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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Les gisements d'or comme témoins de l'histoire géologique du craton oues-africain : apports de la datation / Gold deposits as results of the West-African craton geologic history : Isotopic dating inputs

Le Mignot, Élodie 18 December 2014 (has links)
Le craton ouest-africain héberge de nombreux gisements et occurrences aurifères encaissés dans des terrains paléoprotérozoïques. Ces terrains birimiens se sont formés et accrétés lors du cycle orogénique éburnéen qui s’est déroulé entre 2,25 et 1,98 Ga. Six gisements d’or situés au Burkina Faso et au Ghana ont été étudiés dans le but d’établir une corrélation entre les différentes phases de l’orogenèse et le (ou les) événement(s) minéralisateur(s). L’étude détaillée de la minéralisation de ces six gisements a confirmé leur nature orogénique, mais a également révélé la présence d’un porphyre à Cu (±Au) dans le district minier de Gaoua, Burkina Faso. Par ailleurs, nos observations ont mis en évidence le caractère polyphasé de la minéralisation au sein d’un même gisement. Les datations Re-Os menées sur des sulfures directement liés à la minéralisation en or permettent de distinguer deux grandes périodes métallogéniques au sein de l’orogenèse éburnéenne. La première période se déroule lors de la phase d’accrétion magmatique D1 et de la phase de transition D2, soit entre 2200 et 2120 Ma. Cette période est caractérisée par une minéralisation à faibles teneurs disséminée dans les roches encaissantes. La deuxième période métallogénique prend place lors des stades cassants tardifs de l’orogenèse, aux alentours de 2050-2040 Ma. Elle est représentée par une minéralisation à or visible à plus fortes teneurs, concentrée dans des veines, des brèches et des zones de cisaillement. La mise en évidence de l’existence de minéralisations aurifères précoces pourrait avoir des conséquences sur la compréhension des gisements de type paléoplacer observés notamment au Ghana. Ces minéralisations primaires pourraient en effet constituer la source de l’or des paléoplacers tarkwaïens, mis en place à partir de 2130 Ma, qui demeure inconnue / The West African craton is a region enriched in gold deposits and occurrences which are hosted in Paleoproterozoic terrains. These Birimian terrains formed during the Eburnean orogeny which took place between 2.25 and 1.98 Ga. Six gold deposits situated in Burkina Faso and Ghana were studied in order to define a correlation between the different orogenic phases and the mineralizing event(s). The detailed study of the mineralization of the six deposits confirmed the importance of the orogenic gold deposits in the West African craton. Moreover, the existence of a Cu (±Au) porphyry deposit was revealed in the mining district of Gaoua, southwestern Burkina Faso. Our observations highlighted the polyphased character of gold mineralization within nearly all of the studied deposits. Re-Os dating performed on sulfides directly linked to the gold mineralization permitted two main metallogenic periods to be distinguished. The first period was coincident with the D1 and D2 orogenic phases, occurring between 2200 and 2120 Ma, and representing respectively magmatic accretion and transition towards a collisional regime. This period was characterized by low grade disseminated gold mineralization. The second metallogenic period took place during the later brittle deformational phases of the orogeny, ca. 2050-2040 Ma. This secondary mineralization contains visible gold concentrated in veins, breccias and shear zones, and displays higher gold grades. Geochronological evidence for the existence of early gold mineralization could have consequences for the understanding of paleoplacer-type deposits, observed primarily in Ghana. Indeed, this primary mineralization could represent a potential source for gold found in Tarkwaian paleoplacers, which formed after 2130 Ma, and for which the provenance of the gold remains unidentified
12

Developing a Useful Set of Proxy Elements for the Targeting and Exploration of Gold Deposits, Black Hills, South Dakota

Harp, Michael T. 13 December 2010 (has links)
No description available.
13

Insights into the History of Pyrite Mineralization at the Round Mountain Gold Mine, Nevada: A Detailed Microanalytical Study of the Type 2 Ore

Daniel, Blakemore 03 August 2020 (has links)
No description available.
14

Chemismus paleofluid z ložisek typu "orogenic gold": nové analytické přístupy a případové studie z Českého masívu / Paleofluid chemistry of orogenic gold deposits: novel analytical methods and case studies from the Bohemian Massif

Hrstka, Tomáš January 2012 (has links)
PALEOFLUID CHEMISTRY OF OROGENIC GOLD DEPOSITS: NOVEL ANALYTICAL METHODS AND CASE STUDIES FROM THE BOHEMIAN MASSIF Tomáš Hrstka1 1 Charles University in Prague, Faculty of Science, Institute of Geochemistry, Mineralogy and Mineral Resources, Albertov 6, Praha 2, CZ-128 43 Abstract of the Ph.D. Thesis Fluid inclusions represent a unique tool for understanding the processes leading to the formation of mineral deposits and fluid-rock interactions in general. Orogenic gold deposits in the central part of the Bohemian Massif (Libčice and Kasejovice deposits) were studied in order to provide a better understanding of their genesis. A multifaceted approach was adopted including a broad spectrum of micro-analytical methods. While traditional methods were used as the basis of this study (e.g., microthermometry, SEM and optical microscopy), the application and improvement/development of modern analytical methods (e.g., LA-ICP- MS and Raman spectroscopy) or introduction of alternative innovative techniques (CLSM, Nano- tomography, QEMSCAN) constituted a significant part of this study. This study reveals the importance of the HCO3 - species in hydrothermal fluids (i.e., >100 řC to ~350 řC). Previously, the prevalence of Cl- and other anions was reported for hydrothermal paleofluids and the majority of studies suggested...

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