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-SMALL MINING INTERNATIONAL-=

International Agency forSmall-Scale Mining

Agence internationale pour lespetites exploitations minieres

ISSN 1188-9519

Published forthe information ofthe internationalsmall mining community

Numbers 5-6January 1993

Agrogeology and Small Scale Mining

Small scale mInIng has an extremelyilJ1>Ortant role to play in bringingsustainability to agriculture in thedeveloping world. It can become aprincipal source of local supply ofagrominerals including phosphates,nitrates, liming materials, zeol ites,etc. This issue is exclusivelydevoted to the growing field of"agrogeology."

The papers which follow were preparedby internationally recognizedresearchers and managers work ing inthis field. They deal with a numberof issues related to both agrogeologyand small scale mining. They are byno means exhaustive, but are meantto:

o show the theoretical underpinningfor the agrogeological approach (p 2­5);

o present an overview of agrogeologyand give a detailed breakdown of whatminerals are useful, where, etc.(p. 5-9);

o give examples of the successfulproduction of agrominerals on a smallscale (p. 11-13);

o show some new approaches beingtaken (p. 10, 14);

o give examples of country programsin developing countries (p. 3, 15­6 ;

o show ha some aid agenci as areindeed hinking along these lines(p. 14-15).

Ve would like to en~asi~e here thata number of interna ional agencies

have been and/or are activelyinvolved in agrogeological programs.The International FertilizerDevelopment Centre has carried outextensive research on the directapplication of rock phosphate inSouth America and ~est Africa, mostlyrelated to larger phosphate depositsand large-scale exploitation andprocessing. The InternationalDevelopment Research Centre hassupported a number of agrogeologicalprojects at IFDC and elsewhere. TheBritish Geological Survey has workedon phosphate exploration in Malawi.Appropriate Technology Internationalhas an extensive lime program inCentral America; and UNESCO, theCommonwealth Science Council, theGerman Ministry of EconomicCooperation and the EEC have funded anumber of meetings related toagrogeology. The number and varietyof programs is encouraging; however,some of the other ilJ1>Ortant agencies,such as the development banks, arenotable by their absence.

It is our hope that this specialissue will help promote a widerinterest in and appl ication ofagrogeology worldwide, and make acontribution to the longer term goalof higher and sustainable foodproduction in the developing world,particularly the poorer parts.

av p',? vSpecial Issue Editors.

N.B. References he e beenconsolIdated and can be found onp. 17-18. Photographs were providedcourtesy of C. Pride, P. van Straatenand L. Borsch.

Contents

Agrogeology and Small Scale Mining .• l

The First Twenty-Nine Days: Prospectsfor Agrogeology 2

Sustainable Food Production and Agro-Geology.••.......................... 4

Agrogeologi cal Resources for SmallScale Mining ...•.....••........•..• 5

Current Opportunities ............•.9

Zeo-Agriculture 10

Rock Phosphate as a 0 i rectApplication Fertilizer: A SuccessStory From India ......•...........• 11

Using Rock Fertilizer: SuccessfulCase Studies ...•.................. 13

SMI News '4Development Goals at IDRC .........• 14

Explorat ion and Development Studi esof Phosphate Resources in Zambia - ACase History.•...................• '5

Consolidated References '7

Calendar of Events '8Book Review: Handboo of Small ScaleGOAS Mining for Papua New GUInea(2 Ed.) ..•...•......•••...••••..• 18

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The First Twenty-Nine Days: Prospects for Agrogeologyby Ward Chesworth

Since the Report of the BruntlandCommission, the concept ofsustainability has become afashionable one, with the biggestquestion, of course, being: is h~ncivilization itself sustainable? Asthings stand now, the simple answeris no, and the two maj or reasons haveto do with population and withfarming.

Paul Ehrlich uses a frighteningmetaphor to illustrate thepredicament we face with regards tothe h~n population on earth.Duckweed takes about 29 days to coverhalf the surface of a pond. Such isthe acceleration of exponentialgrowth that it takes only one daymore for the weed to take over thewhole pond. Metaphorically, we h~nbeings are still in the first 29 daysof our tenure of the planet. If wedon't gain control of gallopingpopulat ion, the 30th day wi II dawnand it wi II be too late. The pointhas been made by Malthus in 1803, andin 1832 by John Stuart Mill, whosaid, "society can feed thenecess i tous, if it takes thei I'multiplication under control.... It cannot with impunity take thefeeding upon i tsel f, and leave themultiplying free."

In the hope that population growthwi II yield to control, the rest ofthis paper will be devoted to aconsideration of farming as it iscurrently practised in theindustrial ised world, how sustainableit is and what this has to do withgeology along with some implicationsfor farming practise in developingcountries.

Let us start by asking the question,"What is farmi ng for?" It's forfeeding people, right? Wrong: on aplanet where a billion people gohungry every day, the number onepriority for agricultural research inthe U.S. Department of Agriculture isthe development of new non-food usesfor agricultural products. In NorthAmerica, even where effort and fundsare being invested in food as opposedto non-food agriculture, it is mainlyin terms of issues that would seemfrivolous to an agricul tural ist inEthiopia or Bangladesh: producing aleaner pig, or breeding fruit thatwon't bruise, or engineering cuboidtOl1l8toes that are easy to pack andtransport.

Look at the farming journals andtrade papers in Qrth rica andWestern Europe: there is no mentionof the need to feed people. The

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impression given is that if there hadever been a problem, it has longsince been solved--hence the grainsurpluses, the butter mountains andwine lakes resul ting from over­production. It would seem to followthat since the North has solved theproblem of feeding people, the bestkind of aid we can give to developingcountry farmers is to export Northernfarming systems wholesale to Africa,Asia and South America. That's whatthe Green Revolution dido-highyielding varieties of staple crops,developed in the North, were farmedwith liberal doses of fertilizers andpesticides, aided by elaboratei rri gat ion schemes and supported by ahighly mechanised infrastructure.Unfortunately, for whateverscientific or socio-economic reasons,it never worked in Africa. Even inthose parts of the wor ld where itdoes work, Northern-style farming canonly be a short-term solution becauseit is highly dependent on the energyof fossil fuels. In no real meaningof the word can it be ca II edsustainable.

A corollary of this, of course, isthat high material input agricultureis ul timately unsustainable even inthe North. It is an energy-intensiveintervention into an increasinglystressed ecosystem, and withuncontrolled growth of the h~n

population, a crash is inevitable.The whole system of agribusinessneeds a radical re-thinking before itis too late. Agricultural economistsneed to realise that the second lawof thermoclynami cs is as appl icabl e tothem as to the rest of us.

Let us for now be optimistic and askwhether we can devise an agriculturalystem that is sus ainable. Hi cory

might give us some clues. Farming,as a h~n activity, is roughly10,000 years old. The earliestexamples of well-developed agricul­tural systems that we know of areassociated with the great rivervalleys, and the so-called hydrauliccivilizations of what are now Iraq,Egypt, Pakistan and China. Of these,the examples of Iraq and Pakistanultimately proved to beunsustainable, due principally to theproblem of sal inisation. Thiss i tuati on may have developed partlyin response to climatic changes,although irrigation practices werecertainly a major contributingfactor. Only in Egypt and China dowe find farming systems that have

en stafnea over at least the last5,000 years.

How has this happened, how have theEgyptians and the Chinese managed sowell? The answer is, quite simply,they have been fortunate enough tofind themselves in envirorrnents wheregeological processes have beenconducive to the maintenance of soi lfertil ity. In both locations, newmaterials, rich in plant nutrients,have been added to farmland bygeological forces. In Egypt, theNile brought nutrients from thevolcanic highlands of Ethiopia. InChina, the wind brought loess fromthe Gobi desert. In both regions anatural fertil iser has continuallyand rel iably been added to replacenutrients taken from the soil bycropping.

. If we extend our vi ew to take in thewhole globe, we find that, histori­cally, the most productive soils arefound in areas where fresh,relatively lI1weathered, but eminentlyweatherable materials have been addedto the land surface in the recentgeological past (Chesworth: 1982).In most cases, the addition was "oneoff," without a yearly, sustainedrefertilisation such as the Nileprovides. Consequently, most areasof productive soils have beencontinuously degraded by farming.Iowa, for example, has lost half itstopsoil in less than a century. Theorganic matter content of the prairiesoils of Canada has bottomed out atabout 50X of its virgin value.Nutrient deficiencies are common inareas that formerly were free ofthem.

Assuming that the farmer's watersupply is no problem (and it must beadni tted that th isis by no meansalways a fair assumption), theprincipal problem is one of replacingnutrients removed through cropping.H~n ingenuity has devised manysystems of nutrient replacement: bycrop rotation, adding manures orcomposts, and, finally, artificial orindustrial NPK fertilisers. Nosystem has been entirely successful,although the crop rotations inventedin western Europe in the 18th centuryare as close as we have come so farto a sustainable system. However,this hopeful experiment was largelyreplaced by a dependency onindustrial fertilisers invented inthe 19th century, a technique whichencouraged the development of labour­efficient methods of monoculture. Inbroad terms, the result has been toproduce soils with increasingmicronutrient deficiencies andstructural problems.

exclusively) in developing countries.Energy efficient technologies shouldbe researched and developed formining and using these resources. Interms of their use, appropriatetechniques developed by the world'sfarmers over countless generationsshould be considered as an immenseintellectual resource that may betransferred from one regi on toanother, as the rock mulch techniquehas been transferred to Ethiopia fromlanzarote in Spain.

The ultimate objective is local self­sufficiency, a weaning away fromagricultural systems heavilydependent on fossil fuels andwresting the economic control offarming away from places l ike NewYork, london, Paris and Tokyo. Noneof, this guarantees sustainabil ity,but it gives us a fight ing chance.Provided, of course, that we can stopthe 30th day from dawning.

Dr. Ward Chesworth is a leading lightin the field of agrogeology. Alecturer in the Department of landResource Science at the University ofGuelph, Ontario, CANADA, he has beenactive in studying weathering andformation of soils in Africa andNorth America.

In summary, an inventory of whatmight be called alternativeagrogeological resources needs to bemade, especially (but not

from the soi l. In 1990, thetechnique was transferred toEthiopia, and has resulted in a four­fold increase in corn-yield onexperimental plots, simply throughconservation of water (van Straatenet al.)(see photo below). Thissimple technique can be appliedanywhere a fragmental geologicaldeposit exists. Gravels and coarsesands can be used to create a vapourbarrier, as well as pyroclastics.

What all this suggests is that manycommon rocks can be used to improvethe chemical and physicalcharacteristics of soils. Beingcommon, such rocks have a widedistribution, so that even thepoorest countries contain withintheir borders materials of use to thefarmer. Small mine technologies,under local control, offerappropriate ways of developing suchresources cheaply. Each small minewould service the area immediatelyaround it, thereby cutting down ontransportation costs, as well asproviding jobs and boosting theautonomy of the region served.

-; ..~$"""~

Preparation of rock mulch for moisture retention, Ethiopan Rift Valley.

Consequently, most agronomists noware advocating a reincorporation ofolder techniques-osuch as croprotation, manure and compost--intomodern farming. In addition, therehas been a revival of interest in theuse of geological materials in anunprocessed (or relativelyunprocessed) state. Essentially,this is a return to techniques thatwere the subject of a great deal ofexperimentation in the early part ofthe 19th century, and which have beenrevived in this century by W.O.Keller and by W.S. Fyfe (seeCh <worth: 1983; leonardos et al.:1987). The advantages of usinggeological materials in this way are,first, a decreased reliance on fossilfuels; and second, the addition of abroad spectrun of nutrients in oneappl ication. The disadvantages arethe bulkiness of the materials andthe relatively slow reaction. Thefirst of these disadvantages dictatesthat the resource should be usedlocally, and the second that anappropriate soil be chosen tooptimise reaction, in conjunctionwith simple techniques of increasingreactivity, e.g., coupl ing phosphateswith zeolites, ( lai and Eberl:1986).

As an example, consider the Tanzania­Canada Agrogeology Project (Chesworthet al.: 1989: van Straaten et al.:1992). The principal geologicalresource discovered by the geologicalteam was an apatite-rich residualmaterial weathered from the PandaHill carbonatite in SW Tanzania. Thesoils team at the Uyole AgriculturalCentre then showed that, withoutprocessing, the material could beused to fertilise ferrallitic soilsin the region. There is about a 30years' supply for farmers livingwithin 50 mi les of the source. Atleast two other possible sources forfuture development were found in theregi on (van Straaten et al.: 1992).low grade deposits of this type, ofno intere t to the great multi­nationals, can have a profound impacton local economics and local sel f­SUfficiency (Sheldon and Treharne:1979).

Another poi nt to cons ider is thattraditional farming systems the worldover have gone through generationafter generation of experimentation.It is worth tapping into this fund ofWisdom, making a search for soundtechniques, and choosing those thatcan justifiably be transferred fromone farming community to another.Again, the Guelph agrogeologistsworking with Spanish and Africa~counterparts, have a success to their~redit. For about 200 years, farmers1n the volcanic Canary Islands havecovered thei r oi ls wi th a layer ofscoria (Fernandez-Caldas andTejedor-Salguero: 1989). This actsas a vapour barrier leading to apronounced cut in moisture losses

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Sustainable Food Production and Agrogeologyby William Fyfe

The growth of hUlllln population toover five bill ion now, with almost100 mi II ion edcled each year, hasbeglM"l to mke us increasingly awareof the li~its of the basic parts ofthe planetary life support system.Bioproductivity ultimately dependson:

a solar energy and the temperature ofour environment;

the availability of water viadirect precipitation, or surface orundergrOlM"ld flow;

a the supply of nutrients for thebiosphere which ultimately comes fromthe atmosphere, but more immediatelyderives from the rocks and mineralsof the top kilometre or so of theplanet's surface and in .cst cases,from the stuff called soil.

The state of world food productiontoday gives reason for great concern.In almost all of Africa, food percapita has been declining fordecades. And now, for much of therest of the world, food output percapita has also begun to decl ine.The nat ions where th isis not thecase are those with advancedtechnologies and where the birth rateis dropping below the level ofreplacement. Yet, as recentlyreported by Moldan (1992), humanitynow uses or modifies almost 40" ofthe total net organic productivity ofEarth, making the human race thelargest single appropriator of theplanet's bio-productivity "since lifeappeared on Earth".

When we consider the problem ofsecuring rel iable, sustainable foodproduction for humans, the dominantbasic bio-physical factors arecl imate, water, and the qual i ty ofsoi l. To these must be added anarray of technological influencessuch as farm machinery, energyavailability, chemical technology,and modern biotechnology; but evenwith all these developments,light-soil-water still form thefoundation of our agriculturalsystems.

Understanding the Soil

Soil is the thin interface that formaby react ions of atmosphere andhydrosphere wi th the rocks of thelithosphere. The rocks and mineralswhich occur at this interface arehighly variable. Thua in Iceland orHawaii, they are almost exclusivelyvolcanic products, basalts, which aretransported molten materials from

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depths of tens of kilometres from thedeep earth. In regions near theedges of ice-age fluctuations likemost of Canada and Scandinavia, barerocks of many types l18y be exposed orcovered by glacial sediments whichcomprise a mixture of all .aterialsalong the path of ice-water flow. Inother regions, vast areas may beunderlain by sediments once formed inthe mari ne envi ronlleflt but nowexposed by sea level change ortectonic motion. Thus, on a grandscale, there are very largedifferences in materials from whichsoil forms.

The soil forming process, calledweathering, is basically si~le,

When rocks and minerals react wi thair and water, processes occur whichinfluence the nature of soil. Firstsome minerals, like calcite (calciumcarbonate), si~ly dissolve in waterand are transported towards theocean. Solutions of such mineralscreate porosity in the soil.Miner~ls like felds~rs (KAlSi3~8;NaAlS1 30a; CaAl 2S1208), WlilChcomprise almost ~al~ lhe Earth'scrust, react to form a complex arrayof minerals we call clays, at thesame time releasing Si02 and Ca-Na-Kto the solutions. Clay minerals arehydrated si l icates of complexchemistry with certain very importantfeatures. Typi ca IIy, they are ofextremely fine crystal sizes withvast surface area. They can exchangespecies with those in solution(ion-exchangers), they are excellentabsorbers of species in solution andmay contain traces of dozens ofmetallic elements (Mg, Ca, Na, K, Zn,Cu, etc.). They can absorb andstrongly retain water on theirsurfaces. Th- e ~ lex clayminerals, called smectites, form thenutrient bank and water reservoir ofthe soi l.

Another process of great significanceis the oxidation of iron- andmanganese-bearing primary minerals.Thus, during weathering, a minerallike Fe2Si04 (2Feo + Si02) reactswith oxygen to form Fe2~ + SiO. Itis this process that le&as to t~e redsoi ls typical in many tropicalterrains. And in the pore spaces ofsoil reside a host of bacteria whichplay vital roles in catalyzing themineral-clay reactions, fixingnitrogen, and actfng asion-exchangers. Soil also containsvari ous llIIlOU"Its of resi~l organicmatter, plant roots, plant debris,and big complex organic IIOlecules,which, with the living bacteria andother organisms, playa vital role in

supplying plant nutrients.

The Importance of smectite

One of the classic chemical formulaefor smectite is:

(1/2Ca,Na)O.7(Al,Mg,Fe)4(SiAl)S020(0H)4 nH20.

Essential trace elements such as Zn,Cu, Ni, Co, etc., may substitute forMg, Fe. The nH20 si~ly means thatthe mineral contains various anountsof water, depending on the humidityand temperature. smectites for.. whencommon rock minerals are present.

But if rain water falls for millenniaand leaches the soi l, species areslowly removed and the smectitedegrades to another clay, kaolin(Al2Si~(OH)4)' which contains noessential trace nutrients. The soilis old and tired. This is thesituation with soils in much of thestable Amazon basin where there havebeen few additions of new rock debrisfor millions of years. To assess thequality of a soil rapidly, one needonly look at the chemistry of localdrainage water. In regions of oldleached soils, this water oftenapproaches that of rain water, withlow nutrient value (Fyfe 1989).

Study of the minerals in soil, theirphysical properties and containedmicroorganisms, clearly shows thatfertile soils capable of sustainedagricultural productivity arecomposed of a mixture of primaryrock-forming minerals containing areasonable sample of the chemistry ofthe Earth's crust, plus the majorweathering products of smectiteclays. We elln as el>S the time neededto form a reasonable thickness ofsuch soi l by studying regions wherenew crustal rocks are exposed byerosion or volcanism. The time is onthe order of hundreds of years,depending on rainfall andtemperature. ThUS, for sustainedagriculture, it is necessary toprotect soi l from all forms oferosion. The observations of theWorldwatch Institute, which placesglobal topsoil erosi on at 0,7X peryear - a rate far exceeding soi lformation in most situations - mustbe viewed with alarm.

What informati on is needed to planagricultural development?

As poJXJlation increases, almost allregions of the planet capable ofproducing food are invaded byhumanity. There are few regions now

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where hl.J1l8n activities are notmodifying the land surface. Ourancestors were clever farmers. Whenthey settled a region they were quickto recogni ze those areas wi th goodsoils and adequate water supply.They built their villages in suchregions; today vast cities occupy thesame sites, often expanding over thebest land for food production. Whenwe plan for sustainable foodproduction, what conditions lIUSt bemet?

First, the climate, temperature andrainfall, and light fluxes lIUst besuitable. If water is to be providedby unnatural methods (dams orgroundwater mining), the use lIUSt notexceed the reliable supply orrecharge. And the use lIUSt notdisturb other regions already inproduction. If irrigation is used,the system lIUSt still be adequatelyflushed, or salting will result; mostgroundwaters are more salty thansurface waters.

Marine fish production also dependsheavily on nutrients supplied bycontinental runoff. Satelliteobservations have shown that mostmarine biomass lives near thecontinental margins. Depressingriver flow by irrigation andevaporat i on will lead to depressedfish production, a problem nowoccurring at an alarming scale inmany parts of the world.

There lIUSt be an adequate thicknessof porous so i l • Poros i ty isnecessary for water penetration andstorage, and to provide housing foran array of necessary symbioticorgani sms. The cClqXls it ion of thesoil must in general be close to thatof the average continental crust, andshould contain smectite clays,primary rock and mineral debris. Ifa harvested crop removes x kilograms

of K or Mg or P per' hectare per year,the soil must have the necessaryreserve. If not, the mineralsremoved lIUSt be replaced byfertilizer additions for productivityto be sustained. Before development,the mass balance of all essentialnutrient fluxes lIUSt be determined,including inputs from aerosols, dust,water, minerals, etc. These fluxeswill determine which crop (or forest)is most suitable for a given regime,and what additions lIUSt be made.

Soil porosity and thickness lIUSt bemaintained. Soi l erosion is anatural process. But for sustainedproductivity, erosion rates lIUSt notexceed formation rates. Today, soilerosion can be controlled.

A soi l map should be draftedcontaining all these essential data,including K-Ca-Mg contents, etc. Aswell, there is need for maps showingthe nutrient requirements of variousregions in constituent kilograms perhectare per year; and maps showingthe most suitable biomass for a givenregion.

Can we renew degraded soils?

Through general mismanagement, soilshave eroded and lost adequatenutrient levels in many parts of theworld. There is an urgent need todevelop systems for their renewal.Such problems are complex andspecific to local regions. In manynatural systems, mineral renewaloccurs via periodic flooding whichspreads fine debris or by addition oflayers of new volcanic ash, etc.

Here I suggest just a few approaches:

(a) Sediments may be pumped out ofdams or overloaded river systems andonto local farmland. If locallyavailable, ground rocks may be added.Often this process could be coupled

to careful use of debris from miningand construction.

b) In many situations near giantcities, sewage may be used to addorganics, nitrogen and phosphorus.Many societies have known this forcenturies, but few giant moderncities (e.g. Nairobi, Bombay,Toronto) have such technology. WelIUSt become more commi tted to the useof cClqXlst.

(c) There lIUSt be careful localplaming involving the use of plantcover to reduce erosion and reducecatastrophic runoff.

(d) There lIUSt be a careful choice ofvegetation planted during a periodof renewal (e.g. use of plants likelupins to recharge the soil withnitrogen and organics).

But, in the final analysis, futurehopes lIUSt rest on our abi l i ty toeducate all hl.J1l8ns on how this planetfunctions and all the systems whichcontrol the quality of life supportand the natural fluctuations in thosesystems. We must plan for surplus ­only then can we preservebiodiversity and hope for futuregenerations.

Dr. William Fyfe teaches in theDepartment of Geology, University ofWestern Ontario, London, Ontario,CANADA. One of the pre-eminent geo­chemists of the last several decades,his interests have ranged from issueson mantle geochemistry to thehydrosphere. He has been active in avariety of fields includingagrogeology, for the last decade,working 'in a nunber of developingcountries. During this time, he hasauthored numerous papers and severalbooks.

Agragealagy Resaurces far Small Scale Miningby Peter van Straaten and Calvin Pride

Introduction

Mining and agriculture are strongpillars of a nation's economy. Theyprovide the basis for the survival,development, and comfort of people.~hile agricultural crop productionextracts mineral nutrients from thesurface, mining operations usuallyremove the soils and extract mineralsfrom rocks below. Agri cul tureextracts renewable resources and canbe sustainable; mining extracts non­renewable resources and has finitel lin I

Farming is an extractive process.Plan~s "mine" the soil, extractingnutrlents from soi l solutions

provided by decClqXlsing organicmaterials and the breakdown ofminerals. The speed of release fromorganic and inorganic phases differsvery lIUch, however. Organicmaterials decClqXlse relatively fast,and have a relatively short recyclingtime. The speed of breakdown ofminerals through weathering is muchslower, usually too slow to provideenough nutrients from mineral sourcesfor fast and continuous cultivationtechniques.

Over the last few years a new earthscience discipline has emerged:agrogeology. This new discipline isthe study of geological materials andprocesses that contribute to the

maintenance and improvement of thephys ica l and chemi cal nature ofsoi ls. This inter-discipl inaryapproach combines the knowledge ofagriculturalists with the knowledgeof geologists: soil scientists definethe soi l l imitations and needs, andgeologists find, delineate andcharacterize the geological rawmaterials needed to increase soilproductivity. Practical results ofagrogeological research are thedevelopment of geological resources(e.g. phosphates. potassiumresources, 1imestoneJl, etc. J andtechniques that maintain or increasethe productivity of the soil.

The first phase of an agrogeological

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o conserving nutrients and water.

o improving soil fertility;

o correcting the pH of soils;

• improving salt-affected soils;

o the method and time of application.

the type of crops and theirnutrient requirements;

NitroQen

Of all the essential plant nutrients,nitrogen is probably the mostimportant.

The agronomic effectiveness ofphosphatic rocks is determined by anumber of interrelated factors:

There are only a few biologicalnitrate deposits which are beingexploited, most of them in a smallway. Most of these nitrateaccum~lations developed fromoxidizing animal excreta in caves,where the nitrates are protected fromthe action of water. Theseaccumulations are usually very small.Often, instead of being used as localfertilizers for peaceful purposes,they end up being used as rawmaterial for local gunpowder.

Apart from the rare occurrence ofmineral nitrates, all N-fertil izershave been produced by industrialprocesses synthesizing nitrogen fromthe air (llmining the air") andhydrogen frOll geological fuelresources, such as natural gas orcoal. Nitrates are extremely solubleand are found in their natural formmainly in areas of extreme and longlasting aridity, e.g. in the Atacamadesert of Chile or in Nevada, U.S.A.

• the mineralogy and chemistry of thephosphate rock, the solubi l ity andgrain size;

• the chemical and physical status ofthe soils, especially its pH,moisture holding capacity, P and Castatus and the P-fixing capacity ofthe soil;

Phosphorus

High soil acidity and phosphorusdeficiencies are common growthlimiting factors in many soils, butespecially in highly leached tropicalsoi ls. Low crop yields occurtypically on strongly depletedreddish oxisols and ultisols("lateritic" soils). The lowfertil ity status of these soils is

. large ly due to the low lIIllOU"It ofplant-avai lable phosphorus and thehigh phosphate fixing capacities ofthese soi ls. To be effective,relatively high amounts of solublephosphate fertilizers have to beappl ied on tropical soi ls, becausethe phosphate ion is easily "fixed"to aluminum, iron and manganese oxideminerals_ It has long beenrecognized that major efforts areneeded to develop phosphatefertilizers with lower solubilitywhich are better suited for tropicalsoils.

soili!ll?rovetoAgrominerals

Rocks and minerals are used infarming systems for several purposes,among them:

Like other rocks and minerals,agrogeo log ica l resources are notequally distributed over the earth'ssurface. Rather, they were depositedduring certain times and occur incertain geological environments (vanStraaten: 1987). To discover newagrogeological resources, it is ofutmost importance to recognize thesefavourable geological environments,and favourable geological times ofdeposition, and adjust the selectionof exploration targets accordingly.

Exploration for agrominerals has beencarried out successfully in manycountries. Most of the largedeposits and several smaller depositswere discovered by classicalexploration methods, such asgeological mapping, geochemicalsurveys, radiometric surveys and evengeobotanical surveys. Many othersmaller deposits have been found overthe last few decades, but relativelyfew of these small deposits are beingexploi ted at present. Countries suchas India and China make wide use ofthese local resources; othercountries, such as Zambia, Tanzania,and Ethiopia, are at the stage ofdeveloping some of these smalldeposits now.

zeol ites, limestones, etc.); and"hortiminerals," minerals used in thehorticul tural industry as growthmedia (e.g. vermiculite, perlite,scoria, zeolites)_

:fer "Ii Y

There are 16 elements which have beenrecognized as being essential forplant growth. Of these, carbon,hydrogen, and oxygen are suppl ied bywater and air. Other elements, takenup by the plants from the soilsolution, are the primary macro­nutrients N, P, K, and the secondarymacronutrients Ca, Mg, S. Micro­nutrients include H, Cl, Cu, Fe, Mn,and Zinc. There are other elements,such as Mo, Na, Si, I, Se which, incertain circumstances, increase cropyields or improve the value of thecrops for animals and huaan beings.

I t should be stressed here that allnutrient resources for the productionof ynthetic fertiliz r I wi h hexception of N, are of geologicalprovenance.

• apatite, the principal phosphatemineral;

The best known agrominerals are:

• guano minerals, and complex P- andN-bearing compounds;

• sylvite (KCl) and other, morecomplex K-bearing salts;

o saltpetre, the only naturally­occurring nitrate mineral that occursin sizable deposits;

project is usually that of soilproblem identification. The mostcOlllllOn chemical and physical problemsof soils are:

• K-si l icates, such as K-feldspars,K-micas, glauconite, and K-bearingzeolites, and K-rich tuffs;

o the soi ls are being lost due toerosion.

o calcite and dolomite, both "limingmaterials":

o the moisture of the soils isexcessive (soils are water-logged) orthe soils lose too much moisture dueto evaporation;

• the soils are saline;

o the soi ls are too acid or tooalkal ine;

There are many ways of improving theabove-mentioned problem soi ls, andseveral modes of improvement involvethe use of agrogeological resources.These agrogeological resources needto be located close to farming areas,and they have to be characteri zed andtested for their agronomiceffectiveness.

Agrogeological resources are thosemostly non-metallic minerals androcks from which fertilizers aresynthes fled or wh ich can be appl iedto the soils in unnocIified ormodified forms to improve the natureof the soils.

Agrogeo log i ca l resources

o the soils are not fertile enough,i.e., they tack certain plantnutrients;

o sulphur, sulphides (e.g. pyri te),and sulphates (e.g. gypsum);

• various silicates used to conservenutrients (e.g. zeolite) or used toconserve soil moisture (e.g. scoriaand pumice).

There are also other "agrominerals,"for eXllft1)l e. mi nera ls used ascarriers of pesticides and herbicides(e.g. diatomite, zeolites); mineralsand rocks used as stock feeds and inthe food industry (e.g. clays,

SMI-6

-

The raw materials used for commercialphosphate ferti l izer production areof sedimentary. metamorphic. igneousand biogenic origin. The mostextensive of these resources aremined and processed on a large scale.Large scale operations dominatephosphate mining in Morocco. theUnited States. Russia. and othercountries.

But there are many more phosphatedeposits in the world which have notyet been developed. Most of theseare of medium to small size. Only afew are currently being worked.notably in China. India and SriLanka. In the 196Os, a smallresidual phosphate deposit was minedin East Uganda. GrOl.l'ld-up phosphateswere used as di rect IlIppl icat ion"fertilizer" on grassland. but alsoprocessed wi th soda ash into III moresoluble P-fertilizer.

Considerable knowledge of the geologyand mineralogy of these phosphatedeposits exists. Reasons for notdeveloping more of these locallyavai lable resources include theunfavourable geographic locations,their small size, and the c~lex

coqxls it i on of the phosphates andhence the lack of technologies totrelllt them. There is IlIlso IlIneconomic bias IlIgainst evenconsidering such deposits. Remotedeposits have little attraction forlarge or small sClllle development;however, small deposits close tofarming areas can often havesignificant benefits for a localCOllll'lJni ty. Here, economy-of-scaleconsiderllltions IlIre often outweighedby the cost of transporting highbulk/low vllllue fertilizers. C~lex

phosphate ores require specialattention and the processtechnologies of large industriesmight not be suitable.

A general drawback of mllIny of thesedepos its is thei r low grade and/orthe l solubll i ty of the phosphatemineral apatite, often too low to beagronomically effective. OVer thelast decade, many new and innovativemodification techniques hlllve beeninvestiglllted, including phospho­coqxlsting, bioleaching, fusion,mechanical activation, heap leaching,ion-exchange with llInOther mineral(e.g. zeolites), and in-situacidulation by mixing the rawphosphate with acidifying mineralssuch as pyrites or acidifyingferti l izers. Each individualphosphate resource has to be testedand in some cases one of these "new"techniques might be suitable andllIdaptable. It is clelllr thlllt moreefforts hlllve to be mllIde to developthese small but vital resources and

pt the )Crt" Ion Iff!techniques to suit the localtechnical capabilities.

Potassium

Many soi ls, apart from lackingnitrogen and phosphorus, the two mainmacro-nutrients, also require a large8llIOUI'It of potassium. Crops with ahigh demand for ( include potatoes,bananas, and sugar cane.

(-sal ts: Due to thei r highsolubil ity, ( salts such as sylvite(63% "20) and carnell ite (17X " 0)rarely crop out at the surface of ~heearth. Associated with highlysoluble evaporitic sequences, theyare fOl.l'ld lilt the surface only underextremely arid conditions, foreX8q)le, in the Danakfl depression ofEthiopia. Potash is also recoveredfrOM salt lakes, such as the Dead Seain the Middle East or the Great SaltLake in the US from minerllll brines.

(-silicates: (-silicates IlIre knownfor their low (-release rllltes. Theuse of (-rich minerlllls, such illSleucite (20% (20), "-feldspars (8-14%(20), biotite {6-10% (20), (-zeolites(2-6% (20), IlInd glauconite (6-8% (20)is severely restricted due to theirlow release of plant-llIvllIilablepotlllSS ium. The di rect llIPPli Clllt ion ofgrOl.l'ld (-feldspar has been done inseveral cOU'ltries, including SriLllInka IlInd ColOll'bia, but with limitedsuccess so flllr. Attempts to increasethe plant availabil ity of potassiumfrom siliclllte rocks throughbioleaching (Rossi 1978) and partillllacidulation (Borsch 1990) have metwi th l imi ted success and have notresul ted in cOlllllercial SIllllIll scaleextraction and utilisation illS yet.

Sulphur deficiencies in soils arebecomi ng more and more IlIppll1rent inrecent years, especially in areas faraway from the sea and from industry.These sulphur deficiencies arepartially due to depletion of Sthrough heavy crop removals andintensive cropping, but also due tothe expanding use of S-freefertilizers such as TSP and urea, andthe decreasing USe of fungicides andinsecticides containing sulphur.

Sulphur occurs in rocks and mineralsmainly in the fOnll of elementalsulphur (brimstone. or "burningstoneU). illS sulphides (e.g. pyrite,mllIrcasite). and sulphates (e.g.gypsum, IlInhydrite).

In industry, elemental sulphur islIIIIinly used to produce sulphuric acidfor the manufacture of super­phosphates. It is extracted in largescale operllltions from undergrOl.l'ldsalt domes by the hot WllIter "Frasch"extrlllction process, using superheatedwate. Elertental sulphur fs alsorecovered during the processing of"sour gills" from oi l and gillsoperations. Elemental sulphurassociated with volcanic deposits has

been mined in Sicily, Italy, sincethe 15th century, and is also beingmined from many other volcaniccentres.

The exploitation of a SmllIll sulphur­punice deposit in New Zeal-andinvolves the mining of severllllthousand tonnes of III sulphur­iq>regnated punice breccia whichcontains approximately 10-15%elemental sulphur. It is sold as adirect application fertilizer. Therole of the punice is to retainmoisture in the soil and to provide III

substrate for bacterial growth whichconverts sulphur into plant-availablesulphates.

In recent years, agricultural trialshave also been conducted testingelemental sulphur lIIixed andgranullllted wi th phosphlllte rock.Results from New Zealand showincreased yield responses of ryegrasses following the a~lication ofthese granulated blends (Rajan 1983).The results indicate that the effectof higher yields is not attributed tosulphur as plant nutrient but ratherto the effects of in-situ productionof sulphuric acid, which dissolvesthe phosphates and makes themavailable as plant nutrients.

In many cOU'ltries, pyrite is the rawmaterial for sulphuric acidproduction for the phosphatefertilizer industry. But pyriteshave also been applied directly tothe soil without chemical processing.In India, grOl.l'ld pyrites aresuccessfully used on alluvial soilsof the river Ganges and onunproductive alkaline soils. InBihar State, sulphur-containingpyrites are either applied directlyto calcareous soils or are mixed withphosphate rock. When appl ied to thesoil, the sedimentary pyrites arerapidly oxidized to form sulphuricacid and Fe-sulphates. It is thisin-situ conversion of pyrites tosulphuric acid which affects andpartially acidulates the phosphaterocks, a simple in-situ phosphateacidulation process. In India, it iseconomic to use these local pyriteson calcareous soils because of theiravai labi l i ty and low transport costs.

Pyrites, IlIlone or in cOll'bination withcomposts, have been successfullytested in New Zealand as a cheapmethod of treating iron chlorosis inrice, and bear some potential forspecial applications.

Sulphates, such as gypsum andanhydrite, are used for two purposesin agriculture: as plant nutrients,and as a mineral which improves thephysical properties of salt-affectedso ilS. GypllLlll was al ready used inthe eighteenth century in thesouthern United Stllltes as Nlandplaster" for fertilization purposes.Direct application of gyps~ for

SMI-7

peanut farming is still practised inmany countries.

Small, locally available sulphur,gypsum and pyrite resources are foundin meny countries. It seems obviousthat more of these resources, some ofwhich are well suited for smell scalemining and processing, should betested for their suitability toimprove local S-deficient or alkalinesoils.

Agrominerals to correct soil pH

L1mestOl'le/dolomite for ec'id soils:HIgh soil ac fdi ty is one of theI imf tins f ctora for agri cul ture inmany countries. High leaching rates,unfavourable parent meterials, andCOl'ltinuous appl ication of chemicalfert i l i zers such as 8IIIllOfli um­sulphates are largely responsible forhigh soil acidity and correspondinglyhigh concentrations of toxicaluminum.

Liming materials such as limestones,dolomites, and calcined and slakedlimestones (lime), are used to raisethe pH of acid soils and consequentlydecrease the Al toxicities. Finelyground liming materials have beenapplied to acid soils for centuriesand are sti II being appl ied in manycountries of the world.

The size of mining operations oflimestones and dolomites foragricul tural lime production rangesfrom several thousand tonnes permonth to operations with only a fewtonnes per cropping season. In casesof application to soils with lowbuffering capacities, it is often notadvisable to calcine the limestonesand dolomi tes; rather, they can beused di reet ly.

The application rate of lime orlimestones/dolomites depends targelyon the pH and buffering capacities ofsoils, but is generally in the rangeof several tonnes per hectare. Sincelarge quentiti of liming materialsare requi red per uni t of land, andsince these materials are low value,high bulk products, it is of utmostimportance to find local sources inorder to keep transport costs low.

Locall y avai lable carbonate resourcessuch as calcitic and dolomiticmarbles, carbonatites, sedimentarymatine and lacustrine limestones, andsecondary limestones (calcretes) arerelatively common and are well suitedfor small scale mining andprocessing. Many more small l ime-stone resources could be mined, and,with some advice from agriculturalextension personnel, appl ied on manymore acid soils of the world.

The c f timi 9 rer; lsillustrates the great advantage ofactive cooperation between soi lscientists and geologists in agro'

SMI-B

Small lime operation, lringa,Tanzania.

geology projects. Soil scientistsoutline the areas with high soilacidity, and geologists search foragricuttural limestone/dolomiteresources close to the acid soils.Even if the agricultural carbonateresources are of small extent and notof the qual i ty requi red for cementmanufacture, they are probablysuitable for local acid soils.

Elemental sulphur and pyri tes foralkal ine soi ls: Alkal ine soi ls canalso pose considerable problems forfarming, specifically for farming ofcrops which require a relatively lowpH, such as tea, potatoes, andvarious berries.

To reduce the soi l pH, elementalsulphur or pyrites have been used insome instances. Due to the highappl i cat ion rates of these sulphursources, however, this practice islimited.

Agrominerals to improve salt-affectedalkaline soils

Gypsum: The reclamation of salt­affected alkal ine soi ls consists ofthe removal of soluble salts orexchangeable sodium by adding anamendment which suppl ies solublecalcium. Of all the calciumminerals, gypsum is considered thebest for this purpose. Large amounts(5 to 10 tonnes/ha) of finely groundgypsum are applied to the soils inorder to increase the waterinfiltration and depth of waterpenetration.

The appl; cat; on of gypsun to sa l t·affected soils is economically viableonl y when the gypsum resources areclose to the problem soils.

Agromi I)erats to COnserve soj lmoisture and nutrients

Water is essential for the growth ofplants. It translocates anddistributes the plant nutrients tothe required locations and keeps theturgor of the plant cells and thusthe stability of the plant. Toolittle or too much water are bothdetrimental to plant growth. Lack ofwater strongly influences metabol icprocesses in a plant: the waterturgor decreases, the plant wilts andfinally dies. An excess of waterreduces the ava i labi l i ty of oxygenfor plant respiration in the soi I.Under water-logging conditions, thereis a lack of oxygen which limitsplant growth and, in some cases,increases the development of toxicanaerobic IIletabol ic products. Thecombination of these complexprocesses results in decreased growthand finally death to unspecial izedplants.

Lack of moisture seriously limitscrop yield. This is particularlyserious in arid and semiarid zoneswhere precipitation is limited. Ifthere is not sufficient precipitationduring the growing season, a crop iseither irrigated or must rely onmoi sture reserves stored before thetime of planting. The improvement ofsoil moisture storage or moistureretention is therefore of paramountimportance in cropping systems.Improvements in soi l managementsystems aiM at cutting the highevaporation rate, especially in aridand semiarid areas, by many methods,including mulching and covercropping. The effectiveness of rockmulches to reduce evaporative lossesis well illustrated in the CanaryIslands, where rock mulches have beenappl ied for centuries in vegetableand crop farming (Chesworth et aL.:1983: Caldas and Tejedor Salguero:1987). Recent results from an IDRC­supported agrogeology project inEthiopia indicate that the soi lmoisture content could be conservedconsiderably by mulching with a 3 cmthick layer of volcanic scoria.First field observations showed maizeyields increasing by up to four timesthe control (van Straaten et al.:1991). The experiments are currentlycontinuing with horticultural cropsand fruit trees.

Certain minerals can also be used toconserve and store nutrients. Amongthe nutrient storing minerals, thezeolite group stands out as the mostpromising. These unique hydratedaluminosilicates, found meinly involcanic areas, are characterized bytheir large cation exchange capacity,high ammonium and potassiumselectivity, and high water holdingcapacity. In agriculture, they havebeen tested successfull y for thei r

+ nd + 0 °t fNH4 a K stormg capac1 y, or

their slow nutrient releasecharacteristics, and their ability toincrease the solubility of phosphateminerals. One of the potentialapplications is to cover farmyardmanure and cClq)Ost piles withzeolites, trap the escaping nitrogencompounds, and use these N-zeolitesin the fields as slow-releasenitrogen fertilizers.

Mining of agrominerals

Fertilizer eroducti~ from big minesfor big farms and small farms:Agrominerals, Le., minera s androcks which are used to increase soi lproductivity, are mined on both a bigscale and a small scale. Manyphosphate deposits in Morocco, the USand Russia are mined on a largescale, using huge draglines andsophisticated processing plants--infact, the quintessential large-scale,low-cost mining operations. Sulphurand potash resources are also minedand processed in th is mamer. Theend product is usually a fertilizermaterial that is effective in mostsoi ls, highly concentrated (thereforeeconomic for distant shipping), andeasy to handle. COIIIlIercial fert i­lizers which are mined and processedon this scale are routinely used onlarge scale farms, but considerableamounts of cOlllllercial fertilizers arealso used by small scale farmers, atleast by those who can afford them.

By contrast, there are also manyagromineral mines that operate on asmall scale. There are several smallmi nes that extract sedimentary andmetamorphic phosphates in India, SriLanka and South America for localapplication. There are alsovirtually thousands of small scaleguano operations which haul thephosphorus and nitrogen-rich guanofrom the caves to local markets andfields.

Also, small operations that producelimestones and dolomites for agri­cul tural purposes are not UMCOllIllOn.

More use could certainly be made ofsuch materials, particularly in thetropics where soil acidity is aproblem.

Usually, agrominerals extracted bysmall scale miners are only slightlybeneficiated. They are transportedas bulky and unrefined I118terials tolocal markets and nearby fields wherethey are used directly.

Advantages and disadvantages ofdeveloping and mining small scaleagromineral resources

Among the advantages of developingsmall scale agrOlRinerel depositsclose to farming areas are that smallscale mining and related small scaleindustries can provide some localemployment whi le at the same timeproviding farmers with a valuableproduct to improve their soils. Someof these materials are locally avail­able; their production price andtransport costs are low; and many ofthem have great long-term agronomiceffectiveness. On a wider scale,developing local agrogeologicalresources that can improve the natureof arable soils will lessen thedependence on fertilizer imports andsave scarce foreign exchange. Localagromineral resources may be the onlyrealistic option for the small scalefarmer who cannot afford more expen­sive, mostly imported fertilizers.

It is a truism in geology that forevery very large deposit, there aremany orders of 11I89" i tude more sma ll­and medium-scale deposits of similartype. From the above discussion, itis also obvious that there is enor­mous potential for the increased useof many readily available geologicalmaterials to improve soil fertility.What is clearly needed is a majormulti-disciplinary effort to find,

test and develop these resources forthe use of the small-scale farmer.

There are, of course, somedisadvantages in developing smalldeposits. Among the more obvious aretheir short lifetime, and their loweragronomic effectiveness.

It is clear, however, that withincreasing pressure on the land andthe consequent strain on the soils,more has to be done to develop localresources for the improvement andrestoration of soil fertility. Moreagromineral resources have to befound and mined locally in order foragriculture to become less depelldenton the importing of industrial ferti­lizers which are out of the reach ofmany farmers of the developing world.

The use of locally available mineralsand organic materials for maintainingsoil productivity is a move towards amore sustainable agricultural system.In certain areas, adaptive agricul­tural developnent wi II depend on thefinding and extraction of local agro­mi neral resources, and itis herethat the small scale miners will beable to assist the small scalefarmers. In many cases, the smallscale farmer is the seasonal smallscale miner anyway.

Dr. Peter van Straaten teaches in theDepartment of Land Resource Sciencesat the University of Guelph, inGuelph, Ontario, CANADA. A pioneerin using a multidisciplinaryapproach, he was the driving forcebehind a rutler of Agrogeologicalprojects in Tanzania, Ethiopia andZi II'bebwe •

Dr. Calvin Pride is a geologist andprivate consultant based in St.Pascal Baylon, Ontario, CANADA. HeIs also Vice President of smallMining International.

CURRENT OPPORTUNITIESGhana. Joint-venture partners and technical assistance sought to develop an alluvial gold prospect In the DOrm&aDistrict of the Brong Ahafo Region. For further information, contact Seth Oppong, Aduana Co-operative Gold Prospecting, P.O.Box 657, leumas i .

Ghana. Machinery, financial and technical assistance sought to develop an alluvial gold working on the banks of theBlrin River at Abompe, Eastern Region. Equity or joint-venture investment welcome. Contact Abdullah Abubltr, Manager, Sulelll8flUMohamade Iddrisu Mining Co. Ltd., P.O. Box 11, Bunso, Eastern Region.

United Republic of Tanzania. Entrepreneur with prospecting rights for a gold deposit In the southern highlands ofthe country seeks financial and technical assistance on a joint-venture basis to start a small-scale gold-mining enterprise.Market, surveyed site and manpower available. Contact Christopher Sanga, Director, Lucky Investlllet'lts Ltd., P.O. Box 1675, Mbeya.

Z~ia. China-clay mining company seeks technical know-how, machinery and financial ssistance for the processing ofeh~n. clay into c romics, paints, cistern, floor [ les and other Irems. J.E.Ie. Sangambo, Managing Director, Jeks Enterprise,PrIvate Bag RW 21', Redgewey, Lusaka.

Extracted in part from recent issues of the UNIDO Newsletter.

SMI-9

We may view our present agriculturalpractice with some pride: it is asuperb application of modern scienceand technology, giving large agri­cultural yields for very little humaneffort. But future generations mayview sa.e current practices as beingwasteful, crude and envi ronnentallyunsound. For eXllq)le, some of theproblems facing today's agricultureinclude soil erosion and soil pollu­tion; pollution of grcxrod and surfacewaters by fertilizers and pesticides;drought; lack of phosphorous andtrace nutrients in tropical soi Is;treatment and disposal of animalwastes; and the increasing cost offossi l fuels. What would be a bettertype of agriculture? What aredesirable goals for future agri­cultural research and technology?

It seems clear that future agri­culture needs to be sustainable.This means that the soi l needs, atthe least, to retain its fertility,or, better, to become increasinglyfert ile through the years as it isfarmed. As the soil is imprOVed withtime, so nJst the surrcxroding eco­system, to make an enjoyable, beauti­ful, healthy and productive COll'llU'lityfor humans and other beings. A sus­tainable future means that we cannotcontinue to be heavily dependent oncheap fossil fuel energy.

The field of "zeo-agriculture" (Pondand Mumpton, 1984; Parham, 1989) isin its infancy, but it may help moveus towards more sustainable and en­vironmentally sound farming methods.Zeolites are a family of synthetic ornaturally occurring aluninosilicatecompounds having the general fornJla:

(li, Na, K) (Mg, Ca, Sr,B8)d[Al(a+2d)Sin_~a+2d)02n]·mH20

where the part of the fornJla in thebrackets represents the frameworkatoms, and the rest of the fornJlarefers to exchangeable or fixedcations and water (Gottardi andGalli, 1985). The framework iscomposed of a three dimensionalnetwork of aluminun and silicon atomsthat forms cages and channels havinga variety of sizes and shapes,thereby giving rise to a largeporosity on the molecular scale andto the mineral's use as a molecularsieve (Breck, 1974). Water may beheld in the molecular pores (zeoliticwater), or in the pore space betweencrystals (pore water). The substi­tution of three-valent aluninun forf ur-"alent sili'con ives l"ise to anegative charge on the framework thatis balanced electrically by either

SMI-10

Zeo-Agiiculture

the exchangeable or fixed cationslocated in the cages and channels.

Zeol i tes are useful in 8lIri cuI turebecause of their large porosity andcat ion exchange capac ity, que l it ieswhi ch allow them to be eqlloyed ascontrolled-release carriers of plantnutrients and other soil ametdnentssuch as herbicides and pesticides(Barbarick and Pirela, 1984). Theycan also serve to free nutrientsalready in a soil by ion exchange foruptake by plants (Eberl et al.,1992); to improve soil fertility andwater retention capacity; to removetoxic cations from soils and animals;and to absorb odours in feed lots.Zeol ites not uncommon Iy occur inenormous, near-surface deposits(Mumpton, 1977); therefore they couldbe employed at loW cost on a largescale in agriculture should their useprove to be beneficial andeconomically justifiable.

As there are about 50 differentspecies of zeolites having a varietyof chelllistries and structures, eachtype needs to be tested to prove itsagricultural effectiveness. Zeolitescan be harmful as well as helpful toplant and animal growth. ForeXllq)le, zeolites with sodiun as thech ief exchange ion can be tox ic toplants (Pirela et al., 1984; weber etal., 1984), and I(-poor or ~-poor

zeol ites can scavenge 1(+ or Ca ionsfrom soil solutions and thereby limitplant growth when used in soi Is thatare deficient in these nutrients(Barbarick et al.,1991; Marcille­l(erslake,1991). The zeolite,erionite, is carcinogenic wheninhaled by animals, but otherzeolites tested show no suchbiological activity (Guthrie, 1992).

Despite the above warnings, theintelligent use of zeolites can givegood results. For eXaMPle, zeolitesemployed to treat swine Mnure inorder to prevent nitrogen pollution,improve handl ing characteristics, andremove odour, were subsequent Iy usedas a fertilizer on crops, givingyields comparable to or better thanthose produced us ing convent i ona I,soluble fertilizers (M~ton, 1984,Vidic et al., 1991). NH4 -saturatedzeolite (clinoptilolite) was used tosolubilize phosphate rock in green­house experinaents, leading toimproved P-uptake and yields forsudangrass (Barbarick et al., 1990).Urea-impregnated zeolite chips can beused as a slow' release ni trogenfertill er (Eberl nd l i, 1992).Zeolite, without soil, can be used asa growth mediun for plants ("zeo-

9Y D. D. Eberl

ponics"; Parham, 1989), and is beinginvestigated by NASA as an artificialsoi l for extraterrestri al agri cul ture(Ming et al., 1991). Zeolite hasbeen fed to animals to reduce themoi sture content of feces, to improveweight gain and animal health(Parh.., 1989), to serve as slowrelease carriers of pesticides, totrap heavy metal cont..inants insoils (Leppert, 1990), to decreasethe incidence of intestinal diseasesin animals, to improve the shellstrength of chicken eggs, to removearrmonia from fish tanks and the smellfrom feed lots and poul try houses(Mumpton, 1984).

Based on recent experiments wi thzeol ites, one can imagine anagricultural future in which zeolite­containing fertilizers are appliedonly once every several years. Thesefertilizers would release nutrientsto plants as they are needed by theplants (buffered systems), therebyeliminating fertilizer pollution andtoxicity. These fertilizers alsowould increase soil fertility throughtime by increasing the soil's abilityto hold nutrients and water, and bytapping the soil's own nutrientslocked in sparingly soluble mineralsthrough dissolution by ion exchange(Lai and Eberl, 1986; Chesworth etal. , 1988). Whether or not suchpossibilities for zeo-agriculturewill be real hed will depend on amovement towards agriculturaltechnologies that are advanced andfine-tuned toward ecologicallyfriendly methods. Such advances inzeo-agriculture will require carefulagricul tural experiments with well­characterized zeolites (Shepard,1984) to prove and extend thispromising technology.

0.0. Eberl is a mineralogist with theUS Geological Survey. He has doneextensive work on the use of rockfertilizers and holds the patent on azeolite based fertilizer.

1

by S.L. Chakravorty

Rock Phosphate as a Direct Application Fertilizer:A success story from India

------------------------------Table1

--------_·_---------·--------Table Z

The principal gangue minerals of theore are goethite and clay minerals.The phosphate mineral is fluor­apatite, with the fluorine contentincreasing with increasing P20S (seeTable 2) :

General

the chemi stry vari eson location, one typical

ROM ore gave the following

Wgt •. %

Natural rock phosphate containsphosphorus (P) but not in watersoluble fo"". However, a part of itmay be in citrate soluble form whichon reaction with acid soil prOlllPtlymakes P avai lable to plants. Thenon-ci trate soluble phosphate, in thecourse of time, reacts slowly withthe acid soils and P is graduallyreleased, thus l1IIeeting both theimmediate and long term needs of theplants. Many studies have noted thatrhe residual effect of rock phosphateis greater than that of singlesuperphosphate (SSP).

Use of the Rock

Rock phosphate in powder form iswidely used as direct applicationfertil izer all over the world,especially in the acid soils of theU.S., France, Poland, India and theformer U.S.S.R. Such directapplication is the result ofextensive and large scale scientificand technological studies carried outallover the world in differentcountries under different agro­climatic conditions. The Beldih rockphosphate (sold as Purulia Phos) hasalso been extensively studied bothchemically and agronomically.

Considerations

caO 37.3

P20~ 27.8 *Fe~ 1S.4

Si ~ S.7Al 2 2.9F 2.4

TiO~ 0.9

~~0.80.6

M9~ O.SsrO 0.3Na ° 0.2S ftotal) 0.1Cl 0.01

total 94.9

*(NAC soluble P20s 1.6%)

The IFDC reported that the rock is ametamorphosed sedimentary phosphatedeposit. According to a slbsequentprospecting report of the GeologicalSurvey of India, the material has anaverage ~Os content of 21.6% ofwhich S.7% is soluble in neutralammoniun citrate solution.

Oxide

Al thoughdependings~le ofresults

4

Weight %

32----------._---------------------_._--------------------------------------P20S% 28.78 29.95 31.99 33.97

F% 1.46 2.08 2.10 2.68

CaO 36.32 37.68 39.91 42.82

Fluorocarbonate apatite 67.7

Mn-goethite(fe,Mn)2~H20 16.8

Phlogopite mica(K,Na)z"gsFe(AlZSi60Z0)(OH)4 2.0

HalloysiteAlZSi20S(OH)4·2H20 7.7

IlmeniteFeTi~ 1.6

Qual" z:Si02 1.7

S~le

Mineral/Composition

above 21.10% P20. Slbsequentprospecting along t~e shear zone hasrevealed new deposits which are underdevelopment now. At least one lensin Beldih mine which originallyoutcropped at the surface is of afairly large size, open at depth. Itis also high grade (30% P20S)' Thismaterial is to some extent being usedto "sweeten" the lower grade materialto make it marketable. This avoidswastage and allows conservationconsistent with practical needs andeconomy. This high grade material isonly used sparingly in this manner incase some other gainful use can befound for it.

Table 1 shows the resul ts of modalanalysis of one run-of-mine (ROM)s~le collected in 19n and analyzedby the International FertilizerDevelopment Centre (IFDC), MuscleShoals, Alabama, U.S.A.(NR-607).(from Das, 1979; WBtCHC, 1980;WBNDTC, 1982):

One quarter of the original estimatedreserve of 1.06 mi II ion tomes ofapatite (average grade of 16.34%) has

A detai led socio-economic study inthe area is expected to be carriedout soon, in order to quant i fy thebenefits in real terms to the localpeople from the small scale miningand industrial activities, and toexplore what more can be achieved andhow.

The mineralisation occurs in the formof lensoid bodies of apatite­magnetite rock in a 90 km long shearzone. The host rock is usuallyhighly crushed or brecciated. Theore generally contains fluoro­carbonate apat i te and mart i t i sedmagnetite, with other accessoryminerals. In spite of the high P20Scontent, the presence of about 10 to1S% FeZ~ makes it unsuitable as asource of phosphatic chemicals.Beneficiation has proven to beuneconomi cal except for si~le

washing away some of the clay. Hencedirect application was considered themost judicious use in spite ofinitial opposition from "experts".

Introduction

As a result of elaborate andcomprehensive laboratory and fieldstudies, phosphate powder is todaybeing extensively used, ei ther aloneor mixed with other NPK fertilizers.local demand has increased steadi Iyand is beyond the present capacity ofthe mine. Above all, there is now noprotest from any "experts" aboutmisuse of the rock. The story ofBeldih can therefore be considered asuccess story.

The story of the Beldih rock phos­phate mine in the Purulia district ofthe state of West Bengal is a successstory pointing to the immensepotential to exploit agromineraldeposits on a relatively small scaleand by labour-intensive means. Themi ne was started in 1975, wi th thesale of rock phosphate in powder formas a direct application fertilizer.This was done against the advice of,and in spite of protests from, manymodern "sc ient i f ic" experts, anddespite opposition from the chemicalfertilizer industry. But even today,the mine is operating steadily, whileproviding employment to over 2S0local villagers at wage levels abovethe local average. A large sun ofmoney is thus being pumped into thelocal economy.

- SMI·11

Plants need not only major nutrientssuch as NPK, but also micro-nutrientssuch as mo lybdenl.lll, zinc, manganese,sulphur, copper, etc. which areusually present in rock phosphate butnot necessarily in chemicalfertilizers. Such micro-nutrientsplay an important role in plantgrowth.

Thus where the rock phosphate is oflower grade, it is in many cases morelogical and renunerative to use itdirectly in powder form. Such use ismore justified when a deposit is notamenable to easy beneficiation, or istoo small to sustain a beneficiationplant, and is located in an area ofacid soi ls. The presence ofexcessive quantities of materialsdeleterious to chemical processingsuch as calcite, dolomite, and ironbearing minerals may render aparticular phosphatic rock I.I"suitablefor mak i ng chemi ca l fert i l i zer butnot for direct use. This is exactlythe position with the Beldih rockphosphate.

There are widely varying opinionsconcerning the availability ofphosphorus from apat i te 1n ac idsoils. Many of these opinions haveyet to be verified convincingly.Owing to the wide nunber of variablesrelated to soil and otheragricultural conditions which controlthe solubility of apatite in the soiland the availability of P to plants,the determination of a rock'ssuitability as direct applicationphosphat ic fert i I her should be basedonly on the results of field trials.In India, many such studies have beenmade under varied soil and climaticconditions and on a variety of crops.Against the background of worldexperience, strengthened by theresults of local experimentation,di rect appl icat ion have become moreand more popular in areas of acidsoils because it is both relativelycheap and effective. Moreover, thetotal energy involved in making ther w r Ie phosphate powder is muchless than that involved in makingsuperphosphates. In addition, use ofsuch materi al reduces rather thanincreases soil acidity.

Processing

It is not difficult or costly toprocess raw rock phosphate as adirect application fertilizer. Aftermining of the rock in Beldih, it istransported to the nearby processingplant, Sl.l" dried and hand crushed toless than 10 cm. size (see photo) tobe fed into the jaw crushers(secondary) of appropriate size andcapac i ty. From the secondarycrusher, ore is fed into a pulveriserfitted with a dust catcher. Thepowder th filled manuaLLythrough a chute into polythene linedjute bags for di spatch. There isalso a roller mill in use for higher

SMI-12

Primary crusing: Beldlh Mine.

production of finer materials but thecapital cost involved is alsosomewhat higher. In general,crushing and grinding plants ofmoderate or small sizes, suitable forthe loca l requi rements of sma LLdepos its and sma LL demands, are notvery costly and the technologyinvolved does not need highly trainedworkers.

Rock phosphate with suitablecharacteristics for use as a directapplication fertilizer, can in factbe appLi ed at any grade. From atheoretical standpoint, even a rockphosphate containing only SX PZOS canbe used if the site of use is near.But considering the transport costsof the mater i a l , a more pract ica lmini_ is arOU"d ZO to ZZX PZOs'Where necessary, PZ05 content can Deupgraded to achieve a more marketableproduct, using simple methods.Trying to reach a higher limit (30­3ZX) is usually much more difficultand costly.

From experience, it has been foundthat a powder product of which 90 Xpasses through a 40 BSS sieve wouldbe suitable for direct application.It is not too fine to cause problemsin appl ication yet fine enough forquick dissolution in acid il.

As regards citrate solubility, somerocks are more reactive and some areless so; but, almost al l grades ofrock phosphate avai lable in a cOl.l"trycan be gainfully utilised as directapplication fertilizer in acid soil.The only difference is that theavailability of P to the plant fromsome rock phosphates may be slower.

Regarding the effect of fluorine (F)in fluor-apatite from Beldih, it canbe said that extensive use of suchfluor-apatite has not given rise toany adverse effect so far. Thepresence of iron-bearing minerals hasnot had noticeable effect on theavailability of P to the plant roots.A large number of gronomi ~ udiesof Beldih rock indicate that directapplication of rock phosphate inlateritic soil gives as good a resultas that given by single

superphosphate. Ilhere the soil issandy and deficient in clay, the useof Beldih rock rich in clay alsoenriches the soil.

While acid soil reacts more quicklywi th rock phosphate and releases P,the rock phosphate also reduces theacidity of the soil. Thus when anyland becomes too acidic with regularuse of chemi ca l fert i l i zer, di rectuse of rock phosphate will graduallyrestore the land to a heal thy pHlevel, in addition to supplying P andsome important micro-nutrients. Thepresence of free calci te and dolomi temixed with the phosphate, unlesspresent in large proportions, may notbe much of a prObll!lll in acid soi l.Even where the percentage is somewhathigher, the use of such rockphosphate wi th green manure orcompost will mitigate the problemwhile making more nitrogen available.

Field experiments by WBMOTC showthat direct use of rock phosphate isbeneficial even in near-neutral orneutral soil when used with compostor green manure. Even in alkal inesoi l, rock phosphate powder can beused mi xed wi th a sma l I QUant i ty ofpyrite powder. This also helps toincrease the sulphur content of thesoi l and affects bacterial leachingof non-hl.lllic soils.

Method of Use and Performance

Rock phosphate powder can be useddirectly or mixed with compost orgreen manure (or evensuperphosphate). In acid soils, witha pH value equal to or below 5.S, therock phosphate works very wel l,performing as weLL as SSP in theshort term and much better in thelong term. Ilhen mixed with greenmanure or compost, a betterperformance can be expected even isless acid or neutral soils (pH 6.1­6.6). When compost is charged withrock phosphate powder, it makesvai lable about 20~ more nitrogen

than what is made avai lable byU"Charged compost. Thus this processof composting with rock phosphatepowder increases both avai table N andP.

After broadcasting the powder in the.field and ploughing/puddl ing, 3 to 4weeks may be al lowed under moistconditions before planting ortransplanting is taken up. Sincephosphate is non-migratory, it shouldpreferably be available at root level- for young saplings, at a depth ofabout 5 to 7 cm. ,and for more matureplants at a depth of 15 to ZO em. Ifa layered appl ication at differentlevels is not practical, the rockphosphate should be intimately mixedand puddled wi h soi l down to a d~th

of about ZO cm.

Rock phosphate may be used at therate of 80 to ZOO kg PZOS per hectare

Beldlh Phosphate Mine, West Bengal, India.

in every sowing season (during rainyseason) in acid soil. In other wordsabout 400 to 1000 kg of rockphosphate of zo~ PZOS grade would berequired per hectare. Variation inthe dose has been suggested becausethe response varies depending on thenature of the soil, intensity ofmixing, other conditions of the soil,and also on climatic conditions. Butin any case, an overdose (e.g. 200kg. instead of 80 kg.) would not doany harm. The excess quant i ty willremain in the soil like a bankdepos it and will not be washed awayby the rains. Thus, if for anyreason one is l.I'labl e to buy and userock phosphate in any year, one'scultivation would not suffer. Ifth is pract ice of growi ng wi th rockphosphate during the rainy season andwithout it during the winter isrepeated for three years insuccession, the farmer can grow twocrops a year in the fourth and fifthyear without any phosphaticferti l izer - such is the residualeffect of rock phosphate. The effectmay even be noticed beyond 5 yearsdepending on the quantity appl iedduring the first 3 years. It must beclearly lI'lderstood, however, that forevery crop the requisite quantitiesof N and K should be applied.

Preparation of Rock Phosphate Charged£.2!!J22ll

While preparing compost or greenmanure, rock phosphate is spread inal ternate layers on the compost orgreen manure heap. Considering theneed of about 200 kg. P 0 perhectare, about 4 kg. of 20-i2~ PZOSrock powder may be mi xed wi th everyquintal (of finished dry product) ofcompost or green manure. Incubationstudies indicate that the maximum Pis released after about 4 months ofcomposting. As already indicated,the rock phosphate charging of thecompost also increases nitrogenavailability from the compost by upto ZOX. Thus the charging of compostby rock phosphate doubles thebenefit. Twenty five tonnes of suchcharged compost may be used per

hectare and good crops can be raisedwi thout any other 'fert i l i zer for twocrop seasons.

Pisciculture

In the modern sc ient i f i c method ofpisciculture, calcium and phosphorusare two essential ingredients. Bothof them can be suppl ied by rockphosphate. Rock phosphate powderspread over tanks would thus help thefish spawn grow quickly. Tests withBeldih rock phosphate powder hasproved th is beyond doubt. Comparedto the meagre cost, the benef i tissubstantial.

Conclusion

Modern chemical fertilizers actquickly but are costly both in termsof money and energy. Much of theirnutrient content is lost from thesoil either by leaching and runoff orvia volati I izat;on, thus increasingthe real cost. In a developedcountry where labour is very costlyand agriculture is highly mechanizedand carried out on a large scale, theuse of fast act ing chemi calfertilizers may be justified. But inmany developing countries wherelabour is cheap and capital isscarce, the situation is quite

di fferent. More time can be spentpreparing the ground, as agricultureis less capital and input intensive.

Direct application of rock phosphatepowder not only yields in many caseshigher food production but .is alsomuch cheaper. In addi t ion, theunuti l ized portion remains in thesoil to be made available later.Further, a variety of necessarymicro-nutrients not always availablein chemical fertilizers are alsopresent in rock phos and pranotehealthy plant growth.

Itis therefore necessary thatefforts be made to bring .any more ofthe developing world's smallphosphate deposits into productionwhere justified by transportadvantages. This could lead toenormous savings in energy and anincrease in food production andemployment in rural areas.

Mr. S. L. Chakravorty is the formerManaging Director of the ~est BengalMineral Trading and DevelopmentCorporat ion. He now serves asHonorary Secretary of the NationalInstitute of small Mines CNISM),INDIA, and sits on the SMI's Board ofDirectors.

Using Rock Fertilizer: Successful Case Studies.H. Lindenma)/er, E. North, W. Fyte

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The global correlation of grainproduction with the distribution ofvolcanic, glacial and alluvial soilsillustrates that agriculturalproduct ivi ty is enhanced where Naturehas provided abundant fresh rockdebris. Rock minerals, such asfeldspar, apatite, mica and pyroxene,are the primary sources of plantnu ri en h thilTl car ndnitrogen. These nutrients arereleased by weathering processes asroc~s at the earth's surface are

chemically transformed first tocompl ex clays and eventuall y tosimple clays. An abundance ofcomplex clay minerals characterizesyOl.l'l9, fertile soils and theirpresence maintains cation exchangeand soil moisture retention capacity.Complex clay minerals also controlchemical balance in soi I waters as"leI I as prelllO e ccr,c!' t ions f avourat;ll efor microbiological activity neededfor nitrogen fixation, and theefficient transfer of nutrients from

soils to plants.

Case studies

Brazi I Traditional farmers inAmazonia practice sustainableagriculture on river floodplains,which receive fine grained, nutrientrich sediments from streamsorigin ti"9 in the Ardes IlIO'rItains.Where river banks are steep, highnutrient demanding plants like (corn,beans) are grown on lower terraces

SMI-13

where sediments are depos i ted eachyear. less demanding plants aregrown on higher grOllld, wh ich areflooded peri odi cally, and addi tionalnutrients are made available by smallscale vegetation burning. Thecharred biological debris is notremoved. Both on the lower and upperterraces plant varieties areinterdispersed.

In southern Brazil "organic" farmershave reported IlIJCh higher yields andiq:lroved qual ity of fruits andvegetables (e.g, up to 500X increasesin yields of citrus fruit relative tothose obtained using conventionalmethods). The best resul ts wereachieved by adding a mixture of rock(phosphate rock, granite anddolomite) along with availableorganic material (sugar cane slash,rice husks and wood chips). Thesefarmers maintain that composting isnot necessary in these climates.

Weeds are not controlled, I.I\less theyshade food plants~

Northwestern Ontario - The soils ofNW Ontario have highly variablefert il i ty because they are der ivedmainly from rock debris left asglaciers receded from the regionapprox. 10,000 years ago. Intensivefarming is carried out on theextensive river flood plains coveredby fine-grained glacial sediments.In these areas surface soils havebeen successfully renewed in situ byincorporating less weatheredsubsurface glacial debris into soilsurface layers. This strategy incombination with use of organicmaterial has provided enhancedquality and yields of several fruitsand vegetables grown wi thout chemicaladditives.

An experimental design for smallfarmers interested in evaluating the

8MI News

effects of applying locally availablerocks was tested in NW Ontario bygrowing alfalfa in soils amended withdiabase rock (basalt composition).In this experiment plants grown withdiabase added contained approx. 400" more biomass after three yearsgrowth than those grown in thecontrol plot and SOX more biomassthan those cultivated withsuperphosphate additions. Greaterflower and seed production by plantsgrowing in the al fal fa plot was afurther indication of the higherquality of these plants.

Dr. B.I. Kronberg, D.H. lindenmayerand E. North are with lakeheadUni vers ity, Thl.llder Bay, CANADA. Dr.Kronberg teaches geology, and is oneof a few active in appliedagrogeological research in Canada.Messrs. lindenmayer and North arestudents of Dr. Kronberg.

The SMI secretariat shifted its offices in July of 1992. The official address is now2020 University St. 21st floor, Rm. 149

Box 102, Montreal, PO H3A 2A5, CANADAphone :- (514) 398-2871 ; fax:- (514) 398-8379

The 3rd Amual General Meeting held on October 14, 1992 saw the appointment of four new people to the Board of Directors,including Alexandra ARoako-Mensah, Director, Industrial Research Institute, Ghana; Mr. Paul Fortin, Mining lawyer, Canada; Mr.Tomas Astorga Schneiders, Special Advisor to the Ministry of Mines, Chile; and V.S. Rao, General Manager, Mining, Tata Iron andSteel COlJ1'8ny, India.

Mr. Michael Allison joined the secretariat in late November 1992, taking over the position of Information Specialist.Mr. Allison has worked as a geologist for the Geological Survey of Jamaica and has experience with small-scale mining ofdimension stone.

SMI is collaborating with the United Nations Department of Economic and Social Development and the Goverrwnent of Zimbabwein the organisation of an International Seminar on Guidelines for the Development of Small/Medium Scale Mining. The seminar willbe held in Harare, fra. 15-19 February 1993. With a focus on identifying parameters and conditions that give rise to successin various contexts, the SellIinar ailllS to produce a set of guidel ines for developing countries. The Seminar wi II provide a forumfor participants frOlll developing and industrial ized COWltries to exchange views and experiences and to be exposed to new conceptsand technologies. Representation fra. goverl"lllerlt, international organizations. and the private S~ or is anticipated.Additional information con Obt ined jrom the SHl secretariat or by contacting Ms. Beatrice labonne directly at the UN.(Tel.: (212) 963-8790, or Fax: (212) 963-4340).The Information System Project has begl.l\ in earnest (Issue 4, Feb. 1992). Members and readers are urged to assist thesecretariat in this critical task, by providing references to documentation, equipment, manufacturers, vendors, consultants,government agencies, l.I\iversities and non-government organizations and associations concerned with small-scale mining.

Development Goals at lOReby J.P. Hea

The International DevelopmentResearch Centre (IDRC) was created bythe Parliament of Canada twenty-twoyears ago to support research ofdeveloping countries in the health,agriculture, food, nutritional,information, social, earth andengineering, and environmentalsciences. IDRC's Board of Governors

SMI-14 .

has the distinction of being composedof IJleri)ers coming frOll many countriesand having broad deveIopnentaIexperience. At the United NationsConference of the Envi ronment andDevelopment in JI.I\e 1992, the PrimeMinister invited the United Nationsto propose appai ntments to IDRC I Sboard and supported the UNCED Agenda

21 program as an imperative forsustainable development andprotection of the environ.ent.IDRC's mandate towards goals ofsustainable development is to pursuecapacity building of institutionsthrough partnership with researchersin developing countries and with tiesto the UN and other international

...,.~----.. --- - -- .-----------------------------

'~"'"

i'

gene ie I I.fli vers it i s and r earchinstitutes, non-governmentalorganizations, and the private sectorin Canada and abroad.

IDRC has funded small-scale mIningprojects since 1983 under acollaborat ive program of the EarthSciences and Engineering Divisionwhereby institutions of developingcOl.l'ltries and in Canada participatejointly in research. The aims oftypical projects are to help minersand their cooperatives better exploitartisanal workings and small minesthrough knowledge of the geology ofthe deposits, enhancement of labourskills and use of equipment, safety,beneficiation and processing, andmarketing of ores, gems and minerals.Simi lar projects were supported inquarried construction materials, landuse and geoenvironrnent, water,geotechnics and natural hazards.

In the late 1980s, priorities focusedmore on projects to develop the"social minerals" or those industrialminerals used by cOllllU'lities andsmall enterprises to improve livingstandards. Industrial minerals arerelatively high-bulk and low-valuedcompared to metals and gemstones andthus benefit from a transportation

st wantage where produced locallyand sold into nearby markets.Agrominerals are of specialimportance given the depletion ofnutrients in soils of many developingcOl.l'ltries which lack foreign exchangefor imports of fertilizers, soilconditioners and pesticides. Recenteq:lhasis has been on evaluating thepotential for igneous phosphate rockin East Africa for direct applicationand low-level processing intophosphate fert iIi zers for cOllllU'la Ifarmers. Phosphates, clays,feldspar, carbonates, gypsum,volcanic rocks, sand and gravel,graphite and other industrialminerals which serve localagriculture and industry are labour­intensive and mined by smallenterprises thus helping theeconomies of developing cOl.l'ltries.

In early 1992, a restructuring tookplace at IDRC with the creation ofthe Envi ronnent and Natural ResourcesDivision which combines the formeragricul ture, earth sciences andengineering, and envi ronnental pol icygroups. The new division isresponsive to development needs

through two programs: SustainableProduction Systems and Environmentand Technology Programs. Importantthrusts of the divisions's IIIBndateare institutional change to ensurethe appl ication of research resultsand envirol'1llentally sustainabledevelopment. Priority areas I.nderthe programs are termed GlobalProgram Initiatives. One of theseinitiatives is low-Input Sustainableag r icu l ture wh ich 8IlOI'19 other goa lscalls for the use of agromineralssuch as phosphate, potash and zinc,manganese and other micronutrientsproduced from indigenous resources.

Other important areas related tomining are the prevention of waterand other mine pollution. Projectsare expected in the future to favourcapacity-building of institutions,agrominerals and mining researchhaving goals for sustainabledeve lopment .

Dr. J.P. Hea is an Associate Directorof Programs at IDRC, Ottawa, CANADAand is in charge of agrogeologyactivities in Africa, Asia and latinAmerica.

by L. Borsch

Exploration and Development Studies of Phosphate Resourcesin Zambia - A Case History

BackgrOUnd

In agriculture, phosphate is one ofthe three nutrients essential forhealthy plant growth, the two othersbeing nitrogen and potassium.Unfortunately, phosphate also is veryoften the limiting factor in over­acidic tropical soi ls. It is fixedby chemical reactions with aluminiumand i ron and thus made unavailable toplants. Poor growth and .yield arethe result, even in the presence ofsufficient nitrogen and potassium.

The production of fertilizers inZlIIlOi a at present is based onimported raw materialar semi­f ini shed products of phosphate andpotassium. WIli le there appears to belittle chance of finding substantialpotash occurences in the country, forgeological reasons, abundantphosphate resources are known andhave been explored in quite somedetail during the past years.Unfortunately, none of the four knownoccurences can be considered aneconomic proposition, in theconvent iona l way.

The large Kaluwe cOl'bcrI tit , ne r

luangwa, lusaka Province, is too low·grade, the two syenite-relatedoccurences at Chilembwe, near Sinda,

Eastern Province, and at Sugar loaf,North of "l.IIbla, Central Province,are also too small and comparativelylow-grade to justify a conventionalmining operation, and the largeNkombwa Hill carbonatite near Isoka,Northern Province, has a complexcompos it ion wh ich st ill poses veryserious technical problems.

In addition to these resources,s ntial qu ntiti s of \;l1!lltheredcarbonatite material are fOl.ftt at thefoothills of Kaluwe and Nkombwa Hill,enriched in phosphate but withentirely different characteristicsthan the original carbonatite rock.Th is mater ia l, known as "brownsoils", also does not respond toconventional beneficiation treatment.

Given the apparent technical economicIll8rg ina Ii ty of the known phosphatedeposits with respect to conventionalstandards and the fact thatagricultural requirements were beingmet entirely by imported material, itwas logical to search foralternative, unconventionalapproaches to utilise these resourcesfor the benef i ts of the localgdcul It.

Against this background, "inexDepartment of ZI"CO limi ted started

its research and test work as earlyas 1987.

Research and Test ~ork by MinexDepartment of ZIHCO Limited

As it was clearly I.nderstood that thephosphate ores of the two hugecarbonatite complexes of Nkombwa Hilland Kaluwe were either too complex ortoo poor in phosphate to be ofinterest at the time, "inexDepartment concentrated its studieson the carbonati tes "brown soils" (anestimated 1,200,OOOt containedphosphate) and the two "vein-type"phosphate occurences at Chilentlwe andSugar loaf (approximately 200,OOOtcontained phosphate).

Relatively simple and cheapmechanical beneficiation methodsproved effective, at laboratoryscale, to produce clean concentratesof the phosphate mineral apatite,with acceptable recovery rates, fromthe Kaluwe brown soil, the Chilentlweand Sugar loaf phosphate ores. Th2s~

concentrates wi th 30-35" P 0content, however, are not sui tablefor "direct application", withoutfurther treatmen(, l~ofar s hestability of the mineral prevents itfrom releas ing its phosphate contentinto the soil, thus the phosphorous

SMI-15

does not become available. to theplant. Research thereforeconcentrated on breaking down theapat i te and turni ng it into aphosphate "ferti l iser".

If the insoluble apatite is treated,under controlled conditions, withsulphuric acid, it turns into apartially soluble phosphate coqx>undwhich can be taken up by plants. Theprocess of acidulation is not allowedto go to completion. The objectivebeing to have the phosphate releasedslowly, as plants require it, and notto be entirely washed out. Theproduct is known as "part ia II yacidulated phosphate rock" (PAPR) andhas been propagated as a cheaply andeasily produced alternative productto conventional superphosphates,under ci rcunstances where largeinvestments are not justified.

The product ion and use of PAPR hasbeen strongly promoted by theInternational Fertiliser DevelopmentCentre (!FDC) in Muscle Shoal,Alabama, USA, and close co-operationbetween IFDC, Minex Department andthe Mt. Makulu Research Stationintroduced the idea of PAPRproduction to Zambia at an earlystage of the phosphate explorat ion.In 1987, Minex Department air­freighted 3 tonnes of Chilembwe oreto Alabama to produce PAPR which thenwas air-freighted back to Zambia andfield tested. The crop yields withthis material were as good as thosewith triple super phosphate, and insome cases even better (probably dueto added trace elementavailabilities). These very positiveresul ts encouraged Minex Departmentto set up laboratory-scale productiontests in 1988, at which time 500g ofPAPR was prepared fromunbeneficiated, rich phosphate oreand tried in pot tests. Then, in1989, at a larger scale, testproduct ion was expanded to 300 kgPAPR, using an ordinary concretemixer to blend apatite ore andsui uric acid. The material thenwas tested by the Mt. Makulu ResearchStation staff under various fieldconditions at the Golden ValleyFarms, the Kabwe Regional ResearchStation and the Misamfu RegionalResearch Centre. The results onbeans, soya beans, sunflower andma ize were reported as very good,again in some cases superior totriple super phosphate.

T~ confirm the pr~vious results,Mlnex Department agaIn produced PAPRfor similar field tests in the1990/91 pi ant i ng season us ingapprOXimately 1 tonne of apatite oresfrom Ch i Iembwe and Sugar Loaf.Results again were consistenlypositive.

At this stage, Minex Departmentconsidered its test and developmentwork on the utilisation of these

apatite ores as completed. Theproject has been left in the hands ofthe Zambian Fertiliser TechnologyDevelopment Comnittee who, in co­operation with the School of Mines,University of Zambia, intends to setup a pilot plant.

Minex Department of Zimeo Ltd., wasable to demonstrate, throughdevelppment and test work from 1987to 1990, that a very effectivephosphate fert i l iser can be eas i lyand cheaply produced entirely fromlocal raw materials, phosphate oreand sulphuric acid, using theacidulation technique introduced inZambia by the IFDC. It also has beenshown by producing 1.3t of high­qual ity PAPR test material in 1989and 1990 that "non-viable" (in theconventional sense) phosphateoccurrences can be exploi ted, undercertain circunstances, by a sill1lle"technology", using a crusher, aconcrete mixer and a bucket.

Further research and test work

So far, only unbeneficiated apatiteores, with 10-15X phosphate, havebeen used in the test productionwork; this means that the so producedPAPR carries over 80X barren rockmaterial, this prevents economictransport over large distances to thepotential consumer. Therefore, testseries are being prepared, withseveral professional partiesinvolved, to beneficiate theChilembwe and Sugar Loaf ores to anapatite concentrate of about 30%phosphate for use in PAPR production.

Additional test work has alsoindicated that phosphate rockacidulation with nitric acid may beeasier to perform than with sulphuricacid. Furthermore, nitric acid-PAPRhas two major advantages oversulphuric acid-PAPR: plant-essentialnitrogen is added to the product andpotential shortages of locallyproduced sulphuric acid are avoidedby using readily available nitricacid, also locally produced.However, further tests are requiredto determine economic requirementsfor nitric acid-PAPR production.

In another development project, theUNDESD, in co-operation with MinexDepartment, has prepared afeasibility study for pilot plantproduction of PAPR from the Kaluwe"brown soils".

Not much success has been achieved sofar in utilising the Nkombwa Hill"brown so i l s" wh i ch showcharacteristics entirely differentfrom those of Kaluwe. Apparently,acid leaching is a likely techniqueto extract the 0 , yi l ins ahighly effective phosphate compound.

Apart from research on phosphateresources and utilisation, some

studies and laboratory tests havebeen done on potent ia l sources ofpotash, the second essent ia l pl antnut r ient for wh ich no convent iona lresources are avai lable in Zambia.Abundant common rocks and mineralsrelatively rich in potash have beentested for plant-available potassium.I t was found that certa in types ofrocks and minerals, when finelyground, release appreciablequantities of potassium into theso il • Al though these amounts arerather small, as compared tocommercial fertilisers, they stillmay be sufficient to avert acutepotassium deficiency in certain soilsand for certain crops with highpotassium requirements. The bulky,heavy and quite low-grade rockmaterial certainly does not alloweconomic transport over longerdistances but, on the other hand,these rock types are so abundant thatnearby resources often may beavailable. Substantially moreinvestigations into this subject of"potash from rocks" is necessary.

Conclusion

Minex Department is indeed proud tohave pi oneered the preparat ion ofPAPR in Zambia from local phosphaterock and to be associated with futuredevelopments in the fertiliserindustry with the utilisation of notonly local phosphate deposits, butalso of local sources of potassium.

It is gratifying to note that, withthe advent of the format ion of theZambia Fertiliser TechnologyDevelopment Comnittee, on which MinexDepartment is represented,exploration work and the discovery ofthe Chi lembwe and the Sugar Loafphosphate deposits have not been invain.

L. Borsch is the head of Minex atZIMCO. He has been active indefining and developing local agro­mi ral resourc 5 in Zambia over thepast two decades.

Charging the mixer with phosphaterock.

SMJ-16

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Consolidated References

Chesworth, W. 1983. "Geologicalalchemy: bread from stones."Episodes, p. 32-40.

K.A. and Pirela, H.J."Agronomic and horti­

uses of zeolites: aIn: Pond, W.G. and

F.A. (eds.), p. 93-103.

Murray,Pol itical Economy.London

Ming, D.W., Allen, E.R., and D.C.Golden. 1991. Fertilization bymineral dissolution and ion­exchange (abs.). 83rd AmualMeeting ASA-CSSA-SSSA, Denver,CO, Meeting Program, p. 175.

Rossi, G. 1978. "Potassiun recoverythrough leucite bioleaching:possibilities and limitations."In: MetallUrgical Appl iCJlt Ionsof Bacterial leaching nd Reta edM crobiological Phenomena. Murr.l.E., TONll8, A.E., and J.A.Brierley CEds.) Academic Press,p. 297-319.

M~ton, F.A. 1984. "Flammae etfumus proximi sunt: the role ofnatural zeolites in agricultureand aquaculture." In: Pond, W.G.and M~ton, F.A. (eds.), p. 33­44.

Rajan, S.S.S. 1983. Effects ofsulphur content of phosphaterock/sulphur granules on theavai labi l ity of phosphate toplants. Ferti l izer Research 4:p. 287-296.

Moldan, B. 1992. Geochemistry andthe environnent. In: Planningthe use of the Ear h's surface.Cendrero,A., Lu tig, G.andWolff,F.e. (eds.) Springer Verlag,Berlin, p. 237-251.

Pond, \l.G. and ~ton, F.A., eds.1984. Zeo-agricul ture: Use ofNatural Zeolites in Agricultureand Aguacul ture. Westview Press,BoUlder CO, 296 pp.

M~ton, F.A., ed. 1977. Mineralogyand Geology of Natural Zeolites.Short Course No es 4, Minera­logical Society of America,"ashingron, o.c. 233 pp.

Parham, \l. 1989. "Natural zeol ites.Some potential agriculturalapplications for developingcountries." Natural Resourcesf2rYm, p. 107-115.

Pimentel, D. 1987. Technology andnatural resources. In Resourcesand \lor ld Developnent, McLaren,D.J. and Skinner, B.J. (eds.),John \liley, New York, p. 679-695.

Sheldon, R.P. and Treharne, R.W.1979. "l.ocal phosphate rock ncIlimestone deposits as rawmaterials for local fertilizersupply." In: The Future of SllallPrinciples of1848.

1989. Soi l and globalEpisodes, 12. 249-254.

Fyfe, W.S.change.

Leonardos, O.H., Fyfe, W.S. andKronberg, B.1. 1987. "The useof ground rocks in laterite

y : an i~rovement to theuse of conventional solublefertil hers." Chemical Geology,60, p. 361-370.

Leppert, D. 1990. "Heavy metalsorption with clinoptilolitezeolite: Alternatives fortreating cont8lllinated soi l andwater." Mining Engineering 42,p. 604-608.

lai, 1.M. and Eberl, D.O. 1986."Controlled and renewable releaseof phosphorous in soils frommi x!ures of phosphate rock andNH4 -exchanged cl inoptilol ite,"Zeolites 6, p. 129-132.

sorghun-sudangrass." In review.

Guthrie, G.D., Jr. 1992. "Bio·logical effects of inhaledminerals," American Mineralogy;77, p. 225-243.

Fernandez-Caldas, E., and Tejedor­Salguero, M.K. 1989. "Mulchfarming in the Canary Islands."In Agrogeolagy for A rica,Conrnonweal th Science Ccunei I, p.242-254.

Fyfe, W.S.; Kronberg, B.L.;Leonardos, O.H.; Olorunfemi, N.1983. Global tectonics andagriculture: a geochemicalperspective. AgriCUlture.Ecosystems and Environment, v. 9,p. 383-399.

Eberl, D.O. and Lai, 1.M. 1992.Slow-release nitrogen fertilizerand soil conditioner. u.s.Patent Application US 789,206,15April 1992.

Gottardi, G. and Gall i, E. 1985.Natural Zeol ites. Springer-Verlag, New York, 409 pp.

Maltnus, T.R. 1803. An Essay on thePrinciple of Populo ion.Johnson, london.

Mill, J.S.

1974. Zeol i te Hoi ecul ar

Barbarick,1984.culturalreview."M~ton,

Borsch, l. 1990. "Potential ofpotash-rich rocks and minerals inagriculture. Some preliminarytests." AGIO News, May 1990, p.2.

Chesworth, W., Macias Vazques, P.Acquaye, D. and Thomson, E.1983. Agricultural alchemy :stones into bread. Episodes 1,p. 3·7.

Chesworth, w. 1982. "Late Cenozoi cgeology and the second oldestprofession." Geoscience Canada,v. 9, p. 54-61.

Barbarick, K.A., lai, T.M. and Eberl,D.O. 1991. "Exchange fert i l i zer(phosphate rock plus anmoniun­zeol i tel effects on sorghun­sudangrass." Soil ScienceSociety of America Journal.v. 54, p. 911-916

Barrer, R.M. 1978. Zeol ites andClay Minerals as sorbents andMolecular Sieves. Academic Press,New York, 497 pp.

Caldas, E.F., Tejedor Salguero, M.L.1987. Mulch farming in theCanary Islands. In: Agrogeologyin Africa, Proceedings of seminar23-27 June 1986, Zomba, Malawi.Commonwealth Sci. CouncilTechnical Publ ications 226, p.242-254

Chesworth, W., van Straaten, P.,Sadura, S. 1988. "Solubi l ity ofapatite in clay and zeolitebearing systems." Awl ied Clay~. 2, p. 291-297.

Chesworth, W., van Straaten, P., andSemoka, J.M.R. 1989."Agrogeology in East Africa: theTanzania-Canada project."Journal of African EarthSciences, 9: p. 357-363.

Eberl, D.O., B r rick, K.A. and ai,T.M. 1 2. "Zeol i te (NH4 -cl inapti lol ite) influence onelemental concentrations in

SMI·17

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Shepard, R.A. 1984. "Character­ization of zeolitic materials inagricultural research." In:Pond, W.G. and Mumpton, F.A.(eds.), p. 79-87.

van Straaten, P. 1987."Agrogeologicat resources ineastern and southern Africa."In: AgrOgeol09Y in Africa(Pl'oceedings of a Seminar held23-27 June 1986, Zomba, Malawi).Commonwealth science CouncilTechnical Publication 226, p.242-254.

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van Straaten, P., Semoka, J.M.R.,Kamasho, J.A.M., Mchihiyo, E.P.,et al, 1992. "Report on theresul ts of the Tanzani a-Canadaagrogeology project, phase II(1988-1991)." ~ Universityof Guelph, 127pp.

van Straaten, P., Chesworth, W. andP. Groenevel t. 1991. Agrogeo­logical projects in Ethiopiastill going s rang. AnnualRepor, Department of LandResource Science, University of

Weber, M.A., Barbarick, K.A. andWestfall, D.G. 1984. "Appl ica­tion of clinoptilolite to soilamended with Municipal sewagesludge." In: Pond, W.G. andMumpton, F.A. (eds.), p. 263-272.

CALENDAR OF EVENTS

February 21-24. 2nd AnnualInternational Zinc Conference,Scottsdale, AZ. Contact: Joan

January 31-February 4, 1993. 19thAnnual Conference on Explosives andBlasting Research, San Diego, CA.Contact: International Society ofExplosives Engineers, 29100 AuroraRd., Cleveland, OH 44139, USA.

February 11-13. InternationalSeminar on Mineral Sector in India.Hyderabad, India. Mr. S.K. Sharma,Federation of Indian MineralIndustries, 301 Bakshi House, 40-41Nehru Place, New Delhi-110 019,India.

February 15-19. Guidelines for thedevelopment of Small/Medium ScaleMining, United Nations seminarfocusing on developing countries,Harare, Zimbabwe. Contact: BeatriceLabonne, Chief, Mineral ResourcesBranch, Department of Economi c andSocial Development, Room DC1-864, OneUnited Nations Plaza, New York, NY10017, USA.

November 24-28. Asian Mining '93,international conference andexhibition sponsored by the mining,Geological and MetallurgicalInstitute of India. Contact: A.Banerjee, Co-ordinator, ExhibitionComnittee, MGMI, 29 Chowringhee Road,Calcutta-700016.

September 7-14. Industrial Mineralsof the BaltiC/Fennoscandian shieldand new technologies, Petrozavodsk.Contact: Dr. V. Shchiptsov, Instituteof Geology, Pushkinskaja street 11,Petrozavodsk, Russian Karelia,185610.

June 15-17. International Symposiumon Gold Mining Technology. Contact:ISGMT, Gold Society of China, 1 NorthQing Nian Hu St., An Ding Men Wai,Beijing 100011, China.

May 24-27. 11 th International LeadConference, 'Pb 93'. Vienna,Austria. Contact: Lead DevelopmentAssociation, 42 Weymouth St., LondonW1N 3LQ, England.

June 7-10. Second InternationalS~sium on Mine Mechanization andAutomation. Contact: Ms. LenaCarbin, CENTEK, Lulea University ofTechnology, 951 87 Lulea, Sweden.

Apri l 17-20. Integrated Methods inExploration and Discovery. Sponsoredby the Society of Economi cGeologists, Society of EconomicGeophysicists, Assoc. of Geochemists,and the U.S. Geological Survey.Contact: SEG Conference, Box 571,Golden, CO 80402. USA.

May 23-28. XVIII InternationalMineral Processing Congress. ContactCongress Secretariat, AusIMM, P.O.Box 122, Parkville, Vic., Australia3052.

March 21-26. Minesafe International1993-From Principles to Practice,second international conference onoccupational health and safety in theminerals industry, Perth, Australia.Contact: Minesafe Secretariat, TheChamber of Mines ~nd Energy ofWestern Australia, 7t Floor, 12 st.George's Terrace, Perth, WesternAustralia 6000, Australia.

March 17-19. Mining Investment inNamibia. Contact: Conference Co-ordinator, Private Bag 13297,Windhoek, Namibia.

Rinaldi, American Zinc Association,1112 Sixteenth St. NW, Ste. 240,Washington, DC 20036, USA.

Zinc '93,Contact:

Parkville,

February 14-18. WorldTasmania, Australia.AusIMM, P.O. Box 122,3052Victoria, Australia.

BOOK REVIEWH~ of S-ll SCale Gold Mining for Papua lev Guinee (2nd ed.)

by Mike SlowersPac~fic Resource Publications, Christchurch, 260pp, 1992AvaIlable for 520 US from Small Mining International, 2020 University St., So~ 102, Montreat, Quebec. CA~ADA H3A 2AS.

This monograph is 'intended for goldminers at the village level'. It is

written in extremely simple language,with uncomplicated (but informative)

di agrems and rudimentary (butadequate) mathematics. It covers all

SMI-18

• s

a peets of small-scale gold mining. inPapua-New Guinea (PNG): where to fl~it how to mine it, how to recover Itand how to sell it (and not getripped off !). It covers the scaleof 1 to 100 tonnes per day, from thepan to the mechanized excavator. Asexpected, the book !s emi nent ~ yreadable. It is not WIthout exotIcflavour, being. punctuated with Piginexpressions (slmok, goldston, masket,etc •.. ) and PNG currency (Kina,Toea). The book presents a wealth ofpractical ideas, such as the use ofcut and hanmered copper wi re as I fakegold' to test one's panningabilities, and plans for assembling ahome-made, relatively accurate scale.

The book is very 'protective' ofsmall-scale miners, especially inChapter 10, 'Buying and selling gold,its puri ty and value.' It is thussurprising that cyanide is presentedas even .are poisonous than mercury.The author has the insightful idea ofsugges t i ng add ing a ch lor i ne basedswimming pool powder to cyanidebarren solution prior to discharge tothe environment (to destroy freecyanide). But cyanide also naturallydegrades, and mercury is now known toto be a more serious environmentaland health hazard, because it cannotbe destroyed and it does not degradenaturally.

Al though careful use of mercury isadvocated and explained, Hg remainsthe most serious small-scale goldhazard. One application that isadvocated in the book, at the bottomof the riffles of a sluice box, isindefensible, as discharge to theenvi ronment can hardly be mani toredand prevented. I t may well be thatat the present time, no alternativetechnology is avai lable that wouldreplace it effectively. This clearlyidentifies it as both a sensitiveresearch area and an issue wheregovernment involvement, in the formof stringent legislation andtechnical assistance, is most needed.

The book advocates sluice recoveryfor most applications, and rightlyso, as sluices will recover most goldabove 101 microns (150 mesh) quitesuccessfully. Parameters of sluiceoperation, however, clash withpublished data (Clarkson, 1989, 1990and 1992; Poling and Hamilton, 1986).For example, flow rates of 1300-2000llmin are advocated for a 1m wideSluice, as opposed to a mininun of2400 llmin in Clarkson. Clarkson(~992) also advoca~es, with a 1 mWIde Sluice, 20 m of gravel cerhour, as opposed to Blowers' 1.7 m~.

B~owers advocates rectangularrIffles,S cm high, 2.5 em thick, 10cm apart. Clarkson (1989)recommended expanded metal riffleso~ly if recoverable gold was veryfIne; they are clearly more difficultto oper te, and can yield to packingand extreme gold losses. Regular or

modified angle iron riffles should be5 cm apart. When gold finer than 4mm (6 mesh) is present, regularriffles are not recommended becausethey create extreme turbulence.Clarkson also recommended that theriffle should be vertical rather thanperpendicular to the bottom of thesluices. The tilt angle of the boxeswith angle iron riffles should be 12­15 degrees, which is clearly morethan the 5-15 cm per metre proposedby Blowers.

Blowers also proposes the use of theundercurrent system (a screen whichdiverts fines to two side sluices ata lower ti l t angle for finesrecovery, the main sluice, steeper inangle, treating the oversize).Clarkson's work revealed that the theundercurrent, because of poorscreening efficiency, could lead tounder- and overloading, bothconditions yielding severe goldlosses. Both Clarkson and Blowersrecommend strongly, the use oftrommels to classify the feed as ameans of significantly improving goldrecovery.

The book, in its chapter on 'AdvancedMethods to Catch All the Gold'presents the Knudsen Bowl as a'recent advance.' The Knudsen Bowlwas actually invented about 40 yearsago. Since then, other rotating,single jacketed bowls, such as theAinley, Johnson, Clark and Rogers,have been put on the market. All ofthese uni ts suffer from pecking ofthe riffles, which rapidly limitsfree gold recovery. The Knelsonconcentrator, presented by Blowers asa unit similar to the Knudsen, isactually a double jacketed bowl, oran inner bowl rotating in a jacket ofpressurized water that is injected inthe riffles to prevent packing. Thismakes it a very effective unit torecover free gold over a wide sizerange (Laplante et al., 1989:Llplante and Shu, 1992). The twounits are quite different, and shouldhOt be pre ented a lmll r.

The above flaws do not detract fromthe wea l th of informat ion presentedin the book. It is worth acquiringfor the neophyte as well as theseasoned mineral processor. It is a'textbook case' of how scientific andtechical knowledge can be vulgarized(in the original meaning of the word,vulgaris - for the common people) foreffective dissemination. one canhope that in a third edition, some ofthe weaknesses will be corrected, andthe book will be made international.This would require few modifications,such as replacing PNG currency unitswith US dollars, dropping Piginexpressions, beefing up the referencelist (which has a bit of a localflavour) and the list of usefuladdresses, and finally incorporatingsome techno logy that, wh il stit isnot common in PNG, is commonly used

elsewhere in the world. This wouldlikely incorporate spirals, moreflotation technology, and the onetechnique that has revolutionizedsmall-scale gold production in theU.S.A., heap leaching. The ordermight appear tall, but Blowers' bookprovides a good basis upon which tobuild.

References

Clarkson, R.R., 1989, Gold Losses atKlondike Placer Mines, unpub.report, NEW ERA Engineering Corp.

--, 1990, The Use of Radiotracersto Evaluate Gold Losses atKlondike Placer Mines, unpub.report, NEW ERA Engineering Corp.

--, 1992, The Use of Nuclear Tracersto Evaluate the Gold RecoveryEfficiency of Sluiceboxes, unpub.report.

Laplante, A.R., Liu, L. and Cauchon,A., 1990, Gold Gravity Recoveryat the Mill of Les Mines CamchibInc. , Ch ibougamau, Quebec,International Symposium of GoldRecovery, Salt Lake City, Feb•.

Laplante, A.R., Shu, Y., 1992, TheUse of a Laboratory Centri fugalSeparator to Study GravityRe¥Rvery in Industrial Circuits,2 Annual Meeting of CanBdian

ineral Processors, Ottawa, Paper12, 18 p.

Poling, G.W. and Hamilton, J.F.,1986, Fine Gold Recovery ofSelected Sluice BoxConfigurations, unpub. report.

Dr. Andre Laplante teaches mineralprocessing in the Department ofMining and Metallurgical Engineering,McGill University, Montreal, CANADA.He specializes in beneficiation andrecovery systems for gold ores.

N.B. Clarkson's reports areavai lable form NEW ERA EngineeringCorp., P.B. 4491, Whitehorse, Yukon,CANADA, Y1A 2R8 (phone 403-668-3978),or Northern Affairs Program, 200Range Rd., Whi tehorse, Yukon, CANADA,Y1A 3V1.

SMI-19

SMI BulletinPubl ished by theInternational Agency for Small-Scale MiningL'Agence Internationale pour les Petites Exploitations Minieres

SMI is a non-profit organization dedicated to strengthening andsupporting the small mining sect~r as an aid to rural social and economic

development, especially, but not exclusively, in developingcountries.

Jeffrey Davidson, Michael AllisonEditors

small Mining International - SMI2020 University St., 21st Floor, Room 149

Montreal, QuebecCANADA H3A 2AS

Telephone (514) 398-2871Telefax (514) 398-8379

Jeffrey Davidson, Managing Director

Board of Directors : E. Henk Dahlberg, President, former Director of the Geological Survey and Minister ofDevelopment of Suriname (USA); Calvin Pride, Vice-President, formerly with IDRC's Division of Earth andEngineering Sciences (Canada); Paul Fortin, Secretary, Mining Lawyer (Canada); Jeffrey Davidson, Treasurer,Lecturer, Mining &Metallurgical Engineering Department, McGill University (Canada); Alexandra Amoako-Mensah,Director, Industrial Research Institute, CSIR (Ghana); Tomas Astorga Schneiders, Special Advisor to the Ministryof Mines, on small Scale Mining (Chile); Antony R. Berger, Consulting Geologist and founding Secretary-Treasurerof AGIO (Canada); James McDivitt, Mineral Economist, Colorado School of Mines (USA); Lloyd Quashie, PrivateConsultant, formerly from Ghana (Canada); S.L. Chakravorty, former Managing Director of West Bengal MineralDevelopment Corporation and Honorary Secretary NISM (India); V.S. Rao, General Manager (Mining), Tata Iron andSteel Company (TISCO) and President of NISM (India); Eugene Thiers, Senior Consultant, SRI International (USA);Yang Ke. Vice-President, China National Non-Ferrous Metals Iqx>rt and Export Corp. (China); J.-L. Caty.Directeur de la recherche geologique, Ministere de l'Energie et des Ressources du Quebec (Canada); Rene Dufour,Directeur, Genie Mineral, Ecole Polytechnique de Montreal (Canada); Carlos Oiti Berbert, President, Companhiade Pesquisa de Recursos Minerais - CPRM (Brazil); Deborah E. Ajakaiye, Dean of Natural Sciences, University ofJos (Nigeria); Richard Notstaller, Private Consultant, formerly of Head of Mining Division, AUSTROPLAN(Austria); Ferri Hassani, Director of the Mining Program at McGill University (Canada).

Contributions in Engl ish, French, and SpMish on all aspects relating to _U-scale .ining. including ~c~ingevents and new pj)l ications, as well as c~ts and suggestions, are welc~.

R~ts for infor-.tion on -.bership and slbscription r~ir~tscan be addressed to stU's Managing Directorat the above address.