Cretaceous epithermal gold-silver mineralization and geodynamic environment, Korea

摘要

Epithermal precious-metal mineralization in the Korean Peninsula mainly occurred along NNE-trending major strike-slip fault systems that are associated commonly with formation of pull-apart basins and major volcanic activity during the Cretaceous. Sedimentation in the basins was initiated in the Hauterivian and continued into the Albian, whereas much of the volcanism occurred sporadically from ca. 110 to 50 Ma, with a major episode between ca. 90 and 70 Ma. Epithermal Au-Ag mineralization in Korea took place between approximately 100 and 70 Ma, overlapping with the shallow magmatic activity. Styles of epithermal Au-Ag deposits in Korea include those of the Mugeug-type found in sediment-dominant basins in the central portion, and the Haenam-type in volcanic-dominant basins in the southwest. Epithermal Au-Ag deposits associated with the volcanic-dominant basins in the southern Korea generally formed at very shallow crustal levels (<0.5 kbar) and relatively low temperatures (<300 deg C) from fluids containing large components of less-evolved meteoric waters than those associated with sediment-dominant basins. Orthogonal subduction following oblique subduction of the Izanagi Plate along the Pacific continental margin during the Cretaceous probably represents a major control of magmatism and associated Au-Ag mineralization in the Korean Peninsula. In the Early Cretaceous, the left-lateral strike-slip movements due to the northward (oblique) subduction of the plate resulted in the Gongju-Eumseong and Yeongdong-Gwangju fault systems. Late Cretaceous calc-alkaline volcanic activity and associated caldera-related fractures related to an orthogonal convergence that postdates the NNE-trending strike-slip movements may play an important role in the formation of epithermal Au-Ag deposits. Simultaneously with, or soon after heating related to magmatism, continued movement of strike-slip faults may also have been critical to the ore-forming process, leading to relaxation of local compressive forces, enhancement of crust-scale permeability, and promotion of mixing of ore-forming fluids.