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Geological Society, London, Special Publications; 1995; v. 87; p. 175-189;
DOI: 10.1144/GSL.SP.1995.087.01.15
© 1995 Geological Society of London

Mineralogy and sulphur isotope geochemistry of the Broken Spur sulphides, 29°N, Mid-Atlantic Ridge

Rowena C. Duckworth1,5, Richard Knott1, Anthony E. Fallick2, David Rickard1, Bramley J. Murton3 & Cindy Van Dover4

1 Department of Earth Sciences, PO. Box 914, University of Wales, Cardiff CF1 3YE, UK
2 Isotope Geoscience Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, UK
3 Institute of Oceanographic Sciences, Deacon Laboratory, Wormley, Surrey GU8 5UB, UK
4 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
5 National Key Centre in Economic Geology, Department of Earth Sciences, James Cook University, Townsville 4811, Queensland, Australia

Massive sulphide-sulphate-oxides from the newly discovered Broken Spur hydrothermal field at 29°10'N on the slow-spreading Mid-Atlantic Ridge have been examined to determine their mineralogical, chemical and sulphur isotope characteristics. The chimney and spire samples are dominated by chalcopyrite-isocubanite-pyrrhotiteanhydrite, with the uppermost active areas composed of anhydrite-rich ‘beehive’ structures which act as diffusers for the hydrothermal fluids and scaffolding for the chimney construction. Delicate ‘organ-pipe’ chimney tips grow on the beehive structures. Samples from mounds and the base of active edifices are more enriched in Fe disulphides and sphalerite, with significant amounts of Fe oxyhydroxides and amorphous silica. Sulphur isotope values of sulphides range from –0.8 to 2.4{per thousand}, similar to those reported from the Snakepit hydrothermal vent field. This range is significantly lower than the range reported from the fast-spreading East Pacific Rise, and this may be a function of fluid flow paths in differing hydrothermal settings.





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[Abstract] [PDF]