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GEOREF RECORD

Mineralogy and formation of black smoker chimneys from Brothers submarine volcano, Kermadec Arc

H. A. Berkenbosch, Cornel E. J. de Ronde, J. B. Gemmell, A. W. McNeill and K. Goemann
Mineralogy and formation of black smoker chimneys from Brothers submarine volcano, Kermadec Arc
Economic Geology and the Bulletin of the Society of Economic Geologists (December 2012) 107 (8): 1613-1633

Abstract

Brothers caldera volcano is a submarine volcano of dacitic composition, located on the Kermadec arc, New Zealand. It hosts the NW caldera vent field perched on the steep slope of the caldera walls and includes numerous, active, high-temperature (max 302 degrees C) chimneys and a greater amount of dead, sulfide-rich spires. Petrographic studies of these chimneys show that three main zones can occur within the chimneys: a chalcopyrite-rich core, surrounded by a sulfate-dominated zone, which is in turn mantled by an external rind of Fe oxides, calcite, and silicates. Four chimney types are identified based on the relative proportions of the chalcopyrite and sulfate layers and the presence or absence of anhydrite. Two are Cu rich, i.e., chalcopyrite-sulfate and chalcopyrite-bornite chimneys, and two are Zn rich, i.e., sphalerite-barite and sphalerite-chalcopyrite. Chimney growth begins with the formation of a sulfate wall upon which sulfides precipitate. Later, zone refining results in a chalcopyrite-rich core with pyrite/marcasite and sphalerite occurring predominantly near the outer margins. In chalcopyrite-bornite chimneys, the chalcopyrite core rapidly loses permeability and limits the thickness of the surrounding sulfate layer. In these chimneys, bornite, chalcocite, and covellite form along the outer margin of the chalcopyrite zone as a result of oxidation by seawater. Zinc-rich chimneys display a more vertical zonation and their growth involves an upward-advancing barite cap followed by chalcopyrite deposition (if present) nearer the base. The vertical zonation and lack of anhydrite in these chimneys also implies that larger chalcopyrite and anhydrite deposits may exist subsea floor. The different chimney types are related to subsea-floor permeability, the amount of fluid mixing that occurs prior to venting, and heterogeneous fluid compositions. The occurrence of specular hematite and Bi or Au tellurides associated with chalcopyrite are consistent with magmatic contributions to the NW caldera vent site. These tellurides are the first gold-bearing phase to be identified in these chimneys, and the Bi-Au association suggests that gold enrichment up to 91 ppm is due to scavenging by liquid bismuth. The presence of tellurides in Brothers chimneys have implications for other telluride-bearing deposits, such those in the Urals. Likewise, other aspects of the mineralogy (i.e., textures) and zonation, including the implied subsea-floor deposition, presented here from an active, undeformed environment can aid in understanding ancient volcanogenic massive sulfide (VMS) deposits that have undergone various degrees of metamorphism.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 107
Serial Issue: 8
Title: Mineralogy and formation of black smoker chimneys from Brothers submarine volcano, Kermadec Arc
Affiliation: University of Tasmania, ARC Centre of Excellence in Ore Deposits, Hobart, Tasmania, Australia
Pages: 1613-1633
Published: 201212
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 52
Accession Number: 2013-010682
Categories: Economic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch maps
S36°00'00" - S26°00'00", W180°00'00" - W175°00'00"
Secondary Affiliation: GNS Science, NZL, New Zealand
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: 201308
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