Mineralogy of fine-grained material and of weathered material is of primary importance to understand the erosion processes. Mineralogical change can induce mechanical weakening as well as cementing and thus hardening. Groundwater chemistry plays a fundamental role in weathering processes.

Short courses

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Géochimie des eaux de sources et interaction eau-roche dans les Alpes (in French).

Par Marc-Henri Derron

Résume du cours donné dans le cadre du module “Altération et minéralogie industrielle” du Dr. Ph. Thélin, avril 2000, pour les étudiants de géologie des universités de Lausanne et Genève.

Objet du cours : L’interaction fluide-roche est un des aspects important de l’altération des roches alpines. La composition chimique des eaux de surface est un indicateur des lithologies au travers desquelles les eaux ont circulé et des processus de dissolution des minéraux qui constituent les roches. Le chimisme permet notamment une compréhension des processus érosifs et leur quantification. Le but de ce short-course est donc de mettre en évidence les façons dont les roches alpines influencent la composition chimique des eaux naturelles.

Key publications

  • Dating incipient metamorphism using 40Ar/39Ar geochronology and XRD modeling: a case study from the Swiss Alps

    Contrib Mineral Petrol (1999) 135: 93 – 113. Jaboyedoff M and Cosca MA

    Complete version available on request at: mail@quanterra.org

    Abstract: Six samples from a single lithological unit from the Swiss Préalpes, which has been progressively metamorphosed at very low grade metamorphic conditions (from diagenesis to deep anchizone), have been dated by conventional 40Ar/39Ar step heating techniques. Different size fractions (2-6 mm and 6-20 mm) of dioctahedral phyllosilicates separated from the carbonaceous unit yield 40Ar/39Ar spectra with variably developed staircase patterns, consistent with a mixture of detrital mica and neocrystallized mixed-layer illite/smectite. The lower age intercepts of all 40Ar/39Ar spectrum diagrams converge to ~ 40 Ma giving an imprecise, maximum age for the metamorphism. The illite component of the mixed-layer illite/smectite is interpreted to be neoformed during Tertiary Alpine metamorphism, however distinguishing and quantifying the amount of preexisting illite (detrital mica) and neoformed illite within the mixed-layer illite/smectite, especially for low-grade metamorphic rocks, is critical for determining an accurate age of metamorphism. The percentage of neoformed illite within the mixed-layer illite/smectite has been estimated by comparison of glycolated and air dried X-ray diffraction patterns with NEWMODÓ simulations. In the least metamorphosed samples the mixed-layer illite/smectite contains ~ 66% neoformed illite layer and only accounts for approximately 25% of the total dioctahedral phyllosilicates. This contrasts with the more strongly metamorphosed samples, which contain > 97% neoformed illite layer in the mixed-layer illite/smectite and account for ~ 70% to > 90% of the total dioctahedral phyllosilicates. Phyllosilicate morphologies when viewed by scanning electron microscopy are consistent with these estimates, and are interpreted in terms of disolution/reprecipitation. A plot of the neoformed illite content for progressively metamorphosed samples versus their 40Ar/39Ar integrated total fusion ages yields a straight line relationship with an extrapolated age for 100% neoformed dioctahedral phyllosilicates of 27 Ma, which is interpreted as the age of metamorphism, and is consistent with stratigraphic constraints. Model 40Ar/39Ar age spectra, constructed from the analytical data and modeled results for conditions of progressive metamorphism and varying contributions of detrital and neoformed illite, illustrate the change in degasing properties of progressively metamorphosed samples.

  • “Claim”: a new personal computer-assisted simulation model for teaching mineral exploration techniques (English PDF).

    Bauchau, C Jaboyedoff, M. and Vannier, M. (1993). In: Kirkham, R.V., Sinclair, W.D., Thorpe, R.I. and Duke, J.M., eds. Minerla Deposit Modelling: Geological Assoc. of Canada, Special Paper 40, p. 685-691.

    Abstract: Since 1965, the University of Lausanne and the School of Mines of Paris have jointly developed a mineral exploration practical tuition by simulation techniques. The first models were very empirical, but with the use of large computers, they soon became more complicated and realistic (VANNIER & WOODTLI, 1979). A new model, CLAIM, is being presented here; for the first time, it works on a PC using C language under MS-DOS. This new teaching method is very fast and allows the instant comparison of the students’ results with the model and besides it opens numerous graphic developments.
    CLAIM simulates a 400 sq. km sedimentary copper-bearing district that students have to investigate by means of geochemical samples and various drill rigs, starting from topographic and geologic maps, all simulated.
    Access to information is possible through a drilling function which draws up complete drill logs. The geological setting is created by standard sections and its spatial distribution by displacing the section along trajectories. Topography is drawn from a base level digitalized on a square grid, later eroded and weathered as a function of a lithology-dependant “weathering module”.
    Mineralizations are simulated by so-called “spots” pictured as ellipsoidal clouds and they are introduced by associating them to a lithologic horizon and to X Y coordinates. Lastly, geochemically anomalous zones are created from shallow mineralization maps.
    All these technical functions are accompanied by management programmes enabling progress of the actual game, with budget control, drilling, assays and geochemical samples requests. Here and now, numerous developments appear to be possible.

  • L’enseignement de la prospection minière par simulation sur ordinateur PC. (French PDF)

    Bauchau, C. et Jaboyedoff, M. (1990). Bull. Soc. Vaud. Sc. Nat. 80.1, 49-62.

    Résumé: Depuis 1965, l’Université de Lausanne et l’Ecole des Mines de Paris ont développé un enseignement pratique de la prospection minière par simulation. D’abord très empiriques, les modèles sont devenus plus complexes et plus réalistes grâce à l’apport de l’informatique (VANNIER et WOODTLI, 1979). Un nouveau modèle, CLAIM, fonctionnant pour la première fois sur un PC, en langage C et sous MS-DOS, est présenté ici. Cette nouvelle méthode d’enseignement permet d’obtenir des réponses très rapides et de comparer instantanément les résultats des étudiants au modèle; elle offre en outre de très grandes possibilités graphiques.
    CLAIM simule un district cuprifère de 400 km2, de type stratiforme dans des sédiments, qu’il convient d’investiguer au moyen de prélèvements géochimiques puis de forages exécutés par divers types des sondeuses, tous simulés, à partir de cartes topographiques et géologiques, également simulées. l’accès aux informations se fait par une fonction de forage qui établit des logs de forage complets. Le cadre géologique est créé par des coupes types et sa simulation spatiale par le déplacement des coupes suivant des trajectoires paramétrées. La topographie se construit à partir d’un niveau de base digitalisé suivant une grille carrée, ensuite érodé et altéré en fonction d’un module d’altération dépendant de la lithologie. Les minéralisations sont simulées par des “spots” définis par des ellipsoïdes des et mises en place en les associant à un niveau lithologique et à des coordonnées X Y. Enfin, des zones d’anomalies géochimiques sont créées à partir de cartes de minéralisations superficielles.
    Toutes ces fonctions techniques sont complétées par des programmes de gestion qui permettent le déroulement du jeu proprement dit, avec contrôle budgétaire, commandes des prélèvements géochimiques, des sondages et des analyses. D’ores et déjà de nombreux développements apparaissent possibles, en gîtologie comme dans d’autres domaines des sciences de la terre.

  • An attempt to correlate HRTEM and XRD. Determination of coherent Scattering domain size of illite-smectite interstratification using “illite crystallinity” (English PDF).

    Jaboyedoff M., Kübler B., Stadelmann P., Thélin P. (2001): Soc. Vd. Sc. Nat. 87, 305-319.

    Abstract: The relationships among the Kübler Index (KI), coherent scattering domain thickness, and HRTEM data are examined, using careful modeling of X-ray diffraction (XRD) patterns of air dried, glycolated, and heated samples of interstratified illite-smectite (I-S) from a stylolitic marly limestone. The XRD spectra are decomposed assuming that I-S consists of illite particles can be separated along expandable interlayers; there are also small amounts of two discrete phases mica phases and maybe pyrophyllite. The values obtained for coherent diffraction domain thickness of I-S are compatible with results obtained by HRTEM.