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Chemical and boron isotopic compositions of tourmaline at the Dachang Sn-polymetallic ore district in South China: Constraints on the origin and evolution of hydrothermal fluids

Chemical and boron isotopic compositions of tourmaline at the Dachang Sn-polymetallic ore district in South China: Constraints on the origin and evolution of hydrothermal fluids
Chemical and boron isotopic compositions of tourmaline at the Dachang Sn-polymetallic ore district in South China: Constraints on the origin and evolution of hydrothermal fluids

The Dachang Sn-polymetallic ore district in South China is the second largest tin district in the world with a tin reserve of over one million tonnes. Zn-Cu skarn and stratiform, massive, and vein Sn-Pb-Zn ores are all present in this district. This has led to a debate as to whether the Sn orebodies were formed by Cretaceous magmatic-hydrothermal replacement or Devonian submarine exhalative-hydrothermal sedimentation. Here, we present a systematic investigation of the major, trace element, and boron isotopic compositions of different types of tourmaline in the Dachang ore district. Tourmaline disseminated in the Longxianggai granite and pegmatite veins belongs to the schorl series and has high contents of Li, Zn, and Ga. The δ 11B value of primary magma of the Longxianggai granite is estimated to be about −13‰, close to the global average δ 11B value (−11‰) for S-type granites. Tourmaline from quartz-tourmaline veins in the Longxianggai granite has similar chemical composition to the magmatic tourmaline and likely formed from hydrothermal fluids exsolved from the evolved granitic melt. The δ 11B value of the initial hydrothermal fluids is also calculated to be about −13‰. Tourmalines from the skarn and sulfide ores in the Lamo deposit have higher Mg/(Mg+Fe) and lower Na/(Na+Ca) ratios and higher contents of Be, Ge, Sr, and Sn than magmatic tourmaline. These patterns likely reflect input of elements derived from the host Devonian limestone. The δ 11B values of the hydrothermal fluids are estimated to be between −13 and −10‰, suggesting evolved magmatic-hydrothermal fluids related to the Longxianggai granite. Tourmalines from the stratiform and vein ores in the Changpo-Tongkeng deposit are extremely Mg-rich and mostly belong to the dravite series. They have high contents of Sc, V, Cr, Sr, and Sn and show positive Eu anomalies. The δ 11B values of these B- and Sn-rich fluids are estimated to be between −15 and −10‰, suggesting that the fluids also have a magmatic-hydrothermal origin. These fluids are most likely derived from the same granitic magma source, but may have interacted with the Devonian volcanic rocks.

Boron isotope, Geochemistry, South China, Tin ore deposit, Tourmaline
0026-4598
1589-1608
Zhao, Kui-dong
bd5bd864-d7d0-40b4-ae43-37cdc7632a37
Zhang, Ling-huo
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Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Jiang, Shao-yong
dc929006-69ac-4366-bf2b-dc97527602d3
Xu, Cong
eb846443-63ab-4129-8315-1567e6ed0149
Zhao, He-dong
80aeb4b8-8ed7-4b86-82db-0ac697e3e2c5
Chen, Wei
43d5a7bc-ca02-4943-881e-56f901b5f533
Zhao, Kui-dong
bd5bd864-d7d0-40b4-ae43-37cdc7632a37
Zhang, Ling-huo
cf131ed2-d9ab-43a1-8d7a-0a31b7f69b60
Palmer, Martin R.
d2e60e81-5d6e-4ddb-a243-602537286080
Jiang, Shao-yong
dc929006-69ac-4366-bf2b-dc97527602d3
Xu, Cong
eb846443-63ab-4129-8315-1567e6ed0149
Zhao, He-dong
80aeb4b8-8ed7-4b86-82db-0ac697e3e2c5
Chen, Wei
43d5a7bc-ca02-4943-881e-56f901b5f533

Zhao, Kui-dong, Zhang, Ling-huo, Palmer, Martin R., Jiang, Shao-yong, Xu, Cong, Zhao, He-dong and Chen, Wei (2021) Chemical and boron isotopic compositions of tourmaline at the Dachang Sn-polymetallic ore district in South China: Constraints on the origin and evolution of hydrothermal fluids. Mineralium Deposita, 56 (8), 1589-1608. (doi:10.1007/s00126-021-01045-4).

Record type: Article

Abstract

The Dachang Sn-polymetallic ore district in South China is the second largest tin district in the world with a tin reserve of over one million tonnes. Zn-Cu skarn and stratiform, massive, and vein Sn-Pb-Zn ores are all present in this district. This has led to a debate as to whether the Sn orebodies were formed by Cretaceous magmatic-hydrothermal replacement or Devonian submarine exhalative-hydrothermal sedimentation. Here, we present a systematic investigation of the major, trace element, and boron isotopic compositions of different types of tourmaline in the Dachang ore district. Tourmaline disseminated in the Longxianggai granite and pegmatite veins belongs to the schorl series and has high contents of Li, Zn, and Ga. The δ 11B value of primary magma of the Longxianggai granite is estimated to be about −13‰, close to the global average δ 11B value (−11‰) for S-type granites. Tourmaline from quartz-tourmaline veins in the Longxianggai granite has similar chemical composition to the magmatic tourmaline and likely formed from hydrothermal fluids exsolved from the evolved granitic melt. The δ 11B value of the initial hydrothermal fluids is also calculated to be about −13‰. Tourmalines from the skarn and sulfide ores in the Lamo deposit have higher Mg/(Mg+Fe) and lower Na/(Na+Ca) ratios and higher contents of Be, Ge, Sr, and Sn than magmatic tourmaline. These patterns likely reflect input of elements derived from the host Devonian limestone. The δ 11B values of the hydrothermal fluids are estimated to be between −13 and −10‰, suggesting evolved magmatic-hydrothermal fluids related to the Longxianggai granite. Tourmalines from the stratiform and vein ores in the Changpo-Tongkeng deposit are extremely Mg-rich and mostly belong to the dravite series. They have high contents of Sc, V, Cr, Sr, and Sn and show positive Eu anomalies. The δ 11B values of these B- and Sn-rich fluids are estimated to be between −15 and −10‰, suggesting that the fluids also have a magmatic-hydrothermal origin. These fluids are most likely derived from the same granitic magma source, but may have interacted with the Devonian volcanic rocks.

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Zhao et al 2021 - Accepted Manuscript
Restricted to Repository staff only until 21 February 2022.
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More information

Accepted/In Press date: 3 February 2021
Published date: 21 February 2021
Keywords: Boron isotope, Geochemistry, South China, Tin ore deposit, Tourmaline

Identifiers

Local EPrints ID: 448450
URI: http://eprints.soton.ac.uk/id/eprint/448450
ISSN: 0026-4598
PURE UUID: 41d2c065-f301-4d4a-a01d-e875f844f0dd

Catalogue record

Date deposited: 22 Apr 2021 16:46
Last modified: 25 Nov 2021 23:10

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Contributors

Author: Kui-dong Zhao
Author: Ling-huo Zhang
Author: Shao-yong Jiang
Author: Cong Xu
Author: He-dong Zhao
Author: Wei Chen

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