This reflects the revolutionary change in the history of lead mining since the first discovery of argentiferous lead ores in the Rocky Mountain states in 1864, which became available only after the building of railways.
There are mines of chrome, mercury, cinnabar, argentiferous lead and rock salt.
It is rich in minerals, including chrome, manganese, zinc, antimony, iron, argentiferous lead, arsenic and lignite, but some of these are unworked.
Lead ores (chiefly argentiferous galena) and building stone are found, and iron ore is distributed over the hilly country.
Formerly all argentiferous lead had to be cupelled, and the resulting litharge then reduced to metallic lead.
It is not used in the treatment of ores, but finds application in the case of calcined argentiferous lead and copper mattes.
The mines of argentiferous lead, belonging to Greenwich Hospital, London, were formerly of great value, and it was in order that royalties on the Alston lead mines and on those elsewhere in the county might be jointly collected that the parish was first included within the borders of Cumberland, in the 18th century.
Other pairs of isomorphous argentiferous minerals are: the cubic polybasite, 9Ag2S Sb2S3, and pearceite, 9Ag2S As2S3; and the germanium minerals argyrodite, 4Ag 2 S GeS2, and canfieldite, 4Ag 2 S (Sn, Ge) S2.
In the neighbourhood are mines of argentiferous copper, and the surrounding district and villages are occupied with smelting and similar works.
The most important mineral is a peculiarly rich argentiferous lead, but gold in small quantities, copper, iron, sulphur, alum and arsenic are also found.