Shallow drilling of seafloor hydrothermal systems: The missing link

摘要

In September-October 2002, shallow seafloor drilling using the portable 5 m Rockdrill of the British Geological Survey and the German R/V Sonne has revealed critical information on the sub-surface nature of two distinct hydrothermal systems in the New Ireland fore-arc and the Manus Basin of Papua New Guinea. Drilling of 39 holes at the summit plateau of Conical Seamount close to Lihir Island has indicated that previously discovered epimermal-style gold mineralization reaches to a depth of at least 4.5 m below sea-floor with gold concentrations of up to 14.2 g/t Au over a core section of 30 cm. This discovery significantly extends the known surface extent of gold mineralization (up to 230 g/t Au) at Conical Seamount. Almost 9 m of spectacularly textured massive sulfide core recovered from 10 holes drilled in only two days in the active Roman Ruins black smoker site of the Pacmanus area proves, that massive sulfides extend to a depth of at least 5 m below seafloor. High concentrations of gold, locally up to 57 g/t Au over 20 cm of core length, confirm the gold-rich nature of this particular back-arc deposit. Shallow seafloor drilling is a fast and cost efficient method that bridges the gab between surface sampling and deep (ODP) drilling and undoubtedly will become a standard practice in the future study of seafloor hydrothermal systems and massive sulfide deposits.