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Cerro Bolivar, San Isidro, El Pao, Cerro Altamira, Redondo, La Estrella, Arimagua, Toribio, Frontera |
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Venezuela |
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Fe
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The iron ore deposits of the Bolivar Iron Quadrangle are distributed over a NE-SW elongated area of approximately 80x50 km, while the adjacent El Pao deposit is some 60 km to the NE. The district is located 80 km SW of the Puerto Ordaz at confluence of the Orinoco and Caroní rivers in northern Venezuela, some 520 km SE of Caracas.
Significant deposits include: Cerro Bolivar, Cerro Altamira, Cerro Redondo and La Estrella, Cerro Arimagua, Cerro Toribio, Cerro Frontera and the San Isidro Group.
These deposits lie within the Archaean Imataca Complex which comprises the NW margin of the exposed Guyana Shield segment of the Amazonian Craton. The Complex forms an approximately 500 km long, ENE-trending block, which is overlain by the Orinoco river floodplains to the north, and bounded by the continental scale Guri fault zone to the south, separating it from the Paleoproterozoic (2.2 1.95 Ga) Supamo-Pastora granite-greenstone belt to the south.
The Imataca Complex is predominantly composed of felsic-, quartzo-feldspathic-gneisses, granulites and variably migmatized ortho- and paragneisses, with local anatectic granitoids, that locally contain gradational variations into intermediate/mafic gneisses,granulites. The paragneisses include minor interlayered dolomitic marbles and BIFs that constitute the iron deposits of the Complex. The Complex developed from an Archaean (>3.2 Ga) continental protoliths representing either a differentiated calc-alkaline magmatic series , or metamorphosed clastic/chemical sediments derived from older granitic-greenstone sequences, and which have undergone considerable disturbance plus juvenile accretion during the Neoarchean (~2.8 Ga) times. Transamazonian granulites experienced peak metamorphic conditionsat 1.98 2.05 Ga.
The Imataca Complex rocks have been intensely deformed, metamorphosed and intruded by several 1.98 2.05 Ga. granitic plutons during the Transamazonian orogeny. Metamorphic grade was at granulite facies over most of the northern areas of the Imataca Complex but changed to amphibolite facies towards the south, on approaching the Guri fault zone due to extensive retrograde metamorphism during superimposed cataclastic recrystallization.
The Bolivar Iron Quadrangle represents around 3% of the total area of the Imataca Complex.
The ores have been formed from quartz-magnetite banded iron formations (BIF) which are intercalated in the Imataca feldspathic gneisses. The BIF, which is quoted as carrying around 40% Fe and 40% SiO2, has been upgraded through the supergene leaching of silica and residual concentration of insoluble iron oxides. The ore has an average thickness of 70 m below surface, but can persist to a maximum of 180 m. The highest point on the Cerro Bolivar is 795 m asl. The large size of the ore deposits is attributable to the tight folding and repetition of the iron-bearing units.
The physical ore types include the: i). 'crustal ores', which is found on the tops and upper slopes of hills, consisting of hematite grains in a matrix of secondary goethite and characterised by a remnant banded structure inherited from the protolith the iron formations, and ii). friable ores (60 to 65% < 12 mm fines), which occur below the crust and are composed of porous aggregates of hematite grains which extend downward below a transitional zone of semi-friable, platy ores to depths of as much as 240 metres.
At Cerro Bolivar (1970), the crust ore has approximately 62% Fe, 1 to 2% SiO2, 2% Al2O3. Friable ore had 64% Fe, 0.6% SiO2, 1% Al2O3.
The Cerro Bolivar deposit has been exploited over an area of 12x4 km in a series of pits to the east of the Caroní river. The ore shipped in 1970 assayed 63% Fe, 0.10% P, 0.03% Mn, 1.5% SiO2, 1.5% Al2O3.
The El Pao deposits are 50 km east of the Caroní river. The ore shipped in 1970 assayed 61.7% Fe, 0.05% P, 0.66% Mn, 1.95% SiO2, 4.6% Al2O3.
There are more than five orebodies in the San Isidro district, with very varied shapes and sizes. Individual bodies are up to 3 to 4 km in length, a few hundred metres in width and generally parallel to the regional structure pattern. The base of the ore bodies irregular, with contacts between ore and the unaltered iron-formation beneath being gradational. The maximum vertical thickness of the ore is 260 m, averaging around 60 m. The stratigraphic thickness of iron formation has been structurally enhanced, but is estimated to be approximately from 50 to 150 m. The mean composition of iron ore is 64.41% Fe, 2.62% SiO2, 0.6% Al2O3.
The proven reserves in 2005 of >64% Fe direct shipping ore on a dry basis were 1.7 Gt.
There are another 2.5 Gt of proven ore reserves with 60 to 63% Fe requiring upgrading to be used in steelmaking.
The proven iron ore reserves in the Bolivar Iron Quadrangle are estimated to be around 4.2 Gt within a 14.7 Gt total estimate of proven, probable and possible categories.
The deposits are exploited (in 2006) by CVG Ferrominera Orinoco CA through its Pao Division (the El Pao deposits 80 km southwest of Puerto Ordaz) and its Piar Division (the Cerro Bolivar deposits, 115 km southwest of Puerto Ordaz). These deposits in part support a large HBI plant producing 2.2 Mt pa of hot moulded briquettes by a fluid bed iron ore fines reduction process, at Paula (Puerto Ordaz). Ships of up to 80 000 dwt can berth at Puerto Ordaz from May to November, 50 000 at other times of the year.
The most recent source geological information used to prepare this decription was dated: 2005.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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