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Recovery Practices at Sea The processing of placer minerals at sea has the advantage of reducing the need for the transportation of large quantities of waste minerals which can be rejected on site. Offshore dredging operations in the exposed waters of South East Asia have the processing plant on board to add weight and to increase the stability of the dredgeat sea and alsoto reducethe operatingcost by integratingthe services Koesrnadiet al,, 1975; Donkers, 1980; Lim Che Wan, 1983!. In coastal and protected waters, the processing plant is on a floating platformmooredindependentlyof the dredgeand lyingbehindit, Thisarrangementis commonlyusedwith someof the hydraulictypesof dredgesto increasethe mobilityof thedredge.Thedredgedmaterialis pumped througha floatingpipelinetotheplantforprocessingAnon,1976;Buistetal.,1978;IHC,1983;Kramer,1984!. Comparedwith land-basedoperations,processingat seaimposesrestrictionsdueto the limitedavailability of plantspace,electricpowerandotherfacilities.On modernintegrateddredging/processingoperations,the processingplantconsistsoftwomajorsections:thefeedpreparationanda concentrationsectionwhichhas a numbeorfjigsor conesT,heoperationproducesa bulkconcentrateata highrecoveryanda rejectcontaining sandsg,ravelsandclaymineralsT.hebulkconcentratiesshippedtoshoreforcleaningandupgradingT.his maytaketheformoffurthergravityconcentrationm,agneticandelectrostaticseparationh,eavymedia techniques or flotation. Inthefeedpreparatiosnectionoftheplanthedredgedmateriails disintegrateds,ized,deslirnedandthe densityoftheslurryadjustedO.neortworevolvingscreensperformthefunctionofscrubbingandsizingS,pray waterjets,underpressureinsidetherevolvingscreendisintegrattehelumpymateriaalndciay.Theoversize material,usuallycoyrserthan 16mm,is disposedof. The undersizeis distributedto the first rougherconcen- trators.Therougherconcentrateis passedthroughseveralcleanerandrecleanerstagesbeforea bulk concentrateis obtained.The rejectfromthe rougherconcentratorsisdisposedasfinaltailingsandthe rejects from the cleaner and recleaner concentrators are recirculated. Anyinefficienciyntherecoveryprocesscouldresultin lossesof valuablemineralsi,nthe rejectedtailings, at sea. This may reflecton the returnsof a dredgingoperation,Dankers 980! notedthat mostof the inefficienciesofa processingsystemareduetoanunderdesignedplantcapacitytotreatfeedfluctuationsfrom the dredge and their recirculated products. Forparticularcaseswhena placerdepositcontainsmineralsinanoxidizedstate,partiallyliberated,oras fine and ultra fine particles,processingat sea becomesmorecomplexand impliesextensivestudiespnorto defininga suitableprocessingsystem.In addition,the concentratorsoperatingin the marineenvironment should demonstrate the following: ~ tolerate fluctuations in feed rate, slurry density and particle size. ~ tolerate moderate sea motions and vibrations from the machinery on board. ~ operatewithminimumsupervisionandmaintenance. ~ producehigh recoveryand enrichmentratioswith a minimumpowerconsumption. ~ produce environmentally safe wastes. ~ to be accessible at relatively low cost. Since each placer deposit has distinctive geological and mineralogical characteristics and each equipment performsdifferentlywhen the working conditionschanges,preliminarystudies and testwork are required before the conception of the final design of a dredging/processing operation. Nova Scotia Offshore Placer Gold Deposits Gold has been mined from inland and beach deposits within the province of Nova Scotia since 1862. Early recoveriesofgoldwerereportedfrombeachdepositsat isaac'sHarbor,WineHarbor,TangierHarbor,Gold RiverandtheOvens.Placermining,however,neverassumedanimportantproportionaftertheturnofthe century Malcolm, 1976!. There are approximately190 gold occurrencesin the province Figure 4! categorizedasbeingeitherload,paleoplacerorplacer PonsfordandLyttle,1984;FowlerandMiller,1985!. Mostofthegoldoccurrencesarelocatedinthesouthernmainlandoftheprovinceandaremainlyconfined to the metasedimentaryrocksof the MegurnaGroup,comprisedof quartzites,greywacks,slatesandgranitic intrusions.The Groupunderlays30 percentof the southeasternpart of the provinceand extendsfor approximately40 km offshore,coveringan offshorearea of 26,550km King and MacLean,1976!. The riCh,gOld-bearingrOCkSOfthe Meguma GrOupprOvidea SuitableSOurCeand the prOCeSSeOStglaCial 20PDF Image | Dredging Applications of High Density Polyethylene Pipe
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