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Estrela |
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Para, Brazil |
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Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Estrela Cu-(Mo-Au-Sn) deposit in the Serra dos Carajás District is located ~40 km SE of the city of Parauapebas and ~10 km NNE and ~45 km east of the Cristalino and Sossego IOCG deposits respectively, in Para State, Brazil (#Location: 6° 23' 9"S, 49° 36' 52"W).
Regional Setting
The regional basement in the Serra dos Carajás comprises high grade Mesoarchaean gneisses and migmatites of the Xingú Complex and lesser granulite facies of the Pium Complex, which are overlain by the Neoarchaean supracrustal rocks of the 2.76 to 2.73 Ga Itacaiúnas Supergroup. The latter includes the Grão Pará, Rio Nova, Igarapé Salobo-Pojuca, Igarapé Bahia, and Buritirama groups. These are greenstone-like sequences in which mafic magmatism is dominant. The Itacaiúnas Supergroup is unconformably overlain by the slightly younger siliciclastic Rio Fresco Group and ~ 2.68 Ga Águas Claras Formation sandstone-siltstone succession. These sequences are all intruded by the late Neoproterozoic, ~1.88 Ga A-type granites of the Serra dos Carajás Intrusive Suite, part of a large regional continental magmatic event that covers an area of near 1 million km2, and overlaps the Carajas District. The Estrela copper deposit is situated along the Serra do Rabo fault splay at the eastern termination of the major NW-SE to WNW-ESE trending Carajás Fault.
For details of the regional and local setting see the main Carajás IOCG Province record, in particular Fig. 3 in that record.
Geology
The Estrela Cu deposit is hosted by a 400 m thick sequence of altered bimodal metavolcanic rocks, mainly andesite to rhyolite with minor dacite and banded iron formations, metasediments, and lesser micaceous and carbonaceous schists, as well as minor gabbros. This sequence belongs to the ~2.76 Ga (Sm-Nd isochron age) Grão Para Group of the Itacaiúnas Supergroup. The gabbros are composed of biotite, quartz, albite, tourmaline, fluorite, hastingsite, pargasite, Fe-hornblende and magnetite. The hydrothermally altered calc-alkaline andesites and cogenetic gabbros at the Estrela deposit have been dated at 2579 ±150 Ma (Lindenmayer et al., 2005). These supracrustal rocks dip at 60°S and have been juxtaposed across a Serra do Rabo Fault splay against arenitic sedimentary breccia of the Rio Fresco Group (Lindenmayer et al., 2005; Volp, 2005).
This sequence is intruded by the Estrelinha granitoid (un-related to the Neoarchaean Estrelas Granite Complex ~15 km to the north) along and to the south of, the fault contact. It is porphyritic to equigranular, with a well-defined contact aureole of pyroxene to hornblende hornfels facies, and is cross-cut by aplite, apatite-rich intrusions and pegmatite, and contains abundant pegmatite-stocksheider bodies along its upper contact. The primary granitoid mineralogy comprises quartz + plagioclase + K feldspar + biotite with minor ilmenite. The Estrelinha granitoid is a ferroan, alkali-calcic, and weakly peraluminous (Frost et al., 2001) within-plate granite (Pearce et al., 1984). It is an A-type granite with high SiO2, Na2O+K2O, HFSE and low CaO and Sr (Whalen et al., 1987) and has a negative Eu anomaly, typical of A-type granites. Greisen dominates the apical zone, composed of quartz, fluorite, mica, topaz and sulphides with minor tourmaline and rare mariolictic cavities. The Estrelinha granitoid has been dated at 1875 ±2 Ma whilst a nearby quartz-diorite yielded a date of 1880 ±5 Ma (ID TIMS U-Pb zircon; Lindenmayer et al., 2005). Three aplites gave ages of 1886 ±19 Ma, 1827 ±23 Ma, and 1716 ±9 Ma (U-Th-Pb CHIME monazite; Volp et al., 2006).
The relationship between the granitoids and the gabbroic intrusions is unclear, but Volp (2005) suggests that there are two suites, the majority of which precede the Estrelinha granitoid, although at least one individual intrusion is probably coeval. Lindenmayer et al. (2005) describe these rocks as Palaeoproterozoic porphyritic quartz diorite, orthoclase-albite granite, topaz-orthoclase-albite granite and quartz-alkali-feldspar syenite (episyenite) and conclude they were intruded into the volcanic sequence after the onset of the mylonitic foliation and prior to an episode of brittle deformation.
Volp (2005) interprets structural controls at Estrela to be dominated by granite emplacement features, localised shearing and regional foliation, and fault reactivation. Structural trends suggest steeply-dipping mineralised stockwork veins emanate from the Estrelinha granitoid into the contact aureole. The distribution of mineralisation in country rocks is parallel to sub-parallel with both the lithological boundaries and regional foliation.
Mineralisation and Alteration
Early alteration of the meta-andesites was sodic-calcic, composed of quartz, albite, hastingsite-pargasite, magnetite and ilmenite. This was overprinted by a potassic stage that includes biotite, albite, quartz, tourmaline, chalcopyrite, pyrite, pyrrhotite and molybdenite (Lindenmayer et al., 2005).
Two distinct styles of mineralisation were recognised by Volp (2005), namely i). a proximal stockwork of quartz-biotite-muscovite-fluorite-chalcopyrite veins hosted by the apical zone of the Estrelinha granitoid and its contact aureole; and ii). biotite-pyrrhotite-chalcopyrite mineralisation within the more distal deformed host sequences. Within this zoned pattern, the main mineralisation occurs as millimetre- to metre-scale quartz-rich veins, breccias, and associated alteration within the altered country rocks above the granite cupola. The main stage of veining comprises quartz-albite-biotite-fluorite-chalcopyrite-pyrite-pyrrhotite veins with minor magnetite, ilmenite, epidote, tourmaline, chlorite and molybdenite (Lindenmayer et al., 2005). It is uncertain whether chlorite and epidote are later than albite and biotite (Lindenmayer et al., 2005).
The paragenetic sequence that produced this assemblage evolved from early magmatic to hydrothermal stages, related to decreasing temperature and successive overprinting, infill and alteration. The magmatic stage is represented by aplites and apatite-rich intrusions. At the magmatic to hydrothermal transition, unidirectional solidification textures, mariolitic cavities and pegmatite-stockscheider developed, all with high volatile and REE contents, within the apical zone of the Estrelinha granitoid and the stockwork veins hosting mineralisation. The mineralisation progressed from early molybdenite (and rare cassiterite) followed by magnetite (which does not occur as infill or alteration within the granitoid) and later dominant chalcopyrite-pyrrhotite-pyrite associated with abundant quartz and purple fluorite. Gold has only very rarely been observed within stockwork vein-infill chalcopyrite. Later quartz, chlorite, epidote, hematite and calcite reflect an overprint by cooler fluids along pre-existing structures and reactivation of the Carajás Fault. Rare U-REE minerals have also been observed (Lindenmayer et al. 2005).
An unpublished Re-Os age for deformed molybdenite of 2.7 Ga is quoted by Pollard et al. (2019). However, virtually all other mineralisation dates are younger. Monazite from a quartz-green biotite vein and allanite from a fluorite-sulphide vein gave ages of 1839 ±14 Ma and ~1850 Ma, respectively (Volp et al., 2006). Volp et al. (2006) noted that monazite from the quartz-green biotite vein showed evidence of alteration, but did not specify the nature of the alteration (Pollard et al., 2019). Main stage mineralised veins have also been dated at 1857 ±98 Ma (Sm-Nd whole-rock samples of vein material; Lindenmayer et al., 2005). Age dating of pegmatitic green biotite from stockwork veins gave an age of 1.88 Ga (Ar-Ar; CVRD unpublished company report; quoted by Volp, 2005).
Resource and Dimensions
A preliminary resource estimate of 30 Mt at 0.5% Cu was reported by CVRD (Vale) in 2002. The deposit has a strike length of 1.5 km, width of 500 m, and dips at 60°S. It is exposed from the top of the Serra do Rabo Ridge to a depth of 350 m, and is amenable to open-cut mining.
The most recent source geological information used to prepare this decription was dated: 2019.
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.
Estrela (approximately)
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Selected References:
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Lindenmayer, Z.G., Fleck, A., Gomes, C.H., Santos, A.B.S., Caron, R., Paula, F.C., Laux, J.H., Pimental, M.M., Sardinha, A.S., 2005 - Caracterizacao geologogica do Alvo Estrela (Cu-Au), Serra dos Carajas, Para: in Marini, O.J., Queiroz, E.T. and Ramos, B.W. (eds.), 2005 Caracterizacao do depositos minerais em distritos mineiros da Amazonia. DMNPCT-mineral/FINEP-ADIMB, Conference proceedings, pp. 157-225.
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Pollard, P.J., Taylor, R.G., Peters, L., Matos, F., Freitas, C., Saboia, L. and Huhn, S., 2019 - 40Ar-39Ar dating of Archean iron oxide Cu-Au and Paleoproterozoic granite-related Cu-Au deposits in the Carajas Mineral Province, Brazil: implications for genetic models: in Mineralium Deposita v.54, pp. 329-346.
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Volp, K.M., 2005 - The Estrela copper deposit, Carajas, Brazil: Geology and implications of a Proterozoic copper stockwork: in Mineral Deposit Research: Meeting the Global Challenge. Springer, Berlin, Heidelberg. Proceedings of the Eighth Biennial SGA Meeting, Beijing, China, 18-21 August 2005, pp. 1085-1088.
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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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