The SuSu Knolls Hydrothermal Field, Eastern Manus Basin, Papua New Guinea: An Active Submarine High-Sulfidation Copper-Gold System

摘要

SuSu Knolls comprises three steep-sided conical volcanic peaks, standing on a N-NW-trending ridge in the eastern Manus basin, a complex zone of convergence between the major Indo-Australian and Pacific plates. The knolls consist of three porphyritic andesite-to-dacite domes, each 1.0 to 1.5 km in diameter, with crests ranging from 1,150 to 1,520 m below sea level. An intense hydrothermal plume, with peak transmission anomalies in excess of 40%, originates from SuSu Knolls, and associated hydrothermal venting, with fluid temperatures exceeding 300 degrees C and sulfide mineralization, has been detected on the crests of all three edifices. The most important of these is the 2.47 million metric ton (Mt) Solwara 1 copper-gold deposit on Suzette Knoll, slated for mining by Nautilus Minerals. The porphyritic dacite is commonly strongly altered by reaction with acidic fluids. Fragments of sulfide mineralization, collected as part of the seafloor talus surrounding the crest of North Su and South Su, are characterized by an assemblage of pyrite-(fukuchilite)-enargite +/- covellite-chalcopyrite. By contrast, there are actively venting chimneys on the crest of Suzette that are typically zoned, with chalcopyrite-pyrite-tennantite inner zones and barite-dominated outer zones. The knolls are covered by black sulfidic sediments that contain up to 2.4 wt % Cu and 3.2 ppm Au.