Projects per year

### Abstract

Single component geochemical maps are the most basic representation of spatial elemental distributions and commonly used in environmental and exploration geochemistry. However, the compositional nature of geochemical data imposes several limitations on how the data should be presented. The problems relate to the constant sum problem (closure), and the inherently multivariate relative information conveyed by compositional data. Well known is, for instance, the tendency of all heavy metals to show lower values in soils with significant contributions of diluting elements (e.g., the quartz dilution effect); or the contrary effect, apparent enrichment in many elements due to removal of potassium during weathering. The validity of classical single component maps is thus investigated, and reasonable alternatives that honour the compositional character of geochemical concentrations are presented. The first recommended such method relies on knowledge-driven log-ratios, chosen to highlight certain geochemical relations or to filter known artefacts (e.g. dilution with SiO2 or volatiles). This is similar to the classical normalisation approach to a single element. The second approach uses the (so called) log-contrasts, that employ suitable statistical methods (such as classification techniques, regression analysis, principal component analysis, clustering of variables, etc.) to extract potentially interesting geochemical summaries. The caution from this work is that if a compositional approach is not used, it becomes difficult to guarantee that any identified pattern, trend or anomaly is not an artefact of the constant sum constraint. In summary the authors recommend a chain of enquiry that involves searching for the appropriate statistical method that can answer the required geological or geochemical question whilst maintaining the integrity of the compositional nature of the data. The required log-ratio transformations should be applied followed by the chosen statistical method. Interpreting the results may require a closer working relationship between statisticians, data analysts and geochemists.

Original language | English |
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Pages (from-to) | 16-28 |

Number of pages | 13 |

Journal | Journal of Geochemical Exploration |

Volume | 162 |

DOIs | |

Publication status | Published - 01 Mar 2016 |

Event | GeoMap Workshop - Olomouc, Czech Republic Duration: 17 Jun 2014 → 20 Jun 2014 |

### Keywords

- soil geochemistry
- compositional data analysis, log-ratios, mapping

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## Projects

- 1 Active

## Activities

## Using compositional geochemical ground survey data as predictors for geogenic radon potential

Jennifer McKinley (Speaker)

09 Nov 2015 → 12 Nov 2015

Activity: Consultancy types › Contribution to the work of national or international committees and working groups

## Invited keynote lecture presentation: Investigating potentially harmful trace elements in soils and their bioaccessibility: a compositional data analysis approach at the first GeoMap Workshop (held in Olomouc, Czech Republic, 17-20 June 2014)

Jennifer McKinley (Speaker)

17 Jun 2014 → 20 Jun 2014

Activity: Talk or presentation types › Invited talk

## Cite this

McKinley, J. M., Hron, K., Grunsky, E. C., Reimann, C., de Caritat, P., Filzmoser, P., van den Boogaart, K. G., & Tolosana-Delgado, R. (2016). The single component geochemical map: Fact or fiction?

*Journal of Geochemical Exploration*,*162*, 16-28. https://doi.org/10.1016/j.gexplo.2015.12.005