This document discusses geophysical prospecting methods used to study the structure of the earth's crust. It focuses on electrical resistivity methods, including resistivity profiling and resistivity sounding. Resistivity profiling uses constant electrode spacing to investigate lateral variations in soil resistivity along lines or parallel lines. Resistivity sounding varies electrode spacing with readings taken at the same point to determine resistivity variation with depth. Both methods can be used to distinguish soil layers and prospect for resources like ores, sand, and gravel.

1. SPONDAN BORA

2. INTRODUCTION
 Definition
Geophysical prospecting is the study of the structure
of the earth’s crust by physical methods for the
location and surveying of minerals and ores.
It is an integral part of geophysics.

3. OBJECTIVES
 To determine lithology of the area.
 To identify and locate exploitable reservoirs.
 To detect and delineate geothermal resources.
 Estimate geophysical properties of the geothermal
system.
 To determine the ground water conditions in the
regions.

4. METHODS
 Electrical Resistivity Method


Resistivity Profiling
Resistivity Sounding
 Seismic Refraction Method
 Gravity Geophysical Method
 Magnetic Method
 Geothermal Method

5. RESISTIVITY EXPLORATION

It is a sub surface exploration based on
the measurement of apparent
resistivity of subsurface materials.

7.  Electrode arrangement
• Four metal spikes driven into the ground along a
straight line serve as electrodes.
• While using direct current, the potential electrodes
must be of non-polarizable type.
• For ensuring proper contact with the ground a little
water is poured in the pits a few minutes before
measurement is made.

8. TYPES OF RESISTIVITY SURVEY
 Resistivity profiling
 Used when lateral variation of soil is to be investigated.
 Keeping the electrode spacing constant, readings are taken either
along a single line or along several parallel lines.
 It is use determine the changes in the resistivity characteristics of
materials from one location to another.
 It is used to distinguish between layers of different resistivity.
 Uses
o Prospecting for sand and gravel deposits.
o Prospecting for ore bodies.

9.  Resistivity sounding
 Used when variation with depth is required.
 Keeping the centre of the electrode spread fixed, the electrode
spacing is increased from one reading to the next.
 The sounding data may be plotted either on ordinary graph paper or
on a log-log graph paper.
 Uses
o Estimation of thickness of layer.
o Estimation of depth of sand gravel.
o Estimation of the variation of resistivity with depth.