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South Korea can be divided into five northeast-trending geologic provinces: the Precambrian Gyeonggi and Ryeongnam massifs, the Ogcheon fold belt, the Paleozoic Taebaegsan basin, and the Mesozoic Gyeongsang basin. The Gyeongsang basin occupies the southeast quarter of South Korea and contains Lower Cretaceous post-orogenic fluvial and lacustrine deposits overlain by volvaniclastic and volcanic rocks of middle and Late Cretaceous age. Granitic plutons, ranging in age from 107 to 44 m.y., occur mostly in the Gyeongsang basin, but are also exposed to the north in the Ogcheon zone and Taebaegsan basin.
These plutons are known as the Bulgugsa granites, dominantly composed of granodiorite-quartz monzonite-granite and their porphyritic equivalents, in part are believed to be cogenetic with the Gyeongsang volcanics, which ranges in composition from andesite to basalt. Distribution of the granitic plutons in the Geyongsang basin appears to be structurally controlled by north-northeast, west-northwest, and east-northeast trends, on which circular features are sometimes superimposed.
The majority of mineral deposits in South Korea are closely associated with the Late Cretaeous to early Tertiary Bulgugsa granitic activity. Hydrothermal vein, breccia filling, and porphyry types of copper, iron, lead-zinc, gold-silver, tungsten, and molybdenum deposits characterize the mineralization of the noncarbonate, volcano-sedimentary host rocks in the Gyeongsang basin. In the Taebaegsan basin to the north, however, contact metasomatic (skarn) and hydrothermal replacement types of zinc-lead, gold-silver, tungsten-bismuth, and molybdenum deposits, hosted in thick carbonate beds of the Cambro-Ordovician sedimentary sequence, dominate the country's most productive Taebaegsan mineral belt. The Bulgugsa granites can be correlated with the Chyukoku granites of western Japan in age an accompanying metallogeny.
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