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Mineral Prospecting and Exploration

"Prospecting" is the systematic process of searching promising mineral targets identified during Reconnaissance. The objective is more definitive exploration for increasing geological confidence leading to further exploration.

The prospecting methods are broadly classified into two groups:

  • airborne prospecting methods, and
  • ground prospecting methods.

Airborne Prospecting Methods

The airborne prospecting methods include "remote sensing methods" in which photo geological study is undertaken, and "aerial geophysical prospecting methods". By these methods large areas are covered quickly and target areas are outlined for ground prospecting.

Ground Prospecting Methods

The ground prospecting methods are broadly classified into two groups:

  • surface methods, and
  • geophysical methods

In surface prospecting methods data are obtained by direct observation. Most of the information comes from natural exposures and artificial openings such as pitting, trenching, drilling, etc.

In the geophysical methods, the information is obtained indirectly by studying the physical properties of rocks.

Surface Prospecting Methods

  • Geological mapping.
  • Test pitting, trenching, and aditting.
  • Auguring and wash boring.
  • Drilling.

Geophysical methods

  • Gravity methods
  • Magnetic methods
  • Electrical methods
  • Seismic methods.

Geological Mapping

Before starting the prospecting work, a target area that can yield mineral deposits, is selected. Then its geological map is prepared on a suitable scale. Such a map shows topography, rock outcrops, and structural features such as dip, strike, folds, faults, etc. This sort of map gives an idea of the length and width of the deposit. It also serves as a base map for planning out a trenching, pitting or drilling programme.

Trenching

A "trench" is a narrow linear excavation which is made to expose ore bodies concealed under soil cover. The trenches may be 6 to 9 meter long, 1 to 1.5 meter wide, and 2 to 2.5 meter deep.

They are commonly dug across the strike of the ore body at intervals of 15 to 150 meters. The spacing of trenches depends upon the consistency of data. Prospecting by trenching is generally done when the ore outcrops are narrow and the soil cover is thin (about one meter). The trenching gives reliable information about the geology, structure, extension and grade variation of the ore body. This method has been adopted as a major prospecting method in may iron ore and bauxite deposits.

Pitting

The process of digging rectangular openings to penetrate soil cover to reach ore bodies concealed underneath is called "pitting". The common dimension of pits is 1.2 m x 1.2 m x 6 m. However pits may be sunk to a depth of about 10 meters beyond which they become very expensive. Pitting is a very useful method of prospecting those ore bodies which are flat or gently dipping and lying near the ground surface. For steeply dipping ore bodies and those having linear and narrow outcrops, pitting would not be favourable. The pattern of the layout of the pits may be regular or irregular. In a regular system pits are sunk in rows in grid or triangular pattern. Pitting is an important method of prospecting in many bauxite and iron ore deposits.

Aditting

The "adits" are horizontal openings which are dug in mountainous terrain to explore ore bodies. An adit many be driven across or along the strike of rocks. It should be dug in such a way so that at a later stage it could be used as an opening for exploiting the ore.

Auguring and Washboring

Auguring and washboring are commonly used for prospecting of flat and homogeneous deposits like clays which are concealed under a thin cover of soft and unconsolidated materials. "Auguring " is a simple method of putting down holes of about 2.5 cm in diameter to depths upto 6 meters in soft soils. An auger consists of a screw blade mounted on a steel pipe. It is screwed into the ground by turning on a T-pipe attached to the upper end.

In "washboring" a hole is dug in the soft ground by forcing a jet of water through the wash-pipe. The soil thus eroded comes to the surface a$ a suspension in water where it is examined and identified.

Drilling

Drilling is an important method of prospecting subsurface rocks and ore deposits. In drilling data are collected by direct penetration of subsurface rocks by drill holes. The samples of rocks are obtained in the form of cylindrical cores or rock fragments.

The drill holes provide the following informations.

  • Size, shape and morphology of the ore body.
  • Geological structures and number of lodes present.
  • Nature of the host rocks.
  • Composition and grade of the ore body.

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