546 
MANGANESE DEPOSITS OF INDIA : MINING. [ PaRT III : 
(3) The value of the average ores of the deposit, and of the best ores. 
(4) The character of the ' country ' of the deposit, as regards both 
the soundness of the rock and the abundance of water. 
(5) The costs of mining materials, such as timber, tools and plant, 
when delivered at the mine. 
(6) The cost of labour, both local and imported. 
(7) The cost of employing men with knowledge sufficient to develop 
the deposit in the way proposed. 
The two chief methods of working a mineral deposit — leaving' out of 
account detrital and alluvial deposits, which may be treated by dredging, 
hydraulicking, etc., — are : — 
(a) Opencast working, or quarrying. 
[h] Underground working, or true mining. 
We can now consider the influence of each of the above factors in 
determining the way in which manganese-ore deposits in general, and the 
Indian manganese-ore deposits in particular, should be worked. 
1. It is obvious that if the body or bodies of ore lie at or close to the 
surface, with no or very little overburden, 
£!L1 o7'^th™o:rt oP^'^^-^t work, or quarrying, is all that will 
be necessary. If, however, the ore-body, in the 
form of either bed, lenticle, vein, or irregular mass, extend to some 
considerable depth, it will be necessary to resort to the methods of 
underground mining to win, at any rate the deeper portions of, the ore. 
If it be decided that it will pay to win the ore lying below the depth 
to which opencast working can be carried, it will be necessary to decide 
whether the whole of the ore-body is to be mined, or whether the 
upper portion is to be quarried and the lower mined. 
It is also obvious that before any proper decision can be reached 
on these points it is necessary to know something about the structure 
of the deposit. This can of course be obtained only by testing the deposit, 
first by means of surface prospecting, involving the digging of surface 
cross-cuts or costeans, and trial pits ; and then, if the ore be found to go 
to as great a depth as can be conveniently reached by these methods, 
by putting down shafts or bore-holes. 
It has yet to be proved that deposits of manganese-ore extend to a 
greater depth from the surface than a few 
cse^oTc* depoSrcxtcnd^ hundred feet, say 300 to 500 feet (many of course 
do not extend to greater depths than 50 feet 
