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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 geological 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.