Marine Mining

Transaction

Paper

History of Marine Diamond Corporationand De Beers Marine

Diamonds were first discovered along the westcoast of Africa in 1908 near Luderitz, and by1927, extensive deposits had been found inraised beaches both north and south of theOrange River. Production from onshoredeposits increased and by the 1950s was inexcess of 2 million carats per year along thewhole stretch of coastline.

As a consequence, claims were registeredalong approximately 900 kilometres of thewest coasts of South Africa and Namibia (thenSouth West Africa), and several expeditionswere mounted from Cape Town to search fordiamonds along the coast and on the offshoreislands. However, other than occasional

rumours, there are no records of diamondsbeing recovered from the sea until 1961.

The honour of recovering the first officialdiamonds from the sea goes to Texan oilmanand entrepreneur, Mr. Sam Collins, whoseMarine Diamond Corporation (MDC) recoveredtheir first diamonds on 15 November 1961,netting a total of 45 stones with a combinedweight of 9 carats (ct = 0.2 g) from Wolf Baynear Luderitz.

While tendering for an oil-pipeline instal-lation contract for the Consolidated DiamondMines (CDM), Sam Collins’s interest wassparked by the presence of the shore-basedoperations. His acquisition of a company,Suidwes Afrika Prospekteerders, gave MDCrights to a large concession stretching from theOrange River to Diaz Point at Luderitz.

Sampling operations continued across thelarge concessions, and by the end of March1962, a further 44 diamonds weighing 12carats had been recovered.

Sam Collins, an archetypal Texanentrepreneur, wasted no time in developing abankable reserve, and by May 1962, oil pipe-laying Barge 77 had been converted into adiamond mining platform, and produced 12700 carats by December 1962.

However, during a storm event in June1963, Barge 77 broke her mooring and wasdriven ashore north of Chameis Bay withoutloss of life. A tank landing craft vessel wasquickly converted into the diamond recoveryvessel Diamantkus, and a new barge, Barge111 was constructed as a replacement forBarge 77.

In 1965, a further new barge, Colpontoonwas built, and production peaked at 241 000carats. MDC was also awarded further deep-water concessions in 1963, which extendedapproximately to the edge of the continentalshelf.

A perspective of marine mining within De Beersby K. Richardson*

Synopsis

Although the De Beers group has a long history of placer mining onland, the group only became actively involved in deep water marinediamond exploration and mining in 1983 with the formation of DeBeers Marine. Full-scale commercial mining commenced around1991. Since then, the group marine mining capability has grown intoa formidable fleet of 8 large deep water (>70 m) mining vessels, aswell as other special purpose geosurvey platforms. Marine diamondproduction by the group is expected to be just short of 1 millioncarats in 2006. De Beers operates across the entire value-chainspectrum from geology and geosurvey, through sampling to mining,and finally ore processing into high value concentrate. Supportingthese operations involves significant service activities such asmaintenance, security, logistics and environmental management.Specific challenges exist in terms of developing or acquiringappropriate technology for marine mining. These challenges haveresulted in De Beers operating extensive in-house R&D and projectsdepartments, as well as drawing extensively from technologypartners. An array of computational and test facilities is alsoavailable to support R&D and projects activities. Hydrotransport invarious guises is key to the current approaches to marine miningand ore processing. Use is made of airlift and centrifugal pumpingfor hydraulic hoisting of very coarse gravel, while splitters,launders, dewatering, elutriators, jet pumps, centrifugal pumps,dense medium circuits, pipeline systems, and instrumentation forcoarse abrasive particles are used extensively in the ore processingplant.

* De Beers Marine (Pty) Ltd, Cape Town, SouthAfrica.

© The Southern African Institute of Mining andMetallurgy, 2007. SA ISSN 0038–223X/3.00 +0.00. This paper was first published at the SAIMMConference, Hydrotransport 17, 7–11 May 2007.

393The Journal of The Southern African Institute of Mining and Metallurgy VOLUME 107 REFEREED PAPER JUNE 2007 ▲

A perspective of marine mining within De Beers

Financial woes for the MDC, which had started with theloss of Barge 77 continued, and Sam Collins invited De Beersto participate in the business. After some negotiation, DeBeers secured an option to participate, subject to anindependent survey of the concession area and a decisionwhether to participate. In 1965 De Beers exercised theiroption and became the majority shareholder in the MDC.

The MDC had up to this point been recovering diamondsfrom what is today referred to as the shallow-waters (<30m), and most of the production had come from select highgrade features in Chameis Bay and Bakers Bay. The MDCcontinued to report financial losses, and several vesselsoperated at losses relative to their direct operating costs.Mineral reserves were non-existent, and a form of hand tomouth sampling and mining was practised, relying on theinstincts and luck of the production superintendents.

With the new majority shareholders now exercising theirinfluence, opinions varied at this time (1965) as to the bestcourse of action with the two options considered being: tohalt production while the geosurvey and sampling activitiescontinued until ore reserves had been established and themining methods developed, or, to continue with operations in order to recoup the substantial investment made up to that point.

A compromise was arrived at, and the production fleetwas selectively phased out while survey and samplingcontinued in a much more systematic way. Productiondropped from 241 000 carats in 1966 to only 132 000 caratsin 1967 as the Diamantkus, Barge 111, and Colpontoon werewithdrawn, and a new barge Pomona, with a much enlargedcapacity, was commissioned in July 1967.

Production from Pomona continued and, thanks to thediscovery of a large new reserve feature in Hottentots Bay,production continued to 1971, with output peaking from thisone barge at 239 898 carats in 1970. Due to exhaustion ofreserves, and the anticipated expense of refitting the Pomonaafter 3 years at sea, mining operations closed at the end ofMarch 1971.

The MDC, now under complete ownership by De Beersand unencumbered by operational pressures, focused itefforts on development of an understanding of the marinediamond resources. The operations were vested with CDMand came to be known as CDM marine.

Operations continued to focus on the shallow water areas,but during early 1971 when weather precluded the samplingvessel from continuing work inshore, a series of grabsamples were collected along the coast about 20 km southand north of Chameis Bay out to approximately 100 m waterdepth, so as to determine the presence of any minerals ofvalue. At this stage, marine geological models were almostnon-existent, and the origin of the diamonds in the sea wasstill subject to debate. (It is also worth remembering thatplate tectonics theory was universally only accepted in the1960s.) These grab samples indicated the presence ofsignificant sediments offshore containing concentrated heavyminerals. This was then the first indications of paleo-beachesbeyond 35 m water depth.

The team remaining subsequent to the cessation ofproduction in 1971 was given the brief to confirm the thenconsidered absence of a potential for economic reserves ofdiamonds in the MDC concession areas covering 27 000 km2

in water depths from 35 m to 200 m.

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394 JUNE 2007 VOLUME 107 REFEREED PAPER The Journal of The Southern African Institute of Mining and Metallurgy

Figure 1—West coast map and consessions—Namibia and South Africa

Figure 2—Barge 77—MDC’s first production system

Geophysical surveys, supplemented by vibracoresampling were carried out up to 1974. The information thusgenerated suggested the presence of sediments extensive inarea, but variable in thickness and mineral content.

The most promising results narrowed the area proposedas potential sampling sites to approximately 100 km2, and intotal, 3 297 samples were taken between 1974 and 1977 in70 m to 90 m water depth areas. However, the wholeresource was at that time estimated to contain no more than0.5 million carats and was seen to be too small to support thedevelopment of the mining systems required to operate atthese depths.

As a result, sampling operations moved further offshorein 1977. This exercise seemed to confirm the presence of awidespread low grade deposit in the 100 m to 120 m waterdepth.

There was no announcement of these results at the timebecause of political and business uncertainty, lack ofknowledge of the size of the deposit, and the need to developmining technology.

Sampling continued between 1977 and 1982 with a totalof 9 228 samples taken in the reconnaissance area betweenthe Orange River mouth and the Diaz Point at Luderitz inwater depths of between 100 m and 135 m. As more detailedgeophysical information became available, the area was seento contain wide variations in topography with clear relation-ships between ridges, basins and valleys, and the concen-tration of diamonds. This was used in 1982 as the basis forinterpolation between sampling results on the basis oftopography, thereby enabling the isolation of two largetargets known today as the Northern and Southern TargetAreas.

De Beers Marine formation

By 1983, CDM marine had delineated a deposit of world-classproportions although the total caratage was unknown, andoperations in deep-water deposits moved to an evaluationand ore reserve generation phase. To mine the deposit wouldrequire substantial financial input, and the onshoreoperations at CDM would not be capable of carrying theinvestment. At the same time, South West Africanindependence was being pursued by liberation movementswithin the country. In addition, the South African sea areas(SASA) concessions had been awarded, with De Beersreceiving the 4c and 5c, while 1c was awarded to Alexkor, 2cwas awarded to African Selection Trust Exploration (ASTE),and 3c was awarded to Sedswan.

To allow operations in both South and South WestAfrican waters without disruption of resources whileprotecting the technology that existed at the time as well asthose still to be developed, De Beers Marine (DBM) wasformed as a contracting company that would own proprietarytechnology, and would offer the services to clients byoperating on the concession holders’ behalf, and beingremunerated for this service. At the time, exclusive contractswere signed with CDM and De Beers Consolidated Mines(DBCM) for De Beers Marine to undertake prospectingoperations in their respective grant areas.

During this time, sampling in the SASAs yielded the firstdeep-water diamonds in these concessions in 1984.

The focus for sampling changed after 1983, movingtowards gaining a more detailed knowledge of the geology ofthe existing resource rather than further exploration forextensions to the resource. In addition, after identifying theclear need for the development of technology for mining indeep water, De Beers Marine formed a Mining and ResearchDivision within the company in 1984.

Various mining systems and equipment designs wereconceptualized between 1985 and 1988, while geologicalwork was being carried out simultaneously to support thethinking for mining tool design. Of primary importance wasthe assessment of seabed conditions; and using highresolution seismic surveys supported by visual calibrationusing remotely operated underwater vehicles, someassessment of the footwall was made. In addition, grabsamples were taken in 1988 using a cactus grab capable ofextracting boulders up to a metre in diameter from theseabed.

Prior to making any major financial commitment toacquiring the hardware for mining, security of tenure wassought and received after some negotiation.

The initial approach to mining was based on the samplingtool, and by enhancement and enlargement of thistechnology, the first mining tool was developed. Toaccommodate this equipment, a larger platform was requiredand in July 1986, the 77 m long Pacific Installer waspurchased for conversion by December 1987. The vessel wasrenamed the Louis G. Murray, and included in the conversionwas a large dense medium separation (DMS) section, a drier,and X-ray unit for the final concentration process.Concentrates were to be bagged and transported to CDM inmilk urns.

The first mining device was then similar to the digginghead on the earlier barges, but included the ability totraverse, and while traversing, operated using a bouncingmotion within a frame, thereby enabling the depletion of aswath. This tool underwent modifications at various timesbut was used in essentially the same configuration until June1989, by which time the recoveries had exceeded 42 000carats from the device.

A perspective of marine mining within De BeersTransaction

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395The Journal of The Southern African Institute of Mining and Metallurgy VOLUME 107 REFEREED PAPER JUNE 2007 ▲

Figure 3—Louis G. Murray—first production vessel of modern De Beersoperations


Concerns about the effectiveness of the suspendeddigging head and the controllability of the depletion resultedin the withdrawal of the Louis G. Murray from service in1989 for the conversion to a crawler mining tool. Thisconversion to a crawler vessel heralded the start of the officialproduction phase of De Beers Marine.

The conversion involved the fitting of an A-frame with adocking device to deploy the crawler. The crawler itself wasunmanned, weighed approximately 40 tons, and waspowered by supplying 1100 volts through an umbilical cable.The crawler was tethered by a 100 mm diameter nyloncomposite rope fed through a constant tension winch.

The business end of the crawler was a cutter wheel with ahorizontal suction port supplied by Orenstein & Koppel(O&K). The loosened material was airlifted to the surfacethrough twin 200 mm diameter flexible hoses. Diamondrecoveries were of concern with this first front end deviceand, subsequent to numerous attempts to modify the cutter, asuction box design was decided on in preference to the cuttersystem, this primarily to eliminate the unfavourablerecoveries experienced with the cutter wheel.

The alteration was a success and the vessel regularlymined in excess of 1 000 m2 per day. These successesresulted in the declaration of 28 663 carats from productionin the deep-water deposits in 1990. Subsequently, the crawlerwas modified and a triple box arrangement was commis-sioned, resulting in even higher rates of mining sometimesexceeding 1 500 m2 per day.

The quest for a higher mining rate stems from the need toreduce the cost per square metre mined, as this is the primaryfactor determining the cut-off grade that can be minedeconomically. By reducing the cut-off grade, larger areas canbe moved from resource into reserve, and the life of mine andthe net present value of the resource optimized. To this end,numerous mining tools were conceptualized for the crawler,some of which were tested but returned less than desiredresults.

Plans for an alternative approach to mining wereformulated from 1988 when the opportunity to modify andcombine the technology employed at that time in the offshoreoil drilling and foundation industries became apparent. From

this thinking evolved the concept of the large diameter drill(LDD) mining system with a drill bit tens of square metres inarea coupled to a large diameter reverse circulation riser pipefeeding through a hole in the hull of the vessel, known as amoon pool, and via a compensation system into the plant onboard the vessel. As a result, the Glomar Coral Sea waspurchased in 1989 and converted in Cape Town.

This vessel sailed in February 1991 as the Coral Sea, andafter some commissioning modifications were done, shecommenced mining in April of that year. The recoveries wereconsidered excellent and on the strength of the initial results,a sister ship, the Glomar Grand Banks was purchased in thesame year. The jump in production capacity resulted indiamond recoveries from the deep water concessions reaching159 000 carats in 1991.

The Grand Banks was subsequently converted, withoperational improvement incorporated in the design of thecompensation system to enable operation of the vessel inmove severe swell and wind conditions. With thisimprovement in the weather window came a better utilizationof the capital asset with a commensurate increase in annualmining rate.

While the Grand Banks was being converted, a world-wide search was launched for further vessels that could beconverted to the large diameter drill technology, and twofurther LDD vessels were sourced, both larger than the GrandBanks with an overall length of 138 metres.

Both of these vessels had the advantage of a larger moonpool, which facilitated the deployment of a 30% larger drillbit. The net effect of this was a 24% improvement in produc-tivity for the design. The first vessel to be converted was theDebmar Atlantic, and she was commissioned in 1994, signifi-cantly contributing to the production capacity, and resultingin production of 405 000 carats in 1994, 453 000 carats in1995, and 470 000 carats in 1996.

Approval for the conversion of the Debmar Pacific wasgiven in the last quarter of 1995 and final commissioningwas completed in March 1997, while at the same time, theCoral Sea was withdrawn from mining production to beconverted into a dual-purpose sampling and mining vessel.This step was taken following a significant review ofsampling methods and mineral reserves, which found thatboth were not of sufficient quality to justify the scale towhich the operations had now grown, as well as to justify thesignificant capital risk of each of the expansion projects.

Further capacity expansion came in 1999, which saw thecommissioning of the first !Gariep conversion into a crawlerbased mining system. The front end of this crawler wasbased on continuous miner coal cutting technology, but dueto significant technical difficulties, the technology fell short ofexpectations. Subsequently, the !Gariep underwent a secondconversion into an LDD mining vessel and was successfullycommissioned in 2003.

Production capacity was further increased in 2003 withthe acquisition of the production assets on the Ya Toivomining vessel. This crawler vessel was previously operatedby Namco, which following two episodes of receivership, wasfinally forced to sell all their production and material assets in2003.

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Figure 4—Coral Sea—first large diameter drill (LDD) vessel

The demise of Namco, and the MDC before them,highlights the risks of miscalculated marine mining, and thecritical necessity to have well-defined mineral reserves inplace, as well as deep pockets to carry the explorationoverhead and occasional operational mishaps.

The formation of De Beers Marine NamibiaAs a result of political pressures during concessionagreement renegotiations, De Beers formed a whollyNamibian company in 2001 to operate in the Namibianwaters, and so De Beers Marine Namibia (DBMN) was born.De Beers Marine Namibia, as a fully independent company,now owns or operates a fleet of 5 production vessels in theNamibia concessions, while De Beers Marine continues to

provide survey, sampling, and other select specializedtechnical services to Namibia.

In 2003, DBCM was granted a mining license in the SASAconcessions following an extended period of low priorityexploration and sampling where most of the focus wasdirected towards the Namibian concessions. In addition to theservices provided to DBMN, DBM is currently in the processof converting the mining vessel Peace in Africa anddeveloping the operational readiness plans for a dedicatedmine in this SASA mining licence.

De Beers Marine currently owns or operates a fleet of 3vessel: one destined for production in SASA, one dualpurpose sampling and mining vessel, and one dedicatedexploration sampling vessel; and in addition owns 2 survey


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The Journal of The Southern African Institute of Mining and Metallurgy VOLUME 107 REFEREED PAPER JUNE 2007 397 ▲

Figure 5—De Beers Marine Namibia fleet

Figure 6—De Beers Marine fleet


class autonomous underwater vehicles (AUVs), and surveytowfish equipment, which are typically operated from vesselsof opportunity.

Marine production record

From the inception in 1990, carat production rose rapidly asadditional capacity was added to the fleet. But this rise inproduction occurred against a backdrop of decreasing averagegrade, which by the late 1990s, had almost neutralized theimpact of additional capacity, such as the addition of theDebmar Pacific in 1997. This resulted in a relatively flatgrowth curve prevailing into the early 2000s, as incrementalimprovements in production across the fleet were offset byever decreasing average grades from the resource. Thecommissioning of the !Gariep and the Ya Toivo miningvessels in 2003 added greatly to the total production capacity.This, together with consistent and significant continuousimprovements to the technology used on the LDD vessels andthe Ya Toivo flowing from a concerted R&D campaign,reignited a strong positive growth trend which has continuedto the present.

Total diamond production from the De Beers’ marinemining activities is expected to be close to 1 million carats in2006, and 2005 already marked a historic milestone asmarine production surpassed land production in Namibia forthe first time ever.

The marine mining value chain

The value chain of any mining venture starts withexploration. Marine mining is no different in principle; it ismade more complicated only by the spatially diverse andgeologically complex nature of the deposit. Placer deposits areacknowledged to be difficult and expensive to evaluate due tothe lack of homogeneity in the deposit. The value chain hasevolved to the point were reserve is developed on a rollingbasis, rather than full bankable reserve definition up front.Survey and sampling are conducted in parallel with miningoperations to ensure that an adequate reserve is in place forfuture operations and capital expansion, as well as to replacethe reserves that are depleted annually.

While most of the sampling activity is directed to resourceand reserve generation (evaluation) from well-defined targetlocations within the deposit, a certain fraction is also directedtowards exploration and identification of new targetlocations. This is essential to secure new areas that will berequired in the future as production depletes known areas, as well as to evaluate the comparative economic value ofpotential targets and to seek out the highest net present value options.

Disparate target locations are additionally beneficial whenoperating a large production fleet, as each vessel requires adefinite exclusion zone to ensure safe operating. As newcapacity is introduced, this requirement becomes morepressing.

The typical value chain employed by De Beers in marinemining is illustrated in Figure 8.

The output of the mining activity is a high-valueconcentrate, which for security reasons is sealed on the

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Figure 7—Marine diamond production from De Beers activities1990–2005

Figure 8—Marine diamond mining value chain

Figure 9—Refuelling at sea (RAS)

Figure 10—Helicopter operations for crew transfer

SEISMIC PRFILINGSIDE SCAN SONAR

BATHYSCANSEABED VIDEO

EXPLORATION SAMPLING

GEOLOGICAL MODELS

GLOBAL ESTIMATE

TARGETSELECTION

EVALUATIONSAMPLING

ESTIMATION

MINERALRESOURCE

FACTORDETERMINATION

MINERALRESERVE

MINE PLANNINGSBP AND SHORT-TERM

PRODUCTIONMONITORING

RESOURCE/RESERVE PERFORMANCE(Reconciliation, audit and analyses)

vessel in tin cans (known affectionately as Neptune cans)and dispatched via helicopter to the Namdeb sorthousefacilities.

A complex operation, of this scale, conducted along aremote and somewhat hostile coastline, requires a consid-erable support infrastructure. To this end, both companieshave service departments focused on the main operationchallenges from securing the product, to coordinating themovements of personnel to and from the vessels, tomaintenance of the fleet, and ensuring that activities takeplace in a safe and environmentally responsible manner. Bothcompanies’, activities are ISO 14001 EnvironmentalManagement certified, and high safety standards and cultureare vigorously promoted.

Vessels stay at sea in up to 3-year cycles betweenstatutory inport maintenance, and are refuelled at sea.

Vessels are operated on a 24 hour per day, by 365 dayper year basis, with crew, members working 12 hour shifts,and rotating 28 days onboard followed by 28 days ashore onleave. Crew are transferred to and from the vessels byhelicopter.

Technology acquisition

Very special challenges exist in terms of developing oracquiring appropriate technology for marine mining.

➤ There are no off-the-shelf solutions for mining at 100 m water depth

➤ There are few competitors to learn with or from➤ Failures on the scale of a marine mining vessel are not

tolerated well by management➤ The geology to be mined is under 100 m of water,

making it difficult to visualize and quantify thechallenge.

A strategy has evolved over time at De Beers thatpromotes the development of technologies offline from theproject acquisition stage. In addition, the project acquisitionstage is conducted using standard approaches and practicesconsistent with PMBOK2.

While this approach is not always practical, it is veryimportant for systems and technology for which theengineering sciences are not yet sufficiently developed tosupport verification of a solution by theoretical means.Alternatively, problems that require potentially excessivetheoretical effort in a general case can often be solved for a specific case more easily using a physical model of theproblem.

To this end, De Beers relies on an array of expertise, aswell as computational and physical testing facilities bothinternally and externally within technology partnercompanies.

Because of the unique challenges of marine diamondmining, De Beers has invested heavily in facilities thatsupport the development of technology of the mining tools.

Two large mining tool scale test facilities have beenestablished in the Cape Town area, while a specialized scaletool testing and visualization facility has been established atthe De Beers research laboratories in Johannesburg.

One facility is used primarily for LDD as well as similarrelated tool research and development, while the other isused primarily for crawler-based research and development.These facilities are used to both qualify as well as quantifythe performance of scale models of mining tools.

Testing and technology development at technologypartner facilities is also important to the successfulintroduction of new systems.


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2International Project Management Body of Knowledge

Figure 13—Part of LDD tool research and development facility in CapeTown

Figure 12—Example of scale model test and full scale tool

Figure 11—Technology acquisition and support value chain

Innovation

TechnologyDevelopment

SystemsAcquisitions

Engineering Supportand Services

Capital Management


One example of this is the development of specializedmilling technology for reduction of clays and shell present inthe marine gravels. This development took place at KHI inJapan using specially prepared samples of actual marinegravels collected from concession areas. The collection of thesamples, apart from the security challenges of removingpotentially diamondiferous materials from a restricted area,were a significant challenge.

A further example of technology partner enableddevelopment, is the development of splitter launders use onthe LDD vessels. Material is delivered in the form of an airliftslurry with components of water, air, and solids. After avertical deceleration and partial de-aeration chamber, theslurry must be bridged from the mining system into thetreatment plant, and be equally split and presented onto twovibrating screens. This was to be accomplished using asloping chute (known as a launder), and included a 90º turnforced by design layout constraints. Scale model testing byPaterson & Cooke Consulting Engineers (PCCE) in collabo-ration with the launder designers resulted in a satisfactoryconfiguration being identified.

Independent of the test activity, a computational fluiddynamics (CFD) study was also conducted on the flow in thelaunder to validate the applicability of this numerical tool tothis type of problem. Because of the limitations of coarseparticle flow within CFD analysis, the scale testing was stillessential to confirm the split of soils in addition to the watersplit. Comparison of the CFD with the water flow was good,and this showed the potential of analytical techniques.

DBM is currently involved in a research study to evaluatethe applicability and practicality of coupling CFD with discreteelement modelling (DEM), which would then allow forgeneral solution of fluid and solids coupled problems.

The final step in technology acquisition is usuallyembodied in a conversion or major upgrade project. A recentexample involved the upgrading of the Debmar Pacific in2005, which prior to upgrading was essentially as originallyconverted dating back to 1997. The upgrade involved acomplete new treatment plant and control system, a majorupgrade to the mining system, and replacement engines andalternators, while the vessel also required statutory marinemaintenance as a condition of class. These type of upgradesinvolve an unusually intense period of work in the dry dockand alongside as every effort is made to minimize thedowntime impact to the vessel.

Hydrotransport as key competency and technologies

Problems of fine and coarse particle flow in 2- and 3-phaseflows are particular examples of the complex flows that areencountered routinely in marine mining. As a consequence,hydrotransport can be considered a key competency essentialfor the professional design and application of engineeringsolutions in the marine diamond mining industry.

Hydrotransport is embodied in a large number of unitprocesses used by De Beers in general. Marine mining addsto these with specific applications of hydrohoisting andpumping of particularly coarse slurries. The resultingimportant hydrotransport technologies for marine mining areas follows:

➤ Hydraulic entrainment and fluidization at the mining tool

➤ Gravel pumping and hydrohoisting, including- Centrifugal gravel pumping- Airlift pumping

➤ De-aeration of airlift slurry➤ Coarse slurry splitting

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Figure 14—Part of crawler tool research and development facility in Stellenbosch

Figure 15—Visualization laboratory facility at De Beers Campus,Johannesburg

Test tank

Bogie with services& tool attachment

Miningdirection

z

x

y

Coarse materialtest bed

Drain material Fine materialtest bed

Footwall

➤ Dewatering and sizing of solids➤ Elutriators and overflowing of excess water➤ Jet pumping➤ General centrifugal pumping➤ Fluidizing and eductor extraction out of hoppers and

bins➤ Dense medium separation using hydrocyclones➤ Ferro-silicon dense medium mixing and pumping; and

correct medium maintenance➤ Pipeline systems and networks, particularly for process

water➤ Instrumentation, particularly for coarse and abrasive

solids➤ Wear management, particularly for coarse and abrasive

solids.

While many of the hydrotransport challenges are fairlyconventional, the addition of coarse gravel to the situationleads to interesting and challenging new angles. It is in theup-front processes such as pumping and splitting that thesechallenges are greatest.

Both airlift and centrifugal pumping are used forhydrohoisting of mined material from the sea floor. Airlifts,although somewhat inefficient, are very robust and allowpassage of very large particles. Modern centrifugal gravelpumps are very efficient, but carry a very large overhead with

them. At the required depths of operation, centrifugal pumpshave to be placed well below sea level to ensure sufficient netpositive suction head (NPSH) at the suction, and the electricalchallenges that accompany underwater deployment areconsiderable.


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Figure 16—Launder splitting scale model tests and CFD simulation

Figure 17—Debmar Pacific upgrade projects summary scope

Figure 18—Boulder hydrohoisted by airlift (approximately 450 mm maxdimension)

Figure 19—IHC underwater pump and eMotor for crawler application


Currently airlift and centrifugal pump sizes up to 600 mmin diameter are used to depths of 150 m, and the installedpump power on the Ya Toivo is 1 800 kW. The envisagedinstalled pump power on the Peace in Africa is 2 400 kW andthe diameter increases to 650 mm. These pumping systemsare capable of delivering up to 2 500 tph of solids, and over 9000 m3/h of slurry.

Depending on the pumping system and the downstreamprocess, this slurry may have to be decelerated and de-aerated prior to processing. For the airlift systems used onthe LDD vessels, large de-aeration bins are an integral part ofthe vessel motion compensation system in addition tofulfilling this function.

Splitting of the head feed flow into equal fractions fordewatering and sizing is a particular challenge in marinemining. As the head feed flow rate increases, the flow has tobe diverted to an increasing number of sizing processes.Balancing of these flows is important for downstreamperformance; however, the designs also need to allow forindividual streams to be shut off for maintenance purposes,without significant disruption to the flow split to theremaining streams. PCCE have purpose designed such asplitting device, using rigorous scale testing, for the Peace inAfrica vessel, which should be commissioned by mid 2007.

Dewatering and sizing has traditionally beenaccomplished simultaneously on vibrating screens.

However, the demands of increasing slurry flow rates areresulting in new ways of dewatering becoming the norm.Increasing reliance on static dewatering panels andoverflowing weirs and hoppers is becoming essential.Obviously overflowing must be accomplished in such a waythat ensures minimal risk of diamond loss.

The move to overflowing hoppers, in turn, createsadditional requirements for refluidization of the material sothat it can be further processed. This must be achieveddespite the presence of large, as well as sticky clay materials.

Thus new and challenging technologies must bedeveloped and matured, preferably with minimal impact tooperational assets, that can then be brought to bear in newand upgraded marine mining systems.

Closing remarks

The west coast of Africa has been endowed with a uniquetreasure of placer diamonds located on land and at relativelyshallow water depths. This setting created the conditions forprogressive exploration and mining of these marine deposits.

Sam Collins’s MDC pioneered the exploitation of seadiamonds. De Beers added a long-term sustainability andprofessional impetus to marine diamond mining.

Marine diamond mining is starting to replace land-basedmining of these placer resources as the land resourcesbecome depleted, and the technology and know-how foreconomic marine mining matures.

Marine diamond mining perhaps precedes many othercommodities, which may one day be economically minedfrom the oceans, and hydrotransport will remain one of thekey technologies for all of these future marine miningendeavours.

While marine diamond mining has highlighted some ofthe challenges of marine mining in general, many newchallenges lurk out there in the deep.

References

1. WILLIAMS, R. King of Sea Diamonds: The saga of Sam Collins. Flesch

Publications, Zeekoevlei, South Africa. 1996.

2. FOSTER, R.W. De Beers and the Sea, Internal De Beers Marine Document,

MRU/INT RRT/938

3. HAAGE, D. Deep Water Marine Diamond Mining; Past, Present and Future,

Internal De Beers Marine Document, TSU/INT RRT/99/33. ◆

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Figure 21—Vibrating sizing screen with example oversize material

Figure 20—PCCE balanced head feed splitter

Marine Mining

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