Workshops

WORKSHOPS

2021

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

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. The three-hour short course examined the theory and application of logratio analysis to geochemical data sets for the intention of extracting, visualising and interpreting structure.

Particular attention was 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.

The effect of measurement error including detection limits and structural zeros through interval censoring models and zero replacement approximations. It was also shown 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.

Further, it covered 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 were 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 were 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.

Workshop lectures

Note 1: The video recording of the Workshop can be downloaded from the following YouTube hyperlink:

The IUGS-CGGB Steering Committee acknowledges the assistance of Zacharenia Kypritidou (Department of Economic Geology-Geochemistry, Faculty of Geology and Geoenvironment National and Kapodestrian University of Athens) for the editing of the video recording.

Note 2: The pdf files of the lectures can be downloaded by clicking on the lecture titles.

Eric Grunsky: Extracting, visualising and interpreting structure in geochemical data through compositional data analysis (CoDA): Introduction

Eric Grunsky: Extracting, visualising and interpreting structure in geochemical data through compositional data analysis (CoDA): The Closure Problem

Eric Grunsky: Extracting, visualising and interpreting structure in geochemical data through compositional data analysis (CoDA): Missing Values and Imputation

Michael Greenacre: Compositional Data Analysis: Multivariate Analysis (Animation)

Michael Greenacre: Compositional Data Analysis: Graphical tools and software

Eric Grunsky: Extracting, visualising and interpreting structure in geochemical data through compositional data analysis (CoDA): Process Prediction and Predictive Mapping

PDF files of bibliographic references can be downloaded from the following pCloud hyperlink:

https://u.pcloud.link/publink/show?code=kZGIyNXZNWUT1cYOhlB8RXKmxFxahpjw4o9X

Important note: In case somebody has a browser problem in downloading the presentations from the direct hyperlinks, they can also be downloaded from the above pCloud hyperlink.

Short CVs of Tutors

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 http://www.multivariatestatistics.org. Personal web page: http://www.econ.upf.edu/~michael.

2016

Workshop on Global-scale Geochemical Mapping

On the occasion of the 35^th International Geological Congress and in conjunction with the 3^rd Arthur Darnley Symposium the Task Group (now Commission) organised a two-day Workshop (WK4) on Global-scale Geochemical Mapping, Saturday & Sunday, 27-28 August 2016, Cape Town, South Africa. The first day, 27 August 2016, was devoted to lectures, where the nineteen attendees were given a comprehensive overview of the methods, tools and techniques used in global geochemical baseline mapping, and the training-material was provided to all attendees.

The tutors were Xueqiu Wang (Executive Director of the UNESCO International Centre on Global-Scale Geochemistry and 2^nd Co-Chair of the Commission), and Alecos Demetriades (Chair of Sampling Committee and Treasurer of IUGS Commission):

Demetriades, A., 2016. Introduction to Applied Geochemistry.
Wang, X., 2016. Geochemical mapping: Principles and methodologies.
Wang, X., 2016. China Geochemical Baselines: Quantifying environmental changes.
Demetriades, A., 2016. Sampling at the continental scale.
Demetriades, A., 2016. FOREGS laboratory scheme.
Demetriades, A., 2016. FOREGS quality control scheme.
Wang, X., 2016. Regional geochemical mapping for mineral resources: Examples from China.
Demetriades, A., 2016. Geochemical data management and map generation.
Demetriades, A., 2016. Application of geochemical mapping for mineral exploration and environmental assessment.
Demetriades, A., 2016. Application of geochemical mapping for environmental assessment.

The second day, 28 August 2017, was devoted to the demonstration of sampling techniques used in global-scale geochemical mapping that are described in the FOREGS/EuroGeoSurveys ‘Geochemical Mapping Field Manual’ (Salminen & Tarvainen et al., 1998), which is available from URL: http://tupa.gtk.fi/julkaisu/opas/op_047.pdf. Suitable sampling sites for sampling floodplain, overbank and stream sediments, and residual soil were found in the Cape Farms area to the north of Cape Town.

2012

Seminar on CCOP Geochemical Mapping

The Task Group (now Commission) was co-sponsor to the Seminar on CCOP Geochemical Mapping held at the International Conference Hotel in Nanjing, China, 28-29 March 2012. Other sponsors were the China Geological Survey [http://old.cgs.gov.cn/] and the Coordinating Committee for Geoscience Programmes in East and Southeast Asia [CCOP - http://www.ccop.or.th/]. The seminar was organised by the Institute of Geophysical and Geochemical Exploration (CAGS) of China Geological Survey.

The seminar was attended by 100 participants from 13 CCOP countries (Cambodia, China, Indonesia, Japan, Korea, Lao PDR, Malaysia, Papua New Guinea, Philippeans, Singapore, Thailand, Timor-Leste, and Vietnam), Mongolia, Myanmar, and Brunei.

Lecturers included Dr. Wang Xueqiu (2^nd Co-chair of the Task Group), Dr. David B. Smith (1st Co-chair of the Task Group) and EurGeol. Alecos Demetriades (Chair of Sampling Committee and Treasurer).