Geological Belts, Plate Boundaries, and Mineral Deposits in Myanmar

By Andrew Mitchell

Geological Belts, Plate Boundaries and Mineral Deposits in Myanmar arms readers with a comprehensive overview of the geography, geology, mineral potential and tectonic plate activity of Myanmar. The book focuses on the nature and history of the structural belts and terranes of Myanmar, with particular emphasis on the mineral deposits and their relationship to stratigraphy and structure. The country has a long history of plate tectonic activity, and the most recent plate movements relate to the northward movement of the India plate as it collides with Asia. Both of these are responsible for the earthquakes which frequently occur, making the country a geologically dynamic region. Additionally, Myanmar is rich in mineral and petroleum potential and the site of some of Southeast Asia’s largest faults. However, many geoscientists are only recently becoming familiar with Myanmar due to previous political issues. Some of these barriers have been removed and there is emerging international interest in the geology and mineral deposits of Myanmar. This book collates this essential information in one complete resource. Geological Belts, Plate Boundaries and Mineral Deposits in Myanmar is an essential reference for economic geologists, mineralogists, petroleum geologists, and seismologists, as well as geoscience instructors and students taking related coursework.

• Provides an accessible history of the geological research and mineral exploration and extraction conducted in Myanmar and an overview of its rich mineral resources
• Presents the historical and current plate tectonic activity in the region, offering seismologists and geophysicists a guide to Myanmar’s structural geology and risk for earthquake activity
• Richly illustrated with more than 100 maps, diagrams and photographs to capture the geology of Myanmar and aid in the retention of key concepts
• Focuses on the nature and history of the structural belts and terranes of Myanmar

• Language: English
• Publisher: Elsevier Science
• Release date: Nov 23, 2017
• ISBN: 9780128033838

Andrew Mitchell

Andrew Mitchell obtained his D Phil and a DSc from Oxford and has had an international career in geology. From the early 1960’s to the late 1980’s he was an exploration geologist for the then British Service in Vanu Atu, and in Thailand, Myanmar, Nepal, and the Philippines on Colombo Plan and UN projects. After consulting for various minerals companies in Eastern European and Asian countries from 1990 to 1995, he joined Ivanhoe Myanmar and until 2011 was based in Myanmar responsible for the company’s minerals exploration. He has spent more than half of his career in Myanmar and is familiar with the country’s world-class mineral deposits. He has authored or co-authored about 100 papers on tectonics and mineralization. His first book Mineral Deposits and Global Tectonic Settings (Academic Press, 1981) was followed by Epithermal Gold in the Philippines (Academic Press, 1991).

Book preview

Geological Belts, Plate Boundaries, and Mineral Deposits in Myanmar

Andrew Mitchell

Myanmar Precious Resources Group, Myanmar and Oxford, United Kingdom

Table of Contents

Cover image

Title page

Copyright

Acknowledgments

Part 1

Chapter 1. Introduction

1. Why Myanmar?

2. Morphological Features, Geological Provinces, and Mineral Deposits

3. Geological Blocks, Belts, and Terranes

4. Evolution of Geological Mapping and Mineral Exploration

5. Mineral Deposits and Production

6. Organization of Contents

7. Geographical Names and Geological Terms

Part 2. Myanmar East of the Sagaing Fault

Chapter 2. The Shan Plateau West of the Salween

1. The Plateau and Its Boundaries

2. Stratigraphic Units and Granites

3. Selected Structural Features on the Shan Plateau

4. Mineral Deposits on the Shan Plateau

Chapter 3. Myanmar East of the Salween: The Sibumasu–Mong Yawng Arc Collision and Related Tin Mineralization

1. Early Ideas on a Triassic Collision

2. The Inthanon Suture Zone and Related Magmatic Arc in Thailand and Yunnan

3. Position of the Inthanon Suture Zone in Myanmar

4. Eastern Limit of the Sukhothai (Mong Yawng) Arc in Myanmar

5. Late Triassic Tin Granites in Northern Thailand and Yunnan East of the Salween

6. Tin Granites and Associated Deposits in Eastern Myanmar

7. Manganese and Gold

Chapter 4. The Mergui Group and Equivalents in the Slate Belt, Phayaungtaung and the Gaoligong Range (Northeastern Myanmar)

1. The Slate Belt, the Mergui Group, and the Karen–Tenasserim Unit

2. Mergui and Taungnyo Groups in the Slate Belt

3. The Mergui Group in the Phayaungtaung Area

4. The Mergui Group in the Gaoligong Range, Northeastern Kachin State

5. The Mergui Group and the Chaung Magyi

Chapter 5. Paung Laung–Mawchi Zone

1. Main Features of the Zone

2. Stratigraphy of Zone Segments

3. Minor Intrusions Within the Zone

4. Margins of the Paung Laung–Mawchi Zone

5. Regional Structure of the Paung Laung–Mawchi Zone

6. The Paung Laung–Mawchi Zone Equivalent Northeast of Sedawgyi

7. Mineralization in the Paung Laung–Mawchi Zone

Chapter 6. Granites, Minor Intrusions, and Mineralization in the Slate Belt, Phayaungtaung, and Gaoligong Range

1. Granites and Minor Intrusions in the Slate Belt

2. Tin and Tungsten Mineralization in the Slate Belt

3. Granites and Tin Mineralization in the Gaoligong Range Myanmar and the Tengchong Region of Yunnan

4. Tectonic Setting During Granite Generation and Mineralization

5. Orogenic Gold Deposits in the Slate Belt, Phayauntaung, and the Gaoligong Range

6. Other Mineralization in the Slate Belt

Chapter 7. Mogok Metamorphic Belt

1. Distribution of the Metamorphic Belt

2. Mogok Segment, 96°15′E to Kachin State Border

3. Northern Segment, Eastern Kachin State

4. Central Segment: Wapyudaung to Zawgyi River (Kyaukse South)

5. Shan Scarps From the Zawgyi River to Mokpalin

6. Taninthari Coast, Thaton to Mergui

7. Selected Features of the Mogok Metamorphic Belt

8. Metamorphic Ages in the Mogok Belt

9. The Mogok Metamorphic Belt and the Mergui Group

10. Gemstones in the Mogok Metamorphic Belt

11. Gold Mineralization in the Mogok Metamorphic Belt

12. Lead-Zinc-Silver and Tin Occurrences

13. Ruby Formation, Gold Mineralization, and Uplift of the Belt

Chapter 8. Tagaung–Myitkyina Belt and Katha–Gangaw Range

1. Tagaung–Myitkyina Belt

2. Katha–Gangaw Range

3. Mineral Deposits and Prospects in the Tagaung–Myitkyina Belt

4. Tectonic Events in the Tagaung–Myitkyina Belt

Part 3. Myanmar West of the Sagaing Fault

Chapter 9. Popa–Loimye Magmatic Arc

1. Definition and Arc Segments

2. Kawt-a-Bum–Tatlet–Mt Loimye Arc Segment

3. Wuntho–Banmauk Segment

4. Monywa–Salingyi and Shinmataung Segment

5. Mount Popa Segment

6. Buried Magmatic Arc Beneath the Ayeyawaddy Delta

7. Age and Duration of Subduction-Related Magmatism

8. Arc Basement

9. Continuation of the Arc Beyond Kawt-a-Bum

Chapter 10. Central Burma Depression and Its Petroleum Occurrences

1. Introduction

2. Basins of the Fore-Arc Domain

Chapter 11. The Indo-Burman Ranges and the Arakan Coastal Lowland

1. Introduction

2. Eastern Belt of the Indo-Burman Ranges

3. Western Belt of the Indo-Burman Ranges

4. The Sin Chaung Zone of Exotics and Globotruncana Limestone in the Eastern Belt

5. The Arakan Coastal Lowland

6. Evolution of the Indo-Burman Ranges, Arakan Coastal Belt, and Cretaceous Rocks of the Fore-Arc Basin

7. The Indo-Burman Ranges and the Tagaung–Myitkyina Belt

8. Lateritic Nickel, Chromite, and Copper Prospects in the Indo-Burman Ranges

Chapter 12. Exploration History and Petroleum Geology of Offshore Myanmar

1. Introduction

2. Myanmar Exploration History

3. Rakhine Region

4. Moattama Region

5. Tanintharyi Region

6. Summary and Future Potential

Chapter 13. Hukawng Basin, the Amber Mines, and the Orbitolina Limestone

1. Geology of the Basin

2. The Amber Mines

3. Mid-Cretaceous Orbitolina Limestones

Chapter 14. Jade Mines–Loimaw Uplift

1. Location and Regional Setting

2. Tanai River Section (26°N Uplift)

3. The Hpakant-Tawmaw, Nat Hmaw, and Mawlu-Mawhun Jadeite Areas

4. Indawgyi Mafic Complex and Platinum Group Element Occurrences

5. The Kyaukpahto Mine and Taungzaw and Gegalaw Gold Prospects

6. Nanyaseik Ruby Fields

7. Lateritic Iron Ore Occurrences

8. Relationship of the Uplift to Other Belts

Chapter 15. Kumon Range

1. Location and Regional Setting

2. Geology

3. Alluvial Gold Workings

Part 4. Myanmar East and West of the Sagaing Fault

Chapter 16. Chaun Kan Gneiss and the India Collision Zone in Northwestern Myanmar

Chapter 17. Popa–Loimye Arc, Correlations With Tibet, and Alluvial Diamonds in Myanmar

1. Former Position of the Popa–Loimye Arc Relative to Myanmar East of the Sagaing Fault

2. Continuation of the Popa–Loimye Arc Into Tibet

3. Correlation of Unconformities in the Shan Scarps and Central Tibet

4. Alluvial Diamonds in Myanmar

Chapter 18. Myanmar Orogens and Flysch, Potential for Mineral Discoveries, and Shan Scarps and Jade Mines Cross Sections

1. Alpine Subduction Analogy for Myanmar Orogenic Belts

2. Some Areas of Mineral Potential in Myanmar

3. Extensional Faults and the Mergui Group

4. Cross Section West of the Jade Mines Uplift

Index

Copyright

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Acknowledgments

Through a combination of chance encounters, considerate and geologically oriented mineral exploration employers in a variety of organizations, and some outstanding Myanmar counterparts, I have had the good fortune to enjoy over half my working life as a geologist in Myanmar. This book is largely an attempt to place in a suitable geological framework the cumulative field observations by myself and field parties in Myanmar from 1970 to 1978 and 1995 to 2011 and during numerous subsequent field visits, what I have learned from so many Myanmar geologists and the information in what were until quite recently the printed but mostly unpublished accounts of their field areas.

I am indebted to several groups of people and numerous individuals in addition to those named below. First are those with whom I worked in the field from 1970 to 1978 including initially Dr. Magnus Garson and Dr. Brian Amos from the Institute of Geological Sciences, United Kingdom, and Kyi Soe from Myanmar's Directorate of Geological Survey and Mineral Exploration (DGSE). Dr. Tin Aye, the then Director General of DGSE, kindly invited me to apply for a post on the United Nations-executed Mineral Exploration Project from 1974 to 1978, in which it was a pleasure to work under the guidance of the Project Manager Jussi Huhta and his counterpart Kyi Soe, an outstanding geologist who has been a good friend since my earliest fieldwork in Myanmar. Among the more than 40 DGSE staff attached to the UN project, my counterpart, Zaw Pe, and Tin Hlaing, Nyunt Htay, and Kyaing Sein accompanied me on innumerable river traverses.

Of the field geologists in or associated with Ivanhoe Mines and later Bagan Holdings during the 1995–2011 period, Nyunt Htay is one of the two survivors from the UN project who continues in active fieldwork today, and I thank him for so many years of shared traverses and his penetrating observations. Tin Hlaing, a gifted geologist able to visualize three-dimensional images from air photos without a stereoscope, and Kyaw Min Tun, Myint Thein Htay, Myint Naing Win, and Myint Kyaw are among those who worked longest with me in Ivanhoe Mines. During that time, Ivanhoe benefited and I learned from the experience of Andy Nichols and Ohn Myint Thein, mining engineers at the Modi Taung gold project, each examples of the right person in the right job at the right time. Than Htay, Senior Advisor to DGSE, contributed so much to cordial relationships between DGSE and Ivanhoe Mines during the first years of Ivanhoe's exploration program. Since 2011, thanks to Htun Lynn Shein, owner of Myanmar Precious Resources Group, I have been able to continue participation in Myanmar's mineral exploration, supported by his principal geologists Myint Thein Htay, Kyaw Min Htun, and Myint Oo.

I owe much to Dr. Thura Oo, current Principal of Sagaing University, for sharing his knowledge of Shan Plateau stratigraphy and his company and guidance on numerous field trips since 1998 and to Dr. Win Swe who has shared his knowledge of Myanmar geology willingly with me and his students since 1970.

Among those who contributed so much to agreeable and productive fieldwork, I am hugely indebted to Ko Ko Than and Cho Wai Wai Lwin, Chief Advisor and Senior Secretary to Ivanhoe Mines, respectively, for their dedicated service over 15  years. They ensured successful avoidance of company and personal pitfalls in a country where everything was political, and Ko Ko Than's understanding of government workings and Myanmar mining law was unique and the principle cause of Ivanhoe's success. Equally crucial were the unfussed technical guidance, patience, and support for geologists in the field from Ivanhoe's exploration director Doug Kirwin during the prolonged but ultimately successful search for primary gold in the Slate belt in the late 1990s. David Boehm contributed significantly to the understanding of Myanmar's mineral endowment through Bagan Holdings' support for geological studies of the Monywa copper deposits by the joint venture before the pit was closed and abandoned. Mine production and my knowledge of the geology benefited immensely from the initial guidance of Paul Chare and subsequently from the enthusiastic leadership, operational expertise, and consistent good humor of Philip Blake, mine supervisor at Monywa, in the fascinating years leading up to its sale in 2011.

I welcome this opportunity to thank Professor Sun-Lin Chung of Taiwan National University for his generosity and enthusiasm in undertaking through his Department very many of the zircon U–Pb age determinations referred to in this book. I am also happy to be able to emphasize here the outstanding work of Professor Ba Than Haq, geology professor at Yangon University, for his inspiring but largely unpublished and hence uncited presentations on metallogenic belts in Myanmar beginning in the late 1960s.

Many people contributed directly to the preparation of this book. I thank particularly Mike Ridd, coauthor during the early phase of its writing, who also wrote Chapter 10 and who kindly prepared the illustrations for several chapters. Mike freely shared his wide knowledge of the Mergui Group equivalent in adjacent Thailand but does not share blame for my speculations and perhaps fantasies concerning the glacial Mergui in Myanmar. Andy Racey contributed Chapter 12 and was an invaluable help with detailed comments, suggestions, and discussion on drafts of most of the chapters. It is no fault of his that time permitted only limited revision and incorporation of not all of his careful editorial work. I also thank two reviewers of early drafts of some chapters for suggestions and recommendations that I have endeavored to follow. Than Htun, in addition to many of the geologists mentioned above, kindly responded to requests for geological information and names of who had mapped or drilled what. Cho Wai Wai Lwin prepared the manuscript, Aung Minn Paing drew many of the illustrations, courtesy of Htun Lynn Shein, and I sincerely thank Sandhya Narayanan, Mohana Rajendran, and, in particular, Tasha Frank at Elsevier for patience despite missed deadlines. Finally, I thank my wife Orawin for patience and good humour during my innumerable absences throughout a period vastly exceeding the average geologist's 9  years of active field life, and during my mental absences while the book was in preparation.

Part 1

Outline

Chapter 1. Introduction

Chapter 1

Introduction

Abstract

Geologically, Myanmar can be divided into the post-Jurassic Popa-Loimye magmatic arc in the west and northwest, the continental Shan Plateau, and a late Triassic suture zone and former Permian to Triassic island arc in the Far East. The main purpose of this book is to describe these features, their constituent belts and segments, and the abundant mineral deposits and occurrences within them and to discuss or propose plate boundary–related tectonic or magmatic events to which they may be related. Additional terranes proposed since 1978 include the Western Burma block; Sibumasu (Sino-Burma-Malaysia-Sumatra), which includes all or most of the Shan Plateau but has a very loosely defined western boundary; and the Mt. Victoria Land block, originally envisaged as the exposed part of a Western Burma block basement. Myanmar is also divided into a western and eastern half by the northerly trending Sagaing Fault, on which the western half has moved northward relative to the east since the early Miocene. According to some estimates, this displacement exceeds 300 km, but there is no general agreement. In the south the fault forms the boundary of the Popa-Loimye arc, the northward continuation of the Sunda arc, but in the north what may be the offset arc continues east of the Sagaing Fault through the Tagaung-Myitkyina Belt into northeastern India and Tibet. Because of this uncertainty in displacement, this Introduction (Part 1) is followed by Parts 2 and 3, dealing with geology and mineralization, respectively, east and west of the fault. Most of Part 4 is concerned with structural belts or types of mineral deposit that occur both east and west of the fault. Myanmar's mineral deposits cover a wide variety of types, almost regardless of how they are categorized. Jade exports have recently exceeded in value that of all other minerals combined, eclipsing that of ruby, once the principal gemstone is produced. Very recently Myanmar became the world's largest exporter of tin, from new mines in Wa State; although when these tin reserves decline, their value may soon be overtaken by that of copper from Letpadaung, part of Southeast Asia's largest producing copper deposit near Monywa. The Mawchi mine northeast of Yangon was at one time the world's largest producer of tungsten, and Bawdwin in the northern Shan State the largest base metals mine, producing ore from a Cambrian deposit with similarities to the Miocene Kuroko ores in Japan. Myanmar has also produced up to several percent of world manganese and contains several different types of gold deposit, but the official production figure for gold is an underestimate. The well-received 1994 Mining Law has been modified and superseded, but details and rules are not yet final. There is a widespread desire that individual deposit and national production figures, long provided for oil and gas, be publicly available for every mineral.

Keywords

Blocks and terranes; Gemstones and metals; Magmatic arcs; Mineral production data; Sagaing Fault

Chapter Outline

1. Why Myanmar?

2. Morphological Features, Geological Provinces, and Mineral Deposits

3. Geological Blocks, Belts, and Terranes

4. Evolution of Geological Mapping and Mineral Exploration

5. Mineral Deposits and Production

6. Organization of Contents

7. Geographical Names and Geological Terms

References

1. Why Myanmar?

Myanmar, the second largest country in Southeast Asia, occupies a geologically critical position in the northeast corner of the Indian Ocean (Fig. 1.1), where the northern end of the Sunda–Andaman arc, the world's second-longest arc system, has collided with the Indian continent in the Naga Hills and is juxtaposed with the eastern end of the India–Asia collision zone and Himalayas to the east. For its size and population, Myanmar has a disproportionately large number of world-class metallic mineral deposits, producing offshore and onshore reserves of gas and oil, and an abundance of gemstones, reflecting the country's varied geology. This includes the post-Jurassic Popa–Loimye magmatic arc in the west, and the continental Shan Plateau welded to a Triassic island arc in the east.

The first and primary purpose of this book is to delineate and describe the major structural belts of which Myanmar is comprised, with emphasis on their stratigraphy, their relationships to adjacent belts, and their mineral districts and deposits. A second purpose is to try to relate the main magmatic arc-forming processes and orogenic or mountain-building events to plate movements and ocean closures to increase understanding of the tectonic settings in which most of the metallic, gemstone, and petroleum deposits originated.

Figure 1.1  Regional tectonic setting of Myanmar. EHS , Eastern Himalayan Syntaxis; MBT , Main Boundary Thrust; RRF , Red River Fault; TPFZ , Three Pagodas Pass Fault. Redrawn from Fareeduddin, Dilek, Y., 2015. Structure and petrology of the Nagaland–Manipur Hill ophiolitic melange zone, NE India: a fossil Tethyan subduction channel at the India–Burma plate boundary. Episodes 38, 298–314, with permission of International Union of Geological Sciences.

2. Morphological Features, Geological Provinces, and Mineral Deposits

Until the early 1970s most authorities on Myanmar geology (e.g., Stamp, 1925; Chhibber, 1934a; Tainsh, 1950; Win Swe, 1972; Maung Thein, 1973) recognized four morphological units that were also structural: the Eastern Highlands or Shan–Tenasserim massif that includes the Shan Plateau; the Central Lowlands, or Central Depression; the Arakan–Chin–Naga, Indo-Burman, or Western Ranges; and the Arakan Coastal Plain. With identification of the 1400-km-long Mogok Metamorphic belt as a virtually continuous feature, it became convenient to divide Myanmar geologically into a Western Province or arc system that includes the Popa–Loime magmatic arc, and an Eastern Province comprising the Mogok Metamorphic belt and Shan Plateau to the east. The major Hninzee Fault (Dey, 1968), recognized as a dextral strike-slip structure and renamed Sagaing Fault by Win Swe (1972), coincides with the Province boundary south of Tagaung. To the north where the fault cuts through the Western Province or Popa–Loimye arc system, a possible 300  km or more of dextral displacement was implied by the proposed former continuity of the northeastern end of the Indo-Burman Ranges to the west and the southwestern end of the Tagaung–Myitkyina belt to the east of the fault (Mitchell, 1977). Estimates of spreading rates in the Andaman Sea (Curray et al., 1979) increased this possible displacement to at least 400  km.

Most of Myanmar's major metallic ore and gemstone deposits (Fig. 1.2) and numerous mineral occurrences occur in one of three kinds of geological belt: the first consists of the Cretaceous–Cainozoic magmatic arc in the Western Province, a Triassic arc–continent collision belt in the east of the Shan Plateau, and the late Cambrian Bawdwin Volcanics, a probable arc remnant, on the Plateau's northwestern margin; the second comprises the early to mid-Paleozoic and early Mesozoic carbonate shelves on the Shan Plateau; and the third, Mesozoic ophiolites and orogenic belts formed near plate boundaries since the Cambrian. Former highly productive metallic deposits include the now largely exhausted giant lead–zinc–silver sulfide ore bodies at Bawdwin and the world-class tin–tungsten vein system at Mawchi. More recent discoveries are the Man Makhsan tin deposits east of the Salween River, where current production makes Myanmar the world's largest exporter of tin; the giant high sulfidation epithermal type copper ore bodies near Monywa, producing since the early 1980s; and a major manganese mine and numerous epithermal, orogenic, and skarn-type gold deposits and workings. Myanmar produces the world's highest quality rubies, gem quality jadeite that is currently by far the country's most valuable export, and natural gas from onshore and a growing number of potentially much larger fields in offshore Cenozoic basins.

3. Geological Blocks, Belts, and Terranes

A valuable review of Myanmar's geology in a geosynclinal context is provided in an unpublished presentation by Maung Thein and Ba Than Haq in 1967. By the late 1970s the boundaries of some structural blocks in Myanmar were being interpreted as former terrane or lithospheric plate margins. These included the late Triassic suture zone projected northward from Malaysia and Chiang Rai in Thailand through easternmost Myanmar between the continental Shan-Thai block and a Permian–Triassic magmatic arc to the east, and a speculative plate boundary separating the Shan Plateau from a western Burma block originally thought to have collided with the Shan Plateau after the Triassic (Mitchell, 1979; Hutchison, 1989). With the recognition that Shan-Thai included Sumatra, the block was renamed Sibumasu (Sino–Burma–Malaysia–Sumatra) by Metcalfe (1984); both names are used in this book.

Figure 1.2  Sketch map showing some of the structural belts and major mineral and gemstone deposits of Myanmar. Gas and oil fields in the Central Depression are omitted here because of limited size of individual fields.

The concept of a pre-Miocene Western Burma block or terrane has since 1979 undergone fluctuating popularity and shifts in its supposed eastern boundary, which some authors place either on or near the late Cenozoic Sagaing Fault between Yangon and Putao. Better-defined is the small Burma plate of Curray et al. (1979), initiated in the Miocene and bounded in the east by the Sagaing Fault and in the west by the northward continuation of the Sunda–Andaman subduction or convergence zone into northwestern Myanmar. The proposed Mt Victoria Land block or terrane best exposed as the schists in the Indo-Burman Ranges (Mitchell, 1985) was inferred to underlie the Western Burma block and is within Curray et al.'s younger Burma plate.

Bender (1983) defined the westernmost part of the Shan-Thai block as a distinct structural zone, the Karen–Tenasserim unit. This consists of the late Paleozoic Slate belt or Mergui Group and the southern part of the Mogok Metamorphic belt to the west (Fig. 1.2) and was formerly known to Geological Survey of India geologists as the Shan Scarps. The boundary between the Karen–Tenasserim unit and the Shan Plateau coincides in the north with the Pan Laung Fault of Garson et al. (1976). A narrow belt of Mesozoic sedimentary rocks along this boundary, informally called the Paung Laung–Mawchi zone, has been interpreted as part of either a regional thrust or suture zone on which the proposed dextral strike-slip fault of Ridd and Watkinson (2013) is superimposed.

Structural belts in Myanmar that continue into western China or northeastern India include the high-grade schists, marbles, and migmatites of the Mogok Metamorphic belt (Fig. 1.3) which passes into the Lohit Plutonic Complex in India; ophiolites in the Tagaung–Myitkyina belt which are thought to continue into the Bangong-co suture zone, the Yarlung suture, or possibly both, in Tibet; the Shan Plateau with a Cambrian magmatic arc on its northwestern margin and thick carbonate successions of Ordovician to Devonian and Permian to Triassic age which extend northwards into the Baoshan block in Yunnan and probably into Tibet; and the late Triassic to early Jurassic flysch in the west and northwest of the Shan Plateau which may correlate with late Triassic flysch in the Luxi–Nujiang zone in Yunnan and early Jurassic flysch in central Tibet.

In Myanmar east of the Sagaing Fault regional northerly trending strike-slip faults and related structural complexity are supposedly widespread as a result of the India–Asia collision. We believe that these faults are much less significant than commonly supposed, and that this is demonstrated by the presence of only minor faulted offsets in the northeast-trending segment of the regional Mogok Metamorphic belt northeast of Mandalay.

There is no consensus as to the location and number of Jurassic–Cretaceous closed oceans or collisional plate boundaries in central and western Myanmar. We here infer (see Fig. 5.8) that the Shan-Thai or Sibumasu block and underlying Mogok belt, west of the well-established Triassic Paleo-Tethys suture in eastern Myanmar, lay east of a Meso-Tethys ocean, from which ophiolites were expelled and obducted eastward onto Shan-Thai (Sibumasu). Following a reversal in tectonic polarity, Shan-Thai was thrust westward onto a small Mergui block within Meso-Tethys. During final closure of Meso-Tethys by eastward subduction, late Triassic sediments derived from a West Burma or Mt Victoria block on the subducting plate were overridden by ophiolite and translated westward onto the West Burma or Mt Victoria block from which they were derived. Subsequent events are less speculative: there is almost a consensus that from the late early Cretaceous to the Miocene a Neo-Tethys ocean west of Myanmar subducted eastward generating the Popa–Loimye arc system and that this was succeeded by dextral displacement on the Sagaing Fault.

Figure 1.3  Map showing major structural belts described in text.

4. Evolution of Geological Mapping and Mineral Exploration

Before establishment of the British administration in Upper Burma in 1885 a number of geological reports and accounts of several metallic mineral and gemstone mine sites had emerged. Of particular geological interest was the discovery of Triassic fossils in the then very remote and inhospitable Indo-Burman or Western Ranges (Figs. 1.1 and 1.2) by the Geological Survey of India (Theobald, 1873), a discovery dismissed by many in authority long before its confirmation over a century later.

By the early 1900s systematic geological mapping by the Geological Survey of India was underway and expedited by the availability of one inch to a mile scale topographic maps. For the Survey the main minerals of interest were oil, coal, tin, and, during the two World Wars, tungsten. Numerous Geological Survey of India geologists, among them Brown, Middlemiss, La Touche, Clegg, and Chhibber contributed to the geological mapping of the western part of the Shan Plateau. By the start of World War II geological maps were available for the central plains including the oil and gas fields in the Salin Basin, for the Western Outcrops that border the Chin Hills and Arakan (now Rakhine) Hills in the Indo-Burman Ranges, and for the western and northern parts of the Shan States.

Investigations of many mineral deposits including those of world-class at the Bawdwin lead–zinc–silver mine and the jade mines in the unadministered territory of Kachin State led to publication of related district-scale geological maps. A field party from the Mawchi Mines company (Hobson, 1941) produced what is still the most detailed, although disputed, geological map of an 8000  km² area in Kayah State and adjacent areas. Early work, and the search for tungsten deposits during and after World War I, led to accounts of mineralization and geology (Oldham, 1856; Rau, 1930; Clegg, 1944) of the stratigraphically rather monotonous Tenasserim (now Taninthari) region.

Following World War II, departure of the Japanese and independence from Britain, Myanmar established a Geological Survey with an emphasis on mineral exploration; this eventually became the Directorate of Geological Survey and Mineral Exploration (DGSE). Regional work was limited by the rebellions in Karen and Kachin State and the Shan States and by the White and Red flag communist parties which briefly extended their activities into central Myanmar. All mineral deposits including gemstones were nationalized in the mid-1960s, beginning a long period during which mineral exploration was undertaken only by the DGSE, and mining by the State Mining and Gem Enterprises, under the Ministry of Mines; oil and gas exploration and production were carried out by what became the Myanmar Oil and Gas Enterprise now within the Ministry of Energy.

For some years immediately prior to and after nationalization geological mapping was accorded a very low priority. However, by the late 1960s, bilateral and later multilateral technical assistance and cooperation projects in the mineral sector and geological mapping had recommenced involving initially Swiss, British, Japanese, and German projects with the DGSE and Oil and Gas Enterprise, and United Nations-executed projects with the DGSE and with Yangon Arts and Science University. Projects with DGSE as well as joint programs with the State Mining Enterprises continued until the early 1980s. Subsequent improvement in the security situation then allowed the DGSE to resume systematic geological mapping. Meanwhile oil and gas exploration offshore began in 1972 with the first commercial discovery, Yadana, in 1982. Relative to mining the oil and gas industry benefitted greatly from far lower security risks and greater technical autonomy; from the late 1980s it enjoyed extensive scientific cooperation with geologists from French universities.

With the emergence of the State Law and Order Restoration Council (SLORC) in 1988, and the abolishment of Socialism, the 1994 Mining Law was promulgated. Foreign companies competed through bidding for metallic mineral and oil and gas exploration blocks, and joint ventures were formed with DGSE or State Enterprises. At least 25 exploration blocks for metallic minerals and coal were awarded in 1995–96. In 1997 the SLORC was replaced by the State Peace and Development Council; related administrative adjustments included a change in the ranking of Cabinet ministers relative to that of regional military commanders, and the retirement of virtually all ministers active prior to 1964. From a mineral exploration perspective, the mid 1990s under SLORC were almost a Golden Age relative to the three preceding decades and the subsequent two. Auctions of mining blocks ceased in 1997 although foreign participation in exploration and development of new oil and gas blocks has continued, and the Monywa copper mine has operated successfully as a joint venture and subsequent production share arrangement since 1997. The DGSE continued its systematic regional mapping until recently, happily unaffected by the questionable attitude of international development banks to State-funded geological mapping.

The elections and formation of a parliamentary government in 2010 more or less coincided with the acquisition by Chinese State-controlled companies of the Monywa copper mine and of two of the country's nickel prospects, and with privatization of the Bawdwin and Mawchi mines. The first post-SLORC private sector exploration concession with foreign participation was approved early in 2014. Finalization of revised Mining Rules and Regulations are awaited. Currently the Mines Department in the Ministry of Mines is the regulatory authority for many but not all of the commercial scale mines and for most of the artisanal mining in Myanmar.

University geology departments flourished in the late 1960s and 1970s, despite restricted links to the outside world, partly through the efforts and enthusiasm of the dynamic Mines Minister of the time, Dr. Nyi Nyi. The first accounts of metallogenic provinces in Myanmar were in unpublished presentations by Professor Ba Than Haq in 1970 and 1981. More recently, the university geology departments have been endeavoring to meet a mandated increase in the output of PhDs, and departmental cooperation with foreign institutions is being enthusiastically pursued. At the same time, restrictions on publication of scientific geological articles and on foreign earth science journals, in force with brief interruptions since the mid-1960s, were lifted, stimulating outputs of geological data. The Myanmar Geosciences Society has contributed significantly to this improvement, although geological research is still severely constrained by the minimal university research funds and consequent limits on the duration and location of field investigations.

An authoritative and highly informative account of the development of geology and geological institutions in Myanmar is provided by Win Swe (2009).

5. Mineral Deposits and Production

If jade, ruby, and sapphire are included, Myanmar arguably has the best mineral endowment of any country in Southeast Asia with the possible exception of Indonesia. Geological Survey of India staff were publishing articles on jade, gold, tin, and ruby and sapphire long before World War I, and descriptions of oil field geology date from the 1850s. The mineral deposits have been described in several books, memoirs, and review papers including those by Penzer (1922), Chhibber (1934b), Clegg (1944), Goossens (1978), and Tainsh (1950), and reported together with geology in Bender (1983), Win Swe (2012), and Barber et al. (2017). DGSE produced an unpublished but valuable listing of mineral deposits in the early 1970s.

The above volumes cite early reports of Myanmar's mineral deposits, extensive relative to those of most neighboring countries, and some describe fossil fuels of which oil and gas are included here. On metallic minerals the short paper by Soe Win and Malar Myo Myint (1998) and the more recent article by Gardiner et al. (2016) provide very useful summaries.

Some readers may be disappointed by the lack in this book of production data on minerals and gemstones. Because the focus here is on the geological environments or settings in which the various types of mineralization formed, we describe only the larger and more representative deposits and no attempt is made to provide lists, registers, catalogs, schedules, compilations, compendiums, cadasters, almanacs, or other tabulations of mineral occurrences or of quantities and values of mineral production. Some of this data is available in mining industry or commodity publications. However, official production figures, for example, 100  kg per year currently for gold, are at best only the most approximate of estimates, and a return to the regular release of up-to-date data for all minerals is eagerly awaited.

6. Organization of Contents

Following the Introduction, we divide Myanmar into structural belts (Fig. 1.3) and describe the geology, mineral deposits, and gemstones in each. Although north of the Andaman Sea the country is more or less bisected by the Sagaing Fault with a proposed right-lateral offset of at least a few hundred kilometers, there is no consensus on a displacement of this or any magnitude. We therefore separate the belts on either side of the fault. Those to the east, which include most of the demonstrably older or pre-Mesozoic rocks, are described first in Part 2, and those to the west in Part 3. In Part 4, we mention some possible correlations between magmatic arcs or stratigraphic formations in Myanmar and similar features in Tibet and Yunnan, and describe briefly the distribution of Myanmar's alluvial diamonds that are not limited to any one block.

This book omits a systematic description of faults, largely because any realistic assessment of fault displacement is critically dependent on a rather detailed knowledge of the stratigraphic or structural sequences that are offset. For most of Myanmar, information of this kind is available only in geological maps on at best reconnaissance scale.

7. Geographical Names and Geological Terms

The English language spelling of many place names including rivers was changed by the incoming SLORC administration in 1988. Most of the new names are used in this book, with the exception of those having a particularly well-established geographical name and geological connotation, for example Indo-Burman Ranges, Arakan Yoma or Pegu Yoma, and Mergui. The words mountain and river have a wide variety of equivalents according to the indigenous language of the area. Most common are those for mountain: Bum, Daung, Doi, Loi, and Taung, and for river or stream: Chaung, Hka, Jiang, and Nam. Names and locations of States and Divisions are shown in Fig. 1.4. Most mines in Myanmar are artisanal and so the term deposit is used here for any mineral accumulation that appears to have been worked profitably over many years whether or not at a commercial scale. Elevations are here given in meters but in some cases followed by the equivalent in feet to facilitate location of hill tops on nonmetric maps.

Figure 1.4  Map of States and Divisions of Myanmar.

References

Barber A.J, Crow M.J, Khin Zaw K, eds. Myanmar: Geology, Resources and Tectonics. Geological Society of London Memoir; 2017 (in press).

Bender F. Geology of Burma. Berlin: Borntraeger; 1983 293 p..

Clegg E.L.G. The Mineral Deposits of Burma. Bombay: Times of India Press; 1944 38 p..

Chhibber H.L. The Geology of Burma. London: Macmillan; 1934 538 p..

Chhibber H.L. The Mineral Resources of Burma. London: Macmillan; 1934 320 p..

Curray J.R, Moore D.G, Lawver L.A, Emmel F.J, Raitt R.W, Henry M, Kieckhefer R. Tectonics of the Andaman Sea and Burma. In: Watkins J.S, Monterdert L, Dickerson P.W, eds. Geological and Geophysical Investigations of Continental Margins. vol. 29. American Association of Petroleum Geologists, Memoir; 1979:189–198.

Dey P. Aerial photo interpretation of a major lineament in the Yamethin-Pyawbwe quadrangle. Union of Burma Journal of Science and Technology. 1968;1:431–443.

Fareeduddin, Dilek Y. Structure and petrology of the Nagaland–Manipur Hill ophiolitic melange zone, NE India: a fossil Tethyan subduction channel at the India–Burma plate boundary. Episodes. 2015;38:298–314.

Gardiner N.J, Robb L.J, Morley C.K, Searle M.P, Cawood P.A, Whitehouse M.J, Kirkland C.L, Roberts N.M.W, Tin Aung Myint. The tectonic and metallogenic framework of Myanmar: a Tethyan mineral system. Ore Geology Reviews. 2016;79:26–45.

Garson M.S, Amos B.J, Mitchell A.H.G. The Geology of the Country Around Neyaungga and Ye-ngan, Southern Shan States, Burma Overseas Memoir 2. London: Institute of Geological Sciences; 1976 HMSO, 71 p..

Goossens P.J. The metallogenic provinces of Burma: their definitions, geologic relationships and extension into China, India and Thailand. In: Third Regional Conference on Geology and Minersl Resources of Southeast Asia. 1978 Bangkok, Thailand.

Hobson G.V. Report on a Geological Survey in Part of Karenni and Southern Shan State Memoir Geological Survey of India, 74, Part 2. 1941:103–155.

Hutchison C.S. Geological Evolution of Southeast Asia Oxford Monographs on Geology and Geophysics, 13. Oxford: Clarendon Press; 1989.

Maung Thein. A preliminary synthesis of the geological evolution of Burma with reference to the tectonic development of Southeast Asia. Geological Society of Malaysia Bulletin. 1973;6:87–116.

Metcalfe I. Stratigraphy, palaeontology, and palaeogeography of the Carboniferous of Southeast Asia. Memoires de la Societe Geologique de France. 1984;147:107–118.

Mitchell A.H.G. Tectonic settings for emplacement of Southeast Asia tin granites. Geological Society of Malaysia Bulletin. 1977;9:123–140.

Mitchell A.H.G. Guides to Metal Provinces in the Central Himalayan Collision Belt; the Value of Regional Stratigraphic Correlations and Tectonic Analogies Memoir of the Geological Society of China No. 3. 1979:167–194.

Mitchell A.H.G. Collision-related fore-arc and back-arc evolution of the northern Sunda arc. Tectonophysics. 1985;116:323–324.

Oldham T Notes on the Coal Field and Tin-Stone Deposits of the Tenasserim Provinces. Selected Records in Geology, Government of India. vol. 10. 1856:31–67.

Penzer N.M. The Mineral Resources of Burma Federation of British Industries: Intelligence Department. London: Routledge & Sons; 1922. .

Rau R.S. The geology of the Mergui district. Memoirs of the Geological Survey of India. 1930;55:1–62.

Ridd M.F, Watkinson I. The Phuket-Slate belt terrane: tectonic evolution and strike-slip displacement of a major terrane on the Sundaland margin of Thailand and Myanmar. Proceedings of the Geologists’Association. 2013;124:994–1010.

Soe Win, Malar Myo Myint. Mineral potential of Myanmar. Resource Geology. 1998;48:209–218.

Stamp L.D. An outline of the Tertiary geology of Burma. Geological Magazine. 1925;59:481–501.

Tainsh H.R. Tertiary geology and principal oilfields of Burma. American Association of Petroleum Geologists Bulletin. 1950;34:823–855.

Theobald W. The geology of Pegu. Geological Survey of India Memoir. 1873;10:198–359.

Win Swe. Strike-slip faulting in central belt of Burma. In: Haile N.S, ed. Regional Conference on the Geology of South-East Asia (abs.). 1972 Annex Geological Society Malaysia Newsletter, No 34.

Win Swe. The development of geosciences in Myanmar: a brief overview. Journal of the Myanmar Geosciences Society. 2009;2:1–28.

Win Swe. Outline geology and economic mineral occurrences of the Union of Myanmar. Journal of the Myanmar Geosciences Society. 2012;1:215 Special Publication.

Part 2

Myanmar East of the Sagaing Fault

Outline

Chapter 2. The Shan Plateau West of the Salween

Chapter 3. Myanmar East of the Salween: The Sibumasu–Mong Yawng Arc Collision and Related Tin Mineralization

Chapter 4. The Mergui Group and Equivalents in the Slate Belt, Phayaungtaung and the Gaoligong Range (Northeastern Myanmar)

Chapter 5. Paung Laung–Mawchi Zone

Chapter 6. Granites, Minor Intrusions, and Mineralization in the Slate Belt, Phayaungtaung, and Gaoligong Range

Chapter 7. Mogok Metamorphic Belt

Chapter 8. Tagaung–Myitkyina Belt and Katha–Gangaw Range

Chapter 2

The Shan Plateau West of the Salween

Abstract

The Shan Plateau is part of the small Shan–Thai or Sibumasu continental block, which extends from Malaysia and Thailand through eastern Myanmar into China. East of the Salween River both the block and geological boundary of the Plateau are a late Triassic suture zone. The western margin of the Plateau is the western margin of the Chaung Magyi Group and the Shan Scarp. The late Proterozoic Chaung Magyi Group at the base of the Plateau sequence is underlain with inferred structural break by the Mogok Metamorphic belt. The Chaung Magyi is overlain by the Bawdwin Volcanics beneath an unconformable sequence comprising the late Cambrian Pangyun Formation and an Ordovician to Devonian succession of carbonates, mudstones, and Silurian quartzites. Oolitic sedimentary ironstones occur within the late Devonian succession. Early Carboniferous sandstones and shales of the Taungnyo Group are present near Loikaw on the Plateau's western margin. Silurian–Devonian rocks and the Taungnyo Group are overlain unconformably by the Lower Permian Magiye Conglomerate and Spinomartinia prolifica shale sequence, which underlies the mid-Permian to Triassic Plateau Limestone basal unconformity. Triassic and older strata in the Mandalay–Kyaukse area show low-grade regional metamorphism. Near the Plateau's western margin the Plateau Limestone is overlain by unconfirmed evaporites followed by complexly folded late Triassic to early Jurassic flysch, and late Jurassic to early Cretaceous limestones, coals and very localized volcanic rocks above an unconformity. The conglomeratic Kalaw Red Beds rest unconformably on the flysch and on dolomitic Plateau Limestone. A major orogeny preceded Cambrian arc volcanism and associated deposition of submarine volcanogenic massive Ag Pb Zn sulfides at the Bawdwin mine and may have generated orogenic quartz–gold veins in the Chaung Magyi. A second orogeny probably accompanied the generation of diamictites and eastward emplacement of the Taungnyo Group onto the Plateau as proposed here. Orogeny related to late Triassic collision of Sibumasu with a W-facing Permian–Triassic magmatic arc was accompanied east of the Salween River by intrusion of peraluminous granites and west of the Salween by W-directed thrusting. A further orogeny is inferred during emplacement, probably from the west, of the early Jurassic flysch followed by a reversal in orogenic polarity and eastward subduction. Since the early Cretaceous this part of the Shan Plateau has occupied a back-arc area in which high heat flow may have generated antimony mineralization in anticlines in Upper Paleozoic slates, and perhaps also generated the lead–baryte deposits in Ordovician and younger carbonates. Ruby and sapphire occur in metacarbonates at three localities on the Plateau, which include Mong Hsu, currently Myanmar's main source of gem-quality ruby.

Keywords

Antimony deposits; Bawdwin VMS deposits; Carbonate-hosted lead–zinc; Microcontinent; Orogenies; Ruby–sapphire

Chapter Outline

1. The Plateau and Its Boundaries

2. Stratigraphic Units and Granites

2.1 Late Proterozoic Chaung Magyi Group and the Tawngpeng Granite

2.1.1 Distribution and Lithology of the Chaung Magyi

2.1.2 Age of Chaung Magyi and Tawngpeng Granite

2.2 Cambrian to Devonian, Northwestern Margin of the Shan Plateau

2.2.1 Bawdwin Volcanic Formation

2.2.2 Pangyun Formation

2.2.3 Ordovician to Devonian

2.3 Cambrian to Devonian, Pwin-Oo-Lwin, Mandalay Division

2.4 Cambrian to Devonian of the Southern Shan State

2.5 The Carboniferous Taungnyo Group on the Shan Plateau

2.5.1 Linwe and Loikaw Areas, Shan Plateau

2.5.2 Ngayan Chaung turbidites, Lebyin

2.5.3 Taungnyo Group Equivalents in Yunnan

2.6 Early Permian Magiye Conglomerate, Spinomartinia prolifica Shale, and Yinyaw Formation

2.6.1 Magiye Conglomerate and Spinomartinia prolifica Shale, Kyaukse East

2.6.2 Spinomartinia prolifica Shale at Lebyin

2.6.3 Yinyaw Beds, Loikaw West

2.6.4 The Lower Permian in West Yunnan

2.6.5 Late Paleozoic Unconformities and Glacial Diamictites

2.7 Plateau Limestone Group

2.7.1 Evolving Ideas on Plateau Limestone Stratigraphy

2.7.2 Thitsipin and Moulmein Limestone

2.7.3 Nwabangyi Dolomite

2.7.4 Natteik Limestone

2.8 Uppermost Triassic to Cretaceous, Southern Shan State

2.8.1 Shweminbon Formation and Pinmon East Limestone

2.8.2 Loi-an Formation and Equivalents

2.8.3 Emplacement of the Shweminbon and Loi-an Formations

2.8.4 Patchaung Volcanics

2.8.5 Pinnacle Limestone

2.8.6 Kalaw Red Beds

2.8.7 Late Cenozoic Sediments

2.9 Uppermost Triassic to Cretaceous, Northern Shan State

2.9.1 Pangno Evaporites

2.9.2 Napeng Formation

2.9.3 Tati Limestone and Emplacement of Flysch and Ophiolite

2.9.4 Hsipaw Red Beds

3. Selected Structural Features on the Shan Plateau

4. Mineral Deposits on the Shan Plateau

4.1 Quartz–Gold Veins in the Chaung Magyi Group

4.2 Lead–Zinc–Silver Deposits Associated With Cambrian Rocks

4.2.1 Bawdwin Lead–Zinc–Silver Mine, Northern Shan State

4.2.2 Lead–Silver Mineralization at Yadanatheingi, Northern Shan State

4.3 Carbonate-Hosted Lead–Zinc and Barite Mineralization

4.3.1 The Ordovician Lead Belt

4.3.2 The LonghKeng Zinc (Smithsonite) Deposit

4.4 Sabetaung Copper Prospect

4.5 Sedimentary Ironstone Deposits

4.5.1 Kya-Twinye Ironstone

4.5.2 Paung Pet Iron Deposit

4.6 Thayetchaung Gold–Copper Skarns, Konni Gold Mineralization, and Ye-bu Magnetic Anomaly

4.6.1 Thayetchaung Skarn Mineralization

4.6.2 Konni Gold Prospects

4.6.3 Ye-bu Magnetic Anomaly

4.7 Antimony Deposits and Occurrences

4.8 Gemstone Deposits

4.8.1 Mong Hsu

4.8.2 Wan Ying and Wan Hatt

4.8.3 Genesis of the Ruby

References

1. The Plateau and Its Boundaries

The Shan Plateau is described first because its stratigraphic column, with late Proterozoic, late Cambrian to early Carboniferous, and Permian to Cretaceous strata (Fig. 2.1, Table 2.1) is more complete than that of any other part of Myanmar. The Plateau roughly coincides with the Northern, Southern and part of the Eastern Shan State, and Mandalay Division east of the Shan Scarp and south of the Shweli River (Fig. 2.2). The structurally lowest and westernmost rock unit on the Shan Plateau is the Mogok Metamorphic belt that extends far to the north and arguably also south of the Plateau and is described separately (Chapter 7). Plateau elevations are around 1000–1500  m elevation in the west with dissection and relief increasing eastward where many hilltops are above 2000  m in elevation. The eastern boundary of the Plateau is here defined by the late Triassic suture zone, which is situated east of the Salween River and separates the Plateau from the Mong Yawng block (Chapter 3), part of the Eastern Shan State.

Figure 2.1  Stratigraphic column, Shan Plateau, generalized from western part of Northern and Southern Shan States.

The geology of the Plateau has been established from local surveys by geologists of the Geological Survey of India (GSI), by University of Yangon and other Myanmar university geologists (e.g., Ba Than Haq and Maung Thein, 1970; Maung Thein, 1972; Myint Lwin Thein, 1973; Aye Ko Aung, 2012a,b) and since the late 1960s by the Directorate of Geological Survey and Mineral Exploration (DGSE) alone or jointly with foreign cooperation projects. This mapping has been largely confined to the western and northwestern parts of the Plateau, within 50–100  km of its margin. Reconnaissance mapping to the east, mostly by DGSE, has shown that a stratigraphy similar to that established in the west continues beyond the Salween River. However, this chapter is based mainly on the better-known western and northwestern regions.

Table 2.1

Stratigraphy of the Shan Plateau

Figure 2.2  Map of Shan Plateau showing distribution of Chaung Magyi, Mogok Metamorphics adjacent to Plateau, and localities and selected structures referred to in text. Southern-most area (Moulmein) not shown. NCA , Ngayan Chaung anticline; OGT , Ohn Gyaw thrust; PMZ , Paung Laung-Mawchi zone; T , Taungnima Taung; TMB , Tagaung–Myitkyina belt.

Similarities in the stratigraphy of the Shan Plateau in Myanmar to that of northwestern Thailand, southwestern Yunnan, and western Malaysia have for long been considered to define a small continental block or terrane in which Sumatra was later included. This is the West Malaya block of Stauffer (1974), the Southeast Asia Zone 1 of Mitchell (1976, 1977) subsequently expanded as the Tibet–Western Southeast Asia block (Mitchell, 1979), the Thai–Malay Peninsular block of Ridd (1980), the Shan–Thai block of Bunopas (1981), the Sibumasu block of Metcalfe (1984), and the Sinoburmania of Hutchison (1989). Broad stratigraphic correlations within the block are discussed by these authors, and for example, by Boucot (2002) and Aye Ko Aung (2012a,b).

The Mergui Group or Slate belt and the Mogok Metamorphic belt lie between the northerly trending Shan Scarp in the east and either the Sagaing Fault, or the hypothetical Shan Boundary Fault located east of the Sagaing Fault, and are included in the Shan–Thai or Sibumasu blocks by many authors. Bender (1983) considered that the Mergui Group and Mogok Metamorphic belt formed a distinct geological province, block or terrane, which he called the Karen–Tenasserim unit and was known to GSI geologists as the Shan Scarps, situated west of the Shan Scarp itself. The eastern margin of the Karen–Tenasserim unit, near the base of the Shan Scarp, comprises a narrow structural zone of Mesozoic sedimentary rocks locally bounded by the Pan Laung Fault of Garson et al. (1976), and herein referred to as the Paung Laung–Mawchi zone.

2. Stratigraphic Units and Granites

The term Plateau or Shan Plateau sequence is applied here to the upward stratigraphic succession from the Chaung Magyi Group through a regional late Cambrian unconformity to the early Carboniferous. Younger more widespread units (e.g., Spinomartinia prolifica shale, Plateau Limestone) are included in the Plateau sequence only where underlain by the Chaung Magyi to early Carboniferous succession. Most of the stratigraphic units described in the text are included in Table 2.1.

2.1. Late Proterozoic Chaung Magyi Group and the Tawngpeng Granite

2.1.1. Distribution and Lithology of the Chaung Magyi

The oldest unit on the Plateau, the Chaung Magyi Group, is widely distributed in the western part of the Northern and Southern Shan States and in Mandalay Division. The name was given by La Touche (1913) to the thick metasedimentary unit well-exposed in the south-flowing Chaung Magyi river valley north of Sedawgyi dam, which is 80  km northeast of Mandalay. Here the Chaung Magyi Group occupies a 7-km-wide north-trending belt overlain in the east by late Cambrian rocks which outcrop in the lower part of the west-facing Shan Scarp. To the west a regional fault separates the Chaung Magyi and the Mogok Metamorphic belt.

North of the Chaung Magyi valley the Chaung Magyi Group swings to the east and then southeast around the regional southeast-plunging Kalagwe Syncline. From here the Group continues eastward and then northeast (Fig. 2.2), along the northwestern margin of the Shan Plateau through the Northern Shan State, passing west of the Bawdwin mine and continuing northeastward along the Myanmar–China border beyond Namhkam (Figs. 2.2 and 2.3). The distribution of the Chaung Magyi Group in the Northern Shan State is shown on maps by Chhibber (1934a), Earth Sciences Research Division (1977), and Myanmar Geosciences Society (2014), and for parts of the State by Mitchell et al. (1977). Northeast of Namhkam the Chaung Magyi is intruded by the