Exploration Geochemistry – Basic Principles & Concepts
Soil geochemistry / selective extractions / soil gases © ioGlobal Pty Ltd
Exploration Geochemistry – Basic
Principles & Concepts
Soil Geochemistry
Dr. David Lawie
ioGlobal
www.ioglobal.net
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Soil Geochemistry: Principles and Concepts for Mineral Exploration, Exams of Geochemistry
An overview of soil geochemistry, focusing on its application in mineral exploration. It covers essential principles and concepts, including soil formation, sampling methods, and anomaly detection. The material is structured to guide exploration geologists in understanding how soil geochemistry can be effectively used to identify mineral deposits. Topics include considerations prior to sampling, soil development, anomaly formation, and methods of analysis. It also discusses sampling configurations, such as grid, profile, ridge, spur, and contour sampling, along with regional and semi-regional lag sampling techniques.
Typology: Exams
2025/2026
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Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
Exploration Geochemistry – Basic © ioGlobal Pty Ltd
Principles & Concepts^ Soil Geochemistry
Dr. David Lawie
ioGlobal www.ioglobal.net
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
Outline
Considerations prior to startingScale of samplingSoils and Soil DevelopmentSites for Hosting Anomalies Within SoilsSampling ProtocolsMethods of Analysis & ChallengesAnomaly FormationSome Final Comments
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
From CRC-LEME newsletter
Soil
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
Consideration Prior To Embarking on a Soil Survey^ What elements to analyse for (target, pathfinder, regolith control)Extraction and instrumental finishNature of the soil substrate – residual/transportedSoil profile development, what depth or horizon to sampleLocal variations due to topography, drainage, parent materialOptimum size of sample and whether to sieve or notSpatial configuration of the sampling (square or offset grid, tightspacing along widely spaced lines)QC – Need to monitor the accuracy and representivity of data © ioGlobal Pty Ltd
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
Prospect Scale - Grid
From Rose, Hawkes and Webb 1979
Prospect scale profilesampling to follow upgeophysical anomalies
10 ×
target width either side
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
Prospect Scale - Profiles^ Prospect scale profile sampling tofollow up egg, geophysical anomalies 10 ×
target width either side
Don’t Do This
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
Prospect Scale – Contour Sampling © ioGlobal Pty Ltd
Courtesy Simon Gatehouse
Good for initial reconnaissance oflarge area which has not beenpreviously sampled Relevant where have:
Strongly and deeply dissectedterrainDrainage divides have a poorchance of intersectingmineralisationLogistical difficulty: poor accessinto streams and ridgesbecause of terrain. Speed & Safety: contours often easier tonavigate than ridges in extremetopography
Upper most B horizon tomaximise dispersionCompositing rate variable
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
Semi Regional – Lag Sampling
Swept from the surfaceSieved to 2–6 mmData may be normalised to Fe contentSample grids at 500m by 500m have beenused
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
Regional Soil Data – As in soil
Geological Control
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
Regional Scale – Soils combined with
other surficial data
ZOOM 2
Levelled Cu Data – Nth America
ZOOM 1
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
Always Occur: © ioGlobal Pty Ltd
Weathering of parent materialAddition and partial decomposition of organic matterFormation of structural units
(Profile)
Depending on Environment
Leaching and acidificationClay eluviation (washing of clay from upper horizons)Podzolisation (transport of DOC and Fe & Al from upper h)Leaching of Si relative to Fe and AlReduction (ferric to ferrous)SalinisationErosion
Soil Formation
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
Soil development is initiated by the weathering of thebedrock and the incorporation of organic matter.These processes produce: © ioGlobal Pty Ltd
dissolved matter (bases, silicic acid, Fe, Al etc.); dispersed colloidal particles (e.g. silica, etc.): hydroxyls (Fe, Al, etc.): organic complexes; and, fine particulate matter (clay, clay-sized particles, etc.)
Profile Development
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
++
- ++ +++ + + O + + ++ A1 A2 B C R
Bedrock
Parent material derivedby weathering
Horizons of illuviation(accumulation ofmaterial bydepositionor precipitationfrom percolatingwater).
Some soils show intensely gleyed layers(Horizon G of hydromorphic soils; G mayappear directly beneath A), or layers ofcalcium carbonate (Horizon C
Ca^
of
Organic debris only partially decomposedDark-colored horizon, organic (humus)rich; mixed with mineral matter.Light- Brown to orange-brown horizons.Accumulation of clay minerals or of ironand organic matter; compact blocky,prismatic structure. calcareous soils).
colored horizon of maximum eluviation. Prominent in some soils, faint or absent inothers. Generally loose structure.
Idealised Soil Profile Horizons of maximumbiological activity, ofeluviation (removal ofmaterials suspendedor dissolved in water),or both.
The Solum (the genericsoil developedby soil-formingprocesses)
Modified from Rose, Hawkesand Webb 1979
Exploration Geochemistry – Basic Principles & ConceptsSoil geochemistry / selective extractions / soil gases
© ioGlobal Pty Ltd
Major Soil Groups of the World
FOOD AND AGRICULTURE ORGANISATION OF THE UNITED NATIONS