GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
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Volume 23, Issue 1
Displaying 1-5 of 5 articles from this issue
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  • The kinetics of CoO dissolution in acidic aqueous solutions under surface conditions
    Pujing Pan, Nicholas J. Susak
    1989 Volume 23 Issue 1 Pages 1-10
    Published: 1989
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.23.1
    JOURNAL FREE ACCESS
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    A simple flow-system was designed to study the dissolution of cobaltous oxide (CoO) at surface conditions (25° and 39°C, one atmosphere). Experiments were carried out using solutions with salinities less than 0.01m and pH's of 0.7-3.46. The dissolution was found to be controlled by surface reactions and has a reaction order of 0.67±0.05 with respect to hydrogen ion concentration. The integrated kinetic equation has the form [Co(H2O)62+] =k+/k- [H+]0.67(1-e-Ak_t) where k+ and k- are reaction rates for the forward and reverse reactions, and were determined to be 1.05±0.26×10-10 m-2s-1 and 7.25±1.20×10-10 m-2s-1 respectively. CoO is not stable in acidic aqueous solutions under surface conditions. It gradually transforms into cobalt spinel (Co3O4) and which is effectively insoluble under our experimental conditions. A rate constant of 0.0038 day-1 was estimated for the phase transition reaction (CoO→Co3O4) assuming a first-order reaction model.
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  • Contact relationships between MARID rock and metasomatised peridotite in a kimberlite xenolith
    Frances G. Waters, Anthony J. Erlank, Leon R. M. Daniels
    1989 Volume 23 Issue 1 Pages 11-17
    Published: 1989
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.23.11
    JOURNAL FREE ACCESS
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    A rare kimberlite mantle xenolith displaying a direct contact relationship between a MARID rock and metasomatised peridotite is described. There is an abrupt textural transition from a MARID (phlogopite-K-richterite-diopside) portion, to a 2 cm rind of peridotite (olivine pseudomorphs-phlogopite-K-richterite-diopside-chromite). Small, but significant differences in mineral composition exist across the boundary, the most important of which are lower Fe/Mg ratios in the peridotite rind. Our interpretation is that MARID magmas crystallised and expelled fluids which metasomatised surrounding peridotite wall-rock, and the xenolith has sampled a cumulate-wall-rock contact of this nature.
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  • Ammonium in spilitized basalts of southwest England and its implications for the recycling of nitrogen
    Anthony Hall
    1989 Volume 23 Issue 1 Pages 19-23
    Published: 1989
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.23.19
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    Spilitic alteration increases the ammonium content of basaltic rocks. A series of spilitic rocks from southwest England was found to contain an average of 54 ppm of ammonium ion. Most of this ammonium is fixed as an isomorphous constituent in feldspars and micas, but a small proportion (averaging 5 ppm) is held in an exchangeable form. Subduction of oceanic crust containing ammonium-enriched igneous rocks may be a mechanism for recycling atmospheric nitrogen back into the mantle.
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  • Carbon contents of the magnetite-series and ilmenite-series granitoids in Japan
    Shunso Ishihara, Shigeru Terashima
    1989 Volume 23 Issue 1 Pages 25-36
    Published: 1989
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.23.25
    JOURNAL FREE ACCESS
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    Representative magnetite-series (n=75) and ilmenite-series (n=143) granitoids, and metamorphic rocks (n=11) from the Ryoke Belt, Sanyo Belt, Sanin Belt, Hidaka Belt, Outer Zone of Southwest Japan and Green Tuff Belt, were analyzed for total and noncarbonate carbon contents by combustion and infrared absorption photometry. Noncarbonate carbon contents of the ilmenite-series granitoids (58 and 61 ppm in the average for granodiorite and monzogranite, respectively) are slightly higher than those of the magnetite-series granitoids (39 and 35 ppm), especially of the sodic type (13 ppm for tonalite). Some ilmenite-series granitoids have noncarbonate carbon contents as high as 200-300 ppm at few places. In the carbonate vs noncarbonate carbon contents diagram, common ilmenite-series granitoids have values between those of the sodic granitoids and metamorphic rocks indicating that the ilmenite-series granitoids were formed by mixing of both the igneous and sedimentary source materials. A rather ambiguous separation of the magnetite series from the ilmenite series in these contents may also be due to remobilization of carbon after the granitoids solidified.
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  • On the use of a three-dimensional method in solving the U-Pb two-stage model
    Yong-Fei Zheng
    1989 Volume 23 Issue 1 Pages 37-43
    Published: 1989
    Released on J-STAGE: April 08, 2008
    DOIhttps://doi.org/10.2343/geochemj.23.37
    JOURNAL FREE ACCESS
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    The three-dimensional method is described for treating U-Pb isotopic data obeying a two-stage evolution. The U-Pb discordia plane model and the Pb-Pb isochron plane model are developed respectively, to eliminate the effect of the unknown common lead correction. Calculation formulae of best-fit plane parameters are given and some examples from the literature are recalculated to demonstrate the applicability of the method. The plane-fitting can be a convenient means in U-Pb dating.
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