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- Title
Marine Mineral Exploration With Controlled Source Electromagnetics at the TAG Hydrothermal Field, 26°N Mid‐Atlantic Ridge.
- Authors
Gehrmann, R. A. S.; North, L. J.; Graber, S.; Szitkar, F.; Petersen, S.; Minshull, T. A.; Murton, B. J.
- Abstract
Seafloor massive sulfide (SMS) deposits are of increasing economic interest in order to satisfy the relentless growth in worldwide metal demand. The Trans‐Atlantic Geotraverse (TAG) hydrothermal field at 26°N on the Mid‐Atlantic Ridge hosts several such deposits. This study presents new controlled source electromagnetic, bathymetric, and magnetic results from the TAG field. Potential SMS targets were selected based on their surface expressions in high‐resolution bathymetric data. High‐resolution reduced‐to‐the‐pole magnetic data show negative anomalies beneath and surrounding the SMS deposits, revealing large areas of hydrothermal alteration. Controlled source electromagnetic data, sensitive to the electrical conductivity of SMS mineralization, further reveal a maximum thickness of up to 80 m and conductivities of up to 5 S/m. SMS samples have conductivities of up to a few thousand Siemens per meter, suggesting that remotely inferred conductivities represent an average of metal sulfide ores combined with silicified and altered host basalt that likely dominates at greater depths. Plain Language Summary: Seafloor massive sulfide deposits, formed by high‐temperature hydrothermal activity, provide a potential resource for metals including copper, zinc, lead, gold, and silver. Here, we report the results of a geophysical study to estimate the distribution and size of seafloor ore deposits at the Trans‐Atlantic Geotraverse hydrothermal field, located south of the Azores, on the Mid‐Atlantic Ridge. The Trans‐Atlantic Geotraverse field hosts numerous deposits, all but one of which are hydrothermally inactive. Inactive deposits are economically more valuable but difficult to detect. Our solution is a combination of high‐resolution seafloor and subseafloor mapping techniques. By focusing on exploration using ship‐towed electromagnetic sensing and autonomous underwater vehicle‐based mapping and characterization of their magnetic field, we exploit unique signatures identifying these deposits from their surrounding volcanic rock. These data enable us to delineate the extent of the deposits and provide a first estimate of their thickness. We integrate physical and chemical properties of ore and host rock samples, recovered by drilling, into our interpretation in order to estimate the full economic potential of the deposits. Our results reveal a deposit geometry consisting of a sulfide ore body that is mixed with an increasing amount of silica and altered volcanic rocks at depth. Key Points: Seafloor massive sulfide deposits can be detected/mapped on a large scale with controlled source electromagnetic methodsMultidisciplinary geophysical data analysis and local probing lead to a rigorous interpretation of deposit dimensions and resource potentialSulfide ore content reduces with depth down to a few tens of meters into the deposit's altered basalt and silica‐dominated root
- Subjects
MARINE mineral resources; ELECTROMAGNETISM; HYDROTHERMAL deposits; BATHYMETRIC maps; ELECTROMAGNETIC fields
- Publication
Geophysical Research Letters, 2019, Vol 46, Issue 11, p5808
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2019GL082928