531.25 | 3.76
Sulphur | 127.12 | 15.74
Tin | 459.00 | 4.35
Oxide | 418.75 | 4.77
Zinc | 437.50 | 4.57
Blende | 253.12 | 7.90
Carbonate | 273.12 | 7.32
Silicate | 215.62 | 9.28
Andesite | 165.62 | 12.07
Granite | 162.62 | 12.30
Diabase | 181.25 | 11.03
Diorite | 171.87 | 11.63
Slates | 165.62 | 12.07
Sandstones | 162.50 | 12.30
Rhyolite | 156.25 | 12.80
============================================

The specific gravity of any particular mineral has a considerable
range, and a medium has been taken. The possible error is
inconsequential for the purpose of these calculations.

For example, a representative gold ore may contain in the main
96% quartz, and 4% iron pyrite, and the weight of the ore may be
deduced as follows:--

Quartz, 96% x 12.07 = 11.58
Iron Pyrite, 4% x 6.40 = .25
-----
11.83 cubic feet per ton.

Most engineers, to compensate porosity, would allow twelve to thirteen
cubic feet per ton.

CLASSIFICATION OF ORE IN SIGHT.

The risk in estimates of the average value of standing ore is dependent
largely upon how far values disclosed by sampling are assumed to
penetrate beyond the tested face, and this depends upon the geological
character of the deposit. From theoretical grounds and experience,
it is known that such values will have some extension, and the
assumption of any given distance is a calculation of risk. 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 of
sides exposed or by other phrases. Much discussion and ink have
been devoted to trying to define what risk may be taken in such
matters, that is in reality how far values may be assumed to penetrate
into the unbroken ore. Still more has been consumed in attempts
to coin terms and make classifications which will indicate what
ratio of hazard has been taken in stating quantities and values.

The old t