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An Exploration Drilling is a process of mineral exploration in the mining industry through extraction of rock quantity to probe the contents of known ore deposits and potential sites by withdrawing a small diameter core or chip of rock from the orebody so that geologists can analyse the core/chip by chemical assaying and conduct petrologic, structural and mineralogical studies of the rock. Mineral exploration companies are often broken down into two categories namely; greenfield and brownfield.

Greenfield Exploration refers to unexplored areas, where mineral deposits are not already known to exist which can also be subdivided into grassroot and advanced projects while Brownfield Exploration, also known as near-mine exploration, refers to areas where mineral deposits were previously discovered. Exploration companies search globally for mineral deposits that can be economically mined and processed and mineral exploration is made up of a variety of different activities and techniques of which drilling is one of them, that are used to find a potential discovery which eventually may one day become an operating mine.

The goal of Mineral Exploration Techniques

Many different types of exploration techniques are used in conjunction in order to get enough information to accurately define a mineral deposit. Once enough high-quality geological data has been gathered from exploration activities, a project can be analyzed for economic feasibility.

Management will use this data to make a decision on whether to continue exploration, establish or update a mineral resource estimate, proceed with mine feasibility studies in order to reach production, or pursue other strategic initiatives with the property. The data obtained and used must pass through QAQC (Quality Assurance Quality Control) and thereafter highly validated to give well reliable and informed output for successful mining. Going from a previously unexplored piece of land (“greenfield exploration”) to a well-defined mineral deposit can take years and years of work and huge sums of money can be pumped in though in the first instance the chances of success are very slim such that an exploration company can attempt to withdraw. An example of our own KanyikaNiobium Project and Mkango Resources Songwe Hill Rare Earth Project are living testimonies of how long they carried out their exploration activities. However, the Kayelekera Uranium Project did not take that much years to commence mining since there was already exploration data that existed from the 1980s and was done previously by CEGB (Central Electricity Generating Board) of UK before Balmain Resources took over and was granted an EPL in 1997/98 and later entered into agreement with Paladin Resources to have 90% interest and the remaining 10% equity stake in the project was granted in 2005.

There are many techniques that may be utilized during mineral exploration programs, depending on the mineral deposit type and stage of exploration that is being pursued – as well as the location and budget of the program of which among them is Drilling.

Drilling Techniques

Drilling is the most expensive method of exploration and typically occurs in the later stages of exploration after other methods have already identified a potential deposit     (anomaly). As drilling is an expensive undertaking, detailed study of the area must be made before starting the project. Core logging forms an important aspect of an exploration geologist job and an important stage in the follow up work to an exploration target. There are many different types of drilling methods and all have their place in the universe. Drilling programs are used to collect rock samples at greater depths than surface methods allow. Among others, this page will highlight some of the drilling methods used.

(a) Diamond Drilling (DD)

This method produces a continuous core of rock (in theory) and allows a solid piece of rock core to be collected in such a way that an interval of core allows for much more data to be accurately interpreted.  It consists basically of a hammer unit which is driven by compressed air. This hammer unit imparts a series of short, rapid, blows to the drill steel or rods and at the same time slowly rotates them and sometimes known as down-the-hole hammer and as the name implies, the hammer unit is lowered down the hole at the end of the rods and the diamond drill bit on the end of the hammer unit consists of a large number of chisel ends. Drilled samples are then assayed, and the results will help build a model of the entire deposit. This type of drilling can eventually lead to the entire resource being defined within the boundaries of a chosen cut-off grade but based on the recovery percentage of the core.

(b) Reverse Circulation (RC)

 Reverse circulation drilling produces rock chips which can be sampled under the assumption that they come to the surface in the order in which they were produced and this method returns rock samples in the form of chips that allows sampling but at greater depths. Air is blown down the outside of the drill steel (between it and the wall of rock) and the air and rock chips are carried to the surface on the inside of the drill steel. As the air exits the drill with great blows of dust the rock chips are captured and put in bags for subsequent assaying. In this instance a very large truck is loaded with a tower, drill head, compressor and motor is used. The drill bit is usually of a tri-cone construction (3 cone shaped bits) and a bunch of air blown into the hole to capture the rock chips. This type of drilling is usually a fraction of the cost of diamond drilling but there is controversy surrounding the validity of the samples that are obtained and the method limits the amount of information that can be derived from the sample. Unfortunately, there is no way of knowing what the recovery of chips is and usually it is must be over 100% because the wall of the drill hole caves back a bit and extra rock chips are created and prone to contamination.

(c) Auger Drilling

This method uses an auger as a drilling device. It usually includes a rotating screw   helical blade called a “flighting” to act as a conveyor so as to remove the drilled-out material. The rotation of the blade causes the material to move out of the hole being drilled. Auger drills are used for semi-consolidated soils and produce a core (hollow core) or loose samples (solid core)

(d) Churn drilling

A drill whose cutting action is achieved by raising and dropping a chisel bit. Under this operation, drilling is performed by a heavy string of tools tipped with a blunt-edge chisel bit suspended from a flexible cable, to which a reciprocating motion is imparted by its suspension from an oscillating beam thereby causing the bit to be raised and dropped. It is used to sample gravels by pounding a steel pipe into the ground and then pulling out the material trapped inside the pipe. In churn (cable tool drilling)- heavy chisel like steel is repeatedly jerked up and down by a cable wire.

(e) Sonic Drilling

Cutting or shaping materials with an abrasive slurry driven by a reciprocating tool attached to an audio-frequency electromechanical transducer and vibrating at sonic frequency. This method uses sound waves to consolidate wet deposits like tailings ponds and capture the soils in a tube.

So far, the most common methods which are used in modern day exploration drilling are diamond and reverse circulation drilling methods. The other types of drilling are for fairly specialized cases and because a solid sample is obtained directly can be quite accurate. Of course, it often happens that the sample won’t come out of the pipe sometimes wholly as anticipated by the geologist. The mining industry lives and dies on the accuracy of the samples taken. And the most important samples are taken by drilling so it is important to understand the drilling process ensuring that good questions can be asked. As with anything in life, it is best to find out a bit about the company doing the drilling to       decide as to the validity of the sampling results.  Now that there is a lot of data collected and some interesting mineralization has been discovered, it is time to try and represent the data accurately in space. So the concept of a geological model is produced.

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