Malaysia is awarded with over 33 different mineral types, comprising metallic, non-metallic and energy minerals, worth several billion dollars in economic potential. Mineral exploration is one of profitable industry in this country.
In 2016, the value of non-metallic mineral produced is estimated at RM5.05 billion, whilst the value of metallic and energy minerals produced is estimated at RM1.07 billion and RM0.16 billion, respectively.
The metallic mineral sub-sector produces minerals such as gold, tin, iron-ore, bauxite, ilmenite and other associated minerals. This associated minerals are by-products of tin and gold mining such as silver, zircon, monazite, rutile and struverite.
The non-metallic or industrial mineral sub-sector produce sand, silica, limestone, clays, kaolin, gravel, aggregates, feldspar and mica. Only coal is produced in the energy mineral sub-sector.
Geophysics in mineral exploration involves quantitative measurements of response or contrast in properties between rocks, structures, stratigraphy and mineralization. Specifically, the variations are either on position of objects or function of time.
Interpretation highlights signal “anomaly” of mineral-related features under investigation. Anomaly is significant departure from normal pattern of background values. It must be explained geologically indicating possible occurrences of mineral deposits.
Moreover, geophysical technique is quick and cost-effective path to identify subsurface objects and prioritize drilling targets.
Which Geophysical Method?
Induced polarization (IP) is a geophysical method widely employed in mineral exploration especially in base-metals (metallic minerals) and gold exploration.
The primary advantage of the IP method is its capability under favorable conditions to detect the presence of even small amounts of metallic minerals.
The magnitude of IP response generally increases with the amount of mineralization up to the point where massive sulphide bodies can give large effects.
In addition, induced polarization is a particularly useful method in areas of disseminated mineralization where other geophysical exploration methods are much less effective.
Ground magnetic survey also a geophysical technique suitable in mineral exploration. Although ground magnetic survey measure rock magnetism, they also can help find non-magnetic mineral such as gold.
Ground magnetic survey popular in finding iron ore deposit.
How These Geophysical Techniques Could Help?
Theoretically, during the time of the original current flow, presumably some energy storage took place in the material. Laboratory studies of polarization in various rock types have established that chemical energy is the most important. The chemical energy storage is the result of
a) variations in the mobility of ions in fluids throughout the rock structure.
b) variations between ionic and electronic conductivity where metallic minerals are present.
The effect with presence of metallic minerals is known as electrode polarization or over-voltage. It is generally larger in magnitude than the background IP.
Thus, the presence of metallic minerals is traceable by using IP technique.
Furthermore, after field data acquisition, the collected IP data (measurement) will be undergo inversion process to image the subsurface.
The product or result produced by the inversion process are present in colored contour profile. The profile showing the variations in term of chargeability of the ground to depth.
From here, experienced geophysicist will interpret the prospect area or zone.
Meanwhile, ground magnetic survey measure the magnitude and orientation of the Earth’s magnetic field.
Magnetic field at Earth’s surface depends on field generated in Earth’s core, magnetic mineral content of surface materials and remnant magnetization of surface rocks.
These features produce anomalies in magnetic field then to be used for interpretation.
The most common magnetic minerals found in ground magnetic survey are iron sulphide, pyrrhotite and magnetite. Magnetite when found with sufficient purity and quantity may become an iron ore deposit.
Pyrrhotite often associated with other minerals such as pyrite, another iron sulphide mineral which may contain gold.
Back in the office, geophysicist will processes the collected data using specialized software. Corrections and filters are used to improve the data to reveal precise features and structures.
