The Fluid Evolution Related to Talc Mineralization in the Hwanggangri Area, South Korea

摘要

Scores of talc deposits distributed in the Hwanggangri Mineralized Zone, South Korea are interpreted to have resulted from the contact metamorphic process related to the igneous intrusion of the Muamsa Granite. Talc usually occurs as an alteration product from tremolite, which is crystallized during the prograde stage. It commonly forms fine-grained, fibrous aggregates, or pseudomorphs after tremolite, and abundant tremolite is included as impurities in the talc ore. Quantitative X-ray diffraction analysis has shown that the ores can be divided into three types depending on the concentrations of talc; tale-tremolite ore (talc > 50 percent), tremolite-tale ore (10 percent < talc < 50 percent), and tremolite (talc < 10 percent) ores. Oxygen isotope compositions of those talc ores become higher from 10.9 approx 12.1 through 11.6 approx 12.3 to 11.9 approx 13.2 per thousand with increasing tremolite concentrations, while hydrogen isotope compositions are not so variable, -73 to -69 per thousand. The high value of the calculated delta~(18)O_(H_2O) of the fluids equilibrated with the tremolite may have resulted from the mixing of magmatic water with ~(18)O-enriched CO_2 evolved from the decarbonation reaction during the prograde stage. However, as the decarbonation reaction ceased during the retrograde stage, the inferred oxygen isotope compositions of talc-forming fluids show similar values to those of the igneous fluids.