Effect of double-primer placement on rock fracture and ore recovery

The double-primer placement is based on the principle of shock wave collision. When two shock waves meet each other, the final pressure is greater than the sum of the initial two pressures. Stress analysis indicates that this should be favorable to rock fracture and fragmentation in blasting. This double-primer placement was tested in Malmberget mine by using electronic detonators, aiming to improve rock fragmentation. At the same time, another method, named DRB (Dividing Ring Blasting), was tested, too. Two production drifts in an ore body were taken as test drifts. In each test drift both methods were tried. For comparison, two nearest production drifts to the test drifts were taken as reference drifts. The results showed that on average the double-primer placement recovered more iron ore than either the DRB method or the ordinary method used in the reference drifts. In addition, fragmentation looked much finer and the eyebrow break became much less for the double-primer rings, compared with the reference rings.