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Insights into extinct seafloor massive sulfide mounds at the TAG, mid-atlantic ridge

Insights into extinct seafloor massive sulfide mounds at the TAG, mid-atlantic ridge
Insights into extinct seafloor massive sulfide mounds at the TAG, mid-atlantic ridge

Over the last decade there has been an increasing interest in deep-sea mineral resources that may contribute to future raw metal supply. However, before seafloor massive sulfides (SMS) can be considered as a resource, alteration and weathering processes that may affect their metal tenor have to be fully understood. This knowledge cannot be obtained by assessing the surface exposures alone. Seafloor drilling is required to gain information about the third dimension. In 2016, three extinct seafloor massive sulfide mounds, located in the Trans-Atlantic Geotraverse (TAG) hydrothermal area of the Mid-Atlantic Ridge were drilled. A mineralogical and textural comparison of drill core and surface-grab samples revealed that in recent ceased mounds high-temperature copper assemblages typical for black smoker chimneys are still present whereas in longer extinct mounds the mineralogy is pre-dominated by an iron mineral assemblage. Zinc becomes remobilized early in the mound evolution and forms either a layer in the upper part of the mound or has been totally leached from its interior. Precipitation temperatures of sphalerite calculated using the Fe/Zn ratio can help to identify these remobilization processes. While the Fe/Zn ratios of primary sphalerites yield temperatures that are in very good agreement with fluid temperatures measured in white smokers, calculated temperatures for sphalerites affected by remobilization are too high for SMS. Overall drilling of SMS provides valuable information on the internal structure and mineralogy of the shallow sub-surface, however, additional drilling of SMS, at a greater depth, is required to fully understand the processes affecting SMS and their economic potential.

Drilling, Extinct seafloor massive sulfides, Mid-Atlantic Ridge, TAG hydrothermal area
0009-8558
Lehrmann, Berit
3a90a549-fcd6-4b5e-b361-7d31130d7a2f
Stobbs, Iain J.
bd12fa30-0bdd-4d15-912c-b47de14e260c
Lusty, Paul A.J.
1ef4795f-3882-4b26-900d-c30afc681408
Murton, Bramley J.
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12
Lehrmann, Berit
3a90a549-fcd6-4b5e-b361-7d31130d7a2f
Stobbs, Iain J.
bd12fa30-0bdd-4d15-912c-b47de14e260c
Lusty, Paul A.J.
1ef4795f-3882-4b26-900d-c30afc681408
Murton, Bramley J.
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12

Lehrmann, Berit, Stobbs, Iain J., Lusty, Paul A.J. and Murton, Bramley J. (2018) Insights into extinct seafloor massive sulfide mounds at the TAG, mid-atlantic ridge. Clay Minerals, 8 (7), [302]. (doi:10.3390/min8070302).

Record type: Article

Abstract

Over the last decade there has been an increasing interest in deep-sea mineral resources that may contribute to future raw metal supply. However, before seafloor massive sulfides (SMS) can be considered as a resource, alteration and weathering processes that may affect their metal tenor have to be fully understood. This knowledge cannot be obtained by assessing the surface exposures alone. Seafloor drilling is required to gain information about the third dimension. In 2016, three extinct seafloor massive sulfide mounds, located in the Trans-Atlantic Geotraverse (TAG) hydrothermal area of the Mid-Atlantic Ridge were drilled. A mineralogical and textural comparison of drill core and surface-grab samples revealed that in recent ceased mounds high-temperature copper assemblages typical for black smoker chimneys are still present whereas in longer extinct mounds the mineralogy is pre-dominated by an iron mineral assemblage. Zinc becomes remobilized early in the mound evolution and forms either a layer in the upper part of the mound or has been totally leached from its interior. Precipitation temperatures of sphalerite calculated using the Fe/Zn ratio can help to identify these remobilization processes. While the Fe/Zn ratios of primary sphalerites yield temperatures that are in very good agreement with fluid temperatures measured in white smokers, calculated temperatures for sphalerites affected by remobilization are too high for SMS. Overall drilling of SMS provides valuable information on the internal structure and mineralogy of the shallow sub-surface, however, additional drilling of SMS, at a greater depth, is required to fully understand the processes affecting SMS and their economic potential.

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minerals-08-00302-v2 (1) - Version of Record
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More information

Accepted/In Press date: 4 July 2018
e-pub ahead of print date: 18 July 2018
Published date: 18 July 2018
Keywords: Drilling, Extinct seafloor massive sulfides, Mid-Atlantic Ridge, TAG hydrothermal area

Identifiers

Local EPrints ID: 422985
URI: http://eprints.soton.ac.uk/id/eprint/422985
ISSN: 0009-8558
PURE UUID: 6a6f45e2-b545-433b-b605-cd03adabd404

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Date deposited: 09 Aug 2018 16:30
Last modified: 16 Dec 2019 18:03

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Contributors

Author: Berit Lehrmann
Author: Iain J. Stobbs
Author: Paul A.J. Lusty
Author: Bramley J. Murton

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