Mineral Deposits Have Been Found in the Korean Peninsula

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 nonmarine 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 northeast 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 intermediate 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 accompanied with the Daebo orogeny (Figs. 1 and 4). The isotopic age determinations indicate 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. 5). The Bulgugsa granite series can be sub- divided into three subgroups according to their intrusion ages, distributional localities and petrography; that is, Jindong granite, Bulgugsa granite and masanite in ascending order (S. M. LEE and YOON,1974). The Jindong granites are distributed re- istrictively as small masses near Jindongri, southwest of Masan City. The Jindong granites usually contain altered hornblendes. Some feldspars and quartzes in the granites show cataclastic texture. Judging from those char- Fig. 6 Quartz-alkali feldspar-plagioclase triangular acteristics of the granites, the intrusion age of diagram of Mesozoic granitic rocks in South Korea the granites appears to be earlier than the (after S. M. LEE and YooN, 1974). Bulgugsa granites. The Bulgugsa granites are distributed mainly Jurassic period. The Songrim granite series is in the Gyeongsang basin as large and small distributed restrictively as irregular masses in masses. The Bulgugsa granites are similar to the northern half of the Korean peninsula. No the Jindong granites in the mineralogical exposures of the rocks of the Songrim granite constituents, except for the content of biotite series have been found in the sothern half of which is higher in the Bulgugsa granites than the peninsula (Fig. 4). The intrusion age of in the Jindong granites. the Songrim granite series is estimated to be The masanites are distributed in the area of ranging from 225 to 190 Ma. Masan City and along the eastern zone of the The Jurassic granite series also called Daebo Yangsan fault as irregular masses. The name granite series is distributed as huge masses in of masanite was given first by KOTO (1909) to the central and southwestern regions of the the small mass, disributed near Masan City, of peninsula (Fig. 4). Judging from the lithologi- fine grained and light pinkish colored leuco- cal relationships between the Daebo granite cratic granite with graphic texture. The series and the surrounding granite gneisses and masanite was classified by KOTO into plagio- the distributional patterns with NNE-trending clase-tsingtauite which is an old classificatory of the granites harmonizing with the anticline term not used today any longer. Judging from 240 M. S. LEE MINING GEOLOGY:

Fig. 7 Diagrams of SiO2 versus Na2O+K2O, CaO and FeO+Fe2O3 of Mesozoic granitic rocks in South Korea (after S. M. LEE and YooN, 1974). Fig. 8 Ore deposits and their geologic age in South Korea. Total mine number; 353. Data adopted from Table 1 Metallogenic epochs and accompanied S. M. LEE and YOON(1974). mineral commodities in South Korea. masanite consists of tonalite, quartz monzonite, granodiorite, granite and alkali granite. The rocks of the Daebo granite series con- trast in modal compositions with that of Bulgugsa granite series (Fig. 6). The chemical analyses of those granitic rocks show that the Na2O+K2O contents are highest in the masanite, intermediate in the Bulgugsa granite and lowest in the rocks of the Daebo granite series (Fig. 7). On the contrary, the CaO and Fe2O3+FeO contents are highest in the rocks of the Daebo granite series, intermediate in the Bulgugsa granite and lowest in the masanite (Fig. 7). the mode of occurrence, the intrusion age of the masanite seems to be later than the other Metallogeny two granites. As regards the ore genesis the mineral de- Jindong and Bulgugsa granites comprise posits in South Korea belong to the category three differentiation facies of granodiorite, of epigenetic deposits with the exception of hornblende granite and biotite granite, whereas several iron deposits occurring in Precambrian 31(4), 1981 Geology and Metallic Mineralization in South Korea 241

Of the gold and silver deposits in South Korea, about thirty percent of the deposits are distributed in the granite gneiss of the Pre- cambrian and the rest are associated with the Jurassic and Cretaceous granites. The gold and silver deposits emplaced in the granite gneiss and Jurassic granite are of hypothermal to mesothermal type also called the Korean type gold vein, whereas the deposits in the Cretaceous granites of the Gyeongsang basin are of epithermal type. The distributional Fig. 9 Relationship between granitic rock facies and mineralization in South Korea. Data adopted from patterns and vein systems of the Korean type S. M. LEE and YOON (1974). gold vein deposits seem to be controlled closely by the activity of the Daebo granite. Lead and zinc deposits can be classified into vein and skarn types. The former is emplaced mainly in the sediments and volcanics of the Cretaceous of the Gyeongsang basin and the latter is distributed principally along the same horizon between the lower shale and the upper limestone of the Cambro-Ordovician formation, the Great Limestone Series, in the Taebaegsan area. The famous Sangdong tungsten deposit is also emplaced concordantly in the same horizon. The Pb-Zn skarn type Fig. 10 Relationship between granitic rock types and deposits display vertical mineral zoning con- associated ore deposits in the Gyeongsang basin, sisting of rhodochrosite-pyrite, galena-sphal- Korea. Data adopted from S. M. LEE and YOON erite-pyrite, galena-sphalerite-pyrrhotite, and (1974). pyrrhotite mass with some copper in descend- terrain such as Seosan and Chungju iron ore ing order. On the stratiform skarn type de- deposits. posits, there are alternative explanations about Metallogenic epochs and accompanied min- their genesis; one is epigenetic and the other eral commodities in South Korea are shown in syngenetic. Table 1. According to the relationships be- In the Gyeongsang basin various types of tween the frequency of various ore deposits copper deposits, namely chalcopyrite vein, and their geologic age in South Korea (Fig. 8), breccia pipe, porphyry, and alunite-pyrophyl- various metallic mineralizations are considered lite types are found in the sediments, inter- to be emplaced concentrically during the mediate to felsic volcanics and granites mainly Cretaceous period. By the relationships be- of the southern margin of the basin. In the tween granitic rock facies and various kinds of Ogcheon-Taebaegsan area several skarn type the metallic mineralization (Fig. 9), W-Mo, deposits and vein deposits occur in limestone Cu, Pb-Zn and iron mineralizations are related and granitic rocks, respectively. In the northern closely to granite porphyry and biotite granite, most of the Gyeongsang basin, some native whereas Au-Ag mineralization took place copper deposits are currently found in the mainly in the granite gneiss. Various kinds of basalt flow layer. metallic mineral deposits in association with Several types of iron ore deposits have been the Bulgugsa granite occur predominatingly found in South Korea. The deposits presum- in the Taebaegsan and Gyeongsang basin (Fig. ably of sedimentary type are found in the 10). Precambrian terrain and some skarn type 242 M. S. LEE MINING GEOLOGY:

Table 2 Relationships among metallogenic province, metallogenic epoch, Mesozoic granite series ralated to mineralization and principal mineralization during Mesozoic period in South Korea.

deposits in the Cambro-Ordovician limestone. It is noteworthy that the vein-form deposits associated with skarnization are found in the volcanics of the intermediate composition within the Gyeongsang basin. Tungsten is closely associated with molybdenum in Korea. Tungsten and molybdenum deposits are classified into skarn type scheelite deposits, wolframite-scheelite-molybdenite- chalcopyrite-pyrite-quartz veins and quartz- molybdenite veins. Tungsten deposits usually contain small amount of molybdenum, whereas quartz-molybdenum veins are not accompanied with tungsten. Quartz-tungsten-molybdenum and quartz- molybdenum veins are commonly distributed in the Precambrian gneiss and Cretaceous granites. Generally, tungsten deposits predominate in the north, and molybdenum deposits occur in the south of the southern half of the peninsula. Relationship among metallogenic provinces, metallogenic epochs, Mesozoic granite series related to mineralizations and principal mineralizations during Mesozoic period in South Korea is shown in Table 2.

Metallogenic Province Fig. 11 Metallogenic province and zonal distribution and Zonal Distribution of ore metals in South Korea. Data adopted from S. M. LEE and YOON(1974). With regard to metallogenic province, the southern half of the peninsula can be divided province and Gyeongsang province (Fig. 11). into Precambrian region of Gyeonggi- The Gyeonggi-Yeongnam province is char- Yeongnam province, Ogcheon-Taebaegsan acterized by the mineralization of Korean type 31(4), 1981 Geology and Metallic Mineralization in South Korea 243

gold vein. Some W-Mo mineralizations occur turbance. in the mid-part of the Gyeonggi province. On During the Jurassic period the Daebo orog- the other hand, more extensive W-Mo min- eny took place in the mid-part of the penin- eralization is recognized in the central zone of sula. At this time huge granite intrusions the Ogcheon-Taebaegsan province, and Pb-Zn (Daebo granite series) were emplaced in a belt mineralization in the rest of the province (Fig. shape with Sinian direction of NNE-trending. 11). The distributional pattern of the deposits Following the Daebo orogeny the in the province as well as the mineralogical Gyeongsang group was deposited during lateral zoning are in harmony with the dis- Cretaceous period under the fluviolacustrine tributional pattern and the structural trend of environment. And subsequently granite activity the Ogcheon group, Paleozoic formation sys- (Bulgugsa granite series) took place mainly in tems and huge Daebo granite masses (Fig. 11). the Gyeongsang basin. In the Gyeongsang province, the mineralogi- The edge of the southeastern corner of the cal lateral zoning is represented by a con- Gyeongsang basin has been affected by the centric circular pattern. The central zone is block movement owing to the Yangsan fault. characterized by Mo-W mineralization and Tertiary marine sediments were deposited in the outer zone by Pb-Zn mineralization (Fig. several small basins along the eastern coast 11). Copper mineralizations are dominated in and Quaternary alkaline basalt volcanism the southeastern margin of the Gyeongsang took place along the Jeju and Ulleung island province (Fig. 11). chain. The majority of various metallic mineraliza- Conclusion tions in South Korea are considered to be In the Korean peninsula, two Precambrian formed predominatingly during the Cretaceous massifs whose ages range from about 3,000 to period. 800 Ma are distributed in the areas of the W-Mo, Cu, Pb-Zn and iron mineralizations Gyeonggi and the Yeongnam district. are related closely to granite porphyry and The age unknown Ogcheon group is dis- biotite granite of the Cretaceous granite series, tributed across the central zone of the southern whereas Au-Ag mineralization took place half of the peninsula and the belt of the mainly in the masses of Jurassic granite series Ogcheon group is bounded on the northeast and Precambrian gneiss. by the southwestern margin of the Taebaegsan The gold and silver deposits emplaced in basin where the Paleozoic formations are granite gneiss and Jurassic granite are known distributed. The geological environment of the as "Korean type gold vein". The distribu- Ogcheon group is different from that of the tional pattern of Korean type gold vein Paleozoic formation and it is to be noted that deposits seems to be controlled closely by the the amphibolites presumably originated from Daebo granitic activity. tholeiitic basalt are distributed along the Lead and zinc deposits of vein and skarn border zone. type are emplaced in the Gyeongsan basin The discovery of conodont fossils in the and in the Taebaegsan basin, respectively. uppermost part of the Joseon group lends some The skarn type deposits are distributed along support to the presence of Silurian formations the same horizon of the Cambro-Ordovician in Korea. formation and display vertical mineralogical During the Mesozoic period two tectonic zoning. movements took place in the peninsula. At the Copper deposits are found predominatingly middle to upper Triassic time the Songrim in the southern margin of the Gyeongsang disturbance accompanied with granite activity basin. Some iron deposits of vein type occur- (Songrim granite series) solely affected the ring intermediate volcanics in the southernmost northern part of the peninsula. The Daedong of the Gyeongsang basin are accompanied by group was deposited after the Songrim dis- skarnization. 244 M. S. LEE MINING GEOLOGY

Tungsten is closely associated with molyb- References denum. Tungsten deposits usually contain BURKE, K. (1960): Ore mineral zones related to granite small amount of molybdenum, whereas quartz- in South Korea. Geol. Surv. Korea, Bull. 4, 141 molybdenum vein deposits are not accompanied •`151. with tungsten. Generally, tungsten deposits KIM, J. H. (1977) : Metallogeny of Korea. J. Geol. Soc.

predominate in the north, and molybdenum Korea, 13, 265•`273.

deposits in the south of the southern half of the KIM, O. J. (1971) : Metallogenic epochs and provinces peninsula. of South Korea. J. Geol. Soc. Korea, 7, 37•`59. The three metallogenic provinces can be KOBAYASHI, T. (1953): Geology of South Korea. Univ. established in South Korea, that is, Gyeonggi- Tokyo, Fac. Sci. J., Sect. 2, 8, 145•`293. Yeongnam province of the Precambrian re- KOTO, B. (1909): Journeys through Korea. J. Coll. Sci., Imp. Univ. Tokyo, 26, Part. 2, 207p. gion, Ogcheon-Taebaegsan province, and Gyeongsang province. LEE, H. Y. (1980): Discovery of Silurian conodont fauna from South Korea. J. Geol. Soc. Korea, The Gyeonggi-Yeongnam province is char- 16, 112•`123. acterized by the mineralization of the Korean LEE, H. Y., LEE, M. S. and UM, S. H. (1980) : Geochem type gold vein. In the Ogcheon-Taebaegsan istry of amphibolite in the Hwanggangri area,

and the Gyeongsang provinces rough min- Korea. J. Geol. Soc. Korea, 16, 93•`104.

eralogical zonal distribution is recognized. The LEE, S. M. (1979): Geology and tectonics of Korean

central zone is characterized by Mo-W min- peninsula. Chikyukagaku (Iwanami shoten), 16, eralization and the outer zone by Pb-Zn 355•`384 (in Japanese). mineralization. LEE, S. M. and YOON, S. G. (1974): A relative study on

plutonism and mineralization in Korea. Research Report, Ministry of Sciences and Technology,

Republic of Korea (in Korean).

韓国の地質および中生代花崗岩類に関連する金属鉱化作用

李〓成

要旨:コリア半島の南部は先カンブリア時代の京畿-嶺・中温熱水性Au-石英鉱脈で代表される.これらの鉱床南陸塊,時代未詳の沃川層群,カンブローオルドビス紀のは北々東方向に分布する.しかし,大部分の金属,非金朝鮮層群,上部石炭紀-ペルム紀の平安層群,上部三畳属鉱化作用は白亜紀花崗岩活動に関連して生じたものと紀-下部ジュラ紀の大同層群,白亜紀の慶尚層群,第三考えられる.鉱脈型の鉱床は慶尚盆地で白亜紀堆積岩類紀の陽地・延日層群,そして第四紀のアルカリ火山岩かや中性火山岩類中に主に産出する.経済的に重要なスカら構成される.花崗岩類は3時期,三畳紀(松林花崗岩ルン型鉱床は太白山地域のカンブローオルドビス紀朝鮮系列),ジュラ紀(大宝花崗岩系列),白亜紀(佛国寺花崗層群中の上部石灰岩層と頁岩との間に産出する.鉱床生岩系列)に大別され,半島南部には後2者が産出する. 成区は,京畿-嶺南生成区,沃川-太白山生成区,慶尚生大宝花崗岩に関連する鉱化作用は数多くのコリア型高成区に3分しうる.