WPJ8 1 Gold Dredges

8/2/2019 WPJ8 1 Gold Dredges

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Wo r ld P la c e r J o u r n a l 2 0 0 8

1. Bucket-line mining dred

1.1 History and general descrip

Adredge is a device to remove material f

and the term has come to mean the device is

water. European dredges of the 16th and 17

manual, but Leonardo Da Vinci designed a dre

Venice powered by horses inside a wheel.

Abucket-line dredge digs with a chainbucket with a reinforced lip to undertake the cut

action. Bucket-line dredges are the most ef

underwater mining of minerals, but costly to buil

can last for 40-50 years.

As early as the 1890s the Dutch supplied

dredges to Italy, Argentina and Russia. Large nu

built for placer tin mining, onshore and off-

Indonesia, Malaysia and Thailand. Bucket-line dred

widespread after James Watt invented the steam e

powered industry became the norm. Early buc

where used in the gold rush in New Zealand, A

[1,25,26], Yukon and Alaska [35,36,37], mostly

and New Zealand [28,29].

Most of these dredges stopped working aft

rush was over and scrapped, or left lying somew

become preserved as industrial archaeologicalbecome tourist attractions, such as the Pedro dre

It was a different story in Siberia, the R

Mongolia, China, South America and parts of Afr

many bucket-line gold dredges survive but ne

launched. For instance in Mongolia five lar

bucket-line gold dredges have been launched

Goldfield in the last few years [3,4,5,6].

Bucket-line gold dredges traditionally used

the sluices. The miners believed mercury was sa

[9]. So the fine tailings chutes were the lowest c

of the dredge. The oversize stones were dumped

Modern bucket-line gold dredges achieve B

mercury by relying on more efficient gravitational

rather than leaving barren bare rock in their wake -

via a cyclone to the end of the tailings conveyor ttailings in a carpet of fine tailings as soil-forming

means the agricultural value of the land behind a

dredge can be better then before dredging [18,19,2

This is not so with the Russian bucket-line gol

are essentially the same design of a century ago

mercury they still put the coarse clean stony tailings

tailings, and so the land stays bare for longer.

1.2 Mining versus civil bucket-li

The Dutch, having canals to dig and harb

adapted the bucket-line dredge for civil dredging.

of a mining dredge are too closely spaced to be

dredging where production is paramount. In

buckets need to be spaced out along the buc

which make the dredges more productive,dredging clay. The chain of a civil dredge runs t

the chain of a mining dredge and can exerci

power. In contrast, a Russian-style bucket-line

closed-connected buckets for both mining and civ

A civil dredge can be converted into a m

reducing the bucket size and adding hardened ri

A 1,000-litre (1m3) civil dredge can be turned

mining dredge of the same engine power. Th

heavier a rock bucket of 600-litre weighs the

bucket of 1,000-litre. The walls are cast thicker.

done with a close-connected chain, so Russia

have buckets larger than 600-litre.

, vo lum e 8 , pages 1 -41 .

ges

ion

rom underwater,

floating on theth century were

dging wheel for

f buckets, eachting and digging

fective tool for

d, although they

bucket-line gold

mbers were also

hore, mainly in

ges only became

ngine and steam-

ket-line dredges

stralia, California

made in England

r the early gold

ere. A few have

monuments anddge in Alaska.

ussian Far East,

ica. Not only did

ones are still

e Siberian-built

in the Zaamar

ercury plates in

fe if buried deep

utes at the back

on top [7].

AT by not using

eparation, and

pump fine tailings

bury the coarsematerial. By this

bucket-line gold

].

ld dredges. These

aving abandoned

on top of the fine

ne dredges

ours to deepen,

But the buckets

efficient in civil

civil dredging,

et-line by links,

especially whenice the speed of

se more cutting

dredge has only

il dredging.

ining dredge by

s or rock teeth.

into a 600-litre

bucket is cast

same as a civil

. This cannot be

dredges never

Figu re 4 . b uck et s o f a b uck et - li nBucket line supported on passive rollers.

Figu re 5 . b uck et s o f a b uck et - li nThe classic closely-linked buckets of a bdesign successful for over half a century.Siberian-built bucket-line dredge Northin Mongolia. (photos: Robin Grayson)

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e dredge(photo: Robin Grayson)

e dredgecket-line gold dredge, aHere operating on aDredge of Shijir Alt Ltd


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1.3 Basic and advanced design

Figu re 6. a b asi c b uck et - li ne m in in g dr NOT BAT basic bucket-line dredge with onband risking the dredge becoming stuck in dumpe(drawing: Robin Grayson)

Figu re 7. a l ess b asi c b uck et - li ne m inin

NOT BAT improved by adding a rear stackebut still leaves a wasteland of barren gravel mou(drawing: Robin Grayson)

Figure 8 . an advanced bucket - l ine m ini BAT adding cyclones allow the dredge to acmaterial by dewatering the tailings. Water is retu(drawing: Robin Grayson)

, vo lum e 8 , pages 1 -41 .

edgeard wash-plant, leaving a wasteland of barren mounds of washmaterial.

g dredge

that reduces the risk of the dredge becoming stuck in its own tds.

ing dredgeieve continuous rehabilitation by burying gravel mounds in sludned to the wash-plant as process water. The pond is also kept c

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d gravel,

ilings

e of topsoil-forming fineleaner by this means.


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2.3 Large gold dredges in actio

Figu re 9. b uck et - li ne dr ed ge lea vin g b e

Banana-shaped masses of reject washed oversizebehind. Bayangol Dredge of Altan Dornod Mongo

Figure 10. a fresh banana wi th each swCurved banana-shaped crocodile of reject washeMongolia. Note the 2 chutes at the rear of the drmoving to the left, with the crocodile burying thand the crocodile is high out of the water (photo:

Figure 11. a crocodi le lef t behind by a bPanorama of the crocodile left behind by the Sothe dredge was travelling to the right. (photo: Ro

Figure 12. a dredge pond being preparedA Siberian-built bucket-line dredge in a path cutplacer. A dragline prepares a U-turn for the dred

, vo lum e 8 , pages 1 -41 .

ind bananas in the for m of a crocodile

discharged from the rear of a Siberian-built bucket-line dredge,Ltd, Zaamar Goldfield of Mongolia. (photo: Robin Grayson)

ep of the bucket-line dredged oversize being dumped at the rear of the Toson Alt Dredge indge discharging fine tailings as slurry from the on-board wash-pfine tailings. In this example the pay gravel is near to the surfaRobin Grayson)

ucket-line dredgeth Dredge, the banana-shapes curves are imbricate one upon thbin Grayson)

for th e dredge to entery 2 draglines. Water is pumped from the Tuul River to float thee. A valuable triangle of placer is left. (photo: Robin Grayson)

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leaving a crocodile

the Zaamar Goldfield oflant. The dredge ise so dredging is shallow

e other, indicating that

outh Dredge over the


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large bucket-l ine dredges in placer

Figure 13 . gold be ing lost by a la rge bucThe Shijir Alt North Dredge in action. This powerdealing with Neogene gravels containing red-brostacker dumps vast amounts of red-brown gold-ri

Figure 14 . gold be ing lost by a la rge bucLEFTan informal miner has picked up a gold bRIGHT about 300 artisanal miners recoveringclay is dumped at the rear of the dredge as gold-

, vo lum e 8 , pages 1 -41 .

gold mines

et-line gold dredgeul Soviet dredge is designed for digging and washing clean rivern lateritic clay. The on-board wash-plant cannot cope with such

ch clayey balls. (photo: courtesy of Golden Tiger Corporation)

et-line gold dredgell and is hurrying away to wash it to extract the gold. (photo: Rlacer gold from stiff red clay the North Dredge of Shijir Alt is n

rich lumps. (photo: Gerrit Bazuin)

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gravels, but here ismaterial, and the rear

bin Grayson)ot designed to wash. The


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Wo r ld P la c e r J o u r n a l 2 0 0 8 , v o lu m e 8 , p a g e s 1 -4 1 . www.mine .mn

8

Large bucket- line gold dr edges fordin g a river

Figure 15. large bucket - l ine gold dredge crossing a r iver

The Toson South Dredge shortly after crossing the Tuul river. Notice the plume of dirty water travelling downstream from the disturbedarea and the presence of turbulent rapids where the dredge had crossed the river. (photos: Robin Grayson)

Figure 16. large bucket - l ine gold dredge crossing a r iverThe Toson South Dredge shortly after crossing the Tuul river. In the background (left) is an ESH Walking Dragline busy clearing the

overburden from the path of the dredge. (photo: Robin Grayson)

Figure 17. large bucket - l ine gold dredge crossing a r iverThe Tuul River is being crossed by large gold dredges to recover the gold on both sides of the meandering river. Although this reduces theneed for diversions, it puts a stress on the river due to the release of muddy water. (photo: Robin Grayson)


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Large buckets turn ing around the l

Figure 18 . lower t umbler o f a large buck

Bayangol Dredge, unusual view of the bucket-line

Figure 19 . lower t umbler o f a large buckFront end of the 250m3/hour Toson South Dredg

, vo lum e 8 , pages 1 -41 .

ower tumbler

t-line dredge

raised for inspection. Each bucket has a capacity of 250 litres. (

t-line dredgewith bucket-line raised out of the water. Monpolymet Ltd. (pho

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hoto: Robin Grayson)

o: Robin Grayson)


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Large buckets turn ing around the l

Figure 20. Toson Nor th Dredge, await ingChimed-Erdene inspects the 250-litre buckets. A l

Figure 21. Toson Nor th Dredge, await ingChimed-Erdene inspects the winterised rear stacto Ulaanbaatar and then by 200 low-loaders to Z

, vo lum e 8 , pages 1 -41 .

ower tumbler

assemblyow loader is on the far side of the dry dock. (photo: Robin Grays

assemblyer. The dredge was dismantled in Chelyabinsk in Russia and broamar. (photo: Robin Grayson)

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on)

ght by over 100 rail cars


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Large bucket-line d redges in place

Figure 22 . f ron t end of a bucket - l ine d reFront of the North Dredge, a Siberian-built IZTMlower it to control the dredging depth. The windo

, vo lum e 8 , pages 1 -41 .

r gold mines

ge equipped wit h closely spaced buckets for m iningucket-line dredge, showing the bucket-line and the pulleys and

ws are the control room. (photo: Robin Grayson)

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cables that raise and


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Large bucket-line d redges in place

Figure 23 . f ron t end of a bucket - l ine d reSouth Dredge of Shijir Alt Ltd (Dredge #A-2), wi

, vo lum e 8 , pages 1 -41 .

r gold mines

ge equipped wit h closely spaced buckets for m iningth bucket-line in action. Zaamar Goldfield of Mongolia. (photo: R

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bin Grayson)


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3. Large basic bucket-lin

3.1 Introduction

A bucket-line dredge is here termed

standpoint of BAT if the dredge dumps slurry fr

wash-plant directly into he pond, and therefore

spread over the coarse oversize. Therefore

abandons in its wake a large tract of ridges

oversize that are extremely slow and difficult to rSuch a dredge is also likely to have an on-

that cannot be turned off if you dredge it, you

reduces the operational flexibility of the dredge, m

expensive to switch to stripping off submerged ove

itself a channel to get from one placer to the next.

Figure 24. character ist ic swing of a buckA Siberian-built IZTM bucket-line dredge swinginSouth Dredge of Shijir Alt Ltd. (photo: Robin Gra

, vo lum e 8 , pages 1 -41 .

dredges

basic from the

m the on-board

he fines are not

such a dredge

of barren clean

-vegetate.board wash-plant

ust wash it. This

aking it often too

burden, or to cut

t-li ne dredgeto-and-fro.

son)

3.2 BAT and basic large

Operation al advantages very low operating cost in terms of $ simplicity and high reliability if well

hours/day, 7 days/week is normal. fast rate of mining, constrained only

board wash-plant:

up to 250m3/hour rate of mining is r even higher rate of mining is reason

need less deck space. good even in sticky clay, if buckets h excellent security, with on-board wa

gold concentrate. combines mining with washing and d

Operation al di sadvantages high capital cost. discharging fine tailings into pond m

if wash-water clayey. everything dredged is washed whe

Environmental factors risk to topsoil resource: topsoil usually mixed with the overb washed oversize dumped on fines, t

difficult to re-vegetate. risk to mineral resource: leaves a good clean bottom and cat can remove stones up to twice the s may have problem if extremely larg

leaving some gold behind. risk of dust generation: dredged areas may include islands o

to dust generation. risk of sheet runoff and effluent disc not usually a major factor, assuming

properly designed. risk to surface waters: diversion of rivers, streams and wetl

freedom of movement; and pumping of water in and out of dred

optimum dredge depth. risk to biodiversity: low to high depending on usage,

modify wetlands.

risk of poor land reclamation: dredge mounds have rocky tops and

vegetate naturally; even if dredge ponds are left, net la

wetlands lost; and edge of dredge ponds often cliff-like

Key factor s for BAT high risk of poor or incomplete land high risk of channels of rivers and st

(straightened, steep sided). high risk of damage to topsoil. valley-floor has net land-raising, eve

may stay as new open water areas.

BAT conclusion

Bucket-line dredges of basic type are:

NOT BAT for p lacer mi nin g

Figure 25. cable w inch in act ionPulley for the cable winch in action, steeShijir Alt in the Zaamar Goldfield. (photo

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redges

/m3 mined;maintained 20-22

by space needed for on-

easonable if using sluices.able if using jigs as they

ave a clay rim added.h-plant to recover the

umping, so no trucking.

y hamper gold recovery

ther it has gold or not.

urden and lost; andherefore stony surface is

hes virtually all gold;ize of the bucket; butstones are in the placer,

f dumped oversize, prone

arges:the dredge pond is

ands to enable dredge

ge ponds to maintain

ay or may not severely

no fines, difficult to re-

nd-raising has occurred and

, difficult to lessen angle.

eclamation.eams left canalised

though dredge ponds

ring the South Dredge of: Robin Grayson)


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3.3 Large basic bucket-line gol

Figure 26 . d redge pond lef t beh ind by a NOT BAT path of large bucket-line dredge a

Figure 27. rear end of a bucket - l ine dredRear view of a large IZTM bucket-line dredge in tNote the winterised rear stacker emerging betwe

Figure 28. possib ly t he o ldest work ing drWinterised, heating, plus on-board house. (photo

Figure 29 . tack l ing t he wear and tear ofBucket #35 welded to its cutting lip.South Dredge of Shijir Alt in the Zaamar Goldfiel(photo: Robin Grayson)

, vo lum e 8 , pages 1 -41 .

d dredges in action

ucket-line dredgessisted by 2 draglines at Zaamar difficult to rehabilitate. (phot

e showing w interised rear stacker conveyorhe Zaamar Goldfield, owned by Altan Dornod Mongol.n the pair of huge spuds. (photo: Mongolian Business Developm

edge in the world! somewhere in Siberia: William Kramer of Alluvial Dredging and Mining Services ADMS

ucket lips

of Mongolia.

Figure 30. pu lley fo r cable w inchPulley for cable winch of Toson North DrToson Alluvials Mine of Monpolymet com(photo: Robin Grayson)

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: Robin Grayson)

ent Agency MBDA)

www.adms.nl)

edge awaits assembly.pany.


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3.4 Large basic bucket-line gold dredges Alaska

Bucket-line dredges played a big role in the gold rushes of

North America. In Alaska, the most famous survivor is the Pedro

dredge. Built in California in 1938 by the Yuba Manufacturing

Company, it was shipped to Alaska and assembled. With 3ft3

buckets, it was the smallest in the 12-strong fleet of the

Fairbanks Exploration Co., a subsidiary of the United States

Smelting Refining & Mining Co. (USSR&M). For 20 years it

dredged Pedro Creek, interrupted by WWII, until reserves were

exhausted. Then it was disassembled and trucked to Chicken, andconverted from steam power to diesel-electric. The dredge

operated 5 months a year on lower Chicken Creek from 1958 to

1967, at 2,500yd3/day @ 29 buckets/minute. Then laid up, in

1998 the dredge was hauled a mile to the centre of Chicken,

taking 2 weeks on 120 tyres, at the Chicken Gold Camp, a

camping ground on the site of the original mine camp.

Figure 31. cont ro l room of the Pedro DredgeShowing levers to control operations. (photo: Mike Busby,Chicken Gold Camp & Outpost -www.chickengold.com)

Figure 32 . win ter ized Pedro DredgeWinter scene of Pedro Dredge. (photo: courtesy of Mike Busby,Chicken Gold Camp & Outpost, Alaska -www.chickengold.com)

Figure 33. engine room of the Pedro DredgeShowing the CAT diesel-electric power units installed in 1958.(photo: courtesy of Mike Busby, Chicken Gold Camp & Outpost,

Alaska -www.chickengold.com)

Figure 34. winter ized rear stacker of Pedro Dredge(photo: courtesy of Mike Busby, Chicken Gold Camp & Outpost,

Alaska -www.chickengold.com)

Figure 35. bucket l ine removed f rom Pedro Dredge(photo: courtesy of Mike Busby, Chicken Gold Camp & Outpost, Alaska -www.chickengold.com)


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large bucket-line dredge being transport ed overland

Figure 36. winter ised rear stacker of the Pedro DredgeThe Pedro Dredge in 1998 being hauled a mile overland to the centre of Chicken settlement, taking 2 weeks on 120 tyres.The dredge is now the showpiece of the Chicken Gold Camp, a camping ground on the site of the original mine camp.(photo: courtesy of Mike Busby, Chicken Gold Camp & Outpost, Alaska -www.chickengold.com)


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4. Large advanced bu

4.1 Introduction

A bucket-line dredge is here termed

standpoint of BAT if the dredge dumps slurry fr

wash-plant directly into he pond, and therefore

spread over the coarse oversize. Therefore

abandons in its wake a large tract of ridges

oversize that are extremely slow and difficult to rSuch a dredge is also likely to have an on-

that cannot be turned off if you dredge it, you

reduces the operational flexibility of the dredge, m

expensive to switch to stripping off submerged ove

itself a channel to get from one placer to the next.

A basic bucket-line dredge can be upgrade

the dredge is retrofitted with a lengthy rear sta

ensure oversize is dumped far behind, plus cyclon

as slurry with topsoil-forming properties on top of t

Figure 37. redesign of bucket - line dredgRedesign of a dredge to attach a wash-plant at itSan Antonio de Poto Mine, 4,500m up in the Andconveyor taking pay gravel from the buckets to aplant consisting of a trommel feeding screened sl6-cell IHC trapezoidal sawtooth jigs as primary r2 IHC monomodule jigs and finally an IHC minim(photo: courtesy of IHC Holland - www.ihcholl

Figure 38. redesign of bucket - line dredgView of 6-cell primary jigs fitted to rear of dredge(photo: courtesy of IHC Holland - www.ihcholl

, vo lum e 8 , pages 1 -41 .

ket-line dredges

basic from the

m the on-board

he fines are not

such a dredge

of barren clean

-vegetate.board wash-plant

ust wash it. This

aking it often too

burden, or to cut

to advanced if

ker conveyor to

s to spread fines

he oversize.

- Perurear, at thes. View down

n IHC wash-urry to a pair ofughers, feedingdule jig.nd.com)

- Peru.nd.com)

4.2 BAT and advanced la

To achieve BAT, requires thes on-board wash-plant that can be byp supplies dredged placer to a floating always dumps fine tailings on top of a slurry pump sends fines via a slurr

rear stacker to discharge above and

being freshly dumped by the rear st discharging the fines via a rear chut

discharge above and beyond the codumped by the rear stacker.

layer of soil-forming fines, enables s hydrocyclones dewater slurry to turn i reducing risk of uncontrolled and un

wrong directions; and enabling recycling of water back to t

Operation al advantages low operating cost in terms of $/m3

simplicity and high reliability if wellhours/day, 7 days/week is normal.

fast rate of mining, constrained onlyboard wash-plant: up to 250m3/hour rate of mining is r even higher rate if using jigs as they

good even in sticky clay, if buckets h

excellent security, with on-board wagold concentrate.

by not releasing fine tailings into ponassisting gold recovery.

in some models, dredged material caOR dumping.

combine mining with washing and d

Operation al di sadvantages high capital cost.

Environmental factors risk to topsoil resource: topsoil usually mixed with the overb washed fines dumped on oversize, t washed fines likely to stimulate new new surface is easier to re-vegetate.

risk to mineral resource: leaves a good clean bottom and cat can remove stones up to twice the s may have problem if extremely larg

leaving some gold behind. risk of dust generation: dredged areas may include islands o

dust generation. risk of sheet runoff and effluent disc not usually a major factor, if dredge

risk to surface waters: diversion of rivers, streams and wetl

freedom of movement. pumping of water in and out of dred

optimum dredge depth. risk to biodiversity: low to high depending on usage,

modify wetlands. risk of poor land reclamation: dredge mounds have cover of fines, even if dredge ponds are left, net la

wetlands lost. edges of dredge ponds often cliff-lik

Key factor s for BAT low risk of poor or incomplete land r high risk of channels of rivers and st

(straightened, steep sided). high risk of topsoil loss, but new soil- valley-floor has land-raising, even th

stay as new open water areas.

BAT conclusion

Bucket-line dredges of advanced type a

BAT for placer mini ng

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rge dredges

e characteristics:assed and turned off; orwash-plant.coarse oversize tailings by:y pipeline strapped to thebeyond coarse tailings

cker; orsufficiently high to

arse tailings being freshly

rface to re-vegetate.t into sticky sludge:controllable mobile slurry in

he dredge pond via a pipe.

ined.maintained 20-22

by space needed for on-

easonable if using sluices.need less deck space.

ave a clay rim added;

h-plant to recover the

d, wash-water cleaner,

n be routed for washing

mping, so no trucking.

urden and lost.herefore:topsoil formation; and

hes virtually all gold.ize of the bucket; butstones are in the placer,

f dumped fines, prone to

arges:pond is properly designed.

ands to enable dredge

ge ponds to maintain

ay or may not severely

easier to re-vegetate.nd-raising occurs and

difficult to lessen angle.

clamation;eams left canalised

forming materials spread.ugh dredge ponds may

re:


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5. Medium bucket-line gold dredges

5.1 Introduction

During the last few decades there has been a trend towards

larger bucket-line dredges, with manufacture of medium to small

bucket-line dredges declining perhaps to zero in the west.

However in the rest of the world the manufacture of small

to medium-sized bucket line has continued unabated especially in

China and now Mongolia.In general the non-west dredges are substandard in terms

of materials, safety, energy consumption and digging power.

Often their bucket lines are too weak to scrape bedrock and

stoppages numerous. Yet by about 2000 a few manufacturers in

China rectified the problem, at a cost, by using a Caterpillar (CAT)

chain as the basis for the bucket-line.

The medium CAT bucket-line dredge has bowl-shaped

buckets typical of large bucket-line dredges. But on a

conventional bucket-line dredge, each bowl-shaped bucket is

individually cast from hardened metal and includes a shoe that

constitutes a link in the chain of the bucket line. In contrast each

bowl-shaped bucket of a CAT dredge is of pressed sheet metal

and DOES NOT have a shoe but is fitted by 8 bolts to an endless

CAT chain. As usual the buckets scrape, dig, lift and topple pay

gravel into an on-board wash-plant.

5.2 Operation

The CAT dredge cuts the sideward sweeps that are the

hallmark of an efficient large bucket-line dredge, having bowl-

shaped buckets. To cut its path and cut the desired width of pay-

gravel, the CAT dredge moves forward and sideward. Anchored

by a pair of spuds, one spud is raised while the other spud serves

as an anchor-pivot enabling the dredge to cut an arcuate path

with the assistance of winch-powered onshore cables.

The cutting pass is slow to give time for the buckets to cut

and remove the pay gravel. The return pass is faster as no

cutting occurs. Repeated cutting strips layer after layer.

To commence, the winches lower the bucket-line

underwater. Then engines move the chain of buckets in the

manner of a bike chain strung between 2 cogged axles(tumblers). The submerged tumbler is the cutting site for, as

each bucket turns, the bucket pivots its lip into the sediment

surface so cutting and scooping material. The full buckets

continue up the bucket-line and each bucket in turn is inverted

and emptied as it turns over the upper tumbler. The CAT dredge

can make a cut 30m or more, subject to length of wires on the

winches. The CAT dredge is anchored to either the bank or the

water bottom in order to maintain its position. Typically 4 or 5

cables are used:

a bow winch keeps the bow against the dredge face;

2 front side winches move the dredge sideways;

the side winches also regulate the cut of the buckets; and

a ladder winch regulates the depth of the cut under water.

The CAT dredge has a pair of spuds to assist with forwardcutting power:

digging force is supplied by the spud lowered in the bed andpartly by the front wires; forward movement of the dredge is then achieved by

walking with the spuds; width of swing is restricted by spuds to a width equal to the

length of the dredge; and

with spuds there is a danger the line jumps out of its bottom

tumbler or bending a spud.

5.3 Adoption by placer gold miners

The author is aware of only one CAT bucket-line dredge, innorth Mongolia, but it is expected that a significant number exist

in China and perhaps elsewhere.

5.4 BAT and medium CAT dredges

Operati onal advantages low operating cost in terms of $/m3 mined.

lower capital cost than conventional bucket-line dredge.

high manoeuvrability.

can operate in very shallow water.

CAT chain is very robust and easy to maintain and repair. pressed metal buckets are cheap, easy to make and repair.

bowl-shape of bucket assists wetting of material in bucket.

bowl-shape of bucket assists the sliding out of material.

ease of arranging and modifying the on-board wash-plant.

rapid and inexpensive to move from site to site.

CAT chain can rip weak bedrock to recover gold in crevices.

long reach of rear stacker conveyor avoids dredge being

muck-bound or grounded.

CAT chain enables good progress through stiff ground.

small size and manoeuvrability makes them easy to use in

re-mining areas.

can combine mining with washing and dumping, therefore

no trucking of placer.

Operati onal di sadvantages if placer has sticky clay, buckets may not empty properly. lack of reach for deep placer levels. small buckets prevent dislodging or lifting of large stones. risk of creating an armoured layer of boulders that prevents

proper mining. everything that is dredged has to be washed regardless of

if it is placer or not.

Environmental factors risk to topsoil resource: topsoil usually mixed with the overburden and lost; and washed oversize dumped on fines, therefore leaving a stony

surface that is difficult to re-vegetate. risk to mineral resource: may leave gold behind, even if on-board wash-plant excellent;

risk of dust generation: dredged areas may include islands of dumped oversize, prone

to dust generation. risk of sheet runoff and effluent discharges: not usual, assuming the dredge pond is properly designed.

risk to surface waters: diversion of rivers, streams and wetlands to enable dredgefreedom of movement; and

pumping of water in and out of dredge ponds to maintainoptimum dredge depth.

risk to biodiversity: if in a well-managed placer mine, then no additional risk; but if in wetlands, then severe risk of loss of biodiversity.

risk of poor land reclamation: as for large dredges, plus: tempting to put in inappropriate wetlands, and hard for

inspectors to find them; and potential for reworking tailings left by large dredges, but risk of

leaving chaotic.

Key factor s for BAT tempting to use them illegally in environmentally sensitive

swamps and wetlands.

high risk of poor or incomplete land reclamation.

high risk of channels of rivers/streams left canalised

(straightened, steep sided).

high risk of damage to topsoil. valley-floor has land-raising, even though dredge ponds may


BAT conclusion

Medium-sized CAT bucket-line dredges of basic type are:

NOT BAT for placer m ini ngMedium-sized CAT bucket-line dredges fitted with rear stacker,

cyclones and BAT wash-plant are:

BAT for placer mi ning


19/41


5.5 Medium CAT bucket-line g

Figure 39. CAT bucket - l ine mining dredg

Panorama at the Berleg Mine. The CAT bucket-lin

Figure 40. CAT bucket - l ine mining dredg

Panorama of the CAT bucket-line dredge in actiothe rear stacker, the dredgemasters control roo

Figure 41 . CAT dredge wi th bucket - l ine rPanorama of the mid-sized Chinese-built bucket-stacker and its arcs of dumped oversize, and(photo: Gerrit Bazuin of Ochir LG Ltd -www.och

, vo lum e 8 , pages 1 -41 .

ld dredge in action

at rest in it s dredge pond

e is raised, showing the lower tumbler. (photo: Robin Grayson)

in action

n at the Berleg Mine in Mongolia. Note the electric cable surfacand oversize manhandled from the buckets. (photo: Nick Grays

isedline dredge under test by Ochir LG Ltd in the Berleg Mine in Mhe pair of rear chutes discharging fines from the sluices ofir lg.com)

www.mine .mn

19

ng near the rowing boat;on)

ngolia, showing the rearhe on-board wash-plant.


20/41


21/41


21

electr ical supply to t he CAT bucket-lin e dredge

Figure 48. diesel fuel ar r ives at the mine s iteDiesel fuel is delivered by truck, usually better than this. A riskexists of a diesel spill into a stream during the long journey of thetruck, or by leakage upon arrival. (photo: Robin Grayson)

Figure 49 . d iese l generato r at t he m ine si t e

Diesel fuel drives a diesel engine to generate electricity for theCAT dredge. The risk of soil and water contamination fromleakage of diesel, lubricants and coolant is evident, but moremanageable than if the generator was aboard the dredge.(photo: Robin Grayson)

Figure 50. diesel generator at the mine s iteControl panel of the diesel generator. (photo: Robin Grayson)

Figure 51. elect r ic i ty supply to the CAT dredgeGetting the power cable across the dredge pond to a floatingmoving dredge from the land-based generator requires care. Itcan be via overhead power lines or via a waterproof insulatedcable on the bottom of the dredge pond, as in this instance. Thecable is surfacing on an inflated rubber tyre for a cable connector.(photo: Robin Grayson)

Figure 52. elect r ic i ty supply to the CAT dredgeChecking the cable with the power off. (photo: Robin Grayson)

Figure 53. get t ing the cable aboard the CAT dredgeGetting a submerged power cable aboard a floating movingdredge requires some ingenuity. In this instance the waterproofinsulated cable first comes aboard an island of polystyrene blocksstrapped to wooden planks before boarding the dredge. Thisminimises wear on the cable and reduces the risk of the dredgefouling its own power supply. (photo: Robin Grayson)


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22

drive of t he CAT chain of the bucket-l ine

Figure 54. cabin for v iewing and cont rol l ing operat ionsThe CAT dredge is large enough to support a control viewingcabin for the Dredgemaster. (photo: Robin Grayson)

Figure 55. cont ro l panel of CAT dredgeChecking and upgrading the electrics at the rear of the controlpanel of the CAT dredge. (photo: Robin Grayson)

Figure 56 . cont ro l panel in operat ionThe control panel upgraded and checked, the Dredgemasterrestarts the CAT dredge. (photo: Robin Grayson)

Figure 57. elect r ic motor dr iving the CAT chainThe electric motor, spindles and brakes that control themovement of the CAT chain (photo: Robin Grayson)

Figure 58. dr ive motor for the CAT chainGrease is problematic if it reaches the buckets or on-board wash-plant as gold is oleophilic. (photo: Robin Grayson)

Figure 59. dr ive motor and brake for the CAT chainA brake is essential, not only to slow down and stop the CATchain, but also to stop the laden buckets causing the bucket-lineto reverse its motion. (photo: Robin Grayson)


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23

spuds of the CAT bucket-line dr edge

Figure 60. spud up and spud down Right spud is raised, and the left spud is rammed into the bed ofthe dredge pond. (photo: Robin Grayson)

Figure 61. spud locked on CAT dredgeEach spud is locked to the pontoon. (Robin Grayson)

Figure 62 . spud up and spud down Right spud is raised, and the left spud is rammed into the bed ofthe dredge pond. (photo: Robin Grayson)

cable controllin g the dredge position

Figure 63. cable holding the CAT dredgeThe CAT dredge is secured in place by steel cables hauled to-and-fro to make the dredge move. (photo: Robin Grayson)


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24

raising and low ering of t he CAT bucket-li ne

Figure 64. pul leys for raising/ lower ing the CAT chainPulleys and cables raise/lower the buckets. (photo: Robin Grayson)




25/41


buckets on the bottom tum bler of t

Figure 67 . buckets emerg ing from the wBuckets turn up on the lower tumbler. (photo: Ro

Figure 68 . buckets emerg ing from the wBuckets turn up on the lower tumbler. (photo: Ro

, vo lum e 8 , pages 1 -41 .

heCAT chain

t erbin Grayson)

t erbin Grayson)

buckets on the upper t umbl

Figure 69. bowl - shaped bucke tsBowl-shaped buckets turning over the tobuilt CAT bucket-line dredge, at the Berl

Mongolia. A set of 8 bolts secure the bu(photo: Robin Grayson)

Figure 70. bowl - shaped bucke tsIndicative of a bucket-line dredge desig(photo: Gerrit Bazuin)

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25

r o f CAT chain

ver top tumblerp tumbler of a Chinese-g Mine in north

ket to the CAT chain.

ed for swinging.


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cutt ing lips of bu ckets on the CAT

Figure 71 . we lded l ip of bowl - shaped buThe finger is pointing at the weld of the hardenesteel that forms the cutting edge of the bucket.(photo: Robin Grayson)

Figure 72. l ip lost but st i l l m iningOne of the buckets has lost its cutting edge but sraise sediment to the surface.(photo: Robin Grayson)

Figure 73 . fu ll buckets mean h igh produc

Full buckets mean digging is efficient. However, slost by spillages and dewatering. (photo: Gerrit B

, vo lum e 8 , pages 1 -41 .

hain

ke tmanganese

till manages to

t iv i ty

ome gold will bezuin)

emptying the buckets on th

Figu re 74 . wa t er j e t bl ast i ng o ut

(photo: Robin Grayson)

Figu re 75 . wa t er j e t bl ast i ng o ut


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26

CAT chain

t he buckets

the buckets


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oversize in bucket s on th e CAT cha

Figu re 76 . r em ov in g bo ulder s

Dredge stopped enabling worker to manhandle afrom a bucket and throw it overboard. (photo: Ro

Figu re 77 . r em ov in g bo ulder s

The author standing on boulders manhandled froavoid damaging the CAT dredge. (photo: Nick Gr

Figu re 78 . r em ov in g m am m ot h s

The author with a mammoth tusk recovered by t

(photo: Nick Grayson)

, vo lum e 8 , pages 1 -41 .

in

large boulderbin Grayson)

the buckets toyson)

e CAT dredge.

bushes in buckets on the CA

Figure 79. a la rge p lan t caught in

Clumps of vegetation can be a nuisance.

Figu re 80 . t h ro w in g t h e p lan t ov

Stopping the dredge for a few seconds tRobin Grayson)

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27

T chain

a bucket


rboard

grab the plant. (photo:


28/41


dumpin g w ashed oversize by rear

Figure 81. protect ive apron for end of s tClose-up of the protective apron that shields thethe rear stacker from damage. (photo: Robin Gra

Figure 82. chute feeding the stacker conThe dredge-end of the rear stacker conveyor shconveyor being loaded via a chute. A few stonesonto the dredge. (photo: Robin Grayson)

Figure 83. rear stacker of CAT bucket - l inWashed oversize discharging smoothly via rear stNote the discharge chute from the on-board sluicbackground is a small bucket-line dredge. (photo

, vo lum e 8 , pages 1 -41 .

tacker

cker conveyorischarge end of

yson)

eyorwing there rolling back

dredgecker conveyor.

es. In the: Robin Grayson)

dumpi ng w ashed oversize b

Figure 84 . rear stacker o f CAT buwashed oversize toppling over the end oconveyor.(photo: Robin Grayson)

Figure 85 . rear stacker o f CAT buSweep of the conveyor is dumping a neatop of on earlier layer that is already dry.

www.mine .mn

28

y rear stacker

cket-line dredgef the belt of the stacker

cket-line dredget layer of wet gravel on. (photo: Robin Grayson)


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rear stacker of CAT bucket-li ne dre

Figure 86. rear stacker of CAT bucket - l inWashed oversize discharging smoothly via rear st(photo: Gerrit Bazuin of Ochir LG Ltd -www.och

, vo lum e 8 , pages 1 -41 .

dge

dredgecker conveyor.

ir lg.com)

Figure 87 . rear stacker o f CAT buWashed oversize discharging smoothly v(photo: Gerrit Bazuin of Ochir LG Ltd -w

www.mine .mn

29

cket -line dredgeia rear stacker conveyor.ww.ochirlg.com)


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30

medium -sized CAT bucket-line dr edge in action

Figure 88. path of CAT bucket- l ine dredge being cleared by hydraulic excavatorA hydraulic excavator is dumping overburden into a convoy of trucks to clear the path of the dredge. The dredge is able to mine above thewater level of its dredge pond to a limited extent. As the dredge advances, the sluice tailings are dumped as sandy silt via a pair of sluices,while the sweep of the rear stacker buries this material in a thick layer of gravelly oversize. (photo: Robin Grayson)

Figure 89. cables guiding the path of the CAT bucket- l ine dredgeA pair of cables controlling the sweep of the dredge. (photo: Robin Grayson)


31/41


31

6. Small bucket-line gold dredges

6.1 Introduction

While the history of large bucket-line dredges is quite well

documented, the author has so far failed to find any historical

account of small bucket-line dredges. It seems small bucket-line

dredges only became widespread some time after large bucket-

line dredges in many placer gold regions. Even in Mongolias

modern gold rush, large bucket-line dredges arrived in the 1970sbut it only around 2000 did small bucket-line dredges appeared.

Both large and small bucket-line dredge use an endless

chain of buckets to excavate material, and the buckets typically

dig, lift and topple pay gravel into an on-board wash-plant.

However, small bucket-line dredges have box-shaped

buckets made of welded sheet metal, rather than bowl-shaped

buckets of cast metal typical of large bucket-line dredges.

In this section the term small bucket-line dredge is

synonymous with those dredges equipped with box-shaped

buckets of course this general rule is not always true!

6.2 Operation

Although the box-shaped buckets are cheap and easy to

make and repair, it permits a small bucket-line dredge to only cut

forward slots easily and makes difficult to impossible the cuttingof sideward sweeps that are the hallmark of an efficient large

bucket-line dredge.

A small bucket-line dredge is in essence is a cut-down

version of the basic large bucket-line dredge, but less likely to

have powered winches or powered spuds. In spite of the

essential similarity to a large bucket-line dredge, the differences

are so great that a small bucket-line dredge in fundamentally

different in terms of scale, economics and impact.

Advantages smaller size means much greater manoeuvrability

small enough to mine narrow placers.

shallower draught than larger dredges, giving better access

without grounding.

dredging may be so shallow the stacker can be dispensed

with, albeit risking grounding on mounds of oversize.

proficient at re-mining tailings left by larger dredges - butoverall this is inefficient and prolongs the impact.

often modular, easy to truck, assemble, launch, operate and

then truck to the next site - this makes them popular in

flooded pits, but also in ecologically vulnerable rivers.

small size of the buckets assists in wetting of the contents.

small size and simple construction of the buckets, hence

cheap and quick to make/repair.

onboard wash-plant requires only a small footprint on deck.

onboard wash-plant is easy to adjust, being small and fully

accessible.

Disadvantages cannot reach more that 5-10m deep.

dredge small and so too light to cut tough material.

dredge small and so too light to push tough material.

bucket box-shaped and cannot cut sideward easily. buckets too small to lift boulders - risking carpeting the pond

with boulders that shelters gold particles.

6.3 Adoption by placer gold miners

Worldwide statistics dont seem to exist, but the author has

eyeballed at least 20 Chinese-designed small bucket-line dredges

active in placer gold mining in Mongolia, and travellers tales

suggest large numbers are active in China. None seem to be in

North America, Australia or New Zealand and no information is

available from Africa or the rest of Asia.

6.4 BAT and small bucket-line dredges

Operati onal advantages low operating cost in terms of $/m3 mined. low capital cost (even D.I.Y. versions in China and Mongolia). high manoeuvrability. can operate in very shallow water. small box-shaped buckets are cheap, easy and rapid to make

and repair. small volume of bucket assists wetting material in bucket. ease of arranging and modifying the on-board wash-plant. rapid and inexpensive to move from site to site. small size and manoeuvrability makes them easy to use in re-

mining areas. can combine mining with washing and dumping, therefore no

trucking of placer.

Operati onal di sadvantages problem if sticky clay, as buckets may not empty properly. lack of reach for deep placer levels. box-shaped buckets prevent efficient swing of dredge. small buckets prevent dislodging or lifting of large stones. risk of creating an armoured layer of boulders that prevents

proper mining. small light buckets make it implausible to rip the bedrock for

gold in crevices.

short reach of rear stacker conveyor may cause dredge to bemuck-bound and grounded. lightweight dredge, therefore unable to make good progress

through stiff ground. everything that is dredged has to be washed regardless of if

it is placer or not.

Environmental factors risk to topsoil resource: topsoil usually mixed with the overburden and lost; and washed oversize dumped on fines, therefore stony surface

difficult to re-vegetate. risk to mineral resource: often likely to leave a lot of gold behind, even if the on-board

wash-plant is excellent. risk of dust generation: dredged areas may include islands of dumped oversize, prone

to dust generation. risk of sheet runoff and effluent discharges: not usually a major factor, assuming the dredge pond is

properly designed. risk to surface waters: diversion of rivers, streams and wetlands to enable dredge

freedom of movement; and pumping of water in and out of dredge ponds to maintain

optimum dredge depth. risk to biodiversity: if inside a well-managed placer mine, no additional risk. if used directly in wetlands, severe risk of loss of biodiversity.

risk of poor land reclamation: same as large dredges, plus: tempting to put in inappropriate wetlands, and hard for

inspectors to find them. commonly used in reworking tailings left by large dredges, but

often left chaotic.

Key factor s for BAT tempting to use them illegally in environmentally sensitive

swamps and wetlands. high risk of poor or incomplete land reclamation. high risk of channels of rivers/streams left canalised

(straightened, steep sided). high risk of damage to topsoil. valley-floor has land-raising, even though dredge ponds may


BAT conclusion

Small dredges with box buckets but no rear stacker are:

NOT BAT for placer m ini ng even if BAT wash-plantSmall dredges with box buckets, rear stacker & BAT wash-plant are:

BAT (if placer is difficult to reach by other means) BAT for rewashing t ailings if in a rehabilitation plan


32/41


6.5 Small versus larger bucket-l

Figure 90. box -shaped buckets of smal lThese buckets are cheap and easy to make, but tand lift boulders and are the wrong shape to doBerleg Mine in Eroo valley. (photo: Robin Grayso

Figure 91. box -shaped buckets of smal lNotice the strengthen lip for cutting.Shijir Alt Mine in Tuul valley (photo: Robin Grays

Figure 92. box -shaped buckets of smal lNotice the strengthen lip for cutting. The lip hasto protect the sides of the bucket and allow a littlBerleg Mine in Eroo valley, Mongolia. (photo: Rob

, vo lum e 8 , pages 1 -41 .

ine dredges

dredgeoo small to digswinging cut.

)

dredge

n)

dredgeeen bend round

e side cutting.in Grayson)

Figure 93. bowl - shaped buckets

Bowl-shaped buckets are usual with medredges and allow swinging. These buckBerleg Mine in north Mongolia. (photo:

Figure 94. box -shaped bucke ts

Box-shaped buckets are usual with smallare NOT capable of swinging. These bucBerleg Mine in north Mongolia. (photo:

Figure 95. box -shaped bucke ts

Bucket-line of a dismantled small ChinesTamsag in Mongolia. Notice how weak t(photo: Robin Grayson)

www.mine .mn

32

of larger dredges

ium-large bucket-lineets are on a CAT chain.obin Grayson)

f small dr edges

bucket-line dredge andkets are on a weak chain.obin Grayson)

f small dr edges

-designed dredge at Are chain appears to be.


33/41


6.6 Small bucket-line gold dred

Figure 96 . rear of sma ll d redge wi th stacSmall Chinese-built bucket-line dredge of Ikh AltTuul River, fined by the Ministry of Nature & Envistacker is dumping oversize and slurry is pouring(photo: Gerrit Bazuin of Ochir LG Ltd -www.och

Figure 97 . rear of sma ll d redge wi th stacHaving small buckets, the placer material is alreand the spray bar continues this process. Watdirectly into the Tuul River from the sluiceundersize tailings. Washed oversize is discharginthe rear stacker conveyor.(photo: Gerrit Bazuin of Ochir LG Ltd -www.och

Figure 98. box-shaped buckets of smal l dBOX-SHAPED BUCKETS of small Chinese-built bat the Berleg Mine in Mongolia. (photo: Roel BaLtd -www.ochir lg.com)

, vo lum e 8 , pages 1 -41 .

es in action

kertd mining in the

ronment. A rearfrom the sluices.ir lg.com)

kerdy partly loose,r is discharging

with the muddyfrom the end of

ir lg.com)

redgecket-line dredgezuin of Ochir LG

Figure 99 . box-shaped buckets ofBOX-SHAPED BUCKETS of small Chinesat the Berleg Mine in Mongolia. (photo:Ltd -www.ochirlg.com)

Figure 100. smal l bucket - line dredSmall Chinese-built bucket-line dredge uMine in Mongolia. Slurry is pouring from(photo: Roel Bazuin of Ochir LG Ltd -w

Figure 101. smal l bucket - line goldSmall Chinese-built bucket-line dredge uin the Berleg Mine in Mongolia with MonWashed oversize is discharging withoutpouring from NZ hydraulic sluices.(photo: Gerrit Bazuin of Ochir LG Ltd -w

www.mine .mn

33

small dredge-built bucket-line dredgeRoel Bazuin of Ochir LG

ge in actionnder test in the BerlegNZ sluices.w.ochirlg.com)

dredge in actionnder test by Ochir LG Ltdolian crew.stacker. Slurry is

ww.ochirlg.com


34/41


34

small basic bucket-l ine gold dr edge

Figure 102. small bucket- l ine gold dredge

Mrs Enktuya, Environmental Officer of the Mineral Resources Authority of Mongolia, inspecting the buckets of a small Chinese-built bucket-line dredge, frozen in at the Berleg Mine in north Mongolia. The dredge is used for pilot mining, taking advantage of the high water tableand flooded excavations. (photo: Ms Tsevel Delgertsoo of MBDA)


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small basic bucket-lin e gold dred

Figure 103. construct ion, assembly and la

Remarkable view of assembly and launch of twoDredge of Shijir Alt Ltd in the Zaamar Goldfield o1 pile of red buckets; 2 neat line of red bucke6 dredge almost complete; 7 second dredge

Figure 104. small Chinese-built gold dredgChinese dredge with its bucket-line horizontal, haDredge of Shijir Alt Ltd, Zaamar Goldfield of Mon

, vo lum e 8 , pages 1 -41 .

es

nch of small basic bucket-li ne gold dredges

mall Chinese-style bucket-line dredges, in the midst of the tailinMongolia.ts; 3 bucket-line chain; 4 green tent with workshop; 5 buclmost ready; 8 stock of metal ready for cutting and welding. (

e wit h bucket-line raisedving had partial success at mining horizontally into a bank of tailolia. (photo: Chris Lightfoot)

www.mine .mn

35

s left by the North

et-line fitted to dredge;hoto: Chris Lightfoot)

ngs left by the North


36/41


36

small basic bucket-l ine gold dr edges

Figure 105. small Chinese-built gold dredge with bucket- l ine raisedChinese dredge with its bucket-line horizontal. In the tailings of Shijir Alt Ltd, Zaamar Goldfield of Mongolia. (photo: Minjin Batbayar)

Figure 106. small Chinese-built gold dredge, dismantledThe drive motor, upper tumbler, inclined screen are clearly visible. Ar Tamsag in the Zaamar Goldfield. (photo: Robin Grayson)


37/41


37

chain drive of a small basic bucket-line gold dredge

Figure 107. buckets being emptied onto an inclined screenA rectangular bucket turning over the top tumbler, being flushed by a water jet to remove the pay gravel that drops onto a slopedpunched screen where again spray water is applied. The chute is probably losing a lot of gold. (photo: Robin Grayson)


38/41


small basic bucket-lin e gold dred

Figure 108. shor t cent ra l slu ice instead ofClose-up of the short central sluice, catching dro(photo: Robin Grayson)

Figure 109. dozer removing ta i l ings f rom rLacking a rear stacker, this small Chinese bucket-complicated by the torrents of slurry issuing from

, vo lum e 8 , pages 1 -41 .

es

rear stackerpings from the gap where the rear stacker might otherwise be.

ear of a small gold dr edgeline dredge requires a dozer in attendance to clear away the duthe sluices. Shijir Alt Ltd, Zaamar Goldfield of Mongolia. (photo:

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38

ped oversize Robin Grayson)


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39

sluices of a small basic bucket-line gol d dredge

Figure 110. one of the pair of side sluices await ing slurryOne of the pair of main sluice boxes, pausing while the dozer clears away the tailings. Note the tufted green carpet and the flat bar riffles.(photo: Robin Grayson)

Figure 111. one of the pair of side sluices in act ionFlow resumed, showing the choppy surface of the slurry passing over the flat bar riffles.(photo: Robin Grayson)


40/41


40

chain drive of a small basic bucket-line gold dredge

Figure 112. rear view of small gold dredge with chute instead of a stackerSmall Chinese bucket-line dredge in action. Shijir Alt Ltd, Zaamar Goldfield of Mongolia. (photo: Robin Grayson)

7. Discussion and Conclusions

The study set out to determine the current status of bucket-

line gold dredges in the placer gold industry and found that this

type of mining dredge is still of great economic importance [13,

22,33]. Bucket-line dredges continue to be built for placer gold

mining, particularly small-sized dredges but also large dredges.

The digging end of the bucket-line dredge is the peak of

Best Available Techniques (BAT) from the standpoint of

operational efficiency, production cost and minimal environmental

impact [9,10,11,21,23,24,30,31,32]. The disposal end of thebucket-line dredge is almost BAT when fitted with rear stacker

conveyor [8,14,15], but a major advance can be made by

pumping fines from the on-board wash-plant over the stacked

coarse tailings to encourage soil formation and trigger natural re-

colonisation by plants [19,20].

Bucket-line gold dredges have 100 years of bad press

from contamination by mercury lost from on-board wash-plants,

and from failure to rehabilitate the mined areas after dredging.

However rehabilitation to very high standards are now published,

and there is a fresh awareness among ecologists of the very high

ecological value of abandoned dredge tailings in displaying seral

change with a high degree of naturalness [2,20].

8. Acknowledgements

The author is pleased to acknowledge the assistancegiven by many people and organisations over the last15 years, particularly financial contribution and officesupport by Eco-Minex International Ltd (EMI).

Special thanks are due to: Gerrit Bazuin of Ochir LG Ltdfor sharing his vast expertise on bucket-line dredges;also thanks to Dr. Baatar Tumenbayar of San FrontierProgress NGO, Ms. Garamjav and her team ofMonpolymet Ltd., staff of Altan Dornod Mongol Ltd,staff of Shijir Alt Company, Ms. Tsevel Delgertsoo andRoel Bazuin of Ochir LG Ltd, Willem Kramer of ADMS,and considerable help and encouragement from manymembers of the Alaska Gold Forum.

I am particularly grateful to the owners and managersof over 20 bucket line dredges, large and small, whogranted access to their dredging operations andgenerously shared their experience and ideas.


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9. References

1. Ash, Simon Harry (1932). Safety practices in California golddredging. Washington: United States G.P.O. ii+31 pages.

2. Bazuin, Gerrit (2003). Gold dredging operations in Mongolia- scope for less impacts and more profits. [ABSTRACT] WorldPlacer Journal volume 3.read at: www.mine.mn

3. Bazuin, Gerrit (2003). Successful gold dredging in severewinters. [ABSTRACT] World Placer Journal volume 3.

read at: www.mine.mn

4. Bazuin, Gerrit; Robin Grayson, Frank Mc.Bride and IainBarclay (2000). Review of the Gold Dredges in Mongolia, withcomments on mitigation of environmental impacts. World PlacerJournal, volume 1, pages 90-106.dow nload ACROBAT: www.mine.mn

5. Bazuin, Gerrit; Robin Grayson and Minjin Batbayar (2003).The North Dredge of Shijir Alt in the Zaamar Goldfield ofMongolia. [ABSTRACT] World Placer Journal volume 3.read at: www.mine.mn

6. Bazuin, Gerrit; Robin Grayson and Baatar Tumenbayar(2003). The South Dredge of Shijir Alt in the Zaamar Goldfield ofMongolia. [ABSTRACT] World Placer Journal volume 3.read at: www.mine.mn

7. Cleaveland, Norman (1941). Bucket Line Dredge Methods.Mining Congress Journal volume 27, pages 19-22.

8. Col, M.H.; and W.F. Crockett (1988). Innovative Gold Dual

Dredge Allows Simultaneous Overburden Removal and MineralRecovery. Chapter 28 - Placer Mining and Dredging, 16 pages. In:Gold Mining 88, American Institute of Mining Engineers.

9. Cope, Louis W.; and Leed R. Rice (editors) (1992). PracticalPlacer Mining. Publishers: Society for Minerals, Mining andMetallurgy (SME). 112 pages. Price: $10.00 ISBN: 0-87335-105-3obtainable from: ww w.smenet.org/store/ bookstore/

10. Cotton and Rose (in press). The Grey River gold dredge1985-2004, Australasian Institute of Mining and Metallurgy

AusIMM Monograph on New Zealand Mineral Deposits.

11. Craig, Robert K. (2000). Exceptional Gold Dredging in NewZealand. International California Mining Journal ICMJ, issueSeptember 2000.

12. Demlow, T.C.; P.J. Bosse and P.C. Rusanowski (1989).Bucket-line dredge disposal system turbidity modelling. Pages2955-2966 in: O.T. Magoon and others (editors) Coastal Zone'89. Proceedings of the 6th Symposium on Coastal and Ocean

Management, American Society of Civil Engineers, volume 3.13. Dore, Giovanna; Robin Grayson, Vera Songwe and TonyWhitten (2006). Mongolia - A Review of Environmental and SocialImpacts in the Mining Sector. Environment and Social Development East Asia and Pacific Region, the World Bank, 41 pages.ww w.worldbank.org/ eapenvironment

14. Eddy, Lewis H. (1916). A California Dredge with TwoTailings Stackers. Engineering and Mining Journal 22nd January1916.

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