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Cristalino |
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Para, Brazil |
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Cu Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Cristalino IOCG deposit is located some 40 km to the east of Sossego in a bifurcation of the major regional Carajás Fault in the Carajás district of Para State, Brazil.
For an overview of the regional setting and geological location maps see the Carajás IOCG Province record.
Basement in the area is represented by the Xingu Complex which is >2.86 Ga in age and is composed of a variety of rocks, including the ~3.0 Ga Pium Complex and 2.9 Ga Greenstones. At Cristalino, this basement is represented by the Cruzadão Granite which has been dated at 2831 ±6 and 2848 ±5 Ma, (U-Pb, zircon; Moreto et al., 2011) and does not crop out in the deposit area, but has been intersected at depth by drill core. This basement granite is in sharp unconformable contact with volcanic and sedimentary rocks of the Parauapebas Formation, part of the 2.76 Ga Grão Para Group. These are overlain by the iron formations of the 2.74 Ga Carajás Formation, and cut by the 2743 ±1.6 Ma (Sardinha et al., 2006) Serra do Rabo Granite, the 2.5 Ga Estrella Granite and subsequently by 1.9 Ga granites, but is overlain by the un-metamorphosed 2.7 to 2.6 Ga Águas Claras marine sandstones.
The principal hosts to the Cristalino mineralisation are volcanic rocks of the Grão Para Group, mainly its lower felsic and mafic volcanic rocks within the Parauapebas Formation and, to a lesser extent, banded iron formations of the Carajás Formation. Volcanic rocks of the Parauapebas Formation in the deposit area are variable, both texturally and in alteration intensity, and are cut by mm to cm thick shear zones and veins, also with variable compositions. The mafic volcanic rocks display aphanitic to vesicular textures, and are mostly composed of amphibole, magnetite, allanite and chlorite. The felsic volcanic rocks are less abundant in the mineralised area and have a rhyolitic composition and have been altered to tourmaline, amphibole, K feldspar chlorite-epidote-calcite. In cm thick shear zones, tourmaline and elongated blue quartz crystals define a mineral lineation (Craveiro, et al., 2019). The banded iron formations are accompanied by orange dacite and green andesite with minor basalt and have been hydrothermally altered and disrupted. These iron formations have been upgraded nearby where they constitute part of the Carajás Serra Sul Iron Resources. Both the volcanic rocks of the Grão Pará Group and the Serra do Rabo granite are crosscut by NNW-SSE trending gabbro dykes, likely related to the Neoproterozoic Rio da Onça Gabbro (Tavares 2015).
Hydrothermal alteration is best developed along lithological contacts and NW-SE and NE-SW second order shear zones, particularly within the volcanic rocks of the Parauapebas Formation. It varies in intensity and style, having been imposed within a ductile-brittle to dominantly brittle regime. The initial stages are dominated by a distal sodic assemblage and proximal calcic-ferric alteration. Subsequently, the host rocks underwent a proximal potassic phase, essentially in a brittle regime, followed by a propylitic chlorite-epidote-calcite alteration assemblage (Craveiro et al., 2019).
Sodic metasomatism at Cristalino is characterised by chess-board albite, developed at the expense of the primary plagioclase of the volcanic rocks. This chess-board albite has associated monazite and allanite, with minor quartz and calcite. Scapolite has only been noted occurring distally in outcrops of the Cruzadão Granite, and is regarded as likely also being related to the sodic alteration phase (Craveiro et al., 2019).
Texturally destructive calcic-ferric alteration is represented by actinolite, magnetite and allanite overprinting primary ferromagnesian minerals, with minor coeval apatite, epidote and rare uraninite (Craveiro et al., 2019).
Both Na- and Ca-Fe rich assemblages have been affected by the potassic alteration phase, during which small amounts of biotite initially formed in equilibrium with magnetite, followed by K feldspar growth accompanied by hematite, quartz and titanite (Craveiro et al., 2019).
Tourmaline is predominantly found in felsic volcanic rocks and appears to have been formed: i). early, associated with chessboard albite, allanite and monazite, during the sodic alteration phase; and ii). as subsequent tourmaline-bearing veins and aggregates, in zones previously altered by hydrothermal K-feldspar (Craveiro et al., 2019).
Propylitic chlorite-epidote-calcite association overprints all previous alteration pulses, selectively overgrowing sodic, calcic and ferromagnesian minerals, and destroying pre-existing textures. The infill stages are characterised by K feldspar rich and calcite rich veins, both with variable proportions of quartz, allanite, chalcopyrite, hematite, chlorite and epidote. The former tends to form straight veins that show cm-thick alteration selvages, while the latter, despite having alteration halos with variable thickness, is multi-directional and crosscuts most host rocks and structures, tending to evolve to breccias (Craveiro et al., 2019).
Mineralisation is concentrated in a ~NW-SE, 165° trending, sinsitral transpressive zone of shearing over a drilled length of 2200 m and thickness ranging from ten of metres to 500 m. The shear zone is several hundreds of metres in width and is a splay of the Carajás Fault. The ore zone is generally brecciated and is found in the volcanic rocks of the Parauapebas Formation, below the iron formation, encroaching into the lower sections of the iron formation itself. Iron alteration where it affects the iron formation, has been shown to represent addition, not remobilisation of iron. In general the iron formation forms the upper limit to ore and may have acted as a capping. The hydrothermally altered breccia is composed of 5 to 50% sub-angular to sub-rounded fragments.
Three styles of ore have been identified (after Craveiro et al., 2019):
• Disseminations, which occur either as i). chalcopyrite and pyrite coexisting with up to 50 magnetite, minor allanite and uraninite, chiefly in mafic volcanic rocks, related to the late stages of calcic-ferric alteration or ii). as chalcopyrite accompanied by minor pyrite, hematite and virtually no magnetite, in felsic volcanic rocks, related to the potassic and propylitic alteration.
• Mineralised breccia, which occur inn the main body of the deposit and are preferentially hosted in mafic volcanic rocks. Two styles have been differentiated i). chalcopyrite-pyrite-magnetite breccias that are generally hosted by mafic volcanic rocks that have undergone pre-breccia calcic-ferric alteration to an actinolite-magnetite-allanite assemblage, and are proximal to magnetite-rich zones; and ii). chalcopyrite ±hematite breccias, preferentially hosted in felsic volcanic rocks that have been affected by potassic (K feldspar) and subsequent propylitic and carbonate alteration.
• Sulphide-bearing veins/veinlets - veins and veinlets carrying chalcopyrite and other sulphides in varying proportions are frequently related to chalcopyrite ±hematite breccia bodies and crosscut the host volcanic rocks in multiple directions. They most commonly comprise an assemblage of chalcopyrite-calcite ±pyrite ±hematite ± magnetite/mushketovite, followed by lesser chalcopyrite-K feldspar ±pyrite ±hematite.
Two main mineralisation assemblages/parageneses have been differentiated (after Craveiro et al., 2019):
i). chalcopyrite-pyrite-magnetite-Au occurring as disseminations and breccia-like bodies that are temporally and spatially related to the calcic-ferric alteration; and
ii). chalcopyrite ±Au ±hematite ±pyrite which occur in breccias and sulphide-rich veins hosted mostly in felsic volcanic rocks that have undergone potassic (K feldspar) and propylitic alteration.
In addition to chalcopyrite and pyrite the ore assemblages include magnetite, marcasite, bravoite, cobaltite, millerite, vaesite and gold, with subordinate hematite, bornite, covellite, chalcocite, molybdenite and sphalerite (Huhn et al., 1999). The gold is in the pyrite.
Indications of Cu mineralisation were first noted in the area in the late 1960's to early 1970's. Grid geochemistry and geophysics from 1984 to 87 led to 2 anomalies being drilled in 1988 with some 13 holes in two prospects. The second phase of work was commenced in 1997-98 with more grid mapping, geochemistry and geophysics, culminating in a drill intersection of 38 m @ 1.4% Cu, 0.25 g/t Au between 76 and 114 m depth.
The resultant approximate resource from the subsequent drilling to 2001 amounted to 500 Mt @ 1.0% Cu, 0.2 to 0.3 g/t Au (Huhn et al., 1999). According to CVRD (2010), the reserves amount to 261 Mt @ 0.73% Cu. Pinto (2012) as quoted by Craveiro et al. (2019), stated the deposit comprised 379 Mt @ 0.66 wt.% Cu, 0.3 g/t Au.
The most recent source geological information used to prepare this decription was dated: 2019.
Record last updated: 22/6/2023
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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Selected References:
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Craveiro, G.S., Villas, R.N.N. and Xavier, R.P., 2019 - Mineral chemistry and geothermometry of alteration zones in the IOCG Cristalino deposit, Carajas Mineral Province, Brazil: in J. of South American Earth Sciences v.92, pp. 481-506. doi.org/10.1016/j.jsames.2019.02.009.
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Craveiro, G.S., Villas, R.N.N. and Xavier, R.P., 2020 - A fluid inclusion and stable isotope (O, H, S and C) study of the Archean IOCG Cristalino deposit, Carajas mineral Province, Brazil: Implications to ore genesis: in Ore Geology Reviews v.127, 23p. doi.org/10.1016/j.oregeorev.2020.103822.
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Craveiro, G.S., Xavier, R.P. and Villas, R.N.N., 2019 - The Cristalino IOCG deposit: an example of multi-stage events of hydrothermal alteration and copper mineralization: in Brazilian Journal of Geology, v.49, 18p. doi:10.1590/2317-4889201920180015.
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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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Xavier R P, Monteiro L V S, Souza Filho C R, Torresi I, Carvalho E R, Dreher A M, Wiedenbeck M, Trumbull R B, Pestilho A L S and Moreto C P N, 2010 - The Iron Oxide Copper-Gold Deposits of the Carajas Mineral Province, Brazil: an Updated and Critical Review: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide v.3 pp. 285-306
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Xavier, R.P., Monteiro, L.V.S., Moreto, C.P.N., Pestilho, A.L.S., de Melho, G.H.C., Delinardo da Silva, M.A., Aires, B., Ribeiro, C. and Freitas e Silva, F.H., 2012 - The Iron Oxide Copper-Gold Systems of the Carajás Mineral Province, Brazil: in Society of Economic Geologists, Special Publication 16, Chapter 17, pp. 433-454.
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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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