RestrictedTechnical ReportPP/1977178/2.161.3

BOLIVIADevelopment of scientific knowledgeon mineral resources and strengtheningof scientific manpower in the earthsCiences

Prospection and valuation ofFluvio-Glacial Tin Deposits

by Paul E. Raucq

Serial No.: FMR/SC/GE0I78/166

Paris, 1978

BOLIVIA

PROSPECTION A~ID VALUATION OFFLUVIo-GIACIAL TIN DEPOSITS

by Paul E. Raucq

Rep0rt prepared for the Governmentof Bolivia by the United NationsEducational, Scientific and CulturalOrganization ( U n e s co)

Ul{ESCO

Technical ReportPP/1977-78/2.161.3F~ffi/SC/GEO/78/166(Raucq)31 December 1978

~ UnescG 1978Printed in France

2.

CONTEIlTS

CIRCUMSTANCES AiID OBJECTIVES OF ~rlE ~rrSSION

1.1 Study of detrital deposits by ill&SA

1.2 The CEPIC-CORDI.:PAZ Agl'eelaent ••• •

1.3 Request to Unesco •••••••

SHORT DESCRIPTION OF THE ~rrSSION IN BOLIVIA

2.1 Contacts and difficulties ••••••

2.2 Available documentation and references

2.3 Field and office work ••••••••••

. . . . . . .

Pages

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3

4

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6

3. RESULTS OBTAINED BY IGA-CORDEPAZ

3.1

3.2

3.3

Report on the first stage of operations

Analysis of results • • • • •

Evaluation of results • • • •

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7

8

4.

MAPS

RECOMHE.NDATIONS

4. 1 Principles . . . . . . . . . . . . . . . . . . . .

4.2 Locations and style of digging in the second stage

4.3 Methodology of sampling •••••••••••••••

FURTHER SUGGES'rIONS

5.1 Prospection in selected areas •••••••••

5.2 The study of fluvio-glacial deposits ••••

5.3 Training Bolivian specialists ••••••

Mapa de la Cordillera Real •

Reference Hap . • • • • • • •

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9

10

11

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12

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PREFACE

At the request of the Government of Bolivia and the Univ~Tsidad Mayor deSan Andres de la Paz (Bolivia), a consultant visited the country from 5 to26 August 1978 to aid in the prospection and evaluation of fluvio-glacial tinde~osits in the Andean Cordillera Real, with a view to making recommendations fortheir future exploitation. His mission was financed under Unesco's ParticipationProgramme for 1977-1978, Project No. 2.161.3 - Development of scientific Y~owledge

on mineral resources and strengthening of scientific manpower in the earthsciences.

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1. CIRCUMSTAi'WES AND OBJECTIVES OF THE MISSION

• • U""1•1 Study of detrJ.tal deposJ.ts by T!',ffiA'

The interest of l~SA in detrital deposits bound to recent fluvio-glacialactivities is twofold: scientific and economic.

The first concerns the study of the successive formations and surfacesrelated with the geomorphological history of the Cordillera of the Andes and ofthe Altiplano during late Pleiocene, Pleistocene and modern periods. It is aimedat establishing a definition of the different noraines and pediments and ofvarious inter-glacial ~~a post-glacial formations, including spreading cones,terraces and alluvia. ~his kind of study relies on accurate photo-interpretation(made possible by the availability of a good air cover at a 1/45,000 scale) andof systematic field surveys pernitting sedimentological analyses~ it cen advan­tageously be supported by geochronological measurements, when such are possible.It is the kind of subject which can be dealt with by university students in theirtheses. In the case of UMSA, a favourable element is the presence in the Depart­ment of Geosciences of a grou~ of scientists by agreement with a French group,ORSTOM (Organisation de la Recherche 2cientifique et Technique Outrc-i1er).

From the economic point of view, the Institute of Applied Geology at ill~A

(IGA) has systematically investigated the controversial question of the existenceof workable ore concentrations in fluvio-glacial formations. This problem hasbeen ,artially solved by investigations carried out between 1961 and 1966 byREMINA, 11 Belgian exploration company now named NRC (I'iatural Resources Consultants):

the prospected moraines are poor, except in the case of secondary concen··trations or in inter-glacial, episods:

formations of alluvial nature or fluvial bound deposits may be of economicinterest under certain circ~stances; good international tin prices andprospects are liable to ~prove this appreciation.

The task entrusted by Unesco to this writer, who is a geological adviser toNRC, was made easier by the fact that all REMINA's old files stood at his disposalfor his mission; some of these concerned the areas studied by the IGA. 'Theresultant closer definition of the various geomorphological units made for a moreprecise investigation of R]}1IHA's earlier provisional conclusions.

1.2 The CEPIC - CORDEPAZ Agreel'1ent

In 1977, the economic aspect of this problem attracted the interest of aninstitution involved with the development of the Department of La Paz, COP~EPAZ

(Corporacion Regional de Desarrollo de La Paz): with a view to the exploitationof huge untapped (and even unknown) resources in fluvio-glacial formations on thewestern slope of the Cordillera Real between La Paz and Lake Titicaca, COr~EPAZ

agreed to make a financial contribution toward locating those resources andevaluating tlleir ifl~ortance. The main search was for tin ores, tungsten, copper,lead and zinc.

The long minine tradition of Bolivia rests chiefly upon primary depositslocated in Palaeozoic formations, which are genetically connected with younggranites (Mesozoic or Caenozoic); it was first aimed at the working of veinsmineralized in precious metals, gold or silver. The approach to detrital

+ Universidad Me.yor de San Andres (La Paz).

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occurrences by native diggers almost invariably consisted in a search throughsha~ts or tunnels; this was ~ollowcd by the depletion of richer horizons andpenetration o~ alleged or proven runs. Such methods were entirely inadequate ~or

any appraisal o~the potential o~ large morainicQodies, and could hardly ensuresu~~icient production even ~or a middle-sized venture; they led to unrealisticestimates of reserves. Only a ~ew mines are-at present correctly operated indetrital Geposits, and all of these consist o~ river alluvia.

The assistance provided by CORDEPAZ is the subject o~ an agreement withCEPIC (Centre de Plani~icacion y Coordinacion de la Investigaci6n Cient1~ica y~ecnologica), an U}ffiA body which groups ~ number o~ institutes, including IGA.This assistance took the ~orm o~ collaboration by one geologist sharing the costso~ photo-interpretation, sampling and supervision.

1.3 Request to Unesco

Recourse to Unesco's assistance was justi~ied by the scienti~ic aspects ofthe problem. The ~roject was also potentially valuable ~or graduating studentswho might benefit ~rom contact with new technologies in the preparation of theirtheses.

UMSA's first proposal was ~or an expert to be engeged on the project ~or

one -year. Once the initial investigation had been done, the expert would parti­cipate in a systematic rreliminary prospection, which would in the end yielddetailed information on actual reserves and, ~inally, to the est~blishment o~ anaccurate valuation programme. -

An initial request along these lines was reduced to a three-week consultantmission, within the sphere of prospection and valuation of fluvio-glacial tindeposits; the consultant was to join students in the ~ield to carry out, research.

The consultant had ~~de experience in most forms o~ tin de~osits (especiallydetrital and fluvial), acquired'under various conditions; but practically nocontemporary geologist has any experience of high altitUde glacie~ occurrences.These occurrences are supposed to exist only on the Bolivian Altiplano, wherethey have never been methodically studied. As a matter o~ ~act, the only seriousattempt to prospect moraines, as far as we know, was made in 1965-1966 in El Rodeo(Department of La Paz) by a nOrT retired technician employed by :lE!,rrNA.

On the other hand, o~ the three students presently preparing a licenciatethesis at the IGA, only one is devoting himsel~ to the study o~ detrital rorma­tions of ~luvio-glacial origin and of their mineralization. Naturally there willbe more interest in the subject if such formations prove economically viable.

2. S-HORT DESCRIPrION OF THE HISSION IN BOLIVIA

2.1 Contacts and dif~iculties

The political situation prevailing in La Paz since July 1918 might haveseriously, compromised the mission; m1SA was closed by government order ~uring

that month, and only reopened on 21 August 1978, five days be~ore the date~oreseen for the mission's completion.

However, the goodwill ot all parties involved alleviated these circumstnncesto ensure the full success o~ the nlission. The field work was carried outsatisfactorily9 duplicates existing in CORDEPAZ served as SUbstitutes ~or docu­ments unavailable at the IGA; meetings and discussions took place outside theuniversity; and the prolongationo~ the consultant's stay in La Pez, ~or privateI"J.!'poses, made possible additional conversations with his counterparts.

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In all the consultant was very kindly received by all the official andprivate persons he met during his stay in Bolivia~ he is pleased to acknowledgethis fact.

On the first working day after his arrival he met, as recommended:

the ill~DP Deputy Resident Representative, Mr. E. Velasquez Baquerizo (inlieu of Mr. H. Meyer, away on vacation);

Mr. E. Lorini Tapia, Permanent Secretary of the Bolivian National Commis­sion for Unesco;

Mr. A. Saavedra Munoz, Director of UlISA Geosciences Department (also Deanof the Faculty of Sciences).

His permanent contacts at IGA were the Co-directors of the Institute,Dr. A. Villalpando and Dr. W. Wetzenstein. Other geologists involved in theprogramme and present at most field excursions and conversations were Mr. J. Ponce,of IGA, ~1r. J. Roncal, of CORDEPAZ, and 14r. J. Argollo, the above-mentionedgraduating student. ORSTOf.P s specialists of the Programme of Geodynamics andLimnology, Dr. L.A. Rodrigo and Dr. M. Servant, were requested to perticipate incertain activities, because of their role in the study of the deposits concerned.

The consultant also payed courtesy calls to:

Mr. G.R. Mejia, Executive Director of CEPIC (who gave a reception in hishonour) ;

Mr. E. Sanjines Guillen, General Manager of CORDEPAZ;

~~r. A. Fernandez Castro, Executive Director of GEOBOL (Geological Survey ofBolivia);

Mr. G. Cortez Arce and Mr. W. Swyzen, Co-directors of the UNDP-assistedproject to investigate the Cordillera primary deposits.

2.2 Available documentation and references

Two printed sources were of considerable assistance to the mission:

(a) the partly obsolete treaties by F. Ahlfeld and A. Schneider-Scherbina(1964) - Los Yacimientos minerales y de hidrocarburos de Bolivia,Bol. 5, GEOBOL

(b) a brief preliminary paper by M. Servant (1977) _. Le cadre strati­graphique du Plio-Quaternaire de l'Altiplano des Andes tropicales enBolivie, Rech. Frany • Quaternaire, Suppl. Bull. AFEQ, 1977-1, No. 50.

The consultant had consulted the first of these works prior to his departurefrom Brussels. In addition, comp10te inventory of NRC's archives concerning themissions carried out in Bolivia between 1961 and 1966 (Rill4INA's records) had beenmade, which was completed after interviews with Mr. M. Stilmant, a technician whohas carried out, among the other progre~es, systematic investigations of:

R~o Seco and Milluni fluvio-glacial occurrences, in the area of IGA'sprogramme;

El Rodeo moraine, south of La Paz, in conditions partly similar to thoseencountered in the project area.

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The documents conpiled w~thin the framework of the COR~EPAZ-CDPIC agreementwere analysed, criticized and utilized to great advantage; they were most usefulto an understanding of the facts and simplified the subse~uent definition of thenext stages of investigation. They consist in:

(a) a photogeological map of the area at 1/50,000 scale~

(b) a report on the first stage of operations, headed iiProyecto Horrenasy Aluviones Fla.nco Occidental Cordillera Real, 10 fase i

;, and datedOctober 1977, with attached sampling maps;

(c) results of assays carried out by Daniel G. Griffith, Bolivia laboratory.

2.3 Field and office work

The mission was planned to last from 5 to 26 August 1978. In reality, theconsultant extended his stay in La Paz till 30 August.

During this period five trips in the field took place. Tr~ee were devotedto the identification of moraines, terraces, alluvions and other fluvio-glacialdeposits on the High Plateau (Altiplano) of the area in ~uestion, more especial!yat the foot of Huayna Potosi (6,095 m), Chachacomani (6,150 m) and Illarrpu(6,424 m), three of the highest summits of Cordillera Real. Another took astandard sampling in the flat alld in an assumed fluvio-glacial exposure of thevalley of Rfo Vilaque. The fifth trip was to inspect samples already on hand inthe El Rodeo moraine, at the foot of Cordillera Tres Cruces (out of the limits ofIGA's study) which would serve as elements of comparison.

Three meetings held before the reopening of UMSA enabled the consultant tocollect information on the work done by the project during the first stage and todiscuss the results and methodology for the next stages with those involved.Three further meetings at the IGA, led to the drafting of provisional conclu­sions; amendments were made to the second stage programme and desiderata wereformulated to ensure the full success of the operation. It was agreed that IGA'sDirectors would send to the consultant a detailed programme outline to be initi­ated by the end of September 1978. This programme was to take account of themeans supplied to the project by CORDEPAZ.

3. RESULTS OBTAIUED BY IGA-CORDEPAZ

3.1 Report on the first stage of operations

The area investigated during the first stage of operations extends overapproximately 1,400 square kilometres, between the La Paz-Achacachi road and theCordillera Real, fron Rfo Milluni to Mount Illampu; it belongs to the endoreicbasin of lakes Titicaca and Popoo, at altitudes between 3,800 and 4,800 metres.This area is sharply broken by valleys and crests, corresponding either to olderse~uences, lower Paleaozoic slates, quartzites and Cretacic pink conglomerates,or to fluvio-glacial Pleistocene and Holocene formations.

Recent stUdies have distin~ished four types of glaciations, the oldestb2ing Calvario, and thereafter (in order of seniority) Kaluyo, Sorata, andChoqueyapu.

All of them correspond to morainic formations, the typical morphology ofwhich is evident for Choqueyapu and Sorata though absent for the other two.S~ccessive glaciations were separated by periods of erosion, often followed by

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stages of pedogenesis or fluvio-glacial accumulation (up to 200 m); a singleerosion glacis (Pediment 111) is clear between Kaluyo and Sorata. The Soratamoraine is the more visible in the landscape; Choqueyapu often furrowed thefo~er formations and occurs at a lower level.

Ordinary fluvial erosion and de~osition later developed a regular system ofValleys, with modern alluvions and, in some places, older terraces.

It was the objective of the photogeological analyses carried out by~~. J. Ponce and Mr. E. Vargas accurately to delineate the different formations.The field surveys organized by 1·11'. J. Roncal, assisted by 1-11'. J. Argollo, weresupposed to check and amend this mapping.

A preliminary sampling of the upper part of the different formations wasmade throughout the area in question, samples being taken from shallow wells ortrenches (approximately 1 to 1.5 m deep) and from channels in natural sections.This operation did not explore the area systematically, nor did it endeavour toreach bed-rock, as the funds available were insufficient for a complete sampling.A total of 199 samples (including some from R~o Suches, to the north-west) wereprocessed by gravity with the traditional Bolivian wooden pan; 6 more sampleswere subjected to a granulometric analysis.

The 199 washed samples "rere reduced from an initial weight of approximately60 kilograms (after hand elimination of the coarser elements) to concentrationsweighing between 300 and 600 grams. These were assayed by Griffith's laboratoryfor tin and tungsten (chemical values); 92 of them were also tested for copper~

lead and zinc by atomic absorption.

For tin, contents under 1,000 pp m (1 kg per ton) are thought to be suffi­ciently accurate; higher values lack precision. It was unfortunately impossiblefor the consultant to contact the laboratory.

3.2 Analysis of results

On the basis of the results obtained, the authors of the report on workdone in 1977 consider that copper, lead and zinc grades do not encourage furthersearch for these metals; this is quite normal for concentrates of detritalformations.

The tungsten content was e~so found to be insignificant.

Good tin values (over or near 1,000 pp m) occur frequently in certainareas. Further study of these deposits is recommended in the second stage ofoperations, as far as they are not subject to existing mineral rights. This isthe case of the b~sins of R~os Linkhu, Jallpa and Kellhuani, adjacent to Penasand Achacachi (see attached plan), whereas promising areas extending south­eastward, in the basins of Rros Vilaque and Milluni, are presently encumbered.CORDEPAZ is taking steps to obtain mineral rights to these areas.

The best concentration of heavy minerals (mostly cassiterite) is reportedto occur between the sizes 0.063 and 0.020 mm (about 250 and 400 mesh Tyler).This assumption may be valid for the upper limit, but the elimination of mostof the -fine matter by rapid panning makes the lower figure uncertain.

The authors of the report consider that the most favourable glaciationsfor further cassiterite prospecting are Calvario, Kaluyo and Sorate. This con­sultant thinks that the number of samples in the differer.t formations is notsufficient for any statistical conclusion, especially since the sampling containedthe upper part only of what were very thick formations (30 to 40 m or more).

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His opinion is that, discounting the peculiar circumstances of feeding fromprimary deposits, the lower glaciations seem to be more liable to dilution, whileSorata and Choqueyapu could yield higher concentrations. But he agrees that theareas selected are the most promising, because of the presence of mineralizedflats and terraces.

3.3 Evaluation of results

The main purpose of the project was fulfilled, in so far as it was proventhat viable quantities of minerals occur in different formations related toglaciations on the western slope of the COl'dillera.

The lack of means made it impossible to obtain more spectacular and moreprecise results. Reliable grade and reserve estimates require sampling of thewhole depth of each formation, down to bed-rock; the experts responsible for thisproject were well aware of this fact, as well as of the difficulties encounteredbelow the w3.ter table. In true fluvial formations (flats and terraces), goodsuperficial values may be encouragi~gly indicative for dee?er zones. But inmoraines and fluvio-glacial material, there can be very poor relations (or evennone at all) between the grades obtained through a surface sampling and thoseshowing the average content of the vertical sections underneath. This is truewhenever there is no sedimcntological continuity or relation from one layer toanother, as it is in all cases of turbulent deposition or of deposition connectedwith alternate freezing and thawing in glaciers.

pn the other hand, the figures obtained in the sampling have only relativeimportance; they can ha.rdly be compared to one another. The volumes to beproc~ssed were not necessarily taken evenly. The coarse material which waseliminated during the taking of samples has not been assessed; it may varygreatly fron one sample to another. Furthermore the lack of any assay on the rawnaterial ruled out resenrch into the initial content of the sediment in tin, i.e.any appraisal of the losses sustained while dcsliming and concentrating samples.It may be assumed that these losses represent an important percentage of theexisting cassiterite. But, of course, such failings would be avoided or remediedin an,.v regular sampling.

4. RECOHHENDATIOrm

4.1 Principles

Indications gained from the first stage of prospection should be consideredindependently of any strict correlation between the best values obtained so farand the nost economically viable contents of the deposits. Nevertheless, thetl:ree A areas are on the whole the most promising.

Regular samplings could be organized in these areas: this would be todisi:liss the value of the geonorphological analysis already undertaken. On thecontrary, the latter analysis should be taken as a guide ror further operntio~s:

each formation ought to be investigated separately, eve:l should it prove it.:pOSr­sible to sample every individual unit. If one ravourable unit of each type werestudied, it would be SUfficient.

The experiences of other countries in the transport of detrital cassiteritemust be taken into consideration. In tropical conditions, this mineral is noroallynot round in economic concentrations nuch further than 2 kilometres from primarydeposits: it rr.ay be assu~ed that in no case does this distance exceed 5 kilometres.Il: other words, high grades in alluvial gravels suggest a nearby origin, thisorigin being either mineralized veins or an intermediate host, whence transport

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can occur vith relatively little attrition. The angular shapes of boulders tpebbles and oinerals in glacial foroations show that mora-ines can be such hosts.~is hypothesis should prove useful in the. next stages. Reciprocally, no certaincontinuity can be ascertained between the high grades detected up-stream anddown-strean in the Rlo Jallpa.

Another fact learned iron ex,erience is that the concentration is normallyhigher in an alluvium than in the generatinp; eluvium, and higher again in theeluviun than in the vein-bearin~ rock. A large proportion of the tin resourcesof the world derive from placer cassiterite. Exploration often progresses fromthe flats to primary deposits. This is true for cassiterite, but not necessarilyfor more brittle minerals.

The best concentration /3enerally occurs at the basis of "normal ,1 detritaldeposits (alluvia, terraces and eluvia)~ near bed-rocl:: this is less obvious inthe case of colluvium: it is probably quite different in moraines and fluvio­glacial drift. Anyway, it is advisable to !"lake separate samples of successivelayers in each formation.

Much cassiterite is lost during beneficiation, especially in the finestfractions; for instance, high tin geochemical values are sometimes found inoverburdenstwithno detectable cassiterite. Hence the initial content of thematerial to be processed must be checked with the utmost care.

4.2 Locations and style of digging in the second stage

The Rlo Jallpa should be explored by lines of wells perpendicular to theaxis of the valley; one line should correspond to each of the positive resultsfound in the lower part of the river ~ two lines should be carried out betvTeen theformer ones, the distance between two lines being approximately 600 metres, oneline up-stream and one down-stream should also be envisaged, and so forth, until·payable values vanish. The wells should be 10 metres· apart from each other and,in theory, be dug across the whole width of the flat, from one slope to theother; if this is not possible, owing to lack of financial means,there should beat least three wells per line, one in the thalweg and one on each bench.

Similar lines of wells should be dug in Rfo Kelluani, and ~ossibly also inthe valley of Rfo San Francisco in the small A area (three lines 600 m apart),but this work could be delayed in expectation of positive results in Rfo Jallpa.Anyway, this consultant strongly recommends the execution of three similar linesin the upper Jallpa.

Formations other than alluvia should be sampled perpendicularly to theSupposed flow of the sediments, i.e. roughly parallel with the Cordillera. Themost suitable distance between wells would be in the range of 50 metres, and itshould not exceed 100 netres. However, if this should prove iMpossible, signifi­cant results may 8till be expected if the wells ere 200 metres apart from eachother.

The consultant recommends:

(a) a long line of wells from R~o Kelluani to Rfo Linkhu (4 kIl) and1.5 kilonetre further north-west (except the flats); this line togive information, successively, on fluvio-glacial formations,terraces and older noraines;

(b) a 800 metre line on the left side of Rfo Kelluani across the Soratamoraine;

(c) four wells in the Cboqueyapu moraine: three on the left bank of theupper Jallpa ,and one on the right bank;

(d) two wells in the small A area (R~o San Francisco): one in Sorata andone in Choqueyapu.

A suitable section fnr wells, in accordance with the availability of locallabour, seems to be 1.4 x 0.7 metres, the 10n8 side, in all formations, t&~ing

the strike of the line. Bed-rock has to be hit at all costs and even to bepenetrated for about 20 centimetres if completely'weathered.

It is to be feared that, in uany instances, the well will enter into thewater-table; this will imply the use of pumps and, often, of pit-casings. Fore­casts on the depth pf the water-table will be best obtained through resistivitysurveys.

Indications on the depth of the bed-rock nay be obtained through micro­seismic tests, provided its characteristics are quite different from the proper­ties of the s~diment: this will generally occur in the case of Palaeozoic rocksbut will probably fail if the bed-rock of an alluvium is morainic or fluvio­glacial material. It is assmled that alluvia may reach a depth of 5 metres; andterrace ranges 10 metres~ noraines may exceed 30 metres.

4.3 Methodology of sampling

The log of each well should be accurately surveyed, as e~ch different layeris to be swnpled separately. The first wells, or one well at least in eachformation, should be sampled metre by metre, carefully avoiding any mixture ordistinct lithofacies; the recomnended section corresponds to 1 cubic metre ofnaterial dug out for 1 metre progress. If no no.ticeable grade variation is· notee-oin the veritcal in one single facies, each layer should be sunplcd as a wholebetween its limits.

Each portion of material to be processed (metric or between facies limits)should be nixed and then reduced by successive quarterings to such El. size thatone quarter corresponds approximately to the quantity to be processed; thisprocessed quantity should be exactly 40 litres for each metre depth (1 e,~.m) orfraction thereof; the weathered bed-rock is to be added to the lower gravel. ·Thevolumetric proportion of boulders should be estimated in order to reduce accordinGlythe grades obtained in the gravel.

The gravel should be carefully deslimed and, soon after, sieved on a 10millimetre screen~ the oversize must not be eli~inated ~!ithout a quick exaoina­tion. r,1aterial exceeding 10 millimetres should be washed with the utmost care in avessel permitting two more successive concentrations; a final concentration maybe made in the laboratory, including 9 for instance, a magnetic separation and anestimate of impurities left, in a zinc plate, by HCl reaction.

Calculations should take into account expanding modulus coefficients of 1.2for wet material (river gravels, or any formation below.the water-table) and 1.6for dry material.

In each case, a sample of about 10 litres should be taken in the quarteropposite to the processed s&~ple, for a laboratory assay (without crushing thepebbles), in order to compare the original chemical tin content of the material:this will make possible an estimate of the cassiterite lost during processing endhelp fornulate the problens of recovery. This will be dealt with in the ~hird

st~ge of the study.

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5. FURTHER SUGGESTIONS

5.1 Prosuection in selected areas

The above recommendations will permit:

the identification of workable layers and of zones of reduced interest inthe various formations~

an estimate of cassiterite losses in processing, i.e. a definition of theproblems of beneficiation to be studied in further stages,

the calculation of overall erBdeS for every well and an estimate of pos­sible reserves in the different geomorphological units prospected.

Overall grades are to be determined by the I;gd') method: sum of the productsgrade X depth divided by Sur1 of successive widths of the layers.

Inferred reserves nay be assessed by extending to every unit the dataobtained from the first sampling. ~or flats, average grades will be obtained bydividing the sum of ;'f.d'l products by the sum of Ild" (depths); the areas will becalculated on the basis of the actual flat breadth and an equidistance of 600metres between lines; the figure thus obtained should be reduced by half if onlythree wellS per line have been dug. In other types of formations, the quitearbitrary method of ,linfluence areas" should be used, each of them correspondingto the equidistance between wells and the width of the unit, with a maximum of1,000 metres: of course, the probability will be higher if the wells are peggedevery 50 metres than if they are at distances of 200 metres from each other.

nypothetical resources could be envisaged in other units of the same forma­tions, but there will be no positive basis for this as lone as some direct samplinghas not been carried out.

Before speaking of indicated reserves in any unit, it should be sampled ina regular pattern of 600 x 10 metres for flats, 500 x 50 metres in the otherinstances. Proven reserves need respectively patterns of 100 x 10 metres (or even50 x 5 ID in narrow flats) and of 50 x 50 metres (100 x 50 ID in large units);surfaces will preferably be measured by a planimeter, volumes calculated fromthe averase depth and reserves valuated on the basis of the "gd'; method. Suchproven reserves are practically measured, provided each unit is defined by asufficient n~ber of payable wells (iueally 100, and in no case less than 10 withno low result among the 10), and if the limits are known with sufficient accuracy.

It is suggested that IGA could request the assistance of Unesco towards theend o~ the second sta3e of exploration, for the interpretation of the resultc andto fix the progranllile of the next stage: development prospection and ore benefici­ation. According to the present schedule, Nay 1979 would be an appropriate timefor a one-month consultant mission.

5.2 TIle study of fluvio-glacial deposits

The case of the Cordillera Real and the adjacent Altiplano is unique forthe study of elaciations in a tropical medium. The scientific conclusions ofthis study will be easily extended to other cases, though they represent lesstypical conditions.

The interest involved in this problem is much increased by the possibleeconomic results of research carried out with constant scientific objectives andcontrols. This presupposes a thorough palaeogeogrephic study, a strict definition

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of all fo~ations and surfaces, and an accurate delimitation of the differentsedimentological and geomorphological units. It also implies an investigationinto the possible correlations between primary occurrences, intermediate morainesand fluvio-glacial or alluvial deposits.

~xpected results will concern eventual reserves in the studied areas, andwill probd~ly be extrapolated and utilized for the exploration of other glacialcomplexes in Bolivia and elsewhere; hence the wide general interest of the study.

The study should- comprise:

(a) a complenent to the photogeological analysis, with very close fieldcontrol;

(b) a sedimentological analysis of all formations, possibly usine thematerials produced by the present investigations;

(c) geochronological dating of interbedded volcanic horizons;

(d) an inquiry into mineralizations in.the Cordi~leraJ

(e) a chem1cal and mineralogical study of all formations, by all knownmethods, including classic8.1 spectrography, x-ray spectrography,s~ectro~photonetry, and x-ray fluorescence.

(f) the publication or results, perhaps viithin the "framework of a SYL1­

posium on the Quaternary.

Incentive and support for this kind of study, including part of the co­ordination, seem to be in the sphere of Unesco, because of its scientific approach,its expected conclusions and the eventual economic interest thereof.

Part of the progra.nne could be atta;cl1ed to Unesco, es::?ecially where ques·~

tions' invblving scientific commitoents or training of Bolivian professionals arise.Bilateral co-operation seems possible for some aspects of the study.

5.3 Traininc Bolivian specialists

The studi~s currently U11dor way, as well as those at the planning stagemust develop within the framework of u~A in the Institute of Applied Geology andthe Department of Geosc'iences.. This will result in a transfer of krlowledge andtechnoiogy to the staff And students of these institutions, the :nore so as theywould be involved in c8.rrying out certain aspects of the progr&~e.

A further contribution from Unesco, could be to provide assistance in thetraining of Bolivian specialists in this particular field of study~ by w~y ofgrents for the preparation of graduate theses~

14r. J. Argollo is now completing his study o~.stratigraphic problems of theQuaternary; he ought to receive a scholarship in France for a'post-graduatedegree.

Howev~r, two projects are still pending; each deserves aid ftom outside:

(a) a geo~or~holoGical study of the fluvio-glacial formations of theCordillera and Alti,lano:

(b) an investigation into mirieral~zation in Quaternary detrital forma­tions related with the Cordiilera."

It would appear advisable for both trainees to work six months in Boliviaand study one year in a European academic institution.

1/120 30I Km.

Mapa de la Cordille ra

PLUTONES GRANITlCOS

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