Principles of Mining: Valuation, Organization and Administration

ation (Co

ES OF ORE, AND CLASSIFI

tely. Under the law of averages, the multiplicity of these blocks tends in proportion to their number to compensate the percentage of error which might arise in the sampling or estimating of any particular one. The shapes of these blocks, o

s be an equal distance apart. If they are not equidistant, the average width is the sum of the areas between samples, divided by the tota

he two end-sections be divided by two and the result incorporated in cal

he mine in all these particulars renders any method of calculation simply an approximation in the end. The factors which must remain unknown

ethods of determination of t

however, would not account for the larger voids in the ore-body and in any event, to be anything lik

fferent portions of the mine, and, in examinations, is usually inconvenient and difficult. Yet it is necessary in cases of

hich are usually available from assays of samples and metallurgical tests, and a general inspection as to the compactness of the ore, give a fairly reliable basis for approximation, especially if a reasonable discount be allowed for safety. In

ipal ore-forming minerals and gangue rocks will be useful for approximating the weight of a cubic foot of o

ght

Foot N

ic

To

00

ny 417

de 285

Pyrites

lphate 27

lc

e 198.7

145.6

e 169.

552.5

rite 26

e 321.

te 247.

e 237.

lla 132.

ast) 45

te 315.

te 306

te 237

312.5

te 240.

710.6

468.7

te 406.

Oxide 26

te 221.

te 187.

e 178.1

165.6

lver 84

ar 531

r 127.

59.00

418.

437.5

253.1

te 273.

te 215

e 165.6

e 162.

e 181.

e 171.

165.6

nes 162

e 156.2

erable range, and a medium has been taken. The possible err

n in the main 96% quartz, and 4% iron pyrite, and

6% × 12.0

te, 4% ×

bic feet

porosity, would allow twelve t

TION OF OR

sk. The multiplication of development openings results in an increase of sampling points available and lessens the hazards. The frequency of such openings varies in different portions of every mine, and thus there are inequalities of risk. It is therefore customary in giving estimates of standing ore to classify the ore according to the degree of risk assumed, either by stating the number o

dly abused by the charlatans of mining in attempts to cover the flights of their imaginations. A large part of Volume X of the "Institution of Mining and Metallurgy" has

sight" be defined, it will be easier to teach the laymen its proper use than to abolish it. In fact, the substitu

cy of sample points, and consequently the risk of continuity, will depend upon the detail with which the mine is cut into blocks by the development openings, and upon the number of sides of such blocks which are accessible, most cl

n four sides in blocks of

Deve

on three sides within reason

Ore exposed

Deve

of the ore below the lowest lev

Expe

n the lines laid down above, might be "probable" or even "possible" ore. Likewise, ore may be "fully developed" or "blocked out" so far as it is necessary for stoping purposes with modern wide intervals between levels, and still be in blocks too large to warrant an assumption of continuity of values to their centers (Fig. 1). As to the third class of "possible" ore, it conveys an impression of

ne, showing classification of the ex

pon to a certainty is that which, taking into consideration the character of the deposit, can be said to be so sufficiently surrounded by sampled faces that the distance into the mass to which values are assumed to extend is reduced to a minimum risk. Ore so far removed from the sampled face as to leave some doubt, yet affording great reason for expectation of continuity, is "probab

y a

e is practically no risk

me risk, yet warrantable justifica

uded in the above classes, nor definitel

alteration is that no point in the block shall be over fifty feet from the points sampled. In limestone or andesite replacements, as by gold or lead or copper, the radius must be less. In defined lead and copper lodes, or in large lenticular bodies

ater distance than the above, and such distance must depend upon the collater

dent upon the extension of the deposit beyond the re

to cover both "positive" and "probable" ore is desirable; and where a general term is required,