TAG hydrothermal field: A key to modern and ancient seafloor hydrothermal VMS ore-forming systems

Abstract

The TAG hydrothermal field, situated in the axial valley of the slow-spreading Mid-Atlantic Ridge near 26°N, 45°W, is one of the largest and best-studied seafloor hydrothermal fields in the world. This paper applies what we are learning about the TAG field that may guide exploration for modern and ancient Volcanogenic Massive Sulfide (VMS) deposits. Consideration includes water column and seafloor signals distal to the field and tectonic, magmatic, hydrothermal, alteration, and serpentinization processes with diagnostic features in the axial valley proximal to the field; the role of replacement, sulfate deposition and dissolution, and zone refinement in individual sulfide mounds; the concentration of large deposits by superposition of multiple short espisodes of high-temperature hydrothermal activity (episodes to hundreds of years; episodicity thousands of years); and the clustered mode of occurrence of an assemblage of large sulfide mounds by synchronous and asynchronous episodic hydrothermal activity over more than 100,000 years.