Structural controls on gold mineralization in southeastern Truong Son fold-thrust belt and its significance in regional metallogeny

Transcription

1 Structural controls on gold mineralization in southeastern Truong Son fold-thrust belt and its significance in regional metallogeny Hai Thanh Tran, Truong Xuan Le Hanoi University of Mining and Geology, Hanoi, Vietnam Khin Zaw, Takayuki Manaka CODES Centre of Excellence in Ore Deposits, University of Tasmania, Australia

2 Introduction Current mainland SE Asia is made up of microcontinents or crustal blocks such as the Indochina, Sibumasu and West Myanmar. (Metcalfe, 2013) Indochina Block comprises broken-up remnants of Gondwana, welded with other blocks successively during a number of basin closure and plate-plate assembly. Truong Son Fold-Thrust Belt forms the core of Indochina Block (Metcalfe, 2013) 4/9/2015 2

3 WEST MYANMAR PLATE Myanmar SHAN-THAI PLATE Thailand Laos CHINA SOUTH CHINA PLATE INDOCHINA PLATE SUTURE ZONES Late Silurrian Tam Ky Phuoc Son Early Carboniferous or Late Permian? : Song Ma & Ailaoshan Early Carboniferous or Late Permian? : Dian-Qiong Suture Late Triassic: Jinghong-Nan-Sra Taiwan Kaeo Late Triassic: Changning Menglian- Inthanon-Bengtong Raub Late Cretaceous: Sagaing Cambodia Vietnam Philippines Malaysia Regional tectonic setting of Truong Son Fold-Thust Belt (TSFTB) 4/9/2015 3

4 Introduction TSFTB is limited by: Changning Menglian - Inthanon - Bengtong Raub Suture system: Palaeo-Tethys Suture Zone and Jinghong-Nan- Sra Kaeo system: remnant of a closed Permian back-arc basin behind the Sukhothai island-arc system. Northeastern margin of TSFTB is bounded by Song Ma-Ailao Shan suture Tam Ky - Phuoc Son Suture limits the southern exposed area of TFTB (Metcalfe, 2013) 4/9/2015 4

5 Focus of this presentation Regional lithotectonic framwork of Truong Son Fold-Thrust Belt (TSFTB) General geology of TSFTB Deformational pattern in the TSFTB Major Au (- Cu) mineralization in the TSFTB. NW segment Central segment Southeastern segment Implication of the regional tectonics to gold mineralization in the TSFTB 4/9/2015 5

6 Regional litho-tectonic assemblages of the TSFTB The area comprises numerous lithotectonic assembages of differing composition, age and origin 4/9/2015 6

7 The Precambrian 4/9/2015 7

8 Paleozoic: passive margin, suture-related and arc assemblages Mid. Paleozoicsyn-orogenic intrusives E. PZ pasive margin sediments E. PZ ophiolite remnants 4/9/2015 8

9 Mesozoic: arc, syn-tectonic magma/sedimentary assemblages 4/9/2015 9

10 Cenozoic: open of East Sea basin: regional-wide flood basalt and inter-continental sedimentation 4/9/

11 Deformational pattern in TSFTB Experienced multi-phase deformational history Overprinting of deformational pattern Regional structual pattern controlled by fold-thrust architecture 4/9/

12 Multiple deformational events in TSFTB D 1 shear Triassic Granitoid F 2 `S 1 After Tran et al (in GR 2013)

13 Multiple deformational events in TSFTB B (After Tran et al, in GR 2013) D A C

14 Major tectonic events in the TSFTB 4/9/

15 Major Au (- Cu) mineralization in TSFTB Occurrence of Cu-Au deposits is confined to three main regions; - Northwwest (Phu Bia) - Central (Sepon, Mexi) - Southeastern (Phuoc Son- Bong Mieu) The belt yields 50 % of gold & 60 % of copper resources of Indochina Terrane Gold resources of Indochina Terrane (c.a. 23 Moz) Dalat-Kratie (6.0 %) Unknown (8.9 %) Sukhothai (12.1 %) Loei (24.7 %) Truong Son (48.3 %)

16 Ban Phonxai Pha Gnai Phu Wab Nam Ve Ban Houayxai LCT Phu Kham * Summarised from PanAust website Nam The NNN Phu He Bohr Thong KTL Tharkhek Phu Noum Modified after Brost (2011) NW segment: Phu Bia area Cu & Au deposits associated with L Carboniferous - E Permian ( Ma) magmatic units Cu, Au & Ag resources* comprise; - Phu Kham (1.3Mt Cu, 1.9Moz Au & 17Moz Ag) - Ban Houayxai (2 Moz Au & 17 Moz Ag) - LCT (0.8 Moz Au, 5 Moz Ag) - KTL (0.4 Mt Cu & 0.5 Moz Au) Deposit types include; - Porphyry-related skarn/skarn Cu-Au (e.g., Phu Kham, KTL, Bohr Thong) - Epithermal Au-Ag (e.g., Ban Houayxai, Phu He) - VHMS Cu-Pb-Zn (e.g., Ban Phonxai)

17 Phu Kham porphyry-related skarn Cu-Au Late Carboniferous (c.a. 310 Ma) andesite porphyry intrusions Exoskarns in volcaniclastic unit Orebody on the Mesozoic Khorat red bed Andesite porphyry bornite pyrite chalcocite From Kamvong (2007) Phu Kham North schematic section from Phu Bia Mining (2010)

18 Ban Houayxai Au-Ag deposit* A thick andesite & volcanic breccias (Early Permian; 286 ± 4 Ma) Two Au mineralised systems; - Low/intermediate sulphidation (Ag-rich) epithermal - Sediment-hosted Porphyritic andesite Au-bearing quartz-sulphide vein 1 cm * Information & figures from Brost (2011) & Manaka (2008)

19 Sediment-hosted system at Ban Houayxai Late stage sediment-hosted mineralisation High gold in arsenic pyrites Light sulphur isotope values in vein samples Carlin-like characteristics 40 ppm Au 1.6 ppm Au Pyrite after etched 200 µm 66.8 g/t Au & 316 g/t Ag Photo from Brost (2011)

20 Central portion: Sepon Au-Cu District Cu-Au mineralisation associated with two intrusion centres Early Permian rhyodacite porphyry intrusions Carbonate-rich sedimentary rock sequence Rhyodacite porphyry Modified after MMG (2010) Zircon U-Pb age of ca. 300 Ma*

21 Cu-Au mineralisation at Sepon Supergene Cu Supergene Cu Primary mineralisation; - Porphyry Cu-Mo - Skarn Cu (-Au) - Sediment-hosted Au (Carlin-like) Secondary mineralisation; - Supergene/exotic Cu - Karst fill Au Sediment-hosted Au Dolomite Jasperoid Shale From MMG website From Cromie (2005)

22 Southeastern portion: Phuoc Son Au deposit Indochina Goldfield started exploration in 1995 Olympus Pacific Minerals (now Besra) discovered Bai Dat in 1999 A large intrusion-related Au system

23 Phuoc Son Au deposit, Vietnam 23 2 g/tau and 5.2 g/tag Host rock

24 Metal zonation at Phuoc Son Cu-Au-W-Mo Au-Cu Au Two economic orebodies - Bai Dat - Bai Go A number of gold prospects in tenement Spatial metal association; - Cu-W-Mo in Northwest (skarn & intrusion-hosted) - Pb-Zn in South (sediment-hosted) Pink garnet at Khe Rin Au-Pb-Zn Modified after Besra website

25 Phuoc Son Deposit (Au) Gold is associated with suturing deformation; formed concordant with the thrusting and later modified by late tectonic overprinting Sul Ss1 F2 F3 25

26 Bong Mieu mineralization Ho Ray deposit U 2 Nui Kem deposit Bong Mieu River

27 Bong Mieu mineralization Major generation of mineralization (Au+/-Pb-Zn) 4/9/

28 Bong Mieu mineralization 4/9/

29 Regional metallogenic implication in TSFTB TSFTB hosts numerous types of Au, Cu and related mineralizations Several phases of ore deposition Minerizations partly controled by regional structures and orogenic periods 4/9/

30 Sequence of deformational events and relationship to Au mineralization NP- -O S-D P-T Nui Vu/ Avuong Forms. Chu Lai/ Dai Loc Granites D-C?? Hai Van Granite Time to present KZ?? 4/9/

31 Structural model for mineralization 2 km Modified after Grove et al., 2003 Meteroic fluid Hg-Sb Shallow zone Au-Sb 5 km Deposits in syn orogenic env. 10 km Intermediate zone Au-As-Te Au mineralization Deep zone Au-As (Including Scarn) 4/9/ km Intermediate to high T fluid from deep crust

32 Regional tectonic implication multi-stage crustal growth and thermo-tectonic overprinting (Morley et al. 2013) Cartoon model showing restoration of tectonic configuration of Indochina prior to Cenozoic lateral extrusion of terranes along major faults (constructed from various data) and posible relationship to regional Au-Cu mineralization 4/9/

33 Concluding remarks New works have led to recognition of numerous thermotectonic events that created and/or modified the TSFTB and produced complicated regional tectonic configuration. Many Au (-Cu) mineralized areas have been discovered within the TSFTB. Mineralizations include numerous genetic types, mostabundance are porphyry-related skarn, Carlin type, sedimentary-hosted systems. Two major periods of Au mineralizations were identified. Most of mineralizations either asociated with or controlled by major regional structural breaks. Ore deposition were contemporaneous with 2 major phases of regional orogeny, which took ca. 400 Ma and ca. 250 Ma. Many of Au mineralizations in the TSFTB, however, have not properly investigated. This warrants more comprehensive regional studies to adequately define the generic models and relationship between Au mineralization and regional structures. 4/9/

34 Acknowledgements: This work was supported by a Vietnam s NAFOSTED fund to Hai Tran (Hanoi University of Mining and Geology), Australian Leadership Awards to Hai Tran and the Ore Deposits of SE Asia project led by Khin Zaw (CODES Centre, University of Tasmania, Australia). Thank you for your attention!