As part of continuous improvement efforts to optimise blasting performance and enhance safety at Gold Operation X, engineering trials were designed to trial the effectiveness of Varistem stemming plugs across a series of blasts. These trials aimed to evaluate the operational, economic, and environmental benefits of integrating the Varistem stemming plug technology into the standard blast design.
The primary objectives of the trial were to:
The trial blasts were carefully monitored and documented, with performance metrics compared against baseline data from conventional blasting practices. This case study summarises the findings and provides recommendations for potential full-scale implementation.
The results from the trial are structured according to the objectives. A summary is provided with further detail for each result provided in sub-sections.
A summary of the results is provided in Table 1.
Table 1: Summary of Results – Varistem Stemming Plug Trial at Gold Operation X
| Objective | Result Summary |
|---|---|
| 1. Assess the cost savings resulting from a reduction in explosive column length | Minor savings based on product landed cost at trial volumes, larger savings possible at bulk shipping volumes:
|
| 2. Measure the improvement in fragmentation, with a focus on reducing oversize and enhancing shovel efficiency. | Significant overall improvement:
|
| 3. Quantify the increase in digging rate due to better rock breakage and reduced boulder content. | Significant productivity improvements:
|
| 4. Evaluate the reduction in environmental impact, including lower vibration levels, reduced airblast, and minimised flyrock. | At a distance of 600m, the average PPV was 0.02mm/s and airblast was 0.1Pa (<90dB). No historical results available to compare. |
The original stemming length used at Gold Operation X was 2.7m. The Varistem trial was designed to incorporate a 0.5m airdeck between the explosives column and the stemming material, ultimately resulting in each hole in the trial dataset receiving 0.5m less explosives per hole (approximately 10.8kg per hole). Taking into consideration operation-specific pricing on explosives, this reduction resulted in a saving of approximately $11.48 per hole.
However, the Varistem BP6.5 (for 165mm/171mm holes) used during the trial cost Gold Operation X $11.24 per unit (at a price of $6.43 per unit plus ocean shipping and inland cross-border transportation, taxes and duties). It is important to note that the cost analysis was performed using the Varistem landed cost for a smaller trial shipment. The unit cost to consider for steady-state use is approximately $2.00 less per unit, resulting in a savings per hole of approximately $2.24.
Thus, the economic impact of incorporating the 0.5m airdeck resulted in a net saving per hole of $0.24 for the trial. Following this approach at scale in future would result in a net saving per hole of $2.24. Ultimately, the goal for the trial was to incorporate the Varistem without a net increase in costs, which was achieved.
Fragmentation analysis was done for the Varistem blasts as well as historical blasts using Wipfrag software. Table 2 shows the outcomes of the fragmentation analysis.
Table 2: Summary of Fragmentation Results – Varistem Stemming Plug Trial at Gold Operation X
| D20 | D50 | D80 | |
|---|---|---|---|
| Historical Blasts | 39.28 | 110.075 | 260.67 |
| Varistem Blasts | 38.75 | 109.21 | 243.44 |
| Difference | -1.35% | -0.79% | -6.61% |
From Table 2 it can be seen that the Varistem blasts produced a fragmentation outcome that was 1.35% finer (D20); 0.79% finer (D50) and 6.61% finer (D80) than what was historically achieved in the area. It should be noted that the improvement was achieved at a lower powder factor than before (as a result of the 0.5m airdeck incorporated into the design). The Varistem blasts’ muckpiles showed more uniform results across the blast pattern, as well as better stemming retention.
The fragmentation analysis showed a significant improvement in D80 particle size, which should technically translate to improvements in excavator digging rates and truck-and-shovel productivity. Table 3 shows the digging rates that were measured for historical blasts as well as Varistem blasts.
Table 3: Summary of Digging Rate Results – Varistem Stemming Plug Trial at Gold Operation X
| Excavator | Productivity (tph) | Variance | |
|---|---|---|---|
| Standard Design | Varistem | ||
| PC2000 (Baseline) | 1 100 | 1 100 | |
| PC2000 (Average) | 1 159 | 1 260 | 8.7% |
| PC2000 (Standard Deviation) | 140 | 27 | |
The digging rate for the material that was blasted with the Varistem plugs was, on average, 99tph higher than the historical results (or 8.7% higher). This correlates with the D80 particle size reduction measured during the fragmentation analysis and will ultimately result in reduced cycle times and fuel consumption.
For the trials, vibration and airblast were measured for a single blast. The reason for the single measurement is the proximity of the trial blast area to infrastructure and sensitive areas. Under normal circumstances, the mining operation would not measure vibration and airblast for blasts in the area (as it is not necessary), however, it was decided to do a single measurement for control purposes. Table 4 shows the result.
Table 4: Vibration and Airblast Results – Varistem Stemming Plug Trial at Gold Operation X
| Metric | Outcome |
|---|---|
| Distance | 600m |
| PPV | 0.02mm/s |
| Air blast | 0.1 Pa; <90dB |
From Table 4, it can be seen that the single trial blast (using the Varistem plugs) that was recorded produced a low PPV value and a low airblast value. Although there was no historical data to compare this outcome against, subjective insights from staff on site pointed towards:
The trials were successfully and professionally completed by the drill and blast team on site. The objectives of (1) introducing Varistem into the blast design at a net zero cost were achieved; (2) improving fragmentation and (3) loader productivity were achieved; and (4) reducing the environmental impact was achieved.
The trial blast using Varistem plugs demonstrated notable improvements in fragmentation (D80 at 6.61% finer), digging rates (at 8.70% faster), and environmental safety. Although the cost analysis showed only a slight decrease in per-hole cost of $ 0.24, an expected decrease in the unit price of Varistem plugs for future bulk orders will result in approximately $2.24 saving per hole. Furthermore, a positive impact on the operation’s carbon footprint is expected, attributable to the reduction in explosives consumption and improved blast efficiency.
Additional considerations include a potential increase in manpower requirements due to the additional task of plug insertion and verification.
Given the overall improvements in blast performance, safety, cost efficiency, and environmental sustainability, the drill and blast team on site recommends the continued use of Varistem plugs in production blasting at Gold Operation X. The integration of the Varistem stemming plugs into standard operating procedures will support sustainable and optimised mining operations.
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