Potential sulfur sources for submarine caldera associated mineralization in north-west Wales

In north-west Wales vein mineralization is hosted by the Ordovician Snowdon Volcanic Group, and older sedimentary rocks. Mineralization typically consists of narrow, steeply dipping base metal veins, stockworks, disseminated sulfides and quartz-sulfide cemented breccia zones. Sulfur isotope analyses were carried out on vein sulfides and country rocks to elucidate ore sulfur source/s. The volcanic-hosted and the majority of sedimentary rock-hosted sulfides have delta S-34 from +9.1 to +22.3 parts per thousand, with mean vein delta S-34 of +12.2 +/- 3.7 parts per thousand. The Snowdon Volcanic Group is generally considered to represent a reservoir of isotopically heavy sulphur with mean delta S-34 of +11.7 parts per thousand +/- 4.5 parts per thousand. The sedimentary rock diagenetic sulfides are typically heavier. These values are thus compatible with a typical volcanogenic massive sulfide system, with sulfur originating from a combination of leaching of volcanic host lithologies, and reduction of Ordovician seawater. The delta S-34 ore sulfides from around Snowdon are comparable to those found in Ordovician age volcanogenic massive sulfide deposits globally.