Sb–Au-bearing chalcedonies in hot geothermal systems: insights from the jasperoids of Poggio Peloso (southern Tuscany, Italy)

Detailed characterization was performed on the chalcedonies from the jasperoids of the
Pietratonda–Poggio PelosoSb–Au deposit(southernTuscany,Italy). The main purpose was
to retrieveinformationonthegeothermalfluidsthatformedthechalcedoniesandthesource
of antimony concentrations. Investigations were performed using optical microscopy, laser
ablation inductively coupled plasma mass spectroscopy and X-ray diffraction on both the chalcedonies and the lithotypes cropping out in the area. The results obtained allow the chalcedonies of Pietratonda–Poggio Peloso to be described as a unicum, based on the very high contents of Sb that do not find a comparison in the literature. The textures showed multiple generations of silica that agree well with an environment characterized by multiple injections of mineralizing solutions, bearing variable physico chemical characteristics. The transport likely took place
in analkaline environment, while the acidification of the water may have favoured the precipitation at varying temperatures but not higher than 225°C. The rocks from which the constituents may have been leached are the hosting carbonates and the surrounding metamorphic
rocks. Among the examined rocks, the metamorphic rocks showed the most numerous and
significant correspondences with the chalcedonies and were the only ones in which discrete
amounts of gold contents were found.