April 28, 2020
The geological information that supports activities such as construction and mining is largely obtained through drilling techniques that use a motorised unit to drill into the material being studied (soil or rock). This information contributes immensely to technical and financial feasibility studies for various projects in these sectors.
There are roughly two types of borehole. They are percussion and rotary. To summarise, the first type of drilling occurs when a weight, in free fall, falls on the equipment that is arranged under the rock in order to penetrate it.
The second type, rotary drilling, is when the rock is pierced by rotating movements that cut into it.
The drilling techniques are chosen according to various factors such as:
In general, for investigations aimed at civil works, percussive drilling methods are used, the most common of which is SPT (Standad Penetration Test), which makes it possible to obtain soil penetration resistance indices (ABNT NBR 6484 standard), determine the water level and the physical properties of the drilled material.
One of the main advantages of percussion mode is its low cost per metre drilled, which makes it the most widely used method in research and industrial testing, as it allows for the collection of larger volumes of samples. However, it does have some disadvantages, such as:
To meet the needs of mineral research, the use of rotary drilling methods is considered, the most common being diamond rotary drilling. This drilling method consists of using a set of equipment that works in a mechanised way, cutting the material using diamond cutters, preserving the integrity of the samples that are witnessed every 3 metres of drilling.
Although it is the most expensive method, it has the advantages of preserving the integrity of the drilled material, as well as its ability to pass through any rock material regardless of its degree of cohesion, the possibility of drilling inclined holes to better monitor structures and banding, and the ability to reach much greater depths, which can exceed 1000 metres.
Also widely used in mineral exploration, rotary percussive drilling has a market in the development of mines and the drilling of wells of all kinds, as well as for environmental analysis. It can be used for drilling more compact substrates and, compared to diamond rotary drilling, has lower prices per metre drilled, as well as good productivity.
Like other methods that use percussion, it has disadvantages such as:
A drilling campaign to study a mineral deposit should be planned in such a way as to optimise the representativeness of the mineralised body, reducing uncertainties in both geological modelling and mineral resource estimation.
Borehole cores are the main source of information for direct subsurface research of a mineral deposit, providing samples that promote geological knowledge in greater detail.
Boreholes in mineral deposits are also of great importance in the mining planning stage, helping mine teams to optimise their operations with information that will help, for example, in planning advances in mineralised fronts, predicting areas of high, medium and low grades for possible blending, areas destined for the deposition of waste rock and the establishment of mine infrastructure.