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Constraints on water depth of massive sulfide formation; evidence from modern seafloor hydrothermal systems in arc-related settings

Thomas Monecke, Sven Petersen and Mark D. Hannington
Constraints on water depth of massive sulfide formation; evidence from modern seafloor hydrothermal systems in arc-related settings
Economic Geology and the Bulletin of the Society of Economic Geologists (December 2014) 109 (8): 2079-2101

Abstract

The results of three decades of seafloor research provide the most reliable information on the importance of water depth in massive sulfide formation. Available data from over 130 occurrences show that water depths of seafloor vent sites vary with plate tectonic setting and the regional magmatic and volcanic environment. The shallowest hydrothermal systems in subduction-related settings are hosted by arc volcanoes. These shallow vent sites have a number of features in common with subaerial epithermal systems. Massive sulfide occurrences in arc-related rifts, the most likely setting for many ancient analogs, are generally restricted to water depths from approximately 700 to 2,000 m, with rifts developing within old arc crust at the deeper end of this range. Back-arc spreading centers proximal to arcs host massive sulfide deposits at depths of approximately 1,500 to 2,000 m. The deepest hydrothermal systems occur along mature back-arc spreading centers distal to volcanic arcs where water depths range from approximately 2,000 to 3,700 m. These deeper vent sites probably represent the best modern analogues of ophiolite-hosted massive sulfide deposits. Boiling of the hydrothermal fluids is common at volcanic arcs and in arc-related rifts. In these environments, elevated magmatic gas contents of the hydrothermal fluids can contribute to the widespread occurrence of phase separation and associated gas loss. By contrast, the high ambient pressures in deep marine hydrothermal systems along mature back-arc spreading centers prevent fluids from boiling during their ascent to the seafloor. Boiling controls the maximum temperature at which hydrothermal fluids discharge at the seafloor and, therefore, influences the metal content of seafloor sulfide deposits. Copper-rich massive sulfides typically occur at water depths exceeding approximately 1,000 m, whereas Zn- and Pb-rich occurrences may form at any water depth. Boiling can be an important control on Ag and Au grades but is not the only factor controlling precious metal enrichment in massive sulfides. Shallow marine hot spring deposits can be highly enriched in trace metals such as As, Hg, and Sb. Submarine volcanic arc and back-arc settings are geologically complex and significant variations in water depth can occur over short distances. Paleoenvironmental reconstruction of these environments in ancient volcanic terranes is hampered by the lack of unequivocal volcanological or sedimentological criteria that indicate water depth. The relationships established here using modern seafloor observations provide important constraints on the paleoenvironmental setting of ancient volcanic-hosted massive sulfide deposits.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 109
Serial Issue: 8
Title: Constraints on water depth of massive sulfide formation; evidence from modern seafloor hydrothermal systems in arc-related settings
Affiliation: Colorado School of Mines, Department of Geology and Geological Engineering, Golden, CO, United States
Pages: 2079-2101
Published: 201412
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 186
Accession Number: 2014-105143
Categories: Economic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, sketch maps
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S25°00'00" - S16°00'00", W179°00'00" - W173°00'00"
S05°00'00" - S02°30'00", E148°00'00" - E153°00'00"
N12°00'00" - N21°00'00", E144°00'00" - E147°00'00"
S23°00'00" - S09°00'00", E165°00'00" - E179°00'00"
N26°01'60" - N26°55'00", E127°37'60" - E128°19'00"
S23°00'00" - S15°00'00", W177°00'00" - W171°00'00"
S20°30'00" - S13°00'00", E166°00'00" - E169°00'00"
Secondary Affiliation: Helmholtz Centre for Ocean Research Kiel, DEU, GermanyUniversity of Ottawa, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201452
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