The weekly Butte record., 1862-01-18
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The Arastra.

The arastra is mill to pulverize and ANAL
garnate auriferous quartz. and it is considered
one of the best instruments for doing that
work. Its a circular bed, from eight to twen-
ty feet in diameter, paved with stones, in which
quartz, broken into small pieces, is placed and
ground to powder by dragging muller or
large stone over it. Arastras are of two kinds,
the "rude and the improved" In the rude
arastra, the bed is paved with unhewn, fat,
hard stones, laid usually in common dirt, some
times in clay or cement If laid il cement,
numerous crevices are left between the stones.
In the improved arastra, the paving is done
with stones nicely hewn, of greensboro or very
hard granite. Around the bed is wall of
stone foot high, and in the centre Of the bed
is a post to which are fastened two arms, and
to these. extending across the bed, are fastened
with chains a couple Of mullers, which are to
be dragged round and round in the bed to
grind the quartz. At the end of the arm is
htched mule, which has circular path
along the edge of the bed of the arastra.-
Sometimes only one muller Is used sometimes
two, and in these cases one horse or mule is
sufficient TO DO the work sometimes there are
four mullers used, and then two mules are ne
cessary. The mullers should be long and fat,
of very hard material and coarse grain, and
weigh from five to eight hundred pounds
They are so hung as to have the forward end
about an inch above the bed of the arastra,
while the hind end drags.
When the arastra is to be used, batch Of
quartz broken into fragments Of a quarter of
an inch in diameter or less, and amounting 10
all TO four or FIVE hundred pounds, is put into
an arastra ten feet in diameter-the amount of
quartz being greater if the arastra be larger.
The mule is then hitched up and started, and
If the quartz is very hard it will be ground to
fne powder in about four hours Water is
thea poured in gradually, while the mule still
continues his labor, until the pulverized quartz
and water have taken the consistence of cream.
Quicksilver is now added in the proportion of
an ounce and q quarter to every ounce of gold
in the quartz. The amount of gold is guessed
at from previous examinations and working
rock. The grinding continues for an hour
longer, aud the quicksilver is thereby broken
up into very fine particles, and distributed all
through the pulp, and brought into contact
with every portion of it. The amalgamation
having been completed, large amount of wa
ter is let into the arastra and the mule is driv-
en- around slowly, to dissolve the thick pulp in
the water and allow the particles of quicksilver
and amalgam to settle to the bottom. A quar-
ter or half an hour is sufficient for this, and
then gate at one side of the arastra is opened
and the thin mud is carried away by stream
of water running in on one side and out the
other, leaving the gold and amagam on the
bed of the arastra.
In the rude arastra, the quicksilver amalgam
settles down into the crevices between the
stones of the pavement. After the thin mud
has all been swept away, another charge Of
quartz is put in and the same process is re-
peated. AT the end OF the week, the paving
is dug up, all the dirt between the stones and
attached TO them and under them is carefully
collected and washed, to save the amalgam,
which is then retorted- Hittel.