Geochemistry and Genesis of Hydrothermal Cu Deposits in the Gyeongsang Basin, Korea: Masan Mineralized Area
Choi, Sang-Hoon; So, Chil-Sup; Youm, Seung-Jun; Shelton, Kevin L
published: Jul 7, 1998
ArtNo. ESP154017302002, Price: 29.00 €
Hydrothermal vein-type deposits which comprise the Majin and Woongnam mines are primarily copper deposits, but they have associated gold, zinc, lead, and iron mineralization. The deposits occur within Upper Cretaceous volcanic rocks of the Gyeongsang Basin of Korea. Mineralization can be separated into two distinct stages (stage I, ore-bearing quartz veins; stage II, barren calcite veins) which developed along pre-existing fracture zones. Stage I ore minerals comprise pyrite, arsenopyrite, pyrrhotite, chalcopyrite, electrum, magnetite, sphalerite, galena and hematite. Fluid inclusion data show that stage I ore mineralization was deposited between initial high temperatures (near 330 °C) and later lower temperatures (near 200 °C) from fluids with salinities between 1.4 to 6.9 wt. percent equiv. NaCl. The relationship of salinity and homogenization temperature suggest that ore mineralization at Majin was deposited mainly due to fluid boiling, whereas ore deposition at Woongnam resulted from cooling and dilution via influx of cooler, more dilute meteoric waters. Evidence of fluid boiling suggests pressures decreasing from about 140 to 60 bars. This corresponds to a depth of about 550 m in a hydrothermal system that changed from lithostatic toward hydrostatic pressure conditions. Sulfur isotope compositions of early sulfides of stage I are consistent with an igneous source of sulfur with a δ34SΣs value near 2.0 per mil. Calculated δ34SH2S values show a tendency to decrease with paragenetic time during stage I, from about 2.5 % to - 3.0 %. This pattern, coupled with fluid inclusion evidence and the occurrence of hematite in later stage I veins, indicate progressively increasing oxidizing conditions. Measured and calculated hydrogen and oxygen isotope values of ore-forming fluids indicate meteoric water dominance, with values approaching unexchanged meteoric water with increasing paragenetic time.