Publication Date:
2018-09-18
Description:
Grab samples collected in 1987 from the Valu Fa back-arc ridge in the SW Pacific include sulfide-bearing basaltic andesites and andesitic xenoliths, massive sulfide-barite-silica mineralization, native sulfur, and a large number of Fe-Mn crusts. Sphalerite, pyrite, marcasite, barite, and amorphous silica are the predominant minerals in the massive samples. Smaller amounts of chalcopyrite, galena, tennantite, and covellite have been identified. This assemblage formed at the seafloor from smoker-type hydrothermal fluids with temperatures 〈300°C and high concentrations of reduced sulfur. Sulfide mineralization in basaltic andesites consists of disseminated pyrite and marcasite. The scarity of pyrrhotite suggests precipitation of sulfides under elevated fS2-fO2 conditions and at temperatures that may have been as low as 150°C. Extensive deposits of Fe- or Mn-dominated hydrothermal crusts at the Valu Fa Ridge have formed at considerably lower temperatures (≤20°C). High-temperature hydrothermal products including intergrowths of Cu-Fe-Zn-S intermediate solid solution and pyrrhotite were found in a mineralized xenolith from a subvolcanic level.
Type:
Article
,
PeerReviewed
Format:
text
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