Source document: https://docs-lawep.s3.us-east-2.amazonaws.com/1698069933229.pdf (Guyana)
h. I I G E O L O G I C A L of.

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I < ::'~~ I ,lit j ' , , REPORT ON THE GEOLOGICAL SURVEY.

.. DEPARTMENT l •·· "' l, " •,J·.~ ,1,:·., ~.,;:t I (;k~·· • "t;, ·~w ,., · .,,, .. ~ ,, · ·,;.:,.

'~:'; '~\ 1/, ~1-~t ''ii'•.· ·f FOR THE YEAR 1 9 6 0 ~ t I, .

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..:', ,·· , ' I. II 11 III.

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VII.

REPORT ON TH:C GEOLOGICAL SURVEY DEPAR':'I·t:ENT FOR THE YEAR 1960 CO N TE N TS PAGE I NT ROD UC TIO N Acknowledgements ••• REVIEW OF THE YEAR.

••• Staff • •• ••• ••• .. ,.


• •• • • • ••• ••• Appointments and Promotions Special Duties ••• Leave and Acting nppointments ••• ••• Scholarships _ .. Training Courses • •• • •• • •• • •• Cent rali zat ion Staff Conferences Visi tors Mineral Product ion ••• i., .... ••• ••• ••• •• • GEOLOGICAL SURVEY... ••• ., • ,.

Su.mmary of Field ~.</ork Map Publication Programme;~ ••• Prospecting••• Aia ~UDveys • • • • , • Airborne Geophysical Survey • •.

Tours of Inspection MINERAL DEVELOPMENT • •.

• •.


• • • ••• ••• ••• General Bauxite Chromium Columbite Diamonds Gold Iron Manganese Oil ••• .

·• .

• • • CONF3RENCES AND VISITS WATER SUPPl,Y • • • HEADQUARTERS ••• Administrative .

Office Laboratory ••• Drawing Office· • • • Library ••• • • • ••• • • • ••• • •• ••• ••• • • • .

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.. • • • • • • • • • ••• • • • ••• VIII.


PUBLICATIONS AND REPORTS APPENDIX I Preliminary Geolog ical Reports APPENDIX II List of Senior Staf f of the Geological Survey of British Guian a at 31 December 1960, APPElID IX III Revised St ratig r a phical Table for British Guiana.

Viap o-f British Guiana showing napping progress Provisional Geoloe ical rt.ap of British Guiana.
ILLUSTRATIONS 1 2 2 3 4 4 4 6 6 6 6 ~ 9 9 11 12 13 14 14 15 15 15 20 20 20 21 21 22 22 22 25 26 26 26 26 28 29 ••• ••• ••• ••• ••• ••• ••• ••• ••• • •• ••• .

.. • •• • •• • •• "# • • • •• • •• ••• ••• ••• .... • •• ••• • •• I.

INTRODUCTION The Geological Survey of British Guiana is a Depa r tment responsible to the Minister of Trade and Industry.
It is financed partly under free e~ants from the United Kine;doc out of Colonial Deveiopment and Welfare Funds and partly out of local revenue.

Colonial Developnent and Welfare Scheoe D 2792 came to en and on 31 March 1960 , and a new Scheme, D 4333 came into effect on 1 April 1960, and will run until 31 March 1961.

Under the new Scheme (D 4333) 30% of the Recurrent Expenditure for 1960 was provided out of local revenue, 40% will be so provided in 1961, 50% in 1962, and 60% in 1963.
The remainder, plus Capital Expenditure, will be provi ded from Colonial Developoent and Welfare Funds.

Expenditure for 1960 was as follows: !&£al Funds C.D 1 & w~ Total ·Exeendit ure Scheme D 2792 £ 6,981 £34,575 £41, 55'~ Scheme D 4333 21 s 204 S2132 S: TOTALS _£28 1"88{ £86120:e 241~22 £ll '.i_1 Z82 Under the new scheme £309,048 has been provided of which £182,536 will come from C.D.

& W, fund s, and £126,512 wlll come from local funds.
Under the old Scheme D 2792 a total of £436,930 ~,.ras authorized 11 Th e total amount spent under this scheme was £310,988; £258,578 from C.D.

& w. funds and £52,410 from local funds, leaving -an unexpended balance of · £125,942 .

The principal reason for the funds beinp.

unders pent under the· old scheme was the difficulty in recruitine both senior and junior staff to brine the Department up to the new establishment.

The inevitable delay i n filling these vacancies.


caused the authorized expendit u re to be much less than had been planned.

With the new Scheme D 4333, however; the Depart ment was able to start with a senior staff up to ful l strength, and, owine to the hieh pressure of field wor k, spent nearly up to the full allocation for 1960 .
sum of £16, 000 granted for necessary additional buildings, includine a rock-store, minerals preparation laboratory, garage-workshop and vehicle park remained unspent, as the Public Works Departaent were unable to complete the buildine proe;rao.me, but will be re-voted in 1961.
The Estimates are thus shown to he well-balanced for the c~ntralized $eoloe;ical Survey .. Departoent now set up in British Guiana, and it is hoped that the Survey will continue at full establishment, h ft , ACKNOWLEDGEMENTS 2 The gratitude of the Geological Survey is once again expressed .

to mining companies and small miners for their co-operation during the year.

The Demerara Bauxite _<;:<?m.Pa?:Y.


}~~ted very generously provided funds t o enable Mr D. Bleackley, Senio r Geologist, to visit Leiden Univers i ty while on leave in order to study- methods- of pollen analysis as applied to the dating .and correlation of the coastal sedi ments of British.Guiana in -collaboration with Dr Th.
van der Hammen~·- The Company have _also been very generous with their hospitality at_ Mackenzie and kindly lent the Geological Survey an- Empire drill f or work on latorite deposits of Iron Mo4ntain.

· ~t"~ r ) Thanks are also due to Reynolds Metals.


Company and the Northwest Guiana Mining Company Limi ted for their hospitality to members of the Geological Survey staff during the year~ During 1960 the Compania Shell de Venezuela very generously invited the Director to visit Venezuela as guest of the Coopany to study t h e geology of the Guaya na Shield.

The collaboration of the Director ,· .

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'-··· ·.

_ .and staff of .


the Direcc ion de Geologia of Venezuela, and of Mes_srsc Me.rtin, Sykes, and Associates in this visit is also gratefully recorded.

Mr D. Bleackley, Senior Geologist , was enabled to visit and study the bauxite deposits of Surinam ··· owing to the kindness of the Surinam Aluminum Company and the Billiton Maatschappij who invited him as their guest o The Commi'ss1oner of Lands and Mines and .
members i: , o-f,- hisl staf"f~ ·-kindly ·provided topograph~_c maps, mining informat·ion ·an d aerial photographs whenever possible.

Distri c•t , Conunis'si'oners, · particularly of Kamarang, Mazaruni-Pota·ro and th'e North West District provided a great de~l of h~lp to field·geologists in making arrangements in connection ' w_ith ·expeditions.

· ' Thnnks are also· due to.

the: Principal, Min.era!


Resources Division of the · Ovevs·eas Geological Surveys, for carrying out· chemical analyses of aluminous laterites from the Pakaraima Mountains .and Iron Mountains and for a great deal of a ·dvice on methods of chemical analysis of such minerals.

· II R .E VIEW 0 .

F T H E Y ,EAR The first shipment of oanganese ore from the I-iatthews Ridge mine of ·the Northwest Guiana: Mining Company Limited was made' tn· August 1960.
The start of these mining operations niarked a .i:iiost important milestone in the development of t he raineral resources of British Guiana and brought much rieedeci employment to the North West Districto The company plans to continue exporting at the rate of about 180,000 tons .. per annum., •;c. 3 Prospecting of the ferruginous bauxites discovered i n the Pakaraima Mountains in 1959 has shown that aluminous laterite extends oy.e~ an area of some 1200 square miles.

Much of this material .


is a low-grade ferruginous bauxite with fairly h~gh .s.ilica • In the Kopinang basin, h,o'wever, pitting over .an area o f some 250 square miles showed a large tonnage of promising ferruginous bauxites.

The geolOfP-Cal mapping progracme made great P~ogress and a new record of 7785 square miles with 195 miles of river and railway traverses was achieved.
From the results of the yearis mapping it was concluded that the new stratigraphical table was sufficiently well established to be maintained in the future, and plans were made for the extensive publication of map sheet·s • Guiaµ~ ··to be published in colour at 1:1,000,000 will.be ready by the end of 1961, one year ahead of schedule.
· A draft of the new geological map of British After proving a considerable thickness of off shore sediments by a marine seismic su:rvey the California Oil Company (British Guiana) Limited abandoned their lease; but the area was again applied for by an American group.

A test borehole was completed in the Shelter Belt, Georgetown; by the Pure Water Supply under the supervision of the Geological Survey, to test an .aquifer suspected from previous work.
Below the "An s ands a new aquifer termed the Lower Sands was encountered fr·om 1260-1360 feet with a hydrostatic head of 36 feet· abov·e ground level and a natural flow of 500 imperial gallons per minute of water of a · high degree of puri·ty•• · ·· This Shelter Belt test well was continued until basement rocks were met at .. 1951 feet and a complete section of samples was taken for pollen analysis.

These have proved the· existence of .

Palaeocene beds below the 11An Sands.


Traces bf oil were f ound in cr a cks in the basement .

reeks.

· British Guiana was represented by the Director at the 21st International G.eological Corigress in .

Copenhagen a~d · he exhibited a draft · of the new·.

geological map.

STAFF The Senior Staff continued at full strength and consequently work proceeded at caximum.

pressure.
pressure.

One geologist left the Department on the completion.of his contract and.was ,replaced by a Guianese, thus bringing the .. number of.

,quai'ified Guianese .scientific officers up to .

six, which.

includes one Geophysicist~Hydrologist, two Geologists and three Assistant Geologists.

are still two Guianese Conditional Scholars in the U.K. •There The Chemist-Petro·logist~ Dr • J.

'Schiilin.g, .

wh'..o left the Colony on 27 Jun¢ 1960 on vacation leave has not renewed his contra9t.
4 AJ?pointments ~nd .

'p~-~~~tions .. .

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;Mf _ D. Ble.ack(ey, senior Geologis:t was p~om6:ted to" the· n·ew post of Deputy.

Director (Field) with .. .

~ff'ect from 1 · April 1960 • Mr Cannon was · appointed ~o th~ vacant post of Senior Geologist ·w_ith effect from this date.

• ·Mr M.w.

Carter, Assistant Geologist , ·was promoted G·eolog:i.st with effect from 1 January 1960, · .. + .

Mr M,A,.

Lee was appointed Assista nt Geol.ogist with effect from 26 November 1960.

Mr L,F.
Mr L,F.

Choy, Examiner of Accounts, Grade I, Audit Department, was seconded to this Department · with effect from 17 February 1960 to carry out the duties of Senior Accounting Officer pending approval for the substitution of such a post for t he post of .. Class I Clerk.

He was appointed to the new post ~~ih effect .from 4 June 1960 • .

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Su.b~.equently Mr Choy was seconded to act as Accountant, Land Development Department from 25 August 1960 and his place was taken by Mr V~H.
Campbell, Class I Clerk, Medical Departme~t• I • : ' I-ir R. V. Dr::rkes Class I .

Clerk was transferred to the Medical Department .

with ef.fect from 4 June :I:960 after a period of s~qo~dm~nt t ·o the Audit' .

P~pa rtment f ,rom 1 7 F ebr ua ry.

196 0 •· : = ... ' Mr , c.s •.

Massia_b was appointei;:l ~o .the new post of Class II Clerk with effect from 22 February 1960 • . '

j : Miss c. · Young, ·fir : W~ Davis, · Mr L. : La Rose, Mr S • ' Jagai and :.Miss ··.J.

Jardine.
Jardine.

were appointed .Apprentice Draughtsmen with effect.

· from 1 Mar ch .1960.

Hiss Young and Mr D'~V-is ··were · · subsequently promoted Assista nt Draughtsmen Geological Survey and Drainage .

f1 Irrigation !

'.lepartments r _espectively., , Miss Young 9 s · appo.intment .

too k' effect from 1 March 1960. while Mr Day.is 1 promotion was e ,ffective f _rom ·.

i De_c.ember 1960 • ' ' I • Miss J.A.B.


Dennison was appointed temporary Clerical Assistant (typist Clerk) with e f fect from 1 December 1960 vice Miss· Y~C.

Mayers, Clerical Assistant on ~ a cation leave.

Spediai .·Duties ; •• : .

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D~:; -L:: E~ Ramsahoye, ·G~ophysicist-Hydrologist was1.

seconded t .o th~ .

I't;tre _Wq.t'e r Supply Division, P • W,D.

·.with effect from '8 November 1.96:Q for spec:ial dut'ies; · · .·.

· ' •.
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· · · L.eay~, -a.9d Acting Appointments ' ··n'r ··a.B~ M~Conn e il, Dire ct.pr:-., ·' l eft the Colony on 15 March 1960 on s i x months vacation leave to be spent in the United Kingdom and Europe, and resumed duty 5 ' on :23 •November : after having spent · a period on duty at 'the•· International • Geological Congress in Scandi navia in.addition to ·his .leave; Mr C.G.

Dixon acted : as Dit-ect?r during this: period.


Mr D. Bleackley, Deputy Director (Field) pro ceeded on 145 days vacation leave with effect from · 17 October 1960, to be spent i n the United Kingdom following the expiry of his contract.

Dr E. Williams was appointed to act for him.

Dr J. Schilling, Chemist-Petrologist, departed on 120 days vacation leave · on 27 June 1960 f ollowing the expiry of his contract.

Mr DoD• Hawkes was appointed Acti ng Chemist-Petrologist from 12 December 1960.

Mr J.H.
Mr J.H.

Bateson, Geologist, resumed duty on 3 · May 1960 after vacation leave spent in the United Kingdom.

Mr M.G .

Allderidge, Assistant Geologist, left the Colony on 20 December 1960 on six raontns vacation leave following the expiry of his contract~ Mr R .C.

C.anso41, Assd.stant Geologist, pro:ceeded on · vacation leave with· effect f .rom 1 July -;I.9~0 • on the expiry o f his contract• .

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i, Mr M.WQ Carter, Assistant Geologist, resumed duty on 8 June 1960 after vacation leave spent in the United Kingdom.

Mr F • Johnson, Chief ·Clerk, resumed duty on 28 July1960 · after spending ·appr'oximately seven months vacation leave in ·the ·United Kingdom.

During his absence his ·duties were efficiently carried out by Mr C.E~ Outridge, ·,senior.

Clerk, on secondment from the Post Office.

· Mr K ~ tall,., Senior Assistant Draught sman, went on 162 days va·cation leave wit•h effect .
;from , 16 May 1960.

During his leave he undertook a thr.ee ~ onths course of study at Tolworth at the Directorate of Overseas Surveys.

Mr Lall returhed · to •the Colony and resumed d·uty on 7 December :1960. '

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Mr J.R. Briggs, Senior Field Assistant, resumed duty after six months vacation leave in th.e West Indies.

Mr Do Hope, Technical Assistant, was gra nted 111 days vacation l eave with effect from l · June 1960 to be spent in the ~est Indies and in the Colony.
He reswned duty on 24 September ·1960.

Miss Y. Mayers , Cl~rica1 'lt ssistant, proceeded on six months vacation leave to be spent in -the1United States of America, on 1 Septeober 1960, ~ Higher Degrees · During lris pres ent tou11 of service Mr. D. Bleackley, Senior Geologist, and later Deputy Director '· (Field), made a special study b f ihe bauxites and laterites of .,..

6 · • .Brii1;,ish ~.uiana with special <;m1phasis on their origin, ... : · .geological setting and economic development..

The .

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·results of, his work we re written up · as a thesis .

lavishly illustrated with photographs, profiles and maps and presented at the University of Oxford for the · degree of D.Phil.

This ' work ' has been made available in typescript .

and has been much praised by the g e ological· staff of the bauxite mining coopanie s in British Guiarta.

It will b e publ i shed a s a Bulletin of the Geological S1,1rvey as soon as possible.

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Scholarships Mr G.A.


Sampson and Mr A.S. Persram, formerly Field Assistants, continued the_ir courses of study · at Edinburgh and Glasgow Univ·e rsities respective1y, Both had been awarded Conditional Scholarships to study for the degree of B.Sc.

with honours in geology.
Training Course s Advantage was taken of the numbe r of experienced geologists on the staff during the wet s eason November December to institute a series of lectures on geology and allied subjects for the benefit of the junior staff• CENTRALIZATION The policy of the centralization of the Department in Georgetown and the provision of new buildings,which had been making steady progress, was unfortunately held up · as it das found impossible to arrange for the con struction of the new rock store, assay laboratory and workshop b e fore the end of the year.
Funds had been provided but the Public Works Department could · not '· complete the plans and advertisement of the contract o.wing to shortage of staff.

Parking facilities ,in the compound are also still lacking • ....

The new chemical laboratory was completed and occupied early in the year, and the old laboratory was demolished in readiness for the construction of ·a car park.
On completion of the new rock store and assay -laboratory the roo.aining old building will be demolished to make room for additional parking spac e .

J .. • Additional bedrooms and.

servants' quarters were added to two of :the houses.

in the Geological Survey Compound.

An entrance .fronf .Hadfield Street was completed and will come into use as soon as the parking spaces are 1ai_d .d.01,m,.. , This- w:i,.l], eas e, the severe con gestion at the other .

side of th e ain building.


STAFF CONFERENCES .1 -.

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Two staff conferences of senior officers were held during the year, when administrative matters, especially accounting procedure, were discussed at J.

7 length.

of j~ior ~~q,ff were held and lectures were given by In addition to these a number of conferences :;: g(i}ologists .

as.

part of a programme of In-service training, . '

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VISITORS · On 11 January.


the De_partment was visited by· Hi s Excel:l.~-~.C.f the Gov,ernor, Sir Ralph Grey, K.C.M.G., K. C. V. o .

, O.B.E.

At that time all geolog·is·ts·-werEf at· ·headquar ters an'd ; f.l~mhers of the staff had an opportunity of .explai n ing the nature of their work, methods and resul.ts.

All wer e ·greatly encouraged by the interest shown by His Excellenc y in their.

work and in the pr?gress made by the Depart ment.

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Mr H.A.
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Mr H.A.

Stamers-Smith, C.B.E., Assistant Director of Overseas Surveys·, visited the Department during his visit to the Colony in Janu3:ry when the Direc,t or.

of the.

Geological Survey Department had an opportunity of holding valuable discussions on the subject of .

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::aapping progress, aerial photography and other topics.

· O_n 9: December the Department had a visit from the Hon~ Dr c. Jagan, Minister of Tra4e and Industry.

The Hon.
The Hon.

Minister showed a keen interest in the results being obt_ai~ed by the Departoent and particularly i n the ~pplic~~ion of ~e~ial photography to geological .mapping.

He expressed appreciation of the new develop- ·merits· ±n --the Drawing Office and Darkroom which have greatly speeded up the production of maps.

.

Visits were also mace by numerous other persons, among whom were: Dr Bassett Maguire of w rork l'otani~ al_ Gardens; Mr J.B. Snethlage and Mr S.J.
consultants from the United Nations Tee Mr S .

Mor.ient, Mining Consultant to the Gui ana; Mr M. L. Dewan of the Food and Ai:,.l'icultur e 01:'gan i zation in Rome, Mr J 0 GoH.R.

Diephuis_of trn: Hyd: ologic a l Laboratory in Delft, Dr Watts of McGill Universi~y , Sr E.O .
Mir anda of the Geological Survey .of B~azi l ~ ~ r R. Watson and other members of the Cambridg~ bx pedit ion to British Guiana, and Dr Vine of the Imperial Col lege of Tropical Agriculture$ ih~ssik~ ~pec7alist ,cal Organ 1 zat7 o~; ~l"flment of Bri~ i sh Representatives of th.e following companies also visited the Departoent during the year:~ ,, : African Manganese (Mines Management) Ltd. Colr.iar Surinar.i Oil Co. Demerara Bauxite Company Ltd. Fairey Air Surveys Inc~ Harvey Aluminium.
Inc. Martin, Sykes and Associates, S.A. Minerals Engineering Offshore Exploration·Inc.

Petromina (B.G.)

Ltd. Pickands, Mather and Co. Reynolds Metals Co. Revere Coppe~ and Brass Inc. Rover Company Ltd. · San Francis Metals Co. Ltd. Sinclair·and B.P.

Explorations Inc. Taylor Woodrow (Overseas) Ltd. Union Carbide Ore Co. ~ ' • MINERAL PRODUCTION 8 .
, • , ·, 1 ·Th; .. (~ii~wirig :table gives =~ comparison of' the mineral production of British Guiariil in: 1959 and 1960; the figures were supplied by the Commissioner of Lands and Mines: • ' ' !

... ,' ·Amount· 1959 Value · $ W,I, Amount 1960 Value $ W,I, .

i . '

1';585,872 2,471,190 ' ' !• : •· 62~328 3,085,230 101,003 5,186,504 1 • • !

· hahx:tte .

; · ',,r .

(~ong.'

·~ry, tons) : ', ~- ' ' ' ,' .

Diamonds ( t.~etr ic ~t.s) i . '

Gc>I•d: · ... €OX ·· ' :Troy) ' •• " Grani:te; , : ,(long tons) .
, .

Manganese ; ( ~ong w,et t 'ons) 3, 448 · 190, 3 30. , 67,287 67 2, 87,0 ': ·as, 53<f •.

; : ' 122·,726 .

: . '

l • N ~B.

·.

· Provisional valuation $1 w~I.

= $0,·58 ·u.s.

.

: , l I ' ; • • .

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Value I ~ I . '

.. , ·· Minerals · .

The ·Gomptpoller of Customs and Excise ~ kindly provided the folj.o,·ng .figures for the 'quantity and ' f.o.b.

values of min~a exports for 1960: .

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• • • 1 ' ' .· · · · !


• · ' • I ' ' · ·· · : · ' , ·Export --,,--,-~---:--~~---------------_;;.__...,;,,;--:,:~------ .

, .

Ba'uxite· (l,ong tcms) · • I • , , • , , ; ' · ·, Metal· ah~: •chemical· grade .

Calcined 1, 780,.

297 304,946 ., ·niamorids ' (metric c'arats') ' Uncut diamonds Cut and polished diamonds·.

· Gold (oz.

Troy) 92,224 rt!

•' .

.

,.56 , , ·-= Manganese (long wet tons) ·.

76,765 • .is.~·942, 508 i'o', 378,451 4,733,762 20,019 .

!·.'.

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!·.'.

.

2z 1~9-::;1Q;5 33,233, 845 , " ,... ~, The value of minerals exported exceeds t h e f igure f or 1959 by $ 5,378,539.

This is a very satisfactory result and i s due both t o the first shipments of manganese ore from the new Matthews Ridge Mine, and.

to '.lbhe rising value of diamond exports.

A further increase in the value of minerals exported can be expected in 1961 when the shipping of manganese ore gets well under way.

No gold was exported during the year.

.


-· t. JI 9 The improvement in world trade during 1960 is reflect~ in the increased production o:f. bauxite.

The great increase in diamonds is due to the, devnlopment of the· ·workings in the upper Kurupung River ·.

and to.

the discqvery 6:f a new diamond field in th~ upper Eker·'eku River·~ ... An important developr.ient is the export.

of manganese ··which started in August 1960.


The continued inactivity of •B .• G. Consolidated Goldfields Ltd. and the emphasis on ·t ·he diamond workings continued to have a very adverse effect on· gold production, and the little that was produced all came from S!

!lall workings and was sold locally for the production of jewellery ..
I I I G E 0 L 0 G I C A L SURVEY SUMMARY OP FIELD WORK Field mapping continued very actively as the D~partment was at full strength and additional air p~otographs bacame available.

A further new ·record .. was ~tablished as a total area of 7,785 square miles some revision.
.is was capped at a scale of 1:125,000; included and 195 miles of river and railway traverses were also carried out, The mapping of certain critical areas has confirmed that the subdivisions adopted in the revised Stratigr.aphical Table are suitable and it will be possible to prepare a large number of map~ for.

publication in 1961.

· · Geological mapping and prospecting of ·the aluminous laterites of the Pakaraima Mountains continued .. during the first field -season under the direction of Mr o_ .
Bleackley, Senior Geologist, with the·.

help of Messrs J .H.

Ba:teson, S. Singh, R.C'.

Sansom and J.W., Carter.

, An ·area· of .·one · square mile near the Kopinang Riv.er was drill~d in detail, and reconnaissance surveys carried out over 2,500 square miles disclosed further sheets of gibbsitic ~aterite overlying : dolerite sills at two pifferent levels, ·corres ponding ·to major planation lev:els already defined.
· Mr S. ~ingh continued the- reconnaissance mapping· during the second field season between Monkey Mount.a,i,ri .and Kurungiku and Ebini Mountains, and studied t _he 4.ist:.ributi6n< of .

Contfriuin,f · the gabbros and aluminous la terit es.

reconnaissance work Messrs J.H.

Bat.<,:lSOn and J.,W., Carter prospected the aluminous laterites of tn e · Kopinang and Kamarang-Kukui areas .

respectively., Mr P.B.H.


Bailey, Senior Geologist, mapped the country between the headwaters of the Wenamu and Ekereku Rivers where gold and dianonds are associated with conglomerates of the Roraima Formation.

· A team consisting of Dr E., Williams and Messrs R. T • Cannon, K. Bramley and J. w. Lloyd, carried out further surveys in the upper Bartica and the Barama Waini areas.
The · subj e9 t o.f s ·t,udy_ was the , geological structure of the metasedimentary .formations of the Barama Group, with special ·emphasis on the relations · to the manganese deposits of the Matthews Ridge area~ Mr D.D.

Hawkes carried out field surveys along the Puruni River on the south bank :and .also .

northwards from the Mazaruni River· to the hea.dwaters of the Puruni.

10 .

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:- Ex.tensive granit.es .-occur which have been.


subdivided •and : are associated with etasediments of the Mazaruni , Group.· Ext•ensi ve sills.

and dykes of dolerite occur and· .some · of these appear to be cone-sheets.

Mr M~G-.

Ail.lderidge mapped the country east of the lower P·uruni River., in'cluding Peters Mine and t--.remu Mine.

By paying particular att e ntion tq structure he was.
able· to add much to what was already known about t -his goldfield , which· was once the · most productive in the country but is now desertedo Dr E,.

Williams joined Messrs. Hawkes and Allderidge in tha l a tter part of the first field season in order to map in detail the Puruni River from its nouth to Arabagai , .

Falls.

I ,,. "

Dr Williams in the second field s e ason axarained the rocks exposed aloi'lg the M:azaruni River between Issano and Apaiqua, and in the Meruoe River.
The Mazaruni Group of this region is divided by him into the Cuyuni For~1c1tion and the Haimaraka Formation, which has been considered to b e a possible continuation of the Barama Group.

However, show that the Haimaraka Forcration conform.ably overlies the Cuyuni Formation and is, therefore, ouch younger than the manganiferous horizons of the Barana Group further north.
evidence was found to · Mr R.T. Cannon r e -mapped the Kaburi area later in the year in continuation of nis inve stigation of the rocks of the Bartica region.

Ar:;_phibolites, b,iotite gneisses and hornblende-biotit e gne iss e s are inter- .

banct·ed on a large scale and are a n extension of the Bartica Assemblage.

Hornblend e a northosit ~ occupies a large area in the Kaburi Rive r basin.

This rock consists of large crystals of labrad9rite/bytown~te with interstitial hornblend e o .
During the second field seas on Mr J, W o Lloyd mapped the Waiamu are a, Cuyuni Rive r," wh e r e a series of bedded phyllite s and quartzite s, called the Waiamu Island ·Formation and believed to b e of the Barama Group, is _con~idered to be older than the adjacent sandstones · and i$11e-ous rocks (Cuyuni Foroation) ..

., \ .

.

• , .

.

: :1- .

:· Mr M.G.

Allde:d.dge mapped an area e ast of the lower Puruni ·River ' s 'outh, of the old P'eters Mine road during the second season.
This area is underlain entirely by gneisses and amphibqlite s o f the Bartica A~semblage, with ' a few minor irttrusivesity The origin o f these · rocks is not known, but th e fr e quency with which sillimanite occ1.u:•s sugge sts that ;th e y may have a pelitic origin.

· .... ·, 8' ' .

Mr C.N.

Barr on napped in th e e a rl i e r field seasori ·the · Pott Falls and Omai a ~eas, -both of which have old deserted !

gold' mines-.! '

The rocks ar.e meta- s ediments .


q f th~ · Muruwa F ornation-, with other volcanics and metas e d:unertts· 'qr .'

the t:laza:t-uhi Gr-oup, a ssociated witr1 granites which unde rl.i e a .

larg e pat"t ·.

of th e are a mapped.

The gold •mineralizatiori occurs · marginally to ·the granites.

All have been sheare d to a l c rge e~t e nt and i t is quite possibl·e , that the she ar·in-g, · which.

: is pot, · uniform, may nave some rel a tion ' to the gold .. mine raliza,tion.
· During the second field season.

trrr .

Barroh, ,eontinued · his_ mapping of similar rock-types to the south between the Demerara and Essequibo Rivers.

.

i 1, • 11 Mr 1.1.

Fernandes carried out reconnaissance s~veys· on the gabbro which intrude the Roraima Formation in the upper lpart of the Cuyuni River basin and samples of the bauxiti.c lat.erites and red earth were collected fo~ chemical -analysis.
Reconnaissance prospecting for diamonds was also carried out during a tour of the Weriamu River diamond f i eld.

Mr M. w. Carter mapped.

an area between the Ireng •River and the Blirro~burro River, and the southernmost _part of the Pakaraima Mountains, between the Ireng River and the headwaters of the S1parwii River.

·The rocks mapped fall chiefly into two groups namely, acid and sub-acid porphyries, and rhyolites ~hich may be ex trusive.
These are associated with grahophyres which are believed to be genetically related to the voicanics because a notable feature is the number of transitional rock types which seem to link the two together.

In the area extending from the Mazaruni River aoove·Apaiqua westwards towards the Ekereku River, Mr o. St. John, Field Observer, carried out field mapping and prospected the streams for gold and - c'.iamonds .
The survey extended up on to the top of the Pakara:ima es carpment.- The oldest rocks are foliated volcanics and raetasediments of the Mazaruni Group overlain by the Roraima Formation.

The base of the Roraima is at a low elevation beine: about·river level.
and i t is intruded AGE OF SOUTH SAVANNA GRANITE One of the g reat d~fficulties inherent in the study of the geology of the very old Precambrian rocks encountered in British Guiana is to establish the relative age of t he various formations which we dis tinguish and mark on our geological maps.
Various provisional stratigraphical tables, such as Appendix III in this volume, have been produced from time to time which aim at g ivin g r elative ages b ased on the observed geological and structural relationships of the rocks.

The same difficulty is met in al l countries composed of these ancie nt rocks, and in an attempt to find a solution methods have been developed in recent years for determinations o f age based on the rate of decay of radioact ive minerals.
Such methods are still in an early stage of development and are expensive, hence they have not been applie d hitherto in British Guiana.

Specimens of mona z ite, a radioactiv e mineral of thorium occurring in the South Sava nna Granit e, were · however collected by members of the Atomic Energy Section, Geological Survey of Great Britain, and have _ been analysed.
The results indicate the great age of 2,270 million years (plus or mi nus 1~5 million years)~ This age falls i n the Lower Precamb rian and thus conf1rms the place given to the South Savanna Granite in the stratigraphical table a .

.

.i,.,, >: ' ,. '

reconnaissance map •in .five years.


As a prelirainary i t w'as found necessary to revise the definition of ·the : geological formations of British Guiana and determine as far as possible their actual relat.ion ships; this involved drawing up a new Stratigraphical Table.
The publication of maps was held up until i t was felt that the newly defined rock formations were satisfactory and would, when mapped, give a picture of the geology and structure of British Guiana which would facilitate the interpretations necessary in modern prospecting.
After the last field season of 1960 i t was decided that this stage had been reached, and that the mapping cover would be sufficient by the end of 1961 to warrant, the preparation of a draft geological map of the whole country for ·publication in colour at a scale of 1:1,000,000.

This target should thus be reached one year ahead of schedula.
Arrangements are also being made for the publication during 1961 of a large number of map sheets at a scale ·of 1:200,000 (about 3 miles to 1 inch}_ These sheets are each one quarter of a degree ~square and will be published with geology and topography as lina drawings in black and white, with about 1500 words of geological notes on the sheet itself_ Tha maps are so drawn that the geo1ogical formations can be easily hand coloured by the recipient.
This method is based on the pract:i-r-e of the Geological Survey of Canada, and means that the wor!c of.

the geologist can be placed at the disposal of the public cheaply and very soon after receiving the final draft.

Dr E. Williams and Mr R.T. Cannon h~ve assumed responsibility for producing and editing these map sheets.

Owing to the re<;>re;~_nization of the Drawing Office under the presenti Chief Draughtsman, Mr T .M.
Rahaman, the production of o.aps hns been greatly speeded upo T~e new black end white 1:200,000 quarter degree sheets will be completely drawn at 1:125,000, photographed down and taken to the di.

'.lpositive stage by the Drawing Office staff.

The printing will be done by a local company in direct consultation with the Survey.

be possible ·to produce the maps very rapidly .

'.lnd economically.
'.lnd economically.

If the Drawing Office staff can be maintained at its present level it is hoped to publish 25-30 sheets during 1961, and altogether some 50 sheets covering.about 75% of British Guiana by the middle of 19620 The plnn of publication of the sheets is shown on the map· Figure.
It will thus PROSPi3CTIHG The pr=ncipal object of the survey carried out by Mr o. St. John in the W~kawakapu area was to prospect for gold and diamonds and, if possible, to open the area to prospectors and cut· a trail to provide ::·.access to the recently discovered diamond fields at Ekereku River on the Pakaraiina plateau to the west.

Most .

of the streams prospected contained some gold, which was often fairly coarse ·and at times present in aaounts that would probably repny small ...
I \ 13 ~pa~~r_W<;>fking~ Tha gold is pre s ent both below the p~~~raima ascarprii~nt a nd above it, and normally accqmpanie~ d;i,amorids in tne Ekereku area., Before tll~, expedi;p.ion.'

was concluded a number of local prq$pect6rs foli'owed the lines cut by th e Geological Survey and shortly afterwards .

it · ~'las reported that some had actually found diamonds in a small tributary of Wakawakapu Creek below the escarpment.
After several attempts a route up to the top of the escarpment was eventually found but completion as far as Ekereku River will have to continue in 1961.

The .

cutting of the trail has attracted the attentio n of local prospectors, and when- completed, i t will undoubtedly be much used and i t will be a much.shorter route to the upper Ekereku area than · either.

by the Cuyuni River or by Kama rang.


Mr K. Bramley, during his survey of t h e upper Barima River area, found a · specimen: of hornblendic · r .ock containing niccolite,., Chemical analyses of this and of some soil samples he .cellected _revealed the · ·pres:ence of traces of nickel, -cobalt and molybdenum.

Du~ing the second field season of 1960 Mr Bramley returned to the same area and extended his surveys, and collected more soil samples on a -~~d pattern.
These were nnalysed and tested for lead, copper and zinc.

·When the results were available i t was fow;1d that the hig :.1est propcrtions of the metals in the soils were associated with ·amph,ibolites and with a granite mare;in which· had been mapped during the c-ourse of the 'surveyo in progress.

A further investigation is A IR SURVEYS A ·further contract· for ··aerial photography.
was kindly ar·ranged by the Director a-ta · of Overseas Surveys and photographs were take n with a "wide angle camera · from an altitude of.

15,000 feet giving an approximate scale of 1:51,000o- Unfortunately cloud cover was even worse th~n normal and .
of only about 5,000 square miles were photographedo Although this was rather a disappointment, such photographs as were taken were in areas where they were badly needed and a large :proportion·of them ~av e already ·A large p r oportion been interpreted eeologically., of the Pakaraimas is now covered b y a e ria1- photographs and by interpretine these with the assistance of field surveys carried out during 1960 a nd also in earlier years i t was possible to prepare a series of satisfactory geoloeical ma ps which will be prepared for publication in -black a nd white in t he near future.
It has beeri emphasized ma"r1y ·time /3 that:: aerial photoe;raphy is quite indispens·able f or · the · production of even rea-sonnbly accurate geologica l -maps, · especially in 'tropical countries· ·where g-round ·work is arduous and access difficult.
· The_ ava i ·lability, o:f· aerial photo graphs contributed · largely t;o ·the record square· mileages mapped dur•ing 1959 ·and 1960. raima Mountains as well as in other areas i t was possible to make geological maps a t headquarters with the minimum of previous field surveys, a nd in some cases field· work In ·the· ca-se of the Paka / f •• cart b~ cut to a hinimum throu gh ~sing the compiler's knowled{ie , of the terrain• Without.
continuing aerial ·,, pJ:;tbto~raphy" over that part of th.e country that re 14 mains · to· be covered~ progress iri : geological mapping · r,mst · :inevitably .

'diminish very corisidefably in the · futu;~.· - · · · ·, AIRBORNE GEOPHYSICAL SURVEY With a view to plannine; · the campaie;ns of' airborne geophysical surveyine which will be required to locate any hitherto undiscovered mineral resources in the Interior of British Guiana, a test survey .

flight was arraneed.


This was flown on 31 January by a DC 3 aircraft of ~ero Service Corporation .

equipped with magnetometer·; scintillometer and Radan Doppler navigat i on.

A traverse of 3 56 line miles was flown westward fro!.1 Atkinson Airport to Saxacalli, thence southwest .to the i1ierume chrofi!ium area where a box was flown , • t h ence ·east-northeast to .. Itaki where another box was flo~, thence directly to i.t~inson.
/l comparison between the geophysical records made and the existing geological naps enabled :important comparisons to be made, and it was shown that the Radan Doppler navigation system would bridge eaps in the photographic cov.er.

features were recorded over the.chromium deposit · which will guide more detailed work in the .

future.

Interestine TOURS OF IH.SP3CTION During September the Deputy Director, ·Mr C.G.

Dixon, spent a fortnight in the field with Mr O, St .

John, Field Observer, in the.


Wakawakapu area, l{azaruni River, in order .to study the geol ogical formations and to study the possibilities for developine the.

eold and ni~ing.activities in t h e area .

From 13-15 Octo~er, through the cour.tesy of the 1'1anager of Northwest Guiana Mining Company i.:.raited, Mr Dixon accompanied the Comr.1issioner of Lands and Xines Oja visit to the manganese mines property as guests of the Compc,lny.

.
.

They flew into the lforth West District, to the 1.,;mding pool on the Kaituoa River at the mouth of Sebai Creek, and then went by launch to Port Kaituma.

A •conducted .

tour was made of the bulk loading insta).

:J.,;1.tion and railway terrainus at Port Kaituma, after which , the visitors went to the mL,e by railway.
At T•'latthews Ridge a tour was made of the 1-iines .anc:l the operations were fo l.lowed from the excavat'ion at the wcr king faces, t h rough the assay laboratory atld t4e washing plant to the railway terminus where .

the ore is loaded into the railway trucks .

for tr.ans port to ; Port Kaituma, The hous ine; sc,he es and .

welfare facilities fo.r , staff and workers were in~pected an.d the visitors were \ ,.
'I • • f., ft~ .. .-, ~ .. much impreiS$ed: with the great developments that had -· been achiev,ed in the few years that had elapsed since :th'e.

cqmp_any~ s operations had !>egun.

15 IV HINERAL DEVELOPMENT GENERAL A new phase · i..11: the minern1 devel.opment of British Guiana opened in 1960 .

as Northwest Guiana Mining Company Limited begun exportine; mangane~e ore from their Matthews Ridge mine in August.
In response to the growing world demand tha produc tion of bauxite was·stepped · up and reached a total of 2,471,190 .long tons.

There was ·.

considerable activity in bauxite prospectine by three major companies.

Diamond production, already greatly increased last year, reached a new record of 101,000 metric carats.

This was due to the discovery of diamonds in the Ekereku River apove Sakaika Fa11s which· established yet another· dia~ond fie1d above the scarp of the Pakaraima Mountains.
The entire production was from small workers.

The pro.duction1 of gold continued to decline as porknockers were drawn towards the new diamond finds.

Three areas were ·closed to prospecti~g or mining or the locating of claims , under Section 36(1) of the Mining Ordinance, in order to perm.it the Geological Survey to carry out further detailed investieations for bauxite in the Kopinang-Sukabi are·a, for ·chromite in the Merume area and area.

for iron in .
for iron in .

the Iron and Wamara Hills General BAUXITE The production of ba.uxi te was up by over 800,000 long tons on last year's figure, ref1ecting the improve ment in world business.

Demer.ara Bauxite Company Limited The mining of bauxite durine 1960 was nearly up to capacity again and a total of 2,231,940 t_ona · (dried basis) was · produced, of which 397,180 tons came from the It uni area., of 1,921,468 tons of ba uxite were sold, and carried in 415 vessels to 25 different countries.
This compa res 180,000 ton's were :t,,iarket conditions improved in 1961 and a total .. with 1, 33°2, 307 tons sold in 1959.

· sold to the United States Government stockpile.

The total was .made up as follows: Metallurgical grade Calcined grade Chenical grade 1,513, 53 4 tons 317, 542 90, 392 1,921,468 n ~i vr 16 With the advance of the mine faces the depth of white sand overburden is i ncreasing and a further heavy investment ··in excavating_,.oachinery became ·u..::1- necessary.
· A new dragline with 235- fto boom and 10-yd bucket came into· service 2.t a cost, of ·w .I.

2 million dollars,.

A wheel excavator and allied equipment is also b eing purchased at a further cost of WoI• 3½ ., n.illion dollars.

The new :;1 ~ I"' 615 million.

dollars alumina · plant was nearii.

"'le; cor:ipleti on· nt the end of t he year.

The first unit of the new steam power plant came into operation and digestins operations bagan i n January 1960.
The first shipment of alu.~ina is expected to take place in April 1961. , ..

I ·" a..

The eauging of r~vers with a view to the develop ment of hydro-electric power was continued and two new gaugi ng stations were built for the Government at Hillfoot on the r-fazaruni River and at Itabru on the Berbice River.

Observations were made at four stations uh.de!"

licence, 3S well as at five Goveri'lment stations including those newly constructed.
•• 3xplor~tion wns stepped up dur~ne the year nnd directed towards E.Pvs 561 and 564 situated between tha Demernrn and Berbice Rivers · and to the south of It uni on tha one hand, nnd B~ P ,.· 56 2 in the North West District which li0s south of Mnbaruma between the Venezuelan border and the K~ituma ' River.

South of Ituni the aree .


investigated centred around the drainage systen:.p of Kuruabaru and Ororo kabra Hnrakren Creeks, discharging 'into the Demerara Rivar In at 25 and 125 fee£ respecti vely nbove sea- lavel,.

this area .
this area .

large portions of white sand depositional surface occur· at n general elevation of 21-5-250 feet above sea-level, with several small steep-sided laterite capped hills, havine a core of dolerite or eabbro, risinc about 200-300 feet nbove the surface,whereas in the creek valleys laterized outcrops of basemant rocks are sometimes exposed.
As very few outcrops of b asement rock are exposed in the deep and wid ely spaced valleys it wns decided to do sooe deep drilline to explore for concealed bauxite deposits and further detailed mappi~g was carried out, greatly facilitated by the use of · p r ecision altimeters.

The southern portion of E.P.

564 is drained by tributaries of the· Berb i ce and Demerar~ Rivers and terninated to the south py the scarp of the M~ kari iV.iountain outlier of the Rorabna .

'p6rmation.
'p6rmation.

No laterite hills occur here ~nd the white sand sediments appeC;'r t.o _be underlain by granite, gabbro .

and volcanics.

Explorntion in 3.P.562.

in the Nor:th \Jest District showed that.

tlJ,e hills ris ·e · sharply above tha tidal sweep to heights of 200-3.00 f ee_t, nnd formations of hornblende schists and .

epidiorites were usually cov.ered with a highly f errut:;inbus laterit e cap·.
South of the swampy a rea the· l e nd rises to .2.n.undui'at'ine; surface af an average ~levati on of 100- 150 feet.

· This 'surface, which is not laterized, is covered by lieht~coloured residual clayey sa.nd ' 'derived from granitic• rock which is ofte..-i exposed in· creeks.

interrupted by a Hill to Arukumai.

and lforide wn hills~ The cora of this a hornblende schist whi.
ch is ranee aga1n --cov..si0ts of ~t the surface covered by laterite which is ~est developed r a nge of hills stretchine from Yarikita In the south ·tJ:iis l a.ndscape is J 17 on Yarikita Hill at an altitude of 700 feet above sea-level 8 Reynolds Metals Coapany Limited About 200,000 long tons (dried basis) we re shipped from Everton to the United States, about 50,000 went to the Chemical Industry and the ba l ance to the Government stockpi le.
Drilling was acti ve throughout the year and was encouraging as four boreholes discovered new deposits in widely s eparated areas.

Drilling h as f urnished conclusive evidence of sedimentary sands and clays below the bauxite horizons in t.11.e vicinity of Kurubuka.

~ignite seams were encountered in a borehole beneath the bauxite horizon and sampl es submitted to the Geological Survey were shown to c o ntain pol l en grains which indicate a Palaeocene age for these sediments.
Drilling was continued in the Corent yne area and proved more.

aocouraging as lesser depths of overb urden were encountered • .

Harvey Aluminwn of America As noted last year Harvey Aluminum ha7e r evived their interest· in.British Guiana and during the past year two geologists were engaged in e xploration chief ly in the a rea on the l eft bank of the Essequibo axtending north to .the Supenaam and Pomeroon Rivara.

Soma exploration· was also done on the left bank of the lower Corentyne.
A base camp was estl!blished in the Blue I-1ounta ins area · and included a fully equipped field laboratory, the · base camp was later moved to a point on the Supenaam ,liver.

Petromina (B.G,) Liraited Exploration of the Souther n Ebini and Itaki Hills wae_, · compl~ted in 1959 and North Ebini was tackled during 1960.
Tha laterite bench at t he foot of the Ebini Hil ls l i es between 3 50 and 450 feet abov-e sea .... l e vel and mainly overlies a hornblende-biotite e;ranite~ However a s the hills a re approached outcrops of basic amphibolites and epidiorites occur.

The whit e sands overlying t he massive Ebini Creek laterites were found to be only 15.-20 ems thick .and it is evident that much of the l aterite is detrit al and sand beds occur within it in places.
· Drilling was als o carried out in the I taki but was suspended after affording poor results.

work in the Omai area which is ad jacent to the of the Issano Ro a d is planned for 1961. area Further south During the year an additiona l E.P.

covering 600,000 acres in the Konawaruk-Mowasi- Muruwa a r ea s, · south of the confluence of the Potaro and Essequibo ; was granted-to this company for bauxite exploratio n .

• • :Geological Survey De,)n rtr:a:.--it •,r .

.

, J.

[:,"t:'ec.t- e:'.


:'fort w.:1s pat into th8 explorD.tion 18 c.nd r·~conna ios c:i:1c e of t~-a 2.luninous l ater::..tes discover0d· on the ?

::1karair:10.

Vi:ount ai....'1.S in the p r a-.,rious y~ar m.'.lp~inc was c3rri ad o~t ovar an are~ atout 1 50 mil~s in le::ieth stratc_hinCT aast -southeast frorq.

th~ ?

::'.

!·.nara::ic Rivar val ley to the Kopin~nc Basin and teyond, ~hroueh out.
this ar3a aluminous lat~r~tas, locally enriched to ferruei~ous :au.xites, we re :o~nd ~t two ~2in levels , 1200 snd 1500 faet·a::id 2200 to 2500 ?~e t in el0vatio~, correG::_:)o:1dint7 to pl::ln-1 tion 1-cvels which h::ive ~ wide extent i:1 the G~ctn-~ Shi~ld.

~he laterites hav0 for~3d ty we2therine o~ dolerite wharev ~r this has teen 0X?OS8d o~ ~he ~l~nation levela, a~d ao these c:re prob:-::.'.

)ly grea.ter th.'.l;.1.


25 million ye::1rs i:i age, the · we~the rine processes have ~ean c:.t w:>rk for lo:ig perio.

:s of tir.1e.

The ~ain dap osits have formed ov e r one· of tha thickest of the dolerite _sills intruded into tha iloraiw..a Forr.i::!

:i on, knawn as the i.0war Ko:;,ina:-.e; sill., which varies somewhat in 2.ltitude·.

Owi:::1p; to the re::-.ot~ .


:1nd rue;£3d n2.tur;3 cf the terrain and the thick b•.wh covar, the explor~tion of the deposits is far fror.1 co:;-iplete ;1.~d further C[..:1?~ iens wi+~-.

be :iirectad ':,owards loc.

'.ltinE -th,:3 .

:.

re2.s of higher g r 'cide • . "

'$ ' 1 ~ '-- ., ; .

.. .

.

.. .

2ro~ the work .

:::l re3dy co~)lGt0d it is est.

'.lblishad tha t the I..owar }::opinc:ne dolicrita.

sill.

... has been weathered to .

J.

~terite :ind lithor.1.


:::rc:e over t:'1e major portion of the 1000 square ::.iiles oi its outcrop.

The u:.

:>per 10-15 feet of the ,rio.terite11 is enrid.._,ed in al umLia ·to for::n ~ f arruei...""lous bawd ta or :1:i. uwinous ·1 .

'J.

t~rite, the silic~ cont a:.t is v.:::ria:::le ::):l.-~ incre~oes shz.rply dow:1.wnrds c:.t the tn se of the 1.::-.terit.e to ::'oro a zone o-= rtlithom2.re:e 7•~ Ex:::,lor2.ti•on: h z. s defined -three ~r·e_a s .
of possible econo::1ic intar e st, i ;:-: whic,1.. the character of the lat er itaG differs, 2 s follows: 1 11 In this £.rea ~he Kopin::-.ng River i32Gin.

the upp e r 10 feet of the deposit, · over so~3 300 square ;:::.ilac, is D. ferruginotS ba:i.xite low in· silica with an .

:1veraee analy_sis, bas ad on the sampli:::t of 35 pits, of 40 .• .

!

!-% •.

1 20 2o,,, 6.1% Si0 2 , · 27.6 % Fe a nd L.O.I.

·23.7%.

2.1 %"'I' i0 2 , 3 ,J f • • • 2.

~h~ Su~~ b i Riv ~ r Basin • .


Late rites cover some·250 s~uarc ~ilis but only 3 pits h a va so f e r been s a ::.ipled, 'i'h.es3 prel imin~ry rcsul ts ;1it:;?ler content of silic3, th~ averae;a indicate a annlysis for 2 depth of 16 feet shows 3 4 .

4% ~ 9at m•o -% ,...

.

:o ., a 1,._,_ 2- .1' .Ll.

?, 1o an.

:l 21.8% L.o.::.

... ~ 8"%., o o re ~:, • 2 3 .

:,.._ 2 , • ) o 16 .1., , i n th·e :ns in of the 3'.

The Kc.

::1e.ra:ie-Y..ukui 1--• .rea Up?er i-~~zartu1i Rive°r • o v er c.n a rer.
of sor:10 4,00 square miles and the 3verage analyses of the top 14 ~eet shows·a i n silica:(3i0 2 20;3%) cbnsider nt le i ncrea s e wit!.

a d~crec::se i.."1 iron oxides ",(Fe 2o 3 19.

7%) and · alw:.:..1n:-i.

(Al?0?

3J.3%), 1.6 pits have :iaan sampl ed ~ .

; ;.


/ 19 · The f errue;inous bauxites of Kopinarii appear to be of a slightly higher grcde .the~ those of Oregon ahd compare well with the i7ferru,e;inous bauxitesH of Ghana and the 11r~d :ferl"'.ueinous bauxites n • of·-.. Antrim, N. Ireland~ The material from _the Kainarang ... Kukui and Sukabi areas appe?rs too .high in silica for treatment by pres~~t day coQI!lercicl processes.
~ttempts to be.~eficiate the material by washine and screening, although not conclusive, seen to indicate that it would be possi::-le to reduce the silica content, but the yiald would ~e low e~d much alu.oina lost in the tails.

The grade of mater•ial ~rom the Kopin2.ne; area, as estimated from only 55 ?its (approximately 1 per 10 square niles) appears to be too· low erade for treating by the nornal Bayer process.
The Pederson process utilizes lower grade ores recoverine both_ alumina and iron, but requires low-cost electric power besides laree quantities of lime and coal, ·There is a great undeveloped hydro-electric poteatial in the Pakarai.ma Mountains, but the line and ooal would have to be imported.
· The future of these deposits appear to rest either (1) on the discovery of areas of hieher grade baux~ ite,or (2) the development of a process for the economic extractio n of both alULiina and iron • tinues, and possibilities of the second alternative a re increased by the existence of additional vast deposits o f low-silic~ alum.inous laterites elsewhere in British Guiana, as well as by tha g reat hydro- .

Sxploration con .

electric potential in the rivers descending fror.i.
the Pak:arairaa Eount2.ins.

Pollen Analysis aoELiad to Bauxite Prospecting Since the known hich~grade deposits in the famous T:1.e upper portion of bauxite belt of British Guiana and Surinam disappear to the north below a cover of white sands, Quch attent ion hes been given to the problem of discoverine new deposits beneath the coa stal sedinents.
these consists of a continental-deltaic deposit of alternatine; white s ands and candy cl3ys in which i t is iopossible to establish recognizabla lithological · horizons owin g to the lenticular nature of the beds.

In nn effort to find so~e criteri~ for recog~izing the b~uxite horizon in borehole s the Geologi c al Survey decided to investigs~e ·the possibilities of th e paly nological methods developed now3days to such perfection by the oil cor.1panies.

Professor 'i'h.
Professor 'i'h.

v c::.n d,3r Hammen, e ?Ollen specialist, previously with the Geological Survey of the Republic of Colombia and now attached to the University of Leiden, aereed to act as our consultant and has already obtained very promising results.

He states i n a provisional report that it appears that the sediments beneath the bauxite are ?alaeoce~e in age whereas those above are :.'.
!cuch younger, It a ppears thus very likely that the pollen analysis of borehole samples .will indicate the position of the bau±ite horizon.

A nunber of nining companies have expressed their interest and have .already contributed to the preliminary investigatio na .

- J. '

• 20 • On ?~of• van der Ha~1:;ian 9 s advice the Geological Surv.~y has · proposed a sch;c:ne, to be fi.-rianced by the princi~al bawci.

te mini.

'"J.e; companies ir,.

British Guiana and .


,;3urinan1~· to ena'tle a graduate of the University of i~iden to d~velo~ a ~ractical field method of re coen{zing· the formation:;; a::iove and below the ba:.ixite horizon by neai-1s of poll an grains.

The first reaction of the mini.ie; co::1~an1as nas been f,'.lVOUrable and i t is.

hoped that the scheme will be implemented durine 1961. , .

,: .
,: .

,(- During the test airbor~e eeophysical survey referred to on paga 1.1 a bo:ic was flown over the J:1erume Rivar area where the chror.iium.

mi.,eral ;.-;ierumite occurs.

A :,?ositiva nagnet ic ano:1aly was detected · whose u9per surf .see Wf:lS estimated to lie at D. depth of some ·1500 to 1800 ~eet.

The f~ct · tha_t · ':,his anorn.

:1ly lies .

:.

:..n the erea of greatest concentration o~ the detrital m-arumite indicates that it raay te the deposit.

The ·ara.
The ·ara.

:1 is flat and bush- covered with in s6'r.1e way connected with scarce outcrops end the -lines ·were flown NE-SW ecross the strike of the country.

However the magn~tic anomaly and ee~eral gradie:1.t proved to :)e aligned NE:..SiH and a furt:1.er nore .

detailed r:~aer.,.

:;;tic survey with NW- JB flight- lin e s is being pla:i.~ed.

· Colu.-:1.biu::.
· Colu.-:1.biu::.

Corporation COLUir,:BITE J1ineral prospectir.c operations by this coopany were subordinated to site-work for 2. larea-scale pulp wood op,aratior.. to which the Corporation is com:nitted.

.General DILViOi·E:>S ; · , ( .. t .

<'"\ -,, - · Diamo:1d ::-.1inine or: the pl e.teau areas of the ~ ~, l.,.~ ,;; • ~ .

t"='"?

t J.u r'c-COn Yvers, · - """""a!:\C""!

::l.d • J..:l~.

'"'"''-'"' ra .....

-.rc.l.fil.:..

J.•~oun u~:1S .

'L .. S n la!


'ge;I.y ·:-ec2use of the lesser amounts _of overburden to ba removed before the diar.

:io::d i ferous gravels are l"'eached.. Son8 :::>f the best .

concentra tions have bee:i fo:md to occur in ;>ockat.s of r;rs.v~l in th3 .stream ~eds.

Boulders in swiftly .

~lowi~t rivers hav3 often to be clBared 2.way in order to re a ch the e ravel caueht .in pot ~.oles or· fissures.

.
.

eC1:1ipr.1ent ha.s to :::e used, in shallow w.s.ter the simple In deep wnter c;livin[' · => : 1wate:::>-doggine;·,f method is en?loyed • recoveries h2 va .. ~ee~ mede in t:::.is way, ar:d one :::iiner is report'?d to hE1.·re extracted soc.e 2000 car-:-.

ts in the u::::,par s;r.ereku .

.s.fter c q out three.

r.1onths work • Some very gpod .

Another .

:nethod ol workir-t:r is to climb .down the l a r e; e bo~lders on sc:--ee slo::)~s, which sometimes requires the use .
o·f ropes to ._0 2the .. ~ 't-;;r lantern _ lieht the t:ravels c a ught.

'..:: enec:.-~:-: .

Good · recovaries ar'e reported to h 2ve beei1: r.iad,e .

;:ij, this rae·th<?d also.

. '

.. s .

~ - t 6 / 21 Ekereku River ;·Jithin the Pakaraima I-fountains the i3kere~::i ~iver · became,in itG course on the plateau above Sakaika Fall, the s cene of increasing activity.

1i:ost of the diamonds were produced.by div,ing mathods and came from a section of the river not more thar_ 12 ailes long near Sakai~~a.
I\~~ ... 2-eorge Golas, an associate of i~r i·-1.c.

Correia, estc.blished sev -~r2.l small airstrips ar:.d sr..09s and using as many as three light aeroplanes :11aintai:rnd 2 shuttle service to Ke:marang nirstrip which is now c a:)a;)le o:: takL1.g Dakota aircraft.

Other interests also established the :7easibility of a Grw:1r.1an an;,hibian service ~ro.r.1 either Georr.etown or TUL1erene to 3 a nur..~7:er of shops to su;>ply ..:ainers were quickly cuilt.
I t is doubtful whether this area would hav~ developed without air · transport, :for t:-.e f3w arduous trails to the area are slow and expensive to us3.

landi..~g pool o~ the Ekereku, beside which The Geological Survey opened up the Wak?.wakapu creak area below the Pakaraina escar?ment .

enst of the Ekerekt!

River, WJ.ere both gold and diamonds are now known to occur.

Prospectors are now active in this new area; havine foll~wed the linas cut by the Geological Survey.
A trail was cut westwards ::ron the Eazar· .. mi River up to the ascarpment and this will be continued to the Ekereku e.:irly in 1951.

North West District t ) It was recently re9orted that diamonds are being worked i..--i u-.e North ~;/est District area, about 25 1r.iles south-west of i:abaru.an.

are small - ahout l/8th or I/16th carat in size.


in the Mobai na Creek 'i'ne diaLionds Upper Kurupung - upper Epi11e Diamond mining recained active in the upper Kurupune River 3nd the increase in the overnll production f igures for 1)60 is primarily due to operations in this area.

The ~rocpectors are spreading eastwards to the up~r re:::.ches of the Eping Riv er where some are being supplied tbroueh Inbaimadei airstrip, althougn the Irabaimadai area itEelf has proved disa?poin~ing.
GOLD ~he small miner h~s ·lareely deserted the eold dieei~es for t~e ~ewly discovered dianond fields.

Con£iderable efforts to interest coopanies in large scale dredging have so far wet wit~ little success.

The chi af producing area w2.s the North ~'lest Jistrict.

,.

A drilling ca~ ?aien was ca rried out on holdinES in the Puruni '.liver 'Selow Pe:-ers Tdne but the ec,ld values proved :.i:1economic.
IRON A re~resentative of an i ~9ortant Canadian iron filinine; co:1pa!1y ~,isited ·;::,as Geoloeical Survey and expressed i j terest in the magnetite ceposits in the South Savann3s • 22 of the Rupunu::ii District.

to justify ex?loita~ipn i~ view of the ereat distance fron tidew~ter, but ~urther work is beine carried out and ~~e cocrp~ny will be ~3p~ informed.

;.t present thesel\appear knot Ibrthweat Gui.~ ~1a i'~i:iine Co. Lt~1.

Eini::1.g O?arations co:.::::.


:ianced on 1 Earch 1960 and by th~ end of the year 122,726 tons of mangnnese or0 avarae,-ing over --'.-0% 1-':n h a d c.3an ;>roduced.

119,279 tons ware rc:.il.ed to Port Kait'..l!

':1a w:.-i.ence th,3 ore is shipped t.o 2. stock?ila at Chaguara...1aa, Tr:i,nidad., A tanker has bee n convertec for ~his purpose n~d can neeotinte the c 3nal and deepened C:-1c::.:-.

:1el of the :.
:1el of the :.

(a i tuma :"<.iver, and t h e bar at Waini r:.iouth, cerryi.rre -~ load of ap9rox:i.ma tely 2500 tons.

Shippi;i5 started o:i 5 ,:.."ue;ust and at the end of t~a yacr 76,765 to~s (wat) hAd b~en ex,orted.

The explo:,.

: tio;i of Er· 5-~-3, • , !

\' ;' ir!

the ~utue.

u ~liver lJo .s.re2.

north of the Cuyuni River uas completed.

?ro::lisine; deposits were found tat la,teritas, which 2.re not ext3nsi~re, contc:.in very sr..all amounts of ;:,1anganase.
One tlc,ck of eood grade with lateritic structure was founc., ::.ut a se:'.

).rch in the ar0a .. failed to discover 311y deposit.

_ Gaoloeical Survey .th.'.!

t L.J.ang:::.ni::.~rous phylli t,3s forra c:.

telt in the Be.r9.r:.

:a Group, ir.t.,1ediat.0l y to the north of ti-1,e Ce.-itr2.l Cuym.

:i For::l.:.tion is con:.:irmed.

Th e eastern p£-rt of that '::e::..t :,as baen syst~1l1atic-'.llly proQpectad for :::i.c.

::ie;z.nese ores a:.

'ld is 1,nown to extend a lso to the west o-: :~utu:.~ :.liver.
':i'.

'he conclusion of the 3xplor2.tion °b..3twean Eatti,ews Ridr.a anc!

the Barim~ !liver disclosed deposits o-f '!

:,edded manec:-.

!.1.esa ora i!.1.

', two hills.

Pittinp, c>.nC: t:r-anc~1.inE has estc.blished thc:.t tI,a e-rade is too low ?or ecoz:oaic exploi t ation 2-t present.

OIL 't The California Oil CoQpany (3ritish Gui~na) Ltd. (So Cal) decided to a~3 ndo~ their concessior-.

~he ·:-_;,ari::ie S::lis;:;iic survey carried out i::i.

19 53 indicated · 2. pro~1isinc t!


:ick:.~.ass of sedime::1ts i nside th3 25 fathom ~otton contour, tut the conditions ~or t he accu;:iulation of · workabla reserves o-Z oil were judcad to be unprol!lising .

Since this work was c2rrietl out, howaver, the Geological Sur-rey h~n si-.own th&t Eocene, Pal:'.

).eocene 2nd ~ robably older strata ~re p ra~ent~in t hd oo a stal sedi- 1:...ents, and additio~1 E.l ir..d:.catio!ls of th e :)resence of oil hav ~ beeJ r 3ported.
A further applicatio:i for explore tio!

'l rights has been made ;'.

)y nn Acerican eroup.

V C0 l lFE a .3 l lCES rro.

:.1 19-27 J:>.

!luary the :Uirector :;?aid a visit to Venez-:..tela · s _~ :•,tha.

i::1.T: .. t c.·:.

:.ior~ o -7 the · Coopania Shell de Ve:1ezuela, Thd ·:::i.ajor o~l co:.-;19a:lias of the worli::i ::iow na~rn ::.

r,,ractice o~ studyi..1e the tasaae:..-1t rod".G under- f t • .

( f I ·• .
( f I ·• .

• I ..., t .. \ .. 23 lying oil bearing formations, as much information is thus derived concernine the structure and distribution of oilfields.

Correspondence with the Shell geologists in Venezuela· who were mapping ·.tha Guayana Shield, which forms the b as.ement · o fi · the oil fial ds, led to this generous invitation to visit the areas mapped by them.

Six days were actually spent in the field on the Guayana Shield between the Orinoco River and the border of British Guiana, and ·.

th~.
th~.

par~y.

was ~oincid ~Y e~~J-~is_t_§_ ,·of the· Direccion de Geologia, · M1n1ster10 de Minas e id.£.ocarburos.

Outgrops ' 1of the --•Iinataca Format-ion were studied in some detail·' in view of its economic in.portance as a bearer of iron ores, ·and visits were paid to the two great iron (l) The mines by courtesy of the companies conce~ned - Orinoco Mining Company, a subsidiary of the u.s. Steel Corpo~ation, which mines the iron deposits of Cerro Bolivar and.
has done much valuable research on their geoloeical history, ·and (2) The Iron Mines Company ·of Vene·zue1a at El Pao; a su~sidiary of the .
Bethlehem St_eel Corporation, As a result of this visit it was decided that the Imataca Formation was not present in the North West Dis_trict qf British Guiana• The maneanese deposit at _Upata, also ''in .·the Imataca Foraati6n, is of a type considerably different from the occurrences of manganese in British Guiana, A most interestine _visit was also paid to the office of the Government Geoloe;ist stationed at Ciudad Bolivar.
· Other e;eologica·1 formations which are probably represented in British Guiana were also examined, and problems of , 'correlation discussed with the Government and · company · eeoloeists.- A good measure of agreement was reached.

Very iriteresting -informa~ion was also obtained regarding the altit\ide distvibution of three planation or erosion levels which are now widely recog nized · i-n British 'Guiana~ It is the tropical weathering on these · nearl"y level plains or plat e aux which has resulted ia.
the enormous deposits of aluminous leterite now · known to exist throuehout British Guiana, and it was of very ereat interest to find that the same -series of plateaux existed in Venezuela Guayana.- hi gh grade -of the iron ores at Cerro.
Bolivar and -·El Pa o is also due 'to the same weatheririe; processes acting upon iron..:rich ·forraations exposed on a hieh, and consequently very old, ei'osion surface which can be correla ted, follow ing wide-spread eviden ce, with the Saliparu Surface (2250- 2500 feet) irt the Pakaraima Mountains which carries ferru- .

g inous bauxites 1 -~ - It is now known that the •' • · ' · While in Ca~acas / was invited to visit the well- the Director equipped offices and iabore.tories of:· the Direccion de .
Geologia,· · and had the e;reat pleasure of meetine the Director "a nd ' IJ:is staff, some of whom had attended .

the Inter-Guian_a ' Geologica k Conference in Georgetown 'in- I ·was also priv:i.leeed to i;ieet the the previ·ous y ear~ Minister of Mines and · Hydrocarbons and· very pleased to accept an offer which he kindly made of close collaboration betw~eri t}:ie .

Ge ological Sµrveys · of Venezuela and British Guian~; .
· my' acceptance was · later confirmed by the Minister of· Trade and Ind.U$try on niy r ·eturn to Georgett>wn 4 i. move · ,i.

'.

.l .

~ \ • .

.

.

.

.

.

1.

Geological Survey of British Guiana, Annual Report for 1959, p. 37.

2 4 to o~g~~'.

(~i -~ :;Jci~p.t -~pepition to settle questions of cor.rela;ti_ori and ri.omen'clature on either side of the int ernation~r ,bofaer· ' l a ter in the year failed owing to previous C::Qmtiitment$.~ but will probably take place in 1961 • · · ' · : .

: .
: .

·.-.• u .

· · ,• The Direcit.oz-i · left f ·r the United Kine;dom on long leave on.

'15 Ma'rch, passfne; through Port of SpaL.1.

where three days ·were· spent attending to business connected with his post as Geological Adviser to the Federation of the West Indies.

Cons~ting Geologist of Texaco Trinidad Incorporated to discuss recent developments in the exploration of the coastal sediraents of British Guiana.
A visit wa• also paid to the Four days were also spent in Jamaica visiting the Geological Survey offices, the bauxite mines and other points of geological interest, accompanied by the Director of the Geoloeical Survey and others of h i s staff.

Grateful ncknowledgement is made.~or their kindness, The Director subsequently attended the 21st Inter national Geological Congress held in Scandinavia in August- Septnmber, as official delegate of the Government of British Guiana.
A draft of the new Geological Mnp · of British Guiana and a revised draft .

of the :Mineral Mcp, both ~ta scale of 1:500,000 were exhibited and attracted comment, of British Guianatt by R.B.

McConnell and C.G.

Dixon was re6.d "to the Congress• Comments on the new int-er pretatiori of the geology of British Guiana by JGoverriment and collli"lle~cial geologists familiar with the· Guianns were favourable 9 and publica tians of the new detailed ·.map requested.

J... paper entitled nA eeolop ical map · : ,·.


,.

In addition to hearing r.iany interestine scieri ti:fic 'Before and aft er the official sessions papers and subsequent discussions on subj e cts bear'ing on the type of e;eoloffY, n nd the associated mineral '5 ; deposits, which can be expected in British Guiana, the Director .

::ittended meetings of the Internat i onal Coomission for the Geological Map of the World and other Commissions.
He was an ex officio nember of the Counci l and Bureau and supported the choice of India as the host country for the next .

International Geoloeical Congress to be held in 196 4. in Copenhne;en, .Field Trips wer.e made to study structure!

and economic problems in Norway and Finland.

discussions on the progress of the stu dy of t h e fossil pollens contained in the coastal sediments were held with eeologists representing British Guiana and Surinam bauxi te .
~ining companies and after the Con gress a visit wns paid to Prof. Th.

van der Hammen at Leiden University, who is acting a s Consultant to the Government 9 Detail s were discussed of a Analysis to the problerus of prospecting for b a uxite in the coastal sediments of British Guiana.

·project to appl y the methods of Pollen Important • ... .. ! '
.. .. .. ~ ., .. On the return journey to British Guiana consultations were aeain held with Federal Government offici•ls i n Trini dad, and n visit of inspection wa s paid to'the stockpiling installation of Northwest Guiana Mining Co. Ltd. at Chagua- ~ ramas.

.. Mr n, Bleackley, Senior Geoloeist From 29 .February to 6.

M.1rc~· Mr D. Bleackley visiJed Surin.

;;.m as guest of the.


Surinar.i Alu::tlnum Conpany and the Bill.iton Maatscµappij, He was kindly shown many details of the b~uxite occu rrences in Surinam which were of value in inte.tpreting the bauxite and.

laterite deposits of Sritish Guiana, of which he is making a special study, VI WATER SUPPLY The .investieation of the water supply potential of the coastal artesiun aquifers continued during the year and confirmed that the off-take could be ereatly increased.

Dr L.E.
Dr L.E.

Ramsahoye, Geophysicist Hydrologist was drawn more and more into the prac tical side of water supply work and was finally seconded to Pure :.f3ter Supply in Noveraber 1960, The most important ;:ichievement was the completion( of the test borehole in the Shelter Belt, Georgetown, put down by the Pure Wc.ter Supply for the Geologic.
:11 Survey, The objectives of this borehole started in 1959 were twofold - (a) to collect samples of n complete cross-section of the coastal sediments to b~se~ent with a view to assess ine their oil-bearing possibilities .

and .

.

e~t3blishine a type section to which further work can be referred, and ' (b) to test the potenti31 of an aquifer whic~ previous records indicated s!1ould lie at a depth of 1250-1350 feet and contc:.in c1 purity.
objectives w0re fin ally achieved under the supervision of Hr D. Bleackl ey, Senior Geolo e ist, .

::md Dr L.c.

Ramsahoye., In spite of a g reat many difficulties these f~Ood supply of water o~ ·hip;h chemical The borehole pro¥ed a thickness of 1936 ~cet of sadim_fmts and was completed in solid b.::isement e.mphibolit0 .

:it 1951. feet; speciaens of the core were collected every :ten .feet and e r e now stored a t the Geolo1:ic3l Survey, A complete set of samples of ·.the core was sent to Professor Th.
v.::in der Hammen at Leiden Unfversity for pollen analysis and his report will be available shortly.

The: prelimin.

::iry results of his study 'have been extrem·ely interesting , and encouraeine; in the se::irch for oil; .

::ind they a re rec~rded in other pages of this report.

fourid t,o be lined with · hec:1vy oil which must h,:lVe seeped in, from off-shore bedo.

The cra cks iri the basement rock were The cost o~ the borehole wa s met from a c.n.
& w. [=:-rant su?plemented by a gr ~nt from the Georgetown Sewer~ee nnd ~1foter Comrilissioners whora the well was handed over to on completion.

Dr Ramsahoye reports on the satisfactory results of .

this test well as follows: "Field work in this sphere~ hydrology has been · confine d to work on the deep well a t Shelter Belt.

This well which went ri ght down to basement showed a tota l thickjess o f sediments of approxi r:w.tely 1950 · feet.

Three m:::dn sand horizons were encount e r ed.


The Upper.Sa nd~ frqm 160-295 feet.

The t1A:1 Sa nd from 665-820 feet, and the Lower Sands from 1260-1360 feet.

., 26 HTh0 opportu..""lity wns taken to chack the chnrncteristics of the Upper Sands.

The hydro static hend wns 1 foot above land surface, and permeability 1,000 u.s. units, the·c1 content was 1260 ppm nnd Fe content 60 ppm, Fr on the chemicnl nnplysis i t is obvious .
that thi~s water is quite unsuitable for domestic use, and nny possibility on the use of shallow wells in the Georeetown :1re2.

is ruled out.

The 0 A n Snnds were not ·teste.d becnuse enoue;h informnti on has already been acquired about this aquifer from two previous wells in the Shelter Belt which were completed in these sands.
, 1t7he Lower Sands comprisine the lower £\quif er are mixed erey conrse sand and gravel~ ~he wall was com~leted in these sands usine 60 feet of the standnrd 8-inch everite ::i.nd button screen,.

h ydrostatic head of this nquifer wns 3e feet above ground level nnd the naturnl flow at ~round level was 500 Imp.

enllons per minute.
enllons per minute.

On pumping, this well produced 1,000 enllons par minute with an ndditional draw~down of 24 feet, The cheoical 3nalysis showed a c~loride content of 8 9pn and Fe content of less than 0.2 ppm.

These results surpassed .

:il l expect.

:itions nnd confirmed the existence of Ll very productive o.quifer with water of the highest deeree of·purity hitherto encountered in wells in this coantry.

'!
'!

'he 1YThe res'..llts from this test well will undoubtedly hcve a marked effec~ on the future of artesinn water in this country.

r~ VI HE A JOU ARTERS i,DMINIST PJ,TIV3 OFFICE In spite of much cmJeine nround in nume~ous key posts on the administrntive stiff the work continued most satisfactorily.

A consider:::tle nm.aunt of o.ccou.."1tine; W":EJ occ.
:i.sion•d by the conclusion of Colonial Devalopment ~nd Welf~re Sch0me D 2792 on 31 :M.:i.rch 3nd the start of Sche e D 4333 on 1 April 1960, owing to the need for rcc6nciline the nccounts of the scheme which had just cxpir.3d.
This work wns efficiently concludad by tha ,\ctinc Senior Accou..~tine Officer• Stnff conferences of junior staff were held as po.rt of n plcll1 to conduct in-service trainine, ~nd this wns nmplified by n course of lectures on eeoloey, prospecting nnd allied topics, by senior officers of the De~:)2.rtment.

LABORATORY The conditions under which laborntory work W.'.lS carried out continued to ~e difficult until the naw ln~or3tory w~s occupied and work becnme fully ors~nized.
The most pressine work wns the nnalysis of hundreds of san?les of ~luoinous lnterites collected during prospectine surveys for bnuxite, · Jnd soil samples collected for eeo cheuic nl prospectine.

Pri·ority was e;iven to the laterite s~m?les nnd by the end of th~ ye~r a great denl h~d been done o.nd proe;ress WC\S bei:1e m"de in cntchine up on c rr0ars .l.
I 27 of work i~ this connection, so that it was possible to 6nke ~ $tart on testing soil samples for eco cheniical .Pr.ospectine, Work w:1s also ·held up for a time owing.to acid fumes having corroded the metal - chimney la,ading frora.·.the f!.Ulle cupboards, but this was tempor0rily remedied by the installation of a .chimney .made of more resist.

'.lnt ina tericil, Work wns a lsp decided not · to t.ilke ~ new contr~ct.
interrupted ~ince the Cheoist-Petrologist Nevertheless a eood de3l of wor~ was dona and the record.

for the yenr still coopnres favour .

"l bly with earli'er years.


The new laboratory is -very much better planned· thnn the old one, and a continuad effort is bein5 made to brine the equipment up to date so that eventually the quality and quantity of r~sults ca~riad out will be brought up to the standard .th~t is normally required of modern chemic2l laborator.ies, The ·followine work wns carried out duri_ne the year: Analyses and identifications for the Dept.

-----1209 Sieve · analyses & heavy ~ ineral preparations---- 52 .

1 • .
1 • .

~ • • Thin ·sections prepared-----~--~--~--~---------- 857 Analys _es, etc, for private firms or individuals 20 The total o_f ; the_ above is · 2,l38; nnd the correspond ing figure f:or 1959 is 2,166, but of these, .

during 1960, a total of 1,229 chemical analyses were carried out ae;ainst 476 for 1959.

Thus th-e new labor:itory has already justified itself by nearly trebling t _h3 numoer of chemical analyses carried out.
DRAWING OFFICE The dr3wine office continued to develop rapidly and this was greatly a ssisted by the acquisit ion of a d ark room and m.:ip printinr machine, The .full staff .. is now 11, includine Apprentices,.

o.nd during the wet seasons between expeclition~ a.~ additionnl 15, including Field Observers and Field Assistants, work in the dra wine office under the direction ·of the Chief Drnuehtsman.
, .... .. ···· · The following work was carried out durin{" the year: Prin.ts of mnps •• Pho to scope stencils Maps dra.wn or tr.

:iced ~ a •• •• 3379 67 141 The quantity of ·work c~rried out in 1960 _was much grea ter th~n in 1959.

During 1959 the number of prints m.:!d e, by ammonia-pr in tine i n f);'.

::i.mas, was 1710 ;· diff.erence was due to the new dark room and printing mach.:ine.
The photoscope, in addition to bein,:r used for makine ste nciis of small maps for reprodu~tion on n duplicating mnchine, is now being used for making the ,2 .

.. • 28 ordinary photoeraphic naentives of maps in readiness f o r publication.

3everal hnve nlready b~en made for tha Controllar of Printine nnd Stationery and were used for public.

:ltion by e.,liti::.o-offset process.


Usine special raaterials, i t is now possibla to use the new Oce printing ranchine to onke transparen cies from o~d trncines or line drawines on opaque m.:iterinl.

This is p3rticularly useful for reproducins m~ps containing a ere~t de~l of vary intricate datail , e nd savas time and effort thnt would otharwise be spant in tracing elabor3te aap~ by hand.
It is teing used for makine standard topographic qunrter degree sheets, from which prints may be made for various purposes~ Thase developwents ennblad ~ decision to be made to start the publica t ion or a nur..1bar or black 3nd whita e:eoloe;ical ,maps.

In preparation for the 21st Internntion J.l Geolo eicnl Congress, a new Provisional Geological Map and a revisio;:i of the Hinernl · Mc.p · of 3ritish Gui.

::ma were drawn on a scale of 1:500,000.


Other maps prep3red for specinl purposes were a eaoloeical ma?

of the Colony on~ scal e of 1:2,000,000 for public~tion in black ~nd white, and one on~ s~3le of l:l,000,000 hand coloured, A e;re3t leal of work was done in tracing all maps that ~ccomp~nied papers read at the Fifth Inter-Guiana Geoloeical Conference in 1959.

-- Neentives o:."'

these ware made in reJ.diness for public2- tion.

All maps nre now nrrnne-ed ·.


:md indexed accordin1<: to the number of the degree square to which they refer, and also according to authors.

All astro- fixes ~re now written up in a led~er so that data can ba found readily whenever raquir~d.

The aerial photoeraphs are arrnnged in folders in metal cabinats according to the qu~rter deeree sheets they cover, ~nd each folder is .1.ccompnniad by a record cerd and index maps, photographs covering :1ny .
:\rea can thus be found in n few ninutes, LIBRARY The indexing of books, naeazin0 articles and reports in departmental files h~s been completed4 The followine was : the position at tha end of the year: Putlications cataloeued durine the year-----972 Total cataloe,ued to date----- - - - - -- ------7,433 Nur.1ber o f loans o.ade---- --- - - - - --- - --- - --- New publications received-- - - ------------ - 7 50 690 The Departfilent distributed its publications to 180 1.uliversities, ccillaees, libraries, .
·.oc;ical surveys and other bodies in 47 countries, and the publications of these ~re rec~ived in exchanpa The number of publications sold or distributed free durine 1960 ~re 3S follows: ' ?,µl~etins~----------------------350 .-.

,· · ;,, ' !

·,I • .A-nnua;i" J;lb;lo'rts-.---------------:---303 ' .

_, • !

·- :· :.

.

~t.

:ineral Resources Per.i?hlets-----150 ·· Mips.;.-'.i..!.
:., __ ... ___ ... ____ , _____________ 110 Miscellaneous Pamphlets etc.----665 1,578 The Department also produced cyclostyled copias of .

publications that have e one out of print, in addi tion to other oiscellaneous reports that nre required especially for distribution as follows: Bullatin No.
3-----------~--- 94 Bulletin No, 10----------------195 Annual Report for 1949--------248 :Miner al Resources· Pamphlats---583 Miscellaneous-·-------------- 800 A bibliography of geoloeical and nttnfne; -· literature relating to British Guiana wa~ couii,iled and has a total of 350 published referep.9es~ · It is ·hoped that it may be _2ossicle to issua this · in published forCT during 1961.
A bibliography of 217 unpublished reports was.compiled ~nd -al so a separate bibliogr;;iphy for som~ 150 references·· on bauxite.

The compilation of an index- to m-inera1 · localities in British Guiana and p~blications was started and whe~ this is complete it wi11 be possible to look up · quickl~ all references to .

:, particular ,3conomic min'eral • that have been mentioned in ·,reoorts VII .. PUBLIC k TIO NS .

.

.

.

< • • - • 0 .

.


00 00 :~ L & R E P O R T S The following were p~blished durine 1960: .

.

.. •· ~ ~ .

.

-~.... .

.

Annual Report for _ 1959~ : ·:• · ·.

Addresses to the Op0nine Session: Fifth Inter Guiana Geolog ical Conference, Georgetown.

Tha Takutu Forma tion in British Guiana and the probable aee of the Roraima Formntion by R.B.

McConnell.

Trans.

Rico.

l!lQ.

Ca ribbean Geol.

Conf ., p.163-170; Puerto A Geological :r.-:.

:1p of British Guiana by R. B, McConnell and C.G.


Dixon, Rep. · 21st Int.

Geol.

Congress, Copen hagen 1960, P• 39-50.

Intro-Stra t al Flow md convolute Foldine; by E. Williams.~• M.ae.

:•, v. 97, no.

3, p.208-214.

• ... 30 Contrihut•i"dns t;o -HLaxiquo· -St-ratie;raphique International 11 v.5, fas.

2n Amariqua Centrale, p.18-37 (British Hondtir~s section), -by· C .G.

Dixon-, (Principal ~uthor R. Hofstetter); Paris.

The following unpublished mJps and reports pr0pared: ·R1B.
· McConnall, Director 1960; Report on a visit to Ve~ezuala from 19-27 January, RBM 1/60, ~RP.port on the half.-year July-December 1959;RBM 2/60.

C.G.

Dixon, De2uty Director ·Report on the hJlf-year Ja~unry-June 1 960.

CGD 1/60.

Report to the Advisory Committee on Overseas Geology, and Mineral Resources on the year to AuE"U5t 1959. :ileport ofi a · visit to the Wnkawakapu araa, Mazaruni River, CGD 3/60j ProvisionJl bnse ma?

from herial Photoeraphs of the Wenrunu-Ekereku-1'.Iazaruni-Kamarane; .
:irea; (eeoloeic.

:il); P3/F3.36, scale 1:125, 000 D. Bleackley, Deputy Directbr . ']

DD Occurrences of B~uxite in the Paknraima Mountains, 1/60.

Report on a short visit to Surinam.

: D.B.

2/60, Thesis presented for The BJux:ites 3nd Laterites of British Guiana, degree of D, Phil,, Oxon• D, Ble~ckley, Deputy Diractor and x,w, Carter, Geoloeist.

Report on· (i) Muruwn.

:.Si p.:1rnni; Konawartu{ Expeditions.. DB 3/60.

.

:1nd l i i ) tf.uruw::,.

P,B.H.


Bailey, Senior Geolopist The Knko-Meznruni nreo.. P3HB 1/60.

P I B .

Ht Bail ;::y, Senior Geolo•eis ~-:·£.

and J ,u_.

Bnteson, Geoloeist, Report on a · sh2le loc nlity, Knrnu-uda-:-tipu, KJko River.

PBHB 2/60.

Mo.p showini:,- the Geoloey of the lower Kako River; 1:250,000; PS/FL/10.

1.

?Ul,)LICATIOHS AND REPORTS p·~B -.

H • .

Bailey, Senior Geoloe;ist The Kako - Mazaruni area.

PBHB l/60.
PBHB l/60.

Map showin c -the Geoloa of the lower Kako River; 1:250,000 : PS/Fl/lo • .

· .

· .

.G'.eoloe;.ical map .

qf the .Paruima-Wenamu-Ekereku-area; 1:125,000, (with six fie ures and sections); PS/Fl/17 . '

' , \ .

P .

B,H.Bailev , Senior Geolopist &~J,H.Bateson, Geoloeis t Report on a· shale locality, Karau-uda- tipu, Kako River-.

- PDHB' -·-2/60.

.

.· - · · .

· · .

Geoloe ical map of n ::::irthern flank of Kai;-a_u-uda- tipu, Kako River; 1:20,000; PS/Fl/11.
Section a l~n c a · p o rtion - of ' tl:-e ,.

Uda Creek and tribu taries; 1 ·:3,000'; ·· PS/Fl/12·~ · ·· !

.

; : ( .

• . '

E~· Williams; Senior GeolQE:ist Geoloe;ical ma p o f I'-1atthews Ride;e-Kaitlli!la Railway; 1:125,000.

Pl/FJ/13~ .. Geo;Loe ical -.nap o f part of -the Barama_ River; 1:12~,ooo.

P 2/F1/1s.

• Ge oloc ical -crap of part of t he Bar,ima River; 1: 1 25,000.

Pi/Fl/16.

_ Geolo e ical r.1ap o f Peaina ·Falls- Merume River area; :Mazaruni., 1 : 125~ 000.

?3/:f l/19.
?3/:f l/19.

, E. Williams•• · Senio r Ge o log is t , R, T ,Canno1_:1 & K, Bramlev, GeoloFists Kaituna.

:.Mat t h~ws Rid5 e railway •.

traverse.. EW 3/ 60 .

• 1: · EW ·--4/60.

.

·.

Bar.ima , Ri v 9 r ... · .

.. .. ... .

.

--- .

t r:ai:yers~ ( Ecl, i,pse .Falls = to .

Ko riabo) .

.

... ... ....... .. .

.

... .

..... ·-· .. .. .. .

.. .

-- ... - ~ .

Wi l l1aoo, Seni~r 'Geol o p; ist, J. W,LJ.oyd & D,D.

Hawkes,Geoloeists a nd Am:amuri Rapids:· 'E".V T/6 0 .
...... · ... .. · · ·· Repo rt on the Guyuni-.

tr!=lv~:rs~s between Makapa Hills .. : .· .. .

I r .

.

.

\•-,' ' -· C. N. Barron, Ge o loeist .. .

!

'· Repo rt on the uppe r Berbice-Corentyne Expedition .

CNB ,3~ 4/60.

.,, '· Repo rt on the Canister-:-Core ntyn:e ·Expedition.

CNB 5,6/ 6 0~ I.fap of Kanwatta headwat ers; 1:30,000.

P7/ F 3/13.

Ge ological map of M~c·~;:i 'ivI~~t a in; 1:100,000 .

P7 / F. 3/12.

Geoloe ical .. map ' showili[:.


the Muruwa F ormat ion east of t h e Berbice Rivers; 1:100,000.

P7/ F 3/1 9 .

· Ge o loe-ical map ~ho~ine th e M-1:1.ruwa For.qiation west o f the Berb ic e River; 1:100,000.

P7/ F 3/20.

R,T,C2nno~, Geolopist 1:50,000.

Pl/F3/11.

Geoloeyical map of an area south-east of Arakaka; · P4/Pl/ 24.

- Geological ma_'J?:.

of, Bartica area: 1: 100, 000., .

.. .

.. .. 'iii .. ~· l I , 32 .. · · Geoloei¥al map of Kaburi-Rockstone area: 1:125,000.
P6/Fl/2·6'·: i.~,~, Cahnon and K, Bramley, Geoloe;ists · • Report on the Geology of the area south-east .

Arakaka, ·RT·C 2/60 .

..... - : R.T.Cannon, Geolocist, & J,w.

Carter.Assistant Geologist Preliminary report on the-Ge6loeY of the Waini (SW) quarter de~ree sheet.

RTC 1/60.

.,t ~ J,H, Bateson, Geologist ':.

Use of differential thermal apparatus in the preliminary investigat.ion of aluminous laterites in the Pakaraima Mounta;i.ns.

--.. · " .. · · · · .. : .. ~· - ~-:._•.

:--=.· .. . '

J.W.
:--=.· .. . '

J.W.

Lloyd, GeoloPis,t _;· Report on the G-eoloe;y of the lower Barama and Waini Rivers.

JWL l/60.

Report on tlie Geol·o¢.

of the Waiamu ;_ and Mopay Rivers, Cuyuni River.

JWL 2/60.

Geoloeical map of ··lower Barama .River and Waini : River; 1 : 125,000.

P2/F/17.

, , .

, Geoloeical · n'iap .of.

'W<!~amu and )-1opay Rivers ( Cuyuni.

River); 1; 12 5, 000,.

_ P 3"/F 'J/Z6';· ·· ·- J,W,Lloyd, Geologist & E, Williams, Senior Ge<:>logist -Travers·e of part of the Barama River.

EW 2/60.
EW 2/60.

·,./ ' K, Bramley, Geologist Rewa-Makarapan Expedition report.

KB 1/60.

Kaituma-Barima Expedition report.

KB 2/60.

Upper Barima Expedition, 1959.

KD 1/60 Stars ar-ea, North West District.

KB 4/60.

: Note on the occurrence of Nickel in the Five D1 D1 Hawkes, Geolorist south of the __ Puruni River.

DDH 1/60.

· Provisional report on the·Geolo~ y of an area A ·note on the Petroe;raphy ·of the 'Kopinane; sill.

DDH 2/60.

• • l .f ., , ,, .

\ ,1 " ~.-• 33 A note -on .


the Contact Metamorphis.m .of shales of the R6raima Format~on above the Kopinane sill.

D._DH · 3/ 6.0 • Field repor t on the Geology of an · area between ·the ·i'/laza rw:ii and Puru ni Rivers.

DDH 4/6 0.

Geol oe ica l map of an area south of the Pur u ni River; 1:125,000.

P3/F 3/17, S .

Sineh, Geoloeist survey .

Report 6n the upper Mazaruni-Ekereku-Kamaran e SS 1/ 60., .

.
.

Geological map of Kamarane valley, · and f✓lazaruni River froo Ioba i:mada i to Kuwaima; 1: 125,000.

P5/Fl /9 .

Geological map of the area from Monkey Mottntain to Kurune i ku and Ebini Mountains; 1:125,-000.

P7/Fl /17 .

M, W. Carter, Geolopist Watershed.

M11/C.

1/ 6 0.

Preliminary report, Siparuni-Burro - burro watershed.

MWC 2/60.

F i na l Bxpedition report, Siparuni- Burro - b urro Geo1oeica1 map of Karasabai-Annai area; 1 :100,000, P7 /Fl/19,.

MGA 1 /60, MGA 2/ 6 0 '4 MGA 3/60~ M.G.


Al lderidee, Ass istant Geo loeist The Potaro ( NW) squa r e and adjacent areas .

The northern portion of the Puruni ( SE ) square.

Trav erses o f the Puruni and Kartu ni Rivers .

and Map showin e g eoloGical traverses on the Puriari Mazaruni Rivers.

P 5/F3/ 3 2~ L. L. Fernan~es , Assistant Geol oeist Dist rict.

LLF 1/60.

Report · on a tour of the Goldfields, North West Rep ort on the upp e r Cuyuni Expedition.

LLF 2/60.
LLF 2/60.

Dia g ram showine localities of soil samples taken arouncl a e;alena and sphalerite occurrence, Wenaou River .

P3/Fl/10a.

:~ ' .

, R.C.

Sanso~.

Assistan~ Geolopist 34 Repo rt on the Ko pinane valley and the adjacent ar ea t o the north as f ar as Ayanc anna Mountain.

RCS 1/60. "

J _: ' I .

M~p of , a poit:i)::in ·.of central Kopinane; valley showinc Kopinane drilline proe·ram.rae; 1: 6 , 000.

P7 /Fl/ 3.

J,w.
P7 /Fl/ 3.

J,w.

Carter, Assistant Geoloeist Preliminary report on the · Kukui valley-Chinowien t Ayanea nn a Expedition.

J WC l/60.

Ifap of Bauxite reconnaissance survey; Kukui valley Ayan5a n na-Semane ; 1:12 5,100.

P S/Fl/14.

Map of part o f r~~a rane Hill showine detailed pittine of aluminous laterite deposit ; 1 °: 500 t .

P 5/Fl/15.

o. St. John, Field Observer An inven tory of th e Shell Deposits · on the North West Co ast o f British Guiana.

OStJ 1/60, .
OStJ 1/60, .

Report on the e eoloeical reconnaissance of the .

trails radiatine from-·?

ara:makatoi, Pakaraima Mountains., OSt J 2/60.

.

.

Geol.ogic a1 6a:p: of .. t•:ra-il~ radiatine f rom Paramakatoi; l :100,000. ?

7/Fl/12.

. '

- ~ i ; A,o, Edwards, Fie1d Observer - Repo Ft on drillin e Expedit ion, Iron Mountain .

AOE 1/60.

· ..

:.

:,':__ '.

.

: _ _., I, · -· - - - I' ' • : . '

.

1 1!.e:12009.

Map of J'.re l'i lfount,a ,i n .showin e drill holes; .

?

6/Fl/10.

.

.

.

. '


·· .. , ; ' ' .

.

j ' .

;' I 1.

• , :I ,.

, ii .

l. APPENDIX I 34a PRELIMINARY GEOLOGICAL REPORTS Parui.c.a- Wenamu-Ekereku Area by·P.B .

H. Bailey, Senior Geoloeist.

••• Traversesof the North- West and :t.fazaruni Potaro Districts, by·E.Williarils, Senior ••• Geo logist... · ••• Notes Ol'l •tne Peaima Fa11s-Merume River area, by E.

\'lilli.
\'lilli.

:i.ms., Senior Geolog ist A Preliminary Report on th e Geoloey.of th0 Oaai (NW) Qua rter Deeree Square, by R.T. Cannon, GeoloCTist ••• ••• ••• ••• ••• ·Report on the GeoloBY of east of · Arakaka, by · R;T. Br aoley, Geoloe ists ••• th e 1.rea South Cannon and K. • • • • •• B. c. D. E .

F .

The Ar ea between the Corentyne and Demefara Rivers, North of Can ister Falls , by C.N .

· · · , •• Barron, · Geologist •.

• • •.


\ G. Geology of the Tekwa ri Mountain-Omai Ar ea , Rie ht Bank·Essequibo.River, b y C.N.

Barron; ••• ••• Geologist... ••• H. The Geoloey of an Area between the :r,iazaruni a nd Upper·Puruni River s, by D;D. Hawkes, .. • • • •.. Geoloeist.

• • • • • I .

Geoloa of the Kopinane Valley, by J.H .

Bateson, Geologist • •• • • • J.

The Waiamu and Mopay Area, Cuyuni Rive r, by J. W. Lloyd, Geologist ••• K. The Lower Barama and ·Waini Rivers, by J .w; .
• • • Lloyd, Geoloe;ist t , , • L. The Barima~Barama Watershed, · oy K. Bramley; ••• Geologist ••• • •• ••• Vi .

Geology of the Upper Barima and i\.makura · · · • •• River, by K. Bramley, Geolos ist N. The Upper·Mazaruni-Ekereku-Kaoarane Survey; • •• 1960 by s .

Sine h, Geoloe ist • • • o. J.. t ravers e f r ora Monkey Mountain, across the Enwara.k, Akorobi and Kurungiku 'Mounta in to Ebini Mount~in, bys.

Sine h, Geologist •• • • • .. - . '

.


., .. 35 37 42 45 47 51 53 55 57 59 62 64 67 69 I • ~ ..... .. -.-~ ·-·· .

34b ~ ·• l Geoloe;ist P. The Karasabai-Annai Area, oy ·11.w.

Carter; • •• ... • •• Q.

The Puriari River·; by :r-1,G •.

Allderidee, Assistant Geologist • • • ••• • • • R. The Puruni S .E.

·S-quare north of the Peters Mine Road, by riI.G.

A1lderidee, Assistant· Geologist • t • .... • • • s. Bxploration of AltiIJ1inous Laterites in the Kukui and Kamarane River Val.ley, by M,W;.
••• Carter, i~ssistant Geologist.

- .71 73 75 77 T. Report on the Upper Cuyuni River Expedi t i on 1960, by L.L.

Fernandes, Assistant Geoloeist.

79 , .

fl .

.

.

( ·.

: 1· ·, • • . '

· ~ ..... • r- ... •.

tf ' .

A. PARUD'1'..A-WENAMU-EKEREKU AREA By F 1B.H.

B&iley, -Senio~ Geoloeist .

• .. -.~ i : This rep6rt;rde.

:1ls 'with an :u::e,f :of 500 square_ ~il es in the Pakaraim-n Mountains of western· British Guiann which was survfy"ed on .

b :· reconriaiss.
b :· reconriaiss.

:ince basis during three months i n the l~tter pnrt of 1960~ This ragion lies batween the K~m~r.an~ River in the south nnd the Wennmu.River in the Northwest, nnd includes ·a portion of the Ekereku River arid its tributaries in the enst.

The level of the KamnrQ.ng .

:it Paruima is nbout 1600 feet above se.j level wl-iarens the Wennmu in the neighbourhood of ·.

th~ ' Tshu.nu _and :-<:or.

:ibu mouths is about 750· f .eet above se.

:::i"' level.
:::i"' level.

The Ekereku, over much of the portion surveyed, flows at levels betw0en 2600 and 2100 feet nbove se::i lev.e1:, .. in ,.c?- ,.~orth-enst~rl,y dir e ction,.

The hie;hest ppirit 'in the ' surveyed are~ is the mountain of yw-aritipu ·n t _ p bout "'._4300 feet o. bove sea leve_l ~ 4.

Youneer B.:isic Intrusives 3.

Rornima Formntion 2.

Youngar Granite .

.

· ..

·.!

... ~:.. .·• .

.- Rocks classified within the £1tlz.

'.lrnni Gr.oup oc~ur in the northwest in tha floor and.
sides of ·the Wennmu va110y._ · In the v.:illay floor there are f ·cw axposur·es due to deep weo.therine .

:md these wera eenerally- .3mphibo lites, sometimes schistose.

Two localities in the lower T~hunu.

h::i.d schistose amghi1;olite in pl~~e wit~ folia t _ion directions 010~ : ::md 025 with near ver~ico.1 dips.- At .nnc;>ther loc::1ai:ty, where the Tshuau dro,ps over the lowest .,s.and,stona' ·scarp; .

feldsp.athic porphyri·es .

:ind hornfelses were .

.. observed .


:ts , well ns: aruphibolites; tions of 160° and 170°, steeply dippine to the west, were noted .. foliation direc Biotit.e -.

;gt-nnites occur •in tha· 'lower Tshuau and ':these · are assumed :to be part of .1 Youne;er Granite body· int·~udine the Iilazaruni Group rocks and pre-datinc the· deposition· of the ~or.

'.lioa Formation.

The contD.ct between the Mazaruni Group .


:ind the overlying Roraimn Formation lies nt about 1980 feet above sea level at the Tshuau fall and this is consi stent with observations made at the two places where trails cross the lowest escarpment.

The Roraima Formation consists of fine-to eoarse~ e;rained sandstones, pebbly sandstones, conelonerates, shales ~nd qunrtzites found in horizontal or ~ear In the area surveyed the total horizontal attitudes.

thickness must be in excess of 1500 feet.


The conelo m6rates are the most resistant nnd are responsible f 36 for the scarp faatu:,:•~$ .

t _o tha nq,:-th of the :i<.am.aranp valley and lininp the savanns of Aym.

:i.toi, ond also tha lowest Wen~mu f;3~D.pps to th.e west , of the Kor.

:ibu savannas.

Cone;lo~erate peobles are eener.

:1lly well rounded and are predominnntly of quartz, althoueh sandstone, quartzite and acid volcanic pebbl.as may occur.

T~e rounded pebbles seen sandstones ~re simil.


:i..r, The sandstones are doni::i.:intly quartzose an.cl in _ thi_s· ··c1reo.

f.aldspat,hic -rvarieties are rar-3• .scattered in some Some thin beds of horizont.

:i.1 grey and purpie shales :nay be seen below ·the lowest Wenumu scarp nt ari elevation of 2300 feet on the trail west of Tshu.

:i.u, The u...""lderlying i:-o~ks were obscured by talus.

but the shnles appear confor.muble -with the cone;lomerats above and are classified as Ror3ima.
metamorphosed by the unde~lyinp eabbro sill, ~ccur at 4200 feet on qwaritipu.... ·Hornfelses, shales, · · Observations oz fore.et bedding in Roraime.

s3ndstonos i ndicate depositional · current directions to the west 2nd southwest, which conforms with obsarvations over a1 nre3 includine the Kako, Partnng and Heieka rivars • wide Younger Basic Intrusives occur in the form of two dolerite sills.
The lower~ or Kamarnne, · sill is present in the south and appears t o be about 850 feet thick in the Uluk creek althouch i t may v3ry elsewhere.

Specimens include aueite dolerite and biotitc-pyroxen~ dolerita (with bot~ cli3o- and ortho-?yroxene).

The upper sill occurs on l>waritipu and to the west .

:1nd northwest of that mountcin.

On Uwaritipu the sill a?pears to be 500 feet thick.

Specimens collected include aueite dolerite, biotite- : pyroxene dolerite, noritic dolarit~ and hornblende dolerite.
Prospectine ·of creek ~lluvinls shows thct both GOLD and DIAMONDS are associ~ted with the oonelomerates and that eold oay be a fairly reliable 9indicatorY miner2 l for diamonds in alluvial 5rivel.

Two small diamonds·were ·recovered from a right bank tribut3ry of the Ekereku.

I l • BAILEY, Haieka, river, r. B, H •, ·l-9 59.

A :t-econnaissance.

, aurvey of the Kako und · Kukui river ar~as · of the .u pper Mazaruni Ann• Rep, for 1958.

Gaol.

Sury.

B.G., p.32.

I: ' .

,.

. '

-...·· : !, .

.


• \ I i '-1 ' ' ' .

B. TRAVERSES OF THE NORTH-WEST AlJD MAZARUNI- • I ' : ' P0TAR0 DISTRICTS ' ' ,: by .'

··.

: E.

-_:Wj.

).Ja,ams, Sen.J&J' G,~ogist 1' " : [ ' - ;·,: .

_! '

Dur;i.ng: ·February-April, 196 0, a number of river traverses and a railway traverse were made by the writer with col;I.eagues • .Kiltwna-Matthew~v Ridge Railway Between the 15th and 29th February outcrops o ccurring .
alone tnirty miles of this rnilway yere examined by K. Bramley, R,T.

C~nnon and the writer• The · work was c~rried_ ,9t1t , ur>:der the writer Y s supervision.

:ip.terb'acicted quartzites, manganiferous quartzites, and ~ _udstones .occur best eXposed near :Hat thews' Ridee betwee'ri _the railwey mileposts 26 and 30.
The mudstones are normally represented by clays colour-banded parallel to orie;inal beddine• The quartzites are up to two feet thick~ This sequence is folded in a convolute manner, for the folds die out to a smooth base and top.

The general strike of these rocks is 070-250?

which is also the strike of the axes of convolutions, and they dip 30° to 70° to the northwest.

These rocks are much in truded by feldspar porphyry and the contacts are sharp and variously disposed.
Phyllites and slates, probabiy derived from mud stones, are best exposed between mileposts 17¾ and 19¼, and 25½ and 26 respectively.

They are uually weathered to colour-panded clays.

Their aee relationship.with the qua_rt_zites and mudstones was not determined .. Amongst the phyllites and slates are tabular b odies probably of igneous origin of amphibola schists, recoe nized by Braraley·as such on thin section examination, and e~eenschists.
Quart:i-feldspar porphyry, which intrudes phyllites (milepost 17¾), · is often deeply weathered to ban~ed clays with an extensive.

surface residue of idiomorpffic quartz grains up to 4 mm.

in size.

Plana;:, rias·ses of brownish clays behave tr.ans gressively towards the phy11itas and quartz- feldspar porphyries in which they occur~ The original rock type ieneous origin.
is unknown but appears to ~ave been of A regional foliation,associatad with a low green schist facies · erade of metamorphism, sweeps through all the abovementioned rock types with ·a e eneral ENE-WSW strike,.

'Between r.-iileposts 5¼ and S½· a boundary between.

phyllite and fine-grai.~ed amphibole schists may be· observed, .
:.nd it is avident the:\ t the reeional foliation .. crosses the boundary rsecrdless of rock type, although • ~tsewhere it eenerally appears to be sub-parallel to t~e rock dist~ibution tre~d!

The foliat~pn_ i~ so weil .

: ·· 1.

Bramley, K., Cannon, R,.T., and 'Hilliams, E~ .

,Report .. • ' No.

E'W 3/60, Geol* Surv.

B._G,.. Unpuqlished.

.

... / , .. 38 developed that much of the original textures and structures of the rocks, which may have aided in deterraininB relative aaes , are obliterated.
At milepost 2 is a quarry in biotite-aeeirine eranite2 in which minerals have been alienad, probably by flow.

Simple pegmatites, containine small amounts of fluorite, are associated/4,ith the er~nite • .

, ~ed;i.ur.i-erained dolerite sheets of varying thic~nesses intrude all the rock types encountered in the traverse.

Dislodged blocks of the oarsinal country .


rock occur within the dolerit~ dykes near milepost 30, The dolerites and the biotite-aegirine 5ranite are of later aF,e th~n th~ reeional foliation affectine the other rock types.

Barima River Fron 1st to 6th March, K, Bramley, R.T, Cannon and the writer checked previous work and mapped the rock exposures· in the Bari.ma Rivar between Eclipse Falls and Koriabo 3.
The results of the Kaituma-Matthews' Ridge Railway traverse and this traverse was subsequently successfully made use of by Cannon and Bramley in the regional mapping o"f the area : to the south-east of .

Arakaka4.

· Red; buff, and ·black-b~nded white quartzites are encountered s·om:e three 1:..iles : downstream frora Arakaka • Generally., the •quartzites are fi..11e- and compact.

quartzites occur.

These rocks are considered to be an extensi on ·of the quartzites and mudstones of Matthews• Ridee.
However, horizons of flae;r,-y sericit,e to coarse-grainad Phyllites with occasi·onal e;reenschist horizons outcrop to the north, both.

upstream and downstream, of the quartzites.

Examination by Cannon of a thin section of a rock near Arakaka indicat es that araphibolites, euhedral and cross~cuttine the foliati on, are developed in a quartz-chlorite schist.

A reeional foliation sweeps throue;h these rock types with a general 3-W· trend near Arakaka and NE~SW trend below the Honkey Falls granite_.
The fpliation is associated wit:h· a gree'n-schist · facies of metamorphic erade, Quartz boudins, related in oriein to minor folding of the foliation, occur in a sericite rich· horizon two miles upstream from the ra i lway bridge.

Lineations - of the crests and· trouphs of contorted quart_z ··veins were recorded, .. , Biotite eranite, with feldspar phenocrysts and pPobably·flow · foliation ·occur at Eclipse Falls5 and Monkey·Falis2.

Sim~le pegoatites are rare.

No· .

; ..... '.

• • 2.

Braaley, K. 1960.


Kaitu;:ia-Barima Expedition.

Ann.

Rep. f for 1959.

Geol.

Sury.

J;3_.c; .

, PP• 50-52• 3.

Bra~ley; K., Cannon; R.T., & Wi_lliar:lS, E. Report No.

EW 4/60, Geol_.

),urv.

B.~.• Unpl:1,blished.

4• ca·nnon, R. _T •, a~d Braraley; K. This publi<?a tio~ p. 44-45 5.

Bramley, K,.

.·1960.

Uppor ·aarima Expedition.

Ann.


Rep. for 1959, Geol., ·s.urv~ B.G, ·· PP• 52-54. f;/ 3.q observ~d disturbance of the reeional foliation desci;:ib.ad .a,cov:e is · as~oci a ted with t he emplacement of e:,i.th-~r-: ·gran~tas.

· To : th.~ .

'~~~:t, of Monkey ·Falls granite, .

andalusites are deyeiope<;I fl'lone .

the foliation planes of the phyllites.

,.

· In· .general, the_ir size ·increases to tfle .

L-~ _one .

locality ·laree (up to 2.5 er~nite ~o.µridary • ems.)
andaiusites occur · in a ··psam.mitio horizon.

'i'o the .east ,of .

the, _er,;3-ni_te small ; ·(7 )garnets appear in the phyll:i'tes.

; · · Of interest.is the _occurrence of a belt of schistose eran~te, some sev,en miles downstream from r-:onkey F3.ll~.

is sor.1e three-q:J.arters o:f 2- mil'e in width, and · althoueh ithere is no notable dislocation alone it in the •river.

section there·may,oe l~rge displaceoents elsewhere along its length.

'.
'.

:'his s:1e~r belt, .t:rending ElJE-1,ISW, The -boundary of the Eclipse Faits g ranite exposed in the rive:t;> is marked by schistose rocks, which appeared in- thi::i sect.i.on t.o Cannon to ; b e of apparently · mechani cally sorted layers of quartz, feldspars, apidote and chlorite-biotite.

This shear belt is of a similar · direction to that descri'!

::- ed immediately above.- I1iedium-grained dolerite dykes of NE-SW trend cut all the _rock -types licted above • .
, Lower Barama River 'l'he writ~r visited J.~•T •.

.

Lloyd _ from the 9,th to 18th March, and they mapped.

the rocks exposed in ·_the Barama ~iver ·between Kokeri t Hission aqq St. Bedes t ·.

Mis~ion • .

· .. : Cannon and Carter7 defined ' .th~ .

Ko~erit Formati·on-· as consistingnmainly of schis·t's.

,., • .derived· from .

ps.

?,,r;~,.,litic sediments with a well-defined coneloinerhte·· band a·:nd ,·o·ccasi-0nal pecb.ly horizons • ..
Subordinate pelitic : rocks· occur ·.and .eltered favas; (formerly .

.

au~ite·-andesites) · are inte~calat.ed ;within, .t_he, schistsit (p.'4'5}.

· It was· considered possible that ·the·· format~on reseci.bled: ·the Western and Ce:Ttr:al _C:uyu.1i'i Fornations • In g eneral, these descriptions and conclusions were confirmed durine this ~pedition.

l : • • • All the rocks are foliated ·and a c a taclastic texture is dominant.

Calcite and .
Calcite and .

siderite rhombs, which weather to lar t e limonitic patches, occur ·in a number of horizons.

/the The sediments of/Kokerit Formation.

are turbidites usually _· of fine-erai!led sil;iceous siltstone_s, sandstones, pel::bly sandstones and con e:loaer_a:tes • The .. pebble dis- tribution indicates · poor- sorting and eradat,i_on within · · 6.

7 •.

8.

·'& \ 7illiar.15, .

z. Repor.t No~ .

EW 2/60, Lloyd., J. W ~:, Geol.

Surv·• B.G, ., U:ipublished.

Cannon, 2.T.

& Carter, J.w •.

1960.


Report on the·Geoloey of' the ·Waini Deeree Square.

Ann.

Rep• for 19 59.

PP• ~-4-45,.

Williams, E,, Lloyd, J.w.

& Hawkes, n.n.

· 1960.

Cuyuni River traverse.

P.nn.

Rep. for 1959, Geol.Surv .• B .• .G.pp.39-41• A pr el imi::::i.a ry 1 {SW) ·, Quarter Geo.L.. .. _Surv,.

13,A.

• .

,.

·.s1 .

: - depositional units of norma11·y a foot or so in thickness.
At Maikuru Rock the -conglomerates are coarse with pebbles up to two feet long, and an analysis of the grains lareer than 4 mm in one horizon shows that some 93% were · derived from quartzitic rock types, and 7% fron phyllitic.

Mud stones 9onsidered to be nnormal" deposits, and their · metamorphic derivitives are uncommon in the sequence.

Fine-grai ned igneous rocks occur about a mile up.. stream from Kokerit Mission, and also about four miles upstrean from Mn ikuru Rock.
They are often grey or ereyish-green in colour with saussuritized plngioclase tprobably albite), ragged amphiboles and bundles of chlorite set in a quartzo-feldspathic groundrrnss.

Immediately to the north of the Kokerit Formation exposures, quartzites, normally cr~am coloured, extend from some two miles upstream from Tasawinni to a granitic occurr~ncefive miles downstream.
The quartzites are usually medium-grained, sugary textured, and contain sub-rounded zircons of sedimentary origin; are rich in manganese oxides.

Flaggy sericite-rich horizons occur, which when deeply weathered resemble weathered phyllites.

some layers Quartzites, normally interbedded with phyllites, associated with occurrences·of maneanese oxides are typical of the Barama Group.

It appears l ikely, there~ fore, that the rocks at Tasawinni belone to this group.
The mineralogy, ·textures and structur es of the rocks~of the Kokerit Formation match exactly those of the Western and Central Cuyuni Formations8.
By compari son, the Tasawinni quartzitas are of a similar s-tratie;r·a phical position to the quartzites in the Kutuau River mouth area in the Cuyuni River, and underlie conformably the Kokerit Formation.- · A regional foliation, of a eeneral WSW- ENE trend associated with cataclastic textures and the development of sericite,chlorite; biotite and actinolite-tremolite, occurs throuehout all the rock types.

Pebbles of .pebbly sandstones and conglomerates have been rotated into the foliation planes.

.

;'.
.

;'.

( ( _• : .

: : •, .. ..

Many beddine plane readines were obtained within the Kokerit Formation, although a fold pattern could not be determined.

Puruni River The writer worked in the·Mazaruni-Potaro District from 26th March to 29th April.

Much of the time was .spent with 11.G, Allderidge -mapping· the rocks exposed in the Puru.ni River between its mouth and Paiyuka Falls.
Gneisses and amphibolites of the Bartica Assemblage, foliated in a eeneral N-S direction, are encountered between the Puruni River mouth to near-Peter's M.ne.

.

, .

Younger Granites are represented by a biotite granite I .

I 'f .

.

\ ... .. .. with quartz phenocrysts, which extends from the northern boundary of· the -Bartica · Assemblage to near the Mara-Mara River mouth.
A pre-Younger Grnnite sequence of sediments and fine-grained ieneous rocks occurs between the northern boundary of the biotite granite and a thick dolerite · inclined sheet forming Paiyuka Falls.

This sequence, for purposes ·of field inappine,has been termed the Puruni Formation9.
The Puruni For ation consists of siliceous turbi dites - poorly sort0d but graded cone;lomerat-~s, pebbl y · sandstones and sandstones - interbedded with mudstones, which are believed to·be the 'normal' deposits of the area.

Included within this formation are fine-erained · irngous rocks c·onsisting of feldspar porphyries and rare rhyolites.

The Puruni Formation matches in mineraloey, textures and structures ~he rocks of the Central and Western Cuyuni Formation, and th3 .
Kokerit Formation described above~ Regional mapping has shown that the Puruni and Cuyuni Forwations are in continuity.

A regional· foliation is developed throughout .

the Puruni Foroation -and trends approximately ·wNW-ESE.

The rock constituents have been rotated and entrained in the foliation:.planes, the devalopment of .

which is associated with a gr,3enschist facies erade of metamor phism.

· ------------ Unpublished.

9.

Allderidge, ·M.G.

Report No.

MGA.

2/60,.


Gepl.~ Surv.J:}_.G_~ C. N0'1"ES ON THE PEAil-~ F.t.LLS-MBRUME RIVER .. ii.REA by E, ~villiams 3 Senior Geoloe:ist 42 ;.

• River sections in this area ware·mapped between !-1r J.w.

Lloyd 24th Septaober and 5th Novam~er, 1960. accompanied the writer for the last -three weeks of the expedition.

Theoe notes supplement Bulletin No.

•291 and repetition of inform.

:ition e;iv0n in the publication has been avoided 3S far as possibla.
The oldest examined rocks of the area belong to to the Maz2.runi Group2 which has been defined as correspondine- ..3Xactly to the Volcanic Series3, which .

w~s ·first map·ped in the Maza:.

"uni and Puruni diacond areas.

Provision~lly the eroup is subdivided into · (1) the.
Cuyuni Formation which is defined as consisti~e of those rocks which have been correlated by regioncil L1 mappine 3nd lithology with the Central Cuyuni Formation', the Western Cuyuni ForcationS, the Kokarit Formationu, and the furuni Formcition:7, and (2) the· ;Haimaraka Formation;,formerly known as the Haimaraka Shales.

Regionnl mapp"ine has· ch.own that t!-ie Central ·cuyuni• For:nation is co:iJ.

:.inuous with the Puruni Formation~, and the Western Cuyu!li For1:W.tion.has .been .
.t.raced .to the vicinity of Fleming's Island in the area under .

consideration.

I ' The type area of the Cuyuni Formation is that of the Central Cuyu:ii Formation4, which is~ mappable unit extending froo the Quartzstone eranite to the eneisses a.nd GTanites of the Devil's Hole rranee in the Cuyuni Rivar.

The best section of the formation is exposed in the Cuyuni between Quartzstone eranite and ?igeon Island.
as "consisti3g of laternlly impersistent tongues of pradominantly (1) conglonerates, pabbly sandstones and sandstones, and (2) porphyritic fine-erained ieneous rocks"• -:\Tilliams4 has described the sequence .

/ i.n The Cuyuni Forr.iation/ the ?eaima Falls-:t'lerace River area is represanted by poorly sorted conelomerates and sandstones, with the coarser fraeraents, up t~ 6. i~ches in leneth, usually of quartzite and phyllite.

The finer material of the sedi:J.ents is quartzo-feldspathic.
Between Anabarone xivar coutl-: ·to ~ear Illiwa Island con glot1eretes contain well-rounded fragraents, up to 13 inches in length, of feldspar porphyries in 2. quartzo-faldspathic matrix.

These sedir.1ents 6~ the Cuyuni Formation are believed to be turbidites.
Associated with the older sediments are fine grained ieneou.s rocks, which are c enerally porphyritic and usu~lly of internediate composition10 • Meta dolerites with hornblende schist developed at the marein in soma localitiesl:, appear to ba confined in the main to areas of the Cuyuni Formation.

.

.,,.. .

. '

Th .·.

.


ima aka Formation, forcerly known as the Haima~a""~is a1es, is best exposed in the Mazaruni River between· Issineru River mouth and Ille.ma Island, arid in the Issineru and Hair~araka Rivers~ This is the type area o.f the Formation.

Tl:e tero.

'shales' has been discarded for no true ·shale has been found within the seqµ:ence.
The Haimaraka Formati·on in its type area is a aonotonous sequence of banded erey Dudstones interbedded with greywacke sandstones, · considered to be turbidites.

The sandstones are poorly sorted and eraded with variously shaped frae;ments qf qunrtz, feldspar and mudstone set in a mudstone natrix of quartz, feldspar; sericite and chlorite.

Occasional interc~lations of conglomerate with uudstone ·pebbles have been noted.
To the east or the area in the l-ierume River, this· fonnation is repre sented by a predominant1y deep_r~d coloured mudstone sequence with rare sandstone horizons .• ; .

: i .

.

.

; .

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.

'.

.

.

, (, ... .

.

The Haimaraka Formation is folded about a synclinal axis stee.ply ·piuneine' :to ' tt:e south-east in the Issineru River-Illoma Island area.

Available evidence indicates a conformable relationship between ·the Cuyuni Formation and the overlying Haimarcka Formation of the Mazaruni Group.
In the Merume River area cross-foldine occurs within the Haimarakn Formation resultine in a basin and dome structure.

A secondary reeional foliation, in eeneral striking NW-SE affects the roc!

::s of the rfozaruni Group.

The foliation is more noticeable within the Cuyuni Formation, and quartz, feldspar, sericite, chlorite and biotite have been noted developed within the foliation planes.

River mouth area orie:inal features have been obliterated and ch1orite-f?

)"albite, and quartz-(?


)-albite-sericite schists occur .~ In the Kurupung The Younger Grani~ are represented by biotite granite gneiss, hor~blende-granite, quartz-diorite, eranodiorite and syenites.

Granite country rock contacts have been observed at Enachu, Illiwa Island, the northern eranite boundary in the Epine River and in the Kurupune River where a boundary granitization phenomenon has been observed (McConnell, verbal communication).

REFERENCES 1, POLLARD, E.R.

1956.


The Geology or the Issineru Enachu District, Mazaruni River• British Guiana,.

Bull,.

No.

29, Geo;t_._ Surv.

B.G .. 2, McCONNELL, R.B.

1958.

Provisional Stratieraphical Table for British Guiana.

Ann.

Rep. for 1957, Appendix 1, Geol.

Surv.

B.G~ 3• CONOLLY, H.J.C.

1925.

Preliminary Survey of the Mazaruni and Puruni Diamond Fields, Special Report Report, Geol, S1.U'.~• B .G.

4• LLOYD, J • ~'l., and WILLIAMS, B,.

In press,.


Report on the Geoloe;y of the area between the Arawapai Creek and the Central Cuyuni River.

Fifth Inter Guiana ' Gaolo~ical Conference Georgetown, British Guiana, 1959~ \ 44 5.

WILLIAMS, E·., LLOYD, _J;i-v., and HAWKBS, D.D.

· 1960.

Cuyuni Riv.er t.raverse.

Ann,.

Rep,.

for 1959, Appendix l C, Gool.

'Surv.

B.G.

.

6.

CANNO:N, ~.T, and CARTER, J.W.

1·960,.

h. praliminary report on the geology of the Waini · qu3rter degree square.

Ann.
Ann.

Rep., for 195911 1~·ppendix 1 F, Geol, _Surv.

B.G.

7 .

, WILLIAIV'iS, E,.

This publication P• 38 8.

ALLDERIDGE, M.G.

This putlication p. LLOYD, J.w.

This -~uhlicatioh p. 9.

POLLARD, E.R.

1951.

Report .on theMekuru arec'.

:\, Cuyuni River,.

Ann.

Rep, ~or 1950.

Appendix IV .

Geol.

Surv.

l}_ .. G. 10,.

HA~4ILTON, J.

1951.

Report on the Werush:i,ma-Orlowra area.

Ann.

Rep. for 1950.

AppE:l:ld ix V Geol.

Surv.

B.G • .

• ' • ·- • t' - 1.· .

.

.

.

; .•. '

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r .. A ·• • 0 • I !

·,• .

•.!

: ... .

•·· .. .

J' , I • • _D _.

.A PRELIM:INARY REPORT ON THE G30LOGY OF THE OliIJ.

:;: ( NW) QUJ..R'!

'ER DEGREE SQUARE by R.':' .

·cc.

:mon, Geologist · : A reconna issance l:il:lp on, the scale 1:125,000 .

of the Omai ·( Wi) quarter dei::re.e · square was made .during the second f ield season of 1960.
This square is located between the p a rallels of .latitude 5°30 'N' and 6°N and ·:meridians :·of lone;itude 58~30 9 W, and 59°~:T • .

The followinc eeolog ica~ units were mapped: .

Superficial Deposit§..t.. ;llluvium and laterite White Sand Formation: White and brown sands Yo:unre r Basic L~trusives: Gabbro and dolerite Younger Granites (?
): Biotite g ranite and bioti te nicrogra n it e Uncorrelat:ed: Hornblende anorthosite Bartica Assei:1blage: Porphyroblastic gneisses, b iotite gneisses and granites, hornblende-biotite gneisses and amphibolites.
Amphi b olites, biotite gneisses a nd hornblende-biotite rt large area of porphyroblastic eneisses gneisses are interbandetl on a large scale and are an in the Ba1tica e xtension of the Bartica Ass~1blac;e quarter deg ree s q u are i~mediately t o the north• Occasional irreeula r 2reas of b iotite g r anite occur as sociated with the b iotite gneisses and are part of the same cycl e .

on the Essequibo River ~orms a unique, oappable unit.
Abundant , large {up to three inches), perfectly euhedral, zonad crystals of perthite weather out to form protuber a~ces on the rock surfaces.

The crystals are clearly porphyroblastic enclosinE, hornbl ende, ql.lZl rtz and plagio cla se o f the matrix.

~he ali gnment of the K-feldspars is discordant to the folietion of the surrounding gneisses (as defined by the mafic miner als) and i t is suggested that this localiza tion of K- fel dspa r was formed late in the metamorphic-raetasomatic cycle.
Hornblende anorthosite occupies a lar ge area i n the Kaburi River.

The rock is of striking aspect con sistinc essentially of large placioclases with stitial bla ck amphibole.

The anorthosite is of variab le g rain size; the plagioclase occurs as euhedral crystals froo a half i nch to four or five inches lonE and the umphibole varies fro:.1 sr.iall interstitial areas to large cp~abals, also enclosing t~e plaeioclase, the largest noted b eing- twelve inches lonz.
Prel iminary measurements on the plagioclases i ndica te a composition on the labradorite-bytowitlte border.

The anorthosite has an irree;ular, finer-grained facies near the marein with the Bartica Assenblage which, toeether with the inter " 46 cranulated nature of the fabric, sucg est that the anorthosi:te'was· --probably --in-truded- -into -th?- cneisses of the Bartica AsseQblaee.

· .. , .. : .... ... - .. ' . '

.. .

: .. ..: .


Areas of biotite microcranite around the 1:.iouth o-7 the Kaburi Ri_ver and biotite cranite on the Essequibo River intrude the· Bartica i,ssembl-ae;e and have ten tatively been assigned to the Younger Granite~.

Dolerite dykes intrude all the above rock types, 2nd the Youneer Basic Intrusives are also represented by Arisaru r-:ountain, a latte, laterite·.

:..c2.pped c abhro intrusive approximataly · _9irmllar in outline.
; · White and brown sarids of the · White Sand Fortia tion occupy·a considerable area of the present q u arter deeree square.

The 1ar5e a11uvial flats were mapped: from air photocraphs in addition to the leterite caps occurrine; on ·the amphibolites of Bbini Rills .. -aod the c~pbro of Arisaru b:owitain.

The hornblende anorthosite in the Kacuri River .

.

.

~ .. vn11ay could be a source.

of the .

o:in.~r;3.l -.. FBLW.FAR.

REFERENCES 1.

CANNON, R.T. 1960 .

Ati the 3a~tice Area.

r~port.


.... :, .. ; ·· • .

'· .

·· .. :.

.

: ...

I .

.. .-, • : ~ : I Outlin.e of .. the G.eology of Geol .. .S11r-v. B .r..

Unpublished "' , :.

.

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' .

I ."

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.'

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.. .•.

.

:.

: .... : - .

.

: .. · .. -· .

~ • • • j ,!_ :··_: __ -~-::.'

.. ~--.

.. .

1 · • · ....... .

: :· ~ .

• ·. '

I .. · : ·, i E. REPORT ON THE GEOLOGY OF -THE AREA SOUTH · .. EAST OF ARAI<AKA _, .

:; : by R.T. Camion & K~ Bramley.

Geologists .•·.


47 The followine fomations have been designated and _mapped in this ar~a: Superfici-al De9osits Youneer Basic Intrusives Younger Granites ?or'phyry Intrusions Tenapu Formation .

1':iatthews 9 Ridga Formation Arakaka Formation A11 · the _·above i:-ock types, excapt the Tenapu _Formation, .

were characterized ·by mappine the Kaituma-~:atthews 9 Ridee railway and the Bari.ma River (see paee 34 ab ov e) .
The information so obtained was successfully nade use of in the mappinc of the present area.

The Arakaka and Viatt!l.ews 9 Ridge Fornation should ce considered as an intecral unit with no stratigraphic si5nificance atta ched to the above order.

The Arakaka Formation is 1ominantly pelitic consistine of phyllites and raudstones with subordinate chlorite schists occasionally anphibolitic and representing original basic intrusives) and quartzites.
The Matthews' Ridze Formation consists of interbedded phyllites and quartzites (approxi mately four thousand feet thick) forming a well-defined ridee.
The various rock types at H:atthews 9 Ridge exhibit a distinctive fora of convolute foldine and are locally .matlcaniferouso ~he Tenapu Forraation is considered a large, locally defined area of metamorphosed basic intrusives· with subordinata psaramitic horizons and rare phyllites, The basic rocks (now chlorita schists and amphibolitas) which also invaded the Arakak.a and Matthews' Rid~e Formations / foldine later than the development of convolute/which ante-dates all other phenomena .
Porphyry Intrusions, quartz- feldspar porphyries a nd feldspar porphyries, occur within the above mentioned formations.

All the previous rock types were subject to a low Erade metaoorphism convertine mudstones to phyllites and basic intrusions to chlorite schists, etc.

The meta morphism was within the lower Greenschist Facies and the railway traverse demonstrated that the-impressed foliation is independent of roe~ type distribution.
The railway trav erse also denonstrated that the above foliation was subsequently corrueated.

The air photographs e xaoined in the present area show abundant evidence of folding which proved difficult to astabl ish on the g round and also difficult to relate to foliation.

Faulting accompanied this period of foldin e .

The Younger Granites are represented by the Monkey Falls granite (prob2bly syntectonic) which was emplaced with concomitant contact netanorphism.
The spottine of the phyllites with the occasional development of andalusit e dewonstrated on the Barima River traverse proved a widespread phenomena around the granite. '

Psaomitic horizons within the Arakaka Formation contain garnet, Btaurolite and kyanite.

The latter schists are intimately associated with e~phibolites whi ch were presuoably also formed by the thermal effects of the granite."

: Rocks.
: Rocks.

of the aureole adjncent to the eranite are within the u~per Araphibolite Facies in contrast to the bulk of the rocks in the present nrea which .

:ire within the lower Greenschist Facies.

Retrogressive meta orphisn is shown by some 3 phibo lites within the Ten~?U Formation.

The Barimn River traverse showed that f~ulting and shearine occurrad after e;ranite er.1plncer!lent and .

'.l well defined shear zone was mapped within the cra~ite on this traverse.
The intrusion of the Younger Basic Intrusives was the last major eeolosical event in this area.

The Superficial Deposits consist o~ the alluvial flats of the rivers 2~l irregular, laterite caps on the a~phibolite hills.

; ' ' 49 ·F.

.

,·t r {,, :· · 1~.EPORT mr :'HE !.?.

},A BET~1lEEN THE COR3NTYNE .. .

- .

liND DEr.,r,:Er..i.?J..

RIVEP..S NORTH OF CANNISTER FALLS .-"\• 'I .

.


b~ c, N• Barron I : ' The followine form:,;tions were raapped: 'White Sand Forraatiori Laterite Youneer Bnsic Intrusives Rorairaa Formation Youneer Granites Iwokr.

::i.ma Formation r1uruwa ForDct.ion Sedimentary and volcanic rocks of tha r'iuruwa :lestine on the Iwokrama Formation and Iwokrama Fornations di?

generally southwards under oost of the area, ond are cut by several small granite int'rusions·.
is a considerable outlier of the practically flat lying Rorairaa Fornatio~.

All these rocks are intruded by dolerite sills .

a ;.id dikes which are correlated with the Youneer Ensic .

Intrusives.

The Rornima Formation outlier forr.1s a series of hieh, concentric mesas., whose base is largely concealed by extensive White Sand Formatio"n which cl.so covers·most of the low , lyine country ~round the outlier.
Several of the l~rger dolerite intrusio~s are now covered by vesicular la terite, · ~he Muruwa Formation consists in this area of '::he roe~ is not well e;raded, and graded some 4000 .

fpet of clean quartz.sandstone; with occasional red qr bl&ck cherty e rains.

?etble beds occur.locally, and ·botn tl1,e pebt)las and.

sand grD-ins are rounded to sub-rou.n.ded.

beddine is rarely seen~ but curre:J.t bed.d1ng with · foresets from 6-18 inches·deep and facine rouchly '.rhe matrix is lareely westwards .
is quite con1:.10n.

recry:stalliz.ad , and tha· ·iar-ger era ins raay ·shpw cata-:, elastic effect~~ Pale brown b~otite has developed·· in the v~cinity.

of rare thin strincers of iron oxide r:;ranuleo.

The Muruwa Formation has now been followed from 'i'Jarakabra falls on the Corentyne, to a po1nt some r.1iles wast of the 3erbice river.
· · - Foruin~ a con~orraable transition wit~ tha overlyine volcanics of the Iwokra02 Formation are .a few hundred feet of sandstones a nd red siltstones interbedded with small flows of intermediate composition.

These sedirae~ts, while to those already Qescribed are oore.

often larcely composed of sub-rounded cherty .

erains • including quartzitic types s1miler .

., The Iwokrama Format;io::1.: was examine<i in the areas .
immediately to the north of the Roraimc outlier, Here i:t consists aln:.ost 3n'tiraly of acid flows .with variable amounts of quartz n;.,.d feldspar crys;tals in a stronely flow-banded aphanitic ~ilatrix.

50 The Youneer Granites are .repres~nted _by the Ma rlisc.

:a Gra.nite, cl .. ~n ~l l intrusion on the·· Berbico River, which h a s c~used· some recrystallization of the adjacent Iwokrama vol c anics.

It is a oadium c rain ed, unfoliated rock, with pror..linent red-brow!1.
microperthita, sericitizad oli5oclase, chloritized b rown biotite and iron oxide.

It _carr i es no xenoliths.

The Roraima Formation lies unconformably on volc anics Its base here is of th~ Iwokrama For mation.

Its base is covered by the White S and Formation in the Deiller~ra basin, b ut is well exposed in tha headwate rs .of th0 .

Kamw.

:1tta and i'fa rlissa Rivers, which drain into the Berbic a .
about 200 feet r-'i .S .L., and the outermost scarp, which was exauined in 6 :;_Jl c.c e s, rises to about 600 feet.

The formation consists of co a rse, current-be dded sand stones and pebble cons l omcratas · (increasine upwards) with some 20 feet of red ,fl~ eeY, ripple-marked mudstones around 350 feet i~.s.L.

The crains and pebbles are of rounded quartz .a3d very minor fine-~rained sandstone and ch e rt.
h few thin b eds carry unsort e d anD,Ilar fraenents resemb linc th e underlyinc Iwokr3na volc a nics, a~d these occur both ne~r th e b~se and a ssocia ted with the red sandstones, Secondary ailicific·ation is pro rainen t in f resh sc:.ndstone , and authig•uic r.iuscovi te occurs nccr t ha basa.

~· .. e The Younc er Ba sic ·Iatrusives a re r epr e sent3d down the Roraima • sc ~rp a few s mall intrusio:1s up ?.nd and by a L'.

:lrcc · i :itrusi on.

forr.iinr:; 2.


_ ridee behind Dorinebanc; landin c , on the Berbice ~iver, ?he latter is a medium e;rained · dolerit e for the n.ost part, but a stri ~<.ine; variety, wi th lare;e :?e_ldspar phenocrysts is locally fault3d aeainst it, A flow-banded basal t in th e Eerbica River below Kuia lake nay be a raarginal faci3s o~ the sa!
:lle i:itrusion, Laterite covers the Dorinebane dol e rit e r .idee, a nd also occurs below the s a nd in any placa s · o·n the Muruwe sandstone ridge ,.

2.t a tout 27 5 feet i:·: .s .

L. It ~orms a sh e et o~ Christie hill where i t ris ss to 576 fee t rfi,S .L.

in the south.

Dolerite is e xpos e d around the hill foot, .

.

Th e ~Jh ite Sand Formation is repres ented in the wes t b y an extensive s~d pl a te~u lyine between 200 and iI ,S.L which h a s nowhere "!
)een· penetrated i::y 1 50 fee t t he· Denerara River or its tributaries below Canister Falls; It also hides the base of the Rorai.n~ For21nti'On in -this area.

Its base edee of the plateau.

Further east, brown and white sands attricilted to the f or~~tion stratch between the Berbice ~nd Corentyne Rivers, b ut a lthoug h it.

is much aore dis secte d here, even the ridce forme d.by the harder roc~s o f the Euruwa F orraation, :..s o.1ly axposed in the botto4lS of steep e;tillies in the s2.nd.
is · about 150-:-_200 fee t alone- th e eastern · J: l luvial DIAMONDS have bea:!

:1 worked in the Kar.1atta head, wher e th~ · Mi:ite Sand Formation h 2.s been stripped fror.i the base of t he Ro-raima outlie r. KAOLIN occurs below the white and ~rown sands in ·many places.

There is some alluvial GOLLJ in the Dorin£ba n g area, but the E uruwa and Iwokraril.a Form2tions show no other evidence of cineralization.

.

.

.

, 51 G. GEOLOGY OF THC: TAKWARI MOUNTAIN-O!

'!.lAI AREA, .
'!.lAI AREA, .

'.~i· 'RiGHT BANK · ESSEQUIBO RIVER 'by C. N. Bc.rron Tha s~~vei ' 'cc:1,rri.ed out durine; the second field season.

of, 19.6o ';covei-•s the Essequibo Rive'.!'.'

fromTakwari I-1ountain northwafcis .

to a few miles below.

Omai Landing where it was,,_linked with a curre:it surv.ey by R. T. Cannpn of tlie '.

area to· the 21.ort h. The .


Potaro nnd Konawaruk Rivers wer.a also ·surveyed up to their .lowest falls, and the Yucuriba Itabu was traversed in preference to the Itanime route, previously surveyec;l by M.W.

Carter in 19 58. east bank qf the Esseq1.ii00, and two of these were extended.

as far .as the Demerara River • In addition, lines were cut in1i.

_:ld from the , l·, .

.

--···-·· .

: .


The ro~k (o~mations exioined may ·conveniently b~ arranged in the f~lJowing tentative stratigraphidal succession.

Suparf_icial deI)osits: River alluviu.ra .

!Jhite Sand Formation Laterite (350 750-1000 feet le~els) fe~t and Young.er Basic Intrusives Younge r Granit es Huruwa Formation: Sandstones and j.as.pers Alleero Island Formation: Biotd t~, ·.hornblende-, .. .

.

and.
.

and.

qup.r;t.zitic schists Acid a nd i n termediate fine ~ ~rained ~eneous rocks Amphibolites:: (Orriai are8.J~ .

.

':..

.

.

',''J. '

.

•' .

:c .

.., lPotn r0 11 .. outh area) .

.

-~·--- ·~.

_;_ - .

.

, ... · --:· .

, The above fp,roation_s aria not·· ,necessarily in strati- e;raphic order as .

'their nutual relatio.

!ls are not understood in ev.ery case.

The .Mi.u::-uwa :and Al lecro :Island foron.tions occur to the _south of th~ •main g r an it.e .
mass, and t'he amphibolites and , fine-grained .. 4.G.id .

and int~rmediat3 ieneous rocks l i e to the · rlorth~ the centre of -~h~- arei; .The-{ir·anit'e domina tes • • I ;• · The fo.liation· · of the fine-g:rained ,:;i.e;neoul?

rocks near Potaro mouth' and o·f · the rocks n:aa r 0It1.3:i q._;ip steeply to the SSW and the bandine 2.nd foliation of the Allegro Islaad F ormation is also ne.

::.r vertical but 'str:i.kes NNE.


In the south, the b edding of the 1-iuruwa Formation dips moderately to the SSW and is not foliated.

It is possible tha t shearine observed mainly amon~ the fine-grained igneous rocks may have some control over the occurrence of GOLD.

The amphibolites of the O~ai area consist of a variable assemblage of d~rk, fine- g rained rocks which sometimes show poorly developed ribbin5 on eroded surfaces.
Thin sections show thera to ba plaeioclase amphibolites for the o ost part, with o.bundant epidote and chlorite, A black maneanese mineral o ccurs in sheared quartzitic rocks of this form~tion near the large dyke west of Omai.

and amphibolites on the Demerara ~iv~r, e~st-south-east of ~for.

:::iputa Falls; corralation wit~ the a~phi tol ites of the Omai 3rea, In a ddition there are sooe subvertical quartzites their strike nnd lithology sugeest ,.
52 11.round Tigri F,alls the amphibolites are intruded by acid nnd intermediate .f.irie:.grained icneous · rocks with quartz and oligoclase phenocrysts, which extend up to 7iforaput:-:1 Fc1.lls.

The fine-grained groundinnss is usually somewh~t raetaoorphosed, with the developoent of chlorite, sericite and occasional biotit0; phenocrysts of dark oinerals, pseudomorphosed in chlorite and epidote also occur.

intensely cleaved in c-W and SE-N":v directions, and c~rry nbuadant • chloritoid.
Both these and the amphibo lites are locally cut by qunrtz veins and tension cracks.

;.

round Potaro mouth itself, these rocks are 'i'he :(UL1aka Granite and sioilnr eranit e bodies south of the river, carry quartz and raicr ocline, sooe times enclosine euhedral zoned pl~eioclase crystals, to gethsr with biotite,hornblende, sphene ~nd opaque minerals, nnd is locally foliated.

The Temple Bar Granite is of granoblastic texture, ~nd includes a few xenoliths.
f!lirieraloeically it is characterized by quartz·.

:.olieocl-2.se oicroperthite, and hornblende 2lterine to chlorite.

Sphene is a common accessory.

The "t-faraputa Granite is similar, but carries biotite as the principal d o rk ::1inerc'.ll, to·ge~her with quartz, :-:iicroperthite, albita/ oligoclase, secondary chlorits and sphane.

to a locnl· ;1inera loeica l foliation, it is soneti~es sheared, and even mylonitized, alone; aa E-W or !J1v-S3 direction.
The Warnputa Gr~nite is intruded by the 1-;iineraloeically sirail.

::.r but finer e;rained Yucuriba Granite in the south.

The l a tter is r a rery foliated of sheared, and loc a lly cnrries phenocrysts of potash feldsp a r and olic oclase.

In a ddition To the south, the Yucurib& Gr~nite e ives place to schists of the rillegro Island Foroation which are locally intruded by a sirail nr c rnnite.

These schists include interbanded biotitic, hornblendic and .
quartzitic types, and usually c ~rry nor0 or less epidote· a ·nd chlorite.

Neo.r Takwari Eountain they are in ill-defined ·conta ct with 3pparently ouch less steeply dippinE qua rtz s ~tld stone s of the tl!

!r'uwn Formation, which ~lso includes jasperized banded crreywackes showinc sma ll scale cross bedding and convolute foldinE• Saall rine -sh3p3d bodies less than a qunrter of 3 nilliwetre in size have beea seen in s e veral thin sections of the Or.iai a nd Muruwa sedinents.
They ~ re always well-defined ond appear isotropic between crossed nicols.

· :.

; '• . '

.

H.~ .. ;:THE .GEOLOGY OF AH A.REA BETWEEN THE MAZARUNI .

.

!

1 AND UPPER PURUNI RIVERS .

, :: :,.

:.

_i '.

.. by Donald D, Hawkes, Geologist 53 Ih1rin'e both the field se.

'.lsons of 1960 reconnais sance ···mappfne; wa.s carried out in the south-western portion of the ?uruni dee;ree squnre.
:r.i:uch of the topography is between 300-400 feet in altitude but thick · in1t:t>usions of dolerite form steep and rue;ged hills attainin5 G mnximu,-:i. heiGht of 1900 feet on Sororieng Peak.

The stratigraphical succession wh±oh has been estnbl.ished i:i this area and its ·tentative correlation with the success.i on ··sue;gested for :3ritish Guinn.:.
(l'foConnell :ind Dixon, 19601 ) is shown below: Upper Puruni Regi~nal Succession Superfic¼l· Deposits Superfi_cic::il Deposits White Sarid 'Corentyne Series Basic Intrusions ' ' .

.

Younger Basic Intrusives <'frari.it'ic Roc'ks Younger Granites Metnsedine::itary Group Hazaruni Group Granite-e;neiss Complex ?
The Granite-gneiss Coo plex is a we ll defined unit in the Upper Puruni ~iver where it consists of biotite gneisses and hornbl8nde-~iotite- eneisses with~ pronounced {rn!-SE) r.iiner -:.1logical foliation .

area the relationship 0f t!

:1.e gne iss e s to the Hazaru:~i Group is uncertai~.

In this ~.fue n tra ced tow~rd tne southwest the unit looses to a lare e extent its ide~tity, and is extensively inv~ded b y granodiorites .

Loc nlly, well-foliated eneisses apparently e r~de into non-foli.
:1ted granitic rocks.

The Metasedimentary Group consists of aetamorphosed a:bgj,:1(1:.~.oeous and fine- g r~ined arenaceous sedinents oainly within the ereenschist ~acies , locally attain ine the alb ite-epidote- nmphibolite sub-fncies.

Over the e reater part.of the area the metasediments have an ·Bw foliation.

Huch work both in the field c::..nd labor.

:1tory remains to be done on the Gr~nitic Rocks of this area .
At present two subdivisions have been recogn ized: (1) g r anodiorites and (ii) the leucocratic nicrocline eranite.

The g r anodiorites occur in tha west and are characterized by an abundance of epidote and sphene.

So~e granodiorites CTer ge L~perceptibly · into the g neisses of the Gr anite- g~eiss Complex.

The leuco cratic icroclL~e-eraJite appea rs identical in compo sition and texture to the :<art~bu granite 2 of the Bartica area.
54 • The B3sic Intrusio~§ occur as dykes (trendine Ni3-SW) _ and .. .thick .. inc.J..ined .. sheets.

These doler ites are tholeiitic in ch.

'.lractar and consist esse1'ltially of labradorite, cli'!mpyroxenes and iron ores.
Olivin0 is r a re but ~ay occur in smalf araounts in so~e oarginal faci e s. Two dist"ii,c"tive · f(§ntures are the- or0sence of pigeonite (or hyperstheJe which has inverted from pie;eonite), and ~cid interstitial arens of quartz and micropeematite, LatG st~ec granophyric veins cut the dolarita.intrusions.

It is probable that the topography of the area is forraad by n 35O-foot pla~ntion surface.
The res~dunl hills of this surf ace are capped with deposits of ~Tnite SandsL Su?er~icial Deposits terraces and al luviU<~.

include river REF3:1EHC3S 1 • McConnell, R.B.

and C~G.

Dixon.

·1960.· A Geological E e:!

?

of British Gui ~na.

Rep. Int.

Geol.

Coner., 21st Session, Norden, ?

t. lX, · p. 39-50.

2 • Ca nnon, R.T.

In ?

res~.

T&e Kartabu Granite.

Vth Inter-Guiana Geol.

Conf.

1959.

Georgetown, British Gui2.na.

· \ 'II . )

:,· :'- ~ I\;, -~~1 I • ..


., 7 55 I. GEOLOGY OF THE XO?IHANG VALLEY by J.H, Bateson, Geologist The KopinanE · River empties into the Potaro River at approximately 5°IT, 59o35v ~.

Its valley is surrounded on the north, west nnd southwest -by ~narc of motL~tains with the southern boundary marked by a 200-foot escarp ment.

overlookinc th0 Chennp-au River.


The geological success_ion of tha valley is outlined below: Laterites and gr~vels Upper XopinanCT Sill Kopinang San~stones Kopin a~ e Hornfels' Lower Kopino.ne; Sill Ch ena p' a '11 S .

:l :'!ds ton ~s .. .

The sandstones and hor~fals ·are the local represen · to 3000 tatives of the Roraima Formation - here· represented up sills, a combined thicknens of at least 2000 feet, belong to the Younger Basic Intrusives nnd are of a later date than the Roraimn For~ation.
of sediments, whilst the two feet : .

; Approximately 500 feet of homogeneous fine-grained pink, fawn · and.

white sandstones compose the Che.:::iaplm.

tosether with a thi~ b3nd, about 20 feet Sandstones thick, of interbedded shales.

Thin reoilar beddine is char~cteristic of the sa~dstonas except for the top of the succession where cont~ct with the overlyine sill has converted thee i:-_to i:1at:1quartzites.
The regional dip is shallow, 3-5°, to the southwest with festoon current bedding the domina nt sedime~tory feature.

The overlying dolerite, tha Lower:Kopinang Sill, forms the floor of the Kopin~ng vallay, and itself appe~rs to be conf'ormnble with the S8diments into which it has become intruded.

On tha b~sis of preliminary work s~nsom (1960) 1 subdivided the sill into three zones, a lower noritic dolerite, n normal dolerita ~nd an upper hornblende variety.
Subs0quently this sub-division has been ari.1plified by }1.3.wkes Ul?pendix I).

The top of the sill occurs over a wide area at approximately 2100 feet o~ove M.S.L.

with the base at 1770 feet.

On Kow2.

the top rises to a naximum of 2900 faet.

Overlyincr this sill there is a considerable tn ickness , 250 to 750 feet,of fine-grai~ed, well laminated, dark- · coloured metauorphosed sediments, the Kopinang Hornfels.
These rocks near to t he contact have been completely recrystallized with the developr:ient of sillimanite, cordierite and andclusite et1bedded in a hornfelsic eroundaass of quartz ~nd alkali feldspar.

Further • 56 away from the .

dol~r.ite thay still h _;:ive .

:i typicnl hornfelsic textur·e · 'hut ·with only· th.a · development of cndalusitc nnd cordi e rite.

Thcse rocks have ~n average dip of 2°- 4° to the southwdst.
Rastine upon th3se ~~tasediments are up to 1800 feet of yariously coloured and textur~d qunrtzose sandstones · and int~rb.egd.3d ,jaspe rs of the Kopinang Sandstones.

The sequeace beeins with a b:isal cone;lo r.ierute and pe:i0l.y S.:!ndstone f ac.ies.

which 9.'.

!sses upwards into finer-e;rained pebble-free, dominantly pink, white ~nd fawn sandstones with bnnds of j~spar and jasperized sandstone.
The u~it from conclooerate to jasper is approximately 600 feet thick Jnd is rep eated two or three tiaes i ~ the !80~ ~~et eX?OSed.

Bedding <lips are s~allow, 2-5°, with the ree;ion~l dip to the southwest.

Graded bedding occurs OJ a ll scales accompnnied ':,;!

scourine ~nd f ,estoon beddinr_:-.

:ilestricted to the top of Kowa an~ the hie;her parts of the Kopin2ncr- ~'lokor:mng r-1.

'.lss the Upper Kopinanc Sill, its thic.kness beine; in excess of 800 f eet in botr- these a reas.
Gen0rnlly it is of coarse c r ~ in with lnree pyro1ene crystals p 3 rticularly in the upper layers • .

Snncou sueeests tha t it is of a more ~nsi.c · .corapo si<:.ion, ~nd ther(3t_o._re : ~q.pliE::r· than: .. · the lower sill.

.

:ire exposures i:i · · .

Of the superfici~l deposits the e ravels nre the most icportant froo ~-~ 0corioraic viewpoi~t since they are Dif.rWND benrint;• cqnsiderably over the past few yeirs the sto:1.es .. 6btc1ined are of tood gem quniity.
3xtensive laterites ·a_r~· c;le velqped on the outcrop of the Lowar Kopinane Sill ·usunlly for.mine hard -s urface le.ye.rs up to 8 feet in thicknass.

The · laterites hnve be~~ axarained over the past two years as a poteptial source· of BAUXIT3.

J.. lthouch pro duct,ion has .. decransed RB?

3RENCES 1 ·S gnoom, R.C.

1960.

Report on the Kopinan~ Vallay ·- · · nnd th~ adj~cant ~r ea to the no~th as far as llyc:me;:m~2 ~ountni::1.

GAol •.

Surv.

B.G.

(Unpublished· Report),.

RCS 1/60).

.


..... .. J • THE WAIAMU AUD MOPAY AREA, CUYUNI RIVER 57 by J.W, Lloyd, Geoloe;ist During September na are~:of approxima tely 250 square miles was mapped between the Waikuri River and the Qunrtzstone 5r.:1nit~.

, .

The river flats are restricted i.::£ the area by terraces· th·ough · extensio!lS occur along the consequent creeks.

The lowest terrace at 195 feet above M.s.1.

is extensively developed in the area between Mopay Creek and the Quartzstone eranite.
A higher l evel occurs at 350 faet M:.

-s.1.

Arec}s underlain by the Central Cuyuni Formation are extremely dissected and rise to 7 50 feet alone; the Waiamu- Kopashi (Puruni) watershed~- undulating, sandy clay hills rising to 200 feet and separated by intervening swamps or sandy valleys.

In the aast the Qu.artzstone e;rcmite forms The roe~ of the area nre provisionally grouped i n order ,of _ c:+e.e n.s follows: Yoq.~_ger Basic I:itrusives ·' Younger · Gr.
:1nites Central Cuyu~i Fornation Waiamu Island Foroation The Waiai~m Islnnd Formation outcrops over a l enticular area of .npproxiraately 20 square miles striking southwest w.:1rds from Waiamu Creek aouth to nbout 2 milas inside Waikuri River.

It is composed of a succession of int er bedded phyllites and quartzites, the latt er varyine in width from 6 inches to a qunrter mil e. The thinner bedded members occur nlo~e the northern boundary out cropping extensively nt -ifoiamu Islnnd .
Bedding strike directions are vnriable for they are undulating in the Waikuri-St. John?s Creek area and become tightly folded with vertical axes in :,1aiaou Island.

The te ctonic style of these rocks is dissimilar to that of the n0ighbouring sandston3s and ignaous rocks · and so is considered to be an infaulted older formation.

It should be noted that tha lithology is similar to the Bnrama Group.

The Central Cuvuni Form.

:1tion underlies th~ central and southern portions of the area.
It is composed o f sand stones, conglomerates, quartzites and fine-grained ie;neous rocks.

The sediments are of the greywacke suite and show grading a~d scour structures.

The fine-grained igneous rocks interdigitate with the sediments in the Waiamu-I.fopay area.

They are occasionally porphyritic with chloritized hornblende and feldspar phenocrysts, though karatophyric in composition.

v~sicular vnri~ties occur but it is not known whether they are extrusiv e or not.
they are usually evenly fine- grained and prob~oly The Younger Granites are repres0nted by the Quartzstone granite which forns the eeological feature limitine thG area to the east.

It is a mediur.1-grained hornblende granite well .

exposed in the Quartzstone Islands of the Cuyuni River.

The margin has been exte nsively foliatad ~ - - - - - - - ~------------,=- ' ... 58 by the sace strain which h~s effected the neiehbourine the resultine texture is e;naissose.
ereywacke series; The strain ef·f·ects d-i.r.rinish lnwi.rds from the r.mrEin until only well-sp~ced joints parallel to the reeional folintion ar0 visible in the fiald.

The foliation ha_s resultad in the chloritization of the original hornblende nnd biotite~ The dol0rite dykes of tha YounP.er Basic Intrusives has b-3en intruded int,_o · the ereywackas · off Kutuau Creek Mouth.

Det~ils of structure are observed inland due to ~1Ietn.raorphic ·effects are seen in the lo.ck of outcrop.
the presence of c.1tacl.1site,$," 'schists and [Ileisses, all of the lower Greenschist Fncies er~de, which occur in all rocks older thc:n the Youneer Basic Intrusives • .-: The foliation· directions .

resul tine: from t h is metamorphiso runs nort.

!1.0a.st to southwest · across the .

:1rea.

h.n extensivG "Banka a drill inc proe;ramme carried by Cannon has shown tne area to _be unecononic for any l3ree scale GOLD working.

the c:ire3 but record no mane;aniferous horizons.


no other minerals of economic value nre recorded in the area.

In 19 54 African i'fone;anesa surveyed : ; .

: • 1 ' .

K. THE LOWtR BARAMA AND WAINI RIVERS 59 by J~Wn Lloyd, Geologist During the first field sea~on of February to May an area of approximately 800 square miles was mapped between the lower Barama, Imot.

::ri and Waini Rivers.

The _topography is rather .. ··a-iverse owin c to the complexity of· the e;eology.
The hie;hest areas are in the west where M.S.L.

To the east the country · is dissected but only below the 400-foot contour.

Plateau areas of white sand decrease in height from 500 feet to 300 feet M..S •.

L. in n northerly direction, Pakiria Hill reaches 1300 feet The rocks of the area a re provisionally erouped in order bf aee as follows: White Sand Formation .
Youne;er Basic Intrusives Muscovite Granites and metasom;itism Undifferentia ted Amphiboliies and Diorites Minaba ru-Huiari Igneous Complex Wanaparu Gra nite Warapoko-Baramanni Granite Maka Granite and Gneiss Kokerit Forcation Barama Group The Barama Group extends from the upper Waini to the lower Barana and westwards to form the Barama Barima watershed, northeast - of Tasawinni·~- .

Mudstones and phyllites are comr.1on a nd quartzites are exposed at Tasawinni.
lower Imotai River and upper Waini schists occur which are derived from the Barama Group sandstones.

Biotite-~arnet-staurolite schists are common together with kyanite and sill::i.µiani.

:te., · Orie iri_.

:il .

b~clding planes are found in the 1-owar I.motai.

The schists -are.

with .

: similar rocks described from Pomeroon and Supenaam.
In the .vicinity of Maka Falls, the The Kokerit Formation (Cuyuni Formation) is exposed extensively in the lower Barama and consists of fine- to medium-erained sandstones, pebbly sand stones, conelomera t es,mudstones, siltstones, quartzites, and fine-e;rained i eneous rocks.

Poor sortine; and e;raded bedding .features peculiar to a e;reywacke suite are common but structures such as current beddine and scour ma!

'ks are rare, The conforraabie distribution of the f:tne-g!
'ained i gneous rocks ~ith·'respect to the · sediments and the alie nment of partially minerali zed vesicles su~gest a possible extrusive orieinf , 60 The Maka Granite Gnsiss consists of mediwn-e;rained g ranites and e neisses which occur at Maka falls interdi eitatine with folded Bara.ma schists at the contact.

The fact that the· erariite cut·s·.- ac·ross · met-amoxtphic erades shows i t to be youneer, The Warapoko-Baramanni Granite occurs as isolated .
'.lreas of biotite granite in t,he Warapoko Creek and in tb~ vicinity : of Barama~ni.

Examples of both flow nnd .

cnt~cl.

:lStic ·foliation nre present.

.

The Wanaparu Granite.

found in the Wanaparu Creek is n edium-grainect · biotite .

e;ranite which has a fine crained·, · quart·zitic rock alone; its southern margin in whi ch hornblende porphyro_blasts are developed·.
The Minabaru-Hai~ri -Ie;neous Complex .occ·upies the area between the ·upper Imotai Creek and 'ilJ'aini River and contains all eradations from hornblende dior·it·e to biotite granite.

From central areps occupied by biotite c ranite a continual e;radation can ·be followed throuch biotite e;ranodiorite, biotite hornblende eranodiorite · to hornblende diorite which generally forms the margin.
The intermediate members incorporate xenolithic material predorainantly of biotite composition which are distinct and elongated in the foliation close to the diorite border but ,become diffuse with increasint: acidity.

From field and microscopic evidence it would appear that t he intermediate .rock types are hybrids , rather than differentiates, formed from.

the intermixine of a biotite eranite.

oagma intruded into a hornbl ende diorite.


Undifferenti ated Amohibolites and Dioritas occur in the aureole to the Aranka-Wenaau bathol'ith in the upper Imotai.

The rocks : ar.e of fine.-erained amphibolites, hornblende schists and medium- ·to· coars·e- e;rained diorites.

Muscovite Granites which are coarse- to fine-t:.,--rained, and simple peematites a re interspersed :in phyllite areas between the lower Bnrama and Waini Rivers whare the presence of muscovite becooes increasine ly important eastwards.
The muscovite cranites and per,matites are al~o e;xtensively developed at 11.iaka Falls.

The Yo'unger B'asic Intrusives are chiefly repr-3sented •· .. : ..... ' .. ' .. ...... ' .py a dolerite sheet intrusion of some .1.:8 mile:3 'in leneth which str.ikes alone the eastern side of _,the .Waini River from I1iaka Falls southwards• Gabbro developoents are comLlon.. arid res i dual eranophy:rd .. c veinint occurs at Cannister Fnlls.
I The White Sand Foriiation : , occurs on _isolated flat topped plateaux 'between the lower Bararna and Waini, ~ ·· the lower · fuotai ' a-nd ~rJai rii and alone; the Waini,-Kutuau watershed.

Cu:rsory examination of -the .rocks of the· .Kok.erit · For~ation exposed in the Lower Barama River indicated :h>.ldine. '

Ree;ional- -mappinc sue;cests the existence of a westerly pluneing syncl ine at Kokerit and a westerly p1unein.-ft· anticline near Warakshuru Creek4 .
: · The l(<)kerit and Barama rocks ·have been affected by a late .su!

:)vt:)t"tica,l cata_clastic · foliation.

The Barama schists show .siens ,of more than one metamorphism , I ,.

61 by the presenca of two linaations, corrugations, and sets of boudin and tha development of retroeressive chlorite.
Extensive alluv·ial e;old was worked up until 1938 in the Good Hope Creek area, but although a few traces can still be found throuehout creeks flowine off the Aranka-Wenamu batholith a ureole and Minabaru-Haiari I g neous Complex no deposits of any consequence appear to exist.

~OLUMBITE has been recorded in the Waini and MICA cl.aims h·av·e been taken out in the vicinity of MaI<a 'Falls, but neither of these minerals appear to occur in economic quantiti es.
In the Tasawinni quartzites and occasionally in the phyllites borderine; the Barama River, gANGANES'E staining and veinin8' beco_mes sienificant.

Analysis however shows the content not to rise above 11.30% and mappine; indicat es that the areas are of limited extent, .

.

62 •, ~ • I • by :arn:tl.e-r, Geologist A reconnoissnnc·e map (1:125,000) w2.s produced .

of ·part of the, :::iiddle B-nr:i.w..:1- B:1r.

:u::1a wctarshad, coverinc; an area of some 250 squnre ::tiles.
The ro·cko examined L1 this nren hnv·e- been provi sio:inlly group3d in ord~r o~ aee .

:is follows: .

··.

; -• .. ~ ~1 ,; Superfici~l Youncer B~sic · Intrusivas Youncer ·Grnnites - -~eki .Granite Xok~rit Fornation - Kazaruni Group ?en.

:ipu For2atioti )_ B.'.lr.

'.li:l:.\ Grou~ Pipinni Por~~tion) The Pipiani For1.iation forms the Chi Chi Hilis i L the so~theast of the area, and is conpoo~d - thera, of phyllites, .

:iunrtzit ~G ~:id serf.cite sc!-:.ists.

ICanc.


:ini .~ ) rous deposits :ire fou:id loc.::i.lly.

The fornntion is stroncly foli.

:1tad in .

:i to the boundary of the Teki Gr.

'.lnite but contr~stin~ with the BSE-imw structura l trend of the 2dj oinine; ::okarit Forr.i.:.tion.

T,lebberl describes this ::orraation ia det:J.il and his nc.

::ie is retn inad, but its use limit e d to the rocks of thd type loc.'.l.lity.

iJIP!-SS3 dir~ction, i. a, par.


'.llial The Tenp,Eu Forr:iation 2 is here :n:ide u p of chlorit-3, talc, and sericite sclcists wit.½.

subordin.

'.l te qunrtzita l anses.

Phyllites were ::1.

'.lpped in only one loc.Jlity,.

The folintion jiractions of this forra.

:1tio~ ~r a confor- · D.:lble with those o-:: the neichbourine Kokerit FormLltio:iJ.,.

The :,JS.

::u::imitic schists .

:-.

:id .

'.l.mphibqJ..ites of tha 7enapu Forra.

:ition in the njj~inine nren 2 '' wer e not s een in this .

'.l.re.
'.l.re.

:1, thouc h .

'.l ?romi~ent l.'.lterita-cc v 3red rid ~e ::'ornin c a par-::.

of the southern ooundc:ry to the foro.

::1 tion 1:1a y be underlain by nmphibolite.

The Kokerit Formation3 is conpnral:le to the Cuyuni Foraation of ·:lilliams 1 , nnd consists o-: chlorit 0 .

:1nd sericita schists, quartzit0s, psancitic schists a~d interraedin te volcanics; it is poorly axposed throurhout the c entr.

'.ll 1nd south0r~ part of the a rea.


The schists, p a rticul ~rly the psammitic v.'.lriaties, a re largely of sedinentary oric in, Volcanics are of minor importance and consist of fine:- e rained porphyritic (nue ite phenocrysts) i eneous rocks; were observ.ad, The 0ounda1 .... y between the Ten:lpu Form::-.tion nnd the Xokarit Forr::;.c tion :.s m:1rked by n zone of un- diff eranti.'.

!ted schistose r -xks sorae of which m.:iy ba derived froi:i oetar:iorp hosed 'b.
:1sic intrusiv8S, similar to those of th e Tenapu F orQation but which hav3 been intruded into the w.'.!

r c i~s of th~ Kokerit Formntion.

The formation hes an east-west structural trend which ch,:mges in the eastern .

:1rea to swine; northecs·::.

wnrds .

::md southeastwards c round the '.:.

'eki g raniter.,.

* See also P• 47., no pyroclastics 63 The _.nature of the .contacts between the Kokerit Foroation, Teld.-..

Granite ·and ·r:,fp:i.ani .


Formation is not known in this area thoueh it is sug£asted that the Kokerit Formation unconforraably · ove·rlies the · Pipinni Formation.

adjoining southeastern are.:!

the Kokerit Formation is hornfelsed by the.

Teki Granite3.

In the The Teki Granite occurs ia the eastern part of the c1rea, and .is believed to .extend .northen stwards to Xoriabo, and southwnrcls .

::i.

little beyond the Barama River.


It is a coarse-grained- ::,iot.ite or hornblende-t::iotite e:ranite, apparently unfoliated.

Hornblende-biotite cranite eneisses were J~served on the northern boundary of the cranite.

The ::olintion directions of the Kokerit Forraation swine around t~e granite while those of the· Pipi~ni Foroation are parallel to the eranite bound-'.lry.
Beyond the limit of the ~ield survey in the northeast, aerinl photography shows cha~ees in relief (and joint i ng patterns) which nay indicate chang es in facies of the eranite.

Youneer Basic Intrusives are represented by dhlarite dykes strikine NE-S•il throuchout the a rea.
dolerite body (a:bout l oile i:1 width) occurs in the · northwest cuttine across the Kokarit and Tenapu Formations; i t may be a co~posite dyka as fine- g rained material (typical -of a marginal"f a cies) is found within tha normal r.iediuui- g rained v a riety• was e3countered close to ~his dolerite sucg estine two aees of basic iGtrusives.

;.,_ small body of alt e red ea!

:>bro J.tl important Gold has been obt~ ine d from the .
alluvial flats borderin£ the Bnram ~ Riv 0r on · its ma in tribut.ari es · i;:-i this area (e.e.

the lf.unoooe ~iver) • Gold h a s also been worked from the country.

north of the Chi Ch.i _ I1JJ1s on the borders of the ~e~~ Granite.

Tha econooic po.ssibil ities of the mane;a;nese, in the Pipiani Fqrmation, :1:1ve bee n co;1siderGd "n.t lenc th by Webber 19521 , .. · ' 1 webb.er, B.J.

195~.

li~anganes e Deposits in th e N'orth West Distri.6~, British Guia na, · Qe·o1, Surv, B,G.

Bulletin, 23.
Bulletin, 23.

2cannon, :·~.T.

and Br~ml e y, K. ·1960.

Report No .. RTC 2/60.

.

3 .

Qeol,t1urv 1 B 1G.

Unpublishe d. .

·,.'

' .

.

Gannon; R.T •.

and Carter, J. ,1.

1960.

A preliminary report on · the e;eoloe y of the V!aini (SW) quarter l.nn.

Rep. 1959~ .Qeol, .

Surv, 3,G.

dee r e e ~ .

:i1.

:1n.r a .

4Willia.ras, E. 1961.. Hote s on the .

Peairila Falls-Merune Riy.er a r ea .

.t1.nn.

; · Rep·.

1960.

Geo1, -.. Surv, B 1 G1 ~r:.

GEOLOGY OF TI-~3 U?


?ER BA.RTI•lh AND AVil.-KURil ~lrlzr.s by~.

Bra~ley~ Gaologist* 64 A reconnaissance expedi tioa durinc the second field season, 1960, produced.

a eeoloGical nap (1:125,000) : cover inc an area of soma .

9 50:·squnre .

ni.iies · lyin g between th.e upper Barinfo River and the Am::lkura River • .. .

Th e rocks · of the aren were provisionally crouped .
:i.s f ollows: Superficial deposits· Youneer· Basic Intrusives ' Youneer Granites: i<mnku.ra-Barima Gra::iites Barir:ia-Whc.naraaparu Gneisses Amphibo-le-·· schists and' an1phihol i tes Undiffarentiate<l amphiboles and fine-erained icneous rocks 2uartz and qu~rtz-feldspar por.phyries Bar:i.:nn Group The eeology of the a:t,'ea is dominated -by the Amakura Barinla ·Granites and the Bariraa-Whanamaparu'·G;neisses, wli.ich are b.order.ed to the south by rocks of the Bnrama Group.
The B9rima-;fuanamaparu Gneisses are made up of medium-grained foliated Granite, eran ite eneisses cJd b3ndad gneisses cssoci~ted with araphibolite and amphibole sch_ists .often · occurring as narrow bands p arallel to the EN:z;.

:r..siTstructU:ral trend of the r;:;:ieisses.

The e;neisses form the southern carcin of the coa.plex in cont3ct wit!

: rocks of the Barnma Group, the lnttar often appaarinc as encl~ves within the ·ciarginal e;naisses.
Th e gneisses vary in com.position from eranitic to dioritic t ypes, the latter being foillld on the southwestern marein of the complex.

~iotite, pyroxene or hornble nde may be ._ ... · ..

.

'_ .. ,pr.es.ent as the dorainant fe1"r.,omagriesian minerals.

Close to the amphibolites ar.d a.raphibole schists hornb13nde bacomes the dom.ina:-:it ferromagnesian mineral wi'thi'n the f2'!1.eiss.
The gneisses repr:,_es.ent :t.h~ , ,ee:rly phase in the formation or the complex; by the coarse-erained foliated eranita and the porpny~itic l:: iotit·e e;ranite•·, fc:ilrowed after :i.n unknown intervn.l.

The Bariina-Wh:i.namaparu eneisse~ are panetra~ed by pee;matites, q:uartz-f eldspar ·and quartz veins.

tha later fac i es, represented The· Amakura-Barima Granites include microgranite, _pe~atit.e, aplite ar!d qiartz veins; porphyritic foliated b i otite e ranite; and coarse-erained biotite eranite.
The porphyritic foli ~ted eranite i s characterized by conrse--e;ra in size, ::"oliation (aligned biotite) and potash feldspar phenocrysts (¾-4 ins.

diameter).

Th~se pheno crysts are irreeular in occurrence, locally givine the rock a :pec;ma·:-it.ic appearance.

Th0 phenocrysts !-Revised by E. Williams.

:dis C: ?'

65 are often a l iened parallel to the foliation.


Bioti te i s the dooinant ferrooagnesian ~ineral of the facies ; occ asional saall lanses or schlieren of f i ner- grained biotite rich aaterial are seen within the porphyritic faci~s.

Foliation directions of 140° were observed {n the western a·r ea; · eo.stwards thesa swing throueh a NB._s-,;;.r direction back to the ·SE- 1-n'J direction on the Amakura ~ver in the north~o.st.

Peeu.
Peeu.

'.ltites (quartz, fel dspa r s, biotite and/or a light mica) and quartz veins were _common; dykes of finer-crained biotite erani te were noted .

: Tho coarse-erai~ed ciotite granite facies i s closel y related to the porphyritic facies and can be reearded as a subfacies of the latter.

The fol iation directions · raeasured in each facies ar3 conforraable wi th each other.

· Foli ation is mincraloc ic.

:-1l rather than c3taclastic.


The Baraoa Group rocks in the southeast are de scribed in another reportl • .

)uartz and ·.

)uartz- Feldspar Porph_yries were observed in a Beraraa Riv e r traverse i r. the south,iest of the area, to be in contact with, and penetrated by the Anakura- Barioa Granites.

The porphyrieG hnve a foliation similar to that of the adjoining granitic· rocks .

The extent of these porphyries is not kno~m .


Quartz- rich chlorite- sericite schists, possibly derived from the porphyries were found within the cranitic rocks of the sane area.

Undifferentiated aaphibolites and fina.-grained ign eom rocks of basal tic texture, are closely assoc i ated in the southwest of the area ~rith the fine- c rained ieneous rocks of basaltic texture; insufficient field information was obtnined to mnp thes8 two rock types as indiv i d u al f a cies.

Nowher,3 h c::.
Nowher,3 h c::.

s i t "!J0en possibl e to decide whether the similarity between these i en0ous rocks and a·bnsaltic dyke {=(oun5 er Basic :L-itrusive) · in the c ranitic rocks of the Araakura Rive r was note d. igneous rocks 3re extrusive or intrusiv8, but the The amphibolites and amphibole schists are of unknow:i orie in althouc h, previously, similar rocks of neiehbourin e areas have been referred to as arisinc from clay sedimeJts, volcanics or basic intrusives.
These rocks occur as bands, parallel to the foliation within the eranitic rocks, parti cularly in the Barim:i-Whanamnparu Gneisses~ Lar[;er irrecular bodi e s of amphibolites occur on the mareins of the e neisses.

The amphibole schists appear as nedium- to fine- g rained rocks, mediu.

'.l er0y in colour, with· the schistosity iraparted ~Y al ie ned anphibole crystals.

?h e anphibolites are vario.ble i3 c rain size (lar c est crystals % inch in length) .
The amphibole s,chists may pass locally into amphibolites.

Both amphibolites ~nd amphibole schists a re 9 c netrat e d by quartz veins nnd peematites.

Young3r Basic Intrusives repr e sentine the l atest i g neous activity in the ar e a ar~ not common.

One cohtinuous dolerite dyke ( 25 miles in l e ncth) penetrates the Barirae.- Wh a nama paru e n a isses and has a str.ike rou e nly p~rallel to th~ structural.

trend of the country rock~ .

1.

Bramley, K. 1959.

Upper Bari.ma River Expedition .


Geol, Surv, B .Ge Unpublishe d report . '

.1 .

66 ,\ :.Small dyke of basal tic text ure was noted , ·within the roe.ks of s -~il::-.r appenr e ranite of the Amakur~ ~iv0r; ance were seen i.

't t:1.e southwest of the· a·:I'ea (s''ee above) closely associated with amphibolites~ · Ree;ul ar soil sampling was carri_ed out fo;tlo:wing the discovery of tha nickel niner.

:11: ., n iccolit3.

i n -the Five Stnrs are,'.l (Brar.J.Iey 19 59).


1\nalyses of so i l sa::nples collected are now bei.., e carried oU:t. ·· Diaaonds have been reported fron tha headwaters of the Eobaina Creek in the north3"iist of the area.

It is possibl.

::: that they are derived : from White S-:-:;:1.d which n~y have occurred in t h e area (e.g.

a similar sourc~ to d i amo:1.ds racovered in the Waini Rivar headwaters.)

" ... .

\ ½,.

r ·t, .. ... ' 'J • .

, · ··: ,4b ; r'.


67 N. THE UPPER MAZARUNI-EKEREKU-KAlffiRANG SURVEY, 1960 bys, Sinqh, Geolocist Durine; .th!c first field season a reconnaissance survey was .. made· of.

part of th0 r.J-orthern P3karaima Mountains in cluded iri .

th·e· Karaarane VnlL3y and part of the Upper Maza runi valley, with the objact of investigatinc tha n.:1ture and exta::1t of ,the lo;te!

".iti:,rn.tion of tha e~bbro sills in the area.

• • • I ' ~ : : ' ; ' .


The entire are.2 ls underl:iin by th~ s3dimentary sequence of the Ror-E1ima Forpntion and its intarcalnted sills.

The f'ollowine is a conposite sect~on of · the rock serias.

in· the area: The · U)?p·a~ Sill Thicknass 3cYo-320 faet The M:iddle con{slo;:1er.ates and sn:id.stones, - .

.

1800-22.00 feet Th~ Hiddl~ ·.sill 80-ioo feet The Lower Sill ' 200-250 f cet The lower conglomerates ?

.

.
.

.

The Lower Cone;lomaJ?ates, exposed alone the upper Mazaruni River .froo c:.bout lfosetn rapids .

$.~stwards· towards Iobaimadai, are the oldest beda s~en.

-.in·.·the area.

· They are essentially arkosic qu::!rtz cop..glomerates,.

showi :.ig strong cu;-rent beddine .

).nd frequently _ w~.

:?.therine; to a sur.fac0 of loose white sands.


•., Rocks foroine the i'!Iiddle Cone;lomerate and Sandsto:10s__ are responsible for the escarpments and table mountains to the north and south of the Kaoaranc valh~y includi ne Puluwatipu, Pwipwitipu nnd Karienetipu.

It would appear that the lower part of this series is predorainantly coarse conglomerates with lenses of sandstones which £ive way upwards to pebbly sandston0s containinE lenses of conPlonerates.
Two sh~le horizons can be identified in thii middle aren.

'.lceous series · of the Ror:do.a Forrac1tion; but th~ir actual extent and thickness were not measurabl e. The lower shale horizon was touched at the foot of Eboropu mountain, between the lower dolt3rite sill and the over lyine arenaceous Roraima rocks at a heie;ht of about 1900 feet.

It is for the most part hornfelsed and a search for fossils was nade without success.

The second shale horizon was approxir.


:a te to that occupied · by the middle sill to the north of the z:amnrane valley.

On the south side of the v~lley at a similar h0ight (2800 - 2900 feet} a light brown soft 3nd friable shale is seen alone a·line frora Akopai to t1"1e top of the Karienptipu escarpra~nt~ The dolerite sills are the repr~sentatives of the Younger Basic Intrusives in these parts.

The Lower Sill is about 300 feet thick, thoueh localized thickening up to 400 f aet seems to hnve occurred.
The :Hiddle Sill 3t its thickest point is probably not more than 1 00 feet and is exposed alone n line up Puluwatipu and Kayape .

The Upper Sill is exposed on Eboropu and is about 68 250-300 feet thick.

Thi~ sections f.:iil to show .

:iny sic ns .

of gra vity stra tifica tion within these sills.

- Petroloe;i ·c'o·l ·ly they s ·eem· to b e · noritic·:·i n' · p a rts, thouc h qu a rtz dol arit0 s n r e m~ra common.

,r I Be c .
,r I Be c .

:i us a o f observ ed inclina tions of strntn on both -sid es of t he ~C.:un.

:i r a n c ValL~y, i t is felt tha t :~4 .

a n ticlinn l --Knu1.c.

r a n g Riv er haG c-:>u CT ed its v :1llay a ppro ;,cira3 tely t o the : ~xis o f this n nticlin~.

pa r a l l dl f l exur e is displnya d and thnt the L.:i terites c omaonly o ccur ov e rlyine dol e rit e s and i n the country c ov3 red, thr ee such sills were i d entified.

Their l evels o f occurr ~nce .

:i re on .


:in the lower sill: 2500-2700 a verae:e 1500-2000 f ee t f or feet for th 0 ~iddl e sill; nnd 3700~4 200 feet forthe upp a r Gill.

Th ~ lowe r sill ~lmost entir0 ly floors t h e vall e y of t !le :C_nr:10. r n n e; Riv e r th e Upper l a teritized ov e r most o f n t r e eular int e rv~ ls ov e r the l .

:i t e ritiz ed a reas a nd saopl es tn kan a t 2 ~eet int e rva ls in d e pth.
The r e sults o f chemica l a na lyses o f thes e samples are still p e ndine • • The middl e dole rite sill .is thin and impersistent and not mporta nt f or l a terit e .

The upper sill is e xposed on.

Eboropµ.

and i;s of fres h rock without l a t e rite .

l,:ia zaruni ·Riv e r axamin-ed.

It is deeply t ha ar ea .

i nd tho section of Pits wa re sunk There have ·b e en e;ood strike s o f DIAMONjs in The writer ·s aw ·'diVi"i1r,- .

oper ii'tions a t t his .


::irea durine the f irst p a rt of th e y eo.r, c r ee ks in the , Imb aim~ dai a rea e ood yie lds.. Kuwa~a f a lls b 0low Kam?-ra n c Moll.th, where it is reported tha t _wor~iµ c is verY.

p~ofit~bl e -in tne dry s~ason~ .The most- recent $trikes a r e , however;, 1n the ckereku River o.nd ~ts t~ib ut::q:•y cre~ ks, and· the Imbai.o.adai area was deserted as the deposits proved t o be very ~imited.

a re still e iving r,fany '.

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t I 69 I • •• o. i,;.

TR.A VERSE FROM MONKEY MOUNTAIN, ACROSS THE .

.. ENWARAK, AKOROBI AND KURUNGIKU MOUNTAINS.

TO EBINI MT• • : .

l br s,· '§'1.nph.

Geologist .. - .

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This .

ar e a forms p.:;irt.

of the southe rn Pakarair.11a.

Mountains of British Guiana and was cxpl'ored durine th0 s0cond fi0ld s e ason, with th~ object o-f inva stic n tin c possible occurrcncet of bauxit0 .

* Mountains .

cover most of the are a .


and the terrain is v e ry rucc;ed , The subdu0d undulntin e s ·avanna landscapo extonds northeastwards from Monkey Mountnin t6 the Echile bar River at nn altitude of 1750 to 2200 feet.

The h_ie hest mounta ins a re een,erally f o!

'I)l e d of dola rit e s a nd the · followinc; h e i s hts w0r e measured: Enwarnk Moun~ain is 3200 feet; Akorobi Mountain 3000 feet; Matopi Mountain \2800.

feet.
feet.

the Kurunc;iku Mountains up to 3200 feet; · · The rock sµccession is as foll ows: . '

' Youneer .

Basic Intr~s i v e s: .

Gabb ~o sills and dolerite dyk~s ' Roraima Forma tiori £' Cone lom3r.

:i t 0s ' a nd sandstones · • I ' ' Ma zaruni Group: Acid hypa_byssals qnd pyroclo.sti'cs_ The volc~nic rocks of the Mazaruni Group ar·~ th~ ' olda st rocks of the arej and the ir uppe r surface was touched at different l e vels.
At ona point the Rora ima sandstone s rest on them at 1750 f e et a nd at another at 2000 faet.

They are predominantly a cid volcanics and include hypa b yssal acid rhyolites, qua rtz porphyries, quartz-faldspar porphyries a nd pryoclastic age lome r a t es and·tuffs.

One s pecimen seams to b e spilitic in min e ralog y.
The Roraima Forma tion co nsists ma inly of quartz c ong lomerate s a nd pink to r e d sandstone s. The cone lomer a t e s contn in many a cc e ssory rock fr ae;mants includine quertz porphyry, chert, s a ndstone ~nd con c l omerate.

Echil e b a r s a vanna ther e is an unusua l conc en tra tion of p e bbl e s a nd laree frae;ments of qun rtz porphyry.

Th e sandstone s a r e the domi nant ~ eober o f the Rorair;w. Formation in the nrea.
The y a r e pink and r ed s a ndstone s which are frequently a r e illace ous and wea the r to thin p e bbly late ritic sur fo.

ccs.

Th e e xact rel a t ionship b e tween tha s a ndston es and tha conclomera t e s is unc e rtai n .. Mount a in a r e a the s a ndston0s appeariP ov e rlie the conclo me r a t e .
Els e wh e re i t s e e ms tha t o ne r.ri c ht b e the l a taral e quiva l ent of th~ other• In the Monkey In the The Younge r Basic Intrusive s a r e qua rtz dolerite i n the Rora ima Formc1 tion.

At sills and dykes intrude d l e ast two sills c a n b e i d e ~t if i ed, an uppe r sill a t h e i ghts o f between 2400 f~et a nd 3200 fe et, and a lowe r sill occupyine h e i ghts .

of betwe en 1800 and 2600 f e et.

ML., 0 r a loe ically the s e r o cks o.ppro r t o ba consa n e uin0ous.
De t a ils of the structural rela tionship is not ii Rocks o f forthcomine .

overa l l horizon t n l a tti t ude thouc h minor fl e xur es a nd l ow ane l e dips exist.

F a ultin e has occurred but no consid e r ~ ble displa c em~nts s e8r.1 to h av e tak e n place.

t ~a Roraima Forma tion show an 7'J From.

0yidence in this area and elsewhere in the country, i t --s ·eems-·that '-the Roraina sands·tones·>unconforraably ov0rlie the volcanic rocks of the.

)YI~zaruni Gr.cup • ... .

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, \ The dev01opoent of lat..:;rit0 over th0 dolerite sills is oniy ·localiz-ed , thin and superficial.. A fnir qu~ntity of massive lnteritic ironstone occurs around Waoarak Mountn in but no pror:Iising arens of al uminous laterite were found.
Bands of speculnr haematite occur interbadded with the Roraima sandstones and a specimen subj acted to laboratory analysis yialded 70% _ Fe 2o3 • The th i cke st band observad was about 9 inches.

Diaoonds are still work0d in the area • .

There are two main co ncentrations of porknoc~ers, one around the Monkey r~ountnin nren and the other ip the Upper Ech;:;rak In both these localities .

a sie;nificant .

anount cree:<.

of stones are extracted annually.


The Rornina Mining Conpany is layine down equipment for lnrp,e scaie diamond oper~tion on n River.

It is sienificant that in all the areas, diamond workines are selactively located i n the con~lonerates or in c ro.vels derived from the con~lonerntes.

w concession locntcd _,in t he lower Echilebar Q.Q1g_ is mined as a supplement to di.nmond workin ~s.
It is~ernlly extracted from alluyinl sn~ds which form the upper layers of pits sunk for diar.ionds in the Echero.k area, Th e writer think$ that despit-a th_e fact that minine for dia monds and eold in this area has been c oine; 0:1. s i nce the bee;inni.rie;, of th0 ·century, future prospects nre .still 13ood • .- -- .. .

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P. THE KARASABA I-ANNA I AREA by M, W, Carter, Geologist 71 • -••• • ~~~•~•••••~~' • , . '

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of the Rupunurii·-' D-'.i.strict between Karasabai and Annai ,The cchihtry mapp0d lias iri the n~rther·n savannas .

villa~es, and -~appine was carried out between September a.n'q.

December· 19·60, The formations encountered in the .
:1rea ' tr9Versed may be groupGd ns follows: Youneer Basic Intrusives and sranite porphyry dykes Graphic CTf'anite and e-ranophyres Good Ho.p0-Annai Volcanic Formation The acid volcanics and cranophyres cive rise to steep narrow · ride;es which have an east-west t .rend reflecting the eeological structure of .the reeio~ as a whole.

The dominant structural :feature is, in fact, E-'v:J to WNW-ESE foliation and jointine which affects · the volcanics only; the eranite suite beine massive.
The foliation and jointins dip steeply either to the north or to the south.

_ Flow bandine, when not complex; strikes e enerally east-west, parallal to the foliation, and dips of 45° were recorded, The same dip and strike were also seen in the sediments.

The rocks.

of the Good Hop8-Annai Volcanic Formation are assie;ned to the Mazcruni Group.

Thay are dominantly ieneous with minor pyroclasts and sediments.
The igneous rocks are mainly feldspar porphyries, and erade into rhyodacite and dacit~, and a minor amount of altered andesite also occurs.

The volcanics have in places been thermally metamorphosed or s h eared to produce hornfelses or schists.

One of the meta-volcanics is foliated riebeckite rhyolite and is of interest in view of ~~e occurrence of riebeckite granite at Makarapan Mounta:Li, farther east than the area mapped.

The tuffs are sheared crystal tuffs.


Sediments also are subordinate, may be argillaceous, arenaceous or siliceous, and show current beddinc and eraded bedding.

Some are tuffaceous sediments and match those of the upper Sip4ru::1i area .

:i.lmost exactly.

Hornfelses occur at eranite contacts.

Graphic e;ranite and eranophyres underlie a large part of the a rea mapped.

The doainant rocks are pink c ranophyras, with ninor graphic g ranite, and one very snall outcrop of biotite eranite.
The Good Hope-Ann3i Volcanics are intruded by the e;ranite-e ranophyre.

suite and there are clear siens of contact alteration of the sediments by the eranophyres, while the arenaceous sediments are converted to hornfelses.

Where gabbroic rocks are adjacent to e;ranophyre altaration of the gabbro suggests that the emplacement of these preceded th3 granophyre; if these g3bbros are to be grouped with the Youneer Basic Intrusives, a s appears likely from th3ir petroloey .
:rd structurnl relations, then the crnnophyres would be youneer than the Roraima Formation.

72 -~· .

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.. At one locality, moreover, c:1 dolerite" dyke is cut by a small dyke of f0idspar : porphyr,y,.

, ....

Younger Basic Intrusives nnd granite porphyry dykes.

Numerous dolerite dykes cut.

both th;; vo-lcanics and e;r.:i.no phy:r0s and : have the NE-.SW trend which is .

ch-aracteristic of the dykes of th~· Ybuneer Basic Intrusive~.

in neig h.: bourine nre.ns as well.


: as in other parts of · the Colony.

A few small· dykes of granit~ porphyry cut .the vol9anics and are believed to be ee~etically related to the ernnites • .

Their age relations to the basic i _ntrusives,.

,was not ascer tc:1ined.

Two eabbro plutons occur; ~nd one of these is clearly intrusive into the volcanics.

The other h3s volcanics on one side of it and eranophyre on the other.
Where i t is adjacent to the granophyre the eabbro app0ars to be prog ressively more altered ·a s · the e ranophyre is a pproached, which suceests that some of· the gabbros may be earlier than the g ranophyres.

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: .. ,._ I' ·: l I ' I I I ' Q, THE PURI ARI RIVER ,. '
'· .by MnG • Allderidpe , Assistant Geoloe;ist 73 The triangl e of country between the Puriari River, the Mazaruni River and the eastern.bounda ry · of · the Pur i a ri SE Square was surveye d. The area is entirely underlain by e;neisses and arnphibolites of the Bartica Assembl age, with a few minor intrusives.

The f i eld work was raainly conf ine d to tra v e rs es of the Pur i ar i and Maza run i Riv e rs wh·ere the rocks were best exposed • Mr C.G.
Dixon very kindly carried out microscopic examination of the thin s e ctions and p a rticul ar attention was paid to the basic bodies pres ~nt in the eneisses.

The northern part of the area and the upper part of the Puri a ri Rive r are occupied by high, deeply dissected hills of quartz-feldspar amphibolites, and qua rtz- feldspa r- amphibole schists.
Exposure s are poor and th e relationship of these rocks to the gneisses has not been demonstrated, althoueh it is thoueht that they may·be similar to other bas ic bodies i n the eneiss complex.

Th e rocks at the east of the Mazaruni traverse to coarse- e rained hornblende-biotite e neisses a re medium- with porphyroblastic feldspars.

The foliati on is marked by the orientation of the ferroma a enesian minerals.
Furth er west the gneisses, althouch simila r in composi tion, t ~ke on a banded structur~, the bands beine in the fo r m of e loneat e d lenticles, oft en involved i n ptyematic fold i nc.
Throu e hout the gne iss e s are numerous basic inclusions of hornblende schist, hornblende-biotite schist, biotita schist and biotite-ch l or ite schist, which are generally in the form of boudins a nd l enses paral la l with the foliation of the ene isses , the gn e isses are ptyeoatically folded the basic lenses a r e also involved in the fo ldine.
Oth er basic bodies are oore massive but are interdieitat e d with th e eneisse s at the contncts, pnrallel with the folia tion , A f urth er type occurs where~ basic body partial ly cross cuts the foliation of the cneisses and is partially boudi3ed p a rallel with the foliation.

'¼/hen It is considered that ~11 the structures seen in the gneiss c ompl0x could have been derived by mechanical deformation of rocks which were previously separate masses er l e ucocra t ic and b~sic rock, by a process of .
flow and differential noveaent alon e fo liat i on planes .

As well as the l a r e er b~sic bodies, th e l enticul a r structur e of th e banded gneisses can also be accounted for by the same mechanism.

The oriein of the rocks which we re affecte d by this deformation is not known.

Sillimanite is present in many specimens which may indicate a p e litic orig i n .

Porphyrobl astic feldspars are common but may be the result of .

chemical oobility during or or after the foliation.
74 A number of ·fine-erained.granitic veins cut the eneisses, being particularly prominent at Itaki falls.

They h.:rv-e been- d-emonstrnt.ed _'..t_q .be intimately connected with the joint system ·of the eneisses .

nnd 3ppear to be i ntr,usive in oricin.

Dolerite dykes .

cut the c-,:neisses, in the 1.fazaruni, e;enerally alone joint planes.

Some larger cykes occur to the north of the river and are also present in the area _of amphibolit 9 s. Alluvial .
gold has ·been worked in this r3gion but very littl~ ~oF'lrnow goes on as most·prospectors have In the area to moved up river in search of diamonds.

the north the 5 old in the Peter's and Aremu Mine area is t hought to be associated with intrusive granites at the contact of the eneisses and raetasediments.

This •situation is not repeated here; but eranites intrude the gneiss complex and are very similar to other granites to t he north ~n<;l west associated with alluvial e;old.

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, 75 : · · .. , R.: :·, T·HE PURUlH S,rb > SQUARB· HORTH OF -THE .

, .PETER YS MINE ROAD .

by· M.G.

___ Allde'ridge Asst, Geoloe;ist ) ' ' I • ' ., ' The rock types' occurrinc in the area are in order of 3ge \'.ls follows ·: · Whit e Sands Bnsic Intrusives Granites Puruni Formation: Metasediments Gneisses and Amphibolites- White Sands consistine of pure qu.
'.irtz sands, ·'- ' · · showine evidence of wat.e.r transport, cover a ride:e porth'"of· PeterYs M. ne- Koridbo ·road nnd a lso smaller ' ' ~rea~ oi:i the road itself.

Small outlinas of these · : ··:.

flat· ·surfaced sands occur to the north-west of this <·!r)_._;;irea·.,·' It is estimated that the sands are not less \.

__ .

:' ·'' than 70 ·feet thick .

::i.nd are nt an elevation of approxi mately 400 feet above se~ level, 1; ·' .

11·• !

Basic · Intrusi.a_ve~ in .

the forI!).


qf cioler;ite dykes 'cut a l l the 'r.ock typ~s except tha wh;ite sands.

In the north-weft .. of t,ll9 a:re,3 t~e_y have .

a m.'.l.rked trend a little north 'of ensto They -'.llso cut the amphibolites in : the south nnd.

east of th-e area.

but no definite trend was noted., ,!

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Grnnites: Three ar~as of e r~nites nre present ·.

(a) ,: In the north 3 hc;,rnblende-biotite in this ,- region, e ranit e .

..,, the southern, ext_en~ion ,of.


the Aremu-Quartzstone e;r anite t>eat1s •-intrusive ·relationships to the metn sedicents and to the Gne iss es and aophibol it es .

It is slip;htly fol iated close to .. t.b.J~ .Jn9_r e in, parallal with its cont ncto It is on the southern na~ein of this e ranite th8t th·e · Aremu :M:i.n~ was situ.

:1ted, (b) A porphyritic biotite crnnite outcrops in the Puruni Riv e r between PeterYs Mine landine 3nd Mara Marn creek .raouth.
Towards tha northern oar g in where Peter9s Mine was situ.

:1t0d is a ninernlized shear zone, The main raass of the e ranite is unfoliated but s all areas of· cataclastic £-0liation we re seen.

Its contact with other rock types is not expos e d. (c) In the re e ion of the Puriari River head there is a foliated ' biotite g ranite, nnaed the Puriari ~ranite by Bishopp.

It may be .

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It may be .

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southern extension of the Areou- Q_u<'lrtzstone e r anite linked to the latter below the surface, and thus it probably intrudes the araphi bolites and th e metasediments.

However it is also possible that it is oore intir.lntely connected with the 13neiss and ar.1phibolite c omplex.

76 Metasedi ments of the Puruni Formation (Cuyuni Forrdation*) and subordinate lavas which are contin- uous with those i n the Puruni River uncierlie the central and northwestern part of the region.
The formation is represented by foliated conElomerates, pebbly sandstones, sandstones .

of ~aried p rades, silts and quartzites.

Fine-g rained i e neous rocks are present as a subordinate type.

These rocks are c ata clastically foliated in a fairly constant direction between 280° and 300°.

Metamorphisn of the sericite chlorite g rade h a s taken place.
Amphibolites and Gneisses in the south and east are large hills underlain by amphibolites, a~phibolite schist and minernloe;ically folia.ted gneisses1 These are continuous with the e;neisses and amphibol i tes in the lower Puruni which c~n be tr a ced into the Mazaruni e;neiss cooplex.

The mineralo~ical folia t ion is eenerally in a north e rly or northenst3rly direction.
It is thouc ht that tha e;neissose southeast portion of the Aremu-Qua rtzstone crnnite beloncs to this complex , into whic_h th ~ g ranite has bcen intruded.

Owing to th e di fference in metamorphic erade and type nnd direction of foliation demonstrated in·a detniled traverse of the Puruni River made by E. Willi3 s, it is considered that there is a hiatus between the eneiss nraphibolite complex and the meta sediraents.
/.,:l.rea Aremu and ?eter's Hines are two areas from which lare;e q1,1.antities of eold were ext·ract~d in the past.

Mbre ~ecently only n very fe~ pi6ipectors have worked in the/ owine to difficulty of transport.

· Both minas were situated on the mare;ins of cranites, thouGht to be associated with the contact of th~ meta sedinents and eneisses, nnd a mineralized shear zone is present in the Peter ?s Mine a r ea.
Huch vein quartz is present along th~ line between the two·mines and it seems that the eold is a ssociated with a ·zone of weakness picked out by t he e;ranit~s.

1~ This publication P• 43 ,· .

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, 77 S. .

EXPLORATION OF .. ALill4IliOUS LATERITES IN THE KUKUI AHD KAMARAHG RIVER VALLEyS by J. W. Car t er; Assistant Geologist th · 1959 areas of a luminous laterite were discovered i r1 the I(o'pina n e; Valley ass ocia ted with dolerite sills • .
· ·'Dolerite· :was alr~ady seen in the Kukui Vallay and further to tha east but the e xt ent of lateritization or bauxiti- .

z a tion ·was ·r.10t _known.

A rapid · reconnaissance surve y was c a rried out durine the first field season 1960 in order to delimit the a r ea of lateritization and to test its depth.

A preliminary r.iap wns prepared on the scale of 1:125,000 with attention being paid mainly to dolerite arens.
The e;ener nl succession at ,\yaneanna is as follows: (S.:lndst one ( ~Gabbro (S andstone ~ Con e loaernte ( (Sh,:lle ~Gabbro Ror a ima For ation ~Sandstone or Pebbly Sandstone ( ( Conglomerate In t he Upper Mazaruni Region, the Roraima Formation is wel l e xpos ed on the plateaux and esas collectively known as the Pakara:irJ.a Mountains .
The sandstones, cone lo erates, shales, qua rtzit es and d o l erites a r e predominantly flat-lying g ivine rise to table lands, plateaux and mesas.

La teritization and bauxitization hns dev eloped on f l at planntion surfaces which have very long periods.

Several flat surfaces h ave been n oted i n the r e s ion, tha r.iost inportant of which nre ( .

:i ) the Kan.:irang- Kukui Val ley Surf.

'.lce; Surfn c e and (c) the Kra inarutipu Surfnce.
r emained undisturbad fo r (b) the Puneaik- K3now The Kamarane-Kukui Surf.

:ice is an extensive surfa c e, underlain chiefly by dolerite , in the Kamarane Valley, up the Mazaruni t o the Kukui a nd then further south.

The g eneral level of the sill is between 1550 and 1800 feet M. S .

L .

a nd is u nd e rl a in by sandstone and pebbly sandstone.

• The surface is late ritiz e d throue hout, and in a few places pockets of eood bauxit e were not e d .
The Punpa i k-Kanow Surface dolerite occupies the hic h eround between Phillipa i and Chinowiene , at an a v era g e e levation o f about 2550 f e et M.S .

L. Most of the feat ur es displayed here a re rather similar to those of the Kamarane Kukui surfa c e .

• 7s On the Krai.marutipu Surface at an elev~tion of a pproximtft°ely .3'500 .

feet .

dolerite is also exposed and is lateri-t;._;ized · and ba.uxitized.

However, creeks have cut steeper and deeper valleys so that the topoeraphy is more rueged.
Lateritizati on is not as complete as on the other surfaces and laree masses of fresh dolerite are seen.

Lateritic deposits of the kind found in the Pakaraimas are in common occurrence throuehout the tropical world and have·been formed as special weathering products of basic rocks.

However, the deposit is rich in .iron <lnd only moderately rich in alumina content so that any portions workable as bauxite would be restricted, a nd would have formed due to cer·tain peculiarities in the deposit.
... ~1 ' • 79 T. REPORT ON THE UPPER CUYUNI RIVER EXPEDITION, 1960.

I ', by L.L, Fernandes.Assistant Geolocist · The expedition was c a rried out in t h e first f i eld :season' ·of 1960 · with the object of: (i) Determinine the nature of the lateritic cover over doleritic rocks in the Pakaraima Mountains of the a rea with a view to the possible o ccurrence of bauxite.
(ii) Sunutlne up the diamond and eold minine poten tialities of the a r ea, and (iii) Rev isine the geoloe ica l cap of the area with th~ a ici of aer.:i.

?1 photoe-raphs, The raain physical features of th e area are the hieh pla teau of the Pakaraima Mountains and.the lowl and area bordering the Cuyuni a nd Wenamu Rivers.

The moun tainous reg ion comprises an ext ensive plateau of about 2000-2200 fee t hieh which is d otted with a few outl iers .
that reach up .t 9.. 2500 feet and surrounded b y lower erosion surfaces at about · l500-l'l00 feet and 700-.800 feet.

The plate~:u:,c .. · !.

:i§.ve been deeply i n cised by the rivers with the forra-'.l:tion of steep escarpments and several water falls c A stretch of ,re.l..at.iY:ely low land und·er 500 feet hicrh extends on the rieht ·bank of .

the CuyUhi River between Wenamu and Ekereku Riv-ers,,· The succession represented in the area is as follows: SQ The Youneer Basic I ntrusiv e s 4 .
The Roraima Formation 3o The Youne; er Granites 2.

The Older Bnsic Intrusives 1., The Mazaruni Group The ajority of the rocks of the Ma zaruni Group i@leOUS rocks of int e rme diate (trachytic) a re fine- e r ained composition, The r ocks are sliehtly foliated and usua lly very a l t e red containine; chiefly plaeioclase l.n1 c;.,.

2 c;, ortho clase , secondary chlorite, epidote and calci te w:itn some occasional quartz.
Feldspar porphyries with phenocr ysts of o l ig oclase and o r thoclase are widespr ea d, whil e ther a re scattered occurrenc es of sediments.

(See page above) .

The Haim.arak a For.nation is included in this eroupo It c o nsists o f shales whic h are usually purple in colour but nay be darker coloured near intrusives.

They are intens e ly fold ed and may be inter.bedded with the fine e r ained i gneous r ocks.and sediments noted above .
The rocks of the Mazaruni Group are intruded by Older Basic I ntrusiv es as dykes and sills whi c h .. 80 .

.. are now much altered by metamorphism.

Feldspars are often s .~u~~t:µ"itized .

:i.nd the pyroxenes altered to chlorite.

The Younger Granites are represented by three small outcrops of intrusive e ranites found in the Wenamu River area.

Some specimens displny lnrc e pink orthoclase and plae ioclase An10 crystals, and slieht foliation.
The Roraima Formation in this area comprises about 2500 feet of ·sandstones, quartzites, ~rits, con5 looerntes and shales.

Conelonerates occur near the basa of the forontion whila white and cream coloured s a ndstone pre dominates in the upper part.

The beds are mainly flat lyine; .

The Roraima Formation and the older beds are intruded by a number of Youneer Basic Intrusives as sills and dykes.
Thi ck gabbro sills occurrine within the Roraima Fornation·often cause contact metamorphism of the intruded sedinents.

:_In the investie.

;a tion for bauxite three pits were put down in the weathered mantle over gabbroic rocks.

Positive identification of bauxite has been possible in the results of a nalyses are awaited.

one pit; The lower Ekereku River yielded very poor results in the prospection for diamonds.
Go od diaoond indications and eold colours were seen in the rieht bank tributaries of the Wennou River. '

• ( • I ., , ·~ ,.. A?

PENDIX II 81 GEOLOGICAL SURVEY OF BRITIS H GUI/i.Nf~ S ENIOR ST~FF h ~ 31.12.60 EST i~BL IS I-IltlENT Director . "

.

NAME ••• • • • R. B.

·11cConn ell, C.B.E., Ii.:,.

; • • , D.es Sc, (Lausanne) D, Phil., 1✓:i • I • E • Itl • , F • G • S • , F • R • G .s • 2 Deputy Directors ••• C.G.

Dixon, B.Sc., F.G.S• D, Bl eackley, M.~., D.

Phil., A .

M. I .

I-1 , M., F,G.S .


3 Senior Geologists ••• P, H. A, Martin-Kaye, B.Sc,,~ Ph.D., ~.~.c.s., F.G.s.

ft 9 Ge ologists • • • P , B. H. Bailey, M. ~ ., F.G.S, R, T • Cannon, B .

s c., M.I.:t>·I.

M:,, F , G ,.

S • E. Wil l iams, B.Sc., Ph.D., F .G .s • ••• C. N. Ba rron , B.

A., F.G.S • D, D. Hawkes, M.Sc,, F.G. S .

J.U.

Ba teson, B.Sc., F.G.s.

J .

~ .

Lloyd, B.

Sc., F.G.S.

x:.

Br a mley, .

B,Sc., F ,G .s • s .

S:ineh , B ,Sc.

M. ~ .

Ca r t er, s .


s c. Vac ant Va c ant 3 Assista nt Geologists ••• L, L. Fernandes , B,Sc,, A,R,.S,M, M, G. Allderidge, M, A, J, W. Ca rt e r, B. Sc,, k .

R,S.M.

Chemist- Petroloe ist • • • Vacant Geophysicist-Hydrologist ••• L. B. Ramsahoye, B.Sc~, D.I.C., Ph.

D. 2 Scien tif ic Assistanis Chief Draughtsman Chief Clerk ••• • •• • • • ••• D.O , Pollard Vac a nt T ,M. Rahaman, Graduaty of Technical\ Institute, Trin:iJ:lard.
F. J ohnson S upervisor of Libra ry and Records • • • H , K. Georg e Seni or Accoun ting Offi c e r,.

L. F .

Choy ~A-Seconded t o ~lindward Isla nds • .

_.;;--1, ·:rt~ ip:,.· ~ '-t. _ ,;:.

I .~• _._ ·- :.:.

'I-- ' ~--~~~ent :~: ·~-~~!.


I • p -~~:-',- Upp~ Tertiary ' t-o Pleistocene - •· GEOLOGICAL SURVEY OF BRITISH GUL\HA APPEU~IX III REVISED STR!,TIGRAPHICAL TABLE OF THE GEOLOGICAL UNITS IN BRITISH GUIANA = AGE STRATIGRAPHICAL UNIT ROCK COHPONEHTS AND 1-HHER.l,L DEPOSITS j-2/;, /l , ~ t ,.. 82 Corentyne Group Demerara Formation Marine clays with rare liP.Tiites and sands containine shells.

Includes recent alluvial deposits.

Clays for bricks and ootterv.

shell deoosits (lime).


Coropina Formation Berbice (or i·Jhite Sand) Formation Harine and brackish clays with some lignites and sands.

Marine terrace level.

Sands, sa~dy clays, lignites, and localized basal conglomer- ates.

Conth,ental-deltaic and littoral-deltaic.

Gold, diamonds.

~lass sands.

?

oil (off-shore only).

U n c o n f o r m i t y w i t h lo c a l i z ed b aux i t e d e p o s i t s < ;•'hower Tertiary ..,.and (?)
Cretaceous Rose Hall Group (coastal area) Sands, sandy clays and.clays with some lie;nites towards the t9p.

Some Eocene and Paia~ocene microfossils and pollen erains now under study.

Grou_ p established from borehole cores.

?

Oil (off-shore only).

· Tertiary or Cretaceous ?

Mesozoic ~-- ?

Palaeozoic ~ -~ " Takutu · Forr:1.ation (I':.up~wii District onl Red and grey shales and sandstones with plant remains, ostracods.

Younger Basic Intrusives 1• Doleri tes quartz dolerites.
Quarry stone Roraima Formation Current-bedd;d quartzitic sandstones and .quart z ites with conglomerates and some shales and jasper.

Colour dominantly p i~_ light erey and red.

Diamonds, gold, stone.

____ _ .. r· ·- .. •·, .

""':'.. ; '""- -.~ ·.

r C'v ;f. ..... ..,_.

•:: H ~ a:) '-.

::1 ""' ~ -~ u r.a ~ 11< G r e a t U n c o n f o r cr i t y You,_, eer Granites /,mphibolites -- Biotite and h ornb lende eranites, includine foliated and enei ssic f2 cies .

Gold, columbi te , ?


base meta ls, beryl, etc .. - Aophibolites % h9rnblende schists and eranulites - may belonc eit h er .

to Youne er Granites, Bartica }.ssemblae;e or i ntrusives of v a rious a~es.

Kartabu e r~nite 1-1use-ovite· er~n i te pas sin.e: to muscovite-biotite F,Tie iss • Essequibo Gneiss Group Banded biot it e or h6rnblende- biotite e n e iss, hornbiende- schist .

amnhU)oli t e.. 1:-'.iica .

feldsoar.

nu a rrv stone.

7-2SB ···- Middle to Upper Bartica ,·,ss e rabl ae;e Middl e ?
Baraoa- Mazaruni- i\ sseo.bl ae;e I:la zaruni Group Barama Group Greywacke-sandston e s, pebbly sandst ones and con g lomera tes; l a vas, pyro clastics and aua rtz::j..tes with intercalated muds tones; bas ic intrusive .

r(cksh h ornbl ende schi st and araphibolite~ Go ld.

base meta ls ?

c romium).


Muds tones, quc:.rtzi tes, a r e i l l ites ; fe rous schists and e ondites; phyllites, sericite and sericite- chlorite schists, including metasediments, metavolcan ics bas ic intrusives; b i otite an d biotite-hornbl ende e neiss; hn.-.nhl <>n..-:1 ,;::.

· r;,r,h ;~t-.

.<inn nl.<i.D'iO<'l a.cu:i,_ qn,nhihnl; t,A.

Tib ni::-anAc:::!P.

anl rl_ lavas and tuffs; r:iang-ani- .and ?

u n C 0 n ... -F 0 r m i t y ?


Lower Ru pun u...ri i i~ss embl age ; ,_ .. South Sava n nas Group fllarudi Group - ICenuku Gro up South Savannis biotite g ranite, b i otite gneiss; encl aves of banded bioti e and basic l'!ne iss es .

Monazi te nagnetite .

mic a .

- :1.1etaquartzi~es, ps ~mmit ic metc::sedim ~nts, b i 9tt te schist .

a nd banded biotite e;ne i ss.

S trat i g raphical position uncertain.

Gold.

iron.
Gold.

iron.

Hypersthen e a nd: b i otit e - e:arnet e r anul i tes, charnockitic cneiss and hyperst he:ne · P.-ranites.

".'

.... ,h__,"'9, 1,,,~ -> - - ~ · -c.,-'i"f ;{ ~ ~ - • Iron.

- - - ">1 -~ · 1 .

- • Unc·1 rr e l a ted Kuyuwini Group Rhyolites, ar;id:~si_tes 2.nd cori:-esponding tuffs.

(Possibl y of Middl e Precaobrian ae;e ).

Gneisses a nd e;ranit es Biot ite and hornbl e nde e neiss, gran i t e - une xplored por t ions of Southern Brit ish Guiana.

Mica, etc.

i n p a rtia lly 1rn .


Bauxite and l ateritic ir on ores are asso ciat ed wit h l ateri t ic d e p os its of di ffe r ent a£es .

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