Geochemical sampling technique refers to the specific method, equipment, and procedural approach used to collect, process, and prepare a geochemical sample of a given medium for laboratory analysis. The selection of an appropriate sampling technique is critical to the integrity, representativeness, and scientific value of geochemical data, directly influencing the quality of interpretations made in mineral exploration and environmental programs across bauxite, gold, iron ore, and diamond mining.
Soil sampling techniques vary by depth and equipment used. Hand auger sampling using Jarrett or Ponder augers is commonly employed for shallow (<1 m) soil samples. Mechanical auger rigs extend sampling capability to several metres depth in residual soils and transported cover. Power augers with hollow-stem assemblies allow sample collection at specified intervals through thick regolith sequences, particularly important in bauxite exploration where the full laterite profile must be characterized from surface ferricrete through pisolite, mottled, pallid zone, and saprolite horizons.
In gold exploration under deep lateritic cover (e.g., Yilgarn Craton of Western Australia), specialized sampling techniques have been developed to penetrate thick transported overburden. Vacuum drilling (aircore, rotary air blast) provides cost-effective access to primary bedrock at depths of 30–100 metres, while deep soil gas sampling techniques detect volatilized gold or hydrocarbon anomalies leaking upward through cover.
Rock chip sampling is performed by systematic breaking of fresh or weathered rock outcrops using geological hammers, with care taken to collect representative channel or chip samples rather than selectively high-grade material. In iron ore mines, blast hole cuttings and reverse circulation (RC) drill chips are routinely sampled and analysed for multi-element geochemistry to support grade control block modeling.
Stream sediment sampling techniques require careful selection of the sediment fraction (typically <80 or <180 micron) from active alluvial channels, avoiding contaminated or anthropogenically disturbed materials. Water sampling techniques include filtered and unfiltered aliquots for major ion and trace element analysis, requiring pH, Eh, temperature, dissolved oxygen, and turbidity measurements at the time of collection to preserve hydrochemical integrity.
In diamond exploration, kimberlite indicator mineral (KIM) sampling from stream sediments uses heavy mineral concentration techniques including panning, mini-jig, or Knelson concentrator processing of large sample volumes (often 30–150 kg) to concentrate dense indicator minerals for stereomicroscope examination and electron microprobe analysis.