Geology. Козлова Е.П. - 28 стр.

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                         Prospecting for Mineral Resources

     Before a mineral deposit can be worked, that is, before it can be extracted from
the Earth for use by man, it must first be found. The search for economically useful
mineral deposits is called prospecting. Prospecting work includes three stages:
1) finding the signs of the mineral; 2) finding the deposit; 3) exploring the deposit. To
establish the quality and quantity of a mineral deposit, the type of country rock, etc.
means to prove it and this process is called proving. Prospecting and proving are only
two different processes of mining geological exploration, the latter includes drilling
and driving of openings.
     The aim of prospecting is to search for economically useful deposits, to provide
information on a preliminary estimation of the deposit and the costs of the
geologicals investigation to be made. It also indicates whether it is available to
continue the exploration or not.
     General indications of the possibility of exposing this or that mineral in a locality
can be obtained by study its general topographical relief, the type of ground and its
general natural conditions. Certain deposits are only found in a particular type of
ground. Coal seams, for example, are found in sedimentary formations mainly
consisting of sandstones and shales. Veins, on the other hand, are found in crystalline
(igneous) rocks, and the type of country rock usually determines the type of minerals.
     Prospecting methods may be subdivided into direct and indirect methods. Direct
methods include: 1) geologic and photography mapping; 2) the study of guides of
ores; 3) and the field examination of the surface, supplemented by panning,
trenching, drilling or sampling. Indirect methods are of two kinds: 1) geophysical
methods, which include magnetic, electromagnetic and radioactive surveys, both
from air and on the surface; electrical resistivity; gravimetric and seismic surveys on
the surface; radioactivity and temperature surveys in boreholes; and 2) geochemical
and botanical surveys.
     In geophysical prospecting, gravity, magnetic, electrical, seismic and radiometric
methods are used. Some minerals such as iron and copper are magnetic: first the
compass and later the more sensitive magnetometer have been used to detect them.
The gravimeter, an instrument that can detect minute changes in the Earth’s
gravitational field, can be used for detecting minerals that have densities different
from those of surrounding formations. Electrical method includes using of volmeter
and galvanometer for detecting an electrical potential of minerals. Seismic methods
utilize information gained from the transmission of natural (earthquake) and artificial
shock waves by different underground bodies. Ores of uranium and thorium give off
radiation that can be detected by suitable instruments such as the Geiger counter.
     Geochemical and botanical methods of prospecting involve chemical analysis for
traces of metals, systematic measurement of chemically influenced properties.
Samples of soil, water, rocks, vegetation and humus, gases and air, microorganisms
are collected and tested so that unusual concentrations can be identified.

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