岩鉱
Online ISSN : 1881-3275
Print ISSN : 0914-9783
ISSN-L : 0914-9783
94 巻, 3 号
March
選択された号の論文の1件中1~1を表示しています
論説
  • Chil-Sup SO, Seong-Taek YUN, Chul-Ho HEO, Seung-Jun YOUM
    1999 年 94 巻 3 号 p. 65-82
    発行日: 1999年
    公開日: 2006/08/07
    ジャーナル フリー
    Electrum (79.67-88.68 atom.%Ag)-sulfide mineralization of the Byungjibang mine in the Hwoingsung area represents the first recognized example of mesothermal gold mineralization of late Cretaceous age in South Korea, and was deposited in three stages of mineralogically simple, base metal-rich quartz±calcite veins that filled the fractures in Cretaceous biotite granite and quartz porphyry. The K-Ar dating of hydrothermal vein muscovite indicates that mineralization took place during the late Cretaceous (81.9±1.8 Ma). Fluid inclusion data show that main ore mineralization (stage I) formed from high temperature (225°-370°C), H2O-NaCl(-CO2) fluids with low salinity (1.4-6.7 wt. % eq. NaCl). The deposition of abundant base-metal sulfides (sphalerite, chalcopyrite, galena, etc.) forming distinct sulfide bands was mainly a result of primary boiling and associated CO2 effervescence of the fluid with temperatures between about 320° and 370°C under considerable crustal depths (at least 1.3 to 2.2 km deep). Gold-silver deposition occurred paragenetically later than base-metal sulfide deposition, and was the result of cooling (down to 200°-250°C) and decreasing sulfur activity caused by mixing with meteoric groundwaters. Calculated sulfur isotope composition of ore fluids (δ34SΣS=3.4 to 5.6‰) indicates an igneous source of sulfur in hydrothermal fluids, probably the nearby Cretaceous quartz porphyry dikes. Measured and calculated, oxygen and hydrogen isotope compositions of stage I ore fluids (δ18Owater=3.1 to 7.9‰, δDwater=−72 to −87‰) indicate that the auriferous hydrothermal fluids at Byungjibang formed originally from either a magmatic water or an isotopically highly exchanged meteoric water under low water-rock ratio condition, and evolved through progressive mixing with an isotopically evolved meteoric groundwater (which is represented by stage III fluids; temperature=down to 130°C, δ18Owater=−6.4 to −7.2‰, δDwater=−86‰).
feedback
Top