, 1957; CRAIG, 1953) CO2 + 4H, % CH, + 2H,O it would be possible to calculate the temperature of the mixture when equilibrium was obtained, if the relative quantities of the constituents were known. While a survey of the thermal areas of New Zealand (Fig. 1) was being made to study the carbon isotopes, advantage was taken of the available samples to analyse them with a view to obtaining further information on the processes that produce the discharges. The mass spectrometer provides a convenient method of analysing gas mixtures, some components of which are difficult to determine by conventional gas analysis, e.g. inert gases. The sampling methods used, while being designed particularly to produce isotopically uncontaminated carbon samples, are still quite suitable for general gas collection. The collection of hydrogen sulphide which was not required here would, however, necessitate all metal apparatus being made of stainless steel. * Contribution No. 68 from Institute of Nuclear Sciences, New Zealand. 383
The methods described below are developments of methods ~~sctl previously )JJ workers in the geothermal areas of New Zealand. The gas bubbling from pools was collected in 000 ml bottles by \vater displacement. These bottles described by WILSOS (I!).%). are fit~ted with a :3-in.
NORTH ISLAND mrapiti
i
length of butyl rubber tubing on the inlet, a Hofiman clip and a glass plug, and are evacuated to a few microns pressure before use. Prior to collecting the sample this plug \vas removed and t’he short stem of a shallow but, broad funnel inserted into the tubing. The funnel, the size of which depended on the gas flow from t,he pool. w-as weighted around the edge to reduce buoyancy. Air was removed from the funnel once it was in t’hr pool by inverting it. ‘l’h~ clip was removed and the bott.le filled with water. The’ bottle and funnel nere tIllen winvcrted and placed
Mass spectrometer
measurements
in the thermal areas of New Zealand
385
over the source of gas. The total gas output from the pool was estimated from the time taken to fill the sample bottle, together with an estimate of the proportion of the pool gas output being collected by the funnel. The water outflow was measured by observing the time taken to fill a container of known volume at the outflow, or if this was not possible, the cross-sectional area of the outflow channel and the velocity of the water in it were estimated. Samples of the total discharge of fumaroles were collected in an evacuated flask of several litres capacity containing 8N NaOH. One end of a long length of copper tubing was pushed well down into the vent and the tube flushed with steam before connecting it to the flask. Collection continued until cooling of the flask indicated that no more steam was being condensed. The gas to water ratios were obtained from the relative quantities of carbon dioxide, residual gases and condensate, determined during sample preparation. The apparatus shown in Fig. 2 for collecting gas samples from bores is a development of that described by FERCUSSON and KNOX (1959). The apparatus used by the authors completely separates gas from water and so is not limited by the quantity of water condensed. Because of more efficient cooling and preliminary separation the sample is collected more quickly. The first steam and water cyclone separator operating at as high a pressure as possible removes most of the water, which if not removed would increase the load on the first cooler and dissolve appreciable quantities of gas. The steam from S, at 150-200°C is cooled by the boiling water condenser to 130-170°C. The valve V3 controls the pressure at Pg and consequently the temperature of the steam in the condenser. The second separator, operating at low pressure, removes condensed water, the volume of which is measured, and the steam and gas pass into the air-cooled condenser. The water condensed in the top of this section tends to dissolve some gas on cooling, but this gas is largely removed by the incoming steam containing gas at a much lower partial pressure. The tlow of dry gas from the top of the condenser is observed in the glass gas bubbler containing water and the pressure maintained at approximately one atmosphere by means of the screw clip on the lead into the evacuated flask containing 500 ml of 1ON sodium hydroxide. An average of 35 litres of carbon dioxide and 400 ml of residual gases were obtained from a collection lasting an hour. The collection of bore water and condensate samples was made according to the methods used by ELLIS and WILSON (pers. comm.) by utilizing the lagged stainless steel separator S, shown in Fig. 2. For the water collection the finned tubing was transferred to V, and the outlet led into a 29 litre bottle. The valves were adjusted so that some surplus water was present in the steam discharged. For the collection of condensate the finned tubing was removed from the separator and the valves readjusted so that dry steam was being discharged through V,. Some of this dry steam was led into a 5 litre glass bulb with connections at both ends. When this flask had been thoroughly heated and swept with steam, the outlet was closed off and the flask cooled. Cooling was continued until no further steam was drawn into the flask and the inlet was closed off. The relative quantities of water and steam were calculated from enthalpy values obtained from the Ministry of Works. These values, together with the quantity of carbon dioxide, residual gases and
1
stea
Water
8in.dla.
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1
for
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Globe
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collecting
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Gloss gas
carbon dioxide and residual gases from bores.
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1 ,
4 I I
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dry
STEAM Unless
gas
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COP
bubble<
from
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250lb
bores
1L f&k 10N NoOH
Mass spectrometer measurements in the thermal areas of New Zealand
387
condensate obtained from the apparatus shown in Fig. 2, were used to calculate the ratios of carbon dioxide and residual gases to water. SAMPLE PREPARATION The preparation of gases for mass spectrometer analysis was carried out in a laboratory vacuum system in which were incorporated a trap cooled in dry ice to remove water, a liquid oxygen cooled trap to condense carbon dioxide and a toepler pump to handle non-condensable (residual) gases. The quantities of carbon dioxide and residual gases were determined in calibrated volumes by pressure measurements, and samples for analysis taken in breakseal tubes. Some residual gases were processed further as described in Part II of this paper. To each of the flasks containing the bore condensates was added 100 ml of carbonate free, 10N sodium hydroxide solution to absorb the carbon dioxide. To recover the carbon dioxide gas from this solution from fumarole condensates, and from water samples containing free carbon dioxide and bicarbonate ions, the liquid was acidified, swept with nitrogen and the mixed gases dried and the carbon dioxide condensed as before. A few water samples were swept with nitrogen to remove the free carbon dioxide before acidification and removal of the bicarbonate ion. MASS SPECTROMETERANALYSIS The mass spectrometer used is a 60” Nier type using magnetic ion selection and manual peak height measurement. A calibration of this instrument for the gas mixtures N, and O,, N, and H,, N, and A, A and CH,, and for the argon isotopes was carried out before the analyses were started. As greater accuracy was needed for the argon-nitrogen ratios this calibration was repeated several times during the period in which the measurements were carried out. It is estimated that the accuracy of these A/N ratios is approximately 1-123 per cent of the values given. The accuracy of the other components is approximately 10 per cent of the values given. The measurement of A40/A36 ratios was complicated by the fact that apparatus to remove the nitrogen from the sample was not available at the time when the majority of the samples were analyzed, and it was necessary to measure the A40/A36 ratios by introducing the sample to the mass spectrometer at higher pressures than usual. This is reasonably satisfactory for samples containing more than 1 part of argon per 100 parts of nitrogen, provided there is no mass 36 hydrocarbon contamination present in the sample. Samples which gave A40/A36 ratios less than 240 were rejected, and where possible were held until they could be processed in a system containing both a Calcium furnace (to remove the nitrogen), and a Cu-CuO furnace and a cold trap (to remove the hydrocarbons and hydrogen). The standard deviation of the A4°/A36 ratios given in Table 1 is 5 per cent. RESULTS The analytical parts of nitrogen.
results for individual gases given in Table I are referred to 100 The relative values given for carbon dioxide were estimated
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390
HUISTON
and
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J.
MCCABE
from the relative quantities of carbon dioxide and total residual gases obt,ained iii the chemical separation process. The ratios of argon and carbon dioxide in the gas phase to total water discharge (H,O,) were calculated from the gas to water ratios measured as described above. The tot’al quantity of carbon dioxide in the water expressed in ,umoles per mole of total wat’er. the pH and t’he surface temperature of the water are given where these are available. The output and temperatures of the JVairakei bores are found to vary- w-ith time. The results in ‘Table 1 refer to collections made in April, 1!)5~.
Argon4O/urgons6 ratios Potassium bearing rocks of great age build up quantities of argon 40 due to the K-capture decay of potassium 40. If these rocks are later heated to sufficient temperature to release A 4o then this may appear in the gas discharge and thus upset the calculations which are based on the assumption that’ all the argon in the discharge is of atmospheric origin. Since radiogenic argon is pure AJO but atmospheric argon contains I part of As6 per 295 parts of A40, the presence of radiogenic argon can be determined by measuring the A40/A3’j ratio of the samples as described previously. BOATO et al. (1952) have reported A40/L436ratios up to 100 per cent above the atmospheric value in particular cases, and in the Larderello thermal area the variations range from 10 to 25 per cent, above atmospheric. ZARTMAK> WASSERBERG and REYNOLDS (1961) have reported values ranging from approximately .i per cent above to one hundred times atmospheric for natural gas wells in America. It will be seen in Table I that all ratios, with the exception of that from Hammer Springs, are not significantly different from atmospheric. In the following discussions it has been assumed that virtually all argon is of atmospheric origin. Some radiogenic argon may be present, but it cannot, be detect,ed owing t,o the relativeI) large amount of argon of atmospheric origin which occurs.
A small number of samples were checked at high sensitivity for helium, as the presence of this gas would indicate that uranium bearing rocks occurred underground. These measurements showed that there is approximately 041 parts of helium present per 100 parts of nitrogen. This is of the same order as that present in samples collected from non-thermal gas flows in New Zealand (FARE and ROGERS, 1929) and is approximately 200 times that present in air. Argon-watw
ratios
The ratios of argon to water have been recorded in Table I, where it has been possible to obtain the necessary information. From solubility tables one would expect pure water at 10” C in equilibrium with air to contain 12 ,umoles of nitrogen and 0.32 pmoles of argon per mole of water (,uM/M), i.e. an argon to nitrogen ratio of 2.7 to 100, as dissolved gases together with oxygen and carbon dioxide. The results for the Waikato River between !l’aupo and Wairakei at 11” C’ showed
Mass spectrometer measurements in the thermal areas of New Zealand
391
the presence of 12 ,uM/M of nitrogen and 0.30 ,uM/M of argon which is in good agreement with the above. Thus, if water in equilibrium with air passed underground, was heated, and there was no separation of gas and steam from the water, or addition of gas or water from another source, it would be expected that this ratio of argon and nitrogen would be maintained in a bore discharge. From Table I it will be seen that in all the gas samples measured, the argon to water ratios are less than 0.32 ,uM/M. However, in pools which have a low carbon dioxide content in the gas phase, the partial pressure of argon is sufficiently h.igh for it to be lost to the water phase as dissolved gas. For example, if the total argon output of Awakeri Springs is measured it is found that 0*42 & O-1 PM/M of argon is discharged which is in the range expected. For the other samples measured the correction is very small and the results still give much less argon than expected. One reason for this may be that only part of the water is ground water. However, WILSON (1955) estimates from chloride contents that the magmatic water contribution at Wairakei is about 8 per cent. Thus a more likely explanation for this area is that there has been a separation of gas and water at some point between the water intake and the thermal discharge and that this gas has been lost. For example, an argon to water ratio of 0.03 PM/M would indicate that approximately 10 per cent of the gas remained. This agrees with a gas loss estimate of 90 per cent given by RAFTER, WILSON and SHILTON (1958) based on hydrogen sulphide content of bore discharges. If this was the reason for the low ratios, it would seem that between 80 and 95 per cent of the gas had been lost. The very high carbon dioxide to water ratio and temperature of the Big Donald fumaroles on White Island could be explained by a large proportion of the gas .discharge being of magmatic origin. This could also explain the low argon to water ratio found for these fumaroles without the necessity of postulating a loss of gas mechanism. The high argon content of the gas from the Seven Dwarfs fumarole, however, suggests a large dilution with argon containing water. Argon-nitrogen
ratios
It will be seen from Table I that the measured argon to nitrogen ratios are lower than the 2.7/100 value calculated above from solubility data. Two possible explanations of this will be considered. (i) Fractionation of the gases when argon and nitrogen are lost to the water phase. (ii) The addition of nitrogen from magmatic gases and from ammonia of organic origin. (i) When the discharge is from a pool where argon and nitrogen are lost in the water phase, there is fractionation of these gases. Under equilibrium conditions in the temperature range O-90” C the ratio (A/N) water phase (A/N) gas phase
+ 2.2.
Fig. 3 illustrates the calculated effect of different temperature and carbon dioxide contents on the argon to nitrogen ratio of the gas phase in a pool discharging a
total of 0.31 ,uM/M of argon and 12 PM/M of nitrogen. in the following manner:
These curves are obtained
(‘1
N,- is then calculated from the solubility tables and the percentage of nitrogen in the gas phase. Laboratory experiments on air saturated water at room temperature show that when a portion of the dissolved gas was removed by suddenly decreasing the pressure, the initial argon to nitrogen ratio of the gas and water phases is the same, but after the remaining mixture had been shaken for a few minutes equilibrium conditions were found to exist. Thus the fractionation shown in Fig. 3 will apply only to pools where the gas and liquid phases are in contact for sufficient time for equilibrium to be established. Although the relative solubilities of argon and nitrogen are not known above about 00” C it is probable that the argon still favours the water phase at these temperatures. Thus if the loss of gas underground occurs under equilibrium conditions the argon to nitrogen ratio in the water phase will rise above the 2*7/100 value. However, if equilibrium conditions are not attained, there would be little change in the argon to nitrogen ratio in the \vater remaining. It is possible in some of the pools where the gas discharge is rather slog that equilibrium conditions are reached in the surface discharge and that fractionation occurs. It is also possible that there is much less than 0.32 ,LM/M of argon (due to prior loss of gas) and hence t,hc fractionation is greater than t’hat shown in Fig. 3. Pool lS6 in Geyser Valley may be at1 example of this. The gas to water ratio of this pool was not measured, but’ calculations using equation (4) in the form 4: __ 0-32X where S is the proportion of gas remaining, indicate that it N,: 12x + l.dN,, would be necessary for t’here to be Z/3 loss of gas in the underground water supplying the pool. .In a few pools, A/N values have been measured for both t,ho gas and water phases, and these results are given in Table I. In Rotoma Soda Hprings the ratios are similar and probably indicat,c that equilibrium is not reached. 111 Awakeri Springs the A/N ratio is lower in the gas thaii in the water. This indicates that equilibrium conditions could exist. but, it’ is also possible that cold water of A/S ratio 2*7/100 and hot gas and steal11 of about I .3/100 ratio coultl bo mising just below the surface wit,hont, equilibrium being re-estJabIishetl. ‘I’he latt(xr j)ossibilit> is suggested by t’he work of Felts: I-YSOS (pers. comm.) who tlctc~ctctl considerably more carbon-14 in the \\,ater l)has~~than in t)he gas phase, although i[I a rcpcnt collection to confirm this result insufficient carbon dioxide could be obtained from the gas phase to make a carbon-14 cleterminat,ion.
Mass spectrometer
meesuromonts
in t.he thermal
areas
of New Zealand
393
(ii) The majority of the samples in Table 1 have argon to nitrogen ratios which are lower than can be explained by the system above, as is illustrated by the results plotted in Fig. 3. These results are possibly due to nitrogen being added from both magmatic gases and ammonia of organic origin. ‘NH,
-+ 3H, + N,
If the latter were the main contribution, then t.here should be a linear correlation between the additional nitrogen and the hydrogen content. This is complicated by some of the hydrogen reacting to form other molecules such as methane: 4H, + CO, L+ eH,O
+ CH,
-
1.4
3 \i + !3‘2%
‘I-*
30 Pool
50
60
lem3ermure.
OC
90
Fig. 3. Argon-Nitrogen ration of B pool discharging water which has originally been in equilibrium (at 10’ C) with air, together with some natural pool results.
Jn Fig. 4 a function of the total hydrogen content, obtained by adding to the measured hydrogen an amount of hydrogen equal to four t.imes the measured methane, has been plotted against a function of the surplus nitrogen, which is defined as all the nitrogen above the quantity needed to give an argon to nitrogen ratio of 2*7/100. These functions, which are respectively the ratio of total hydrogen to argon and surplus nitrogen to argon, were used as being equivalent to total hydrogen t.o water and surplus nitrogen to water ratios, assuming that there had been no gas loss. It will be seen, in Fig. 4, that with the exception of two Big Donald samples, the concentration of tot.al hydrogen is very approximately proportional to the square of the surplus nitrogen concentration. As the relationship is not a first order one, the ammonia decomposition does not appear to be the major contributor to the surplus N,. Furthermore, since a
394
and TV.
J. R. HCLSTOW
J.
MCCABE
relationship does appear to exist, there may be some other equilibrium in existence. It has not been possible, however, t,o identify a particular reaction which might be responsible for this relationship.
Since conditions underground are reducing, it would be expect,ed that very little oxygen should be present in the samples collected from t,he discharges. The difference in oxygen content between surface and underground is shown in the I
I
I
10
/
I lo“
(7 ’
Total Fig. 4. Relationship
of “Surplus
Xtrogon”
r,$
hydrogen/argon
to “Total
Hytlrogcn“
in geot~hormal tlisrhargrs.
oxygen to nitrogen ratios for the Hutt River at Silverstream of 59/100, and the same water after having passed through the Hutt’ Valley artesian system with a ratio of 3/100. It will be seen from Table 1 that the samples from most of the bores and fumaroles contain about 0.3 parts of oxygen per 100 parts of nitrogen. This may be due to air contamination of the sample. If this were so, it would represent l-5 per cent air in the residual gas. Although samples from some pools, namely, Whale Island (R477/1 and 6), Onepu (R473/1), Waiotapu and h’gawha, are of the same order, the tendency is for pool samples to contain more oxygen. In the Geyser Valley (Wairakei) samples for example the lowest oxygen content is 5-2 parts per 100 parts of nitrogen. It is worthwhile considering whether this is due to air contamination of the sample. If this occurred, then in the worst case, pool 186, the collection would need to be one third air. As however the gas pressures in the bottles were
Mass spectrometer
measurements
in the thermal areas of New Zealand
398
measured in the first step of the chemical separation and were found to vary by only &5 per cent at 65 cm of mercury, it is improbable that this is due to leakage into the bottles after collection. It thus appears likely that the oxygen content of these samples is at least partially real. ALLEN and DAY (1935) found the oxygen contents in pool samples from Yellowstone Park, U.S.A., to be larger than normal for air contamination and suggested that this might be due to dissolved oxygen carried down by locally descending surface water. This appears to be the most likely explanation for the oxygen present in these Geyser Valley pools, particularly as they are all below the level of the surrounding country. Chemical equilibrium
between CO, and CH,
Previous workers (CRAIG 1953, ELLIS 1957) in this field have considered the chemical and isotopic equilibrium of methane and carbon dioxide in geothermal discharges. The overall mechanism usually suggested is the reaction: CH, + 2H,O<,, + CO, + 4H, It is probable that carbon monoxide is an intermediary in the reaction, but the chemical equilibrium constants are such that the concentration is normally very low, and was not detected by the authors. In Table 2 values of K, calculated by Ellis for the above reaction are given where
Table
2.
Values of equilibrium constant for methane-carbon dioxide reaction T” K 1000 700 600
-
K, (atmospheres0) 2.78 x 1O-2 4.21 x 102 7.40 x 104 8.73 x 10’ 2.75 x 10la
It will be seen that there is considerable variation of K, with temperature. In Table 1 the equilibrium temperatures have been calculated for chemical equilibrium of the gases analysed. In making this calculation the partial pressure of water vapour has been taken to be that of saturated water vapour at that temperature. On the assumption that there is only a small gas phase, the partial pressures have been calculated using the molar concentrations derived from Table 1 together with gas solubility data obtained from Ellis and Fyfe (1957) and from the Handbook of Physics and Chemistry. Some extrapolation was necessary -for the methane data. It will be seen from Table 1 that in general there is reasonable agreement between temperatures based on chemical equilibrium and on geothermograph measurements, especially considering the possible errors in the chemical measurements.
396
J. K. HULSTOS
and \is. 5. McCxaz
(1957) concluded that the agreement between field results and those calculated was an indication that magmatic gases approach a state of chemical equilibri~~ni. It will also be seen from Table 1 that, the llydrogen contents of two samples collected from Big Donald Mound on White Island are widely different,. The difference in the calculated equilibrium temperatures is, however, in the same direction as that estimated when the samples were collected. Bs the reaction given above is normally thought to be rather dew at the temperatures involved here it was decided to conduct a laboratory experiment. Carbon dioxide, hydrogen and water were heated in a steel bomb at al)proximately 250” f ’ for a period of t-we months. 1Jhe contents of the bomb were then analysed on the mass spectrometer and the methane found to be just above the mass spectrometer background. From this it was estimated that the reaction has a half time of at’ least five years in a typical bore. Because catalysts or poisons could easily change the rate in the ~~x~(~ergroundsit~~atioI~s,these e~perimel~ts were not ~ursued~ ELLIS
The use of argon as a tracer of atmospheric gases indicates that there has been a considerable loss of gas in many areas, particularly at Wairakei. This would tend to support the hypothesis that in the latter area the water has travelled some distance horizontally before reaching the bores sampled here. The argon to nitrogen ratios are in most cases much lower t~han expected for gas collected from heated ground water. The square of tSlic concentration of nit’rogen in excess of that expected from ground water appears to be proportional to the t’otal hydrogen concentration. The I~resence of appreciable oxygen perceIltages in pool samyies is ~,ho~~gl~tt,o be due to contamination with shallow groundwater containing dissolved oxygen. The AJ0/A36 ratios of the samples measured were not significantly different from t’hat obtained from argon of atmospheric origin, except in the case of Hnnmer Springs. Comparison of temperatures calculated assuming t,ho existence of chemical equilibrium between CO, and CH, with t)emperatures measured, show reasonably good agreement and thus tend to indicate that these gases at least approach a state of chemical equilibrium.
REBEREXCES ALLJXN E. T. and DAY A. L. (1935) Hot, Springs of the Yellowstone Nat,ional l%rk.
Carnegie Inst., Washington, P&l. A-0. 466, 525 pp. BOAT0 G. C&I%ERI G, and SAWI!ANGELO RiI.(1952) !qpn Isotopt~s in ~8,txard i&~% ~~zmw Cimento 9, 44-49. c&wckitn. et C’owwchim. A&l, CRAIG H. (1953) The Geochemistry of the Stable Carbon Isotopes. 3, 53-92. ELLIS A. J. (1957) Chemical ~~~lilibriunl in ~~~~at~c Gases. Bm,er. J. Sri. 255, 4tii-431. ELLIS A. J. Pomona1 Communication. ELLIS A. J. and FYFIZ I%',S. (1957) Hydrothermal Chemistry. Rev. .Vwr. dppI. C'kern.7, 261416. FARR C. C. and ROGERS M. N. (1929) Helium in Sew Zealand. ,V.%. J. Sri. Tech. 10, 300408. FERGUSSOW f:. J. and K~:ox P. B. (1959) The Possibilities of Nat,iond Radio-carbon as a Ground Water Tracer in Thermal Areas. X.Z. J. Sci. 2, 431-441.
Mass spectrometer
measurements
in the thermal areas of New Zealand
397
Handbook of Chemistry and Physics. 38th Edition. p. 1608. Chemical Rubber Publishing Co., Ohio. RAFTER T. A. WITSON S. H. and SHILTON B. W. (1958) Sulphur Isotopic Variations in Nature. Pt 5-Sulphur Isotopic Variations in New Zealand Geothermal Bore Waters. N.Z. J. ii’& 1, 103-126. WILSON S. H. (1953) The Chemical Investigation of the Hot Springs of the New Zealand Thermal Region. Proo. Seventh Pacific Science Congress 2, 449-469. WILSON S. H. (1955) Geothermal Steam for Power in New Zealand-Chemical Investigations. N.Z.D.S.I.R. Bull. 177, pages 27-42. WILSON S. H. Personal Communication. ZARTMAN R. E., WASSERBURG G. J., and REYNOLDS J. H. (1961) Helium, Argon, and Carbon in Some Natural Gases. J. Geo~~~,~s.Res. 61,277-306.