!PERSATUAN GEOLOGI MALAYSIA NEWSLETTER

The unknown mineral was recovered, together w:i th cobbles and boulders of country rock contai~ing veins of cassiterite. The romeite is in the form of...

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. Geological Society of Malaysia



!PERSATUAN GEOLOGI MALAYSIA

NEWSLETTER

September 1973

Number 44

CONTENTS Page GEOLOGIC NOTES P.C. Leong & F.L. Yap: Occurrence of Romeite at Tai Lee Mine, Sg. Siput Utara, Perak

1

Leslie R. Beddoes, Jr.: The Changing Exploration Scene in Australasia Abstracts of Papers: GSM Seminar on Mineral Exploration and Evaluation, 8th September 1973

10

REPORT OF MEETINGS Annual Convention of the Indonesian Petroleum Association, Jakarta, June 4 and 5, 1973

15

Meeting of 7th September: D.E; Karig .

18

R.H. Murphy and

GSt1 Seminar on Mineral Exploration and Evaluation, Kuala Lumpur, September 8th 1973

20

NEWS OF THE SOCIETY Bulletin 6

21

Membership

22

Issued bimonthly by the Geological Society of Malaysia, c/o Department of Geology, University of Malaya, Kuala Lumpur, Price to non-members: MZ1/copy. Bock issues MZO·50 to members.

GEOLOGICAL SOCIETY OF MALAYSIA Officers - 1973/74 President

Vice-President

R.W. Murphy Esso Exploration Inc. P.O . Box 57, Tanglin Post Office Singapore l~

S.H. Chan Dept. of Geology University of Malaya Kuala Lumpur

Honorary Secretary

Assistant Secretary

€-.H. Lei-gb

Dept. of Geography University of Malaya Kuala lumpur

C.H. Yeap Dept. of Geology University of Malaya Kuala Lumpur

Treasurer

Editor

E.V. Gal'lgadharam Dept. of Geology University of Malaya Kuala Lumpur

B.K. 'fan Dept. of Geology University of Malaya Kuala Lumpur Immediate Past President P.H. Stauffer Dept. of Geology University of Malaya Kuala Lumpur

Councillors 1973/74 K.Y. Foo Geological Survey lJalan Gurney Kuala Lumpur

K.W. Choy Conzinc Riotinto P.O. Box 291 Kuala Lumpur

T.H. Tan Geology Department University Kebangsaan K\,lala Lumpur

Councillors 1973/75

S.C. Toh C<;mzinc Riotint:;o P.O. Box 291 Kuala Lumpur

E..H. Yin Geological Survey P.O. Box 1015 Kuala Lumpur

Address of the Society:

M. K. Choo Associated Mines P.O. Box 2125 Kuala Lumpur

K.M. Leong Geological Survey Kota Kinabalu Sabah

LS. Chong Geological Survey P . 0 . Box l~n5 Ipoh, Perak

Geological Society of Malaysia c/o Dept. of Geology University of Malaya Kuala Lumpur

GEOLOGICL NOTES

Occurrence of RomeiteatTai Lee Mine, Sg. Siput Utara, Perak P.C. Leong and F.L. Yap, Malaysia

Geological Survey of Malaysia,

Ipoh,

As far as is known, no previous occurrence of romei te in Malaya has been reported, although stibiconite and romeite have been encountered in Sarawak. Attention was first drawn to the mineral through a dark green, fairly hard pebble being sent tb the Geological Survey for identification by the owner of Tai Lee Mine near Sg. Siput. The specimen was found among .the gravel on the mine floor. The Tai Lee Mine is operating as a gravel:1>unip mine now, but in the past, at the beginning of the century, the .¥,~a has been worked as a lode mine known as Loke Yew's Lode. The Lode o6curred as a network of small tin-bearing veins. in chert and shale. A brief description has been given by Savage (1937). The unknown mineral was recovered, together w:i th cobbles and boulders of country rock contai~ing veins of cassiterite. The romeite is in the form of pebbles ranging from 3cm in diameter to lumps of 5cm x 8cm x 7cm and varying in color from yellowish green to chocolate brown, presumeably depending on the Fe 2+ and Fe 3+ 'contents. It is often veined and encrusted with, iron oxides. Spec'if~c gravity is about 5.1; and hardness about 5.' The mineral is isotropic and in microsection is observed to be made up of an aggregate of extremely minute grains. A Debye-Scherrer powder photograph shows the strongest 14 lines to be very close to those of titanian romeite on the ASTM cards (see Table I). However, chemical analysis shows th~ mineral to have the following composition.

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4.80% 0.30 ,

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16.40 MgO

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,PbO,

trace

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Fe203

1. 36 0.38 '

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Ti0 2

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------------"Specific

Gra~ty

S.16

It will be noted that the titanium content is only in trace quant~cy while the sodium content is 4.80%, indicating that the mineral should be reg~ded ,as ,a sodium rome.ite. , No powder diffI:'9-ction data on sod:iull romei te is available at the Geological: Survey for comParl.son, but it appears reaSO~l­ able to assume that the d spacing values will not be vastly different from those of titanian romeite.

3

It is not easily exPlained: hoW-the rome;i te had originated as other' antimony minerals ·hav;e. so far. pot been foup.d at Tai Lee Mine. However jamesonite has been known to occur in the" Sungei Siput. area. It is intended that further investigations will be conducted in the mine', ·this note being merel,.y .a preli.minary report of findings to date. " ,,'" ..... ."

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REFE'RENCE .,

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SAVAGE, H.E.F., 1937, The Geology of the Neighbourhood of'Stingei Siput~ Perak;··Federated)1alay States ,,..with an. Account of the Mineral Deposits. G.epl,.og~~a:},. ..SUI'vey~: ~einbir:·~~ •. ·L... '·'··::f· . . .,. ...

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X-ray Diffraction Data' ':'.'. ::':'. 14 'stI'6ngestlines in-dexe. 4:

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Relative Intensities . III' + .: ,Qiiknown. ·Mip.1t~~. ,' .....

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+ Cu target,

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filter 30kV and 26rnA.

* Cu target, Ni filter.

Exposure 3· ilOUI's

.'

The. Changi.ng Exploration Scene in Australasia~;+ i ;':

. I"

.~.,

':'. Leslie R. Beddoes, 'Jr. )'Cities Service .Eastr:Asia, Inc, ,L

_

Si~oapor",

,-

Petroleum and mineral exploration in", Aust·ri:di.a, Papua New Gui-pea and New Zealand are currently undergoing changes brought about by .an interplay of political and economic factors. Australia is marking time and taking a step or two backward, while a new ~aborGovernment prepares their new set of exploration rules. ,

Papua New Guin~a,' approadh.ing independence as a:"n;a1;i.on ,. presents a climate of uncertainty as near-term internal struggles mas~ long-term policies within a country of substantial natural resource potential. New Zealand's change is far more subtle and toward the progressive, An expanding economy, guided by stable government policies is looking for indigeneous mineral power sufficiency and possible export markets. We, the explorers,are di:r~ctly' effected by any such increase or decrease in exploration requirements, due to economic timing and/ or political rules. To a large degree, the interplay of politics and economics creates the' exploration. cycles with which we are so familiar, and over whic'li'xwe "ha:ve'little ·control. . ,

'

Let us now review, each country, separately, it:l.regard to: its political climate, economics of exploratio::l and developement ;'and explbra1:ion "acti vity •...... - ..- ... __ . .'

cur.rerif· :.'

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AUSTRALIA·

Political Situation: Australians elected a new government, the Labor Government, into power in early December, 1972, replacing the Liberal Government who had . ruled for the past 23 years. LaborYs nationalism and socialism pollcies~ well announced prior to the election, have drawn loud cries of concern from private enterprise and State Governments. New Labor policies have had some harsh effects upon exploration and development of petroleum and minerals in their establishment of:- . fa)

Federal control over export of: all mineral and energy resources: e.g, approval of export projects, product prices, and corporate composition of exporting companies;

* Address

delivered to Geological Society of Malaysia - July 6, 1973

. '+'The opinions expresSi:d in trn..s .paper are solely those of the author and not· 'the Society., . "l: ". " . ': . . '. .......... .. .

5

(b)

Federal control of oil and mineral expltration rights for all offshore areas. These rights are now held by each State . . . ~ -".

(c) . Feder.al· CCOlltroi over all pi pe"1.inesea.rryl:ng oil arid natural gas, : both' onshore and offshore. (d)

A National Minerals and . Pe.tpoleum Authority" to' explore', for,. produce, refine, and transport petroleum and minerals. .

(e)

A cons'ervationpolicy for energy .fuels and minerals to satisfy projected needs of Australia.

(f)

A decreaseoffor.eign investment .and participation in all exploration and de~~iopmEmtvent·ureg· involving' natural· :resources. . The ·Minister· for Minerals and Energy recently quoted that 62% of' . Australia" S ndneralsand 70% o;eher crude oil and natural gas are owned'or'contIiolled by foreigns8mpanies.·

The Government is'serfbusly contemplating a production-sharing type. of ventl,lre for future exploration. Since many of Labor's'policies are in ,direct' conflict.with the previ6us system, a certain amount of time 'is'needed to implement the newc'oncepts and to' set-up, st.af:f:ai:ld run the "large ,newly created G6yernmentagencies, In the meant~ine.,';\t.4e Labor . Government has . iJIiposed 'the. following restrictions on. . exploration:; . . :

(a)

(b)

,'. (c)

The Labor Government has not and will not appt'ov~: any farmout/ farmi~p~oposals on petroleUm or mineral exploration leases anywhere iIi Australia where: the. compan,yinvolved in the farmin .is foreign owned or controlled. " J . " To restrict foreign capital from entering Australia for explqra.tion or'developmentprojects, a 25% deppsitpf all . fo:r.e,j,gi-i,: ~.:ioan,il :capi tal is required to be I>.J;.a:oi2a"w,lth the Federal Reserve Bank for a ·tv~o year period ".intet'est free, Overseas finai'1ce for domestic enterprises ,may' be channelled ~hr:~u,&h the. Australian Industries Development Corporation (AI~C) and avoid this 25 go deposit ' . Generation of local risk capital for Australian explorers discoUl"'l"lged early this year, when the Government announced that it was' d'isallowir..g tax deductions for private or corporate investors in exploration'ventures,.

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(d). The Gqyernment' s financial as:;istance to explorers through the 1957 Petroleum Search Subsidy Act is also'to terminate, effective June 30) 1974.

6

. ': i

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Labor's timing' is eri tical, and "di-~ected toward two ·:impor.tant events;. :The first is "offshore acreage relinquishments". One-half of each offshore lease around Australia will be turnsd-:back' tP,··a: ! ':.. government body for re-distribution from mid-1974 through:mid-:1976 • .the Labor, ~qvernment w~nts this acreage returned to a Federal body, rather than to each State, as would now be the case. . ., '. " The ,s.econd. important event is another scheduled Federal election, in late 1975, where Labor must show some results for their new' policies. "':

Ecpnomic

f~ctors'

of Exploration and Development Projects

. Hithin this. changing political climate,.· the economics of exploration ventures within Australia are currently'notfavorabl!e ·anddo not encourage new exploration interest. However, many of these ,factors are held-over from the previous Government's policies. A few brief elements o'f'product pricing, costs, taxes and royalties are as follows:1 I'

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'• • •

. • , •

• .'

. ~ ':

a price' s:chedule" . determined in 1968, by the previousGo'\l'ernme~1: to ,be' effective-until September 1975. The current price of Bass 'Strait oil'is tJS$2.94/bbl. (F.O. B• loading terminal). This is 'clbout' 70 ~ 80 cents "l>elow import parity and the producers have long been requesting a price' 'rise' for indigeneous crude.

1. .: Crude Oil Pricing wi thin Australia is set' at

Natural Gas Prices have been fixed thpough tough negotiation between producers and government agencies. Profit margin is. small and, . consequently, little risk capital is being generated. Mineral Prices are somewhat bett~r~. cmd appea;t' to b~. based upon competi ti ve world market prices. S.everal ,iron-ore and coal contracts havtf been re-negotiated' to recover cont~act prices lost in the l • . .. recent U.S. Dollar devaluat~on. ,'. 2.

Exploration costs are relatively high:due to remoteness of many of the operations, and lack of available services and equipment to ','., 'create a competitive climate. • . •

.

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3.'::'·Royalty for oil and gas is basically. 10%, but. has been increased to l2!% in several Bass Strait fields as ana,iternative to production lease relinquishment. :',..

4.

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cUrrent 'taxes' are 4 7~% on produced incomo,,. after all allowable exploration costs have been deducted. .

7

Current Exploration Scene '':lbeeff~~ts of political reorganization of natural resources along

wi,t}:l",lack:o~', fa'Vor~le 'exploration economics ~ have, had a predictable clampening, eft=e~t upon exploration acti vi ty • Most petroleum ,exploration

acti vity-,is centered '011 the Northwest Shelf, where 4 rigs arecUrreIltly active and 3 more will be working here before the end of 1973. ' . Since 1968, the, Northwest Shelf has increasingly proved to be ,~' major,',hydrocarbon province. With an approximate success ratio 1.' in 4, compared to the North Sea's reported in 1 in 25 ratio, some 19+ trillion cubic feet of gas and 700+ million barrels of oil and condensate have so far been discovered in 5 fields.

of

Mineral -Exploration anddeveloprilent of new ventures have also be~n slowed do'WIl by the, ~estricti6n of foreign capital and uncertainti.es ofgovemment policies. The G6v~rilment' s close look" at all deals inVOlving foreign participation has '1l shelfed'; many large project propo~als. , i

PAPUA NEW, GUINEA Political Situation With encoragement from the United Nations and Australia, Papua New Guinea is on the verge of independence. In the current t'imetable of events, Papua New Guinea should be self-governing by the en,dof 1973. ".J;n.dependence should follow soon after, from rilid-1974 to :'early 19'75. ,,' ,As with so many emerging nations, Papua New Guinea has seripus internaLpI'ObleI!ls. Struggles are currently in progress for lan,Q.ri , rights, as well as political power,with the concept being that the land held at the time of independence will be honored by the new government. Tension and conflicts are intensifying as time for independence approaches. The Government party in power appears to be solidly based, and general guidelines have been proposed for mineral and petroleum .exploration ~d,development. These are favorable, since Papua New :Guinea,iSi:filage)[''t9 eIl~ourage projects using local labour and generating , substantiaL income. ': " ' , . '.. . . . . .'

Aust'raitan and international companies, are currently he~YilY invol ved in mining and petroleum ventures in Papua New Guine'a, and the Australian Bureau of Mineral Resources is completing geological and geophysical investigation of Papua New Guinea's natural resources.

8

Economic Factors Papua New Guinea is still.tied to Australia's economic and exploration policies. However, their Administrator has recently. showed autonomy by further encouraging various exploration projects. Exploration companies are concerned about post-ind,ependence policies, but thoBB close to the situation are optimistic. It is speculated': that Papua New Guinea may also adopt a production-sharing concession agreement for "petroleum exploration, similar to that in operation in many other parts of Southeast Asia. Papua New Guinea does not have any oil or gas production to date , but does have substantial copper production at Bougainville. Major economic factors in Papua New Guinea, are high costs of explo.ratl.on project·s (due to the geography, complex geology, and operational and logistica~ support required) - and the magnitude of success necessary to create a viable project •. Papua New Guinea. has smail internal needs for natural resources and would probably 'export most minerals and petroleum discovered ·there. Officia.ls have, . however, expressed a distinct desire to internally process natural' resources to the maximum extent prior to export. Farrnouts have not beel!' frozen· in Papua New Guinea, and several companies are actively seeking partners to assist evaluate their acreage while subsidy is still in effect. Also, Papua New Guinea does not ha,ve the 25% surcharge on incoming capital, as does Australia. CurreritExploration Scene Since petroleum subsidies will remain in effect for projects completed before 30 June, 1974, there has been a recent rush of petroleum exploration· activity. This follows abundant seismic work completed during the past.few years. Mineral evaluation work is .also increasing in various par·ts of Papua New Guinea, mainly by large· Australian' and international companies. NE~.J ZEALA,,~~J :';"/'"

Political Situation. A Labor Government carne into power in New Zealand- in O~~ober, 1972. Reforms made by this government wera progressiveCl.nd the collIitry is enjoying a booming economy. Mining and petroleum legislationihas been .._upd'at~d and export policies decided for natural resources.

9

;Economic ,F:a:ctdrs ~

.. - .

, ,New, Zealand has a relatively small internal market' for, natural' , resou'P9.~s'c:ind 'islooki'ngfor export situations, to ,improve her trade balarige. 'It is anehergy rich country with hydro:':"electric power, thel'mC!.l po~er'~ abundant coal reserves, and naturai gas'~' New Zealand's old mining and oil legislation contained long lease terms liberal'work obligations~ and low royalties ,(5% on petroleum) ,but, these were made more strigent by recent legislation.,; E,xplo:ration costs are al?out comparable to' those in Australia. New Zealand does not discourage foreign investments; however, strictly controls the percentage of generated profits that can be repatriated. ' g

In a new-type of involvement, the New Zealand Government announced a few, ,months ago that they would buy, one half-interest in the offshore Mauf gas-coride1'iS;~te' field, disrrovered by Shell~BHP-Todd in 1969, and will then be 50:"50 partner for its development. Cu:rre~t

,Exploration

~ctivity

", On~hore petroleuJll'e'Xploration is relatively inactive, reflecting iack,'ofquaiity prospects and a long history of exploration effort. . ,".. ."'. . . .: . ~.

.

.

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Offshore exploration, however;,shall shortly' enter a'se~ond cycle of exploration drilling when Hunt Oil's new PenrOd 74, semi-submersible reaches New Zealand late this year for at least a four well program off the southeast coast of N€w Zeland. Other offshore operators, with defined prospects) may either use Hunt's rig or bring in another for several additional wells during 1974. Mineral exploration in New Zealand is increasing in tempo, as the price incl'eases and a favorable framework for exploration is maintained. ' ,'. . ~" of~nerals

SUMMARY ,;.,

. :,,";

.,.~; L., In Australia, the new Labor Government is e'i=fectively nationalizing l~ir ~atUrar,resotirces. Their policy is to:. "buy-back ,Australiall from ,fOPEdgn intet\ests, get directly involved, in eXploration'~ cind .conserve

natirraI'resources to fulfill Australia's future needs. ...... ..

.,

-'

,

Australia's Il shut-down;; attitude has, and will continue to, shift oil and mineral exploration companies, and experienced personnel into regions where exploration is encouraged. It is interesting to note that

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even Australian oil and mineral explorers, as well as the international comp~ies, are increasing their exploration effort outside of Australia. 'Areas such 'as South~ast Asia, where' so many partipipation opportuni-ties are evolving, will benefit from,AustraJ.ia's curreritattitude. Discovery of major natural resources in Southeast Asia could also fulfill some of the market potential counted on' by Australian explorers. In 'Papua New,Guinea~ the transitibnfrom territorial rule·to selfrule tonational,indepenqence, presents .achallengingset of circumstances. Internal ~md. exte:rnal pre~sures' 'are~t p,lay on the revol virig nebula forming this new nation. It is anticipated, however,that an increasingly unified Government will, emerge to continu.e a reasonable' environment for exploration.' . , 'New press ing atti tude gas, and

Zealand is.changing gears toward a more progl:'essive and atti tude for dev~lopment of i tS",natur'al resources • This has and will continue to encourage exploration for oil and. for minerals. '

Exploration companies and explorationists are predictibly responding'to these changes, witqi-flexibility learned e,arly in each of our careers. Exploration, nO... ,matter how aesthetic we conceive it, to be, is connnercially guided by the interplays 'of internationcil and internal ~olitics, and economics of the time • .

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Abstracts of Papers:

GSM Seminar on Minerai Exploration and Evahiation" 8th September 1973

The performance of the Bangka drill under offshore conditions and some problems associated with bore-hole evaluation Choo Mun Keong, ;

':

Associated Mines (M) Sdn. Bhd., Selangor

.

Investigations into the,performance"of the·,con,ven~ional Bangka drill under Qffshore c.ondi t.io~s' O,ff the west' coast of T'nailand revealed that the drilling system has SOme inherent mechanical'limitations. Overall ground sample and cassiterite recoveries were .. found to" be generally poor and erratic.

11

'The'low-volume' recoveries,pJ;'esented problems in ,the ,accurate determination of bore-hole grade and three possibleine:t.hods of· grade" determination are outlined. ' " . " '. ',.,. . Further investigations into the pro~lem of cassiterite and ground sample recovery using a modified Bangka drill incorporating a flushing unit showed that significant quantities of cassiterite and ground sample were,Z;ecoveI"ed on: flushing those hore-holes which_werl?.considered to be "adequately bottomed and cleaned l1 by conventional. Bangka dr'iI1ing. The results of a test programme in which 18 bore-holes drilled by the conventional Bangka system w~re subsequently flushed for ;:my remaining material indicated that sampling of an individual bore-hole'by conventional Bangka drilling was not truly representative as the failure to recover total cassiterit~'f1as riot balanced by a proport;i;,opa+, loss in ground sample. The We;ignted a:verage.'gradeof the 18 .bor~·.,r~su,lts obtaineci bYconven-. tional Bangka: drilling'. was however app:ro~imateiy, equal to the' w~ighted average bf the gt'a:des-~based on the total.,'c'~~.:i..terite and gro,und' samPle recovered by combined conventional Bangka drilling:anc;l flushing; hepqe , on average,. a reasonably reliable average grade estimate' was still . obtainabl~by "bonventional Bangka drilling.

0" • •

---oooOOooo--~

Evaluation of alluvial deposits by homogepeous bloCking'" Lee Wbye Kwong,

Associated Mines (M) Sdn.Bhd.,' Selangor

Folidwing a study of· the' evaluation meto.od\=l pr~cti~~d in the Associated Mines group of companies, a new approach to ore compl.i'ation has been evolved placing particular emphasis on the geological and metallurgical aspects of the area being evaluated. The method involves the division of the area under consider.ations into geological blocks which are homogenous in respect ofsucn'parameters as vertical and lateral mineral distribution, bedrock topography, bedrock type, depth) etc. Stress is laid on the determination of recoverable reserves. ,

Though the evaluation method is particul'a'rily designedf~r' dredging pinnacled limestone, it is equally applicable in opencast mining operations and in di'ffet-ent hedriock environinEmts. ,',

operat~9ns'over

A fin?lore reserve ·block.pi~ is produced'showingdetail'ed information,.·.'1.I$e:f1U fr;>r short,C!-l1d long t,eI'IJI mine planning,- facilitating fairly quick re-evaiuation 'account of changes!!l dredp.:E~··:course':o .. ~edging

on

12

depth, etc. and, in new projects, for economic investigations to ensure the best investment·return. ---00000000---

The D~t'erinination of Free Tin Content in Bore-hole Concentrates . C.H. Yeap, Jabatan Geologi,tiniver.siti·Malaya, Mc;ilaysia Sediments cored from dill-hol~s are normally .washed 'and dressed into'acassHerite concentrate and a discard beavy mineral (amang) concentrate. The former is normally assayed direct to: give the tin conterit,while varioUs techniques are used to deterTninerepoverabie tin content in the . latter • .; . . .: " "; :-.. '~\

. . ' ~ i ,-;;

The practicability of using point-counting to determine tin-content amang concentrates was investigated. Artificial amang samples wer~ made up to simulate actual concentrates from a known prospect. These artificial samples were split into 5 size fractions and point-counted. Weights of cassiterite for each fraction are calculated from the grain-count (volume) percent and specific gravities of the constituent minerals. It is, shown that though the point-count method gives an error of up to 25 percent, this error recalculated to total bore"'value·'isileSs·than one percent, and is a reasonable figure when inaccuracies of the field prospecting method are taken into account. Ease and rapidity of this method calls for its wider practice. The use of ast~ndard assay figure to report'· field concentrates is questioned, .for this . leads to' either over-evaluation or·under.-.evaluation as the case may be. . !' i . ' .

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Biogeochemi~a~ Metl1od. of ExploI'ation

Tan TeongHing,

Jabatan Kajibumi, lliliver-siti Kebangsaan·~· Malaysia

The biogeochemical.method has rarely been used in this country, as an aid to mineral explpration. The studies, based on"tb~analytical data obtained from .the analyses of plant materialsc~llected from ·certai1!

13

parts of the Kledang Range forests (Perak), indicate that there is variation' betwe.en the :metal contents iIi plants growing close to an<;1 within the, zones, of mineralisa'tion and those removed from the, zones of mine:r.aiisation .• '. The vCiriation in the' metal contents in the plants • ' enables
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Genera.1ly.where there' is a 'high metal content in the soils,. thf3, , plants growing ,on :these soils have a comparatively high concentrations. of metals in their tissues. The pattern of the biogeochemical anQrnalies, therefore has a spatial relationship to that of the geochemical soil anomalies. , Owing to the wide varieties of plantepecies in the tropical forests, a collective study of the metal content in all, the plants, in the are~provid~s. significant inforination regarding the pattern of mineralisation in the' area. The biogeochemical. studies reveal that plants in the tropical environment behave :.'9>9 ~riorinal accumulator-s particularly towards 'copper" zinc and lead ~ Th.e" me;t4~d is, however ~ not a' particularly satisfa~t...,. '; ory one, for the search for concealed tin;' tUngsten, arid arsenic, ,de~~ '. ; " sits. ' """ ' . '. '" : Leaves of pl~~rt~ .,are the. most· .sui table biogeochelilical sample~.'.,· since they accumUlate relatively high' concentrations: of· metal~." " partictM-a..rly. copp~r? zinc and lead. Twigs and roots are, nevertheless ~ su~:t.able sin~~ they do give comparable anomalies over areas of minerali.sation. . , ---00000000'--- ,,'

A

~eoretical

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Study of Gravity Anomalies caused by Limestone Pinnac2.::;::.;

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S."H."Chan;Jabatan Geologi, ,Upiversiti Malaya, Mal,aysia The ~~sultsof a theoretical study of the gravity anomalies ca~ed by limestone pinnacles are 'pr~sented. The purpose oftbis study is .to find out what the possibility is in using gravity method of,. geophysical explo;,ation ,for ~apping limestone pinnacles concealed under a cover of alluv~um •.•. Akn9wledge of the limestone'pinnacles wi th.. regard to their spatial.dist.ribution. ~ sizes,' and' depths below the ground' surface, is: 9f imp
14

In this study gravitational profiles corresponding to two-dimensional models are computed to.slmulate actual gravity anomalies which might be observed over. the limestone pinnacles. Two-dimensional models . are used becaus.e the computations involved in this case are easier than in the case in which three-dimensional models are employed. It is also found that in this.case the analysis of two-dimensional anomalies provides information almost identical to that derivable . from the study of anomalies associated with th~ three-dimensional models. Study of the densities of limestone and alluvium shows that aden''sity contrast varying from about 0.5 to slightly over 1.0 g/cm3 exists between the limestone and the alluvium. Witp such a density contrast, an isolated limestone pinnacle of dimensions, say a height of 60 feet and radii of 10 and 40 feet at the top and bottom respectively, can' cause a gravity anomaly detectable by gravity meter' 'with a sensitivity of 0.01 milligal. A number of pinnacles occurring in close proximity to each other produce a.1I!uch larger gravity anomaly th~m an isolated pinnacl-e ~'.. .Owing to the . superposition of' gravi tat~onal . effecits of the indi vidual pinnacles ~ the anomaly associated with' 'su'ch a group of pinnacle has no resolution with regard to the number of pinnacles present and their relative positions. However, when the pinnacles are separated at sufficient distances apart, the presence of each individual pinnacle can definitely be ide~tified :fr>om the gra:vi ty anomaly. ":"!'"

. Computed' ·anomcil.ies associated with pinnacles buried in a deep trough show that such pinnacles are difficult to detect because their gravitational effects are almost completely masked by those caus'ed by the walls of the~ough. This is especially true when the density contrast between trough and alluvium is larger than the density contrast between pinnacle and alluvium. The resolution of a gravity anomaly may be improved by computing the second vertical derivative of the gravity field. The profile of the second vertical derivative computed from the anomaly~associated with a pair of pinnacles separated by a small distance apart reveals clearly the position of each pinnacle along the traverse. Other possible techniques for increasing the resolu~ion of gravity data are downward continuation and digital filtering. Based on the results' of this the.oretical study one J!lay conclude' . that gravity method can be utilized for mapping limestqne pinnacles .. provided that the anomalies' associated with these pinnacles are of sufficient order of magnitude. However, a word of warning is in order. Great care must be exercised in carrying out the actual field measurements because the anomalies to be expected, as indicated by this study,

15

are going to be small and can easily masked by 'noises' associated with the observations. Geologic data and data from other sources . are necessary for proper interpretation of the gravity nieasut;ement~. ---00000000-- ... · .': .

A ¢ompute~':p~io~,amme ,for theevaluC'7tionof ,p~~cer dflflling data Toh Swee Cheng)

Conzin'cRiotinto Malaysia Sdn. Bhd>, Selangor

.TQe'PNgramrne is d~slgned to yie1:d the, basic. data formats necessary for th~ interpretation. and description!'.of placer. deposits. Borelog information is proces.s~dinto masternles':1 for use ·'iri. an integrated series of computer' stibprog:ramkl~:s. : This.;r>aw information can be modified by subsequent contr.ol cords, which' tn,ay,::incorporate assay corrections, ground recovery revisions, and' changing cutoff decisions by management. Programme, reports consist of. bor,e }l,ists, ore· r~.Slerve summaries, - pJ,~sand . cross':"sect;i6ns " ·frequency·taples, and rolling., mean distributl.ons. ' . '.,.." . . ''.

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REPORT OF MEETINGS :

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Annual Convention 'of the Indonesian Petroleum Association ,Jakarta;',;, June 4 and 5, 1 9 7 3 . :;._ .. .., =.. ~ ..

" The'secondannualconve~tion 'of the Indonesian Pettioleum AssociatIon' (IPAY,was. held in Jakarta on 'JUn~ 4' and 'S, 1973 and was· followed (by three"fieYd'excursions to, Java and the south a;r>m of Sula .... ·.,. wesi (Celebes). Between 300 and 400 participants heard 'twenty.··· technical papers, which may be classified as follows: Six field studies.,orfi-e;Ld area reports:

Ar~~.·~~ .Sumatr~(Mobil)· .... . Jati~arang,. JaY-a (Pertamina) NE Java Fields (Pertamina-Lemigas) Tarakan, Kalimantan (Tesoro) Attaka, Kalimantan (Union) Kasim-Jaya, West Irian (Trend)

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Nine· regional

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st~dies:.

Lower-Middle Miocene, N. Sumatra (Pertarnina) S. Sumatra Paleotopograp9Y and Sedimentation (Stanvac) South China Sea Plate Tectonics (AGIP) Banyumas Area, Java (Pertarnina) SW Java (BEICIP - Lemigas) Reefs, SW Java (Lemigas) Java Sea Structure, (Pertamina) Offshore Mahakam, Kaiimantan' (To'tal ~ BEtCIP-Lemigas ) SahulShelf, AustrCilia (B~, <:;al)b~rra) Five other papers: Oil Industry in Indonesia (Dept;. Mines) Helicopter Driiling Operations, Central:Sumatra (Caltex) Pipelines, Central Sumatra (Stanvac) Wax Pla.J;lt. Operation (Pertamina) . ·Offshore Storage (Chicago Bridge)

Even. though fourteen of the speakers were talking in a language not their own, the quality of presentation was high •. The quality of the written papers was extraordinarily good, and a large amchlh't· of :: well-organized data was presented. Oil Field Studies: Three papers of timely interest to petroleum geologists were the oil field studies of the Arun, Attaka, and Kasim-Jaya fields. Mobil's Arun field is a giant gas-condensate accumulation stra.tigrap9ically trapped in a Middle Miocene reef sitting on a north-trending basement high ~d se.aled by marine shales. Although reserve estimates are not available, productive 'thickness 'approaches 500 feet and. ultimate field size may be in excess of 30,000 acres. .' The Attaka field, discovered in 1970 by Union in the East Kalimantan Mahakam deltabffshore area, is a major oilfield in: an Upper Miocene tc? Pleis.tocenedeltaic complex. The major acc~mulationsare,in d~lta . front sands above' and below a delta plain lobe. Trapping is' stJ;'\,1c~iwa.l. Production ofabout'lOO~OOO'b/d of low 'sulfur 35~:- ,43 0 oil will he:' attained by the end 'of 19'73. Petromer-Trend's Kasimand Jaya discoveries in West·Irian were described by Richard Vincelette in ~ o~tstanding conference paper from the standpoint of both content and delivery •. The area offers an elegant demonstration of how a small company Wc:iS able to make signifi-

17

cant discoy.~:ries by coupling a bold exploration idea with solid geology, acuteairphoto in.teri?:tIe~~tiorl, and a·very limited seismicbuclget. VincelettE) wa,s cortvinb-ed't;hat buried··reefs muSt : exist in'Ylest Irian,' much as. the, De'Vonian'~eef:'pi'a:Y·'bf Albetita. He 'isolatedsmall.f.a.uit, :,'. block· areas' on' ciirphdtos and· re~soned that these faults were pr~ba.i)lY·· reef flank faults on pinnacle reefs with great vertical extent. A,,;·· limi ted but careful CDP seismic program then was used to define drilling locations. The two discoveries to date - Kasim and Jaya - have ~il columns of 250-400 feet, calculated porosities of up to 42%, and inplace,reser'ves of up to 2000 bbl/ac.ft. For a truly fact-packed article on a matUI"e producing region, the· on the fields of NE Java is a classic. 150,000,000 bbl~,have,1:)~!?n produced f1:.om Middle ,Miocene to Pliocene'quartz sandstones and ~aicarE!1?i.tes in 's'ome 27 elongate narrow, asymmetric E,TW trending,. ::' anticlines~" The fields are classified· as to structural, subtype~ and " illustrated by maps and cross-sections. Production histories are. s~-, rized, basin evolution depicted, and timing of trap formation and oil migration sketched. Tabular data includes year of discovery, cummulative prouuction, peak production, number and depth of wells, areal and vertical closU!"e,nUmber of reservoirs, geometrical information on the anticlines, and remarks on the producing intervals. Pertam~~a, ~~icle

Regional Papers: Regional presentations included two on Sumatra, foU!" on Java and the Java Sea, one on East Kalimantan, and one on the South China Sea. A cardinal featU!"e of the newel" work is the resolution of previous stratigraphic problems by the applicatibn of the worldwide,' Tertiary planktonic ,f()raminiferal zonations. An eXce.lle'9tPertamina. paper on 'the Lower and Middle·· Miocene"of North. Sumatra"ip9,lu~~d:new stratigraphic information ','on . 25 wildca:t rre~ls, setting into a r'egicma,1. framework the subsurfa~e formations, wpich, h~v~ . been the targets of recerit successful drilling: 'the 'AI"un, Lime~ton.eiand the AlUI".Siw;ah L~m~stone.

""Stanvac· Ys discussion of the relationship between paleptopography, and Tertiary sedimentation in South SUJ1\atra not only- demonstrated, the, . , paleogeogt',aphicpatterns but also included an updated basement map of . the ar~a.' ' .. A., fi:rst piat~,tict6nic interpretation of. the South Cbina Sea ~ppeare in Dr M. Pupiliii!~:I1\GIP :;-sponsored paper:.,· The argument: is caref~ly.;,. thought ouf.. and' do6uriient~d.':" including some: new· data from the South China Sea :wells. " ,

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In a facies study of the.offshore Mal;lakam delta.area, including Attaka'and several other major' discoveries, the TOTAL-BEICIP-r,emigas group documented in exemplary fashion a prograding Upper Tertiary' tropical delta and the locus of oil accumulations within the deltaic setting. FiC?ld'Trips: Three short field excursions followed the presentations of formal papers: SW Java (one day), Central Java (two days) and the South Arm of Sulawesi: (three days) ~ The field trips were well organized and only led. ,The quality of the ,field mappin'g is quite high and it was a great pleasure to :view at first hand areas which had previously, been known only through, .•. " Ii terature' ~ ;,;

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R:W. Murphy

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Meeting of 7th September:

R.W. Murphy and D.E. Karig

A meeting of the Society was held at 8.00 p.m. on the evening of 7th'September 1973 in the Department of Geology, University of Malaya. The speakers for the evening was Mr R.W. Murphy and D.E. Karig who both spoke on some' aspects of Island Arcs. The meeting was attendeo by approximately 40 members and ended at 9.45 p.m. Mr R.W. Murphy of Esso Exploration Inc., Singapore spoke on liDiverSity of ,Island Arcs ll with Japan, Philippine and Northern Mollucas as examples of island arcs systems. Although these three island arcs complexes show many common charac~·' ertics, detail studies of their surface geology suggests great diversity in their geological development., Mr"Murphy presented geologic and geochronological data which he has interpreted cs 'evidence ,for long . continued but not necessarily continol,ls; subduction at the s~te 'of the,. present day Japanese Islands. Implicit in his discussion is the asduTllPtion that the pre-Neogene core of Japan was formerly attached to the . Asian mainland and that the Japanese Sea is a marginal sea which has

been created by horizontal separation and insertion of young basaltic crust betWeeriJapan and the. mainland. The two other arcs, the Philippines and the Northern' Molll.,1Cas, l:;>o'-fh"relatively young but .~oth composite' in nature appear .to 'be :Ln:the stage o:f\,:ontinental construction out6f elements which were o;riginally oceanic·'5iI1·Origin. ,: ,.-.:.- :

Mbst of the materials presented in his 'talkhave alre.9.dy appear:ed in his paper in The APE A Journal, 1973, pp'~" 1-9-25 and members interested in·this'aspect of the Island Arcs System may request for reprints of,: this article from the author. ' ,.. Following Mr Murphy' s.presentation . there was' a brief. inforfl\al": talk by Dr D.E. (Dan) 'Karig of the University of: California at Santa Barbara, whose papers on the origin of limarginal basins',' are. well.known to students of plate tec't;on;i,cs. Dr Karig had recently been a particF pant in Leg 31 of the JOII;l:E;S, deep sea drilling project in the western Pacific, and was visi ting,,-~qc4-aLumpur on his way back from the isl,and of Nias,- off Sumatra,wher~ he examined apart of the outer, non-' volcanic arc of an active island arc system. DilKarig- spoke abO\,lt the detailed structure of island' arcs., ' Identifiable structural9.nd t~pographic' subdivisions of an island arc include, starting from the outside, that is: the· side of .t,he down going slab: (1) the trench, whose bottom is the site of the actuai dislocation plane between the- two'lithosphere slabs, (2)·the, ipner trench wall, a steep slope formed mainly of deformed sediments, (3) the trench-slope break, which may be expressed as an outer, nonvolcanic string of islands, but more commonly as a submarine shoal or even just a break in Slope, (4) the shallow basin of the arc-trench gap, which receives sediment mainly from the inner side~ (5) the upper slope discontinuity, a major fault or flexure, with the outer side displaced downward, ( 6 ) the frontal,' arc, a mechanically rigid and stable region which may be composed of any sorts of rocks, (7) the volcanic arc itself, and (8) the marginal basin separating the arc system from, in most cases, a continent some distance behind. Although the basin in the arc-trench gap'1s shallow, its sedimentary fill may be quite thick (as much as 5 km or more) and,':coll'!tllonly is tilted toward the frontalarc~ indicating the sense of displacement on the upper slope discontinuity. " . The depth of a trench seems, to dependoD., 'amorrg 'othep thipgs, the depth of the ocean over the down:-going plate ,.( the: dee~r this" i~" the d~eper the trench); the amount of sedimehtbeing supplied tq:'the',trenc2. (the'niore sediment, the shallower the trench); and whether the trench ts'ih a marginal basin or'~:.Qce~ Joceanic'trenches"are deeper), • j



20

The make-up of the inner trench wall and of tr~nch-slope break are of considerable interest, and at least three varieties can be;:recognized, (1) the "Mariana-Tonga!: type? in Vlhich little oceanic ·sediment·, is supplied, and the inner trench wall consists of slivers of oceanic crust as well as oceanic sediments, forming a 'platform' on which arcderi ved $.ediments can accumulate:)', (2) the H Sumatrali type, in which much oceanic sediment is supplied, ',but only limited amounts from the arc, and the thick sediment pile may be puS?hed uplnto 'an actual.island chain. ,. ,with an unfilled basin between it and the frontal arc, and (3) the - 1I Aleutian!! type, in which'much sediment is supplied from both sides, and j:he, whole region between the front<;l,l'arc and the trenchslopeb,reak.beComes a sedimented platform, the'basin being filied. .. ..

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Some drill holes into, the lower' part of the inner trench wall made during JOIl)ES Leg 31 seem to verify, the ,hypothesis that·sediments caught in the 'jaws' of the trench bottom. are deformed'into packets of isoclinally folded (and sUrprisingly dewatered 'and compacted) material, whi~h are slid into position in the base of the inner trench wall, push:ng up the previous packets, which gradually rotate from a near..-horizontal posi tion to ste.eper and steeper dips, and indicate that the deformatioE and dewatering take place in a relatively short time.' . Preliminary results of JOIDES ,Leg 31 will appear soon in 'Nat,ure.

PHS 00000000---

GSM Seminar on Mineral Exploration and Evaluation, Kuala Lumpur,': Septemb.er8th '1973 , This seminar lias Driginally scheduled to be held ort 4th· August but was postponed due to the untimely death. of the hono'urable Deputy Prime Minister of Malaysia"Tun (Dr) Ismail Al Haj. The abstracts of the papers presented at this: seminar appear earlier in this Newsletter for the l:>enefit.of those'members who were notable to attend. Besides the valuable contributions made by the speakers and other members participating in the discussions which followed eachpresentation, this meeting is notable on two other counts. For the first tim::!

2],

in the Society's history, a seminar or discussion meeting was held with a theme which is priminarily of interest to the mining community in , . this country. .The presence at this meeting of representative "froin ..... most of the leading Mining CGmpanies operating inthis'region,q.ugers well for future undertakings along similar lines. Dr S.H. Chan, ,the . Seminar organizer expressed the hope that other organizations in this country serving the mining community would in future join with the Geological Society in sponsoring more seminars and discussion meetings of this nature. This meeting is also the first Society function to be held in the Geology Department of the Un 1. vet'si ty Kebangsaan. The Sociei:y . would, , like to record its appreciation for the use of the excellent facilities and the cooperation of the staff of the University.

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NEHS OF THE SOCIETY· ;,

Bulletin 6 Most members and participants at the Conference s~ould have received their free copy of the Proceedings, Regional Con:ference on the Geology of Southeast Asia. This Bulletin was published' at' 'the end of July but due mainly to a shortage of packing material there was some delay in posting them to the various individuals. The Council has decided that all members of the Society (except for Student members category two) would receive a free copy of·this Bulletin. This decision was taken mainly in view of the Society's sound financial standing arising largely to the generous donations made to the Society for the Conference and the publication arising from it. ---00000000---

22 -.':'.

MembeI'ship .

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2 n~w.Fu11 me~e~~ and 1 new 'student membeI'S weI'e elected to the

Society~'

Fui1 u.einbers Graham MooI'croft Mii1er c/o Getty Oil Development Co. 275 A1fI'ed.~tI'eet NOI'th NOI'th.. Syciney , ,..... AVST~LIA,. .

.. bavid ·t.eslie Mathias . Box 3972, G.P.O. Sydney, N.S.W. AUSTRALIA ' .

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Student membeI'S Kha1id b. Omat' No. 1217 Road 17/48 Peta1ing Jaya

Yeoh Gaik Chooi 6 Ja1an SS2/20 Petaling Jaya

Kenny Oh Woo Pui 2 LoI'ong Tiong Nam Enam Kuala LumpUr', MALAYSIA

Faiza1 Daud ·5/30 James StI'eet WindsoI', Vic. 3181 AUSTRALIA

Seet Chin Peng c/o 18 Ja1an 14/36 Peta1ing Jaya

Au Yong Mun Heng 13 Ja1an 21/2 Peta1ing Jaya

KI'ishnan DhaI'mat'ajan No. 133·2, 17/48A Petaling Jaya.

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