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Showing 121 to 124 of 124 (0.066 seconds)Spelling suggestions: "subject:"hydrothermal"" "subject:"hydrothermally""
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Altération de l'île volcanique de Mayotte (Comores) : approches par géochimie des eaux et isotopie du silicium sur les roches de profils d'altération / Alteration of the volcanic island of Mayotte (Comoros) : approaches by water geochemistry and silicon isotopes on rock weathering profilesPuyraveau, Romain-Arnaud 05 October 2016 (has links)
Dans cette étude, nous cherchons à dresser le bilan de l’altération à l’échelle de l’île de Mayotte (en surface et en souterrain), à contraindre l’impact des facteurs de contrôle dominant l’altération, puis à caractériser les processus impliqués dans les fractionnements des isotopes du silicium à l’échelle du profil d’altération.Deux campagnes d’échantillonnage incluant des eaux de rivières et des eaux souterraines ont été réalisées en saison humide et sèche, complétées par le prélèvement mensuel de 5 rivières. La prise en compte des crues (3 % de l’année) dans le calcul des taux d’altération moyens annuels en rivière a entraîné une augmentation de ≈32 % du bilan annuel. Le taux d’altération chimique global de l’île de Mayotte s’élève à 94 t/km²/an (81 t/km²/an en surface & 131 t/km²/an en souterrain). Nos résultats mettent en avant le rôle prépondérant des écoulements souterrains dans le transport de matériel dissous directement à l’océan. La contribution du domaine souterrain au bilan de l’altération diminue avec l’âge des formations, soulignant l’implication de l’âge des roches du bassin versant comme paramètre clé dans le contrôle des taux d’altération.Les isotopes du Si ont été analysés sur des roches totales le long de profils d’altération associés à différentes conditions d'altération du régolite : météorique (basse température) ou hydrothermale (haute température). À l’échelle du profil, les deux types de régimes ont montré un appauvrissement en 30Si en fonction du degré d’altération. À l’échelle du minéral, le fractionnement des isotopes du Si s’est révélé plus négatif pendant la précipitation de kaolinite secondaire à haute température qu’à basse température. / In this study, we seek to establish the weathering budget at the scale of the island of Mayotte (rivers and groundwater), to constrain the impact of dominant control factors to the weathering both locally and at a global scale, and then to characterize the processes involved in the fractionation of silicon isotopes across the weathering profile.Two field campaigns, in order to sample river water and groundwater, were carried out during wet and dry season, supplemented by the monthly monitoring of 5 rivers. By taking account of river floods (3% of the year) in the calculation of average annual weathering rates in the river has increased the annual weathering budget by ≈32%. The overall rate of Mayotte Island chemical weathering is 94 t/km²/yr (81 t/km²/yr from surface & 131 t/km²/yr from underground). Our results highlight the important role of groundwater flow to the dissolved material export directly to the ocean. The contribution of groundwater to the weathering budget decreases with the age of the geological formations, highlighting the involvement of the age of the rocks of the watershed as a key parameter in the weathering rates control.Si isotopes were analyzed for whole rock along two weathering profiles associated with different alteration conditions of the regolith: meteoric (low temperature) or hydrothermal (high temperature). At the weathering profile scale, the two types of alteration regimes showed 30Si depletion as a function of the degree of weathering. At the mineral scale, Si isotope fractionation was more negative during the secondary kaolinite precipitation at high temperatures than at low temperatures.
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Magmatic-Hydrothermal Events, Mineralogy and Geochemistry of Tourmaline Breccia in the Giant Río Blanco – Los Bronces Porphyry Copper Deposit, Central ChileHohf Riveros, Michael 26 April 2021 (has links)
The Río Blanco–Los Bronces (Chile) is one of the richest endowed porphyry copper-molybdenum districts worldwide, where about 20% of the known mineralization is hosted by tourmaline-cemented hydrothermal breccia.
This work seeks: (1) to find a relationship between tourmaline chemical and/or isotopic composition and the degree of mineralization in the breccia, (2) to constrain the source of the mineralizing fluid in the breccia, and (3) to determine of the composition and age of intrusive units in three new exploration projects and correlate them with the known intrusive rocks of the mine areas. Tourmaline from mineralized and barren breccias has similar boron isotopic compositions but differences in Mg/(Mg+Fe) ratios, Al-contents and Al-Fe correlation, which may have exploration value. Boron and sulfur isotopes results are consistent with a magmatic source of hydrothermal fluids. Results of whole rock geochemistry and U-Pb and 40Ar/39Ar geochronology of intrusive units, breccia and late-stage veins are combined with previous U-Pb, Ar/Ar and Re-Os ages to elucidate the magmatic and hydrothermal history of the district.:1 Introduction
1.1 Motivation of the study and statement of research questions
1.2 Scope of the study
2 Porphyry copper deposits (PCDs)
2.1 Introduction
2.1.1 Global copper inventory
2.1.2 Definition and classification of PCDs
2.2 Regional scale characteristics of PCDs
2.2.1 Tectonic setting
2.2.2 Space and time distribution
2.2.3 Porphyry stocks and their pluton and volcanic connections
2.2.4 Wall-rock Influence
2.3 Deposit-scale characteristics
2.3.1 Porphyry stocks and dikes
2.3.2 Hydrothermal breccia
2.3.3 Alteration-mineralization zoning
2.4 Processes of PCD formation
2.4.1 Arc magmatism
2.4.2 Magmatic volatiles
2.4.3 Genetic models
3 Regional setting of the study area
3.1 Tectono-magmatic setting
3.2 Metallogenic belts
4 Río Blanco – Los Bronces mining district
4.1 Mining history
4.2 District geology
4.2.1 Stratified rocks
4.2.2 Plutonic and hypabyssal intrusions
4.2.3 Structures
4.2.4 Alteration and mineralization
4.2.1 Geochronology database
5 Results
5.1 Plutonic units
5.1.1 Petrography
5.1.2 Whole rock (WR) geochemistry
5.1.3 Geochronology
5.2 Mineralization
5.2.1 Petrography
5.2.2 Tourmaline occurrence and composition
5.2.3 Sulfides and sulfates
6 Discussion
6.1 Time-space relationships of intrusion, brecciation and hydrothermal alteration
6.2 Stable isotope constraints on fluid source and evolution
6.2.1 Oxygen, hydrogen and sulfur isotopes
6.2.2 Boron isotopes
6.3 Tourmaline as a redox indicator and significance for exploration
7 Summary and conclusions
8 References
Digital supplement
Appendix (Methods)
9 Appendix Methods
9.1 Optical microscopy (OM)
9.2 Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS)
9.3 Whole rock chemical analysis
9.4 Electron microprobe analyses (EMPA)
9.5 Boron isotopes
9.6 Sulfur isotopes
9.7 40Ar/39Ar dating
9.8 Zircon separation and characterization
9.9 U-Pb zircon LA-ICP-MS dating
9.10 U-Pb zircon CA-ID-TIMS dating
9.11 Single zircon evaporation as screening method
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Das Lagerstättengebiet Zobes-Bergen im Vogtland und benachbarte Uranvorkommen im Bereich des Bergener GranitmassivsHiller, Axel, Schuppan, Werner 23 March 2017 (has links)
Der Band enthält einen regionalgeologischen Überblick zur Region und die Beschreibung der Lagerstätten Zobes und Bergen sowie weiterer Uranvorkommen des Vogtlandes nach ihrem geologischem Aufbau und ihrer Erkundung. Am umfassendsten untersucht war die Gangmineralisation in der Uranlagerstätte Zobes. In ihr trat außerdem eine schichtgebundene Scheelit-Sulfid-Vererzung auf.
Nach Abschluss von Uranbergbau und -erkundung in Sachsen und Thüringen bleiben die geowissenschaftlichen Erkenntnisse und Erfahrungen von grundsätzlichem Interesse. Sie können als Grundlage für künftige regionalgeologische Forschungen und rohstofforientierte Untersuchungen dienen.
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Geochemie Porifera-reicher Mud Mounds und Mikrobialithe des Mittel- und Oberdevons (Westaustralien, Nordfrankreich) / Geochemistry of Porifera-rich mud mounds and microbialites of the Middle and Upper Devonian (Western Australia, Northern France)Hühne, Cathrin 07 November 2005 (has links)
No description available.
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