What is SP?

SP can stand for Self Potential, Spontaneous Potential or Streaming Potential. Whichever is used, it is referring to a passive investigation method that records the natural voltages in the ground, without injecting any current from an instrument.  

The SP phenomenon is an effect of the movement of ions through the subsurface. This can occur around massive sulfide ore bodies, for instance, or due to the flow (streaming) of water in porous materials, such as till, affecting the concentration of electrolytes (e.g. soluble salts, acids and bases) in the ground. The presence of clay can also influence the measured SP values due to the inherent electrical charge associated with clay particles.

SP effects are normally measured in mV, and considered a bulk measurement around the measurement location – i.e. they have no depth associated with them. Results are normally analyzed in relative terms, looking for regions of significant change, and using the pattern of change as an indicator of what may lie beneath.  

 An SP measurement requires just two electrodes (i.e. a pair of potential probes) but they must be made of non-polarizing material as the insertion of metal electrodes into the ground can create greater voltages than the natural SP your are trying to record. The electrodes are then attached to your regular resistivity equipment, such as a Terrameter LS 2.

SP is most commonly used for identifying large sulfide ore bodies but also has applications in identifying water seepage (for instance in earth dams), pollution plumes and clay areas. 


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