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Corumba, Urucum, Santa Cruz
Mato Grosso do Sul, Brazil
Main commodities: Fe Mn

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The Corumba - Urucum district is located in western Mato Grosso do Sul, Brazil, along the border with Bolivia. It hosts extensive manganese rich ironstones of late Neoproterozoic age. The district is some 170 km in length, the greater part of which is in Bolivia. An approximately 30 km strike length of mineralisation is found in Brazil, where the iron formation reaches a thickness of up to 300 m. Resources are stated as being as much as 36 Gt at an average grade of 54% Fe, embracing higher grade enriched zones containing 890 Mt @ 63% Fe.
(#Location: Urucum - 19° 11' 23"S, 57° 36' 17"W; Santa Cruz - 19° 13' 7"S, 57° 35' 4"W).

The host Jacadigo Group is preserved in a series of 8 tabular mountains that rise up to 1000 m out of the swampy lowlands of the Pantanal. Basement is represented by gneisses and amphibolites, with lesser schists and quartzites of the Rio Apa cratonic block, cut by 889 to 1200 Ma granitoids. These are overlain by the:
Jacadigo Group - which is 150 to 700 m thick, and overlies the Rio Apa basement with an angular unconformity. It comprises:
  The Urucum Formation - a basal conglomeratic and sandy braided stream deposits containing volcanogenic detritus and arkose beds. The lower section of this formation is mainly diamictite/conglomerate and siltstones, whilst the upper segment is predominantly sand-sized facies, with reworked hematitic, silt- to pebble-sized mud rip-up clasts. The latter grades upwards into a marine setting in the lower portion of the overlying Santa Cruz Formation, where the first ice-rafted dropstones appear (Trompette et al., 1998).
  The Santa Cruz Formation, which is up to 300 m thick, comprises hematite-rich banded iron formation with manganese oxide intercalations and lens of diamictite containing boulder size ice-rafted dropstones. It is interpreted to have been deposited in a marginal rift basin to shelf, occurring as iron and manganese-rich sediments overlying the fluvial deposits of the Urucum Formation. These sediments were essentially composed of iron, silica and carbonate, and form banded iron formations and ironstones with jasper, hematite and carbonate, interspersed with layers of manganiferous, arkosic, fine to coarse grained clastic sediments and conglomerates. The maximum thickness of the formation recorded in drilling is 396 m, whilst the thinnest is only 40 m. Polgári et al. (2021) state that it has been established that the Santa Cruz Formation is Ediacaran, aged ~547 ±3 Ma (39Ar/40Ar; after Piacentini et al., 2013), consistent with the presence of Corumbella fossils (Biondi and Lopez, 2017; Biondi et al., 2020), estimated at ~550 Ma.
  The base of the Santa Cruz Formation is marked by the appearance of dropstones and the change from carbonate cement to manganese and iron oxides in the host cross bedded sandstone of the 80 m thick lower member. This member carries a basal 0 to 7 m thick manganese rich horizon (Mn1) with concretionary/nodular, detritus-rich and layered massive ores. The upper member is almost exclusively composed of chemical sediments. It commences with a widespread band of layered massive manganese ore that is 0 to 3.5 m thick (Mn2). This is followed by a 70 to 270 m thick monotonous sequence of hematite-jaspilite which covers an area of 120 km
2. A third 0 to 2.35 m thick manganese horizon (Mn3) is intercalated with the hematite-jaspilite 40 to 45 m above Mn2, while a fourth such band, Mn4 which is 0 to 1.4 m thick, is found a further 45 m higher. Mn3 and Mn4 are again layered massive manganese oxide beds. Erratic dropstone from 0.05 to 1 m across are found sporadically throughout the chemical sediments.
  The Jacadigo Group is correlated with the Cuiabá Group of the Northern Paraguaia Fold Belt. The iron formation of the Santa Cruz Formation is both interbedded with, and overlain by, pebble to boulder glacial diamictite of the Puga Formation equivalents.
Corumbá Group - a carbonate rich succession which unconformably overlies and surrounds the Jacadigo Group. The diamictites are overlain by the carbonate facies succession that is regarded to be equivalent to the Araras Group of the Northern Paraguaia Fold Belt (Trompette et al., 1998; Silva et al., 2016), such that the Araras-Corumbá carbonate platform is continuous along the southern and eastern margins of the Amazon craton and Rio Apa Block and into the Chiquitos-Tucavaca Aulacogen/Rift (Freitas et al., 2011) report the presence of Ediacaran fossils within the Corumbá Group. This group has been subdivided into the:
  - Cadiueus/Puga Formation - glacio-marine diamictite, overlain by glacial outwash deposits. The top of the Puga diamictite is marked by an erosional surface that has been intensely pyritised and chloritised during burial diagenesis, overlain by an 18 m thick, light grey, intraclast-bearing, granitic gneiss-pebble to cobble conglomerate that is pervasively trough-cross-bedded. The youngest detrital zircon from this formation has been dated at 706 ±9 Ma (U-Pb zircon; Babinski et al., 2013), a 695 ±17 Ma from within shaly beds in the Urucum district iron formation succession (Frei et al., 2017).
  - Cerradinho Formation - 60 m of dropstone-rich shallow, tidal, shelf-marine facies sandstone and rhythmites, comprising dark-grey to black, thinly bedded, chlorite-rich, feldspathic sandstones with interbedded black laminated siltstone (Hiatt, et al., 2020).
  - Bocaina Formation - dominantly stromatolite-rich dolostone to dolomitic limestone and limestone, sometimes silicified and oolitic, representing a regionally extensive shallow and warm water carbonate platform. It is generally at least 300 m thick, but may be as much as 1000 m, with ~350 m of limestone to dolomitic limestone and 300 m of dolostone. It has transitional contacts with the Cerradinho and Tamengo below and above respectively, but also oversteps the former to rest directly on the Jacadigo Group and Rio Apa basement.
Weathered Corumba iron formation   - Tamengo Formation, an ~200 m thick carbonatic-clastic sequence that discordantly overlies the Bocaina Formation. It is characterised by black limestones, grainstones and organic siltstones, and is predominantly composed of limestone with subordinate shales, siltstones and sandstones, as well as intercalations of marl and volcanic ash. Carbonate breccias of sedimentary and/or tectonic origin are also evident.
  - Guiacurus Formation, a thick succession of grey laminated siltstones and finer-grained pelite that both overlies, and is laterally equivalent, to the Tamengo Formation. The base of the Guiacurus Formation is interpreted to lie on or close to the base of the Cambrian (Walde et al., 2015).
In summary, Polgári et al. (2021) conclude that from sedimenatalogical studies the Santa Cruz Formation formed as an in-fill of an ancient marginal basin with iron and manganese-rich sediments overlying fluvial the Urucum Formation, while limestones from the Tamengo and Bocaina Formations were deposited in the shallow marginal rim

The fresh jaspilitic ores of the lower Santa Cruz Formation average 50% Fe, while supergene enriched sections carry up to 67% Fe.

The higher grade, enriched ores occur in two forms, namely:

i). canga - Fe-hydroxide-cemented breccias of hematite-jaspilite - occurs as a sub-recent weathering crust in places, and
ii). 'colluvial' ore in the form of weathered 0.01 to 10 m blocks of hematite-jaspilite which form debris cones and fans on the flanks of the tabular mountains.

The un-enriched hematite-jaspilites are predominantly composed of micro-crystalline hematite and crypto-crystalline red jasper forming alternating bands on a micro- and macro-scopic scale. In finely laminated ores, spherical and concentric aggregates of hematite and jasper are preserved.

Mining has occurred in two mining areas, Urucum to the west and the Santa Cruz Mine on the southeastern part of the Morro Grande plateau. I has also involved open pit extraction of iron ores and underground mining of manganese.

Image: Weathered and supergene enriched iron formation at the Courumba iron deposit.

Rio Tinto operated the Corumbá iron ore mine through it's 100% owned subsidiary Mineraçao Corumbaense Reunida, with the output being transported by barge down the major Paraguay River to Argentina. Vale, who also exploits iron and manganese from its nearby Urucum mine, purchased the iron operations from Rio Tinto in 2009. On 6 April, 2022, Vale sold their stake in Mineraçã Corumbaense Reunida S.A. and associated companies involved in the operation at Corumba to J&F Mineraçã Ltda.

The most recent source geological information used to prepare this decription was dated: 2021.     Record last updated: 14/3/2023
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.


Santa Cruz

  References & Additional Information
   Selected References:
Angerer, T., Hagemann, S.G. Walde, D.H.G.,  2021 - Diagenetic and supergene ore forming processes in the iron formation of the Neoproterozoic Jacadigo Group, Corumba, Brazil: in    J. of South American Earth Sciences   v.105, 28p. doi.org/10.1016/j.jsames.2020.102902.
Angerera, T., Hagemann, S.G., Walde, D.H.G., Halverson, G.P. and Boyce, A.J.,  2016 - Multiple metal sources in the glaciomarine facies of theNeoproterozoic Jacadigo iron formation in the Santa Cruz deposit. Corumba, Brazil: in    Precambrian Research   v.275, pp. 369-393.
Biondi, J.C. and Lopez, M.,  2017 - Urucum Neoproterozoic-Cambrian manganese deposits (MS, Brazil): Biogenic participation in the ore genesis, geology, geochemistry, and depositional environment: in    Ore Geology Reviews   v.91, pp. 335-386.
Biondia, J.C., Polgari, M., Gyollai, I., Fintor, K., Kovacs, I., Fekete J. and Mojzsis, S,J.,  2020 - Biogenesis of the Neoproterozoic kremydilite manganese ores from Urucum (Brazil) - A new manganese ore type: in    Precambrian Research   v.340, 27p. doi.org/10.1016/j.precamres.2020.105624.
Frei, R., Dossing, L.N., Gaucher, C., Boggiani, P.C., Frei, K.M., Arting, T.B., Crowe, S.A. and Freitas, B.T.,  2017 - Extensive oxidative weathering in the aftermath of a late Neoproterozoic glaciation - Evidence from trace element and chromium isotope records in the Urucum district (Jacadigo Group) and Puga iron formations (Mato Grosso do Sul, Brazil): in    Gondwana Research   v.49, pp. 1-20. doi.org/10.1016/j.gr.2017.05.003.
Gutzmer, J., Chisonga, B.C., Beukes, N.J. and Mukhopadhyay, J., C.A.,  2008 - The geochemistry of banded iron formation-hosted high-grade hematite-martite iron ores: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore, Reviews in Economic Geology   v.15 pp. 157-183
Huang, Q., Viehmann, S., Walde, D.H.G. and Li, W.,  2021 - Iron isotope constraints on the metal source and depositional environment of the Neoproterozoic banded iron- and manganese deposits in Urucum, Brazil: in    Geochemistry,   v.81 NA. doi.org/10.1016/j.chemer.2021.125771.
Klein C, and Ladeira E A,  2004 - Geochemistry and Mineralogy of Neoproterozoic Banded Iron-Formations and Some Selected, Siliceous Manganese Formations from the Urucum District, Mato Grosso do Sul, Brazil: in    Econ. Geol.   v99 pp 1233-1244
Piacentini, T., Vasconcelos, P.M. and Farley, K.A.,  2013 - 40Ar/39Ar constraints on the age and thermal history of the Urucum Neoproterozoic banded iron-formation, Brazil: in    Precambrian Research   v.228, pp. 48-62.
Polgari, M., Biondi, J.C., Gyollai, I., Fintor, K. and Szabo, M.,  2021 - Origin of the Urucum iron formations (Neoproterozoic, Brazil): Textural and mineralogical evidence (Mato Grosso do Sul - Brazil): in    Ore Geology Reviews   v.139, 25p. doi.org/10.1016/j.oregeorev.2021.104456.
Urban H, Stribrny B, Lippolt H J  1992 - Iron and Manganese Deposits of the Urucum District, Mato Grosso do Sul, Brazil: in    Econ. Geol.   v87 pp 1375-1392

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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