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PROCEEDINGS PIT IAGI LOMBOK 2010 The 39 th IAGI Annual Convention and Exhibition KALIMANTAN MINERAL RESOURCES: AN UPDATE ON EXPLORATION AND MINING TRENDS, SYNTHESIS ON MAGMATISM HISTORY AND PROPOSED MODELS FOR METALLIC MINERALIZATION Setijadji, L.D. 1,4 ., Basuki, N.I. 2,4 , & Prihatmoko, S. 3,4 1 Department of Geological Engineering, Gadjah Mada University, Yogyakarta 55281, Indonesia 2 Study Program of Geology, Institut Teknologi Bandung, Bandung 40132, Indonesia 3 P.T. AGC Indonesia (Ivanhoe Mines Ltd), Jakarta 12520, Indonesia 4 Indonesian Society of Economic Geologists (MGEI) ABSTRACT Kalimantan, the Indonesian part of Borneo island, contains significant amount of known metallic mineral deposits and potential for future discoveries in Indonesia. However, a synthesis on its geological history, magmatism and metallic mineralization is still lacking. This paper explains results of an init ial effort to compile all relevant data regarding the magmatic history and metallic mineralization in this island. Additionally, update on current mining industry in Kalimantan and future potential developments are included. There is a major change in mining industry activities in Kalimantan following the new reform in Mining Law. Current activities are done by small to medium-scale players working on various commodities, including iron, base metals and quartz sands. Real exploration programs are limited as activities concentrate on evaluation of known prospects and efforts to bring productions from existing prospects or re-open old mines. A long geodynamic history produced different events of magmatism since the Late Paleozoic. More evident magmatic arcs are found for the Cretaceous and younger events. Subduction zone magmatism might come to end after Late Cretaceous in many parts of the island, from which syn- and post-collision magmatism became more prominent. Metallic mineralization can be divided into two major periods. First is the Cretaceous or older events, in which mineralization is dominated by granitoid-related skarn iron and base metals mineralization, geographycally located within the Schwaner and Meratus Mountains. Second is the Middle to Late Miocene gold and base metals mineralization associated with Sintang Intrusions. Miocene gold-bearing intrusions are not products of ordinary subduction-zone magmatism, but they are derived from basalts source during major tectonic events following subduction. Gold exploration programs should include study on petrogenesis of intrusive rocks. Suture zones of Late Cretaceous-early Tertiary age should be tested for their potential of orogenic gold mineralization. INTRODUCTION On 29-30 th March 2010, Indonesian Association of Geologists (IAGI) and Indonesian Society of Economic Geologists (MGEI) conducted a seminar entitled Kalimantan Coal and Mineral Resources (KCMR) at Balikpapan city, East Kalimantan. We refer Kalimantan here as the Indonesian parts of the island of Borneo. During this two-day seminar, various projects on coal and mineral resources in Kalimantan were presented and discussed. Presented papers cover almost all geographical regions and various mineral commodities, deposit styles and sizes, such as porphyry, epithermal (LS-HS), skarn, iron ores, and bauxites. Several new ideas and technologies were presented and discussed, such as exploration on deeper targets, older terrane (Mesozoic host rocks), and application of spectral geology. The seminar also noted that despite Kalimantan can be considered as a relatively mature
Transcript
Page 1: KALIMANTAN MINERAL RESOURCES: AN UPDATE ON … · 2018-12-21 · seminar entitled Kalimantan Coal and Mineral Resources (KCMR) at Balikpapan city, East Kalimantan. We refer Kalimantan

PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

KALIMANTAN MINERAL RESOURCES: AN UPDATE ON EXPLORATION ANDMINING TRENDS, SYNTHESIS ON MAGMATISM HISTORY AND PROPOSED

MODELS FOR METALLIC MINERALIZATION

Setijadji, L.D.1,4., Basuki, N.I.2,4, & Prihatmoko, S.3,4

1Department of Geological Engineering, Gadjah Mada University, Yogyakarta 55281, Indonesia2Study Program of Geology, Institut Teknologi Bandung, Bandung 40132, Indonesia

3P.T. AGC Indonesia (Ivanhoe Mines Ltd), Jakarta 12520, Indonesia4Indonesian Society of Economic Geologists (MGEI)

ABSTRACT

Kalimantan, the Indonesian part of Borneo island, contains significant amount of known metallic mineraldeposits and potential for future discoveries in Indonesia. However, a synthesis on its geological history,magmatism and metallic mineralization is still lacking. This paper explains results of an initial effort tocompile all relevant data regarding the magmatic history and metallic mineralization in this island.Additionally, update on current mining industry in Kalimantan and future potential developments areincluded. There is a major change in mining industry activities in Kalimantan following the new reform inMining Law. Current activities are done by small to medium-scale players working on variouscommodities, including iron, base metals and quartz sands. Real exploration programs are limited asactivities concentrate on evaluation of known prospects and efforts to bring productions from existingprospects or re-open old mines.

A long geodynamic history produced different events of magmatism since the Late Paleozoic. Moreevident magmatic arcs are found for the Cretaceous and younger events. Subduction zone magmatismmight come to end after Late Cretaceous in many parts of the island, from which syn- and post-collisionmagmatism became more prominent. Metallic mineralization can be divided into two major periods. Firstis the Cretaceous or older events, in which mineralization is dominated by granitoid-related skarn iron andbase metals mineralization, geographycally located within the Schwaner and Meratus Mountains. Secondis the Middle to Late Miocene gold and base metals mineralization associated with Sintang Intrusions.Miocene gold-bearing intrusions are not products of ordinary subduction-zone magmatism, but they arederived from basalts source during major tectonic events following subduction. Gold explorationprograms should include study on petrogenesis of intrusive rocks. Suture zones of Late Cretaceous-earlyTertiary age should be tested for their potential of orogenic gold mineralization.

INTRODUCTION

On 29-30th March 2010, Indonesian Associationof Geologists (IAGI) and Indonesian Society ofEconomic Geologists (MGEI) conducted aseminar entitled Kalimantan Coal and MineralResources (KCMR) at Balikpapan city, EastKalimantan. We refer Kalimantan here as theIndonesian parts of the island of Borneo. Duringthis two-day seminar, various projects on coal andmineral resources in Kalimantan were presented

and discussed. Presented papers cover almost allgeographical regions and various mineralcommodities, deposit styles and sizes, such asporphyry, epithermal (LS-HS), skarn, iron ores,and bauxites. Several new ideas and technologieswere presented and discussed, such as explorationon deeper targets, older terrane (Mesozoic hostrocks), and application of spectral geology.

The seminar also noted that despite Kalimantancan be considered as a relatively mature

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

exploration island, in fact no comprehensive datainventory on mineral resources and integratedgeologic model of the whole Kalimantan has beendone. Therefore, as an important result derivedfrom the above seminar, MGEI considers the needto produce an update of mineral resourcesinventory and geological model for the wholeKalimantan. It is done through integrating the datadelivered during the seminar with other existingpublications and conducting several follow-updiscussions by inviting prominent researchers andmineral explorers working in Kalimantan.

This paper is part of the first result of compilationefforts, with special attention on metallic mineraldeposits. Discussion will start with the update ofcurrent status of mineral industry in this island, asresults of the new political and mining reformfollowing the 1998’s economic crisis and reformin Indonesia. Following part will evaluate themagmatic history and metallic mineralization, asresults of current compilation works. Otheraspects are covered within the other two papersconcerning the basin development and diamondorigin in Kalimantan, which are presentedtogether with this paper in a special session on theKalimantan geology during the 39th IAGI AnnualConvention and Exhibition in Lombok island,Indonesia.

SOURCE OF DATA COMPILATION

Geoscience datasets compiled in this studycomprise geology, mineral occurrences,radiometric ages and petrochemical data onigneous rocks. Basic information on Kalimantanmineral deposits was derived from exceptionalcompilation work by Van Leeuwen (1994), whichis then enriched by newer materials includingpapers, internet and KCMR seminar results. Dataon geology of Kalimantan are mainly derivedfrom many published geological map sheets byGeological Survey Indonesia at scale 250.000, andprospect maps from many papers. Petrochemicaland radiometric data are mainly compiled fromGeological Survey Indonesia from their projectsin West-Central Kalimantan (e.g. De Keyser andRustandi, 1993) and Meratus (e.g. Hartono et al.,2000; Heryanto and Panggabean, 2010), and datafrom certain area such as Kelian (Van Leeuwen etal., 1990; Davies et al., 2008), Mt. Muro(Simmons and Browne, 1990) and Masupa Ria

(Thompson et al., 1994). Data from Malaysianparts of Serawak and Sabah are mainly compiledfrom Hutchison (2005).

KALIMANTAN MINERAL INDUSTRYBEFORE 21st CENTURY

Kalimantan, with its massive land mass andcomplex geological history, is endowed with hugepotential of economic mineral deposits (e.g. gold,copper, diamond and bauxite) and other importantgeological resources such as coal andhydrocarbon. The mining industry in Kalimantanhas started more than 1,000 years ago. Gold hadbeen worked from alluvial deposits since 4th

century and especially during the 18th century theWestern Kalimantan (Sambas area) was the site ofgold rush (Van Leeuwen, 1994; Gunter, 2010a).Alluvial diamonds have been known since the 7th

century. There are also records on mining andprocessing of iron ore between 5th and 10th

century. The foundation for modern-day mineralindustry was laid by the Dutch, who undertookexploration and development since the 19th

century (Van Leeuwen, 1994). Early investigationprograms for metallic deposits in Kalimantanincluded investigation on tin in Ketapang regionin 1820s (De Keyser and Rustandi, 1993) andgold deposits in Sambas region in 1880s (Gunter,2010a).

Since the Indonesian independence and theintroduction of the foreign investments throughthe Contract of Work (COW) scheme, regulatedby the Mining Law No. 11/1967, Kalimantanattracted many major exploration projects. Initialprojects under early generation of COW weredominated by bauxite project in the West andSouthwestern Kalimantan by ALCOA since 1969(Van Leeuwen, 1994). The result was thediscovery of 10 bauxite deposits in WestKalimantan, totaling 1,300 Mt ore with an averagegrade of 30% Al2O3, with the Tayan (270 Mt) asthe biggest one.

Uranium exploration in West Kalimantan duringperiod 1974 and 1988 resulted in the discovery ofKalan deposit, in the form of fault breccia bodieswithin metasediments nearby Mesozoic graniticintrusives, with a total resource of 11,000 tonnesof U3O8 (Sarbini and Wirakusumah, 1988 in VanLeeuwen, 1994).

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

Intensive porphyry copper search during the early1970s that swept the majority of Indonesianarchipelago did not actually reach Kalimantan,probably due to the lack of recognition of Tertiarymagmatic arcs in this island.

Exploration for primary gold in Kalimantan wasstarted by RTZ/CRA in 1975 that lead to thediscovery of Kelian deposit. The real massiveexploration activities in Kalimantan occurredduring the “Revised Third Generation of COW”(Van Leeuwen, 1994) that attracted interests fordiscovery and development of smaller-sizedeposits. During the epithermal gold boom in1980s, the majority of COWs signed in Indonesiaduring the period 1985 and 1992 were dominantlylocated in Kalimantan. Van Leeuwen (1994)recorded following alluvial gold prospects hadbeen drill tested during this period: Monterado,Sungai Raya, and Kapuas in West Kalimantan,and Ellahula, Cempaga Buang, and Tewah inCentral Kalimantan. Meanwhile, the primary golddeposits were drilled at Kelian and Muyup (EastKalimantan), Mt. Muro, Masupa Ria, Mirah, andGunung Mas (Central Kalimantan), Buduk (WestKalimantan), Sungai Keruh and Timburu (SouthKalimantan).

Among these deposits, two alluvial gold deposits(Monterado and Cempaga Buang/Ampalit) cameinto production but only for a short period. Thebiggest success story was the discovery of theKelian gold deposit that entered into mining stagein early 1992 with a total resource of 92.1 Mt ofore grading 2.61 g/t Au (Davies et al., 2008).Kelian was the biggest gold-only mine inIndonesia until its mining closure in 2005. Alongwith Kelian, several smaller gold deposits werealso discovered within an apparently NE-SWtrending Oligo-Miocene magmatic belt in centralKalimantan, such as Mt. Muro (Simmons andBrowne, 1990; Moyle et al., 1995), Masupa Ria(Thompson et al., 1994), Mirah and Muyup.Among these, Mt. Muro became the secondprimary gold mine in Kalimantan, operated byAurora Gold. The discovery of the CentralKalimantan Gold Belt was major achievement asthis belt was not recognized during the Dutchperiod. Carlile and Mitchell (1994) then proposedthe occurrence of the Neogene CentralKalimantan Arc that spans from Sabah in NE

through the Gold Belt in the South and bends tothe West to reach Singkawang.

Although numerous lead-zinc occurrences wereidentified since the Dutch period in Kalimantan,minor systematic exploration effort for lead andzinc has actually been undertaken. Van Leeuwen(1994) noted two lead-zinc deposits being drilled,i.e. Riam Kusik in West Kalimantan and Long Laiin East Kalimantan. Riam Kusik consists ofnarrow veins of massive sulfides along Cretaceouslimestone-dyke contact, while Long Lai consistsof irregular skarn deposits by Cretaceous-Eocenesandstone-siltstone intruded by Oligocene granite.Another base metal skarn deposit is discovered inRuwai, Central Kalimantan, associated withcontact metamorphism between Paleozoicsedimentary rocks and Cretaceous granite(Setijadji et al., 2010).

With exception cases of Kelian and Mt. Muro, themajority of other projects suffered severely fromthe low commodity prices in the late 1990s, theBre-X Minerals scandal on the Busang golddeposit in 1997 and global economic crisis in1998. Many COW projects were terminated andalmost no exploration activities were done during1998 to early 2000s.

KALIMANTAN MINERAL INDUSTRYTODAY

Despite the current high commodity prices foralmost all metals that started around 2003,Indonesia including Kalimantan do not benefitfrom significant increasing global explorationspends during the last several years. Many partiesclaim that the current Mining Law and overallregulations related with mining industry are notwelcomed by foreign companies.

Such situation started since the wave ofreformation following the 1998’s economic-political crisis gradually has brought to thefundamental changes to decentralize the miningsystem. Among all geological resources, only oiland gas are now still regulated by the centralgovernment; other commodities includingminerals are transferred to the districtgovernments. The reformation culminated by therelease of Mineral and Coal Mining Law No.4/2009. This Law groups mineral resources as

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

radioactive, metal, non-metal, and coal, peat, andoil shale. Among other restrictions, the law aimsto shorten the period of mining contracts. Asresults, actually there are very limited funds beingspent for exploration and no new deposits havebeen discovered since the mid 1990s. Since theclosure of Kelian gold mine in 2005, Kalimantanhas now lost its position as a primary goldproducer in Indonesia.

Existing gold projects are now mainly evaluationand further exploration programs on knownprospects discovered during the 1980-1990sexploration period, such as Buduk (Gunter,2010a), Jelai (Gunter, 2010b), Seruyung (Rura etal., 2010), and Mansur-Beruang district (Geiger etal., 2010). There are also small-scale goldoperations in East, Central and West Kalimantan.Among them, the Mt. Muro gold mine in CentralKalimantan is the biggest one, operated by StraitsResources Ltd. that took 100% ownership of Mt.Muro since 2004. In its 2008 annual report, StraitsResources reported ore reserves at Mt Muro of1,800kt with gold content of 433,000oz Au andannual production 80,000oz Au(http://www.mining-technology.com/projects/mt-muro/). Other gold operations have smaller scale,such as the case of Buduk mine in Singkawangdistrict, West Kalimantan (Gunter, 2010a).

In better sight, the current mineral industry hasencouraged the births of many national miningenterprises, mostly funded by Chinese and Indianinvestors. Commodities of interest have growndramatically into various minerals, such as iron,base metals, bauxites, zircon, and quartz sand.Revival of interest on bauxite has drawn P.T.Antam to continue its Tayan project and evenexpand its exploration areas into Mempawah andLandak districts in West Kalimantan that resultedin delineation of larger bauxite district in WestKalimantan (Surata et al., 2010). Iron deposits arenow being explored and exploited in SchwanerMountains region in West-Central Kalimantan,such as Kendawangan (Subandrio and Kuswanto,2010), Ketapang (Aribowo, 2010) and Lamandaudistricts (Setijadji et al., 2010) and in the MeratusMountains and surroundings in SouthernKalimantan. Lateritic iron ore is reported to bemined at Sebuku island, Kotabaru, SouthhKalimantan. Zinc and lead are now produced fromthe Ruwai deposit in Lamandau district, Central

Kalimantan (Setijadji et al., 2010). Many of theseiron and base metal deposits are associated withCretaceous granitic rocks especially within theSchwaner Mountains. As geology andmineralization styles within Cretaceous and oldermagmatic arcs in Indonesia are not well studiedyet, current interests on these deposits giveopportunities to study the geology and mineralpotentials of Kalimantan Mesozoic magmaticbelts.

MAGMATIC HISTORY

Existing radiometric data (272 records) suggest along history of magmatic events in Kalimantanthat started since 319 Ma (Late Carboniferous)until almost Recent (Figs. 1 and 2). The oldestigneous rock to be dated so far is the S-type LumoGranite, located near Buntok, NW MeratusMountains whose 260-319 Ma (LateCarboniferous-Early Permian) ages were derivedfrom K-Ar dating on biotite and muscovite(Hartono et al., 2000). Heryanto and Panggabean(2010) proposed that this granite was formed atintra-cratonic setting not related with subduction.Late Paleozoic to Triassic-Jurassic magmatism(263-201 Ma) occurred in the Ketungau Basin andSemitau Ridge in Sanggau district, WestKalimantan, whose compositions range fromgranite to amphibolite and collectively named theEmbuoi Complex (Supriatna et al., 1993). Theorigin and tectonic setting of this rock assemblageis poorly known. Meanwhile, the Jurassicmagmatism was recorded in the MeratusMountains as the Purui Dalam Granite (only oneK-Ar date of 155 Ma and was interpretedassociated with Jurassic subduction zone (Hartonoet al., 2000; Heryanto and Panggabean, 2010).

Cretaceous subduction zones occurred in the NWand SE Kalimantan, forming two pairs of trench-magmatic arc belts (e.g. Carlile and Mitchell,1994). In the SE corner of Kalimantan, theMeratus Mountains was formed by northwest-wards subduction (part of the Sumatra-Meratusarc). This subduction produced overlapping Earlyto Late Cretaceous granitoids typical of VolcanicArc Granite (VAG) emplaced within the MeratusMountains and northern part of Pulau Laut(Hartono et al., 2000). The Early Cretaceousgranitoids are dominated by intrusive rocks calledthe Batang Alai (Balawayan) Granites (118-101

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

Ma), while the Late Cretaceous magmatismproduced the dominated volcanic rocks named theHaruyan Volcanics.

Meanwhile, from the NW Kalimantan, thesouthwards subduction zone during theCretaceous resulted in the Schwaner MountainsGranitoids. The Early Cretaceous I-type granitoids(124-99 Ma) formed in the Singkawang regionand northern part of the Schwaner Mountains,forming the 500km long ESE trending magmaticarc called the Schwaner Arc by Carlile andMitchell (1994). These granitoids are typical ofVAG whose magma affinities are dominated bymedium-K and high-K granodiorite (MensibauGranodiorite) and tonalite (Sepauk Tonalite). TheLate Cretaceous I-type granitoids (91-66 Ma)were emplaced south of the older ones, forming aseparate yet partly overlapping Sunda Shelf Arc(its name was given by Carlile and Mitchell,1994). The distribution of dated Late Cretaceousgranitoids is rather a rectangle area (about 200 x170 km) than a typical arc. In Ketapang region,such granitoids are named the Sukadana Granite(De Keyser and Rustandi, 1993). The LateCretaceous granitoids in general are more alkalinethan the Early Cretaceous one, but in overall stillshow VAG characters. Hutchison (2005) and theIndonesian-Australian joint team (e.g. Amiruddinand Trail, 1993; Supriatna etal., 1993) preferredpost-subduction origin for the Late CretaceousSukadana Granites. Indeed, parts of the SukadanaGranite show transitional signatures into syn-collision and within-plate granite, suggesting thetermination of subduction and the beginning ofcollision at the end of Cretaceous. In severallocations, such as Lamandau, the Late Cretaceousgranites are intruded by diorite to basalt dykes ofprobably Early Tertiary age. Some LateCretaceous granitoid rocks were also formed andemplaced along the collision zone north of theSchwaner Mountains (Menyukung Granite) thatalso show a transition signature from the VAG towithin-plate granite. Syn-collision LateCretaceous magmatism seems to occur along thecollision zone at the northern boundary of theSchwaner Mountains. The extension of LateCretaceous silicic volcanics is recently recognizedto reach the Kelian district (Davies et al., 2008) onwhat previously thought to be Late Eocene (VanLeeuwen et al., 1990).

The timing of termination of southwardssubduction post Late Cretaceous is still matter ofdebate. Arc magmatism seems to be terminatedpost the Late Cretaceous (~65.5 Ma). There wasthen a period of no magmatic event during thePaleocene, which was followed by Eocenemagmatism that started at 51 Ma (Soeria-Atmadjaet al., 1999). Through the Tertiary, magmatism-volcanism formed a long arc starting from theSingkawang district at the western end to theTawau or Dent Peninsula (Malaysia) at thenortheastern end; this arc is referred to be theTertiary Central Kalimantan Arc (Carlile andMitchell, 1994). Tertiary magmatism alsooccurred in the Meratus Mountains (Eocene-Miocene) that produced scattered and overlappingbasaltic to dacitic volcanic and subvolcanic rocks(Hartono et al., 2000). This Tertiary magmaticbelt in Meratus Mountains is previously notknown (e.g. Carlile and Mitchell, 1994).

Within the Central Kalimantan Magmatic Arc,dated Eocene igneous rocks are found as thin arc(width approximately 50km) found in all sections(Singkawang to Dent Peninsula) and aredominated by acid volcanics. They consist of thePiyabung, Nyaan, Serantak and Muller Volcanics,and whose affinities are low-K (tholeeitic) tomedium-K (calc-alkaline). Soeria-Atmadja et al.(1999) and Priadi (2010) concluded them asproducts of (new) southward subduction in theNW of Kalimantan. It means that there was newlyinitiated subduction zone in the Eocene along theNW Kalimantan (boundary between Indonesiaand Malaysia) that was different from theCretaceous one. The Late Oligocene to Miocenemagmatism forms a wider arc, probably 75-150km wide that might be consisted by doublevolcanic chains in several parts. Magma affinity isdominated by calc-alkaline whose compositionsrange from andesite, dacite and rhyolite with fewbasalts (Soeria-Atmadja et al., 1999). Volcanicedifice groups include the Kelian, Mount Muro,Masuparia and Sintang Intrusions. The SintangIntrusions occur as hundreds of stocks, sills anddykes that cut the sedimentary sequence of theKetungau and Melawi Tertiary basins (Hutchison,2005). They often form high inselbergs, whichmay reach a height of 1000 m rising from thesurrounding area. In many cases no associatedlava flows and volcanics have been found; some

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

researchers suggest that the volcanic parts havebeen completely eroded.

The origin of Late Oligocene to Miocene magmasis still controversial and probably different amongdifferent locations. In western Sarawak, two kindsof intrusions can be distinguished (Prouteau et al.,2001 in Hutchison, 2005). The Early Miocene(22.3-23.7 Ma) intrusions in the northern part aredominated by high-K to medium-K calc-alkalinediorites and microdiorites that show all the usualcharacteristics of subduction-related magmas. Onthe other hand, the younger Middle to UpperMiocene (14.6-6.4 Ma) intrusions to the South(Bau area) are dominated by microtonalites anddacites that share some of the subduction-relatedcharacteristics, but in addition they display thetypical adakitic magma. Adakites are interpretedto have resulted from melting of basalt, which isdifferent from the typical source of subductionzone, i.e. peridotite. The separation between theabove two episodes of intrusions was at least 8Ma.

Adakites versus typical subduction-zone magmasare also identified in Kalimantan, and they occurwithin almost all geological epochs (Fig. 3). Thisphenomenon can be interpreted that within themajority of subduction-related magmas inKalimantan, there was always other source(basalt) that produced the melts. The most strikingfeature is on the Sintang intrusion suite within theCentral Kalimantan Arc that strongly showsadakitic characters. We conclude that nonsubduction zone magmas became more frequentlypresent after the Middle Miocene.

In the Sabah area in NE Borneo, separatemagmatic evolution may be present especiallyduring the Neogene. Earlier suggestion was thatfrom the Paleogene until the Early Miocene, therewas southward-directed subduction of the proto-China Sea that produced the Middle to LateMiocene (12.9–9Ma, Rangin et al., 1990) ages forNeogene magmatism in the Semporna and DentPeninsulas. The southward subduction precededthe collision at Late Miocene that resulted in theemplacement of Mount Kinabalu granites (13.7-6.4 Ma, Rangin, et al., 1990; Hutchison, 2005).The questionable whole-rock dating results byRangin et al (1990) and the lack of tomographicevidence for a dipping slab, has challenged Hall

(2002) to use the geological configuration ofSabah to propose that the Neogene subduction inthe Dent and Semporna Peninsula was actuallydirected towards the northwest, as the southernend of the Sulu Arc.

The youngest phase of magmatism in Kalimantanis presented by widespread basaltic lava flows ofPlio-Pleistocene age. This unit includes the NiutVolcanics in western Kalimantan (4.9 Ma,Supriatna et al., 1993), Metulang Volcanics incentral Kalimantan (2.41-0.97 Ma, Pieters et al.,1993; Abidin, 1996 in Daview et al., 2008), andKunak basalts in Dent and Semporna Peninsula(<2.95 Ma, Hutchison, 2005). Origin of this basaltis considered to be within-plate magmatism withtholeiitic composition (Soeria-Atmadja et al.,1999; Priadi, 2010; Macpherson et al., 2010).Nevertheless, several Metulang volcanics fromcentral Kalimantan show certain adakiticsignature.

METALLIC MINERALIZATION

Metallic mineral deposits are discussed based ontheir geological ages and domains. We start withPaleozoic-Mesozoic geologic domain and finish itwith Neogene events. Due to the lack of reliableage data on mineralization, discussion on spatialassociation between certain mineral occurrencesand geologic domain is not necessarily implyingthat mineralization events occurred at the sameperiod with the hosting geologic domain.

Late Paleozoic-MesozoicIn Kalimantan, the Late Paleozoic-Mesozoicdomain is known to be present in two geologicdomains, i.e. the Meratus in SE Kalimantan andthe Schwaner Mountains in W-SW Kalimantan(Fig. 4). These units may represent magmatismproduced during the collision and amalgamationevents of Gondwanaland fragments during theLate Paleozoic and Mesozoic era. There isactually another Paleo-Mesozoic magmaticsystem in the Dent-Semporna Peninsula, but it isnot discussed here due to its location that is inMalaysia.

Pre-Cretaceous granitoids are sparsely found andtheir association with metallic mineralization ispoorly understood. The Lumo granite in NWMeratus Mountains (260-319 Ma, Carboniferous-

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

Early Permian) is the oldest magmatic rock,characterized by S-type granite supposed to formwithin plate (Harmoko et al., 2000; Heryanto andPanggabean, 2010). Although theoretically suchgranite may carry tin, so far no information aboutthe presence of tin placer is reported in this area.In the Sanggau area, West Kalimantan, the EarlyPermian to Early Jurassic Embuoi Complex(Supriatna et al., 1993) is spatially associated withseveral occurrences of placer gold, placerdiamond as well as primary gold, base metals,uranium and mercury, but their genetic link is notclear. Triassic and Jurassic granitoids are probablyof subduction origin and are present at limitedexposure in Meratus and Singkawang areas. Theirgenetic association with mineralization is stillpoorly known, although at Singkawang they arespatially related with many mineral occurrences.

The Cretaceous granitoids become the backboneof the Schwaner Mountains in the west andsouthwest Kalimantan, and can be divided intotwo separate areas. First is the Singkawang clusterthat consists of the Early Cretaceous, medium-Kcalc-alkaline I-type granitic rocks. Here we find ahigh concentration of various metallicmineralization of Au, Cu, Mo, Pb, Zn, Bi, Mn andHg spatially associated with various Mesozoic andTertiary intrusive rocks (Suwarna and Langford,1993). It is not clear which intrusive stage wasactually responsible for certain mineralizationstyle. However, as many occurrences showfeatures of deeper level of emplacement (e.g.abundance of base metals) that are significantlydifferent from typical epithermal mineralizationassociated with Middle Tertiary Sintangintrusions, we believe that many are geneticallylinked to Mesozoic granitoids.

Within the Schwaner Mountains, there is strongindication of metallic mineralization, includingprecious metals, associated with Early CretaceousI-type granitoids (e.g. Sepauk Tonalite andassociated volcanics), located at the northern partof the Schwaner Mountains. In the Nangapinohsheet area, Amiruddin and Trail (1993) describedthe occurrence of Kalan uranium deposit withinthis sheet, hosted by the Paleozoic-Triassic PinohMetamorphics associated with both Early andLate Cretaceous granitoids. Operations on placergold as well primary gold-lode mines were alsoreported to be done from intensely kaolinitised

Sepauk Tonalite. Amiruddin and Trail (1993)therefore suggested that the Sepauk Tonaliteapparently contain gold over a wide area. Primarygold mineralization is also reported to occurwithin Pinoh Metamorphics. On the other hand,no such direct evidence was found for primarygold in the Sintang intrusions in that region,although some alluvial deposits are likely toderive from these rocks. Several occurrences ofiron and base metal mineralization were reportedto be hosted by Pinoh Metamorphics, with tracesof gold and silver.

Within the Late Cretaceous Sukadana Granite,occurrences of iron, base metals and some goldwere reported. Iron occurrences were alreadyknown since the Dutch era, but it was just recentlythat iron becomes exploration target by severalIndonesian companies. In southern SchwanerMountains (Ketapang and Lamandau districts),there are clusters of probably skarn-type Fedeposits found as small pockets of magnetitebodies spatially associated with Late CretaceousSukadana Granites (Aribowo, 2010; Setijadji etal., 2010). Some deposits show banding featuresthat may resemble features of a Banded IronFormation (Subandrio and Kuswanto, 2010), butthe others support the iron skarn mineralizationmodel. All iron deposits are spatially associatedwith Cretaceous I-type granitoids that intrudedhost rocks of sedimentary and/or metamorphicrocks.

Setijadji et al. (2010) observed from the Ruwaideposit in Lamandau district, Central Kalimantan,the typical mineralization associated with epizoneof I-type granitoids. At contact zone between thistype of intrusion and carbonate-bearingsedimentary rocks, a zoning skarn mineralizationwithin a lateral distance of about 3 km isobserved. Skarn deposits are strongly controlledby structure and favorable stratigraphy. Atproximal zone directly at contact with intrusiverock, Fe skarn deposits are formed enveloping theintrusion with magnetite as the main ore mineral.Meanwhile approximately 3 km away, still withinthe same structural trend, several distal Zn-Pb-Agskarn deposits are found.

Several iron ores are found within the MeratusMountains, such as nearby the Batu Licin region,are probably associated with Cretaceous

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

granitoids. Lateritic iron is reported to be mined atSebuku island; the nearest Cretaceous granitoid isfound at the nearby Laut island. Carlile andMitchell (1994) concluded several gold-bearingquartz and quartz-carbonate veins at Timburu andSungai Keruh as part of the Cretaceous events.Sungai Keruh is hosted by a potassic alteredmonzonite porphyry intruded into volcanics andsediments resembling mixed features of bothepithermal and porphyry-style mineralization(Van Leeuwen, 1994). Meanwhile, the Timburu ishosted by silicified and brecciated ultramaficrocks around phyllically altered quartz-dioriteporphyry intrusions; quartz texture suggests amesothermal condition (Van Leeuwen, 1994). Asrecently Tertiary igneous rocks are also identifiedto be present in this region (Harmoko et al., 2000),there is also possibility that actually thehydrothermal events occurred during the Tertiaryrather than Cretaceous.

TertiaryGold mineralization is so far the most promisingmetal to reach industrial scale mining operationsin Kalimantan. The biggest known gold depositsso far are dominated by low-sulfidation gold-carbonate-base metals system (Kelian, Mt. Muro)but other gold deposits types are also present,such as low-sulfidation Au-Ag (Jelai), high-sulfidation Au (Seruyung), sediment-hosted Au(Bau in Serawak), porphyry Cu-Au (Beruang,Mansur and Mamut) and skarn Au (Buduk). Themost striking similar features among thesedeposits are their spatial association with narrow,shallow level, and acidic intrusive rocks calledcollectively as the Sintang Intrusions. SintangIntrusions are typically present as hundreds ofstocks, sills and dykes that cut the older rocks, andthey often form high inselbergs that can reach aheight of 1000 m rising from the surroundingarea. As in many cases we do not find the syn-intrusion volcanics nearby, there probably uniquepetrogenesis of this rock suite. As discussed inearlier section, Sintang Intrusions have adistinctive adakite signature that differs fromtypical characteristics of subduction-relatedmagmas. Rather, adakites are interpreted to haveresulted from melting of basaltic source such asoceanic crust derived from older subductionand/or basalt underplate.

The ages of several gold and copper deposits havebeen constrained relatively well, and the majorityfalls into the Middle to Late Miocene. The Keliangold deposit was long time considered to beformed around 20 Ma (Van Leeuwen et al., 1990)which is now confirmed by state-of-the-art zirconU-Pb dating on ore-bearing quartz-phyric rhyolite(19.8 ± 0.1 Ma) and quartz-feldspar-phyricrhyolite (19.5 ± 0.1 Ma) (Davies, 2002 in Davieset al., 2008). The Bau gold deposit was emplacedfrom series of ore-bearing microtonalites anddacites that were firstly emplaced around 14.6 Ma(Proteau et al., 2001 in Hutchison, 2005). Theaverage age of Mamut porphyry copper deposit inKinabalu was dated to be 9 Ma (Hutchison, 2005).

There are some interesting common features thatapply in many gold and base metalsmineralization in Kalimantan that actually are notcommon features for other Indonesian islands.First, the melts that produced gold mineralizationin Kalimantan are not derived from typicalsubduction-zone magmatism, i.e., many gold-bearing intrusions have adakite characters.Second, there is strong evidence of spatial andgenetic links between gold mineralization andintrusions, including the epithermal and sediment-hosted types. Third, the lack of syn-intrusionvolcanic rocks being found at the proximity ofgold deposits. In term of geodynamic perspective,the emplacement of major gold and base metalsmineralization can be correlated with majortectonic events beyond the ordinary, long-lastingsubduction processes. The emplacement of Kelianat approximately 20 Ma was coincident with theinitiation of counter-clockwise rotation of Borneo,in which the location of Kelian-Mt.Muro-Masuparia at that time was approximately at therotation pole (Hall, 1996, 2002). The Bau goldmineralization was generated after new adakiticmagma was generated about 15 Ma (during theevent of counter-clockwise rotation). Finally,Mamut copper porphyry was emplaced around 9Ma at the time of termination of the rotation andthe collision period.

Talking about collision, it is challenging to testthe presence of orogenic gold in the westernKalimantan, i.e. Lupar or Boyan suture zone(Hutchison, 2005; Metcalfe, 2006). This suturezone, located along the boundary betweenIndonesia and Malaysia, was the site of multi

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

collision events. Major collision event took placeduring the Late Cretaceous or Early Tertiary.Active continental margin-type of Cretaceoussubduction, the presence of alluvial gold andoccurrences of Sb and Hg mineralization are someof critical evidence that indicate the orogenic goldpotentials. Such potential may also be present atthe Meratus Mountains, however this site lacksthe evidence of Au, Sb and Hg occurrences.

QuaternaryMineral accumulations during the Quaternary arefound as alluvial gold, diamond and zircon,lateritic iron and bauxite deposits. Alluvial gold isalmost found within all geologic domains, withthe main concentration at West Kalimantan(Monterado, Mempawah) and Central Kalimantan(Cembaga Buang, Tewah). Three separate areasare known to hold alluvial diamond, i.e.Martapura in South Kalimantan, Muarateweh areain Central Kalimantan, and Mempawah area inWest Kalimantan. Quartz sands are widespreadwithin Central and West Kalimantan, from whichzircon is mined in several sites such as at KotaWaringin Barat district, Central Kalimantan.Lateritic iron is reported to be mined at Sebukuisland. The main bauxite-prospective region is theSchwaner Mountains in West Kalimantan (Surataet al., 2010). Placer tin is reported to be present atlimited area in the Ketapang region.

CONCLUDING REMARKS

The reformation of mining regulation in Indonesiaand the China-India factors have resulted in themajor change in mining activities in Kalimantan.The players change from major companies,working on gold-related targets into variouscommodities for small- to medium-scaleresources. Real exploration programs are few asactivities concentrate on upgrading the knownprospects into production or re-open old mines.

Metallic mineralization can be divided into twomajor periods. First is the Cretaceous or olderevent, which is dominated by granitoid-relatedskarn iron and base metals mineralization,especially within the Schwaner and MeratusMountains. Second is the Middle to Late Miocenegold and base metals mineralization associatedwith Sintang Intrusions. Such gold-bearingintrusions are not products of ordinary

subduction-zone magmatism. Rather, they arederived from basaltic source melted due to majortectonic events such as collision, faulting andregional rotation. As results, the widely acceptedmodel of the presence of Central Kalimantan GoldBelt that extends from Singkawang at the west toSabah and is synonymous with the distribution ofthe Central Kalimantan Arc (e.g. Carlile andMitchell, 1994) should be revised. We proposethat the Central Kalimantan Gold extends fromSabah in the north to somewhere around Mirahgold deposit in the south. Gold occurrences areconcentrated along the backarc part of magmaticarc (east to southern parts), while copperoccurrences at the volcanic front side (west andnorthwest). This belt is separated from the Bau-Singkawang gold district in western part (Fig. 4).For exploration targeting, studying the melt originof intrusive rocks is important tool to define theirmetallic potentials, especially gold. Testing newideas of different styles of gold mineralization,such as orogenic gold along the suture zones,opens more opportunities for future newdiscoveries.

ACKNOWLEDMENTS

The authors thank to all colleague geoscientistswho contributed during the IAGI-MGEI seminaron Kalimantan Coal and Mineral Resources(KCMR) in Balikpapan in March 2010. Thiscompilation work was initiated and supported byDr. A. Bachtiar. Following geoscientists areacknowledged for their discussions: Dr. A.Kadarusman, P.E. Pieters, A.S. Subandrio, A.H.Satyana and Prof. H.D. Tjia. Mary Silaban isthanked for her coordination.

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

FIGURE 1: The dated Tertiary igneous rocks in Kalimantan

FIGURE 2: The dated Pre-Tertiary igneous rocks in Kalimantan

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

FIGURE 3: Occurrences of adakite in Kalimantan

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PROCEEDINGS PIT IAGI LOMBOK 2010The 39th IAGI Annual Convention and Exhibition

FIGURE 4: Compiled database on metallic mineral occurrences in Kalimantan


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