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Volume 32 (1998)
- Issue 6 Pages 351-
- Issue 5 Pages 281-
- Issue 4 Pages 213-
- Issue 3 Pages 143-
- Issue 2 Pages 71-
- Issue 1 Pages 1-
Volume 32, Issue 2
Displaying 1-6 of 6 articles from this issue
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Yong-Fei Zheng, Bin Fu1998 Volume 32 Issue 2 Pages 71-89
Published: April 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSAn empirical model for predicting oxygen diffusivity from anion porosity is presented for a wide range of minerals. It is based on the examination of experimental diffusion data under anhydrous and hydrothermal conditions. The relationship between activation energies and pre-exponential factors in all minerals is assumed to obey a common compensation law regardless of diffusion medium (H2O, OH-, CO2 or O2). However, the H2O molecules and OH- groups are relatively small in volume and thus can migrate within mineral structures with given anion porosities easier than the CO2 and O2. As a result, the rates of oxygen diffusion in minerals under hydrothermal conditions are greater than those under anhydrous conditions. The Arrhenius parameters for oxygen diffusion in about 130 minerals have been estimated for the anhydrous and hydrothermal conditions, respectively. The empirical results on oxygen diffusivity are internally consistent for the minerals of geochemical interest and thus can be applicable to oxygen isotope geospeedometry during cooling of high-temperature mineral assemblages.View full abstractDownload PDF (4958K) -
C. Lin, M. D. Melville, I. White, B. P. Wilson, D. Yu1998 Volume 32 Issue 2 Pages 91-101
Published: April 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThree cores of Holocene sediments were investigated from an infilled sand barrier estuary, eastern Australia. The estuary formed as a result of drowning of the previous river valley following the postglacial marine transgression. The sedimentary environments evolved over time at the investigated site from a saline prodelta to a less saline delta front to fresh flood overbank sedimentation. Both prodelta and delta front sediments contained large amounts of pyrite, but pyrite accumulation was limited in the riverine flood overbank sediments. The accumulation of pyrite in the estuarine sediments appears to have been controlled by the combined effect of sedimentation rate and the supply of organic matter, while palaeowater salinity relating to the supply of sulfate ion did not limit pyrite accumulation except for the top 1 metre of the freshwater sediments. The degree of pyritization (DOP) of the investigated estuarine sediments is comparable to that of aerobic marine sediments (Raiswell et al., 1988), although the concentrations of organic C, reactive Fe and pyrite-S were much greater. This may be attributed to higher availability of organic matter and reactive Fe compounds, and consequently pyrite-S enrichment in an embayed estuary than in the open sea. Owing to the presence of large amounts of pyrite, the investigated estuarine sediments posed great acid potential upon the oxidation of pyrite. In general, increasing pyrite concentration in the sediments resulted in increasing acid potential, but this was also accompanied by an increase in self-neutralizing and buffering capacity (NBC) of the sediments although the finely-grained prodelta sediments tended to have greater NBC values than did the coarser delta front sediments on an equivalent pyrite concentration.View full abstractDownload PDF (2801K) -
Maozhong Min, Junqi Wu1998 Volume 32 Issue 2 Pages 103-115
Published: April 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThe Devonian-Carboniferous carbonate rocks in South China host several important uranium deposits, which are characterized by their occurrence in solution collapse breccias and by the mineral association of pitchblende, coffinite, carbonates and Fe, Pb, Cu, Zn, Ni sulfides. The deposits represent an economically new, important uranium deposit type in China. The results of sulfur, carbon, oxygen and hydrogen isotope studies on fluid inclusions, carbonate and pyrite from three typical deposits of this type, i.e., Sanqilinyi, Sanbaqi and Saqisan, provide information concerning the nature of the fluids and sources of sulfur and carbon responsible for uranium mineralization. The δ34S values of pyrite from the ores and host carbonate range from 1.0 to -39.8‰ and from 8.2 to -38.1 ‰, respectively. Depletion in 34S and a wide range of the δ34S values for sulfide indicate that the sulfur in both the ores and host carbonates is biogenic. The δ13C values of calcite from the ores range from 2.9 to -4.4‰, which are similar to those of the host carbonate, ranging from 3.3 to -1.8. The majority of δ13C and δ18O values of carbonate from the deposits lie within the range for carbon and oxygen isotope compositions that exist in marine sedimentary carbonate. The similarity between the sulfur and carbon isotope compositions of the ores and host carbonate indicates that the sulfur and carbon as well as metallic elements in the ores may have derived from the host marine sedimentary carbonate. The δ18O and δD values of the mineralizing fluids range from 12.6 to -2.1‰ and from -26.8 to -54.8‰, respectively. The oxygen and hydrogen isotope data demonstrate that the mineralizing fluids were derived from metamorphic water and were mixed with shallow groundwater. Such fluids may have been released by faulting and shearing, which also opened the channel ways for circulation of minerarizing fluids and facilitated their mingling with meteoric water.View full abstractDownload PDF (3386K) -
Sheng Xu, Kozo Uto, Yoon Ku Kim1998 Volume 32 Issue 2 Pages 117-123
Published: April 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSK-Ar dating was performed for four volcanic rocks from three stages of the Ulreung Island, situated off eastern coast of the Korean Peninsula. The results are consistent with volcano-stratigraphic succession. Presently accumulated data of age and chemical compositions indicate that the subaerial volcanism of Ulreung Island was active from late Pliocene through Pleistocene and well comparative with that of Oki-Dogo Island being located about 60 km off the coast of SW Japan in the Sea of Japan.View full abstractDownload PDF (1858K) -
Hodaka Kawahata, Atsushi Suzuki, Hidekazu Ohta1998 Volume 32 Issue 2 Pages 125-133
Published: April 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSSinking particles play an important role in the transfer of atmospheric CO2 into the deep sea. We deployed six moorings of sediment traps across the transect at 175°E from 0°N to 46°N in the central Pacific. Mean organic matter fluxes along the transect generally reflected primary productivity. Mean opal fluxes showed similar profile, but increased markedly between 34°N and 46°N. The increase in mean total fluxes was accompanied with the increase in fluxes of organic matter and opal. Carbonate contents generally decreased from the equatorial to the subarctic regions. The opal/carbonate ratios increased from mid to high latitudes. These trends are essentially compatible with the prevalent plankton community structure in the upper ocean. Diatoms predominate over calcareous nannoplankton and foraminifera in higher latitudes. In spite of different plankton communities flourishing along the 175°E, C/N atomic ratios of sinking particles varied within a small range (6.0-8.7). The high export flux of organic carbon and high Corg/Ccarbonate ratio in sinking particles were potentially responsible for diminished partial pressure of CO2 in surface water in the middle latitudes of the central Pacific during late spring.View full abstractDownload PDF (2254K) -
Tasuku Akagi, Shun'ichi Nakai, Akimasa Masuda1998 Volume 32 Issue 2 Pages 135-141
Published: April 20, 1998
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSRare earth elements in REE-rich minerals were determined accurately by isotope dilution mass spectrometry (IDMS). The chondrite normalized REE patterns of some specimens showed regular relative aberrations, which are similar to that of the “tetrad effect”. We have introduced a background curve passing normalized values of La, Nd, Gd, Er and Lu, to measure the aberrations. The relative differential variations of some of the minerals are not small, but have been overlooked due to large overall variations of the chondrite normalized values.View full abstractDownload PDF (1548K)
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