Europe has very few sources of tin. Therefore, throughout ancient times it was imported long distances from the known tin mining districts of antiquity. These were the Erzgebirge along the modern border between Germany and Czech Republic, the Iberian Peninsula, Brittany in modern France, and Devon and Cornwall in southwestern Britain (Benvenuti et al. 2003, p. 56; Valera & Valera 2003, p. 11). There are several smaller sources of tin in the Balkans (Mason et al. 2016, p. 110) and another minor source of tin is known to exist at Monte Valerio in Tuscany, Italy. The Tuscan source was exploited by Etruscan miners around 800 BC, but it was not a significant source of tin for the rest of the Mediterranean (Benvenuti et al. 2003). Even at that time, the Etruscans themselves had to import additional tin from the northwest of the Iberian Peninsula, and later from Cornwall (Penhallurick 1986, p. 80).
Source: Tin sources and trade in ancient times – Wikipedia
Tim B.
https://en.wikipedia.org/wiki/Cassiterides