Athenian silver ores were exploited from the Bronze Age. The earliest evidence for processing silver ore anywhere in the Aegean is from Lambrika (on the Koropi-Vari road) and dates to about 3,000 BC, Archaeological Reports for 2003-4 (2004) 8.
The Laurion silver mines expanded significantly in the early fifth century BC when new rich veins were discovered; this was reputedly the source of the money used, on Themistokles' suggestion, to build the 200 triremes with which the Athenians fought the Persians at the Battle of Salamis.
Extensive remains of mining, ore dressing and smelting are visible in the area. Field walkers should beware unmarked mine shafts.
The photo to the left is a gallery, going horizontally into the hill, with some of the waste excavated rock used to pack and shore up the old entrance hole.
The photo to the right is a shaft, going down into the hill.
And this is remains of a furnace.
Contact me if you want high quality versions of these photos.
Refs: For the process of turning rocks in the Laurion into Athenian silver coins, see T E Rihll 'Making money in Classical Athens' in D Mattingly & J Salmon (edd) Economies beyond Agriculture, Routledge 2000, pp. 115-142.