Sulfide composition and microthermometry of fluid inclusions in the Leg 111 sheeted dike section of Ocean Drilling Program Hole 504B, Costa Rica Rift

Hole 504B of the Ocean Drilling Program is dedicated to the study of crustal structure and hydrothermal processes in 5.9-m.y.-old oceanic basement. Continuing the work of previous legs, hole 504B was extended 212.3 m to a total depth of 1562.3 m below seafloor (bsf) during leg 111 in 1986. Quartz-sulfide veins occur at a depth of 1369–1388 m bsf in basalts of the sheeted dike complex. The ore minerals are predominantly pyrite, less chalcopyrite, rare Corich Cu-Fe-S phases, and a thiospinel (linnaeite/carrollite). Microprobe analyses yield a high Co content in zoned vein pyrites (>8 wt %) as well as in the Cu-Fe-S phases (>5 wt %). Up to 35.8 wt % Co was detected in the thiospinel. A Co/Ni ratio of >100 distinguishes the vein pyrite from pyrite in the basaltic wall rock and from pyrite formed as an alteration product of olivine (Co/Ni