sentences:  These later mines were both open-cast and underground, mostly to exploit the island's numerous karst hosted calamine deposits for their lead and silver.Gold, copper and iron were also found; the Byzantines quarried marble on the island.In the early 20th century, mining companies (most notably the Speidel mining company) exploited the island's zinc-lead rich calamine ores, with a yield of around 2 million tonnes, and a processing plant at Limenaria produced zinc oxide.