Epithermal-type gold mineralization at Conical Seamount: A shallow submarine volcano south of Lihir Island, Papua New Guinea

Gold-rich polymetallic (Au+Ag+As+Sb+Hg+Zn+Cu+Pb) sulfides have been recovered from the top of Conical Seamount, a shallow (1050 m water depth) submarine volcano just south of Lihir Island in the New Ireland Fore-Are, Papua New Guinea. Gold contents up to 45 ppm (avg. 16 ppm, n=26) with accompanying high Ag, As, Sb, and Hg concentrations occur in samples from a clay-silica(-alunite) altered area at the summit plateau. Mineralization includes realgar, orpiment, stibnite, and sulfosalts such as freibergite in association with the more common sulfides sphalerite, galena, chalcopyrite and pyrite. Native gold has been found in several samples and is usually associated with galena and sphalerite and not related to later As-Sb mineralization. Sulfur isotope ratios of sulfides in the range of -0.2 to -8.6 parts per thousand delta(34)S (avg. -3.5 parts per thousand delta(34)S, n=14) and the occurrence of alunite with typical magmatic habit and sulfate sulfur isotope ratios of +7 parts per thousand delta(34)S indicate a magmatic contribution to the hydrothermal system. Mineralization and alteration at Conical Seamount resemble that of typical subaerial epithermal gold deposits not previously recognized at the modern seafloor.