Regional variations of sulfur isotope compositions for metallic deposits in the Taebaeksan Mineralized District, South Korea

摘要

Metallic ore deposits of various genetic types are distributed in the Taebaeksan mineralized district in South Korea. The different basements or host rocks for these deposits vary across the northern and southern regions of the district with the Baegunsan Syncline as its center. Previous and newly analyzed sulfur isotope data of 374 sulfide minerals collected from 45 ore deposits were reviewed to compare the genetic characteristics of the two regions. Metallic deposits in the study area were classified into skarn, hydrothermal replacement, and hydrothermal vein based on genetic types and W-Mo, Fe-Cu(-Mo-Pb-Zn), Pb-Zn(-Cu-Au- Ag), and Au-Ag(-Cu-Pb-Zn) deposits with regard to ore species. For each genetic type, average sulfur isotope values were found to be 6.8aEuro degrees, 7.7aEuro degrees, and 6.3aEuro degrees in the northern region, and 2.3aEuro degrees, 3.6aEuro degrees, and 3.5aEuro degrees in the southern region, respectively. Average sulfur isotope values for each of the ore species were 11.3aEuro degrees, 2.6aEuro degrees, 6.6aEuro degrees, and 6.9aEuro degrees in the northern region, and 1.3aEuro degrees,-0.2aEuro degrees, 4.2aEuro degrees, and 3.3aEuro degrees in the southern region, respectively. The results indicate that sulfur isotope compositions for both genetic types and ore species are distinctly higher in the northern region than in the southern region. These differences could be ascribed to different sulfur isotope compositions of basement and host rocks that provided sulfur to ore minerals during the evolution of hydrothermal fluids, though the mineralizing fluids were originated from magmatic source. In the northern region, higher delta 34S values of ore sulfurs could be attributed to high delta 34S values of sulfate and sulfide in carbonate rocks formed in seawater. On the contrary, lower delta 34S values of sulfide minerals in the southern region seem to be attributed to metasedimentary rocks that have lower delta 34S values as a result of bacterial sulfate reduction.