Operations, if planned to be conducted for a long term of years and therefore warranting the installation of large and expensive plants, should be based upon the holding of extensive ore-bearing ground. Here enters the notion of the shape and size of a mining property.
With some kinds of mining ground, the best form for the holdings would probably be a compact, approximately equilateral tract, covering a reasonably large acreage. This would be the case with ores that occur in sedimentary beds, for instance, where it is advisable to have the mining plant centrally located so as to work expeditiously the entire area. This would apply to a region like the Cripple Creek District, which contains innumerable veins running in all directions but displaying no outcrops.
In other instances, the most desirable shape might be long, narrow strips so laid off as to contain the strikes of persistent lodes or veins, as those of the wonderful Comstock Lode region. It is not acreage that counts here so much as lineal extent.
In the Transvaal, land is held in rectangular blocks. The first owners of the ground took it up for agricultural purposes. This same statement is also true of the mining properties in the Joplin District of Missouri and Kansas.
In the case of the South African properties, every company has definite boundaries to which operations may be planned. Hence it is possible for the management to so plant any mine as to operate it at a given rate for a predetermined life of the enterprise. The work is planned to maintain a certain output that will exhaust the ore bodies in just so many years, and all the equipment may thus be purchased with the forecast that it will serve its purpose and perform its economic share within the prescribed time.
This notion will be more readily understood when we consider the various types of ore bodies. With properties wherein there is no possible way of predicting the number, size, and worth of discoverable ore bodies, the life is wholly problematical and it is therefore difficult for a manager to decide how much he should expend in the initial equipment.
[X
MINE OPENINGS.]
In every new mining project, there is much to be considered concerning the expediency of opening up through shafts, inclines or adits. More attention has lately been given to this subject than formerly. There are very good reasons for the selection of any one of these kinds of mine openings.
The words shaft, incline, and tunnel have been handled with careless meanings by mining men. It is time that some definitions be accepted so that everybody will use these terms with the same meanings.
A shaft has loosely been any steep opening sunk through the ground. An incline—sometimes spoken of also as an incline shaft—has been taken to mean an opening resembling a shaft, but not very steep and not approaching verticality. Right here, there has been too much latitude of speech and it has entailed the necessity of many awkward explanations.