Research cruise SO299 to the New Ireland Basin, Papua New Guinea, discovered the active Karambusel vent field that combines characteristics of magmatic-hydrothermal venting and hydrocarbon seepage. The vent field is located at an eruptive centre on the western flank of Conical Seamount, previously known to host epithermal-style mineralization near its summit. Mineralization at Karambusel consists of disseminated sulfides and polymetallic epithermal amorphous silica veins crosscutting altered ankaramite breccias. Gold occurs as up to 20 µm sized electrum grains (Au/Ag = 5-12) in the matrix of amorphous silica veins and associated with Zn-As-Sb-Ag sulfosalts resulting in bulk rock concentration of up to >30 ppm Au. The main Au precipitation stage was overprinted by a younger Hg- (up to 500 ppm), Sb- (up to 5850 ppm), and As-rich (up to 6.5 wt.%) stage possibly related to the currently active venting of methane-rich, low-temperature (up to 50°C) fluids. Variable δ34S (-14 to 2‰) in sulfides from different stages suggest complex S isotope fractionation processes related to magmatic, hydrothermal, and biogenic processes.
Here, we use a combined approach of bulk methods and high-resolution sulfide trace element and S isotope micro-analysis to reveal the enrichment processes of vein-style submarine precious metal mineralization. Comparison of our results with the Au-rich mineralization at the summit of Conical Seamount (up to 230 ppm Au) and with the world-class Ladolam Au deposit (50 Moz Au) on nearby Lihir Island will allow us to develop a comprehensive mineralization model for Karambusel, which may also be linked to active hydrocarbon seepage.