BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 52 , Issue 8
Bulletin of the Geological Survey of Japan
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Article
  • Pin’an WANG
    2001 Volume 52 Issue 8 Pages 327-345
    Published: November 30, 2001
    Released: April 25, 2015
    JOURNALS FREE ACCESS
    Sanjiang orogen is a NS-trending collisional orogenic belt between Indian plate and Yangtze block of the South China plate, and also an important metallogenetic belt in southwestern China. The collision process between Eurasia plate and Indian plate started from Mesozoic times, which resulted in strong and frequent magmatic activities then after. After Cenozoic, the stronger and more frequent tectono-magmatism and volcanic eruptions provided fracture spaces and plenty of heat sources for epithermal activity in this area. As an active geothermal field, the Rehai geothermal field situates in the southern part of the Sanjiang orogen, and is composed of two sub-scale geothermal fields-the Huanggua-qing-Liuhuang-tang in northeast and Reshui-tang in southwest. Rocks that outcrop in this geothermal field are mainly late Cretaceous granitoids with minor late Tertiary and Quaternary volcanics, sandstone and conglomerate. Strong volcanisms in Pliocene to Pleistocene were recognized and early Pleistocene dacite and andicitic terrestrial volcanics distribute in the Huanggua-qing-Liuhuangtang geothermal field (i.e. Rehai geothermal field in narrow sense). 62 hot spring groups occur along a NS-striking main fault in the Rehai geothermal field. Hydrochemical types of the spring water are mainly Na-Cl-HCO3 and Na-HCO3-Cl types, secondly Na-SO4 type, Na-Cl type, Ca-Na-HCO3-SO4 type and Mg-Ca-HCO3 type.Temperature of spring water on the surface is 24~102°C, and pH value is 2~9.8. Geothermometers of SiO2, Na/K, Na-K-Ca, and Na-K-Ca-Mg, of the hot spring waters in the Rehai geothermal field, were used to evaluate the reservoir temperature, which yielded results of >270~100℃ from below 600 m to the surface. The hydrothermal alteration and gold mineralization process are still going on in that area, and the Lianghe gold deposit was formed between the Zao-tang River and the Xiao-shui River in Liuhuang-tang-Huanggua-qing geothermal area in the northeast sector of the geothermal field. This deposit is about 6 km2 in area, with several kinds of spring sinter, hydrothermal alteration and breccia, and is one of the most recently formed hot spring-type gold deposits in China.Au content in hot spring water, surface sinter, bottom sinter, acid leaching zone, and stockwork quartz veins, is 0.01~0.16 ppb, 0.001~0.63 ppm, 0.004~0.17 ppm, 0.001~0.73 ppm, and 0.003~4.65 ppm, respectively. Ag content in silica cap reaches 0.001~54.5 ppm. Based on the average of Au and Ag content, Au/Ag ratio is always less that 0.1 (1 : 10~1 : 19). δ18OH2O,δDH2O, and δ13CCO2, values of hot spring waters in the Tengchong Lianghe area are -12.3‰~-5.1‰, -68.9‰~-55.7‰,and -5.2‰~-1.6‰,respectively. δ34S values of hot spring water, native sulfur, and sulfides such as pyrite, are mainly -2‰~+2‰. Liquid composition of fluid inclusions in quartz from breccia of Liuhuang tang area is H2O 72%, H2S 28%; vapor composition is CO2 67.1%, H2S 12.6%, and H2 20.3%. The δ18O values for quartz from quartz veins in the Lianghe gold deposit are between 5.0‰ and 8.8‰ (averaged 7.3‰ for 10 samples), and 2.3‰~12.4‰ (averaged 7.6‰ for 6 samples) for silicified Pliocene sandstone (whole rock). Soil and rock geochemical investigation results suggest a tendency of high concentration or anomalies of Bi, Li, Rb, As, Sb, Hg, and Sn in or near hot spring areas, and Mn, Ni, Co, Pb, and Zn around or out of hot spring areas.
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  • Shigeru TERASHIMA, Atsuyuki OHTA, Noboru IMAI, Takashi OKAI, Masumi MI ...
    2001 Volume 52 Issue 8 Pages 347-369
    Published: November 30, 2001
    Released: April 25, 2015
    JOURNALS FREE ACCESS
    A total of 240 alluvial soils collected from the southern to northeastern Kanto district, Japan, were analyzed for major and minor elements to characterize the geochemical map of soil. It has been considered that these alluvial soils originated mainly from elastic materials derived from basement rocks and altered volcanic ashes. The chemical composition change of elastic materials from basement rocks in alluvial soils reflects the geology of catchment areas, whereas the change of altered volcanic ashes depends mainly on erupted volcanoes. The vertical variations of the elemental concentrations in alluvial soils are generally smaller than volcanic ash soils. Several sand layers derived from basement rocks are found in the cores. Compared to the mud layers, sand layers are poor in Al2O3, TiO2 and heavy metals, but rich in alkali and alkali earth metals in most cases. The elution and/or deposition of chemical elements result from the decreasing grain size during weathering. Compared to the volcanic ash soils, the alluvial soils are rich in alkali and alkali earth metals, and depleted in Al2O3, TiO2 and heavy metals. The sedimentation rate of alluvial soils is estimated about 0.3 to 1.2 mm/yr at some places. It is less than or equal to the rate of recent lake sediments, but much higher than volcanic ash soils (0.03-0.08 mm/yr).
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  • Kuttickat Paul SHAJAN
    2001 Volume 52 Issue 8 Pages 371-382
    Published: November 30, 2001
    Released: April 25, 2015
    JOURNALS FREE ACCESS
    Geochemical study of bottom sediments of the Periyar and Muvattupuzha rivers, Cochin estuary and the adjoining nearshore continental shelf was carried out to understand the distribution and enrichment pattern, sources, possible factors responsible for the enrichment and depletion of elements and environmental contamination of the systems. The river sediments are sand to sandy silt, estuarine sediments are sandy silt to clay and inner shelf sediments are mud. The study indicate that the sediment texture is the major controlling factor in the distribution of elements here. The fine grained sediments of the inner shelf and estuary are rich in MgO, CaO, Al2O3, TiO2, Fe2O3, Na2O, P2O5, K2O, MnO, Li, Sc, V, Cr, Co, Ni, Cu, Zn, As, Rb, Ta, Zr, Nb, Pb, LOI and poor in SiO2. The organic rich sediments exhibit a similarity in the distribution of elements like Fe2O3, Al2O3, MgO, P2O5, Cu, Ni, Co, Cr and V. The other possible factors for the enrichment of certain elements are the presence of metal scavenging phases like Fe/Mn hydoxides and the higher content of heavy minerals in the area.The higher concentration of Fe2O3, MgO, P2O5, Zn, Ba, Pb, Cd, Bi and Cr in many samples indicates that all the sampling units are anthropologically contaminated, with the Periyar river and it’s estuarine area showing maximum heavy metal contamination in the study area.
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