Study on structural controlling factors in fluid-flow : application to dykes and ore-deposits = 유체유동의 구조적 제어요소에 대한 연구 : 암맥과 광상에의 적용

다국어 초록 (Multilingual Abstract)

Classification of dyke intrusion patterns and inferred paleostress conditions

Dyke has commonly been considered as a simple planar intrusive structure. However, recently various dyke patterns and structures have been reported. The concerns on dykes may be related with exploration of mineral resources, one of the recent hot issues in geology. Dyke intrusion patterns are mainly controlled by the interrelationship between characteristics of source magmas, local stress conditions and preexisting structures. The subjects of previous studies on dykes are mainly mineralogical or geochemical studies, analysis of specific intrusion pattern and deduction of heat source area. However, one of the main concerns in recent dyke studies is fluid properties in rocks as conduits.
Fault and fracture are the main controlling factors in fluid flow such as magma, groundwater, hydrothermal solution, hydrocarbon in rock masses. Therefore, the characteristics of fracture and fault for fluid flow are a hot issue in modern structure geology. Studies on dyke intrusion pattern may give an insight into understanding the interrelationship between fluid flow and fractures. In this study, various dyke intrusion patterns discovered in Korea are analyzed and classified, and their associated stress conditions are inferred from the dyke geometries. Based on these geometric and kinematic analyses, the relationship between dyke intrusion patterns and controlling factors are interpreted.
The basic dyke classification depends on the similarity of intrusion pattern. We established four main categories and made more branch types depending on specific shapes and differences. Furthermore, intrusion mechanisms and controlling factors are interpreted to understand the interrelationship between dyke intrusion patterns and related factors. The controlling factors on dyke intrusion patterns inferred from this study are extension direction, stress condition, pre-existing fracture, and shear senses. Therefore, precise analysis on specific intrusion patterns can provide useful information about principal stresses and pre-existing structures. Based on these analyses and classification, classification charts for dyke intrusion patterns and controlling factors are proposed here. This classification charts might be very useful to infer local tectonic stress conditions and their effects to associated intrusion patterns.

국문 초록 (Abstract)

이번 연구에서는 관입암류에서 나타나는 특징적인 관입형태들을 분석 및 분류하고 이들을 운동학적 지시자로 활용하여 고응력을 해석하고자 하였다. 먼저 각 암맥들 간의 형태학적 유사성을 토대로 암맥의 관입형태를 유형별로 분류하였으며, 암맥의 확장방향과 발달방향 사이의 관계와 특징적인 관입형태를 이용하여 관입시의 운동학적 정보를 획득하였다. 이러한 정보와 암맥의 변형특성을 이용하여 암맥의 관입 전, 중, 후의 응력변화를 추정하였다.
관입암체들에서 발달하는 관입특성인 암맥의 직진성 또는 굴절성, 암맥들의 분절이 만나는 부분에서의 특징, 암맥 내 구조적 요소의 발달 유무 등을 기준으로 연구된 암맥들을 분류하였다. 그 결과 기존에 존재하던 단열, 관입시의 응력상태, 확장방향 등이 암맥의 형태와 방향성 및 두께를 결정하는 주요한 요소임이 밝혀졌다. 따라서 이런 요소들이 상호 복합적으로 작용하는 암맥의 관입형태를 정밀분석 할 경우 암맥이 관입할 당시 최소수평주응력의 방향뿐만 아니라 관입특성에 대한 많은 정보를 얻을 수 있다. 특히, 지그재그형 암맥의 두께와 확장방향에 대한 기하학적 분석은 암맥관입시 각 단열방향의 확장 폭에 대한 정보뿐만 아니라 기존단열의 방향과 암맥 관입시의 최소수평주응력에 대한 정보를 제공한다.
이런 암맥의 관입형태와 특성을 분석하고 분류하는 연구는 마그마 관입 이전에 발달한 단열에 대한 정보, 마그마 관입시의 응력조건, 관입후의 구조운동 등에 대한 매우 유용한 정보를 제공 한다. 또한, 절대연령측정을 통한 암맥의 연대가 밝혀질 경우 더 정확한 관입 전, 후의 구조운동 시기에 대한 정보도 얻을 수 있을 것으로 사료된다.

다국어 초록 (Multilingual Abstract)

Study on structural controlling factors in fluid-flow : application to dykes and ore-deposits

Abstract of the whole thesis

Fault and fracture are the main controlling factors in fluid flow such as magma, groundwater, hydrothermal solution, hydrocarbon in rock masses. Therefore, the characteristics of fracture and fault in fluid flow are a hot issue in modern structure geology. The purpose of this study is understanding the relationship between structure features and fluid-flow. For this purpose, I investigated a Au-Ag ore-deposit and dyke intrusion patterns in Korea .
In the case of modern low-sulfidation epithermal systems, it is even possible to examine the chemical and physical properties of Au-Ag-rich ore fluids. In ancient fluid convection systems, such as the Moisan low-sulfidation epithermal deposit in SW Korea, it is important to fully characterise structural relationships and understand their formational history over time. In this study, I examine the structural genesis of the Eunsan and Moisan deposit and interpret how these structures have influenced fluid flow, and the formation and positioning of Au-Ag ore-bodies.
Dyke has commonly been considered as a simple planar intrusive structure. However, recently various dyke patterns and structures are reported. Dyke intrusion patterns are mainly controlled by interrelationship between characteristics of source magmas, local stress conditions and preexisting structures. The subjects of previous studies on dykes are mainly mineralogical or geochemical studies, analysis of specific intrusion pattern and deduction of heat source area. However, one of the main concerns in recent studies is fluid properties in rocks as reservoirs. Studies on dyke intrusion pattern may give an insight into understanding the interrelationship between fluid flow and fractures. In this study, various dyke intrusion patterns, discovered in Korea, are analyzed and classified, and their associated stress conditions are inferred from the dyke geometries. Based on the geometric and kinematic analyses, the relationship between dyke intrusion patterns and controlling factors are interpreted.

다국어 초록 (Multilingual Abstract)

Structural genesis of the Eunsan and Moisan low-sulphidation epithermal Au-Ag deposits, Seongsan district, south Korea

Gold-Ag mineralisation at the Eunsan, Moisan, and Chunsan low-sulphidation epithermal deposits are hosted by Cretaceous volcanic and volcaniclastic rocks of the Yuchon Group. These rocks are interbedded with epiclastic fluvial, alluvial, and lacustrine sedimentary rocks. Bedding in the district is subhorizontal and is locally cut by WNW-striking, subvertical, fault-hosted, Au-Ag-bearing veins. The veins formed at about 77.5 Ma, following the main episodes of volcanism (98-71 Ma), plutonism (86-68 Ma), and high-sulphidation epithermal mineralisation (98-91 Ma) in the Seongsan district. The Au-Ag-bearing veins in the low-sulphidation epithermal deposits formed in response to district-wide, NE-SW-directed extension and associated horst-and-graben-style dismemberment of the stratigraphy. During this event, ore fluids were focussed along WNW-striking faults and were concentrated in areas within the fault that experienced low-mean stress, such as intersections between the main WNW-striking fault and NNW-striking fault splays at Eunsan. In contrast, ore fluids were less focussed at the Moisan and Chunsan deposits due to the development of regularly-spaced fractures, resulting in a system of subparallel, sheeted Au-Ag-bearing veins. A secondary control on the development of ore zones is the intersection between mineralised WNW-striking structures and volcanic and volcaniclastic rocks of the Haenam Formation. The greater 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 the subvertical WNW-striking, fault conduit and the formation of wider ore zones in these host rocks. At the Eunsan deposit, the intersection between the WNW-striking, subvertical, mineralised vein and the shallowly, SW-dipping lithological contact between the Haenam Formation and Uhangri Formation defines a 20° westward plunge to the Eunsan ore body. A resumption in NE-SW-directed extension during the second district-wide deformation event resulted in up to 100 m of vertical displacement of the strata and ore bodies along WNW-striking faults. Subsequent deformation events resulted in N-to NNE-striking, brittle faults that offset the WNW-trending veins and post-mineralisation faults. Past exploration in the Seongsan district has been hindered by the lack of outcrop. Future exploration requires the systematic testing of WNW-trending mineralised structures along strike from the Eunsan, Moisan, and Chunsan deposits, with particular focus in areas that experienced local dilation during the mineralisation event and areas that are presently buried under deep transported sediments. Geophysical exploration tools, such as induced polarisation surveys, may help identify areas for drill testing.

목차 (Table of Contents)

• CONTENTS
• Abstract of the whole thesis
• Structural genesis of the Eunsan and Moisan low-sulphidation epithermal Au-Ag deposits, Seongsan district, south Korea
• List of Figures
• List of Tables
• Abstract
• 1. Introduction 1
• 2. Geological setting of the Seongsan district 4
• 3. Methodology 9
• 4. Geology of the Eunsan deposit
• 4-1. Lithostratigraphy 11
• 4-2. Structures
• 4-2-1. Deformation event 1 at Eunsan (DE1) 13
• 4-2-2. Deformation event 2 at Eunsan (DE2) 15
• 4-2-3. Deformation event 3 at Eunsan (DE3) 18
• 4-2-4. Deformation event 4 at Eunsan (DE4) 18
• 4-3. Hydrothermal alteration associated with Au-Ag
• mineralisation 22
• 4-4. Distribution and morphology of ore zones 23
• 5. Geology of the Moisan deposit
• 5-1. Lithostratigraphy 26
• 5-2. Structures
• 5-2-1. Deformation event 1 at Eunsan (DE1) 29
• 5-2-2. Deformation event 2 at Eunsan (DE2) 31
• 5-2-3. Deformation event 3 at Eunsan (DE3) 33
• 5-2-4. Deformation event 4 at Eunsan (DE4) 33
• 5-3. Hydrothemal alteration associated with Au-Ag
• mineralisation 35
• 5-4. Distribution and morphology of ore zones 36
• 6. Discussion
• 6-1. Genetic model for the Eunsan and Moisan deposits
• 6-1-1. Deformation event 1 at Eunsan (DE1) 38
• 6-1-2. Deformation event 2 at Eunsan (DE2) 41
• 6-1-3. Deformation event 3 at Eunsan (DE3) 41
• 6-1-4. Deformation event 4 at Eunsan (DE4) 42
• 6-2. Implications for exploration in the Seongsan district, Korea 44
• 7. Conclusion 47
• References 49
• Summary (in Korean) 51
• Classification of dyke intrusion patterns and inferred paleostress conditions
• List of Figures 54
• Abstract 57
• 1. Introduction 59
• 2. Dyke intrusion patterns
• 2-1. Single type 61
• 2-2. Multiple type 76
• 3. Controlling factors 79
• 4. Inferring paleostress
• 4-1. Case A: Cross-cutting 84
• 4-2. Case B: Restoration 84
• 5. Conclusion 88
• References 89
• Summary (in Korean) 93
• Acknowledgements 94