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Tapajos and Alta Floresta Gold Provinces - Serrinha, Ouro Roxo, Pe Quente, Luizao, Juruena
Main commodities: Au

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The Tapajós Gold Province within central Brazil lies within the southern half of the major NNW-SSE trending Palaeoproterozoic (2.03 to 1.88 Ga) Tapajós-Parima tectonic province (or Ventuari-Tapajós geochronological domain) which is composed of a back-arc sequence, four volcano-plutonic arcs and intra-arc sedimentation and is located immediately to the west of the central Archaean Amazonian province that is the core of the Amazon Craton.

The ESE-WNW trending, 800 x 100 km Alta Floresta Gold Province comprises a belt of placer and intrusion-related gold deposits that lie along the southern section of the northeastern margin of the Paleoproterozoic (1.82-1.54 Ga) Rondonia-Juruena tectonic province (Rio Negro-Juruena geochronological province), which is parallel to and immediately to the SW of the Tapajós-Parima tectonic province.

According to Santos et al. (2001), the Tapajós and Alta Floresta gold provinces contain a series alluival/eluvial and predominantly small primary gold deposits, including:
i). orogenic, turbidite-hosted: disseminated and quartz-pyrite veinlet deposits within the lower greenschist-facies metaturbidites of the Jacareacanga Group, and emplaced in ductile structures;
ii). orogenic, magmatic arc-hosted: disseminated and pyrite-quartz-carbonate vein deposits, hosted by metamorphic rocks (Cuiú-Cuiú Complex) and formed under a ductile-brittle regime, with the Ouro Roxo deposit as a type example;
iii). intrusion-related, epizonal quartz-vein deposits (~1860 Ma), occurring as vertical to subvertical quartz-pyrite veins and pyrite disseminations filling extensional brittle faults; and
iv). intrusion-related, epizonal, disseminated/stockwork deposits (with some similarities to porphyry-type deposits), the type-example being the Serrinha deposit in the Alta Floresta province, which is spatially and genetically related to the Matupá granitic Massif (1872±12 Ma). At this deposit, the Matupá Massif comprises a single biotite monzogranite, known as the Matupá Granite, which outcrops as isotropic undeformed and little-fractured blocks. The gold mineralization is disseminated and restricted to the intense hydrothermally altered zones where it is associated with pyrite, sericite, chlorite and/or albite. Hydrothermal magnetite and rutile accompany the pyrite. Gold is in the native form, included within, or filling fractures in pyrite. The Fazenda Brasileiro Au mine at Serrinha is quoted as containing at least 15 Mt @ 8 g/t Au.
The deposits listed above have individual resources of that range from 5 to 60 t of gold.

According to Assis et al. (2017), most of the gold systems in the Alta Floresta Gold Province are hosted by oxidised, I-type, calc-alkaline to subalkaline, medium- to high-K, metaluminous to weakly peraluminous granitic intrusions. They describe mineralisation occurring as:
i). disseminated (e.g., Luizão, Serrinha, Juruena, X1 and Pé Quente) and structurally controlled vein-type (e.g., Paraíba, Buriti and Pezão) Au ±Cu (Bi, Te, Ag, Mo), predominantly comprising pyrite with variable concentrations of chalcopyrite and hematite (Moura et al., 2006; Paes de Barros, 2007; Assis, 2011; Rodrigues, 2012; Trevisan, 2012; Serrato, 2014). Host intrusions include biotite tonalite (1901±6.8 Ma) and monzonite (1979±31 Ma) for the Pé Quente, syenogranite-monzogranite (1970±3 and 1964±1 Ma) for the Luizão, and biotite granodiorite (1904±4.6 Ma) and quartz-feldspar porphyry (1784±10 Ma) for the X1 gold deposits. The host granites within the gold-rich zones are strongly altered to sericite-muscovite+chlorite+quartz (phyllic) and contain abundant pyrite with variable amounts of chalcopyrite±molybdenite±hematite accompanied by subordinate barite, sphalerite, galena, and Bi-Te-Ag-bearing phases. These zones overprint more extensive and pervasive potassic alteration comprising orthoclase-microcline±hematite, which is preceded by more localised sodic alteration with albite ±quartz. Gold commonly occurs as <180 µm inclusions in pyrite, although pyrite-molybdenite is frequently associated with gold at the X1 deposit. Gold-related pyrite from Luizão and Pé Quente and molybdenite from the X1 deposits were dated (Re-Os; Assis et al., 2017), giving ages of 1792±9 to 1784±11 Ma for Pé Quente; and 1805±21.5 to 1782±8.9 Ma at Luizão. The X1 molybdenite yields ages of 1787±7 and 1785±7 Ma. These ages are markedly distinct from those of their host granites but display a close temporal association with the quartz-feldspar porphyry intrusion at the X1 deposit.
ii). disseminated Au±Mo±Cu deposits (e.g., Ana and Jaca) composed of pyrite and variable amounts of chalcopyrite and molybdenite, and
iii). structurally controlled vein-type Au+Zn+Pb±Cu deposits (e.g., Franscisco, Bigode and Luiz), with pyrite and significant concentrations of sphalerite, galena, and minor digenite and chalcopyrite (Assis, 2011; Trevisan, 2015). The gold in these deposits occurs predominately as inclusions (<185 µm) in pyrite and less commonly in chalcopyrite and as free Au.

Official production figures estimate 159 tonnes of gold were mined in the Tapajos Gold Province between 1959 and 1996. Ninety percent of this was taken from thousands of recent placer deposits, as well as Tertiary paleoplacers located about 10 to 20 metres below the recent surface.

Gold at the mouth of the Tropas River in 1958, striggering the discovery of several other alluvial gold deposits during the 1960s. The Tapajós gold province became the main gold producer in Brazil in the 1970s to the 1990s, largely exploited by up to ~80 000 artisanal miners (garimpeiros). The annual reported gold production between 1975 and 1990 was of the order of 60 to 80 t, although this represent only a small portion of the gold being mined.

Following exhaustion of some of the alluvial±eluvial deposits, small-scale mining turned to primary ores, with the discovery of several hundred lode gold occurrences mainly in the Tapajós and Alta Floresta domains. The Brazilian Geological Survey has registered 178 sites of exposed primary ores; 140 in the Tapajós domain and 38 in the Alta Floresta domain. Normally, only ~15 to 120 m thick supergene zones from above the fresh rock have been mined by open pit, although in a few cases underground workings have also been attempted. In 2016, the Alta Floresta Gold Province became the focus of copper exploration.

The most recent source geological information used to prepare this decription was dated: 2012.     Record last updated: 1/12/2017
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:
Assis, R.R., Xavier, R.P. and Creaser, R.A.,  2017 - Linking the Timing of Disseminated Granite-Hosted Gold-Rich Deposits to Paleoproterozoic Felsic Magmatism at Alta Floresta Gold Province, Amazon Craton, Brazil: Insights from Pyrite and Molybdenite Re-Os Geochronology: in    Econ. Geol.   v.112, pp. 1937-1957.
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.
Caetano, J., Rye, R.O., Nunes, C.M.D., Snee, L.W.. Correa-Silva, R.H., Monteiro, L.V.S., Bettencourt, J.S., Neumann, R. and Neto, A.A.,  2005 - Paleoproterozoic high-sulfidation mineralization in the Tapajos gold province, Amazonian Craton, Brazil: geology, mineralogy, alunite argon age, and stable-isotope constraints: in    Chemical Geology   v.215, pp. 95-125.
Juliani C, Correa Silva R H, Monteiro L V S, Bettencourt J S and Nunes C M D,  2002 - The Batalha Au-granite system Tapajos Gold Province, Amazonian craton, Brazil: Hydrothermal alteration and regional implications: in    Precambrian Research   v119 pp 225-256
Klein E L, Harris C, Renac C, Giret A, Moura C A V and Fuzikawa K,  2006 - Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil: in    Mineralium Deposita   v41 pp 160 - 178
Lamarao C N, Dall Agnol R and Pimentel M M,  2005 - Nd isotopic composition of Paleoproterozoic volcanic and granitoid rocks of Vila Riozinho: implications for the crustal evolution of the Tapajos gold province, Amazon craton: in    J. of South American Earth Sciences   v18 pp 277-292
Moura, M.A., Botelho, N.F., Olivo, G.R. and Kyser, T.K.,  2006 - Granite-Related Paleoproterozoic, Serrinha Gold Deposit, Southern Amazonia, Brazil: Hydrothermal Alteration, Fluid Inclusion and Stable Isotope Constraints on Genesis and Evolution: in    Econ. Geol.   v101 pp 585-605
Santos J O S, Groves D I, Hartmann L A, Moura M A and McNaughton N J  2001 - Gold deposits of the Tapajos and Alta Floresta Domains, Tapajos-Parima orogenic belt, Amazon Craton, Brazil: in    Mineralium Deposita   v36 pp 278-299

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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