Geochemical soil sampling is one of the most straight forward exploration techniques to gather information of a prospective area and can be performed with simple field equipment. A computer-based GIS-system is the key tool during the planning phase. The option to export data to a field GPS to track these points in the field afterwards is one big advantage of using the computer-based GIS-system. The exploration area is gridded on a regular, predefined spacing (raster), which is derived from the total amount of samples or from empirical values. Labeled field maps and GPS are necessary for orientation in the field. the field equipment itself consists of a metal shovel, a plastic shovel, sample labels and cotton bags as well as a notebook for field samples and a phot camera for documentation. The gathered samples are derived from the B-horizon, as most elements are enriched in this specific soil horizon. To guarantee a suitable quality control, field duplicates, standards and blank samples are added to the actual field samples for subsequent lab analysis.
Example of an element distribution map with nugget effect
After receiving and assuring the quality of the lab results, an internal quality control is carried out using the added duplicates, standards and blanks to inform the lab in case of significant differences. The first step is a descriptive analysis of the elements of interest and the creation of element distribution maps. Geostatistical methods such as IDP (inverse distance to power), kriging or a radial basic function are used to generate element distribution maps. These maps show the spatial distribution of the particular elements and provide a first hint for further exploration. Up to three elements can be displayed in one RGB (red-green-blue) map. This three element RGB plot is a first step to avoid nugget effects and maps with „spotted dogs“-areas. In general a multi-element approach can be of greater use then single element plots.
Example of a Principal Factor Analysis (PFA) for different elements from geochemical samples
Subsequently, an analysis of the correlation matrix and a principal component analysis (PCA) are performed to better understand the geochemical processes. Each component represents an individual geochemical process and can be plotted individually on a map. The spatial distribution of these principal components enhance the understanding of the local geochemical distributions and the ore forming processes.
Correlation plot of various elements from a geochemical sampling campaign
Linking soil geochemistry with topography, geological mapping, geophysics and other data enhances the resulting 3D model. This 3D model is used for visualization and further planning. Geological and geochemical areas or structural elements can be interpolated, displayed or exported for other software applications.
My name is Thomas Unterweissacher. I am a geologist and head of GEO Unterweissacher GmbH. Here we present our projects and interesting facts.
