Stable isotope and geochronological study of the Mawchi Sn-W deposit, Myanmar: Implications for timing of mineralization and ore genesis

Aung Zaw Myint, Kotaro Yonezu, Adrian J. Boyce, David Selby, Anders Scherstén, Thomas Tindell, Koichiro Watanabe, Ye Myint Swe

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Myanmar is endowed with abundant Sn-W mineralization, pre-eminent amongst which is the world-class Mawchi deposit. In the Mawchi area, N-S trending vertical or steeply dipping quartz veins are hosted by both Eocene granite and Carboniferous to Early Permian metasediments. Three stages of ore formation are recognized; (i) tourmaline-cassiterite stage (ii) main ore stage and (iii) sulfide stage. Tourmaline, cassiterite and pyrite-I are early-formed minerals and are representative of the first stage. Their deposition continued together with wolframite, scheelite, molybdenite, arsenopyrite, pyrite-II, fluorite and danalite, which form the second stage. This was followed by the successive deposition of sulfides such as chalcopyrite, sphalerite, galena and Pb-Bi sulfides. A 40Ar/39Ar magmatic biotite plateau age of 41.50 ± 0.16 Ma (MSWD = 2.5) is determined for the Mawchi biotite granite which we interpret as the time the granite cooled through the biotite blocking temperature, and is consistent with a previously reported LA-ICP-MS U-Pb zircon concordia age of 42.72 ± 0.94 Ma (MSWD = 2). A molybdenite Re-Os model age of 42.4 ± 1.2 Ma indicates that Sn-W mineralization was synchronous with late Eocene granitic magmatism. Our 40Ar/39Ar hydrothermal muscovite plateau ages from the tourmaline granite (40.14 ± 0.14 Ma; MSWD = 1.48) and quartz vein selvages (40.80 ± 0.12 Ma; MSWD = 0.47) define the timing of hydrothermal alteration and simultaneous veining that accompanied the late stage of ore forming at Mawchi. Fluid inclusion microthermometry from cassiterite, scheelite, quartz, and fluorite reveals that ore fluids in the cassiterite-tourmaline stage and main ore stage are characterized by moderate homogenization temperatures (Th = 260–345 °C) and salinities (4.5–15.7 wt% NaCl equiv), while the sulfide stage is characterized by lower temperatures (Th = 175–260 °C) and moderate to low salinity (2.5–13 wt% NaCl equiv). The mean δ34S of all sulfides is 2.9 ± 2.9‰ which is suggestive that the overall system is dominated by magmatic sulfur. The similarity of δ34S values in galena and Pb-Bi sulfides (−1.3 to 2.7‰) suggest that sulfur, and inference the Pb and Bi were transported by a common fluid, probably of magmatic origin. The calculated δ18OH2O of the hydrothermal fluid associated with cassiterite and tourmaline is 7.3–8.4‰. Scheelite and quartz deposition is characterized by lighter δ18OH2O values (2.1–4.9‰) indicating that the ore fluid might be mixed with another source of water, perhaps, meteoric. Hydrogen isotopic compositions (δD = −51 to −121‰) again indicate that origin of the ore fluid is magmatic, but δD (∼−120‰) is low enough to support the δ18OH2O data that suggests, in part, a meteoric water component to the hydrothermal fluids at Mawchi.

Original languageEnglish
Pages (from-to)663-679
Number of pages17
JournalOre Geology Reviews
Volume95
DOIs
Publication statusPublished - Apr 1 2018

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Isotopes
Ores
Sulfides
cassiterite
stable isotope
tourmaline
Deposits
mineralization
Quartz
sulfide
Fluids
scheelite
granite
biotite
molybdenite
Fluorspar
fluid
fluorite
quartz vein
galena

All Science Journal Classification (ASJC) codes

  • Geology
  • Geochemistry and Petrology
  • Economic Geology

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Stable isotope and geochronological study of the Mawchi Sn-W deposit, Myanmar : Implications for timing of mineralization and ore genesis. / Myint, Aung Zaw; Yonezu, Kotaro; Boyce, Adrian J.; Selby, David; Scherstén, Anders; Tindell, Thomas; Watanabe, Koichiro; Swe, Ye Myint.

In: Ore Geology Reviews, Vol. 95, 01.04.2018, p. 663-679.

Research output: Contribution to journalArticle

Myint, Aung Zaw ; Yonezu, Kotaro ; Boyce, Adrian J. ; Selby, David ; Scherstén, Anders ; Tindell, Thomas ; Watanabe, Koichiro ; Swe, Ye Myint. / Stable isotope and geochronological study of the Mawchi Sn-W deposit, Myanmar : Implications for timing of mineralization and ore genesis. In: Ore Geology Reviews. 2018 ; Vol. 95. pp. 663-679.
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abstract = "Myanmar is endowed with abundant Sn-W mineralization, pre-eminent amongst which is the world-class Mawchi deposit. In the Mawchi area, N-S trending vertical or steeply dipping quartz veins are hosted by both Eocene granite and Carboniferous to Early Permian metasediments. Three stages of ore formation are recognized; (i) tourmaline-cassiterite stage (ii) main ore stage and (iii) sulfide stage. Tourmaline, cassiterite and pyrite-I are early-formed minerals and are representative of the first stage. Their deposition continued together with wolframite, scheelite, molybdenite, arsenopyrite, pyrite-II, fluorite and danalite, which form the second stage. This was followed by the successive deposition of sulfides such as chalcopyrite, sphalerite, galena and Pb-Bi sulfides. A 40Ar/39Ar magmatic biotite plateau age of 41.50 ± 0.16 Ma (MSWD = 2.5) is determined for the Mawchi biotite granite which we interpret as the time the granite cooled through the biotite blocking temperature, and is consistent with a previously reported LA-ICP-MS U-Pb zircon concordia age of 42.72 ± 0.94 Ma (MSWD = 2). A molybdenite Re-Os model age of 42.4 ± 1.2 Ma indicates that Sn-W mineralization was synchronous with late Eocene granitic magmatism. Our 40Ar/39Ar hydrothermal muscovite plateau ages from the tourmaline granite (40.14 ± 0.14 Ma; MSWD = 1.48) and quartz vein selvages (40.80 ± 0.12 Ma; MSWD = 0.47) define the timing of hydrothermal alteration and simultaneous veining that accompanied the late stage of ore forming at Mawchi. Fluid inclusion microthermometry from cassiterite, scheelite, quartz, and fluorite reveals that ore fluids in the cassiterite-tourmaline stage and main ore stage are characterized by moderate homogenization temperatures (Th = 260–345 °C) and salinities (4.5–15.7 wt{\%} NaCl equiv), while the sulfide stage is characterized by lower temperatures (Th = 175–260 °C) and moderate to low salinity (2.5–13 wt{\%} NaCl equiv). The mean δ34S of all sulfides is 2.9 ± 2.9‰ which is suggestive that the overall system is dominated by magmatic sulfur. The similarity of δ34S values in galena and Pb-Bi sulfides (−1.3 to 2.7‰) suggest that sulfur, and inference the Pb and Bi were transported by a common fluid, probably of magmatic origin. The calculated δ18OH2O of the hydrothermal fluid associated with cassiterite and tourmaline is 7.3–8.4‰. Scheelite and quartz deposition is characterized by lighter δ18OH2O values (2.1–4.9‰) indicating that the ore fluid might be mixed with another source of water, perhaps, meteoric. Hydrogen isotopic compositions (δD = −51 to −121‰) again indicate that origin of the ore fluid is magmatic, but δD (∼−120‰) is low enough to support the δ18OH2O data that suggests, in part, a meteoric water component to the hydrothermal fluids at Mawchi.",
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T1 - Stable isotope and geochronological study of the Mawchi Sn-W deposit, Myanmar

T2 - Implications for timing of mineralization and ore genesis

AU - Myint, Aung Zaw

AU - Yonezu, Kotaro

AU - Boyce, Adrian J.

AU - Selby, David

AU - Scherstén, Anders

AU - Tindell, Thomas

AU - Watanabe, Koichiro

AU - Swe, Ye Myint

PY - 2018/4/1

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N2 - Myanmar is endowed with abundant Sn-W mineralization, pre-eminent amongst which is the world-class Mawchi deposit. In the Mawchi area, N-S trending vertical or steeply dipping quartz veins are hosted by both Eocene granite and Carboniferous to Early Permian metasediments. Three stages of ore formation are recognized; (i) tourmaline-cassiterite stage (ii) main ore stage and (iii) sulfide stage. Tourmaline, cassiterite and pyrite-I are early-formed minerals and are representative of the first stage. Their deposition continued together with wolframite, scheelite, molybdenite, arsenopyrite, pyrite-II, fluorite and danalite, which form the second stage. This was followed by the successive deposition of sulfides such as chalcopyrite, sphalerite, galena and Pb-Bi sulfides. A 40Ar/39Ar magmatic biotite plateau age of 41.50 ± 0.16 Ma (MSWD = 2.5) is determined for the Mawchi biotite granite which we interpret as the time the granite cooled through the biotite blocking temperature, and is consistent with a previously reported LA-ICP-MS U-Pb zircon concordia age of 42.72 ± 0.94 Ma (MSWD = 2). A molybdenite Re-Os model age of 42.4 ± 1.2 Ma indicates that Sn-W mineralization was synchronous with late Eocene granitic magmatism. Our 40Ar/39Ar hydrothermal muscovite plateau ages from the tourmaline granite (40.14 ± 0.14 Ma; MSWD = 1.48) and quartz vein selvages (40.80 ± 0.12 Ma; MSWD = 0.47) define the timing of hydrothermal alteration and simultaneous veining that accompanied the late stage of ore forming at Mawchi. Fluid inclusion microthermometry from cassiterite, scheelite, quartz, and fluorite reveals that ore fluids in the cassiterite-tourmaline stage and main ore stage are characterized by moderate homogenization temperatures (Th = 260–345 °C) and salinities (4.5–15.7 wt% NaCl equiv), while the sulfide stage is characterized by lower temperatures (Th = 175–260 °C) and moderate to low salinity (2.5–13 wt% NaCl equiv). The mean δ34S of all sulfides is 2.9 ± 2.9‰ which is suggestive that the overall system is dominated by magmatic sulfur. The similarity of δ34S values in galena and Pb-Bi sulfides (−1.3 to 2.7‰) suggest that sulfur, and inference the Pb and Bi were transported by a common fluid, probably of magmatic origin. The calculated δ18OH2O of the hydrothermal fluid associated with cassiterite and tourmaline is 7.3–8.4‰. Scheelite and quartz deposition is characterized by lighter δ18OH2O values (2.1–4.9‰) indicating that the ore fluid might be mixed with another source of water, perhaps, meteoric. Hydrogen isotopic compositions (δD = −51 to −121‰) again indicate that origin of the ore fluid is magmatic, but δD (∼−120‰) is low enough to support the δ18OH2O data that suggests, in part, a meteoric water component to the hydrothermal fluids at Mawchi.

AB - Myanmar is endowed with abundant Sn-W mineralization, pre-eminent amongst which is the world-class Mawchi deposit. In the Mawchi area, N-S trending vertical or steeply dipping quartz veins are hosted by both Eocene granite and Carboniferous to Early Permian metasediments. Three stages of ore formation are recognized; (i) tourmaline-cassiterite stage (ii) main ore stage and (iii) sulfide stage. Tourmaline, cassiterite and pyrite-I are early-formed minerals and are representative of the first stage. Their deposition continued together with wolframite, scheelite, molybdenite, arsenopyrite, pyrite-II, fluorite and danalite, which form the second stage. This was followed by the successive deposition of sulfides such as chalcopyrite, sphalerite, galena and Pb-Bi sulfides. A 40Ar/39Ar magmatic biotite plateau age of 41.50 ± 0.16 Ma (MSWD = 2.5) is determined for the Mawchi biotite granite which we interpret as the time the granite cooled through the biotite blocking temperature, and is consistent with a previously reported LA-ICP-MS U-Pb zircon concordia age of 42.72 ± 0.94 Ma (MSWD = 2). A molybdenite Re-Os model age of 42.4 ± 1.2 Ma indicates that Sn-W mineralization was synchronous with late Eocene granitic magmatism. Our 40Ar/39Ar hydrothermal muscovite plateau ages from the tourmaline granite (40.14 ± 0.14 Ma; MSWD = 1.48) and quartz vein selvages (40.80 ± 0.12 Ma; MSWD = 0.47) define the timing of hydrothermal alteration and simultaneous veining that accompanied the late stage of ore forming at Mawchi. Fluid inclusion microthermometry from cassiterite, scheelite, quartz, and fluorite reveals that ore fluids in the cassiterite-tourmaline stage and main ore stage are characterized by moderate homogenization temperatures (Th = 260–345 °C) and salinities (4.5–15.7 wt% NaCl equiv), while the sulfide stage is characterized by lower temperatures (Th = 175–260 °C) and moderate to low salinity (2.5–13 wt% NaCl equiv). The mean δ34S of all sulfides is 2.9 ± 2.9‰ which is suggestive that the overall system is dominated by magmatic sulfur. The similarity of δ34S values in galena and Pb-Bi sulfides (−1.3 to 2.7‰) suggest that sulfur, and inference the Pb and Bi were transported by a common fluid, probably of magmatic origin. The calculated δ18OH2O of the hydrothermal fluid associated with cassiterite and tourmaline is 7.3–8.4‰. Scheelite and quartz deposition is characterized by lighter δ18OH2O values (2.1–4.9‰) indicating that the ore fluid might be mixed with another source of water, perhaps, meteoric. Hydrogen isotopic compositions (δD = −51 to −121‰) again indicate that origin of the ore fluid is magmatic, but δD (∼−120‰) is low enough to support the δ18OH2O data that suggests, in part, a meteoric water component to the hydrothermal fluids at Mawchi.

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