δ¹⁸O values of unaltered, primary minerals from two Cretaceous rocks of komatiitic affinity and from associated rocks from Gorgona Island, Colombia, indicate that the komatiitic samples, have δ¹⁸O values ≥ 6.0 whereas the associated tholeiitic igneous rocks have greater (Ce/Sm)_N ratios and δ¹⁸O values near 5.5. δ¹⁸O values of the komatiitic rocks, in conjunction with their low LREE contents and high ε_Nd values, suggest derivation from sources that were extensively depleted by prior melting events and different from those of some of the associated rocks. The divergence between the δ¹⁸O values of primary chromite, olivine and pyroxene in the komatiitic rocks is in accordance with petrographic relations which suggest substantial undercooling took place during their emplacement. δD and δ¹⁸O values of chrysotile from the komatlitic samples are characteristic of those for serpentines formed from meteoric water at Gorgona rather than from seawater. This post emplacement alteration has also affected the ⁸⁷Sr/⁸⁶Sr ratios.

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Albite and basalt glasses were dissolved in distilled water and 0.01 and 0.0001M HCI solutions at 47, 80 and 120°C. The compositional change of solutions was traced. At an initial stage of dissolution, elemental ratios in solution differ from those in the starting materials, thus showing the glasses dissolve incongruently. With increasing duration of experiments the release rate of elements becomes congruent, and the incongruency of the glass and the solution decreases. At the later stage, the dissolution is again incongruent, mainly owing to precipitation of secondary minerals. The release rate of each element is proportional to aⁿ_H+, where n is from 0.5 to -0.2. The activation energy for the release of elements from the glasses is from 15 to 40kJ/mol. The value is smaller than that reported for crystalline silicates. Reaction pathways on activity diagrams show that the solutions after the longest experimental duration of each series are saturated or slightly supersaturated with secondary minerals. The concentrations of Al, Ca, Mg and Fe in such solutions for the same glass series are either constant or decrease with increasing temperature at the approximately same pH, while those of Si and Na increase. Concentrations of all elements decrease with increasing pH. The pathways showed a trend approaching to an equilibrium state. The typical sequences of precipitation of secondary minerals were suggested to be amorphous silica → stable polymorphs of clay minerals (e.g., kaolinite) in strongly acid solutions, and metastable polymorphs of clay minerals (e.g., allophane and halloysite) → quartz in weakly acid solutions. We conducted two step experiments. Solutions which dissolved the glasses at high temperature were let stand or reacted with fresh glasses at low temperatures. The compositional difference between the solutions obtained at high and low temperatures suggests formation of some secondary minerals, and also dissolution of the glass during the experiment. The compositional change of solution caused by precipitation and dissolution of minerals as a result of change in the solution is explained by the solubility product of a mineral, defined in terms of total molality of related element at fixed temperature, pressure, pH and in case of need, at fixed P_O2, P_CO2, m_cl and m_s. Various alteration patterns in geothermal fields were discussed for a model of hydrothermal convection system on the assumption that groundwater flows nearly in equilibrium with rocks, at least with secondary minerals. The alteration was investigated on the basis of compositional change of hydrothermal solution by combining the experimental results obtained after long isothermal runs at different pH's and temperatures. The results of the two step experiments are also considered. This approach is systematized by different trends of the solubility products as described above for silica and other oxides, hydroxides and silicates in function of temperature and pH, and used to clarify processes observed in the field, such as silicification, argillization, quartz vein formation and zonation of wall rock alteration products.

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K-Ar age determinations were carried out on two lamprophyre dikes intruded into the Sambagawa metamorphic rocks at Shingu in the central part of Shikoku Island, Southwest Japan. These dikes are very distinctive among Neogene igneous rocks in Shikoku because of their abundant mantle xenoliths and carbonate minerals in the fresh groundmass, and of their unique chemical compositions. In order to eliminate the effect of extraneous argon from xenoliths and carbonates, removal of large crystals and acid leaching experiments were done for three grain size fractions. Apparent ages ranging from 18.6±0.7Ma to 21.6 ±2.0Ma were obtained for both rocks. However, positive correlation between apparent ages and atm. ⁴⁰Ar% suggests that samples contain initial argon which is not atmospheric. The well defined isochron age of 17.7±0.5Ma is obtained from all samples with the initial ⁴⁰Ar/³⁶Ar ratio of 310±5 in the ⁴⁰Ar/³⁶Ar-⁴⁰K/³⁶Ar diagram. As the initial ⁴⁰Ar/³⁶Ar ratio is higher than that of atmosphere, apparent ages do not show any geologic meaning, and the isochron age of 17.7±0.5Ma gives the intrusive age of dikes. The Shingu lamprophyres are much older than other Miocene igneous rocks in Shikoku ranging in age from 14 to 12Ma, and both magmatisms could be genetically independent. As the Shikoku Basin kept opening in a northeast-southwest direction at 18Ma, it could not subduct significantly beneath Southwest Japan from the south when the Shingu lamprophyres intruded into the Sambagawa metamorphic belt. Petrogenesis of the Shingu magma could be related to the rifting of the back arc basin, the Japan Sea.

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In order to estimate possible silver sulfide complexes in ore solutions, the solubility of Ag₂S was measured between 25° and 250°C in NaOH-H₂S-H₂O solutions of 0.0 to 4.1 m NaHS concentration. Solubility changes as a function of temperature, total reduced sulfur concentration ΣS (m_H2S + m_HS-) and pH. A maximum solubility of 2140ppm Ag was obtained at 250°C in 4.1 m NaHS concentration under P_H2S of 29.1 atm. From these solubility data, reactions to form silver sulfide complexes are estimated as follows: Ag₂S + H₂S = Ag₂S(H₂S), Ag₂S + H₂S + HS^- = Ag₂S(H₂S) (HS)^-, Ag₂S + H₂S + 2HS^- = Ag₂S (H₂S) (HS)₂^2- and Ag₂S + 2HS^- = Ag₂S (HS)₂^2-. The equilibrium constants for these reactions are given in Table 2. Assuming that such silver sulfide complexes as above are in an ore solution, Ag₂S (argentite or acanthite) is precipitated in response to changes of temperature, pH and total sulfur concentration (ΣS). Decrease of pH and ΣS is more effective than that of temperature. Silver sulfide complexes are more important than silver chloride complexes in ore solution of high ΣS, neutral to slightly alkaline pH and geologically reasonable chloride concentrations.

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Strontium isotopic compositions were determined in thirty-two volcanic rock samples collected in thirteen volcanic centers of the 41°30′ - 46°S region of the Southern Volcanic Zone (SVZ) of the Andes. This region is just north of the Chilean triple junction, where the Chile Rise subducts under the South American plate. The along-arc variation of ⁸⁷Sr/⁸⁶Sr ratios of volcanic rocks from the SVZ (33°S-46°S) is complex and shows a wave-like pattern, which does not correlate either with the age pattern of the subducted Nazca plate or with the thickness of the continental crust. Furthermore, the variation of the Sr-isotope composition in along-arc direction does not seem to correspond to those of other geochemical parameters examined up to now of SVZ rocks. We interpret this Sr-isotopic variation in terms of either locally different crust-magma interactions or heterogeneities in the mantle wedge. Effects of subduction of the Chile Rise on the ⁸⁷Sr/⁸⁶Sr ratios are not obvious.

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Some investigators argue that there exist large-scale elemental and isotopic heterogeneities of rare gases in the solar system. It can be shown, however, that their conclusions are based on the use of an overly-simplified model and a careless interpretation of the existing rare gas isotope data.

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The experimental evidence for correlated elemental and isotopic ratios of rare gases in meteorites is indisputable and totally independent of model or interpretation. More effort needs to be made to understand this observation if models proposed to explain the existence of isotopic anomalies in the early solar system are to be credible.

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