Sumatra, an Emerging World-Class Magmatic Gold Belt

PROCEEDINGS OF SUNDALAND RESOURCES 2014 MGEI ANNUAL CONVENTION 17-18 November 2014, Palembang, South Sumatra, Indonesia

89

Sumatra, an Emerging World-Class Magmatic Gold Belt

Adi Maryono1, Danny H. Natawidjaja2, Theo M. van Leeuwen3, Rachel L. Harrison3 and Budi Santoso1

1PT J Resources Nusantara, Equity Tower, 48th Floor,SCBD Lot 9; Jl. Jend. Sudirman, Kav 52-53, Jakarta 12190, Indonesia

2Geo-Technology Research Center, Indonesian Institute of Sciences (LIPI) 3Independent Consultants

ABSTRACT

The island of Sumatra has a long history of gold mining that dates back to the 4th century but large scale gold production and discovery of world-class gold deposits did not happen until recent times. With the advent of a three-fold increase in gold production to 300koz per annum in 2013, and the discovery of world-class gold deposits at Martabe and Miwah, Sumatra has become an emerging world-class magmatic gold belt. The island contains a total known endowment of 27.19 million ounces of gold, 151.13 million ounces of silver and 9.20 billion pounds of copper from 32 deposits and prospects. Prime gold sources are from high-sulfidation epithermal deposits that account for 41.3% by resource discovery with the largest deposit being Martabe (8.20 million ounces).

Two distinctive metallogenic systems, the Aceh-Toba Metallogenic (Au-Cu+Mo) Province in Northern Sumatra and the Barisan Metallogenic (Au-Ag) Province in Central and Southern Sumatra along with two discrete clusters of Au-Cu-base metals (the Lubuk Sikaping and West Jambi Clusters) reflect distinctive tectonic and geologic histories. The Aceh-Toba Metallogenic Province has dominant high sulfidation epithermal and porphyry occurrences, developed in Northern Sumatra covering the Aceh and Batak Tumors, two broad uplifted zones with very active N-S trending seismicity, corresponding to the longest and most complex tectonic and geologic history since 4 Ma. The Barisan Metallogenic Province, characterized by abundant low sulfidation epithermal Au-Ag occurrences, occupies Central and Southern Sumatra, in areas with simpler tectonic and geologic history and dominated by kinematics and architecture of the Sumatra Fault Zone (SFZ). The Lubuk Sikaping and West Jambi Clusters occur within the districts caused by local uplifts in Central Sumatra due to the relict components of the subducted Investigator Fracture Zone (IFZ) beneath the island and/or the movement of the SFZ.

Main gold mineralization across the island formed during a discrete time period from 1 to 4 Ma, represented by three mineralization styles; low sulfidation epithermal at Lebong Donok (1.2 to 1.3 Ma); high sulfidation epithermal at Martabe (1.2 to 1.3 Ma) and porphyry style at Upper Tengkereng (1.95 to 2.08 Ma) and Beutong (4.0 Ma). Other stages of mineralization in the form of massive sulfide deposits at Dairi, sediment-hosted gold deposit at Sihayo and skarn at Sungai Tuboh, developed in much older times at 19.0 Ma, post-Oligocene and 40+2 Ma respectively compared to the main mineralization stage.

On a regional scale Northern Sumatra displays unique tectonic and geologic features similar to the world-class fertile Au-Cu metallic provinces which are associated with compressive tectonic environments, thickened continental crust, and active uplift and erosion e.g. Eastern Sunda, Central and Northern Chile and Northern Luzon. Formation of high sulfidation epithermal Au-Ag deposits at Martabe and Miwahand porphyry Au-Cu prospects at Tengkerengis thought to have been closely associated with an inferred kink or tear of the subducting IFZ beneath the Aceh and Batak Tumors. Permeability architecture of the upper crust in particular with the key role of the Sumatran Fault System is important aspects at district and deposit scale levels. The Neogene magmatism is key for district fertility selection criterion as the main gold and gold-copper mineralization formed during a discrete time period from 1 to 4 Ma. These key geologic features, spatially and genetically associated with ore emplacement and its environment, can provide important selection criteria for prospective districts.


90

Sumatra - Introduction The island of Sumatra has a long history of gold mining history that dates back to the 4th century by ancient Chinese, Hindu immigrants and the local natives. Early gold production was primarily taken from alluvial mining e.g. Woyla in Aceh. Major gold production was mined by the Dutch from primary gold deposits at Lebong Donok and Lebong Tandai in Bengkulu from 1896 to 1941 which accounted for 61.5% of total production of 130 tonnes (Van Leeuwen, 1994). Modern gold exploration in Sumatra commenced in 1985 after the introduction of the Contract of Work System (CoW) to promote foreign mining and exploration investment during the 1980s gold rush. Intense exploration activities took place from mid-1980s to late-1990s including a re-examination of the old Dutch mines. As a result, a number of gold mines have developed in more brown field areas at LebongTandai (1985), Rawas (1990) and Way Linggo (2003), and several other new gold discoveries that are being brought to production. With the recent successful commissioning of Martabe in 2012, the island of Sumatra has continued to sustain its prolonged history of being a gold producer. Inspite of continued declining gold production in the country, gold production of Sumatra has jumped 300% from 100koz to 300koz per annum since 2013 which warrants its recognition as an emerging world-class magmatic gold belt (Fig. 1). Future gold production is expected to increase with the development of new mines at Talang Santo, Sihayo and Tembang. However lack of new gold discoveries during recent time reflects the lack of greenfield exploration activities during periods of distressed gold prices and continued legal uncertainties. This paper seeks to appreciate the island’s gold endowment with recent and increasing production, regional tectonics and geology where gold deposits occurred. A brief description of some major gold deposits isalso discussed to draw key selection criteria at

regional and district scale for the benefit of future exploration programs.

Sumatra -Gold Endowment The total metal endowment of the island of Sumatra is dominated by gold with significant amounts of associated silver and copper but insignificant other metals (iron, lead and zinc). The island contains a total known endowment of 27.19 million ounces of gold, 151.13 million ounces of silver and 9.20 billion pound of copper. These figures include all resource categories available in the public domain from 32 deposits and prospects. Of these, two are active mines, twelve are abandoned Dutch mines, and four are under development. Present and past production statistics have been primarily generated from epithermal gold deposits. Prime gold sources in Sumatra are from high-sulfidation epithermal deposits that account for 41.3% (11.24 million ounces) with the largest deposit being Martabe. Porphyry and low sulfidation epithermal deposits are the second largest for 7.69 and 6.62 million ounces respectively. Other deposit types of sediment-hosted gold, skarn and VMS account for less than 7 %. The high sulfidation epithermal deposit at Martabe contains 8.2 million ounce of gold (G-Resources Group Ltd., 2013), becoming the first epithermal deposit exceeding the 5 million ounce threshold in the country (Figs. 2 and 3). Although low sulfidation epithermal style mineralization is superior of the population (17 deposits) across the island, it contributes only 24.3% of total gold endowment. Porphyry style mineralization in Sumatra to date contains little or no gold of economic quantities unlike the Grasberg and Batu Hijau occurrences in eastern Indonesia.

Sumatra -Regional Tectonics and Geologic Framework

The island of Sumatra is the northwest oriented physiographic expression on the western edge of Sundaland, a southern extension of the Eruasian Continental Plate. Tectonic elements


91

Figure 1.Gold production profile of Indonesia showing a sharp production increase from Sumatra due to the commissioning of the high sulfidation epithermal Au-Ag deposit at Martabe in 2012.

Figure 2. Distribution of active gold and gold-copper mines and major gold and gold-copper deposits (+2 and +5 million ounces of gold) in Indonesia.

of the island show a normal trench-arc system consisting of the trench-slope break, outer-arc ridge, fore arc basin, inner magmatic arc and back arc basins toward east (Fig. 4). These tectonic and geologic elements have been complicated by the subducted slabs of the

Investigator Fracture Zone (IFZ) and Wharton Old Spreading Ridge (WOSR), the Sumatran Fault Zone (SFZ), the Mentawai Fault System (MFS) and broad regional uplifts (Natawidjaja, 2007). Such geologic history provides the perfect environment for this island terrain to


92

Figure 3. Distribution of gold resources across Sumatra, showing major gold deposits with +3 and +5 million ounces of contained gold

Figure 4. Neotectonic domains of Sumatra (Natawidjaja, 2007) showing the Northern and Central Domains with a long and complex geologic history, and the Southern Domain

with the simplest outer arc, fore-arc, and Sumatran fault geometries

host multiple deposits of both scientific and economic interest. Sumatra’s present-day tectonic and geologic configuration is controlled by the oblique

trench-subduction system along with three major fault systems, the Sumatra Fault Zone (SFZ), the Western Andaman Fault (WAF) and Batee-Singkil Fault (BSF). Continued subduction is attested by a Wadati-Benioff Zone (WBZ) that

50 – 60mm/year


93

extends to depths of 200 km and regular volcanic activity along the Barisan Mountains with volcanic centers within a few tens of kilometers of the western coast. Sumatra can be divided into three tectonic domains; the Northern, Central and Southern Domains (Fig 4; Sieh and Natawidjaja, 2000; Natawidjaja, 2007): The Northern Domain is the structural

junction where the SFZ is juxtaposed against the BSF and WAF. The northern domain has experienced the longest history in its tectonic evolution of the Sumatran Fault Zone, since 4 Ma.

The Central Domain is the most complex structurally and is associated with the transtension and fragmentation of the fore-arc region, the subduction of IFZ and WOSR (during the past 15 Million years), the N-S high-seismicity zone, and the equatorial bifurcation of the SFZ.

The Southern Domain shows the simplest outer arc, fore-arc, and Sumatran fault geometries. The Domain representsthe youngest structural development of the SFZsince 2 Ma ago to date and shows more regular than the remaining domains.

Similar to the tectonic history, regional geology of Sumatra shows the Northern part has more complex features with older rock package of the Permo-Carboniferous basement than the Southern part of the island. The Northern Sumatra is underlain by continental crust of the Permo- Carbonniferous Tapanuli Group (Cameron et al., 1980; Pulunggono and Cameron, 1984) that resembles closely with the Phuket Group of Southern Thailand and the Singa and Kubang Pasu Formations of Perlis and the Langkawi Island of NW Malaysia (Garson et al 1975; Gobbet 1973). The group is mainly composed of three formations (Bohorok, Kluet/Kuantan and Alas). Four magmatic arcs overly the basement rock packages (Fig.5), summarized from previous authors on the basis of distribution of volcanic and plutonic rocks along with supporting age

dating data (Katili, 1973; Rock et al., 1983; Bartolini and Larson 2001; Barber et al., 2005; Carlile and Mitchell, 1994) as follows: The Pre-Cretaceous Magmatic Arc is defined

on the basis of Rb-Sr age determinations on feldspars obtained from drilling consisting of West and East Sumatra Permian Plutonic-Volcanic Belts(Katili, 1973, Rock et al. 1983).

The Cretaceous Magmatic Arc resulted from extensive plutonism associated with volcanism of the continental margin Jurassic-Cretaceous Plutonic Arc (Barber et al., 2005). This magmatic pulse in Sumatra coincides with the rapid formation of the Pacific Plate (175-170Ma, Bartolini and Larson 2001), which led to a world-wide flare-up of subduction magmatism. This magmatic arc extends along the inferred southern edge of Sundaland from north Sumatra through the tip of west Java to east Kalimantan, named as the Sumatra-Meratus Arc by Carlile and Mitchell (1994).

The Tertiary magmatic Arc started with a short-lived plutonism in the early Eocene. Intense Tertiary magmatic activities have commenced since Early Miocene when the present fore arc – arc – back arc became established along with basin development. The Tertiary magmatic activities have been generally facilitated by and confined along the Sumatran Fault Zone (SFZ).

The Quaternary Magmatic Arc develops as magmatism continues towards Quaternary period with the latest giant magmatic event of the Toba Volcano eruption as the subduction system beneath the island remains active. Similar to the Tertiary arc, the Quaternary magmatic activities have been generally facilitated by and confined along the Sumatran Fault Zone (SFZ).

Sumatra -Metallogenic Provinces

Gold-silver-copper endowment and distribution of metal occurrences have been primarily confined along the 1,900km length and vicinity of the Sumatran Fault Zone. Four distinctive metallogenic provinces of gold, silver, copper and base metals are recognized from the


94

Figure 5.Regional Geology of Sumatra and distribution of magmatic arcs (from several sources: Carlile and Mitchell, 1994; and geological maps of the Geological Survey of Indonesia).

Figure 6. Distribution of metal occurrences and metallogenicprovices (two major provinces of Au-Cu and Au-Ag and two clusters of Au-Cu-base metals).

distribution of mineral occurrences. They consist of two major provinces of Au-Cu+Mo (here termed the Aceh-Toba Province) and Au-Ag (termed the Barisan Province) in the northern and southern parts of the island respectively and two discrete clusters of Au-Cu-base metals (the Lubuk Sukaping and West

Jambi Clusters) identified in the middle part of the island (Fig. 6). The first metallogenicprovince is characterized by Au-Cu+Mo, stretching from an arbitrary line at Padang Sidempuan to the northern tip of Aceh here termed the Aceh-Toba Metallogenic


95

Figure 7.The subducted IFZ (Investigator Fracture Zone) and WOSR (Wharton Old

Spreading Ridge) beneath Sumatra that have triggered regional magmatism, active NS trending seismicity and broad uplifted districts of the Aceh and Batak Tumors.

Province. This province is dominated by the presence of porphyry Cu-Au, porphyry Cu-Mo and high sulfidation epithermal Au-Ag-Cu deposits and related occurrences. Economic high sulfidation epithermal Au-Ag-Cu deposit at Martabe and porphyry Cu-Au prospects in the southern part and porphyry Cu-Au at Tengkereng and high sulfidation epithermal deposit at Miwah are the prime examples. Molybdenum is contributed by the only porphyry Cu-Mo occurrence at Tangse Aceh. The second major province is characterized by Au-Ag and runs from an arbitrary line at Padang Sidempuan to the southern tip of the island to Bandar Lampung, here termed the Barisan Metallogenic Province. This province is confined along, and accommodated by, dilational jogs, step-overs and splays of the Sumatran Fault System with the simplest outer

arc, forearc, and Sumatran fault geometries. Abundant low sulfidation and intermediate sulfidation epithermal Au-Ag deposits and occurrences are developed within this province. A series of economic deposits of intermediate to low sulfidation epithermal Au-Ag in character are also represented in the province from Lebong Tandai in the north to Way Linggo in the south. In fact, the Barisan Province of Sumatra extends further to the West and into Central Java with dominant low sulfidation epithermal Au-Ag occurrences (Maryono et al., 2012). Economic low sulfidation epithermal deposits at Pongkor and Cibaliung represent province in Java. Two other metallic provinces appear as two discrete clusters of Au-Cu-base metals that occur in the middle parts of the island, one in an

Martabe


96

area from Padang to Gunung Seblat (here termed the West Jambi Cluster) and another one in an area around Payakumbuh to Lubuk Sikaping (here termed the Lubuk Sikaping Cluster). These two metallogenic clusters are dominated by the occurrences of skarn, porphyry, high-sulfidation epithermal and massive sulfide (volcanogenic and Mississippi valley types) occurrences. A number of Au-Cu-base metals occurrences have been identified in these areas including high sulfidation epithermal and porphyry prospects at Bujang, skarn prospect at Muara Sipongi and massive sulfide prospect at TanjungBalit.

Sumatra - Gold Occurrences and Settings Metal endowment and occurrences of Au, Ag, Cu and base metals appear to have shown patterns as discussed in the metallogenic provinces concentrated along the Sumatran Fault Zone and magmatic arcs. The Aceh-Toba Metallogenic Province occupies the northern part of the island in two broad uplifted regions (Aceh and Batak Tumor) after Natawidjaja (2007), these areas are characterized by compressive environments, thickened crust, oceanic plateaus, active uplifts and erosion (Fig. 7). The Aceh and Batak Tumors have undergone a long and complex tectonic and structural evolution due to an impact of the subducted Investigator Fracture Zone (IFZ) and the Wharton Old Spreading-center Ridge (WOSR). The structural history began with dextral plate motion, accommodated by the West Andaman Fault (WAF) between 15 to 4 Ma. The Aceh segment of the SFZ and the Batee-Singkil Fault system developed from 4 Ma. The Seulimeum segment, west of the Aceh segment and the rest of the SFZ was the last to develop from 2 Ma, and have continued taking up the right-lateral movement along the tectonic margin until the present day. The culmination of the Batak Tumor is the Toba-caldera Lake, the largest Quaternary caldera on earth (Natawidjaja, 2007). The Toba highland coincides with the Investigator Fracture Zone (IFZ) that is presently subducting beneath the Sumatran plate. The eastward movement of

the subducting IFZ for the past 15 Ma seems to be responsible for the bending in the subduction isobath and shifting in location of the volcanic-arc zone. The subducted IFZ, which is now related to the high-seismicity zone, may also cause cross-strike tear zones within the Sumatran crust and result in upwelling of giant magmas beneath the Batak Tumor. Similar to other fertile metallogenic districts, major high sulfidation epithermal and porphyry projects including the world-class high sulfidation epithermal Au-Ag deposit at Martabe (8.2 million ounce of gold; G Resources, 2013) and Miwah (3.27 million ounces of gold, Taylor, 2011) are thought to have formed along the N-S trending crustal structures of the subducted IFZ beneath the island (Fig. 7). In the Circum Pacific Region, the formation of giant porphyry Cu-Au deposits has been closely associated with subduction of aseismic ridges, seamount chains and oceanic plateaus beneath oceanic island and continental arcs (Cooke et al., 2005). Continued active regional uplifts in the northern part of Sumatra can be observed from projections of the benioff zones, flat slab subduction, active seismic activities, volcanic arc shift, widespread regional magmatism, the presence of large intrusive bodies, exposures of the Tapanuli Group basement and basin configuration. Torn slabs beneath the Batak Tumor are indicated by the widening benioff zone of 200km projection that separates subducted slabs with flattened dip toward north and deeper dip towards the south as well as N-S trending high-seismicity zones as surface expression of subducted IFZ beneath the Batak and Aceh Tumors. This is a similar geologic setting to the Eastern Sunda Arc where Batu Hijau formed along the eastern margin of the Roo Rise plateau that correlates with an arc-normal northeast trending structure (Kerrich et al., 2000 and Garwin, 2002). Sumatra - Gold Mineralization Styles and Ages There are at least six gold mineralization styles that have been unequivocally identified to date in Sumatra; porphryry, skarn, high sulfidation epithermal (HSE), intermediate sulfidation


97

epithermal (ISE), low sulfidation epithermal (LSE) and sediment-hosted (SHG). They can generally be grouped into two: intrusion related and non-intrusion related styles. Other mineralization styles exist but do not have appreciable amounts of gold (e.g. massive sulfide deposits). The intrusion related styles are represented by porphyry and skarn deposits at the deeper crustal level with overlying HSE in the upper part of the system. They are both associated with calk-alkaline magma. Porphyry (and skarn) Cu-Au mineralization at Beutong and HSE Au-Ag mineralization at Martabe are two classic examples respectively. The Beutong deposit contains 3.0Mt copper equivalent from 505Mt @ 0.47% Cu and 0.12 g/t Au with some portion of high grade including the skarn. Juxtaposing porphyry and HSE gold mineralization types is exemplified by the Upper Tengkereng Porphyry Cu-Au mineralization style, associated with multiple intrusive diorite-tonalite porphyry intrusions that are highly telescoped with HSE overprinting. A large lithocap alteration zone at surface overlies porphyry Cu-Au mineralization at Tengkereng (Hamid et al., 2014). This is similar to a telescoped system of overlying HSE over porphyry Cu-Au mineralization at Tumpangpitu in East Java where gold and copper enrichment took place during a later HSE epithermal stage (Harrison and Maryono, 2012). Martabe is the best example of HSE, consisting of a number of deposits over a strike length of 7 km. It is characterized by multiphase phreatomagmatic breccias (at least two ages) that host high-grade mineralization where they are in contact with mineralizing fluids in zones of structural complexity (Levet et al., 2003). It shares similarity to the other HSE style mineralization of Miwah but with less phreatomagmatic phases. Interestingly Miwah is thought to have been connected to a buried porphyry-type intrusion (Williamson and Fleming, 1995). The presence of the multiphase and extensive phreatomagmatic breccias in

both deposits demonstrates that the geological environment was very dynamic and is interpreted to be a favorable setting to host a prolonged (magmatic) hydrothermal system thus multiphase or bigger systems could be formed. With the current resource of 8.20 Moz of contained gold, Martabe is a world class gold deposit. The non-intrusion related styles, ISEand LSE mineralization styles are well represented by Lebong Tandai and Way Linggo respectively. Lebong Tandai is volcanic-hosted (intermediate sulfidation) epithermal gold deposit. The mineralization is exclusively in the form of tabular quartz-cemented breccias bodies which are localized along faults. The sulfide minerals occur as either a single cockade band around the clasts in the breccia, or as polymineralic aggregates disseminated throughout the breccia cement (Jobson et al. 1994). While WayLinggo is a small but classic LSE Au-Ag deposit style formed in Tertiary andesite/dacite pyroclastics with the ore body forming typical LSE quartz veining and siliceous sinter (Andrews at al., 1991). Like Martabe, Way Linggo is associated with arc-parallel master fault segments of the Sumatra Fault Zone. Another gold mineralization style in Sumatra is represented by Sihayo. At Sihayo, gold mineralization is hosted by regolith and silicified breccias that formed by karst dessolution under phreatic conditions and subsequent collapse. Using general classification Sihayo may be called a ‘sediment hosted’ gold type deposit. The main gold and gold-copper mineralization across the island from the northern to the southern parts of Sumatra are very young and formed during discrete time periods of 1 to 4 Ma or during the Pliocene-Pleistocene period. Epithermal gold mineralization was formed between1.2 to 1.3 Ma at Martabe (Sutopo, 2011) and 1.2 to 1.3 Ma at LebongDonok (Henley and Etheridge, 1995). A number of epithermal deposits (e.g. Miwah, Lubuk Sikaping, Mangani, Balimbing and Salida) are reported to have formed during Pliocene to Pleistocene times (Williamson and Fleming,


98

1995; Rock et al., 1983; Kavalieris et al., 1988; Grey, 1935; Krief and Oen, 1973). Porphyry style mineralization occurred during the same period; 1.95 to 2.08 Mafor Upper Tengkereng (Norman, 2013) and 4 Ma for Beutong (Kusnanto, pers. comm., 2014). This is in line with the main gold-copper mineralization stage in the Eastern Sunda Arc which is related to the Pliocene and Pleistocene magmatism (Maryono et al., 2012). Similarly, overwhelming numbers of mineralization ages in the South Western Pacific region (about 45.1% or 321.2 million ounces of total gold endowment) were formed during the Neogene (Maryono and Power, 2009). Other mineralization events formed much older than the main gold mineralization and were developed in the form of massive sulfide depositsat 19 Ma forDairi (Hendrawan, pers. Comm., 2014), at post-Oligocene for Sihayo (Jones, pers comm., 2004) and skarn mineralization styles at 40+2 Ma for Sungai Tuboh and at 54+2 Ma for Bukit Rajah (JICA, 1988).

Sumatra - Summary and Implications for Exploration

With the advent of a three-fold increase in gold production to 300koz per annum in 2013 and the discovery of world-class high sulfidation epithermal deposits at Martabe and Miwah, Sumatra has become an emerging world-class magmatic gold belt. Future gold production is expected to increase with the development of new mines at Talang Santo, Sihayo and Tembang. In total the island contains known gold-silver-copper endowment of 27.19 million ounces of gold, 151.13 million ounces of silver and 9.20 billion pounds of copper, compiled from 32 deposits and prospects. Sumatra still offers large exploration ground with magmatic arcs stretching for more than 1,650km along the length of the island in areas which still remain under-explored. Two distinctive metallogenic provinces are recognized; the Aceh-Toba Metallogenic Province (Au-Cu+Mo) in the Northern Sumatra,

and the Barisan Metallogenic Province (Au-Ag) in the Central to the Southern Sumatra along with other two discrete metallogenic clusters of Au-Cu-base metals (the Lubuk Sikaping and West Jambi Clusters) as differentiated by two distinctive tectonic and geologic histories. On a regional scale the Northern Sumatra displays unique tectonic and geologic features similar to the world-class fertile Au-Cumetallic provinces which are associated with compressive tectonic environment, thickened continental crust, and active uplift and erosion e.g. Eastern Sunda, Central and Northern Chile and Northern Luzon (Cooke et al., 2005; Maryono et al., 2012). Formation of dominant high sulfidation epithermal Au-Ag and porphyry Au-Cu deposits/prospects is thought to have been closely associated with subduction of aseismic ridges, torn slabs, and oceanic plateaus beneath the Aceh and Batak Tumors in the Northern Sumatra. Significant deposits at Martabe, Miwah and Tengkereng are thought to be related to an inferred kink or tear of the subducting IFZ. These areas are characterized by continued active regional uplifts, widening benioff zones, N-S trending active seismic activities, volcanic arc shift, widespread regional magmatism, the presence of large volcanic-magmatic bodies and range-basin configuration. Permeability architecture of the upper crust in particular with the key role of the Sumatran Fault System plays important aspects at district and deposit scales. Although gold mineralization is spread across the magmatic arcs and geological times since Late Cretaceous, the main gold mineralization stage across the island formed during discrete time period of 1 to 3 Ma or during Pliocene-Pleistocene period. Therefore Neogene magmatism is key for district fertility with robust magmatic links as small discrete intrusions for major intrusion-related mineralization styles. These key geologic features, spatially and genetically associated with ore and its environment can provide selection criteria for prospective districts. These criteria will enable explorers to draw priority gold deposit types, exploration targets and focus.


99

Acknowledgement

This paper was initiated by a joint study of the first two authors of this paper in 2007 for the purpose of understanding the geology and mineral occurrences of Sumatra, and new discoveries. Brian K. Levet is gratefully acknowledged for his encouragement and support. This manuscript benefited considerably from the insightful review of David Cooke and Colin Davies. Great thanks are for Iryanto Rompo for the materials and continued support and Raden Aditya Suryadarmafor the excellent drawing.

REFERENCES Andrews, M.J., Dods, G.H. and Hewitt, W.V.,

1991, Methods and approach to exploration for hard rock and alluvial gold in Indonesia. In: Proceedings World Gold '91. Australian Institute of Mining and Metallurgy, 259-269.

Aron J. M., Sieh, K., Abrams, M., Duncan, C.A., Hudnut, K. W., Avouac, J.P., Natawidjaja, D. H., 2006, Uplift and subsidence associated with the great Aceh-Andaman earthquake of 2004; JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, B02407.

Arribas, A. Jr., 1995, Characteristics of high-sulfidation epithermal deposits, and their relation to magmatic fluid, In J.F.M. Thompson (ed.), Magmas, Fluids, and Ore Deposits, Mineralogical Association of Canada Short Course Vol. 23.

Barber, A.J., Crow, M.J., Milsom, J.S., 2005, Sumatra:Geology, Resources and Tectonic Evolution, GEOLOGICAL SOCIETY MEMOIRS NO. 31, The Geological Society London, The British geological Survey.

Bartolini, A. and Larson, R.L., 2001, Pacific microplate and the Pangea supercontinent in the Early to Middle Jurassic. Geology, 29, 735-738.

Basuki, A., Sumanagara, D.A., Sinambela, D., 1994. The Gunung Pongkor gold-silver deposit, West Java, Indonesia. J. Geochem. Expl. 50: 371-391.

Cameron, N.R., Clarke, M.C.G., Aldiss, D.T., Aspen, J.A. and Djunuddin, A. 1980, The

geological evolution of northern Sumatra. In: lndonesian Petroleum Association, Proceedings of the 9th Annual Convention, Jakarta, 1980, 9, 149-187.

Carlile, J.C. and Mitchell, A.H.G., 1994, Magmatic Arcs and Associated Gold and Copper Mineralization in Indonesia, Journal of Geochemical Explor., v. 50, p. 91, Elsevier Sci. Publish. Co.

Cooke, D.R., 1996, Case studies of western Pacific porphyry Cu-Au deposits in Indonesia: CODES Key Centre, University of Tasmania, Economic Geology Short Course notes (unpublished).

Cooke, R.D., Hollings, P., and Walshe, J., 2005, Giant Porphyry Deposits: Characteristics, Distribution, and Tectonic Controls, Bulletin of the Society of Economic Geologist Vol. 100, No.5, pp. 801-818

G-RESOURCES, 2013, Mineral Resource and Ore Reserve Statement at 30 June 2013, Company News Release.

Garson, M.S., Young, F.B., Mitchell, A.H.G. and Tait, B.A.R., 1975, The Geology of the Tin Belt in Peninsular Thailand around Phuket, Phangnga and Takua Pa. Institute of Geological Sciences, London Overseas Division, Memoirs, 1.

Garwin, S., 2002, The geological setting of intrusion-related hydrothermal systems near the Batu Hijau porphyry copper-gold deposit, Sumbawa, Indonesia: Society of Economic Geologists Special Publication 9, p.333–366.

Gustafson, L.B. and Hunt, J.P., 1975, The porphyry copper deposit at El Salvador, Chile: Economic Geology 70, pp. 857-912.

Gobbett, D.J. and Hutchinson, C.S., 1973, Geology of the Malay Peninsula (West Malaysia and Singapore). Wiley Intersciences, New York, 5.

Grey, D.W.J., 1935, Notes on Balimbing mine, west coast of Sumatra. Bulletin Institution of Mining and Metallurgy, 1-20.

Hall, R., 2002, Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations. Journal of Asian Earth Sciences, 20: 353-431.

Hamid, D., Ardiansyah, S. and Safrihadi, B.,


100

2014, Discovery, Exploration History and Geology of the Upper Tengkereng Porphyry Gold and Copper Deposit, Gayo Lues, Aceh, Barisan Gold Corporation

Hamilton, W.B., 1988, Plate tectonics and island arcs. GSA Bull. 100: 1503-1527.

Hamilton, W. B., 1979, Tectonics of the Indonesian Region. Professional Paper 1078, U.S.G.S., Washington, DC, 345 p.

Harrison, R.L., and Maryono, A., 2012, Tumpangpitu porphyry-high sulfidation epithermal deposit, Tujuh Bukit project, Indonesia - geology, alteration and mineralization: Red Metals Symposium presentation, CODES, University of Tasmania, 51 p.

Hedenquist, J.W., White, N.C., and Siddeley, G., (Ed.), 1990, Epithermal Gold Mineralization of the Circum Pacific: Geology, Geochemistry, Origin and Exploration II, Assoc. of Explor. Geochemist. Spec. Publication No.16b, Elsevier Sci. Publish. Co., Amsterdam.

Hedenquist,J.W., Arribas, A. and Gonzales-Urien,E., 2000, Exploration for epithermal gold deposits. SEG Reviews 13, pp. 245-277.

Hendrawan, D., 2014, Personal Communication. JICA 1988. Report on the cooperative mineral

exploration of Southern Sumatra, Consolidated Report. Japan International Cooperation Agency, Metal Mining Agency of Japan, February 1988.

Jobson, D.H., Boulter, C.A. and Foster, R.P., 1994, Structural controls and genesis of epithermal gold-bearing breccias at the Lebong Tandai mine, Western Sumatra, Indonesia. Journal of Geochemical Exploration, 50, 409-428.

Katili, J.A. 1973, Geochronology of west Indonesia and its implicationon plate tectonics. Tectonophysics, 19, 195-212.

Kerrich, R., Goldfarb, R., Groves, D., and Garwin, S., 2000, The geodynamics of world-class gold deposits: Characteristics, space-time distributions, and origins: Reviews in Economic Geology, v. 13, p. 501–551.

Kirkham, R.V., and Dunne, K.P.E., 2000, World distribution of porphyry, porphyry-associated skarn, and bulk-tonnage epithermal deposits and occurrences:

Geological Survey of Canada Open File 3792a, 26 p.

Kusnanto, B., 2014, Personal Communication. Levet, B., Jones, M.L. and Sutopo, B., 2003, The

Martabe gold project,Sumatra, Indonesia. Paper presented at SMEDG-AIG Symposium 2003, Asian update on mineral exploration and development, Sydney, 10 October 2003.

Lindgren, W.W., 1933, Mineral deposits. John Wiley & Sons, New York.

Marcoux, E., Milési, J.-P., 1994, Epithermal gold deposits in West Java, Indonesia: geology, age and crustal source. J. Geochem. Explor. 50: 393-408.

Marcoux, E., Milési, J.-P., Sitorus, T., Simandjuntak, M., 1996, The epithermal Au-Ag-(Mn) deposit of Pongkor (West Java, Indonesia). Indon. Mining J. 2: 1-17.

Maryono, A. and Power, D., 2009, Regional Framework Study on Papuan Fold Belt, Newmont internal company report (unpublished).

Maryono, A., Setijadji, L.D., Arif, J., Harrison, L.R., and Soeriaatmadja, E., 2012, Gold, Silver and Copper Metallogeny of the Eastern Sunda Magmatic Arc Indonesia, Proceeding MGEI BESA 2012.

Metcalfe, I., 1996, Pre-Cretaceous evolution of SE Asian terranes. In Hall, R. and Blundell, D.J. (Eds.), Tectonic evolution of Southeast Asia, Geological Society Special Publication, 106: 97-122.

Milési, J.P., Marcoux, E., Sitorus, T., Simandjuntak, M., Leroy, J., Bailly, L., 1999, Pongkor (west Java, Indonesia): a Pliocene supergene-enriched epithermal Au-Ag-(Mn) deposit. Mineral.Deposita 34: 131-149.

Natawidjaja, D.H., 2007, Special report of the project study, “Structural Architecture and Tectonics of the Sumatra Fault Zone”, 24th of July 2007, Report to Newmont Asia Pacific, pp. 1-11.

Nishimura, S., Nishida, J., Yokoyama, T., and Hehuwat, F., 1986, Neo-tectonics of the strait of Sunda, Indonesia. Journal of Southeast Asian Earth Sciences, 1: 81-91.

Norman, M., 2013, Written communication on age dating for Upper Tengkareng

Pulunggono, A. and Cameron, N.R., 1984, Sumatran microplates, theircharacteristics


101

and their role in the evolution of the Central andSouth Sumatra basins. In: Indonesian Petroleum Association, Proceedingsof the 13th Annual Convention, 13, 1221 - 1443.

Rock, N.M.S., Aldiss, D.T., Aspen, J.A., Clarke, M.C.G., Djunuddin, A., Kartawa, W., Miswar, S.J., Thompson, R. and Handoyo, R., 1983, The Geology of the Lubuksikaping Quadrangle (0716), Sumatra Scale 1 : 250 000. Geological Survey of Indonesia, Directorate of Mineral Resources, Geological Research and Development Centre, Bandung.

Sillitoe, R.H.,1989, Gold deposits in western Pacific island arcs: The magmatic connection: Economic Geology Monograph 6, pp. 266-283.

Sillitoe, R.H., 2000, Gold-rich porphyry deposits: descriptive and genetic models and their role in exploration and discovery: Reviews in Economic Geology 13, 315-345.

Sieh, K. and Natawidjaja, D., 2000, Neotectonics of the Sumatran fault, Indonesia. Journal of Geophysical Research 105(B12): doi: 10.1029/2000JB900120. issn: 0148-0227 - Harry Doust, Ron A. Noble, Petroleum systems of Indonesia, Marine and Petroleum Geology, Volume 25, Issue 2, February 2008, Pages 103-129, ISSN 0264-8172, 10.1016/j.marpetgeo.2007.05.007.

Sutopo, B., 2011, The Martabe Au-Ag High Sulfidation Epithermal deposits, Sumatra: Implications for Ore Genesis and Exploration, University of Tasmania, PhD.Thesis, 329 p.

Taylor, I.A., 2011, A Technical Report on Exploration and Resource Estimation of the Miwah Project, Sumatra, Indonesia, Prepared by Mining Associates Pty Limited for East Asia Minerals Corporation.

Van Leeuwen, TM., 1994. 25 Years of mineral exploration and discovery in Indonesia. In: T.M van Leeuwen.J.W. Hedenquist, L.P. James and J.A.S. Dow (Editors), Indonesian Mineral Deposits -- Discoveries of thePast 25 Years. J. Geochem. Explor.+ 50: 13-90.

Williamson, A. and Fleming, G.J., 1995, Miwah prospect high sulphidation Au-Cu mineralisation, northern Sumatra, Indonesia.

In: PACRIM '95. Australian Institute of Mining and Metallurgy, 637-642.

Documents

Sumatra, an Emerging World-Class Magmatic Gold Belt