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Esta revisão incorpora novos dados isotópicos e químicos para correlação quimioestratigráfica de sucessões, predominantemente carbonáticas, na América do Sul (Argentina, Bolívia, Brasil, Paraguai e Uruguai). Estas sucessões, depositadas durante eventos de extensão, aparecem como espessos estratos carbonáticos/siliciclásticos em bacias epicontinentais ou foram acumulados sobre margens passivas em bordos de cratons (ex.: São Francisco, Amazonas, Bloco Rio Apa, Pampia e Río de La Plata) como três megasequências: glaciogênica, plataforma marinha carbonática (sobre diamictitos glacio-marinhos) e predominantemente continental siliciclástica. Em cinturões circunjacentes a cratons, sucessões carbonáticas contendo material vulcanoclástico/siliciclástico foram, na maioria dos casos, fortemente deformados. A idade precisa de sedimentação destas sucessões permanece em debate, mas recentes dados paleontológicos e geocronológicos têm consideravelmente restringidos os intervalos de deposição. Neste trabalho, reportamos trends isotópicos de alta resolução de C, O, Sr e S medidos em amostras bem preservadas e usamos principalmente isótopos de Sr e C em consonância com observações litostratigráficas/biostratigráficas, para estabelecer correlações detalhadas destas sucessões. Propor uma correlação quimioestratigráfica entre bacias Neoproterozoicas na América do Sul é o principal objetivo deste trabalho. This report reviews and incorporates new elemental and isotope chemostratigraphic data for correlation of Neoproterozoic carbonate-dominated successions in South America (Argentina, Bolivia, Brazil, Paraguay and Uruguay). These thick mixed carbonate/siliciclastic successions were largely deposited in epicontinental basins or accumulated on passive margins on the edges of cratons (e.g. São Francisco, Amazonia, Rio Apa Block, Pampia and Río de la Plata paleocontinents) during extensional events related to the rifting of the Rodinia Supercontinent. From the stratigraphic point of view, these successions occur as three mega-sequences: glaciogenic, marine carbonate platform (above glaciomarine diamictites or rift successions), and dominantly continental to transitional siliciclastics. In the orogenic belts surrounding cratons, carbonate-dominated successions with important volcanoclastic/siliciclastic contribution have been, in most cases, strongly deformed. The precise ages of these successions remain a matter of debate, but recently new paleontological and geochronological data have considerably constrained depositional intervals. Here, we report high-resolution C, O, Sr, and S isotope trends measured in well-preserved sample sets and mainly use Sr and C isotopes in concert with lithostratigraphic/biostratigraphic observations to provide detailed correlations of these successions. The establishing of a high-level and definite chemostratigraphic correlation between Neoproterozoic basins in South America is the main goal of this work.

p. 71 - 83 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-01-10T19:18:01Z No. of bitstreams: 1 0895981110000416-main.pdf: 2060599 bytes, checksum: f1ab9079c334ca980deb2aa5bbb75add (MD5) Made available in DSpace on 2012-01-10T19:18:01Z (GMT). No. of bitstreams: 1 0895981110000416-main.pdf: 2060599 bytes, checksum: f1ab9079c334ca980deb2aa5bbb75add (MD5) Previous issue date: 2010 This paper aims at establishing a tectonic and temporal framework to characterize the metallogenic processes that contributed to the origin of the mineral provinces in the northern São Francisco Craton. Many Archean mineralizations (eg. massive sulfide zinc, lead, zinc and copper, besides magnesiteetalc, ironetitaniumevanadium, iron, chromite and manganese) were generated before the assembly of the Craton. Deposits of chromite, nickel, gold and emerald were produced during the Paleoproterozoic orogenic cycle, when the Craton was amalgamated into the Atlantica paleocontinent. An extension event is recorded in the Neoproterozoic, during the breakup of Rodinia, associated with deposits of phosphorite and uranium. Kimberlite diamond and gold mineralization were generated during the Brasiliano orogenic cycle, coeval with the amalgamation of West Gondwana. A long-lasting and rather uniform crustal stress is recorded in the area during the Cambrian period. Resetting of the isotopic and magnetic systems that affected the Neoproterozoic sediments of the Irecê Basin at about 520 Ma was attributed to the regional-scale fluid migration and mineralization in the aftermath of the Brasiliano orogenic cycle.

p.346–361 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-01-13T12:32:35Z No. of bitstreams: 1 S1342937X06001985-main.pdf: 2869794 bytes, checksum: 3ceabc4f60938ee86c2d118b04156918 (MD5) Made available in DSpace on 2012-01-13T12:32:35Z (GMT). No. of bitstreams: 1 S1342937X06001985-main.pdf: 2869794 bytes, checksum: 3ceabc4f60938ee86c2d118b04156918 (MD5) Previous issue date: 2007 The cratonic blocks of South America have been accreted from 2.2 to 1.9 Ga, and all of these blocks have been previously involved in the assembly and breakup of the Paleoproterozoic Atlantica, the Mesoproterozoic to Neoproterozoic Rodinia, and the Neoproterozoic to Phanerozoic West Gondwana continents. Several mineralization phases have sequentially taken place during Atlantica evolution, involving Au, U, Cr, W, and Sn. During Rodinia assembly and breakup and Gondwana formation, the crust-dominated metallogenic processes have been overriding, responsible for several mineral deposits, including Au, Pd, Sn, Ni, Cu, Zn, Mn, Fe, Pb, U, P2O5, Ta, W, Li, Be and precious stones. During Rodinia breakup, epicontinental carbonate-siliciclastic basins were deposited, which host important non-ferrous base metal deposits of Cu–Co and Pb–Zn–Ag in Africa and South America. Isotope Pb–Pb analyses of sulfides from the non-ferrous deposits unambiguously indicate an upper crustal source for the metals. A genetic model for these deposits involves extensional faults driving the circulation of hydrothermal mineralizing fluids from the Archean/Paleoproterozoic basement to the Neoproterozoic sedimentary cover. These relations demonstrate the individuality of metal associations of every sediment-hosted Neoproterozoic base-metal deposit of West Gondwana has been highly influenced by the mineralogical and chemical composition of the underlying igneous and metaigneous rocks.

p. 263–304 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-01-26T15:59:26Z No. of bitstreams: 1 S016913680500020X-main.pdf: 2085935 bytes, checksum: ca02adfba2f94589150a37f9ca97e874 (MD5) Made available in DSpace on 2012-01-26T15:59:26Z (GMT). No. of bitstreams: 1 S016913680500020X-main.pdf: 2085935 bytes, checksum: ca02adfba2f94589150a37f9ca97e874 (MD5) Previous issue date: 2005 The Proterozoic sediment-hosted Zn–(Pb) sulfide and non-sulfide deposits of the São Francisco Craton, Brazil, are partially syn-diagenetic and epigenetic and were probably formed during extensional events. The majority of the deposits occur within shallow water dolomites. The Pb isotopic data of sulfides are relatively homogeneous for individual deposits and plot above the upper crust evolution curve of the Plumbotectonic model. Some of the deposits are characterized by highly radiogenic lead (206Pb/204Pb ≥ 21) originating from the highly radioactive crust of the São Francisco Craton. Pb and S isotopic data suggest the sources of metal and sulfur for the deposits to be the basement rocks and seawater sulfates in the sediments, respectively. The relatively high temperatures of formation (100 to 250 °C) and moderate salinity (3% to 20% NaCl equiv.) of the primary fluid inclusions in the sphalerite crystals suggest the participation of basinal mineralizing fluids in ore formation. The steep paleo-geothermal gradient generated by the radioactively enriched basement rocks probably assisted in heating up the circulating mineralizing fluids.

p. 302-305 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2011-09-09T13:12:28Z No. of bitstreams: 1 10647-35962-1-PB.pdf: 2214213 bytes, checksum: 33ee842d48602ada35981ac07a2c8305 (MD5) Made available in DSpace on 2011-09-09T13:12:28Z (GMT). No. of bitstreams: 1 10647-35962-1-PB.pdf: 2214213 bytes, checksum: 33ee842d48602ada35981ac07a2c8305 (MD5) Previous issue date: 2000-06 ntegrated studies carried out on the Proterozoic sediment-hosted Pb-Zn sulfide deposits of the São Francisco Craton, Brazil, allowed the estimation of (1) ages of the host sequences, (2) timing of mineralization, (3) possible sources of met al and sulfur, (4) temperature and salinity range of mineralizing solutions, (5) sources of fluids and (6) possible mechanisms of fluid flow. Contrary to the deposits from other Proterozoic basins, the Brazilian deposits do not contain world class met al reserves. This can probably be attributed to the lack of sufficient investments in exploration and mining development research activities. However, the sulfide deposits of the São Francisco Craton do share several important geological, structural, isotopic and fluid characteristics with some of the giant deposit types. Using these data we develop a more realistic met allogenic model for the Proterozoic sediment-hosted Pb-Zn sulfide deposits.

p. 315-317 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2011-09-09T13:25:35Z No. of bitstreams: 1 10650-35965-1-PB.pdf: 648069 bytes, checksum: fded09c47a370c7fd708ee275dd10069 (MD5) Made available in DSpace on 2011-09-09T13:25:35Z (GMT). No. of bitstreams: 1 10650-35965-1-PB.pdf: 648069 bytes, checksum: fded09c47a370c7fd708ee275dd10069 (MD5) Previous issue date: 2000-06 The Pb-Zn (Ag) mineralizations of Nova Redenção, Una-Utinga Basin, are hosted by dolarenites, dolomicrites and siliceousferruginous breccias of the Salitre Formation, Una Group. An ore reserve of about 2.5 Mt, with average grade of 6,1% Pb, 0,5% Zn, 32 ppm Ag and 10 ppm of Cd has been estimated by Companhia de Pesquisa de Recursos Minerais (CPRM) in the main sector of the deposit. The mineralization is composed mainly of galena and sphalerite, which occur in different ways (disseminated, stratabound, oolith and brecciacement, filling stilolytes/pockets, and veins). The orebodies are directly associated with N50°W trending regional fractures and faults, which are thought to represent deep basement structures reactivated during and after the Neoproterozoic carbonate basin sedimentation. Relationships between sulfides and the shallow sedimentation facies are striking. Several evidences of early-formed sulfates have been observed, including length-slow or lutecite-type microcrystalline quartz, aggregates of quartz with gypsum structure, microcrystalline pseudo-fibrous silica nodules, indicating both a lithostratigraphic and a sedimentary facies control. The study of primary fluid inclusions in sphalerites contemporaneous to galena showed the presence of moderate to high (around 24.3wt% eq. NaCl) aqueous solutions, containing Ca, K and Mg salts. The homogenization temperatures (TH) have a mean value of 185°C. Previous sulfur isotopic studies (d34S) (Misi et al. 1999) in cogenetic galenasphalerite pairs also indicated temperatures in the range 140°-180°C. Sulfur isotopic data in sulfides and sulfates suggested that sulfur was derived from seawater, possibly by thermochemical reduction (Misi et al. 1999). The characteristics of the mineralization along with the obtained fluid inclusion and isotopic data permit to suggest the following met allogenic model for the Nova Redenfao deposit: high concentration of met al brines have migrated throughout deep reactivated structures of the basement, forming sulfides by thermochemical reduction of sulfur present in the basin. The stratigraphic and sedimentary facies control is indicated by the presence of sulfates formed probably by sea-water evaporation in shallow zones of sedimentation.

p. 47-65 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-01-23T17:15:44Z No. of bitstreams: 1 S1342937X0570126X-main.pdf: 1967218 bytes, checksum: 7266d6bc53bafa83043e421d29708a29 (MD5) Made available in DSpace on 2012-01-23T17:15:44Z (GMT). No. of bitstreams: 1 S1342937X0570126X-main.pdf: 1967218 bytes, checksum: 7266d6bc53bafa83043e421d29708a29 (MD5) Previous issue date: 1999 Integrated studies of seven Proterozoic sediment-hosted, Pb-211-Ag sulfide deposits of Brazil, permit the estimation of the age of the hosting sequence and the mineralization, the nature of the sulfur and metal sources, the temperature range of sulfide formation and the environment of deposition. These deposits can be classified into three groups, according to their ages. (a) Archean to Paleoproterozoic: the Boquira deposit, in Bahia state, consists of stratiform massive and disseminated sulfides hosted by parametamorphic sequences of grunnerite-cummingtonite+magnetite that represent a silicate facies of the Boquira Formation (BF). Lead isotope data of galena samples indicate a time Span between 2.7 and 2.5 Ga for ore formation, in agreement with the stratigraphic position of the BE The relatively heavy sulfur isotope compositions for the disseminated and stratiform sulfides (+8.3 to +12.8 %O CDT)suggest a sedimentary source for the sulfur. (b) Paleo to Mesoproterozoic: stratiform and stratabound sulfides in association with growth faults are present in the Canoas mine (Ribeira, in Parana state) and in the Caboclo mineralization (Bahia state). They are hosted by calcsilicates and amphibolites in the Canoas deposit, whereas in the Caboclo area the mineralization is associated with hydrothermally altered dolarenites at the base of the 1.2 Ga Caboclo Formation. The interpreted Pb-Pb age of the Canoas mineralization is coeval with the 1.7 Ga host rocks. Sulfur isotopic data for Canoas sulfides (+1.2 to +16 %O CDT) suggest a sea water source for the sulfur. The range between -21.1 and +8.8 %O CDT for the Caboclo sulfides could suggest the action of bacterial reduction of seawater sulfates, but this interpretation is not conclusive. (c) Neoproterozoic: stratiform and stratabound sulfide deposits formed during the complex diagenetic history of the host carbonate rocks from tlieMorro Agudo (Bambui Group), Ired and Nova RedenCIo (Una Group), yield heavy sulfur isotope values (+18.9 to +39.4 %O CDT). The uniform heavy isotope composition of the barites from these deposits (+25.1 to +40.9 %a) reflect their origin from Neoproterozoic seawater sulfates. The latestage, and most important, metallic concentrations represent sulfur scavenged from pre-existing sulfides or from direct reduction of evaporitic sulfate minerals. Lead isotope data from the Bambui Group suggest focused fluid circulation from diverse Proterozoic sediment sources, that probably was responsible for metal transport to the site of sulfide precipitation. (d) Late Proterozoic to Early Paleozoic: lead-zinc sulfides (+pyrite and chalcopyrite) of Santa Maria deposits, in Rio Grande do Sul, form the matrix of arkosic sandstones and conglomerates, and are closely associated with regional faults forming graben structures. Intermediate volcanic rocks are intercalated with the basal siliciclastic members. Lead isotope age of the mineralization (0.59 Ga) is coeval with the host rocks. Sulfur isotopic values between -3.6 and +4.1 are compatible with a deep source for the sulfur.

Texto completo: acesso restrito. p.87–100 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2013-01-30T14:23:23Z No. of bitstreams: 1 Misi.pdf: 2104937 bytes, checksum: dae3326343dfa94be452f0114d8265ec (MD5) Made available in DSpace on 2013-01-30T14:23:23Z (GMT). No. of bitstreams: 1 Misi.pdf: 2104937 bytes, checksum: dae3326343dfa94be452f0114d8265ec (MD5) Previous issue date: 1998 The Una Group, Irecê Basin (Bahia state) is correlative with the better known Bambuí Group of the São Francisco Basin (Minas Gerais state); these basins are remnants of widespread carbonate platform that covers > 300 000 km2 of the São Francisco Craton in Brazil. The Irecê area contains a well-controlled stratigraphic succession hosting economic phosphate deposits and sulfide mineralization. Una Group strata comprise a basal siliciclastic sequence, mostly composed of glacial diamictites (Bebedouro Formation), followed by a carbonate succession that is several hundred meters thick, the Salitre Formation. An angular unconformity separates the two units. The carbonates of the Salitre Formation are characterized by 87Sr/86Sr ratios ranging between 0.70745 and 0.71776, and δ13C values ranging between −4.4 and +9.4‰ PDB. The carbonates also contain beds and nodules of barite and gypsum with highly positive δ34S values (+25.2 to +32.8‰ CDT). The ‘best preserved’ carbonate samples selected on the basis of their Mn and Sr concentrations as well as their ratios, yield 87Sr/86Sr values of 0.70745–0.70765. Comparison of these values with the secular strontium isotopic curve for the Neoproterozoic seawater suggests a 600 (to 670) Ma age for the Salitre Formation and for its correlative units in the São Francisco Basin.

This report reviews and incorporates new elemental and isotope chemostratigraphic data for correlation of Neoproterozoic carbonate-dominated successions in South America (Argentina, Bolivia, Brazil, Paraguay and Uruguay). These thick mixed carbonate/siliciclastic successions were largely deposited in epicontinental basins or accumulated on passive margins on the edges of cratons (e.g. São Francisco, Amazonia, Rio Apa Block, Pampia and Río de la Plata paleocontinents) during extensional events related to the rifting of the Rodinia Supercontinent. From the stratigraphic point of view, these successions occur as three mega-sequences: glaciogenic, marine carbonate platform (above glaciomarine diamictites or rift successions), and dominantly continental to transitional siliciclastics. In the orogenic belts surrounding cratons, carbonate-dominated successions with important volcanoclastic/siliciclastic contribution have been, in most cases, strongly deformed. The precise ages of these successions remain a matter of debate, but recently new paleontological and geochronological data have considerably constrained depositional intervals. Here, we report high-resolution C, O, Sr, and S isotope trends measured in well-preserved sample sets and mainly use Sr and C isotopes in concert with lithostratigraphic/biostratigraphic observations to provide detailed correlations of these successions. The establishing of a high-level and definite chemostratigraphic correlation between Neoproterozoic basins in South America is the main goal of this work. RESUMO: Esta revisão incorpora novos dados isotópicos e químicos para correlação quimioestratigráfica de sucessões, predominantemente carbonáticas, na América do Sul (Argentina, Bolívia, Brasil, Paraguai e Uruguai). Estas sucessões, depositadas durante eventos de extensão, aparecem como espessos estratos carbonáticos/siliciclásticos em bacias epicontinentais ou foram acumulados sobre margens passivas em bordos de cratons (ex.: São Francisco, Amazonas, Bloco Rio Apa, Pampia e Río de La Plata) como três megasequências: glaciogênica, plataforma marinha carbonática (sobre diamictitos glacio-marinhos) e predominantemente continental siliciclástica. Em cinturões circunjacentes a cratons, sucessões carbonáticas contendo material vulcanoclástico/siliciclástico foram, na maioria dos casos, fortemente deformados. A idade precisa de sedimentação destas sucessões permanece em debate, mas recentes dados paleontológicos e geocronológicos têm consideravelmente restringidos os intervalos de deposição. Neste trabalho, reportamos trends isotópicos de alta resolução de C, O, Sr e S medidos em amostras bem preservadas e usamos principalmente isótopos de Sr e C em consonância com observações litostratigráficas/biostratigráficas, para estabelecer correlações detalhadas destas sucessões. Propor uma correlação quimioestratigráfica entre bacias Neoproterozoicas na América do Sul é o principal objetivo deste trabalho.