The history of Kythnos, as well as that of the other western Cyclades from the beginning of the 3rd millennium BC, is intertwined with the existence of metal ores, particularly copper and iron ores on them. Prehistoric copper mining and smelting sites have been identified on the island, and small Early Cycladic installations have been located nearby.
The surface research on the east coast and the northwest part of the island, carried out by I. Bassiakos and O. Filaniotou, has made a significant contribution. The work was based on geological field surveying and metallurgical-geochemical analyses.
In the northwest part of the island, the copper mines at Aspra Kelia and Petra are to be associated with the copper smelting sites of Pounta, Sideri and Paliopyrgos-Aspra Spitia. At these sites on the surface lie slag and fragments of smelting furnaces (many of which have perforations), potsherds and tools. At Aspra Spitia (Paliopyrgos), the quantity of copper slag and fragments of furnaces present is impressive, mainly around the ancient tower that survives having been integrated into a newer monastic cell. Small Early Cycladic installations related to the above mining activities have been identified in the area (Kakovolo, Aspra Spitia).
The northeast coast of the island is dominated by Skouries, a plateau with steep slopes towards the sea to the north of the Agios Ioannis peninsula, at a point exposed to the winds. Judging by the large quantities of copper slag here, it seems that this is a prehistoric site of intensive smelting over a long lifespan. According to the analyses, arsenical copper was produced in Skouries and the site was dated with C14 to the Early Cycladic period.
South of Skouries another site of smelting is Lefkes and is probably related to the nearby Zogaki where among the remains of modern mines, copper minerals (malachite and azurite) have been identified
During historical times, copper gives way to iron. Classical and Roman mines have been identified in Zogaki, Kanala and Milies near Dryopida, as well as in the Katafyki cave. In Vryokastro (an ancient city) a large number of iron slags on the surface testify to intense mining activity.
Modern mining activity began on Kythnos in 1880 and stopped in 1940. Impressive installations from this activity are visible today in various parts of the island (Kakovolo, Zogaki, Lefkes, Dryopida).
