International Journal of Coal Geology 81 (2010) 151–162

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International Journal of Coal Geology

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Distribution of sulfur and pyrite in coal seams from Basin (East , ): Implications for paleoenvironmental conditions

Sri Widodo a,⁎, Wolfgang Oschmann b, Achim Bechtel c, Reinhard F. Sachsenhofer c, Komang Anggayana d, Wilhelm Puettmann e a Department of Mining Engineering, Moslem University of Indonesia, Jln. Urip Sumoharjo, Makassar, Indonesia b Institute of Geosciece, J.W. Goethe-University, Altenhöferallee 1, D-60438 Frankfurt a.M., Germany c Department of Applied Geoscience and Geophysics,University of Leoben, Peter-Tunner-Str.5, A-8700 Leoben, Austria d Department of Mining Engineering, Bandung Institute of Technology, Jln. Ganesa 10, I-40132 Bandung, Indonesia e Institute of Atmospheric and Environmental Sciences, Dapartment of Analytical Enviromental Chemistry, J.W. Goethe-University, Altenhöferallee 1, D-60438 Frankfurt a.M., Germany article info abstract

Article history: Thirteen coal samples from three active open pit and underground coal mines in the Kutai Basin Received 12 August 2009 (, Indonesia) were collected. According to our microscopical and geochemical investigations, Received in revised form 29 November 2009 coal samples from Sebulu and Centra Busang coal mines yield high sulfur and pyrite contents as compared to Accepted 3 December 2009 the Embalut coal mine. The latter being characterized by very low sulfur (b1%) and pyrite contents. The ash, Available online 13 December 2009 mineral, total sulfur, iron (Fe) and pyrite contents of most of the coal samples from the Sebulu and Centra Busang coal mines are high and positively related in these samples. Low contents of ash, mineral, total sulfur, Keywords: Kutai Basin iron (Fe) and pyrite have been found only in sample TNT-32 from Centra Busang coal mine. Pyrite was the fl Pyrite only sulfur form that we could recognize under re ected light microscope (oil immersion). Pyrite occurred in Sulfur the coal as framboidal, euhedral, massive, anhedral and epigenetic pyrite in cleats/fractures. High Framboidal concentration of pyrite argues for the availability of iron (Fe) in the coal samples. Most coal samples from Ombrogenous the Embalut coal mine show lower sulfur (b1 wt.%) and pyrite contents as found within Centra Busang and Topogenous Sebulu coals. One exception is the coal sample KTD-38 from Embalut mine with total sulfur content of 1.41 wt.%. The rich ash, mineral, sulfur and pyrite contents of coals in the Kutai Basin (especially Centra Busang and Sebulu coals) can be related to the volcanic activity (Nyaan volcanic) during whereby aeolian material was transported to the mire during or after the peatification process. Moreover, the adjacent early Tertiary deep marine sediment, mafic igneous rocks and melange in the center of Kalimantan Island might have provided mineral to the coal by uplift and erosion. The inorganic matter in the mire might also originate from the ground and surface water from the highland of central Kalimantan. © 2009 Elsevier B.V. All rights reserved.

1. Introduction ascending or descending solutions in cracks, fissures, or cavities or by alteration of primarily deposited minerals. Most of the inorganic matter in coal is present as minerals which The dominant mineral of coals is usually composed of sulfides, are dispersed throughout the coal macerals. Individual grains of clay, carbonates, and quartz and sometimes additional phosphates, minerals vary largely in size from less than one micrometre to tens or heavy minerals, and salts as minor contributions to inorganic matter hundreds of micrometres. Sometimes mineral-rich layers are even of coal. In most coals, sulfides are preferentially composed of pyrite thick enough to be visible on the coal surface (Taylor et al., 1998). and marcasite but pyrite is in general dominating by far (Balme, 1956; Mineral components in the coals were classified in three groups Mackowsky, 1943). according to their origin (Stach et al., 1975): (1) Mineral from the Sulfides can be categorized as either syngenetic (primary), early- original plants; (2) mineral that formed during the first stage of the diagenetic or epigenetic (secondary) in origin. During peatification, coalification process or which was introduced by water and wind into syngenetic or early-diagenetic fine-crystalline or fine-concretionary the later coal deposits; and (3) mineral deposited during the second pyrite appears, commonly in the form of framboids. Syngenetic pyrite phase of the coalification process, after consolidation of the coal, by formed during accumulation of the peat and/or during early (humification) processes, and is usually small in size, and intimately dispersed throughout the coal (Renton and Cecil, 1979; Reyes- Navarro and Davis, 1976). Occasionally, the cell walls of plant material ⁎ Corresponding author. Tel.: +62 411 454775; fax: +62 411 453009. have been replaced by pyrite (Taylor et al., 1998). Falcon and Snyman E-mail address: [email protected] (S. Widodo). (1986) suggest that the accumulation of pyrite in coal might also arise

0166-5162/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2009.12.003 152 S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162 from the aeolian and fluviatile import of iron-rich mineral at the time The island of Kalimantan and in particular the Kutai Basin has of peat accumulation followed by in-situ precipitation. Epigenetic experienced a complex tectonic history from the to the pyrite is incorporated in the coal after compaction or partial present day. The Kutai Basin was formed during early Tertiary times consolidation (Reyes-Navarro and Davis, 1976) and is generally and was filled-up with clastic sediments progressing from the much larger (coarse grained) and fills cracks, cleats, and cavities western to the eastern part of the basin. This basin was subdivided (Renton and Cecil, 1979). The formation of epigenetic pyrite is into the Upper Kutai Basin, consisting of Paleogene outcrops with dependent primarily on the availability of reduced sulfur, dissolved volcanics possessing a strong northwest–southeast struc- cation (ferrous iron) and a suitable site for formation i.e., cleat tural grain, and the Lower Kutai Basin with Miocene strata cropping (Casagrande et al., 1977; Spears and Caswell, 1986; Demchuk, 1992). out in a north–northeast-trending structure. The Meratus Mountains Moreover, epigenetic pyrite might be precipitated from water to the southwest and the Central Kalimantan Mountains to the north percolating into fractures, cavities and pores present in coal seams of the Kutai Basin have an ophiolitic basement together with long after accumulation of the peat (Falcon and Snyman, 1986). Paleogene strata striking dominantly in a north–northeast direction In general, coals deposited in paralic basins contain more pyrite (Clay et al., 2000). than those in limnic basins. Among the paralic deposits, coal seams The coal mining companies are located in the vicinity of the Mahakam which have been influenced by marine transgressions are consistently River, Kutai Basin, East Kalimantan Province (Fig. 2). The precise characterized by a particularly high content of pyrite and sometimes geographic position of Sebulu coal mine is S00°26′40.4″/E116°52′54.1″ also of organic sulfur, especially in the upper part of the seams (Balme, and Centra Busang coal mine is S00°44′22.2″/E116°89′16.6″,whereasthe 1956; Dai et al., 2002; Mackowsky, 1943). In sulfur-rich humic coals, Embalut coal mine is situated S00°33′34.9″/E117°12′15.5″.CentraBusang pyrite in the form of fine grains or fine concretions is particularly is located in the Busang village, East Kutai and Sebulu coal mine in common in microlithotypes containing a high proportion of vitrinite; the Sebulu village, Kutai Kertanegara regency, East Kalimantan province. these forms also tend to be common in sapropelic coals. In the absence The Embalut coal mine is located in Embalut village, Kutai Kertanegara of other criteria (such as marine fossils or coal balls), a relatively high regency, East Kalimantan province. Coal seams in the Centra Busang and proportion of synsedimentary or early-diagenetic pyrite can be useful Sebulu mines were found in the Pulau Balang Formation with Middle for seam correlation. Miocene age, and coal seams in the Embalut mine was found in the Pulau Many previous investigations (Anggayana et al., 2003; Baruah, 1995; Balang (Middle Miocene age) and Formation with Upper Dai et al., 2002, 2003, 2006, 2007, 2008; Dai and Chou, 2007; Elswick Miocene age (Fig. 3). et al., 2007; Frankie and Hower, 1987; Kortenski and Kostova, 1996; Previous studies of the sedimentary evolution of the Kutai Basin, Lόpez-Buendía et al., 2007; Querol et al., 1989; Renton and Bird, 1991; based on field survey and oil wells, have shown that the Tertiary Strauss and Schieber, 1989; Turner and Richardson, 2004; Wiese and sequences are broadly regressive in general with a (dominantly) Fyfe, 1986) have described the characteristics, type, morphology, offshore marine argillaceous sequence of Palaeocene age followed by genesis, and distribution of pyrite in coal seams from different deposits. a coal bearing deltaic and coastal plain succession of Miocene age. Our investigation deals with sulfur and pyrite occurrences in the Shoreline progradation was generally towards the east (Samuel and Miocene coal seams from Centra Busang, Sebulu and Embalut coal Muchsin, 1976; Rose and Hartono, 1978 in Land and Jones, 1987). mines, Kutai Basins, East Kalimantan, Indonesia. The primary purpose of According to Supriatna and Rustandi (1986) the the study is to explain why most Miocene coal seams from Kutai Basin succession in the Kutai Basin includes from bottom to top the have very low sulfur contents, whereas in some coal seams higher sulfur following formations: Pamaluan, Bebuluh, Pulau Balang, Balikpapan, contents are observed. The second purpose is to identify the types of Kampung Baru Formation and alluvial. The Pamaluan Formation (up pyrite and factors affecting their appearance and it's relation with to 1500 m thick) consists of sandstones with insertion of claystone, paleoenvironmental conditions during deposition of the coals. shale, limestones, and siltstone. It formed in a deep marine environment during Late and Early Miocene times. The Lower Miocene Bebuluh Formation (up to 900 m thick) consists of limestones with 2. Geological setting insertion of sandy limestones and argillaceous shales. The deposition of the formation occurred in a shallow sea. The Bebuluh Formation Kalimantan is surrounded by marginal basins of South China, Celebes interfingers with the Pamaluan Formation. The Pulau Balang Formation and Sulu seas, microcontinental fragments of south China in the north, and of Early to Middle Miocene age overlies the Bebuluh Beds concordantly. mainland SE Asia (Indochina and peninsular Malaysia) in the west (Moss It is composed of graywackes, quartz sandstones, limestones, claystones, and Chambers, 1999). Kalimantan was interpreted as the product of dacitic tuff and coal insertion. The thickness of coal seams ranges from Mesozoic accretion of oceanic crustal material (ophiolite), marginal basin 3 to 4 m. The depositional environment can be characterized as deltaic fill, material and microcontinental fragments onto the Paleozoic to shallow marine according to Supriatna and Rustandi (1986).The continental core of the Schwaner Mountain in the SW of the island (Fig. 1; formation is approximately 900 m thick. The Middle to Upper Miocene Hall and Nichols, 2002; Hutchison, 1989; Moss and Wilson, 1998; Widodo Balikpapan Formation (1000–1500 m thick) uniformly overlies the et al., 2009). Pulau Balang Formation and consists of quartz sandstone, clay with During early Tertiary times, Kalimantan formed a promontory of insertion of shale, and coal seams 5 to 10 m thick. The deposition of the the Sundaland Craton: the stable eastern margin of the Eurasian plate Balikpapan Formation occurred in a delta environment. The Upper (Hall, 1996; Metcalfe, 1998). In the east, Kalimantan is separated from Miocene to Kampung Baru Formation disconcordantly overlies by the deep Makassar Basins (Fig. 1), formed during the Balikpapan Formation. It is composed of quartz sandstone with Paleogene times (Situmorang, 1982). The main areas of eastern, insertion of clay, shale, silt and approximately 3 m thick coal (lignite). central and northern part of Kalimantan are coated by Tertiary The deposition of the Kampung Baru Formation up to 900 m thick, sediments (Fig. 1) which were deposited in fluvial, marginal-marine sedimentary succession occurred in a delta. Alluvium deposit (alluvial) or marine environments. consists of sandy clay and clayey sands. Tertiary sedimentation in these areas occurred at the same time with, and subsequent to, a period of widespread Paleogene extension and subsidence, which may have commenced in the middle or 3. Samples and method earlier (Moss and Wilson, 1998). A number of Tertiary sedimentary basins, of which the Kutai Basin is the largest, are identified across Coal samples were collected in-situ with channel sampling method Kalimantan (Moss et al., 1997). from three active surface mines in the Centra Busang (3 samples), S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162 153

Fig. 1. Simplified geology of Kalimantan (modified from Moss and Wilson 1998; Hall and Nichols, 2002).

Sebulu (2 samples), and Embalut (8 samples) coal mines, Kutai Basin, particles of about 1 mm in diameter were used for preparation of East Kalimantan, Indonesia. polished sections, which were embedded in a silicone mould The sample preparation and microscopic examination generally (diameter 40 mm) using epoxy resin as an embedding medium. followed the procedures described by Taylor et al. (1998). Coal After hardening, the samples were ground and polished. Microscopic 154 S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162

Fig. 2. Geographic map showing the locations of Sebulu, Centra Busang and Embalut coal mines in the Kutai Basin, East Kalimantan, Indonesia. analyses were performed by a single-scan method with a Leica MPV Ash yields were determined following standard procedure DIN microscope using reflected white and fluorescent light. At least 300 51719 using dry coal samples. One gram of each coal sample is heated points were counted for coal macerals and mineral. Pyrites were 2 h to 815 °C (±15 °C) in a muffel furnace, the residue was then counted separately from the other minerals (for example, clay, cooled to room temperature and weighed. carbonate, quartz) which were counted together in one group. For trace element analyses, carried out by ACTLABS, Ancaster,

Total sulfur contents were determined using an automated Leco Canada, the coal ash (0.5 g) was dissolved in aqua regia (0.5 ml H2O, SC-344 carbon sulfur analyzer. A weighed coal sample is mixed with 0.6 ml concentrated HNO3 and 1.8 ml concentrated HCl). After iron chips and a tungsten accelerator and is then combusted in an cooling, samples were diluted to 10 ml with deionized water and oxygen atmosphere at 1370 °C. The moisture and dust are removed homogenized. The digestion is near total for base metals, but will only from the combustion product and the SO2 gas is measured by a solid- be partial for silicates and oxides. The solutions were then analyzed state infrared detector. using a Perkin Elmer OPTIMA 3000 Radial ICP-MS for the 30 elements

Fig. 3. Sedimentary sequences and the distribution of some fundamental parameters of the Embalut, Centra Busang and Sebulu coalfield, Kutai Basin, East Kalimantan, Indonesia. S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162 155 suite. A series of USGS-geochemical standards were used as controls. contents and total sulfur. The correlation coefficients are r2 =0.96 (Fe vs The iron (Fe) is one of the elements to be discussed in this paper. pyrite contents), and r2 =0.86 (Fe vs total sulfur). Whereas, iron (Fe) contents of Embalut coal samples are low and range from 0.15 to 1.32%. Highest content are found in the sample KTD-38 with a value of 1.32%. 4. Results and discussion Fig. 7 also shows a positive correlation of iron (Fe) contents to the pyrite contents and total sulfur in the coal samples from Embalut coal mine. 4.1. Ash, mineral, total sulfur and iron (Fe) contents The correlation coefficients are r2 =0.97 (Fe vs pyrite contents) and r2 =0.99 (Fe vs total sulfur). Ash yields, minerals, total sulfur, and Fe contents in the coal The sum of total sulfur and iron (Fe) is close to the amount of ash samples from Centra Busang, Sebulu and Embalut coal mines are for Centra Busang and Sebulu coals (Table 1). This indicates that a summarized in Table 1 and cross-correlation are shown in Fig. 4. The large proportion of the mineral in the coal samples must be composed ash yield of the Centra Busang and Sebulu coals varies from 1.40 to of pyrite. In the two samples (TNT-30 and TNT-33) the sum of the 5.80 (wt.%, db). The Embalut coal samples show higher variability in total sulfur content and the Fe content exceeds the ash content. In ash yields (1.33 to 8.98 wt.%, db). Four coal samples from Embalut these samples some of the sulfur must be organically bond sulfur, yield more than 2 wt.% (db) ash (Table 1) while ash contents lower which evaporates together with the organic matter during heating. than 2 wt.% (db) are found in the samples KTD-36, KTD-35, KTD-43, The lowest total sulfur content (0.14 wt.%) of the Centra Busang and and KTD-37 (Table 1). The ash contents of Cetra Busang and Sebulu Sebulu coal mines is observed in TNT-32, which provided a very low 2 coals show a positive correlation to the total sulfur+Fe (r =0.83). ash yield of 1.40 wt.%, db. This allows to estimate the non-pyritic Embalut coals show also a positive correlation between ash contents mineral content to approximately 1 wt.%. to the total sulfur+Fe (r2 =0.77). The mineral contents of Centra Busang and Sebulu coals vary from 4.2. Pyrite content and pyrite types in the coal seams 0.70 to 5.60 (vol.%). Mineral is predominantly composed of pyrite. Clay and carbonates are also found in a significant quantity. Quartz is Based on microscopical analyses, the amount of pyrite in the observed only in a trace proportion. In the coal samples from Centra Centra Busang and Sebulu coal samples varies from 0.4 to 4.3 vol.% Busang coal mine, mineral contents vary from 3.70 vol.% (TNT-30, seam (Table 1). In comparison, most of pyrite contents of Embalut coal BL-4) over 1.60 vol.% (TNT-31 BL-7) to 0.70 vol.% (TNT-32, BL-7.1). The samples are lower than in Centra Busang and Sebulu coals and pyrite coal samples from Sebulu coal mine show mineral contents between is only observed in three samples (KTD-36, KTD-43 and KTD-38). 2.3 vol.% (TNT-33) and 5.6 vol.% (TNT-34). The mineral contents of Differences in the pyrite contents of coals from Centra Busang, Sebulu Centra Busang and Sebulu coals show a strong positive correlation to the and Embalut coal mines are reflected by the type of pyrite found (i.e. ash contents (r2 =0.96; Fig. 4). Unlike to the Centra Busang and Sebulu framboidal, euhedral, massive, anhedral, and epigenetic/syngenetic coals, mineral in the Embalut coals is dominated by clay minerals. pyrite in cleats and fractures). Carbonate, pyrite and quartz are found in small amounts. The mineral contents of Embalut coals vary from 0.30 to 2.0 (vol.%). Most of mineral contents are lower than 2 vol.%. The mineral contents (from micro- 4.2.1. Framboidal pyrite scopical analysis) of Embalut coal mine show a negative correlation to Framboidal forms of pyrite are categorized as syngenetic (Dai et al., the ash contents in the coals (r2 =0.05, Fig. 5). 2007). Some authors proposed that the type of this pyrite originates The studied coal samples from the Centra Busang and Sebulu coal from pyritization of sulfur bacteria (Casagrande et al., 1977; mines have relatively high total sulfur contents (up to 3.15 wt.%; Casagrande et al., 1980; Kortenski and Kostova, 1996; Lόpez-Buendía Table 1). Total sulfur contents show a positive correlation to the ash et al., 2007; Querol et al., 1989; Renton and Cecil, 1979). Kortenski and contents in the samples (r2 =0.67; Fig. 4). On the other hand, most Kostova (1996) also proposed the possibility of pyritization of other samples from the Embalut coal mine show very low total sulfur kinds of bacteria which might have coexisted along with the sulfur contents (≤0.2 wt.%). Sole exception is the coal sample KTD-38 from metabolizing bacteria and supported the decomposition and assim- Pulau Balang Formation with a total sulfur content of 1.41 wt.%. The ilation of the plant tissue. correlation of total sulfur to the ash contents in the Embalut coal mine Moreover, it has been suggested that framboidal pyrite might be also shows a positive correlation (r2 =0.84, Fig. 5). generated from mineral solutions in inorganic material (Dai et al., Iron (Fe) contents in the samples from the Centra Busang and Sebulu 2002, 2003; Kortenski and Kostova, 1996). Other theories (Wilkin and coal mines fall within the range of 0.17 to 1.51 wt.%. As shown in Table 1 Barnes, 1997) suggested for the formation of framboidal pyrite is in and Fig. 6, the iron (Fe) contents in the coal samples from Centra Busang first step the activity of biogenic processes i.e., pyritic fossilization of and Sebulu coal mines show a strong positive correlation to the pyrite bacterial colonies, and in a second step further growing of framboidal

Table 1 Ash yield, minerals (from microscopical analysis), total sulfur, pyrite (from microscopical analysis) and iron (Fe) contents in the studied coal samples.

Samples Seams Formations Coal mines Ash Mineral Total sulfur Pyrite Fe (wt.%, db) (vol.%) (wt.%, db) (vol.%) (wt.%)

KTD-42 21 Balikpapan Embalut 2.66 1.3 0.05 0.0 0.18 KTD-36 18 1.33 1.6 0.05 0.2 0.15 KTD-35 17 1.65 0.3 0.06 0.0 0.21 KTD-43 12 1.61 1.0 0.07 0.3 0.17 KTD-40 10 5.05 0.7 0.20 0.0 0.20 KTD-39 9 2.81 1.0 0.10 0.0 0.22 KTD-38 8 Pulau Balang 8.98 1.0 1.41 0.7 1.32 KTD-37 7 1.77 2.0 0.18 0.0 0.20 TNT-30 BL-4 Pulau Balang Centra Busang 3.50 3.7 3.15 3.0 1.15 TNT-31 BL-7.9 1.90 1.6 1.10 1.0 0.34 TNT-32 BL-7.10 1.40 0.7 0.14 0.4 0.17 TNT-33 ST Pulau Balang Sebulu 2.10 2.3 1.69 2.0 0.51 TNT-34 STU 5.80 5.6 2.92 4.3 1.51 156 S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162

Fig. 4. The variation and cross correlation of ash to the mineral matter, total sulfur, Fe and pyrite contents in the coal samples from Centra Busang and Sebulu coal mines. pyrite by organic processes, based on laboratory syntheses over a 30 appears as single bodies or solitary. In Embalut coal sample wide range of thermal conditions. Bacterial framboidal pyrite framboidal pyrite is not observed. preserves the independence of the separate globules even when they form aggregates (Kortenski and Kostova, 1996; Querol et al., 1989; Renton and Cecil, 1979). 4.2.2. Euhedral pyrite During peatification, syngenetic or early-diagenetic fine-crystal- Euhedral pyrite is recognizable as well shaped pyrite crystals line or fine-concretionary pyrite appears, commonly in the form of (Kortenski and Kostova, 1996). Querol et al. (1989) described euhedral framboids. pyrite in the coal samples from Maestrazgo Basin, northeastern Spain. The Centra Busang and Sebulu coal samples contain bacterial Kortenski and Kostova (1996) observed this type of pyrite in the coal framboidal pyrite in high abundance. An example is shown in sample samples from Bulgaria and divided euhedral pyrite into isolated and TNT-34 (Fig. 8a). In some samples such as TNT-30 from the Centra clustered varieties and isolated anhedral crystals and aggregates of Busang coal mine the primary framboidal pyrite shows an overgrowth euhedral crystals. Most of the euhedral pyrite is syngenetic and is by secondary pyrite which is generally associated with clay minerals generated during deposition of peat and/or during early humification. In (Fig. 8b). In most of the framboidal pyrite globules the crystals are general, the crystals of euhedral pyrite are small in size and intimately densely intergrown and consist of some aggregates as previously dispersed throughout the coal (Dai et al., 2007, 2008; Renton and Cecil, described by Skripchenko and Berberian (1975;inKortenski and 1979; Reyes-Navarro and Davis, 1976; Turner and Richardson, 2004). Kostova, 1996). Most of bacterial framboidal pyrite in the sample TNT- Isolated euhedral pyrite was found only in small amounts in sample

Fig. 5. The variation and cross correlation of ash to the mineral matter, total sulfur, Fe and pyrite contents in the coal samples from Embalut coal mine. S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162 157

Fig. 6. Cross correlation of the concentration ratios of Fe (wt.%) to the pyrite content (vol.%) and total sulfur (wt.%) in the coal samples from Centra Busang and Sebulu coal mines.

TNT-34 from Sebulu coal mine (Fig. 8c). Clustered euhedral pyrite could anhedral pyrite was divided into two types, the replacement anhedral not be detected in all analyzed samples. pyrite and the infilling anhedral pyrite (Kortenski and Kostova, 1996; Wiese and Fyfe, 1986), which are of late syngenetic and epigenetic origin, respectively. The anhedral pyrite in the sample from Centra 4.2.3. Massive pyrite Busang and Sebulu coal mines was found in small amounts. Massive pyrite is usually found as cleat-/cell-fillings, cementing or Replacement anhedral pyrite was deposited in the lumens of coating framboids, euhedral or detrital minerals (Querol et al., 1989). densinite maceral (Fig. 8f). The replacement anhedral pyrite was a Massive pyrite has also been found as a replacement of organic matter result of mineralization of cell wall and described to originate from in different macerals (Querol et al., 1989). Many authors denoted replacement of plant material or massive pyrite replacement of pyrite grains with irregular shapes and different sizes by the term organic matter (Kortenski and Kostova, 1996; Querol et al., 1989; massive pyrite (Dai and Chou, 2007; Grady, 1977; Kortenski and Wiese and Fyfe, 1986). Anhedral pyrite was not found in the Embalut Kostova, 1996; Wiese and Fyfe, 1986). Renton and Bird (1991) coal samples. described this type of pyrite as irregular. Massive pyrite was found in most coal samples from Centra Busang and Sebulu. The homogeneous massive pyrite was generally porous 4.2.5. Epigenetic pyrite in cleats and fractures and not compact, which is due to the inclusion of relict organic matter The term epigenetic pyrite in cleats and fractures is used for pyrite and clay minerals during the crystallization processes. Homogeneous deposited in fractures or cleats which determine the path of solutions massive pyrite was present in lenticular or irregular form. Fig. 8d and penetrating a coal seam. There are two types of epigenetic pyrite in e show the homogeneous massive pyrite in the coal samples of the cleat and fracture: infilling and replacing epigenetic pyrite. The Sebulu mine (sample TNT-34). This type of pyrite was not observed in infilling epigenetic pyrite in cleat and fracture has again been divided the Embalut coal samples. in two types: fracture and cleat filling (Kortenski and Kostova, 1996; Querol et al., 1989; Renton and Cecil, 1979). Epigenetic pyrite in cleats 4.2.4. Anhedral pyrite and fractures is observed only in a very small quantity in the studied Anhedral pyrite corresponds to pyrite forms whose shape depends coal samples. Infilling epigenetic pyrite in cleats and fractures was on the shape of the plant debris in which they were deposited. The observed in the Centra Busang coal samples (e.g., TNT-30, Fig. 8f). The

Fig. 7. Cross correlation of the concentration ratios of Fe (wt.%) to the pyrite content (vol.%) and total sulfur (wt.%) in the coal samples from Embalut coal mine. 158 S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162

Fig. 8. All photos taken under oil immersion. (a) Bacterial framboidal pyrite (Py) from the Sebulu coal mine (TNT-34), (b) overgrowth framboidal pyrite (Py) from the Centra Busang coal mine (TNT-30), (c) euhedral pyrite (Py) from the Sebulu coal mine (TNT-34), (d) massive pyrite (Py) from the Sebulu coal mine (TNT-34), (e) massive pyrite (Py) from Sebulu coal mine (TNT-34), (f) epigenetic pyrite (Py) in cleats/fractures and anhedral pyrite (Py) from the Sebulu coal mine (TNT-30), (g) replacing epigenetic pyrite (Py) in cleats/fractures from the Sebulu coal mine (TNT-30), (h) replacing epigenetic pyrite (Py) in fractures from Embalut coal mine (KTD-38) (i) and replacement massive pyrite (Py) from Embalut coal mine (sample KTD-38).

pyrite grains were deposited in the fractures and cleats of the coals formation (Casagrande et al., 1977, 1980; Dai et al., 2008; Demchuk, and are of epigenetic origin. Replacing epigenetic pyrite from Sebulu 1992; Taylor et al., 1998; Wiese and Fyfe, 1986). coal samples is shown in the Fig. 8g. The grains of pyrite replaced The amount and type of pyrite identified in the coals from Centra (filled) the cell lumens. Replacing epigenetic in fracture pyrite was Busang, Sebulu and Embalut differs significantly. In the Centra Busang also found in the Embalut coal samples (Fig. 8h). The pyrite from the and Sebulu coals both syngenetic and epigenetic pyrites appear. Embalut coal sample can be characterized as massive fracture filling Syngenetic framboidal pyrite is partly overgrown by epigenetic pyrite. pyrite with density-fill in the lumens or fractures (Fig. 8i). Typically, primary framboidal pyrite occurs in coals and carbonaceous shales overlain by marine strata (Taylor et al., 1998). In case of the Centra Busang and Sebulu coals, the high abundance of mineral might 4.3. Interpretation of coal depositional environment and the difference of originate from the erosion of Early Tertiary marine sediments of the pyrite in coals Central Kalimantan ridge (Fig. 9), delivering sufficient iron and sulphate for pyrite formation under subaquatic conditions (Fig. 9). It is Enrichment of minerals in coal suggests that the peat was assumed that the Centra Busang and Sebulu coals have been evolved deposited under topogenous conditions resulting in increased from a topogenous peat deposited under wet forest swamp conditions (richer) nutrient supply (minerals/detrital influx). In contrast, coals (Fig. 9). This interpretation is verified by the high proportion of ash, of low mineral content are generated in general from ombrogenous mineral, sulfur, pyrite and iron contents in the Centra Busang and peat bogs with low nutrient supply (minerals). Supply of mineral to Sebulu coals. the topogenous peat occurs preferentially by surface water and In the Embalut coals, pyrite is found only in epigenetic form ground water, while in ombrogenous peat bogs the supply takes place resulting from post depositional processes. The absence of framboidal through atmospheric deposition. Pyrite is sometimes the dominating pyrite is consistent with the formation of the coal from an inorganic matter present in the coal and the morphology of pyrite can ombrogenous peat. This type of peat receives the water through help to reconstruct the environmental condition during and after peat heavy rainfall and the groundwater table lying below the peat forming S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162 159

Fig. 9. Scheme of possible formation of paleo peat in the Centra Busang, Sebulu and Embalut coal mines with both topogenous and ombrogenous peat types in the Kutai Basin. surface. Ombrogenous peat occurs only in humid climates where the have K–Ar ages of 48–50± 1 Ma (Fuller et al., 1999; Pieter et al., annual rainfall is higher than the total yearly evaporation. Ombro- 1987). genous peats are not constrained by surface morphology, forming Today the Kutai Basin is the most important coal producing basin even on mountain summits with a high annual rainfall. Hall and in Kalimantan. Based on our investigation (proximate, ultimate and Nichols (2002) suggested that rainfall in Kalimantan is very high and trace element analyses) to some coal seams in the Kutai Basin (Loa the tropical weathering is very intense, as well as probably greater Janan, Kendisan, Loa Duri, Loa Ulung and Embalut coal mines), almost average heights and local relief early in the Neogene. Kalimantan all coal seams have very low sulfur and iron, as well as low pyrite receives a yearly rainfall of 2000 to 4000 mm distributed uniformly contents. throughout the year (Fig. 9). These conditions are favourable for However, the coals from Centra Busang and Sebulu coal mine ombrogenous peat formation. Formation of peats within East have higher sulfur and iron as well as pyrite contents compared to Kalimantan may be governed by the dynamics of the water table, as the coal deposits located east of Kalimantan. According to the demonstrated in Fig. 9. paleogeographic map of Kalimantan (Fig. 10), Centra Busang and Sebulu coal mines are located relatively close to the upper Kutai Basin. The Upper Kutai Basin is bordered with early Tertiary deep 4.4. Relation of paleogeography, geology and tectonic setting with the marine sediments, mafic igneous rock and melange in Central presence of mineral contents in the coal samples Kalimantan Ranges (according to geological map of Kalimantan). Therefore the increasing amount of ash, mineral, total sulfur, iron In order to gain information about the origin of mineral, sulfur and pyrite in the Centra Busang and Sebulu coals can be related to and iron (Fe) in the Kutai Basin (especially in Centra Busang and the highland Nyaan volcanic activity during the Tertiary or might be Sebulu coal mines), paleogeography, geology and tectonic events caused by the supply of sediments from early Tertiary deep marine have to be considered. The early Miocene to middle Miocene was a strata, mafic igneous rocks and melange from the Central Kaliman- period of major plate readjustments with the rotation of Kalimantan tan. In this case ground and surface water play a major role in the (from 20–20 Ma; Hall 1996, 1997). This resulted in the deformation transport of inorganic matter from the highland of Central and uplift of Kalimantan and a major influx of volcanogenic clastics Kalimantan to the lowland of the Kutai Basin (East Kalimantan). into the Kutai Basin from the uplifted terranes in the western part of Erosion in Kalimantan is also very high and implies that the crust the basin. Collision of microcontinental blocks with a significantly more than 6 km has been removed from the highest zone along the northwest Kalimantan margin (Palawan Trough) mountainous part of Kalimantan in the Neogene. Kalimantan was resulted in uplift that produced the Central Kalimantan Mountains surrounded by deep basins ready to receive sediment (Hall and (Clay et al., 2000). Nichols, 2002). Three suites of volcanic and intrusive rocks were recognised During the Miocene the depositional setting changed from within the Tertiary of Kalimantan: the Nyaan Volcanics, the Sintang extensive carbonate shelves to deltaic deposition and progradation Intrusive Suite, and the Metulang Volcanics (or Plateau Basalts). One occurred on the eastern side of Kalimantan, particularly in the of the igneous activities that occurred in the Kutai Basin is the felsic Tarakan–Muara and Barito Basins (Ahmad and Samuel, 1984; Moss Nyaan volcanism. The Nyaan Volcanics in the Uppper Kutai Basin and Wilson, 1998; Netherwood and Wight, 1992; van de Weerd and 160 S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162

Fig. 10. Paleogeographic map for 21 Ma, early Miocene and predicted situated of Centra Busang and Sebulu coals (modified from Moss and Wilson, 1998).

Armin, 1992). The predominance of deltaic sedimentation around 5. Conclusions the northern and eastern parts of Kalimantan (), particularly around the deep Kutai Basin, suggests that most of the major river Total sulfur content of Centra Busang and Sebulu coal mines were system were draining into these areas. Abundant detritus was positivelycorrelatedtoash,mineral,andiron(Fe)contentsinthecoal supplied from the uplift and denudation of the center of the island studied.Totalsulfurcontentwasgenerallyhighinthecoalsamples.Pyrite and coeval volcanism (Moss and Wilson, 1998; Moss et al., 1997; occurred in the Centra Busang and Sebulu coals as bacterial framboidal Tanean et al., 1996). pyrite and intergrown framboidal pyrite, euhedral pyrite, massive By the end of Miocene the drainage system within Kalimantan pyrite,anhedralpyriteandepigeneticpyriteincleatsandfractures.High Island was similar to the present day. The Mahakam delta had concentrationofpyritearguesfortheavailabilityofiron(Fe)inthecoal prograded to near its present day position by the late Miocene samples. On the other hand, most of sulfur contents of Embalut coal (Addison et al., 1983; Land and Jones, 1987) and siliciclastic samplesarelower(b1 wt.%) than Centra Busang and Sebulu coals. One marginal marine and deltaic deposition predominated in this area exceptionisthecoalsampleKTD-38withtotalsulfurcontentof1.41 wt.%. (Moss and Wilson, 1998). The Makassar Straits remained a deep IntheEmbalutcoalsamples,pyritewasobservedonlyasmassivepyrite water basin separating Sulawesi from Kalimantan, although as the andepigeneticpyriteincleatsandfractures. land area increased in eastern Kalimantan due to the progradation of Epigenetic and syngenetic pyrites were found in high quantities in deltas, the distance across this seaway was progressively reduced. coal samples. Epigenetic pyrite might be deposited by percolating S. Widodo et al. / International Journal of Coal Geology 81 (2010) 151–162 161 water into fractures, cavities and pores within the coal seam long after Grady, W.C., 1977. Microscopic varieties of pyrite in West Virginia coals. Transactions of Society of Mining Engineers. American Institute of Mining Engineers 262, initial accumulation of the peat. The reason for the rich ash, mineral, 268–274. total sulfur, iron (Fe) and pyrite contents of coals in the Kutai Basin Hall, R., 1996. Reconstructing Cenozoic SE Asia. In: Hall, R., Blundell, D.J. (Eds.), Tectonic (especially of Centra Busang and Sebulu coals) can be related to the evolution of Southeast Asia: Geological Society of London, special publication, vol. 106, pp. 153–184. Nyaan volcanic activity during Tertiary and/or to the supply of Hall, R., 1997. Conezoic plate tectonic reconstructions of SE Asia. In: Fraser, A., Matthews, Tertiary marine sediments, mafic igneous rocks and melange S., Murphy, R.W. (Eds.), Petroleum Geology of Southeast Asia: Geological Society of outcropping in the central of Kalimantan. Activities of ground and London, Special Publication, vol. 126, pp. 11–25. surface waters played also a major role and brought mineral into the Hall, R., Nichols, G., 2002. Cenozoic sedimentation and tectonics in Borneo: climatic influences on orogenesis. In: Jones, S.J., Frostick, L. (Eds.), Sediment Flux to Basins: mire of Centra Busang and Sebulu coals. Causes, Control and Consequences: Geological Society, London, Special Publication, vol. 191, pp. 5–22. Acknowledgements Hutchison, 1989. Geological evolution of South-east Asia. Oxford Monographs on Geology and Geophysics 13. Kortenski, J., Kostova, I., 1996. Occurrence and morphology of pyrite in Bulgarian coals. This study has been carried out within BIK-F. The first author (Sri International Journal of Coal Geology 29, 273–292. 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