The importance of magmatic degassing at a mineralized, submarine volcano: The case of Conical Seamount, Papua New Guinea

Conical Seamount is an active submarine volcano of the Tabar-Lihir-Tanga-Feni island chain (TLTF) in north-eastern Papua New Guinea. This island chain is located within the New Ireland Basin and the related alkaline to shoshonitic magmas are ascending through a thick sedimentary sequence. The TLTF hosts several Cu-Au mineralized volcanic centers. Conical Seamount is a rare example of a submarine epithermal-style mineralization and is considered to be a juvenile analogue of the Ladolam world-class gold deposit located on the nearby island of Lihir.

Recent research assessed important crustal magmatic processes as precursors for the mineralization at Conical Seamount. More specifically, the presence of a degassing crustal magma chamber has been found to be critical for the metal concentration and transfer into the epithermal system. This may explain why other seamounts in the TLTF island chain remain barren (unmineralized).

Here we present new volatile (H₂O, CO₂, F, Cl, S) as well as major and trace element data of clinopyroxene-hosted melt inclusions. These data along with fluid inclusion data allow us to further constrain the volcanic plumbing system, more specifically the pressure (i.e., depth) of the crustal magma chamber, the degassing stage and sulfide saturation processes. Chalcophile elements and Au in particular are scavenged within sulfides concomitant with the magmatic fluid exsolution, leading to ideal conditions for the transfer of metals into the ore-forming system.