Gold mineralization of the Thone Myae Song area, Sagaing Region, northern Myanmar

https://doi.org/10.1016/j.jseaes.2021.104749Get rights and content

Highlights

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    Central Magmatic-Volcanic Belt (CMVB) hosts several Au-Cu ore types and Thone Myae Song deposit.

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    Formation of CMVB is related to the eastward subduction of Indian Ocean floor during the Cretaceous.

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    Sericite-carbonate alteration is important as confines to the margins of mineralized veins.

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    Fluid immiscibility was a major trigger to the precipitation of gold and base metals at EE3 deposit.

Abstract

Several gold deposits are found in the Central Magmatic-Volcanic Belt (CMVB) of Myanmar, which forms a nearly N–S-trending, 1500-km-long arc extending from the Andaman Sea to northern Myanmar. The CMVB consists of Cretaceous granitoids intruded into folded andesites and pillow basalts (Mawgyi Andesite) which rest on cherts, talc-schists, mudstones and phyllites. The EE3 gold deposit is part of gold mineralization in the Thone Myae Song area, located in the Kawlin–Wuntho block in the northern part of the CMVB. The orebodies occur as sulfide-bearing massive quartz veins hosted by Mawgyi Andesite. Based on the mineral assemblages and cross-cutting relationships, three mineralization stages are identified in the EE3 gold deposit: Stage-I quartz-carbonate-sulfide veins; Stage-II quartz-carbonate veins intersecting the Stage-I veins; and Stage-III quartz-carbonate-sulfide veins parallel to the Stage-I veins. The main hydrothermal alteration minerals are sericite, epidote, chlorite and calcite. Three main types of fluid inclusions were distinguished from the mineralized quartz veins hosted by Mawgyi Andesite: liquid-rich aqueous fluid inclusions (Type A), vapor-rich aqueous inclusions (Type B), and H₂O-CO₂-NaCl inclusions (Type C). The latter occurs only in the Stage-I veins. The ore-forming conditions are estimated from fluid inclusions in the Stage-I, Stage-II and Stage-III veins to be at 180 °C and 28 bars, 176 °C and 26 bars, and 158 °C and 21 bars, respectively. The formation pressures of the Stage-I, Stage-II and Stage-III mineralization correspond to a shallow depth of 300 m, 280 m, and 225 m, respectively. Based on the ore and alteration mineral assemblages, and estimated temperature and pressure conditions of the mineralization, the EE3 gold deposit was formed in an epithermal condition.

Introduction

Myanmar has long been known to be richly endowed in ore deposits of tin, tungsten, copper, gold, silver, zinc, lead, gemstones, jade and hydrocarbons (Chibber, 1934a, Chibber, 1934b, Brown, 1936, Griffith, 1956, Marlar Myo Myint, 1998; Gardiner et al., 2014; Khin Zaw, 2017, Khin Zaw et al., 2017; Mitchell, 2018). The Thone Myae Song area is one of the high-grade gold occurrences in the (Banmauk-Wuntho district), northern Myanmar. The EE3 gold deposit is an important occurrence in the Thone Myae Song area and located 35 km to the south from Banmauk Township, Sagaing Region, Northern Myanmar. Gold Mineralization is hosted in Mawgyi Andesite at the Thone Myae Song area. The Mawgyi Andesite has been interpreted by Mitchell (1993) to represent an oceanic volcanic arc thrusted over the West Myanmar Block as a nappe during the Cretaceous. Gold mineralization in the Banmauk-Wuntho district occurs generally as gold-bearing quartz or quartz-carbonate veins with ore grades from 20 to 100 g/t Au and has been mined by local companies (Mitchell et al., 1999). Presently, there is scant summations of the mineralogical significance of the Banmauk-Wuntho district, with no comprehensive works on deposit geology, host rock alteration, ore mineralogy, and fluid mineralization properties. In this paper, we introduce regional and local geological settings and present new mineralogical, sulfur isotope and fluid inclusion data for the EE3 gold deposit of the Thone Myae Song area. Our aims are to elucidate the genesis of the deposit including further discussion on the implications for gold mineralization in the CMVB.

Section snippets

Regional geological setting

Gold deposits in Myanmar occur in six main tectonic belts: (1) porphyry-type copper ± gold ± molybdenum and related epithermal gold mineralization as well as intrusion-related and orogenic gold mineralization in the Central Magmatic Arc or Central Magmatic-Volcanic Belt (CMVB); (2) orogenic gold mineralization along the Tagaung–Myitkyina Belt; (3) skarn-type gold and gold-copper mineralization in marble and granite within the Mogok Metamorphic Belt; (4) sedimentary rock-hosted epithermal gold

Local geology

The geological map of the Banmauk-Wuntho district is shown in Fig. 2b. The Banmauk-Wuntho district lies in the northeastern part of the Kawlin-Wuntho block and it is located at the northern segment of the CMVB (Barber et al., 2017; Khin Zaw, 2017, Khin Zaw et al., 2017; Mitchell, 2018). Locally the Kawlin-Wuntho block is composed of intermediate to felsic igneous rocks and bordered in the west by the Chindwin Basin and in the east by a 1500-km-long N–S-trending right lateral strike slip fault

Samples and methods

A total of about 200 samples of volcanic rocks, altered rocks, and ores were collected during field investigations. Fifty-five samples were collected from the underground workings at the EE3 gold deposit. Thirty petrographic thin sections and 40 polished sections were prepared to examine textural characteristics of the rocks, alteration minerals and ore minerals with a Nikon Eclipse E600 POL microscope equipped with an AdvanCam-U3II camera. A scanning electron microscope equipped with energy

Deposit geology

Three orebodies are being mined in the Thone Myae Song area. EE3, Myauk Let Sho, and Thapan Aing, which are here referred to as deposits, and with this study focusing on the EE3 gold deposit (Fig. 3). Collectively, gold mineralization in the Thone Myae Song area occurs as massive veins, stockworks and disseminations and the general orientation of quartz veins is N–S.

The principle stratigraphy is composed of Mawgyi Andesite (Cretaceous), phyllite and mudstone of the Shwedaung Formation (Upper

Whole-rock composition

A total of 25 samples from the EE3 gold deposit were selected for whole-rock composition analysis (location of samples in Fig. 8), including fresh and hydrothermally altered volcanic rocks. The results of whole-rock major and trace element analyses are listed in Table 1. The SiO2 concentrations of the volcanic rocks in the EE3 gold deposit range between 44.8 wt% and 73.5 wt%. The Al2O3 concentration of varies between 5.2 wt% and 18.3 wt%. The K2O content ranges from 0.1 wt% to 2.6 wt%, while

Hydrothermal alteration and alteration mineral assemblages

Samples from the EE3 gold deposit are plotted on an alteration box plot diagram using the alteration index (AI) against the chlorite-carbonate-pyrite index (CCPI) proposed by Large et al. (2001). The samples from the EE3 gold deposit display (1) chlorite-carbonate alteration, (2) sericite-carbonate alteration, and (3) epidote-carbonate ± albite alteration. The data show that one sample is plotted in the least altered box, and the other samples are near the epidote/calcite boundary. Rock samples

Mineralization style

The style of mineralization includes massive quartz-sulfide vein, stockwork, dissemination and veinlets. Based on field observations (cross-cutting relationship) and ore mineralogy, three main vein types were identified in the EE3 gold deposit: (1) massive N–S-trending, steeply dipping, quartz-carbonated-sulfide veins (Fig. 10a, b), which are in turn classified as the first-generation Stage-I veins; (2) E–W-trending quartz-carbonate Stage-II veins that crosscut the N–S-trending Stage-I veins (

Sulfur isotopes

The δ34S values of nine pyrite grains of the EE3 gold deposit Stage-I veins range from −3.0‰ to + 0.5‰ (Fig. 13a) and the δ34S values of nine pyrite samples of Stage-III veins range from −2.4‰ to −1.1‰ (Fig. 13b). The determined δ34S values are summarized in Table 2 and shown in histograms (Fig. 13a, b). The range of δ34S values are relatively narrow, with a unimodal distribution.

Fluid inclusion petrography

Fluid inclusions in the quartz veins of the EE3 gold deposit were examined in this study. The fluid inclusions are petrographically classified as primary and secondary in origin based on the criteria by Roedder (1984). Those fluid inclusions aligned along growth zones in quartz crystals were interpreted as primary inclusions, as well as occurring as isolated inclusions, in random distributions, or in clusters are also categorized as primary in origin (Fig. 14a, b, c, e, f, h, i). Secondary

Source of sulfur

The bulk sulfur isotopic composition of the fluids can be interpreted from the δ34S values of sulfides assuming the absence of sulfate. There are three major reservoirs on Earth, with different sulfur isotopic compositions: (a) mantle or magmatic sulfur (0% ± 3‰); (b) seawater sulfate (+20‰, present as SO₄2−); and (c) reduced sulfur or biogenic sulfur in sedimentary rocks (less than0‰) (Hoefs, 1975). In this study, the δ34S values of the sulfides narrowly range from −3‰ to + 0.5‰, indicating a

Conclusions

The EE3 gold deposit consists of hydrothermal veins hosted by the Mawgyi Andesite, which can be classified into three stages: Stage-I N–S-trending quartz-carbonate-sulfide veins, Stage-II E–W-trending quartz-carbonate veins, and Stage-III N–S-trending quartz-carbonate-sulfide veins. Based on alteration mineral assemblages, three alteration zones were identified in the EE3 gold deposit: (1) proximal (sericite-carbonate alteration), (2) intermediate (epidote-carbonate ± albite alteration), and

CRediT authorship contribution statement

Htet Sandar Aung: Data curation, Writing - original draft. Kotaro Yonezu: Supervision. Akira Imai: Writing - review & editing. Thomas Tindell: Supervision, Conceptualization, Methodology. Koichiro Watanabe: Visualization, Investigation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We would like to express our gratitude to the Japan International Cooperation Agency (JICA), Shigen No Kizuna Program, for the PhD scholarship to the first author and for its financial support. The first author thanks Dr May Thwe Aye for facilitating the scholarship program and project. Special thanks to Professor Khin Zaw who read earlier versions of the manuscript and provided helpful advice for the manuscript. We are greatly indebted to, and appreciative of, two anonymous reviewers for their

References (58)

  • S.M. Sterner et al.

    Synthetic fluid inclusions in natural quartz I. Compositional types synthesized and applications to experimental geochemistry Geochim

    Cosmochim. Acta.

    (1984)
  • Barber, A.J., Khin Zaw, Crow, M.J., 2017. The pre-Cenozoic tectonic evolution of Myanmar. In: Barber, A.J., Khin Zaw,...
  • M.E. Barley et al.

    Jurassic to Miocene magmatism and metamorphism in the Mogok Metamorphic Belt: implications for the India-Eurasia collision in Myanmar

    Tectonics

    (2003)
  • Belousov, A., Belousova, M., Khin Zaw, Manaka, T. 2012. Holocene gravitational collapse and explosive eruptions of...
  • R.J. Bodnar

    Revised equation and table for determining the freezing point depression of H2O-NaCl solutions

    Geochim. Cosmochim. Acta

    (1993)
  • J.C. Brown

    India’s Mineral Wealth: A Guide to the Occurrences and Economics of the Useful Minerals of the Indian Empire

    (1936)
  • H.L. Chibber

    The Geology of Burma

    (1934)
  • H.L. Chibber

    The Mineral Resources of Burma

    (1934)
  • Cho Cho Aye et al.

    The nature and distribution of gold in the ores from Kyaukpazat Mine, Myanmar

    Journal of Myanmar Academy of Arts and Sciences

    (2007)
  • P.L.F. Collins

    Gas hydrates in CO2-bearing fluid inclusions and the use of freezing data for estimation of salinity

    Econ. Geol.

    (1979)
  • DGSE (Department of Geological Survey and Exploration), 1976. Geology and Exploration Geochemistry of the...
  • H.R. Fan et al.

    Ore-forming fluids associated with granite-hosted gold mineralization at the Sanshandao deposit, Jiaodong gold province

    China. Miner. Depos.

    (2003)
  • N.J. Gardiner et al.

    The metallogenic provinces of Myanmar

    Appl. Earth. Sci.

    (2014)
  • S. Griffith

    The mineral resources of Burma

    Min. Mag.

    (1956)
  • J.L. Haas

    The effect of salinity on the maximum thermal gradient of a hydrothermal system at hydrostatic pressure

    Econ. Geol.

    (1971)
  • S.G. Hagemann et al.

    PTX conditions of hydrothermal fluids and precipitation mechanism of stibnite gold mineralization at the Wiluna lode-gold deposits, Western Australia: Conventional and infrared microthermometric constraints

    Miner. Depos.

    (2003)
  • D.J. Hoefs

    Geochemistry of Stable Isotopes

    Angew. Chem. Int. Ed.

    (1975)
  • D.J. Hoefs

    Stable Isotope Geochemistry

    (2009)
  • Khin Zaw, 2008. Origin of sedimentary rock-hosted gold deposit at Kyaukpahto, Kawlin–Wuntho District, Northern Myanmar....
    • View full text
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