Page 28 - js expolaratıon

When an electrical current is applied to some materials a phenomenon known as “induced polarization
(IP)” occurs, with a charge being acquired. When the current is switched off the charge dissipates over
time, in a similar way that a car’s battery slowly goes flat if the car is not regularly used.
An induced polarization survey is usually run at the same time as a resistivity survey. The resistivity
method can be adapted to an induced polarization method with the addition of switches and changes to
the instrumentation. One of the main advantages of doing the two types of surveys together is to save
time as well as associated costs.
The collection of induced polarization data involves measuring the voltage at certain times after the
current is switched off, usually over a period of a few seconds. There are two switches in the layout. The
switch on the recorder part of the circuit, which measures the decaying voltage, is left open until the
moment the current is switched off.

The layout of electrodes and
instrumentation for an IP survey.

Different materials have different IP
responses. Disseminated or
dispersed sulphide grains within a
large body of rock, for example
porphyry and strataform
deposits usually have a strong IP
response. Small semi-massive
sulphide bodies generally have a
weak IP response. In gold
exploration, associated minerals
such as pyrite and arsenopyrite may be present in sufficient quantity in the neighboring rock to cause an
IP effect. Therefore gold mineralization may be indirectly detected using the IP method.

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