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JURUTERA, May 20066

Gravel Pump Tin Mining in Malaysia...........................................................................................................................................................................................................................

By: Ir. Yap Keam Min, FIEM, MICE, MIEAust, P.Eng, C.Eng (A former tin miner)

INTRODUCTION

Gravel pump was the most commonmethod of tin mining in Malaysia. TheChinese have been using this methodfor decades in Perak and Selangor. TheKinta valley in Perak was once therichest tin ore field in the world andpractically every low lying land in theregion contained tin. The tin depositsin Selangor were generally locateddeep in the ground, some up to 100m.

Gravel pump was popular becauseof its low capital cost and itseffectiveness in alluvial mining. A lotof people could and did venture intomining especially in the Kinta valleywhere tin ore occurred in shallowerdepths. Gravel pump could minegrounds with irregular bedrocks whichthe dredge could not. The depositsbetween the limestone pinnacles wereusually rich in tin.

The obvious principle in mining isto extract as much tin as possible in theearly stages of operation so as to coverthe capital cost. One problem thatminers faced was the short mininglease. The lease was usually for fiveyears and the miner might not getrenewal after the lease expires.

Most of the mining equipmentssuch as pumps, liners, impellers andsteel pipes were manufactured locally,mainly in Perak.

Since the collapse of the world tinmarket in 1985, the tin mining industryhas been on a very steep decline. Thenumber of tin mines now operating inMalaysia is less than 25, a far cry fromthe 1000’s in the 1970s, producing amere 3000 tonnes.

PROSPECTING FOR TIN

Wash boring (Figure 2) was the mostcommon method used to prospect foralluvial tin ore. It was less expensivecompared with drilling for primary tindeposits. Samples were collected forevery 1.5m and washed for tin ore. The tinwould then be weighed, dried and kept inplastic bags (Figure 3). The type of soil forevery layer would also be recorded.

OVERBURDEN STRIPPING

The removal of non ore bearing earthor overburden could be done either bydry or wet stripping. In dry stripping,the earth would be excavated bytractors and moved by trucks to thedump site. It is similar to earthworks inconstruction but only in massive scaleand minus the compaction.

Wet stripping would normally bedone by monitors and gravel pump,

Abstract

This paper gives a review of gravel pump tin mining in Malaysia. Most of the major operations ofgravel pump mining are highlighted. Although most of the information provided is historical innature, the operations can still be adopted today. Malaysia has the technology and experience inalluvial mining but we do not have that much more prospective land for profitable tin mining.

Figure 2: Prospecting for tin using the washboring method

Figure 4: Wet stripping of the overburden bygravel pump

Figure 3: Tin ore samples from prospecting works

Figure 1: A gravel pump tin mine in Tronoh,Perak (1952). The engine used was large in sizebut low in capacity. Interestingly one engine runboth the water and gravel pumps. The engine hadto be housed in a big hut.

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and would be similar to actual miningexcept that the earth materials werepumped directly to the tailings dump(Figure 4). It would be more expensiveand time consuming than dry stripping.However, in very soft ground such aspeat soil where the trucks cannot work,wet stripping had to be used.

GRAVEL PUMP MINING

Gravel pump method evolved from theground sluice used in gold mining.Early ground sluice for gold mininginvolved diverting a stream of waterfrom the river along wooden groundsluice. Earth was shovelled into thesluice and agitated; the flow of waterwould the carry the lighter materialsleaving behind the heavier gold.

Early tin mining was also along theriver banks and when mining had togo inland, pump was used to providewater and for dewatering the mine pit.Chinese miners used chain pumpwhich was operated by a water wheel.The British introduced centrifugalpumps run by steam engines of 8-12 H.P.Later diesel engines were used .Thesize of the pumps was 100mmdiameters in the early years, steadilyprogressing into larger ones (up to450mm) due to higher capacityengines. Electrical engines were alsocommon especially in shallower minesor where power was available.

Gravel pump mining involvedusing high pressure water jets knownas ‘monitors’ (Figure 5 ) to break theore bearing stratum (or karang); andthe slurry would then be washed to asump in the pit floor. The groundwould normally be kept steep so thatthe slurry could slide easier to thesump. The monitors were usuallylocated near to the working face to beeffective. A gravel pump (Figure 6)would pump all the material up to anelevated ‘palong’. The common size ofthe gravel pump would be 350mm anddriven by a 620 H.P. diesel engine. Themaximum lift of the pump would beabout 30m and deep mines wouldrequire several gravel pumps.

Excavators would be used to digand break up the clayey material.Clayey deposits are tough for themonitors to break down. Further more

tin ore could stick to lump of clay andflow to the tailings. Excavators werealso used to dig tin deposits lyingbetween limestone pinnacles. Bulldozers were used to push the materialsdug by the excavators to the sump forthe gravel pump.

The mine face could be steepespecially near the land boundaries(Figure 7). Miners usually mine close tothe border especially when the depositis rich. Since mine face is usuallytemporary, miners do take risk.

PALONG

Palong is the most important structurein the tin mine because it is where thetin ore is saved. Figure 8 shows aclassic palong which is a raritynowadays. The efficiency of the orerecovery would depend on its design.

A poor design would result in tin oreending up in the tailings.

The pumped materials from thegravel pump would have to go througha fixed (Figure 9) or a revolvingtrommel screen to discharge largegravel, stones and large lumps of clay.

Palong is essentially a big woodensluice box and the early palong hadsingle or twin lanes. Palong for goldmining normally has two lanes and agentle slope (Figure 10). Typicaldimensions of palong are 50m long, 2mwide lane of at least 12 lanes. Transversetimbers (100mmx50mm) are placed asriffles to agitate the slurry and formeddies as shown in Figure 11. As theheavy materials accumulate and when it

becomes difficult to agitate, additionaltimbers are added on the original ones.The tin ore is trapped in the riffles.

The most important feature ofpalong is its gradient of the floor. A toosteep slope will result in lower recoveryof ores but a gentle one will reduce theflow of the slurry and will hamper theoperation. The gradient of palongdepends on the soil of the tin bearingstratum. For tin bearing layers in clay,gradient is normally 1:13 and for sandykarang, the slope should be steeper, 1:11.For dry stripping mining the slope is 1:9because of the much larger volume of

Figure 5: Monitors and the gravel pump

Figure 6: The gravel pump; Gravel pump methodis named after this equipment

Figure 7: Mining slopes can be steep

Figure 8: A Palong; a rare sight nowadays

Figure 9: A fixed screen to screen the largematerials such as gravel and stones

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materials needed to be treated. Most ofthe tin ore is caught at the top 10m of thepalong. A well designed and managedpalong can recover 80% of the tin ore.

DRY MINING

In the mid 1980s when the constructionindustry was in doldrums, manyearthworks contractors had noprojects. Instead of leaving their heavyequipments and trucks idle, someenterprising contractors ventured intotin mining. The contractors enteredinto joint venture with miners in apercentage of ore won basis.

The method they used is known asdry mining. Excavators were used to digthe tin bearing earth onto dump trucksto move to a collection area in front ofthe palong. Monitors were used tobreak, loosen and agitate the materialswhich flow to a palong by gravity. Thismethod is known as dry mining becauseno gravel pump is used. (Hence, thegravel pump is now known as wetmining).This method is very ideal forsandy karang. This has proven to be ahighly effective method of mining aslarge volume of tin ore bearing earth canbe treated. The other operations are thesame as gravel pump method.

The advantages of the dry miningare as follows:1. Selective mining; only workable

grade of tin bearing materials are transported to the palong.

2. Reduction in tailings slime whichresults in the water being less turbid. Clearer water is essential forore dressing

3. Larger volume of ore bearing earth per month can be mined. The dry method can treat twice as muchkarang as the wet method.

4. Much reduced machinery andequipment down time as compared

with the wet method.5. Safer operation for mines workers.

Flooding of the mine hole is not crucial as mining equipments and workers are not in the pit.

TAILINGS

Gravel pumps produce tremendousamount of tailings sand and slime.They are pumped from the tail end ofpalongs to retention ponds (Figure 12)which usually consists of a series ofsedimentation ponds. Slime iscontained in the initial pond and watercan overflow into the next pond. Sandis at the apex of the tailing and slime isstored in sedimentation ponds. As thevolume of the tailings increases, the

heights of the bunds are increased,usually with dry stripping overburden.

Tailings can also be dumped in ex-mining pool as shown in Figure 13.There would be a lot of saving frompumping cost as the tailings goes to thepool by gravity. Tailings dumps haveto be maintained and inspected daily.

DRAINAGE

Drainage is one of the most importantoperations in gravel pump mining.Closed-circuit system of drainage isnormally practised. Water is re-cycledfor use. One of the common problemsin open cut mining is ground watercontrol. Mine has to be drained bypumps and in deep mine, dewateringcan be non stop. For this reason, somedeep mines work 24 hours.

TIN ORE WASHING AND

DRESSING

Tin ore is normally recovered by apalong-jigs plant as shown in Figure 14.The recovered concentrates or roughconcentrates from the palong (Figure 15)are transported to the tin washing plantlocally known as “tin shed”. This is alsothe ‘safe’ where tin ores are kept beforetransporting to the smelters. Therecovered concentrates are washedusing small palong known as lanchute.There is a premium for higher

Figure 10: An example of a gold mining palong

Figure 11: A naked palong-showing the riffles fortrapping tin ore

Figure 13: Tailings dumped into ex-mining poolby gravity

Figure 14: Washing of the palong using jigs

Figure 15: Rough concentrates recovered from the jigs

Figure 12: Tailings retention ponds

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concentrates when the ore is sold to thesmelters. Nitric acid is often used toremove impurities. The more efficientmines have concentrating tables (Figure16) for dressing the materials which givea higher recovery rate. Tin ore is thendried in a furnace and packed into bagsfor sale. The residual after extracting thetin ore is known as amang whichcontains other heavy minerals and asmall percentage of tin ore. Coarse tinore has more impurities and has to becrushed and grinded. Larger minesprocess their own amang utilisingcrushers, grinding and magneticseparators to extract the tin ore. Figure17shows a typical magnetic separator.

TIN ORE BY-PRODUCTS

Sand is the most common by- productof the tin mining operation and theconstruction industry has for manyyears benefited from the abundantsupply of it. The closure of the tinmines has caused suppy problem.Some of the by-products of tin are rareearth minerals such as monazite andxenotime. These heavy minerals areradioactive; uranium and thorium canbe extracted from them. Zircon isanother by- product of tin ore. Theseminerals are extracted from the amang.These minerals were initially unknown

to tin miners and amang factoryowners alike and for many years thesewere left as waste. The discovery ofthese minerals had made a few amangowners rich.

STEPS TO VENTURE INTO

TIN MINING

1. Identification of land based on localknowledge or known deposits

2. Apply for prospecting permit fromthe state government

3. Start prospecting for ore4. Application for mining lease.5. Apply to the mines department for

Hydraulic Licence6. Start mining

State governments will only issuemining lease if the project is viable andthe environmental consideration is taken.A proposed rehabiliting programmeshould be provided. Miners will alsohave to give a guarantee (usually in theform of a bank guarantee) to fulfill thefilling and leveling condition.

CONCLUSION

Gravel pump method is very effectivefor mining alluvial tin ore. It has beendeveloped through years of experience.The three most important items ingravel pump mining are tin ore content,water and tailings dumps. Without anyof the items, the mine cannot operate.Obviously the land must be workableand profitable. Water is crucial forhydraulic mining and closed circuitsystem of drainage is practised. Thereshould be adequate dumps for tailingsand overburden earth. Gravel pumpmay not be effective in areas where thereare a lot of boulders. Dry mining whichhas evolved from gravel pump is nowthe preferred method. It has theadvantages of selective mining, largervolume of materials can be treated andreduction in tailings slime. Malaysianminers are the most efficient hydraulicminers in the world and they shouldexport their expertise. �

REFERENCE

[1] Gullick JM, Kuala Lumpur1880-1895.PelandukPublications, 1988

Figure 16: Concentrating or shaking table for tinore dressing

Figure 17: Magnetic separator to dress tin ore