Workshop Title:  Extracting, visualising and interpreting structure in geochemical data through compositional data analysis (CoDA)


The workshop material will be found in the Workshop web page

Workshop Presenters:  Eric Grunsky, Michael Greenacre


Workshop Date:   Thursday, 18 November  2021                      


Workshop Description:


Geochemical data collected from government and exploration industry surveys are derived from un-modified (bedrock) to modified (weathered, transported) media that are comprised of minerals.  Minerals are ordered structures governed by atomic forces which impose “structure” (mineral stoichiometry) in the way the elements are associated.  Rocks, till, soils and other forms of sample media are mixtures of minerals and thus represent a complex array of structured mineral material.  In order to discover and interpret the structure in geochemical data, a range of statistical methods are required.


Because geochemical data are compositional, the issue of closure can be dealt with using logratios, as advocated by John Aitchison.  This three-hour short course will examine the theory and application of logratio analysis to geochemical data sets for the intention of extracting, visualising and interpreting structure.


Particular attention will be paid to the role of selecting ratios of minerals as well as ratios involving amalgamations of minerals, where these are either pre-specified or identified statistically.  The objective is to simplify the understanding of compositional data so that the geochemist can interpret the essential relationships between the minerals based on a few key ratios.


We will examine the effect of measurement error including detection limits and structural zeros through interval censoring models and zero replacement approximations. We will also show how amalgamation can greatly reduce the zeros problem in many cases and also how correspondence analysis can be especially useful with data sets with very many zeros.


We will also cover the situation where the objective is to understand differences between samples, after accounting for correlation across space or time.


Different methods of visualisation of a compositional data set will be highlighted, as a means of facilitating the interpretation and understanding of its structure.  Univariate, bivariate and multivariate graphical displays adapted to the compositional nature of the data will be presented.


All methods presented will be coded in R and demonstrated during the short course, and participants will have access to the R scripts for their own analyses.


Final Workshop Programme:


15:00-15:15   Introduction:  Compositional data for geologists (Eric Grunsky).

15:15-15:45   Compositional data analysis (CoDA):  Effects of closure (normalisation), subcompositional coherence, logratio transformations, role of amalgamations; introduction to Kimberlite data (Eric Grunsky).

15:45-16:00   Problem of data zeros: Detection limits; zero replacement (Eric Grunsky).

16:00-16:30   Multivariate analysis: Dimension reduction of logratios; using Principal Component Analysis (PCA); equivalence of analysing centred logratios (CLRs) and all pairwise logratios; variable selection to simplify analysis; use of amalgamations; use of additive logratios (ALRs); all applied to Kimberlite data (Michael Greenacre). 

16:30-16:45   Coffee break - Please stay on-line in order not to miss the start of the second session

16:45-17:15   Graphical tools to aid understanding of geochemical data: univariate, bivariate and multivariate displays; alternative use of chi-square distance and correspondence analysis, which can handle data zeros; software tools are indicated during the presentation (Michael Greenacre).

17:15-18:00   Predictive geochemical mapping in the geospatial domain; two case studies (Eric Grunsky).

18:00             Answers to questions and closing session with a surprise ....!!!

Eric Grunsky is a professional geoscientist (P.Geo. Ontario) whose career has included field mapping and applied research at: the Geological Survey of Canada, Ottawa, the Division of Exploration and Mining, CSIRO, Australia, the Alberta, British Columbia and Ontario provincial geological surveys. His research has focused on the application of multivariate statistical methods and spatial statistics applied to geochemical data. He was the recipient of the Krumbein Medal (2012) and the Felix Chayes Prize (2005) by the IAMG, in recognition for his work in applied geochemistry. Eric has published extensively in peer-reviewed journals and government reports. He has also presented numerous short courses for the interpretation of geochemical survey data. He served as Secretary General for the International Association for Mathematical Geosciences (IAMG) [2016-2020] and as a council member of the CoDa Association. He is a fellow of the Association of Applied Geochemists (AAG) and a member of the Geochemical Society. Eric is an Adjunct Professor at the University of Waterloo, Canada and a member of the Science Advisory Board for the pan-Canadian research initiative, Metal Earth.

Michael Greenacre is Professor of Statistics at the Universitat Pompeu Fabra, Barcelona. He specialises in applied multivariate analysis and has written six books on correspondence analysis and related methods, as well as four co-edited books on data visualisation.  Most recently he published the book Compositional Data Analysis in Practice. He has given short courses in 15 countries on all five continents, including an annual course for the last 15 years on multivariate data analysis for ecologists in Tromsø, Norway, and a workshop on compositional data analysis for biochemists at the Alfred Wegener Institute in Germany. Author of over 90 research publications in international journals, including several on compositional data analysis, some of his books are also published online at   Personal web page:





Note:  For details about events organised by CGGB refer to


Goldschmidt2021 - Lyon France 4-9 July 

"Geochemical mapping at all scales for all reasons". Special session organised by CGGB in Theme 12c



The Critical Minerals Forum

Americas - 12 February 2021 - The role of geological survey organizations to advance critical mineral research
Pre-recorded presentations live stream 11.00 - 13.00 EST
Live plenary and discussion 13.00 - 14.30 EST
The pre-recorded presentations for this session will be available online starting on 08 February.

Europe and Africa - 19 February 2021 - The past, present, and future directions of critical mineral research
Pre-recorded presentations live stream 11.00 - 13.00 CET
Live plenary and discussion 13.00 - 14.30 CET
The pre-recorded presentations for this session will be available online starting on 15 February.

Asia and Oceania - 26 February 2021 - Geoscience to support critical mineral discovery
Pre-recorded presentations live stream 11.00 - 13.00 AWST
Live plenary and discussion 13.00 - 14.30 AWST
The pre-recorded presentations for this session will be available online starting on 22 February.

For more information, including registration details, please visit:


UNESCO Lecture Series - Earth Materials for a Sustainable and Thriving Society

Organised in collaboration with IUGS and iCRAG 


Dates: Starting on 26 January 2021 and ending on 9 March 2021 (6 sessions in total on 26 Jan., 2 Feb., 9 Feb., 16 Feb., 2 Mar. & 9 Mar. 2021) 


The lectures will be delivered in webinar format by recognised global experts, who will frame their presentations in the context of the United Nations Sustainable Development Goals. The Series will boost knowledge on Earth materials and contribute to better informed local, regional, and international discussions. The lectures will be freely accessible and recordings will be made available online soon after presentation.


More information and registration at:



CoDA Association virtual conference, CoDAWork 2021

Thursday, 17th of June 2021, 14h-17h  (UTC+1). 
Online CoDa-Day is free of charge but it requires registration by filling out a form, at the latest by 31st of May 2021, at:
More information at:



The planned Session and Workshop that the IUGS Commission on Global Geochemical Baselines was organising on the occasion of the 36th International Geological Congress (Delhi, India) with the title: Challenges and Opportunities of Global-Scale Geochemical Mapping (4th Arthur Darnley Symposium) may still be organised as a virtual congress and workshop.

 2-9 August 2020 - POSTPONED TO AUGUST 2022 DUE TO THE COVID-19 PANDEMIC:  Conference theme: Environment, Health, GIS and Agriculture in the Big Data Era3 conferences combined:  (a) 5th International Symposium on Environment and Health; (b) 6th International Conference on Environmental Pollution and Health, and (c) 7th International Conference on Research Frontiers on Chalcogen Cycle Science and Technology The IUGS Commission on Global Geochemical Baselines and the EuroGeoSurveys Geochemistry Expert Group are organising a session with the title:  Geochemical mapping at all scales: evidence from soil, sediment, water and plants.  Session conveners:  Philippe Négrel and Alecos Demetriades.  Deadline for abstract submission will be announced in due course.  Galway, Ireland.