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Multispectral discrimination of spectrally similar hydrothermal minerals in mafic crust: A 5000 km2 ASTER alteration map of the Oman–UAE ophiolite

Multispectral discrimination of spectrally similar hydrothermal minerals in mafic crust: A 5000 km2 ASTER alteration map of the Oman–UAE ophiolite
Multispectral discrimination of spectrally similar hydrothermal minerals in mafic crust: A 5000 km2 ASTER alteration map of the Oman–UAE ophiolite

Multispectral remote sensing of hydrothermal alteration in volcanogenic massive sulfide (VMS) ore systems in mafic crust is relatively uncommon, in part due to the short-wave infrared spectral similarity of several key alteration minerals: epidote, chlorite, actinolite, and serpentine. In this study, we developed regional mosaic generation and classification workflows for Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery to discriminate these minerals over the entire crust of the Semail ophiolite (Oman–UAE). Spectral discrimination was achieved through adaptation of the ASTER (pre-)processing workflow to the specific mapping targets, available datasets, and location of this study. Necessary steps included the pre-selection of ASTER scenes without residual atmospheric water features, mosaic normalization based solely on overlapping target outcrops, correcting cross-mosaic ramp errors, and alteration map classification based on image-derived reference data. The resulting alteration map, validated through comparison with field mapping and sampling, is the most areally extensive continuous survey of hydrothermal alteration yet presented for oceanic crust, providing a renewed framework for research and mineral exploration of Earth's largest ophiolite. Our map confirms that the vast majority of the upper oceanic crust is regionally altered to a spilite type secondary mineral assemblage. Localized areas of epidosite alteration, marking focused hydrothermal flow paths, are confined to the upper oceanic crust, whereas areas of previously unrecognized but intense actinolite alteration are common in both the lower and upper oceanic crust. Our methodological developments expand the standard considerations necessary for regional geological mapping using infrared image mosaics. They further demonstrate the underappreciated capability of multispectral data for mapping spectrally similar rock types. Although the specifics of the method are necessarily optimized for the Oman–UAE ophiolite, re-optimization based on local reference data should allow similar results to be achieved in other well-exposed mafic-hosted VMS districts.

Alteration, ASTER, Hydrothermal, Mafic, Multispectral, Oman, Ophiolite, VMS
0034-4257
Belgrano, Thomas M.
6135b1b8-ca0f-41a6-a94a-6b6c3513dee3
Diamond, Larryn W.
2f4d31e5-b7df-41bb-9be1-975c823fc883
Novakovic, Nevena
a56cfbfb-2152-4109-ae72-e9c6e9f53495
Hewson, Robert D.
55380186-fdab-43c4-be7e-20bad4163fa7
Hecker, Christoph A.
d675dcaa-715a-4f3d-8533-afb8bdeb617c
Wolf, Robin C.
62e5a807-2968-42c2-8d92-aba7dc9d8e40
de Doliwa Zieliński, Ludwik
09fc15c6-1585-4d8d-a187-90f29770d4cd
Kuhn, Raphael
d74006aa-3aaa-47e2-b485-a2313b562d47
Gilgen, Samuel A.
634e2d69-8d77-4a8f-8e10-e01695f7aa7d
Belgrano, Thomas M.
6135b1b8-ca0f-41a6-a94a-6b6c3513dee3
Diamond, Larryn W.
2f4d31e5-b7df-41bb-9be1-975c823fc883
Novakovic, Nevena
a56cfbfb-2152-4109-ae72-e9c6e9f53495
Hewson, Robert D.
55380186-fdab-43c4-be7e-20bad4163fa7
Hecker, Christoph A.
d675dcaa-715a-4f3d-8533-afb8bdeb617c
Wolf, Robin C.
62e5a807-2968-42c2-8d92-aba7dc9d8e40
de Doliwa Zieliński, Ludwik
09fc15c6-1585-4d8d-a187-90f29770d4cd
Kuhn, Raphael
d74006aa-3aaa-47e2-b485-a2313b562d47
Gilgen, Samuel A.
634e2d69-8d77-4a8f-8e10-e01695f7aa7d

Belgrano, Thomas M., Diamond, Larryn W., Novakovic, Nevena, Hewson, Robert D., Hecker, Christoph A., Wolf, Robin C., de Doliwa Zieliński, Ludwik, Kuhn, Raphael and Gilgen, Samuel A. (2022) Multispectral discrimination of spectrally similar hydrothermal minerals in mafic crust: A 5000 km2 ASTER alteration map of the Oman–UAE ophiolite. Remote Sensing of Environment, 280, [113211]. (doi:10.1016/j.rse.2022.113211).

Record type: Article

Abstract

Multispectral remote sensing of hydrothermal alteration in volcanogenic massive sulfide (VMS) ore systems in mafic crust is relatively uncommon, in part due to the short-wave infrared spectral similarity of several key alteration minerals: epidote, chlorite, actinolite, and serpentine. In this study, we developed regional mosaic generation and classification workflows for Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery to discriminate these minerals over the entire crust of the Semail ophiolite (Oman–UAE). Spectral discrimination was achieved through adaptation of the ASTER (pre-)processing workflow to the specific mapping targets, available datasets, and location of this study. Necessary steps included the pre-selection of ASTER scenes without residual atmospheric water features, mosaic normalization based solely on overlapping target outcrops, correcting cross-mosaic ramp errors, and alteration map classification based on image-derived reference data. The resulting alteration map, validated through comparison with field mapping and sampling, is the most areally extensive continuous survey of hydrothermal alteration yet presented for oceanic crust, providing a renewed framework for research and mineral exploration of Earth's largest ophiolite. Our map confirms that the vast majority of the upper oceanic crust is regionally altered to a spilite type secondary mineral assemblage. Localized areas of epidosite alteration, marking focused hydrothermal flow paths, are confined to the upper oceanic crust, whereas areas of previously unrecognized but intense actinolite alteration are common in both the lower and upper oceanic crust. Our methodological developments expand the standard considerations necessary for regional geological mapping using infrared image mosaics. They further demonstrate the underappreciated capability of multispectral data for mapping spectrally similar rock types. Although the specifics of the method are necessarily optimized for the Oman–UAE ophiolite, re-optimization based on local reference data should allow similar results to be achieved in other well-exposed mafic-hosted VMS districts.

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Accepted/In Press date: 30 July 2022
e-pub ahead of print date: 17 August 2022
Published date: 17 August 2022
Additional Information: Funding Information: The ASTER imagery used in this study was made available by NASA (USA) and METI (Japan), and NASA Land Processes Distributed Active Archive Center (LP DAAC) are thanked for data access. We thank the Ministry of Energy and Minerals (MEM), Sultanate of Oman, for their long support of this project, in particular Hussein Azubaibi, Mohammed Al Araimi, and Mohammed Al-Battashi. Khalid Al-Tobi and the team at National Earth Secrets Co. (Muscat) provided much appreciated logistical support. We thank Ali al Hashmi (MEM), Alannah Brett-Adams, Lisa Richter, Nicolas Zuluaga, Ivan Mercolli, Lea Weyermann, Fabian Scherer, and in particular, Samuel Weber (all University of Bern) for assistance during field mapping. The ITC, University of Twente facilitated spectroscopic measurements and Freek van der Meer, Frank van Ruitenbeek and colleagues are thanked for their advice. TMB acknowledges support from the SNSF and from the Southampton Marine and Maritime Institute, University of Southampton . This project was otherwise entirely funded by the University of Bern and by Swiss National Science Foundation (SNSF) Grant 200020-169653 to LWD. Funding Information: The ASTER imagery used in this study was made available by NASA (USA) and METI (Japan), and NASA Land Processes Distributed Active Archive Center (LP DAAC) are thanked for data access. We thank the Ministry of Energy and Minerals (MEM), Sultanate of Oman, for their long support of this project, in particular Hussein Azubaibi, Mohammed Al Araimi, and Mohammed Al-Battashi. Khalid Al-Tobi and the team at National Earth Secrets Co. (Muscat) provided much appreciated logistical support. We thank Ali al Hashmi (MEM), Alannah Brett-Adams, Lisa Richter, Nicolas Zuluaga, Ivan Mercolli, Lea Weyermann, Fabian Scherer, and in particular, Samuel Weber (all University of Bern) for assistance during field mapping. The ITC, University of Twente facilitated spectroscopic measurements and Freek van der Meer, Frank van Ruitenbeek and colleagues are thanked for their advice. TMB acknowledges support from the SNSF and from the Southampton Marine and Maritime Institute, University of Southampton. This project was otherwise entirely funded by the University of Bern and by Swiss National Science Foundation (SNSF) Grant 200020-169653 to LWD. Publisher Copyright: © 2022 The Authors
Keywords: Alteration, ASTER, Hydrothermal, Mafic, Multispectral, Oman, Ophiolite, VMS

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Local EPrints ID: 471134
URI: http://eprints.soton.ac.uk/id/eprint/471134
ISSN: 0034-4257
PURE UUID: c1cd5a25-787d-442d-80c3-c3c382b42c16

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Date deposited: 27 Oct 2022 16:36
Last modified: 27 Oct 2022 16:47

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Contributors

Author: Larryn W. Diamond
Author: Nevena Novakovic
Author: Robert D. Hewson
Author: Christoph A. Hecker
Author: Robin C. Wolf
Author: Ludwik de Doliwa Zieliński
Author: Raphael Kuhn
Author: Samuel A. Gilgen

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