Varistem® Stemming Plug  Pilot Project at a South African Underground Platinum Mine

Introduction and Project Background

ERG Industrial conducted a Varistem® stemming plug pilot project at a South African underground platinum mine between May 2024 and June 2024. This pilot project aimed to demonstrate the energy retention capabilities of the Varistem® stemming plugs towards the primary goal of improving advance per blast.

The advance per blast refers to the distance (in meters) moved forward or into the rock mass after a blast. The planned advance per blast typically depends on the mining depth below the surface, geological and rock engineering considerations, the mining method and layout, the drill and blast parameters and design capabilities, and the production requirements. Not achieving the planned advances for each blast results in the mine not achieving the required production tonnages. This means that the mine’s actual production does not align with the annual budgets and estimates. There are several reasons that could potentially lead to poor advances.

These include, but are not limited to:

• Poor drilling practices
• Poor or inadequate cut design or flawed blast design
• Poor performance of explosives (This can be due to poor product quality, reactive ground or water in holes, etc.)
• Poor charging practices
• Inadequate confinement of the explosives in the blastholes (This can be due to fractured ground and seeping of explosives, poor tamping practices, etc.)
• Poor execution of the blast design

The planned advance at the mine is 3.1m for every blast, using standard tamping cartridges to confine the blast holes. However, over recent months, the mine only achieved approximately 79% of this advance on average. The average advance per blast is summarised in Table 1.

Table 1: Average advance per blast at an Underground Platinum Mine in South Africa

The overall average advance per blast for the three months before the Varistem® implementation was 2.46m per blast, which is 0.64m (21%) less than the planned 3.1m advance rate. This leads to an average lost blast volume per blast of 10.24m3, considering an 8.0m x 2.0m panel.

Considering the current advances achieved by the mine and an initial high-level audit of the mine’s drilling and blasting practices – it was determined to trial the Varistem® stem plugs to improve on the achieved advances. The main objective for this pilot project was, therefore, to improve the average advance per blast and simplify the tamping procedure of blastholes. The Varistem® plug is a tool that can be used in various ways to address specific site-specific challenges, based on the site requirements. For this pilot project, the full effect of the plug was trialled. This was done by replacing the current tamping cartridges with the Varistem® plug only – i.e. no other means of confinement was used during this trial.

Project Methodology

The testing methodology was simple – no changes will be made to the drill and blast design. The only difference will be the addition of the Varistem® stemming plug. Advances will be measured for each blast and compared to historical advances in the same area, which will demonstrate the impact of the use of the Varistem® stemming plug on advance.

In an attempt to ensure that there is minimal impact on the quality of drill and blast execution, the ERG Industrial team was only on-site to train teams on the use and installation of the Varistem® plug and was not present during the execution of the trial. The main motivation for this is that, generally, when an auditor or consultant is present during activities, the overall discipline and execution of tasks seem to be noticeably better than normal. (Note: no changes were made to the drill and blast practices. The intention was to purely trial the impact of the Varistem® plug.)

Once the pilot project had been concluded and the full datasets became available, a cost-benefit analysis was conducted to determine the financial impact of the change in advance.

Results

A total of twelve blasts were taken with the Varistem® plugs between 05 June 2024 and 10 June 2024. Two of these blasts were excluded from the analysis due to poor conditions and execution – yielding outlier data points that will skew the overall analysis of the results. This exclusion allowed for a more representative dataset and analysis of the achieved results.

The advances achieved for the blasts that formed part of this pilot project, i.e. using the Varistem® plug as confinement instead of tamping cartridges, are given in Table 2.

Table 2: Advance per blast achieved with Varistem® plug as means of confinement for the dataset

From the data presented in Table 2, it should be noted that out of the ten blasts, four achieved an advance of more than 3.0m – i.e. 40% of blasts during the trial achieved ‘full advance’ (as defined by the mine). The average advance across the trial blasts is 2.82m which is a significant improvement (11%) from the historical advance averages achieved.

Based on the average advance achieved historically (pre-trial) and the advances achieved during the pilot project, the estimated volume blasted per month was calculated and is shown in Table 3 and graphically represented in Figure 1.

Table 3: Blast volume based on the achieved advances

Figure 1: Blast Volume estimates based on historic advances and Varistem® achieved advances

Based on the historical data and the advances achieved using the Varistem® plugs, a financial analysis was conducted assuming the existing drill and blast practices continue and the achieved advances using the Varistem® plug remain consistent with the trial results.

Financial Analysis

To be able to conduct a financial analysis illustrating the long-term benefits of continued use of the Varistem® plugs based on the results achieved during the pilot project, assumptions were made specific to the value of the orebody and the potential revenue generated. The assumptions used for the financial analysis of the Varistem® pilot project are summarised in Table 4 (minerals recovered per blast), Table 5 (blasting operational assumptions), and Table 6 (value of the ore).

Orebody value assumptions: 6E UG2

• Density = 4.0 t/m3
• Grade = 3 g/t
• Gram to Ounce Conversion Factor: 1g = 0.035274 oz
• Recovery Factor: 80%

Table 4: Recovered Minerals per blast (assuming a 6E UG2 grade of 3 g/t)

Table 5: Assumptions for blasting operation

Table 6: Assumptions for the 6E UG2 Ore Value

Based on the assumptions summarised above, the value added over 12 months (annually) could be estimated and analysed.

Table 7 indicates the estimated value added per panel per blast, considering the average advance achieved when using the Varistem® stemming plugs, using the historic and measured (trial) advance rates.

Table 7: Estimated Value added by replacing the standard tamping cartridges with Varistem® plug per blast

Simply considering the average gain across all datasets during the pilot project, a Net value of over R 58,000 was achieved per panel per blast. Table 8 below presents a breakdown of the gains and losses achieved per blast reflecting the individual advances achieved per panel per blast during the pilot project testing. Considering the combined value of all ten panels from the pilot test (trial), a total value gained of over R 600,000.00 is shown.

Table 8: Breakdown of Gains and/or Losses achieved during the Pilot Project

As a projected impact of including the Varistem® plug, based on the results achieved in the trials and on the assumptions made, the following annual financial benefit can be forecasted for five panels at a blast frequency of 25 blasts per month.

Table 9: Financial Value Added across five blasts (assuming 25 blasts per month)

Assuming a consistent average advance of 2.46m per blast across all 66 panels at the mine, the following estimates can be made to indicate the potential value-added for the mine with the improved measured Varistem® advance rates (2.82m per blast). The Net value added, i.e. taking into account the cost of the Varistem® plug, across all 66 panels with an average advance of 2.82m per panel per blast, amounts to R 1.91 billion annually.

Table 10: Value per blast – based on the assumed 6E UG2 ore value and assumed average advances

Conclusion

This significant predicted financial gain of over R 1.91 billion is based on only improving the average advance per panel per blast from 2.46m to 2.82m by simply replacing the standard tamping cartridges with the Varistem® stemming plug. Considering the impact of the Varistem® plug in this pilot project and combining it with improved drill and blast practices and QAQC procedures, it can be presumed that the combination of these activities will result in increased advance performance and financial gains.

If you would like to find out more regarding the Varistem® stemming plug, improving your drill and blast practices and QAQC procedures, contact us today.