Download MINERAL PROSPECTING

MINERAL PROSPECTING
Mineral exploration is based on scientific understanding and the use of modern equipment.
It involves geological mapping, geophysical and geochemical techniques and satellite
imagery. The results of all these then have to be combined.
GEOLOGICAL MAPPING
A geological map is a pictorial record of surface or underground geological data. This is
the first step in exploration as for example, certain types of minerals are only found with
certain types of rocks, e.g. kimberlites are host rocks for diamonds and nickel is
associated with basic or ultrabasic rocks.
Aerial photos are often used as the basis for mapping as they show topography,
vegetation and distribution of rock outcrop.
The ultimate purpose of the map is to select the most likely areas for minerals so that more
expensive techniques can be employed where they are most likely to be successful.
GEOPHYSICAL TECHNIQUES
TYPE OF SURVEY
Seismic Methods
(Reflection and refraction)


Magnetic Methods
(magnetometer survey)
PARTICULAR
APPLICATIONS
Reflection surveys –
particularly useful for
petroleum exploration
and the search for traps
such as anticlines.
Refraction surveys –
useful for site
investigations for civil
engineering where
thickness of layers is
important.

Identifying magnetic iron
ores e.g. magnetite,
ilminite and pyrrhotite.

Identifying salt domes,
so useful in petroleum
exploration
ADVANTAGES/
LIMITATIONS
Gravity Methods
(gravimeter survey)
Identifying underlying rocks
which are more or less
dense than the surrounding
rocks




Electrical Methods
(resistivity survey) Most
rocks are poor conductors
and have high resistivity
unless they contain
groundwater or metallic
sulphide

Electromagnetic Method
(electromagnetic survey)



Identification of dense
sulphides.
Identification of dense
igneous rocks such as
gabbro.
Identification of less
dense bodies such as
salt domes.
Identification of fault
structures which bring
rocks of different density
together(useful for ores
or petroleum).
Studies of water table
depth.
Identifying metallic
sulphide deposits.
Determining thickness of
cover of loose sediments
(sand and gravel ) on
bedrock.
Location of ore mineral
deposits, particularly
metallic sulphide
deposits which are better
conductors
GEOPHYSICAL METHODS carried out in boreholes include measuring the hole diameter,
gamma ray logging, resistivity logging, and density logging (see previous notes)
GEOCHEMICAL SURVEYS
Samples are collected,
analysed in the lab and
interpreted
REMOTE SENSING
Radiation is absorbed and
reflected in different ways by
different materials. This
emitted and reflected
radiation may be monitored,
analysed and displayed
visually
FOSSIL IDENTIFICATION
Follow up after ground
based mapping, or from
boreholes
Stream and soil samples
can be tested to check the
deviation from normal
concentrations of an
element in an area. This
shows anomalies e.g. for
Cu, Fe. Pb,.
Other substances may be
pathfinders e.g. arsenic is a
clue to the presence of
sulphides.
Satellite pictures of a granite
intrusion – the granite shows
up as a different colour –
minerals such as pegmatites
may be nearby.
Hydrothermal veins and
metasomatic deposits are
associated with large
plutons
Oil and gas exploration –
microfossil may be important
in correlating rocks in
boreholes or identifying
reservoir rocks.
Coal exploration –
microfossils used to
correlate rocks.
Macrofossils (goniatites)
used to correlate age of
rocks