40AR-39AR LASER MICROPROBE STUDY OF FLUIDS IN DIFFERENT COLOR ZONES OF A HYDROTHERMAL SCHEELITE CRYSTAL FROM THE DAE-HWA-W-MO MINE, SOUTH-KOREA

Laser Probe analyses of Ar isotopes in fluid inclusions in five neutron-irradiated zones from a single scheelite crystal indicate the presence of two fluid components: (1) a Cl-rich hydrothermal fluid containing excess 40Ar; and (2) a meteoric fluid containing dissolved Ar with a 40Ar/Ar-36 ratio similar to the atmospheric value, and low Cl content. Core to rim variations indicate increasing dilution of the hydrothermal fluid with the meteoric component; however, the expected decrease in 40Ar/Ar-36 ratio is not recorded. At present the explanation of this is not clear, however, two possibilities are that either the dilution was accompanied by a complex process of boiling and fluid mixing, or that the 40Ar/Ar-36 ratio of the hydrothermal fluid increased with time due to leaching or diffusive loss of 40Ar from country rock minerals within the hydrothermal system, without significant addition of Cl.