Noble gas evidence for two fluids in the Baca (Valles Caldera) geothermal reservoir

Noble gas elemental and isotopic abundances were measured in steam from four wells in the Baca geothermal reservoir located in the Valles Caldera, New Mexico. The ${}^{40}\text{Ar}{}^{36}\text{Ar}$ ratio and noble gas elemental abundances relative to ³⁶Ar are all strongly correlated with 1/³⁶Ar, the inverse of the argon content. Ratios of (α,n)-produced ²¹Ne1 and radiogenic ⁴⁰Ar1 to total ⁴He (dominantly radiogenic) are nearly constant at 2.1 × 10?8 and 0.20, respectively. The ${}^3\text{He}{}^4\text{He}$ ratio covers a restricted range of 3.9 to 4.8 times atmospheric. The high ³He content of the gas indicates the presence of a helium component ultimately derived from the mantle. Kr and Xe isotopic compositions are close to atmospheric; excess ¹²⁹Xe1 is <0.25% of the total ¹²⁹Xe.The high degree of linear correlation among the various noble gas results strongly suggests that the Baca reservoir contains two distinct fluids that are produced in varying proportions from individual wells. The noble gases in fluid A (~2900 mg/1 C1) are air-like, but with lighter gases and isotopes preferentially enriched. The fluid A ³⁶Ar content is low, only 13% that of 10°C air-saturated water (ASW). The second fluid, B (~ 1700 mg/1 C1), is the dominant carrier of the radiogenic and mantle-derived gases. The heavier non-radiogenic gases are preferentially enriched in fluid B, and its ³⁶Ar content is very low, only 5–7% ASW. The source of the noble gases in fluid A is tentatively ascribed to leaching of the relatively young (<1.4 m.y.) volcanic Bandelier Tuff. The radiogenic gases and mantle-derived helium in fluid B suggest a deeper source, possibly including gases escaping from a magma.     

Intensive sampling of noble gases in fluids at Yellowstone: I. Early overview of the data; regional patterns

The Roving Automated Rare Gas Analysis (RARGA) lab of Berkeley's Physics Department was deployed in Yellowstone National Park for a 19 week period commencing in June, 1983. During this time 66 gas and water samples representing 19 different regions of hydrothermal activity within and around the Yellowstone caldera were analyzed on site. Routinely, the abundances of five stable noble gases and the isotopic compositions of He, Ne, and Ar were determined for each sample. In a few cases the isotopes of Kr and Xe were also determined and found to be of normal atmospheric constitution.Correlated variations in the isotopic compositions of He and Ar can be explained within the precision of the measurements by mixing of only three distinct components. The first component is of magmatic origin and is enriched in the primordial isotope ³He with ${}^3\text{He}{}^4\text{He}\text{≥ 16}$ times the air value. This component also contains radiogenic ⁴⁰Ar and possible ³⁶Ar with ${}^{40}\text{Ar}{}^{36}\text{Ar}\text{≥ 500}$, resulting in a ${}^3\text{He}{}^{36}\text{Ar}$ ratio ≥ 41,000 times the air value. The second component is assumed to be purely radiogenic ⁴He and ⁴⁰Ar (${}^{41}\text{He}{}^{401}\text{Ar}\text{= 4.08 ± .33}$). This component is the probable carrier of observed excesses of ²¹¹Ne, attributed to the α,n reaction on ¹⁸O. Its radiogenic character implies a crustal origin in U. Th, and Krich aquifer rocks. The third component, except for possible mass fractionation, is isotopically indistinguishable from the noble gases in the atmosphere. This component originates largely from infiltrating run-off water saturated with atmospheric gases.In addition to exhibiting nucleogenic ²¹¹Ne, Ne data show anomalies in the ratio ${}^{20}\text{Ne}{}^{20}\text{Ne}$, which correlate roughly with the ${}^{21}\text{Ne}{}^{22}\text{Ne}$ anomalies for the most part, but not as would occur from simple mass fractionation. Some exaggerated instances of the ${}^{20}\text{Ne}{}^{22}\text{Ne}$ anomaly occur which could be explained by combined mass fractionation of Ne and Ar isotopes to a severe degree coupled with remixing with normally isotopic gases. Otherwise exotic processes have to be invoked to explain the ²⁰Ne data.Relative abundances of the non-radiogenic and non-nucleogenic noble gases (²²Ne, ³⁶Ar, ⁸⁴Kr, and ¹³²Xe) are highly variable but strongly correlated. High Xe/Ar ratios are always accompanied by low Ne/ Ar ratios and vice versa. Except for water from the few cold (T < 20°C) springs analyzed, none of the samples have relative abundances consistent with air saturated water and the observed variations are not readily explained by the distillation of air saturated water.In characterizing each area of hydrothermal activity by the highest ${}^3\text{He}{}^4\text{He}$ ratio found for that area, we find that within the caldera this parameter is somewhat uniform at ~7 ± 1 times the air value. There are exceptions, most notably at Mud Volcano, an area located along a crest of recent and rapid uplift. Here the maximum ${}^3\text{He}{}^4\text{He}$ ratio is ~ 16 times the air value. Also noteworthy is Gibbon Basin which is in the vicinity of the most recent rhyolitic volcanism and exhibits a ${}^3\text{He}{}^4\text{He}$ ratio ~ 13 times the air value. Immediately outside the caldera the maximum $\text{sol}{}^3\text{He}{}^4\text{He}$ ratio decreases rapidly to values < ~3 times the air value.     

3He4He ratio,noble gas abundance and K-Ar dating of diamonds—An attempt to search for the records of early terrestrial history

The ${}^3\text{He}{}^4\text{He}$ ratios measured in 27 Southern Africa diamond stones, four from Premier Mine and the rest of unidentified origin, range from 4.2 × 10^?8 to 3.2 × 10^?4, with three stones above 1 × 10^?4. We conclude that the initial helium isotopic ratio (${}^3\text{He}{}^4\text{He)}{}_0$ in the earth was significantly higher than that of the planetary helium-A (${}^3\text{He}{}^4\text{He = 1.42 × 10}{}^{\mathrm{?4}}$), but close to the solar helium (${}^3\text{He}{}^4\text{He ? 4 × 10}{}^{\mathrm{?4}}$).The apparent K-Ar ages for the twelve diamonds of unidentified origin show enormously old age, indicating excess argon-40. ${}^3\text{He}{}^4\text{He}$ evolution in diamonds suggests that the diamonds with the high ${}^3\text{He}{}^4\text{He}$ ratio (>2 × 10^?4) may be as old as the earth.Noble gas elemental abundance in the diamonds relative to the air noble gas abundance shows monotonie decrease with a decreasing mass number.This paper discusses the implications of these observations on the early solar system and the origin of diamonds.     

Variability of the He3 and Ne21 production rates in ordinary chondrites

Al²⁶ and noble gas contents of 6 ordinary chondrites with $\text{He}{}^3\text{Ne}{}^{21}$ ratios above 6.0 or below 4.0 are used to infer the variability of the production rates of He³ and Ne²¹ (P_He³ and P_Ne²¹). The ratio of the observed Al²⁶ content to a calculated, normal value is taken as a measure of the change of P_Ne²¹ from its normal value. The corresponding change in P_He³ is then computed from the observed $\text{He}{}^3\text{Ne}{}^{21}$ ratio and an average value of P_He³.According to these calculations which exclude orbital effects, P_He³ will be near the average value in meteorites with high $\text{He}{}^3\text{Ne}{}^{21}$ ratios, while P_Ne²¹ will be about 30 per cent below normal. In meteorites with low $\text{He}{}^3\text{Ne}{}^{21}$ ratios, P_He³ may be depressed by as much as 25 per cent from normal while P_Ne²¹ may be 15–20 per cent above the average.     

Radium content and the 226Ra228Ra activity ratio in groundwater from bedrock

The relative abundance of ²²⁶Ra and ²²⁸Ra were determined in the groundwater from 125 drilled wells containing from < 0.1 to 51.3 pCi/l of ²²⁶Ra. The determination of ²²⁸Ra was carried out with a liquid scintillation counter by measuring only the weakly energetic β particles emitted from ²²⁸Ra. Thus the interference from the daughter nuclides of ²²⁶Ra was avoided, without specific separation of ²²⁸Ac. The direct measurement of ²²⁸Ra made the method decisively simpler and faster in terms of the chemistry involved.The concentration of ²²⁸Ra was found to be independent of the amount of ²²⁶Ra present in the samples. The concentrations of ²²⁸Ra were nearly the same over the whole range of ²²⁶Ra concentrations and the average $\text{sol}{}^{226}\text{Ra}{}^{228}\text{Ra}$ ratio sharply increased as the ²²⁶Ra content of water increased. The ${}^{226}\text{Ra}{}^{228}\text{Ra}$ ratio in the drilled wells varied from 0.3 to 26. Abnormally high ${}^{226}\text{Ra}{}^{228}\text{Ra}$ ratios were found in areas with known uranium deposits as well as in several drilled wells at other locations. The abnormally high ${}^{226}\text{Ra}{}^{228}\text{Ra}$ ratios present in groundwater suggest that the radioactivity anomaly is caused by uranium deposits and not by common rocks. In samples with a low radioactivity level the average ${}^{226}\text{Ra}{}^{228}\text{Ra}$ ratio was slightly below unity, corresponding to the typical U/Th ratio of granite, the most common kind of rock in the study area. The samples from the rapakivi area proved to be exceptional in that they had a low ${}^{226}\text{Ra}{}^{228}\text{Ra}$ ratio independent of the concentration of ²²⁶Ra.     

Trapped solar wind noble gases and exposure age of Luna 16 lunar fines

He, Ne, Ar, Kr and Xe concentrations and isotopic abundances were measured in three bulk grain size fractions prepared from sample L-16-19, No. 120 (C level, 20–22 cm depth) returned by the Luna 16 mission. The expected anticorrelation between the concentrations of trapped solar wind noble gases and grain size is observed. Elemental abundances of solar wind trapped noble gases are similar to those previously found in corresponding grain size fractions of the Apollo 11 and 12 fines. The trapped ratio ${}^4\text{He}{}^{20}\text{Ne}$ varies in the soils from different lunar maria due to diffusion losses. A rough correlation of ${}^4\text{He}{}^{20}\text{Ne}$ with the proportion of ilmenite in these samples is apparent. The elemental and isotopic ratios of the surface correlated noble gases in Luna 16 resemble those previously found in Apollo fines. Based on ²¹Ne, ⁷⁸Kr and ¹²⁶Xe a cosmic ray exposure age of 360 my was determined. This age is similar to those obtained for the soils from other lunar maria.     

He,Ne and Ar isotopes in inclusions of some iron meteorites

He³, He⁴, Ne²¹ and Ar³⁸ contents were determined in 18 metal, troilite, sehreibersite and graphite inclusions of 9 iron meteorites, by total outgassing and stepwise heating. The $\text{He}{}^4\text{He}{}^3$ ratio in metal phase ranges from 3.85 to 4.65, but in non-metallic samples, from 6.70 to 30.5. The results for cosmogenic isotopes of helium, neon and argon disagree appreciably with data on accelerator-irradiated targets. It should be noted, however, that some inclusions have lost considerable amounts of gas by diffusion.Uranium contents of 22 troilite and sehreibersite samples were determined by the fission track technique. The average uranium content of troilite is 0.4-0.7 ppb. Excess He⁴ of unknown origin was observed in troilite inclusions. If one assumes that the excess He⁴ was produced by uranium decay in situ, then the apparent U-He⁴ age is at least 5.9 × 10⁹ yr.     

Ground water geochemistry of 228Ra, 226Ra and 222Rn

²²⁸Ra, ²²⁶Ra, and ²²²Rn activities were determined on over 150 ground water samples collected from drilled, public water supply wells throughout South Carolina. A wide range of aquifer lithologies were sampled including the crystalline rocks of the Piedmont and sedimentary deposits of the Coastal Plain. A significant linear relationship between log ²²⁸Ra and log ²²⁶Ra (n = 182, r = 0.83) was indistinguishable between Piedmont and Coastal Plain ground water. Median ${}^{228}\text{Ra}{}^{226}\text{Ra}$ activity ratios for the Piedmont, 1.2, and Coastal Plain, 1.3, ground water are close to estimated average crustal ${}^{232}\text{Th}{}^{238}\text{U}$ activity ratios of 1.2 to 1.5 corresponding to Th/U weight ratios of 3.5 to 4.5. A linear correlation was also found between log ²²²Rn and log ²²⁶Ra for Piedmont (n = 68, r = 0.62) and Coastal Plain (n = 89, r = 0.64) ground water. However, the median ${}^{222}\text{Rn}{}^{226}\text{Ra}$ activity ratio for Piedmont ground water, 6100, was much higher than for Coastal Plain ground water, 230. Higher excess ²²²Rn activities may be due to greater retention of ²²⁶Ra by the chemically active Piedmont aquifers compared to the more inert sand aquifers sampled in the Coastal Plain. The relationship between log ²²⁸Ra and log ²²⁶Ra was used to predict total Ra (${}^{228}\text{Ra +}{}^{226}\text{Ra}$) distributions in Appalachian and Atlantic and Gulf Coastal Plain ground water. Predictions estimate that 2.4% of Appalachian and 5.3% of Atlantic and Gulf Coastal Plain ground water supplies contain total Ra activities in excess of the 5 pCi/l limit established by the U.S. Environmental Protection Agency. These predictions also indicate that 40–50% of these ground water wells may be overlooked using the presently suggested screening activity of 3.0 pCi/l of ²²⁶Ra for ²²⁸Ra analysis.     

Spallation production of 3He, 21Ne,and 38Ar from target elements in the Bruderheim chondrite

The concentrations of noble gas isotopes of He, Ne and Ar have been measured in eight mineral separates of the Bruderheim chondrite. The cosmic-ray-produced nuclides ²¹Ne and ³⁸Ar were correlated by a computer least-squares fitting program with the elemental composition in each separate of potential targets for nuclear production yielding the following production equations: $\text{[}{}^{21}\text{Ne, 10}{}^{\mathrm{?8}}\text{cm}{}^3\text{/g] = k(0.45[Mg] + 0.085[Si] + 0.060[S] + 0.017[Ca] + 0.0044[Fe + Ni])}$; $\text{[}{}^{38}\text{Ar, 10}{}^{\mathrm{?8}}\text{cm}{}^3\text{/g] = k(2.6[K] + 0.37[Ca] + 0.08[Ti + Cr + Mn] + 0.021[Fe + Ni])}$ with elemental concentrations in weight per cent and k equal to the reciprocal of the cosmic-ray exposure age of Bruderheim. The P(S)/P(Cr + Mn + Fe + Ni) weight production ratio for ³He was determined to be 1.53; relative productions of ³He from O, Mg and Si and ²¹Ne from Al proved to be incalculable.     

The solubility of noble gases in water and in NaCl brine

A direct-sampling, mass-spectrometric technique has been used to measure simultaneously the solubilities of He, Ne, Ar, Kr, and Xe in fresh water and NaCl brine (0 to 5.2 molar) from 0° to 65 °C, and at 1 atm total pressure of moist air. The argon solubility in the most concentrated brines is 4 to 7 times less than in fresh water at 65 °C and 0°C, respectively. The salt effect is parameterized using the Setschenow equation.

$\text{ln}\text{[}\text{β}{}^{\mathrm{i}}{}_{\mathrm{o}}\text{(T)}\text{β}{}^{\mathrm{i}}\text{(T)}\text{= MK}{}^{\mathrm{i}}{}_{\mathrm{M}}\text{(T)}$

where M is NaCl moiarity, βⁱ_o(T) and βⁱ(T) the Bunsen solubility coefficients for gas i in fresh water and brine, and Kⁱ_M(T) the empirical salting coefficient. Values of Kⁱ_M(T) are calculated using volumetric concentration units for noble gas and NaCl content and are independent of NaCl molarity. Below about 40°C, temperature coefficients of all Kⁱ_M are negative. The value of K^He_M is a minimum at 40°C. K^Ar_M decreases from about 0.40 at 0°C to 0.28 at 65 °C. The absolute magnitudes of the differences in salting coefficients (relative to K^Ar_M) decrease from 0° to 65°C. Over the range of conditions studied, all noble gases are salted out, and K^He_M ? K^Ne_M < K^Ar_M < K^Kr_M < K^Xe_M.From the solubility data, we calculated $\text{Δ}\text{G}{}^0{}_{\mathrm{tr}}$, $\text{Δ}\text{S}{}^0{}_{\mathrm{tr}}$, $\text{Δ}\text{H}{}^0{}_{\mathrm{tr}}$ and $\text{Δ}\text{C}{}^{\mathrm{O}}{}_{\mathrm{p,tr}}$ for the transfer of noble gases from fresh water to 1 molar NaCl solutions. At low temperatures $\text{Δ}\text{S}{}^0{}_{\mathrm{tr}}$, is positive, but decreases and becomes negative at temperatures ranging from about 25°C for He to 45°C for Xe. At low temperatures, the dissolved electrolyte apparently interferes with the formation of a cage of solvent molecules about the noble gas atom. At higher temperatures, the local environment of the gas atom in the brine appears to be slightly more ordered than in pure water, possibly reflecting the longer effective range of the ionic fields at higher temperature.The measured solubilities can be used to model noble gas partitioning in two-phase geothermal systems at low temperatures. The data can also be used to estimate the temperature and concentration dependence of the salt effect for other alkali halides. Extrapolation of the measured data is not possible due to the incompletely-characterized minima in the temperature dependence of the salting coefficients. The regularities in the data observed at low temperatures suggest relatively few high-temperature data will be required to model the behavior of noble gases in high-temperature geothermal brines.     

Inert gases in a terra sample: measurements in six grain-size fractions and two single particles from Luna 20

The inert gases have been measured in six size fractions covering the range below 500 μm, in a single feldspathic fragment weighing 523 μg, and in an agglutinate particle weighing 465 μg. The two size fractions between 125 and 250 μm as well as 250 and 500 μm were separated into magnetic and non-magnetic portions, which were measured separately. Like the Apollo and Luna 16 fines, the terra fines represented by Luna 20 are very rich in trapped solar-wind gases, but they contain relatively less He⁴ and Ne²⁰, which is revealed by their average $\text{He}{}^4\text{Ne}{}^{20}$ ratio of 35 and $\text{Ne}{}^{20}\text{Ar}{}^{36}$ ratio of 2.9. Obviously the terra materials are less retentive for solar-wind He and Ne than typical mare fines such as 10084. Whether this is due to the relatively small TiO₂ or the relatively large plagioclase content of the former is not resolved. ($\text{Ar}{}^{36}\text{Kr}{}^{84}\text{)}{}_{\mathrm{trapped}}$ and ($\text{Ar}{}^{36}\text{Xe}{}^{132}\text{)}{}_{\mathrm{trapped}}$ ratios are relatively large; the average values are 2800 and 14400, respectively. The apparent Ne²¹ radiation ages of all the size fractions are in the range 209–286 × 10⁶ yr; the average is 260 × 10⁶ yr. This is in the range of values known for the Apollo and Luna 16 fines. The feldspathic fragment has a much greater apparent Ne_c²¹ age of 780 × 10⁶ yr. The Ar⁴⁰-Ar³⁶ systematic reveals the presence of two Ar⁴⁰ components, because Ar⁴⁰ = (1.41 ± 0.076)Ar³⁶ + (0.490 ± 0.130) × 10^?4 (cm³ STP/g). The $\text{Ar}{}^{40}\text{Ar}{}^{36}$ slope of 1.41 is not inconsistent with an origin of the sample from a relatively old terra region.     

Radium isotopes in saline seepages,south-western Yilgarn,Western Australia

Water samples from saline seepages in the south-western Yilgarn Block of Western Australia contain high activities of the four naturally-occurring radium isotopes. Activities of up to 310 $\text{pCi}\text{l}$ for ²²⁶Ra and 1720 $\text{pCi}\text{l}$ for ²²⁸Ra were measured and the ${}^{228}\text{Ra}{}^{226}\text{Ra}$ ratio averaged 6.1. Activities of the two short-lived radium isotopes were also high. ²²³Ra activities of up to 94 $\text{pCi}\text{l}$ were found with an average ${}^{226}\text{Ra}{}^{223}\text{Ra}$ ratio of 3.3, considerably lower than the natural abundance ratio of 21.4. Activities of up to 23 $\text{pCi}\text{l}$²²⁷Ac, the long-lived ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 22 years}$) grandparent of ²²³Ra, were also measured. The analysis of surface granite samples, the probable source rocks of the radium, gave $\text{Th}\text{U}$ activity ratios of around 1.5. The higher ${}^{228}\text{Ra}{}^{226}\text{Ra}$ ratios of the waters were attributed to readily leached ²²⁸Ra in the weathered granites as a result of thorium remaining after weathering. Leach experiments on U-Th ore by NaCl solutions showed that all four radium isotopes were equally leached. Sulphate anions reduced the ²²⁶Ra and ²²⁸Ra leaching to a greater extent than for ²²³Ra and ²²⁴Ra, suggesting that the latter isotopes were being supported in solution by parent isotopes. In particular this suggested ²²⁷Ac was leached into the sulphate solution but this does not fully account for the amount of ²²⁷Ac seen in the seepage waters.     

Isotopic composition of noble gases in geothermal fluids of the Krušné Hory Mts., Czechoslovakia,and the nature of the local geothermal anomaly

The contents and isotopic composition of all noble gases in the fluids from two localities (Karlovy Vary and Franti?kovy Lázně) in Western Czechoslovakia are given. The data show: (1) atmospheric Ne, Ar, Kr and Xe, which indicates meteoric recharge; (2) excess He, attributed to radiogenic contributions; (3) a small excess of Ne, but the data shed no light on its origin. Even though there is no evidence of any juvenile component in these mineral waters, part of the dissolved He is believed to be of deep (mantle) origin.Correlation between the ratio ${}^3\text{He}{}^4$He and heat flow has been reported in the literature: our data enabled a direct test of this relationship and proved its fairly good validity. The combined interpretation of the heat flow and isotopic composition shows that the local heat flow anomaly in the Kru?né Hory graben is of deep origin and was produced by the mass outflow which occurred during the Alpine activation of the Bohemian Massif.     

Helium accumulation in groundwater,I: An evaluation of sources and the continental flux of crustal 4He in the Great Artesian Basin,Australia

The rate of accumulation of ⁴He in the groundwaters of the J-aquifer of the Great Artesian Basin, Australia has been determined using ¹⁴C and hydrologic ages. For groundwaters less than 50 Kyr in age, the ⁴He accumulation rate is 4.6 × 10^?12 HeAU (where ) in close agreement with in-situ production rate of ⁴He (3.95 × 10^?12 HeAU) based on U and Th concentrations of 1.7 and 6.1, respectively, of the sandstone. For groundwaters older than 100 Kyr, the rate of ⁴He accumulation is 2.91 × 10^?10 HeAU based on hydrologic ages; or 74 × the rate of in-situ production. The rate of ⁴He “production” due to weathering of the aquifer rock is calculated to be ~10^?16 HeAU, indicating that the weathering input of ⁴He is insignificant. If the groundwater of the GAB can be considered as a trap for the total crustal production of ⁴He, the rate of ⁴He accumulation under a steady-state flux is calculated to be 3.02 × 10^?10 HeAU, in agreement with the measured accumulation rate. It is concluded that over long times the ⁴He accumulation rate in groundwater aquifers may be controlled by the whole crust flux of ⁴He.     

Rare gases and 36Cl in stony-iron meteorites: cosmogenic elemental production rates,exposure ages,diffusion losses and thermal histories

Metal and silicate portions from 13 mesosiderites, one pallasite, Bencubbin (“unique”) and Udei Station (‘iron with silicate inclusions’) have been analysed for their content of He, Ne and Ar; in most cases ³⁶Cl could be determined as well. ³⁶Cl-³⁶Ar cosmic ray exposure ages fall between 10 and 160 Myr. Half of the metal samples show a deficit of spallogenic ³He (up to 30%) which we ascribe to a loss of tritium. The observed depletion of ³He in the silicates is correlated with their mineralogical composition: feldspar has lost its ³He in all cases, pyroxene definitely in one and possibly in five others, while olivine has been affected in only two meteorites. The thermal histories during their exposure to the cosmic radiation have been different for different meteoroids. Nevertheless, with the exception of Veramin, the data are compatible with the assumption of a continuous diffusion loss during a considerable fraction of the exposure era. For Veramin, however, an episodic event late in the exposure history is required. The exceptionally high ${}^{39}\text{Ar}{}^{36}\text{Cl}$ ratio in the metal, which is due to a high ³⁹Ar activity, indicates that the event occurred during the last 500,000 years or so and resulted in an extremely excentric orbit (large aphelion).Production rates of ^38,39Ar from Ca and ^21,22Ne from Mg are given. The ratio $\text{P}{}^{38}{}_{\mathrm{Ca}}\text{P}{}^{21}{}_{\mathrm{Mg}}$ is close to unity. The ratios $\text{P}{}^{38}{}_{\mathrm{Ca}}\text{P}{}^{38}{}_{\mathrm{Fe}}$ vary between 20 and 50, and are not correlated with the absolute production rate of ³⁸Ar from metal. The ${}^{22}\text{Ne}{}^{21}\text{Ne}$ production ratio from Mg is found to be close to but below unity.Of the mesosiderites only Veramin shows unambiguous evidence for primordial rare gases with larger amounts and a higher ${}^{20}\text{Ne}{}^{36}\text{Ar}$ ratio in the olivine, suggesting in situ fractionation to have at least been partly responsible for the abundance pattern found. Bencubbin contains large amounts of strongly fractionated primordial gases, but again part of the fractionation may have occurred in situ. Udei Station shows an excess of (3.5 ± 0.6) × 10^?10 cm³ STP ¹²⁹Xe/g in the non-magnetic portion.