The Amazonian Craton hosts world-class metallogenic provinces with a wide range of styles of primary precious, rare, base metal, and placer deposits. This paper provides a synthesis of the geological database with regard to granitoid magmatic suites, spatio temporal distribution, tectonic settings, and the nature of selected mineral deposits. The Archean Caraj as Mineral Province comprises greenstone belts (3.04 e2.97 Ga), metavolcanic-sedimentary units (2.76e2.74 Ga), granitoids (3.07e2.84 Ga) formed in a magmatic arc and syn-collisional setting, post-orogenic A 2-type granites as well as gabbros (ca. 2.74 Ga), and anorogenic granites (1.88 Ga). Archean iron oxide-Cu-Au (IOCG) deposits were synchronous or later than bimodal magmatism (2.74e2.70 Ga). Paleoproterozoic IOCG deposits, emplaced at shallow-crustal levels, are enriched with NbeYeSneBeeU. The latter, as well as SneW and Au-EGP deposits are coeval with ca. 1.88 Ga A 2-type granites. The Tapaj os Mineral Province includes a low-grade meta-volcano-sedimentary sequence (2.01 Ga), tonalites to granites (2.0e1.87 Ga), two calc-alkaline volcanic sequences (2.0e1.95 Ga to 1.89e1.87 Ga) and A-type rhyolites and granites (1.88 Ga). The calc-alkaline volcanic rocks host epithermal Au and base metal mineralization, whereas CueAu and CueMo ± Au porphyry-type mineralization is associated with sub-volcanic felsic rocks, formed in two continental magmatic arcs related to an accretionary event, resulting from an Andean-type northwards subduction. The Alta Floresta Gold Province consists of Paleoproterozoic plutono-volcanic sequences (1.98e1.75 Ga), generated in oceaneocean orogenies. Disseminated and vein-type Au ± Cu and Au þ base metal deposits are hosted by calc-alkaline I-type granitic intrusions (1.98 Ga, 1.90 Ga, and 1.87 Ga) and quartz-feldspar porphyries (ca. 1.77 Ga). Timing of the gold deposits has been constrained between 1.78 Ga and 1.77 Ga and linked to post-collisional Juruena arc felsic magmatism (e.g., Colíder and Teles Pires suites). The Transamazonas Province corresponds to a NeS-trending orogenic belt, consolidated during the Transamazonian cycle (2.26e1.95 Ga), comprising the Lourenço, Amap a, Carecuru, Bacaj a, and Santana do Araguaia tectonic domains. They show a protracted tectonic evolution, and are host to the pre-, syn-, and post-orogenic to anorogenic granitic magmatism. Gold mineralization associated with magmatic events is still unclear. Greisen and pegmatite SneNbeTa deposits are related to 1.84 to 1.75 Ga late-orogenic to anorogenic A-type granites. The Pitinga Tin Province includes the Madeira SneNbeTaeF deposit, Sngreisens and Sn-episyenites. These are associated with A-type granites of the Madeira Suite (1.84 e1.82 Ga), which occur within a cauldron complex (Iricoum e Group). The A-type magmatism evolved from a post-collisional extension, towards a within-plate setting. The hydrothermal processes (400 C e100 C) resulted in albitization and formation of disseminated cryolite, pyrochlore columbitization, and formation of a massive cryolit...
ABSTRACT. The Alta Floresta Gold Province (AFGP) is located in the central-southern portion of the Amazon Craton. In its eastern segment there are more than one hundred gold deposits hosted in volcanic and plutonic rocks of medium to high content of potassium. In many of these deposits the gold ore is correlated spatially and genetically related to magmatic-hydrothermal systems and mainly hosted into the silicification, potassic and sericitic alterations. In this context, this work focuses on understanding the geological context of the region and the possibility of expanding new exploratory frontiers through techniques further traditional geological mapping.The processing and interpretation of airborne magnetic and gamma-ray spectrometry data of the Juruena-Teles Pires Project (Phase 1) allowed the production of a new regional geological map of the eastern portion of the AFGP. Additionally, theoretical models showed that despite the limitations of the reduction to the pole at low latitudes, the magnetic enhancements proposed can be applied to real data through the use of directional filtering to eliminate the features generated in the magnetic declination direction. The Total Horizontal Derivative of the Tilt Derivative (THDR-TDR) method proved the best enhancement for the interpretation of the structures, showing a structural complexity similar to that proposed for the evolution of the province. The interpretation of the products based on the gamma-ray spectrometry channels allowed the reinterpretation of different geological units, including the individualization of a new high-potassium intrusive unit, which in the context of AFGP may have metallogenetic potential.Keywords: Alta Floresta Gold Province, airborne geophysical data, geological interpretation. RESUMO.A Província Aurífera de Alta Floresta (PAAF) situa-se na porção centro-sul do cráton Amazônico. Em seu segmento leste, ocorrem mais de uma centena de depósitos auríferos hospedados em rochas plutônicas e vulcânicas de médio a alto potássio. Além disso, em muitos desses depósitos o minério aurífero apresenta relação espacial e genética com alterações hidrotermais, preferencialmente alterações do tipo potássica e sericítica. Nesse contexto, o trabalho enfoca o entendimento do contexto geológico dessa região e a possibilidade de expansão de novas fronteiras exploratórias por meio de técnicas que vão além do mapeamento geológico tradicional.Assim, através do processamento e interpretação de dados aeromagnetométricos e aerogamaespectrométricos do projeto Juruena-Teles Pires (Fase 1) gerou-se um novo mapa geológico regional da porção leste da PAAF. Adicionalmente, por meio de modelos teóricos observou-se que apesar das limitações da redução ao polo em baixas latitudes, os realces magnéticos propostos podem ser aplicados aos dados reais mediante o uso de filtros direcionais que eliminem os artefatos gerados na direção da declinação magnética. O método Inclinação do Sinal Analítico do Gradiente Horizontal Total (ISA-GHT) mostrou-se como o realce mais adequado ...
This review paper aims to integrate geological, tectonic and metallogenetic data, including new data, and propose a regional model for the gold (and base metal) mineralization in the south Amazonian Craton to support the mineral exploration concerning magmatic–hydrothermal deposits. The Proterozoic evolution of the Amazonian Craton comprises the accretion of terrains to the Archean Carajás Mineral Province. In the Tapajós and Juruena mineral provinces, located at the south part of the Amazonian craton, a long-lived ocean–continent subduction event produced ca. 2.0 to 1.77 Ga continental magmatic arcs. Extensive lava flows, volcaniclastic, sedimentary, and plutonic rocks were originated during at least four major orogenic magmatic events (ca. 2.1, 1.9, 1.88, and 1.80 Ga) and two post- to anorogenic events (ca. 1.87 and 1.77 Ga). Gold mineralization occurs in: (i) alluvial/colluvial occurrences, (ii) orogenic carbonate–sulfide-rich quartz veins in shear zones, (iii) stockworks, veins, and dissemination in granites, (iv) contact of basic dikes, (v) well-preserved high-, intermediate- and low-sulfidation epithermal mineralization, and (vi) porphyry-like and intrusion-related gold systems associated with late- to post-orogenic epizonal granites. The estimated historical gold production, mainly in secondary deposits, is over 27 Moz at the Tapajós and 6 Moz at the Juruena provinces. A total resource of over 5 Moz Au is currently defined in several small to large primary gold deposits. Andesite to rhyolite, volcaniclastic, and clastic sedimentary rocks (1.96–1.88 Ga) host epithermal (high-, intermediate-, and low-sulfidation) Au–(Ag–Pb–Zn) mineralization, whereas Au–Cu and Cu–M–Au mineralization is hosted in sub-volcanic tonalitic to granitic plutons. Advanced argillic alteration (alunite, pyrophyllite, enargite) associated with high-sulfidation mineralization occurs in ring volcanoes around nested volcanic calderas. This zone grades outward to propylitic or chlorite alteration, often covered by silica caps with vuggy silica. Lava flows and volcaniclastic rocks within faults or associated with volcanic edifices and rhyolitic domes host low- and intermediate-sulfidation mineralization. Low-sulfidation alteration zones typically have adularia and illite or sericite. Chalcopyrite, sphalerite, galena, pyrite, digenite, and manganiferous calcite are related to intermediate-sulfidation gold mineralization. Late- to post-orogenic evolved oxidized I-type granitoids host alkalic-type epithermal and porphyry-like gold mineralization. Porphyry-style hydrothermal alteration is analogous to those of modern systems, with inner sodic and potassic (potassic feldspar ± biotite or biotite) alterations grading to propylitic, muscovite-sericite, chlorite–sericite, and chlorite alterations. Potassic alteration zones are the locus of Cu–Mo mineralization, and gold-rich zones occur in muscovite/sericite–quartz–pyrite alteration. The Paleoproterozoic epithermal and porphyry-like mineralization in these large provinces defines a new frontier for the exploration of world-class gold deposits in the worldwide Proterozoic arc-related magmatic terrains.
Disponível on-line no endereço www.igc.usp.br/geologiausp -207 -Resumo O garimpo aurífero do Papagaio, localizado em Paranaíta, Mato Grosso, insere-se no setor noroeste da Província Aurífera de Alta Floresta, sul do Cráton Amazônico. Está hospedado em dacito porfirítico inicialmente afetado por alteração potás-sica, sobreposta por forte alteração sericítica pervasiva e, por fim, por alteração propilítica. O minério é representado pela paragênese pirita + calcopirita + esfalerita ± galena ± calcocita ± covelita e ocorre associado a sistemas de veios de quartzo e stockworks que truncam os setores de alteração potássica e sericítica. Estudos de inclusões fluidas dos veios mineralizados e estéreis presentes no garimpo permitiram identificar três grupos de inclusões fluidas: tipo I) inclusões aquocarbônicas; tipo II) aquosas bifásicas; tipo III) aquosas tri a multifásicas. Nos veios mineralizados houve a crepitação das inclusões do Tipo I a 325ºC. Foram encontradas temperaturas de homogeneização de 115,1 a 216,2ºC e salinidades entre 0,5 a 24,0% para as inclusões do Tipo II. Nos veios estéreis, as inclusões do Tipo II resultaram em temperaturas de homogeneização total entre 135,9 e 190,3ºC e salinidades de 26,0 a 30,2%. No Tipo III a homogeneização total ocorreu entre 323,2 e 402,9ºC com salinidade superior a 40,0%. Portanto, fluidos de elevada temperatura e salinidade com características de origem magmática tiveram um papel essencial na formação das zonas mineralizadas do garimpo. Nesse contexto, a colocação de corpos subvulcânicos teria sido essencial na gênese da mineralização aurífera do Papagaio, pois teria servido como fonte de calor, fluido e metais para a instalação de um sistema magmático-hidrotermal profundo, relacionado ao ambiente dos depósitos do tipo pórfiro e intrusion-related gold systems (IRGS).Palavras-chave: Cráton Amazônico; Província Aurífera de Alta Floresta; Inclusões fluidas; Microtermometria; Fluidos magmáticos. AbstractThe Papagaio artisanal gold mining in Paranaíta, Mato Grosso, Brazil, is located in the northwest sector of Alta Floresta Gold Province, in the southern Amazon Craton. Mineralization is hosted in porphyritic dacite initially affected by a potassic alteration that is superimposed by a strong pervasive sericitic alteration and, finally, by propylitic alteration. The ore paragenesis consists of pyrite + chalcopyrite + sphalerite ± galena ± chalcocite ± covellite that is located in a quartz veins systems and stockworks that cuts hydrothermal potassic and sericitic alteration zones. Studies of fluid inclusions of the mineralized and barren veins present in the mining identified three groups of fluid inclusions: type I) aqueous-carbonic inclusions; type II) aqueous biphasic inclusions; type III) aqueous tri-to multiphase inclusions. In the mineralized veins, the type I inclusions decrepitated at 325ºC. Type II inclusions have homogenization temperatures of 115.1 to 216.2ºC and salinities of 0.5 to 24.0%. In the barren veins, type II inclusions yielded total homogenization temperatur...
Resumo A Província Aurífera de Alta Floreta, centro-sul do Craton Amazônico, representa uma unidade tectônica essencialmente composta por sequências plutônicas-vulcânicas geradas em ambiente de arcos magmáticos que se desenvolveram e se agregaram progressivamente no decorrer do Paleoproterozoico. No segmento leste desta província, na região de União do Norte (Peixoto de Azevedo, MT), rochas plutônicas e vulcânicas são as hospedeiras de depósitos auríferos com sulfetos de metais de base (esfalerita+galena±di genita±calcopirita), alguns atualmente em explotação por garimpeiros. O arcabouço geológico desta região consiste de uma unidade vulcanoclástica de origem epiclástica que aloja várias suítes graníticas. Na unidade vulcanoclástica predominam grauvaca-feldspática e arenito arcoseano lítico vulcanoclásticos, possivelmente depositados em bacia de retroarco do tipo foreland, em margem ativa, cuja área fonte teriam sido vulcânicas intermediárias. As suítes intrusivas são representadas por plútons que variam em composição de (1) granodiorito, (2) sieno-monzogranito a, (3) álcali-feldspato granito porfi rítico e monzogranito porfi rítico (Pórfi ro União do Norte). Todas essas unidades são ainda cortadas por diques de vulcânicas máfi cas a félsicas. No conjunto, essas unidades são recobertas pelos sedimentos arenáceos da Formação Dardanelos. Dados geoquímicos obtidos para as unidades plutônicas-vulcânicas indicam magmatismo eminentemente cálcio-alcalino de alto K, magnesiano, metaluminoso e subordinadamente alcalino, peraluminoso e ferroso. Evidências de campo em conjunto com os dados litogeoquímicos indicam que as séries magmáticas representam a evolução do ambiente tectono-magmático, desde a geração de rochas mais primitivas em ambiente de arco vulcânico (granodiorito; granito tipo I) até o alojamento de corpos altamente evoluídos (Pórfi ro União do Norte; granito tipo A) em arcabouço pós-colisional.Palavras-chave: Província Aurífera de Alta Floresta, granitos tipo I e A, petrografi a, geoquímica. Abstract Geological setting and geochemistry of the plutonic-volcanic units from the União do Norte region, eastern portion of the Alta Floresta Gold Province (MT).The Alta Floresta Gold Province, eastern portion of the Amazon Craton, represents a tectonic unit composed primarily of plutonic-volcanic sequences generated in a continental arc during the Paleoproterozoic. Particularly in the União do Norte region, easternmost segment of this province and within the municipal limits of Peixoto de Azevedo (MT), the plutonic and volcanic rocks are the host of gold deposits with base metal sulphides (sphalerite+galena±chalcopyrite±digenite), some currently under exploitation by local prospectors (garimpeiros). The geological setting of this region consists essentially of an epiclastic volcaniclastic unit and granitic suites. The former unit contains feldspathic-arenite and feldspathic-wake volcaniclastics interpreted to have been deposited in a retroarc foreland basin in an active continental margin. The main source area for thes...
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