The lord grants a lease or set for 21 years, reserving a power to put an end to the term, if the mine should not be effectually worked; he likewise agrees for a certain proportion of the ores to be delivered to him on the mine in a merchantable state, or their value in money: he provides for a power of inspecting the works at all times, and binds the adventurers to maintain and leave at any determination of their grant all the shafts, adits, and levels, perfect, and in good condition, as to timber, where required.
The proportions of ore paid to the land-owner, called the lord's dues, vary considerably, according to the circumstances of different mines, and the nature of the prospects under which they may be undertaken. A deep old mine which has been abandoned, is undertaken with a chance of less profit and a certainty of greater risk, than a new and promising discovery. In the first case encouragement is often held out, by fixing very moderate dues, while in the other, so much is too frequently demanded and given, as to prevent that share of profit accruing to the adventurers which is due to the great risk constantly attendant on all mining pursuits.
In the deep expensive mines the lord's dues do not often exceed a fifteenth or eighteenth part of the whole produce of ore, and sometimes they do not amount to more than a twenty-fourth, or even a thirty-second proportion.
In the newer mines the dues are often as much as a tenth or twelfth part of the produce, and there are mines which pay an eighth; but this is the case only in such as were undertaken when the prices of metals were much higher than at present, and where an unusual produce has enabled the concerns to exist in spite of such a heavy deduction from their produce. The dues are delivered to the lord, or to his agent on the mine, free of all expense, or are commuted for a proportionate part of the money arising from the sale of the whole.