The phoscorite-carbonatite complex in the Sokli alkaline-carbonatite massif, northern Finland, comprises five stages of intrusions of phoscorites and carbonatites (P1-C1, P2-C2 and P3-C3 for phoscorites and calcite carbonatites; D4 and D5 for dolomite carbonatites). The phoscorites and calcite carbonatites at Sokli usually occur as pairs with the same mineral assemblages. Pyrochlore is found in the majority of rock types in the Sokli phoscorite-carbonatite complex, shows wide compositional variation and seems to preserve evolution trends of host rocks. Crystallization of pyrochlore begins from the P2-C2 phoscorite and calcite carbonatite and continues up to the latest D5 dolomite carbonatite. Pyrochlore in the early stage P2-C2 rocks has high U and Ta contents. These elements suddenly decrease from the P3-C3 rocks, on the other hand, Th and Ce contents increase. The compositions of the late generations from the D4 and D5 rocks are close to that of an ideal end-member pyrochlore with formula (Ca,Na)₂Nb₂O₆F. The Nb/Ta ratio and F content of pyrochlore increase from P2-C2 to the latest D5 dolomite carbonatite. The composition and evolutionary history of pyrochlore from the phoscorites are distinguished from those of the associated calcite carbonatites. Pyrochlore from the calcite carbonatites shows larger A-cation deficiencies compared to those from the paired phoscorites. Ta and Zr contents are slightly higher in pyrochlore from the calcite carbonatites, whereas Ti is generally higher in pyrochlore from the associated phoscorites. Moreover, pyrochlore from the phoscorites always shows a longer and more complex crystallization history compared to that of the same stage carbonatites. This indicates that the chemical condition was clearly different in the two systems during the crystallization of pyrochlore. Based on these results, together with the previous mineralogical and geochemical studies on the Sokli phoscorite-carbonatite complex, we propose a liquid immiscibility process as the most possible segregation mechanism of the two associated rocks. The composition of pyrochlore in the late dolomite carbonatites is distinct and always lies on the evolutional trend of the earlier varieties. This implies that the dolomite carbonatites are the final magmatic products of the Sokli phoscorite-carbonatite system.

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The southern Central India craton (also known as Bastar craton) has experienced several episodes of mafic magmatism during the early Precambrian time. These mafic igneous rocks are emplaced as dyke and volcanic rocks. A set of mafic dyke swarm and few exposures of mafic volcanics, both emplaced in the Neoarchaean time, contain high-SiO₂ (>52 wt%), high-MgO (>8 wt%), and low-TiO₂ (mostly <0.5 wt%) and classified as boninites on IUGS classification scheme. Al₂O₃/CaO ratio classifies these high-Mg mafic igneous rocks into high-Ca and low-Ca (Type 3) boninites. High-Ca boninites show typical boninitic geochemical characteristics, whereas low-Ca variety shows geochemical characteristics similar to the high-Mg norites. Siliceous high-magnesium basalts (SHMB) show similar geochemical properties as observed for the high-Mg norites. Early Precambrian high-Mg norites are reported from the rift setting environment but, on the other hand, boninitic magmatism represents an enigmatic style of magmatism and commonly formed at convergent margin settings. Most boninites are Phanerozoic in age and rarely reported from the Archaean terrains. The established geological and tectonic setting of the Archaean Bastar craton clearly suggests existence of a stable continental rift environment in the region since the Archaean time. Thus, report of Neoarchaean boninite-like rocks in an intracratonic setting is an important feature noticed in the Archaean terrain of Indian peninsula. A highly refractory mantle source region is required to form boninitic magma. Refractory lithosphere may be result of extensive extraction of mafic magma during Mesoarchaean. The preservation of refractory reservoir beneath the Bastar craton for long period of time corroborates a high degree of crustal stability during the Meso-Neoarchaean time. Trace element modelling suggests that high-Mg mafic igneous rocks under study are product of different pulses of boninitic magma produced by ∼20-25% melting of a refractory mantle source.

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Major and minor elements of successively collected 70 Middle Triassic radiolarian bedded cherts from the Mino Belt in central Japan were studied. In order to reveal pre-diagenetic, primary geochemical signatures related to marine biogeochemical cycles, composite data of chert-shale couplets in addition to raw data were examined. The results show that Mn, Cu, Sr, Ba and P were supplied significantly by non-lithogenic excess fractions. Positive correlation with SiO₂/TiO₂ suggests that accumulations of Ba, Sr, Mn and Cu were closely related to sedimentation of biogenic silica; Mn and Cu were probably incorporated into oxides, whereas Ba into barite. Relationship between SiO₂/TiO₂ and excess-Ba, proxy for surface productivity implies that regeneration of silica from sinking radiolarian tests was not significant. This may have been caused by an expected relatively short travel time of radiolarian tests from the ocean surface to the bottom, reflecting their large size compared with diatoms. Positive correlations between CaO and P₂O₅ imply that apatite species are host phases for P and Ca. Although conodont composed of apatite is abundant in both chert and shale, their CaO/P₂O₅ ratio differs markedly from those of cherts and shales. Other apatite species, possibly carbonate apatite of diagenetic origin, are present in the bedded cherts and contribute to excess-P accumulation. Early diagenesis is believed to have modified only slightly primary geochemical features of the studied bedded cherts. This suggests relatively oxic depositional environment for the bedded cherts, under which regeneration of redox sensitive elements were not active.

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Mineral chemistry, major and trace elements and Sr-Nd isotopes are presented for basalts and trachybasalts from the Quaternary alkaline Tepi shield from southwest Ethiopia. The lavas are variably porphyritic with phenocrysts of olivine (Fo_67-87), clinopyroxene (Wo_45-47En_38-40Fs_13-16), plagioclase (An_57-68) and Ti-magnetite set in a microcrystalline matrix. Although there are two high-MgO lavas (10.6-10.8 wt.% MgO), the majority of specimens are more evolved (MgO = 4.7-6.2 wt.%). The major element variations can be explained by olivine + clinopyroxene ± plagioclase fractionation, most likely consistent with low P fractionation. The geochemical variations observed in the Tepi lavas are interpreted in terms of variable open system fractional crystallization of a magma sourced from primitive mantle like source.

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The present work aims at providing experimental evidence for weathering as a direct consequence of plant physiology, and the importance of the proximity of fine roots to rock in the weathering process. Discussion is based on the release of different elements from andesite rock particles by the three crop species: rice, maize, and soybean. We designed two types of hydroponic crop pots, in which fine roots were allowed (or not allowed) to contact rock particles by using coarse (or fine) net bags. A plant-free control was also run. Experiments were carried out in a controlled glasshouse for 35-38 days. The pH in the media of all the planted pots decreased by about 1-1.5 units from the value of blank pots during the experimental period, but it did not differ significantly between the coarse and fine net pots. The release of elements in the presence of the plants was calculated by subtracting the depletion of media from the amount absorbed by the plants. We observed a positive effect of plants on the release of elements from the rock particles. The amounts of Ca, Mg and Mn released increased by a factor of 4-12, 4-28, and 4-7, respectively, except for Ca for rice. The amount of Si released was also higher in all the planted pots. Between the coarse and fine net pots the released amounts of Ca and Mn differed significantly for maize (p < 0.05) and that of Si for soybean (p < 0.05). In the case of Fe and Al, the fine net pots gave a greater release than did the coarse ones. A significant difference was found only in the rice pots (p < 0.05 for Fe and p < 0.001 for Al). Maize showed the greatest growth of the three species and significantly higher release of some elements in the coarse net pot than in the fine net pot. This implies that weathering may be caused partially by the direct contact of fine roots with rock particles, together with the alteration of rhizospheric conditions by the roots.

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Microthermometric and stable isotope studies of fluid inclusions were conducted for the Poongjeon talc deposit which formed as alteration products of calc-silicate minerals during the retrograde stage of contact metamorphism related to the intrusion of the Cretaceous Muamsa Granite of South Korea. Two types of quartz vein are observed in the deposit. Vein I, which occurs in marble, is characterized by both mixing and unmixing process of fluid inclusions. Repeated boiling of carbonic fluids produced high X_CO2 fluids abundantly and low X_CO2 or aqueous fluids a little. Occasionally mixing took place between halite ± sylvite-bearing fluids and carbonic fluids. As for vein II, which occurs typically at points of amphibolite-metapelite contact, the fluid mixing model can be applied to the coexistence of abundant CH₄ ± H₂O, H₂O-CO₂-CH₄ fluids with variable CH₄/CO₂ ratios (X_CH4 > 0.1), and minor high X_CO2 fluid inclusions. The CH₄-rich inclusions seem to be derived from the reheating of C-bearing metapelite during contact metamorphism.
Occurrences of halite ± sylvite-bearing inclusions along trails in both vein I and II are chronologically behind other primary inclusions and are closely related to the talc mineralization. The mineralizing fluids would have been derived directly from a water-saturated crystallizing melt and the entrapment occurred between 150 and 700 bars at 260°-390°C. The δ¹³C_CO2 values, 0.1-2.4‰, of inclusion fluids of vein I seem to have resulted from the isotopic exchange of magmatic carbon with ¹³C-enriched CO₂ liberated from the decarbonation for calc-silicate formation. Distinctly lower δ¹³C_CO2 values, -3.5 to -1.7‰, in vein II could have originated from the strong effect of metasediment-derived fluids. Higher δ¹⁸O_H2O values of vein I and lower δD values of vein II, both of which belong to the magmatic water range, seem to have similar evolution history as δ¹³C values. Geologic structures such as faults and contacts between different rock units seem to have promoted infiltration, mixing, and unmixing of fluids of diverse origins.

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Organic-inorganic reactions during thermochemical sulfate reduction (TSR) are the main cause for the destruction of hydrocarbons in deep carbonate sediments. In this paper, thermal simulation experiments on C₁—C₃ hydrocarbons and solid calcium sulfate were carried out using an autoclave operated at high temperature and high pressure. The gas and solid products were characterized by advanced analytical methods including microcoulometry, gas chromatography and FT-IR. The kinetics and thermodynamics were investigated on the basis of the experimental data, and the results showed that the reactions of C₁—C₃ hydrocarbons and solid calcium sulfate can proceed spontaneously in the laboratory to produce H₂S, H₂O, and CaCO₃ as the main products. From the kinetic calculation, it is found that these three reactions are zero order reactions with activation energies of 152.9 kJ/mol, 131.0 kJ/mol and 120.6 kJ/mol, respectively. When extrapolated to geological temperatures, the time needed to reach 50% conversion at the temperature of 200°C for the reaction between CH₄ and CaSO₄ is 1.44 million years.

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We performed batch dissolution experiments on different sized granite and biotite in pure water, in order to better understand the source and geochemical behavior of fluoride in groundwater. Very high concentrations of fluoride (up to 6-10 mg/l) were observed from granite leaching. Correlations between leached ions suggest that fluoride possibly originates from dissolution of biotite. After ∼500 hrs, fluoride concentration gradually decreased because of the supersaturation with respect to fluorite as a result of the build-up of sufficient Ca ions by dissolution of Ca-bearing plagioclase. Biotite dissolution experiments also showed that the fluoride concentrations are controlled by the attainment of fluorite saturation, which depends on the removal of Ca ion by adsorption and/or cation exchange on the surface of clay minerals. In summary, this study indicates that occurrence and behavior of fluorine in groundwater are mainly controlled by fluorite precipitation as a function of Ca concentration which depends on several geochemical processes such as dissolution of Ca-bearing minerals, calcite precipitation, and adsorption and/or cation exchange.

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Anthropogenic pollution of groundwater was investigated from the source area to the uppermost densely populated city, Dujiangyan, along the Minjiang River, a tributary of the Yangtze River, in the Sichuan Basin, in China, based on the chemistry of major dissolved ions and stable isotopic ratios (H, O and S). In the source area above 2,900 m, groundwaters were rarely polluted by human activities. Groundwater pollution was found to be limited to populated areas, where the pollutants come mainly from household wastes. The groundwaters in Dujiangyan and the surrounding area were mixtures of waters from the upper streams along the Minjiang River and local precipitation. The groundwater of this area was found to contain high amounts of anthropogenic Cl^-, NO₃^--N, and SO₄^2-. Among these anions, most SO₄^2- was derived from air pollutants. The present study demonstrates that air pollution seriously affects the quality of groundwaters in areas where the Minjiang River emerges from the bottom edge of the Sichuan Basin.

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