First insights on the metallogenic signature of magmatic fluids exsolved from the active magma chamber of Vesuvius (AD 79 "Pompei" eruption)

Fluid inclusions hosted in sanidine from xenoliths, representing the crystallization front of the AD 79 magma chamber of Vesuvius, offer a rare opportunity to track the composition of magmatic fluids exsolving at the peripheral part of a growing K-alkaline magma chamber disrupted by an explosive eruption. This work demonstrates that the exsolving magmatic fluids have a complex composition taking in evidence the great capability of metal transport by means of these solutions. Inclusions are particularly enriched in Zn, Mo, W, Sb, Bi, Tl and Pb. Metals display two different positive correlations: 1) Pb–Zn–Tl–Bi; 2) Mo–W. The different trends may reflect the different complexing agent for these elements (probably chloride for Pb–Zn–Tl–Bi and probably hydroxyl for Mo–W). The occurrence of a “silicothermal” component in these fluids may furthermore favor the metal transport of these solutions. This is probably a major, previously underestimated process in the enrichment of some metals in magmatic–hydrothermal systems. This hypothesis may challenge conventional ideas on fluid-phase mass transport of components by means of magmatic–hydrothermal fluids, and should be taken into account in future works on these topics.