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Short description of the Peruvian coal basins
International Journal of Coal Geology 58 (2004) 107 – 117 www.elsevier.com/locate/ijcoalgeo
Short description of the Peruvian coal basins Eitel R. Carrascal-Miranda a, Isabel Sua´rez-Ruiz b,* b
a UNI, Lima, Peru Instituto Nacional del Carbon (CSIC), Ap. Co., 73, 33080 Oviedo, Spain
Received 1 January 2003; accepted 27 May 2003
Abstract This work synthesizes the main general characteristics of the Peruvian Coal Basins in relation to age, coal facies and coal rank. Peruvian coals are located in a series of coal basins from the Paleozoic to the Cenozoic age. Paleozoic coal seams are mainly of Mississippian age (Carboniferous). They are of continental origin and their reduced thickness and ash content are their main characteristics. Mesozoic coal seams (Upper Jurassic – Lower Cretaceous) are located in the so-called Peruvian Western Basin and in the depressions close to the ‘‘Maran˜on Geoanticline’’. They were originated in deltaic facies under the influence of brackish and fresh waters. Some of these coal basins (those distributed in the central and northern parts of Peru) are relatively well known because they are of economic importance. Finally, Cenozoic coal seams (Tertiary) are found in both paralic and limnic basins and their reserves are limited. All the Peruvian coals are of humic character and are vitrinite-rich. Their rank is highly variable and normally related with the different orogenic events which strongly affected this region. Thus, Paleozoic and Mesozoic coals are of bituminous to anthracite/meta-anthracite coal rank while peats, lignite and subbituminous coals are found in Cenozoic basins. D 2004 Elsevier B.V. All rights reserved. Keywords: Peru; Coal; Coal basins; Paleozoic; Mesozoic; Cenozoic; Coal facies; Organic petrology
1. Introduction The Peruvian Andes Range contains a large number of coal basins which correspond to three successive geological ages: Upper Palaeozoic (Carboniferous), Upper Jurassic – Lower Cretaceous, and Tertiary. The present distribution of the coal basins is in the form of strips subparallel to the already known morphostructural units: Cordillera de la Costa, Llanuras Pre-Andinas, Cordillera Occidental, Franja de Volcanes, Franja Interandina, Cordillera Oriental, Franja Subandina, * Corresponding author. Tel.: +34-985-11-9090; fax: +34-98529-7662. E-mail address: [email protected] (I. Sua´rez-Ruiz). 0166-5162/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2003.05.004
and Llano Amazonico. The estimated coal potential of the different coal basins is about 1 Gt, the most important being those of the Mesozoic and Cenozoic (Tertiary) age. In general, there is very little information relating to Peruvian coals, coal facies, and sedimentary paleoenvironments. In the best of cases, information is limited to the sedimentary environment of the coalbearing formations. Thus, most bibliographic references are inventories of general or local coal resources (Agramonte, 1978; Siderperu´, 1980; Sa´nchez, 1985; Ministerio de Energı´a y Minas, 1990; Ingemmet, 1992; Carrascal Miranda et al., 2000), inventories of coal for specific coal mines (Weibenbach, 1986), or general geologic studies of different areas in which
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basins with coals are included (Pearson, 1981; Velez, 1994; Alleman, 1985; Ojeda Chavez and Mendoza, 1985; Agramonte, 1985). The most recent research work has been carried out by Dunı´n-Borkowski (1981, 1983, 1984, 1985, 1994), Medina (1991), Carrascal Miranda (1996), Carrascal Miranda et al. (1994a,b,c, 1997, 2000), and Carrascal Miranda and Sua´rez-Ruiz (1995a,b,c, 1997, 2002) who focused mainly on the distribution of coals and coal beds in the main Mesozoic and Tertiary basins. These works also provide some information related to the sedimentary environment or other features of coal seams such as composition and coal rank. Using geological, petrological, and geochemical studies of the most important coal seams from the Oyon, Santa, Alto Chicama (Mesozoic), and Yanacancha (Tertiary) Basins (which contain half of the known coal reserves in Peru), Carrascal Miranda (1996), defined the sedimentary environments in which the coals were generated. Carrascal Miranda et al. (2000) also synthesized the knowledge that exists about depositional paleoenvironments in relation with the other coal basins. Below is a brief description of the main coal basins of the Cenozoic, Mesozoic and Paleozoic age (Fig. 1 and Table 1).
2. Peruvian Coal Basins 2.1. Cenozoic coal fields Cenozoic coals (Dunı´n-Borkowski, 1981) are located in basins that developed mainly during the Lower – Upper Tertiary age. Most of these coals are lignites and their reserves are limited. 2.1.1. Loreto Basin Coal seams are concentrated in the Pebas Formation (Miocene) in the Loreto Basin (Peruvian Amazonia) located northeast of Peru (Fig. 1). They continue laterally into the Colombia and Brazil areas and form a part of the Llanura Amazo´nica (Amazonic Plain) which is made up of a thick sequence of Cenozoic molasse-type sediments that cover the Mesozoic rocks. The Pebas Formation is made up of lutites, clays, and lenticular levels of lignite (Palacios, 1994). These coal seams are thinner
(Steinmann, 1929), undeformed, and show high mineral matter content, especially pyrite. They are of humic type, the occurrence of mollusc fragments being common in the coal seams. The coal mainly derives from herbaceous vegetation in which ferns with palynomorphs such as Verrucatasporites, Psilatasporites, and fungal spores are predominant (Carrascal Miranda et al., 2000). The geological aspects, their petrographic composition, the content and the type of mineral matter, indicate that coals from the Loreto Basin (Table 1) originated in a marsh of estuary type influenced by brackish waters and under humid conditions in a paralic basin (Carrascal Miranda et al., 2000). These coals are peat and brown lignites, with high ash (18.0 –48.0%) and sulphur contents (0.5 – 8.0%). 2.1.2. Tumbes –Piura Basins Coals of the Cenozoic age are also found in the Mancora (Oligocene) and Zorritos (Miocene) Formations of the Tumbes Basin and in the Ostrea Formation (Middle Eocene) in the Piura Basin, both of which are located on the northwestern edge of Peru (Fig. 1). These formations are made up of a sequence of sandstones, lutites and coal beds (Palacios, 1994). Palynological data has shown that the Rhizopora bruguiera, Iriartites tumebezensis berry, Ficus winslowiana and ferns (Cruzado, 1985) were the vegetation which contributed to the formation of the coal deposits in these basins. Coals are lignites with a huminite reflectance lower than 0.30%. As in the case of the Loreto Basin, the coals also originated in an estuary paleoenvironment of a paralic basin (Table 1) under the influence of brackish waters and humid conditions. 2.1.3. Yanacancha Basin Finally, the Yanacancha Coal Basin (Lower – Middle Tertiary) is an intramontane basin in the north part of the Andes (Fig. 1). Its coal seams are in the Porculla Formation and their rank is subbituminous/ high volatile bituminous (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rez-Ruiz, 1995a,b; Carrascal Miranda et al., 1996a, 2000). The Porculla Formation unconformably overlies the folded sediments of the Upper Cretaceous age and reaches 150– 200 m thickness, representing the eastern edge of volcanism. The formation is made up of two mega-
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Fig. 1. Distribution of the coal basins in Peru (modified from Dunı´n-Borkowski, 1981; Medina, 1991).
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Table 1 Coal facies studies in Peru (by Carrascal Miranda, E.R. and Sua´rez-Ruiz, I.) Method
Depositional environment/ other comments
Age/area
ASTM rank
seam development, stratigraphy
continental depositional environments, limnic basins
Mississippian/ Paracas Basin and coal fields in the southern and central Peru (Ambo Group)
l.-an
seam development, stratigraphy
subsident coastal plains periodically covered by the sea level, paralic basin.
Callovian/Yura Basin (Yura Group)
hvb-san-an
Benavides (1956) Wilson (1963) Cobbing et al. (1981) Dunı´n-Borkowski (1984, 1985) Carrascal Miranda and Sua´rez-Ruiz (1995c) Carrascal Miranda et al., (1996a,b, 2000) Carrascal Miranda (1996)
seam development, stratigraphy, organic petrology, chemistry
littoral/deltaic to sedimentary paleoenvironment, coal seams in deltaic facies; humid conditions paralic basin.
Berriasian/Oyon Basin (Oyon Formation)
mvb-an
1.54 – 5.50
Benavides (1956) Gastan˜aga (1979) Dunı´n-Borkowski (1981) Carrascal Miranda (1996) Carrascal Miranda et al. (1996a, 2000)
seam development, stratigraphy, organic petrology, chemistry
deltaic sedimentary paleoenvironment, delta plain facies and deltaic/fluviatile basin
L. Valanginian and Tithonian – Berriasian/ Santa Basin (Chimu and Oyon Formations)
an-man
>4.1
Steppenbeck (1929) Benavides (1956) Wilson (1963) Escudero (1979) Agramonte (1985) Dunı´n-Borkowski (1981, 1985) Carrascal Miranda et al. (1994a,b,c, 1996a, 2000) Carrascal Miranda (1996)
seam development, stratigraphy, organic petrology, chemistry
deltaic sedimentary paleoenvironment, facies from lower delta plain, to upper delta plain, humid conditions, paralic basin.
L. Valanginian/Alto Chicama Basin (Chimu Formation)
an-man
>4.3
Mclaughlin (1921) Dunı´n-Borkowski (1983, 1984,1985) Carrascal Miranda and Sua´rez-Ruiz (1998) Carrascal Miranda et al. (2000)
seam development, stratigraphy, organic petrology, chemistry
deltaic – fluviatile environments, delta plain facies in transition to fluviatile facies, humid conditions, probably paralic basin
Neocomian/Jatunhuasi Basin (Goyllarisquizga Group)
hvb-an
0.5 – 2.55
seam development, stratigraphy
deltaic paleoenvironments close to the shoreline, humid conditions, probably paralic basin
Neocomian/Goyllarisquizga Basin (Goyllarisquizga Group)
sb
Author
Paleozoic coal basins Broggi (1927) Steinmann (1929) Rassmuss (1947) Newell et al. (1953) Carrascal Miranda et al. (2000) Mesozoic coal basins Benavides (1962) Marocco and del Pino (1966) Wilson et al. (1967) Guevara (1969) Pecho (1981) Dunı´n-Borkowski (1985) Carrascal Miranda et al. (2000)
Mesozoic coal basins Page (1960) Wilson (1963) Dunı´n-Borkowski (1983, 1984,1985) Carrascal Miranda et al. (2000)
Reflectance (%)
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Table 1 (continued) Author
Method
Depositional environment/ other comments
Age/area
ASTM rank
Reflectance (%)
seam development, stratigraphy, organic petrology, palynology
estuary influenced by brackish waters, humid conditions,
Oligocene – Miocene/ Tumbes Basin (Mancora and Zorritos Formations); M. Eocene/Piura Basin (Ostrea Formation)
l.
0.25 – 0.30
Dunı´n-Borkowski (1981) Casten˜eda (1991) Carrascal Miranda (1996) Carrascal Miranda et al. (1996a) Carrascal Miranda and Suarez-Ruiz (1995a,b, 1997)
seam development, stratigraphy, organic petrology, chemistry
paralic basins peat swamps under humid conditions, in fluviatile – lacustrine environments, limnic basin
L. – M. Tertiary/Yanacancha Basin (Porculla Formation)
sb/hvb
0.5 – 0.6
Steinmann (1929) Palacios (1994) Carrascal Miranda et al. (2000)
seam development, stratigraphy, organic petrology, palynology
estuary influenced by brackish waters, humid conditions, paralic basin
Miocene/Loreto Basin (Pebas Formation)
peat – l.
0.17 (punctual data)
Cenozoic coal basins Cruzado (1985) Palacios (1994)
sequences of reworked pyroclastic material, tuffs, breccias of andesitic, rhyolitic, and dacitic composition. In the middle of this stratigraphic series and in the first sequence, this reworked material is interbedded with thin sandstone levels, siltstones, clays, lutites, and conglomerates that fill up the channels. All of this is covered by tuffs which grade into siltstones, lutites, and coal beds constituting a coal unit of 8 m thickness. A second sequence of pyroclastic and detrital material without coal lies on top of the previous sequence. The coal unit represents a depositional environment of a shallow fluviatile – lacustrine floodplain of fresh water in which the lime and clay sediments represent the flood plains (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rezRuiz, 1995a,b, 1997; Carrascal Miranda et al., 1996a, 2000). The coals are of humic type, and the organic material derives from herbaceous vegetation and woody trunks (trees). The principal (main) coal seam in this basin was generated in a swamp in which humid conditions predominated. The corresponding facies are of limnic type influenced by fresh water (Table 1). The coal rank (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rez-Ruiz, 1995a,b, 1997; Carrascal Miranda et al., 1996a), which increases in the vicinity of the fault structures, is from subbituminous to high volatile bituminous (vitrinite reflectance 0.5 –0.6%).
2.2. Mesozoic coal fields Mesozoic coals originated in the subbasins of the ‘‘Peruvian West Basin’’ and also in the depressions close to the ‘‘Maran˜on Geoanticline’’ (Fig. 1) during the short emergence periods that occurred in the Upper Jurassic and Lower Cretaceous (Dunı´n-Borkowski, 1981). The development of the Peruvian West Basin occurred from the south (Yura area of the Callovian age) towards the north of Peru (Goyllarisquizga Group of the Neocomian age). Thus, according to Escudero (1976), the oldest coals are those of the Yura Basin (Carumas area, Fig. 1), while the youngest coals (Aptian) are located north of Peru in the Farrat Formation (Petersen, 1975). However, the most important Mesozoic coal basins are those distributed in the central and northern parts of Peru (Fig. 1) in the Peruvian West Basin such as the Chiclayo, Cajamarca, Alto Chicama, Santa, Alto Pativilca, and Oyon Basins. The few coal deposits found in the local depressions of the Maran˜on Geoanticline (Central Peru, Fig. 1) are concentrated in the Goyllarisquizga and Jatunhuasi Basins (Petersen, 1975). The stratigraphic sequences of the Peruvian West Basin are different from those of the Maran˜on Geoanticline. The former are thicker, well defined (Wilson, 1963), and contain the most important coal deposits from a commercial point of view. Those of the Maran˜on
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Geoanticline are irregular, isolated (Petersen, 1975), and of reduced size. In general, Mesozoic coals were originated in deltaic facies (Table 1) under the influence of both fresh and brackish waters as part of a major delta, whose materials derive from the Maran˜on Geoanticline and the Brazil and Guiana Shields. The rank of Mesozoic coals varies from bituminous to anthracite and meta-anthracite coals (Dunı´n-Borkowski, 1981; Carrascal Miranda, 1996; Carrascal Miranda et al., 2000), in agreement with their relative location in the above-mentioned strips and their proximity to the major thermal events. 2.2.1. Jatunhuasi Basin The Jatunhuasi and Goyllarisquizga Basins are small coal deposits located in the depressions near the Maran˜on Geoanticline (Fig. 1). In the Jatunhuasi Basin, the representative sedimentary sequence is the Goyllarisquizga group (Neocomian age) which is made up of white and yellow quartzitic sandstones interbedded with dark lutites and relatively continuous coal seams of variable thickness (Mclaughlin, 1921). This basin was also deformed by the Andean Orogeny. Coals show a relatively high ash content but lower than in the case of the Goyllarisquizga coals. On the other hand, the high sulphur content is characteristic (4 – 5%). From a petrographic analysis (Pearson, 1981; Carrascal Miranda and Sua´rez-Ruiz, 1998; Carrascal Miranda et al., 2000), a variable rank from bituminous to semianthracite and anthracite was established for these coals with vitrinite reflectance values ranging between 0.57% and 2.51%. The more evolved coals are those located near the magmatic intrusive bodies (Fig. 1). Coals are of autochthonous/alochthonous character (Carrascal Miranda and Sua´rez-Ruiz, 1998; Carrascal Miranda et al., 2000) and their organic fraction mainly derive from ligneous material as well as from shrubby and herbaceous vegetation. The coals were generated in delta plain environments in transition to fluviatile facies under humid paleoclimatic conditions (Table 1). The basin was probably a paralic basin (Carrascal Miranda et al., 2000). 2.2.2. Goyllarisquizga Basin The Goyllarisquizga Coal Basin was subjected to different Andean Orogeny phases and, thus, it is very faulted and deformed. The coal seams are found in
two coal bearing series in the basal part of the Goyllarisquizga Group (Neocomian age), the formation representative of this basin. This group is about 500 m thick and is made up of sandstones, coal seams, interbedded with volcanic material, clays and calcareous sandstones (Page, 1960). In general, the coal seams are of lenticular shape and reach a thickness of up to 3 m. They laterally change into coal shales and coal lutites. Thus, their ash content is high and variable and can reach 60% (Carrascal Miranda et al., 2000). In addition, these coals show high sulphur (mainly pyrite) content (3%). Although there has been some controversy concerning the coal rank (Broggi, 1927; Page, 1960), petrographic data and chemical analysis results suggest a subbituminous coal rank for the Goyllarisquizga coals. The coal seams are of autochthonous character and they were generated in a deltaic paleoenvironment (Wilson, 1963) close to the shoreline in a paralic basin under humid paleoclimatic conditions (Table 1). At the regional level (Fig. 1), this basin correlates with the Jatunhuasi Basin and both basins contain the less evolved coals of Mesozoic age (Carrascal Miranda et al., 2000). 2.2.3. Alto Chicama, Santa and Oyon Basins These three basins are known for their vast coal reserves of commercial value. They are located in the central and northern parts of Peru (Fig. 1). In addition, their coal seams, the most important of the Mesozoic age, are mainly concentrated in two formations: the Oyon (Tithonian – Berriasian age) and the Chimu Formations (Lower Valanginian age), the latter belonging to the Goyllarisquizga Group (Lower Cretaceous: Valanginian –Aptian time). Previous geological studies carried out on these basins are scarce and of general character such as those of Steppenbeck (1929), Steinmann (1929), Benavides (1956), Cossio (1964), Cossio and Jae´n (1967); Wilson (1963), Wilson et al. (1967), Cobbing (1973), Cobbing et al. (1981), and those mentioned above: Dunı´n-Borkowski (1981, 1983, 1984, 1985), Medina (1991), Carrascal Miranda (1996) and Carrascal Miranda et al. (1994a,b,c, 1997, 2000), Carrascal Miranda and Sua´rez-Ruiz (1995c). Benavides (1956), in his stratigraphic study of the formations found in the Oyon, Santa and Alto Chicama areas (Fig. 1), pointed out that the units are
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made up of a sedimentary sequence in which the Oyon and Chicama Formations (Upper Jurassic) are a substratum. Thus, the Chicama Formation (Tithonian) in the centre and the north of Peru represents marine facies (Wilson, 1963). The Oyon Formation (Berriasian) is partially equivalent to the Chicama Formation, with the difference that the latter is made up of siltstones, sandstones, and in addition contains coal beds. It represents the coal-bearing series for the Oyon Basin and is one of the coal-bearing series for the Santa Basin (Fig. 1). The Oyon Formation is made up of marine and continental facies (Wilson, 1963) originated in sedimentary environments which evolved from littoral to deltaic facies and finally to a floodplain facies. Moreover, the Oyon Formation could be laterally equivalent to the lowest part of the Chimu Formation located north of Peru (Cobbing et al., 1981). Above the Chicama and Oyon Formations is the Goyllarisquizga Group (Lower Cretaceous) made up of the Chimu (Lower Valanginian), Santa (Upper Valanginian), Carhuaz (Hauterivian – Aptian) and Farrat (Upper Aptian) Formations. Only the Chimu Formation has significant coal seams which can be identified in the Santa and Alto Chicama Basins (Fig. 1). The Chimu Formation has been described by Steppenbeck (1929) and Benavides (1956), and its coal seams studied by Carrascal Miranda et al. (1996a,b). This Formation is made up of orthoquartzites, siltstones, sandstones, shales and coal beds. It originated in continental – coastal environments in which deltaic facies predominated (Wilson, 1963; Kopex-Minero Peru´, 1975; Escudero, 1979; Cobbing et al., 1981; Dunı´n-Borkowski, 1984; Carrascal Miranda, 1996). The coal seams represent deltaic and transition deltaic/coastal environments (Carrascal Miranda, 1996). The Santa Formation, without coal, corresponds to a shallow marine environment. The Carhuaz Formation in the Alto Chicama Basin contains small coal intercalations of lenticular morphology (Kopex-Minero Peru´, 1975). This Formation also seems to have originated in a deltaic environment with sporadic marine invasions (Benavides, 1956; Wilson, 1963; Cobbing et al., 1981). The Farrat Formation in the Alto Chicama Basin also has a few thin coal beds (Escudero, 1979) generated in a delta sedimentary environment.
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Above the Goyllarisquizga Group are the Calcareous formations. They are representative of the Middle – Upper Cretaceous. These formations include the Inca (Lower Albian), Pariahuanca (Lower Albian), Chulec (Middle Albian), Pariatambo (Middle – Upper Albian), Jumasha (Cenomanian – Turonian), Celendı´n (Upper Turonian – Coniacian), Casapalca (probably Santonian), and Huaylas (probably Santonian), without coal. They originated in sedimentary environments from shallow marine, neritic marine, and euxinic marine to continental clastic deposits. On top of these Calcareous Formations are the volcanic materials of the Calipuy Group described in this part of Peru by Cossio (1964), and assigned to the Lower –Middle Tertiary by Cobbing et al. (1981). These materials discordantly cover all of the Cretaceous series. 2.2.3.1. Alto Chicama Basin. In this basin are 16 coal levels which are not very persistent laterally (they do not appear in all the coal fields) with a variable thickness which can reach up to 4 m. These coal seams are concentrated in two coal-bearing series of the Chimu Formation that are also controlled by tectonic structures of great development. As in the case of the other Mesozoic coal basins, there are several coal fields being commercially exploited. Petrographic and chemical data (Carrascal Miranda, 1996; Carrascal Miranda et al., 1994a,b,c, 1996a, 2000) suggest that the coals are of humic type and of high rank (anthracites and meta-anthracites, vitrinite reflectance >4.5%) generated in a paralic basin from the same type of vegetation as in the case of that of the Oyon and Santa Basins, in a deltaic sedimentary paleoenvironment (Table 1). The sedimentary facies were transitional from the lower delta plain to upper delta plain influenced by both fresh and brackish waters. Two aspects are important in this basin: the structures of ball coals found in two of the coal seams (Lipiarski and Szyminiak, 1977; Hower and Fishel, 1990) which seem to be related to the tectonic activity (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rez-Ruiz, 2002) promoted by the Andean Orogeny in this basin and the high (14 – 24%) sulphur content (mainly elemental sulphur) found in the coals from the Shulcahuanca and Callacuyan coal fields (Southeastern Peru, Fig. 1) which are of a thermogenetic nature
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due to the fluids from the magmatic activity (Carrascal Miranda, 1996). 2.2.3.2. Santa Basin. In this basin and lying on top of the Chicama Formation are the same sedimentary formations (Lower and Upper Cretaceous age) as in the Oyon area. There are two coal-bearing series in the Santa Basin. The first, with a thickness of 250 m, is located in the Oyon Formation (Tithonian – Berriasian age), while the second which can reach up to 500 m is found in the Chimu Formation (Lower Valanginian age). As in the case of the Oyon and Alto Chicama Basins, the coal seams are controlled by tectonic structures. Therefore, their thickness and lateral continuity is highly variable. Coals from this basin are evolved (Carrascal Miranda, 1996; Carrascal Miranda et al., 1996a, 2000), showing anthracitic and metaanthracitic coal rank (vitrinite reflectance values >4.11%) which is a consequence of the metamorphism of regional character that affected the Santa Basin. All the coals are of a humic type, mainly composed of vitrinitic macerals. The mineral matter content is variable (ash contents between 4.0% and 30.0%) with very low sulphur percentages ( < 1.0%). These coals were generated in a sedimentary environment typical of a delta plain influenced by fresh and brackish waters under humid conditions in a paralic basin (Table 1). 2.2.3.3. Oyon Basin. In the Oyon Basin (Fig. 1), the aforementioned clastic and calcareous formations (Lower and Upper Cretaceous) can be found. The general stratigraphic sequence is deformed and unconformably covered by the Calipuy Group (Lower – Middle Tertiary). The coal seams, interbedded with lutites and sandstones, are located in the 400– 500 m thick Oyon Formation (Tithonian – Berriasian age). The lenticular coal seams show a variable thickness. Petrographic and chemical data (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rez-Ruiz, 1995c; Carrascal Miranda et al., 1996a,b, 2000) have shown a coal rank which varies from medium volatile bituminous coals to meta-anthracite (vitrinite reflectance from 1.54% to 5.50%) in the different coal fields. The coals are also of a humic type (mainly composed of the vitrinite maceral group), with an organic fraction derived from trees, shrub, and herbaceous materials. Their mineral content is variable (ash content between
10.0% and 34.0%) and the total sulphur percentages are relatively low (< 1.85%). The coals were generated in deltaic environments (Table 1) in which the humid paleoclimatic conditions contributed to the development of marshy facies in a typical paralic basin. 2.2.4. Yura Basin The coal potential of the Callovian Yura Basin (Fig. 1) is of little economic value. The coal seams are thinner (< 1 m) and of lenticular shape. They are found in the Labra, Gramadal, and Hualhuani Formations near Arequipa and in equivalent formations in other areas of South Peru (Dunı´n-Borkowski, 1985). The coal deposits are of humic type and of autochthonous/alochthonous origin (Carrascal Miranda et al., 2000). The sedimentary paleoenvironments (Table 1) were subsident coastal plains that were periodically covered by the sea (Dunı´n-Borkowski, 1985). Chemical data show that coals from the Yura Basin are bituminous, semianthracite, and anthracite rank. The higher rank coals are located near intrusive rocks such as the Coast Batholith. 2.2.5. Other coal basins Other Mesozoic coal fields are found in the Cajamarca, Chiclayo, Alto Pativilca, and Oriente Group Basins. However, these basins are almost unknown and information about them is very scarce. Thus, specific data about their coal facies or the sedimentary paleoenvironments of the coal seams are nonexistent. 2.2.5.1. Cajamarca Basin. Five coal seams of variable thickness (0.8 – 2.0 m) and located in the Chimu Formation are described for the Cajamarca Basin. Their coal rank is also variable, from bituminous to anthracite (Medina, 1991), and their ash and sulphur contents are relatively low (>12% and 1.2%, respectively). 2.2.5.2. Chiclayo Basin. Some isolated and sporadic outcrops of coals are found in this basin. They are also located in the Chimu Formation as well as in San Pedro Formation (Valanginian age). They are of anthracitic coal rank (Medina, 1991) and their coal facies and economical potential are unknown.
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2.2.5.3. Alto Pativilca Basin. This basin represents a transition between the Chicama Formation of marine nature and the Oyon Formation of continental origin (Carrascal Miranda et al., 2000). No information about the coals is reported. It is only known that the coal seams are of reduced thickness. 2.2.5.4. Oriente Group Basin. In the Sub-Andean region (Amazonas –San Martin) is the Oriente Group Basin (Fig. 1). Coal seams are located (Medina, 1991) in the Cushabatay Formation (Neocomian age) which is contemporary to the Goyllarisquizga group (Dunı´nBorkowski, 1985). The coal seams in this formation are thin (Valdivia, 1966; Soto, 1979) and their coal rank is from bituminous to anthracite, particularly in northern Peru. No data about the sedimentary paleoenvironment of these coal deposits are reported in the bibliography. 2.3. Palaeozoic coal fields Paleozoic coal fields are located in the Eastern Range (Cordillera Oriental) in the southern and central parts of Peru (Fig. 1). Other minor coal fields are found in small basins of the Paracas (South of Lima) coastal area (Fig. 1). For all the basins, the coalbearing formation is the Mississippian Ambo Group (Newell et al., 1953), which is made up of sandstones, conglomerates, coal shales, and thin coal levels with a lenticular shape and high ash content (until 60%). The number of these coal levels is in general small. However, in the coastal area of Paracas, the Ambo Group shows a large number (8) of coal seams (Rassmuss, 1947). The Paleozoic coal resources are reduced because of the thinner and discontinuous character of its coal seams which in addition, laterally change into coal shales and coal lutites. The scarce bibliographic references to the coal rank of these Paleozoic coals suggest a variable rank from anthracite (in Huanuco, Cerro de Pasco and Puno areas) to bituminous (Madre de Dios and Puno areas), subbituminous (Paracas), and lignite (Madre de Dios and Titicaca Lake areas) from the central to the southeastern part of Peru (Fig. 1). In general, Paleozoic coals are of humic type and they were generated in limnic basins (Steinmann, 1929). Various authors (Table 1) suggest a depositional environment of continental type for the coal-bearing Ambo Group.
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References Agramonte, J., 1978. Inventario preliminar del carbo´n en el Peru´. Ministerio de Energı´a y Minas, Lima, Peru´, 85 pp. Agramonte, J., 1985. Geologı´a del Sector Sureste de la Cuenca carbonı´fera de Alto Chicama. Primer Simposium Nacional del Carbo´n. UNI, Lima, Peru´, 11 pp. Alleman, V., 1985. Paleontologı´a de los carbones paleozoicos peruanos. Primer Symposium Nacional del Carbo´n. UNI, Lima, Peru´, 12 pp. Benavides, C.V., 1956. Cretaceous system in Northern Peru. Am. Mus. Nat. Hist. Bull. New York. USA 108, 491 – 552. Benavides, C.V., 1962. Estratigrafia pre-Terciaria de la regio´n de Arequipa. Bol. Soc. Geol. Peru 38, 5 – 37. Broggi, J., 1927. La industria carbonera en el centro del Peru´. Sintesis de la Minerı´a Peruana en el Centenario de Ayacucho, vol. 2 Pt. 2. Ministerio de Fomento, Lima, pp. 1 – 93. Carrascal Miranda, E.R., 1996. Caracterizacio´n y estudio de los carbones de las Cuencas de Oyo´n, Santa, Alto Chicama y Yanacancha de Peru´. PhD Thesis. University of Oviedo, Spain, 411 pp. Carrascal Miranda, E.R., Sua´rez-Ruiz, I., 1995a. Petrographical and geochemical study of the ‘‘Principal’’ coal seam, Yanacancha Basin (Tertiary) of Peru. In: Pajares, J.A., Tascon, J.M.D. (Eds.), Coal Science and Technology, 24. Coal Science, vol. 1. Elsevier, Amsterdam, pp. 211 – 215. Carrascal Miranda, E.R., Sua´rez-Ruiz, I., 1995b. Geologı´a, petrologı´a y geoquı´mica de los carbones de la Cuenca Intramontan˜osa de Yanacancha (Terciario)—Peru´. Bol. Soc. Geol. Peru´, 47 – 67 (Vol. Especial Jubilar Alberto Benavides). Carrascal Miranda, E.R., Sua´rez-Ruiz, I., 1995c. Rank distribution of coals from the Oyon basin (Upper Jurassic) of Peru. 47th Annual Meeting of the ICCP, Poland. ICCP News, vol. 12, pp. 11 – 12. Carrascal Miranda, E.R., Sua´rez-Ruiz, I., 1997. Composition, depositional environment and rank distribution of Porculla Formation Coals in Yanacancha Basin (Peru). 49th Annual Meeting of the ICCP, New Zealand. ICCP News, vol. 16, 13. Carrascal Miranda, E.R., Sua´rez-Ruiz, I., 1998. Caracterı´sticas petrogra´ficas de los carbones Mesozoicos del centro y norte del Peru´. Anales del I Congreso Panamericano de Minerı´a, Lima, 11 pp. Carrascal Miranda, E.R., Sua´rez-Ruiz, I., 2002. Las estructuras geome´tricas en ‘‘bolas de carbo´n’’ en algunas capas de la Formacio´n Chimu´ en la Cuenca de Alto Chicama (Peru´). Hipo´tesis sobre su origen y formacio´n. XI Congreso Peruano de Geologı´a Geologı´a Regional, Estratigrafı´a y Tecto´nica. Trabajo 7. Lima, Peru´, 13 pp. Carrascal Miranda, E.R., Martı´nez-Tarazona, M.R., Rodrı´guez Moinelo, S., Prado, J.G., Sua´rez-Ruiz, I., 1994a. Etude pre´liminaire des anthracites et meta-anthracites des secteurs NW et SE du Bassin Pe´ruvien Alto Chicama (Cre´tace´ Infe´rieur). Bull. Cent. Rech. Explor. Prod. Elf-Aquitaine, Mem. (BCREDP), Spe´cial Publ. 18, 63 – 67. Carrascal Miranda, E.R., Martı´nez, L., Sua´rez-Ruiz, I., 1994b. Estudio por microscopı´a o´ptica y electro´nica de los carbones de la Cuenca Alto Chicama (Creta´cico Inferior)—Peru´. VIII Peruano
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de Geologı´a. Resu´menes extendidos. Sociedad Geolo´gica del Peru´. Pub. Espec., Lima, Peru´, pp. 58 – 62. Carrascal Miranda, E.R., Martı´nez Tarazona, M.R., Sua´rez-Ruiz, I., 1994c. Caracterizacio´n quı´mica y ana´lisis de la materia mineral de la Cuenca Alto Chicama—Peru´. VIII Peruano de Geologı´a. Resu´menes extendidos. Sociedad Geolo´gica del Peru´. Pub. Espec., Lima, Peru´, pp. 55 – 58. Carrascal Miranda, E.R., Sua´rez-Ruiz, I., Martı´nez, L. 1996a. Distribution du rang des charbons des principaux bassins houilliers du Perou. 16e`me Re´union des Sciences de la Terre. Resumes des Communications, Chap. Du sol au se´diment, Symposium 12, Evolution de la matie`re organique, cycles (bio-) ge´ochimiques, diage`nese thermique. Orle´ans, Francia, 122. Carrascal Miranda, E.R., Sua´rez-Ruiz, I., Martı´nez, L., 1996b. Analysis of the evolution and rank distribution of coals from the Oyon Basin (Upper Jurassic) of Peru. Geogaceta 20/3, 651 – 653. Carrascal Miranda, E.R., Sua´rez-Ruiz, I., Martı´nez-Tarazona, M.R., 1997. Mineral matter and trace elements distribution in Mesozoic coals from Peru. In: Ziegler, A., van Heek, K.H., Klein, J., Wanzl, W. (Eds.), Proceedings of the 9th International Conference on Coal Science. ICCS´97 Essen, Germany. vol. 1, pp. 413 – 416. Carrascal Miranda, E.R., Matos Avalos, C., Silva Campos, O., 2000. Carbo´n en el Peru´. Ingemmet. Ser. B, Geol. Econ. Lima, Peru 7, 150 pp. Casten˜eda, J., 1991. Carbo´n Yanacancha. Exploracio´n y resultados. Informe Interno Compan˜´ıa Adminco Exploraciones, Lima. Peru´, 15 pp. Cobbing, J., 1973. Geologı´a de los cuadra´ngulos de Barranca, Ambar, Oyo´n, Huacho, Huaral y Canta. Bol. Serv. Geol. Minas, Lima. Peru´ 26, 172 pp. Cobbing, J., Pitcher, W., Wilson, J., Baldock, J., Taylor, W., McCourt, W., Snelling, N.S., 1981. Estudio geolo´gico de la Cordillera Occidental del Norte de Peru´. INGEMMET, Bol. Lima, Peru´ 10/D, 252 pp. Cossio, A., 1964. Geologı´a de los cuadra´ngulos de Santiago de Chuco y Santa Rosa. Bol.-Com. Carta Geol. Nac. Peru´ 8, 69 pp. Cossio, A., Jae´n, H., 1967. Geologı´a de los cuadra´ngulos de Puemape, Chocope, Otuzco, Trujillo, Salaverry y Santa. Bol. Serv. Geol. Minas, Lima. Peru´ 17, 141 pp. Cruzado, J., 1985. Lignitos en Formaciones Terciarias del Peru´. Primer Symposium Nacional del Carbo´n. FIGMM-UNI. Lima, Peru´, 18 pp. Dunı´n-Borkowski, E., 1981. Los carbones en el Peru´: posibilidades de su explotacio´n. Bol. Soc. Geol. Peru´ 68, 32 – 52. Dunı´n-Borkowski, E., 1983. Ensayo preliminar sobre el carbo´n del grupo Goyllarisquizga (facies Meridionales y Orientales). Bol. Soc. Geol. Peru´ 70, 13 – 24. Dunı´n-Borkowski, E., 1984. Ensayo preliminar sobre el carbo´n del grupo Goyllarisquizga (facies Occidentales). Bol. Soc. Geol. Peru´ 73, 15 – 55. Dunı´n-Borkowski, E., 1985. Los carbones Mesozoicos del Peru´. Bol. Soc. Geol. Peru´ 75, 65 – 71. Dunı´n-Borkowski, E., 1994. El Geosinclinal Andino en los departamentos de La Libertad y de Cajamarca (parte Sur) entre el
Jura´sico y el Albiano Inferior. VIII Congreso Peruano Geologia, Lima, Peru, pp. 174 – 178. Escudero, J., 1976. Reservas carbonı´feras Peruanas. Usos del carbo´n en siderurgia, abastecimientos y tecnologı´as. ILAFA, Santiago de Chile, pp. 91 – 96. Escudero, J., 1979. El carbo´n del Alto Chicama. Bol. Ing., Lima. Peru´ B/2, 79 pp. Gastan˜aga, A., 1979. Fuentes de carbo´n mineral en el Peru. Conversatorio. ‘‘Perspertivas de reduccio´n directa en el Peru’’, 35 – 62. Guevara, C., 1969. Geologı´a del cuadra´ngulo de Characato (hoja 33t). Bol. Serv. Geol. Minas 23, 53 pp. Hower, J.C., Fishel, K.W., 1990. Anisotropy of coal reflectance. An example from the na 5 seam (‘‘Bollas’’) meta-anthracite, Peru. Soc. Org. Petrol. Newsl. 7/3, 10 – 11. Ingemmet, 1992. Evaluacio´n de reservas carbonı´feras. Cuenca de Santa. Programa Carbole´ctrica Rı´o Santa. Info. Inter. Ine´d. Electroperu´. Kopex-Minero Peru´, K.W., 1975. Estudio geolo´gico de los yacimientos de carbones minerales. Zona Coina – Callacuya´n. Cuenca del Alto Chicama. Katowice y Lima (Inf. Ine´dito) 1/2, 240 pp. Lipiarski, I., Szyminiak, R., 1977. Balls Coal from Alto Chicama. Peru. Ann. Soc. Geol. Pol. XLVII-3, 451 – 458. Marocco, R., del Pino, M., 1966. Geologı´a del cuadra´ngulo de Ichun˜a. Bol.-Com. Carta Geol. Nac. 14, 57 pp. Mclaughlin, D.H., 1921. Yacimiento de carbon de Oyo´n. Cerro de pasco Corporation, Lima. 34 pp., A.T. Ingemmet A0585. Medina, H., 1991. Cuencas Carbonı´feras en el Peru´ y mapa geolo´gico catastral por tipos de carbo´n. Anal. VII Congreso Peruano Geologia, Lima, Peru´, pp. 643 – 647. Ministerio de Energı´a y Minas, H., 1990. Reservas Carbonı´feras de Peru´Inf. Inern. Ine´d. Oficina Nacional de Planificacio´n, Lima, Peru´. Newell, N.D., Chronic, J., Roberts, T., 1953. Upper Paleozoic of Peru. Mem.-Geol. Soc. Am. 58, 276 pp. Ojeda Chavez, M.J., Mendoza, A., 1985. Distribucio´n de elementos traza en carbones peruanos. Primer Symposium Nacional del Carbo´n. UNI, Lima, Peru´, 26 pp. Page, J.S., 1960. Geologı´a del carbon. Convencio´n de Ingenieros de Minas del Peru´, Lima, vol. 6. Anales, Instituto Ingenieros de Minas, Lima, pp. 8 – 21. Palacios, O., 1994. Geologı´a de los cuadra´ngulos de paita, Piura, talara, Sullana, Lobitos, Quebrada, Seca, Zorritos, Tumbes, Zarumilla. Bol.-Inst. Geol. Min. Metal., Ser. A Carta Geol. Nac. 54, 190 pp. Pearson, D.E., 1981. Report to the United Nations Revolving Fund For Natural Resources Exploration on a Coal Mission to Peru´. Victoria, Canada. Infor. Int., 12 pp. Pecho, G., 1981. Geologı´a de los cuadra´ngulos de Chalhuanca, Antabamba y Santo Toma´s (hojas 29-p, 29-q y 29-r). Bol.-Inst. Geol. Min. Metal., Ser. A Carta Geol. Nac. 35, 94 pp. Petersen, R., 1975. Coal resources of Peru. Geol. Am. Spec. Pap. 179, 35 – 42. Rassmuss, J., 1947. La Perforacio´n por Carbo´n en Paracas. Cuerpo de Ingenieros de Minas, Lima. 4 pp. (A.T. Ingemmet A0562). Sa´nchez, A., 1985. Reservas carbonı´feras de Peru´. Inf. Inter. Ine´d. Ministerio de Energı´a y Minas, Lima, Peru´.
E.R. Carrascal-Miranda, I. Sua´rez-Ruiz / International Journal of Coal Geology 58 (2004) 107–117 Siderperu´, J., 1980. Proyecto carbonı´fero de Oyo´n. Inform. Interno Ined. Empresa Sideru´rgica de Peru´, 20 pp. Soto, F., 1979. Facies y ambientes deposicionales Creta´cicos. Area centro-sur de la Cuenca de Maran˜o´n. Bol. Soc. Geol. Peru´ 60, 223 – 250. Steinmann, G., 1929. Geologı´a del Peru´. Carl Winters Universitatsbuchhandlung, Heidelberg, 488 pp. Steppenbeck, R., 1929. Geologia des Chimatales in Nordperu und seiner Anthracitta – Gerstaetten. Geol. Paleont. Abhand. Neue Folge, Gustav Fisher Verlag Jena. B 16/20. Valdivia, H., 1966. Seccio´n medida en el Pongo de Tiraco. Petroperu´. Area de Investigacio´n y desarrollo, Lima. (Internal report).
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Velez, E., 1994. Geologı´a de los mantos de la Cuenca carbon´ıfera de Gazuna – Oyo´n. Inf. Interm. Ine´d. Compan˜ia Minera Gazuna. Weibenbach, N., 1986. Factibilidad del proyecto de Antracita – Mina Ambara y Huayday. Lucma—Peru Grundstofftechnik GMBH-ESSEN, Germany. Wilson, J.J., 1963. Cretaceous stratigraphy of Central Andes of Peru. Bull. Am. Assoc. Pet. Geol. 47, 1 – 34. Wilson, J., Reyes, L., Garayar, J., 1967. Geologı´a de los cuadra´ngulos de Mollebamba, Tayabamba, Huaylas, Pomabamba, Carhuaz y Huari. Bol. Serv. Geol. Minas, Lima, Peru 16, 95 pp.
Short description of the Peruvian coal basins Eitel R. Carrascal-Miranda a, Isabel Sua´rez-Ruiz b,* b
a UNI, Lima, Peru Instituto Nacional del Carbon (CSIC), Ap. Co., 73, 33080 Oviedo, Spain
Received 1 January 2003; accepted 27 May 2003
Abstract This work synthesizes the main general characteristics of the Peruvian Coal Basins in relation to age, coal facies and coal rank. Peruvian coals are located in a series of coal basins from the Paleozoic to the Cenozoic age. Paleozoic coal seams are mainly of Mississippian age (Carboniferous). They are of continental origin and their reduced thickness and ash content are their main characteristics. Mesozoic coal seams (Upper Jurassic – Lower Cretaceous) are located in the so-called Peruvian Western Basin and in the depressions close to the ‘‘Maran˜on Geoanticline’’. They were originated in deltaic facies under the influence of brackish and fresh waters. Some of these coal basins (those distributed in the central and northern parts of Peru) are relatively well known because they are of economic importance. Finally, Cenozoic coal seams (Tertiary) are found in both paralic and limnic basins and their reserves are limited. All the Peruvian coals are of humic character and are vitrinite-rich. Their rank is highly variable and normally related with the different orogenic events which strongly affected this region. Thus, Paleozoic and Mesozoic coals are of bituminous to anthracite/meta-anthracite coal rank while peats, lignite and subbituminous coals are found in Cenozoic basins. D 2004 Elsevier B.V. All rights reserved. Keywords: Peru; Coal; Coal basins; Paleozoic; Mesozoic; Cenozoic; Coal facies; Organic petrology
1. Introduction The Peruvian Andes Range contains a large number of coal basins which correspond to three successive geological ages: Upper Palaeozoic (Carboniferous), Upper Jurassic – Lower Cretaceous, and Tertiary. The present distribution of the coal basins is in the form of strips subparallel to the already known morphostructural units: Cordillera de la Costa, Llanuras Pre-Andinas, Cordillera Occidental, Franja de Volcanes, Franja Interandina, Cordillera Oriental, Franja Subandina, * Corresponding author. Tel.: +34-985-11-9090; fax: +34-98529-7662. E-mail address: [email protected] (I. Sua´rez-Ruiz). 0166-5162/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2003.05.004
and Llano Amazonico. The estimated coal potential of the different coal basins is about 1 Gt, the most important being those of the Mesozoic and Cenozoic (Tertiary) age. In general, there is very little information relating to Peruvian coals, coal facies, and sedimentary paleoenvironments. In the best of cases, information is limited to the sedimentary environment of the coalbearing formations. Thus, most bibliographic references are inventories of general or local coal resources (Agramonte, 1978; Siderperu´, 1980; Sa´nchez, 1985; Ministerio de Energı´a y Minas, 1990; Ingemmet, 1992; Carrascal Miranda et al., 2000), inventories of coal for specific coal mines (Weibenbach, 1986), or general geologic studies of different areas in which
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basins with coals are included (Pearson, 1981; Velez, 1994; Alleman, 1985; Ojeda Chavez and Mendoza, 1985; Agramonte, 1985). The most recent research work has been carried out by Dunı´n-Borkowski (1981, 1983, 1984, 1985, 1994), Medina (1991), Carrascal Miranda (1996), Carrascal Miranda et al. (1994a,b,c, 1997, 2000), and Carrascal Miranda and Sua´rez-Ruiz (1995a,b,c, 1997, 2002) who focused mainly on the distribution of coals and coal beds in the main Mesozoic and Tertiary basins. These works also provide some information related to the sedimentary environment or other features of coal seams such as composition and coal rank. Using geological, petrological, and geochemical studies of the most important coal seams from the Oyon, Santa, Alto Chicama (Mesozoic), and Yanacancha (Tertiary) Basins (which contain half of the known coal reserves in Peru), Carrascal Miranda (1996), defined the sedimentary environments in which the coals were generated. Carrascal Miranda et al. (2000) also synthesized the knowledge that exists about depositional paleoenvironments in relation with the other coal basins. Below is a brief description of the main coal basins of the Cenozoic, Mesozoic and Paleozoic age (Fig. 1 and Table 1).
2. Peruvian Coal Basins 2.1. Cenozoic coal fields Cenozoic coals (Dunı´n-Borkowski, 1981) are located in basins that developed mainly during the Lower – Upper Tertiary age. Most of these coals are lignites and their reserves are limited. 2.1.1. Loreto Basin Coal seams are concentrated in the Pebas Formation (Miocene) in the Loreto Basin (Peruvian Amazonia) located northeast of Peru (Fig. 1). They continue laterally into the Colombia and Brazil areas and form a part of the Llanura Amazo´nica (Amazonic Plain) which is made up of a thick sequence of Cenozoic molasse-type sediments that cover the Mesozoic rocks. The Pebas Formation is made up of lutites, clays, and lenticular levels of lignite (Palacios, 1994). These coal seams are thinner
(Steinmann, 1929), undeformed, and show high mineral matter content, especially pyrite. They are of humic type, the occurrence of mollusc fragments being common in the coal seams. The coal mainly derives from herbaceous vegetation in which ferns with palynomorphs such as Verrucatasporites, Psilatasporites, and fungal spores are predominant (Carrascal Miranda et al., 2000). The geological aspects, their petrographic composition, the content and the type of mineral matter, indicate that coals from the Loreto Basin (Table 1) originated in a marsh of estuary type influenced by brackish waters and under humid conditions in a paralic basin (Carrascal Miranda et al., 2000). These coals are peat and brown lignites, with high ash (18.0 –48.0%) and sulphur contents (0.5 – 8.0%). 2.1.2. Tumbes –Piura Basins Coals of the Cenozoic age are also found in the Mancora (Oligocene) and Zorritos (Miocene) Formations of the Tumbes Basin and in the Ostrea Formation (Middle Eocene) in the Piura Basin, both of which are located on the northwestern edge of Peru (Fig. 1). These formations are made up of a sequence of sandstones, lutites and coal beds (Palacios, 1994). Palynological data has shown that the Rhizopora bruguiera, Iriartites tumebezensis berry, Ficus winslowiana and ferns (Cruzado, 1985) were the vegetation which contributed to the formation of the coal deposits in these basins. Coals are lignites with a huminite reflectance lower than 0.30%. As in the case of the Loreto Basin, the coals also originated in an estuary paleoenvironment of a paralic basin (Table 1) under the influence of brackish waters and humid conditions. 2.1.3. Yanacancha Basin Finally, the Yanacancha Coal Basin (Lower – Middle Tertiary) is an intramontane basin in the north part of the Andes (Fig. 1). Its coal seams are in the Porculla Formation and their rank is subbituminous/ high volatile bituminous (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rez-Ruiz, 1995a,b; Carrascal Miranda et al., 1996a, 2000). The Porculla Formation unconformably overlies the folded sediments of the Upper Cretaceous age and reaches 150– 200 m thickness, representing the eastern edge of volcanism. The formation is made up of two mega-
E.R. Carrascal-Miranda, I. Sua´rez-Ruiz / International Journal of Coal Geology 58 (2004) 107–117
Fig. 1. Distribution of the coal basins in Peru (modified from Dunı´n-Borkowski, 1981; Medina, 1991).
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Table 1 Coal facies studies in Peru (by Carrascal Miranda, E.R. and Sua´rez-Ruiz, I.) Method
Depositional environment/ other comments
Age/area
ASTM rank
seam development, stratigraphy
continental depositional environments, limnic basins
Mississippian/ Paracas Basin and coal fields in the southern and central Peru (Ambo Group)
l.-an
seam development, stratigraphy
subsident coastal plains periodically covered by the sea level, paralic basin.
Callovian/Yura Basin (Yura Group)
hvb-san-an
Benavides (1956) Wilson (1963) Cobbing et al. (1981) Dunı´n-Borkowski (1984, 1985) Carrascal Miranda and Sua´rez-Ruiz (1995c) Carrascal Miranda et al., (1996a,b, 2000) Carrascal Miranda (1996)
seam development, stratigraphy, organic petrology, chemistry
littoral/deltaic to sedimentary paleoenvironment, coal seams in deltaic facies; humid conditions paralic basin.
Berriasian/Oyon Basin (Oyon Formation)
mvb-an
1.54 – 5.50
Benavides (1956) Gastan˜aga (1979) Dunı´n-Borkowski (1981) Carrascal Miranda (1996) Carrascal Miranda et al. (1996a, 2000)
seam development, stratigraphy, organic petrology, chemistry
deltaic sedimentary paleoenvironment, delta plain facies and deltaic/fluviatile basin
L. Valanginian and Tithonian – Berriasian/ Santa Basin (Chimu and Oyon Formations)
an-man
>4.1
Steppenbeck (1929) Benavides (1956) Wilson (1963) Escudero (1979) Agramonte (1985) Dunı´n-Borkowski (1981, 1985) Carrascal Miranda et al. (1994a,b,c, 1996a, 2000) Carrascal Miranda (1996)
seam development, stratigraphy, organic petrology, chemistry
deltaic sedimentary paleoenvironment, facies from lower delta plain, to upper delta plain, humid conditions, paralic basin.
L. Valanginian/Alto Chicama Basin (Chimu Formation)
an-man
>4.3
Mclaughlin (1921) Dunı´n-Borkowski (1983, 1984,1985) Carrascal Miranda and Sua´rez-Ruiz (1998) Carrascal Miranda et al. (2000)
seam development, stratigraphy, organic petrology, chemistry
deltaic – fluviatile environments, delta plain facies in transition to fluviatile facies, humid conditions, probably paralic basin
Neocomian/Jatunhuasi Basin (Goyllarisquizga Group)
hvb-an
0.5 – 2.55
seam development, stratigraphy
deltaic paleoenvironments close to the shoreline, humid conditions, probably paralic basin
Neocomian/Goyllarisquizga Basin (Goyllarisquizga Group)
sb
Author
Paleozoic coal basins Broggi (1927) Steinmann (1929) Rassmuss (1947) Newell et al. (1953) Carrascal Miranda et al. (2000) Mesozoic coal basins Benavides (1962) Marocco and del Pino (1966) Wilson et al. (1967) Guevara (1969) Pecho (1981) Dunı´n-Borkowski (1985) Carrascal Miranda et al. (2000)
Mesozoic coal basins Page (1960) Wilson (1963) Dunı´n-Borkowski (1983, 1984,1985) Carrascal Miranda et al. (2000)
Reflectance (%)
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Table 1 (continued) Author
Method
Depositional environment/ other comments
Age/area
ASTM rank
Reflectance (%)
seam development, stratigraphy, organic petrology, palynology
estuary influenced by brackish waters, humid conditions,
Oligocene – Miocene/ Tumbes Basin (Mancora and Zorritos Formations); M. Eocene/Piura Basin (Ostrea Formation)
l.
0.25 – 0.30
Dunı´n-Borkowski (1981) Casten˜eda (1991) Carrascal Miranda (1996) Carrascal Miranda et al. (1996a) Carrascal Miranda and Suarez-Ruiz (1995a,b, 1997)
seam development, stratigraphy, organic petrology, chemistry
paralic basins peat swamps under humid conditions, in fluviatile – lacustrine environments, limnic basin
L. – M. Tertiary/Yanacancha Basin (Porculla Formation)
sb/hvb
0.5 – 0.6
Steinmann (1929) Palacios (1994) Carrascal Miranda et al. (2000)
seam development, stratigraphy, organic petrology, palynology
estuary influenced by brackish waters, humid conditions, paralic basin
Miocene/Loreto Basin (Pebas Formation)
peat – l.
0.17 (punctual data)
Cenozoic coal basins Cruzado (1985) Palacios (1994)
sequences of reworked pyroclastic material, tuffs, breccias of andesitic, rhyolitic, and dacitic composition. In the middle of this stratigraphic series and in the first sequence, this reworked material is interbedded with thin sandstone levels, siltstones, clays, lutites, and conglomerates that fill up the channels. All of this is covered by tuffs which grade into siltstones, lutites, and coal beds constituting a coal unit of 8 m thickness. A second sequence of pyroclastic and detrital material without coal lies on top of the previous sequence. The coal unit represents a depositional environment of a shallow fluviatile – lacustrine floodplain of fresh water in which the lime and clay sediments represent the flood plains (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rezRuiz, 1995a,b, 1997; Carrascal Miranda et al., 1996a, 2000). The coals are of humic type, and the organic material derives from herbaceous vegetation and woody trunks (trees). The principal (main) coal seam in this basin was generated in a swamp in which humid conditions predominated. The corresponding facies are of limnic type influenced by fresh water (Table 1). The coal rank (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rez-Ruiz, 1995a,b, 1997; Carrascal Miranda et al., 1996a), which increases in the vicinity of the fault structures, is from subbituminous to high volatile bituminous (vitrinite reflectance 0.5 –0.6%).
2.2. Mesozoic coal fields Mesozoic coals originated in the subbasins of the ‘‘Peruvian West Basin’’ and also in the depressions close to the ‘‘Maran˜on Geoanticline’’ (Fig. 1) during the short emergence periods that occurred in the Upper Jurassic and Lower Cretaceous (Dunı´n-Borkowski, 1981). The development of the Peruvian West Basin occurred from the south (Yura area of the Callovian age) towards the north of Peru (Goyllarisquizga Group of the Neocomian age). Thus, according to Escudero (1976), the oldest coals are those of the Yura Basin (Carumas area, Fig. 1), while the youngest coals (Aptian) are located north of Peru in the Farrat Formation (Petersen, 1975). However, the most important Mesozoic coal basins are those distributed in the central and northern parts of Peru (Fig. 1) in the Peruvian West Basin such as the Chiclayo, Cajamarca, Alto Chicama, Santa, Alto Pativilca, and Oyon Basins. The few coal deposits found in the local depressions of the Maran˜on Geoanticline (Central Peru, Fig. 1) are concentrated in the Goyllarisquizga and Jatunhuasi Basins (Petersen, 1975). The stratigraphic sequences of the Peruvian West Basin are different from those of the Maran˜on Geoanticline. The former are thicker, well defined (Wilson, 1963), and contain the most important coal deposits from a commercial point of view. Those of the Maran˜on
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Geoanticline are irregular, isolated (Petersen, 1975), and of reduced size. In general, Mesozoic coals were originated in deltaic facies (Table 1) under the influence of both fresh and brackish waters as part of a major delta, whose materials derive from the Maran˜on Geoanticline and the Brazil and Guiana Shields. The rank of Mesozoic coals varies from bituminous to anthracite and meta-anthracite coals (Dunı´n-Borkowski, 1981; Carrascal Miranda, 1996; Carrascal Miranda et al., 2000), in agreement with their relative location in the above-mentioned strips and their proximity to the major thermal events. 2.2.1. Jatunhuasi Basin The Jatunhuasi and Goyllarisquizga Basins are small coal deposits located in the depressions near the Maran˜on Geoanticline (Fig. 1). In the Jatunhuasi Basin, the representative sedimentary sequence is the Goyllarisquizga group (Neocomian age) which is made up of white and yellow quartzitic sandstones interbedded with dark lutites and relatively continuous coal seams of variable thickness (Mclaughlin, 1921). This basin was also deformed by the Andean Orogeny. Coals show a relatively high ash content but lower than in the case of the Goyllarisquizga coals. On the other hand, the high sulphur content is characteristic (4 – 5%). From a petrographic analysis (Pearson, 1981; Carrascal Miranda and Sua´rez-Ruiz, 1998; Carrascal Miranda et al., 2000), a variable rank from bituminous to semianthracite and anthracite was established for these coals with vitrinite reflectance values ranging between 0.57% and 2.51%. The more evolved coals are those located near the magmatic intrusive bodies (Fig. 1). Coals are of autochthonous/alochthonous character (Carrascal Miranda and Sua´rez-Ruiz, 1998; Carrascal Miranda et al., 2000) and their organic fraction mainly derive from ligneous material as well as from shrubby and herbaceous vegetation. The coals were generated in delta plain environments in transition to fluviatile facies under humid paleoclimatic conditions (Table 1). The basin was probably a paralic basin (Carrascal Miranda et al., 2000). 2.2.2. Goyllarisquizga Basin The Goyllarisquizga Coal Basin was subjected to different Andean Orogeny phases and, thus, it is very faulted and deformed. The coal seams are found in
two coal bearing series in the basal part of the Goyllarisquizga Group (Neocomian age), the formation representative of this basin. This group is about 500 m thick and is made up of sandstones, coal seams, interbedded with volcanic material, clays and calcareous sandstones (Page, 1960). In general, the coal seams are of lenticular shape and reach a thickness of up to 3 m. They laterally change into coal shales and coal lutites. Thus, their ash content is high and variable and can reach 60% (Carrascal Miranda et al., 2000). In addition, these coals show high sulphur (mainly pyrite) content (3%). Although there has been some controversy concerning the coal rank (Broggi, 1927; Page, 1960), petrographic data and chemical analysis results suggest a subbituminous coal rank for the Goyllarisquizga coals. The coal seams are of autochthonous character and they were generated in a deltaic paleoenvironment (Wilson, 1963) close to the shoreline in a paralic basin under humid paleoclimatic conditions (Table 1). At the regional level (Fig. 1), this basin correlates with the Jatunhuasi Basin and both basins contain the less evolved coals of Mesozoic age (Carrascal Miranda et al., 2000). 2.2.3. Alto Chicama, Santa and Oyon Basins These three basins are known for their vast coal reserves of commercial value. They are located in the central and northern parts of Peru (Fig. 1). In addition, their coal seams, the most important of the Mesozoic age, are mainly concentrated in two formations: the Oyon (Tithonian – Berriasian age) and the Chimu Formations (Lower Valanginian age), the latter belonging to the Goyllarisquizga Group (Lower Cretaceous: Valanginian –Aptian time). Previous geological studies carried out on these basins are scarce and of general character such as those of Steppenbeck (1929), Steinmann (1929), Benavides (1956), Cossio (1964), Cossio and Jae´n (1967); Wilson (1963), Wilson et al. (1967), Cobbing (1973), Cobbing et al. (1981), and those mentioned above: Dunı´n-Borkowski (1981, 1983, 1984, 1985), Medina (1991), Carrascal Miranda (1996) and Carrascal Miranda et al. (1994a,b,c, 1997, 2000), Carrascal Miranda and Sua´rez-Ruiz (1995c). Benavides (1956), in his stratigraphic study of the formations found in the Oyon, Santa and Alto Chicama areas (Fig. 1), pointed out that the units are
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made up of a sedimentary sequence in which the Oyon and Chicama Formations (Upper Jurassic) are a substratum. Thus, the Chicama Formation (Tithonian) in the centre and the north of Peru represents marine facies (Wilson, 1963). The Oyon Formation (Berriasian) is partially equivalent to the Chicama Formation, with the difference that the latter is made up of siltstones, sandstones, and in addition contains coal beds. It represents the coal-bearing series for the Oyon Basin and is one of the coal-bearing series for the Santa Basin (Fig. 1). The Oyon Formation is made up of marine and continental facies (Wilson, 1963) originated in sedimentary environments which evolved from littoral to deltaic facies and finally to a floodplain facies. Moreover, the Oyon Formation could be laterally equivalent to the lowest part of the Chimu Formation located north of Peru (Cobbing et al., 1981). Above the Chicama and Oyon Formations is the Goyllarisquizga Group (Lower Cretaceous) made up of the Chimu (Lower Valanginian), Santa (Upper Valanginian), Carhuaz (Hauterivian – Aptian) and Farrat (Upper Aptian) Formations. Only the Chimu Formation has significant coal seams which can be identified in the Santa and Alto Chicama Basins (Fig. 1). The Chimu Formation has been described by Steppenbeck (1929) and Benavides (1956), and its coal seams studied by Carrascal Miranda et al. (1996a,b). This Formation is made up of orthoquartzites, siltstones, sandstones, shales and coal beds. It originated in continental – coastal environments in which deltaic facies predominated (Wilson, 1963; Kopex-Minero Peru´, 1975; Escudero, 1979; Cobbing et al., 1981; Dunı´n-Borkowski, 1984; Carrascal Miranda, 1996). The coal seams represent deltaic and transition deltaic/coastal environments (Carrascal Miranda, 1996). The Santa Formation, without coal, corresponds to a shallow marine environment. The Carhuaz Formation in the Alto Chicama Basin contains small coal intercalations of lenticular morphology (Kopex-Minero Peru´, 1975). This Formation also seems to have originated in a deltaic environment with sporadic marine invasions (Benavides, 1956; Wilson, 1963; Cobbing et al., 1981). The Farrat Formation in the Alto Chicama Basin also has a few thin coal beds (Escudero, 1979) generated in a delta sedimentary environment.
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Above the Goyllarisquizga Group are the Calcareous formations. They are representative of the Middle – Upper Cretaceous. These formations include the Inca (Lower Albian), Pariahuanca (Lower Albian), Chulec (Middle Albian), Pariatambo (Middle – Upper Albian), Jumasha (Cenomanian – Turonian), Celendı´n (Upper Turonian – Coniacian), Casapalca (probably Santonian), and Huaylas (probably Santonian), without coal. They originated in sedimentary environments from shallow marine, neritic marine, and euxinic marine to continental clastic deposits. On top of these Calcareous Formations are the volcanic materials of the Calipuy Group described in this part of Peru by Cossio (1964), and assigned to the Lower –Middle Tertiary by Cobbing et al. (1981). These materials discordantly cover all of the Cretaceous series. 2.2.3.1. Alto Chicama Basin. In this basin are 16 coal levels which are not very persistent laterally (they do not appear in all the coal fields) with a variable thickness which can reach up to 4 m. These coal seams are concentrated in two coal-bearing series of the Chimu Formation that are also controlled by tectonic structures of great development. As in the case of the other Mesozoic coal basins, there are several coal fields being commercially exploited. Petrographic and chemical data (Carrascal Miranda, 1996; Carrascal Miranda et al., 1994a,b,c, 1996a, 2000) suggest that the coals are of humic type and of high rank (anthracites and meta-anthracites, vitrinite reflectance >4.5%) generated in a paralic basin from the same type of vegetation as in the case of that of the Oyon and Santa Basins, in a deltaic sedimentary paleoenvironment (Table 1). The sedimentary facies were transitional from the lower delta plain to upper delta plain influenced by both fresh and brackish waters. Two aspects are important in this basin: the structures of ball coals found in two of the coal seams (Lipiarski and Szyminiak, 1977; Hower and Fishel, 1990) which seem to be related to the tectonic activity (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rez-Ruiz, 2002) promoted by the Andean Orogeny in this basin and the high (14 – 24%) sulphur content (mainly elemental sulphur) found in the coals from the Shulcahuanca and Callacuyan coal fields (Southeastern Peru, Fig. 1) which are of a thermogenetic nature
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due to the fluids from the magmatic activity (Carrascal Miranda, 1996). 2.2.3.2. Santa Basin. In this basin and lying on top of the Chicama Formation are the same sedimentary formations (Lower and Upper Cretaceous age) as in the Oyon area. There are two coal-bearing series in the Santa Basin. The first, with a thickness of 250 m, is located in the Oyon Formation (Tithonian – Berriasian age), while the second which can reach up to 500 m is found in the Chimu Formation (Lower Valanginian age). As in the case of the Oyon and Alto Chicama Basins, the coal seams are controlled by tectonic structures. Therefore, their thickness and lateral continuity is highly variable. Coals from this basin are evolved (Carrascal Miranda, 1996; Carrascal Miranda et al., 1996a, 2000), showing anthracitic and metaanthracitic coal rank (vitrinite reflectance values >4.11%) which is a consequence of the metamorphism of regional character that affected the Santa Basin. All the coals are of a humic type, mainly composed of vitrinitic macerals. The mineral matter content is variable (ash contents between 4.0% and 30.0%) with very low sulphur percentages ( < 1.0%). These coals were generated in a sedimentary environment typical of a delta plain influenced by fresh and brackish waters under humid conditions in a paralic basin (Table 1). 2.2.3.3. Oyon Basin. In the Oyon Basin (Fig. 1), the aforementioned clastic and calcareous formations (Lower and Upper Cretaceous) can be found. The general stratigraphic sequence is deformed and unconformably covered by the Calipuy Group (Lower – Middle Tertiary). The coal seams, interbedded with lutites and sandstones, are located in the 400– 500 m thick Oyon Formation (Tithonian – Berriasian age). The lenticular coal seams show a variable thickness. Petrographic and chemical data (Carrascal Miranda, 1996; Carrascal Miranda and Sua´rez-Ruiz, 1995c; Carrascal Miranda et al., 1996a,b, 2000) have shown a coal rank which varies from medium volatile bituminous coals to meta-anthracite (vitrinite reflectance from 1.54% to 5.50%) in the different coal fields. The coals are also of a humic type (mainly composed of the vitrinite maceral group), with an organic fraction derived from trees, shrub, and herbaceous materials. Their mineral content is variable (ash content between
10.0% and 34.0%) and the total sulphur percentages are relatively low (< 1.85%). The coals were generated in deltaic environments (Table 1) in which the humid paleoclimatic conditions contributed to the development of marshy facies in a typical paralic basin. 2.2.4. Yura Basin The coal potential of the Callovian Yura Basin (Fig. 1) is of little economic value. The coal seams are thinner (< 1 m) and of lenticular shape. They are found in the Labra, Gramadal, and Hualhuani Formations near Arequipa and in equivalent formations in other areas of South Peru (Dunı´n-Borkowski, 1985). The coal deposits are of humic type and of autochthonous/alochthonous origin (Carrascal Miranda et al., 2000). The sedimentary paleoenvironments (Table 1) were subsident coastal plains that were periodically covered by the sea (Dunı´n-Borkowski, 1985). Chemical data show that coals from the Yura Basin are bituminous, semianthracite, and anthracite rank. The higher rank coals are located near intrusive rocks such as the Coast Batholith. 2.2.5. Other coal basins Other Mesozoic coal fields are found in the Cajamarca, Chiclayo, Alto Pativilca, and Oriente Group Basins. However, these basins are almost unknown and information about them is very scarce. Thus, specific data about their coal facies or the sedimentary paleoenvironments of the coal seams are nonexistent. 2.2.5.1. Cajamarca Basin. Five coal seams of variable thickness (0.8 – 2.0 m) and located in the Chimu Formation are described for the Cajamarca Basin. Their coal rank is also variable, from bituminous to anthracite (Medina, 1991), and their ash and sulphur contents are relatively low (>12% and 1.2%, respectively). 2.2.5.2. Chiclayo Basin. Some isolated and sporadic outcrops of coals are found in this basin. They are also located in the Chimu Formation as well as in San Pedro Formation (Valanginian age). They are of anthracitic coal rank (Medina, 1991) and their coal facies and economical potential are unknown.
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2.2.5.3. Alto Pativilca Basin. This basin represents a transition between the Chicama Formation of marine nature and the Oyon Formation of continental origin (Carrascal Miranda et al., 2000). No information about the coals is reported. It is only known that the coal seams are of reduced thickness. 2.2.5.4. Oriente Group Basin. In the Sub-Andean region (Amazonas –San Martin) is the Oriente Group Basin (Fig. 1). Coal seams are located (Medina, 1991) in the Cushabatay Formation (Neocomian age) which is contemporary to the Goyllarisquizga group (Dunı´nBorkowski, 1985). The coal seams in this formation are thin (Valdivia, 1966; Soto, 1979) and their coal rank is from bituminous to anthracite, particularly in northern Peru. No data about the sedimentary paleoenvironment of these coal deposits are reported in the bibliography. 2.3. Palaeozoic coal fields Paleozoic coal fields are located in the Eastern Range (Cordillera Oriental) in the southern and central parts of Peru (Fig. 1). Other minor coal fields are found in small basins of the Paracas (South of Lima) coastal area (Fig. 1). For all the basins, the coalbearing formation is the Mississippian Ambo Group (Newell et al., 1953), which is made up of sandstones, conglomerates, coal shales, and thin coal levels with a lenticular shape and high ash content (until 60%). The number of these coal levels is in general small. However, in the coastal area of Paracas, the Ambo Group shows a large number (8) of coal seams (Rassmuss, 1947). The Paleozoic coal resources are reduced because of the thinner and discontinuous character of its coal seams which in addition, laterally change into coal shales and coal lutites. The scarce bibliographic references to the coal rank of these Paleozoic coals suggest a variable rank from anthracite (in Huanuco, Cerro de Pasco and Puno areas) to bituminous (Madre de Dios and Puno areas), subbituminous (Paracas), and lignite (Madre de Dios and Titicaca Lake areas) from the central to the southeastern part of Peru (Fig. 1). In general, Paleozoic coals are of humic type and they were generated in limnic basins (Steinmann, 1929). Various authors (Table 1) suggest a depositional environment of continental type for the coal-bearing Ambo Group.
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