Alexander Grigorievich, as far as we know your company conducted drilling on a number of tailing dumps in Kazakhstan. Could you tell us about the main objective of this project?

We performed drilling in order to obtain objective information on the content of commercial components in tailings and their distribution within the tailing dump, as well as for the collection of representative technological samples for development of operational procedures for processing. The fact is that because of appearance of new technologies today there is a possibility to reprocess mature tailings with a low content of commercial components. This is important not only for our company, because it is not a secret that the mineral resource base of existing enterprises is being exhausted. Therefore, the involvement in processing of mature tailings with a low content of commercial components allows us to obtain additional end products.

What scope of work was performed by your company and what type of drilling did you use?

We performed evaluation of three tailing dumps. The total scope of drilling amounted to about three thousand meters. The RC drilling technology (RC means “reverse circulation”) was used. This method was chosen by us not by chance, as tailings are special loose materials, somewhere very moistened. That is why use of any other method of drilling would not give us a possibility to get objective information. Due to this technology, we are able to obtain the material that characterizes the specific horizon of a tailing dump.

What percentage of the material is considered to be representative for the proper evaluation of the tailings?

As RC drilling technology is used in geological prospecting and exploration not for a long period of time, this percentage is not specified in any regulatory documents yet. However, by analogy with the core drilling 75–80% of material yield shall be considered sufficient.

What challenges did you face and what solutions were found?

The tailing dumps, as a rule, are watered and the biggest challenge is to perform drilling for obtaining objective information for a particular network. In this case, it is considered to be the most appropriate to perform works in winter, when the upper part of the tailing dumps is frozen. Thus, on one of the tailing dumps we could not come to the site and we had to perform drilling from the dam. This can lead to non-objective evaluation. Therefore, we plan to perform further works on the tailing dumps at a time when their upper part is frozen, as it allows performing works safely. Naturally, this leads to significant inconveniences as the separation of drilled material and collection of samples at sub-zero temperatures are complicated. For example, we have a task to evaluate one of the tailing dumps in eastern Kazakhstan. The dams are made there by filling the soil on the impounded tailings, i.e. inside the tailing dumps. If we drill from the dam, we will cover about 15% of the tailing dump area and even less in terms of its volume. Naturally, such indicators make it impossible to obtain an objective picture.

What results were achieved and how did the findings influence the further work?

The end result of tailing dump evaluation is development of operational procedures for tailings processing, which describes the technology of extraction of metals and answers the question of economic feasibility of their processing. The work of geologists in this chain is to conduct drilling, collect samples and analyse the standard samples. The results obtained for standard samples make it possible to determine the volume of tailings, reserves and content of commercial components. Technological samples, the amount of which is calculated in tons, are transferred to an organization that is developing a process procedure. The development of process procedure is supervised by engineers of ore dressing. Therefore, we know nothing about the end results. I can only say that the result obtained from the samples collected, as a rule, differs from the information that we have according to TMF passports (technogenic mineral formation), which include data on dumps, tailings. This is due to the fact that the data in TMF passports are added on the basis of operational data of concentration plant discharge. Another important point is that in a TMF passport we have an average content of commercial components in the entire volume of a tailing dump. The results of drilling will make it possible to obtain data on distribution of a certain metal by the content at different horizons of a tailing dump. It is known that any concentration plant in different periods receives different extraction of metals and, respectively, material with different content of commercial components is discharged into the tailings. For example, when launching a mill, during the period of elaboration of technology and attainment of projected capacity, metals with the content higher than those specified in process procedure can be discharged into the tailings. We cannot know for sure now how these metals are distributed within a tailing dump. And only this type of drilling allows us to determine the specific content of metal by layers.
To what extent is it reasonable to perform similar works in the future?

It is absolutely reasonable, as if we are guided only by TMF passport data, we can get a distorted picture and biased information on the economic feasibility of tailings processing. This work makes it possible to perform the following main tasks: 1) to perform an objective calculation of reserves of commercial components; 2) to select a representative technological sample for the development of the operational procedures for tailings processing; 3) to accurately determine the economic feasibility of their processing.

What would you recommend to your colleagues who would like to use your experience?

If we speak about tailing dumps, I for sure recommend using RC drilling. I do not know any other option. Of course, there are new techniques in the world, such as vibration drilling, but we do not have them here. We are of the opinion that the most objective results at exploration of tailings can be obtained only when using RC drilling. In addition, the possibilities of this technology allow selecting material with the weight of 17–20 kg from one meter of penetration while drilling with the diameter of 123 mm. This amount is enough for collection of both standard samples and technological samples with the weight of from first tons to first tens of tons.