Transcript Sample Preparation for Geochemistry Analyses

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
 Chemistry for Geologists (first year)
 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
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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
Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA
Goals for Lab Activities
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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
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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
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
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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
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
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Sample Preparation Laboratory
• 1 Hydraulic rock breaker
• 3 Stell crushers
• And also other tools…
 Hammers
 Sieves
 Paper
 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:
 Perform a typical procedure
for preparing solid rock
samples for analyses.
 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:
 Representative fractions of sample to analyze
 Sample storage
 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
 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
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:
 Thin sections
 Powder
 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
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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
Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA
Rock Sample Preparation: AC-04
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Lab Activity 04: Sample decomposition-solution
Acid digestion (open and closed systems)
Alkaline fusions
Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA
Rock Sample Preparation: AC-04
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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
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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
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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
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:
 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.
Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA
Difficulties
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Restricted funds
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Absence of Technical Support
Time for assessment
insufficient
this
discipline
is
• Labs off-routine
 Students missing classes
 References:
• Scarcity
• Native language: English
Laboratório de Petrologia Aplicada à Pesquisa Mineral – CPGG – IGEO – UFBA
Solutions
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Limit field activities to nearby the University
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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 GeoChronos 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 GeoChronos 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