Magma evolution and epithermal ore formation at Conical Seamount, Papua New Guinea

The Tabar-Lihir-Tanga-Feni (TLTF) island chain in northeastern Papua New Guinea hosts the world-class Ladolam gold deposit on Lihir island as well as several other Au prospects. Several young seamounts are located around Lihir and were studied in detail by three RV Sonne cruises in 1994, 1998 and 2002. While most of these seamounts are considered barren, Conical Seamount, located southeast of Lihir island, shows evidence for epithermal-style mineralization and has been interpreted as a submarine analogue to the Ladolam deposit. It offers a rare opportunity to study a porphyry-epithermal ore system at a juvenile stage and compare it to a mature system nearby.

In the first phase of our research project, we focus on the igneous system underlying the epithermal ore-forming system at Conical. We study the lavas as well as minerals and glass inclusions to reconstruct melting processes, magma evolution and ore fertility using detailed petrology, in situ geochemistry and thermobaric modelling. Special emphasis is given to volatile as well as trace metal and metalloid contents in bulk rocks, glasses and glass inclusions. Mineral zonations and the compositional diversity of pyroxene-hosted glass inclusions point towards repeated magma recharge and the potential existence of multiple magma stagnation levels. While the high melt oxidation state (∆ log fO2 of +0.5 to +2 relative to FMQ) at Conical is advantageous for the enrichment of chalcophile elements in the evolving melt, high volatile contents may promote early fluid exsolution and the transfer of metals and metalloids into the epithermal system.