Analysis of the Effectiveness of the Mine Cycle Acceleration with Double Blasting Method at Kencana Underground Mine, PT Nusa Halmahera Minerals, Indonesia

The Underground Gold Mine Kencana, operated by PT Nusa Halmahera Minerals (NHM), utilizes the cut and fill mining method. The mining cycle carried out in the Kencana underground mine is completed within 1 × 24 h for headings with a type-3 RMR (fair). PT NHM employs the double blasting method to expedite the mining cycle from 1 × 24 to 1 × 12 h. This research aims to assess the effectiveness of the double blasting method in terms of cut advance and activity duration. The standard activity duration time for the 1 × 12 h mining cycle is formulated using the PERT method based on 91 historical mining data points. The PERT method can formulate activity durations by considering uncertainties in activity duration using a three-time estimation method. The evaluation results state that the cut advance achieved using the double blasting method is higher by up to 5% compared to the conventional method, enabling this method to enhance cut advance by 110% longer than the conventional method when performed twice within 24 h. The activity duration formulated using the PERT method yields 9.38 h, with a completion probability before the task deadline of 93%. The utilization of activity time consists of 55.3% active time, 23% idle time, and 22% buffer time. The obtained values are superior when compared to the time utilization of the conventional method.