Programa de Pós-Graduação em Geologia e Geoquímica - PPGG/IG

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2603

O Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA) surgiu em 1976 como uma necessidade de desmembramento do então já em pleno desenvolvimento Curso de Pós-Graduação em Ciências Geofísicas e Geológicas (CPGG), instalado ainda em 1973 nesta mesma Universidade. Foi o primeiro programa stricto sensu de Pós-Graduação (mestrado e doutorado) em Geociências em toda Amazônia Legal. Ao longo de sua existência, o PPGG tem pautado sua atuação na formação na qualificação de profissionais nos níveis de Mestrado e Doutorado, a base para formação de pesquisadores e profissionais de alto nível. Neste seu curto período de existência promoveu a formação de 499 mestres e 124 doutores, no total de 623 dissertações e teses.

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Aspectos geológicos e metalogenéticos do depósito de ouro hospedado em metaconglomerados e metarenitos paleoproterozoicos Castelo de Sonhos, Província Tapajós, sudoeste do Pará
(Universidade Federal do Pará, 2015-04-06) QUEIROZ, Joana D’arc da Silva; KLEIN, Evandro Luiz; http://lattes.cnpq.br/0464969547546706
Castelo de Sonhos, located in the central-south sector of the Amazonian Craton, near the boundary between the Tapajós and Xingu-Iriri tectonic domains, is a gold deposit hosted in metaconglomerates and metasandstones of the Castelo dos Sonhos Formation (<2080 Ma U-Pb SHRIMP). Subvolcanic rocks and granitoids were identified in boreholes that drilled the deepest parts of the deposit area. Some of these rocks are intrusive into the Castelo dos Sonhos Formation, while for others rocks, the contact relationships could not be determined with confidence. In general, these rocks show calc-alkaline to alkaline affinities and their geochemical patterns indicate that they are related to volcanic arc or post-collisional tectonic settings. The subvolcanic rocks are represented by a porphyritic dacite with age of 2011 ± 6 Ma (U-Pb LA-ICP-MS).The granitoids were classified as biotite granodiorite, biotite monzogranite, muscovite monzogranite, respectively dated at 1976 ± 7 Ma, 1918 ± 9 Ma and 1978 ± 6 Ma (U-Pb SHRIMP), and an undated syenogranite. These ages represent three to four distinct magmatic events and indicate that the studied rocks are coeval to four major units from Tapajós Domain: the Cuiú-Cuiú Complex (2033-2005 Ma), the Comandante Arara Formation (2020-2012 Ma), the Creporizão Intrusive Suite (1998-1957 Ma), and the Tropas Intrusive Suite (1907-1892Ma). Despite the temporal correspondence, the geochemical data show no direct correspondence with the units cited above. Notwithstanding, the intrusion relationship between some of the studied rocks and the metasedimentary rocks of the Castelo dos Sonhos Formation establishes a temporal, spatial and possibly stratigraphic relationship between this formation and the Tapajós Domain. The intrusive contact relationship between the porphyritic dacite and metasandstones of the Castelo dos Sonhos Formation allowed us to determine at 2011 ± 6 Ma the minimum sedimentation age of this unit. The primary gold mineralization at Castelo de Sonhos deposit is stratabound and restricted to a metaconglomerate package and interlayered metasandstones. The mineralization distribution is erratic and does not seem to follow special features or structural control. In the matrix of the metaconglomerates, gold occurs as intergranular particles, occasionally associated with magnetite, and also within quartz grains (medium to coarse sand), which probably represent fragments of auriferous veins. In general, the gold particles show subrounded to rounded shapes, mild to moderately rough surfaces. The particles seldom contain inclusions, and only of magnetite. The chemical composition is homogeneous and characterized by high Au/Ag ratios. These characteristics indicate a syngenetic origin for gold within the metaconglomerates package. Therefore, the age of mineralization is limited by the time x interval of deposition of the Castelo dos Sonhos Formation (2011 ± 6 Ma to ca. 2080 Ma). On the other hand, the occurrence of gold in fracture planes of metasandstones indicates an epigenetic origin for this style of mineralization. The epigenetic mineralization is related to concurrent metamorphic, magmatic and deformational processes that affected the sedimentary sequence of the Castelo dos Sonhos Formation and caused the remobilization of gold originally hosted in metaconglomerates. It is likely that the interaction of these processes associated with infiltration of meteoric waters contributed to the generation and flow of oxidizing hydrothermal fluids, which have percolated through the metaconglomerates package and were able to solubilize some of the gold, and re-precipitate it accompanied by ferruginous films, in fracture planes of the metasandstones. As a conclusion, a modified paleoplacer model is proposed here to explain the hybrid nature (syngenetic and epigenetic) of the gold mineralization in the Castelo de Sonhos deposit.
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Caracterização petrográfica, geoquímica e geocronológica U-PB das rochas de alto grau metamórfico do Complexo Tartarugal Grande, sudeste do Escudo das Guianas, Amapá
(Universidade Federal do Pará, 2016-10-26) PAIVA, Hanna Paula Sales; GORAYEB, Paulo Sérgio de Sousa; http://lattes.cnpq.br/4309934026092502
The Tartarugal Grande Complex is represented by a high rock metamorphic association degree of Paleoproterozoic with Archean relics, which occurs on the northern edge of the Amapá Block, in the context of Maroni-Itacaiúnas Province, southeast of the Guyana Shield. In this region, the Tartarugal Grande Complex meets gneiss and granulite rocks, dominated enderbitic and charnockitics types, forming elongated rocks and marked by lineament NW-SE direction, characterized as transcurrent and thrust shear zones. This unit is formed by an intricate combination of high-grade metamorphic rocks and this study aimed to characterize these rocks petrographically, geochemically and geochronology discussing the processes in this metamorphic terrain. Petrographic analyzes identified five types of rocks classified as charnockitic granulite, charnoenderbitic granulite, enderbitic granulite, mafic granulite and leucogneisses Migmatization features as neossomes also present in felsic granulites (charnockitics, enderbitics and charnoenderbitics) and gneisses. The felsic granulites are the dominant rocks in the area, while the mafic granulites occur as smaller rocks, metric dimensions, embedded in other granulites and gneisses. The leucognaisses are commonly associated with enderbitic/charnockitic granulites, showing sudden contacts with these rock types. The lithogeochemical studies in these rocks indicated that the Tartarugal Grande Complex predominance of acid rock with silica content between 61 and 75%, and peraluminous, due to the presence of minerals such as biotite, garnet and cordierite. The mafic granulites are dominantly basic types (SiO2 between 48 and 55%) with high Fe2O3 levels (12 to 26%), MgO (5 to 19%) and CaO (2 to 12%). In geochemical classification diagrams felsic granulites and leucognaisses are located in granite field, while the mafic granulites plots in gabbro field. In AFM diagram, the felsic granulites have characteristics of collisional calc-alkaline suite and mafic granulites are basaltic types of tholeiitic suite. In the multi-element diagrams felsic granulites out more significant anomalies of Ti and P, in addition to the strong negative anomaly of Nb, characteristic of subduction environments. The mafic granulites shows, mostly signed with sub-horizontal pattern. For the rare earth elements (REEs), felsic granulites at moderate enrichment of light REEs, for heavy REEs with low Eu anomalies (ratio Eu/Eu* = 0.19 to 5.51). The mafic granulites had a lower degree of fractionation and recorded insignificant Eu anomalies (ratio Eu/Eu* = 0.44 to 1.07). The leucogneisses shows very similar to the felsic granulites signature, but have different genesis. In the discrimination diagrams of tectonic environments, it was established magmatic arc environment related to the subduction zone. U-Pb geochronological analyses in situ zircon crystals by LA-ICP-MS done in charnoenderbitic granulite, enderbitic granulite, garnet–biotite leucogneisse and charnockitic granulite, provided average ages of 2045 ± 14 Ma, 2084 ± 7.9 Ma, 2617 ± 25 Ma and 2671 ± 10 Ma respectively. These results represent the formation age of the protoliths of these rocks. Ages obtained by other studies by Sm-Nd whole rock-garnet between 2.02 and 1.98 Ga indicate a high grade metamorphic event near the age placement of plutons. The parageneses characteristics of the rocks found in the search area are represented by: mesopertitic Mc + Qtz + Pl + Opx + Bt (charnockitic granulite); Pl + Qtz + mesopertitic Mc + Opx ± Bt (charnoenderbitic granulite); Pl + Qtz + mesopertitic Mc + Opx + Bt ± Cpx ± Hbl (enderbitic granulite); Pl (An60) + Opx + Cpx + Hbl (mafic granulite) and; Qtz + Mc + Pl ± Bt ± Grt ± Crd (leucogneisses) and these associations indicate that the rocks was subjected to conditions of regional metamorphic granulite facies in temperature conditions between 780 and 850°C and pressure between 5 and 7 kbar. Not extensive meltings (anatexis) are also common in the area where masses of sienogranitics compositions originated under high temperature conditions from granulites and gneisses. In addition, characteristics indicative of cooling were found in these rocks, such as partial or total replacement of pyroxene by biotite and/or hornblende, garnet by biotite and cordierite by pinit. Thus, in accordance with results of studies already developed in the area and indicated by datings performed in this present study, it was concluded that the Tartarugal Grande Complex comprises rocks that were involved during magmatic events in Neoarchean and Rhyacian, followed by high-grade metamorphism in Paleoproterozoic end and related thermo-tectonic Transamazonian event. This event deformed pre-existing types and rebalanced minerals rocks, resulting in a complex association of granulites and gneisses with different ages, origins and deformation intensities.
Acesso aberto (Open Access)
Estudos de inclusões fluidas e de isótopos estáveis no depósito Moreira Gomes do campo mineralizado do Cuiú-Cuiú, Província Aurífera do Tapajós, Estado do Pará
(Universidade Federal do Pará, 2013-08-29) ASSUNÇÃO, Rose de Fátima Santos; KLEIN, Evandro Luiz; http://lattes.cnpq.br/0464969547546706
Moreira Gomes is a recently discovered deposit (preliminary resources of 21.7 t Au) of the Cuiú-Cuiú goldfield, an importante and historical mining área of the Tapajós Gold Province, Amazonian Craton. The mineralized zone is about 1200 m long, 30-50 m wide, and is followed to at least 400 m in depth. The zone is controlled by a subvertical, east-west-trending structure that is related to a left-handed strike-slip fault system. The host rocks in the deposit are predominantly tonalites dated at 1997 ± 2 Ma that are attributed to the magmatic arc or post-collision Creporizão Intrusive Suite. Hydrothermal alteration and mineralization are predominantly of the fissure-filling type and locally pervasive. Sericitization, chloritization, sulfidation, silicification, carbonatization and epidotization are the observed alteration types. Pyrite is by far the predominant sulfide mineral and bears inclusions of chalcopyrite, galena, sphalerite and minor hesite and bismuthinite. Gold occurs predominantly as inclusions in pyrite and subordinately in the free-milling state in quartz veins. Ag, Pb and Bi have been detected by semi-quantitatiive analysis. Three types of fluid inclusions, hosted in quartz veins and veinlets, have been identified. (1) Type 1: one- and two-phase CO2 inclusions; (2) Type 2: two- and three-phase H2O-CO2-salt inclusions, and (3) Type 3: two-phase H2O-salt inclusions. CO2 is largely the predominat volatile phase in the CO2-bearing inclusions. The CO2-bearing types 1 and 2 are interpreted as the product of phase separation of an immiscible fluid. This fluid presentes low to moderate density, low to moderate salinity (1.6 to 11,8 wt.% NaCl equivalent) and was trapped chiefly at 280° to 350°C. In Type 3 fluid, the chemical system may contain CaCl2 and/or MgCl2, salinitye varies from zero to 10.1 wt.% NaCl equivalent. Only locally salinities up to 25% have been recorded. This fluid was trapped mainly between 120° and 220°C and is interpreted as resulting from mixing of a hotter and more saline aqueous fluid (in part derived from phase separation of the H2O-CO2 fluid) with a cooler and dilute aqueous fluid. As a whole, the fluid inclusions indicate phase separation, pressure fluctuations, mixing, and reequilibration during trapping. The isotopic composition of inclusion fluids and of the fluid in equilibrium with hydrothermal minerals (quartz, chlorite, and calcite) show δ18O and δD values that range from +0.5 to +9.8‰, and from -49 to -8‰, respectively. The δ34S values of pyrite (-0.29‰ to 3.95‰) are probably related to magmatic sulfur. Mineral pairs show equilibrium isotopic temperatures that are compatible with the fluid inclusion homogenization temperatures and with textural relationships of the hydrothermal minerals. Isotopic results combined with mineralogical and fluid inclusion data are interpreted to reflect a magmatic-hydrothermal system that evolved in at least three stages. (1) Exsolution of a CO2-bearing magmatic fluid between 400°C and 320-350°C and up to 2.1 kbars (6-7 km in depth) followed by phase separation and main precipitation of the hydrothermal assemblage composed of chlorite-sericite-pyrite-quartz-gold. (2) Cooling and continuous exolution of CO2 producing a CO2-depleted and slightly more saline aqueous fluid that was trapped mainly at 250°-280°C. The predominant hydrothermal assemblage of stage 1 continued to form, but epidote is the main phase at this stage. (3) Mixing of the stage 2 aqueous fluid with a cooler and dilute aqueous fluid of meteoric origin, whis was responsible for the main carbonatization phase. The composition of the hydrothermal assemblage and the fluid and isotopic composition indicate that the mineralizing fluid was neutral to slightly alkaline, relatively reduced (only locally, more oxidezed conditions have been attained, resulting in the precipitation of barite). H2S (and/or HS-) might have been the main súlfur species in the fluid and Au(HS)-2 was probably the gold transporting complex. Gold deposition occurred as a consequence of a combination of mechanisms, such as phase separation, mixing and fluid-rock interaction. The Moreira Gomes is a granite-hosted gold deposit that interpreted to be a product of a magmatic-hydrothermal gold system. The age of ore formation (~1.86 Ga) is consistent with the final stages of evolution of the widespread high-K, calc-alkaline Parauari Intrusive Suite, although the ttransitional to predominantly alkaline Maloquinha Intrusive Suite cannot be ruled out. Notwithstanding, the deposit does not show the classic features of (oxidized or reduced) intrusion-related gold deposits of Phanerozoic magmatic arcs.
Acesso aberto (Open Access)
Estudos de inclusões fluidas e isótopos estáveis nos alvos Jerimum de cima e Babi, campo mineralizado do Cuiú-Cuiú, Província Aurífera do Tapajós, Cráton Amazônico: implicações para os processos genéticos
(Universidade Federal do Pará, 2015-08-18) SILVA JUNIOR, Carlos Alberto dos Santos; KLEIN, Evandro Luiz; http://lattes.cnpq.br/0464969547546706
The Cuiú-Cuiú goldfield is located near the central portion of the Tapajós Gold Province in the south-central portion of the Amazonian Craton. This goldfield is one of the oldest prospecting areas of the province and holds multiple more or less developed prospects and gold deposits (Central, Raimundinha, Pau da Merenda, Guarim, Jerimum de Cima, Jerimum de Baixo, Nho, Moreira Gomes, Babi and other less known). As contribution to the understanding of the metallogenic evolution of the Cuiú-Cuiú goldfield in general, this study focused on the mineralized Jerimum de Cima and weakly mineralized Babi targets and aimed: (1) to define the sulfide mineralogy associated with gold mineralization and its textural relationships with the host rocks; (2) to define the physical and chemical characteristics of the mineralizing/hydrothermal fluids through petrographic, fluid inclusions and stable isotopes (C, O, S) studies trying to identify what caused the hydrothermal alteration in rocks from these targets and that enabled more significant mineralization at Jerimum de Cima (and other targets/deposits), whereas Babi is only weakly mineralized (not economic). The petrographic study identified strongly hydrothermally altered host rocks, with obliterated primary characteristics. In the Jerimum de Cima target the host rocks are biotite-hornblende tonalite, monzogranite and granodiorite. In the Babi target, titanite monzogranite, biotite monzogranite, biotite-hornblende tonalite, and brecciated monzogranite are the hydrothermally-altered rocks. Sericitization, silicification and sulfidation occur strongly in the Jerimum de Cima target, whereas carbonatization and chloritization occur usually in both targets. Pyrite, sphalerite, chalcopyrite and galena, in decreasing order of abundance, are the sulfide minerals, with large predominance of pyrite. Fluid inclusions (FI) trapped in quartz crystals occur in small groups, in isolation, or in trails. In decreasing order of abundance, there are three types of FI: two-phase aqueous (Type 1), aqueous-carbonic (Type 2) and carbonic (Type 3). The microthermometric results show that the aqueous FI at Jerimum de Cima homogenized between 105 and 387°C, and have salinities that range from 0,0 to 18 wt.% NaCl equivalent; whereas the aqueous-carbonic type has final homogenization temperatures between 144 and 448°C, salinities of 1,0 to 7,8 wt.% NaCl equivalent, and bulk density ranging from 0,6 to 1,0 g/cm3. At Babi the aqueous FI are the only type present. These FI homozenized between 136 and 410°C and show salinities from 0,7 to 13,2 wt.% NaCl equivalent. The aqueous-carbonic FI are interpreted as a product of fluid immiscibility (phase separation). The absence of CO2–bearing inclusions in the Babi target is possibly a consequence of late-timing of fluid trapping during the evolution of the hydrothermal system, after the CO2 consumption, with only aqueous FI being trapped. Stable isotope analyses of hydrothermal minerals present in veins and alteration zones indicate mineral precipitation between 305 and 330°C and between 108 and 205°C, which is in line with the fluid inclusion honogenization temperatures and indicate more than one stage of mineral precipitation. The data also suggest magmatic and meteoric sources for the fluids. As a whole, our data are compatible with a magmatic-hydrothermal gold systems (intrusion-related), and with mixing of magmatic and meteoric fluids. The lack of CO2 at Babi might explain the weak mineralization in this target.
Acesso aberto (Open Access)
Estudos isotópicos (Pb, O, H, S) em zonas alteradas e mineralizadas do depósito cupro-aurífero Visconde, Província Mineral de Carajás
(Universidade Federal do Pará, 2013-06-05) SILVA, Antonia Railine da Costa; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Cu-AuVisconde deposit is located in the Carajás Mineral Province, northern Brazil, about 15 km east of the world-class Sossego deposit. It lies within a regional WNW–ESE-striking shear zone that marks the contact between the ~2.76 Ga metavolcano-sedimentary rocks of the Carajás Basin and the basement units. Other Cu- Au deposits with similar characteristics (Bacaba, Castanha, Alvo 118, Cristalino, Jatobá) occur along this shear zone. They have been included in the IOCG class, although much controversy exists regarding their genesis, particularly with respect to the mineralization age and source of fluids, ligands and metals. TheVisconde deposit is hosted by Archean rocks, mainly felsic metavolcanic rocks (2968 ± 15 Ma), the Serra Dourada granite (2860 ± 22 Ma), and gabbro/diorites. These rocks are variably sheared and reveal various types of hydrothermal alteration with strong structural control. The earliest types are the sodic (albite-scapolite) and sodic-calcic alterations (albiteactinolite ± tourmaline ± quartz ± magnetite ± scapolite ± epidote), which promoted ubiquitous replacement of the rock primary minerals and precipitaton of disseminated chalcopyrite, pyrite, molybdenite and pentlandite. Oxygen isotope data of representative minerals from these stages show that the hydrothermal fluids were hot (410 – 355°C) and 18O-rich (δ18OH2O = +4.2 to +9.4‰). The following potassic stage is characterized by intense biotitization of the rocks, which developed concomitantly a mylonitic foliation highlighted by the remarkable orientation of biotite flakes. This mica precipitated from fluids with similar oxygen isotope signature to that of the previous stages (δ18OH2O = +4.8 to +7.2‰, at 355°C). Microcline and allanite are other typical minerals of this stage, in addition to chalcopyrite that deposited along the foliation planes. At lower temperatures (230 ± 11°C), 18O-depleted fluids (δ18OH2O = -1.3 to +3.7‰) generated a calcic-magnesian mineral assemblage (albite + epidote + chlorite ± actinolite ± calcite) present mostly in veins and contemporaneous with the main mineralization. The δ18OH2O and δDH2O data indicate that the hydrothermal fluids were initially formed by metamorphic and formation waters, possibly with some contribution of magmatic water. At later stages, there was a considerable influx of surface water. The resulting fluid dilution and cooling might have accounted for the abundant precipitation of sulphides (chalcopyrite ± bornite ± chalcocite ± digenite) mainly in tectonic breccias, whose matrix contains up to 60% sulphides. These breccias represent the most important ore bodies, although sulphides also occur in veins together with sodic-calcic minerals. The mineral associations assign a Cu-Au-Fe-Ni-ETRL-B-P signature to the ore. The sulphur isotope composition (δ34SCDT= -1.2 to 3.4‰) is compatible with a magmatic source for sulphur, which could have been either exsolved from a crystallizing granitic magma or dissolved from sulphides originally present in preexisting igneous rocks. Additionally, it indicates relatively reducing conditions for the fluid. Dating of chalcopyrite by Pb leaching and total dissolution techniques yielded ages of 2736 ± 100 Ma and 2729 ± 150 Ma. Despite the large errors, they point to a Neoarchean age for the mineralization and preclude a Paleoproterozoic mineralizing event. The age of 2746 ± 7 Ma (MSDW = 4.9; Pb evaporation on zircon), obtained for a non-mineralized granitic intrusion present in the deposit area and correlated to the Planalto Suite, was considered as the minimum age for the mineralization. Thus, the Visconde deposit genesis could be related to the 2.76-2.74 Ga transpressive tectonothermal event that was responsible for the inversion of the Carajás basin and generation of granitic magmatism in the Carajás and Transition domains. Such an event should have triggered devolatilazion reactions in the Itacaiunas Supergroup rocks, producing metamorphic fluids or even driving off water trapped in the pores of the basin rocks. These fluids migrated along regional shear zones and reacted with both the basin and basement rocks through which they moved during the ductile regime. The subeconomic concentrations of the Visconde deposit might be the result of the absence of prominent structures that would otherwise favor a greater influx of fluids, as it seems to have been the case in the Sossego and Alvo 118 deposits.
Acesso aberto (Open Access)
Estudos isotópicos e de inclusões fluidas no depósito central do campo mineralizado do Cuiú-Cuiú, província aurífera do Tapajós, estado do Pará
(Universidade Federal do Pará, 2014-01-09) ARAÚJO, Ana Claudia Sodré; KLEIN, Evandro Luiz; http://lattes.cnpq.br/0464969547546706
Central is a gold deposit of the Cuiú-Cuiú goldfield, located in the Tapajós Gold Province, Amazonian Craton. The deposit is hosted in a NW-SE-trending structure and the mineralized zone is followed by 800 m along the strike and 450 m along the dip, and is 50-70 m thick. The ore bodies are hosted in a monzogranite dated at 1984±3 Ma and ascribed to the Parauari Intrusive Suite. Resources are estimated in 18.6 t Au. The hydrothermal alteration is predominantly of the fissure-filling type and sericitization, chloritization, silicification, carbonatization and sulfidation are the main alteration types. Pyrite is the predominant sulfide mineral, whereas chalcopyrite, sphalerite and galena are subordinated phases occurring in fractures and rims of pyrite. Gold particles occur in fractures of pyrite and contain subordinate amounts of silver. Three types of fluid inclusions are hosted in quartz veins and veinlets. Type 1 is the least abundant and is composed of one- (CO2vapor) and two-phases (CO2liq-CO2vapor) inclusions; Type 2 comprises two- (H2Oliq-CO2liq) and three-phases (H2Oliq-CO2liq-CO2vapor) inclusions; Type 3 is the most abundant type and consists of two-phases (H2Oliq-H2Ovapor) inclusions. CO2 is the volatile phase in CO2-bearing inclusions (types 1 and 2) and these inclusions were produced by phase separation of an aqueous-carbonic fluid. The density of this fluid is low to moderate (0,33 - 0,80 g/cm³), as is the salinity (11.15 - 2.42 wt.% NaCl equiv.). The homogenization temperatures show a peak at 340ºC. Type 3 inclusions have NaCl as the main salt component, the global density varies from 0.65 to 1.11 g/cm³, and the salinity ranges from 1.16 to 13.3 wt.% NaCl equiv. The homogenization temperature shows bimodal distribution, with peaks at 120-140ºC and 180ºC. Fluid inclusion and mineral (quartz, chlorite, calcite) isotopic compositions show δ18O and δD values of +7.8 to +13.6 ‰ and -15 a -35 ‰, respectively. Pyrite shows δ34S values of +0.5 to +4.0 ‰ and δ13C values ranging from -18 to -3.7 ‰ were obtained in calcite and CO2 inclusion fluids. The fluid δ18OH2O and δDH2O values plot in the field of metamorphic waters with a weak shift towards the meteoric water line. However, considering the absence of known metamorphic event at the time of mineralization at Central, the fluids are interpreted as belonging to a magmatic-hydrothermal system. Accordingly, the aqueous-carbonic fluids were exsolved from felsic magmas related to the latest phases of evolution of the Parauari Intrusive Suite and the carbonic and aqueouscarbonic fluid inclusions were trapped in this phase, predominantly at 340°C. The continuous exsolution lead to progressive decrease in the CO2 contents of the magmas and to increasing predominance of aqueous fluids. At this time, the fluids might have interacted with meteoric waters and most of the low-temperature aqueous inclusions were trapped. It is possible that part of the aqueous fluid inclusions (those with the highest trapping temperatures) represent local mixing of the different fluid sources. These observations allow to interpret Central as a magmatic-hydrothermal gold deposit related to the final stages of evolution of the Parauari Intrusive Suite.
Acesso aberto (Open Access)
Evolução geológica pré-cambriana e aspectos da metalogênese do ouro do cráton São Luís e do Cinturão Gurupi, NE-Pará/ NW-Maranhão, Brasil
(Universidade Federal do Pará, 2004-07-06) KLEIN, Evandro Luiz; GIRET, André; HARRIS, Christopher; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
In the Gurupi region, located at the border between the Pará and Maranhão states in northern Brazil, igneous and metamorphic rocks crop out as part of the Parnaíba Structural Province. Early geochronological studies, based on the Rb-Sr and K-Ar methods have shown two geochronological domains. The rocks that crop out towards the Atlantic margin showed a Paleoproterozoic signature, around 2000 Ma, whereas the rocks that crop out towards the inner portions of the continent showed a Neoproterozoic signature, especially between 800 and 500 Ma. These domains have been then defined as the São Luís Craton and Gurupi Belt, respectively. Several lithostratigraphic propositions have been developed throughout more than two decades. However, these propositions always lack robust geochronological support. Geotectonic models discussed a one- or two-phase evolution for the Gurupi Belt, also lacking robust geochronological and isotopic data to consubstantiate the interpretations. Furthermore, among the several gold deposits that occur in both the cratonic and belt areas, only a few have geological and genetic information. These subjects are addressed in more or less depth by this thesis. New propositions for the regional lithostratigraphy and geological evolution have been achieved in this work by revaluating the available geological, geochemical, geochronological and isotopic dataset, as well as by adding new geochronological data on zircon (Pb-evaporation, U-Pb ID-TIMS, and LAM-ICP-MS) for most of the igneous and orthometamorphic rocks in the region. Whole rock Nd isotope data have also been obtained, allowing the discussion of crustal accretion and reworking. The results show a rather complex geological evolution with intensive and extensive crustal growth between 2.24-2.15 Ga and crustal reworking, involving melting, migmatization, metamorphism, and deformation around 2.10 Ga. The following results have been obtained for the São Luís Craton: Aurizona Group, metavolcano-sedimentary sequence, maximum age of 2241 Ma (juvenile) that possibly evolved until c.a. 2200 Ma; Tromaí Intrusive Suite, calc-alkaline, metaluminous tonalites of oceanic island arc, 2168 Ma (juvenile); Areal Granite, calc-alkaline, weakly peraluminous, 2150 Ma (mixing of juvenile and arc materials). In the Gurupi Belt, the following results have been obtained: Igarapé Grande Metatonalite, small and localized granoblastic tonalite, 2594 Ma; Itapeva Complex, weakly migmatized tonalitic orthogneiss, 2167 Ma (mostly juvenile); Chega Tudo Formation, metavolcano-sedimentary sequence (back-arc basin?), 2150-2160 Ma; Maria Suprema Granite, syntectonic, peraluminous muscovite-bearing granite, 2100 Ma (similar to other peraluminous granitoids in the Gurupi Belt). The Gurupi Group is tentatively placed in the Paleoproterozoic (>2160 Ma), but this must still be proved. The above data are interpreted on a plate tectonics basis, as follows. An oceanic basin is open at ca. 2260 Ma and is followed by the onset of subduction, formation of island arcs and voluminous calc-alkaline magmatism in oceanic settings, and concomitant reworking of the arcs between 2170-2150 Ma. This set of oceanic terranes has been accreted (soft-collision) onto an Archean continental margin to southwest (Archean part of the Amazonian Craton or a present day concealed cratonic nuclei). The collision provoked the metamorphism, deformation, and partial melting of the newly formed Paleoproterozoic crust and of part of the Archean bloc, or their erosive detritus, migmatization, and emplacement of peraluminous granitoids at 2100-2080 Ma. The region has been the locus of a second event in the Neoproterozoic. A continental rift developed in the bloc that was assembled in the Paleoproterozoic, as attested by the intrusion of a nepheline syenite (Boca Nova) at 732 Ma. Sedimentary rocks that filled this rift (Marajupema Formation) have detrital zircon crystals that show the youngest ages around 1100 Ma. The rift evolved probably to an oceanic basin, as suggested by the widespread occurrence of detrital zircons with ages around 550 Ma in small sedimentary basins that have been filled with immature sediments. The precise time of orogenesis climax that followed basin closure, with mass transport from SSW to NNE and accompanying metamorphism, is not yet constrained. Equivocal geochronological information point to 650-520 Ma (zircon of the nepheline syenite, Rb-Sr and KAr ages in minerals). The metallogeny of selected gold deposits occurring in both the São Luís Craton and the Gurupi Belt is addressed using varied information, such as geology, chlorite chemistry, fluid inclusion geochemistry, and stable (O, H, C, S) and radiogenic (Pb) isotopes. Structural and textural relationships, and Pb isotope data indicate a post metamorphic peak and late- to posttectonic timing for the gold mineralization with respect to the Paleoproterozoic events (post 2080 Ma). At a regional scale, the deposits show a similar signature characterized by formation temperatures between 280° and 380°C; pressures of 2-3 kbars; low-salinity (5 mass % NaCl equiv), reduced and moderately dense aqueous-carbonic (CO2 <20 mol%, traces of CH4 and N2), showing strong evidence for phase separation. Stable isotope studies suggest distinct sources for fluids and solutes. The carbonate, graphite, and fluid inclusion carbon comes from two sources: a depleted organic source, and an unknown source that may be magmatic, metamorphic or mantlederived (or both). Sulfide sulfur derived directly from magmas or from the dissolution of magmatic sulfides. Combined oxygen and hydrogen isotopes attest a metamorphic source for the fluids. Therefore, dehydration and decarbonization reactions during the metamorphism of the Paleoproterozoic metavolcano-sedimentary sequences appear to have produced the mineralizing fluids. Gold was transported as a reduced sulfur complex, such as the Au(HS)2 - and precipitated in response to the breakdown of this complex due to phase separation and fluid-rock interactions. The geological and genetic constraints are consistent with the orogenic gold model, found in metamorphic belts of all ages. As a whole the results of this study have implications for the understanding of the Paleoproterozoic and Neoproterozoic orogenies that built up the South American Platform and for the assembly and break-up of the Atlantica, Rodinia, and West-Gondwana supercontinents. The geological scenario outlined here for the Paleoproterozoic shows good correlations with those found especially in the southeastern Guyana Shield and in the southern portion of the West- African Craton. For the Neoproterozoic, the available information is still insufficient to draw major correlations.
Acesso aberto (Open Access)
Evolução petroquímico-metalogenética das rochas e mineralizações associadas à suite Vila Nova na Serra do Ipitinga (NW do Pará)
(Universidade Federal do Pará, 1997-05-08) FARACO, Maria Telma Lins; MCREATH, Ian; http://lattes.cnpq.br/5299851252167587
The Vila Nova Metamorphic Suite in the 'pitinga Hills (NW Pará) consists of a supracrustal sequence of mafic and ultramafic metavolcanics, cordierite-antophyllite - and quartz-chlorite-bearing rocks underlying chemical (oxide and silicate-type BIFs) and clastic metasediments. Part of the basic lavas was hydrothermally altered under greenschist facies conditions, similar to mid-ocean-ridge axis hydrothermal systems, creating quartz-chiorite-bearing rocks (which occur as large clots within the metavolcanic sequence) and hydrothermal syndepositional exhalative volcanogenic sulphide deposits, formed by pyrrhotite, pyrite, chalcopyrite and sphalerite with associated Au and Ag and traces of galena, molybdenite and silver telluride. The temperature range of generation of these host rocks, dalculated from AI-saturated chlorite, is 273°C to 320°C, with an average value of 308°C. Afterwards, metamorphism under amphibolite facies transformed the basic volcanics to amphibolites, and part of the quartz-chlorite to cordierite-antophyllite rocks. Geothermometric calculations using the cordierite-antophyllite pair, point to 547°C for the generation of these rocks. Present-day mineralogical associations of BIFs and clastic metasediments were formed during that metamorphism. All the metavolcano-sedimentary sequence was deformed by brittle-ductile shearing and transformed in present-day NW-SE trending shear belts with subvertical-NE dip. The deformational shearing episode yielded mylonites, polymetamorphic and hidrothermalized rocks, showing retrogressive metamorphic paragenesis. There was also hydrothermal alteration produced by granitic fluids. Gold is present in three typologies: associated to volcanogenic sulphides, sheared Iodes, and supergene altered rocks. Platinum anomalies were registered in many hydrothermalized rocks, but not in association with sulphide mineralization. Four hydrothermal events were identified. Fluid inclusion studies indicated tweive types of inclusions which pointed to finco fluid systems, one consisting of a CH4-rich aqueous-carbonic phase and the other of an aqueous phase with sahnites ranging from 40% CaCl2 equivalent to near pure water. The first is related to sulphide-bearing rocks and the second to the shearing episode. The homogenization temperatures of the fluid inclusions in the sulphide mineralization's host-rocks, point to 250°C-450°C to the origin of these rocks. The CH4-isochores and the temperature range of generation of the host-rocks, provide a pressure range of 0,7 kb to 2,3 kb for the mineralization. The protoliths of mafic metavolcanics are subaikaline tholeiitic basalts. Komatiitic basalts were also characterized, suggesting the presence of a komatiitic affinity to the magmatism. The lithochemical study revealed a volcanic environment similar to back-arc basins to the Vila Nova Suite. The Nd isotopic study yielded model ages between 2.26 Ga and 2.19 Ga for Vila Nova metavolcanics, while the BIF's REE patterns are equivalent to many Paleoproterozoic banded iron-formation of the world. This is in agreement with the 2.11 Ga (Sm/Nd) and 2.25 Ga (U/Pb) ages from French Guyana and Guyana's rocks, correlatives to Vila Nova Suite. The petrological, lithochemical, metallogenetic and isotopic data from the Vila Nova metamorphic suite account also for its correlation with the paleoproterozoic birimian metavolcano-sedimentary belts of the West African craton.
Acesso aberto (Open Access)
Geocronologia e geoquímica isotópica dos depósitos de Cu-Au Igarapé Bahia e Gameleira, Província Mineral de Carajás (PA), Brasil
(Universidade Federal do Pará, 2002-05-10) GALARZA TORO, Marco Antonio; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
Copper sulfide + Au ore deposits are common in the Carajás Mineral Province and systematically occur in Archean metavolcano-sedimentary sequences associated or not with granitoid intrusions. Two of these deposits, Igarapé Bahia and Gameleira, have been chosen for a geochronological and isotopic study with the purpose of not only determining their ages, origin and relationships with the host rocks, but also the formation and evolution of the crustal segments within which both deposits are located. The Igarapé Bahia Group hosts the Igarapé Bahia deposit and is composed of mafic metavolcanic (MVR), metapyroclastic (MPR) and meta sedimentary rocks (MSR), besides banded iron-formations and hydrothermally altered breccias zone (HBZ). The whole rock pile is crosscut by mafic dikes (MIR). The Cu-Au ore forms disseminations to massive bodies, mostly occurring in the HBZ which marks the contacts between the MVR and the MSR/MPR rock units. Petrographic and geochemical data about the MVR (basaltic meta-andesites), MPR (laminated and lapilli metatuffs) and MIR (quartz diorites) show them all to be derived from mafic magmas of tholeiitic affiliation, in spite of the alteration evidence. These rocks also show geochemical similarities (major and trace elements, including REE) with the coeval Grão Pará Group volcanic rocks. Chloritization (dominant), carbonation, sulfidation and magnetitization are the most important types of hydrothermal alteration. The ore is chiefly composed of chalcopyrite with variable amounts of pyrite, bornite and chalcocite. Chrorite, magnetite, siderite are abundant as gangue minerals, whereas tourmaline, molybdenite, fluorite and biotite are subordinate. Pb-Pb dating on zircon yield crystallization ages of 2745±1 Ma and 2747±1 Ma for the MVR and MPR, respectively. Similar whole-rock ages were obtained for the MVR (Pb-Pb / 2776±12 Ma and Sm-Nd / 2758±75 Ma) and the MPR (Pb-Pb / 2758±36 Ma). A Pb-Pb age of 2764±22 Ma for the chalcopyrite and gold suggests the mineralization to be contemporaneous with the host Igarapé Bahia Group. Similar Pb-Pb ages are recorded on chalcopyrite from the HBZ (2772±46 Ma), MVR (2756±24 Ma), MPR (2754±36 Ma) and MIR (2777±22 Ma), and in gold from the MVR (2778 Ma). All these geochronological data support a syngenetic to late syngenetic origin of the Igarapé Bahia Cu-sulfide + Au ores. Pb-Pb ages of 2385±122 and 2417±120 Ma obtained by leaching of the BHZ chalcopyrite may indicate a period of remobilization probably related to tectonic reactivations of the Carajás-Cinzento Strike-Slip System. δS18 values of +0.1 to +4.2%0 in ZBH sulfides (mostly chalcopyrite) corroborate both the involvement of magmatic hydrothermal fluids and exhalative deposition, whereas δC13PDB values of -7.28 to -15.78‰ in ZBH siderite suggest the mantle as a likely source for the homogeneous CO2- rich fluids responsible for the carbonate precipitation (carbonatic source) although, if it does not have evidences of the existence of this type of rock in the Carajás region. In turn, δO18PDB values of -15.51 to -20.96%0 in the same siderite indicate some contribution of meteoric waters to the fluids that altered the breccias. The Gameleira ore deposit is hosted by the Archean Igarapé Pojuca Group which consists of mafic metavolcanic rocks (MVR), amphibolites, schists, banded iron-formations and hydrothermalites. Neoarchaean mafic intrusive rocks (MIR), Paleoproterozoic quartz-feldspathic apophyses and granitoids crosscut all the Igarapé Pojuca rocks. Petrographical and geochemical data allow the MVR and MIR to be classed, respectively, as basaltic meta-andesites and quartz diorites of tholeiitic affiliation. The schistose rocks can be classified as plagioclase-quartz-biotite schist. Biotitization, chloritization, sulfidation, tourmalinization and silicification are the most remarkable types of hydrothermal alteration. The ore occurs chiefly in veins and veinlets and is characterized by selvages of chalcopyrite, pyrite, pirrhotite, bornite, molybdenite, rare cubanite, besides quartz, tourmaline, fluorite, chlorite and biotite. The MVR seem to be contemporaneous with those of the Grão Pará, Igarapé Bahia and Igarapé Salobo groups, adopting the age of the Grão Pará Group as the age of formation of these rocks. Dating of the MIR (Pb-Pb on zircon) yields a value of 2705±2 Ma interpreted as the crystallization age of these rocks and similar to those found for the mafic sills (2.70 to 2.65 Ga) that occur in the neighboring Águas Claras deposit. Pb-Pb ages of 2615±10 and 2683±7 Ma on zircon from a saprolith of the Igarapé Pojuca Group domain probably represent rocks coeval with those sills. Pb-Pb ages of 2646±30 Ma (MVR / whole-rock), 2422±12 Ma (vero sulfides) and 2218±14 Ma (leaching of chalcopyrite) are indicative of a superimposed event on the Igarapé Pojuca metamorphic rocks, either the emplacement of granitoid intrusions (1.87-1.53 Ga) or the reactivation of the Caraj ás-Cinzento Strike-Slip System. This event probably caused remobilization of pre-existing ore as well as (partial or total) resetting of the Pb isotopic system. Both the Igarapé Bahia and the Igarapé Pojuca groups, and other greenstone-like metavolcano-sedimentary sequences of Carajás, overlie a basement made up of rocks that are contemporaneous with the Xingu and Pium complexes as well as with the Arco Verde tonalite, which are the likely sources of the inherited zircon found in the MVR and MIR of the Igarapé Bahia Group and dated at 3.03-2.86 Ga. Therefore, the ranges of 3.03-2.86 and 2.76-2.74 Ga represent, respectively, well-defined periods of crust formation and expressive volcanism in the northern portion of the Carajás Mineral Province. Sm-Nd model ages (TDM) of 3.17-2.99 Ga, obtained for the rocks of both the Igarapé Bahia and Gameleira deposits are consistent with those determined for the basement rocks and granitoids that occur in the Carajás Mineral Province. ΕNd(t) values for these rocks (-0.36 to -2.12) indicate nor only participation of older crust material in the parental magmas but also that magmas were generated in a continental rift environment. This supports the current hypotheses about the tectonic environment of formation of the Itacaiunas Supergroup to which belong both the Igarapé Bahia and the Igarapé Pojuca groups. In conclusion, both studied deposits seem to have a similar primary genesis, but distinct further history in the Neoarchaean and Paleoproterozoic times, which certainly affected their mineralizations.
Acesso aberto (Open Access)
Petrografia, geoquímica e assinatura isotópica de PB de formações ferríferas associadas à gênese das cavernas da Serra Sul, Carajás – PA
(Universidade Federal do Pará, 2016-06-17) CABRAL, Erica da Solidade; MACAMBIA, Joel Buenano; http://lattes.cnpq.br/4842128592488825; TORO, Marco Antonio Galarza; http://lattes.cnpq.br/8979250766799749
Geospeleological studies in hosted caves in banded iron formation (banded iron formation - BIF's), type jaspilite, which is the iron protore the S11D body, Serra Sul, showed that these rocks are at different stages of weathering, allowing classifies them into three groups: 1) non-altered jaspilite, 2) altered jaspilite and 3) Iron Ore. Samples BIF’s were collected both in caves and in correlated drillholes stratigraphically to S11D-0035 cave. This stratigraphic correlation was established from the construction of geological section, which allowed us to determine the likely initial lithological setting of the cave and its stratigraphic level. It was concluded that the cave is in the lower portion of the Carajás formation near the contact with the Parauapebas Formation. Petrographic observations showed that jaspilite is characterized by alternating centimetric bands of opaque mineral composed of hematite-1, magnetite and maghemite and subordinate siliceous bands formed by chert and granular quartz. While the non-altered jaspilite consists predominantly of hematite-2 and subordinately hematite-1 and magnetite, banding is absent because the band of silica minerals, which is more soluble, it was almost in its entirety leached, which led to the generating dissolution cavities. In addition, they also observed neo-formed mineral phases, goethite and hematite-3. The chemical analysis of rocks of different groups corroborate the petrographic evidence. Samples of non-altered jaspilite SiO2 content ranges from 40.0 to 44.5% and Fe2O3T content from 53.9 to 58.3%, and the other oxides present, Al2O3, MnO, P2O5, TiO2, CaO, MgO, Na2O, K2O, have very low levels, as well as in other types. In contrast, the rocks are classified as altered jaspilite higher concentration of iron (from 87.9 to 97.1%) and lower SiO2 content (0.3 to 1.1%). The iron ore classified as representing the most advanced stage change, has a high content of Fe2O3T, ranging from 96.2 to 98.3% and low amounts of SiO2 from 0.4 to 1,0%. In all three groups of rock a low content of ETR was observed and, from bottom to top of the weathering profile is observed an increase in the amount of these elements, from 6 to 18 ppm. The ratio La/Eu ranges from 1.3 to 2.2 ppm non-altered jaspilite, from 0.2 to 1.6 ppm altered Jaspilite and 0,1 to 0,8 ppm Iron Ore. This decrease in iron ore may be due to less mobile behavior of HREE relative to LREE in the advanced stages of weathering. The positive anomaly Eu (Eu/Eu* > 1), typical of the BIF's was observed in all samples from different groups change. The Pb-Pb isotopic analyzes in non-altered jaspilite indicate 206Pb/204Pb ratios ranging from 15.247 to 26.111, the ratio 207Pb/204Pb ranges from 15.292 to 16.300, and the ratio 208Pb/204Pb ranges from 34.596 to 37.614. The figures suggest that these rocks are less radiogenic and have isotopic signature similar to the upper crustal rocks. In jaspilite Changed the isotopic ratios 206Pb/204Pb ranging from 16.827 to 23.244, the 207Pb/204Pb from 15.635 to 16.279, and 208Pb/204Pb from 34.715 to 38.811. In Iron Ore the 206Pb/204Pb ratios ranging from 15.702 to 22.845, 207Pb/204Pb from 15,369 to 16,221, and 208Pb/204Pb from 35,169 to 38,467. Therefore, changes were observed in the isotopic signature over change profile suggesting that there were no metamorphic events, tectonic reactivations, percolation of hydrothermal fluids or any other event that upset the Pb-Pb geochronometer and would add materials (Pb) come from other sources. The genesis and evolution of the caves, in addition to chemical processes, relief plays an important role, acting at two different times. First, facilitating the infiltration and percolation of rainwater and channel them to underground portions of the plateau, causing the dissolution of the siliceous layer and the formation of iron ore, loss of rock volume, reduction of layers and concomitant formation of caves. In a second step these caves are exposed by relief denudation processes that favor the retreat of the slopes. Therefore, the analysis of chemical processes with the help of petrography and geochemistry showed that the dissolution and leaching processes are the primary processes in the formation of caves linked to erosive processes provide its evolution. The analysis of chemical processes indicates common origin (weathering) for both the caves and for iron ore, probably contemporary.
Acesso aberto (Open Access)
Quartzo magmático e hidrotermal do depósito de ouro São Jorge, província aurífera do Tapajós-PA: petrografia, MEV-CL e implicações metalogenéticas
(Universidade Federal do Pará, 2015-08-05) SOTERO, Aldemir de Melo; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
The São Jorge Deposit (DSJ), located in the municipality of Vila Riozinho, Gold Tapajós Province, southwest of Pará state, is hosted on 1.89 Ga monzogranite rocks, hydrothermalized at different intensities, belonging to the Younger São Jorge granite. Four morphologicaltextural types of quartz (Qz1, Qz2, Qz3 e Qz4) were identified through images of scanning electron microscopy-cathodoluminescence (SEM-CL) in the mineral assemblages proposed by Borges et al. (2009) to the area of the São Jorge gold deposit. In the most preserved rocks (assemblages 1 and 2), rich in amphibole and biotite, occur anhedral crystals of primary magmatic quartz, with moderate to high luminescence (Qz1). In the altered rocks (assemblages 2 and 3), post-magmatic to hydrothermal fluids affected the granite and percolated fractures in Qz1 and crystallized Qz2 not luminescent (dark). In the most intensely altered rocks (assemblage 4), successive alteration, dissolution and recrystallization processes gave rise to zoned subhedral (Qz3) and euhedral (Qz4) quartz crystals, typically hydrothermal, the latter being host of the gold mineralization. The textural evolution of quartz is directly related to hydrothermal fluids that affected the rocks of the Younger São Jorge granite. Backscattered electrons images (ERE) and semiquantitative analysis by energy dispersive spectroscopy (EDS) identified two generations of gold: Au1, enriched in Ag (4.3 to 23.7%) and included or associated to crystals of Py; Au2, enriched in Te (1.1 to 17.2%) and included in Qz4. The study of quartz crystals by SEM-CL provided important morphological and textural information for understanding of the hydrothermal processes that acted in the mineralized area of the São Jorge gold deposit, allowing the application of this methodology in studies of quartz of other hydrothermal deposits.

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