Lead mining was an important industry in Healeyfield Parish for many years. Healeyfield lead mine was situated at Dene Howle, about half a mile west from the crossroads at Castleside. The mine closed in 1891 after a long history dating back some 800 years, and yielded not only lead but also large quantities of silver. It was owned by the Dean and Chapter of Durham Cathedral, pre-reformation called the Benedictine Priory of Durham and was a supplier of silver to its Mint.
In addition to the various mines, a mill for smelting lead ore was built before 1800 in the Castleside area. The former site of the smelting mill is the starting point for the Healeyfield Parish Walk with the Healeyfield Smelt Mill Flues recognised as an archaeological site.