Petrology of hydrothermal mineralization: a vertical section through the TAG mound

Knott, R., Fouquet, Y., Honnorez, J., Petersen, Sven and Bohn, M. (1998) Petrology of hydrothermal mineralization: a vertical section through the TAG mound Proceedings of the Ocean Drilling Program: Scientific Results, 158 . pp. 5-26. DOI 10.2973/

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Mineralogical, textural, chemical, and isotopic features of a vertical section through the active Trans-Atlantic Geotraverse
(TAG) hydrothermal mound reveal the nature of subsurface mineralization. The multistage growth and evolution of the TAG
mound occurs by the following processes: (1) near-surface (<10 m depth) hydrothermal precipitation of porous Fe-Cu-Zn sulfide
and Si-Fe-oxyhydroxides; (2) modification of surface material within the mound (>20 m depth) by sequential overgrowth,
recrystallization and mineral dissolution; (3) hydrothermal mineralization within the mound, forming Fe-Cu sulfides, anhydrite
and quartz; and (4) alteration and mineralization of basalt basement beneath the mound. During the long history of hydrothermal
activity, these processes have driven the TAG mound toward a mineralogy dominated by pyrite and depleted in Cu, Zn, and
trace elements. The basement beneath the mound is ultimately altered to pyrite-quartz.
Sulfur-isotope composition of sulfides in the range +4.4‰ to +8.9‰ requires a deep hydrothermal source with elevated
d34S to generate an end-member fluid with estimated d34S of +5.5‰. Vein-related sulfide mineralization is isotopically light,
whereas sulfide disseminated in altered basalt is isotopically heavy. The systematic variations between sulfide generations and
a general increase with depth are a result of sulfate reduction in a shallow seawater-hydrothermal circulation system developed
around the hydrothermal feeder zone. This generates hydrothermal fluid and sulfide mineralization with a maximum d34S of
+8.9‰. Mixing between this shallow circulated fluid and the end-member hydrothermal component would explain the variations
of up to 3‰ observed between different sulfide generations in the mound.

Document Type: Article
Keywords: ODP Leg 158, Petrology, hydrothermal mineralization, TAG mound
Research affiliation: OceanRep > GEOMAR
Refereed: Yes
DOI etc.: 10.2973/
ISSN: 1096-7451
Projects: ODP
Date Deposited: 18 Feb 2008 17:24
Last Modified: 15 May 2019 11:54

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