Sossego - Sequeirinho-Pista-Baiano, Sossego-Curral,

Para, Brazil

Main commodities: Cu Au
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The Sossego IOCG deposits are located some 40 km to the south of the Carajás townsite in the state of Para, Brazil. It is approximately 80 km SE of Igarapé Bahia and Alemao, and 40 km west of Cristalino. It is also ~30 km east of the main Carajas Serra Sul iron operation (#Location: 6° 25' 10"S, 50° 3' 55"W).

For details of the setting of the deposits see the Carajas IOCG Province record.

Mineralisation is hosted along a regional WNW-ESE-striking shear zone that defines the contact between the metavolcano-sedimentary rocks of the ~2.76 Ga Itacaiúnas Supergroup and the basement tonalitic to trondhjemitic gneisses and migmatites of the ~2.8 Ga Xingu Complex.

Both the Itacaiúnas Supergroup and Xingu Complex rocks are intruded by granite, granophyric granite, gabbro intrusions and late dacite porphyry dykes in the deposit area. The ages of these rocks are uncertain, although a Pb-Pb zircon age of 2734±4 Ga for a biotite-hornblende granite and a U-Pb zircon age of 2765±39 Ga for a tonalite-trondhjemite (Sardinha et al., 2004) close to the deposit area, are considered the best estimates. In addition, the Palaeoproterozoic Rio Branco granite intrusion crosscuts the hydrothermally altered volcanic and intrusive rocks in the deposit area. This field relationship, together with the lack of hydrothermal alteration and mineralisation of the granite, indicate it was emplaced much later than the formation of the copper-gold ore at Sossego (Xavier et al., 2010).

An ~1.88 Ga A-type alkaline to subalkaline magmatism event extends over an area of ~1000 x 1500 km of the Amazon craton and is represented in the Carajás domain by the Serra dos Carajás Intrusive Suite (Machado et al., 1991; Tallarico et al., 2004).

An extensive, >20 km2, zone of scapolite alteration representing distal sodic alteration surround the Sossego deposits (Villas et al., 2005; Sousa, 2007). This alteration is characterised by plagioclase replacement and by scapolite in both mafic and felsic protoliths. Scapolite veins, with widths ranging from mms to >1 m, commonly crosscut basement and supracrustal units and have a biotite-scapolite-hastingsite rich halo that grades outward to chlorite.

In the Sossego deposit area, deformation is represented by cm- to metre-wide mylonitic zones, which are regionally crosscut by NE-striking faults. Rocks in the immediate footwalls of these faults are intensely mylonitised with biotite-tourmaline-scapolite and siliceous alteration developed prior to or synchronous with the shearing (Xavier et al., 2012).

The ore is located in two adjacent centres, Sossego Hill (the Sossego-Curral zones) and the larger Sequeirinho (the Pista-Sequeirinho-Baiano zones) which has a length of 1.6 km and thickness of 150 to 200 m in its central section. These two centres are separated by a major high angle fault. The original resource within Sequeirinho and Sossego was distributed ~85 to 15% respectively.

The Sequeirinho-Pista-Baiano orebodies are characterised by deeply emplaced magnetite-(apatite) and albite-actinolite-rich zones, whereas the Sossego Hill (Sossego-Curral) orebodies have predominant potassic and chlorite alteration typical of shallow crustal levels. Dating of hydrothermal monazite (U-Pb LA-MC-ICPMS) and molybdenite (Re-Os NTIMS) of the Sequeirinho-Pista orebodies rendered ages of ~2.71 to 2.68 Ga, while ore-related monazite of the Sossego-Curral orebodies yielded ages of ~1.90 to 1.88 Ga (Moreto et al., 2015). This implies two periods of IOCG style mineralisation at Sossego. The first occurred during coupling of ductile sinistral transpression with NNE-directed oblique shortening and Neoarchean magmatism at ~2.7 Ga. The second, shallowly emplaced Palaeoproterozoic system, formed after progressive exhumation of the deeply emplaced Neoarchaean IOCG deposits, and was coeval with the emplacement of 1.88 Ga A-type granites which may have caused regional circulation of magmatic and externally derived fluids along crustal discontinuities (Moreto et al., 2015). This second Palaeoproterozoic event was also responsible for other deposits in the region including

The Sequeirinho ore zone lies along a NE striking sinistral fault, associated with a positive magnetic anomaly, and comprises an S-shaped, tabular, subvertical body. It has been subjected to regional sodic (albite-hematite) alteration, overprinted by sodic-calcic (actinolite-rich) alteration accompanying with the formation of massive magnetite-(apatite) bodies. Both alteration assemblages exhibit ductile to brittle-ductile fabrics and are cut by spatially restricted zones of potassic (biotite and potassium feldspar) alteration that grades outward to chlorite-rich assemblages (Monteiro, et al., 2007).

The Sossego Hill zone is a subcircular, vertical, pipe-like orebody, with a central breccia surrounded by a stockwork of sulphide veins, faults, and shear zones (Morais and Alkmim, 2005; Carvalho, 2009; Domingos, 2009). The orebodies within the zone display only weakly developed early albitic and very poor subsequent calcic-sodic alteration, although they have well-developed potassic alteration assemblages that were formed during brittle deformation that produced breccia bodies. The matrix of the breccias commonly displays coarse mineral infill suggestive of growth into open space (Monteiro, et al., 2007). The potassic alteration assemblages, which mark the onset of mineralisation, grade outward to a widespread zone of chlorite and late hydrolytic (sericite-hematite-quartz) assemblages crosscut by calcite veins (Carvalho et al., 2005; Monteiro et al., 2008, ).

The orebodies are commonly brecciated. The Sequeirinho breccias contain rounded fragments of hydrothermal magnetite, actinolite and apatite or rocks with low angularity. The Sossego ore breccias comprise fragments of potassic-altered host rocks (e.g., granophyric granite) with high clast angularity, characteristic of breccias that underwent minor transport.

The sulphides of both groups of orebodies were initially accompanied by potassic alteration and a subsequent more important assemblage of calcite-quartz-epidote-chlorite. In the Sequeirinho orebodies, sulphides range from undeformed to deformed, while at the Sossego Hill orebodies they are undeformed. Very late stage, weakly mineralised hydrolytic alteration is present in the Sossego Hill orebodies (Monteiro, et al., 2007).

The dominant sulphides are chalcopyrite with subsidiary siegenite and millerite, and minor pyrrhotite and pyrite in the Sequerinho orebodies, although pyrite is relatively abundant in the Sossego Hill bodies.

Chalcopyrite occurs in the breccia matrix associated with pyrite, gold, siegenite, millerite, Pd melonite, hessite, cassiterite, sphalerite, galena, molybdenite, thorianite, and monazite. The resulting Fe-Cu-Au-Co-Ni-Pd- LREE signature characterises the Sossego deposit.

In early 2001 the total resource was quoted as 355 Mt @ 1.1% Cu, 0.28 g/t Au, encompassing a mineable reserve of 219 Mt @ 1.24% Cu, 0.33 g/t Au at a 0.4% Cu cut-off and stripping ratio of 3.3:1 wate:ore.

At the commencement of mining in 2004, reserves were quoted by CVRD as 250 Mt @ 1.0% Cu. Montiero, et al., (2007) published a reserve of 245 Mt @ 1.1% Cu, 0.28 g/t Au.

Mineralisation (gold) was initially discovered by garimperos (prospectors) in 1984 within CVRD concessions. The area was tendered to Phelps Dodge in 1996 and the first major intersections were in early 1997.

In 2001 the project was controlled by Mineracao Serra do Sossego, a 50:50 joint venture between Phelps Dodge do Brasil and CVRD.   In 2002 CVRD bought Phelps Dodge's share and commenced mining in 2004 with a nominal capacity of 93 000 tya of Cu in concentrates.

Remaining ore reserves at 31 December 2017 were (Vale 20-F form report to the US SEC, 2017):
    Proved Reserves - 110.7 Mt @ 0.68% Cu;
    Probable Reserves - 9.4 Mt @ 0.66% Cu;
    TOTAL Reserves - 120.1 Mt @ 0.68% Cu, with a recovery range of 90 to 95% of contained Cu.

The most recent source geological information used to prepare this summary was dated: 2012.    
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.

  References & Additional Information
   Selected References:
Bettencourt, J.S., Juliani, C., Xavier, R.P., Monteiro, L.V.S., Bastos Neto, A.C., Klein, E.L., Assis, R.R., Leite Jr., W.B., Moreto, C.P.N., Fernandes, C.M.D. and Pereira, V.P., Vit  2016 - Metallogenetic systems associated with granitoid magmatism in the Amazonian Craton: An overview of the present level of understanding and exploration significance: in    J. of South American Earth Sciences   v.68, pp. 22-49.
Bettencourt, J.S., Juliani, C., Xavier, R.P., Monteiro, L.V.S., Bastos Neto, A.C., Klein, E.L., Assis, R.R., Leite Jr., W.B., Moreto, C.P.N., Fernandes, C.M.D. and Pereira, V.P., Vit  2016 - Metallogenetic systems associated with granitoid magmatism in the Amazonian Craton: An overview of the present level of understanding and exploration significance: in    J. of South American Earth Sciences   v.68, pp. 22-49.
Huang, X.-W. and Beaudoin, G.,  2019 - Textures and Chemical Compositions of Magnetite from Iron Oxide Copper-Gold (IOCG) and Kiruna-Type Iron Oxide-Apatite (IOA) Deposits and Their Implications for Ore Genesis and Magnetite Classification Schemes: in    Econ. Geol.   v.114, pp. 953-979.
Monteiro, L.V.S., Xavier, R.P., Hitzman, M.W., Carvalho, E.R., Johnson, C.A., Souza Filho, C.R. and Torresi, I.,  2008 - Spatial and temporal zoning of hydrothermal alteration and mineralization in the Sossego iron oxide copper gold deposit, Carajas Mineral Province, Brazil: paragenesis and stable isotope constraints: in    Mineralium Deposita   v.43, pp. 129-159.
Monteiro, L.V.S., Xavier, R.P., Hitzman, M.W., Juliani, C., Souza Filho, C.R. and Carvalho, E.R.,  2008 - Mineral chemistry of ore and hydrothermal alteration at the Sossego iron oxide-copper-gold deposit, Carajas Mineral Province, Brazil: in    Ore Geology Reviews   v.34, pp. 317-336.
Moreto, C.P.N., Monteiro, L.V.S., Xavier, R.P., Creaser, R.A., DuFrane, S.A., M.A., Tassinari, C.G., Sato, K., Kemp, A.I.S. and Amaral, W.S.,  2015 - Neoarchean and Paleoproterozoic Iron Oxide-Copper-Gold Events at the Sossego Deposit, Carajas Province, Brazil: Re-Os and U-Pb Geochronological Evidence: in    Econ. Geol.   v.110, pp. 809-835.
Moreto, C.P.N., Monteiro, L.V.S., Xavier, R.P., Creaser, R.A., DuFrane, S.A., Melo, G.H.C., Delinardo da Silva, M.A., Tassinari, C.G. and Sato, K.,  2014 - Timing of multiple hydrothermal events in the iron oxide-copper-gold deposits of the Southern Copper Belt, Carajas Province, Brazil: in    Mineralium Deposita   v.50, pp. 517-546.
Oliveira J L, Fanton J, Almeida A J  2001 - Discovery and geology of the Sossego copper-gold deposit, Carajas District, Para State, Brazil: in  2001 SME Annual Meeting & Exhibition, Feb 26-28, Denver, Colorado, Technical Programs    Abstract 1p
Williams, P. J., Kendrick, M.A. and Xavier, R.P.,  2010 - Sources of Ore Fluid Components in IOCG Deposits: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.3, pp. 107-116.
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
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.
Zhu, Z.,  2016 - Gold in iron oxide copper-gold deposits: in    Ore Geology Reviews   v.72, pp. 37-42.

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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