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Structural genesis of the Eunsan and Moisan low-sulphidation epithermal Au–Ag deposits, Seongsan district, Southwest Korea |
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| Authors: | Seok-Jun Yang Paul Duuring Young-Seog Kim |
| Institution: | 1. Department of Earth & Environmental Sciences, Pukyong National University, Busan, 608-737, South Korea 2. Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, 305-350, Republic of Korea 3. Centre for Exploration Targeting, University of Western Australia, Crawley, WA, 6009, Australia |
| Abstract: | The Seongsan district in the Jindo–Haenam basin of southwest Korea comprises Precambrian gneissic basement, overlain and intruded by Cretaceous volcanic (98–71 Ma) and plutonic (86–68 Ma) rocks, respectively. Haenam Formation volcanic and volcaniclastic rocks are the dominant rock type exposed in the district and are the main host to high-sulphidation (82–77 Ma) and low-sulphidation (79–73 Ma) epithermal deposits. The Eunsan and Moisan low-sulphidation epithermal deposits have similar vein mineralogy, zoned hydrothermal alteration mineral assemblages, structural framework and interpreted deformation events. These similarities suggest that they formed by district-scale hydrothermal fluid flow at about 77.5 Ma. At this time, ore fluid movement along subvertical WNW-trending faults was particularly focussed in dilatant fault bends, jogs, and at intersections with N-trending splays. At Eunsan, Au–Ag ore shoots coincide with these areas of structural complexity, whereas at Moisan, narrower ore zones correspond with several parallel, poorly connected veins. A secondary control on the location of ore zones is the intersection between mineralised WNW-striking structures and rocks of the Haenam Formation. The higher permeability and porosity of these rocks, in comparison with mudstones and siltstones of the underlying Uhangri Formation, resulted in the more efficient lateral migration of ore fluids away from subvertical faults and into wall rocks. The intersection between subvertical WNW-striking faults and the gently dipping Haenam Formation imparts a low angle SW plunge to both ore bodies. WNW-striking post-mineralisation faults displace ore zones up to 100 m and complicate the along-strike exploration and mining of WNW-trending ore zones. Future exploration strategies in the district involve the systematic testing of WNW-trending mineralised structures along strike from known deposits, with a particular emphasis on identifying structurally complex areas that experienced local dilation during the mineralisation event. Poorly exposed regions have historically been under-explored. However, based on the proposed exploration model for the Eunsan and Moisan deposits, these areas of poor outcrop are now considered important target areas for hidden ore bodies using ground-based geophysical exploration tools, such as seismic surveys. |
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