1. Introduction The Gyeongsang Basin formed in Cretaceous Period is located in the southeastern tip part of the Korean Peninsula (Fig. 1). The basin comprises sedimentary, vol- canic, and plutonic rocks of the Cretaceous to Early Tertiary. In particular, igneous activities occurred along the belt connecting the southeastern China - southeastern Korea (Gyeongsang Basin) - southwestern Japan from the Late Cretaceous to Early Tertiary. This belt seems to be closely related with the subduction of Pacific and Kula plates during the same period (Park, 1994). There are about six hundreds hydrothermal deposits including vein-type Au-Ag, Cu, and Pb-Zn, and hydrother- mal clay deposits (pyrophyllite-kaolin-sericite) within the Gyeongsang Basin. The hydrothermal mineralization in this basin is controlled by geological and geotectonic environments such as igneous activities, fracturing, and hydrothermal activities. In this study, we interpret the spa- tial and temporal relationship between the mineralization and fracturing which took place within the Gyeongsang Basin. Characteristics of metallogenic provinces and geo- logical structures were anatomized on the basis of the published data such as geology, parent rock, deposit type, vein strike, mineralization age, fault, and lineament extracted from satellite image data in this study. Park (1994) interpreted that the epigenetic mineraliza- tion of the Gyeongsang Basin is related with the intrusion activity of Bulguksa granite by the spatial distribution of hydrothermal metallic ore deposits and by the temporal relationship based on the mineralization age. Chang (1994) interpreted that the mineralization of the Gyeong- sang Basin is related with the igneous activities based on the Pb isotopic data of ore (galena) and the Bulguksa granite. Moon (1994) interpreted that the formation envi- ronments of Miryang pyrophyllite, Bobae and Sangdong sericite deposits are related with volcanic activities based on the sericite age, alteration mineral assemblages, and stable isotopic data of clay minerals. Koh et al. (2000a) suggested that the epigenetic hydrothermal alteration which formed hydrothermal deposits such as pyrophyl- lite, sericite, and porcelain stone in South Korea is close- ly related with Cretaceous post-volcanic activities in the Gyeongsang Basin based on the age data of volcanic rocks, sericite, and alunite, and on the geochemical data RESOURCE GEOLOGY, vol. 53, no. 3, 175–192, 2003 175 Mineralization Characteristics and Structural Controls of Hydrothermal Deposits in the Gyeongsang Basin, South Korea Sang-Mo KOH, Chung-Ryul RYOO and Min-Sub SONG Korea Institute of Geoscience and Mineral Resources, 30 Gajeong-dong, Yuseong-gu, Daejeon, Korea 305-350 [kohsm@kigam.re.kr] Received on July 12, 2002; accepted on July 5, 2003 Abstract: Hydrothermal deposits in the Gyeongsang Basin show the genetic relationship with igneous activity from Late Cretaceous to Early Tertiary in the spatial and temporal viewpoints. Many hydrothermal Au-Ag-Cu-Pb-Zn and clay deposits are dominantly distributed within the Gyeongsang Basin. The Gyeongsang Basin is divided into seven metallogenic provinces by spatial distribution. The age ranges of igneous activity and mineralization are 140~40 Ma and 100~40 Ma, respectively, and the most dominant age ranges of the both activities are from 90 Ma (Coniacian) to 50 Ma (Eocene). The age consistency between igneous activity and mineralization suggests that this age range is the climactic period of the hydrothermal activity of the Gyeongsang Basin. The metallogenic epochs in the Gyeongsang Basin are divided into three epochs of 100~80 Ma (western part of the Gyeongsang Basin), 80~60 Ma (central part of the Gyeongsang Basin), and 60~40 Ma (eastern part of the Gyeongsang Basin). The mineralization and igneous activity tend to become young eastward in the Gyeongsang Basin. NNW-SSE mineralized veins from 100 to 80 Ma in the western part of the Gyeongsang Basin are interpreted as the control of the parallel tensional fissures caused by NNW-SSE compressional stress. NW-SE mineralized veins from 80 to 60 Ma in the central part of the Gyeongsang Basin seem to have been formed under the same stress as that of the Gaeum and Yangsan Fault Systems. Namely, NW-SE tensional stress is associated with a conjugate set of fracturing of the WNW-ESE Gaeum Fault System and NNE-SSW Yangsan Fault System. Also NE-SW mineralized veins from 60 to 40 Ma in the eastern part of the Gyeongsang Basin seem to be controlled by the NE-SW fractures. The fractures are related with NE-SW com- pressional stress and are developed as secondary fractures within the dextral strike slip Yangsan Fault System. Keywords: Gyeongsang Basin, hydrothermal, mineralization, age, metallic, non-metallic, compressional stress, tensional stress, conjugate fracturing, Yangsan Fault System, Gaeum Fault System