By David Stewart and Tamara Wiseman

This paper examines how a proactive drill and blast optimisation programme using advanced technology will generate a measurably positive impact on primary crusher throughput; reduction in secondary breakage and fines; and improved efficiencies in the loading and hauling of shot rock.

quarry located in the south-eastern United States is a greenfield site established in 2011. The quarry lies in the eastern part of the Georgia Piedmont area. It is within a distinctive, northeast-trending belt of relatively high-rank metamorphic rocks known as the Kiokee Belt, a poorly mapped sequence of units that largely consist of amphibolite, and various schists and gneiss that are host for relatively young granite bodies and associated pegmatite and aplite dikes. The operation is currently using a 50” × 62”( 1.27m × 1.52m) Jaw Crusher as their primary crusher and anything larger than 48”( 1.22m) is considered oversize. The operation is also using a Caterpillar 992K loader and two haul trucks: a Caterpillar 777 and a Komatsu 785.

The operation was not achieving their desired production goals. Data collected during the benchmarking phase determined that production was averaging 932 short tons( 845.5 metric tons) per hour through their primary crusher. Target production for the crusher is 1 000 short tons( 907 metric tons) of rock per hour through the primary, with a goal of 65 000 short tons( 58 967 metric tons) per week. The quarry was unable to maintain this level of production on a regular basis. Along with production issues, the quarry was also experiencing extensive highwall damage, rolling floors, oversize, and hard digging at the toe of the highwall. Several potential causes for these issues were identified: geological

conditions such as prominent seams; blast design and front row borehole placement; and drilling accuracy. Figure 1 is an overview of the site.

The primary goals of the programme were uniform fragmentation, an increase in crusher throughput, improving the highwall by eliminating back break and back shatter preconditioning, and maintaining grade control through optimized drilling and blasting performance.

In conjunction with their drilling company, the quarry implemented a drill and blast optimisation programme using drill monitoring systems, drill navigation, a 2-D laser profiling system, 3-D photogrammetric profiling technology and borehole surveying equipment, and a GPS survey system. The deployment of the various technology was done in multiple phases as the need for more detailed profiles, blast design, borehole deviation, and blast performance analysis were identified.

Optimisation programme – Phase One

Phase One focused on the geological issues observed in the pit. Prominent seams located in the pit, which intersected with boreholes in a blast, allowed explosives gasses to vent through the blast face and adjacent boreholes during a blast.

The LIM system was implemented for drill monitoring. The system monitors drilling parameters such as tool feed pressure, air pressure, torque pressure, as well as tracking steel changes. This data can then be used to determine the depth where a cave or prominent seams intersect a borehole. This information is vital to ensure the appropriate weight of explosives or decking material is loaded in a borehole at the correct borehole depth. Figure 3 is an example of the report from the drill monitoring system.

Along with the drill monitoring data, 2-D profiles of the blast face were taken at individual borehole locations. These profiles were then used to adjust decking and explosives loading within the borehole. The adjustments demonstrated a visible reduction in the venting of gases through seams and out of the blast face, but only marginally improved crusher throughput and oversize reduction.

Because the initial Phase One changes showed only a marginal improvement in productivity and highwall improvement, a second phase of the programme was developed and implemented to address these areas of poor performance further.

Figure 2

12 _ QUARRY SA | JANUARY 2017