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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 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.

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 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.

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.

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.