the type of for mation peneration rate v aries widel y from 10 20 m per hour t he Khumani operation At the King Mine on the Khumani com ple x the drilling feet is dominated b y Atlas Copco s diesel po w ered Pit V iper 271 rigs Unlik e at Sishen Khumani chooses to use t h e h i g h p r e s s u r e v e r s i o n o f t h e P V 2 7 1 with DTH Do wnTheHole hammers to tackle the ore beds that are w ell kno wn for their e xtreme hardness Ho w e v er the ore here is generall y w ell e xposed and the mine benefts from a lo w stripping ratio of 07 09 w hereas other mines in the area need to manage a ratio of around 27 The benches are 104 m high and holes are drilled v er ticall y to a depth of 114 m including 1 m of subdrilling In drilling the o v erb urden the usual drill patter n is 55 m x 65 m as allo w ed b y the rock type such as sandstone shale and w eathered material The underl ying ore is often v er y hard here and some drill bits last onl y tw o hours DTH drilling is used with 165 mm bits and Secoroc 64 hammers and others b ut the mine is con tinuousl y tr ying to reduce drilling costs Ger rit Loedolf f Manager of Mining Operations at Khumani e xplains that a cur rent priority is to e xamine rotar y drilling options for 251 mm holes Lar ge diameter holes reduce drilling cost and used in con junction with electronic b lasting reduces b lasting cost as w ell W e will be using the con v er ted PV 271 because of suffcient compressor capacity to ensure adequate chip fushing The big gest enem y of a tricone bit is drill chippings in the hole and incor rect bailing v elocities can ha v e an impact on drill rod life In s witching from 165 mm to 251 mm holes it is e xpected that the drill patter n will change to 6 m x 6 m and that the v ol ume of b lasted rock per hole will increase from 16 m 3 to appro ximatel y 36 m 3 In addition to changing drill pipes the con v ersion will require lo w ering the pres sure of the compressor to the minimum le v el as w ell as changing the carousel rod suppor t the break out systems and tool handling accessories The tricone bits will initiall y be from Secoroc b ut Loedolf f sa ys that the mine will test a v ariety of products including bits used b y neighbouring mines D r i l l r i g a v a i l a b i l i t y a t K h u m a n i i s increasing A v ailability of the PV 271 rigs is in e xcess of 85 percent and R OC L8 rigs are abo v e 75 percent repor ts Loedolf f As e xper tise and maintenance practices Nor thern Cape miner s display their strong belief in the future Here Pit V iper 271 drill rigs hard at work at Khumani s King mine Mining Constru C tion 1 2013 7