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Alexandra Guedes Fernando Noronha Marie-Christine Boiron David A. Banks 《Chemical Geology》2002,190(1-4):273-289
In order to identify and characterise fluids associated with metamorphic rocks from the Chaves region (North Portugal), fluid inclusions were studied in quartz veinlets, concordant with the main foliation, in graphitic-rich and nongraphitic-rich lithologies from areas with distinct metamorphic grade. The study indicates multiple fluid circulation events with a variety of compositions, broadly within the C–H–O–N–salt system. Primary fluid inclusions in quartz contain low salinity aqueous–carbonic, H2O–CH4–N2–NaCl fluids that were trapped near the peak of regional metamorphism, which occurred during or immediately after D2. The calculated P–T conditions for the western area of Chaves (CW) is P=300–350 MPa and T500 °C, and for the eastern area (CE), P=200–250 MPa and T=400–450 °C. A first generation of secondary fluid inclusions is restricted to discrete cracks at the grain boundaries of quartz and consists of low salinity aqueous–carbonic, H2O–CO2–CH4–N2–NaCl fluids. P–T conditions from the fluid inclusions indicate that they were trapped during a thermal event, probably related with the emplacement of the two-mica granites.
A second generation of secondary inclusions occurs in intergranular fractures and is characterised by two types of aqueous inclusions. One type is a low salinity, H2O–NaCl fluid and the second consists of a high salinity, H2O–NaCl–CaCl2 fluid. These fluid inclusions are not related to the metamorphic process and have been trapped after D3 at relatively low P (hydrostatic)–T conditions (P<100 MPa and T<300 °C).
Both the early H2O–CH4–N2–NaCl fluids in quartz from the graphitic-rich lithologies and the later H2O–CO2–CH4–N2–NaCl carbonic fluid in quartz from graphitic-rich and nongraphitic-rich lithologies seem to have a common origin and evolution. They have low salinity, probably resulting from connate waters that were diluted by the water released from mineral dehydration during metamorphism. Their main component is water, but the early H2O–CH4–N2–NaCl fluids are enriched in CH4 due to interaction with the C-rich host rocks.
From the early H2O–CH4–N2–NaCl to the later aqueous–carbonic H2O–CO2–CH4–N2–NaCl fluids, there is an enrichment in CO2 that is more significant for the fluids associated with nongraphitic-rich lithologies.
The aqueous–carbonic fluids, enriched in H2O and CH4, are primarily associated with graphitic-rich lithologies. However, the aqueous–carbonic CO2-rich fluids were found in both graphitic and nongraphitic-rich units from both the CW and CE studied areas, which are of medium and low metamorphic grade, respectively. 相似文献
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Ahmed Barakat Christian Marignac Marie-Christine Boiron Mohamed Bouabdelli 《Comptes Rendus Geoscience》2002,334(1):35-41
The gold showings at Bleida are hosted in Late Pan-African N50–80 °E quartz–hematite–chlorite 1 tension lenses that are related to the activity of major sinistral sub-east–west thrusts. Ores result from three superimposed stages of fluid migration. Gold occurs in microcracks offsetting the earlier minerals. Fluids evolved from COHN compositions with a saline component to boiling aqueous fluids. Pressure and temperature decreased from 50 MPa and 300 °C to less than 4 MPa and 150 °C. Thus, the gold showings at Bleida were formed in a typical geothermal (epithermal) setting, likely controlled by the Late Pan-African magmatism. To cite this article: A. Barakat et al., C. R. Geoscience 334 (2002) 35–41 相似文献
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Jean?VallanceEmail author Marie-Christine?Boiron Michel?Cathelineau Serge?Fourcade Michel?Varlet Christian?Marignac 《Mineralium Deposita》2004,39(3):265-281
The Moulin de Chéni orogenic gold deposit is the only granite-hosted deposit of the Saint-Yrieix district, French Massif Central. It occurs in 338±1.5 Ma-old peraluminous leucogranites and is characterized by intense microfracturing and bleaching of the granite in relation to pervasive sulfide crystallization. Formation of quartz veins and gold deposition occurred in two successive stages: an early mesozonal stage of quartz-sulfide (Fe-As-S) deposition, usually devoid of gold and a late epizonal stage of base metal and gold deposition. Both stages postdate peak metamorphism and granite intrusion. The genesis of the deposit is the result of four successive fluid events: (1) Percolation of aqueous-carbonic metamorphic fluids under an assumed lithostatic regime of 400–450 °C, at a maximum depth of 13 km; (2) Formation of the main quartz lodes with coeval K-alteration and introduction of As and S from aqueous-carbonic fluids percolating along regional faults. Arsenopyrite and pyrite deposition was linked to the alteration of Fe-silicates into K-feldspar and phengite at near-constant iron content in the bulk granite. Temperature was similar to that of the preceding stage, but pressure decreased to 100–50 MPa, suggesting rapid uplift of the basement up to 7.5 km depth; (3) The resulting extensional tectonic leads to the deposition of gold, boulangerite, galena and sphalerite in brecciated arsenopyrite and pyrite from aqueous fluids during a mixing process. Temperature and salinity decrease from 280 to 140 °C and 8.1 wt% eq. NaCl to 1.6 wt% eq. NaCl, respectively; (4) Sealing of the late fault system by barren comb quartz which precipitated from dilute meteoric aqueous fluids (1.6 wt% eq. NaCl to 0.9 wt% eq. NaCl) under hydrostatic conditions at 200–150 °C.Editorial handling: B. Lehmann 相似文献
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Summary Four metamorphic/hydrothermal fluid systems were identified in detailed microthermometric and spectroscopic investigations carried out on fluids trapped in late-stage quartz veins sampled throughout the Witwatersrand Basin. These include aqueous, H2O-CO2-rich, H2O-CH4-CO2-rich and CH4-N2-rich fluids. Early inclusion populations are dominated by H2O- and CO2-rich fluid systems. Cross-cutting these early fluid populations are trails of inclusions that contain CH4, C2H6, N2, H2 and H2S (vapour-rich inclusions). Fault-related quartz veins, in particular, are characterized by these later fluid types. A common feature of some of these later fluids is the presence of hydrocarbons and daughter crystals. A very late phase of aqueous fluids occurs in most samples as transgranular inclusion trails. P-V T-X considerations as well as chlorite geothermometry, mineral assemblages and burial conditions suggest entrapment temperatures of between 200°C and 400°C and locally up to 500°C. Fluid chemistry suggests that the post-depositional C-O-H fluids affecting the sediments have oxygen fugacities between Q-F-M and Ni-NiO in the range 300°C to 400°C. This accounts for the widespread preservation of detrital uraninite and gold remobilization along major fluid conduits.
Charakterisierung von post-sedimentären Fluiden im Witwatersrand-Becken
Zusammenfassung Vier verschiedene Arten von metamorphen/hydrothermalen Flüssigkeitseinschlüssen wurden im Zuge von detaillierten mikrothermometrischen und spektroskopischen Untersuchungen an Flüssigkeiten in Proben von spätgebildeten Quarzgängen aus dem Gesamtbereich des Witwatersrand-Beckens identifiziert. Bei diesen Flüssigkeiten konnten wässerige, H2O-CO2-reiche, H2O-CH4-CO2-reiche und CH4-N2-reiche Typen unterschieden werden. Bei frühgebildeten Einschlüssen dominieren H2O- und CO2-reiche Flüssigkeiten. Die frühen Einschlüsse kommen entlang verheilter Bruchflächen vor und werden von einer späteren, gasreichen Generation durchkreuzt, die CH4, C2H6, N2, H2, und H2S enthält. Insbesondere Quarzgänge, die an Verwerfungen gebunden sind, enthalten Flüssigkeitseinschlüsse des letzteren Typs. Einige dieser Flüssigkeiten haben die Anwesenheit von Tochterkristallen und hydrokarbonischer Komponenten gemeinsam. Eine sehr späte Generation von wäßrigen Flüssigkeiten kommt in den meisten Proben in der Form von trans-granularen Einschlussbahnen vor. Berücksichtigung von P-V-T-X Bedingungen und Chlorit-Thermometrie, von Mineralparagenesen und Überlagerungsmächtigkeit weisen auf Bildungstemperaturen zwischen 200 und 400 °C, lokal bis zu 500 °C. Die Zusammensetzungen der Flüssigkeiten deuten an, daß die spät-bis post-diagenetischen C-O-H Flüssigkeiten, die auf die Sedimente einwirkten, Sauerstoffugazitäten im Bereich zwischen Q-F-M und Ni-NiO, für Temperaturen von 300 bis 400 °C, hatten. Dies erkärt, warum detritischer Uraninit in weiten Bereichen des Beckens auftritt und warum Remobilisierung von Gold entlang von Zonen hoher Fluidwegsamkeit stattfinden konnte.相似文献
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Aurélien?EglingerEmail author Clément?Ferraina Alexandre?Tarantola Anne-Sylvie?André-Mayer Olivier?Vanderhaeghe Marie-Christine?Boiron Jean?Dubessy Antonin?Richard Marc?Brouand 《Contributions to Mineralogy and Petrology》2014,167(2):967
In the Pan-African Lufilian belt (Western Zambian Copperbelt), uranium mineralizations, preferentially scattered in kyanite ± talc micaschists (metamorphosed evaporitic sediments) or concentrated along transposed quartz veins provide an opportunity to (1) understand the time/space relationship between the ore minerals and the deformation of the host rocks, (2) identify the different fluid events associated with specific stages of quartz deformation and (3) characterize the ore fluid geochemistry in terms of fluid origin and fluid/rock interactions. In the U occurrences studied in Lolwa and Mitukuluku (Domes region, Western Zambian Copperbelt), two mineralizing stages are described. The first generation of ore fluids (53–59 wt% CaCl2, 13–15 wt% NaCl; N2–H2 in the gas phase of fluid inclusions) circulated during the high-temperature quartz recrystallization, at 500–700 °C. This temperature is in agreement with the P–T conditions recorded during the crustal thickening related to continental collision at ca. 530 Ma. LA-ICPMS analyses show the presence of uranium within this fluid, with a concentration mode around 20 ppm. The second generation of ore fluid (21–32 wt% NaCl, 19–21 wt% CaCl2; CO2–CO in the gas phase of fluid inclusions) percolated at lower temperature conditions, at the brittle–ductile transition, between 200 and 300 °C. This temperature could be related to the exhumation of the high-grade metamorphic rocks at ca. 500 Ma. The formation of H2 and CO is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions. Finally, a late fluid (14–16 wt% NaClequiv) circulated in the brittle domain but seems unrelated to U (re-)mobilization event. 相似文献
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Philippe Lach Julien Mercadier Jean Dubessy Marie‐Christine Boiron Michel Cuney 《Geostandards and Geoanalytical Research》2013,37(3):277-296
Advances in the quantification of rare earth elements (REE) at the micrometric scale in uranium oxides by laser ablation‐inductively coupled plasma‐mass spectrometry are described. The determination of the best analytical conditions was tested using a uranium oxide (Mistamisk) the concentrations of REE in which were previously estimated by other techniques. Comparison between the use of U or Pb as an internal standard clearly showed a diameter‐dependent fractionation effect related to Pb at small crater diameters (16 and 24 μm), which was not found for U. The quantification of REE contents in uranium oxide samples using both matrix‐matched (uranium oxide) and non‐matrix‐matched (NIST SRM 610 certified glass) external calibrators displayed no significant difference, demonstrating a limited matrix effect for REE determination by LA‐ICP‐MS. Moreover, no major interferences on REEs were detected. The proposed methodology (NIST SRM 610 as external calibrator and U as internal standard) was applied to samples from uranium deposits from around the world. The results showed that LA‐ICP‐MS is a suitable analytical technique to determine REE down to the μg g?1 level in uranium oxides at the micrometre scale and that this technique can provide significant insights into uranium metallogeny. 相似文献