Dynamics of Ore MEtal TRansport in Alkaline Porphyry systems (DOMETRAP)

The DOMETRAP project aims at understanding the enrichment and transport processes of metals and metalloids including their pathways in alkaline porphyry-epithermal systems. The main focus is on the Tabar-Lihir-Tanga-Feni (TLTF) island chain in northeastern Papua New Guinea that also hosts the world-class Ladolam gold deposit on Lihir island. Several seamounts are located around Lihir and were studied and sampled during RV Sonne cruises SO-94 in 1994, SO-133 in 1998 and SO-166 in 2002. While seamounts are generally considered barren, Conical Seamount, located southeast of Lihir island, shows evidence for epithermal-style mineralization (Petersen et al., 2002) and has been interpreted as a submarine analogue to the Ladolam deposit (Müller et al., 2003). Investigating this submarine system thus means studying a porphyry-epithermal ore system at a juvenile stage. The fertility of the melt to form an ore deposit will be determined and detailed in a first stage through petrological characterization and geochemical analyses (using electron microprobe and LA-ICPMS): whole rock, mineral and glass inclusion chemistry. Beside the major elements, this part of the project will specifically focus on volatile content (Cl, S, F) and trace metal and metalloid contents (e.g. Au, Cu, Ag, As, Bi, Mo, Sb, Se, Te, Tl). Tracking these elements combined with the calculation of the melt oxidation state will help determining the origin and enrichment process of metals in alkaline porphyry-epithermal systems.

The second stage of the project focuses on the magma degassing and fluid exsolution. Therefore, an extended suite of volatile elements (CO2, H2O, S, Cl, F) will be determined in glass inclusions through Secondary Ion Mass Spectrometry (SIMS). Additionally, fluid inclusions will be studied using microthermometry combined with LA-ICPMS. Finally, the local plumbing system will be reconstructed through thermobarometry and the analysis of diffusion profiles in ante-, xeno- and phenocrysts (e.g. clinopyroxene, plagioclase, olivine).

Figure 1: Map of the North-East of Papua New Guinea (left) / Map of Lihir island and surrounding volcanic field (right).

Figure 2: Polarized light Photomicrographs (A, B, C) and electron microscope Photomicrographs (D). A: Glass inclusion in a Clinopyroxene (39RD30-40). B: Magmatic sulfides (37RD0-20). C: Fluid inclusions (white arrows) in Clinopyroxene (29RD0-15). D: Clinopyroxene with concentric zonation (42RD10-22)

References

Müller, D., Franz, L., Petersen, S., Herzig, P. M., & Hannington, M. D. (2003). Comparison between magmatic activity and gold mineralization at Conical Seamount and Lihir Island, Papua New Guinea. Mineralogy and Petrology, 79(3–4), 259–283. doi.org/10.1007/s00710-003-0007-3

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.