Basic Principles of Mineral Exploration

The knowledge of elements associated with mineral deposits is one of the major requirements for geochemical exploration. Awareness about the economic size of deposits, the mineralogical form of the elements, the size of the elemental anomalies, etc are some of the other prerequisites.

The primary objective of geochemical exploration is to locate specific anomalies. The collected data should be statistically analysed by using computers.

Massive sulfide deposits for instance, contain some amounts of arsenic and gold, in addition to copper, lead, etc.

Calorimetry, atomic absorption spectro photometry, x- ray fluorescence, inductively couples plasma emission spectrometry, inductively coupled plasma mass spectrometry, etc are important methods applied in geochemical exploration.

Measurement of density, magnetism, resistivity, speed of sound, etc does provide information about concealed geology. Airborne geophysical surveys are the quickest and the cheapest ways to provide data about geology in wider areas. Cesium vapor magnetometer, and proton magnetometer are some of the most widely used instruments for magnetic surveys. Magnetic minerals produce easily detectable anomalies.

Metal sulfides and oxides are denser than their surrounding rocks. The gravity field at the surface of the earth is influenced slightly by density variations in the underlying rocks. This principle is the basis of gravity method.

Other geophysical methods are radio metrics, resistivity, spontaneous polarisation, induced polarisation, seismic refraction, reflection, bore hole geophysics.

The appearance of outcrops is variable and it depends on several factors. Some of the exploration techniques are, the location of out crops and detecting old workings. A copper deposit in Indonesia was recognised due to its green stained top. Similarly, iron deposits in Brazil were detected as they protruded through rain forests.

In addition to topographic anomalies, most of the outcropping mineral deposits do show variations or anomalies in their colors. For instance, black and white outcrops indicate the probable occurrence of manganese and zinc respectively. Similarly, red outcrops generally indicate the presence of mercury. In western Australia, weathered sulfides overlie base metal or gold deposits.

Aerial photographs provide reliable geological information in areas of clear and perfect exposures. They yield better information even if the outcrop exposure is about 5%.

After identifying the mineralized zones, and acquisition of land, the next steps in the exploration process are generation of targets for drilling, physical examinations. through pitting or trenching. Utmost care needs to be taken while planning drilling activities at all stages.

Pit or trench is ideal in regions of poor exposure of out crops to confirm the bed rock source of anomalies. The preparation of geological maps is one of the major processes of mineral exploration.