Fluid inclusion and stable isotope studies of gold- and silver-bearing vein deposits, South Korea: Geochemistry of a te-bearing Au - Ag mineralization of the Imcheon mine

Sang Hoon Choi, Seong Taek Yun, Chil Sup So

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Abstract

Mesohypothermal, tellurium-bearing gold - silver vein mineralization of the Imcheon mine was formed in mineralogically complex quartz - sulfide veins that filled fault fractures in Precambrian gneiss and Mesozoic granite. Ore grades average 15 g/ton gold with a gold/silver ratio of 1 : 3. Mineralization was deposited in three stages (I to III) of veins: stage I is ore-bearing, whereas stages II and III are barren. Major ore mineralization during stage I is composed of three mineralization phases which show a progressive change in ore mineralogy and mineral composition with increasing paragenetic time: early Fe - sulfide mineralization → middle base-metal sulfide mineralization accompanying active gold deposition → late telluride mineralization. This shift in mineralogy reflects a progressive decrease in temperature with a concomitant increase in fugacity of tellurium. Fluid inclusion and stable isotope data indicate a complex history of boiling and later cooling and dilution of ore fluids. Stage I mineralization occurred from dominantly aqueous (but containing little CO2) fluids with a wide range of temperature (200° -430 °C) and salinity (0.5-10.0 wt % NaCl equiv.) under a depth of about 1 km below the paleosurface. Early Fe - sulfide was deposited at temperatures of 350°-430 °C from boiled magmatic fluids (δ34SΣs = 3 ‰, δ18Owater = 7.1 to 8.5 ‰, δDwater = - 70 to - 74 ‰). Middle base-metal sulfides + Au mineralization resulted from lower temperature fluids (260°-350 °C, δ18Owater = 2.3 to 4.2 ‰, δDwater = - 76 to - 8.2‰) through continued boiling and concomitant meteoric water mixing. Gold precipitation was mainly a result of a decrease of activity of reduced sulfur by sulfide precipitation and/or H2S loss accompanying boiling. Late telluride mineralization resulted from the continued cooling (down to 200°-260 °C) and concomitant increase in fTe2 of ore fluids, likely due to the meteoric water inundation. This meteoric water mixing is evidenced by decrease in oxygen and hydrogen isotope compositions of hydrothermal fluids (down to δ18Owater = - 0.1 to 1.2 ‰ and δDwater = - 85 to - 88 ‰). Comparison of Imcheon with other Au - Ag ( - Te) deposits indicates that the complex sequence of Fe - sulfide, base-metal sulfide, and telluride mineralization is a natural consequence of repeated inundation of a hydrothermal system by progressively cooler meteoric groundwaters.

Original languageEnglish
Pages (from-to)33-59
Number of pages27
JournalNeues Jahrbuch fur Mineralogie, Abhandlungen
Volume171
Issue number1
Publication statusPublished - 1996

Keywords

  • Au - Ag( - Te)
  • Fluid inclusions
  • Geochemistry
  • Imcheon mine
  • Korea
  • Mesohypothermal quartz veins
  • Stable isotopes

ASJC Scopus subject areas

  • Geochemistry and Petrology

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