Epithermal systems of the Seongsan district, South Korea an investigation on the

geological setting and spatial and temporal relationships between

high and low sulfidation systems

Thesis submitted by Christopher David Bowden, BSc (Hons, JCUNQ)

for the degree of Doctor of Philosophy in the School of Earth Sciences at

James Cook University of North Queensland

STATEMENT OF ACCESS

I, the undersigned, author of this work, understand that James Cook University will make this

thesis available for use within the University Library and, via the Australian Digital Theses

network, for use elsewhere. I understand that, as an unpublished work, a thesis has significant

protection under the Copyright Act and;

I do not wish to place any further restriction on access to this work.

20th July, 2007

_________________________ ______________

Christopher David Bowden Date

Bowden, C.D. ii

STATEMENT OF DECLARATION

I, the undersigned, the author of this work, declare that this thesis is my own work and has not

been submitted in any form for another degree or diploma at any university or other institution

of tertiary education. Information derived from the published or unpublished work of others has

been acknowledged in the text and a list of references is given.

20th July, 2007

_________________________ ______________

Christopher David Bowden Date

Bowden, C.D. iii

ELECTRONIC COPY DECLARATION

I, the undersigned, the author of this work, declare that the electronic copy of this thesis

provided to the James Cook University Library is an accurate copy of the final printed thesis

submitted, within the limits of the technology available.

20th July, 2007

_________________________ ______________

Christopher David Bowden Date

Bowden, C.D. iv

ACKNOWLEDGEMENTS

Firstly I would like to thank Doug Kirwin from Ivanhoe Mines Ltd. and Roger Taylor for

initiating this project. They also provided guiding direction early on and showed continued

support and patience throughout the project. Special thanks also to Doug and Ivanhoe Mines

Ltd. for providing all of the logistical and financial support that was necessary for the success of

this project. Several other people within Ivanhoe Mines Ltd. provided invaluable assistance and

deserve thanks, including, but not limited to Craig Panther, Miles Worsley and Chris Wilson.

Several external analytical procedures were required for this project. Thanks goes to Jodie

Miller for providing oxygen and hydrogen isotope analyses, Keith Harris for providing sulfur

isotope analyses and Jim Dunlap for providing stepwise 40Ar/39Ar analyses.

I am indebted to my primary supervisor, Andrew Allibone, for taking the time to work with me

in developing so many aspects of this project from a bunch of ideas into a readable thesis. I

can’t imagine many other supervisors reviewing with as much patience and thoroughness as

Andrew did. I have learnt a lot from Andrew and this work would not be the standard it is

without his help, thanks mate.

Numerous other colleagues have reviewed various parts of this thesis, including: Tim Baker,

Nick Oliver, Graham Shields, Pat Williams, Bill Collins, Mike Rubenach, Roger Taylor and

Peter Pollard. Thanks to these people for their contributions to this project.

Thanks also to the examiners, who have taken time out of their busy schedules to review and

examine this manuscript.

Finally, to all my friends and family, thanks also to you for your support, belief, encouragement

and patience during this project.

Bowden, C.D. v

ABSTRACT

Two distinct styles of epithermal Au-Ag deposits have been recognised globally for the past 25

years or so, low-sulfidation or adularia-sericite systems and high-sulfidation or acid-sulfate

systems. Both types of epithermal systems occur in a volcanic arc setting at regional scale, but

generally they are not found together at the district scale and the extent to which they are

genetically related is often not clear. The Seongsan district of South Korea however, does host

high-sulfidation style clay-sulfate-silica deposits that are exploited as commercial sources of

kaolinite and dickite. The district also hosts several low-sulfidation Au-Ag mineralised

epithermal systems that have only been recognised recently. Little is known about their

geological setting, any structural controls on their location, or their relationship, if any, to the

nearby clay-sulfate-silica deposits.

Advanced argillic alteration in the Seongsan district has been mined as a source of clay rather

than Au and Ag. The region therefore also offers as opportunity to assess the controls on clay

ore as well as Au-Ag ore development in a high-sulfidation/acid-sulfate environment.

The primary objective of this project is to investigate the geological setting and the spatial and

temporal relationships between the high and low-sulfidation epithermal systems in the Seongsan

district of South Korea. The Seongsan district provides the opportunity to examine if the two

distinctly different types of epithermal systems are coeval parts of a single hydrothermal event,

or separate events formed by different fluids at different times.

The Cretaceous Yuchon Group that hosts the epithermal systems of the Seongsan district

comprises a sequence of pyroclastic ignimbrite flows and subplinian, plinian and phreatoplinian

fall and surge deposits. Sub-volcanic intrusive domes, flows and proximal to distal pyroclastic

and volcaniclastic deposits formed during later stages in the magmatic history. These are all

intercalated with epiclastic fluvial, alluvial fan, and lacustrine sediments. The volcanic rocks in

the Seongsan district represent an ancient continental silicic volcanic succession. No evidence

of a caldera setting was seen in the Seongsan district despite previous workers assumptions to

the contrary.

Both low- and high-sulfidation systems are often localised along faults that comprise zones of

brittle fractured rock a few cm to 10s of metre wide. Two phases of fault movement and

alteration have affected the Seongsan district. Advanced argillic alteration is localised along a

network of brittle faults whose internal geometry and slickenlines indicate that high-sulfidation

Bowden, C.D. vi

hydrothermal activity occurred during sinistral strike-slip movement. Quartz-Au-Ag veins and

associated adularia alteration are localised along younger normal faults. Synchronous

reactivation of some strike-slip faults resulted in deformation of the advanced argillic alteration.

The structural framework of the Seongsan district was determined to have developed under two

distinctly different stress regimes, characterised initially by wrenching (district-scale stress

regime 1; σ1 north-northeast – south-southwest) followed by extension (district-scale stress

regime 2; σ3 north-northwest – south-southeast).

40Ar/39Ar stepwise heating age data indicate adularia in the low-sulfidation systems crystallised

between 77.4±0.5Ma and 78.1±0.3Ma. When coupled with published age data on the high-

sulfidation deposits, this new data shows that the advanced argillic and adularia-phyllic

alteration occurred between 1.3Ma and 5.5Ma apart. Epithermal systems of the district formed

during two discrete hydrothermal events, although they could be considered as two parts of a

long-lived cycle of crustal convergence, subduction, volcanism and associated hydrothermal

activity.

A lack of workable primary fluid inclusions resulted in negligible information being obtained

from microthermometric fluid inclusion analyses. Mineral phase relations show that the high-

sulfidation systems formed under oxidised, acidic, SO4-dominant conditions, whereas the low-

sulfidation systems formed under reduced, near-neutral pH, H2S-dominant conditions. Fluids

associated with the Au-Ag-bearing paragenetic stages were of intermediate- to low-sulfidation-

state, regardless of which epithermal system they formed in. Oxygen and hydrogen isotopic

ratios show that a meteoric-derived fluid characterised by a δ18O range of -8 to 1‰ and δD of -

65 to -100‰ formed the low-sulfidation Au-Ag vein systems, whereas a magmatic fluid

characterised by a δ18O range of 2 to 7‰ and δD of -145 to -40‰ formed the high-sulfidation

systems. Sulfur isotopic ratios of pyrite (-9 to 0‰ δ34S) and alunite (5 to 7‰ δ34S) from the

high-sulfidation systems show marked fractionation, and imply a SO4-dominant, magmatic-

steam origin for fluids that formed the advanced argillic alteration. The relatively narrow range

of δ34Ssulfide from the low-sulfidation systems implies that the associated phyllic-argillic

alteration formed from fluids in which H2S was the dominant sulfur species.

Epithermal systems in the Seongsan district shares many similarities with those in the Comstock

district of Nevada, Mt Skukum in Canada, southern Kyushu in Japan and the Mankayan district

in the Philippines. All districts show a superimposition of low- on high-sulfidation style

alteration (±mineralisation) coupled to a change in structural setting from compression/

wrenching to extension, typically over a period of ca. 1 to 2Ma. This suggests that, although

Bowden, C.D. vii

rare, districts that host both high- and low-sulfidation systems share a common structural and

hydrothermal evolution.

Rhyolitic to dacitic host rocks and SO4-dominant conditions play critical roles in the

development of clay deposits. Metalliferous mineralisation requires sulfur speciation to be H2S-

dominant, whereas host rock composition is less critical.

The Seongsan district is possibly the first documented area in Korea, if not globally, that hosts

both high- and low-sulfidation epithermal systems that produce economic clay/sulfate and Au-

Ag from the same district.

Bowden, C.D. viii

LIST OF CONTENTS

STATEMENT OF ACCESS ............................................................................................ ii

STATEMENT OF DECLARATION .............................................................................. iii

ELECTRONIC COPY DECLARATION ....................................................................... iv

ACKNOWLEDGEMENTS.............................................................................................. v

ABSTRACT..................................................................................................................... vi

LIST OF FIGURES ....................................................................................................... xvi

LIST OF TABLES......................................................................................................xxvii

Chapter 1......................................................................................................... Chapter 1: Introduction to the epithermal systems of the Seongsan district, South Korea 1.1 INTRODUCTION .................................................................................................1-2 1.1.1 Epithermal Au-Ag deposits and their related hydrothermal systems ......1-2 1.1.1.1 Comparison of sulfidation-state with descriptive models for epithermal

systems ..................................................................................................................1-7 1.1.2 Epithermal systems of the Seongsan district: research themes ...............1-13 1.2 PRIMARY OBJECTIVE AND DETAILED AIMS OF THIS RESEARCH.1-17 1.3 GENERAL GEOLOGY OF THE SEONGSAN DISTRICT...........................1-19 1.3.1 Orogenies, tectonics and regional geology .................................................1-19 1.3.1.1 Basement Precambrian metamorphic complex ......................................1-19 1.3.1.2 Tectonics of the area prior to the Late Cretaceous (ca. 80Ma) .............1-19 1.3.1.3 Mesozoic igneous activity prior to the Late Cretaceous (ca. 80Ma)......1-19 1.3.1.4 Cretaceous Yuchon Group sediments, intrusive and volcanic rocks......1-21 1.3.1.5 Tectonics of the area during the Late Cretaceous to Early Tertiary......1-22 1.3.1.6 Plutonic activity during the Late Cretaceous to Early Tertiary .............1-23 1.3.1.7 Tectonics of the area after the Cretaceous .............................................1-23 1.3.2 Metallogenic overview of Korea, with a focus on the south-west ............1-27

1.3.2.1 Jurassic to Early Cretaceous ..................................................................1-27 1.3.2.2 Late Cretaceous to Early Tertiary ..........................................................1-27

1.4 PREVIOUS WORK WITHIN THE SEONGSAN DISTRICT .......................1-30

Chapter 2

Bowden, C.D. ix

Chapter 2: Lithostratigraphy and structure of Cretaceous volcanic and sedimentary rocks in the Seongsan district, South Korea 2.1 INTRODUCTION .................................................................................................2-2 2.1.1 Previous lithostratigraphic and structural work in the Seongsan district2-2 2.2 LITHOSTRATIGRAPHIC UNITS AND THEIR RELATIONSHIPS ............2-3 2.2.1 Uhangri Formation (Ums).............................................................................2-6 2.2.2 Haenam Formation ........................................................................................2-6 2.2.2.1 ‘Hwangsan Tuff’ (HVf) a lithic fiamme tuff flow deposit .........................2-8 2.2.2.2 Heterolithic crystal-rich lapilli tuffaceous sediments (HVxo) ................2-10 2.2.2.3 Igneous complex one (Ic1 ) ......................................................................2-10 2.2.2.4 Co-ignimbrite volcanic deposit HVci (or where differentiated, HVxi, HVac & HVai)...............................................................................................................2-12 2.2.2.5 Hwangsan mudstone and siltstone (Hms)...............................................2-14 2.2.2.6 ‘Hwangsan Volcaniclastics’ (HV) - undifferentiated .............................2-18 2.2.3 Discordant Cretaceous sub-volcanic intrusions and extrusions ..............2-25

2.2.3.1 Igneous complex two (Ic2 ) ......................................................................2-25 2.2.3.2 Mafic dykes (Dm)....................................................................................2-25 2.2.3.3 Altered volcaniclastic debris flow breccia (AVdb) .................................2-28 2.2.3.4 Igneous complex three (Ic3 ) ...................................................................2-28 2.2.3.5 Pebble dykes (Dp) ...................................................................................2-31

2.2.4 Quaternary Units .........................................................................................2-31 2.2.4.1 Reclaimed land, colluvium and minor alluvium (Qa).............................2-31

2.2.5 A facies model for the Seongsan district: deduced from observed lithostratigraphy ...................................................................................................2-31 2.2.6 Correlation of Cretaceous Bulguksa Series granitoids with igneous rocks of the Seongsan district.........................................................................................2-32 2.3 STRUCTURAL FRAMEWORK OF THE SEONGSAN DISTRICT............2-34 2.3.1 Introduction..................................................................................................2-34 2.3.2 Nature of faults in the Seongsan district....................................................2-34 2.3.3 Orientation, continuity, sense and direction of movement on faults in the district ....................................................................................................................2-34

2.3.3.1 East-northeast striking faults..................................................................2-34 2.3.3.2 North striking faults ................................................................................2-41 2.3.3.3 East-southeast striking faults..................................................................2-44 2.3.3.4 Gently dipping faults...............................................................................2-54

2.3.4 Timing of fault movement relative to Ic1, Ic2, AVdb and Ic3. ..................2-54 2.3.5 Structural paragenesis for the Seongsan district ......................................2-56

Bowden, C.D. x

Chapter 3: Alteration, mineralisation, paragenesis and geological setting of epithermal deposits and prospects in the Seongsan district, South Korea 3.1 INTRODUCTION .................................................................................................3-2 3.2 ALTERATION ASSEMBLAGES........................................................................3-3 3.2.1 Primary mineral assemblages .......................................................................3-3 3.2.2 Propylitic alteration .......................................................................................3-3 3.2.3 Advanced argillic 1 alteration.......................................................................3-3 3.2.4 Advanced argillic 2 alteration.......................................................................3-6 3.2.5 Advanced argillic 3 alteration.......................................................................3-6 3.2.6 Siliceous alteration .......................................................................................3-12 3.2.7 Silicic alteration............................................................................................3-12 3.2.8 Phyllic alteration ..........................................................................................3-12 3.2.9 Adularia alteration.......................................................................................3-16 3.2.10 Carbonate (late-stage) alteration..............................................................3-16 3.3 VEINING AND INFILL MATERIAL ..............................................................3-19 3.3.1 Clay-sulfide vein/infill assemblages – associated with advanced argillic alteration ................................................................................................................3-19 3.3.2 Quartz-dominated vein assemblages..........................................................3-21

3.3.2.1 Quartz± carbonate vein assemblages .....................................................3-21 3.3.2.2 Quartz± adularia± sulfide± metal vein assemblages...............................3-21

3.3.3 Carbonate-only vein assemblage ................................................................3-21 3.3.4 Quartz textures and vertical zonation........................................................3-22 3.3.5 Adularia textures .........................................................................................3-22 3.3.6 Composition of carbonates..........................................................................3-24 3.4 PARAGENESIS ...................................................................................................3-26 3.4.1 Overprinting alteration assemblages: development over time or space …? . .......................................................................................................................3-26 3.4.2 Paragenetic events within the Seongsan district .......................................3-27

3.4.2.1 Paragenetic events in systems that are dominated by hypogene advanced argillic alteration ................................................................................................3-27 3.4.2.2 Paragenetic events in systems that are dominated by phyllic-adularia alteration.............................................................................................................3-29

3.5 GEOLOGICAL SETTING OF EPITHERMAL DEPOSITS AND PROSPECTS WITHIN THE SEONGSAN DISTRICT ........................................3-49

Bowden, C.D. xi

3.5.1 Geological setting of the Seongsan epithermal deposit.............................3-49 3.5.1.1 Host rocks and field relationships at the Seongsan epithermal system ..3-49 3.5.1.2 Structural setting of the Seongsan epithermal system ............................3-51

3.5.2 Geological setting of the Ogmaesan epithermal deposit...........................3-52 3.5.2.1 Host rocks and field relationships at the Ogmaesan epithermal system 3-53 3.5.2.2 Structural setting of the Ogmaesan epithermal system ..........................3-53

3.5.3 Geological setting of the Eunsan epithermal deposit................................3-56 3.5.3.1 Host rocks and field relationships at the Eunsan epithermal system .....3-56 3.5.3.2 Structural setting of the Eunsan epithermal system................................3-56

3.5.4 Geological setting of the Moisan epithermal prospect..............................3-58 3.5.4.1 Host rocks and field relationships at the Moisan epithermal system .....3-58 3.5.4.2 Structural setting of the Moisan epithermal system................................3-58

3.5.5 Geological setting of the Chunsan epithermal prospect ...........................3-61 3.5.5.1 Host rocks and field relationships at the Chunsan epithermal system ...3-61 3.5.5.2 Structural setting of the Chunsan epithermal system .............................3-61

3.6 CLASSIFICATION OF THE SEONGSAN EPITHERMAL SYSTEMS ......3-64 3.7 SUMMARY OF RESULTS FROM THIS CHAPTER ....................................3-66 Chapter 4 Chapter 4: 40Ar/ 39Ar geochronology of adularia from the hydrothermal systems in the Seongsan district, South Korea 4.1 INTRODUCTION .................................................................................................4-2 4.1.1 Previous geochronological work in the Seongsan district ..........................4-2 4.2 NEW 40Ar/39Ar GEOCHRONOLOGICAL DATA ON THE EPITHERMAL SYSTEMS OF THE SEONGSAN DISTRICT .........................................................4-3 4.2.1 Geochronology methods ................................................................................4-3

4.2.1.1 Introduction ..............................................................................................4-3 4.2.1.2 Geochronology sample selection and paragenesis...................................4-3 4.2.1.3 Geochronology final sample preparation and analysis............................4-3

4.2.2 Geochronology results ...................................................................................4-4 4.2.3 Interpretation of geochronological data ......................................................4-7

4.2.3.1 Lengths of hydrothermal activity ..............................................................4-7 4.2.3.2 Apparent ages versus actual ages of formation........................................4-7 4.2.3.3 Comparison of high- and low-sulfidation age data: implications for the timing and length of each hydrothermal system ...................................................4-9 4.2.3.4 Correlation of low-sulfidation age data with igneous events ...................4-9

Bowden, C.D. xii

4.3 SUMMARY OF RESULTS FOR THIS CHAPTER ........................................4-10 Chapter 5 Chapter 5: An investigation into the origins and characteristics of fluids in the epithermal systems in the Seongsan district, South Korea 5.1 INTRODUCTION .................................................................................................5-2 5.2 MICROTHERMOMETRIC ANALYSIS OF FLUID INCLUSIONS .............5-2 5.2.1 Previous microthermometric fluid inclusion work in the Seongsan district . .........................................................................................................................5-2 5.2.2 Sample selection for fluid inclusion microthermometry ............................5-3 5.2.3 Fluid inclusion morphology, classification and paragenesis ......................5-3 5.2.4 Fluid inclusion microthermometric results .................................................5-4 5.2.5 Interpretation of the microthermometric results......................................5-13 5.3 GEOCHEMICAL CONDITIONS OF FORMATION: IMPLICATIONS FROM MINERAL STABILITIES...........................................................................5-14 5.3.1 Previous constraints on the temperature during alteration in the Seongsan district ....................................................................................................................5-14 5.3.2 Alteration conditions: implications from mineral stabilities ...................5-14

5.3.2.1 Advanced argillic alteration assemblages ..............................................5-14 5.3.2.2 Phyllic-adularia alteration assemblages ................................................5-15

5.3.3 Sulfate-sulfide mineral stabilities: further constraints on conditions of formation ...............................................................................................................5-20 5.4 OXYGEN & HYDROGEN ISOTOPE CONSTRAINTS ON FLUID ORIGINS AND CHARACTERISTICS .....................................................................................5-23 5.4.1 Previous oxygen and hydrogen isotopic work in the Seongsan district ..5-23 5.4.2 Oxygen and hydrogen isotope methods .....................................................5-23 5.4.3 Oxygen and hydrogen isotope results ........................................................5-28 5.4.4 Interpretation of the oxygen and hydrogen isotope data .........................5-32

5.4.4.1 A brief comment on the isotopic composition of exsolved fluids ............5-32 5.4.4.2 Hydrological evolution based on calculated fluid-rock isotopic exchange... .......................................................................................................................5-32 5.4.4.3 Interpretation of fluid-rock isotopic exchange at various temperatures and fluid to rock ratios...............................................................................................5-37

5.5 SULFUR ISOTOPE CONSTRAINTS ON FLUID ORIGINS AND CHARACTERISTICS...............................................................................................5-40

Bowden, C.D. xiii

5.5.1 Previous sulfur isotopic work in the Seongsan district.............................5-40 5.5.2 Sulfur isotope methods ................................................................................5-40 5.5.3 Sulfur isotope results ...................................................................................5-42 5.5.4 Interpretation of sulfur isotope data ..........................................................5-47 5.6 TRACE METAL DATA: LOOKING FOR A GEOCHEMICAL SIGNATURE .......................................................................................................................5-50 5.6.1 Methodology .................................................................................................5-50 5.6.2 Trace metal data: Seongsan and Ogmaesan compare and contrast .......5-51 5.6.3 Trace metal data: Eunsan, Moisan and Chunsan compare and contrast ..... .......................................................................................................................5-54 5.7 SUMMARY OF RESULTS FOR THIS CHAPTER ........................................5-57 Chapter 6 Chapter 6: A comparison of the epithermal systems in the Seongsan district with epithermal systems elsewhere 6.1 INTRODUCTION .................................................................................................6-2 6.2 RELATIONSHIPS BETWEEN HIGH-, INTERMEDIATE- AND LOW-SULFIDATION EPITHERMAL SYSTEMS............................................................6-3 6.2.1 Definitions and setting the scene...................................................................6-3 6.2.2 Relationships between different styles of epithermal systems in the Seongsan district .....................................................................................................6-4 6.2.3 Comparison of the Seongsan and other districts that host high-, intermediate- and low-sulfidation epithermal systems........................................6-5

6.2.3.1 Seongsan and Comstock ...........................................................................6-6 6.2.3.2 Seongsan and Mt Skukum .........................................................................6-7 6.2.3.3 Seongsan and Kyushu ...............................................................................6-7

6.3 CONTROLS ON THE DEVELOPMENT OF HIGH-SULFIDATION CLAY/ SULFATE OR GOLD-SILVER±COPPER DEPOSITS ..........................................6-9 6.3.1 Clay deposits: key characteristics.................................................................6-9 6.3.2 Au-Ag±Cu high-sulfidation deposits: key characteristics ........................6-13 6.3.3 Thoughts on why some high-sulfidation systems develop an intermediate- to low-sulfidation mineralising stage and others do not…?..............................6-14 6.3.4 Implications for the hydrothermal fluid evolution in the Seongsan district . .......................................................................................................................6-16

Bowden, C.D. xiv

6.4 IDENTIFICATION OF HIGH-SULFIDATION EPITHERMAL SYSTEMS PROSPECTIVE FOR METAL AND/OR CLAY/SULFATE MINERALISATION. .......................................................................................................................6-17 6.4.1 Composition of host rocks ...........................................................................6-17 6.4.2 A fore-arc versus back-arc tectonic setting ...............................................6-18 6.4.3 The H2S:SO4 composition of a system........................................................6-18 6.4.4 Chemical zonation within magmatic alunites............................................6-19 6.4.5 Background Au values in early stage high-sulfidation style alteration ..6-19 6.4.6 So, what is the key thing to look out for…?...............................................6-20 6.5 EXPLORATION MODELS FOR EPITHERMAL CLAY/SULFATE AND GOLD-SILVER DEPOSITS IN SOUTH KOREA.................................................6-20 6.5.1 Possible evidence of a caldera setting for the Seongsan district…? ........6-20 6.5.2 Deep-seated roots: faults and/or intrusives ...............................................6-24 6.5.3 Implications for the Seongsan district and similar terranes: exploration targetting criteria for clay/sulfate and Au-Ag epithermal deposits .................6-24 6.6 TARGETTING EPITHERMAL CLAY/SULFATE AND GOLD-SILVER DEPOSITS AT THE CONTINENTAL SCALE IN EAST ASIA .........................6-26 6.6.1 Comparison of southern Korea to similar terranes in China, Japan and Russia .....................................................................................................................6-26 6.7 THESIS SUMMARY...........................................................................................6-29 6.7.1 Synthesis of results: main conclusions and outcomes of the research.....6-29 6.7.2 Future recommendations: possible follow-on research themes...............6-31 References ................................................................................................................ R-1 Appendices: Appendix 1: Sample inventory.....................................................................................A-2 Appendix 2: Microprobe data ......................................................................................A-5 Appendix 3: Stepwise 40Ar/ 39Ar data ........................................................................A-14 Appendix 4: Fluid inclusion raw data.......................................................................A-16 Appendix 5: X-ray diffraction raw data ....................................................................A-18 Appendix 6: Geological map of the Seongsan district............................................. insert

Bowden, C.D. xv

LIST OF FIGURES

Chapter 1

Fig. 1-1 Distribution of principal Au-Ag epithermal deposits distinguished as either high- or low-sulfidation systems from: a), the circum-Pacific region; and b), Europe. From Hedenquist et al. (2000). The box around Korea represents approximate outline of Figure 1-8A. ............................................................................................... 1-3

Fig. 1-2 Grade-tonnage plot showing the size of epithermal Au mineralisation from deposits classified as either high-

or low-sulfidation. From Hedenquist et al. (2000). ......................................................................................... 1-4 Fig. 1-3 Proposed schematic sections of end-member volcanotectonic settings and commonly associated epithermal

and related mineralisation types from Sillitoe & Hedenquist (2003). In general, high-, intermediate- and low-sulfidation epithermal systems do not occur in close proximity to each other although each is part of a broad spectrum of epithermal-type systems found in volcanic-hypabyssal settings. For an explanation of hydrothermal plumbing in epithermal systems, refer to Figure 1-6.................................................................. 1-6

Fig. 1-4 A schematic two-stage model for alteration and ore deposition in high-sulfidation hydrothermal systems after

Cooke & Simmons (2000), modified from Arribas Jr (1995). Alteration Stage A is the ground preparation stage, whereby magmatic gases generate an acid sulfate high-sulfidation hydrothermal fluid that is responsible for the initial stage of residual silica alteration and surrounding more extensive advanced argillic alteration (typically barren with respect to Au and Ag). Ore Deposition is thought to involve either of two possible scenarios, Stage B1 involves gold deposition from acid chloride low-sulfidation waters, or Stage B2 involves gold deposition from acid chloride brines. ....................................................................................................... 1-9

Fig. 1-5 Schematic model of low-sulfidation alteration and mineralisation, from Hedenquist et al. (2000), modified

from Buchanan (1981). Fluid flow is typically focussed through structures. Alteration haloes generally develop around the primary fluid zones, which are typically coincident with the vein systems, in contrast to the more pervasive and extensive high-sulfidation system alteration haloes.......................................................... 1-9

Fig. 1-6 Illustration of the generalised hydrothermal plumbing and settings of epithermal systems relative to plutonic

activity within a calc-alkaline stratovolcano volcanic arc setting with a low differential stress to mildly extensional tectonic setting. Modified from Hedenquist et al. (2000); fluid data from Cooke & Simmons (2000). Although these systems share a common hydrothermal and tectonic setting, this spatial representation of all epithermal systems occurring together is not commonly observed. ...................................................... 1-11

Fig. 1-7 A log ƒS2 vs. temperature diagram showing mineral sulfidation reactions at 1 bar. Sulfidation reactions used

to define sulfidation state are in bold. Shaded areas represent sulfidation fields for arc volcanic rocks and active hydrothermal systems. From Einaudi et al. (2003); for details of reactions, calculations and sources of original data see Einaudi et al. (2003; Fig. 4). Mineral abbreviations this figure: arg = argentite; asp = arsenopyrite; bn = bornite; cc = chalcocite; cp = chalcopyrite; cv = covellite; dg = digenite; en = enargite; hm = hematite; lo = lollingtonite; mt = magnetite; orp = orpiment; po = pyrrhotite; py = pyrite; qtz = quartz; rl = realgar; tn = tennantite.................................................................................................................................... 1-12

Fig. 1-8 Location of the Seongsan district within the Chollanam Province, South Korea. A: Korean peninsula with

location of the Chollanam Province, B: Seongsan region with major clay-sulfate deposits inferred to be correlatives of high-sulfidation systems and C: Seongsan district with the location of epithermal systems recognised to date........................................................................................................................................... 1-14

Fig. 1-9 Satellite mosaic image of the Seongsan district. This figure highlights to some extent the amount of farming

and patchy outcrop of the district. This image has been produced to underlay Figure 1-8C. ........................ 1-15 Fig. 1-10 Tectonic development of East Asia from Late Jurassic to Late Cretaceous. Shaded parts indicate ancient and

modern sea-coasts; ‘v’ pattern indicates igneous activity............................................................................... 1-20 Fig. 1-11 Cretaceous tectonics of Korea. This figure roughly coincides in time with high-sulfidation activity in the

Seongsan district. A: Cretaceous sinistral strike-slip fault systems of Far East Asia, and B: Cretaceous sedimentary basins of the Korean peninsula, the Kyonggi massif (labelled ‘A’), the Okchon Fold Belt (labelled ‘B’), the Yongnam massif (labelled ‘C’) and major regional scale fault systems. Numbers and hatching pattern refer to Cretaceous sedimentary basins. The Haenam basin (labelled as ‘3’) in the southwest is host to the Seongsan district. The Haenam basin is bounded to the west and east by the sinistral strike-slip Chonju and Kwangju Faults. Dashed lines represent terrane boundaries between the Kyonggi massif, the Okchon Fold Belt and the Yongnam massif (‘A’, ‘B’ and ‘C’); mostly these boundaries are fault bound. From Lee (1999). .. ............................................................................................................................................................... 1-24

Bowden, C.D. xvi

Fig. 1-12 Schematic cross section looking north showing Cretaceous back arc tectonic setting for the Chollanam Province. The tectonic setting was sinistral strike slip under a transtensional regime with the development of pull-apart basins. This tectonic regime was followed shortly after by a transpressional regime. During the Late Cretaceous to Early Tertiary, Korea began to experience minor extensional tectonics. By the Miocene the volcanic arc in the right of the figure, which later evolved into modern day Japan, began to drift eastward as the opening of the Sea of Japan begun. From Chough et al. (2000). ............................................................. 1-24

Fig. 1-13 Regional geology of the broader area around the Seongsan district. This figure is at approximately the same

scale as Figure 1-8B. The box outline around Seongsan and Ogmaesan shows the area illustrated in Figure 1-8C. Geology and structure within this figure are from Koh (1996). .............................................................. 1-25

Fig. 1-14 Compilation of previous 40K/40Ar age data by Kim & Nagao (1992) grouped by host rocks and Cretaceous

Bulguksa granitoids within the Seongsan district and more regionally and previously dated alteration sericites and alunites from the Seongsan and Ogmaesan deposits (combined this figure; see Chapter 4 for further detail). 1 and 2 refer to two ages obtained for the Weolchulsan granite by Kim & Nagao (1992). ............................. 1-26

Fig. 1-15 Metallogenic provinces of the Jurassic to Early Cretaceous (left) and Late Cretaceous to Early Tertiary

(right). From Kim & Lee (1983). .................................................................................................................. 1-29 Fig. 1-16 A schematic representation of possible paleo-setting corresponding to the transition between the deposition

of the Uhangri Formation and the deposition of the Haenam Formation. From Chun & Chough (1995). .... 1-31 Fig. 1-17 The most commonly inferred position for a potential Haenam caldera and location of high-sulfidation clay-

sulfate-silica deposits within the broader region, from Kim & Nagao (1992). For a more thorough review of a caldera setting in the Seongsan district, refer to Chapter 2, Section 2.3.6. ..................................................... 1-34

Fig. 1-18 Surface geological map of the Seongsan area and cross section as determined by Koh & Chang (1997).

Geological units used in this map and section are unusual (see legend), and the structural mapping is limited. .. ............................................................................................................................................................... 1-35

Fig. 1-19 Alteration and structural mapping of the Seongsan area after Koh & Chang (1997)................................. 1-36 Fig. 1-20 Alteration zonation map of the Ogmaesan mine area after Kim (1992a)................................................... 1-37

Chapter 2

Fig. 2-1 Schematic facies architecture of the Seongsan district volcanic and sedimentary rock sequence, looking west. Due to the large area of the district and the complex nature of inter-tounguing units, local variations will inevitably exist. HV is represented here undifferenciated with semi-schematic representations of some intercalated units. Refer to text for further detail regarding untis differentiated within HV. Refer to text for explanation of unit abbreviations. Igneous compleses (Ic) are discordant; the Hwawon Formation and Uhangri Formation unconformably overlie the Sani Granite; and AVdb unconformably overlies Ic2 and HV.............. 2-4

Fig. 2-2 Simplified geological map of the Seongsan district, from detailed 1:5,000 scale mapping (Appendix 6).

Boxes around Ogmaesan, Moisan, Eunsan, Chunsan and Seongsan highlight prospect areas. A number of cross sections at 1:5,000 scale (Appendix 6) and at prospect scale (Chapters 2 and 3) have also been produced. ................................................................................................................................................................. 2-5

Fig. 2-3 Well bedded and laminated upper Uhangri Formation grey mudstones and siltstones (Ums) from the type-

section exposure ca. 4km north of field area, with conformably overlying massive Hwangsan Tuff member (HVf) of the basal Haenam Formation. ............................................................................................................ 2-7

Fig. 2-4 ‘Hwangsan Tuff’ (HVf), a lithic fiamme tuff flow deposit, (equivalent to an ignimbrite). A: Unaltered

outcrop of generally massive HVf with lithics and fiamme at location ca. 4km north of mapped area, just above the contact with the Uhangri Formation (259,452mE, 3,833,732mN; Ums, scale bar = 10cm). B: fiamme-rich drill core sample of HVf (sample EN005 170m, scale bar = 1cm). C: lithic-rich drill core sample of HVf (sample EN006 176m, scale bar = 1cm)........................................................................................................... 2-9

Fig. 2-5 Heterolithic lapilli tuffaceous sediment (HVxo). A: drill core (scale bar = 1cm). B: thin section (XPL; scale

bar = 1mm). Both samples are from MS008 129.5m. Shows the generally clast supported nature of HVxo and generally uniform component size of quartz and plagioclase crystals; some quartz crystals are embayed. Matrix in this sample is carbonate-illite altered.............................................................................................. 2-11

Bowden, C.D. xvii

Fig. 2-6 Igneous complex 1 (Ic1) A: General morphology of Ic1 (sample MS008 82.5m; scale bar = 1cm). B: Evidence for multiple intrusions includes crosscutting relationships like this (sample MS001 136.5m; scale bar = 1cm). C: peperite, formed from generally coherent intrusive/extrusive magma/lava mixing with wet sediment resulting in peperitic texture of mixed intrusive ± sediment (I) and sediment ± intrusive (S) (sample MS001 186.5m; scale bar = 1cm). D: Thin section of ‘A’ (XPL; scale bar 1mm). ....................................... 2-13

Fig. 2-7 Crystal rich ignimbrite (HVxi). A: drill core (scale bar = 1cm). B: thin section (XPL; scale bar = 1mm).

Both samples are from MS008 57.6m. Note the development of fiamme, the dark green colour of the rock and the abundance of crystals and lithics. ............................................................................................................. 2-15

Fig. 2-8 MS001.17 Co-ignimbrite ash tuff (HVai). HVai is similar to HVxi but contains less crystals and lithics. A:

drill core (scale bar = 1cm). B: thin section (XPL; scale bar = 1mm). Both samples are from MS001 72.5m.... ............................................................................................................................................................... 2-15

Fig. 2-9 Hwangsan mudstone and siltstone (Hms). A: drill core sample of very finely laminated black to dark grey

mudstone and siltstone units (sample EN002 150m; scale bar = 1cm). B: outcrop showing small-scale mudstone-siltstone intercalated laminations with horizontal bedding and internal slumping, most likely due to wet sediment thixotropic deformation (sample location •124)....................................................................... 2-16

Fig. 2-10 Hwangsan mudstone and siltstone (Hms) at surface at Moisan. A: folding of bedding as a result of post

deposition tectonic activity (sample location •087). B: cross-bedding indicating a sub-aqueous environment for the deposition of Hms sediments that overlie Ic1 at Moisan (sample location •082). ............................... 2-17

Fig. 2-11 Laminated ash tuffaceous sediments (HVlm). A: finely laminated grey sedimentary units with stylolaminae

separating underlying ash to lithic tuff (sample CH002 207m; scale bar = 1cm). B: blackish carbonaceous flecks within weakly laminated grey tuffaceous sedimentary unit (sample EN002 156m; scale bar = 1cm). 2-19

Fig. 2-12 Volcaniclastic sandstone (HVs). A: drill core sample (scale bar = 1cm). B: thin section (XPL; scale bar =

1mm). Both samples are from EN002 143m. ................................................................................................ 2-20 Fig. 2-13 Lapilli tuff (HVo). A: drill core sample (scale bar = 1cm). B thin section (XPL; scale bar = 1mm). Both

samples are from EN002 136.5m. .................................................................................................................. 2-20 Fig. 2-14 Ash tuff (HVa). A: drill core sample showing euhedral to subhedral plagioclase phenocrysts in a very fine-

grained ash tuff groundmass. Phenocrysts now altered to clay. (scale bar = 1cm) B thin section of ‘A’ showing plagioclase phenocrysts now altered to clay (illite) (XPL; scale bar = 1mm). Both samples are from CH006 93.5m. ................................................................................................................................................ 2-22

Fig. 2-15 Lithic tuff (HVl). A: drill core sample, ash tuff on the left hand side, lithic tuff on the right hand side

showing a marked increase in amount and size of lithic fragments, (scale bar = 1cm). B thin section of ‘A’ showing lithic tuff in thin section showing clasts variably altered to clay (kaolinite) with other fragments including crystals and lithics (XPL; scale bar = 1mm). Both samples are from EN004 36.3m..................... 2-23

Fig. 2-16 Pumice tuff (HVp). A: drill core sample comprising numerous pumice fragments in a very fine-grained ash

groundmass (scale bar = 1cm). B thin section of ‘A’ showing leaching of pumice fragments (XPL; scale bar = 1mm). Both samples are from CH003 90m and show moderate to strong leaching leaving relic pumice..... 2-24

Fig. 2-17 Igneous complex 2 (Ic2). A: regionally Ic2 forms numerous small dome-shaped hills, such as Ogmaesan. B:

outcrop showing intrusive contact, shearing and locally deformed HV units on the margins of an Ic2 intrusion (sample location •012; scale bar ca. 1m). C: rock slab (sample •12.1; scale bar = 1cm) shows weak flow-banding and strong iron oxide development. D: thin section of ‘C’ showing plagioclase phenocrysts in very fine-grained dacitic groundmass (scale bar = 1mm). Note: A, B, C and D sample location shows evidence of previous mining for clay-sulfate-silica deposits, hence samples show strong pervasive advanced-argillic alteration development and as such, primary textures are difficult to distinguish. ......................................... 2-26

Fig. 2-18 Mafic dyke (Dm). A: Dm dyke exposed within the Ogmaesan clay-silica mine. The Dm dyke is parallel to

the plane of the photo and wall-cutting but is only ca. 1 to 2m in width (sample location •20; scale bar ca. 5m). B: rock slab from ‘A’ shows a green highly altered sample of Dm in which relict plagioclase phenocrysts are still visible (scale bar = 1cm) and C: in thin section showing relic subhedral pyroxene in upper left and lower right and relic plagioclase phenocrysts in centre, both now strongly clay-silica altered (scale bar = 0.5mm)....... ............................................................................................................................................................... 2-27

Fig. 2-19 Altered volcaniclastic debris flow breccia (AVdb) in outcrop showing the highly varied habit of AVdb

comprised of pebble- to boulder-sized clasts of various underlying units hosted in a fine- to medium-grained dacitic tuffaceous matrix that is now highly friable and typically green reflecting strong quartz-chlorite-illite alteration (sample location ca. 250m west-southwest of •134; scale bar ca. 30cm). ...................................... 2-29

Bowden, C.D. xviii

Fig. 2-20 Igneous complex 3 (Ic3). A: outcropping through AVdb showing that Ic3 intruded after the deposition of AVdb (sample location •178; scale bar ca. 10m). B: close-up of outcrop surface showing strongly spherulitic texture indicative of rapid accent and devitrification. C: rock slab of ‘B’ showing various glassy sections and spherulites (sample SS 178; scale bar = 5mm). D: thin section of ‘C’ showing spherulites in thin section (XPL; scale bar = 1mm). ........................................................................................................................................... 2-30

Fig. 2-21 Chronological compilation of previous 40K/40Ar age data by Kim & Nagao (1992) for the host rocks and

Cretaceous Bulguksa Granitoids within the Seongsan district and more regionally as distinguished within Figure 1-14 (granitoids: Jiyoungsan, Weolchulsan1 & 2, Weolgangdu and Jangseong). 1 and 2 refer to two ages obtained for the Weolchulsan granite by Kim & Nagao (1992), but as the age data are significantly different, they have been chronologically differentiated in this figure. Also included in this figure are the previously dated alteration sericites and alunites from the Seongsan and Ogmaesan deposits (combined this figure; see Chapter 4 for further detail) and relative timing for the observed igneous complexes of the district (i.e. Ic1, Ic2 and Ic3) as based on cross-cutting field relationships, represented by dashed horizontal lines....................... 2-33

Fig. 2-22 The character of faults within the Seongsan district. A: example of a narrow north-striking fault plane in

the Baekam pit (location •234; scale bar ca. 5m), looking north. The fault cuts gently dipping beds. Steeply plunging slickenlines (not shown) within the narrow zone of cataclasite imply dominantly dip-slip offset. B: north bounding fault of the Seongsan Fault Zone, looking east-northeast along strike, an example of a wide fault zone in the Bukok pit (location •213; scale bar ca. 50cm). The fault shows brittle fracturing and shear/cataclasite development. C: slickenlines associated with the fault plane in ‘B’ imply dominantly dip-slip offset. Figure 2-22 continued next page. ....................................................................................................... 2-35

Fig. 2-22 (continued) D: a narrow steeply south-dipping fault plane at the Moisan prospect looking east. Bedding

attitudes change from gently to steeply dipping as the fault is approached from the hanging wall side (right of figure). Bedding within 10m of the fault plane in the hanging wall dips ca. 30-50º towards the south, whereas bedding in the footwall dips less than 10º in either direction (see also Fig. 2-33). Steepening of bedding dips in the hanging wall and cross section construction from diamond drill core (Section 2.3.3.3) implies that locally this fault underwent a component of reverse movement at some time in its history (location •088; scale bar ca. 50cm). ............................................................................................................................................................ 2-36

Fig. 2-23 Summary structural map of the Seongsan district. Faults include those observed in outcrop and drill core,

and others inferred from structure contour analysis. Bedding attitudes are for the HV unit only and show a general gently southwest dipping attitude. Localised deviations are due to depositional variations, slumping and localised faulting. Note: not all bedding attitudes measured in the field have been shown on this figure. Rose diagram show fault strikes measured in outcrop.................................................................................... 2-37

Fig. 2-24 Strike slip movement on the Seongsan Fault Zone. ‘A’: Seongsan plan view enlargement (Fig. 2-23)

showing strike of faults with inferred sinistral sense of movement. The faults are generally steeply dipping, ca. 80º to the south; fault line type as per Figure 2-23. ‘B’: Photo looking ca. northeast on short linking fault within the Seongsan Fault Zone, showing gently southeast plunging slickenlines. The orientation of the slickenlines implies dominantly strike-slip movement with a smaller component of dip-slip movement. The asymmetry of the fault array implies a sinistral sense of strike-slip movement (photo courtesy Panther, et al., 2000). ‘C’: plan view of the principle components for the inferred stress field for sinistral strike-slip movement on the Seongsan Fault Zone, with σ1 resolved as σ1n - normal stress and σ1s - shear stress on the main fault plane orientations. ......................................................................................................................... 2-39

Fig. 2-25 Normal movement on the Seongsan Fault Zone. ‘A’: Seongsan plan view enlargement (Fig. 2-23) showing

strike of faults and sense of normal movement. Faults are generally steeply dipping ca. 80º to the south. Faults shown in grey do not show evidence for having undergone normal movement, but were active during sinistral strike-slip movement (Fig. 2-23). ‘B’: Photo looking ca. northwest on north-bounding fault of the Seongsan Fault Zone, showing steep southeast-plunging slickenlines whose orientation implies dip-slip movement. The lack of slickenlines on steeply dipping cm-scale jogs suggests a normal rather than reverse sense of movement (north-block up). ‘C’: plan view of the principle components of the inferred stress field during normal dip-slip movement on the Seongsan Fault Zone. .................................................................... 2-40

Fig. 2-26 Structure contoured intersections of bedding and lithological contacts with topography east of Eunsan.

‘A’: simplified Seongsan location map from Figure 2-23, highlighting the area east of Eunsan shown in detail in ‘B’. ‘B’: analysis of bedding attitudes (HV and Hms units) and exposures (locations •095 and •236) support the existence of a fault east of Eunsan that strikes ca. northeast. See main text for comments on inferred fault movements including sense and direction of shear. Ic2 directly south of Eunsan within AVdb is inferred to be a rafted block within AVdb rather than a discrete intrusive. Ic2 to the east within AVdb is thought to be in place with AVdb draping over it. Apparent offset of AVdb is discussed in detail within the main text......................................................................................................................................................... 2-42

Bowden, C.D. xix

Fig. 2-27 North-striking faults. ‘A’: detailed map of north-striking faults located north of the Seongsan Fault Zone (see side inset for location). Map shows that bedding strikes parallel to the fault plane, as highlighted by bedding form lines. ‘B’: photo looking north along the north-striking fault, location highlighted in ‘A’, which illustrates the apparent normal sense of movement on this fault (scale bar = ca. 5m). ................................... 2-43

Fig. 2-28 North-striking fault east of Ogmaesan. ‘A’: location map for enlarged area shown in ‘B’. ‘B’: detailed

map showing the inferred north striking fault. The presence of this fault is inferred from outcrops of brittle fractured rock at location •064 and stratigraphic offset across the inferred fault position, evident from cross section construction (EE’, Appendix 6) and structurally contoured intersection of bedding and topography projections. The position of the Hms unit on the east side of the fault has been inferred based on structurally contoured intersection of bedding and topography projected from Moisan and Eunsan. The inferred locations of Hms are offset despite no distinct change in bedding attitudes across the fault. ........................................ 2-45

Fig. 2-29 Eunsan structural analysis. 'A': location plan map (see Figure 2-23 for location; note: Ic2 is interpreted as a

rafted block within AVdb). 'B': cross section looking northwest showing section EN002 and EN005. 'C': cross section looking northwest showing section EN004 and EN001. 'D': cross section looking northwest showing section EN006 and EN008. This Figure has been used to determine the sense and offset across the main Eunsan Fault (see text for details). Alteration and mineralisation zonation at Eunsan will be discussed in detail within Chapter 3. Dashed lines inferred; solid red is fault/vein; solid yellow is carbonate vein; annotation 'F' labels fault; AVdb overlies HV unconformably; lithology labels as per Section 2.2. .................................... 2-46

Fig. 2-30 Structure contour analysis of Hms to resolve net movement on the Eunsan Fault. ‘A’: plan view of

Eunsan, with structure contours for the basal contact of the selected Hms unit. Pierce points from diamond drill holes are shown by solid dots, with depths to the basal contact and local thickness of Hms unit in brackets. A 3.5m thick interval was arbitrarily chosen. For the north-block, the basal contact for a 3.5m thick interval of Hms occurs at the pierce point proximal to the fault at the western end (highlighted by the shaded grey area). For the south-block, by averaging the thickness between pierce points, a 3.5m thick interval should occur at the -46m structure contour (highlighted by the shaded grey area). ‘B’: cross section view in the plane of the fault looking north-northeast. The thick line is the intersection of fault with topography. The pierce points of the basal contact depth for the 3.5m thick interval of Hms with the Eunsan Fault are shown with a dashed line linking them. Based on this analysis, the net movement on the Eunsan Fault as highlighted by dashed line, was ca. 150m of sinistral strike-slip with ca. 11m of north-block up dip-slip. ...................................................... 2-47

Fig. 2-31 Simplified block diagram showing the Eunsan vein-spur geometry, including a projected horizontal level-

plan view through the intersection of the main vein and spur. This vein-spur relationship is based on limited observations early in the mines development history; however it is supported by the gentle west-northwest plunges of the higher-grade lodes at the main vein-spur intersections. .......................................................... 2-49

Fig. 2-32 Resolving the net movement on the Eunsan Fault. The net movement on the Eunsan Fault was determined

previously (Fig. 2-30). Additionally, the last phase of movement on the fault was determined to be dip-slip (see text for details). In order to resolve a last movement on the Eunsan Fault of dip-slip with the net movement on the fault, an earlier phase of sinistral strike-slip movement with a significant component of north-block up dip-slip must have occurred. .................................................................................................. 2-50

Fig. 2-33 Moisan structural analysis. 'A': location plan map (see Figure 2-23 for location). 'B': cross section looking

northwest showing section MS008 and MS001. 'C': cross section looking northwest showing section MS022 and MS021. This Figure has been used to highlight the geological and structural complexity as compared with Eunsan, and to some degree to determine the sense and offset within the Moisan Fault Zone (see text for details). Alteration and mineralisation zonation at Moisan will be discussed in detail within Chapter 3. Dashed lines inferred; annotation 'F' labels fault; lithology labels as per Section 2.2. ................................... 2-52

Fig. 2-34 Detailed map and photograph documenting localised movement on faults at Moisan. ‘A’: detailed plan

map highlights the change in bedding attitudes as the fault is approached; and shows that the fault plane generally dips steeply to the south (see Figure 2-23 for location). ‘B’: photograph (as seen previously in Fig. 2-22D) looking southeast showing field relationships of disturbed bedding locally at fault plane (scale bar = ca. 50cm). Cross section construction (Fig. 2-32B) and structural interpretation of fault movements (Fig. 2-34) implies that locally this movement comprised a component of reverse dip-slip movement and a component of normal dip-slip movement; see text for further details. .................................................................................. 2-53

Fig. 2-35 'A': location plan map (see Figure 2-23 for location). 'B': cross section looking northwest showing section

CH002 and CH006. This Figure has been used to some degree to determine the apparent horst and graben like structure at Chunsan (see text for details). Alteration and mineralisation zonation at Chunsan will be discussed in detail within Chapter 3. Dashed lines inferred; annotation 'F' labels fault; lithology labels as per Section 2.2 (note: AVdb within the volcanic pile here does not correlate to the extensive surface deposit of AVdb; additionally, HVf is inferred to occur ca. 180 to 200mRL below Chunsan based on district-scale cross section reconstruction - see Appendix 6, BB' cross section)....................................................................................... 2-55

Bowden, C.D. xx

Fig. 2-36 Structural paragenesis of the Seongsan district; based on determined stress fields of various faults. Each prospect lists the #dominant fault kinematics and *inferred prospect-scale stress fields; which can be categorised into either 1 of 2 district-scale stress regimes. This data is shown mapped )right), highlighting faults and inferred movements at surface during each of the district-scale stress regimes. See text for further analysis and interpretation of the tectonic setting based on this data.............................................................. 2-57

Chapter 3

Fig. 3-1 Propylitic alteration in thin section. ‘A’: example of propylitic altered sample showing completely albitised and carbonate-altered feldspar with overprinting very weakly developed phyllic alteration, evident as patchy illite replacement of the matrix (XPL, EN001 174m, scale bar 0.5mm). ‘B’: relic propylitic alteration evident as albitised and carbonate-altered feldspar with phyllic and adularia-altered feldspar overprints (XPL, MS001 186.5m, scale bar = 0.25mm)............................................................................................................................ 3-5

Fig. 3-2 Advanced argillic 1 and 2 alteration in thin section. ‘A’: advanced argillic 1 alteration comprises

predominantly quartz and kaolinite (dark mottled material) (XPL, sample location Ogmaesan ●042, scale bar = 0.25mm). ‘B’: advanced argillic 2 alteration comprises quartz, kaolinite, minor alunite and dickite. The dark coarser material is dickite which is more crystalline and coarser than kaolinite in ‘A’ (XPL, sample location Ogmaesan ●040, scale bar = 0.25mm). ‘A’ and ‘B’ are both at the same scale, highlighting the increase in the clay minerals crystallinity and size between samples of advanced argillic 1 and advanced argillic 2 alteration.... ................................................................................................................................................................. 3-7

Fig. 3-3 Sulfide mineralisation associated with advanced argillic 2 alteration. ‘A’: advanced argillic 2 dickite-pyrite

alteration (central) forms darker grey zones richer in pyrite. The locally abundant zones of pyrite in this sample are selectively replacing reactive components within the host rock; the more diffuse pyrite is associated with dickite alteration. Both texturally distinct types of pyrite alteration are hosted within dickite alteration and field relationships consistently show that both are associated with dickite alteration. The light grey to buff to pink coloured diffuse overprint is advanced argillic 3 alunite alteration, which contains no significant associated sulfide (sample location Ogmaesan ●036, 0.03ppm Au, <0.5ppm Ag; scale bar = 2cm). ‘B’: Au-Ag mineralisation comprising dickite+pyrite±argentite infill associated with advanced argillic 2 alteration within the Seongsan system. Au-Ag mineralisation where present includes both disseminated dickite+pyrite±argentite as alteration and localised occurrences of vein-style mineralisation (SS001 186.35m, 1.59ppm Au, 8.6ppm Ag; scale bar = 2cm). ............................................................................................................................................... 3-8

Fig. 3-4 Reflected light thin sections showing pyrite mineralisation associated with advanced argillic 2 alteration in a

groundmass predominantly of quartz + dickite. ‘A’: pyrite from Ogmaesan showing growth zones associated with varying As content (sample location Ogmaesan ●016, 0.05ppm Au, <0.5ppm Ag; scale bar = 0.5mm). ‘B’: pyrite from Seongsan showing growth zones associated with varying As content (SS002 148.24m, 0.27ppm Au, 5.1ppm Ag; scale bar = 1mm). .................................................................................................... 3-9

Fig. 3-5 Advanced argillic 3 alteration. ‘A’: alunite occurring as coarse laths that replace phenocrysts and fine laths

that replace matrix along with quartz and minor relic dickite (XPL, sample location Ogmaesan ●059, scale bar = 0.25mm). ‘B’: sample of ore material from the ‘Alunite Pit’ at Seongsan showing pervasive alunite+dickite alteration as alunite laths and coarse dickite. Dark material in the top left corner is black ink on the thin section (XPL, alunite ore; sample location ●199, scale bar = 0.25mm). ..................................................................... 3-10

Fig. 3-6 EDS spectra from microprobe analyses of alunite from Seongsan (upper; sample SS 199) and Ogmaesan

(lower; sample OG 59) showing their relatively simple K, Al and S composition (alunite = KAl3(SO4)2(OH)6). . ............................................................................................................................................................... 3-11

Fig. 3-7 Siliceous ± silicic alteration in thin section. The sample comprises texturally destructive silicification with

minor leaching resulting in the development of vughs in the siliceous-altered rock. The vughs are presumed to be relic phenocryst sites that nucleated leaching. No evidence is preserved which would show whether leaching occurred of primary clay-altered or silicified phenocrysts. (XPL, sample location Ogmaesan ●050, scale bar = 0.5mm).......................................................................................................................................... 3-13

Fig. 3-8 Phyllic alteration in thin section. ‘A’: medium-grained illitic clay replacement of albitised relic feldspar

altered during the propylitic stage (XPL, EN004 68.5m, scale bar = 0.25mm). ‘B’: coarse-grained illitic clay (illite+titanite/rutile(leucoxene)+pyrite) replacement of a biotite phenocryst (centre) plus fine-grained illitic clay replacement of the rock groundmass (XPL, MS013 118m, scale bar = 0.5mm). .................................... 3-14

Fig. 3-9 ‘A’: chemographic volume plot illustrating the relationship of some true dioctahedral micas (phengite series)

to interlayer-cation-deficient dioctahedral micas (glauconite / illite series) (adapted from Rieder, et al., 1998).

Bowden, C.D. xxi

‘C’ axis = viAl / (viAl + viFe3+); ‘R’ axis = viR2+ / (viR2+ + viR3+) - where ‘vi’ refers to the octahedral cations; ‘I’ axis = total interlayer cations. Solid dots refer to end-member micas as (1): celadonite [KFe3+MgSiO4O10(OH)2], (2): alumino-celadonite [KAlMgSiO4O10(OH)2], (3): muscovite [KAl2AlSiO3O10(OH)2], (4): [KFe2

3+AlSi3O10(OH)2], (5): [Fe23+Si4O10(OH)2] and (6): pyrophyllite

[Al2Si4O10(OH)2] – where ‘’ refers to a vacancy. Two blow-out slabs show the phengite series and the glauconite/illite series in further detail. Most dioctahedral micas from epithermal systems plot within the plane (2), (3), (6) as shown in ‘B’. ‘B’: Seongsan district phyllic alteration micas plotted on the alumino-celadonite – muscovite – pyrophyllite plane as determined from microprobe analyses. Fine interstitial micas (solid dots); coarse phenocryst replacement micas (crosses). Eunsan phyllic micas (n=5; green data), Moisan phyllic micas (n=9; red data) and Chunsan phyllic micas (n=5; blue data). See main text for discussion; see Appendix 2 for sample list. ...................................................................................................................................................... 3-15

Fig. 3-10 Adularia alteration in thin section. ‘A’: phyllic-altered albitised feldspar partially replaced by illite and then

overprinted by adularia, which forms clear grey irregular patches that lack illite (EN004 133m, scale bar 0.25mm). ‘B’: phyllic-altered albitised feldspar partially replaced by illite and then overprinted by adularia, which forms clear grey irregular patches that lack illite (MS001 186.5m, scale bar = 0.1mm). ..................... 3-17

Fig. 3-11 Ternary plot showing the composition of feldspars associated with propylitic alteration (solid dots) and

feldspar overgrowths during adularia alteration (open dots) from the Seongsan district. Grey shaded areas show detailed sections of the data from the main ternary plot. Propylitic altered feldspars range from Ab96.7Or1.7An1.6 to Ab100 (Eunsan and Moisan; n=21), adularia altered feldspars range from Or92.0Ab5.7An2.3 to Or100 (Eunsan, Moisan and Chunsan; n=84). No primary unaltered feldspars were found in the Seongsan district, but reaction pathways for feldspars forming from fluids of different initial temperatures are shown by the dashed lines with arrows indicating direction of cooling temperature (from Tuttle & Bowen, 1958). These pathways highlight that end-members orthoclase and albite are highly unlikely primary products. Their presence within the Seongsan district is evidence for hydrothermal alteration and highlights the distinctly different compositions of feldspars from the respective alteration assemblages. See Appendix 2 for sample list and raw data. ................................................................................................................................................... 3-18

Fig. 3-12 Semi-schematic diagram based on numerous observations from Eunsan and Moisan illustrating the vertical

zonation of vein quartz textures with associated approximate primary Au±Ag and base-metal grade relationships. ................................................................................................................................................... 3-23

Fig. 3-14 Rare carbonate and phyllic alteration overprinting dickite alteration at Seongsan. ‘A’: carbonate veinlets

with selvages of phyllic alteration and interstitial phyllic alteration; both overprinting earlier dickite alteration (sample SS001 298.5m, scale bar = 0.25mm). ‘B’: primary biotite phenocryst (centre) replaced by a mixture of coarse platy illite and leucoxene with fine interstitial illite (i) overprinting carbonate (c) (top half) leaving corroded but optically continuous patches of carbonate (note the parallel cleavage between patches); both carbonate and illite are associated with phyllic-carbonate alteration which overprints earlier dickite alteration (bottom half) (sample SS001 298.5m, scale bar = 0.25mm). .......................................................................... 3-30

Fig. 3-15 Quartz veins within the Seongsan system that cut earlier advanced argillic alteration. ‘A’: From SS002

(134.9m; scale bar = 3cm), continuous pieces of quartered HQ core totalling ca. 30cm of vein material that comprises pseudo-colloform to pseudo-crustiform banded quartz, quartz after bladed carbonate, massive chalcedonic quartz, comb quartz and minor saccharoidal quartz. Dark bands of sulfides in the interval 134.87m to 135.23m (0.36m) assayed 0.13ppm Au, 1.3ppm Ag. Host rock in the top left is strongly advanced argillic 2 altered. ‘B’: From DDH 87-1 (Seongsan Clay Mining Co., 92.8m; photo courtesy of Ivanhoe Mines Ltd.), ca. 5cm of vein material comprised of pseudo-colloform banded quartz with bladed carbonate dissolution textures. The interval 92.8m to 93.8m (1m) re-assayed by Ivanhoe Mines Ltd. returned 0.41ppm Au, 3.9ppm Ag (Panther et al., 2000). These veins are similar in texture to mineralised veins in the phyllic-adularia alteration dominated Eunsan and Moisan systems implying similar but minor hydrothermal activity occurred within the Seongsan system late in the paragenesis. ........................................................................................................ 3-31

Fig. 3-16 Relic bladed carbonate veins now pseudomorphed by quartz. Bladed carbonate veins are overprinted by

adularia and siliceous alteration, which implies that they developed pre or synchronous with the onset of phyllic alteration (Table 3-3). Quartz flooding that pseudomorphs bladed carbonate occurs paragenetically later. ‘A’: quarter core at Eunsan; quartz flooding hosts significant Ag mineralisation from acanthite in darker silica (EN042 23m, 2.82ppm Au, 696.80ppm Ag; scale bar shows cm intervals). ‘B’: Chunsan; quartz pseudomorphing bladed carbonate (CH006 34.6m, 0.33ppm Au, 1.80ppm Ag; scale bar = 1cm). ................ 3-33

Fig. 3-17 Adularia-Au-Ag mineralisation at Chunsan cross cutting earlier advanced argillic alteration. 'A' and 'B'

show advanced argillic 1 alteration (kaolinite-silica alteration±leaching). 'B' now overprinted by siliceous alteration. 'C' and 'D' show relic patches of advanced argillic altered and leached rock overprinted by quartz-adularia-Au-Ag mineralisation (Figs. 3-18 & 3-19) and associated siliceous-adularia alteration. 'A' - CH006 180.5m (1m @ 0.08ppm Au & 5.6ppm Ag); 'B' - CH003 61.5m (1m @ 0.27ppm Au & 10.0ppm Ag); 'C' - CH003 135.5m (1m @ 1.93ppm Au & 88.4ppm Ag); 'D' CH003 146.5m (1m @ 1.14ppm Au & 54.8ppm Ag). Diamond drill core all ca. 5cm across. ............................................................................................................ 3-34

Bowden, C.D. xxii

Fig. 3-18 Quartz-adularia-sulfide-Au-Ag mineralisation at Chunsan. Age data in Chapter 4 shows that disseminated adularia-Au-Ag mineralisation formed before vein adularia-Au-Ag mineralisation (Table 3-3). ‘A’: drill core showing massive disseminated adularia-sulfide (CH003 115m, 24.02ppm Au, 70.2ppm Ag; scale bar = 2cm); ‘B’: thin section shows massive abundant rhombic adularia crystals in siliceous-altered rock with pyrite (opaque material) (XPL, CH003 115m, 24.02ppm Au, 70.2ppm Ag; scale bar = 1mm). ............................... 3-35

Fig. 3-19 Quartz-adularia-sulfide-Au-Ag mineralisation at Chunsan. Main photo showing abundant adularia-sulfide-

Au-Ag mineralisation in thin section (RL, CH003 115m, 24.02ppm Au, 70.2ppm Ag; scale bar = 1mm). Note the euhedral rhombic adularia crystals. adu = adularia; py = pyrite; t/t = tennantite/tetrahedrite; cpy = chalcopyrite. Upper line diagram outline showing microprobe spot analyses (see Appendix 2 for microprobe data). Adularia alteration is directly associated with sulfide-Au-Ag mineralisation at Chunsan.................... 3-36

Fig. 3-20 Crystalline quartz-only veins. ‘A’: sub-parallel steeply south dipping quartz-only stringer veins with

siliceous altered selvages that make the rock resistant to weathering (sample location Moisan ●087, 0.30ppm Au, 0.8ppm Ag). ‘B’: slab of ‘A’ highlighting the void space which is common to these quartz-only veins. Similar veins also occur at Eunsan but rarely at Chunsan............................................................................... 3-38

Fig. 3-21 Eunsan first and second vein breccia event. ‘A’: the first vein-breccia event (left side) is overprinted by

quartz dominant infill associated with the second vein-breccia event (right side). The first vein-breccia event is characterised by the distinctive silica rimmed clasts (left side) set within colloform banded to massive chalcedonic infill. Subsequently, re-brecciation during the second vein-breccia event has incorporated broken fragments of this first vein-breccia (evident as incomplete rimmed clasts) within the second vein-breccia matrix of mesocrystalline to crustiform-colloform banded quartz infill with acanthite, pyrite, and late-stage carbonate (far right side). ‘B’: sulfide dominant second vein-breccia event (centre) overprinting first stage vein-breccia event (left and far right side). 1 – colloform banded silica infill from first vein-breccia event (equivalent to left side in ‘A’). 2 – clast within second vein-breccia event showing characteristic first vein-breccia event silica rim. 3 – pyrite-acanthite-native Ag infill. 4 – overprinting late-stage carbonate infill. Photos courtesy Nicholson (2003), both scale bars = 3cm. ....................................................................................................... 3-40

Fig. 3-22 Eunsan second vein breccia material with quartz-adularia-sulfide matrix infill. Main photo shows the

sulfide mineralisation in thin section. This sample is unusually anomalous in visible chalcopyrite (cpy) compared to the majority of Eunsan mineralisation. Ag mineralisation is manifested as trace electrum grains hosted within quartz-adularia matrix. The grey mineral in the lower right corner is most likely proustite (Ag3AsS3); electron microprobe data returned 22.85wt% for S and 6.73wt% for As; total wt% 29.58 (RL, EN006 72m 1.66ppm Au, 230.60ppm Ag; no assay data for base metals; scale bar = 0.1mm). Upper line diagram outline shows the position of microprobe spot analyses (see Appendix 2 for microprobe data). ...... 3-41

Fig. 3-23 Moisan quartz±sulfide mineralisation paragenetically equivalent to the second vein-breccia event at

Eunsan. ‘A’: crustiform crystalline to mesocrystalline quartz+adularia infill with some Ag-rich sulfide formed during the second vein-breccia event (MS008 147.8m 0.77ppm Au, 78.8ppm Ag; scale bar = 2cm). Adularia is distinctive as buff coloured vein material. ‘B’: sulfide dominant veining comprising black silica-sulfide rich breccia with colloform sulfide-quartz infill material (MS001 110m 493.00ppm Au, 1300.0ppm Ag; scale bar cm graduations)............................................................................................................................................... 3-42

Fig. 3-24 Moisan quartz±sulfide vein material paragenetically equivalent to the second breccia event at Eunsan.

Main photo shows the sulfide mineralisation in thin section. This sample contains significant pyrite (yellow) and Fe-poor sphalerite (grey) set in a quartz matrix. Fe-poor sphalerite wt% totals range from 60.72% to 96.48% and some chalcopyrite wt% totals are less than 60.72% possibly indicating Ag substitution (RL, MS007 76m 1.60ppm Au, 73.40ppm Ag; no assay data for base metals; scale bar = 0.25mm). Upper line diagram outline shows the position of microprobe spot analyses (see Appendix 2 for microprobe data). ...... 3-43

Fig. 3-25 Moisan base-metal mineralisation. ‘A’: diffuse quartz-base-metal-sulfide veining (Fe-poor

sphalerite+galena±minor chalcopyrite) (MS021 90.25m 0.94ppm Au, 34.4ppm Ag, 216ppm Cu, 2093ppm Pb, 4802ppm Zn; scale bar = 2cm). ‘B’: coarse crystalline banded quartz-base-metal-sulfide±late stage carbonate veins (MS016 79.7m 5.15ppm Au, 39.8ppm Ag, 899ppm Cu, 313ppm Pb, 258ppm Zn; scale bar = 2cm). .. 3-44

Fig. 3-26 Seongsan alteration zonation superimposed over geology and structure. Key relationships highlighted are

that the advanced argillic alteration is formed around the principle faults of the Seongsan Fault Zone, and as a result, form tabular, steeply dipping east-northeast and east-southeast striking zones. 'A': plan view of the Seongsan system, focused around the Bukok and Alunite open pits showing lithology, structure and alteration zonation, and diamond drill hole collar locations and traces for Ivanhoe Mines Ltd. (SS001 and SS002) and Seongsan Mining Co. (vertical holes 88-9, 88-6, 87-1 and 90-18) (see Fig. 2-2 for map bounds location). 'B': cross section view as outlined in 'A' (looking west) showing lithology, structure and alteration as determined from surface mapping and some diamond drill hole data. Due to a lack of available diamond drill hole data for this area and very limited underground access, alteration zonation and lithologies have primarily been projected from surface, hence they may appear simplified but they cannot be resolved any further based on current data. Propylitic alteration boundaries have been inferred and may actually occur well outside the Seongsan system.

Bowden, C.D. xxiii

Note: the view in 'B' shows an extended cross section compared to that outlined in 'A'. DDH: 88-6 (Seongsan Mining Co.) is ca. 100m off section to the west and SS001 is ca. 80m off section to the west. Alteration assemblages comprise the following: prop = propylitic; AA1, AA2, AA3 = advanced argillic 1, 2, 3 (see Table 3-1); and q = siliceous. Relic patchy phyllic and carbonate alteration observed at Seongsan overprinting advanced argillic alteration (as documented in Section 3.4.2.1) occur within SS001 at 298m. Dashed lines inferred; annotations 'F' label faults and 'und' label underground mining operations in section; lithology labels as per Section 2.2. See main text for further detail......................................................................................... 3-50

Fig. 3-27 Ogmaesan alteration zonation superimposed over geology and structure. 'A': plan view of the Ogmaesan

system, in the vicinity of the main breccia and Ogmae mine open pits showing lithology, structure and alteration zonation (see Fig. 2-2 for map bounds location). ‘B':- cross section view as outlined in 'A' (looking northwest) showing lithology, structure and alteration as determined from surface mapping. This cross section is at the same scale as the Seongsan cross section (Fig. 3-26). Due to the lack of diamond drill hole data in this area, alteration zonation and lithologies have been projected from surface, hence may appear simplified, but can not be resolved any further. Note: the view in 'B' shows an extended cross section compared to that outlined in 'A'. Alteration assemblages comprise the following: AA1, AA2, AA3 = advanced argillic 1, 2, 3 (see Table 3-1); and q = siliceous. Dashed lines inferred; annotation 'F' labels faults; lithology labels as per Section 2.2. See main text for further detail. .................................................................................................. 3-54

Fig. 3-28 Eunsan alteration zonation superimposed over geology and structure (from Fig. 2-29). Siliceous alteration,

adjacent adularia alteration and related auriferous veining are localised around the main Eunsan Fault. Lithological unit labels have been removed (see Fig. 2-29 for labels). ‘A’, ‘B’, ‘C’ and ‘D’ views as per Figure 2-29. Alteration assemblages comprise the following: prop = propylitic; phy = phyllic; adu = adularia; q = siliceous; and c = carbonate (see Table 3-1). See main text for further detail. ............................................... 3-57

Fig. 3-29 Moisan alteration zonation superimposed over geology and structure (from Fig. 2-33). Siliceous alteration,

adjacent adularia alteration and related auriferous veining are localised along the main faults that make up the Moisan Fault Zone. Lithological unit labels have been removed (see Fig. 2-33 for labels). ‘A’ and ‘B’ views as per Figure 2-33. Alteration assemblages comprise the following: prop = propylitic; phy = phyllic; adu = adularia; arg = advanced argillic 1; adv arg = advanced argillic 2/3; and q = siliceous (see Table 3-1). See main text for further detail. ...................................................................................................................................... 3-60

Fig. 3-30 Chunsan alteration zonation superimposed over geology and structure (from Fig. 2-35). Siliceous

alteration, adjacent adularia alteration and related auriferous veining are localised around the faults that make up the Chunsan Fault Zone. The phyllic-adularia alteration and associated mineralisation at Chunsan overprints earlier advanced argillic alteration (see Section 3.4.2.2). Lithological unit labels have been removed (see Fig. 2-35 for labels). ‘A’ and ‘B’ views as per Figure 2-35. Alteration assemblages comprise the following: prop = propylitic; phy = phyllic; adv arg, AA1, AA2, AA3 = advanced argillic 1, 2, 3 (see Table 3-1); and q = siliceous. See main text for further detail..................................................................................... 3-62

Chapter 4

Fig. 4-1 Step-wise 40Ar/39Ar apparent plateau age data (this study) on adularia from the low-sulfidation systems of the Seongsan district (Chunsan system CH003 115m; Eunsan system EN006 72m; Moisan system MS008 148m). Adularia from each sample show well-defined apparent plateau ages between 78.4 and 76.9Ma (77.7±0.8Ma).................................................................................................................................................... 4-5

Fig. 4-2 New step-wise 40Ar/39Ar apparent plateau age data for the low-sulfidation systems of the district (* - this

study) with previous 40K/40Ar apparent age data for various rocks and alteration in the district and surrounding region (Kim & Nagao, 1992). In addition, field relationships constrain the ages of igneous complexes within the Seongsan district. Adularia ages are consistently younger than those of alunite from nearby high-sulfidation systems consistent with field relationships (Chapter 3). Dark grey areas highlight age range whereas light grey areas highlight analytical error of age range....................................................................... 4-6

Chapter 5

Fig. 5-1 Fluid inclusions from Eunsan, Moisan and Chunsan. This Figure highlights how small most fluid inclusions are. ‘A’: sample CH003 115m (scale bar = 0.1mm) fluid inclusions in quartz as minute, pseudo-secondary to secondary inclusions in variably radiating trails. ‘B’: sample EN006 81m (scale bar = 0.2mm) fluid inclusions

Bowden, C.D. xxiv

in quartz as minute, pseudo-secondary to secondary inclusions in densely packed arrays. ‘C’: sample EN006 72m (scale bar = 0.05mm) fluid inclusions in calcite as minute, pseudo-secondary to secondary inclusions typically in variably oriented trails. ‘D’: sample CH003 115m (scale bar = 0.05mm) minute liquid-only (type 1) and liquid-rich (type 2a) fluid inclusions. ‘E’: sample EN ●092 (scale bar = 0.1mm) typically liquid-rich (type 2a) and lesser gas-rich (type 2b) fluid inclusions. Note the irregular and necked nature of the fluid inclusions. ‘F’: sample MS006 51.6m (scale bar = 0.05mm) type 3a fluid inclusions with no CO2 phase evident at room temperature, but heating-freezing experiments show the presence of clathrate. ..................... 5-6

Fig. 5-2 Histogram of final melting temperatures (combined ice (<0ºC) and clathrate (>0ºC)). ‘A’: data from this

study, highlighting the distinctive character of secondary inclusions from Moisan compared to Eunsan and Chunsan; ‘B’: data for the Seongsan deposit from Koh (1996), highlighting the distinctive character of fluid inclusions from Seongsan compared to Eunsan, Moisan and Chunsan. ......................................................... 5-10

Fig. 5-3 Histogram of homogenisation temperature. ‘A’: data from this study, highlighting the low but fairly

continuous range of homogenisation temperatures from Moisan, Chunsan and Eunsan; ‘B’: data for the Seongsan deposit from Koh (1996). ............................................................................................................... 5-11

Fig. 5-4 Homogenisation temperature versus salinity plot. ‘A’: data from this study, showing the more saline

character of fluid inclusions from Moisan compared to those from Eunsan and Chunsan; ‘B’: data for the Seongsan deposit from Koh (1996), which shows a greater spread of salinities than Eunsan, Chunsan and Moisan............................................................................................................................................................ 5-12

Fig. 5-5 ‘A’: Calculated pressure-temperature curves in the system Al2O3-SiO2-H2O based on 1Kb stability

relationships and thermodynamic data (Hemley et al., 1980). Calculated temperature dehydration reactions for kaolinite at 1Kb are 273±10ºC for kaolinite-pyrophyllite-quartz (quartz saturated) and 300±10ºC for kaolinite-pyrophyllite-diaspore (quartz under-saturated). ‘B’: Calculated pressure-temperature curves in the system Al2O3-SiO2-H2O at low water pressures based on 1Kb stability relationships and derived thermodynamic data. Dashed lines show temperatures from chosen pressures. For quartz saturated system: 0.1Kb = ca. 260ºC, 0.3Kb = ca. 264ºC, 0.5Kb = ca. 267ºC; for quartz under-saturated system: 0.1Kb = ca. 288ºC, 0.3Kb = ca. 292ºC, 0.5Kb = ca. 295ºC............................................................................................................................... 5-17

Fig. 5-6 Mineral stability relationships in the system Al2O3-SiO2-H2O at 1Kb H2O after Hemley et al. (1980). The

lack of diaspore, pyrophyllite, corundum and andalusite constrain the temperature of formation of advanced argillic alteration to ca. <280ºC. Grey shaded area represents the inferred stability field for advanced argillic 1 and 2 alteration (quartz-kaolinite/dickite). ..................................................................................................... 5-18

Fig. 5-7 Mineral stability relationships in the system K20-Al2O3-SiO2-H2O-SO3. ‘A’ and ‘B’ are experimentally

determined at 200ºC and 300ºC; ‘C’ and ‘D’ are calculated at 200ºC and 300ºC. Quartz is present and total pressure is 1Kbar. Figures and thermodynamic data from Hemley et al. (1969). The shaded areas in ‘B’ represent stability ranges for transitional alteration zones as labelled. These shaded areas highlight that the high- and low-sulfidation alteration assemblages formed under distinctly different conditions..................... 5-19

Fig. 5-8 Log ƒO2 versus pH diagram at 250ºC and log ΣS = -1.7 (which approximates the Seongsan system, see Fig.

5-14). Figure and thermodynamic data from Heald et al. (1987). Dark grey shaded areas represent the maximum range of likely stability fields for advanced argillic altered systems (top left: Seongsan and Ogmaesan) and phyllic-adularia altered systems (lower centre: Eunsan, Moisan and Chunsan). Light grey shaded areas represent possible but less likely stability fields. AA1&2 = advanced argillic 1 and 2 alteration assemblages; AA3 = advanced argillic 3 alteration assemblage; adu-phy = adularia-phyllic alteration. AA1&2 and AA3 are separated by the alunite-kaolinite stability boundary. Sulfur isotope studies (Section 5.5) show that Seongsan and Ogmaesan are SO4-dominant and that Eunsan, Moisan and Chunsan are H2S-dominant. See main text for discussion.................................................................................................................................. 5-21

Fig. 5-9 Log ƒO2 versus log ƒS2 pH diagram at 250ºC. The log ƒO2 is constrained from Figure 5-8. Figure and

thermodynamic data from Heald et al. (1987). Grey shaded areas represent inferred stability fields for advanced argillic altered systems (top right: Seongsan and Ogmaesan) and phyllic-adularia altered systems (lower centre left: Eunsan, Moisan and Chunsan). The Au-Ag bearing sulfides at Seongsan are geochemically similar to those found within Eunsan, Moisan and Chunsan, highlighting that distinctly different fluids formed the advanced argillic alteration and Au-Ag mineralisation............................................................................. 5-22

Fig. 5-10 Oxygen, hydrogen and sulfur isotope analyses undertaken at each prospect............................................ 5-24 Fig. 5-11 δ18Owater and δDwater results for samples analysed during this study (Table 5-4). Ranges of residual

magmatic water remaining in intrusion after degassing and crystallisation (Taylor, 1974), composition of water initially dissolved in felsic melts (Taylor, 1992), and low-salinity vapour discharges from high-temperature volcanic fumaroles (Giggenbach, 1992) are shown in grey and discussed further in the main text. ‘X’ = hypothetical fresh granodiorite/dacite (from Criss & Taylor, 1986). Remaining data (labelled) are plotted

Bowden, C.D. xxv

according to sample type. AA1, 2, 3 = advanced argillic 1, 2, 3; qtz = siliceous altered; adu = adularia altered. ............................................................................................................................................................... 5-31

Fig. 5-12 δ18Owater and δDwater plot as shown in Figure 5-11 (see Figure 5-11 for description) with calculated

exchange pathways based on paleo-meteoric water (solid thin curves) and paleo-magmatic water (dashed thin curves) at equilibrium with hypothetical fresh dacite/granodiorite with 1wt% water content over a range of fluid to rock weight ratios (R = 10 to 0.001) and temperatures (150 to 400ºC). See main text for discussion and interpretation. ................................................................................................................................................. 5-36

Fig. 5-13 A histogram showing the distribution of δ34S isotopic compositions for sulfate (alunite) and sulfide (pyrite)

minerals analysed from the Seongsan district. Alunites tend to have heavier isotopic compositions while associated pyrites in the high-sulfidation systems have particularly light isotopic compositions. Pyrites from the low-sulfidation systems tend to have an intermediate composition.......................................................... 5-44

Fig. 5-14 Summary of δ34S isotopic compositions for alunite and pyrite from the Seongsan district. The grey shaded

area represents the range for calculated δ34SΣS as determined from Figure 5-15. This figure highlights the disproportionate relationship between sulfur isotopic compositions in co-existing alunite and pyrite in the Seongsan and Ogmaesan systems................................................................................................................... 5-45

Fig. 5-15 δ34Ssulfate - δ34Ssulfide plot of alunite and pyrite mineral separates from Seongsan and Ogmaesan. Despite

extensive examination, no directly co-existing sulfate-sulfide mineral pairs were identified. However, these alunite and pyrite samples formed during the same paragenetic stage and hence would have probably formed from the same fluid of fixed δ34SΣS. As no sulfate minerals were identified within the low-sulfidation prospects only data from Seongsan and Ogmaesan can be plotted on this figure. This figure highlights that the sulfate and sulfide minerals at Seongsan and Ogmaesan formed under strongly oxidised, SO4-dominant conditions. See main text for further description and interpretation of this figure. ....................................... 5-46

Fig. 5-16 Multi-element versus Au diagrams showing data from Seongsan (black dot) and Ogmaesan (red dot). See

main text for discussion and interpretation of results. Dashed blue line represents average crustal abundances: 0.004ppm Au; 0.07ppm Ag; 55ppm Cu; 12.5ppm Pb; 70ppm Zn; 1.8ppm As; 0.08ppm Hg; 0.2ppm Sb; 1.5ppm Mo; 0.17ppm Bi; and 10ppm Th (Levinson, 1974). .......................................................................... 5-53

Fig. 5-17 Multi-element versus Au diagrams showing data from Moisan (black dot), Eunsan (red dot) and Chunsan

(blue dot). See main text for discussion and interpretation of results. Dashed blue line represents average crustal abundances: 0.004ppm Au; 0.07ppm Ag; 55ppm Cu; 12.5ppm Pb; 70ppm Zn; 1.8ppm As; 0.08ppm Hg; 0.2ppm Sb; 1.5ppm Mo; 0.17ppm Bi; and 10ppm Th (Levinson, 1974). ................................................ 5-55

Chapter 6

Fig. 6-1 A1: North Island of New Zealand showing the location of the Taupo Volcanic Zone (TVZ). A = andesite dominated, R = rhyolite dominated. A2: The broad structural framework of the main calderas (numbered) within the TVZ. Grey areas within A2 are lakes or sea. T = Lake Taupo, R = Lake Rotorua. Calderas: 1 = Rotorua, 2 = Haroharo (in Okataina Volcanic centre), 3= Kapenga, 4 = Reporoa, 5 Mangakino, 6 = Maroa, 7 = Whakamaru and 8 = Taupo (modified from Rowland & Sibson, 2001 and Milner et al., 2002; after Houghton et al., 1995). B: The broad structural framework for the main calderas (numbered) within southeast Korea. OFB = Okchon Fold Belt, Pre-K = pre-Cretaceous Formations, KS = Cretaceous sedimentary Formations, KV = Cretaceous volcanic Formations, KG = Cretaceous granites, TS = Tertiary Formations. Calderas: 1 = Geumseogsan, 2 = Hwasan, 3 = Choijeongsan, 4 = ?, 5 = Unmunsa, 6 = Chisulryeongsan, 7 = Daeunsan, 8 = Jangsan, 9 = Jinrye and 10 = Palryeongsan (modified from Koh et al., 2002 and pers. comm. Reedman, July 2004). C: The broad structural framework of the Seongsan district (surface exposures of ‘Kv’ – nomenclature from B – Cretaceous volcanic rocks).............................................................................................................. 6-23

Fig. 6-2 Magmatic belts of East Asia, distinguished by the dominant plate subduction causing the magmatism (by

either the Farallon-Izanagi or Kula-Pacific as indicated by hatching; see: Fig. 1-10). Modern day Japan has been split and rotated back to its approximate position during magmatism, although note that paleo Japan would be a different outline to modern day Japan due to post Cretaceous volcanic activity and accretion. Figure after Kinoshita (1995). ........................................................................................................................ 6-27

Bowden, C.D. xxvi

LIST OF TABLES

Chapter 1 Table 1-1 Classification schemes for epithermal systems. Modified from Sillitoe & Hedenquist (2003).................. 1-5 Table 1-2 Principle field-oriented characteristics of epithermal deposit types. From Sillitoe & Hedenquist (2003). .....

............................................................................................................................................................... 1-10

Chapter 3 Table 3-1 Alteration types and associated mineral assemblages observed in the Seongsan district. Alteration types

(left column) are listed from generally the most to the least volumetrically abundant alteration type. Alteration mineral assemblages (right column) are listed from the most to the least commonly observed mineral within a given alteration type. Alteration minerals highlighted in bold signify key alteration mineral/s for each alteration type. 1 - the process of siliceous alteration is silicification. 2 - silicic alteration type is also commonly called residual silica, or vuggy silica. 3 – phyllic alteration type is also known as either ‘sericite’ or ‘illite’ alteration................................................................................................................................................ 3-4

Table 3-2 A broad classification of vein assemblages, infill material, infill forms and associated metals within the

Seongsan district. See text for further detail. Individual systems show some localised variations as discussed within Section 3.4. ^ - associated metals are not always present. py = pyrite; dick = dickite; kao = kaolinite; qtz = quartz; carb = carbonate; adu = adularia; cpy = chalcopyrite; sph = sphalerite; ten/tet = tennantite/tetrahedrite; tell = tellurides........................................................................................................... 3-20

Table 3-3 Paragenetic events for all epithermal systems in the Seongsan district. Key relationships highlighted are

that advanced argillic alteration dominates in some systems, whereas phyllic-adularia alteration dominates in others; however, Chunsan, and to a lesser degree, Seongsan epithermal systems comprise significant amounts of both alteration types. In addition, field relationships show that advanced argillic alteration pre-dates phyllic-adularia alteration across the district. Furthermore, field relationships also show that advanced argillic alteration and associated mineralisation formed on and around structures that were active during district-scale stress regime 1, whereas phyllic-adularia alteration and associated mineralisation formed on and around structures that were active during district-scale stress regime 2. Line thickness relates to abundance/intensity, with a thicker line indicating greater abundance/intensity. See Section 3.5 for further discussion between timing of structural and alteration/mineralisation events................................................................................ 3-48

Table 3-4 Classification of the Seongsan district epithermal systems. Descriptive nomenclature is based on the

framework of Cooke & Deyell (2003), adapted from earlier geological frameworks of Berger & Henley (1989), Hayba et al. (1985) and Heald et al. (1987). This descriptive nomenclature allows the varied nature of the different systems to be highlighted, which may not be the case with using traditional classification schemes. Sulfidation-state is from Hedenquist et al. (2000) incorporating both the common usage of the term to characterise a particular deposit as well as examination of the sulfidation-state of the metalliferous ore-forming sulfides. This highlights the potentially ambiguous and at times limiting nature of the sulfidation-state terms. Analogous references are also provided for reader familiarity. .......................................................... 3-65

Chapter 5 Table 5-1 Fluid inclusion types, morphological summaries and classification, based on inclusions from this study and

Koh (1996). * - fluid inclusion types 3a (both this study and Koh, 1996) generally do not show a CO2 phase at room temperature, therefore can only be distinguished from type 2a fluid inclusions during microthermometric analysis. If CO2 is found to be present, then the fluid inclusion can be categorised as type 3a as opposed to type 2a. ............................................................................................................................................................. 5-7

Table 5-2 Fluid inclusion samples. ^ = mineral paragenesis. # = fluid inclusion paragenesis –pseudo-secondary to

secondary (PS/S). Pseudo-secondary to secondary fluid inclusions formed from a fluid trapped later than that which produced the mineral hosting the fluid inclusions. ~ = dominant fluid inclusion type – represents the dominant fluid inclusion type, as defined in Section 5.2.2.2 (see also Table 5-3). L:V = liquid to vapour ratio. qtz = quartz; cal = calcite; adu = adularia; sil = siliceous. ................................................................................ 5-7

Bowden, C.D. xxvii

Bowden, C.D. xxviii

Table 5-3 Summary fluid inclusion heating and freezing data from this study and from Koh (1996). ^, # and ~ as per description in Table 5-2. L:V = liquid to vapour ratio. * - highlights Tm data corresponding to final melting temperatures for clathrate. ** - highlights data that is an average of both final ice and clathrate melting temperatures, as such is misleading to average Tm, as data is bimodal............................................................ 5-9

Table 5-4 Oxygen and hydrogen isotope data for samples from the Seongsan district. SS = Seongsan; OG =

Ogmaesan; EN = Eunsan; MS = Moisan and CH = Chunsan. Calculated δ18Owater and δDwater results highlighted in grey are at the preferred temperatures based on the mineral assemblages; and these data are used in Figures 5-11 & 5-12. ^ as per description in Table 5-2. R = rock sample, M = mineral separate. HS = high-sulfidation, LS = low-sulfidation. Alteration types: prop = propylitic; adu = adularia; phy = phyllic; dick = dickite; qtz = siliceous±silicic; sil (p-a) = siliceous (phyllic-adularia related); sil (aa) = siliceous (advanced argillic related); alu = alunite; kao = kaolinite. OG 51 +157mRL; OG 59.1 +130mRL; OG 40 +85mRL; OG 42b +82mRL. .....................................................................................................................................5-29 to 5-30

Table 5-5 Calculated δ18O and δD values for a paleo-meteoric and paleo-magmatic fluid in isotopic equilibrium with

a hypothetical fresh dacite (1wt% H2O) over a range of fluid to rock weight ratios and temperatures. See main text for further detail. ..................................................................................................................................... 5-35

Table 5-6 δ34S isotope data for pyrite and alunite mineral separates from the Seongsan district. ............................ 5-43

Chapter 6 Table 6-1 Selected geological characteristics of some epithermal systems and those of the Seongsan district. HS, IS,

LS = high-, intermediate- and low-sulfidation. adv. arg. = advanced argillic; alt. = alteration. ^ = age data done this study. qtz = quartz, py = pyrite, adu = adularia, en = enargite, lz = luzonite, t/t = tennantite/tetrahedrite, cpy = chalcopyrite, sph = sphalerite, gal = galena, acan/argen = acanthite/argentite, goldf = goldfieldite (Cu variably substituted by Ag-Au in the series to tennantite/tetrahedrite). TVZ = Taupo Volcanic Zone. ...................................................................................................................................6-11 to 6-12