CO2 and H2O SIMS measurements of clinopyroxene-hosted silicate melt inclusions from Conical Seamount, Papua New Guinea.

Conical Seamount, in Papua New Guinea, is a shoshonitic seamount that hosts epithermal-style mineralization (Petersen et al., 2002). A shallow crustal magma chamber appears to be the main difference between Conical Seamount and the other, barren seamounts nearby. It is characterized by dynamic convection, extensive fractional crystallization and frequent magmatic replenishment (Gautreau et al., 2024). This magma chamber appears to be critical for the transfer of metals and volatiles into the exsolving fluid phase and is thus of key importance for epithermal ore formation (Gautreau et al., 2024).

In this study, we aim at presenting the first robust constraints on volatile contents and saturation as well as the timing of magmatic degassing underneath Conical Seamount. Thus, we quantified CO2 and H2O concentrations in silicate melt inclusions contained in clinopyroxene crystals to determine the different magma stagnation levels below Conical Seamount. We used the CAMECA 1280-HR Secondary Ion Mass Spectrometer (SIMS) at the GFZ facility in Potsdam. These data will be used to model pressure and temperature conditions of the silicate melt (e.g., Iacovino et al., 2021).

At the end of the analytical session, all SIMS pits were imaged with an optical microscope in reflected light mode to check the exact location of each analysis and whether other minerals, inclusions or cracks were hit. If SIMS pits touched cracks or inclusions, the corresponding analyses were considered as outliers. If the central part of the SIMS craters (5 µm in diameter) touched the pyroxene crystal hosting the silicate melt inclusions, then the calculated CO2 and H2O concentrations were considered as minimum values. Visible crystals in the melt inclusions are mentioned for each measurement point in the notes. Finally, we exclude results for volatile contents outside of the range of the basaltic glass reference materials (i.e., > 5,900 µg/g for CO2 and > 8.8 wt.% for H2O; Scicchitano et al., 2024).

Gautreau, L., Hansteen, T.H., Portnyagin, M., Beier, C., Frische, M., Brandl, P.A., 2024. Understanding the links between volcanic systems and epithermal ore formation : A case study from Conical Seamount , Papua New Guinea. LITHOS 482–483, 1–18. https://doi.org/10.1016/j.lithos.2024.107695
Iacovino, K., Matthews, S., Wieser, P.E., Moore, G.M., Bégué, F., 2021. VESIcal Part I: An Open-Source Thermodynamic Model Engine for Mixed Volatile (H2O-CO2) Solubility in Silicate Melts. Earth Sp. Sci. 8, 1–55. https://doi.org/10.1029/2020EA001584
Petersen, S., Herzig, P.M., Hannington, M.D., Jonasson, I.R., 2002. Submarine Gold Mineralization Near Lihir Island , New Ireland Fore-Arc , Papua New Guinea 97, 1795–1813.
Scicchitano, M.R., Shishkina, T.A., Wilke, F.D.H., Wilke, M., Botcharnikov, R.E., Almeev, R.R., 2024. Basaltic glasses for quantification of CO2 and H2O content by Secondary Ion Mass Spectrometry (SIMS). GFZ Data Services. https://doi.org/10.5880/GFZ.3.1.2024.009