The choice of drilling and sampling method is fundamental in the evaluation of mineral deposit resources.

Sonic drilling is a relatively new method that finds its place in specific geological and exploration conditions. It is not a universal method but rather the only one in certain complex situations.

Where Sonic drilling finds its application in geological exploration:

- Sampling of overburden deposits, especially from layers of unconsolidated or weakly cemented rocks, such as soil, sand, or clay. This method allows for obtaining continuous, undamaged samples along the entire length of the borehole, enabling accurate interpretation of lithostratigraphic sedimentary sequences, particularly in modern deposits.

- Drilling and sampling of "capping" overburden deposits, such as calcretes, silcretes, duricrusts, basalt flows, or large boulders. This makes it valuable in situations where there is interlayering of soft and hard rocks of small thickness.

- Reconnaissance of alluvial deposits - suitable for exploring alluvial gold deposits, where representative samples are required due to loose sediments.

- Drilling of technogenic deposits, such as tailings and dumps, slag, construction waste dumps, and other industrial waste.

- Remote or hard-to-reach areas - despite Sonic drilling being relatively expensive compared to some other drilling methods, its mobility and efficiency in obtaining high-quality samples can justify the expenses, especially when there are significant logistical challenges or short timeframes for conducting research.

- Investigation of objects previously considered unpromising, impractical for exploration and development, such as tails or dumps of rocks with unsorted material and low contents.

Ultrasonic drilling machines use vibration (in the supersonic wavelength range) of the drill rod and drill bit to penetrate the rock mass. The driller aims to achieve maximum vibration (resonance) at the drill bit, where the surrounding particles either consolidate (in loose material) or break apart (in hard rock).
Sonic drilling can be conducted dry, but when passing through hard rocks and in deep boreholes, drilling fluids are required. The main disadvantage of this technique is its relatively high cost, approximately three times higher than the cost of RAB or one and a half times higher than the cost of RC. As the depth of the boreholes increases, the penetration rate decreases, and at depths greater than 30 meters, the RC method appears to be more economical. Despite this cost, sonic drilling can be ideal for remote areas where there are already high logistical costs, research seasons may be short, and excellent sample recovery rates are required. In some cases, drilling unconsolidated or unsorted deposits, such as tails and dumps of deposits, Sonic is the only way to obtain a high-quality and representative sample. Supersonic drilling is certainly not a solution for every project, but it has potential for projects that were previously considered impossible. SRK recognized the significant potential of sonic drilling as early as 2010. SRK Exploration specialists recommended using supersonic drilling rigs on a platinum mining project in alluvial deposits, which was experiencing difficulties reconciling exploration and mining results. Ultrasonic drilling was perfect for this project, providing excellent sample recovery in soft rock formations and the ability to drill through thick layers of alluvial boulder deposits. All boreholes were completed without failures, and the results showed metal contents three times higher than when using other drilling methods (such as auger and pneumatic percussion), allowing the company to maximize profit from the research results. Since then, SRK has used sonic drilling in various projects and has developed extensive experience and understanding of the advantages and disadvantages of this technique. SRK recommended using sonic drilling on a project in Romania to assess dumps containing high-quality slag and waste, as well as reinforced concrete and other industrial debris. For the evaluation of oxidized ore dump contents at the Almalyk copper-porphyry deposit, a sonic drilling program was recommended. It is known that gold and copper contents have industrial significance, but to develop the processing project, it is necessary to assess these resources. Traditional drilling methods did not yield positive results, and most drilling contractors terminated contracts after losing a large amount of drilling equipment despite relatively small amounts of drilling. Test drilling of a small number of boreholes allowed for local assessment of the content levels, collection of high-quality technological samples, and understanding the practical capabilities of the Sonic method. However, the lack of experience among drilling contractors prevented the full implementation of this methodology at the Almalyk cluster mines.

Picture 2: Dumps of the Almalyk deposit. Example of dumps with unsorted material of various sizes and composition
SRK has repeatedly recommended to major mining companies in Kazakhstan to use this drilling method for the evaluation of tailings and ore dumps. It is evident that there is a need for high-quality and reliable assessment of such assets by many companies. The implementation of this technology in Kazakhstan is crucial for the efficient management and extraction of maximum benefits from the exploited natural resources.

Zaure Kunanbayeva
Geological Consultant, SRK Consulting

Grigory Granovsky
Senior Geological Consultant, SRK Consulting