MINERALIZATIONS IN OPHIOLITE-RELATED VOLCANOGENIC MASSIVE SULFIDE DEPOSITS FROM THE MODENA PROVINCE, EMILIA-ROMAGNA REGION, ITALY

The Northern Apennine External Ligurian units include sequences of pillow lavas associated with serpentine and gabbro breccias, radiolarian cherts, limestones, and abundant serpentinized subcontinental mantle peridotites (Rampone et al., 1995; Zaccarini & Garuti, 2008 and reference therein). In these units, various types of Volcanogenic Massive Sulfide (VMS), i.e., metal deposits associated with hydrothermal events in submarine environments (Piercey, 2011), occur at different stratigraphic positions in the ophiolite sequence. In the Boccassuolo ophiolite (Modena Province, Emilia-Romagna region), they consist of crosscutting stockwork ore bodies emplaced into pillow basalts (Zaccarini & Garuti, 2008). Forty samples from two historically dismissed mine districts of the Boccassuolo ophiolite, Boccassuolo and Montecreto, were collected to determine their metal contents and mineralization genesis. Both barren and mineralized samples were selected to better constrain the mineralization enrichment tenor. Whole-rock major and trace elements were analyzed to determine the original host-rock composition and progressive formation of ore bodies. Barren samples are variably weathered basalts and basaltic andesites. On the basis of Rare Earth Elements (REE) contents and Nb/Y and Zr/Y ratios, they show Ocean Continent Transition Zone (OCTZ) chemical features with low-Ti contents (up to 2.52 wt.%), T-MORB affinity, and a garnet signature (Dyn/Ybn: 1.2-1.4), in agreement with Cyprus-type deposits (Saccani, 2015; Zaccarini & Garuti, 2008). In opposition with these, mineralized samples belonging to VMS deposits are Pb-poor (up to 3 ppm) and Cu- Zn rich (up to 0.6 and 0.3 wt.%, respectively), comparable with mafic VMS types, although not Ag-enriched, as seen in other examples worldwide (e.g., Piercey, 2011; Zaccarini & Garuti, 2008). Boccassuolo samples consist of veins, mainly formed by albite and tiny sulfide minerals (1mm maximum), while Montecreto ones are mainly made of quartz and largest sulfides (up to 1.5 cm). XRD and EMPA analyses on selected Montecreto samples reveal a sulfide association of pyrite, in particular Au-enriched pyrite chalcopyrite, sphalerite, pyrrhotite and kësterite. EMPA results show clinochlore-type chlorite, as well as titanite and ilmenite as the main oxides phases in barren samples. These preliminary data identify the different proximity related to the VMS feeding system.