In November, the World Gold Council published a report on the global market for the yellow metal in Q3 2022, according to which demand for it increased by 28% over the same period last year to 1181 tons, thereby returning to pre-pandemic levels.
The top three global producers remain unchanged, with only Russia showing a positive trend and increasing turnover. Having caught up with and surpassed Australia in 2022, it is now second only to China. Consumption is also not standing still, primarily thanks to central banks, the jewelry industry and investors. In Russia, for example, 20.5 tons of coins and bars were purchased this year - five times more than last year.
Historically, most of the gold was mined in river beds, which eroded the exposed rock nuggets and carried them downstream. Today the bulk of the precious metal is produced by developing deposits formed through geochemical processes. The development of deposits with the content of a useful component of 1.5-2 grams per ton is considered to be profitable, and this is not more than 0.0002 per cent. At the same time, from year to year their exploitation becomes more and more technologically complex and expensive.
Drilling and blasting, located at the beginning of the gold production chain, determines the subsequent efficiency of all technological processes, as well as their cost. Therefore, improving the quality of pit development directly affects the profitability of mining. It is at this stage that the mining engineer needs to ensure the output of the optimal fraction of the blasted rock mass and determine the degree of displacement of the ore body after the explosion as reliably as possible.
One of the ways to minimize costs is computer modeling of the process of explosive demolition of the rock mass. How feasible is it? Forpost decided to find out from Anastasia Plesakova, a final-year student at the Blasting Department of the St. Petersburg Mining University. The sphere of her scientific interests includes preliminary prediction of the results of an explosion in the GEOMIX mining and geological information system and the subsequent use of the data obtained in real-life conditions. Industrial practice Anastasia passes on the objects of the largest domestic gold mining company "Polyus", the total gold production of which at the end of the first half of 2022 amounted to 1 186 thousand ounces, i.e. over 36 tons.
Each explosion is unique
A mining system is unpredictable: even different parts of the same deposit have unique structures and properties, so it is quite difficult to guess how a massif will behave in an explosion. Especially given the scale of modern gold mining and the high productivity of the equipment used. This explains the industry's need for ever-improving technologies to study the structure of a rock mass and predict its response to an explosion.
"The field tests required to obtain field statistics can take a long time, and with simulation, everything can be done quickly, without direct blasting. It also allows us to run multiple blast scenarios and choose the best one for specific mining and geological conditions," explains Anastasia.
Digital modeling of massif destruction reduces not only time but also resource costs: preliminary selection of blasting parameters allows predicting the shape of the fault and distribution of gold-bearing ore in it. Accordingly, to reduce the number of zones with its uncertain content.
"For example, this is relevant for deposits of Kuranakh ore field in Aldan region of the Republic of Sakha (Yakutia), which are developed by Polus Aldan. They are characterized by an uneven distribution of the useful component, in addition, they are a mixture of hard and soft rocks within the boundaries of one block. In this case, modeling is also useful: if we know where the soft sandy-clay rocks are and where the hard limestone is, for example, then we can proportionally distribute the amount of explosive or apply a dispersed charge," says Anastasia.
Of course, it is impossible to completely avoid displacement of the ore body and its mixing with the waste rock in the process of explosion. However, engineers and scientists can easily minimize the negative "side effect" and improve the quality of ore that goes to the gold mill.
"Digital modeling helps predict displacement and mark new block boundaries after blasting as accurately as possible. Engineers do this by controlling what is called deceleration time, that is, by selecting the optimum length of pauses between each successive row of wells, and these pauses are measured in only tens of milliseconds. Their sequence and tempo has a direct impact on the shape of rock failure," comments Anastasia Plesakova.
It can also help justify the required consumption of explosives. The economic benefit from optimizing its volume can be quite significant. For example, at some fields developed by major Russian companies the wells are up to 20 meters deep, and the charge column contains up to 1.5 tons in TNT equivalent. Of course, errors in planning will result in significant losses.
The human factor
Based on the mine development plan and geological data, which includes information on the grade and distribution of ore in the massif, engineers draw conclusions on how best to divide it into blocks for drilling and blasting operations. They outline the contours of the sections, designate diameters, drilling depths and angles, borehole charge weights, and adopt an initiation pattern that will provide the desired direction of block displacement for subsequent excavation.
By entering the initial parameters into the program and changing them, specialists receive several models, which also contain information about the volume of blasted rock mass, shape and height of the breakage, position of ore bodies, size of heterogeneous zones and volumes of rock mass thrown on neighboring blocks. All this is presented in the form of graphic documentation, drawings and animated explosion process, which clearly shows the destruction of the mass in time. Based on the results obtained, engineers can compare several blast variants on the same block and choose the most suitable one for the given conditions.
"All decisions issued by GEOMIX are analyzed by humans: at each stage, geologists, surveyors, blasting engineers and other engineers make adjustments to the models and make final decisions on whether the forecast is correct or not. The suitability of the best model, which is approved by the technical manager, is confirmed in the field tests." - clarifies Anastasia Plesakova.
Let us remind you that blast modeling is only one of the advanced technologies implemented by the domestic company GEOMIX, with which the St. Petersburg Mining University has a cooperation agreement. The platform allows to perform most calculations during construction and reconstruction of mining production remotely, as well as to accumulate a statistical database on mines from all over the country.