Long hole drilling applied to narrow reef mining - SAIMM

1 LONG hole drilling applied TO narrow REEF MINING199 ObjectiveThe purpose of this report is to chronicle the interactionbetween Anglo Platinum and sandvik Tamrock during thedevelopment and application of Long hole drilling as aviable, practical method of narrow reef mining . Appendix Iidentifies the people from Anglo Platinum and SandvikTamrock who participated in the in long hole drilling and blasting wereconducted in a number of mines during the late 1950s andearly 1960s. Some of the advantages envisaged were: The face would require no daily examination No barring down or immediate face support required No sockets to clean Only a few well drilled holes rather than large numbersof short blast holes Avoidance of poorly-marked holes, inaccurate drillingand improper charging Better supervision and better face 50 mm in diameter were drilled parallel to thestope face by pneumatic rock drills from advance strikegullies.

2 Holes were charged with amon gelignite holes were traced with detonating cord to ensurepropagation of the explosive along the entire hole was blasted onto a rolling scatter number of reasons have been cited for the failure ofthis mining method. The two most important were: problems in controlling hole deviation which wasexacerbated by the fractured ground difficulty of charging up holes in fractured ground, dueto relative movement of rocks along fracture surfacesover the hole idea of drilling a few long holes parallel to the facerather than a large number of short blast holesperpendicular to the face was an attractive option tomechanize narrow reef particular project started in trialThe Union Section of Anglo Platinum purchased a Solo H606 RA long hole drilling rig from sandvik Tamrock in1997.

3 In order to evaluate long hole drilling as a basis forface mechanization. The Solo series of drill rig was selectedbecause it combines high drilling performance and gooddrilling accuracy with high versatility with a compact mining method proposed by a consultant to AngloPlatinum was based on the current trackless mining methodpractised by Union Section. The trackless mining method isbetter described as a trackless development and transportmethod. Reef strike drives were installed approximately 40metres apart on dip using trackless equipment. Reef wasmined using hand-held pneumatic rock drills and scraperwinches and the excavation was supported by sticks andcrush pillars at the top of the panel.

4 Rock scraped from thepanel was loaded by Lad Haul Dumps (LHDs), trammed toan inclined haulage, and loaded into trucks for transport tothe surface. It was intended that the Solo would drill from the bottomadvance strike drive to the top advance strike drive. Blastedrock would still have to be scraped from the panel. It is alsodifficult to understand how well the support would the initial motivation it was stated that drillingaccuracy was of the utmost importance. Previous work bySandvik Tamrock had shown that, in other parts of theworld, 20 metre long holes could be drilled with a deviationnot exceeding 100 mm provided that: holes were collared with low thrust pressure operating percussion pressure was kept low often notexceeding 10 MPa drilling was to be with tubes, not early 1998 initial trials with the Solo H 606 RA wereinconclusive; attempts were made to drill 40 metre longholes from one advance strike drive to another.

5 Difficultywas experienced in measuring hole straightness andaccuracy, there was no survey of the holes, and no blastingwas done to expose hole long hole mining system was then defined, with acorresponding face mining system, which led to the designof a test programme for the Solo drilling experience at TelferThe proposed face mining system was based on a miningmethod that is practised at Telfer Gold Mine in WesternAustralia. Telfer has a series of domed reefs that dip atangles of less than 20 to more than 40 . The ore bodies areall thin, with widths from metres to metres. Figure 1shows the face layout. Experience at Telfer indicated thefollowing: The spacing and size of the dip pillars should be basedon the rock mechanics of Union Section The length of the face is determined by the ability tocorrectly position the blast holes.

6 Positioning of blastholes is a function of hole straightness and holedirection. Blast holes in Telfer were drilled 64 mmdiameter with retrac bits from sandvik . Extension steelwas T38 by metre lengths. A guide rod was fittedimmediately behind the bit. To achieve greateraccuracy operators drill at relatively low percussionand thrust pressures. Results show that very goodaccuracy is achieved in 20 metre stopes and only fairaccuracy in longer stopes. In 34 metre long stopes10 15% of the holes are not sufficiently accuratelypositioned and have to be re-drilled. All blast holes arePICKERING, Long hole drilling applied to narrow reef mining . International Platinum Conference Platinum Surges Ahead ,The Southern AfricanInstitute of mining and Metallurgy, hole drilling applied to narrow reef PICKERINGS andvik, TamrockPLATINUM SURGES AHEAD200drilled as up holes.

7 Attempts have been made toincrease face lengths by drilling up and down holes but this resulted in too many bridges and increased thedifficulty of getting the ore out of the stope. A veryimportant lesson from Telfer was that as all holesbreak through, operators are able to check the drillingaccuracy regularly, and make the necessaryadjustments. Face advance is dictated by the time taken to drill theholes, the burden between the holes and the number ofholes blasted at any one time. At Telfer, where thereare excellent footwall and hangingwall contacts, holesare drilled centrally in the orebody with a burden of in the 20 metre long stopes. In the 34 metre longstopes the burden was reduced to metres.

8 A singleoperator drills 120 150 metres in a 12-hour is in rings of five holes. All long holes aredouble primed and loaded with ANFO, leaving anuncharged collar of between one and metres A process of rapid raising is essential to realize thebenefits of increased rates of face of the raise could be by hand or dropraising Face cleaning at Telfer, where the dip is less than 32 ,is by means of a scraper mounted in a frame that sits inthe bucket of an LHD. When the dip exceeds 32 thestope is water-bombed using the LHD bucket full for long hole stoping systemIn November 1998 it was agreed that the vision for a LongHole Stoping System should encompass the followingobjectives: a totally mechanized system a necessity for change in the existing mining layout all hand held drilling on the face to be eliminated no support should be required in the long hole drilledarea in effect the stope should be man- free the final mining system should be more profitable tothe company than the existing mining was also argued that some elements of the proposedfinal system should be trialed.

9 The purpose of the trialswould be to determine the parameters on which the finaldesign of the system was to be based. A trial that focusedon the following was initiated: drilling accuracy drilling performance or drilling rate throw of the blasted rock effect of the blast on the hangingwall blast design for the most efficient breaking of the fullchannel UG2 at Union SectionA site for trial drilling was selected at Union Section. Thesite was at an intersection between one of the advancestrike drives and a decline roadway, giving a triangular-shaped section of reef. This position was selected because itwould be possible to drill varying lengths of holes from theASD to the roadway.

10 Experience from Telfer had clearlydictated the methodology of drilling into an opening as themost effective way of determining hole results are shown in Tables I and II. All the drilling was carried out by an operator trained bythe Tamrock Drill Master for the previous abortiveexperiment. He was supported by an experienced Tamrocktechnician/operator, with additional advice provided by theTamrock Drill Master. Holes at the first site were drilledwith 64 mm Retrac bits and T38 male/female rods. In thesecond stage of the drilling , trial T38 Guide Tubes werefitted immediately behind the Retrac initial focus of the trial was to determine holeaccuracy. Accuracy is a combination of hole direction andhole straightness.