2 the copper deposit of batu marupa

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THE COPPER DEPOSIT OF BATU MARUPA IN CENTRAL SULAWESI,INDONESIA

Rudarsko-geoloSko-naftni zbornik

Ivan JU RK OV I~ nd I Boiidar ZALOKAR IRudarsko-geolofko-naftniakultet SveuEiliJta u Zagrebu, Pierotijeva 6, YU-41000 Zagreb

Key-words:Forms of the copper ore bodies, paragenesis, microp- Kljuine Oblici bakarnih rudnih tijela, mineralni sastav,hysiography, genesis mikrofiiografija, postanak IetiSta

UDC 553.43 Izvorni znanstveni ELanak

Vol. 2

The authors give in this paper the tectonic framework of the A ~ t o r i aju u ovom radu tektonsku gradu otoka Sulawesi (Ce-island Sulawesi (Celebes) as well as the results of field and lebes) kao i rezultate terenskih i laboratorijskih istrdivanjalaboratory researches into the copper deposit of Batu Marupa bakamog lefista Batu M ~ N P ~Sangka ro~ i) SrediSnjem dijelu(Sanp karopi) in the central part of the island. otoka.

The tectonic framework of Sulawesi

str. 29-33

Plate tectonic models of the Indonesian Archipe-lago have been constructed by H a m i l t o n (1970,1973) and K a t i l i (1971, 1973). According toK a t i 1 (1973) a double volcanic-plutonic arc withopposing Benioff zones existed during Permian andCretaceous times in this area. The Tertiary Sunda-Banda east-west trending arc had its origin in aspreading centre situated in the Indian Ocean, whilethe north-south trending Sulawesi-Mindanao arc-trench system was generated by a spreading centresituated in the Pacific Ocean. The Sulawesi andHalmahera arcs came into existence in the earlyand late Tertiary period when the Pacific Plate chan-ged its movement to a westnorthwest direction.

K a t i 1 (1978) explains the special, bizzare formof the islands Sulawesi and Halmahera (fig. 1.) bythe following view: >>Thecontinuous northwardmovement of the Indian Ocean Plate and the west-ward thrust of the Pacific Plate along the SorongTransform Fault, accompanied by the counter-clock-wise movement of New Guinea, have producedcomplicated tectonic structures such as the K-shapedform of Sulawesi and Halmahera, bending theBanda arc westward and pushing Sulawesi and Hal-mahera towards the Asian continent, as well as theopening of the Makassar Straitcc. This happenedduring the Miocene time 19-13 m.y. B. P., on thebasis of palaeomagnetic studies.

The Sulawesi-Mindanao volcanic-plutonic arc,striking perpendicularly to the Banda arc extendsfrom western Sulawesi to Mindanao and it is charac-terized by granites and volcanics that have beenradiometrically dated: granites 3,35-31,O m. y.; vol-canites 4,25-17,8 m.y. B. P. The Tertiary Sulawesisubduction zone follows eastern Sulawesi, theTalaud Ridge and the submarine Mayu Ridge. Itis characterized by the presence of ophiolites ormklange in the island ( K a t i 1 , 1974).

Zagreb, 1990.

MineralizationEastern and south-eastern Sulawesi containsabundant lateritic nickel deposits in the ophiolitecomplex: Larona, Soroako, and Pomalaa. In ophio-lite Acoje, in Latau there are also nickel and pla-tinum sulphides. All these deposits originate froma subduction zone generated by the Pacific Ocean.They are related to collision zones and transform

faults.The western arc of Sulawesi is characterized bycopper-silver-gold porphyry doposits occurring in anarea where the underlying crust is oceanic in natureand is characterized by a steeply dipping Benioffzone (Katili, 1984).Porphyry prospects are Tap, Tomb, Malala (withMo) in the Gorontalo area, northern arm of Sula-wesi; Sassak is in the central part of the island.The copper deposit of Batu Marupa

The mineralized area is situated some 35-40 kmnorth of Makale, which is the administrative centreof the Tana Toradja Province, some 60 km north-west of Polopo port, in the gulf of Bone. Makaleis connected with Padang, the capital of the islandby a road 350 km in length. The ore deposits areconnected by a road to Polopo port.In North Toradja there are three copper depo-sists: B a t u M a r u p a (Singkaropi), M a r i r i andT a 1 m b a n g a n, exploited during World War I1by the Japaneses or prepared for exploitation.According to V a n B e m m e 1e n (1949) Talimban-gan is an iron-ore deposit.

The exploitation of copper ore during World War I1 wasmost intensive on the ore deposit of Batu Marupa. The Japaneseconstructed an access road, leading to the mine, and they alsoerected some primitive smelting plants, but on retreating, theydestroyed them again. According to information obtained fromthe local population, the Japanese used to convey to Polopoport 2-3 trucks of selected ore daily, i.c. 10-15 tons of ore


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30 Rudarsko-geoloSki-naftni zbornik, Vol. 2, Zagreb, 1990

S U L A W E S l S E A

A OPHIOLITE-RELATED Ni-LATERITES A N 0 CHROMITE DEPOSITSNlKALJNl LATERlTl I L E ~ I ~ T AROMITA VEZANA NA OFlOLlTEPORPHYRY COPPER OEPOSITS RELATED TO MAGMATIC ARCPORFIRNA B M A R N A L E ~ I ~ T AEZANA NA MAGMATS61 LUKBATU MARUPA PROSPECT = I S T R A ~ N IRA D BATU MARUPA& CTIVE SUBDUCTION ZONE = AKTIVNA ZONA SUBDUKCIJE

C, T RANSFORM FAULT (IF) TRANSFORMNI RASJED

SANGIHE

F L O R E S S E A0

SUMBAWAU ALORO @ ~ P ~ ~ d- .Q @OL E S S E R S U N D A I S L A N D S 100 200 300 400 W N m

IFig. (SI.11 LOCATION OF BATU MARUPA P R O S P E C TP O L O ~ A JL E ~ I S T AB A T U MARUPA

B A N D A S E A

with 3-5% of Cu. The Mariri deposit, situated about 5 km The author (B. Zalokar) visited and examinednorthwest of Batu Marupa is a somewhat smaller one. The ore only the B~~~M~~~~~deposit, the other two depo-of the same type, but on a smaller scale, was extracted and theore from this deposit was transported in quantity to Singkaropi. sits were inaccessible at the time of his visit.The ore deposit of Talimbangan is situated farther from Mariri.According to information obtained from the local population, The ore deposi t of B a t u M a r u P is situatedthe Japanese were assuming that the o re deposit of Talimbangan on the southern slopes of the volcanic domes ofis larger and of greater economic value than that of Batu Marupa, Popomalangi (+ 1242 rn) and Bidong Pangpano (+and had the constmction of a km long 1250 m) which are prominently elevated among theroad an d started to open and develop the mine, but the interrup-tion of the war had prevented them from realizing their plans surrounding hills and mountains by their morpholo-further. gy. The highest of the mountain peaks is Bidong


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I . JurkoviC and B. Zalokar: The Copper Deposit 31Lepong (+ 1580 m) The ore occurrences areencountered at an altitude of 1100-1200 m.The broader area of the ore deposit is composedof magmatic rocks ranging from acid and interme-diary to basic volcanic rocks. The hydrothermal alte-ration processes, preceding direct mineralization,had affected vast areas and had been very intensive,so that the immediately surrounding rocks haveremained almost entirely altered. The three rockspecimens analysed by Prof. V. Majer (Universityof Zagreb) showed as follows: the firs rock specimenshows a completely altered rock with rounded, cor-roded crystals of quartz, which indicates that theoriginal rock belongs to the group of dacites. Thesecond rock specimen shows an obvious porphyrystructure. The predominant phenocrysts are the pla-gioclases, polysynthetically twinned. They havecolumnar or lath-like forms. Members ranging frombasic andesine to labradorite were dealt with onthe basis of their index of refraction. Some of thescarce salic phenocrysts belong to sanidine. Thecoloured minerals are considerably scarcer, the mostfrequent among them being pseudomorphoses ofuralitized amphibole after pyroxene, The matrix ofthis rock is holocrystalline, composed of columnarplagioclase and laths and leaves of amphibole, somechlorite, while magnetite and devitrified volcanicglass are subordinate constituents. The third rockspecimen represents a rock of indistinct porphyrystructure that was promoted by the general reduc-tion of the size of the phenocrysts, so that theamount of them in the matrix has become compa-ratively small. The main phenocrysts are polysynthe-ticaly twinned and they belong to andesine by theirrefraction index, or to more basic members.. Asphenocrysts, there is augite besides plagioclase (theangle of extinction is about 40"). Magnetite occursas an accessory mineral. Kaolin substance, someuralite and chlorite are the supergene products. Inthe druses, there are low-temperature albite andchalcedony. The rocks in the immediate surroun-dings of the ore deposit, as weU as in the sterileportions within the ore bodies, are almost entirelysilicified; besides small to fine-grained quartz andchalcedony there is, sporadically, some clayey sub-stance.Further away from the ore bodies, the rocks arealso entirely altered, but there are, besides aggrega-tes of fine and small-grained quartz, rarely coarse-grained quartz, as a product of silicification, twoother silicate minerals not precisely identified, deve-loped as products of hydrothermal alteration.Forms of th e ore bodies

The ore bodies are developed in the form ofsmall or large lenses, inside a completely alteredintermediary subvolcanic rock. Some ten ore bodies,viz. ore outcrops, were known down to 1962. Thelargest in size among them is an ore body, some60-70 m in length, and about 15-18 m wide. Theother ore bodies, viz. their outcrops, are considera-bly smaller in size, but the works formerly carriedout by the Japanese during the World War I1 didnot have the character of exploration work, and

their activities were concentrated on the exploitationof the largest ore body. There is no access via theold adits, for they are partly caved in and destroyed.Paragenesis of the ore samples

A great number of the ore specimens were takenfrom the old ore dump comprisig some 2500-3000tons of hand-picked ore. Macroscopically, it maybe seen that three types of ore are dominant inthat area: the y e 11 o w t y p e in which chalcopyriteprevails among the copper minerals, the b l a c kt y p e with chalcocite and small-grained sphaleriteprevailing, and the i m p r e g n a t i o n t y p e withpyrite in intensively silicified mother rock. Detailedmicroscopical study carried out by I. JurkoviC hasestablished the following parageneses:A. Y el lo v o r e (n a me d ~ o k o r e < >island( > K u ro k o r e<


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32 Rudarsko-geoloSki-naftni zbornik. Vol. 2. Zagreb. 1990P y r i t e is the oldest among the ore minerals. In concentrations of metal components in the mineralsome places it is very abundant. It occurs usually solutions.in the form of regular colloidal spherules or dro- The w e deposit may be genetically determinedplets, either aggregated to colonies or to irregular as a hydrothermal subvolcanic deposit, related tomasses of various size. These spherules and droplets intermediate effusive magmatic activity.of pyrite manifest a concentrically banded structure.

If developed in the form of metacwsts, it is to a Discussiongreat extent replaced by tetrahedrit; and chalcopy-rite, so that only some relicts are left. We s t e r v e 1d (1952) stated that the western arcs h a 1e i t is relativery abundant in some of of Sulawesi is characterized by the Middle Miocenethe polished sections, extraordinarily Sunda Orogen, while the Eastern Sulawesi containsdense chalcopyrite exso~utionsof ~cr osc opi c ize deposits related to the Late Cretaceous to Middlein the form of lamellae and discs. In addition to Miocene Molucass Orogen. According to S t a n t 0 nchalcopyrite there are large amounts of colloidally (1972) a fundamental connection exists between Par-formed pyrite. Besides the exsolutions in the spha- P ~ Y Vopper deposits and volcanic arc structures;lerite mass, replacing of chalcopyrite was also obser- deposits of this type are most likely to be formedved along the boundaries of grains, i.e. along the in the more mature portions of modern volcanicfissures or the boundaries between quartz and spha- arcs. K a t i l (1974) interpreted the geology andlerite. mineralization by means of the plate tectonic theory.T t a h e d i t is the main ore mineral in some He distinguished mineralization in western Indone-of the specimens, mainly replacing pyrite and chal- sia from that in eastern Indonesia, the first beingcopyrite. lts basic are the high degree related to the spreading centre of the Indian Oceanof fine-porous structure with inclusions of quartz, and the latter generated by the spreading of theand also of galena and chalcopyrite. structure is Pacific Ocean. The Tertiary mineralization in Sula-zonar, certainly as a result of abrupt cooling. wesi and in other group of islands in eastern Indo-various tints are noticed microscopica~~y,t may be nesia is more important in comparison to the Suma-assumed that it contains isomorp~ica~yome other tra-Lesser Sunda Islands, due to the fact that thedifferent metals. crustal elements generated by the Pacific Oceanch a 1 i I occurs as exsolutions in spha- spreading centre are apparently richer in metals thanlerite, c h a 1c0 p y r i t e 11 replaces sphalerite and those of the Indian Ocean- Occurrences of porphyrypyrite and is itself replaced by tetrahedrite. copper in northern and central Sulawesi demons-ch a 1 i and a 1 a are accessory mine- trate that this volcanic-plutonic arc of Pacific originrals. is rich in copper mineralization. Differences in theG h i , 1 i d i e , a 1a h i composition of the mantle beneath the spreadingare the most abundant among the hypergene min- centres of the Indian Ocean and the Pacific Oceanrals. are responsible for differences in mineralization inwestern and eastern Indonesia. T a y 1o r and H u t -C. I m p r e g n a t i o n t y p e of m i n e r a l i z a t i o n c h i s o n (1978) emphasized that the group of South-East Asia copper deposits is related spatially andThis Ore was named the genetically to rocks generated in ocean basins orminers nkeiko oreblackore


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I. Jurkovik and B. Zalokar: The Copper Deposit 33K a t i 1 i, J. A. (1978): Past and present geotectonic position ofSulawesi, Indonesia. - Tectonophysics, 45, 289-32K a t i l i , J. A. (1984): Southeast Asia: Tectonic framework,resources occurrences and related problems in SoutheastAsia. - In J. A. Katili and J. A. Reinemund %SoutheastAsia: Tectonic framework, earth resources and regional pro-grams, 18-68, IUGS, Publ. No 13, Bangkok,ThailandS t a n t o n, R. L. (1972): Ore Petrology. - McGraw-Hill BookComp., 713 p. USA

T a y 1o r , D . & H u t c h s o n, C. S. (1978): Patterns of mine-ralization in Southeast Asia, their relationship to broad-scalegeological features and the relevance of plate tectonic con-cepts and their understanding. Proc. of the 11th Common-wealth Mining and Metallurgical Cong., H ongkong, 6 8,l-1 5V a n B e m m e l e n, R. W. (1949): The Geology of Indonesia,732 p., The HagueW e s t e r v e 1d, J. (1952): Phases of mountain building and mine-ral provinces in the East Indies. Proc. of the 18th Int. G eol.Cong., XIII, 235-255, Gr ea t Britain .

Bakarno leWe Batu Marapa a srediinjem Sulawesi-n, IndonezijaIv an J U R K O V I ~ nd IBoZidar ZALOKAR I

Kretanjem indijske ploEe prema sjeveru i navlaknjem paci-fiEke pl& uzduZ Sorong transformn og rasjeda prem a zapadu,uz istodobnu rotaciju otoka Nove Gvineje suprotno kretanjukazaljki na satu, u zrokovali su po K a t i li-u (1978) kornpliciranutektonsku strukturu i bizaran oblik u vidu slova nKa otoka Sula-wesi (Celebes) i Halmahere. Ti procesi su se zbili izmedu mio-cena i pliocena. U zapadnom kraku Sulawesi-a do otoka Minda-nao razvio se vulkansko-plutonski magmatski luk s granitima ivulkanitirna za koji su vezana porlirna bakarna IeZiSta dok jetercijama zona subdukcije locirana u istoborn kraku Sulawesi-aproteZuCi se duZ submarinskog hrpta Mayu i o t d n o g h r p t aTalaud, a karakterizirana je lateritskim nikaljnim IeiiStima i poja-vama kromita (sl. 1.).Autori su istra2ii morfologiju i paragenezu bakarnog leZiStaBatu Marupa koje se nalazi u sredignjem dijelu otoka Sulawesiok o 40 km sjevernije od grada Makale i oko 60 km sjeveroza-padno od luke Polopo. Japanci su za vrijeme drugog svjetskograta eksploatirali bakarnu rudu i talili bakar u primitivnim talio-nicama. Ruda je sadrZavala 3-5 % Cu.RudiSte se nalazi na juhim padinama vulkanskih doma Popo-malangi i Bidong Pangpano na visinama od 1100 do 1200 m.Okolina bakarnog le%&a izgradena je od magmatskih stijena tijidiierencijati variraju od kiselih preko intermedijernih do bazibnijih varijeteta. Sv e su stijene vrlo intenzivno hidrotermalno izmi-jenjene. Najsnabija je silifikacija, a zatim kaolinizacija. Mikro-skopski je ist&no vk3e tipova alteriranih stijena.Rudna tiiela. niih desetak, imaiu o b li e maniih i l i v& l e b .NajveCe t ijelo, .kdje su ~ a ~ & c inienzivno ekspfoatirali, imalo jedimenzije 70mx18m, ostala su bila manja ili nedovol jno i s t r hn a .

Broini uzorci rude s naouStenih starih kuoiSta detalino suispitan; u reflektiranoj po ldz ira no j svjetlosti i itvrde ne s; para-geneze i mikrofiziografske karakteristike identificiranih minerala.U&na su tri razlitita tipa rude:s u t a r u d acc s pirotin om , pirito m i halkop iritom ka o glav-nim mdnim mineralima te s tetrae dritom , sfaleritom, galenitom,

halkozinom, neodigenitom i enargitom kao sporednim sastojcimaDarageneze;n c.r n a r u d au s piritom, sfaleritom i tetraedrito m kao glav-nim rudnim mineralima te h alkopiritom, halkozinom i galenitomkao akcesorijama;~ i m p r e g n a c i o n a u d a u s piritom i nematnom kolifiinomostalih minerala u potpuno silificiranoj stijeni.Kvarc je dominantan mineral jalovine, u znatnoj koliEini imai kaolinita.Osnovna je karakteristika glavnih minerala u oba prvonave-dena tipa rude da su puni inkluzija i da su intimno prorasli sakcesornim mineralima. Puni su izdvajanja submikroskopskih imikroskopskih dimenzija, a osim toga karakteriziraju ih tipitnekoloidalne strukture n a r e t o u wcrnoj rudiu. Svi navedeni feno-meni indiciraju subvulkanski karakter orudnjenja iz jako koncen-triranih mineralnih otopina kojima su se temperatura i tlak naglosmanjivali.LeZiSte Batu ~ i r u ~ ae bakarno lefizte nastalo unutar mag-matskog luka za vrijeme faze subdukcije u subvulkanskom nivou.

2 the copper deposit of batu marupa

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