r, such
as the character of the surface and the rock to be intersected,
the time involved before reaching production, and capital cost.
As shafts must bear two relations to a deposit,--one as to the
dip and the other as to the strike,--they may be considered from
these aspects. Vertical shafts must be on the hanging-wall side
of the outcrop if the deposit dips at all. In any event, the shaft
should be far enough away to be out of the reach of creeps. An
inclined shaft may be sunk either on the vein, in which case a
pillar of ore must be left to support the shaft; or, instead, it
may be sunk a short distance in the footwall, and where necessary
the excavation above can be supported by filling. Following the
ore has the advantage of prospecting in sinking, and in many cases
the softness of the ground in the region of the vein warrants this
procedure. It has, however, the disadvantage that a pillar of ore
is locked up until the shaft is ready for abandonment. Moreover, as
veins or lodes are seldom of even dip, an inclined shaft, to have
value as a prospecting opening, or to take advantage of breaking
possibilities in the lode, will usually be crooked, and an incline
irregular in detail adds greatly to the cost of winding and maintenance.
These twin disadvantages usually warrant a straight incline in the
footwall. Inclines are not necessarily of the same dip throughout,
but for reasonably economical haulage change of angle must take
place gradually.

[Illustration: Fig. 8.--Longitudinal section showing shaft arrangement
proposed for very deep inclined deposits.]

In the case of deep-level projects on inclined deposits, demanding
combined or vertical shafts, the first desideratum is to locate
the vertical section as far from the outcrop as possible, and thus
secure the most ore above the horizon of intersection. This, however,
as stated before, would involve the cost of crosscuts or rises and
would cause delay in production, together with the accumulation
of capital charges. How important the increment of interest on
capital may become during the period of opening the mine may be
demonstrated by a concrete case. For instance, the capital of a
company or the cost of the property is, say, $1,000,000, and where
opening the mine for production requires four years, the aggregate
sum of accumulated compound interest at 5% (and most operators
want more from a mining investment) would be $216,000. Under such
circumstances, if a