The San Francisco call., 1904-02-22
Gold Dredging.
BY MALCOLM MCDOWELL

some time examining, investigating
and testing the newest and decidedly
the most novel method used for rob
bing the earth of the yellow metal
gold dredging. Apparently he is thor
oughly satisfied with this unrOmantie
development for placer mining, for he
wants sixty OF these floating gold ex-
tracing machines which, according to
experts VII become the principal
agents for supplying the world with
gold
Gold dredging is one Of the new in
oustries About ten or twelve years
ago II was done il a small way in New
Zealand and Australia, and soon after
il appeared in Oroville, Cal To-day
they are using dredges-and the same
kind Of an outfit could be employed TO
-eXcavate a canal or cut a drainag ge
ditch-in the orange groves of Cali
fornia and operating them by cleo
tricity generated by water power many
miles distant In Colorado the endless
chain Of steel buckets is lifting the
gold bearing material out Of its bed
within sight Of high bars and gulehes.
where a few years ago the cradle and
pans of the old-time placer miners,
those heroes Ct Bret Harte and Mark
Twain, caught the grains and nuggets
for which men risl1ed their lives and
souls
It's all different now. Placer mining
1t used 10 be called the poor mans
chance"-is done on a wholesale basis.
Skilled mechanics, with improved ma
chinery, go down TO bed rock or hard
pan, forty five feet sometimes, after the
gravel and sand, which carries the
gold. and do it much after the fashion
Of other mechanics. who with similar
machinery deepen river channels or
cut through sandbars in harbOrs. This
new industry has developed a new
breed of mining engineers. 1t is a com
posite Of hydraulic engineer, gold
prospectOr. placer miner, topograph-
ical engineer and boat builder. One
such is ". ". Dyar, general manager
Of the American Gold Dredging Com
pany. operating near Breckenridge,
Colo.
Said he: "Gold dredging is just be-
ginning. It has taken US some years
L. develop the machinery we now eni-
plOy. There seems TO be no doubt that
this method OF gold mining will be-
come one Of the great industries II
csr be said. in a general wa- that
wherever there is a large deposit Of
gravel and clay carrying free gold
in short, wherever there are placer
mines-gOld can be dredged In most
placer mining districts there are
gulches and slopes having sufficient
grade TO mine by ground sluicing CT
ordinary 'hydraulicking
Ground sluicing is simply running
water over the ground, picking the
material and shOveling il into small
sluice boxes. leaving enough grade 20
run the water OF. In ordinary hy-
EyCraulicking water is brought to the
working in pipes under pressure and
5etting from nozzles called giants
washes down the gold bearing ma
teriaL These were the two methods Of
placer mining up 20 the time dredE-
Ing made its appearance. The neces-
Sitv for using dredGes grew ont Of
this condition. the high bars and
gulches were worked by ground sluic-
i-, ard hydraulicking because there
was enough grade 10 carry the water
ad tailings down hiIl-aWay from the
work But down below these high bars
and guicbes We're larger valleys con-
tanning gold-bearing gravel beds in
carry of the tailings These fatter
gravel beds are very extensive. and
generally richer in gold. IN order to
'sluice' this material il was necessary
dig il and then lift it 10 a height
which would give the requisite grade
for properly working the material. The
dredge does this. 1t is a self-containad
machine which scoops out and lifts up
The material. screens out the large
powders and coarse rocks and then
sluices the material with the water
which il raises with its own pumps.
The dredge consists Of a scow or pom
toon from 100 TO I40 feet long and about
forty feet wide. It's principal feature
is the endless chain OF steel buckets
which works upon the upper body Of the
boat and which can be raised or low
cred at the forward or digging end by
means Of steel cables. The steel buck
ets-according 70 the size Of the dredge
have each a capacity OF three to ten
cubrc feet
The power for operating the chain of
buckets is applied at the upper end Of
The ladder bv means of a fat sided
drum called lumber As it revoIves
ii gives motion TO the buckets which
descend through the water into the
. gravel bed. each bucket scooping out
its. capacity of material and conveying
h Up 10 be dumped into a hopper At
The forward or cutting end OF the lad
der is another tumbler which has large
nanges on its sides so that the buck
cts cannot slip of.
The scooped UP. dripping wet mate
rial falls through the hopper on to
screens. On some dredges these screens
are revolving cylinders; on others they
are fat screens which are continuously
shaking 50 as TO facilitate the screen
ing process. In both cases, however, |
water under pressure is sprayed upon |
the screens to wash clean the powders
and fragments of rocks. The powders |
and other coarse material which does