Mercury deposits in metamorphic settings: the example of Levigliani and Ripa mines, Apuane Alps (Tuscany, Italy)

Abstract

In addition to the world-class epithermal deposits in the Monte Amiata area (Southern Tuscany), mercury production in Tuscany is recorded from the Levigliani and Ripa deposits in Apuane Alps. Both deposits are hosted by sedimentary and subordinate volcanic rock sequences, belonging to the Apuane Metamorphic Complex (AMC), metamorphosed in the greenschist facies during the Apenninic orogeny (ca. 27–8 Ma). At Ripa, mineralization is very simple, consisting of cinnabar with minor pyrite in quartz gangue. Its emplacement is obviously controlled by shear structures produced during the second Apenninic deformation event (D 2). At Levigliani, both the setting and the mineral assemblage are more complex. Mineralization is confined to a lithologic horizon comprised of carbonatic chloritic phyllites and calc-alkaline metabasites. The mineralizing process spanned the entire tectono-metamorphic Apenninic event. A first mineral assemblage (cinnabar I+zincian metacinnabar+pyrite) was formed under conditions presumably not far from the metamorphic thermal peak, whereas a second assemblage (cinnabar II+mercurian sphalerite+pyrite±native mercury±chalcopyrite±galena±pyrrhotite±grumiplucite) was formed in a retrograde stage. In both deposits, the overall P– T– X features of fluid inclusions in quartz are similar to those previously established for syn-metamorphic hydrothermal circulation in AMC. At Ripa, the syn-D 2 shear structures provided a hydrologic trap for mercury mobilized from an unknown source. At Levigliani, the strict lithological control, the protracted nature of the mineralizing process, and the similarities to the setting of Palaeozoic peri-Mediterranean mercury deposits, suggest a small scale remobilization from a pre-existing anomaly.