BENEFITS RELATED TO THE APPLICATION OF MASS BLASTS IN OPEN CUT MINING

Transcription

1 BENEFITS RELATED TO THE APPLICATION OF MASS BLASTS IN OPEN CUT MINING José Vergara, Carlos Muñoz, Natalia Ortega. Advanced Technology Solutions, Orica Mining Services Latin America August 2015 Document reference David Avilés Drill & Blasting Manager, CAP Minería Mina Los Colorados.

2 MASS BLAST OBJECTIVES LOS COLORADOS CASE STUDY TECHNICAL SOLUTIONS RESULTS FOR WALL CONTROL FRAGMENTATION RESULTS CONCLUSIONS 2 CONFIDENTIAL: Information contained in this document is strictly confidential.

3 THE OBJECTIVES OF MASS BLASTING Traditional Blasting Included a Production blast plus a separate wall control blast. Mass Blasting Blasting the entire bench cutback width toe crest. Traditional Blast Mass Blast Mass Blast

4 ADVANTAGES OF MASS BLASTING The benefits of Mass Blasting for mine productivity are: Reduce the number of blast events Reduce blast delays and evacuations. Reduce damage to walls. Larger drilling and excavation areas Better distribution of explosive energy Improved fragmentation. Increased excavation rates. P&H <3500 tph P&H <4500 tph P&H >5500 tph 5 4

5 CASE STUDY CAP LOS COLORADOS Is a Kiruna Iron Ore type deposit in the Atacama Region of Northern Chile. 84M tons / Year open-cut operation producing 10.4M ton of Magnetite Iron Ore 5

6 MASS BLAST - TECHNICAL SOLUTION Two trials were designed, fired and monitored using: Trial Tonnes Description Computer based blast designs Electronic timing was used to manage energy distribution Advanced finite vibration prediction modeling. Near field vibration monitoring Separate production & trim blast. Blasting entire cutback width toe crest Bore hole camera inspections were conducted before and after blasts to determine rock mass damage 850 Kth Production Trim 950 Kth Production Trim 6

7 TIMING DESIGN TO MANAGE GEOTECHNICAL ISSUES A presplit blast is fired 1000 ms before initiating the combined production and trim blast. Blasts were split into 300 k/tonne panels to reduce peak vibration levels. 500ms timing breaks are used to prevent superposition Blast sequencing is made possible by using electronic timing. Mass blast 500 ms Presplit Buffer 500 ms 500 ms 7

8 VIBRATION PREDICTION MODELLING Traditional Blast Small narrow blast dimensions in the trim area designed to channel vibrations away from wall structures. Traditional Blast High impact in the rock mass, generate cracking in the failure zones. 8 Mass blast Novel timing designed to channel vibrations away from walls. Mass blast Mass blast minimizes generation of new fractures in the failure zones.

9 DRILL & BLAST DESIGN PARAMETERS : Measurement Trial 1 Trial 2 TRIAL 1 Hole Diameter 26 cm 31 cm Bench height 15 m 16 m Burden 7.5 m 7.5 m Spacing 10.5 m 10.5 m Charge factor 200 gr/tonne 200 gr/tonne Total Energy 3.53 MJ/tonne 3.53 MJ/tonne Bulk Product Fortan Extra 50 Fortan Extra 50 Priming per hole 3 x EBS 3 X EBS TRIAL 2 9

10 WALL CONTROL MEASUREMENT TRIALS 1 & 2 Application of presplit and buffer row. Maintained the trim blast to a width of 35m. Near field vibration monitors (GT, GT2) (disposable triaxle geophones). Borehole camera inspections for near-field damage (BH1, BH2, BH3,, BH9). GT Borehole Inspection Holes GT2 Borehole Inspection Holes 10

11 MEASUREMENT RESULTS FOR WALL CONTROL BLAST TRIAL 1 & 2 Presplit filters reduced near field vibrations (ppv) by 47 & 50% before and after presplit. Borehole camera inspections indicated no damage inside all monitoring holes. PPV in front of PPv forward presplit 50% PPv PPV back behind presplit BH 6 (10m) Before mass blast BH 6 (10m) After mass blast 11 11

12 FRAGMENTATION RESULTS Photo fragmentation image analysis of trial shots. Both trial shots reduced the P80.distribution P80 (inch) Baseline 7.4 Trial Trial

13 CONCLUSIONS Blast size has increased from approx. 250,000 to 950,000 tonnes No adverse effects to wall stability. Near field vibration (ppv) remained below 500 mm/sec, well below the geotechnical design limit of 720 mm/sec The borehole examinations showed no difference in damage behind the presplit line. Fragmentation improved. The mass blasts replaced three or more standard blasts Drilling & the Truck / Shovel productivity increased. The mine owner estimates the total productivity benefits to be valued over US $ 2M per annum Consequently a combined mass Production + Trim blast has been adopted as standard practice 13

14 14