Principles of Mining: Valuation, Organization and Administration

of Mines (

TERVAL BETWEEN LEVELS; PROTECTION OF LEVELS; WINZES AND

ARY DEV

fter the initial entry. They are all expensive, and the

t down, they must be ten to fifteen feet higher than the floor of the crosscut. Where loading into skips is to be provided for, bins must be cut underneath and sufficient room be provided to shift the mine cars comfortably. Such bins are built of from 50 to 500 tons' capacity in order to contain some reserve for hoisting purposes, a

tation arrangement for skip

tation arrangement for skip

ons. Among them is that, where haulage is confined to few levels, storage-bins are not require

reased by making the connections with the shaft at every second or even every third level, thus not only saving in the construction cost of crosscuts and stations, but also in the expenses of scat

t of loading chutes

phasis. This is, that the tendency of ore-fissures to be formed in parallels warra

tation arrangement for skip

VE

applied to all openings on one horizon, crosscuts included. Levels are for three purposes,-for a stoping base; for prospecting the deposit; and for roadways. As a prospecting and a stoping base it is desirable that the level should be driven on the deposit; as a roadway, that it should constitute the sh

0 feet below, and repeating the operation. This interval gradually expanded, but for some reason 100 feet was for years assumed to be the proper distance between levels.

ining the vertical interval bet

larity of t

method of excavatio

nd the metho

follow that every level need be a through roadway to the shaft or even a stoping base. In such deposits, intermediate levels for prospecting alone are better than complete levels, each a roadway. Nor is it essential, even where frequent levels are required for a sto

y costly to pull spoil out of, and rises too high become difficult to ventilate, so that there is in such cases a limit to

from stopes to the roadway, the levels must be comparatively close together. Where deposits are very flat, under 20°, and walls fairly sound, it is often possible to use a sort of long wall system of stoping and to lay tracks in the stopes with self-acting inclines to the levels. In such instances, the inter

te *: P

rvals given are me

ed stopes, in dips over about 45°, intervals of 150 to 200 feet are possible. In filled stopes intervals of over 150 feet present difficulties in the maintenance of ore-passes, for the wear and tear of longer

icient points of stoping attack to keep up a certain output. This must pa

g.

he subheading for a stoping base is driven far enough above or below the roadway (depending on whether overhand or underhand stoping is to be used) to leave a supporting pillar which is penetrated by short passes for ore. In overhand stopes, the ore is broken directly on the floor of an upper sublevel; and in underhand stopes, broken directly from the bottom of the sublevel. The method entails leaving a pillar of ore which can be recovered only with

sets (Figs. 19, 30, 43), by dry-walling with timber caps (Fig. 35), and in some localities by steel sets. Stulls are put up in various ways, and, as their us

S AND

up overhand. When the connection between levels is completed, a miner standing at the bottom usually refers to the opening as a rise, and when he goes to the

out or is assisted by gravity in one case, and in the other has to be shoveled and hauled up. Moreover, it is easier to follow the ore in a rise

d of passageways for material to be used below. Where stopes are to be filled with waste, more winzes must be kept open than when other methods are used, and these winzes must be in sufficient alignment to permit the continu

THE EARLY PRO

tion, dip, strike, etc.,-so much at least as may be necessary to determine the works most suitable for their extraction or values warranting purchase. In outcrop mines th

ch considerable scale, even for prospecting, that the initial outlay does not warrant any anticipation of revision. Such works have to be located and designed after a

tion and in their application to loose material; but inability to determine the exact horizon of the spoil does not lend them to narrow deposits, and in any event r

ations. The core amounts to but a little sample out of possibly large amounts of ore, which is always of variable character, and the core is most unlikely to represent the average of the deposit. Two diamond-drill holes on the Oroya Brownhill mine both passed through the ore-body. One apparently disclosed unpayable values, the other seemingly showed ore forty fee

le that it is especially affected by the angle at which stratification or lamination planes are inclined to the direction of the hole. A hole has been known to wander in a depth of 1,500 feet more than 500 feet from the point int