Principles of Mining: Valuation, Organization and Administration

op

TOPES; OVERHAND STOPES; COMBINED STO

to indicate all the operations of ore-breaking, support of excavations, and transportation between levels. It is used further as a noun to designate the hole left when the

overn the method of st

The

dth of th

racter of

ost of m

aracter o

e simply an inquiry into the broad principles which govern the adaptability of special methods. A logical arrangement of di

the subject may

s of ore-

f supporting

of transpor

OF ORE-B

gement for blasts is therefore to set the holes so as to preserve a corner for the next cut; and as a consequence the face of the stope shapes into a series of benches (Fig. 22),-inverted benches in the case of overhand sto

g.

king face gives rise to the usual primary clas

erhand

rhand

bined

s no longer a logical basis of distinction, for underhand holes in overh

g.

ws downward and to stand upon the ore when at work, it was almost universal before the invention of powder; and was applied more generally before the invention of machine-drills t

g.

the stopes. To support the walls in bad ground in underhand stopes would be far more costly than with overhand stopes, for square-set timbering would be most difficult to introduce, and to supp

n at the passes not present in overhand stoping, for with that method several chutes are available for discharging ore into the levels. Where the walls require no support and no selection is desired in the stopes, the advantage of the men standing on the solid ore to work, and of having all down holes

inal section of a

that is broken upward from one level to the next above. There are t

cut overhand stope-l

ase at the level (Figs. 25 and 26). Horizontal or flat-backed stopes can be applied to almost any dip, while "rill-stoping" finds its most advantageous application where the dip is such that the ore will "run," or where it can be made to "run" with a little help. The particular application of the two sys

overhand stope-lon

' phthisis. A further advantage in the "rill" cut arises in cases where horizontal jointing planes run through the ore of a sort from which unduly large masses break away in "flat-back" stopes. By the descending cut of the "rill" method these calamities can be in a measure avoided. In cases of dips over 40° the greatest advantage in "rill" stoping arises from the possibili

overhand stope-lon

ried back more or less parallel with the winzes, and thus broken ore after blasting lies in a line on the gradient of the stope. It is, therefore, conveniently placed for mechanical stope haulage. A further advantage is gained in that winzes may be placed long distances apart,

dinal section of

here there is considerable dip to the ore. This space is so narrow that it is of doubtful advantage in any case, and 40 inches is more

he ore, thus stripping the ore and enabling it to be broken separately. This permits of cleaner selection of the ore; but it is a problem to be worked out in each case, as to whether roug

nprofitable ore being broken down and used as waste. Where values fade into the walls, as in impregnation deposits, the width of stopes depends upon the limit of payability. In these cases, drill-holes are put into the walls and the drillings assayed. If the ore is found profitable, the holes are blasted out. The gauge of