In Eastern Liguria, manganese ores occur as stratiform layers (0.01-0.1 m thick) or massive lenses (5-20 m thick) near the base of chert sequences (“Diaspri di Monte Alpe” Formation) overlaying Jurassic ophiolites. These stratiform ores, which were formed by Mn-oxide fractionation form hydrothermally metalliferous-bearing siliceous muds  during turbiditic re-sedimentation, consist of rhythmic interlaying of braunite-bearing levels (5-15 cm thick) and hematitie-rich cherts.

Tectono-metamorphic re-equilibration (80 Ma), under prehnite-pumpellyite facies conditions (T=275 ± 25˚C; P= 25 ± 0.5 Kbars), affected  ophiolites and their  sedimentary covers, inducing mobilizations and thickening of stratiform ores at the fold hinges were massive lenses, up to some tens of meters, formed. Braunite + quartz is the stable assemblage replacing the sedimentary oxides and hydroxides. During this stage a complex network of veins and fractures developed, mostly in the massive lenses; reaction processes, triggered by mobilized fluids along fractures and brecciated layers, developed Mn-silicate and/or Mn-carbonate assemblages, at the expense of braunite and quartz.

Circulation of fluids, under decrasing P-T metamorpgic conditions, along later extensional fractures, induced the further concentration of dispersed elements such as Ba, Sr, As, V, and allowed the genesis of a great variety of rare and new minerals.