Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1939-11-04
DOodIebug Development
Boon To Placer mining

Of the standard type OF placer
dredge. The type of distribution
which seems most successful was
patented in 1905 on a dredge at
Orville. California.
With this system the fines,
after passing the screen, are caught
in a steel collecting pan under the
screen The collecting pan slopes
toward the head of the sluices with
slope Of / y inches to the foot.
The pulp passes through this
sluice over the rifles and at the
lower end is subdivided into equal
portions. which pass through laun-
ders to the head of the secondary
tables in which it is spread out ov-
or twice or three times the width
over which it passed in the prim-
airy sluice. This spreading out ef-
facts a secondary concentration. The
secondary tables slope toward the
stern of the washer enabling ready
failing disposal This system of con-
centration has been successful in
over 100 dredges. and many plants
which were unsuccessful with 9TH
er types of rifles were remodeled
and made successful and profitable
with this system.
The great advantage of this prac-
tice is that unless the operator is
in exceptionally high ground, it
will not be necessary to clean up
more than once a month instead OF
every week.
There is a great variety Of riff
files in use on dredges. but the
standard seems to be a rifle made
of one-inch angle irons or the wood
rifles with steel or rubber face.
The angle iron rifles are more
sturdy and wear longer than eth
or of the other types. though there
70 now on the market new all
rubber rifles which promise to
be superior to all the other types
and are said to wear many times
longer.
Some Of the newer drv-land ma
chimes like the Judson-Pacific are
equipped with the bowl type gold
saving devices or iigs The use of
jigs. bowls and centrifugal ANAL
eamators are better adapted to the
dry-land rigs than the floating be-
cause Of the stability of the outfit.
The bobbing of a floating dredge
from the deposition of the material
in the hopper interferes with the
operation of the bowls and jigs by
the shifting of the vertical axis.
Jigs also depend upon stable foun-
dations so that water levels may
be properly maintained.
The floating type, for successful
operation, should have a fairly soft
bedrock that may be scraped clean
with the bucket or much of the
values will be left behind. The
standard type of the dredge has the
advantage of the buckets following
closely and being moved over the
bedrock much more evenly, thus
cleaning more Thoroughly than is
possible with a dragline bucket.
The dry-land type of washer en-
ables the bedrock to be studied and
carefully cleaned by hand, which
is seldom necessary.
In this article. l have tried to
present the development and the
process of naming the new indus
try Of manufacturing and operat-
ing small two-unit gold dredges.
Though the industry is still in the
development stage and no satisfac-
tory conclusion has been reached
in its naming, it is thriving and is
being successful. 1t is understood
that all washers do not hold to
the description given, but all follow
the same principle and the field is
rapidly standardizing.