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A aplicação dos métodos Lógica Nebulosa (FuzzyLogic) e Pesos das Evidências (Weights of Evidence) na estimativa da favorabilidade para ocorrência de depósitos de Pb e Zn na área da Bacia de Irecê (Bahia) aborda dois enfoques distintos da modelagem em ambiente de Sistemas de Informações Geográficas: o primeiro, simulando as idéias de um especialista sobre determinado fenômeno, e o segundo, obtendo medidas estatísticas da associação espacial para usar no prognóstico de novas ocorrências do mesmo fenômeno.

More than three hundred mafic-ultramafic bodies of different sizes, containing copper sulfide mineralization, are present in the Curaca River Valley Copper Province, northeastern Sao Francisco Craton, Bahia State, Brazil, covering an area of about 1700 km2. The basement, supracrustal sequence, and mafic-ultramafic intrusive rocks underwent granulite facies metamorphism and were reworked during the evolution of the Itabuna-Salvador-Curaca Orogeny, resulting in retrograde metamorphism to the amphibolite facies, partial migmatization, and intrusion of granitic and syenitic rocks. During the slow and progressive rise of the terrain, hydrothermal reactions mainly along shear zones retrogressed part of these rocks to assemblages characteristic of the greenschist metamorphic facies. The main orebodies with copper sulfide minerals are associated with pyroxenite, mica-rich (glimmerite) and noritoid rocks. The present investigation focuses on the major Caraiba, Sussuarana, Surubim, and Vermelhos deposits. Chalcopyrite and bornite compose the ore, in a ratio of 70–30%, with copper grade varying between 0.69% and 1.4%, and associated gold and silver. The sulfide minerals are invariably accompanied by magnetite. Two mineralization styles are distinguished: (i) disseminated in non-altered mafic-ultramafic rocks; and (ii) tectonic controlled related to hydrothermal alteration zones. New geochronological data show that quartz-microcline metasomatites of the Caraiba Mine contain Neoarchean inherited zircons (upper intercept at 2723 ± 51 Ma), related to the early stages of magmatism, whereas Orosirian ages (2047 ± 12 and 2042 ± 15 Ma) are related to the main hydrothermal mineralization activity. Norite from the Surubim Mine has a Paleoproterozoic age (2047 ± 11 Ma), and the dated gabbro shows Pb loss in the Neoproterozoic, probably related to the Brasiliano Orogeny (670–490 Ma). Previous studies have demonstrated that the main hydrothermal event is Paleoproterozoic. Phlogopite Ar-Ar dating from the Caraiba Mine yields plateau-ages around 2000–2100 Ma. A cluster of δ34S values approaching zero is related to interstitial sulfide minerals in the least-altered ultramafic rocks, while values above and below zero are related to remobilized sulfides. These data support the hypothesis of the existence of a primary (magmatic) mineralizing event, alleged to have precipitated disseminated, interstitial sulfide minerals, and a second (hydrothermal) event, responsible for the economically more important mineralization, which is structurally controlled and related to significant potassic alteration. The sulfide minerals are associated with different generations of magmatic and hydrothermal magnetite, as well as distal plagioclase and microcline alteration halos. The combination of these features reaffirms the concept that the Curaca Valley deposits may be part of the same alteration system, as described in IOCG deposits, with the deepest deposits being located further south. Based on the data obtained during the present study, it is possible to establish a tectono-metallogenic evolutionary model to explain the genesis of the copper mineralization in the Curaca Valley. The mafic-ultramafic bodies were emplaced as multiple intrusions in Neoarchean arc-related gneisses and chemical sediments, along with bornite and chalcopyrite mineralization. The sulfide minerals that preserve the characteristics of this stage are chalcopyrite or bornite, both with δ34S values around 0‰V-CDT. A continental collision affected the Caraiba arc and the related sequences between 2100 and 2080 Ma. During this Rhyacian-Orosirian orogeny, deformation and amphibolite-granulite facies metamorphism, the rocks underwent partial melting, and sapphirine formation developed. Between 2050 and 2020 Ma, the main mineralization stage took place at Caraiba, Vermelhos, and Surubim, which corresponds to an earlier stage in the Sussuarana deposits. The southern deposits were formed deeper than those to the north, resulting in less extensive potassic alteration and related hydrothermal mineralization. The sulfide minerals of the deeper deposits have negative δ34S (between 0‰ and −6.81‰), to slightly positive values, where the igneous protoliths are best preserved. This alteration took place near the brittle-ductile boundary, mainly associated with ductile structures. The latest stage of mineralization took place between 1950 and 1920 Ma, in the Caraiba, Vermelhos and Surubim deposits, along with major sulfide remobilization in Sussuarana. This stage was characterized by the participation of oxidizing fluids, possibly meteoric waters, which raised the δ34S values up to +11.77‰.

The Precambrian basement of Northeastern Brazil is the product of Rhyacian block convergence. The main deformation and intrusion of crustal granitoids occurred between 2.15 and 1.8 Ga ago. This large area has been subjected to long-lasting and rather uniform stresses during the Cambrian period. Gold provinces in Bahia represent metallogenetic products of distinct tectonothermal events. Gold mineralization took place during the Paleoproterozoic collision and the Cambrian convergence, respectively, accompanied by heat flow, crustal deformation, and granite intrusion. The tectonic framework of the region was reconstructed at ca. 700 Ma ago, considering the hypothesis of wrench-fault tectonics. The new hypothesis provides geological evidence and metallogenic constraints that make further investigation necessary, with reference to well-established São Francisco Craton concept and its peripheral fold belts.

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.

The Vazante Group, as originally described, is a thick marine carbonate-dominated succession adjacent to the Brasilia Fold Belt, on the western border of the Sao Francisco Craton, in south-central Brazil. The sedimentary dolomites of this group contain economically important Zn–Pb and phosphate deposits, but age constraints for the host rocks and mineralization have been controversial. New geochronological data and geological observations have indicated that the upper and middle sections of the Vazante succession belong to a Mesoproterozoic sequence that was thrust over a Neoproterozoic succession correlative with the Bambui Group. This new stratigraphic framework has significant implications for metallogenic exploration models in both intra-cratonic and passive-margin basins of the Sao Francisco Craton. Although hosted in Mesoproterozoic units, most of the Zn–Pb mineralization occurred in the Neoproterozoic by circulating hydrothermal fluids during the prolonged breakup of the Rodinia supercontinent. The possibility that an initial stage of mineralization occurred earlier is considered. Phosphorite generation in the Neoproterozoic units is conceivably related to glacial events. The refined stratigraphy combined with a new mineralization model will significantly contribute to the exploration strategy for phosphate and sulfide deposits in the Mesoproterozoic and Neoproterozoic successions of the Sao Francisco Craton and beyond.

A new Re–Os radiometric age date for an organic-rich shale horizon from the Vazante Group in Brazil, coupled with geological observations, provide evidence for late Mesoproterozoic glacial episodes, conflicting with the general view of greenhouse conditions marked by a eustatic high stand at this time. Field observations of a reverse fault juxtaposing older Mesoproterozoic sedimentary rocks above younger Neoproterozoic strata provide a new stratigraphic framework and reconcile the apparent inversion of U–Pb detrital zircon ages through the succession. Combined, the geochronological, geochemical and stratigraphic evidence suggest that the Vazante Group sediments accumulated along a passive margin of the Sao Francisco craton and are correlative with the neighboring Paranoa Group. Biomarker, sulfur isotope and iron speciation analyses support the interpretation of a strongly stratified water column during post-glacial transgression and deposition of one of the bituminous shale horizons. The relationship of the glaciogenic Vazante Group to other late Mesoproterozoic successions, such as the non-glacial Atar Group in West Africa and Bylot Supergroup in arctic Canada, however, remains enigmatic.

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.

The Bebedouro Formation (Fm.) is a Neoproterozoic glaciogenic succession at the base of the Una Group on the Sao Francisco Craton. The glaciogenic sequence is composed of diamictites, pelites and sandstones with a variety of lithofacies that are grouped into four associations: (i) ice-contact, (ii) pro-glacial, (iii) ice-rafted and (iv) aeolian (extraglacial). Thus, the Bebedouro Fm. is interpreted to have been deposited in a shelf marine environment where glacio-proximal sedimentation dominated. It variably overlies Palaeoproterozoic/Archaean basement and Mesoproterozoic metasedimentary rocks of the Chapada Diamantina Group. The overlying carbonate succession (Salitre Fm.) is informally subdivided into five mappable units. Unit C, at the base, is composed of red argillaceous dolostone with typical negative δ 13 C signatures averaging –5.1‰ (VPDB). Unit B consists of grey laminated limestones that grade upward into grey dolostone with tepee structures of Unit B1; both have δ 13 C values around 0‰. The overlying Unit A consists of interbeds of greyish marl, shales and siltstones grading upward into massive black organic-rich limestone with oolitic and pisolitic beds of Unit A1. Positive δ 13 C signatures averaging +8.5‰ VPDB characterize the black limestones of Unit A1. 87 Sr/ 86 Sr ratios of well-preserved samples of these carbonate units show values of 0.70745 and 0.70765. These units can be correlated litho- and chemostratigraphically with formations of the Bambui Group (Sao Francisco Basin) to the west.

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 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.

The Neoproterozoic Vazante Group at the western border of the Sao Francisco Craton, Brazil, hosts the largest Zn–Pb district in South America. Several authors have classified this mineral district as Mississippi Valley-type (MVT), based on the intimate association with carbonates and the epigenetic character of most ore bodies. In this paper, we present 47 new lead isotope data from four deposits located along the 300 km N–S Vazante–Paracatu–Unai linear trend. Pb isotope ratios indicate sources with relatively high U/Pb and Th/Pb ratios. Considering the 206Pb/204Pb and 208Pb/204Pb ratios as indicative parameters for the source, we suggest an upper crustal source for the metals. The small variation on the Pb isotope ratios compared to those observed in the classical MVT deposits, and other geological, fluid inclusion and sulphur isotopic data indicates a metallogenic event of long duration. It was characterized by focused circulation of hydrothermal fluids carrying metals from the basement rocks and from the sedimentary pile. The data obtained are more compatible with an evolution model similar to that of IRISH-type deposits. The existence of three Pb isotopic populations could be the result of regional differences in composition of the source rocks and in the fluid–rock interaction since the mineralization is a long-term process.

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.

The Proterozoic sediment-hosted Zn–(Pb) sulfide and non-sulfide deposits of the Sao 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 ( 206 Pb/ 204 Pb ≥ 21) originating from the highly radioactive crust of the Sao 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.

The Vazante Formation consists of approximately 1700 m of mainly microbial mats and stromatolitic reefal lenses that were deposited on shallow marine platform and have been entirely dolomitized. Samples representing different dolomite generations were taken from three boreholes covering the entire spectrum of the Vazante carbonates. Dolomites can be classified, based on petrography and geochemistry, into four generations ranging in crystal size between 4 m (almost micritic) and 3 mm and occurring as both replacements and cements. The Sr/Ca molar ratios, calculated for the dolomitizing fluid (0.0006–0.0138), suggest a contribution from a non-marine, possibly meteoric, water component. The 18 Oa nd 13 C values vary from − 0.1 to − 14.3‰ (PDB) and 0.2 to − 2.3‰ (PDB), respectively. Fluid-inclusion study suggests that dolomitization must have commenced at a temperature lower than about 50 °C. A mixing-zone model of dolomitization for Dolomites I–III satisfies the constraints from elemental chemistry, 18 O, 87 Sr/ 86 Sr and fluid inclusions. The petrographic and chemical criteria of the latest generation, Dolomite IV, reflect conditions of deep burial environment at temperatures above 120–130 °C. The 13 C values show only small variations at the base of the formation, followed by a major negative plunge ( 4‰) at the top, this plunge correlated with the Sturtian glacial phase. In contrast to C-isotopes, only few samples may have retained their near-primary 87 Sr/ 86 Sr values of 0.70614–0.70734. The lowest 87 Sr/ 86 Sr value (0.70614), from fibrous cement in the upper part of the formation, correlates with the negative 13 C shift and is also consistent with the Sr-isotope signature proposed for the glacial Sturtian seawater. The 34 S values, obtained from sulfates trapped in carbonates, range between 10.8 and 16.9‰ with a jump to 21.3‰ in the overlying formation. All isotope signals are within the range suggested for the early Neoproterozoic seawater, but the Precambrian baseline is poorly known and additional work is required to confirm this tentative assignment. © 2001 Elsevier Science B.V. All rights reserved.

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 Una Group, Irece Basin (Bahia state) is correlative with the better known Bambui Group of the Sao Francisco Basin (Minas Gerais state); these basins are remnants of widespread carbonate platform that covers > 300 000 km2 of the Sao Francisco Craton in Brazil. The Irece 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 Sao Francisco Basin.

The Irece Basin is a relatively small late Proterozoic basin within the Sao Francisco craton of northeast-central Brazil. Stratabound Zn-Pb-Ag sulfide and phosphate-rich units occur within a 50-m-thick tidal-flat sequence of dolomitic limestone and cherty dolostone within the lower Salitre Formation of the Una Group. Phosphate is concentrated in stromatolitic structures; metallic mineralization is represented by stratiform masses and disseminations of sulfide minerals in a tidal-flat sequence that has relict evaporitic structures. Zn-Pb-Ag sulfide concentrations in the Irece area are associated with parallel laminated, silty dolostone with shallow-water sedimentary structures, including laminar stromatolites, mud cracks, tepee structures, collapse breccias, length-slow quartz nodules, and pseudomorphs after evaporitic sulfates. Sulfide minerals include pyrite, sphalerite, galena, marcasite, jordanite, tetrahedrite, and covellite, in order of decreasing abundance. Nodular and bladed sulfide forms are pseud...

Lead- and sulfur-isotope investigations were performed at the Boquira sediment-hosted lead-zinc deposit in Bahia state, Brazil. This deposit, hosted by banded iron formation of metamorphosed oxide, carbonate, and silicate facies, was the most important lead mine in Brazil for nearly 40 years, until 1991, when mine operations ceased as a result of inadequate proven reserves. The lead-isotope data indicate an Archean-Paleoproterozoic age (2.5 to 2.7 Ga) for the deposit, and the lead is inferred to have been derived from crustal sources, probably from the basement rocks. The δ34S values for the layered sulfides are in the range from +8.3 to +12.8‰. The high positive values indicate that the sulfur was derived from the sediments by thermochemical reduction of Archean/Paleoproterozoic marine seawater; Boquira is a rare sediment-hosted galena-sphalerite deposit of this age. The study emphasizes the need to prospect marine sedimentary areas of Archean age for possible economic deposits of Pb and Zn.

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.

In this review we provide a correlation scheme for Neoproterozoic palaeoclimatic events in southwestern Gondwana based on combined carbon and strontium isotope variations informed by emerging radiometric constraints on glacial deposits. Strontium isotope ratios in particular hold promise as chronostratigraphic tools if well-preserved samples can be identified, and if long-term trends through the Neoproterozoic show a regular progression to more radiogenic values. Based on analyses of high Sr limestone samples from cap carbonate lithofacies, we recognise four discrete glacial events in southwestern Gondwana, including two Sturtian, one Marinoan and one Gaskiers ice age. Notably, the Namibian Maieberg cap carbonate – considered by many to be a Marinoan archetype – sits stratigraphically below a profound positive carbon isotope excursion (called the Huttenberg anomaly) and is correlated using Sr isotope ratios with an identical post-glacial cap in Brazil dated at ca. 740 Ma by Pb-Pb carbonate techniques. If correct, the Pb-Pb age constraint places the Ghaub ice age and its equivalents into the Sturtian epoch.

Carbonate strata of the Una Group represent late Proterozoic platform sedimentation in the Irece Basin of east-central Brazil. The Irece Basin contains a basal siliciclastic sequence (the Bebedouro Formation) composed of diamictites dominantly of glacial origin that is overlain by lacustrine carbonate sediments. These are succeeded by the Una Group, a marine carbonate sequence that totals several hundred meters thick. The marine units consist of a basal laminated limestone and dolomitic limestone sequence that grades upward into dolostone and cherty dolostone; a middle sequence dominated by gray argillaceous limestones, shales, and siltstones; and an upper sequence of black organic-rich lime grainstones. Stratabound phosphate- and sulfide-rich units are present within a 50-m-thick tid l flat sequence of dolomitic limestone and cherty dolostone in the lower Una Group. Shallow-water sedimentary structures include stromatolitic laminae, columnar stromatolites, mudcracks, teepee structures, collapse breccias, length-slow quartz nodules, and other pseudomorphs after evaporitic sulfates. Conventional petrography supported by cathodoluminescence and scanning electron microscopy of the carbonate strata reveals a complex diagenetic history representing four major diagenetic environments: Marine, Reflux, Meteoric, and Burial. Carbon and oxygen isotope analyses of diagenetic carbonate generations yield distinct populations that support the environmental interpretations. Concentrations of fine-grained carbonate fluorapatite are present in stromatolitic carbonate units in the Irece-Lapao area. Three types of primary phosphate concentrations have been defined: columnar stromatolitic, laminar stromatolitic, and intraclastic. The presence of resedimented phosphatic clasts and of phosphatic units interbedded with barren dolostones suggest that the formation of stromatolitic phosphorite was an early-diagenetic process. Carbon and oxygen isotope data for calcite, dolomite, and carbonate fluorapatite, as well as sulfur isotope data from sulfates and sulfides, suggest the presence of an anoxic environment during the formation of the Irece phosphorites. Postglacial enrichment of the basin waters in phosphate is considered to be a critical aspect of phosphatizat on. Bacterial degradation of organic matter in the stromatolites probably was responsible for local phosphate enrichment of pore waters and resulted in concentration of carbonate fluorapatite by direct precipitation or by replacement of calcium carbonate.

Os chapéus de ferro associados ao depósito de Canoas mineralizado em Zn-Pb, em Adrianópolis (PR) e ao depósito de O\'Toole mineralizado em Ni-Cu, em Fortaleza de Minas (MG), contém concentrações anômalas desses metais base. O intemperismo químico do minério sulfetado produziu uma série de feições mineralógicas e geoquímicas características que são diagnóstico para a prospecção mineral e identificação do tipo de depósito mineral. Análises por espectrometria de raios X para elementos maiores e traços, difratometria de raios X, espectroscopia Mössbauer, análises microssituadas, foram utilizadas para este estudo. No depósito de Canoas existem três ocorrências de chapéus de ferro, Canoas 1, Salvador 1 e Salvador 2, os quais apresentam diferenças nos teores de metais base dosados que pode estar relacionado ao tipo de minério e maturidade do chapéu de ferro. O chapéu de ferro de Canoas 1 ocorre sobre o minério primário e assemelha-se a uma zona de sulfato-carbonato. Os chapéus de ferro de Salvador 1 e Salvador 2 apresentam feições e mineralogia características de chapéus de ferro maduros. A associação jarosita-goethita e em menor proporção hematita é a principal feição mineralógica dos chapéus de ferro de Canoas. As jarositas são uma fase transitória e armadilhas para o Pb. No depósito de O\'Toole o intemperismo e alteração supérgena dos sulfetos primários de Ni-Cu evoluíram para uma zona de pentlandita-violarita ou zona de cimentação ou transição. O chapéu de ferro ocorre sobre a zona de transição e tem feições, texturas e mineralogia típicas de um chapéu de ferro maduro e evoluído. Durante os processos de lixiviação dos sulfetos, metais tais como Pb, Zn, Cu, Ni e Co são dissolvidos e podem ser co-precipitados com compostos de Fe ou serem adsorvidos em duas superfícies. No primeiro caso eles são incorporados na estrutura dos minerais de Fe por substituição isomórfica, causando distorções nas dimensões da cela (continua) (dependendo) unitária, dependendo das diferenças entre os raios iônicos. No chapéu de ferro de Canoas a incorporação de Pb e Zn na estrutura da goethita não ficou claramente demonstrada. Para as amostras de chapéu de ferro de O\'Toole as análises sugerem que o Cu e Ni foram incorporados estruturalmente na goethita. Gossans associated with the Canoas zinc-lead ore deposits, in Adranópolis (PR), and O\'Toole nickel-copper ore deposit, in Fortaleza de Minas (MG), contain anomalous concentrations of these base metal. The chemical weathering of sulfide lodes has produced a series of characteristic mineralogical and geochemical features that are diagnostic for mineral prospection and identification of ore body type. X-ray spectrumetrie analysis of major and trace elements, difractrometry of the X-ray, Mössbauer spectroscopy, microprobe analysis, were used in this study. In the Canoas deposit there are three gossan occurrences, Canoas 1, Salvador 1 and Salvador 2, which have differences in accumulation that may be related to the ore type and gossan maturity. The Canoas 1 gossan is over the primary ore and appears to be a sulphate-carbonate zone. The Salvador 1 and Salvador 2 gossans presented features and mineralogy that are characteristics of the mature gossans. The jarosite-goethite association and to a lesser extent hematite is the principal mineralogical feature of the Canoas gossans. The jarosites are the transitory Pb-bearing phases. In the O\'Toole deposit the weathering and supergene alteration of primary nickel-cooper sulphides evolved to the pentiandite-violarite zone or cementation zone. The gossans is over the cementation zone and has features, textures and mineralogy typical of mature evolved gossans. During the sulphide leaching processes, metals such as Pb, Zn, Cu, Ni and Co are dissolved and can either co-precipitate with Fe compounds or be adsorbed onto their surfaces. In the first case they are incorporated into the Fe-mineral structurs by isomorphous substitution, causing distortions in the unit-cell dimensions, depending on the ionic radii differences. In the Canoas gossan incorporation of the Pb and Zn into the goethite structure are not clearly demonstrated. For the O\'Toole gossan samples the analysis suggests that Cu and Ni structurally incorporated in the goethite lattice.

A região de Vazante-Paracatu representa o maior distrito zincífero conhecido no país, e inclue vários depósitos importantes, tais como, Vazante, Morro Agudo, Ambrósia e Fagundes, entre outros. Fagundes é um depósito \"stratabound\", caracterizado por forte silicificação, que antecede a mineralização, dolomitização, texturas de preenchimento de espaços abertos e texturas zonadas, refletindo oscilações no conteúdo de elementos traço na esfalerita. A esfalerita dos estágios diagenéticos a tardi-diagenéticos de mineralização apresenta baixo conteúdo de ferro (0.20 to 0.80%), relativamente baixa razão Zn/Cd ratios (89 - 305) e altos conteúdos de Ge (até 2200 ppm), que podem indicar afinidade com salmouras oxidadas. Veios e brechas tardias refletem estágios intermediários de mobilização, possivelmente relacionados com deformação dúctil-rúptil. A mineralização de Ambrósia é epigenética e, predominantemente, controlada por falha, sendo hospedada por dolomitos brechados, tectonicamente imbricados a filitos e ardósias. As feições típicas de alteração dos dolomitos hospedeiros da mineralização incluem recristalização, silicificação localizada, e substituição por dolomita baroque e dolomita ferrosa. Pirita, marcassita e esfalerita com galena subordinada ocorrem em veios, usualmente brechados. A esfalerita de Ambrósia apresenta os conteúdos mais altos de Fe (0.21 to 2.54%), as menores concentrações de elementos menores e traços, e as razões Zn/Cd mais elevadas (1510) em relação à esfalerita de Vazante e Fagundes, sugerindo processos de substituição hidrotermal relacionados com a interação de fluidos tardios. O depósito de Vazante difere dos demais depósitos da Faixa Vazante-Paracatu, principalmente devido à mineralogia do minério willemítico. As relações entre a formação da willemita e o desenvolvimento de microestruturas, sugere que a mineralização willemítica e o desenvolvimento da Zona de Falha de Vazante são episódios coevos. Os estágios diagenéticos a tardi-diagenéticos de mineralização característicos de Morro Agudo e Fagundes, associam-se ao escape, principalmente ao longo de falhas, de fluidos quentes (> 250°C), moderadamente salinos e oxidados, com baixa razão Zn/Cd, que adquiriram metais, e tornaram-se radiogênicos durante a migração por seqüências clásticas nas partes mais profundas do sistema hidrotermal. A deposição do minério é resultante da mistura desses fluidos metalíferos, com baixo conteúdo de enxofre reduzido, com fluidos de temperatura moderada (140 a 190°C), salinidade elevada (15 a > 23% peso equiv. NaCl), relativamente reduzidos, com composição próxima à do sistema H2O-\'NaCl IND.2-\'CaCl IND.2\'. Esses fluidos são semelhantes a salmouras bacinais e representam fontes potenciais de \'H IND.2\'S. O processo de mistura é progressivo e resulta em tendências covariantes entre os valores de \'delta\'\'POT.34\'S dos sulfetos e do conteúdo de elementos menores e traços na esfalerita, refletindo a predominância de uma fonte de enxofre isotopicamente mais leve e aumento do conteúdo de Fe e das razões Zn/Cd nos estágios finais de evolução do sistema mineralizante, relacionados a estilos epigenéticos de mineralização. Estes estágios tardios vinculam-se a pulsos tardios de fluidos expulsos da bacia, devido aos esforços compressivos finais associados ao desenvolvimento da faixa de dobramentos. No depósito de Vazante, a assinatura dos isótopos de enxofre e conteúdo de elementos menores e traços na esfalerita indicam grande homogeneidade que não pode ser explicada por processos de mistura de fluidos. Assim, a evolução fluidal em Vazante é controlada predominantemente por interação fluido-rocha, envolvendo os fluidos metalíferos oxidados, de mais alta temperatura (< 250°C) e baixo conteúdo de enxofre reduzido. A mistura entre esses fluidos metalíferos quentes e fluidos meteóricos canalizados na zona de cisalhamento, possibilitou o estabelecimento de condições de alta f\'\'O IND.2\'/f\'\'S IND.2\', responsáveis pela mineralização willemítica de Vazante. The Vazante-Paracatu region represents the biggest zinc district known in Brazil, which includes various important zinc deposits such as Vazante, Morro Agudo, Ambrósia and Fagundes, among others. The deposits are hosted by metapelitic-dolomitic sequences of the Vazante Group and have contrasting geological characteristics. Fagundes is a stratabound ore type deposit, characterized by strong hydrothermal alteration, such as silicification and dolomitization, open-space filling textures and depositional growth zoning in sphalerite due to oscillatory variations in minor element concentrations. The primary sphalerite displays low Fe content (0.20 to 0.80%), relatively low Zn/Cd ratios (89 - 305) and high Ge content (up to 2200 ppm), which could indicate affinity with oxidized brines derived from a carbonate-evaporite-shale dominated basin. Later veins and breccia ore types reflect several intermediate stages of mobilization, possibly related to ductile-brittle and brittle deformation, which are responsible for obliteration of primary crystallization features accompanied by sphalerite compositional modifications. Ambrósia mineralization is mainly fault-controlled and related to brecciated dolomite, which is tectonically imbricated with black shales and slates. Observed typical features are host rock recrystallization, minor silicification, baroque dolomite and Fe-dolomite crystallization. Pyrite, marcasite, sphalerite and minor galena occur in brecciated comb-veins, and veinlets infillings. The Ambrósia sphalerite displays the highest Fe (0.21 to 2.54%) and lowest trace-metal content relative to Fagundes and Vazante, which reflect different mineralizing fluid evolutionay stages. The Ambrósia Zn/Cd average ratio (1510) in sphalerite suggests that the hydrothermal substitution processes took place due to the interaction of preexistente mineralization with a later fluid Phase. The Vazante deposit differs from all the other deposits of the district, and it appears to be due to the observed willemitic ore. The relationships between willemite formation and the development of microstructures, suggest that willemitic mineralization and deformation are synchronous episodes closely related to the Vazante shear zone. Fluid inclusions studies, about the three deposits, indicate a wide range of variability of temperatures between 280 and 180°C for pre-ore and ore-stages and 190 to 140°C for mobilization or post-mineralization. The sulfide ore deposition is related to fluid mixing between a hot, oxidized metalliferous fluid (> 250°C), which has moderate salinity, low reduced sulfur content and low Zn/Cd ratio, and a H2O-\'NaCl IND. 2\'-\'CaCl IND. 2\' brine with moderate temperature (140 a 190°C), high salinity (15 a > 23% weight equiv. NaCl) and high sulfur content. Covariant trends of \'delta\'\'POT.34\'S and trace element content in sphalerite, indicate progressive mixing process during the fluid evolution and predominance of the low-temperature brine during the epigenetic stages of mineralization. The homogeneity of \'delta\'\'POT.34\'S values and of trace element-content in sphalerite from Vazante, indicates that mixing process are not important for the Vazante sulfide deposition. The fluid-rock interaction, involving the high-temperature metalliferous fluid, represents the more important mechanism for sulfide ore deposition. ln this way, the willemitic mineralization is related to mixing of meteoric and metalliferous fluid with low reduced sulfur content, channeled into the shear zone. This scenario which might favor the f\'\'O IND.2\'/f\'\'S IND.2\' conditions required for the experimentally predicted willemitic assemblage stability.

O estudo teve como objetivo a análise estratigráfica do Grupo Corumbá. Esta unidade aflora na região central da América do Sul com exposições no Planalto da Bodoquena e nos arredores do Maciço de Urucum, constituindo parte da Faixa de Dobramentos Paraguai e da cobertura cratônica. A Faixa de Dobramentos Paraguai, relacionada ao evento orogenético Pan-Africano - Brasiliano, ocorre a sudeste do Cráton Amazônico e a leste do Bloco Rio Apa, onde compreende metassedimentos neoproterozóicos, de baixo grau metamórfico, que se estendem sobre o cráton. São características desta unidade geotectônica a deformação polifásica, com dobras isoclinais e falhas de empurrão de vergência para oeste e noroeste, e o escasso registro vulcânico básico. Apresenta extensão de 1500 Km, com exposições em Goiás (sudoeste), Mato Grosso e Mato Grosso do Sul, formando o conjunto um grande arco com a convexidade voltada para o cráton. Apesar das diversas e controvertidas subdivisões estratigráficas propostas para as unidades aflorantes, é possível distiguir três conjuntos. O inferior é representado pelo Grupo Cuiabá, caracterizado por metassedimentos predominantemente pelíticos de caráter turbidítico. O conjunto médico é marcado por sucessões carbonatas (Grupo Corumbá e Formação Araras) recobrindo sedimentos glácio-marinhos (Formação Puga). O superior é representado por arenitos e folhelhos continentais (Grupo Alto Paraguai). As unidades carbonáticas pertencem ao Grupo Corumbá, na porção meridional da faixa, e à Formação Araras ao norte, originadas em contextos ambientais e estratigráficos distintos. O Grupo Corumbá é representado por sucessão de aproximadamente 700m de espessura. Apresenta, na base, conglomerados, arenitos e pelitos (formações Cadiueus e Cerradinho) passando a dolomitos (Formação Bocaina) e calcário e pelitos carbonosos (Formação Tamango), recoberto por espesso pacote pelítico (Formação Guaicurus). Na Formação Tamengo, são encontrados os fósseis metazoários Cloudina e Corumbella, enquanto que na Formação Bocaina há abundante registro estromatolítico associado a ocorrências de rochas fosfáticas. O Grupo Corumbá, como um todo, possui registro estratigráfico típico das demais sucessões neoproterozóicas pós-glaciação Varanger, relacionado a rifting de supercontinente neoproterozóico, provavelmente o Pannotia. A investigação de isótopos de C e O permitiu identificar, na Formação Tamengo, a variação de \'\'delta\' POT.13\'\'C IND.PDB\' de valores negativos (\'-3GRAUS\'\'/ IND. 00\') para positivos (\'+5GRAUS\'\'/ IND. 00\'), interpretada como incursão positiva ediacariana, também encontrada em demais sucessões carbonáticos pós-glaciação Varanger. O Estudo de fácies sedimentares possibilitou definir duas sequências estratégicas relacinadas à evolução de bacia rift-to-drift, aqui definida como Bacia Corumbá. A primeira sequência (estágio rift), essencialmente terrígena, é constituída pelas formações Cadiueus e Carradinho. A segunda (estágio drift) abrange as formações Bocaina, Tamengo e Guaicurus. Separando as duas sequência (estágio rift), essencialmente terrígena, é constituída pelas formações Cadiueus e Cerradinho. A segunda ( estágio drift) abrange as formações Boicaina, Tamengo e Guaicurus. Separando as duas sequência, foi indentificada marcante superfície erosiva, denominada Superfície de Aplainamento Pedra Branca. A Formação Araras, exposta na porção norte e nordeste e Faixa Paraguai, na Serra das Araras e no Sinclinal da Guia, apresenta distribuição faciológica relativamente mais homogêniea do que a encontrada no Grupo Corumbá. A metade inferior da Formação Araras é formada por calcários calcíticos e ritmitos ( calcário/folhelho carbonoso) e a superior por dolomitos com estromatólitos. A deposição destes carbonatos teria ocorrido em provável mar epicontinental, com passagem gradativa para sedimentação continental das formações Raizama, Sepotuba e Diamantino. Fechando a evolução geológica da Faixa Paraguai, ocorreram deformações tectônicas brasilianas, mais intensas nas porções orientais da faixa, seguidas de magmatismo granítico pós-tectônico, com idade a redor de 500 Ma. This thesis reports the results of the stratigraphic analysis of the Neoproterozoic Corumbá Group, that crops out in the Bodoquena Plateau and adjacent to the Maciço do Urucum, in Mato Grosso do Sul, Brazil, central South America, Rocks of the Corumbá Group constitute part of the Paraguay Mobile Belt and partially cover the southeast margin of the Amazon Craton. The Paraguay Mobile Belt (Pan-African-Brasilano orogenetic event) in a 1500-km-long arc convex towards the craton. It is characterized by low-grade metamorphic and sedimentary rocks subjected to polyphase deformation, with isoclinal folds and inverse faults with westward and northwestward vergency. Three principal successions are recognized in this region, the lowest represented by the Cuiabá Group, which is made up of pelitic sediments of turbiditic character. The intermediate succession is marked by the carbonates of the Corumbá Group and Araras Formation. The uppermost succession comprises the continental sandstones and shales of the Paraguia Group. The carbonate units were deposited in two distintic sedimentary environments and stratigraphic contexts. The Corumbá Group occurs in the southern portion of the Paraguay Mobile Belt and the Araras Formation in the north. The Corumbá Group reaches 700m in thickness and presents from the bottom to top: conglomerates, sandstones and pelitic sediments (Cadiueus and Cerradinho formations); dolostones (Bocaina Formation), limestones and carbonaceous shales ( Tamengo Formation); and shales ( Guaicurus Formation). Through the study of sedimentary facies, it was possible to recognize two stratigraphic sequences related to the evolution of a rift-to-drift basin, here defined as the Corumbá Basin. The lower terrigenous sequence (rift stage) is composed of the Cadiueus and Cerradinho formations. The upper sequence (drift stage) includes the Bocaina, Tamengo and Guaicurus formations. These sequences are separated by na outstanding erosional surface here called Padra Branca Unconformity. Among the fossils in the Corumbá Group are the metazoan fossils Cloudina and Corumbella in the Tamengo Formation and stromatolites, which may be associated with phosphatic rocks, in the Bocaina Formation. The investigation of stable isotopes (C, O) revealed a variation of \'\'delta\' POT.13\'\'C IND.PDB\' from negative (\'-3GRAUS\'\'/ IND. 00\') to positive values(\'+5GRAUS\'\'/ IND. 00\') , interpreted here as the Ediacaran Positive Excursion which is found in all other post-Varanger carbonatic successions. The Araras Formation ( in the northern part of the Paraguay Mobile Belt) presents a more homogeneous facies distribution than the Corumbá Group. The lower part of this formation is composed of calcitic limestones and rhythmites (limestones/carbonaceous shale) and the upper presents stromatolitc dolostones. These carbonates were deposited under epeiric marine conditions that geve way upwards to terrigenous sedimentation of the Raizama, Sepotuba and Diamentino formations. The final stages in the geological evolution of the Paraguay Mobile belt was marked by intense Brasiliano tectonic deformation in this eastern portion followed by pos-tectonic granitic magmatism at about 500 Ma.