Complex geochemical evolution of hydrothermal fluids related to breccia pipe Cu-W mineralization of the Dalseong mine, Korea
Chul-Ho Heo, ; Seong-Taek Yun, ; Chil-Sup So, ; Sang-Hoon Choi, ; Seung-Jun Youm,
published: Jun 22, 2001
ArtNo. ESP154017602001, Price: 29.00 €
The Cu-W deposit of the Dalseong mine, Korea, occurs within a steeply plunging, pipe-like breccia zone (40-90 m by 120-240 m in horizontal dimension) of intensely altered andesitic rocks and lies about 1.5 km of a Cretaceous quartz monzonite stock. The hydrothermal mineralization occurs mainly as two stages (stages 1 and 2) of open space filling in breccia blocks (mainly, < 1 to 30 cm in size). stage 1 mineralization is classified into early matrix mineralization and late ore zone mineralization. the ore zone mineralization of stage 1 consists of quartz, tungstates, base-metal sulfides and carbonates, and is further divided into three mineralization periods: early w-mo; middle base-metal sulfides; and late bi-bearing sulfides and sulfosalts. stage 2 mineralization occurs as barren carbonate veins. fluid inclusion data indicate a complex evolution of the hydrothermal fluids. the earliest recorded fluid in quartz of the matrix mineralization of stage 1 is found as hypersaline (31-42 wt. % equiv. nacl) fluid inclusions that are homogenized totally at high temperatures (440-550 °c), and was likely formed by condensation of an immiscible magmatic vapor phase. later fluids trapped in quartz of the early to middle periods of stage 1 ore zone mineralization occur as lower salinity (< 20 wt. % equiv. nacl), lower temperature (th-tot = 250-400 °C) fluid inclusions that consist of various types (aqueous vapor-rich, aqueous liquid-rich, liquid CO2-bearing, and halite-bearing). These fluid inclusions suggest the presence of compositionally heterogeneous fluids formed by fluid boiling and associated CO2 immiscibility. Fluid inclusions in quartz of the middle to late periods of stage l ore zone mineralization are aqueous liquid-rich and very low in total homogenization temperature (250-330 °C) and salinity (down to 12 wt. % equiv. NaCl), and record the history of mixing with cooler meteoric groundwater. Measured and calculated O and H isotope compositions of hydrothermal fluids gradually decrease with time (and decreasing temperature): δ18OH2O values, from 6.3 to-1.0‰; and δDH2O values, from -73 to -99 ‰. This indicates the influx of progressively increasing amounts of meteoric groundwater into an early, W-Mo-depositing magmatic hydrothermal system. This increasing influx of meteoric water resulted in successive deposition of base-metal sulfides, Bi-bearing minerals, and finally carbonates.