Esacanaba Trough
A transect of holes (Holes 1038A to 1038I) was made in the vicinity of Central Hill in Escanaba Trough with the highest priority to drill through the massive sulfide deposits and into the alteration zone near the center of the hydrothermal upflow zone. A primary objective was to establish the causes of the major compositional differences between the deposits at Middle Valley and Escanaba Trough. A series of shallow RCB exploratory holes was targeted primarily at the exposed mounds of massive sulfide in order to establish the extent, composition, and drillability of the massive sulfide in this area prior to starting a deeper drill hole.
Massive sulfide recovered from Central Hill suggests that the mineralization forms only a thin (5-15 m) veneer over the sediment. No major intersection of massive sulfides was recovered.The absence of a well-developed vein-dominated feeder zone in the sediment under the sulfide mounds indicates that hydrothermal venting was probably diffuse and short lived. This is consistent with the lack of chimneys and the general occurrence of high temperature pyrrhotite crusts on the sediment observed during submersible dives. Massive sulfides consist predominantly of massive pyrrhotite and vuggy pyrite. Sphalerite is locally abundant and is associated with pyrrhotite.
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