Mercury in groundwater from the Mt. Amiata area (central Italy)

The Mt. Amiata geothermal area is well-known for the presence of the (homonymous) extinct Quaternary volcano and its residual hydrothermal activity. Additionally, several epithermal Hg-ore bodies are widely distributed in the area and are prevalently represented by stockworks and mantos depositional structures, whose genesis is intimately linked to the volcano-geothermal setting of this province. These peculiar features made this site the fourth largest and most important mining district worldwide (World Class Deposit) for mercury exploitation where the operations started around the mid-‘800s and officially ended at Abbadia San Salvatore mine (ASSM) in 1982. The industrial exploitation was based on two main exploitation and production sites, ASSM and Siele mines, respectively, and in other minor “satellite” centers (e.g. Solforate, Abetina (Argus), Morone, Cornacchino, Pietrineri, Cortevecchia, Montebuono). Metallic mercury, also called “quicksilver”, was used in agricultural practices, medical purposes, thermometric devices, cosmetics, weapon industry and as a pigment. Through the last decades, several geochemical studies dealing with mercury metallogeny and environmental issues related to the past mining activities have been performed. Currently, monitoring and remediation programs, started in 2009, are still going on at the ASSM site. In the framework of collaboration with the local water management company, aimed at better definition of the hydro-geochemical characteristics of the main groundwater bodies hosted in the Mt. Amiata area, over 130 spring water samples (including thermal waters and waters discharging from some dismissed mine drainage tunnels) were collected and analyzed for water chemistry. Among the analyzed (by ICP-MS) trace species, Hg is here considered for discussion along with the detected concentrations of other heavy metals such as As and Sb. Another goal of this research was indeed that to support the local authorities with useful hints on the most appropriate strategy to adopt (in terms of both availability and quality assessments) for the management of freshwater resources in the area. The detected mercury concentrations were ranging between <0.1 and 11 mg/L. The average values of Hg measured in water samples from the cold Mt. Amiata aquifer (volume of about 55*106 m3, hosted in the Quaternary volcanics) were around 0.2-0.3 mg/L, whereas concentrations up to 2.5 mg/L were occasionally found in correspondence to the outlets of some hypothermal springs from the area. Locally, higher mercury concentrations were recorded in other springs discharging from different portions of the regional carbonate aquifer cropping out in the close surroundings of the volcanic edifice. Water chemistry appeared to be mainly governed by water-(mineralized)rock and gas-water interactions, although secondary processes are also likely.