The majority of documents are either accounts of the keepers of the king's mines of tin and other minerals in Devon and Cornwall, that is, they are records either of the period of direct administration by the Crown, or more commonly, records of the Duchy of Cornwall; or are coinage rolls relating to the production and sale of tin in the same counties. A few records relate more widely to the Crown's prerogative rights over the extraction of minerals found beneath the surface of the soil.
Records relating to mines in Cornwall and Devon are mostly those of the Duchy, remaining in the Exchequer records by virtue of the physical interrelation between the Duchy Office and the Courts of General Surveyors, which originally shared the same premises, and the Augmentations Office, which assumed audit of the Duchy's accounts in 1547: a relationship and overlap of personnel which frequently continued under the auditors of the Land Revenue. Records of mines in other counties are placed here purely on account of their subject matter. Most appear to be records of the King's Remembrancer's Office.
For other records concerning mines and quarries of both the Crown, the royal duchies, and of private persons, see Public Record Office, Records Information no 83 'Sources for the history of mines and quarries'. Exchequer depositions taken by commission, E 134, are a particularly important source, and can be used as a key to related documents in particular equity proceedings heard in the Exchequer. The supplementary list of the 'Mines' section of E 101 includes a few cross references to strays now in LR 12.