Geology and geochemistry of the Sambo Pb-Zn deposit, Republic of Korea

Abstract

The Sambo lead-zinc deposits are composed of fissure-filling quartz-barite veins within Proterozoic biotite schist which has been intruded by granite and granodiorite stocks. K-Ar dates of biotite and muscovite from the intrusions are 177 + or - 4 and 164 + or - 3 m.y., suggesting a Jurassic age for Pb-Zn-Ba mineralization. This age is in agreement with data for metallogenic epochs in Korea. Ba-rich Pb-Zn deposits are related to a Jurassic-Early Cretaceous epoch, whereas Ba-poor Pb-Zn deposits are generally related to Late Cretaceous-Tertiary igneous activity. Mineralization at Sambo consists of three distinct stages of quartz-barite veins (I, II, and III) which were separated in time by tectonic fracturing and brecciation events. Ore textures of Stage II suggest rhythmic deposition. Five successive mineralization cycles of Stage II, each with up to seven nearly monomineralic bands, are recognized. Fluid inclusion data suggest that each stage evolved from early high temperatures (near 300 degrees C) to later lower temperatures (less than 200 degrees C). Sulfur isotope and fluid inclusion evidence indicates that galena, sphalerite, and barite were deposited at temperatures near 160 degrees to 265 degrees C from solutions with salinities ranging from 2 to 17 equivalent weight percent NaCl. Fluid inclusion evidence of boiling suggests pressures of less than 100 bars during portions of stage II mineralization. This pressure corresponds to depths at the time of mineralization of between 500 and 1,250 m.--Modified journal abstract.