Dragline Dredging Methods

BRITISH COLUMBIA DEPARTMENT OF MINES
Hon.HERBERT ANSCOMB, Minister
JOHN F. WALKER, Deputy Minister
BULLETIN No. 16
DraglineDredgingMethods
Compiled by
STUART S. HOLLAND
1942
This Bulletin is in large part a reprint from United
States Bureau of Mines Information Circular 7013
VICTOIIIA, R.C.:
Photoaffset by C H ~ L EF.
S BANPI~U).
Printer to the
1042.
King's
Most Excellent Majsty.
CONTEPJTS
Page
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HISTORY AND DEVELOP1IZNT
LINITATIONS 'OF Mn~ T H O D.................1...............................................................
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Values .......................................................................................................
Depth .................................................................. ..................................................................................................................................
..
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Bottom
Character of t h e g r a v e l ................................................................................................................................................ '
Surface ........................... ................................................................................................................................................................................. .
Q u a n t i t y .............................................................................................................................................................................................................
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SAMPLIIJG AND RECOVERY
FLOATING
PLANTS
BIBLIOGRAPHY
1
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I ................................................................ :..............................................................
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5
6
6
7
7
7
8
9
13
36
ILLUSTRATIONS
Page
Figure
.Figure
-Figure
T y p i c as le t - u p
'and
excavator.
1
2
,
3
I
for f l o a t i n g washer
'2
......................................................................................................................................
E s s e n t i a fl e a t u r e s
of a f l o a t i n g
.....................................................................
washerandgoldsavingplant.
14
Methods of r e b u i l d i n gb u c k e tt e e t h
21
.................................................
PHOTOGRAPHS
Facing
page
.Plate I
A.
The f i r s t d r a g l i n ed r e d g et o p e r a t e
Operation of A . G . Watkins
on SimilkameenRiverabout
2 m i l e s upstream from. P r i n c e t o n . ......................................................................................................
6
View of washingplantshowingthe
s t a c k e r and s l u i c e s which d i s c h a r g e
a t t h e s t e r n . .............................................................................................................................................
6
in B . . C.
B.
P l a t e I1
5
A.
Operation of NorthAmericanGoldfields
L t d . o n low Fraser-River bench ups t r e a mf r o mA l e x a n d r i aF e r r y .T a i l i n g
it
p i l e sl i eb e h i n dt h es h o v e l ,b e t w e e n
andtheFraser
River, andback o f . t h e
washing plant. ....................................................................................................................
:................... 14
'
B.
Sideview of t h e washing p l a n t showing
bucket dumping i n t o t h e h o p p e r , r i f f l e
t a b l e s d i s c h a r g i n g a t t h e s t e r n , enclosed engine room. and c o n t r o l h o u s e
on u p p e r d e c k , a n d s t a c k i n g b e l t l e a d i n g off t o t h e r i g h t . ...........................................................................................
...........
14
,.
'DRAGLINEDREDGINGMETHODS
HISTORY
'
AND
DEVELOPMENT
A dragline dredge isa placer mining machine comprising two
separate units (see Plates
I and 11). The gravel is dug by a
standard dragline shovel which travels over the ground under its
own power usually by means
of caterpillar tracks (someof the
large shovels are "walkers"). The bucket, havinga capacity of
from.one to three cubic yardso r more, is suspended from
a
structural steel boom50 feet or more in length. The gravel is
washed ina separate unit whose equipment
is on a barge floa.ting
in apond. For washing the gravel and separating the gold from
it, the barge has
a revolving screen (trommel) and riffle-tables
similar tothose used on bucket-line dredges. The dragline shoveldigs away at theedge of the pond andcasts thegravel into the
hopper of the washing plant. The pond consequently advance: as,
by being warped along
tKe digging proceeds and the barge follows
by winches with cables anchored
on shore. The coarse tai1in.g.s
the
are dischargedfrom abelt-conveyo;, and sand-sluices. fill
pond be'hind the dredge.
"In the early daysof placer mining, depositsof goldbearing gravels were
found that.could not
be hydraulicked or
worked by hand. .The principal result
of efforts to work such
deposits mechanically has been the development
of the gold
bucket-line dredge. The first efforts were mainly unsuccessful
but the modern gold dredge is an efficient machine.1
"During the past45 yearssteam shovels and other mechanical.
excavators have been
used,fcr mining gravel deposits not susceptible
to dredging. The technique for dragline and power-shovel mining
has not been developed to
a comparable degree with dredging. Most
of the operations have been spasmodic and, except
in relatively
'few cases, unsuccessful up to about 1934.
"However, standard washing, screening and gold-saving- *quipment similar to that used on bucket-line dredges is now.empl.oyed
on floating washing plants and permits continuous operation."
The successful development.of dragline .dredging equipment
and methods has largely taken place in California in recent years.
The first plant was
a home-made boat built at Oroville about 1932
equipped with a perforated tronmel 24 inches in diameter and about
12 feet long whose maximum capacity with
a l/Z-yard bucket was
The material in'quota'tion is reprinted
from Uni,ted Statef; Bureau
of Mines Information Circular 7013.
- 1 -
I
N
I" C h a n n e l
A
width up to 150 feet-
B
Figure I.-Typical set-up,for floating washer and. excavator(not drawn to scale).
Reprinted from U. S. Bureau of Mines Infornation Circular 7013.
I
about 200 yards per day. Although the equipment had many mechanical
defects, basically it used the principles embodied in the monster
dredge installed recently at Dayton, Nevada, which a uses
14-cubic
yard dragline and whose washing plant ahas
oapacity of 15,000
cubic yards per day. From modest beginnings dragline dredges have
been perfected mechanically and at the same time their limitations
discovered so that the proportion of failures has been considerably
reduced and'their value, in working certain types of placer ground,
200 dragline
recognized. There are at the present time more than
dredges operating in the Western United States,l by far the greatest
number being in California.In British Columbia the first dragline
dredge began operationsin 1941. .Credit for being the first to
the
operate in the Province goes to the one which began on
working
3 miles ,up-stream from Princeton.
A second
,Sirnilkameen River about
and somewhat larger dredge operated by North American Goldfields
2 miles above Alexandria Ferry
Ltd. is on the Fraser River about
and began work about mid-July 1941.
"Most of the unsuccessful ventures owe their failureinto
adequate sampling of deposits; the gravel did not contain the
anticipated-amountof gold. Other factors contributing to
failure have been poor washing-plant design, selection
of'a setup not adaptedto the deposit, and lack of experience. ALthough
this type of mining is primarily
a dirt-moving job, only
a few
of the excursions into the field by excavating cofitractors and
sand and gravel men have proved successful. The majority
of the
unsuccessful ventures have been run by men without'previous
placer-mining experience; most of
the.suocessfu1ventures are
run by men with this experience.
"To be successful, gold mustbe recovered at Low cost per
cubic yard of gravel, and the success of ofthe
most enterprises
is determined by the number of cubic yards handled per man shift.
A successful plant must
be designed'to fit
existing conditions;
proven.equipment is
used by virtually all successful operators.
"The excavating machines are built by established responsible
companies; mechanical troubles have been
largely eliminated. On
the other hand, washing
and gold-saving equipment have been
standardized only in the floating plants
in California.
"The most efficient screening an'd washing device for placer
on dredges. As far as is
mining is the trommel of the type used
loiown no installations using flat screens
for washing and fine.
sizing of placer gravels have proved successful.. Riffles, as
used on dredges, are efficientin recovering gold, except.fine
or flaky rusty particles. Jigs have been used as an auxiliary
Mining World, vol.3, No. 10, 1941, p. 14.
to riffles to increase the over-all extraction in some places.
There are numerous other gold-saving devices, but, with the
of these have proven successexception of the Ainlay bowl, none
ful in practice, principally because
of their limited capacity.”
- 4 -
LIMITATIONS OF METHOD
dmgline
There are certain definite limitations to the ofuse
dredges that apply both to the character of the deposit and the
method of working it. To sustaina successful operation the placer
deposit should be favourable Bs to (1) values, ( 2 ) depth 3f
gravel, (3) character of the bottom or bedrock,,(4) character
of the gravel,
(5) surface and (6) quantity (yardage).
Unusual conditions and those unfavourable in some degree
be overmay
come to a certain extent by modification
in design or method of
operation, o r they may not be critical if the gold values ars
sufficiently high.
"Areas suitablefor mining by dragline dredges consist
essentially of small shallow deposits too small to amortize the
cost of bucket-line dredges, too low-grade to be worked by hand
methods, and unsuitedf o r various reasons to hydraulic mining.
each deposit is a problem in itself and the type and size
of
equipment mustbe selected and the methods of treatment adapted
to fit the particular conditions.
"In some instancesa balance must be struck between lower
operating costs attainable with bucket-line dredges and the
lower first costsof pl.ants usinga dragline and a floating
of
washing plant. The operating casts per cubic yard at plants
the latteT type usually are double that for dredges. Generally
is le'ss than at
the cost at mines using floating washing plants
o f 'similar capacities which i:n
those with movable land plants
turn are less costly to operate than mines with stationary
plants . I '
or stationary land plants will not
Operations using movable
be considered in this report inasmuch as their 'operating cos.ts
.are high and furthe'rmore thereis at present practically no
standardized plant design. On the other hand tha design of
floating washing @'ants has been perfected
in recent years
and has become more
or less uniform.
of the gravel and the character
"The character and depth
of bedrock are determining factors
in the selectionof a floating type o f washing'plant. The gravel mustbe amenable to
digging with draglines as these machines are for
usedexcavating.
As the deptho f gravel,increases,larger equipment is needed
on
floating plants. Deep ponds must be maintained in working higher
banks to keep the
boat,from grounding on the sand tailings,or
be disposed of back of the pond. Moreover,
this material must
for stacking the oversize rock.
long conveyors are needed
"Digging is under water, and
under the best conditions :more
gold is lost than in dry pits. This additional
loss of gold is
- 5 -
balanced-againsthigher costs with other types
of plants.
A rough, hard bedrock cannot be cleaned adequately
under,water
by draglines;it would preclude the use aof,floating plant."
This factor in British Columbia should be recognized by
operators. In addition to water for washing, the floating
plant requires a pond to float the boat. Xater flows rapidly
from the pond-thr.ough loose gravel'a and
steady inflowis.
necessary to replenish it.
all
Values
The lowest limitof profitable average valuesin a deposit
An
cannot be fixed because every deposit and operation varies.
experienced operator should
h o w approximately what recoveries
may be expected after tests have been
made.
The higher the values,
the-greater the difficulties th'at may
be overcome; lower values require more'favourable conditions. High
values are aptto'occur under conditions unfavourable for dragline
dredging. Coarse gold is quite likely to be associated with heavy
gravel and,may be erratic in distribution. If most of the values
are on bedrock, the distribution is apt b'e
to within narrow.limits
laterally and the gold be difficult to recover. Gold that is
dniformly distributed areally is more likely to occur from the
f o r draglining.
surface down. This is the most favourable condition
Although the depth to which gravel can be successfully worked
may be modified by adapting the equipment to special conditions,
nevertheless, it is more definite than any of the.other limitations
on the
imposed by this method of dredging. The lower limit depends
on the pond. Four feet
depth of water necessary to float the plant
is sufficient for the u.sual size plant.
The,higber limit of depth ranges ordinarily from 15 to 25 feet
up to 200 feet the
but for exceptionally large shovels with booms
depth .dug may be as much100
as feet. A dragline witha l 1/4-yard
bucket and a 50-foot boom works efficiently
at 15 feet depth; beyond this depth there is
a sacrifice of speed. Larger draglines
power dig to 25 feet without apparent
with longer booms and more
loss of efficiency. It is considered good practice for the length
of the boom to be three times thetodepth
be dug., The increased
output of the larger dragline
requires a larger washing plant.
and consequently requires
a larger
This increases the investment
reserve of yardageto justify the increased cost. These initial
costs are apt to be more offset
than
by lower production costs.
Since greater depth of gravel increases the yardage
in a given
area, the deeper deposits are most likely to provide better reserves.
- 6 -
P l a t e I A . The f i r s td r a g l i n ed r e d g e
t o o p e r a t ei n B. C.
Operation of A . 0. Wstkins on Sirnilkameen River
about 2 miles up-stream from Princeton.
P l a t e I B. View of ,washing p l a n t showing t h es t a c k e r
and s l u i c e s which discharge a t t h e s t e r n .
Bottom
i s t h e n a t u r e of
One of t h e i m p o r t a n t p o i n t s t o b e c o n s i d e r e d
thebottom o r bedrock. I t i s most d e s i r a b l e t h a t it shouldpeel
off e a s i l y so t h a t f r o m 6 i n c h e s t o a f o o t o r more may bedug.
a few inches
Thus s e v e r a l p a s s e s w i t h t h e d r a g l i n e b u c k e t d i g g i n g
of bottom each time
w i l l c l e a n up t h e h i g h e r v a l u e s u s u a l l y f o u n d
of t h e g r a v e l .
near the bottom
On t h e o t h e r h a n d , i n
B r i t i s h Columbia,bedrrock i s seidom
on t h e k i n d of r o c k , it m.ay be
weathered,consequently,depending
h a r d ,r o u g h ,c o n t a i nd e e pc r e v i c e s ,a n db ed i f f i c u l t
if n p t imp o s s i b l et od i g .
Under suchcircumstancestherecovery
of all
thebed-rockgold
would be impossible so t h a t t h e t o t a l r e c o v e r a b l e
gold might not be sufficiently great to justify
working t h e d e p o s i t .
However p l a c e r d e p o s i t s i n which t h e g o l d i s more o r l e s s
uniformlydistributedthroughoutgravellying
above a s o f t c:lay
o r sandbedofferopportunities
f o r e a s y d i g g i n g and s u c c e s s f u l
I t i s importantalways t o c o n s i d e r t h a t
c l e a n i n g of thebottom.
it i s n o t t h e t o t a l g o l d c o n t e n t
of t h e g r a v e l t h a t c o u n t s b u t
t h e amount of r e c o v e r a b l e g o l d .
Character of t h e G r a v.e"l
T h e r ea r ew i d ev a r i a t i o n si np l a c e rg r a v e l .
I t may b e f i n e
o r c o a r s e ;a n g u l a r o r rounded:sandy
or c l a y e y ; l o o s e , o r t i g h t .
For d r a g l i n e d i g g i n g t h e most f a v o u r a b l e g r a v e l i s medium sj.ze
1 8 i n c h e si nd i a m e t e r
andsandyratherthanclayey;bouldersover
of t h e washing
are troublesome t o handle and must be kept out
p i a n t by a g r i z z l y over' t h eh o p p e r .
Very c o a r s eg r a v e l i s
d i f f i c u l tt od i g .
The hand1,ing o f b o u l d e r sr e p r e s e n t s a l o s s
o f d i g g i n g t i m e and consequently of gold production and must
be
compensated by higkier v a l u e s . I n g e n e r a l , sandy g r a v e l i s l o o s e
and may n o t h o l d up t h e g o l d , b u t s u c h g r a v e l
i s easy t o d i g and
e a s y t o wash. Clayeygravel i s t i g h t andharder t o d i g and wash.
The' presence of c l a y c o n s t i t u t e s a s p e c i a l problem as, it mustbe
h e l d i n t h e trommel l o n g e r b y b a f f l e s
o r c o u n t e r s p r a y s i n order
t h a t it may bebroken up b e f o r e it g e t s o n t o t h e r i f f l e - t a b l e s .
Some c l a y r o l l s i n t o b a l l s which as t h e y p a s s o v e r t h e t a b l e s
will p i c k up goldandcarry
it o v e r t h e dump. Reasonablyclean
g r a v e lw i t ha b o u t
40 p e r c e n t . s a n d
i s i d e a l f o r draglinedredging.
Surface
.The t o p o g r a p h i c a l r e l i e f of a p l a c e r d e p o s i t i n f l u e n c e s
t h e p r a c t i c a b i l i t y of dredgingand t h e c o s t of t h e o p e r a t i o n .
or r o l l i n g ,b r o k e n
o r SLOPThe s u r f a c e may be f l a t andsmooth,
i n g . I t may b ec l e a r , wooded o r bushy. The most d e s i r a b l e
,
s u r f a c e i s f l a t andsmooth without bru-sh or timber.Dredging
may
b e c a r r i e d on i n r o l l i n g or broken country i f t h e pond c a n \ b e
carried across the irregularities without too
much e x t r a work.
A caterpillar tractor with
a bulldozerbladeand
a power t a k e off i s a na l m o s ti n d i s p e n s a b l ep a r t
of theequipment.
With it
a road can be levelled
for t h e d r a g l i n e , b a r r e n o v e r b u r d e n ' r e moved, and dams b u i l t a c r o s s b a s i n s
o r d e p r e s s i o n s where t h e
ground i s t o o uneven f o r t h e , d r a g l i n e c o n v e n i e n t l y t o do t h e
work.
A dredgecanascend
a 3 percent.slopewithout
much
d i f f i c u l t y andcandescend
a s l o p e of 2 degrees with about
t h e same e f f o r t .S t e e p e rg r a d e s ,
as much as 5 p e rc e n t . ,c a n
and l o s s of t i m e .
be managed i n an emergency b u t a t g r e a t e r c o s t
The c l e a r i n g of wooded l a n d may c o s t a s much a s $100 an
a c r ef o rd e n s e l y
wooded, heavytimber.This
i s a heavycharge
against a shallowplacerdepositandforthatreasoqcleared
land has a d i s t i n c t a d v a n t a g e .
Quantity
The d e p o s i t mustbe
l a r g e enough so t h a t t h e , r e c o v e r a b l e
gold w i l l y i e l d a p r o f i t a f k e r p a y i n g o f f t h e investment.
E s t i m a t i n g t h e s i z e of a d e p o s i t i s a problem t h a t r , e q u i r e s
The mostfavourable
experienceand an ample s a f e t y f a c t o r .
d e p o s i t s have a l a r g e volume o f g r a v e l which n e c e s s i t a t e s a
largerinitialinvestmentbut
whichenablesloweroperating
c o s t s t o beattained.
The p l a n t of a d r a g l i n e d r e d g e i s b u i l t f o r e a s y p o r t a b i l i t y
and it may be moved a t comparatively small c o s t from one small a r e a
t h e exto another providing the distances are not too great and
The c o s t of moving theplantmustbe
pense of movingreasonable.
added t o t h e t o t a l c o s t
of operatingthedifferentsmallareas.
- 8 -
SAMPLING MID RZCOVERY
"The percentage o f gold recovered in placer mining
is seldom
definitely known. Recovery percentages are likely to be misleadi,ng
unless the relation between the method
of sampling and the rnabor
method of saving the gold is considered. Most of the placer operations visited reported their recovery to be nearly
100 per cent.
or higher. In each case the figureis based on the estimated
by
amount of gold present in the deposit, as indicatedsmpling.
When the method used to recover the gold from the samples from
pits o r shafts closely simulates the procedure used
in the operat100 per cent.
ing plant, the indicated recovery usually is nearly
'
"Variations willbe.caused by the thoroughness
of sampling
the ground. Moreover, refined methodsof washing the samples may
o r careless
be the causeof low indicated recovery at the plants,
a higher recovery than expected
handling of the samples may indicate
"In drilling gravel depositsa factor generally is used in
of the samples to allow
for losses
calculating the gold content
in treating the ground.,
"The.entireamount of gold contained in anyplacer deposit
washing plants either on dredges
rarely is recoverable standard
by
o r on the types described in this paper. This is due mainly to
the physical conditionof the gold andits relation to gangue
minerals in the deposit. Often fine and rusty gold and that. .
in riffles o r quickembedded in gangue material is not caught
silver ana is lost. Therefore, the methodof estimating the
mount of recoverable go12 in abed of gravel that most nearly
approaches the methodused to work the deposit is considered
the safest method of estimation.
"Gardner and Johnson1 have discussed sampling and estimation
of gold placers. The most common^ methods of obtaining samples at
the placers discussedhere.are from pits or shafts. These are dug
by hand o r with a dragline shovel.
."Gold usually is distributed more uniformly along the channel
than across it. Usually pits are spaced along the channel
o r across
it to compensatefor the variation in the two directions. The dis100 from
tance between the rows across the channel was found to vary
to 1,200 feet,
and the distance between individual pits
in each row
shculd.dewas from 30 to'200 feet. The spacing in each direction
.of the gravel.
pend upon the uniformityof the gold content
Gardner, E. D. & Johnson, C. EI., "Tlacer Mining in the Western
United States," PartI, Information Circular 6 7 8 6 , 1934, pp. 26-46.
- 9 -
A' measured volume of gravel is taken
f o r a sample by
of tine pit, inmaking a uniform cut from the top td the bottom
cluding in it a proportionate amount of bed-rock. Usually, this
sample is washed in
a rocker-or long tom; the clean-up is
amalgamated and the gold is 'recovered and weighed.
I!
"The percentage of recovery obtained after working the
gravel is calculated from this estimate.An estimate based on
the practice'of crushing, pulverizing, and recovering the gold
by fire assaying is not practicable; while it may be more accurate
as a measure of the total
mount of gold actuallyin the sample,
it is misleading, since it does not angive
accurate estimate of
the gold it is possible to recover by placer
mining'methods.
"Prospecting of a gravel bed by the Wyandotte Gold Dredging
Shafts 3 by
6 feet in crosssection were sunk
by hand to the false bed-rock.
A windlass was'
used in the deeper pits and water was pumped
by aout
gasoline
engine-powered pump when necessary. The distance between rows
across the channel was500 feet and between shafts in the rows
about 200 feet: 30 pits were sunk.on 75 acres.
.Co. has been.described by Magee.1
"A sample was taken
by making a cut1 foot wideby 6
inches deep from the top tobottom'at
the
one end of the shaft.
Check samples were taken from the. opposite end when necessary.
the^ volume and weight of each sample were determined.
"The sample was puddled
in atub of water to completely
disintegrate it and it was then washed
in a rocker. The washed
material was r u n through the rockera second time and discarded.
The .clean-up was panned down amalgamatedwith
and
Quicksilver:
and weigkied.
the gold was extracted
4 to 90 cents per, cubic
"The valueof samples ranged from
yard in gold. Erratically high sample r&sults were discarded.or
checked. The average grade obtained for the whole tract was
18'1/2 cents per cubic yardin gold. Actual recovery based on
100 per cent.
this estimate was finally more than
"For some subsequent sampling,
a Denver mechanical gold
pan was usedto work down the samples.. The results were said
to be misleading, as the two crepe-rubber mats and the amalgamating pan re'covered more fine and coated gold than it was possible
to catch in the riffles during the major operations; The operators
concluded thata rocker or siuice-box furnished them the best
comparison for actual recovery.
1 Magee, James F., "A Successful Dragline Dredge": Tech pub.No.
No. 757, Amer. Inst. of Min. and Met.Eng., 1936, p. 9.
" S a n p l i n g ,a sp r a c t i c e db y
3 . T . F i s h e r Co., A t l a n t i c , C i t y ,
Wyo., has been described
by Ross andGardnerl as f o l l o w s :
'The d e p o s i t was sampled by driving pipes. through
A s i n g l e r o w of h o l e s 1 5 0 t o
300 f e e t
t h eg r a v e l .
of t h e
a p a r t was p u t down f i r s t a l o n g t h e c e n t r e l i n e
channel. Rows of h o l e s l/Z m i l ea p a r t were t h e n d r i l l e d
i n t h e rowswere 20 t o 60 f e e t
acrossthedeposit;holes
a p a r t . The spacing depended upon s u r f a c ei n d i c a t i o n s .
-The holes extended through the
decomposed bed-rock t o
i n depth.
s o l i d r o c k and a v e r a g e d 1 4 f e e t
%
?The samplingdevice was a 4-inch c a s i n g w i t h a
The diameter of t h e s h o e was
Keystone c u t t i n gs h o e .
of t h e p i p e ; t h e s a m p l e s
were
slightlylessthanthat
r e t a i n e d in t h ep i p e when i t was withdrawn. The c a s i n g s
were driven down t o r e f u s a l ' w i t h a . l o c a l l y made p i l e
d r i v e r .T h i sc o n s i s t e d
of a 275-pound hammer, a .ZO-foot,
4-legged,polederrick,and
a Chevroletautomobileengine
a n dt r a n s m i s s i o ns h a f t .T h e ' c a b l e
for r a i s i n g t h e h m e r
ran through a sheave a t t h e t o p of t h e . d e r r i c k t o a drum
on t h e t r a n s m i s s i o n s h a f t .
The whole assembly was on a
p a i r of s k i d s and was moved forward by i t s own power; t h e
end of t h ec a b l e was a t t a c h e d t o a deadrnan. The sampliag
o u t f i t c o s t $300 z o . 6 u i l d .
'The c a s i n g s were p u l l e d by means of a s e t of wire
blockshaving 4 and 5 sheaves. The cablefromthebloclrs
was wound on t h e drum by t h e e n g i n e .
About h a l f t h e , t i m e
it was n e c e s s a r y t o s t a r t t h e c a s i n g w i t h j a c k s s e t
a g a i n s t a c l m pp u ta r o u n 2t h et o p
of t h e p i p e .
ThTee
sets o f . c a s i n g s wereused.
A p u l l e dc a s i n g was l a i d on
saw h o r s e s and t h e g r a v e l removed i n 6 - i n c h s e c t i o n s by
means of a s p e c i a l spoon; each s e c t i o n of g r a v e l w a s
panned.
'Thecrewconsisted
of t h r e e men. The m a n . i n ' c h a r g e
panned while the machine
was being moved up and'the n e x t
p i p ed r i v e n .
A l l t h r e e men p u l l e dt h ec a s i n g s .
A total
of 140 h o l e s was p u t dowr, i n 2 1/2 months'time a t a c o s t
of $2,200 e x c l u d i n g t r a v e l i n g expenses. The c o s t p e r
f o o t was $1.12. -From 4 t o 7 h o l e s were d r i v e n d a i l y
when f u l l t i m e was spentinsampling.Fourholes
were
l o s tb e c a u s et h ep i p eh i tb o u l d e r s .I nt h e s ec a s e s
new
h o l e s were d r i v e n a l o n g s i d e .
''
Ross, Charles L . & Gardner, E . D . , P l a c e r MiningMethods of
6846,
E . T . F i s h e r Co., A t l a n t i c C i t y , Myo: I n f o r m a t i o nC i r c u l a r
2-3.
June
1935,
Bureau of Mines,
pp.
-
11
-
‘ A f t e rt h es a m p l i n g
was c o m p l e t e d , t h e a r e a
was
plotted and the grade and
amountof
g r a v e l was c a l c u l a t e d .
This was followed by sinking
46 s h a f t s a t a v e r a g e d r i l l h o l e st h r o u g h o u tt h et r a c t .T h e s es h a f t s
were 4 by 6
f e e t andweresunkwithouttimbering.
The gravelfrom
Where t h es h a f t s
t h e s h a f t s was washed i ns l u i c e - b o x e s .
were wet, t‘ne water pumped f r o m them w h i l e s i n k i n g was
used i n washing.Otherwise,sluicing
was d e l a y e du n t i l
w i t h w a t e r . A Larson,2-inc’h,
high
t h es h a f tf i l l e d
s p e e d , c e n t r i f u g a l p u q powered by a 1 1/2 horsepower
g a s o l i n e e n g i n e was used t o h a n d l e t h e w a t e r .
‘Twomen
sank a s h a f t e a c h d a y , . w h i l e t h e t h i r d
washed
t h eg r a v e l .
The c o s t of s i n k i n gt h es h a f t s
‘andwashing
t h e g r a v e l was $1.90 t o $4 per cubic yard
of g r a v e l .
‘The v a l u e of the^ g r a v e l i n t h e a r e a t e s t e d , a s
19 c e n t s p e r
c a l c u l a b e df r o mt h ed r i l lh o l e s ,a v e r a g e d
a t $20.67 p e ro u n c e ) .
The r e s u l t s of
c u b i cy a r d( g o l d
sluicing the gravel from the’ shafts indicated
a value
15 p e r cent. hygher (21,8 c e n t sp e ry a r d ) .A c t u a l
recovery i n washing has b e e n v e r y n e a r l y 25 c e n t s p e r
The discrepancy
c u b i c y a r d (42 c e n t s a t $35 perounce).
a l l colours
may he e x p l a i n e d by t h e f a c t t h a t . i n s a m p l i n g
a
v
a
l
u
e
of
1
c
e
n
t
o
r
more
were
discarded.’”
having
- 12
-
FLOATING PLANTS
"GraveL is washed in
a revolving screen; the undersize is distributed toa bank of cross table's
on each side of the trommel, from
on each side,
which it discharggs into banks of longitudinal sluices
and Finally flows to the pond at the rear of the boat. Gold . is collected in Hungarian-type riffles installed in the sluices. The oversize is discharged from the
tromel to a stacker belt and piled, at
the rear. Figure 2 shows (diagrammatically) the essential features
of a typical floating plant.
Hulls
'
.
'or steel; the smallest one
"Hulls are constructed of wood
visited was 17 by 35 feet and3 1/2 feet in depth; the largest was
50 by 50 1/2. feet and 2 1/4 feet in depth; the customary size is
30 by 40 by 3 1/2 feet for boats with
a capacity of 100 to 130 cubic
f o r a 3-cubic
yards per hour." According to Lordl the average boat
48 by 3 1/2 feet made up of
6 pontoons sach 34
yard shovel is 34 by
feet.long and 8 feet wide. "The sizeis very important;.inaddition
to beingable.to carry the load, the hull should be large enough to
give as much stability the
to plant as practicable in order to
minimize swaying and tipping caused by intermittent dumping of gravel
into the hopper. Swaying interferes with the efficiency of the
sluices, and sudden tipping causes sand to bank in places
and upset
the even flowover.the riffles. The latest practice is to use steel
pontoons about 8 by 30 by'3 feet in size, fastened together by bolting
them to:steel members-laid,across the deck. The first cost of the
steel pontoon is greater than thatof wood; the steel hull, however,
has a much longer life. When the plant is dismantled and mosed to
a new site, the pontoon sections are separated and moved along with
it. An ultimate saving of steel over wood hulls
is claimed by
manufacturers. Hulls made of wood are constructedon the si-te and
abandoned when the operation is finished.
"The superstructure is made of wood
o r steel. The engine and
winch room on the upper deck is covered with corrugated iron.
Occasionally the entire plant is enclosed, particularly
in colder
climates.
Hopper
"A hopper, usually about 15 to 1/2
15 feet above the surface,
of the boat. This i s made
of the pond, is constructed at the front
of metal supported by steel
or wood underpinning; it slopes
downward, terminating in a metal chute that conveys the gravel to the
feed end of thetromel. Manufacturers recommend that the hopper
1 Lord, W. S. Mining World
V o l . 3 No. 10, 1941, p. 14.
- 13
-
Figure 2.--Essential features
of a floating washer and gold-saving plant.
Reprinted from U. S. Bureau of Mines 1nfomtion.Ciroular 7013.
P l a t e I1 A. Operation of North American GoldfieldsLtd. on
low Frasar River bench up-stream from Alexandria Ferry.
Tailingpilesliebehind
the shovel, between it
and t h e Fraser River, andback of t h e
washingplant.
P l a t e I1 B. Side v i e w of t h e washingplantshowing
bucket dumping i n t o t h e hopper, r i f f l e t a b l e s d i s charging a t the stern, enclosed engine
room and
c o n t r o l house on upper de&, and s t a c k i n g
b e l t l e a d i n g off t o t h e r i g h t .
belinedwith
2 t o 4 i n c h e s . o f wooden plank, over which i s l a i d a
wearingsheet of s t e e l p l a t e shaped t ot h eh o p p e r .
The wearing .
s h e e t may be renewed economically without renewing the entire
h o p p e r ;t h e wood s e r v e s a s a cushion."
Water n o z z l e s a r e a r r a n g e d a t t h e d i s c h a r g e
end of t h e hopper
and by proper arrangement partly
wash t h e g r a v e l and feed it i n t o
I t i s c l a i m e dt h a th a l ft h ew a s h i n gs h o u l db e
done
thetrommel.
i n a welldesignedhopper.
The r e s t of t h er e q u i r e dw a t e r
is
s u p p l i e d by a s p r a y p i p e i n t h e - t r o m m e l .
A grizzly, usually level, with
from 8- t o 1 8 - i n c h s p a c i n g
thebopper.
The usualspacing
between t h eb a r s i s mountedabove
i s 1 2 i n c h e s .R a i l r o a dr a i l s
up t o 90 pounds p e ry a r da r eu s e d
o f t h eg r i z z l y .
f o rb a r s .
They a r e i n v e r t e d t o p r e v e n t b l i n d i n g
Oversize boulders and t r a s h ( s t u m p s a n d r o o t s ) a r e t h r o w n b y
hand
i n t o t h e pond.
If
Troimel
54 a n d ' 6 0 i n c h e s i n diameterand
"'The trommelsusedare48,.
from18 t o 32 f e e t i n l e n g t h .
About 4 f e e t on eachend i s b l a n k *
t op r o t e c tt h e t r u n n i o nr o l l e r s
anddrive'mechanism.
An a d d i t i o n a l
4 t o 8 feet i s blanton the feed end
of t h e tronimel t o provide a
i n t h e more modern
s c r u b b e rf o rt h eg r a v e l .
The blankupperends
a l i n i n g of highcarbon o r o t h e r a b r a s i v e
trommels a r e p r o v i d e d w i t h
made
r e s i s t i n g steel t op r o t e c tt h es h e l l .C o n s i d e r a b l es a v i n g ' i s
by t h i s p r o c e d u r e , a s t h e l i n i n g
may beburnedoutandreplaced
more c h e a p l y t h a n t h e o u t e r , s h e l l .
"Most of t h e s c r e e n s of t h e trommels a r e 16 t o 20 f e e t l o n g ,
o r 5-fOOt sections.Usual1y;eachsection
i s made
made up of4of t h e s h e l l .
up of four r o l l e d - s t e e l p l a t e s f o r m i n g t h e p e r i p h e r y
The b l a n k s e c t i o n s a r e t i e d t o g e t h e r
endwise a c r o s s t h e s c r e e n a r e a
w i t h four heavy railroad rails, the base flanges
ofwhich a c t a s t h e
longitudinalbuttstraps
and t o which t h e r e p l a c e a b l e scree:n s e c t i o n
p l a t e sa r eb o l t e d .P e r i p h e r a lb u t ts t r a p sa b o u t
4 i n c h e s wide and
halfaninchthickcover'thejoints
between abuttingSectio:?s of
s c r e e n s t o which t h e y a r e b o l t e d .
"Some o p e r a t o r s p r e f e r ' w e l d e d j o i n t s ; t h e s e a r e c h e a p e r t o
constructbutare
more c o s t l y t o m a i n t a i n . .
Th.e worn sectionmust
beburnedoutand
new p a r t s welded i n .
"Screens usually are perforated with holes with
a minitnun
of t h e i rl e n g t h .
Depending on
diameter of 3/8 inchalongmost
t h e maximum s i z e of g o l d n u g g e t s - f o u n d d u r i n g t e s t i n g , t h e l a s t
w i t h . h o l e s 1/2, 5/8, o r 3/4
s e c t i o n of screen nay be perforated
one
i n c hi nd i a m e t e r .
lnlhen f l a t o r elongated nuggets arefound,
o r more of t h e l a s t s e c t i o n s sometimes a r e p e r f o r a t e d w i t h s l o t s .
'
These are formed by punching
or drilling two holes,
3/8 inch in
diameter.or' larger, near each other and cutting out the intervening metal.
I
.
"The bridge between holes
in the screen commonly is diminished
gradually f o r each succeeding section, to give an equal distribution
of the undersize to the sluices.
A less common methodis to start
with smaller holesin the first section and increase the size in
succeeding sections, keeping the bridging the same.
'
'
"The intermittent loads dumped into the hopper cause surges
of gravel through the screen and sluices. To equalize the flow,
some trommels have been equipped with
a spiral type of retarding
ring that acts as
a feeder. The spiral ring makes' or
onemore
turns along the lengthof the blank scrubber section; Considerable
by this
success is claimed by the operators in regulating
flow
the
method.
"The degreeof cementation found in various gravel deposits
varies over a wide range. Some are entire'ly unconsolidated, and
a strong stream of water introduced by
a spray pipe within the
trommel is sufficient entirely to disintegrate the masses and free
the gold. Other gravelsmay be cemented'or may contain layers of
clay; when this condition exists, it is often found necessary to
of the trommel.
increase the scrubbing section up to half the length
of angle iron, usually are
Lifter bars, comprising short pieces
of the trommel to increase cascading and to
bolted to the inside
aid in the disintegration of,the gravel. Retarding rings are also,
commonly used in addition to lifter bars give'the
to
water more
of a screen decreases
time to act on clayey masses. The capacity
as the time required to disintegrate the gravel increases.
"Best practice indicates thatall clay shouldbe entirely
bi-oken downinto a pulp, regardless of whether it contains gold.
Obviously, if gold is eritrapped .in clay balls, it will be lost
with the rock oversize. Clay passing through the screen has been
a f gold and car'ried them
off with
noted to have collected flecks
the tailings.
"The slope of the tromels .usually is1 1/2 inches to,a'foot.
14 to 19 i-.p.m:, with 15 r.p.m. the
.Speed of rotation ranges from
most common.
.Sluices
.
and
Riffles
"Sluice-boxes with riffles (called riffle-tables
on'dredges)
are used on all the boats
for recovering the gold; at one plant,
however, (Jasper-Stacey) jigs are employed in the flow sheet in
addition to riffle-tables. Sluice-boxes usually are made of about
No. 12-gage steel; those in use generally range from4824 to
-
16 -
'
inches in width and
6 to 9 inches in depth: A typical arrangement
is shown in Figure2. The slope is between1 1/4 to 1 1/2 i:nches
per foot; the latter.' grade is favored. The width, area, and slope
of the sluices havean important bearingo n the gold-saving
efficiency of the plant. .An even distributionof sand across the
width of the sluice is necessaryf o r good work. The side swayof
the boat has
a tendency to'pile the sand up at the edges; this
tendency increases with the width. The 48-inch width is un30 inches is probably
a better maximum.
doubtedly too great;
"The ,characterof the deposit and its contained gold de.termines
the table area required per cubic of
yard
material handled hourly.
In average ground in which about50 per cent;of the material
passes through the screen, manufacturers recommend at ,300
least
'and preferably600 square feetfor plants with a capacity of 150
cubic yards per hour.
"The slope of the tables shouldbe adjusted to the character
of the material handled. The slope is increased when fines tend
or when the gravels contain
an undue ;?roperto pack in the rlffles
tion of sand." A common slope is 1 1/2 inches to thefoot.
"Wooden riffles are used
in the sluices
on most of the boats;
1/8- or 1/4-:inch
these consistof 1- by 1-inch slats topped with
by 1 1/8 or 1 1/4-inch strap iron. The overhang of the strap iron
is on the downstream side. The top of the wooden memberof the
riffle is usuaily cut on a bias to make the strap iron lie f:Lat;
this hasa tendency to cause cascading as the pulp passes down
the sluice. Usually, the riffles are made up in sections
of 10
each; they are held togetherby header slats at each end. GeneralOJ? the
ly the widtho f the riffle is 1/8 inch less than the width
box; to facilitate its removal.
Riffles-madeof 1 1/4- by 1 1/4inch angle are favored
by many. The top of the riffle may be
placed parallel to the bottom of t h e box, but usually it i s
horizontal. The overhang is downstream. The iron riffles are I
by being welded onto strap headers
on each
made up into sections
end or by being fitted into notches in wooden strips. Riffles
are spaced 1 to 1 1/2 inches apart. One o r the other of these
types of riffles is usedin all the plants. They are supplemented
by expanded metalor wire screen laidon burlap, carpet,o r
matting. Usually, these auxiliary riffles follow the main type
f o r the purposeof catching fine and rusty gold not .caught by
the standard riffles."
If the gold is fine
and flaky, not easily amalgamated,
or
if there is an excessive
amount of black sand itis probably
advisable not to use usual
the
wooden riffles. A firm, shortpiled slightl$-ccrrugated Brussels carpet has been found to be
an effective gold-saver for the fine, flaky
gold that is found
of the Fraser River. The carpet
is
along the bars and benches
- 17
-
usedwithouttheprotection
of e x p a n d e d m e t a l s c r e e n w i t h t h e d i s t i n c t a d v a n t a g e of n o t c o l l e c t i n g t o o much black sand whichneeds
t o behandled i nt h ec l e a n - u p .T h i st y p e
of r i f f l e i s . u s e d b y
thedredgeoperated
byNorthAmericanGoldfieldsLtd.
a t Alexandria
, .
F e r r y on t h e F r a s e r R i v e r .
"Special riffles'or traps are installed at the heads
of t h e
c r o s s s l u i c e s on t h e b o a t s i n t o which t h e q u i c k s i l v e r i s charged.
A common type comprises a number of 1- by 1 - i n c h c r o s s s l a t s n a i l e d
t o g e t h e r .A l t e r n a t es l a t s
have a s e r i e s of 1/2- by 2-inch n o t c h e s ;
.the s l a t s e c t i o n s a r e p l a c e d w i t h t h e i r l e n g t h a c r Q s s t h e s l u i c e .
Othertypescompriseboardswithhblespartlyboredthrough
them
o r i r r e g u l a rd e p r e s s i o n s .
The
and moulded rubbermatswithround
betterconstructedsidesluicesusually
have a s t r a p iron 1 t o
1 1/4 inchhigh,welded
on edge a t t h e lowerends; t h i s p r e v e n t s
l i v eq u i c k s i l v e r from p e n e t r a t i n g beyond t h i s p o i n t .T r a p s
cons i s t i n g of r e c t a n g u l a r d e p r e s s i o n s i n the bottoms are used
at the
.lower ends of t h e s i d e s l u i c e s ; o c c a s i ' o n a l l y e x t r a t r a p s a r e i n s t a l l e d f a r t h e r up i n t h e b o x e s . "
. .
I t i s p o s s i b l e t h a t p l a c e r g o l d ji&s may d i s p l a c e r i f f l e s f o r
u s e on f l o a t i n g washing p l a n t s . J i g s
work w e l l on f i n e g o l d and
on c o n c e n t r a t e s w h i c h c a r r y v a l u e s
not e n t i r e l y f r e e d from i t s
m a t r i x ; or
platinum o r o t h e r p r e c i o u s m e t a l s a r e p r e s e n t
in
a p p r e c i a b l eq u a n t i t i e s .J i g s
w i l l o f t e ni n c r e a s et h ep e r c e n t a g e recovery per cubic yard.
is
A properinstallationrequiresroygher
a n dc l e a n e rj i g s ,s a n d
pump, g r i n d i n g m i l l and amalgamator'plates o r an amalgamating barrel.
One f u r t h e r a d v a n t a g e i s t h a t notime i s l o s t f o r t h e c l e a n - u p .
' D e s c r i p t i o n of .Jasper and Stacey
Mine
"The o p e r a t o r s of t h e J a s p e r a n d S t a c e y
Mine a t Lincoln,
Ca'lif., h a v e d o n e c o n s i d e r a b l e p i o n e e r i n g i n . m e t a l l u r g y a s a p p l i c a b l e ,
t o t h e t y p e of t r e a t m e n t p l a n t s u n d e r d i s c u s s i o n . ' S t a n d a r d p r a c t i c e
i s followed'in digging and washing; an innovation has been applied
i n savingthegold.
com"The g r a v e l i s washed i n a 60-inchby 32-foottrommel,
scrubber
s
e
c
t
i
o
n
,
t
h
r
e
e
1
0
f
o
o
t
6
f
o
o
t
s
c
r
e
e
n
s
e
c
t
i
o
n
s,
prising a
and a & f o o tb l a n kd i s c h a r g es e c t i o n .P e r f o r a t i o n sa r ea l l
3/81/2 i n c h e s ,
i n c hd i a m e t e r ; t h e b r i d g i n g i s 1 1/2, 3/4,and
r e s p e c t i v e l y , for e a c hs c r e e ns e c t i o n .
"The .undersize from the
trommel d i s t r i b u t i n g b o x e s g o e s t o
a
bank o f . t h r e e 30-inch'-wide b y 3 - f o o t - l o n g d o u b l e - d e c k r i f f l e
t o t w o 42- by 42-inch'Bendelari
t a b l e s on each side, and thence
j i g s on a s i d e . The j i g s have 5-fOOt head room, a 1 3/8-inch
A bed of
s t r o k e , and p u l s a t e a t t h e r a t e ' o f 124 perminute.
- 18
-
250pounds of No. 10 s h o t i s used i n each j i g . The overflow
of j i g s p a s s e s o v e r
two 5 - f o o t s l u i c e s andthence
fromeachpair
a dewatering
through30-inchby45-footlongitudinalsluicesto
t a n k . The sand i s r a i s e d by a b u c k e te l e v a t o rt o
a steelshice,
edge o.f t h e
fromwhich it i s d i s c h a r g e d o n t o t h e r o c k p i l e a t t h e
pond.
"The hutch product from the primary
j i g s i s pumped t o a c l e a n e r
j i g .T h e , b e d
of t h ec l e a n e rc o n s i s t s
of 350pounds of No. 1 3 and
250 pound's of No. 10 s h o t . The p u l s a t i o n s a r e 136perminute.
"The overflow Prom t h e c l e a n e r j i g f l o w s b y g r a v i t y b a c k t o
one of therougher j i g s . The hutchproduct flows b y g r a v i t y t o
rod m i l l d i v i d e d midway by a p a r t i t i o n . S i x
a 36-inchby7-foot
on t h e o t h e r .
3-inch rods a r e u s e d on one s i d e and f i v e 4 - i n c h r o d s
The nil1 t u r n s a t 1 9 r . p . m .
"The pulp from t h e mill i s d i s t r i b u t e d o v e r two s e t s of 1 2 by36-incharnalgmplates
in s e r i e s . The p u l pf r o mt h ep l a t e s
3 f e e t o f quiokgoesthrough a 17-inchbyl0:footsluice,with
s i l v e r t r d p s and 7 f e e t of wooden H u n g a r i a n r i f f l e s , and thence
t o one of t h e t a i l s l u i c e s .
of t h e g o l d i s recovered i n t h e
"The o p e r a t o r s s t a t e t h a t m o s t
double-deckcrossriffles
and d i s t r i b u t o r s u n d e r t h e ' t r o m m e l .
About 25 p e r c e n t . of therecoveredgold
i s saved i n t h e jig::.
Recovery i s s a i d t o havebeenraisedabout
25 p e r c e n t . by use
of t h e j i g s . "
-
19 -
EXCAVATING EQUIPMENT
DraglineShovels
'
'
"Diesel-engine power u n i t s a r e u s e d
on 18 of 24 d r a g l i n e s
'(examinedbyGardnerandAllsman
in.California)thatservefloatingwashers;fourarepoweredwithelectricmotorsand
two w i t h
g a s o l i n ee n g i n e s .
" D r a g l i n ee x c a v a t o r ss e r v i n gf l o a t i n gp l a n t sr a n g e
in size'
f r o m 1 1/4- t o 3 - c u b i cy a r d sb u c k e tc a p a c i t y ;t h e
1 1/4- and 1 1/2c u b i cy a r ds i z e sa r e
more common. A common p r a c t i c e i s t o buy a
dragline equipped with .a bucket 1/4-cubic yard smaller than the
r a t e d c a p a c i t y of t h e machine t o p r o v i d e r e s e r v e
power f o r conr
o f t h e u n i t , andreducerepairs.
t i n g e n c i e s ,p r o l o n gt h el i f e
Cables
'
"Shovelsareequippedwith
a h o i s t and a boom s u p p o r t c a b l e ;
o c c a s i o n a l l y some of t h es m a l l e rs h o v e l sa r ee q u i p p e dw i t h
a cablet y p e crowd. The d r a g l i n e . ,i na d d i t i o nt oh o i s t
and boom c a b l e s ,
r e q u i r e s a dragcable.Usually,cablesrecommendedbytheexcavator
dealerareused;theyareconstructedtowithstandextreme
wearand
sudden s t r a i n s and musthave
maximum f l e x i b i l i t y . The boom support
cablesaresuvjecttolittle
wearand
last indefinitely.
" O r d i n a r i l y ,h o i s ta n dd r a gc a b l e sa r er u nt of a i l u r e .
The
d r a g c a b l e . o n a d r a g l i n e g e n e r a l l y i s a n e i g h t h of a n i n c h l a r g e r
i n d i a m e t e rt h a nt h eh o i s t ,
owing t o t h e h a r d e r s e r v i c e i n d i g g i n g
o v e rh o i s t i n g .O c c a s i o n a l l y ,b o t hc a b l e sa r e
of t h e same diameter;
thehoist,beingtwicethelength
of t h e d r a g , may b e c u t t o make
two d r a g c a b l e s , t h e r e b y i n c r e a s i n g t h e u l t i m a t e l i f e
and usefulness
of t h e c a b l e .
"According t o a v a i l a b l e d a t a , t h e a v e r a g e l e n g t h
of s e r v i c e
forhoistcables
on d r a g l i n e s was from 150 t o 900 h o u r s , t h e
500 h o u r s f o r a l l - o p e r a t i o n s l i s t e d .
The
averagebeingabout
l i f e of d r a g c a b l e s r a n g e d
from 150 t o 400 h o u r s , w i t h ' a n a v e r a g e
f o r a l l of about 200 h o u r s .
.
Teeth
-
"A c o n s i d e r a b l e s a v i n g i n c o s t
of s u p p l i e s i s claimedby
most of t h e p l a c e r o p e r a t o r s
who u t i l i z e same method of b u i l d i n g
of t e e t h a r e u s e d ;
one
up worn b u c k e tt e e t h .T h r e eg e n e r a lt y p e s
t y p e c o n s i s t s oftwo p a r t s , t h e b a s e ( o f t e n c a l l e d a n a d a p t e r )
and t h e p o i n t ; a s e c o n d t y p e i n c o r p o r a t e s t h e b a s e a s a n i n t e g r a l
may 'beremoved; t h e t h i r d
p a r t of' t h e b u c k e t , a n d o n l y t h e p o i n t
t y p e i s made up of t h e b a s e a n d p o i n t
i n one s i n g l e d e t a c h a b l e
unit. The c o s t of teeth^ v a r i e sg r e a t l y ,d e p e n d i n gm a i n l y
upon t h e
t y p e , s i z e and m a t e r i a l fromwhich t h e y a r e made.
-
20"
I
1
I
I
I
I
+
"Cut' to width of tooth
I
I
I
STEEL APPLICATOR BAH
REBUILT I'OUI'H
A. Steel applicator bar
B. Welding-rud filling
C. Hard face
D. Point before rebuilding
,
TYPICAL REPOINTS FOR TEETH
F i g u r e 5.--Xethods
bf
rebuilding d i p p r and bucket t e e t h .
Reprinted f r o m U. S. Bureau of Mines Information C i r c u l a r 7013.
-
21
-
"The life of teeth varies because of the wide range in hardness and. abrasive qualities of the gravel at different mines.
"Several methods of rebuilding and prolonging the life of
teeth are in use. Some operators reconstruct the entire point
from welding rod. Aqother method is to weld
on repointers; when
these are used,
care'is taken notto wear into the stock of the
is
tooth or it will have to be rebuilt before the repointer
applied. The use of applicator bars has found favor with many
f r o m several manufacturersof
operators; these may be bought
by them. The bars
steel products and are highly recommended
are of man6anese steelor some other suitable steel, and come
into.sizes the
in lengthsof several feet; they may be cut
width of a tooth. These are welded
on and filled.out to size
with welding rod. A surface of hard facing applied to the
in prolonging the life of
point is proving to be economical
teeth at some places. Figure
3 shows a typical applicator bar
and its application toa tooth with hard facing added. Typical
repointers are also shown.
"An arc-welding machine is considered by many small-scale.
mechanical placer operators to be essential equipmenta for
complete plant,
Bulldozers
"A bulldozer comprisinga tractor with caterpillar treads
and road blade mounted
in front is considered
an indispensable
part of the mechanical placer operation. Its chief use is for
clearing away trees and brush and levelling ofahead
the dragand and occasionally
line. It i s used, also, ,to build roads dams
to strip a few feet of barren clayor soil overburden."
-
22
-
"Five principal typesof power motors and combinations
of the small-scale mechanical 'type
thereof are common at plants
(1) electric power for excavator and washing plant, (2) :Diesel
engines for b o t h , (3) Diesel shovel and Diesdl electric plant,
(4) gasoline-powered shovel and plant, and (5) Diesel shovel
and electrically powered treatment plant.
on
"The choice of the most economical power plant depends
a number of variables, and each particular case must
be dedded
on its merits. The Bodinson Manufacturing Go.,
I n c . , of Sail
Francisco, Calif., submits the following table showing first
costs for' various power plantsfor a mine with a dragline aild
opera-tion.
floating treatment plant and costs after two of
years
,
c
125-horsepower dragline and 85-horse2ower on boat
Cost of
Operatpower ing oost,
plant
years
2
Direct
electric
power
Diesel engines, both
shovel and boat
Salvage,
value
at end of
2 years
Net cost at
end of 2 years'
operation
$ 4,214
$14,790
$1,685
9,100
7,644
3 ,'4ao
1.3,264
4,800
1.3,867
1,000
25,175
Diesel shovel, Diesel
6,475
12,192
boatelectrtc
on
Gasoline engines, both
23,275
2,900
boat
shovel
and
Diesel shovel, electric
power purchased for
7,912
boat
$17,318
"This table indicates that Diesel power is most economical,
although it shows little advantage
in economy over the Diesel
shovel and Diesel electric plant. The latter has advantages
of electrical drives and elimination
owing to the convenience
of transmission machinery. Most recently purchased excavators
and boats are Diesel-powered. Gasoline seldom is used except
on
the older excavators. Generally, Diesel power has an advant.age
-
23
:
over electricity, due to the isolation and wide extent
of placer
deposits. The initial cost of constructing power lines'and installing transformers to serve equipment that is used on deposits
having a life of sometimes a year' or less is prohibitive. Part
of the line and transformers must be moved continually to keep
up with advancing operations; long trailer cables that are maintained from transformer to equipment demand attention.. Zlectrically-powered and controlled excavators ordinarily give
smoother operation and mcre,positivecontrol than Diesel power;
however, the modernDiesel engine isbeing improved rapidly.
'Considering all factors, Diesel power is more economical than.
of the type
'electricity or gasoline for the average placer mine
considered in this circular.
"Fuel and power consumption per cubic yard for shovels and
draglines has a wide range. Variations on excavators of the
same size and type are due mostly
to physical conditions.in the
gravel and to the relative experience
of operators rather than
to the efficiencyof power units of the same degreeof repair."
-
24-
-
WATER
~.
f o r disintegrating and washing the
"Water is used primarily
gravel and flushing it through the sluices.In addition, a
relatively large amount is used during
a olean-up.
"Disintegration and washing usually start by spraying
water onto the gravelin the hopper. Further washing is done
with a spray pipe with 'holes drilled inside and running the
entire length of the trommel,or by sprays that shoot into
the lower end of the screen. Occasionally, a.smal1 amount
of water is added in the sluices to prevent choking. From
700 to 1,800 gallons1 of water
used on the
per cubic yard was
floating plantsfor washing the gravel and runningit .throu(;h
the sluices;a boat with jigs in addition to sluices used
2,500 gallons per cubic yard. The range
on movable and
450 to 2,000 gallons per cubi.c
stationary land plants was
yard where tromels were used for washing. At the JettRoss mine, where the gravel was not screened,
3,200 gallons per
oubic yard was used.
"The amountof water required to wash
a cubic yardof
gravel is governed mainly by the amount
of clay and relative
coarseness of the gravel. Gravel containing littleor no
clay anda large amount of oversize can
be washed with a
minimum of water (the oversize is handled mechanically);
a
up
large amountof clay in fine sandy gravels will require
to three times the amount. Usually, about
700 or 800 galloris
per cubic yard and not over 1,000 gallons per cubic yard is
sufficient for washing an average gravel. Some of the plants
discussed were'not using enough water, often from necessity,
and.others undoubtedly were using too
much. An insufficient:
supply with a muddy return causes the densityof the pulp to
be too high, which prevents some fine
gold from settling down
into the riffles. Too great a supply of water causes the
of the
riffles to run naked at times, thereby causing some
settled gold to be boiled out of the riffles and carried
away with the tailing. At the best managed plants the water
supply to the sluices
is cuto f f immediately wheneverthe feed
of gravel is interrupted.
"The amount of water required to maintain
a pond sufficient
for a floating washer depends
upon the relative porosity of the
gravel and bed-rock. The minimum requirements appear to be about
, 35 to 50 miners ' inches,2 although20 miners inches were used at
These are U. S. gallons equal to0.833 of an Imperial gallon.
2
1 miners' inch equals9.3 Imp. gallons per minute.
-
25 -
one s m a l l p l a n t w o r k i n g i n t i g h t g r a v e l a n d w i t h
a limitedwater
was found t o beused a t a few
supply; 100 t o . 1 5 0 m i n e r s ' i n c h e s
o p e r a t i o n s , owing m o s t l y t o t h e abundance of w a t e r .
"The b e s t p r a c t i c e f o r f l o a t i n g p l a n t s
of a b o u t 100 cubic
yardsperhourcapacityappearstobetousean&inchcentrifugal
pump t o c i r c u l a t e t h e wash waterand a 3- or 4 - i n c h a u x i l i a r y pump
for c l e a n i n gu p .
Water u s u a l l y i s suppliedbythe8-inch
pump
working against about a-40-foot pressure head
andconsuming 25 t o
30 horsepower. A 3- or 4-inch pump w i l l r e q u i r ea b o u t 5 t o 10
horsepower.
"Cleanwater pumps a r e not recommended, a s t h e r e c i r c u l a t e d
w a t e rc o n t a i n s some s a n d t h a t c u t s
down t h e i r e f f i c i e n c y . "
-
26
-
"The crewf o r operation of an excavator and floating plant
on a 3-shift basis usually,comprises3 excavator operators,3
oilers, 3 winchmen who operate the washing plant,
a boat master
to supervise the work,
a welder, and a utility man to run the
bulldozer,. do trucking, and other miscellaneous work. The sluices
are cleaned upby the crew on shift during the time the plant is
shut down for this pbrpose.
"Actual labour requirement for movable land plants
is a
little higher thanf o r floating plants, probably partly due to
lack of standardization of operations.
"Additional labour is required in all types
of dredgin.;
for ground testing. The mount is governed by the method and
thoroughness of sampling."
-
27
-
TABLE 1 - %sost of p l a n t s a c d o n e r a t i n c c o s t s
T
.
..
I
N
m
I
.....
.
........
.........
............
.........
........
.
.......
.......
......
...........
.........
Folsom. ..........
L i l l y ...........
Schwegler.. ......
Cooley ..........
Lynx Creek
,.
Fay.
Consuelo
Richter
Cinoo Mineros..,
Penn.
England
Xidlsnd..
Gold A c r e s . . . . : .
Pioneer 1
Pioneer 2
Pioneer 3.
Carlson-Sandbur@
Olson
Collins
.............
......
./.
Fsirplay..
Priokly Pear..
kcavator
-
$18,500
28,500
8, ooo
22,500
39,600
18,000
-
22,000
22,000
30,000
-
21,000
20,270
18,500
-
C a s t of
-
Tisoellaneour
$10,000
10,lOC
15,000
$9,000
12,ooc
16,000
12,000
15,000
.
21,000
14,000
22,8OC
10,000
r
plant
Boat
__
-
at plaoerninesusingfloatingtreatmentplants
c o s tp e rc u b i cy a r d
fiscellaneous
-
-
8,400
$37,500
47,000
4,000
YZ7,OOO
-
omrat
v44,400
lo., 000
34,500
100,000
40,000
40,000
-
60,000
-
8,600
10,600
43,600
52,800
-
9,000
-
Total
lJo.10
2J.
-
5J.
$0.0179
,0153
.15
QJ.10
g.09
g,.
09
y.09
QJ. 09
g.09
g.11
g.055'
-.
- 1
g.10
16,400
125
-
3 j 18
.25
4f.
30
-
1/ I n c l u d e sd i r e c t ,r e n e r a l ,
m.d d e n r e c i a t i o n ; l a b o r $0.05, power $0.02, o t h e r 0 o s t s, 80.03; e x c l u d e sr o y a l t i e s
Cost fbr 1 9 3 6 i n c l u d e s d e p r e c i a t i o n b u t d o e s n o t i n c l u d e
&ner's t i m e a s s u p e r i n t e n d e n t or r o y a l t i e s . "
5/ I n c l u d e s d e p r e c i a t i o n oirer a 4 - y e a rp e r i o db u tn o t
owner's wages as s u p e r i n t e n t t e n t o r i n t e r e s t
on the^
investment.
Excludes wages o f Ower andtwo sons who c o n s t r u c t e d t h e p l a n t .
5/Excludes waees o f owner andtwo sons.
Does n o t in:lu.de
d e p r e c i a t i o n of equipment.
I n c l u d e s $ 5 , 5 0 0 f o r 8. b u l l d o z e r and two l i g h t d r a g l i n e s h o v e l s that would n o t d i g the gravel.
. 8/ Does n o t i n c l u d e d e p r e c i a t i o n ; c o s t s
O O V ~ P a periodfrom
A p r i l 5, 1935, t o J a n .
1, 1936.
E x c l u d e s r o y a l t y and d e p r e c i a t i o n : i n c l u d e s c i e a r i n g .
Includes depreciation but not royalties.
'&l Based on h a n d l i n g 4 , 0 0 0 c u b i c y a r d s
per d a y a n d i n c l u d i n g d e p r e c i a t i o n .
h e r ' s wages n o t i n o i u d e d .
expens.es.
E s t i m a t e f o r f i r s t 6 weeks'operationand'includespreliminarynon-recurring
4
l
J Includes 5 t o 7 centsdepreciation.
-4/
3
3
&
Reprintedfrom
11
y.12
12
5J.111
U. S. Bureauof
Mines Information Circular 7013.
C O S T S
Cost of P l a n t s
' "The c o s t of p l a n t s( i n , C a l i f o r n i a ) , where d a t a were
a v a i l a b l e , i s g i v e ni nT a b l e
I . P r i n c i p a lf a c t o r sg o v e r n i n g v a r i a t i o n i n c o s t of f l o a t i n g p l a n t s havebeenwhether
equipment i s new or secondhandand
thedailycapacity.
The
c o s t of washing p l a n t s v a r i e s l e s s w i t h i n c r e a s e s i n c a p a c i t y
than does tKe cost
of excavation."
Note:
The t a b l e on the'prebeding page r e p r e s e n t s c o s t s of equip1936 and 1937. B o t h .
mentand
o p e r a t i o ni nC a l i f o r n i ai n
would b e h i g h e r a t p r e s e n t .
The f o l l o w i n g , t a b l e l i s t s the approximate (American) costs
ofplants,quoted
by H. S . Lord i n The Mining World f o r October
1941.
Dragline
1
1-2 cu.
yd.
Boat
CapacAty
1200-1500 2000-2500 4000-5000 5000-6000 1.0-12,000
Dragline
Boat
2 Buckets
Welder
F i e l d Shop
T r a c t o r and
Bulldozer
. T r u c k s ,e t c .
Totals
2 cu.
yd.
$25,000
20,000
3,600
1,000
1;000
$636,000
28,000
7,000
2,000
10,000
2,000
$59,600
4',400
1,000
1,000
3 cu.
yd.
$53,000
50,000
5,200
1,000
1,500
10,000'
3,000
$82,400
$123,700
5 cu.
yd.
$B 90,000
100,000
9,000
1,000
,3,000
1.2 cu.
yd.
$250,000
200,000
20,000
1,000
10,000
10,000
5,000
10,000
$218,000
$501,000
10,000
:Cost of Mining
a t p l a c e r mines
"Table I g i v e s c o s t s of miningpercubicyard
where f l o a t i n g w a s h e r s , a r e ' u s e d .
The c o s t s a r e b a s e d upon e s t i m a t e d
y a r d a g e s ,s i n c ea o t u a lm e a s u r e m e n t sr a r e l ya r e
made.
"The: u n i t . c o s t a t p l a c e r s u s i n g f l o a t i n g washers, excluding
from 9 t o 15 c e n t s
fairp play, and Folsom,range
the Prickly Pear,
percubicyard.
When a l lc o s t se x c e p tr o y a l t i e sa r ei n c l u d e d ,
12 c e n t sp r o b a b l y would b ea b o u ta v e r a g e .R o y a l t i e su s u a l l ya r e
10 o r 15 p e r c e n t . of t h e r e c q v e r e d g o l d . "
- 29 -
. I t should be pointed out that the crew
for a small p l a n t
i s almost as g r e a t a s f o r one handling 5000 yardsperday.
There i s however a s l i g h t l y g r e a t e r power c o s t for t h e l a r g e r
i f a ta n xo p e r a t i o nt h ey a r d a g e , h a n d l e d
plant.Consequently
w i l l decrease
b e i n c r e a s e d b y lC00 y a r d s a day t h e c o s t p e r y a r d
p r o p o r t i o n a t e l y .F u r t h e r m o r eo t h e rf a c t o r ss u c ha st y p e
of
ground worked a n 2 l o s t t i m e t h r o u g h
break-down or i n handling
It i s
bouldershave a pronounced zff'ect on t h e p e r u n i t c o s t .
important.therei'orethattheplantbekeptrunning
as s t e a d i l y
as p o s s i b l e i n o r d e r t o wash t h e maximum d a i l y y a r d a g e p o s s i b l e .
More s p e c i f i c c o s t s a r e g i v e n i n t h e f o l l o w i n g
summaries:
Wyandotte Gold Dredging C 0 . l
C r o v i l l e D i s t r i c t , Cal.
1935 t o Jan. 1, 1936(557,764
April5,
cubic yards mined)
Draglinewith 1 1/4-yard bucket on a 50-foot boom d i g g i n g t o a
depth of 9 1/2 feet; bed-rock i s decomposed g r a n i t e .
.~ ,
Barge :
Cents per
c u .y d .
2.51
0.90
0.32
-0.01
Payroll
Maintenance
F u e l ,o i l ,s u p p l i e s
Shop
I
_
.
Total
Shovel:
Payroll
Maintenance
Fuel, o i l , supplies
3.74
-
1.40
1.60
0.32
I
_
Total
General :
3.32
P
0 .r2o2s p e c t i n g
Clearing
W a t ei nr ,s u r a n c e , . e t c .
0.99
0.77
I.90
Total
oTpoetraealxtcp
i ne9eg
n.n0tss4e s
This doesnotinel-udedepreciation
I
and property payments.
Magee, J . F.;DraglineDredging,
p.123.
-
30
C.I.M.M.
-
T r a n s .v o l .x L . 1 9 3 7
Lincoln GoldDredging Company1
Klamath R i v e r , Cal.
March 1 5 t o S e p t . 3 ,
1939(485,910cubicyardshandled),
of ground20 f e e t of which
Draglinewith2-yardbucket,depth
8 t o 10 f e e t was s t r i p p e d by s e p a r a t e s h o v e l .
Centsper
cu.yd.
No. 1 Dredge U n i t
. D r a g l i n ep a y r o l l
D r a ' g l i n ef u e l & o i l i n g
Dragline maintenance
Dredge p a y r o l l .
Dredge f u e l and o i l i n g
Dredke maintenance
Depreciation
Taxes
0.937
0.812
1.07
0.911
0.567
0.366
0.794
0.243
5.702
Total
No. 2 Unit
- u s e df o rs t r i p p i n g
i n c l u d e sp a y r o l l ,f u e l ,
maintenance,depreciati.on
and t a x e s .
Total
. T r a c t o ru n i t s
2.16
f o r stripping
P a y r o l l ,f u e l ,m a i n t e n a n c e
d e p r e c i a t i o n and t a x e s
,
3.065
,
Administration and g e n e r a l ' e x p e n s e s
1.95
- .
Total
12.877
cents
Note t h a t t h i s i s t h e t o t a l o p e r a t i n g c o s t p e r c u b i c y a r d b u t
c l u d e s r o y a l t i e s andexploration.
Austin, V. OperatingCosts
v o l .1 4 1 ,
No. 9,1940,'p.57.
on t h e KlamathRiver,
- 3 1 - .
ex-
E. and IY. J .
SanAndreas
Gold Dredging Co. 1
(744,584
cubic
yards
mined).
J a n . 1 t o Dec. 31, 1939
Dragline w i t h 2-yard bucket on a 60-foot boom d i g g i n g an
a v e r a g e d r i f t of 11 f e e t b u t , a s rnueh a s 20 f e e t a t t i m e s .
Averageminedper hour of a c t u a l r u n n i n g t i m e - 1 3 4 c u b i c y a r d s .
Cents per
eu.yd.
Dredge o p e r a t i o n
- i n c l u d i n gl a b o u r ,
f u e l ,w a t e r ,
s u p p l i e s ,r e n e w a l s ,
,r e p a i r s
Generalexpenses
-
8 :05
s u p e r v i s i o n ,o f f i c e , '
etc.
Indirect expenses -insurance, taxes,
etc.
Royalties
-
0 .,60
i n c l u d i n g1 0p e rc e n t .
of,
g r o s sg o l d ,m i n e r a lr i g h t s
purchased.
P r o s p e c t i n g andmoving
leases.
2.53
dredge,abandoned
1.64
.
c o sT
t so t a l
Allowance
d e p r e c ifaot ri o n
.
0..
62
13.44
1.70
T co ot aslt s . i n c l u ddienpgr e ccie1an4t1ti5so n
I n t h i s o p e r a t i o n muchof
t h e gold was i n t h e b e d - r o c k
and consequently from 2 t o 4 f e e t of s l a t e b e d - r o c k was t a k e n
ui) by c l e a n i n g f r o m t h r e e a n g l e s , p a r a l l e l t o t h e c u t a n d
by
two c r o s sc u t s .F u r t h e r m o r el a r g eb o u l d e r s
were c a s ta s i d e
andhandledby
a bulldozer.and consequently the yardage per
hour was. c o n s i d e r a b l y l e s s t h a n t h a t
of o t h e r o p e r a t i o n s u s i n g
t h e same s i z e d r a g l i n e u n d e r
more f a v o u r a b l ed i g g i n gc o n d i t i o n s
Thurman, C . H
p.29.
Dragline GoldDredging,
- 32 -
The Kiner,Sept.1941,
H. S. Lord in.The Mining World for October
1941 lists the
following costs as having applied ato
3-cubic yard plant that
handled 1,243,000 cubic yards in 333 working days under fairly
favourable conditions.
Cents per
cu. yd.
Payroll
2.64
. Repairs
0.06
Gas, oil and fuel
0.. 69
Other expenses
0.30
-Compensation etc.
0.23
Insurance and taxes
0.09
Cable
0.07
Welding
0.06
material
Freight and express
Total field cost
0.03
4.97
'Depreciation
2.01
.General office
expense
0.40
Total
cents
7.38
In the above statementno items are included for interest
on investment. income taxes, depletion, prospecting, moving ex-
penses or royalties. These~varywidely but must be included in
the total cost per yard mined.
.
-33-
NORTH AMERICAW
GOLDFIELDS LTD.
up-stream
from
The North Amerlcan Goldfields Ltd., Box
67,
Quesnei, B. C
holdplacerleasescovering
a low benchon the east sideof the Fraser
River and extending for about
1 1/2 miles
Alexandria Ferry.
is ab0u.t 10 feet above the high
The surface of the bench
water level of the Fraser River. The gravel, which is duga to
depth of 9 or 10 feet is loose, fairly porous, contains little
clay and hasfew,.if any boulders larger than 12 inches across.
Bed-roc2 lies at a depth of 15 feet or more. The gravel contains
fine, flaky gold in the upper part with in
little
the gravel
which lies below the depth dug. The surface may be underlain by
off by aD7
from.2 to 5 feetof barren silt which is stripped
caterpillar.
The shovel isa 21/2-cubic yard Lima 'dragline operating
a
2 1/2-yard Page bucketon a 60-foot boom. the shovel is run by
a
a ~ 2 6 0H.P. C m i n s Diesel engine. The hoist cable used is
1 1/8 inch.
1-inch diameter,. and the drag,
is carried on a boat 40 by 32 feet,
The washing equipment
large
built on the ground from Douglas fir. Because there no
are
a hopper, havingno
boulders the bucket dumps directly into
grizziy, which feeds the gravela to
tromel 54 inches in diameter
and 26 feet'long. There isa 5-foot blank section at each end
of the tromel. The screen sectionis 16 feet long having3/8th
inch holes.spaced widerapart'at the front end. It revolves at
14 R.P.M.
The stacker belt is
50 feet long and 30 inches wide running
at 150 feet per minute.and driven by an eiectric motor at the
outer end.
There is about800 square feetof riffle-tables havinga
grade of 1 l/2 inches to the foot at the head end and ausing
hafd surface, slightly-corrugated Brussels carpet.
The power plantis a 100-h.p. International Diesel engine
belt-connected toa drive shaft which operates the trommel and
pump and direct-connectedto a generator which supplies power
for the electric motor running
the stacker.
j
The dredgeworks two 10-hour shifts per day
and operates
from 16 to19 hoursja day. Gravel dug averages about
130 cubic
yards per hour of operating time. The riffles are oleaned up
f o r greasing
once a day when the shovel and dredge are shut-down
and oiling,. The total crew comprises2 shovel runners'at $1.25
an houi-, 2 greas.ers at 5 5 b per hour, 2 dredge operators at 656 ' '
an hour, 1 bulldozer operator (on day shift) at$1 an hour, 1 cleanup man (on day shift), 1 office pan, and the superintendent.
- 34 -
The p l a n t r e p r e s e n t s
a c o s t of about $90,000.
There are other
low b e n c h e s . a l o n g t h e F r a s e r R i v e r h a v i n g
s i m i l a rp h y s i c a lc h a r a c t e r i s t i c st ot h e
one beingmined.These
arepotentialdredgingareas
which need,however,
t o be
thoroughly sampled for valuesand total yardage before mining
i s warranted..
-
35
-
..
.
BIBLIOGRAPHY
A u s t i n , A.V.
Operating Cost of Dredging on t h e Klamath
River 3 . 8: "I J . vol.141,
No. 9, 1940,
p.57.
Averill, C . V.
C a l i f o r n i a J o u r n a l of Mines & Geology,
vol. 34, NO. 2, 1938, , pp. 96-111.
Catalogue o f t h e Dodinson Mfg. Co.,2401BayshoreBoulevard,
San F r a n c i s c o .
Gardner, X . D. and
Allsman, P. T .
Lord,
n. S.
Tower Shovel
and
Dragline
Placer
Mining
Uni'ced S t a t e s Bureau of Mines, Inf.
7013, 1939.
Modern Dragline Dredging, Mining
v o l . 3, NO. 10, 1941,
pp.
14-16.
World,
Magee, J . F
Dragline Dredging, C . I . M . M . Trans.
117-125.
V o l . XL, 1937,
pp.
Peele, R.
Mining
Xngineers
Handbook, Wiley
John
Sons, New York, 1941,p.
10-600.'
Thurman, C . H.
Dragline Gold Dredging, The Miner,
Vancouver,Sept.1941,pp.29-32.
-
36
-
Circ.
&