| Summary: | Tese de doutoramento, Ciências do Mar, Universidade de Lisboa, Faculdade de Ciências, 2016 Underwater hydrothermal vent fields are known since the 1970s and occur in a variety of oceanic settings, each field with unique particularities. The potential importance of these hydrothermal deposits for the global economy is growing and each new discovery opens new ground for exploration for metal resources. The Arctic Ocean presents itself as an opportunity to study new interesting areas and numerous hydrothermal systems (active and inactive) were already discovered (or detected) along the Arctic Mid Ocean Ridge (AMOR). The AMOR is an ultra-slow spreading ridge, in which, according to modern views, there is a reduced but more focused magma supply, capable of sustaining long-lived hydrothermal circulation which increases the potential for the formation of large polymetallic hydrothermal deposits. Jan Mayen and Loki’s Castle are two hydrothermal vent systems discovered in 2005 and 2008 respectively in the Mohns Ridge, a segment of the AMOR. The work presented here originated from the need to understand these vent fields from a ore resource viewpoint, in order to evaluate the possible economic interest of each area. Sediments from each area were studied to establish the possible extent of hydrothermal influence in the surrounding terrains. Additionally, rocks of basaltic nature helped to constrain the geochemical influences on the hydrothermal fluid and understand the nature of the hydrothermal products generated on the seafloor. And finally, hydrothermal products composed of chimney structures and, in the case of Loki’s Castle, also sediments from the hydrothermal mound were studied to understand the polymetallic sulfide paragenesis of each system. There was a first macroscopic approach on these samples, followed by X-ray diffraction to better comprehend the expected mineralogy. Selected samples were polished and studied in reflected light and analyzed in the electron to understand the mineral chemistry in each vent ...
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