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Rock Samples and Geochemical Analysis

Rock Samples and Geochemical Analysis. Maria de Lourdes Rosa & Débora Correia Rios Federal University of Bahia Earth Sciences Institute Brazil.

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Rock Samples and Geochemical Analysis

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  1. Rock Samples and Geochemical Analysis Maria de Lourdes Rosa & Débora Correia Rios Federal University of Bahia Earth Sciences Institute Brazil Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

  2. Geochemistry at the Federal University of Bahia - Brazil

  3. Geochemistry at the Federal University of Bahia (UFBA) - Brazil • Brief Description • 2 Disciplines of Geochemistry • Chemistry for Geologists (first year) • Geochemistry (fourth year) • For who? • Undergraduate students of Geology • Background: • Introductory Geology

  4. Chemistry for Geologists Course • Syllabus - Lectures (60%) • Lab Activities (40%) • 48 students/semester • 2 Teachers • 75 hours/semester • 30 h Lectures • 45 h Laboratory Activities

  5. Laboratory Activities • 15 Laboratory Activities: 1 per week • The laboratory practices are for students to recognize what is involved in modern geochemistry analyses of these geological materials: • Rocks and minerals • Water • Soil and sediments

  6. Goals for Lab Activities • Types of materials subject to geochemical analysis. • Procedures and care in sampling. • Tools for sample preparation. • Avoiding contamination and common errors. • Analytical Instruments at UFBA: • ICP-AES • AAS • XRF • Microprobe

  7. Rock Sample Preparation: AC-01 • Lab Activity 01: What do geochemical analysis mean? • Research about geochemical analysis. • Websites • Earth Sciences Institute Library • At this point, we will discuss different kind geologic samples and ways of reporting geochemistry data. • Tables • Qualitative versus quantitative analyses • Major, minor and trace constituents • Chemical form

  8. Rock Sample Preparation: AC-01 • Lab Activity 01: What do geochemical analysis mean? • Students will discuss the analyses as measurements which provide quantitative information about the chemical composition of a sample and the importance of the results.

  9. Rock Sample Preparation: AC-02 • Lab Activity 02: Sampling • Sample Collection • Sample scheme: What to collect? • Geochemical investigation: How to proceed? • How many and how much: number and size of samples that I need • Which tools should be used? • Identification: Sample protocols • Field Activity • Neighborhood • Granite outcrops

  10. Rock Sample Preparation: AC-02 • Lab Activity 02: Sampling • Students must understand the importance of sampling and of a well planned field study and the importance of these steps in the geochemical analysis.

  11. Rock Sample Preparation: AC-03 • Lab Activity 03: Classic Sample Preparation • Granulometric Reduction • Polished slice • Rock powder • Mineral Concentration • Effects of these choices on the results

  12. Rock Sample Preparation: AC-03 • Sample Preparation Laboratory • 1 Hydraulic rock breaker • 3 Stell crushers • And also other tools… • Hammers • Sieves • Paper • Storage containers…

  13. Rock Sample Preparation: AC-03 • Sample Preparation Laboratory Reciprocating rock crusher • During these steps, students will: • Perform a typical procedure for preparing solid rock samples for analyses. • Discuss the media used to fabricate the equipments and risks of sample contamination.

  14. Rock Sample Preparation: AC-03 • Sample Preparation Laboratory • During these steps, students will see: • Representative fractions of sample to analyze • Sample storage • Possible sources of systematic errors

  15. Rock Sample Preparation: AC-03 • Mineral Concentration Laboratory • 2 Swing mills • Tungsten carbide pot • Agate pot • 1 Ball mill • Hardened steel balls • 1 Mineral Separator Table • 2 Frantz • Isodynamic magnetic separator • Heavy Liquids • Bromophorm Shatter Box

  16. Rock Sample Preparation: AC-03 • Mineral Concentration Laboratory • Other skills and goals for this activity are to concentrate mineral grains. Students will be taught that some geochemical procedures require a pure mineral sample and that a single mineral can be physically separated from the rock.

  17. Rock Sample Preparation: AC-03 • Lab Activity 03: Classic Sample Preparation • At the end of this step, students will be able to prepare their samples: • Thin sections • Powder • Mineral concentration • Now, they have samples ready for XRF (powder - solid disc) and Electron Microprobe analysis (thin section).

  18. Rock Sample Preparation: AC-04 • Lab Activity 04: Sample decomposition-solution • Here, following the physical preparation procedures, students will perform one or more stages of chemical processing. • The Lab environment • Safety in the geochemistry lab • Equipments • Glasses • Reagent purity and blanks

  19. Rock Sample Preparation: AC-04 • Lab Activity 04: Sample decomposition-solution • Acid digestion (open and closed systems) • Alkaline fusions

  20. Rock Sample Preparation: AC-04 • Lab Activity 04: Sample Decomposition-Solution • By the end of this activity, rock samples were converted into solution by a variety of procedures. • Therefore, we will emphasize the procedures producing solutions suitable for analysis by ICP-AES and AAS.

  21. Geochemical Analyses: AC-05 • Lab Activity 05: Running Samples • ICP-AES – AAS – XFR – Microprobe ICP-AES AAS

  22. Geochemical Analyses: AC-05 • Lab Activity 05: Running Samples • From the analytical viewpoint, students will perform the analyses using the instrumental methods available at the Federal University of Bahia. • Additionally they will be able to evaluate the differences in methods and results by comparison • Time to get an analysis • Precision and accuracy • Costs

  23. Student Evaluation • Students work in groups of four (3 groups per class) • For each activity a preliminary report • A seminar by the end of the term including: • A final write-up: first time they are expected to write up their own data • An oral presentation • Seminars allow comparison between the groups. Each one uses a distinct analytical method.

  24. Difficulties • Restricted funds • Time for assessment this discipline is insufficient • Absence of Technical Support • Labs off-routine • Students missing classes • References: • Scarcity • Native language: English

  25. Solutions • Limit field activities to nearby the University • Buy some books ourselves • Limiting the course reference to the ones available • Resuming and translating some texts and making them available to students • Emphasizing operating methods • Looking for working labs in other institutes

  26. Nice News… • The GeoChronos Net: • A Brazilian national Earth Sciences Project creating the Geochronological, Geodynamic and Environmental Net.

  27. The GeoChronos Net SHRIMP • University of São Paulo LA-ICP-MS • Federal University of Pará • University of Brasilia • Federal University of RS

  28. Acknwledgments 510

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