2. The presence of gold in the property, and the existence of the ordinary facilities for mining operations.
3.
The knowledge of how to extract the gold in the property, and
the provision of suitable appliances for the purpose.
Mr. Lock mentioned the several conditions under which gold occurs, viz:—
(1.)
In the form of scattered grains and nuggets, in alluvial deposits,
having been liberated by natural causes from its original matrix; (2.)
In the form of grains and leaves, in mineral veins (principally
quartz), still enveloped in its matrix, but not associated with any
other metals, and technically known as "free" gold; (3.) In the form of
grains, imbedded in and most intimately associated with (not chemically
combined with) various other metallic compounds, chiefly sulphides and
arsenides, and commonly known by the comprehensive term " pyrites,"
disseminated throughout veins of quartz or other mineral.
The
first class Mr. Lock passed over, as there is less difficulty and
making expense in treating it. The process of crushing and stamping was
then described, the best forms of stampers and proper order of their
drop being detailed, Mr. Lock said :—
I
would here direct attention to a class of stamps recently brought into
notice, which though requiring certain modifications to fit them for
gold ore crushing, yet are decidedly a step in the right direction—I
refer to \V. Rasche's, of Melbourne, " direct acting " batter}',
Husband's and Sholl's Pneumatic stamps and Patterson's " Elephant"
stamps. They are all based upon one principle: the battery consists of
two stamps only, driven at a great speed (150 to 200 blows per minute),
and weighing only 2 to 1 cwt. each, their main differences lying in the
means adopted for securing the speed. The perfection of stamping, so
far as quantity is concerned, would be gained by allowing each stamp in
a battery to work independently, and to surround it on all sides by
screens. One reason why some of the stamps in Victoria and America
crush so much more than others, is, that they have screens both at the
back and at the front of the battery. An excellent little stamp for
prospecting purposes has been quite lately invented by Dunham. It can
be driven by mule or hand-power, and is exceedingly portable ; the
stamp is surrounded by screens, and consequently, permits the maximum
of duty to be reached.
The
appliances for arresting the gold (both free and pyritous) rendered
separable by the stamping operation were then described, these being
divided into the mercury or amalgamation methods and the
blanket-tables. Under the first head Mr. Lock said :—
A
very effective arrangement of blanket-tables and mercury troughs,
adopted by the largest Victorian companies, is as follows :—The
material leaving the stamps is led into a trough, having a perforated
plate at the bottom to keep back any coarse stuff, by which it is
easily distributed; thence it passes into three connected troughs,
containing mercury, dropping from the first into the second, and from
the second into the third. Each of these troughs, is fitted with a
splash-board, which, reaching down to within a certain distance of the
bottom compels the falling matter to penetrate the mercury more or less
before escaping over the lip of the trough. Each trough has a tap hole
on one side, by means of which the amalgam may be drawn off. The whole
of the contrivance is under lock and key, which prevents stealing. At
the end of the blanket-table, another similar trough is placed, through
which the material passes before entering the waste-trough. The amalgam
formed in all these troughs is periodically removed.
The
causes of success and failure of the blanket-tables were also
described, as well as the treatment of the blanket sand by barrel
amalgamation. The treatment of the tailings, a matter of considerable
trouble, and largely neglected in well-paying mines, was then gone
into, it being shown how much gold at present lost might be saved. Mr.
Lock then described the operations necessary for separating the ore
from the pyrites, in which amalgamation also takes a part,
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