MINING GEOLOGY, 31(4), 235～244, 1981 Geology and Metallic Mineralization As•¬ociated with Mesozoic Granitic Magmatism in South Korea* Min-Sung LEE** Abstract: The southern half of Korean peninsula is composed geologically of Geyonggi-Yeongnam massif of Precambrian, Ogcheon group of age unknown, Joseon group of Cambro-Ordovician, Pyeongan group of late Carboniferous to Permian, Daedong group of late Triassic to early Jurassic, Gyeongsang group of Cretaceous, Yangbuk arid Yeonil groups of Tertiary, and alkaline volcanics of Quaternary. Three groups of granites are distributed in the peninsula, that is, Triassic granite series (Songrim granite series), Jurassic granite series (Daebo granite series) and Cretaceous granite series (Bulgugsa granite series). In the southern half of Korean peninsula, the latter two are widespread. The mineral deposits related to Daebo granite series are many hypothermal to mesothermal Au-quartz veins known as Korean-type gold vein. These are distributed in NNE direction. The majority of metallic and nonmetallic mineralizations in the southern half of the Korean peninsula is considered to have been formed associated with the Cretaceous granite series. The vein-type deposits are mainly emplaced in the Cretaceous sedi ments and intermediate volcanics in the Gyeongsang basin. Economically important skarn type deposits are found along the same horizon between shale and upper limestone of Cambro-Ordovician formation in the Taebaegsan area. The southern half of the Korean peninsula can be divided into three metallogenic provinces of Gyeonggi- Yeongnam province, Ogcheon-Taebaegsan province and Gyeongsang province. Daebo orogeny during Jurassic to early Introduction Cretaceous period and Bulgugsa granite series Mineral deposits have been found in the of late Cretaceous to early Tertiary periods. Korean peninsula throughout various geologi- Studies from the viewpoint of metallogeny cal periods. Particularly epigenetic mineraliza- related to granitic magmatism were performed tions associated with granitic magmatism took first by BURKE(1960) and subsequently done place in pre-mid-Proterozoic and Mesozoic to by O. J. KIM (1971) and S. M. LEE (1974). early Tertiary times. Majority of various kinds The metallogeny of Korea is comprehensively of metallic mineralization, however, is con- summarized by J. H. KIM (1977). sidered to be related to granitic magmatism This paper attempts to deal, from a some- during Mesozoic to early Tertiary periods. what different point of view, with the metallic In the southern half of the Korean peninsula, mineralizations associated with granitic mag- two major granitic activities are recognized, matism of Mesozoic period in South Korea namely Daebo granite series accompanied with chiefly based on the pre-published papers and * Paper presented at the Symposium on Granitic some additional geological data. Magmatism and Associated Mineralization in Japan Geological Settings and Korea, held in Tokyo on January 27, 1981. The manuscript received on March 15; accepted on June The Korean peninsula is located in the 22, 1981. ** Department of Earth Sciences, Seoul National southeastern margin of the North China University, Seoul 151, Korea. craton, and is separated by the Tsushima Keywords:Gyeonggi massif(京 畿 陸 塊),Yeongnam strait from the southwestern part of the mobile massif(嶺 南 陸 塊),Ogcheon belt(沃 川 帯),Taebaeg- belt of the Japanese island arc. san basin(太 白 山 盆 地),Gyeongsangbasin(慶 尚 盆 The Precambrian basement composed mainly 地),Daebo granite(大 宝 花 崗 岩),Bulgugsa granite of granite gneiss and schist crops out in the (仏 国 寺 花 崗 岩),Jindong granite(鎮 東 花 崗 岩), form of massif in the Gyeonggi district in the Masanite(馬 山 岩),Sangdong tungsten deposit (上 東 重 石 鉱 床). northern region and the Yeongnam district in 235 236 M. S. LEE MINING GEOLOGY: 31(4), 1981 Geology and Metallic Mineralization in South Korea 237 Cambrian. The northeastern margin of the Ogcheon belt is in contact with the southwestern margin of the Taebaegsan basin comprising the Joseon group of Cambro-Ordovician age and the Pyeongan group of late Carboniferous to early Triassic age (Fig. 1). The Daedong group of Jurassic and the Gyeongsang group of Cretaceous have subordinate distribution in the basin (Fig. 1). The Joseon group is represented by thick marine calcareous sediments and is uncon- formably overlain by the Pyeongan group. The Pyeongan group is composed mainly of non- marine sediments and of important coal meas- ures of Permian age. Silurian-Devonian hiatus between the Joseon group and the Pyeongan group had been postulated. Lately Silurian conodont fossils were found in the uppermost part of the Joseon group (H. Y. LEE, 1980). On the basis of the sedimentary facies, the formations of the Ogcheon and the Joseon groups can be classified into the eugeosynclinal and the miogeosynclinal sedimentary deposits respectively, according to the classical classifica- tion of the geosynclinal deposits. The Ogcheon belt is bounded on the north- east by the southwestern margin of the Taebaegsan basin of the Paleozoic formations and on the southeast by the northwestern margin of the Yeongnam massif of the Pre- cambrian formations (Fig. 1). Fig. 2 Major stratigraphic units and their ages in It is to be noted that the geological environ- South Korea. ments of the Paleozoic formations in the the southern region of the southern half of the Taebaegsan basin and the Precambrian forma- peninsula (Fig. 1). The isotopic age datings tions in the Yeongnam massif are different from indicate that the Precambrian age ranges from that of the Ogcheon group and that the about 3,000 to 800 Ma (Fig. 2). amphibolites are distributed along the border The Ogcheon group consists mainly of zone mentioned above. The amphibolites seem metamorphosed pelitic rocks, pebbly mudstone, to belong to tholeiites (H. Y. LEE, et al., thin limestone layer, and some mafic volcanics. 1980). The group is distributed in a belt shape with In view of such geological facts, emplace- northeast-trending across the central zone of the ment mechanism of the amphibolites along southern half of the peninsula (Fig. 1). The the border zone is considered to be an im- geological age and the depositional environ- portant question in the study of the tectonic ments of the group have not been well clarified settings of the Korean peninsula. yet. Thus two different opinions of its geologic During the Mesozoic period two tectonic age have been presented by the Korean geolo- movements of the Songrim disturbance and the gists; one is Precambrian and the other post- Daebo orogeny took place in the Korean 238 M. S. LEE MINING GEOLOGY: trusions were emplaced in a belt shape with NNE-trending (also called Sinian direction) in the area of the mid-part of the peninsula (Figs. 1 and 4). Following the Daebo orogeny, the Gyeongsang group was deposited during Cretaceous period under the fluviolacustrine environment in association with mainly inter- mediate volcanism. And subsequently granite activity took place mainly in the area of the Fig. 3 Tectonic province of South Korea. Gyeongsang basin (Fig. 1). Presumably at the early Tertiary time, the eastern corner of the Gyeongsang basin was cut by the Yangsan fault having NNE trend (Figs. 1 and 3). Accordingly the eastern block of the fault has been affected by the block movement owing to the faulting. At the Tertiary period, Yangbuk and Yeonil groups which are composed mainly of marine sediments accompanied with volcanics were deposited in several small basins that were formed along the eastern coast of the peninsula (Fig. 1). After that the Quaternary volcanic activity of alkaline basalt took place in Jeju island, Ulleung island and several places along the eastern coast of the peninsula (Fig. 1). The volcanic chain is corresponded to a part of the Penin-Korean volcanic chain proposed by KOBAYASHI(1953). The major stratigraphic units and their ages in South Korea are shown in Figure 2. On the basis of lithology, stratigraphy and tectonic history, the southern half of the peninsula can be geologically divided into Gyeonggi, Ogcheon, Taebaegsan, Yeongnam, Fig. 4. Distribution of granitic rocks in Korea (after western Gyeongsang, and eastern Gyeongsang S. M. LEE, 1979). tectonic provinces (Fig. 3). Mesozoic Granitic Rocks peninsula (Fig. 2). At the middle to upper Triassic time the Songrim disturbance accom- The granitic rocks of the Mesozoic period panied with granite activity solely affected the can be divided into three series; Triassic northern part of the peninsula. granite series, Jurassic granite series and The Daedong group of nonmarine clastic Cretaceous granite series, based on their intru- sediments was deposited in isolated lakes after sion ages and distributional localities. the Songrim disturbance (Fig. 1). The Triassic granite series also called During the Jurassic period the Daebo orog- Songrim granite series accompanied with the eny attacked more severely the mid-part of Songrim disturbance is presumably a product the peninsula. At this time huge granite in- of the igneous activity during Triassic to early 31(4), 1981 Geology and Metallic Mineralization in South Korea 239 axes of the folded belt, Daebo granite series is considered to be syntectonic intrusives ac- companied with the Daebo orogeny (Figs. 1 and 4). The isotopic age determinations indi- cate that the age of the Daebo granite series ranges from 183 to 135 Ma (Fig. 5). The Daebo granite series can be petrographycally classified into tonalite, granodiorite and granite (Fig. 6). The Cretaceous granite series (also called Bulgugsa granite series) within the Gyeongsang basin of the southern region of the peninsula is Fig. 5 Frequency distribution of radiometric ages of distributed concentrically in smaller irregular granitic rocks in South Korea. The number of meas- urements is 85. masses than the Daebo granite series (Figs. 1 and 4). Results of the isotope datings indicate that the age of the Bulgugsa granite series range from 120 to 68 Ma (Fig.