Mineralogy, sulphur isotope geochemistry and the development of sulphide structures at the Broken Spur hydrothermal vent site, 29 degrees 10 ' N, Mid-Atlantic Ridge

IB Butler, AE Fallick, RW Nesbitt

Research output: Contribution to journalArticlepeer-review

Abstract

A large collection of hydrothermal sulphides from the Broken Spur hydrothermal vent site, including representative samples of mound sulphide materials, has been characterized using optical mineralogy and sulphur isotope analysis. Young mound sulphides from Broken Spur have a pyrrhotite-dominated mineralogy unusual for bare ridge vent systems. However, pyrrhotite is metastable and is ultimately converted to iron disulphides. Mature sulphides are indurated, recrystallized and contain abundant quartz. Sulphide mound materials are developed by three major processes: (i) coalescing of chimney structures; (ii) accumulation of talus from mass wasting and (iii) precipitation and growth in response to hydrothermal flow. Progressive maturation of mound materials is by modification of primary textures, development of mineralogical zoning and replacement of metastable phases. Sulphur isotope analysis of 35 mineral separates returned delta(34)S values of -0.5 to +3.2 parts per thousand. These values are similar to those previously measured for Broken Spur and Snakepit, but are distinctly S-32 enriched compared to the TAG active mound and some Pacific sites. Seawater entrainment and sulphate reduction within the subsurface feeder zone below Broken Spur mounds do not appear to be important processes at Broken Spur, in contrast to the TAG active mound.

Original languageEnglish
Pages (from-to)773-785
Number of pages13
JournalJournal of the Geological Society
Volume155
Publication statusPublished - Sep 1998

Keywords

  • Mid-Atlantic Ridge
  • sulphides
  • sulphur
  • isotopes
  • hydrothermal vents
  • EAST PACIFIC RISE
  • REACTIONS FORMING PYRITE
  • IRON(II) MONOSULFIDE
  • AQUEOUS-SOLUTIONS
  • MASSIVE SULFIDES
  • H2S OXIDATION
  • SULFUR
  • MARCASITE
  • SYSTEMS
  • 125-DEGREES-C

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