Navegando por Assunto "Granito - Pará"

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Geologia, controle estrutural e geocronologia das rochas hospedeiras e do minério: implicações para o modelo genético do depósito aurífero do Palito, Província Tapajós, Itaituba-PA
(Universidade Federal do Pará, 2016-09-24) SERRA, Vitor Felipe Hage; TORO, Marco Antonio Galarza; http://lattes.cnpq.br/8979250766799749
The Palito gold deposit, located at east portion of the Tapajós Gold Province, southwestern Pará State, comprises a nearly vertical mineralized quartz vein system, hosted by the Palito and Rio Novo Paleoprooterozoic granites and controlled by a sinistral strike-slip brittle-ductile shear zone, trending to NW-SE direction, which belongs to the regional Tocantinzinho lineament. The host granites are two oxidized calc-alkaline monzogranite stocks of Orosirian age and magmatic arc affiliation, correlated to the Parauari Intrisive Suite. The thicker lodes of the veining system are hosted by the major shear, along the N40-50W direction, whereas the thinner veins are housed by faults and fractures of second order and oblique to the main shear direction, both at low angle (around 20), moderate angle (nearby 50) and high angle (around 80). Such a structural situation is compatible with the Riedel system, with the major lodes parallel to the main shear direction (D), associated with low-angle veins (in R and P faults), moderate-angle gash veins (in extension T fractures) and high-angle veins (in R’ an X faults). Stockwork veinlets also occur as a minor ore type. The veins are always involved by a well-developed, normally brecciated, hydrothermal alteration halo. Phyllic alteration (quartz + phengite + pyrite) and chloritization are the two main hydrothermal alteration types, associated to minor potassic alteration (K- feldspar), carbonatization (calcite + sericite + quartz) and sufidation (pyrite + chalcopyrite + sphalerite). Three generations of hydrothermal veining quartz are well characterized in the Palito gold deposit. The youngest low-angle veins (R and P) are made up by quartz1, whereas the later thicker lodes (D) are composed by quartz1 and 2. Tension gash quartz veins may occur at any time of the hydrothermal system evolution and are made up by both quartz1 (youngest gash veins) and quartz2 and 3 (later gash veins). Gash veinlets of quartz3 correspond to final stages of the Palito hydrothermal process. The gold ore, hosted chiefly by quartz1 and 2 veins, is always associated to iron and copper sulfides (pyrite and chalcopyrite), besides sphalerite. Pyrrhotite, bismuthinite, galena, native bismuth and gold are minor metallic phases. Three generations of pyrite and chalcopyrite and one generation of sphalerite were recognized. Chalcopyrite1 replaces pyrite1 and it is replaced by sphalerite, which, in turn, is replaced by chalcopyrite2. Pirite2, coeval to sphalerite, occurs in mineralized veins as anhedral masses replacing tiny remnant grains (islands) of chalcopyrite1, showing concave or corroded edges. Gold is always associated or included in chalcopyrite1 and 2 and pyrite2, bismuthinite and native bismuth crystals. Veinlets of pyrite3 and chalcopyrite3, crosscutting sulfide masses in transtension zones of tiny sinistral faults, are the latest sulfide generations. Two generations of phengite and chlorite were identified in the gangue minerals, being veinlets of phengite2, chlorite2 and carbonate the last one. Fluorite, rutile, zircon and ilmenite still occur as minor gangue phases. The Pb-Pb age of 179417 Ma, obtained for the Palito ore, was interpreted as rejuvenation of the Pb-Pb system caused by Sthaterian alkaline granitic magmatism (Porquinho Intrusive Suite) related to the third extensional deformation phase. The geological features of the Palito gold deposit, as structural controlled veining style of ore bodies and hydrothermal alteration halos, predominating sericitization and cloritization and metallic association (Au-Cu-Bi-Zn) of the ore, all favor classification of the Palito deposit as intrusion-related vein gold deposits. It is a non-porphyritic intrusion-related deposit type, possible related to alkaline granites of the Maloquinha Intrusive Suite, which occur around the Palito deposit. The granitic magma should has provided the ore fluids and metals and the shearing should has controlled the fluid circulation and ore deposition of the Palito deposit.
Acesso aberto (Open Access)
Geologia, petrografia e geoquímica do Trondhjemito Mogno e rochas arqueanas associadas, Terreno Granito-Greenstone de Rio Maria - SE do Pará
(Universidade Federal do Pará, 2009-07-15) GUIMARÃES, Fabriciana Vieira; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Geological mapping alongside petrographical and geochemical studies in the occurrence area of the Mogno Trondhjemite in the Rio Maria Granite Greenstone Terrain (RMGGT) led to the identification of two distinct TTG facies. The Mogno Trondhjemite designation was maintained for the dominant facies with NW-SE to E-W structural style and distributed over east and west through the mapped area. The association identified on the central-west portion of the area, with NE-SW and N-S dominantly foliation was defined as a new stratigraphic unit called Mariazinha Tonalite. In the mapped area it was also possible to individualize another unit, the Grotão Granodiorite which intrudes Mariazinha Tonalite and it was proposed the redefinition of Parazônia Tonalite which now is to be called Parazônia Quartz-diorite. Geochronological data (Almeida in prep.) revealed that Mogno Trondhjemite and Mariazinha Tonalite are not part of the second generation of TTG rocks from the RMGGT because they yield ages older than 2.87 Ga. Also, the Parazônia Quartz-diorite is similar in age with the sanukitoid association of the RMGGT. Mogno Trondhjemite and Mariazinha Tonalite are mainly composed by quartz and plagioclase with biotite and magmatic epidote as the main ferro-magnesian minerals. Their geochemical characteristics are compatible with Archaean TTG granitoids with high Al2O3 contents, relatively poor in ferromagnesian elements and display ETR patterns with moderate to strong fractioning of ETRP and smooth Eu anomalies. The Grotão Granodiorite is a leucogranite composed by plagioclase, quartz and potassic feldspar with biotite and epidote as the main ferromagnesian minerals. This leucogranite has metaluminous to peraluminous character and has a distinct geochemical behaviour in comparison with RMGGT TTG granitoids and the Xinguara Granite (Leite 2001, Leite et al. 2004). In K-Na4 Ca digrams the Grotão Granodiorite escapes from the trondhjemitic trend as it shows enrichment in K in relation to TTG granitoids, but with minor K contents related to the Xinguara Granite and the biotite-granodiorite studied by Medeiros (1987). Parazônia Quartz-diorite shows compositions varying from quartz-diorite to granodiorite. The Parazônia Quartz-diorite is very similar to the sanukitoid rocks from the RMGGT (Oliveira et al. 2006, 2009), even though the Parazônia Quartz-diorite also displays some remarkable differences in relation to Bannach intermediate rocks, such as minor values of silica and Mg#.
Acesso aberto (Open Access)
Geologia, petrografia e geoquímica dos granitóides arqueanos de Sapucaia - Província Carajás-PA
(Universidade Federal do Pará, 2013) TEIXEIRA, Mayara Fraeda Barbosa; DALL'AGNOL, Roberto; http://lattes.cnpq.br/2158196443144675
Geological mapping performed in the eastern portion of the Transition Subdomain, Carajás Province, southern of Canaã dos Carajás and the northern of Sapucaia cities, allowed the identification, individualization and characterization of a variety of Archean rocks, previously encompassed in the Xingu Complex. The oldest unit identified in this area is a hornblende tonalite, correlated to São Carlos Tonalite (~2.93 Ga), which is exposed as blocks or outcrop and commonly present foliation (NW-SE to E-W) or homogeneous aspect. Its geochemical signatures differ from the typical Archean tonalite-trondhjemite-granodiorite (TTG) associations due to show enrichment in TiO2, MgO and CaO, low contents of Sr, and Rb contents similar to samples with lower concentrations of silica, which are reflected in higher Rb/Sr ratios and lower Sr/Ba ratios. The REE patterns reveal low to moderate fractionation of HREE compared to LREE, and discrete or moderate negative Eu anomalies. It is stratigraphycally followed by TTG association correlated to Colorado Trondhjemite (~2.87 Ga) which displays gray color, medium-grained, and commonly a NW-SE to E-W foliation. In the southern of area, outcrops a body of 40 km 2, which comprises a small mountain of porphyritic leucogranodioritic rocks named Pantanal Leucogranodiorite . It is emplaced at TTG association and crosscutted, on its western portion, by deformed leucogranites. The Pantanal Leucogranodiorite shows peraluminous character and calc-alkaline affinity, with high contents of Ba and Sr. The REE patterns show nosignificant Eu anomalies and HREE are strongly fractionated, which is geochemically similar to Guarantã Suite (~2.87 Ga) from the Rio Maria Domain. Its origin may be related to low degrees of melting of TTG, probably accompanied by interaction with fluids enriched in K, Ba and Sr, derived from a metasomatized mantle. The leucogranites exhibit A-type geochemical signature and reduced character, and may have originated from the melt of dehydrated peraluminous calcic-alkaline rocks, during the Neoarchean. In the eastern portion of the Pantanal Leucogranodiorite was also identified ahornblende-biotite monzogranite which is geochemically similar to oxidized A-type granites, correlated to Neoarchean Vila Jussara Suite. Also, it correlated to Neoarchean subalkaline magmatism in the northern area, occur two granitic stocks. They comprise (i) tonalite to granodiorite with geochemical signature similar to oxidized A-type granites and show affinity with Vila Jussara Suite; and (ii) monzogranites which show reduced A-type granites signature and could be compared to Planalto Suite. At northern of the study area was identified an association of mafic-enderbitic rocks which comprises intensely deformed and recrystallized hornblende norite, pyroxene-hornblende gabbros, pyroxeneix hornblende monzonite, hornblende gabbros, amphibolites and enderbites, which are represented in the geological map as a WNW-ESE small elongated body , and a semicircular body controlled by shear zones. The textures observed in these rocks indicate that recrystallization occurs under relatively high temperatures, 6000C or above, and those rocks show metamorphic features. The geochemical behavior of these rocks suggests that the hornblende-norite, hornblende-gabbros and amphibolites are tholeiitic subalkalines, whereas enderbites, pyroxene-hornblende gabbro and pyroxene-hornblende monzonite exhibit calcalkaline signature. The low La/Yb ratios for mafic rocks indicate low degree of fractionation, whereas the high La/Yb ratios for enderbites reveal significant fractionation of HREE during formation and differentiation of its magmas, and the concavity of HREE pattern indicates probably influence of amphibole fractionation during its evolution. In the central and northcentral of area was recognized biotite-monzogranites with peraluminous and calc-alkaline signature and distinct REE patterns, which allowed us to distinguish two groups. The first shows higher REE enrichment, weak enrichment in LREE relative to HREE, and exhibit moderate negative Eu anomalies, indicating no significant fractionation of phases enriched in HREE and show possibly affinity with Bom Jesus Granite from Canaã dos Carajás area. The second group shows a sharp fractionation of HREE relative to LREE, with discrete or absent Eu anomalies, and concave HREE patterns indicating that amphibole was important phase during the fractionation of these rocks, like Serra Dourada and Cruzadão granites, also located in the Canaã dos Carajás area. This comparison should be enhanced as soon as further geochemical and geochronological data are available in order to a correlation can be evaluated.
Acesso aberto (Open Access)
Geologia, petrografia e geoquímica e suscetibilidade magnética do Granito Paleoproterozoico São João, Sudeste do Cráton Amazônico, Província Carajás
(Universidade Federal do Pará, 2013-06-04) LIMA, Paulo Henrique Araújo; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
The São João granite (SJG) is an anorogenic batholith of circular form, with an area of approximately 160 km2, which cuts Archean units of the Rio Maria Granite-Greenstone Terrain, southeastern Amazonian Craton. It consists of four distinct petrographic facies: biotite-amphibole monzogranite (BAMG), biotite-amphibole syenogranite (BASG), amphibole-biotite monzogranite to syenogranite (ABMSG) and biotite monzogranite to syenogranite (BMSG). The SJG has a metaluminous to weakly peraluminous nature, FeOt/(FeOt+MgO) ratios varying from 0.94 to 0.99 and K2O/Na2O from 1 to 2, shows geochemical affinities with the intraplate granites, A-type granites of A2 subtype and ferrous granites, suggesting a crustal source for its origin. The SJG has higher contents of LREE compared to HREE and a sub-horizontal pattern for the latter. The negative anomalies of Eu rising from less evolved towards more evolved rocks (BAMG → BASG→ ABMSG→ BMSG). Magnetic susceptibility data (MS) allowed the identification of six populations with different magnetic characteristics, where the highest values of MS relate to the less evolved facies and the lowest to the more evolved facies. The comparison between SJG and the granite suites of the Carajás Province shows that it displays strong geological, petrographic, geochemical and MS similarities with the granites of the Serra dos Carajás suite, and may be preliminarily included in the same.
Acesso aberto (Open Access)
Petrografia, geoquímica e suscetibilidade magnética do granito Gradaús, Província Carajás, SE do Pará
(Universidade Federal do Pará, 2017-10-31) CARVALHO, Thiago Andrade de; LAMARÃO, Claudio Nery; http://lattes.cnpq.br/6973820663339281
The Gradaús Granite (1882±9 M.y.), located in Pará State, to the West of Bannach city and to the North of Cumaru do Norte, southeastern portion of Amazonian Craton, it is an anorogenic batholith with an area approximately 800 km², it is part of an intense granitic magmatism event that occurred during the Paleoproterzoic in the Carajás Province. It outcrops metasedimentary rocks of Rio Fresco Group, which lays on archean units of Rio Maria Domain. It compreends two distinct petrographic group: monzogranitics, composed by biotite-monzogranite and porfiritic-biotite-monzogranite, and syenogranitics, composed by biotite-anfibolesyenogranite, biotite-syenogranite and porfiritic-biotite-syenogranite. The magnetic suscetibility (MS) data allowed to identify three populations with differents magnetic characteristics, moderate to low MS values (< 3.53 x10-3 SIv) classify it as a moderately reduced granite. The Gradaús Granite shows contents of SiO2 >75%, MgO <0,2%, CaO <1%, FeOt between 1-2% and Al2O3 between 11,3 e 12,9%, metaluminous to peraluminous nature, 0.94 to 0.97 FeOt/(FeOt+MgO) ratios, K2O/Na2O ratios between 1 and 2 and higher LREE contents than HREE ((La/Yb)n=9.40). The LREE shows a moderate fractionation pattern ((La/Sm)n=4.61), while the HREE shows a subhorizontalized pattern ((Gd/Yb)n=1.40). The Eu anomalies are moderate to accentuated in the monzogranitic and syenogranitic rocks (Eu/Eu* 0.43-0.02), and slightly accentuated in the porfiritic ones (Eu/Eu* 0.25-0.03). It shows geochemical affinity to intraplate A-type granites, A2 subtype and ferroan granites. It shows petrografic, geochemical, geochronological and MS similarities to São João and Seringa granites, not yet placed in none of the three granitic suites of Carajás Province. The comparative study between these three granites to those which compreends the Jamon, Velho Guilherme and Serra dos Carajás granitic suites shows that these granites presente greater similarities to the granites that integrate the Serra dos Carajás Suite.