geochemical surveys

• Geochemical surveys determine what might be there. 
• Used in mineral exploration. 
• Elements from the ore body are dispersed by glaciers/rivers to weathering and erosion, dispersed elements can be traced back to their source. Used when original deposits are covered. 
• Stage 1 - orientation survey to find the geological setting of ore body, establish a background concentration of element. 
• Stage 2 - reconnaissance survey over a large area. 
• Stage 3 - detailed survey to focus on area of interest, taking readings at close distances. 
• Geochemical methods:

  • River water analysis 
  • Rivers sediment analysis 
  • Vegetation surveys 
  • Soil analysis 
• Stream water analysis from groundwater because it can dissolve elements from an ore body and transport them distance before emerging in streams. Samples can be taken at intervals then analysed and plotted onto a map. Measures small concentrations of metal and seasonal changes in discharge distort readings. 
• Streams sample soils of drainage basins, sediments samples are taken and analysed. Reduction in concentration downstream due to runoff from surface and tributaries. Sample each tributary upstream of confluence so anomalies do not become diluted. Results plotted as symbols on maps, areas of importance become apparent. 
• Panning is sediment and water swilled in  pan, the higher density minerals settle at the bottom of the pan. 
• Biogeochemical surveys - collection of plant matter, burning to produce ash and the analysis for metal concentrations - higher levels linked to mineralisation. 
• Geobotanical surveys involve the recognition of a particular plant species that grow in certain soils rich in metals. 
• Stressed vegetation can occur due to toxic minerals in the soil, either due to a lack or excess of a minerals. 
• Soil analysis - not all terrains are suitable for water sampling - arid areas. Soils are sampled at intervals at a predetermined depth. Closest survey spacing gives the most detail but is expensive. Highest concentration is above ore body but not always, secondary dispersion occurs due to soil creep or groundwater flow and river sedimentation or glacial transport.