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Baseando-se em interpretações paleoambientais utilizando dados geoquímicos, os mármores e as rochas calcissilicáticas do Vale do Jacurici, centro-norte da Bahia, demonstraram estar associados a um paleoambiente de deposição marinho raso Paleoproterozoico. Essas rochas encontram-se deformadas, metassomatizadas e metamorfizadas em condições de anfibolito alto a granulito. São intruditas pelo Sienito de Itiúba e pelo Complexo Máfico-ultramáfico Vale do Jacurici, mineralizado em cromita, relação que sugere idade mínima paleoproterozoica para a sucessão. Os estudos realizados em testemunhos de sondagem permitiram a caracterização de mármores, diopsiditos e rochas calcissilicáticas granulitizadas. São identificadas assinaturas marinhas preservadas em padrões de elementos terras-raras (ETR + Y), bem como anomalias negativas de Ce, positivas de Y e Gd e relações Y/Ho próximas aos valores da água do mar (60–168) nos mármores. Foram constatados padrões de contaminação crustal que indicam componentes provenientes de input terrígeno, resultando em relações positivas Zr versus Hf, enriquecimento relativo de metais traços, ΣETR + Y e razões Pr/Yb[SN], padrões Y/Ho (< 30) e anomalias menos acentuadas, sobretudo nas rochas calcissilicáticas. A presença de magnitudes variáveis de anomalias positivas de Eu pode refletir contribuição de assinaturas das águas dos mares arqueanos residuais e influência de fluidos magmáticos tardios. A ocorrência de valores anômalos de P2O5 nos mármores (1,38 e 4,56%) e diopsiditos (2,07 e 2,3%) relacionada às razões Y/Ho (parâmetro de contaminação detrítica na bacia) sugere assinaturas de zonas limítrofes entre contribuição terrígena e marinha, bem como evidencia controle estratigráfico preservado nas concentrações de fósforo. Esses dados indicam um paleoambiente influenciado por eventos climáticos globais favoráveis à fosfogênese, envolvendo alta disponibilidade de oxigênio, cenário semelhante aos registros em bacias paleoproterozoicas mineralizadas em fosfato sedimentar

Greenstone belts and volcano-sedimentary sequences are essential features to understand the tectonic framework of Precambrian terranes worldwide. The Sao Francisco Craton, eastern Brazil, hosts several of these supracrustal belts related to its Archean-Paleoproterozoic evolution. The Rio Salitre Complex (RSC) is a Paleoproterozoic greenschist-metamorphosed volcano-sedimentary sequence deposited over Archean orthogneisses of the northern Sao Francisco Craton. Here, we present a tectonic model for the Rio Salitre Complex, integrated with regional and global contexts, based on geology, structures, whole-rock geochemistry, U–Pb zircon geochronology, and Lu–Hf isotopes. The RSC comprises the Baixo Vale do Rio Salitre (BVRS), formed by Lower and Upper Subunits, and the Sobradinho Unit. The BVRS Lower Subunit is composed of ultramafic, mafic, and felsic metavolcanic rocks, chemical, and minor clastic metasedimentary rocks. The BVRS Upper Subunit comprises clastic metasedimentary rocks, while the Sobradinho Unit consists of chemical and clastic metasedimentary rocks. The RSC units display evidence of shallow to deep marine platformal deposition in an intra-cratonic rift (abundance of pelitic facies, presence of phosphorites, iron formations, graywackes, arkoses, and cross-bedded quartzites). RSC phosphorites are a register of a global Paleoproterozoic phosphogenic event. The volcanics of the Rio Salitre Complex compose a bimodal suite. The mafic and ultramafic metavolcanics exhibit komatiitic, tholeiitic, and alkaline affinities. Enriched REE, trace elements patterns, and incompatible element ratios indicate a continental rift environment for the mafic and ultramafic metavolcanic rocks. These features also suggest enriched mantle-derived melts, with a variable crustal contribution. The porphyritic rhyolites and aphyric high-silica rhyolites have subalkaline to alkaline features, with enriched REE and trace element profiles and negative Eu, Nb, and Ti anomalies. U–Pb SHRIMP dating of porphyritic rhyolite resulted in a concordia age of 2161.1 ± 4 Ma (MSWD: 1.1). Archean Lu–Hf TDM ages with negative eHf(t) values (from −8.90 to −2.70), and an isolated Paleoproterozoic TDM age (2440 Ma) with positive eHf(t) value (+3.96), related to the geochemical features, indicate that RSC felsic metavolcanics were originated from melting of multiple Archean crustal sources (continental and slab), with minor contributions of Paleoproterozoic juvenile material, and emplaced in a continental rift environment. 2.0 Ga foliated metagranites and metagranodiorites (locally augen) intrude the RSC rocks, resulting in local hornblende-hornfels metamorphism. The RSC supracrustal lithotypes register D1’, D1″, and D2 structures. D1′ structures are mainly represented by N–S high-dip angle schistosity, N and SSE plunge folds, and high-rake mineral stretching lineation (Lx’); while D1″ corresponds to NE-SW transpressional shear zones, NE-SW low-dip angle crenulation cleavage, and medium to low-rake mineral stretching lineation (Lx1″). The D2 structures are related to, locally quartz-filled, fractures, in addition to NE-SW and ENE-WSW oriented faults. The structural framework reflects a two-phase deformation, with a ductile to ductile-brittle, W-E frontal to NW-SE oblique D1 phase, and a late brittle, NE-SW D2 phase. Late hydrothermal activity resulted in quartz veins and pyrite-pyrrhotite-(chalcopyrite) concentrations. The documented aspects of the Rio Salitre Complex are consistent with evolution in a Rhyacian-Orosirian continental rift basin, inverted by the influence of orogenic belts, approaching from northwest and southeast.

The Jacobina Range mountain chain is located in the northeastern part of Bahia state, Brazil. It is 250 km long, with N–S direction located at the eastern border of the Gaviao-Lencois block, and corresponds to the northern portion of the Contendas-Mirante-Jacobina Lineament. There are several structurally controlled Au-bearing quartz veins hosted by metasedimentary rocks of the siliciclastic Jacobina Group and Vale do Coxo metaultramafic schists that are exploited by artisanal miners. Four of these deposits were mapped. They are hosted by two Paleoproterozoic fault systems, named from east to west, as Pindobacu and Maravilha. The Pindobacu fault system, D1 phase, second-order thrust, and reverse faults hosts both central and oblique mineralized veins at Morro da Palmeirinha and Maravilha deposits, respectively. The Maravilha fault system, D2 phase, second-order transpressive fault, hosts the mineralized central shear vein at the Jaqueira deposit. The D3 phase, second-order normal faulting hosts mineralized central shear vein at Mina Velha. The sericitic alteration is dominant in the D1 and D2 phase deposits, while sulfidation prevails in the D3 phase. Gold grades are lower at the deposits with schist as host rocks when compared to deposits were quartzite is the predominant host rock. Chlorite geothermometry showed that the hydrothermal system temperature conditions ranged between 303 °C and 346 °C at Jaqueira and the primary H2O + CO2+NaCl (type I) and H2O + NaCl (subtype II.a) fluid inclusion assemblage seems to be heterogeneously entrapped during the phase separation, which was triggered by a decrease in pressure, with retrometamorphic conditions, during the orogenic uplift at the Jacobina Range. Later, this assemblage was reequilibrated according to the hydrothermal system temperature conditions. The vapor-rich H2O + NaCl fluid inclusion assemblage subtype II.d suggests a possible magmatic contribution in fluid composition at the Mina Velha deposit. The H2O + NaCl, secondary subtypes II.b and II.c fluid inclusion assemblages from Jaqueira and Mina Velha deposits are of uncertain origin. The hydrothermal mineralization at Jacobina Range is interpreted as an orogenic mineral system, and the following elements were characterized: (1) participation of orogenic and possibly magmatic fluid composition; (2) the fault systems in a compression-driven fluid flow type acted as conduits of the mineralizing fluids, and the second-order structures were the throttle of the hydrothermal system; (3) the later phases of tectonic evolution were the driver; (4) the inductor of gold precipitation was fluid-rock interaction; (5) dispersion in the gold content occurred when schist host rocks are present.

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.

The Neoproterozoic successions of the Sao Francisco Craton are primarily represented by the Bambui and Una groups, deposited in cratonic epicontinental basins, and by the Vazante and Vaza Barris/Miaba groups, which accumulated on passive margins on the edges of the craton. The epicontinental basins comprise three megasequences: glaciogenic, carbonate platform (marine) and dominantly continental siliciclastics. Possible correlative sequences are observed in the passive margin deposits. At least two major transgressive–regressive sea-level cycles occurred during the evolution of the carbonate megasequence, which lies above glaciomarine diamictites of probable early Cryogenian (i.e. Sturtian) age. C, O, Sr and S isotope trends from analyses of well-preserved samples, together with lithostratigraphic observations, provide reasonable correlations for most of the Neoproterozoic successions of the Sao Francisco Craton. The 87 Sr/ 86 Sr record of these successions, ranging from 0.70769 to 0.70780, supports the proposed correlation with the Bambui, Una and Vaza/Barris successions, and with the basal units of the Vazante Group. In addition, C-isotope positive excursions ranging from +8.7 to +14‰ and negative excursions from –5.7 to –7‰ VPDB in the Bambui, Una and Vaza-Barris successions provide key markers for correlations. The precise ages of the sedimentation in these successions remains a matter of debate, but organic shales of two units of the Vazante Group have been dated by Re–Os techniques in two different laboratories, both yielding Mesoproterozoic ages. The Neoproterozoic and Mesoproterozoic successions preserve significant glaciogenic deposits.

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 Sao Francisco Craton. Many Archean mineralizations (eg. massive sulfide zinc, lead, zinc and copper, besides magnesite–talc, iron–titanium–vanadium, 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 Irece Basin at about 520 Ma was attributed to the regional-scale fluid migration and mineralization in the aftermath of the Brasiliano orogenic cycle.

The Lapa Formation is a thick carbonate sequence (∼900 m) that constitutes the upper part of the Vazante Group on the S˜ Francisco craton, Brazil. It conformably overlies a previously unrecognized glacial diamictite unit of poorly constrained age. The sequence, above the glacial unconformity, consists predominantly of organic-rich shale, subtidal rhythmic dolomicrites and microbialaminites, and intertidal stromatolites. Four boreholes, spanning different depositional settings, were sampled at highresolution and investigated for their petrographic and chemical criteria to evaluate their degree of preservation. The δ 13 C and δ 18 O values of well preserved Lapa carbonate microsamples range from −8.2‰ to 3.3‰ (VPDB) and from −13.6‰ to −0.9‰ (VPDB), respectively. Each of the δ 13 C profiles of the investigated cores reveals two strong negative excursions of up to 8‰, an event in post-glacial dolomicrites immediately above the glaciogenic unit and a 10 m interval of organic-rich shale, and a second near the top of the sequence associated with a shale interval. Based on the observation of dropstones and sedimentary iron formation in the underlying diamictite, as well as the distinguishable carbon isotope trends, the Lapa Formation is considered as a cap carbonate lithofacies. The age of the Lapa Formation is presently unknown but the least radiogenic 87 Sr/ 86 Sr value (∼0.7068), associated with a negative carbon isotope excursion, matches that from the Rasthof Formation in Namiba on the Congo craton, which is radiometrically constrained to be younger than ca. 750 Ma.

Integrated studies of seven Proterozoic sediment-hosted, Pb-Zn-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 BF. The relatively heavy sulfur isotope compositions for the disseminated and stratiform sulfides (+8.3 to +12.8 ‰ 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 ‰ CDT) suggest a sea water source for the sulfur. The range between −21.1 and +8.8 ‰ 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 the Morro Agudo (Bambui Group), Irece and Nova Redencao (Una Group), yield heavy sulfur isotope values (+18.9 to +39.4 ‰ CDT). The uniform heavy isotope composition of the barites from these deposits (+25.1 to +40.9 ‰) reflect their origin from Neoproterozoic seawater sulfates. The late-stage, 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. Geological, petrographic and isotopic data of the deposits studied suggest that they were formed during periods of extensional tectonics. Growth faults or reactivated basement structures probably were responsible for localized circulation of metal-bearing fluids within the sedimentary sequences. Sulfides were formed by the reduction of sedimentary sulfates in most cases. Linear structures are important controls for sulfide concentration in these Proterozoic basins.

The Sao Francisco and the Congo cratons represent sectors of a Neoproterozoic palaeocontinent preserved from the Brasiliano-Pan African orogeny, recorded in their marginal belts. The boundaries between the Sao Francisco Craton and the surrounding belts are marked by intensive folding and overthrusting. In the interior of the craton, Neoproterozoic sedimentary covers are horizontal or gently deformed, forming isolated basins. The term Sao Francisco Basin includes Palaeo- and Mesoproterozoic successions but in this chapter it is restricted to the Neoproterozoic sedimentary successions of the Sao Francisco Supergroup, characterised by a glaciogenic unit at the base and an argillaceous–carbonatic–arkosic unit at the top. The Neoproterozoic evolution of the Sao Francisco Craton, including its marginal belts and sedimentary cover, is reviewed. The lithostratigraphy, Neoproterozoic mineralisations (lead, zinc, fluorine, barium and phosphates) and geochronological and stable isotope studies are also presented. The geological record of glacial events and stable isotope data of related cap carbonates are also discussed.