To divulgate geoscientific research by means of the publication of carefully analysed, original papers concerning academic and applied themes in the various Geology areas.
Universidade de São Paulo. Instituto de Geociências
Minerais e equivalentes sintéticos do sistema Fe2-O3-SO3-H2O
The study of the Fe2-O3-SO3-H2O system needs revision because the papers concerning the subject stress either chemical or mineralogical aspects. The Fe(III)-sulfates occurring as minerais may be grouped in the following manner: a) Hydrogen-sulfates: Fe:S = 1:2 : rhomboclase*, "leucoglaucite". b) Sulfates ("normal"): Fe:S = 2:3 : quenstedtite, coquimbite*, paracoquimbite, kornelite*, lausenite*. c) Hydroxy- and oxy-sulfates: Fe:S = 7:9 : ferricopiapite*. Fe:S = 1:1 : fibroferrite, hohmannite, amarantite, butlerite*, parabutlerite, metahohmannite Fe:S = 3:2 : hydronium jarosite*. Fe:S = 4:1 : "glockerite". Fe:S = 8:1 a 16:3 : unnamed*. The minerais marked by an asterisk have been synthesized, and the products (H3O)Fe4(SO4)2, Fe2(SO4)3, Fe(OH)(SO4) and Fe4(OH)10(SO4) are known only as synthetic compounds. Minerais within quotation marks have been inadequately described. It is concluded that seven well characterized and two incompletely described minerais have not yet been synthesized. On the other hand, four compounds are known only as syntheüc products.
Regression with variables subject to imprecision: an approach using the Monte Carlo method
A Monte Carlo approach is presented for the problem of least squares fitting of points with correlated errors. The method consists of the definition of an uncertainity space based on absolute error and random sampling for each data point. This procedure is repeated a large number of times (typically 1000 times) and a regression is obtained for each set of data. The results are stored and described statistically at the end of the process. Comparisons were made with results obtained by conventional methods applied to Rb/Sr isochrons, without any significant discrepancies. The main advantage of the method now proposed is its simplicity and the possibility of graphical representation of variability
Preliminary petrographic and geochemical considerations on the precambrian mafic dykes of the Ilhéus-Olivença area, Bahia
Problemas de terminologia morfológica e anatômica em língua portuguesa e de nomenclatura binomial de fitofósseis e vegetais atuais: relatório de debate
In Memoriam: Elias Dolianiti (1911-1985)
Stratigraphy and age of fini-proterozoic basins of Parana and Santa Catarina States, southern Brazil
The Itajaí, Corupá, Campo Alegre, Guaratubinha, Camarinha and Castro basins are the most important register in the northern half of southeastern Brazil of geological events wich occurrec at the end of the Neoproterozoic and beginning of the Cambrian. The Itajaí and Camarinha basins are thought to be foreland basins while the rest are late-collision extensional basins. The volcanisir in these basins is related in time and genetically to the alkaline-peralkaline magmatism of the Serra dc Mar Suite. The main phase of basin installation is related to extensional events which separate twc compressive phases at the end of the Proterozoic (~ 650-600 Ma) and the beginning of the Cambrian (550-530Ma).
Hydric potentiality study of the sedimentary aquifer of the Azángaro formation in the Ilave Puno area
This works presents the assessment of groundwater resources of the Azángaro Formation dominantly composed of lacustrine deposits, located in the Peruvian territory, Department of Puno. The area of interest is part of the Titicaca Lake Basin, which is about 3840 m a.s.l., and covers 180 km2 .The local morphology of the area is characterized by a soft waved plain surface contrasting with a set of elongated hills or isolated slopes. This geomorphological pattern was developed over volcanic and sedimentary formations from Cretaceous to Tertiary. These rock sequences exhibit great structural complexity and are related to the tectonic evolution of the Peruvian Andean Cordillera. The unconsolidated deposits of the Azángaro Formation, which represem the aquifer system, were hidrogeologically investigated using lithological data from 25 wells and 37 vertical electrical soundings besides hydrodynamic tests. The physical space of the reservoir comprises three distinct facies units recognized within the local stratigraphic column and geological profiles. The middle layer unit, makes the bulk of the aquifer of interest mainly due to its morphology as defined by the vertical electrical soundings. The thickness of the aquifer is variable from 30 to 60 m, composed of sands and graveis. The specific yields are of the order of 10 to 20 m3/h.m
Large scale magmatic banding in mesozoic basic sill of the Paraná basin, Campinas, São Paulo State, Brazil
O método isotópico Re-Os: características e potencialidades
Geochemistry and Petrology of the Cana Brava stratiform complex - GO mafic and ultramafic rocks and their
The Cana Brava body is a 2.0 Ga, anorogenic, stratiform complex whose layers dip from 30º to 50º NW. The massif is made up of five units, composed of layers containing several associations of cumulus phases and variable amounts of inter-cumulus minerais. Transitions between units are characterized by changes in the composition and/or in the relative abundance of these phases. Stratigraphically, the lowest sequence is composed of amphibolites (PICB1), overlain by serpentinites (PICB2), metawebsterites (PICB3) and metagabbroic rocks (PICB4 and PICB5) at the top. This sequence was originally formed by microgabbros, peridotites, websterites and gabbroic rocks. The rock sequence of the complex can be attributed to a single magmatic fractionation. There is no evidence of multiple injections. Metamorphic events affected the different units heterogeneously. The gabbroic rocks (PICB4 and PICB5) were the least transformed; hence their chemical compositions are close to the original ones. Units PICB1 to PICB3 were the most affected by post-magmatic processes. Geochemical evidences suggest that PICB1 may be the chilled border of the massif. However, due to post-magmatic phenomena, the composition of the parent magma was calculated using the chemical compositions and inferred volumes of units PICB2 to PICB5. For PICB2 and PICB3 the compositions of mineral phases were utilized. The possible Cana Brava parent magma is olivine-tholeiite, similar to the majority of the complexes utilized for comparison. Its amount of normative olivine is within the range for liquids derived from 25 to 35% of mantle melting. Phase equilibria condictions point to pressures under 6-7 Kbar during crystallization. The possible parental magma of the Cana Brava complex is compared with the alcali-olivine basaltic magma of the Palmeirópolis metavolcano-sedimentary sequence, and with the possible parental magma of the Serra da Bota satellite body.
Stratigraphic analysis of the Camaquã group facies, provenance and paleocurrents (Proterozoic-Fanerozoic tectonic-sedimentary evolution of the Camaquã Basin, RS
The open pit of the Uruguai Mine, in the Minas do Camaquã region, presents the best exposures of the Camaquã Group. Stratigraphic analysis of facies, paleocurrents and provenance show that the Camaquã Group deposits are organized in two lithostratigraphic units: Rhythmites and Sandstones at the base of the exposure and Conglomerates and Sandstones at the top. The top unit was divided by the CBC (Companhia Brasileira do Cobre) team into three sub-units: Lower Conglomerate, Intermediate Sandstone and Upper Conglomerate. The Rhythmites and Sandstones unit is represented by marine turbidites and sandstones of shallow water and transitional environments. The Lower Conglomerate unit is composed mainly by pebbly conglomerates and sandstones formed in subaqueous fans. Provenance and paleocurrents analysis of these two units indicate source áreas composed of volcanic acid rocks, granites and metamorphic rocks located S and SW. The Upper Conglomerate is composed by cobble and boulder conglomerates of alluvial fan environment, derived from mylonites and granites located SE and reworked sedimentary rocks of the lower units of the Camaquâ Group.
Alkaline dikes and plugs of the Vale do Ribeira region, limit of Paraná and São Paulo States: mineral chemistry
Rocks of phonolitic composition l.s. are found in the Ribeira Valley area mainly as dikes and plugs associated with alkaline complexes or also as small dikes intruding into granitic rocks of the Três Córregos massif. These rocks have been described in Banhadão, Itapirapuã and Mato Preto complexes, in Barra do Teixeira, Barra do Ponta Grossa and Sete Quedas plugs and also as dikes in a few places such as Morro do Chapéu, Cerro Azul and along the road Sete Quedas-Dr. Ulisses (SQ-Dr. U). Petrographically, they are classified as peralkaline phonolites (the most common type), phonolites, trachyphonolites and phonolitic nephelinites. Main minerais include alkali feldspar (in general rich in K 20 and less commonly in Na20); clinopyroxenes, varyingin composition from calcic (diopside, hedembergite and augite) to sodic-calcic (aegirine-augite) and up to sodic (aegirine) types; and nepheline. In minor amount are found biotite (titanium-biotite or titaniferous biotite); titanian garnet (in phonolitic nephelinites and also in Banhadão peralkaline phonolites); amphiboles and opaques (Mato Preto phonolites). On the basis of mineral chemistry, the investigated rocks can be placed into two groups showing different degrees of evolution. More primitive rock-types are represented by phonolitic nephelinites and phonolites while more evolved ones correspond to trachyphonolites and mostly to peralkaline phonolites.
Sequences and stratigraphtc hierarchy of the Paraná basin (Ordovician to Cretaceous), southern Brazil
The Paraná Basin, a vast sedimentation area during Paleozoic and Mesozoic times, holds a stratigraphic record ranging in age from late Ordovician to late Cretaceous and comprising six supersequences or unconformity-bounded units (Milani, 1997): Rio Ivai (Ordovician-Silurian), Paraná (Devonian), Gondwana I (Carboniferous-early Triassic), Gondwana II (middle-lateTriassic), Gondwana III (late Jurassic-early Cretaceous), and Bauru (late Cretaceous). Three of them coincide with major Paleozoic transgressive-regressive cycles, and the others are Mesozoic continental sedimentary packages with associated igneous rocks. These supersequences are the remnant record of successive phases of sediment accumulation alternating with times of erosion. The evolution of each supersequence was constrained by a p art icular tectonic and climatic setting. The Rio Ivaí supersequence is closely associated with basin inception and its geometry suggests that deposition was to some extent controlled by normal faulting. The Paraná supersequence deposited during a time of widespread marine flooding over the cratonic area of southwestern Gondwana. From the deposition of the Gondwana I supersequence onward true intracratonic conditions were established. Sharing Gondwana's dessication trend the Paraná Basin sedimentation history culminated with extensive desertic conditions during the Jurassic. The Lower Cretaceous Serra Geral continental flood basalts are related to the initial moments of South Atlantic rifting, and the upper Cretaceous Bauru continental cover ended the history of the basin. The hydrocarbon potential of the Paraná Basin is related to two well defined source beds: the Devonian shales (Ponta Grossa Formation) and the upper Permian bituminous shales and limestones (Irati Formation). Sandy reservoirs can be found in the lower Devonian Furnas Formation, in the upper Carboniferous/lower Permian Itararé Group and in the lower Permian Rio Bonito Formation. The role of intrusive bodies in the maturation of source rocks and in the trapping of hydrocarbons seems to be crucial and deserves more investigation.
The Cambro-Ordovician of the Borborema Province
This paper describes some volcano-sedimentary deposits that characterize the time interval from Neoproterozoic IE to the early Ordovician, typical of the Borborema Province, Northeast Brazil. They are usually designated molassic deposits and comprise coarse-grained immature rocks with common lateral gradation to pelitic lithologies of continental environments. The volcanism varies, but is mostly acid to intermediate. Two major types of basins may be identified: The first type is connected with the formation and evolution of pull apart depressions along the major shear zones (or lineaments) as part of the escape-tectonics phase of the Borborema Province (LL type basin). The second type is formed by foreland (foredeeps) and intradeeps (distal rifts) related to the late and post-tectonic evolutionary processes of the Sergipano Belt, a "miogeoclinal" orogen positioned at the northeast border of the São Francisco Craton. In both cases, the preservation of these deposits - usually scarce and scattered throughout the province - was only possible due to the immediate protection by younger Paleozoic covers (Silurian and younger) of syneclises and Mesozoic rifts (generated above these syneclises). Presently, the thickest and largest occurrences of these deposits do not crop out as they are beneath the Paleozoic basins according to geophysical and other subsurface data. Some of these Eo-Paleozoic rifts have been pointed out as precursor rifts for the development of the Parnaiba Syneclise.
Periodic noise suppression techniques applied to remote sensing images
The image data collected by the JERS-1 OPS, SPOT and AVHRR systems are affected by a variety of periodic (coherent) noise problems, which can be severe in many cases. This paper examines some of these defects and also describes and evaluates a series of methodologies to recover partially or totally the information contained in these data by means of: (i) filtering in the spatial domain (convolution filters), (ii) Principal Components Analysis (PCA) and (iii) filtering in the frequency domain (using Fast Fourier Transforms). Filtering in the spatial domain using relatively small convolution filters can be successfully applied to tackle elementary periodic noise problems. However, variations of theoretically efficient kernels experimented in this study were only able to minimise the effect of such complex noise structures at the expense of significant modification or complete loss of important raw image data. Principal Component Analysis transforms the data so that the noise component is cast into one or more of the high-order principal components. Our experiments show that this technique is able to confine the noise in the higher order PCs, but a significant amount of residual noise was present in the low-order components. Filtering in the frequency domain proved to be a suitable technique to achieve image restoration whilst preserving most of the raw scene information intact. Conventional Fourier operators like the Notch Filter and the Low-pass Elliptically Symmetric Filter (with a Gaussian-shaped intensity profile) can tackle the problems with some noisy images quite reasonably. However, such filters are unable to recover images on which the amplitude of the noise varies heterogeneously producing a series of impulses from low to high frequencies. Both the Zonal Notch Filter (based on the difference of the Fourier spectra of two channels) and the Synergistic Filter (which relies on the convolution theorem) are designed to contour this problem. These are interactive restoration methods that can successfully eliminate or minimise the effects of multiple two-dimensional periodic structures superimposed on both multi-channel and single channel data, respectively.
Evaluating geoscan AMSS MK-II for gold exploration in the Fazenda Maria Preta District, Rio Itapicuru greenstone belt, Bahia State, Brazil
The Rio Itapicuru Greenstone Belt (RIGB), located in north-eastern Brazil, is an important gold producing region. It hosts two important mining districts, the Fazenda Brasileiro and the Fazenda Maria Preta, owned by Companhia Vale do Rio Doce (CVRD), plus a number of gold occurrences, all associated with hydrothermal alteration along shear zones. In 1992, Geoscan multispectral scanner data were acquired for mineral exploration purposes over more than 7,500 km² in this greenstone belt. Geoscan AMSS is a 24-band airborne scanner, with 5 meter spatial resolution. Standard image processing techniques, applied immediately after data acquisition, defined some spectral anomalies, particularly due to silicification and oxidation, which could be due either to hydrothermal alteration or to weathering processes. We have reprocessed the Geoscan data over a portion of the RIGB in order to define possible anomalies due to hydrothermal alteration minerals, using the feature-oriented principal component selection (FPCS) technique, modified for use with Geoscan data. Laboratory reflectance spectra of residual soils were acquired to establish superficial expression of hydrothermal minerals that occur in sub-surface and to guide image processing and interpretation. This led to the production of "mineral component" images, in which the spatial distribution of some minerals are shown. Results of the spectral analysis of soil samples showed that goethite may be used as a surface indicator of hydrothermal alteration and that it is not possible to differentiate the alteration zones from surrounding rocks based on the hydroxyl or carbonate spectral features.
Reflectance spectrometry of rocks from the comstock lode (Virginia City, Nevada, USA) and its comparison with X-ray diffraction
This paper presents the results of mineralogical analysis of hydrothermal altered rocks from the Comstock Lode, near Virginia City, Nevada, USA, using two different techniques: reflectance spectrometry and X-ray diffraction. These results are discussed based on their quickness, accuracy and low costs. The applicability to mineral mapping using high spectral resolution remote sensing images is also briefly discussed. Comparison of the results obtained for both techniques have a good degree of correlation, showing that reflectance spectrometry represents an expedite, simple and relatively inexpensive technique, capable of mapping numerous minerals in the field or in laboratory.
Remote sensing strategies for lithological mapping of pan African assemblages in arid environments: a case study in Eritrea, NE Africa
Over a 30 year period, when major advances were made in understanding the evolution of the Arabian-Nubian Shield, military conflicts prevented the geological mapping and tectonic interpretation of Eritrea, NE Africa. The indication of small occurrences of ultramafic rocks through ancient work in the NW extremity of the country prompted many workers on regional tectonics to propose the line of the Barka river as a Neoproterozoic (Pan African) suture. Several attempts based on remote sensing data have been considered to resolve about the existence of such structure in this region. These previous approaches, based on Landsat TM band ratios, fail comprehensively in Eritrea both to unequivocally map ultramafic occurrences and to serve as a good basis for lithological mapping, producing inconclusive and divergent overall results. In this paper we attempt to verify and amplify the hypothesis of a suture zone in N W Eritrea, employing a novel remote sensing strategy and detailed field work. Using statistically-selected Landsat TM enhanced false colour composites together with renditions from residual information of favored Principal Components (pseudo-ratios), we demonstrate that many important components of the Pan African Terranes of Eritrea - i.e. ophiolitic assemblages - can be mapped with a high degree of confidence. This remote sensing strategy transcends the problems encountered in previous approaches in Eritrea and can potentially serve as a powerful tool for geological mapping of similar arid terrains elsewhere.
Digital image processing and enhancement of gravity data as an aid to the definition of the structural framework of the north Tucano-Jatobá basins, Northeastern Brazil
Digitally processed and enhanced gravity data in raster format were used to improve the definition of the main structural features in the northern part of the Reconcavo-Tucano-Jatoba Rift. Image processing techniques included: (a) conversion of Bouguer and residual-Bouguer gridded data into contrast-enhanced gray-level images; (b) generation of enhanced hybrid pseudo-color composites; and (c) generation of a gravity digital elevation model in perspective views. The integrated analysis of this dataset permitted the recognition of subtle trends and intensity-related spatial variations in gravity data, tentatively related to the following tectonic units of the RTJ Rift: ramp platforms, structural lows and highs, along-length horsts, grabens, faulted borders and extensional faults.
Integration of gis technology, remote sensing and multivariate analysis in the delimitation of physiographic units for pedological mapping
This study was based on an association of techniques and equipment that could lead to the delimitation of physiographic units not merely restricted to the photointerpreter's criteria. A data matrix was evaluated which was obtained from the crossing, by means of Geographic Information System (GIS), of a regular grid with cells 300 x 300 meters and a drainage base map of the study area and bands 3, 4, 5 and 7 from TM-LANDSAT and a slope map generated in a GIS. The variables collected in each cell of the regular grid were: long, medium and short channels from the first to the seventh order, weighted slope and the grey levels (DNs) in bands, resulting in a matrix with 1167 individuals with 27 variables, whose data were subjected to cluster analysis. This analysis provided dendrograms which enabled the separation of groups of individuals represented by cells from the regular grid, aiming at creating pictograms to serve as "guides". These guides overlaid upon properly treated and handled orbital HRV-SPOT images oriented the discrimination of physiographic units on the color monitor of the image processing system. Among the variables used, those referring to drainage network were best for cluster analysis of regular grid cells. The variables relief and grey levels of TM-LANDSAT image also presented satisfactory results with the methodology applied.
Digital processing and geological interpretation of TM-LANDSAT images of the area east of the Camaquã mine in Rio Grande do Sul State, Southern Brazil
The Camaquã basin was formed during the closing stages of the accretion of Gondwanaland. The sediments were deposited over mylonites of the Porongos Complex. Two sequences of silici-clastic sediments are present, the lower Santa Bárbara Formation and the upper Guaritas Formation, which is intruded by the Rodeio Velho calc-alkaline rocks. Relief is strongly controlled by lithology and structure, with an overall rectilinear drainage pattern. Vegetation is formed by grasses together with subordinate bushes and trees which are either scattered over the countryside or form small woods and dominates the spectral response. Soil cover is thin and rock outcrops are common, although subordinate. Based on field data, statistical parameters for atmosphere-corrected bands 2, 3, 4, 5 and 7 were set up, and served as a base for the digital processing. Greater lithological contrasts were obtained by Principal Component Analysis (PCA) through comparison of results of statistical analysis of the transformed parameters and of the original bands. A preliminary analysis of the images thus obtained led to the identification of different spectral patterns. The component PCI reflects textural patterns related to the relief and the different albedos. In PC2, the spectral response of trees highlighted the Porongos Complex and the Rodeio Velho andesites, while grasses accentuated areas of fine-grained sandstones of the Santa Bárbara and Guaritas Formations. In PC4, the sandstones and conglomerates of the two sequences, together with quartzite hills of the basement complex, are prominent.
Provável modelo de origem e evolução dos horizontes ferruginosos da Bacia de São Paulo com base na geoquímica de superfície
This paper presents the mineralogical, micromorphological and geochemical evolution and as well as geographic distribution of iron crusts in the São Paulo Basin. Two types of crusts were identified, an older one near the surface and a younger type in the subsurface within underlying sediments. Both derive from the underlying sediments through variations in the water table which propitiated iron hydroxides precipitation at the contact between a porous, permeable sediment above, and impermeable sediments below. The ferricrusts are found in at least three leveis within the sediments of the basin, which are from the bottom to the top: 1) about 20 m below the surface with ochre-colored clay covered by sandy silt; 2) 5 m below the surface with purplish clay overlain by sand and, finally, 3) the surface crust where it characteristic features of ferricrust are evident. Geochemical diagrams show that the uppermost crust is enriched in Fe2O3 and poorer in AI2O3 than the other two layers crusts. Micromorphological analysis shows that the surfícial ferricrust are marked by larger grain size than in the deeper crusts, which show relic textural features of the original sediments. This feature is not found in the surface ferricrust.
Diamantes de capa verde: freqüência, distribuição e possível origem nos depósitos diamantíferos de Minas Gerais
Mottled green diamond crystals and green-coated diamonds are common in diamondiferous sedimentary deposits of Minas Gerais. Diamonds with this characteristic were studied in the most significant áreas of the Espinhaço Province and compared with diamonds of the Coromandel region. The frequency of green-coated diamonds in these deposits varies but is relatively high in the Espinhaço deposits with values of 25% or higher, locally up to 90%. On the other hand, in the Coromandel deposits this value is less than 0,5%. We discuss the two main hypotheses for the origin of the green coatings, i.e., radiation damage in situ, or the presence of chromophorous elements in the externai part of the crystals. Analitycal data reveal both factors contributed to the green color. However, the relative contribution of each to the intensity of green coloration has yet to be determined.
Magmatismo alcalino do Paraguai: uma revisão e atualização das províncias
The tectonic-magmatic event at the border of the Paraná basin in southera Brazil (Mato Grosso do Sul State) and Eastern Paraguay is evidenced by the existence of several foci of alkaline rocks. The recent accumulation of knowledge on this magmatism, active between the Permo-Triassic and Oligocene, makes it crucial that it be reviewed and leads to an updated proposal for assembling the known occurrences mainly on the basis of petrographic, geochemical and geochronological evidence. Despite unsatisfactory information on some occurrences, the available data allow definition of six provinces (Alto Paraguay, Rio Apa, Amambay, Central, Misiones and Asunción), each characterized by remarkable differences in rock composition and time of emplacement into the crust. Although little work has been done in Paraguay on the relation between geographic distribution of the alkaline magmatism and tectonic elements, three main types of association can be suggested: a) cratonic margins or tectonically stable áreas, for example, the Alto Paraguay and Rio Apa Provinces; b) structural ares or tectonic alignment, exemplified by the Amambay Province, and c) continental rift, as is the case for the Central, Misiones and Asunción Provinces.
Trace elements and Pb isotope variations in galena from the onça gold deposit, Mato Grosso, Brazil: fluid mixing from hydrothermal and crustal sources
This study deals with the petrography of sulfídes and quartz veins, Pb isotopes, major and trace elements in galena, microthermometry and Raman spectrometry of fluid inclusions, with the objective of delineating temporal and spatial aspects of the fluid circulation patterns during the origin of the Onça gold deposit, Mato Grosso State, Brazil. The Pb isotope and mineral chemistry data indicate variable sources for the Pb isotopes, major (S and Pb) and trace elements (Sb, Ag, Zn and Se), with increases or decreases of the contents during the growth of the galena crystals. The results suggest that the variation may be due to the contamination of the hydrothermal solution by mixing with components derived from supracrustal host rocks of Pontes e Lacerda metavolcanic-sedimentary sequence. The mineral chemistry and fluids inclusion studies suggest two possible sources for the hydrothermal solutions: (1) deep solutions that originated during the regional metamorphism represented by the Aguapeí metamorphic event where the solutions present aqueous-carbonic composition and Iow salinity. Geologic control of the mineralization is in agreement with this hypothesis because the ore bodies are syntectonic with foliation formed during the Aguapeí event; (2) high contents of base metais indicates a plutonic influence in the origin of the fluids. Geologic controls also are in agreement with this hypothesis because pegmatitic intrusion was synchronous with the mineralizations. The Pb isotope and fluid inclusion relations allows the conclusions that the compositions of the hydrothermal solutes were variable during the emplacement of the quartz veins and the growth of galena crystals. The earlier solutes had hydrocarbons and were more radiogenic, whereas the later solutes had base metais and were less radiogenic. The Onça deposit originated during a metamorphic event by the effect of hydrothermal solutions related to plutonism, and with an important contribution from the host rocks as recorded by the influence of isotope, major and trace element compositions on the growth of ore-forming minerais.