Tarshish, which means 'to smelt,' was a source not only of silver, but also other refined metals such as iron, tin and lead (Ezekiel 27:12). Recent lead isotope ore provenance analyses of silver found at Akko, Dor, Ein Hogez and Tell Keisan in southern Phoenicia, indicate that Biblical Tarshish was located on the island of Sardinia.
For more, see (off-site link): Silver at Tarshish