Teaching Geochemistry Workshop Rock Samples and Geochemical Analysis

Teaching Geochemistry Workshop 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

Geochemistry at the Federal University of Bahia - Brazil Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Geochemistry at the Federal University of Bahia (UFBA) - Brazil § Brief Description • 2 Disciplines of Geochemistry ü Chemistry for Geologists (first year) ü Geochemistry (fourth year) § For who? • Undergraduate students of Geology § Background: • Introductory Geology Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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 Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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: ü Rocks and minerals ü Water ü Soil and sediments Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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 Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Rock Sample Preparation: AC-01 § Lab Activity 01: What do geochemical analysis mean? • Research about geochemical analysis. ü Websites ü Earth Sciences Institute Library • At this point, we will discuss different kind geologic samples and ways of reporting geochemistry data. ü Tables ü Qualitative versus quantitative analyses ü Major, minor and trace constituents ü Chemical form Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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. Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Rock Sample Preparation: AC-02 § Lab Activity 02: Sampling • Sample Collection ü Sample scheme: What to collect? ü Geochemical investigation: How to proceed? ü How many and how much: number and size of samples that I need ü Which tools should be used? ü Identification: Sample protocols • Field Activity ü Neighborhood ü Granite outcrops Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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. Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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 Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Rock Sample Preparation: AC-03 § Sample Preparation Laboratory • 1 Hydraulic rock breaker • 3 Stell crushers • And also other tools… ü Hammers ü Sieves ü Paper ü Storage containers… Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Rock Sample Preparation: AC-03 § Sample Preparation Laboratory Reciprocating rock crusher • During these steps, students will: ü Perform a typical procedure for preparing solid rock samples for analyses. ü Discuss the media used to fabricate the equipments and risks of sample contamination. Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Rock Sample Preparation: AC-03 § Sample Preparation Laboratory • During these steps, students will see: ü Representative fractions of sample to analyze ü Sample storage ü Possible sources of systematic errors Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Rock Sample Preparation: AC-03 § Mineral Concentration Laboratory • 2 Swing mills ü Tungsten carbide pot ü Agate pot • 1 Ball mill ü Hardened steel balls • 1 Mineral Separator Table • 2 Frantz ü Isodynamic magnetic separator • Heavy Liquids ü Bromophorm Shatter Box Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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. Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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: ü Thin sections ü Powder ü Mineral concentration • Now, they have samples ready for XRF (powder - solid disc) and Electron Microprobe analysis (thin section). Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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 ü Safety in the geochemistry lab ü Equipments ü Glasses ü Reagent purity and blanks Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Rock Sample Preparation: AC-04 § Lab Activity 04: Sample decomposition-solution üAcid digestion (open and closed systems) üAlkaline fusions Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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. Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Geochemical Analyses: AC-05 § Lab Activity 05: Running Samples • ICP-AES – AAS – XFR – Microprobe ICP-AES AAS Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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 ü Time to get an analysis ü Precision and accuracy ü Costs Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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: ü A final write-up: first time they are expected to write up their own data ü An oral presentation ü Seminars allow comparison between the groups. Each one uses a distinct analytical method. Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

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 Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Solutions § § Limit field activities to nearby the University § § Emphasizing operating methods Buy some books ourselves Limiting the course reference to the ones available Resuming and translating some texts and making them available to students Looking for working labs in other institutes Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Nice News… § The Geo. Chronos Net: • A Brazilian national Earth Sciences Project creating the Geochronological, Geodynamic and Environmental Net. Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

The Geo. Chronos Net SHRIMP • University of São Paulo LA-ICP-MS • Federal University of Pará • University of Brasilia • Federal University of RS Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA

Ackn wledgments 510 Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA