AMC has conducted numerous studies to reduce dilution for mechanized narrow vein (NV) mining methods in operating mines. Methods have included longhole open stoping (LHOS) and mechanized cut and fill (CAF). Dilution can be classed as planned or unplanned. Planned dilution accounts for waste material incorporated into the stope when designing practical mining shapes. Planned dilution will depend on the vein geometry, thickness, orebody dip, and local ground conditions. Unplanned dilution consists of waste which is mined due to overbreak, which may result from poor drilling or blasting or as any waste incorporated during mucking. This article presents a high-level discussion of a study conducted by AMC to determine the optimum (minimum) dilution that could be reasonably applied to a NV orebody.
The dilution study began with vein characterization. The broad aim was to identify the general variability in vein width, geometry, and lateral extent (strike and dip) and, as far as practicable, to identify geotechnical conditions that may determine the applicability of various mining methods. The findings included:
Using the results of the vein characterization study, it was concluded that the minimization of dilution for LHOS and CAF would be based on:
AMC utilized the following formulae to determine dilution. Dilution ratios were calculated for planned and unplanned dilution. Total dilution is the sum of planned and unplanned dilution (Figure 1.1 and Figure 1.2 ). This method has been selected from numerous alternatives for calculating dilution.
The optimum dilution is a trade-off against ore recovery. Given the value of the ore for this case study, recovery was given priority over dilution, with a target recovery of 100%.
AMC used benchmarking and case studies to identify dilution experienced at different NV mines, guide equipment selection, drill-and-blast (D&B) designs, and technical services procedures and recommendations.
AMC examined the existing fleet of stope equipment (jumbos, LHDs, longhole drills, and bolters) at the mine and established optimal D&B designs for the selected vein widths, dips, drift profiles (square and shanty), drift size (height and width), and mining methods, which could immediately be implemented to reduce dilution, without additional equipment purchases.
AMC also identified the optimal fleet of stope mining equipment for dilution minimization. This requires the purchase of small, low-profile equipment and reduced development sizes.
AMC completed a comprehensive analysis to determine the minimized dilution for both LHOS and CAF using the formulae discussed. All of the selected vein widths, dips, drift profiles, and drift sizes were examined to minimize dilution and maximize recovery. The drift sizes considered had to accommodate either existing or optimal equipment.
In general, minimum dilution is achieved using the optimal equipment and smaller ore drives for the LHOS methods, or the lowest practicable drift heights for CAF.
Minimum dilution for LHOS ranged from 66% (1.5 m stope width, 0.5 m vein width) to 9%. For a 5 m vein width a minimum dilution of 9% is achievable in good ground with a 20 m sublevel interval and either a 5 m wide by 3 m high ore drive or a 5 m wide x 5 m high ore drive; in fair ground, the dilution projection increases to 10%.
Key results for CAF method was 28% for a 1.5 m vein width and 11% for a 5 m vein width.
AMC used the ideal stope and drive dilution results for the basis to create D&B designs, which included: slot raise, production rings and powder factors (PF) for LHOS. The D&B designs for CAF included: drill patterns, suggested explosive loading and PFs.
An example of LHOS design for an irregular vein shown in Figure 1.3.
The three main areas to target idealized dilution includes: drive dimension optimization, D&B practices, and overall quality control.
Subscribe for the latest news & events
Contact Details
Useful Links
News & Insights