The formation of gold-rich seafloor sulfide deposits: Evidence from the Beebe hydrothermal vent field, Cayman Trough
| Autor: | Matthew R. S. Hodgkinson, Alexander P. Webber, Bramley J. Murton, Stephen Roberts, Rachel A. Mills |
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| Rok vydání: | 2017 |
| Předmět: |
chemistry.chemical_classification
Beebe Hydrothermal Vent Field 010504 meteorology & atmospheric sciences Sulfide Geochemistry engineering.material 010502 geochemistry & geophysics 01 natural sciences Seafloor spreading Hydrothermal circulation Geophysics chemistry Geochemistry and Petrology Ultramafic rock engineering Seawater Chimney Pyrrhotite Geology 0105 earth and related environmental sciences |
| Zdroj: | Geochemistry, Geophysics, Geosystems. 18:2011-2027 |
| ISSN: | 1525-2027 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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