The 19th century was a period which saw Cornish mining technology used to deepen some of the mines in search of richer ore deposits. However, as the lead veins narrow with depth, this proved unsuccessful, and attention was switched to resmelting the leadrich waste slag and slimes left over from previous medieval mining.
Lead is found at low levels in Earth's crust, mainly as lead sulfide. 4. However, the widespread occurrence of lead in the environment is largely the result of human activity, such as mining, smelting, refining and informal recycling of lead; use of leaded petrol (gasoline); production