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The formation of gold-rich seafloor sulfide deposits:: evidence from the Beebe hydrothermal vent field, Cayman Trough

The formation of gold-rich seafloor sulfide deposits:: evidence from the Beebe hydrothermal vent field, Cayman Trough
The formation of gold-rich seafloor sulfide deposits:: evidence from the Beebe hydrothermal vent field, Cayman Trough
The Beebe vent field (BVF) in the Cayman Trough has built an auriferous massive sulfide deposit on the ultra-slow spreading mid-Cayman spreading centre. The genesis of auriferous sulfide deposits at mid-ocean ridges is not fully understood, although there is a growing recognition that slow and ultra-slow spreading centres are conducive to gold mineralization. Analysis of hydrothermal precipitates from the BVF indicates that the highest gold contents are present within “beehive diffusers”, which have developed a highly porous pyrrhotite framework. The beehive structure allows vent fluids to effuse slowly, while allowing ingress of seawater to cool the fluid. The prevalence of pyrrhotite in the beehive samples, lack of sulfates, association between pyrrhotite and gold grains, and results of thermodynamic modelling, suggests gold precipitation occurred under highly reduced conditions even during mixing with seawater. In contrast, high temperature chimneys, with a single orifice, maintain high temperatures to the primary vent orifice and much of the gold is lost to seawater. Despite this, both chimney types are relatively gold enriched, which points to a further underlying cause for high gold at the BVF such as interaction of hydrothermal fluids with ultramafic lithologies in the basement. The final gold composition of the deposit is partially controlled by loss of gold during mass-wasting of the material, with gold depletion most prevalent in blocks formed at beehive-type chimneys. The BVF demonstrates that the overall gold content of a massive sulfide deposit is the sum of basement, precipitation, and surface processes.
2011–2027
Webber, Alexander P.
c9b7b1e3-ea40-4740-805e-914806eeaeb7
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
Murton, Bramley J.
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Mills, Rachel A.
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Hodgkinson, Matthew R.S.
2e2ab582-a6af-4f26-9427-9a95023681da
Webber, Alexander P.
c9b7b1e3-ea40-4740-805e-914806eeaeb7
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
Murton, Bramley J.
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12
Mills, Rachel A.
a664f299-1a34-4b63-9988-1e599b756706
Hodgkinson, Matthew R.S.
2e2ab582-a6af-4f26-9427-9a95023681da

Webber, Alexander P., Roberts, Stephen, Murton, Bramley J., Mills, Rachel A. and Hodgkinson, Matthew R.S. (2017) The formation of gold-rich seafloor sulfide deposits:: evidence from the Beebe hydrothermal vent field, Cayman Trough. Geochemistry, Geophysics, Geosystems, 18 (6), 2011–2027. (doi:10.1002/2017GC006922).

Record type: Article

Abstract

The Beebe vent field (BVF) in the Cayman Trough has built an auriferous massive sulfide deposit on the ultra-slow spreading mid-Cayman spreading centre. The genesis of auriferous sulfide deposits at mid-ocean ridges is not fully understood, although there is a growing recognition that slow and ultra-slow spreading centres are conducive to gold mineralization. Analysis of hydrothermal precipitates from the BVF indicates that the highest gold contents are present within “beehive diffusers”, which have developed a highly porous pyrrhotite framework. The beehive structure allows vent fluids to effuse slowly, while allowing ingress of seawater to cool the fluid. The prevalence of pyrrhotite in the beehive samples, lack of sulfates, association between pyrrhotite and gold grains, and results of thermodynamic modelling, suggests gold precipitation occurred under highly reduced conditions even during mixing with seawater. In contrast, high temperature chimneys, with a single orifice, maintain high temperatures to the primary vent orifice and much of the gold is lost to seawater. Despite this, both chimney types are relatively gold enriched, which points to a further underlying cause for high gold at the BVF such as interaction of hydrothermal fluids with ultramafic lithologies in the basement. The final gold composition of the deposit is partially controlled by loss of gold during mass-wasting of the material, with gold depletion most prevalent in blocks formed at beehive-type chimneys. The BVF demonstrates that the overall gold content of a massive sulfide deposit is the sum of basement, precipitation, and surface processes.

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Accepted/In Press date: 27 April 2017
e-pub ahead of print date: 1 June 2017
Published date: 16 July 2017
Organisations: Ocean and Earth Science, Faculty of Natural and Environmental Sciences, Geochemistry, Marine Geoscience, National Oceanography Centre

Identifiers

Local EPrints ID: 408029
URI: http://eprints.soton.ac.uk/id/eprint/408029
PURE UUID: 3d4dd6ff-6c52-4b9d-8cf7-5ad552b517f1
ORCID for Stephen Roberts: ORCID iD orcid.org/0000-0003-4755-6703
ORCID for Rachel A. Mills: ORCID iD orcid.org/0000-0002-9811-246X

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Date deposited: 10 May 2017 01:03
Last modified: 19 Mar 2022 05:01

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Contributors

Author: Alexander P. Webber
Author: Stephen Roberts ORCID iD
Author: Bramley J. Murton
Author: Rachel A. Mills ORCID iD
Author: Matthew R.S. Hodgkinson

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