Mineral Deposit of Sulawesi_Theo M. Van Leeuwen and Peter E. Pieters

7/22/2019 Mineral Deposit of Sulawesi_Theo M. Van Leeuwen and Peter E. Pieters

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PROCEEDINGSOFTHESULAWESIMINERALRESOURCES2011SEMINARMGEIIAGI

2829November2011,Manado,NorthSulawesi,Indonesia

1

MineralDepositsofSulawesi

TheoM.vanLeeuwenandPeterE.Pieters

ABSTRACT

Sulawesi can be divided into three geologicalmetallogenic provinces: 1) Northern Sulawesi, which consists of

series of Late Cenozoic calcalkaline magmatic arcs built on a basement of Early Cenozoic tholeiitic basaltic

volcanicsunderlainbyoceaniccrust;itcontainsnumerousmineraldepositsandoccurrencesofpredominantlyLate

MiocenePlioceneage, includingporphyryCuAuMo,high, intermediate,and lowsulphidationepithermalAu

Ag, sedimenthosted Au, intrusionrelated base metalAu, skarn, and VMS styles of mineralization; 2) Western

Sulawesi,composedofLateCenozoichighKcalcalkalinetoultrapotassicigneoussuitesoverlyingaseriesofEarly

Cenozoic sedimentary rocks and subordinate calcalkaline volcanics deposited on a basement of metamorphic

complexes and Late Cretaceous flysch deposits; mineralization styles include porphyry Mo, porphyry CuAu,

intrusionrelated(?)Au,intrusionrelatedbasemetalAu,andVMS;and3)EasternSulawesi,comprisingawestern

metamorphicbeltandeasternophiolitebelt,whichare interthrustedwithMesozoicEarlyCenozoicsedimentary

rocks and unconformably overlain by Late Cenozoic postorogenic sequences; weathering of the ophiolite has

givenrisetoanumberofNiandFelateritedeposits,andchromitebeachsands;goldmineralizationofuncertain

originislocallyhostedbymetamorphicandpostorogenicsedimentaryrocks.

MineralexplorationandminingactivitieshavebeenundertakeninSulawesisincetheturnofthe19thcentury,but

byworldstandardslargepartsoftheregionremainunderexplored.Todateonlytwocommoditieshavebeenmined

onasignificantscale,viz.goldwithatotalproductionofabout90t(excludingartisanalmining),andnickeltotaling

about4.8Mt. Golddepositsfoundtodateareofsmalltomodestsize(


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Table1.MaingeologicalandmetalogeniccharacteristicsofNorthern,WesternandEasternSulawesi

NORTHERNSULAWESI WESTERNSULAWESI EASTERNSULAWESI

Tectonicsetting IslandArc Continentalmargin Suture

Basement Oceanic(backarc)crust Continental fragments;

accretionary

rocks/mlange; overlain

byLateCretaceousflysch

deposits.

Continental fragments;

accretionary

rocks/mlange;

ophiolites; Mesozoic

Paleogene sedimentary

terranes.

Paleogene

magmatism

LowK tholeiitic, bimodal

(basalticfelsic);

submarine; intense,

widespread.

Calcalkaline:

intermittent and

localized.

Neogenemagmatism MediumK calcalkaline,

predominantly andesitic;

also bimodal during

latest PliocenePleistocene.

Voluminous highK calc

alkaline (mostly

granitoids); and

shoshonitic to ultrapotassic.

Minor,localized.

Paleogene

sedimentation

Minor;deepsea. Synrift siliciclastics

overlain by platform and

deeper marine

carbonates; pelitic

sedimentsinthenorth.

Neogene

sedimentation

Siliciclastics in isolated

basins, including Plio

Pleistocene Celebes

Molasse.

Marine sediments and

volcaniclastics; Plio

Pleistocene Celebes

Molasse.

Widespread deposition

ofCelebesMolasse.

Main mineralization

types

Porphyry CuAu; high,

intermediate, and low

sulphidationepithermal

AuAg; sedimenthosted

Au.

PorphyryMo; intrusion

relatedAu.

LateriticNi&Fe.

Otherstyles VMS; intrusionrelated

base metal Au;

FeAuskarn alluvial Au;

Febeachsands.

VMS; intrusionrelated

base metal Au;

FeAuskarn; Mn

ironstones.

Primary and secondary

chromite; alluvial Au;

epithermalAu,Sb.


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Figure1.RegionaltectonicsettingofSulawesi(afterWilsonandMoss,1999)

Figure2.DigitalterrainmodelSulawesi


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areaof172,000km2. It is themostmountainous

of the larger islands within the Indonesian

archipelago. Withtheexceptionofsomenarrow

stretches of coastal lowland and intermontane

plains, the terrain consists entirely of mountain

rangeswith thehighestpeaksbeing inexcessof

3000m (Figure 2). Unlike the other larger

islands/island groups in Indonesia, which are

partlyborderedbyextensiveshallowshelfareas,

the seabottomoff theSulawesi coastsdrops in

mostplacesrapidlybelow100m,andthe1000m

bathymetriclineislocatedatadistanceofonlya

few10sofkilometersorlessfromthecoast.

TheislandhasapeculiarKshape,consistingof

four peninsular known as Arms, which are

separated by deep gulfs and united in central

Sulawesi(Figure3A). ThenarrownorthtrendingpartoftheNorthArm,iscommonlyreferredtoas

theNeck.

The Sulawesi region can be divided into four

distinct geological and metallogenic provinces,

namedhere (modifiedafterSukamto,1978),the

Northern, Western and Eastern Sulawesi

ProvincesandBanggaiSulaProvince (Figure3B).

As the latter province does not contain any

significantknownmineralization, ithasnotbeen

included

in

this

review.

The

main

geological

and

metallogenic features of the other three

provincesareshowninTable1.

Thepresentpaperconsistsoffourparts. Thefirst

partdescribes thehistoryofmineralexploration

and mining in Sulawesi. It is followed by an

overviewoftheregionalgeology. Themainpart

of thepaper comprisesadetailed reviewof the

various mineral deposit types found in each of

the three provinces together with some

additional exploration history data. In the last

section we discuss how the various deposit

typesaredistributedinspaceandtime,whenand

howtheywerediscovered,andhowtheyfeature

in Sulawesis mining industry. It also briefly

addressespastandpresentexplorationtrends.

Anumberofsourcesofinformationareavailable

for the history of exploration and mining in

Sulawesi,andtheregionsmineralresources. For

the Dutch colonial era these include the

Jaarboek van het Mijnwezen (Mining

Yearbook), ter Braake (1944), van der Ploeg

(1944), and van Bemmelens (1949) Economic

Geology of Indonesia. A publication by the

Indonesian Mining Association and Mining and

Metal Agency of Japan (IMAMMAJ, 1995), the

anually published Register of Indonesian

Gold/RegistrerofIndoPacificMining,andvarious

trade journals record mineral exploration

activities post1967. Several review papers on

thecopperandgoldmineralizationofNorthern(+

Western) Sulawesi have been published (Carlile

et al., 1990; Kavalieris et al., 1992; Soeria

Atmadja et al, 1999; Pearson and Caira, 1999).

Paperson individualdepositsandprospects can

be found in various proceedings and journals.

Mostoftheseareincludedinthereferencelistof

thepresentpaper. MoredetailedinformationiscontainedinCOWcompanyreports,whicharean

open file in the library of Pusat Sumber Daya

Geologi (PSDG). Unfortunately a number of

reports are missing,often the more informative

ones, and the quality of the reports is rather

variable (some discuss at great length weather

conditions, topography, etc but give little

geological information). Websites of foreign

junior companies are another source of

information, although they tend to focus on

trench

and

drill

results.

Recently Pusat Sumber Daya Geologil published

two geochemical atlases covering the northern

and southern halfs of Sulawesi, which include

mapsforthefollowingelements: As,Co,Cr,Cu,

Fe,K,Li,Mn,Ni,PbandZn (PSDG,2008). They

also compiled a mineral resources atlas for

Sulawesi as part of a series of atlases for the

entire country (PSDG, 2010). It comprises a

series of maps for each Kabupaten

(administrative district), including geology and

minerallocationsmaps,andalistofmetallicand

nonmetallicmineralresources(nameofdeposit,

coordinatesand resource figure). Nogeological

information or references are given, limiting

somewhat its usefulness for mineral

explorationists.

Forthisreviewwehavemadeextensiveuseofa

GIS databasecalledIndonesianMineral Deposit

Database(IMDD),thatwehavebeencompiling


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Figure3.Sulawesi. (A)Geographicdivision;(B)Geologicalmetallogenicprovinces

Figure 4. Simplified geological map of Sulawesi (modified after

Sukamto,1975b;Hamilton,1979;Silveretal.,1983;Parkinson,1991)


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Table2.HighlightshistoryofmineralexplorationandmininginSulawesi

Year Results

18961908 SmallquantitiesofAuproducedatSumalata.

18961929 Palelehmine; 6.2tAu,5tAg,550tPb.

1900 G.Panidiscovered.

19001921 Totokmine;3.7tAu.

1911 AbendanonrecognizesNiFelateritepotentialofESulawesi.

19131931 ThreeminesinBolaangMongondowdistrict;5tAu,4tAg.

19161919 SeveralNiandFelateritedepositsfound,includingPomalaaandSoroako.

1938 NilateriteminingstartsatPomalaa.

1968 Large2ndgenerationCOWareaawardedtoPTInco.

1969 SasakporphyryCuAuprospectidentified.

1970 SecondgenerationCOWawardedtoEndeavourResources;BahodopiNilaterite

depositdiscovered.

19721973 TapadaaandTombulilatoporphyryCudistrictsidentified.

19741975 Discovery of the Cabang Kiri, Cabang Kanan and Kayubulan Ridge porphyry

prospects.

1976 Commercial ferronickel production starts at Pomalaa; Malala porphyry Mo

discovered.

1977 3rdgenerationcontractsignedbyRioTinto.

1978 CommencementofnickelmatteproductionatSoroako.

19801982 Drill testing of Cabang Kiri, Cabang Kanan, Kayubulan Ridge and Sungai Mak;

[email protected]%Cu,0.47g/tAu.

19831984 Motombotohighsulphidationsystemdrilled.

19861987 Twentytwo4th

generationCOWssigned.

1987 Severaldiscoveriesmade, includingBulagidun(porphyryCuAu),Binabase(HS),

andTototopo,Anggrek,Tanoyan(IS).

1988 MiningofchromitebeachsandscommencesinESulawesi

1989 MeselandAwakMasdiscovered.

1994 TokaTindungandPoboya discovered.

19941997 115th7

thgenerationCOWssigned.

1998 RiskaandMasabofound

1999 Palopodistrictdiscovered.

2004 MiningstartsatRiska;annualproductionca50.000ozAu.

2008 GoldrushatBombanainvolving>20,000localminers.

2011 FirstgoldpouredatTokaTindung;annualproductionca160,000ozAueq.


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since 2005 (van LeeuwenandPieters,2011). It

contains all available relevant descriptive

information about deposits and prospects,

including location details, commodity, deposit

type, host rock, mineralization, alteration,

structure, resourcedata,explorationhistoryetc.

Most of the data in IMDD are derived from

sources mentioned above and unpublished

companyreportts.

Thepresentpaperisaimedprimarilyatgeologists

engaged in mineral exploration in Sulawesi and

those who wish to assess its mineral potential.

The focus is on providing descriptions of the

more significant mineralizing districts and

individualdeposits.

2.0 HistoryofMineralExplorationandMining

inSulawesi

The documented history of mineral exploration

andmining in Sulawesi spans aperiodofabout

125 years, but traces of iron slag with a Ni

content of 12% found at an archeological site

near Lake Montano suggests there was already

someminingactivity more than1000 yearsago

(Bulbecks, 2000, in Rafianto, 2011). The

highlights

of

the

past

125

years

are

summarized

in Table 2 and discussed below in some more

detail.

Local gold mining activity in Northern Sulawesi

wasrecordedasearlyas1813andhascontinued

uptothepresentday,itsintensitydependingon

the price of gold and economic conditions.

BritishmapsofSulawesipublished in1885show

agoldmine intheRatatotokdistrict,namedMt.

Tottik. Mining there was done by local people

from the neighbouring province of Bolaang

Mongondowtoprovidegoldfortheirchief.

In1848,thegovernmentoftheNetherlandsEast

Indiesdecidedtoinvestigatethemineralrichesof

thearchipelago. Itwas thought that sixmining

engineers would be sufficient to carry out the

task. Theywereemployedby HetMijnwezen

(BureauofMines),founded in1852,thattwenty

years later began to publish Jaarboek van het

Mijwezen (MiningYearbook). Initiallythefocus

wasonJava,SumatraandBorneo. Investigations

inSulawesistartedmuchlater,aroundtheendof

the 19th century.The reason for this was

threefold: i)Sulawesiwashighly inaccessible; ii)

theislandhadnotyetbeenpacified;andiii)very

little was known about its mineral endowment

(Rutten,1927).

The first government mining engineer to

investigate some of the gold deposits known at

that time in Northern Sulawesi was van Schelle

(1889). Private enterprise soon followed,

prompted by historical reports of artisan gold

mining in the region. Between 1896 and 1929

fourundergroundmineswereoperated(Table2)

and in the Ratatotok district elluvial deposits

were also exploited using hydraulic mining

methods. Inadditiontwounsuccessfulattemptswere made to carry out underground mining at

G. Pani between 1900 and 1910. Mining of

nearbyalluvialsproducedonlymarginallybetter

results. Also not overly impressive were the

results of alluvial mining at Tapaibekin in the

Doup district. When more than 50 years later

geologists of Endeavour Resources undertook a

mineral survey in the central part of the North

Arm they observed short trial adits in even the

mostremotepartsoftheregion,suggestingthat

it

had

been

thoroughly

covered

by

the

early

gold

prospectors(Trailetal.,1974).

Truscott (1901) published a description of gold

minesandprospects intheNorthArmknownat

the time, presenting highly optimistic

evaluations. Healsonotedthatcopperdeposits

in the hinterland of Gorontalo were being

developed,butno further recordsareavailable.

Attempts toproduce copperatBuhu,Molosipat

andBukalintheearly1900sallfailed.Twoofthe

gold mines in Northern Sulawesi were

investigated in some detail by government

engineers and geologists, namely Sumalata

(Molengraaff, 1902) and Totok (Ratatotok)

(Koperberg,1900;Hirsh,1911). Theoriginofthe

goldmineralizationatTotok,which ishostedby

limestone,wasexplainedintwoways: i)thegold

wasoriginallyderivedfromrocks locatedfurther

inland and transported by the Totok river at a

timethatitslevelwasseveralhundredsofmeter

higherthanatpresent. Goldandsilicawerethen


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dissolvedanddepositedfromdescendingfluidsin

fracturesand cavities in the limestone,believed

to be younger than underlying andesite, and ii)

the limestonewas intrudedby theandesiteand

gold deposited from associated hydrothermal

fluids.

During the early part of the 20th century

government geologists discovered several

preciousmetal,basemetaland ironoccurrences

in central Western Sulawesi, including at Sasak,

which more recently has been explored for its

porphyry copper potential. A rather curious

copper occurrencewas found in the Latimojong

Mountains,wheresmallpocketsofnativecopper

arepresentinslates,thesocalledKoperLeienor

CopperSlates(vanBemmelen,1949),thesedays

knownas ToradjaFormation.

Far more important (from a presentday

perspective) was the work done in Eastern

Sulawesi. Abendanon (191517), who

investigated the region in 1909/10 was the first

to observe the presence of extensive ultramafic

rocksandtheirlateriticweatheringproducts. He

wasconvincedthatironandnickeloreswouldbe

found in this part of the island. Following his

recommendation,amore systematicsurveywas

initiated

in

1915,

and

in

a

relatively

short

period

of time significant iron and nickel laterite

resourceshadbeenoutlined. Oneof these, the

Larona Fe laterite deposit was explored in

considerable detail outlining proven reserves of

370Mt (airdried)averaging49%Fe (Dieckmann

and Julius, 1925). Extensive studies were

undertakenintheensuingyearsonthepossibility

of establishing an iron and steel industry in

Sulawesi, butwithout much success, one of the

reasons being the lack of known coking coal

depositsinIndonesia.Theoutlookfordeveloping

the more Nirich laterite deposits was equally

discouragingbecauseofthelowNicontents(0.50

1.15%), whereas at the time grades of 3.5

4.0% were required. Using the rich nickel

deposits of New Caledonia as a model efforts

were subsequently directed towards finding

highergradegarnierite(Nisilicate)ore. Afteran

extensivesearch thistypeoforewasdiscovered

inthehillssouthofLakeMantanoatSoroakoand

near Malili (Pomalaa). In 1934, two private

companiesweregiventherighttofurtherexplore

and develop these deposits. By applying a

method of selective mining, which involved

careful stripping of overburden and removing

peridotite boulders, dry ore of 3.5% Ni was

producedatPomalaa,andshipped to Japanand

Germany, starting in 1937. By 1940, a

government engineer had succeeded in

developing a new process for the treatment of

theseNisilicateoresonsite,butbefore itcould

beappliedJapaneseforcesinvadedIndonesia. By

that time a totalofabout150.000 tof ore had

beenexported(Darmono,2009).

Before the outbreak of the Pacific War the

Japanese had obtained nickel ore from Canada

andNewCaledonia,butthesesourceswerenow

cut off. Sulawesi became an important newsource to supply their war industry. The Dutch

miningoperationsweretakenoverbySumitomo

Metal Mining, which built a smelting plant to

produceNimatte,butbeforeitwascompletedit

was destroyed by the allied forces. Between

1942and1945a totalof184.000tofnickelore

was produced (Darmono, 2009). The Japanese

alsocarriedoutlimitedminingforbasemetalsat

SangkaropiincentralSulawesi.

After

the

Dutch

returned

in

1946

they

resumed

nickel mining, but only for three years. Eight

years later NV Perto (Pertambangan Toraja)

shipped nickel ore still remaining in stock piles

fromtheJapaneseoccupationtoJapan. In1961,

it became PT Pertambangan Nickel Indonesia, a

stateownedenterprise,whichthenmergedwith

several other stateowned mining companies to

become PT Aneka Tambang (Antam). This

company has been operating thePomalaamine

since 1968. In the central part of Eastern

Sulawesi, including the Soroako area, all

explorationactivitiesweresuspendeduntil1965

becauseoflocalinsurgency.

Following the promulgation of new foreign

investment and mining laws in 1967, Indonesia

offered for tender several areas with known tin

and nickel laterite potential, including a large

block in Eastern Sulawesi. This concession was

awardedin1968toaconsortiumheadedbyINCO

(International Nickel Cooperation) of Canada.


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The consortium company, which includes

Sumitomo Metal Mining as a shareholder, is

usuallyreferredtoasPTINCO. Intheearlyyears

the company carried out extensive exploration

with the assistance of the Geological Survey of

Indonesia(GSI) and about 40 geology students

from the Institute Teknologi Bandung (ITB).

Initiallytheexploration focuswason thecoastal

areas, but in mid1969 it shifted to Soroako,

wherefouryearslaterminedevelopmentbegan.

Soon afterwards oil prices escalated and the

international nickel market deteriorated. In

ordertocounterthesenegativedevelopmentsPT

INCO built a hydroelectric plant and tripled

annual production capacity to 45,000 tonnes of

nickel matte, but it had to wait until 1988,

following an improvement in the nickel market,

to see its operations become profitable (vanLeeuwen,1994).

The first company to carry our gold and base

metal exploration in Sulawesi was Newmont,

which between 1967 and 1969 undertook

reconnaissanceandlimitedfollowupworkinthe

NorthArmwithporphyrycopperdepositsasthe

main target. They examined recorded

mineralizationanddiorite rockseasilyaccessible

from the north and south coast, and in the

hinterland

of

Gorontalo

and

the

Bone

Valley,

and

made more detailed investigations around the

abandonedG.Panigoldmine,andatafewother

localities,includingtheBuhucopperprospect.

Intheearly1970stwoothercompaniesinitiated

porphyry copper searches, namely Endeavour

Resources,ajuniorAustraliancompany,andRio

Tinto. The former obtained a 2nd generation

ContractofWork(COW),knownasBlockII,which

coveredanareaof12,000km2inthecentralpart

oftheNorthArm. Theirobjectivewastotestthe

hypothesis that thePhilippines porphyry copper

belt might extend into northern Sulawesi, an

initiative thatwas rewardedby thediscoveryof

porphyryCu stylemineralization in theTapadaa

andTombuililatodistricts. Followinga literature

study and the second years survey work that

revealedthatgoldmineralizationwaswidespread

inBlockII,thescopeofthesurveywasextended

toincludealluvialandhardrockgoldtargets.

The two porphyry districts were investigated in

moredetailinjointventurewithKennecottfrom

1973 to1976. In1980,Utah International took

controlofEndeavourslocalcompanyandcarried

out an intensive exploration campaign in the

Tombuililato district until 1982. Together these

efforts resulted in the discovery of three

porphyry prospects in the Tapadaa district and

five porphyry prospects in the Tombuililato

district, including Cabang Kiri, Kayubulan Ridge

andSungaiMakwithacombinedresourceof296

Mt @ 0.57% and 0.47 g/t Au (van Leeuwen,

1994). In addition high sulphidation AuCu

mineralizationwasfoundatMotomboto.

RioTintoappliedfora largeCOWarea,Block III,

located to the west of block II and covering an

areaof17,200km2in1973,whichwasgranted in1977. In the intervening years reconnaissance

geochemical sampling identified 18 anomalous

areas,followupofwhich ledtothediscoveryof

the Malala (Anomaly B) porphyry molybdenum

deposit in theTolitolidistrict. Drillingbetween

1978 and 1982, partly in JV with SANTOS of

Australia,outlineda [email protected]

MoS2, which was not economically viable at

prevailingmolybdenumprices.

Further

south,

GIS

carried

out

reconnaissance

geochemical surveys in the late 1960searly

1970s, outlining three areas anomalous in base

metals, i.e. Sasak, Seko and Sangkaropi. These

were subsequently investigated together with

Antam, and drilled. Porphyry Cu mineralization

was found in the former two locations, but

appearedtobeoflowgrade(0.3 0.4%Cu)andof

limited extent. In the Sangkaropi area, three

VMS deposits were subjected to detailed

exploration that failed to outline an economic

resource.

Inthoseearlyyearsexplorationwasoftencarried

out under conditions reminiscent of the Dutch

days, requiring a true pioneering spirit. This is

exemplified by the story of the Kuda mati

berdiri(standingdeadhorses)(Geomin,2010). In

1975, Antam decided to drill test Seko, located

200km to thenorthofSangkaropiatanaltitude

of 1000m, which could for the most part be

reached only on foot. The party included 30


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porters and 70 horses. As the track followed

mostly mountain ridges grass and water were

very scarce. After 10 days one of the horses

refusedtomoveevenaftersomeof its loadhad

been decreased. It took a while to realize that

the poor animal was already dead, probably

because of dehydration. A number of other

horses died the same way without falling over.

Thelocationwasfinallyreachedafter30days.

By the mid1980s the porphyry search was

virtually over and the focus shifted to gold. In

Northern Sulawesi the gold search was

spearheadedbyBHPMinerals (whichhad taken

over Utah in 1984), soon to be joined by

Newmont,Ashton,PlacerDome,andNewHope

Colliers. A total of thirteen 4th generation

COWsweresignedinthelate1986and1987.

The gold exploration undertaken during the

second half of the 1980s and early 1990si

Northern Sulawesi was quite successful.

Newmont discovered a sedimenthosted gold

district in an area of old Dutch workings

(Ratatotokdistrict). Itsubsequentlydevelopeda

mine (Mesel), which between 1996 and 2004

produced1.9MozAu. Anothergolddistrictwas

identified by Ashton at the northern tip of the

North

Arm

centred

on

Toka

Tindung.

This

company was also involved in the discovery of

high sulphidation gold mineralization in the

BinabaseBawone area on Sangihe island. BHP

drilledfivegoldprospects,includingMotomboto.

In addition, a high resolution aeromagnetic

survey identified several targets, only some of

which were followed up. A reevaluation of the

Tombuililato district resulted in a geological

resource estimate of up to 356 Mt @ 0.6% Cu,

0.37 g/t Au, including a mining reserve of

[email protected]%Cu,0.43g/tAuand118

Mt @ 0.94% Cu, 0.40 g/t Au at a strip ratio of

~2.75:1 (BHP Minerals Sulawesi, 1997). Finally,

New Hope Colliers geochemical sampling

identified a number of gold anomalies which

were subsequently followed up by Newcrest,

resulting in the discovery of gold mineralization

atTototopoandPetulis.

Concurrentlywiththesigningofthe13COWs in

Northern Sulawesi, nine 4th generation COW

agreements were entered into for areas in

Western Sulawesi, but serious exploration was

carried out only by Aberfoyle Resources, which

held a block containing Sasak and Sangkaropi

(relinquished in 1994), and new Hope Colliers,

which discovered the Awak Mas deposit in the

LatimojongMountains.

In Eastern Sulawesi PT Palmabim commenced

exploration for chromite beach sands in the

Bungkuareawhereitoutlined700,000tonnesof

recoverable chromite. The deposit was put into

operationin1988.Ithassincebeencloseddown

(yearnotknown).

The 1990s witnessed the signing of one 5th

generation Cow by Newcrest covering most of

the old Endeavour Block II, and two 6thgeneration COWs, also located in Northern

Sulawesi (Newmont in the Bolaang Mongondow

district, and Aurora Gold, which had acquired

Ashtons areas in 1993,in an area adjacent to

their Toka Tindung COW), and eight 7th

generationCOWs,allbutonelocatedinWestern

Sulawesi, including twoblocksheldbyRioTinto

andonebyNorthLtd). The lattercompanyhad

selected a large block in central Western

Sulawesi, which based on the widespread

occurrence

of

potassic

alkaline

volcanic

and

intrusive rocks combined with the presence of

known porphyry mineralization (Sasak) was

believed to have good potential for finding

Parkestype porphyry copper deposits. (The

Parkesmine inAustraliawasoperatedbyNorth

at the time). Arguably themostcomprehensive

investigations were carried out by Newcrest,

which between 1993 and 1998 covered their

entire COW area in Northern Sulawesi with

drainage reconnaissance sampling, resulting ina

largenumberofanomalies. Manyofthesewere

investigatedin1996/97. Atotalof168prospects

were identified (including previously known

ones),twelveofwhichweredrilltested, inmost

casesdowngradingtheireconomicpotential.

The highlights of the 1990s include Newmonts

discovery of the Northern Lanut trend, which

contains several styles of mineralization,

including highsulphidation epithermal gold

mineralization. Work by Aurora outlined a


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mineraldistrictaroundTokaTindung,containing

seven epithermal gold systems. In Western

Sulawesi, Rio Tinto discovered the Masabo

porphyry copper and the Poboya gold deposits.

Rather surprisingly the latter deposit was

previouslynotknowndespitebeing locatedonly

7km from the provincial capital Palu and next

doortoPoboyavillage,formingadistinctoutcrop

withhighgoldgrades. RioTintoalsodiscovered

towards the end of the decade the La Sampala

laterite deposit in Eastern Sulawesi, believed to

beoneofthe largestundevelopednickellaterite

resources in the world. Around the same time

Antam found several new gold prospects near

Palopo Sulawesi.Thecompanyalso initiatedan

intensive exploration programme in Eastern

Sulawesi with the objective to find additional

nickel laterite resources to supply theirferronickelplantatPomalaa. Severalprospective

areaswereoutlined.

As elsewhere in Indonesia, the combined effect

of the Busang scandal (the largest fraud in the

history of mining, which was committed in East

Kalimantan), the Asian economic crisis, and

domestic political instability that took place

towardstheendofthe20thcenturyhadasevere

impact on the mineral exploration activities in

Sulawesi

(and

elsewhere

in

Indonesia).

Most

foreigncompanies,bothbigandsmall,withdrew

fromtheregionorcurtailedtheiractivities.

The first decade of the 21st century saw some

important new developments: 1) regional

autonomy gave the local government of

Kabupaten(Districts,subdivisionsofProvinces)a

significant direct say in mining and related

matters ;2)anewmining lawwaspromulgated

in 2009, which among other initiatives

introduced a tender system for new areas,

abolishedtheCOWsystem,whichuptothenhad

been the cornerstone of Indonesias modern

miningindustry,andpromotedprocessingofore

toatleastasemifinishedstatewithinIndonesia;

3)commoditypricesstartedtorisearound2004,

which spurred an increase in domestic

involvement in exploration and mining,

particularly of nickel laterites; and 4) the

explorationfocuswasonknown,moreadvanced

prospects.

Some of the highlights of the decade include

commencementofgoldproductionatRiskaand

Toka Tindung, and revisiting of some old tired

prospects. At Riska, which was discovered by

Newmont in 1988, Avocet Mining started

productionin2006withanannualproductionof

about50,000ounces. TokaTindungwasbought

by Archipelago Resources in 2002; after long

delays the first goldwaspoured in2011 witha

forecastedannualproductionof160,000ounces.

Gunung Pani (looked at by 7 companies since

1967) and Awak Mas (investigated by 5

companies since 1988) are presently under

detailed investigations by One Asia Resources

Ltd. The Tombulilato porphyry Cu and Malala

porphyry Mo deposits, discovered in the mid

1970s, are being reinvestigated by BumiResources and Victory Moly West respectively.

The former company also acquired the Poboya

golddeposit,butuptillnowhasbeenprevented

from carrying out exploration because of illegal

mining activities.The latter company has

expanded its activities into nickel laterite and

base metal explorations in central Sulawesi.

Antam started exploration at Esang, which had

been discovered during North Ltd regional

exploration programme in central Western

Sulawesi

a

decade

earlier.

A

new

arrival

on

the

scene isGoldenPeaksResourceswhich recently

acquired the Palopo gold property in Western

Sulawesi and the Tanoyan and Anggrek gold

prospects in Northern Sulawesi. And finally, in

2008 seven domestic companies started nickel

laterite production, all being relatively small

operations.

Theonly importantnewdiscoverythathasbeen

reported since 2000 is the rich alluvial gold

depositatBombanainSESulawesifoundbylocal

villagers in2008. It is the first indicationof the

presence of potentially significant gold

mineralizationinEasternSulawesi.

In summary, thedocumentedhistoryofmineral

explorationandmininginSulawesicanbedivided

intosixstages:

1) 1813 1888. Local gold mining activities in

various parts of Northern Sulawesi, which


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12

have continued intermittently until the

presentday.

2) 1889 1941. Exploration by the Netherlands

EastIndiesgovernmentandprivateenterprise

that resulted in the development of several

goldandnickellateritemines.

3) 19421967. Relatively small scale nickel

laterite mining by Japanese, Dutch and

IndonesianStatecompanies.

4) 1968 1984. Exploration with the main focus

on nickel laterite and porphyry copper

deposits; initially reconnaissance surveys of

largetractsofland,followedbymoredetailed

investigations of selected areas; mine

developmentatSoroako.

5) 1985 1999. Focus shifts to gold; 23 COWs

signed; exploration mix of regional surveys

and prospect evaluation; several significant

gold discoveries made, one of which (Mesel)

wasdevelopedintoamine(nowclosed).

6) 2000 present. Activities that began to

decrease sharply in the late 1990s pick up

again around 2004/5 with increased

involvement

of

domestic

companies,

mainly

in

nickel laterite exploration and mining; focus

on known gold and nickel laterite

deposits/districts; two gold mines developed

(RiskaandTokaTindung).

3.0 Geology

Inthischapterwebrieflydescribethegeologyof

the Northern, Western and Eastern Provinces.

Theformertwoprovincesareoftentreatedasa

single tectonostratigraphic unit, referred to as

theWestSulawesiPlutonVolcanicArc (WSPVA),

whereas the Eastern Sulawesi Province is

commonly divided into a western Central

Sulawesi Metamorphic Belt and an Eastern

OphioliteSulawesiBelt.

SeparatingtheWSPVAintotwodifferententities,

as first proposed by Taylor and van Leeuwen

(1980), isbasedon therecognitionofsignificant

differences intectonicsetting,ageandcharacter

of rockunits (Table1).The tectonic relationship

between the two domains is not clear. They

probably formedamoreor less continuousbelt

throughout the Cenozoic, but were definitely

connectednot laterthantheEarlyMiocene (van

Leeuwen and Muhardjo, 2005). A simplified

geologicalmapofSulawesiisshowninFigure4.

3.1 NorthernSulawesiProvince

TheNorthernSulawesiProvinceoccupiesa large

part of the North Arm and the row of islands

extending to the north as far as Sangihe Island

(Figure 3B). The EW part of the North Arm,

referred to as the Gorontalo section (van

Bemmelen, 1949), is made up of Cenozoic arc

volcanics and associated sedimentary rocks.TowardstheeasttheNorthArmbendssharplyto

aNEtrendandthisregion,theMinahasasection,

islargelycoveredbyPliocenetoRecentvolcanics.

The young volcanic arc continues northwards

through the Sangihe Island group and is often

referred toas the SangiheArc. Like the restof

Sulawesi, Northern Sulawesi consists of

mountainous terrain, although rarely reaching

altitudes higher than 2000m. The landscape of

thenorthernpartoftheprovinceisdominatedby

the

presence

of

(partly

eroded)

volcanic

cones,

someofwhicharestillactive,likeLokonVolcano,

which erupted as recently as October 2011.

Several grabenlike depressions occupy the

centralpartoftheGorontalosection.

The rock sequences that make up Northern

Sulawesicanbedividedbroadlyintothreegroups

thatareseparatedbyregionalunconformities. In

thispaper theyare informallyreferred toas the

Early,Mid andLateCenozoicgroups.

TheoldestgroupconsistsofathickpileofMiddle

EoceneLate Miocene submarine oceanic arc

volcanics,namedPapayatoVolcanics(Trailetal.,

1974;vanLeeuwenandMuhardjo,2005),which

arewidely exposed in the southwestern part of

theGorontalosectionforminga275kmlongbelt,

andarefoundfurthereastassmallerexposures.

This unit consists of a thick series of basaltic

volcanics that occur in bimodal association with

much less voluminous felsic rocks. It contains


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13

subordinate intercalations of red calcareous

mudstone, red limestone, greywacke, and

radiolarian chert, and is intruded by basaltic

dykes, locally occurring as dyke swarms, and

stocks of gabbro and diorite. The basaltic

volcanics include massive, autobrecciated or

pillowed lava flows, and volcanic breccia. The

bulk of the mafic and felsic rocks have

geochemicalcompositionsthataretypicaloflow

K tholeiitic island arc (IAT) volcanics, but some,

thought to have been produced late in the

evolutionofthevolcanicarc,showahighKcalc

alkalineaffinity(Elburgetal.,2003;vanLeeuwen

and Muhardjo, 2005), and contain small

volcanogenicmassivesulphidedeposits.

Near Labanuki on the north coast of the

Gorontalo section, the Papayato Volcanics areunderlain by basalts, which show geochemical

similaritieswithbasalts that form thebasement

of the Celebes Sea and are interpreted to

represent backarc basalts (Priadi et al., 1997).

Bothbasaltsequencesareoverlainbygreenand

blackmudstone. These similarities suggest that

the Labanuki basalts formed as part of the

CelebesSeacrust(Ranginetal.,1997). Anumber

ofauthorshavesuggestedthatmostoftheNorth

Arm isunderlainbysimilarcrust (e.g.Taylorand

van

Leeuwen,

1980;

Kavalieris

et

al.,

1992;

Rangin

etal.,1997).

TheEarlyCenozoicrockscommonlydisplaysteep

dips, and in places are highly deformed

(Koperberg,1929;Trailetal.,1974;Kavalieriset

al.,1992). This,togetherwiththepresenceofa

regional unconformity separating the unit from

the MidCenozoic group (Koperberg, 1929;

Ratman, 1976; Carlile et al., 1990; Pearson and

Caira, 1999) indicate that a significant tectonic

eventtook place in the Early Miocene (van

LeeuwenandMuhardjo,2005). Thecauseofthis

eventisnotcertain. Ithasbeensuggestedthatit

may be related to the collision between the

North Arm and either a small continental

fragment or the Sula Spur (van Leeuwen and

Muhardjo,2005;SpakmanandHall,2010).Inthe

latter scenario the Sula Spur was subsequently

fragmented during extension caused by

subductionrollbackindeBandaregion.

TheMidCenozoicgroupoccupiesa largepartof

the Gorontalo section, and is locally exposed in

the southern part of the Minahasa section. It

consists of a predominantly volcanic unit

(Bilungala Volcanics), a mixed sedimentary

volcanic unit (Dolokopa Formation), and several

sedimentary units, including the Ratatotok

Limestone, which hosts Mesel and associated

gold deposits. The volcanic rocks consist

predominantly of andesitic lava flows and

pyroclastics, debris flows, and related

volcaniclastics,markingmultipleperiodsofuplift

anderosionduringthedevelopmentofthemid

Cenozoicvolcanicarc (PearsonandCaira,1999).

Felsicrocksarecommonlypresentinsomeareas,

includingtheTombulilatodistrict(Perello,1994).

The base of the MidCenozoic group has beenobservedonlyinafewlocalities,whereitconsists

of chaotic masses of Papayato Volcanics

fragments or poorly sorted conglomerates (Trail

etal.,1974;vanLeeuwenandMuhardjo,2005).

Thesequenceisintrudedbycomagmaticbodies,

varying in size from dykes and stocks to

batholiths of diorite, quartzdiorite and

granodiorite (e.g.Trailetal.,1974;Pearsonand

Caira, 1999). Limited radiometric age dating

results (Lowder and Dow, 1978; Polv et al.,

1997;

Pearson

and

Caira,

1999)

suggest

that

batholithsizedbodieswereemplacedduringthe

EarlyMiddleMiocene(1612Ma),irregularstock

and dykelike intrusions of diorite and

monzodiorite composition during MiddleLate

Miocene times, and small stocks and plugs of

quartz diorite composition during the latest

Miocene (85 Ma). According to Pearson and

Caira (1999) the batholiths were probably

exposedbyoneormoreperiodsofintraMiocene

erosion. Published geochemical data for the

volcanicandplutonicsuitessuggestthattheMid

Cenozoic was dominated by mediumK calc

alkalinemagmatism(Polvetal,1997). Porphyry

CuAuMo and intrusionrelated base metal Au

mineralization is commonly associated with the

MiddleLate Miocene suites. However, most

depositsaresmalland/oroflowmetaltenor.

ThestructureoftheMidCenozoicrockshasbeen

studiedinmostdetail intheTombulilatodistrict,

where several periods of lowangle thrusting


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14

were followed by development of highangle

northerly trending faults, which was succeeded

by several stages of easttrending block faulting

(Perello, 1994). A regional unconformity

between theMid and LateCenozoic sequences

marks a major tectonic event that is generally

believed to be related to the collision of the

BanggaiSulacontinental fragmentwithSulawesi

(e.g.Perello,1994;PearsonandCaira,1999).

The Late Cenozoic, which was the most

productivemineralizing period, witnessed

widespread and intensive volcanism. The Early

Pliocene Wobudu Breccia, exposed along the

north coast of the Gorontalo section, is

composedalmostentirelyofbasaltictoandesitic

agglomerates, breccias, pyroclastics, and lava

flows(Trailetal.,1974). Alongthesouthcoast,aseries of dominantly dacitic volcanics and co

magmatic highlevel intrusions are exposed,

named Pani Volcanics (Trail et al., 1974). They

form major caldera complexes that have

developed within the SW corners of large arc

parallel and arcnormal fault rhombs, and host

significant gold mineralization (Pearson and

Caira, 1999). Similar rocks are found in the

Tombulilato district, where they have been

named Motomboto Volcanics by Perello (1994).

K/Ar

dating

suggests

the

two

units

were

formed

between5.3and2.0Ma (Perello,1994;Polvet

al., 1997; Pearson and Caira, 1999). Significant

porphyryCuAuandepithermalAumineralization

isassociatedwiththismagmaticevent.

ThePinogoVolcanics(Trailetal.,1972)constitute

a volcanicsedimentary succession that occurs

overadistanceof170kmalong thesouthcoast,

from40kmwestofTototopotomorethan60km

eastofTombulilato,whereitisupto300mthick.

Isolatedremnantsarepresentwithinthecentral

LimbotoBone riftvalley,andup to40km to the

north. The unit is thought to have formed in

latest PliocenePleistocene times, a period

dominated by explosive volcanism (Kavalieris et

al.,1992;Perello,1994;PearsonandCaira,1999).

Thevolcanicsarecharacterized,atleastinpart,by

a bimodal association of basaltic andesite and

rhyolite(Kavalierisetal.,1992). Throughoutthe

Gorontalo section diatreme and irregular

magmatichydrothermalbrecciabodiesappearto

postdate and intrude the Pani Volcanics. They

include postmineralization diatreme breccias at

theCabangKiriandSungaiMakporphyrycopper

deposits(CarlileandKirkegaard,1985).

Volcanic units in the Minahasa section include

the locally named Maen Volcanics and Toka

Tindung Breccia (Wake et al., 1996), which are

contemporaneouswiththegoldmineralizationin

the Toka Tindung district and of Late Pliocene

age, and the Tondano Tuff of Effendi (1976),

whichare the resultofexplosiveeruptions from

the Tondano caldera, now occupied by the

Tondano Lake. Quaternary to Recent volcanics

maskmostof theolderrocks in theSangiheArc

(i.e. northern Minahasa section to Sangihe

Island).

The Late Cenozoic units are mostly flat lying to

gently dipping. Significant subrecent vertical

movements in the Gorontalo section are

evidenced by the elevation of young coral

limestone up to height of 5501000m, and the

formationofbroaddepressions(Rutten,1927).

The Gorontalo section is dominated by three

structural elements: i)long ESE trending fault

corridors, which are arcparallel structures; ii)

regularly

spaced

NW

NNW

arc

normal

fault

zones;andiii)shortNEENEarcnormalconjugate

faults (Carlileetal.,1990;Kavalierisetal.,1992;

Pearson and Caira, 1999). Carlile and al. (1990)

andKavalierisetall.(1992)observethatmuchof

the most recent faulting along the arcparallel

structures comprisenormal verticalmovements,

resulting in uplifted EW trending mountain

chainsandgraben.IntheMinahassasectiontwo

fault sets dominate: i) NE, showing vertical

movement,andii)NW,whichprobablycomprises

an orthogonal tensional fracture system

comparable to the Gorontalo section (Carlile et

al.,1990).

3.2 WesternSulawesiProvince

IntermsofgeomorphologyandgeologyWestern

Sulawesi can be divided into three parts:

Southwest (SW), Central West (CW) and

Northwest (NW) Sulawesi (Figure 3B). SW

Sulawesi is geomorphologically separated from


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15

CWSulawesibyaNW trendingdepression filled

with Quaternary sediments, which may mask a

major structure. It differs from the rest of the

province inbeing less tectonicallydeformedand

less mountainous, lacking large Neogene

granitoid bodies, and having Neogene volcanics

with isotopic and trace element characteristics

that are different from those found in CWNW

Sulawesi(e.g.ElburgandFoden,1999). Themain

differencesbetweenCWandNWSulawesiarein

the nature of Late EoceneEarly Miocene

sedimentation (dominantly carbonate and

dominantly siliclastic respectively) and the

relative scarcityofNeogene volcanicdeposits in

thelatterarea. CWSulawesihasthemostrugged

terrain, with many mountain ridges between

20003000m altitudes reaching a maximum

heightof3495m.

Western Sulawesi contains an almost complete

stratigraphic sequence ranging between Late

Cretaceous and Recent, which developed on a

basement of continental fragment and

accretionary/mlange rocks. It represents

severalmajorperiodsofsedimentation,including

Late Cretaceous flysch, Eocene synrift

siliciclastics, Late EoceneMiddle Miocene

platformanddeepermarine carbonates,Middle

Miocene

Early

Pliocene

shallow

marine

deposits,

and latest Cenozoic synorogenicsedimentary

successions. The sedimentation cycles were

accompaniedorinterruptedbyseveralmagmatic

eventsthattookplaceduringthePaleocene,mid

Eocene to midOligocene, Early Miocene, and

Middle Miocene to Pliocene, locally continuing

into the Quaternary (e.g. van Leeuwen and

Muhardjo,2005;vanLeeuwenetal.,2010).

PreTertiaryaccretionary/mlangecomplexesare

exposed in theBantimalaandBarrublocks inSW

Sulawesi and in the Latimojong Complex in SW

Sulawesi. They consist of imbricated tectonic

slices of both continental and oceanic rocks,

whichhavebeenmetamorphosedtogreenschist

amphibolite and blueschist facies (Sukamto,

1986;Wakitaetal.,1996;Maulanaetal.,2010).

The complexes have been interpreted by

Parkinson et al. (1998) to belong to a

dismembered midCretaceous accretionary/

subduction zone that extended from central

Eastern Sulawesi through southern Western

SulawesiandSEKalimantantocentralJava.

Three metamorphic complexes are exposed in

NW Sulawesi, i.e. the Palu, Karossa and Malino

MetamorphicComplexes,whicharecomposedof

continental fragments derived from the

AustralianNewGuineamargin,andinthecaseof

theformer twocomplexes,alsocontainslicesof

oceaniccrust(vanLeeuwenandMuhardjo,2005;

vanLeeuwenetal.,2007). ThePaluMetamorphic

Complex hosts a gold deposit named Poboya,

which is of uncertain origin. The metamorphic

complexes are believed to form part of asingle

large fragment (or composite fragment) that

underlies most of Western Sulawesi, the

MakassarStraits,JavaSeaandEastJava,andhas

been named the East JavaWest Sulawesi Blockby Hall (2009). This author interprets the

fragment(s) to have been separated from NW

Australia in the Jurassic and accreted to the SE

SundalandmargininthemidCretaceous.

The basement complexes are unconformably

overlain by weakly metamorphosed Late

Cretaceous flysch deposits, which occur

widespread throughout the province and in CW

Sulawesi host significant gold mineralization.No

mineralization,

other

than

minor

sediment

hostedCuoccurrences,hasbeenfoundtodatein

the unconformably overlying siliciclastics and

carbonate sequences which were deposited in

midEocene to midMiocene times. Volcanism

thattookplaceduringthisperiodappeartohave

been intermittent and localized, as a result of

which no major continuous volcanic arc

developed (van Leeuwen and Muhardjo, 2005;

van Leeuwen et al., 2010). The volcanic rocks

arecalcalkaline in composition and generally

believed tobe related toactive subduction (e.g.

Yuwono et al., 1986, 1988; Elburg et al., 2002,

2003). The only mineralization known to be

associated with the Early Tertiary volcanism is

Kurokotype VMS near Sangkaropi in CW

Sulawesi.

A major tectonic event took place in the early

MiddleMioceneunderextensionalconditions. It

wascharacterizedbyblockfaultingthatresulted

inlocalunconformitiesand developmentofa


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Table 3 SelectedfeaturesofporphyryCuAuMosystemsinNorthernSulawes

Prospect

Name

Hostrocks Alteration Mineralization Vertic

exten

(cm

Type Mineralogy

Bulagidun hydrothermal collapse

bx associated with

diorite &qtz diorite

stocks

(upper)muscchlorthqtzillkaol;

(inner)btqtzmgt

(outer)chlepi.

sulphide

cement

fillingbx

cpypymgt;Auwith

cpy and in native

form

500

Dunu diorite porphyry &

tourmalinebx

(inner)btqtzalb

(outer)chlactepi

stk&bxfilling cpypo(pymo); Au

withCp

Tapadaa qtz diorite; andesite

volcanics

(early)qtzchlbtanhalbmgt

(late)ser+qtzdiaspandpyroph.

stk&dissem pycpybo; chalc

blanket up to 40m

thick

100

CabangKiri qtz diorite stock;

(andesitevolcanics)

1.(top)kaoldiaspal2.clayserchlmgt3.chlmgt4.(bottom)qtzseralbchlmgt

bt

stk&dissem cpypybomgt,

chalccovpy

400

Kayubulan

Ridge

pipelike breccia

complex

qtzmgtbt overprintedby serill

chl

Stk&dissem cpypybo 150

SungaiMak diorite porphyry, sill

like

qtzmgtbt overprinted by serill

chlvuggysialkaol

Stk&dissem chalcblanket,upto

176m;+pycp

200

Source: vanLeeuwenandPieters(2011)

Abbreviations(Tables35): A=alteration;act=actinolite; al=alunite;alb=albite;ad=adularia;and=andalusite;anh=a

ba=barite;bo=bornite;bt=biotite;bx=breccias;carb=carbonate;chalc=chalcocite;chald=chalcedony;chl=chlorite;

=

diaspore;

dissem

=

disseminations;

en

=

enargite;

epi

=

epidote;

ga

=

galena;

HR

=

host

rock;

ill

=

illite;

kaol

=

kaolinitemolybdenite;musc=muscovite;orth=orthoclase;py=pyrite;pyroph=pyrophyllite;po=pyrrhotite;qtz=quartz;ser=se

stibnite;stk=stockwork;


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major strikeslip fault in SW Sulawesi (Walanae

FaultZone),alongwhichanoceanicfragmentwas

emplaced (van Leeuwen et al., 2010). Another

oceanic fragment exposed further north, the

LamasiOphioliteComplex,mayhaveaccretedto

theWesternSulawesicontinentalmarginaround

thesametime.

Thetectoniceventheraldedtheonsetofaperiod

of widespread shoshonitic to ultrapotassic

magmatismthatlastedtotheEarlyPliocene,and

locally continued into the Quaternary

(Lompobatang Volcano). Over 5000m thick

deposits of volcanic, comagmatic intrusive,

volcaniclastics and intercalated sedimentary

rocks cover large parts of SW and CW Sulawesi

(e.g. Sukamto, 1982; Bergman et al., 1996). In

NWSulawesi,theirdistributionismorerestricted(Elburg et al., 2003). The potassicultrapotassic

suiteshavebeenreferredtoasHKseriesbyPolv

et al. (1997).In CW and NW Sulawesi, the HK

seriesmagmatismwasaccompaniedbyadistinct

magmatic event that started around the

beginning of the Late Miocene and produced

large volumes of granitoids and subordinate

amounts of tuffs that were exclusively felsic in

nature and of highK calcalkaline composition,

theCAKseriesofPolvetal. (1997). Thisevent

lasted

until

the

Pleistocene,

making

the

granites

oneoftheyoungestintheworld.

Most of the mineral deposits and occurrences

found inWesternSulawesiarerelatedtotheHK

andCAKmagmatism. TheyincludeporphyryMo,

porphyryCuAu,intrusionrelatedbasemetalAu,

and probably also the Awak Mas and Poboya

golddeposits,andothersfoundinthesamebelt,

which in this paper we refer to as intrusion

relatedAudeposits.

Synorogenicsedimentary deposits of Plio

Pleistocene age, collectively known as Celebes

Molasse (Sarasin and Sarasin, 1901) occur

widespread throughoutWesternSulawesi. They

reflect a major tectonic event, involving rapid

uplift, folding and thrusting (? gravity sliding) in

CWandNWSulawesi. Thiseventhaspreviously

beenattributedtocollisionbetweentheBanggai

Sula microcontinent and the East Arm (e.g.

Bergman et al., 1996; Hall and Wilson, 2000).

However,thereisincreasingevidencetosuggest

that the CWNW SulawesiNorth ArmGorontalo

Bayregionhasbeen inextensionsince theEarly

Pliocene,whichmayhavebeendrivenbyrollback

of the subduction hinge at the North Sulawesi

Trench (Cottam et al., 2011). However, the

extremelyrapidratesandlargeamountsofuplift

andsubsidence in the region (ca3kmand>2km

respectively) suggest that significant flow of

lower crust, from beneath basins towards

topographically elevated areas, may also have

beenacontributingfactor(Hall,2011).

3.3 EasternSulawesiProvince

TheeasternSulawesiProvincecomprisestheEast

andSoutheastArms, theeasternpartof central

Sulawesi,andthe islandofButon. Theterrain isinmanyplacesveryrugged. This,combinedwith

thehighlytectonizednatureoftheregion,means

thatitsgeologyisstillpoorlyunderstood.

As discussed by Hamilton (1979), the province

consists of several quasicentric arcuate belts,

which are composed of, from west to east: 1)

shearedmetamorphicrocks,2)highly tectonized

mlange of ophiolitic, metamorphic, and

MesozoicPaleogene rocks; the latter also

occuring

as

more

coherent

masses;

and

3)

predominantlyophioliticrocks. Afourthzoneof

imbricated Mesozoic and Paleogene rocks that

fringes the southeast margin of the East Arm

belongs to theBanggaiSulaProvinceandmarks

the collision zone between the BanggaiSula

continentalfragmentandtheophioliteterraneof

theEastArm. Therocksthatconstitutethefour

zonesareunconformablyoverlainbysyntopost

orogenic sedimentary deposits (Celebes

Molasse).

Metamorphic rocks form a 460km long, 80km

wide zone, including the Pompangeo

Metamorphic Complex in central Eastern

Sulawesi (Parkinson, 1991; 1998), and the

MehonggaandTeimosiMetamorphicComplexes

in the SE Arm (Rusmana and Sukarna, 1985).

Severalsmallermassesoccuratthesouthendof

the SE Arm and on Kabaena Island. In central

Sulawesi,themetamrphicbeltisboundedonthe

west by a profound tectonic dislocation, the


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18

Median Line (Brouwer, 1947), against Western

Sulawesi,andtotheeastitgradesintoatectonic

mlange. In the SE Arm, the southwestern

boundaryofthemetamorphiczoneismarkedby

a narrow strip of ophiolite, whereas a major

strikeslip fault (Lawanopo Fault) forms the

northeastern boundary, separating the

metamorphiczonefromtheophiolitezone.

The metamorphic rocks include both blueschist

and greenschistamphibolite facies (e.g.

Parkinson,1998;Helmersetal.,1989;1990). In

central Eastern Sulawesi an increase in the

degreeofmetamorphiccrystallizationisapparent

fromeasttowest(Brouwer,1947). Thistogether

withthestyleofdeformationofthePompangeo

Schists is consistent with successive

underthrustingofslicesofdowngoingmaterialina westdipping subduction, which based on

limited K/Ar dating of the schists probably took

place during the midCretaceous (Parkinson,

1991;1998). Parkinson (1998)suggeststhatthe

protolithsofthemetamorphicsconsistsinpartof

Jurassic sedimentary rocks, similar to the ones

exposed in small terranes to the east. Until the

recent discovery of gold in metamorphic rocks

near Bombana in the SE Arm the metamorphic

complexeswereconsideredtohavelittlemineral

potential.

The contact zone between the metamorphic

rocks and the ophiolite is marked by a tectonic

mlange in central Eastern Sulawesi, which is

composed of a highly complex mosaic of

tectonized and metamorphosed ophiolite

fragments, schist fragments and variably

disruptedMesozoicsedimentaryrocks.K/Arages

of 2832 Ma suggest that the mlange was

formed during the middle to late Oligocene,

possibly as the result of eastward subduction

beneath the ophiolite terrane, that was

subsequently thrusted westward over the

metamorphicbasement(Parkinson,1996).

Largeophiolitemassesaredistributedovermost

of the East Arm and the northwest part of the

Southeast Arm, and on the adjacent islands of

ButonandKabaena. Theycoverover15,000km2

andareknownas theEastSulawesiOphioliteor

ESO (Simandjuntak, 1986). From an economic

pointofviewthisisthemostimportantrockunit

in Eastern Sulawesi, as it has given rise to

extensiveNilateritedepositsandchromitebeach

sandsdeposits.

A complete, but highly imbricated ophiolite

sequence has only been observed in the East

Arm, whereas elsewhere only the lower,

ultramafic portion of the sequence is present.

Theageoftheophioliteispoorlyconstrained. A

widerangeofK/Arageshavebeenobtainedfrom

ESO rocks, varying from Cretaceous to Miocene

(Mubroto et al., 1994; Monnier et al., 1994;

Simandjuntak, 1986), which are difficult to

interpret. IthasbeensuggestedthatCretaceous

deepmarinepelagicsedimentaryrockswhichare

spatiallyassociatedinseveralplaceswiththeESO

may represent the uppermost part of thesequence(e.g.Kndig,1956). Variousoriginsand

timingofemplacementhavebeenproposed for

theESO. It is likely,however, that theESO isa

compositeterranewithmorethanoneoriginand

ofdifferentages(HallandWilson,2000).

MesozoicPaleogene sedimentary rocks are

mostlyinterthrustorininterminablefaultcontact

with the metamorphic basement and ophiolite

sequencesthroughoutEasternSulawesi. Broadly

speaking,

they

consist

of

fluvial

to

shallow

marine

siliciclastics and subordinate carbonates of late

TriassicJurassicage thatwere formedalong the

Australian continental margin, and Cretaceous

Oligocene deep marine, pelagic sedimentary

rocks,whichwere laiddownonfragmentsrifted

from the margin and transported westwards to

theSulawesiregion(e.g.PigramandPanggabean,

1984;Villeneuveetal.,2001;Surono,2008).

Synto postorogenic deposits are widely

distributed throughout Eastern Sulawesi. They

can be divided into clastic and carbonate

sequenceswith coarsegrained clastic sediments

dominating (Surono, 2008). Deposition started

earlier in the southern part of the province

(around the Early Miocene) than further north

(MiddleLateMiocene).


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19

4.0 Mineraldeposits

Inthischapterwepresentareviewofthevarious

mineralization styles thatareknown tooccur in

the Northern, Western and Eastern Sulawesi

Provinces.Examplesofeachtypearedescribedin

some detail as either individual deposits or

mineral districts, for which a brief summary of

their exploration history is also given. We have

assignedthemto17categories,whichareshown

in Figure5 togetherwith theirmap symbols for

Figures 6, 25 and 35. In this paper we have

adopted the most widely used nomenclature.

The reader will be familiar with most of the

terms,butafewneedfurtherexplanation.

1) High, intermediate and lowsulphidation

epithermalAu

Ag.Thisbroadgroupofepithermal

mineral deposits has been subjected to over a

dozenclassificationschemessincethelate1970s,

which in part reflects the wide range of

characteristic features displayed by orebodies

belonging to this group (Simmons et al., 2005).

The currently most widely used terminology of

high, intermediate and lowsulphidation, terms

introducedbyHedenquist (1987),Hedenquistet

al(2000)andEinaudietal (2003), isbasedupon

the sulphidation state (or sulphur fugacity) of

sulphur

bearing

minerals

that

occur

in

the

epithermal mineral assemblage. Intermediate

sulphidation isarelativelynew term,whichwas

previously included in the lowsulphidation

category. Sillitoe and Hedenquist (2003)

emphasize the linkage between sulphidation

types and volcanotectonic settings; most high

sulphidation deposits are generated in calc

alkalineandesiticdaciticarcsunderneutralstress

state or mild extension conditions, and

commonly show a close connection with

porphyry Cu deposits; intermediatesulphidation

deposits occur in a broadly similar environment

but lack such close relationship; and most low

sulphidation deposits are associated with

volcanicsuitesinabroadspectrumofextensional

settings.

Corbett and Leach (1998) divided the low

intermediate sulphidation deposits into two

broad groups. The first group dominates in

magmatic arcs and displays an association with

intrusionsgradingawayfromtheintrusionsource

as; quartzsulphideAu+/Cu, carbonatebase

metalAu and epithemal AuAg. The second

group,termedadulariasericiteepithermalAuAg,

dominates in rift settings. Corbett (2007)

subsequentlyrenamed the lattergroupbanded

chalcedonyginguro epithermal veins. Where

appropriatewerefertothisclassificationscheme

inthetext.

2)IntrusionrelatedbasemetalAu. Thiscategory

includes vein deposits which usually contain

significantamountsofbasemetal sulphidesand

show,orareinferredtohave,acloseassociation

with (porphyry) intrusions. It overlaps with the

quartzsulphideAu+/CucategoryofCorbettand

Leach(1998).

3)Intrusionrelated Au. This category has been

assigned toa fewdeposits inWesternSulawesi,

includingAwakMas,MangkalukuandPoboya.As

discussed below, the origin and classification of

thesedepositsisproblematic.Wedescribethem

in4.2.4under the (moreneutral)heading Gold

inmetamorphicterrains

Asformanymineraldepositsandoccurrences in

Sulawesi there is no detailed information

available,

assigning

them

to

a

particular

category

can be quite subjective. In a few cases where

therewastoolittletogoby,oranoccurrencedid

notseemtofitanyofthecategories,weassigned

themtothenotclassifiedcategory.

For each of the three provinces we have

prepared a map showing mineral localities and

the names of deposits/prospects or mineral

districts mentioned in the text. The maps were

compiled from the Indonesian Mineral Deposit

DataBase(vanLeeuwenandPieters(2011).

4.1 NorthernSulawesiProvince

Northern Sulawesi is relatively well endowed

with mineral deposits and prospects (Figure 6).

Asdiscussedearlieritisaregionofbothpastand

presentgoldminingactivity.Anumberofmineral

styles have been recognized todate. These are

porphyryCuAuMo,high,intermediate and


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20

Figure5.MineralizationtypesfoundinSulawesiandtheirsymbolsusedinFigures6,25and35

Figure 6. Northern Sulawesi. Distribution of mineralization types, and location of prospects and

mineralizeddistrictsmentionedinthetext;forsymbolsseeFigure5


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21

lowsulphidation epithermal AuAg, sediment

hosted Au, brecciahosted base metalAu

mineralization, intrusionrelated base metalAu

veins, FeAu skarns, and CuPbZn volcanogenic

massive sulphides (VMS). The VMS

mineralizationistheonlystyleassociatedwiththe

Paleogenevolcanicactivity. All theotherswere

formed during the Miocene and particularly

Pliocenemagmaticepochs. Tables3and4show

selected features of the more significant

Northern Sulawesis porphyry copper and

preciousmetalsystemsrespectively.

4.1.1 PorphyryCuAuMomineralization

More than 40 porphyrystyle deposits and

occurrences have been identified, which

commonlyoccurinclusters. Theycanbedividedinto two groups, Late Miocene and Pliocene.

Their main features have been described by

PearsonandCaira(1990).

The Late Miocene group (e.g. Bahumbang, and

Dunu)arehostedby irregulardykelikebodiesof

dioritetoquartzdioritecompositionintrudedinto

comagmatic basaltic andesite andesite

volcanics. A central quartzbiotitemagnetite

zonegradesoutwards to chloriteepidotecalcite

alteration,

and

upwards

to

quartz

sericite

carbonateclayassemblages. Albite ispresent in

someprospects. Advancedargillic lithocaps are

absent. In some deposits sheeted quartz veins

are well developed (e.g. Petulu) but most are

characterized by quartz stockworks. The

porphyry systems are poorly mineralized,

showing the following zonation: central

chalcopyrite+molybdenite pyrite+chalcopyrite

pyrite leadzinc. Gold is associated with

chalcopyrite. Molybdenite commonly occurs in

earlyveins. RatherunusualisBulagidun(4.1.1.2)

whereCuAumineralization ishostedbyaseries

ofhydrothermalbrecciasdevelopedperipheralto

a biotite altered, but unmineralized diorite

complex.

ThePliocenesystemsshowbothsimilaritiesand

differenceswiththeMiocenesystems. Examples

include the Tapadaa district (4.1.1.3) and

Tombulilato district (4.1.1.4) and Taware on

Sangihe Island (4.1.1.5). With a few exceptions

(e.g. Taware) the Pliocene systems are better

mineralized. They are centred on multiphase

cylindricalstocksanddykesshowingfractionation

to more felsic endmembers (quartz diorite to

dacite porphyry) that are associated with co

magmatic volcanics of dacite composition.

Diatreme breccias are commonly present.

Alteration zonation consists of a central quartz

albitemagnetitebiotitechlorite core, an outer

chloriteactinolitemagnetite zone,andanupper

sericitekaolinitealunitediaspore zone. Quartz

sulphide stockworks are well developed. Higher

gold grades show a strong association with

bornite,magnetiteandchalcopyriteinthecentral

zone thatgradeoutwards toa pyrite zone with

supergenechalcocite. Au:Curatiosarerelatively

high.

4.1.1.1 Bahumbung

Bahumbung is the only Miocene porphyry Cu

prospect thathasbeendescribed insomedetail

(Lubis et al., 2011). It consists of several

mineralizedcentresupto500x400mindiameter.

The area was identified during Newcrests

regionalexplorationprogrammeinthelate1990s

asaCuAuanomaly. Itwasinvestigatedinmore

detail by Ivanhoe Mines Ltd in the late 2000s,

including

groundmagnetics

and

drilling

of

3

deep

holes(1,544m)and13shallowholes(561m).

The prospect area is underlain largely by

andesitic lava, tuff and volcanic breccias

belonging to theBilungalaVolcanics. Theseare

accompanied by minor dacitic volcanics and

intruded by multiple intrusives ranging in

compositionfromdioritetoaplite. Threediorite

units have been recognized, referred to as Old,

IntermediateandYoungDiorite.

TheOldDiorite (onlydetected intwodrillholes)

ischaracterizedbystrongalteration(potassicand

pale green mica), moderate to high density

quartz stockwork, and moderate copper grades

(0.3%0.4%). The Intermediate Diorite has a

lowerdensityofquartzstockwork(upto3%)and

lower copper grades (0.10.3%), and is

moderately altered (PMG). The Young Diorite

occurs as latemineral dykes with low sulphide

andCucontents,


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22

Potassicalterationhasaffectedmoststronglythe

Old Diorite and andesitic wall rocks. Very fine

grained secondary biotite and magnetite

completely replace mafic minerals, and are

intergrown with actinolite in veinlets. The

alteration is associated with quartz stockwork

zones, varying in intensity from 3 to 10%, and

0.4%)havebeenobtainedfromstronglyaltered

andesiticwall rocks adjacent to the Old Diorite.

Palegreenmicaalterationischaracterizedbythe

presence of shreddy chlorite and green sericite,

which replace earlier secondary biotite and

primary feldspar. In rocks that are not tooweathered chalcopyrite and pyrite can be

observed.

Sericitechloritemagnetite alteration is

associated with the Young Diorite. Mafics are

replacedbychloriteandmagnetiteaccompanied

byvariousamountsofpyrite. Primary feldspars

are partially or totally altered to sericite. This

alterationassemblage isprominent inore zones

ofanumberofmajorPhilippineporphyryCuAg

deposits

(Sillitoe

and

Gappe,

1984),

but

at

Bahumbung contains only very little

chalcopyrite.Molybdenite appears to be mostly

associated with sericitechloriteclay alteration

overprintingpotassicalteration.

4.1.1.2 Bulagidundistrict(Figure7)

This district is located 170km WNW from

Gorontaloand10kminlandfromthenorthcoast.

It is the largest known Miocene system in

Northern Sulawesi, covering an area of 50km2,

and encompassing five separate prospects of

porphyry, vein and skarn styles, of which the

largest known is the Bulagidun prospect. The

districtisoutlinedbya790ppmCu80#stream

sediment anomaly, while Au anomalism is

centredonBulagidun,andPbandZnanomalies

are related to peripheral vein systems. It is

coveredbydense tropical rain forestwith steep

relief(500to1700m).

Thedistrictwas identified in1987byBHPduring

followup of stream sediment and panned

concentrategeochemicalanomalies. Systematic

exploration until 1991, including ~8000m of

drillingoutlinedageologicalresourceof14.4Mt

@ 0.68 g/t Au and 0.61% Cu in three separate

breccia bodies. Further investigations were

carried out by Newcrest and Cyprus in 199697

involving detailed surface work and drilling

(Bulagidun,2793m;Matinan9,760m;Matinan6,

1484m). The results of the two campaigns are

discussed by Lubis et al. (1994), PT Newcrest

Nusa Sulawesi (1999) and Pearson and Caira

(1999).

ThegeologycomprisesadeeplyerodedMiocene

volcanic centre within a sequence of

volcaniclastics and immature sediments coveredby andesite lava, which in turn is overlain by

andesite pyroclastics and volcanogenic

conglomerates. Two samples of unaltered

andesitelavayieldedKArwholerockagesof9.4

Ma. The sequence is intruded by a sequential

fractionation intrusive suite consisting of seven

partially superimposed plutons that range in

composition from pyroxenebiotite diorite to

quartzbiotite feldspar porphyry and aplite.

Limited whole rock analyses presented by Lubis

et

al.

(1994)

suggest

that

the

igneous

rocks

in

the

BulagidunareabelongtothemediumandhighK

calcalkalineseries.

A regional scale NNWtrending arc normal

structurepassesthroughthewesternpartofthe

system. A setofNEtrending faultsbracket this

system linking it across to another arc normal

structure, 20km to the east. Intrusive bodies

forming aligned circular features, 2 to 4km in

diameter, are centred on the Bulagidun and

Matinan prospect areas, suggesting a collapsed

magma chamber at depth. Mineralization is

strongly controlled by EW structures and

intersections with crosscutting NS structures.

This pattern is consistent with dextral

transpressuring of the arc normal structures.

Twelve breccia pipes have been mapped in the

system.

The Bulagidun/Matinan alteration system

extendsover7k min an EN Edirectionwitha


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23

Figure7.SimplifiedgeologicalmapofBulagidundistrictandprospect locations (modifiedafterPT

Newcrest

Nusa

Sulawesi,

1999)

Figure 8. Simplified geological map of Tapadaa district and prospect locations (modified after PT

NewcrestNusaSulawesi,1999)


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24

Figure9.SimplifiedgeologicalmapofTombulilatodistrictandprospect locations

(modifiedafterPerello,1994)

Figure10.CartoonshowingporphyryCudepositstylesintheTombulilatodistrict


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25

width of 3km. It is concentrically zoned with a

biotite core (2000mx300m) surrounded by an

albitemagnetite zone thatgradesoutwards into

an albitesericitepyrite assemblage. Another

shell of epidotechloritecalcite surrounds these

assemblages. Sericiteclay

chloritequartzcarbonate alteration, both

pervasiveandstructurallycontrolled,crosscutall

theearlyassemblages. WholerockKArdatingof

thisassemblageyieldedanageof8.75Ma. Late

stage claypyrite alteration occurs as narrow

zones along faults and fractures. Disseminated

blebs and fracture fillings of radiating black

tourmaline are found in biotite magnetite and

sericiteclaychlorite altered rocks. It typically

constitutes 12% of the rocks, but locally may

attainvaluesof1020%.

StylesofhypogeneCuAumineralization include

a porphyryrelated collapsedrawing down

brecciainfillinatleast7brecciapipes(Bulagidun)

and disseminated mineralization controlled by

microlitic cavities in the causative intrusions,

representing orthomagmatic mineralization

(Matinan9). Drillingofthemainbrecciapipehas

demonstratedthatthemineralizationextendsto

greater than 500m depth. The dominant

sulphides are chalcopyrite and pyrite (largely in

veinlets

and

breccia

matrix).

Molybdenite

is

locally abundant, whereas bornite, galena and

sphalerite are rare. Gold is associated with

chalcopyrite and pyrite in solid solution or as

minuteintergrowths.

Breccias are fragment supported with angular

fragments ranging in size from cm to 10s of m

withlittleornorockflourmatrixandnoevidence

ofhydrothermalstreamingorfragmentedmilling.

The breccia void spaces are filled with coarse

grained, pegmatitic, hydrothermal minerals,

whichhavea remarkably consistentparagenesis

across the system, from earliest to latest;

magnetite (replaced by specularite in places),

apatite, biotite (partly replaced by chlorite),

molybdenite, quartz, tourmaline, chalcopyrite,

galena, pyrite, ankerite. A characteristic of the

Bulagidun district is the apparent lack of quartz

stockworkdevelopmentassociatedwithzonesof

CuAu mineralization. Preliminary fluid inclusion

studiesshowawiderangeofhomogenenization

temperatures (180oC to 700oC) and salinities,

suggesting multiple separate stages of

hydrothermal fluid and mixing between saline

magmaticanddilutemeteoricfluids.

Quartz veins,partly sheeted,occuradjacent (up

to 500m lateral distance) to the mineralized

breccias. They are up to 2m thick and contain

minorsphaleriteandgalena. Inexcessof10g/t

Auwas recorded in surface samples,but indrill

holesonly0.52g/tAuwasobtained. Insome

placesmeterwidezonesofabundanttourmaline

occurincloseproximity.

A large tabular body of magnetiteepidote

garnetpyrrhotite skarn (Matinan6) is found

within the propylitic zone, 2km to the NNW of

thecentralCuAuzoneatBulagidun. Itcontainspatchygoldmineralizationinnativeform.

4.1.1.3 Tapadaadistrict(Figure8)

Discovered in1971byEndeavourResources,the

district was investigated in some detail by

Kennecott between 1972 and 1974, including

1,222mofdiamonddrilling. Four smallsystems

were outlined (Tapadaa South, Central and

North, and Mogi Wapo), each containing

between

2

and

15

Mt

@

0.2

0.4%

Cu

in

primary

ore and a total of 20 Mt @ 0.61.0% Cu in

supergeneenrichedore(vanLeeuwen,1994). In

1994,NewcrestobtainedalargeCOWareawhich

included the Tapadaa district. It undertook

regionaltoprospectscalesurfacework,whichled

tothediscoveryofafifthsystem,TapadaaWest.

The best result obtained was 252m of chip

sampling averaging 0.39% Cu and 0.13 g/t at

TapadaaSouth.

LiteratureontheTapadaadistrict inludespapers

byLowderandDow(1977;1978)andareportby

PTNewcrestNusaSulawesi(1999).

ThedistrictgeologyconsistsofMioceneBilungala

Volcanics, which are primarily andesitic to lithic

tuffs. They have been intruded by a series of

porphyritic diorite stocks and dykes on the

western margin of the Miocene Bone batholith.

These have been subdivided into premineral

weakly porphyritic diorites, synmineral quartz


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26

diorite plugs and quartzdacite porphyry dykes,

and postmineral andesite porphyry dykes.

Pleistocene Pinogu dacite tuffs (some with

mineralized clasts) unconformably overlie much

ofthearea,includingpartofthemineralizationat

TapadaaNorthandCentral.

TheTapadaaprospectsliewithina>90mppmCu

elliptical halo defined by stream sediment

sampling. Internal to this isa>4ppmMohalo,

thatonly includes Mogi Wapo. PlotsofCuand

Au in rock show small Au bull eyes (>0.1 ppm)

within largerCu (>500ppm) zones. AtTapadaa

West the largest Au anomaly measures

460mx400m. Porphyry mineralization appears

almost continuous from Tapadaa South through

to Tapadaa North, except where obscured by

postmineral Pinogu Volcanics over an area of100300m by 3000m. Mogi Wapo measures

about200mx1000m, andTapadaaWest has the

smallest exposure (200x400m). Mapping by

Newcrest has shown that the Tapadaa West

mineralization is hosted by the Bilungala

Volcanics,andnotbydioriteintrusiveasthought

by previous explorers. This introduces the

possibilityofa largerconcealed intrusivehosted

system.

The

porphyry

prospects

occur

in

a

NW

trending

structurally controlled blocks. Copper

mineralization isassociatedwithearlyalteration

consisting predominantly of quartzchlorite

biotiteanhydrite, and in areas of better grades

(0.20.4%)alsogreensericiteandalbitetogether

withalbitequartzandmagnetitequartzveinlets.

TwosecondarybiotitesamplesyieldedKArages

of5and2.5Ma. Sulphidecontents(chalcopyrite,

bornite,pyrite)are typically low. Sulphidesand

magnetite are present mostly as fracture infill,

andalsoasdisseminationsandinquartzveinlets.

There appears to be a positive correlation

between primary Cu grades and magnetite

concentrations.

The early alterationmineralization assemblages

areoverprintedbysericite+quartzorclay,quartz

sericitediaspore, and/or andalusitepyrophyllite

assemblages. Corundum and specularite are

associatedwithhighpyritecontents. Supergene

blankets,up to30m thick,are locallydeveloped

underlying of strongly leached pyritic zones in

advancedargillicrock.

4.1.1.4 Tombulilatodistrict(Figure9)

TheTombulilatodistricthasbeenanexploration

teaserformanyyears. Followingitsdiscoveryin

1971byEndeavourResources,Kennecottcarried

out exploration between 1972 and 1975 which

ledtothediscoveryofCabangKiriwhere1,070m

[email protected]%Cu

and 0.75 g/t Au, Kayubulan Ridge with an

estimated [email protected]%

Cuand 0.35 g/tAubased on surface data only,

and Cabang Kanan. Following Kennecotts

withdrawal in1976,Endeavourdrilled6holesat

Kayubulan Ridge, one of which intersected

significant mineralization. Between 1980 and1982 Utah International embarked on a major

exploration programme involving 5 drilling rigs

and2helicopters. Thethreeknowndepositsplus

a new discovery, Sungai Mak, were drill tested

(~1600m)outliningacombinedresourcesof296

Mt @ 0.57% Cu and 0.47 g/t Au. The original

Endeavour COW was terminated in 1986. Two

years later BHP entered into a JV with Antam

whichobtainedtwosocalledsuperKPsoverthe

district. In 1991, a national park was declared

over

the

area

and

all

work

ceased.

After

a

2

year

exploration permit was obtained from the

MinisterofForestry in1996BHPembarkedona

heliborne magnetic survey, which identified a

numberofanomalies,twoofwhichappeared to

beassociatedwithpreviouslyunknownporphyry

stylemineralization,i.e.GunungLintahandWest

Kayubulan Ridge. Because of uncertainties

pertainingtothenationalparkandotherreasons

BHPwithdrewinlate1997. Recentlythedistrict

was excised from the park and exploration title

wasawardedtoBumiResources.

TheTombulilatodistrict(LowderandDow,1978;

CarlileandKirkegaard,1985;Carlileetal.,1990;

Perello, 1994; BHP Minerals Sulawesi, 1997) is

composed of a >3400m thick volcano

sedimentary sequence in which three main

stratigraphic units are recognized: i) Bilungala

Volcanics (Upper Miocene base Pliocene)

divided intoa LowerMember (tholeiiticbasaltic

and spilitic volcanics), Middle Member


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(alternating andesitic and felsic volcanics with

minor sedimentary intercalations), and Upper

Member (subaerial andesitic fragmental

volcanics); ii) Motomboto Volcanics (Upper

Pliocene), which consists of subaerial felsic to

intermediatevolcanic rocks; iii)PinoguVolcanics

(Pleistocene), characterized by poorly

consolidated, subaerial bimodal volcanics.The

sequence is intruded by strongly porphyritic

bodies of andesitic to dacitic composition, and

equigranular bodies of granodioritic to dioritic

composition. Field relationshipsand twowhole

rocksKAragesof2.35and2.05Ma suggests a

LatePlioceneagefortheseintrusions. Afoliated

granodioriteexposedintheNEpartofthedistrict

isprobablyMiddleMiocene(orolder).

The structure of the Tombulilato district ischaracterized by northerly striking highangle

faults, normally a few metres wide and

containing

Documents

Mineral Deposit of Sulawesi_Theo M. Van Leeuwen and Peter E. Pieters