Análise morfotectônica da Bacia do rio Santo anastácio, sp, através de parâmetros fluviomorfométricos e de registros paleossísmicos

Fluvial morphometry is method of great value regarding neotectonic analysis of extensive areas because streams, besides representing one of the main agents in the relief modeling, quickly adjust their thalwegs to even the most gentle crustal deformations. The purpose of this paper is to present the application of some morphometric techniques in the Santo Anastácio River hydrographic basin in order to identify recent tectonic deformations. Additionally, we show liquefaction structures identified in the basin and interpreted here as seismites linked to ancient earthquakes (magnitudes greater than 5). The morphometric survey includes longitudinal stream profile analysis, RDE (declivity versus stream length) index application, and the sinuosity study of the Santo Anastácio River channel. Geologic substrate comprises Cretaceous siliciclastic rocks of the Caiuá and Bauru groups, locally covered by Cenozoic sediments (alluvial plains, terrace deposits, colluvial aprons, as well as in situ regoliths). Considering that liquefaction structures affect dark clay layers of 32.340±320 year BP age (14C dating), a lower age limit for the ancient earthquake is triggered in that region. The authors believe that neotectonic understanding of the Western São Paulo State Plateau is important to the geologic and geomorphologic evolution of that landscape and to the consequent territorial planning and occupation.

Permian-polysulphide-siderite-barite-haematite deposit Rude in Samoborska Gora Mts., Zagorje-Mid-Transdanubian zone of the Inner Dinarides

Samoborska Gora Mts. is situated within the westernmost part of the Zagorje-Mid-Transdanubian zone of the Internal Dinarides. The Samoborska Gora Mts. predominantly consists of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralisation is hosted by Permian siliciclastic sediments, below gypsum and anhydrite strata. The central part of the deposit consists of a 1.5 km long stratabound mineralisation, grading laterally into ferruginous sandstone and protruding vertically into a gypsum-anhydrite layer. Siderite-polysulphide-barite-quartz veins are located below the stratabound mineralisation. The stratiform part of the deposit is situated above the stratabound and consists of haematite layer with barite concretions and veinlets. Late stage galena-barite veins overprint earlier types of mineralisation. The Rude ore deposit was generated by predominantly NaCl +/- CaCl(2)-H(2)O solutions. Detrital quartz from stratiform mineralisation contains fluid inclusions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150 degrees C to 230 degrees C. Stratabound/siderite-polysulphide-barite-quartz vein type mineralisation was derived from solutions with salinities between 5 and 19 wt. % NaCl equ., homogenizing between 60 degrees C and 160 degrees C, while late stage galenabarite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100 degrees C to 140 degrees C. Fluid inclusion bulk leachate chemistry recorded Na(+)> Mg(2+)>K(+)>Ca(2+)>Li(+) and Cl-> SO(4)(2-) ions. Sulphur isotope composition of barites and overlying gypsum stems from Permian seawater sulphate, supported by increased Br(-) content, which follows successively the seawater evaporation line. The sulphur isotopic composition of sulphides varies between -0.2 and + 12.5 parts per thousand , as a result of thermal reduction of Permian marine sulphate. Ore-forming fluids were produced by hydrothermal convective cells (reflux brine model), and were derived primarily from Permian seawater, modified by evaporation and interaction with Permian sedimentary rocks. Rude deposits in Samoborska Gora Mts. may be declared as a prototype of the Permian siderite-polysulphide-barite deposits (products of rifting along the passive Gondwana margin), in the Inner Dinarides, and their equivalents extending northeastward into the Zagorje-Mid-Transdanubian Zone and the Gemerides, and southeastward to the Hellenide-Albanides.

The Yanque prospect (Peru): from polymetallic Zn-Pb mineralization to a nonsulfide deposit

The Yanque nonsulfide Pb-Zn deposit (inferred resources 12.5 Mt @ 3.7% Pb and @ 3.5% Zn) is located in the Andahuaylas-Yauri ore province (Cuzco, southern Peru). The deposit occurs within a base metal mineralized district, centered on the medium-sized Dolores porphyry copper. A thorough geological, mineralogical and geochemical study has carried out in order to define: the relationships between the Dolores Cu-porphyry ore and the Yanque Zn-Pb polymetallic mineralization, and the characteristics of the economic nonsulfide concentrations. Both sedimentary and igneous rocks constitute the backbone of the Yanque-Dolores area. The sedimentary lithologies belong to the Soraya, Mara and Ferrobamba Fms. (upper Jurassic-middle Cretaceous). The Yanque orebody is hosted by the Mara Fm., which prevailingly consists of a siliciclastic sedimentary breccia. The original sulfide mineralization consisted of galena, pyrite and sphalerite. The host rock has been affected by a strong hydrothermal alteration, characterized by prevailing sericite/illite, as in the typical porphyry-related phyllic-argillic alteration stage, and by minor kaolinite, dolomite and quartz. Minor element geochemistry, characterized by Sb, As, Mn, Ag and locally also by Cu, points to magmatic-hydrothermal related mineralizing fluids. The Pb isotopic compositions from Dolores and Yanque sulfides are similar, and are typical of the Tertiary magmatically-derived ores in this part of Peru. The hydrothermally altered rocks at Yanque have the same Pb isotopic compositions as the sulfides, thus confirming the hypothesis that the Yanque primary Zn-Pb mineralization may have been produced by hydrothermal circulation related to the emplacement of the Dolores Cu-porphyry, as it is the case of other porphyry Cu systems associated with polymetallic mineralization elsewhere. However, no simple genetic model for the mineralization involving just one fluid circulation episode is able to explain the data. The Yanque economic nonsulfide ore association consists of sauconite, hemimorphite, smithsonite and cerussite, which result from the weathering and alteration of the original sulfide mineralization. Zinc is allocated mainly in sauconite (Zn-smectite), rather than in carbonates: a factor strictly related to the prevailing siliciclastic character of the host rock. Distinctive features of the Yanque orebody are the comparable ore grades for both Pb and Zn (3.5% Zn and 3.7% Pb), and the inverse supergene chemical zoning. In fact, contrary to other supergene ores of this type, zinc prevails in the top zone of the Yanque deposit, whereas lead content increases with depth. Considering the different mobility of the two metals in solution, it may be assumed that most of the primary zinc that was the source for the Yanque nonsulfides was originally located far from the position occupied by the galena mineralization, whose remnants have been observed on site. Zinc sulfides may have been originally contained in the eroded rock volumes that surrounded the actual deposit: the zinc-rich solutions have possibly migrated through the siliciclastic Mara Fm. and precipitated the nonsulfide minerals by porosity filling and replacement processes. In this sense, the Yanque secondary Zn-Pb deposit could be considered as a special type of “Exotic” mineralization.

ELA-ICP-MS U-Pb zircon geochronology of regional volcanism hosting the Bajo de la Alumbrera Cu-Au deposit: implications for porphyry-related mineralization

ELA-ICP-MS U-Pb zircon geochronology has been used to show that the porphyritic intrusions related to the formation of the Bajo de la Alumbrera porphyry Cu-Au deposit, NW Argentina, are cogenetic with stratigraphically well-constrained volcanic and volcaniclastic rocks of the Late Miocene Farallon Negro Volcanic Complex. Zircon geochronology for intrusions in this deposit and the host volcanic sequence show that multiple mineralized porphyries were emplaced in a volcanic complex that developed over 1.5 million years. Volcanism occurred in a multivent volcanic complex in a siliciclastic intermontane basin. The complex evolved from early mafic-intermediate effusive phases to a later silicic explosive phase associated with mafic intrusions. Zircons from the basal mafic-intermediate lavas have ages that range from 8.46 +/- 0.14 to 7.94 +/- 0.27 Ma. Regionally extensive silicic explosive volcanism occurred at similar to8.0 Ma (8.05 +/- 0.13 and 7.96 +/- 0.11 Ma), which is co-temporal with intrusion of the earliest mineralized porphyries at Bajo de la Alumbrera (8.02 +/- 0.14 and 7.98 +/- 0.14 Ma). Regional uplift and erosion followed during which the magmatic-hydrothermal system was probably unroofed. Shortly thereafter, dacitic lava domes were extruded (7.95 +/- 0.17 Ma) and rhyolitic diatremes (7.79 +/- 0.13 Ma) deposited thick tuff blankets, across the region. Emplacement of large intermediate composition stocks occurred at 7.37 +/- 0.22 Ma, shortly before renewed magmatism occurred at Bajo de la Alumbrera (7.10 +/- 0.07 Ma). The latest porphyry intrusive event is temporally associated with new ore-bearing magmatic-hydrothermal fluids. Other dacitic intrusions are associated with subeconomic deposits that formed synchronously with the mineralized porphyries at Bajo de la Alumbrera. However, their emplacement continued (from 7.10 +/- 0.06 to 6.93 +/- 0.07 Ma) after the final intrusion at Bajo de al Alumbrera. Regional volcanism had ceased by 6.8 Ma (6.92 +/- 0.07 Ma). The brief history of the volcanic complex hosting the Bajo de la Alumbrera Cu-Au deposit differs from that of other Andean provinces hosting porphyry deposits. For example, at the El Salvador porphyry copper district in Chile, magmatism related to Cu mineralization was episodic in regional igneous activity that occurred over tens of millions of years. Bajo de la Alumbrera resulted from the superposition of multiple porphyry-related hydrothermal systems, temporally separated by a million years. It appears that the metal budget in porphyry ore deposits is not simply a function of their longevity and/or the superposition of multiple porphyry systems. Nor is it a function of the duration of the associated cycle of magmatism. Instead, the timing of processes operating in the parental magma body is the controlling factor in the formation of a fertile porphyry-related ore system.

A scientific note: Foragers deposit attractive scent marks in a stingless bee that does not communicate food location

National Science Foundation NSF IBN[0316697]

Guadalupian algae-sponge reefs in siliciclastic environments - the reefs at Lengwu (South China) compared with the reef at Iwaizaki (Japan)

Guadalupian reefs occur locally in Guangxi, Guizhou, Yunnan and Western Zhejiang, South China. Two types of Guadalupian reefs can be recognized, one is developed in carbonate platforms, e.g. those in the juncture areas of Guangxi, Yunnan and Guizhou; the other occurs in a littoral clastic shelf. The Lengwu reef in Western Zhejiang is a representative of the latter type, which is a major topic of this paper. Lengwu algae-sponge reef, more than one hundred meters in thickness, are composed mainly of sponges, hydrozoans, algae, bryozoans, microbes and lime mud. Reef limestones sit on the mudstone interbedded with fine sandstone of the proximal prodelta facies and are overlain by coarse clasts of the delta front sediments. Lengwu reef displays a lens-shaped relief, dipping and thinning from the reef core, which is remarkably different from the surrounding sediments, showing a protruding relief. Sponges and microbe/algae form bafflestone, bindstone and framestone of the reef core facies. Fore-reef facies is characterized by lithoclastic rudstone and bioclastic packstone. Reef limestone sequence is composed of three cycles and controlled by sea level changes and sediment influx. Such reef is unique among the Guadalupian reefs in South China, but seems similar in some aspects to lwaizaki reef limestones of south Kitakami in Japan. Algae and microbes growing around sponges to form rigid structure in Lengwu reef are a typical feature, which is distinctly different to Guadalupian reefs in a stable platform facies of Guizhou, Yunnan and Guangxi, South China.

Different mineralization styles in a volcanic-hosted ore deposit: the fluid and isotopic signatures of the Mt Morgan Au-Cu deposit, Australia

Quantitative laser ablation (LA)-ICP-MS analyses of fluid inclusions, trace element chemistry of sulfides, stable isotope (S), and Pb isotopes have been used to discriminate the formation of two contrasting mineralization styles and to evaluate the origin of the Cu and Au at Mt Morgan. The Mt Morgan Au-Cu deposit is hosted by Devonian felsic volcanic rocks that have been intruded by multiple phases of the Mt Morgan Tonalite, a low-K, low-Al2O3 tonalite-trondhjemite-dacite (TTD) complex. An early, barren massive sulfide mineralization with stringer veins is conforming to VHMS sub-seafloor replacement processes, whereas the high-grade Au-Cu. ore is associated with a later quartz-chalcopyrite-pyrite stock work mineralization that is related to intrusive phases of the Tonalite complex. LA-ICP-MS fluid inclusion analyses reveal high As (avg. 8850 ppm) and Sb (avg. 140 ppm) for the Au-Cu mineralization and 5 to 10 times higher Cu concentration than in the fluids associated with the massive pyrite mineralization. Overall, the hydrothermal system of Mt Morgan is characterized by low average fluid salinities in both mineralization styles (45-80% seawater salinity) and temperatures of 210 to 270 degreesC estimated from fluid inclusions. Laser Raman Spectroscopic analysis indicates a consistent and uniform array Of CO2-bearing fluids. Comparison with active submarine hydrothermal vents shows an enrichment of the Mt Morgan fluids in base metals. Therefore, a seawater-dominated fluid is assumed for the barren massive sulfide mineralization, whereas magmatic volatile contributions are implied for the intrusive related mineralization. Condensation of magmatic vapor into a seawater-dominated environment explains the CO2 occurrence, the low salinities, and the enriched base and precious metal fluid composition that is associated with the Au-Cu. mineralization. The sulfur isotope signature of pyrite and chalcopyrite is composed of fractionated Devonian seawater and oxidized magmatic fluids or remobilized sulfur from existing sulfides. Pb isotopes indicate that Au and Cu. originated from the Mt Morgan intrusions and a particular volcanic strata that shows elevated Cu background. (C) 2002 Elsevier Science B.V. All rights reserved.

Occurrence of storm-generated bedforms along the inner continental shelf - Southeastern Brazil

Levantamentos sonográficos desenvolvidos em duas áreas da plataforma interna adjacente ao estado do Espírito Santo revelam formas de fundo cuja origem é fortemente relacionada a eventos de tempestades. Estas são caracterizadas por alternâncias de bandas de areias finas sobrepostas, de forma alternada, a um fundo de areias grossas, gerando manchas de areias grossas intercaladas abruptamente com faixas de areias finas a profundidades de 25-30 m para GUA e de 05-08 m para BES. Em ambas as áreas as faixas de areias grossas apresentam marcas de ondulação geradas por ondas com orientação levemente paralela a linha de costa. A sedimentologia de GUA é composta por areias finas a muito finas lamosas carbonáticas com cascalhos siliciclásticos e a de BES por areias grossas e médias com cascalhos biodetríticos. Desta forma, é clara a ação de correntes/ondas de tempestade no fundo marinho de GUA e de BES; porém, a classificação quanto ao comportamento hidrodinâmico e ao transporte de sedimento é necessária para as estimativas sobre a formação, transporte e manutenção das feições encontradas.

The Farol Deposit (Depósito do Farol) – a Pleistocene beach deposit from Cape Mondego (Figueira da Foz, West Central Portugal)*

Among the Pleistocene and Holocene units recorded near the marine cliffs of Cape Mondego (Figueira da Foz, West Central Portugal) stands out the Farol Deposit (Depósito do Farol), at an altitude of ±95 m above present sea level. It is a marine terrace with three exposures of interstratified conglomerates and sands, overlapped by calclititic-fanglomerates. This sedimentary setting indicates that deposition took place in a seashore environment influenced by the proximity of a marine palaeocliff. The deposit has an interesting subfossil fauna with abraded and fragmented shells of Nucella lapillus (LINNÉ, 1758), Patella vulgata (LINNÉ, 1758) and Littorina littorea (LINNÉ, 1758), suggesting the existence of an environment with colder surface seawater, when compared with the present day Portuguese seashore. These specimens belonged to marine communities adapted to live in intertidal rocky platforms, which have been exposed to the cyclic action of waves and tidal flows, on the swash and surf zones. The Farol Deposit can be related to an Early/Middle Pleistocene “cold-water” episode, earlier to the Isotopic Stages 7 and 11. This episode occurred before the deposition of the units Quiaios Sands (Areias de Quiaios) and Cantanhede Sands (Areias de Cantanhede) (Sicilian?), but later than the Arazede Sands (Areias de Arazede) and Marinha das Ondas Sands (Areias de Marinha das Ondas) (Early Pleistocene).

The role of deposit insurance and bank’s asset size in the 2008 financial crisis

In this paper we analyze the role of deposit insurance in providing the market with liquidity in times of financial turmoil. To do so, we look at the variation in insured and uninsured deposits between 2005Q3 and 2011Q3, controlling for liquidity, solvency and capital adequacy indicators, and find evidence that deposit insurance does provide some confidence in keeping funds in banks in times of turmoil. Additionally we follow an event study methodology to assess the impact of deposit insurance oriented policies on bank holding companies stock market returns, and find a TBTF effect.

Using customer lifetime value to improve the prediction of bank deposit subscription in telemarketing campaigns

Customer lifetime value (LTV) enables using client characteristics, such as recency, frequency and monetary (RFM) value, to describe the value of a client through time in terms of profitability. We present the concept of LTV applied to telemarketing for improving the return-on-investment, using a recent (from 2008 to 2013) and real case study of bank campaigns to sell long- term deposits. The goal was to benefit from past contacts history to extract additional knowledge. A total of twelve LTV input variables were tested, un- der a forward selection method and using a realistic rolling windows scheme, highlighting the validity of five new LTV features. The results achieved by our LTV data-driven approach using neural networks allowed an improvement up to 4 pp in the Lift cumulative curve for targeting the deposit subscribers when compared with a baseline model (with no history data). Explanatory knowledge was also extracted from the proposed model, revealing two highly relevant LTV features, the last result of the previous campaign to sell the same product and the frequency of past client successes. The obtained results are particularly valuable for contact center companies, which can improve pre- dictive performance without even having to ask for more information to the companies they serve.

The size of the underground economy in Germany: A correction of the record and new evidence from the Modified-Cash-deposit-Ratio approach

Based on the Ahumada et al. (2007, Review of Income and Wealth) critique we revise existing estimates of the size of the German underground economy. Among other things, it turns out that most of these estimates are untenable and that the tax pressure induced size of the German underground economy may be much lower than previously thought. To this extent, German policy and law makers have been misguided during the last three decades. Therefore, we introduce the Modified-Cash-Deposit-Ratio (MCDR) approach, which is not subject to the recent critique and apply it to Germany for the period 1960 to 2008. JEL: O17, Q41, C22, Keywords: underground economy, shadow economy, cash-depositratio, currency demand approach, MIMIC approach

Francoisite-(Ce), a new mineral species from La Creusaz uranium deposit (Valais, Switzerland) and from Radium Ridge (Flinders Ranges, South Australia): Description and genesis

The new mineral francoisite-(Ce), (Ce,Nd,Ca)[(UO(2))(3)O(OH)(PO(4))(2)]center dot 6H(2)O is the Ce-analog of francoisite-(Nd). It has been discovered simultaneously at the La Creusaz uranium deposit near Les Marecottes in Valais, Switzerland, and at the Number 2 uranium Workings, Radium Ridge near Mt. Painter, Arkaroola area, Northern Flinders Ranges in South Australia. Francoisite-(Ce) is a uranyl-bearing supergene mineral that results from the alteration under oxidative conditions of REE- and U(4+)-bearing hypogene minerals: allanite-(Ce), monazite-(Ce), +/- uraninite at Les Marecottes; monazite-(Ce), ishikawaite-samarskite, and an unknown primary U-mineral at Radium Ridge. The REE composition of francoisite-(Ce) results from a short aqueous transport of REE leached out of primary minerals [most likely monazite-(Ce) at Radium Ridge and allanite-(Ce) at La Creusaz], with fractionation among REE resulting mainly from aqueous transport, with only limited Ce loss due to oxidation to Ce(4+) during transport.

Remediation of a marine shore tailings deposit and the importance of water-rock interaction on element cycling in the coastal aquifer

We present the study of the geochemical processes associated with the first successful remediation of a marine shore tailings deposit in a coastal desert environment (Bahia de Ite, in the Atacama Desert of Peru). The remediation approach implemented a wetland on top of the oxidized tailings. The site is characterized by a high hydrauliz gradient produced by agricultural irrigation on upstream gravel terraces that pushed river water (similar to 500 mg/L SO(4)) toward the sea and through the tailings deposit. The geochemical and isotopic (delta(2)H(water) and delta(18)O(water), delta(34)S(sulfate) , delta(18)O(sulfate)) approach applied here revealed that evaporite horizons (anhydrite and halite) in the gravel terraces are the source of increased concentrations of SO(4), Cl, and Na up to similar to 1500 mg/L in the springs at the base of the gravel terraces. Deeper groundwater interacting with underlying marine sequences increased the concentrations of SO(4), Cl, and Na up to 6000 mg/L and increased the alkalinity up to 923 mg/L CaCO(3) eq. in the coastal aquifer. These waters infiltrated into the tailings deposit at the shelf-tailings interface. Nonremediated tailings had a low-pH oxidation zone (pH 1-4) with significant accumulations of efflorescent salts (10-20 cm thick) at the surface because of upward capillary transport of metal cations in the arid climate. Remediated tailings were characterized by neutral pH and reducing conditions (pH similar to 7, Eh similar to 100 mV). As a result, most bivalent metals such as Cu, Zn, and Ni had very low concentrations (around 0.01 mg/L or below detection limit) because of reduction and sorption processes. In contrast, these reducing conditions increased the mobility of iron from two sources in this system: (1) The originally Fe(III)-rich oxidation zone, where Fe(II) was reduced during the remediation process and formed an Fe(II) plume, and (2) reductive dissolution of Fe(III) oxides present in the original shelf lithology formed an Fe-Mn plume at 10-m depth. These two Fe-rich plumes were pushed toward the shoreline where more oxidizing and higher pH conditions triggered the precipitation of Fe(HI)hydroxide coatings on silicates. These coatings acted as a filter for the arsenic, which naturally infiltrated with the river water (similar to 500 mu g/L As natural background) into the tailings deposit.

Bitumens in the late Variscan hydrothermal vein-type uranium deposit of Pribram, Czech Republic: Sources, radiation-induced alteration, and relation to mineralization

The late Variscan (275-278 Ma) Pribram uranium deposit is one of the largest known accumulations of uraniferous bitumens in hydrothermal veins. The deposit extends along the northwestern boundary of the Central Bohemian pluton (345-335 Ma) with low-grade metamorphosed Late Proterozoic and unmetamorphosed Cambrian rocks. From a net uranium production of 41,742 metric tons (t), more than 6,000 t were extracted from bitumen-uraninite ores during 43 years of exploration and mining. Three morphological varieties of solid bitumen are recognized: globular, asphaltlike, and cokelike. While the globular bitumen is uranium free, the other two types are uraniferous. The amount of bitumen in ore veins gradually decreases toward the contact with the plutonic body and increases with depth. Two types of bitumen microtextures are recognized using high-resolution transmission electron microscopy: amorphous and microporous, the former being less common in uraniferous samples. A lower Raman peak area ratio (1,360/1,575 cm(-1)) in mineralized bitumens (0.9) compared with uranium-free samples (2.0) indicates a lower degree of microtextural organization in the latter The H/C and O/C atomic ratios in uranium-free bitumens (0.9-1.1 and 0.09, respectively) are higher than those in mineralized samples (H/C = 0.3-0.8, O/C = 0.03-0.09). The chloroform extractable matter yield is Very low in uranium-free bitumens (0.30-0.35% of the total organic carbon,TOC) and decreases with uranium content increase. The extracted solid uraniferous bitumen infrared spectra show depletion in aliphatic CH2 and CH3 groups compared to uranium-free samples. The concentration of oxygen-bearing functional groups relative to aromatic bonds in the IR spectra of uranium-free and mineralized bitumen, however, do not differ significantly. C-13 NMR confirmed than the aromaticity of a uraniferous sample is higher (F-ar = 0.61) than in the uranium-free bitumen (F-ar = 0.51). Pyrolysates from uraniferous and nonuraniferous bitumens do not differ significantly, being predominantly cresol, alkylphenols, alkylbenzenes, and alkylnaphthalenes. The liquid pyrolysate yield decreases significantly with increasing uranium content. The delta(13)C Values of bulk uranium-free bitumens and low-grade uraniferous, asphaltlike bitumens range from -43.6 to 52.3 per mil. High-grade, cokelike, uraniferous bitumens are more C-13 depleted (54.5 to -58.4 parts per thousand). In contrast to the very light isotopic ratios of the high-grade uraniferous cokelike bitumen bulk carbon, the individual n-alkanes and isoprenoids (pristane and phytane) extracted from the same sample are significantly C-13 enriched. The isotopic composition of the C13-24 n-alkanes extracted from the high-grade uraniferous sample (delta(13)C = -28.0 to 32.6 parts per thousand) are heavier compared with the same compounds in a uranium-free sample (delta(13)C = 31.9 to 33.8 parts per thousand). It is proposed that the bitumen source was the isotopically light (delta(13)C = 35.8 to 30.2 parts per thousand) organic matter of the Upper Proterozoic host rocks that were pyrolyzed during intrusion of the Central Bohemian pluton. The C-13- depleted pyrolysates were mobilized from the innermost part of the contact-metamorphic aureole, accumulated in structural traps in less thermally influenced parts of the sedimentary complex and were later extracted by hydrothermal fluids. Bitumens at the Pribram deposit are younger than the main part of the uranium mineralization and were formed through water-washing and radiation-induced polymerization of both the gaseous and liquid pyrolysates. Direct evidence for pyrolysate reduction of uranium in the hydrothermal system is difficult to obtain as the chemical composition of the original organic fluid phase was modified during water-washing and radiolytic alteration. However, indirect evidence-e.g., higher O/C atomic ratios in uranium-free bitumens (0.1) relative to the Upper Proterozoic source rocks (0.02-0.05), isotopically very light carbon in associated whewellite (delta(13)C = 31.7 to -28.4 parts per thousand), and the striking absence of bitumens in the pre-uranium, hematite stage of the mineralization-indicates that oxidation of organic fluids may have contributed to lowering of aO(2) and uraninite precipitation.