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Critical role of caldera collapse in the formation of seafloor mineralization: The case of Brothers volcano

Critical role of caldera collapse in the formation of seafloor mineralization: The case of Brothers volcano
Critical role of caldera collapse in the formation of seafloor mineralization: The case of Brothers volcano
Hydrothermal systems hosted by submarine arc volcanoes commonly include a large component of magmatic fluid. The high Cu-Au contents and strongly acidic fluids in these systems are similar to those that formed in the shallow parts of some porphyry copper and epithermal gold deposits mined today on land. Two main types of hydrothermal systems occur along the submarine portion of the Kermadec arc (offshore New Zealand): magmatically influenced and seawater-dominated systems. Brothers volcano hosts both types. Here, we report results from a series of drill holes cored by the International Ocean Discovery Program into these two types of hydrothermal systems. We show that the extent of hydrothermal alteration of the host dacitic volcaniclastics and lavas reflects primary lithological porosity and contrast- ing spatial and temporal contributions of magmatic fluid, hydrothermal fluid, and seawater. We present a two-step model that links the changes in hydrothermal fluid regime to the evo- lution of the volcano caldera. Initial hydrothermal activity, prior to caldera formation, was dominated by magmatic gases and hypersaline brines. The former mixed with seawater as they ascended toward the seafloor, and the latter remained sequestered in the subsurface. Following caldera collapse, seawater infiltrated the volcano through fault-controlled perme- ability, interacted with wall rock and the segregated brines, and transported associated metals toward the seafloor and formed Cu-Zn-Au–rich chimneys on the caldera walls and rim, a process continuing to the present day. This two-step process may be common in submarine arc caldera volcanoes that host volcanogenic massive sulfide deposits, and it is particularly efficient at focusing mineralization at, or near, the seafloor.
0091-7613
de Ronde, Cornel E.J.
b6e8fa3b-0dd8-43c1-a066-a9c603e52bde
Humphris, Susan E.
fd7fef75-a84d-4f24-9a7b-502f43cfe159
Hofig, Tobias
8397796e-fb32-4460-971b-94cc356a3e55
Reyes, Agnes
aecbdacc-d253-4969-ad8f-9c8cc506766b
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
IODPExpedition 357 Science Party,
0fe8e786-3c07-4f5d-ab9f-8b9cc38025ca
de Ronde, Cornel E.J.
b6e8fa3b-0dd8-43c1-a066-a9c603e52bde
Humphris, Susan E.
fd7fef75-a84d-4f24-9a7b-502f43cfe159
Hofig, Tobias
8397796e-fb32-4460-971b-94cc356a3e55
Reyes, Agnes
aecbdacc-d253-4969-ad8f-9c8cc506766b
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
IODPExpedition 357 Science Party,
0fe8e786-3c07-4f5d-ab9f-8b9cc38025ca

de Ronde, Cornel E.J., Humphris, Susan E., Hofig, Tobias, Reyes, Agnes, Roberts, Stephen and IODPExpedition 357 Science Party, (2019) Critical role of caldera collapse in the formation of seafloor mineralization: The case of Brothers volcano. Geology. (doi:10.1130/G46047.1).

Record type: Article

Abstract

Hydrothermal systems hosted by submarine arc volcanoes commonly include a large component of magmatic fluid. The high Cu-Au contents and strongly acidic fluids in these systems are similar to those that formed in the shallow parts of some porphyry copper and epithermal gold deposits mined today on land. Two main types of hydrothermal systems occur along the submarine portion of the Kermadec arc (offshore New Zealand): magmatically influenced and seawater-dominated systems. Brothers volcano hosts both types. Here, we report results from a series of drill holes cored by the International Ocean Discovery Program into these two types of hydrothermal systems. We show that the extent of hydrothermal alteration of the host dacitic volcaniclastics and lavas reflects primary lithological porosity and contrast- ing spatial and temporal contributions of magmatic fluid, hydrothermal fluid, and seawater. We present a two-step model that links the changes in hydrothermal fluid regime to the evo- lution of the volcano caldera. Initial hydrothermal activity, prior to caldera formation, was dominated by magmatic gases and hypersaline brines. The former mixed with seawater as they ascended toward the seafloor, and the latter remained sequestered in the subsurface. Following caldera collapse, seawater infiltrated the volcano through fault-controlled perme- ability, interacted with wall rock and the segregated brines, and transported associated metals toward the seafloor and formed Cu-Zn-Au–rich chimneys on the caldera walls and rim, a process continuing to the present day. This two-step process may be common in submarine arc caldera volcanoes that host volcanogenic massive sulfide deposits, and it is particularly efficient at focusing mineralization at, or near, the seafloor.

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Final-Brothers-with Diagrams - Accepted Manuscript - Accepted Manuscript
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Accepted/In Press date: 14 May 2019
e-pub ahead of print date: 6 June 2019

Identifiers

Local EPrints ID: 432415
URI: https://eprints.soton.ac.uk/id/eprint/432415
ISSN: 0091-7613
PURE UUID: 65c40f18-3e0f-4ef4-b6b2-a7dff61c48ae
ORCID for Stephen Roberts: ORCID iD orcid.org/0000-0003-4755-6703

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Date deposited: 12 Jul 2019 16:30
Last modified: 10 Dec 2019 01:58

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