Native copper and α-copper–zinc in sediments from the TAG hydrothermal field (Mid-Atlantic Ridge, 26°N): nature and origin

Abstract

Native copper and α-copper–zinc occur as strands and elongated grains (up to 300 μm in length) within the sediments from the Trans-Atlantic Geotraverse (TAG) hydrothermal field (Mid-Atlantic Ridge, 26°N). They are remarkably similar in composition and crystal structure to copper and copper–zinc occurrences found in other natural environments. The results of mineralogical studies are discussed in terms of the possible mechanisms of native metal formation in the complex TAG field: with an asymmetric and highly-fractured rift valley, and mature active and relict sulfide mounds. Native copper and α-copper–zinc grains disseminated in the TAG sediments are either inherited from: (1) primary magmatic or metamorphic crustal source; (2) hydrothermal deposits; and (3) the alteration of primary deposits, or formed (1) authigenically, or (2) biogenically within/on the sediment cover. Native metallic particles could have been formed as accessory minerals disseminated in the ridge crest basic rocks and/or massive sulfide mounds. Degradation of these rocks and mass wasting of the mounds have liberated the metallic grains which have, in turn, been deposited into adjacent sediments.