Mining Constru C tion 1 2013 25 Drill and Blast Supervisor s Handik S etiaw an and J os Bernadus Manulang a The DM30 II the latest rig to join the Atlas Copco rig feet enables the mine to drill a wider variety of holes J er ry Mur thi the second generation owner of drilling contractor Nariki Minex S ejati says he appreciates the ver satility of the new DM30 II On a monthl y basis Pit 1 produces 700 000 tonnes w hereas Pit 2 produces 300 000 tonnes The stripping ratio is 7 to 1 Mining be g an at an ele v ation of 90 meters and is cur rentl y at 20 meters abo v e sea le v el Exploration is continuing to deter mine the total depth of the coal for mation The mine is operating on a fv ey ear e xca v ation plan including the opening of a third pit Prima Sarana Gemilang mine The for mation breaks w ell with an 8 or 9 m b urden and 9 to10 m spacing Handik Setia w an and Jos Ber nadus Manulang Drill and Blast Super visors e xplain that the y are still adjusting the patter n based on v aria tions in cla y or sandstone rock In addition the y ha v e to contend with a la y er of coral in Pit 1 that lo w ers producti v ity from an a v erage of 56 m per hour do wn to 40 m Pit 2 a v erages 48 m per hour drill ing with the DM30 II T he r e a r e ei g ht s ea m s be in g mi ne d here Drilling is generall y done during a 10hour period each da y although min ing operation s continue 24 hours a da y in tw o shifts The benches in both pits are 8 m high The coal sits on a 30 de g ree incline in seams ranging from 5 to 30 m in thick ness The coal in Pit 2 r uns at 5 800 kcal w hereas Pit 1 is 6 000 kcal Although the coal in Pit 2 is of a lo w er quality the seams are generall y thick er and easier to mine