Insights on the role of alkaline magmatic systems for epithermal gold potentials : a case study of Conical Seamount, Papua New Guinea
Alkaline porphyry-epithermal systems represent main gold sources throughout the world. The Tabar-Lihir-Tanga-Feni (TLTF) island chain in north-eastern Papua New Guinea exhibits a particular metal endowment, especially exemplified by the giant Ladolam gold deposit on-shore Lihir island with more than 47.1 Mt Measured and Indicated Resources. In the past decades, increased attention has been given to the seamounts off-shore Lihir. Conical Seamount, located south to Lihir, has been well documented because of the hosting gold-mineralization, which is the site where epithermal-style mineralization was discovered on the seafloor first. However, the magmatic system of Conical Seamount underlying such a prominent gold mineralization has not been well constrained and remained widely unknown. This work identifies and describes the main stages of magmatic evolution underneath Conical Seamount along with their importance for the metal transport and deposition. In a broader context, this study addresses the strong link between alkaline magmas and epithermal mineralization. A detailed petrographic study combined with geochemical measurements of different magmatic samples recovered during several cruises conducted with the research vessel SONNE (SO94, SO133, SO166 and SO299) was carried out. Conical Seamount is characterized by several key features for the metal enrichment, transport and deposition: subduction-modified mantle source, significant fractional crystallization, shallow magma chamber marked by metal extraction through sulfide precipitation and fluid exsolution. However, magmatic rejuvenation through the ascent of a new, more hydrous parental magma appears to be an additional necessary stage prior to epithermal mineralization.
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