Induced Polarization (IP Induced Polarization (IP ), background ), background • • IP phenomena have been noted by Conrad Schlumberger in IP phenomena have been noted by Conrad Schlumberger in 1912, i.e. earth materials discharge after applied current is 1912, i.e. earth materials discharge after applied current is switched off switched off → → capacitance effect or chargeability capacitance effect or chargeability • • Electrically conductive materials exhibit delayed voltage Electrically conductive materials exhibit delayed voltage response or over response or over - - voltage effect voltage effect • • IP parameters response to disseminated mineral grains (rather IP parameters response to disseminated mineral grains (rather than massive ore) than massive ore) • • Equipment used in IP measurement is similar to (but much Equipment used in IP measurement is similar to (but much more elaborate than) that employed in more elaborate than) that employed in resistivity resistivity work work → → IP and IP and resistivity resistivity surveys are usually conducted at the surveys are usually conducted at the same time same time

Induced Polarization (IP)

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Induced Polarization (IPInduced Polarization (IP), background), background

•• IP phenomena have been noted by Conrad Schlumberger in IP phenomena have been noted by Conrad Schlumberger in 1912, i.e. earth materials discharge after applied current is 1912, i.e. earth materials discharge after applied current is switched offswitched off

→→ capacitance effect or chargeabilitycapacitance effect or chargeability

•• Electrically conductive materials exhibit delayed voltage Electrically conductive materials exhibit delayed voltage response or overresponse or over--voltage effectvoltage effect

•• IP parameters response to disseminated mineral grains (rather IP parameters response to disseminated mineral grains (rather than massive ore)than massive ore)

•• Equipment used in IP measurement is similar to (but much Equipment used in IP measurement is similar to (but much more elaborate than) that employed in more elaborate than) that employed in resistivityresistivity workwork

→→ IP and IP and resistivityresistivity surveys are usually conducted at the surveys are usually conducted at the same timesame time

Induced Polarization (IPInduced Polarization (IP), origin), origin

•• Exact cause of IP phenomena are still unclear, but two main Exact cause of IP phenomena are still unclear, but two main mechanisms of electrochemical process are reasonably mechanisms of electrochemical process are reasonably understoodunderstood

→→ grain or electrode polarizationgrain or electrode polarization

→→ membrane polarizationmembrane polarization

•• Chargeability is measured by sending a pulsating current to the Chargeability is measured by sending a pulsating current to the ground that creates an exchange of ions between mineral ground that creates an exchange of ions between mineral grains and surrounding pore fluids.grains and surrounding pore fluids. When the current is When the current is stopped, the voltage drops and then gradually dissipates.stopped, the voltage drops and then gradually dissipates.

•• Chargeability is related to the ratio of the Chargeability is related to the ratio of the overvoltageovervoltage to the to the applied voltage, and the lapse time it takes the ground to applied voltage, and the lapse time it takes the ground to ““unchargeuncharge”” after the transmitter is cut off.after the transmitter is cut off.