Chemical and mineral compositions of hydrothermal sulfide deposits from the Lucky Strike hydrothermal field, Mid-Atlantic Ridge

Several hydrothermal sulfide structures were sampled using the Mir manned submersibles in the relatively shallow Lucky Strike vent field, Mid-Atlantic Ridge. Bathymetric position of these structures varies by approximately 100 m. Investigation of chemical and mineral compositions of hydrothermal ore occurrences led to the conclusion that the initial high-temperature ore-bearing solution ascending toward the surface became unstable and experienced phase separation beneath the ocean floor. The phase separation was responsible for bathymetric control of hydrothermal ore formation within the field.

Major and trace element abundances at DSDP Hole 72-516F

Anomalously high values of Ir have been detected in association with the Cretaceous/Tertiary boundary in about a dozen marine or continental sections laid down about 65 Ma in many different parts of the world (Alvarez et al., 1981). One possible exception is the Cretaceous/Tertiary boundary region in DSDP Site 356, in the South Atlantic off the coast of South America. In a detailed study of that section, the maximum Ir abundance was about 0.2 ppb, much lower than the 3-90 ppb found in most of the other marine locations (authors' unpublished data on the Cretaceous/Tertiary region of Site 356, 1982). A study of Hole 516F, which is not too far from Site 356, could show whether the very low (or missing) Cretaceous/Tertiary Ir anomaly at Site 356 is characteristic of this region of the South Atlantic.