Deep ore min­ing goes cut­ting edge

CityPress - - Business - JAN DE LANGE busi­ness@city­press.co.za

A new type of drilling sys­tem for sink­ing shafts could mean that many un­der­ground bod­ies of ore that were pre­vi­ously too ex­pen­sive or risky to get to can now be mined.

In the next two years, Mas­ter Drilling, the min­ing in­no­va­tor with its gi­ant drilling ma­chines, will build a de­vice that can sink a 2km deep mine shaft twice as fast as us­ing ex­plo­sives could.

It will also be about a third cheaper than the ex­plo­sives, which were for more than a cen­tury the only af­ford­able and re­li­able way to sink un­der­ground shafts.

It is also con­sid­er­ably safer and a lot less harm­ful to the en­vi­ron­ment.

Mas­ter Drilling, which de­vel­ops its world-renowned tech­nol­ogy in dusty Fochville, Gaut­eng, has de­signed the sys­tem and is now call­ing for ten­ders for its con­struc­tion.

Louis Germishuys, chief op­er­at­ing of­fi­cer of shaft de­vel­op­ment at Mas­ter Drilling, said: “We ex­pect to be ready to sink the first shaft with the sys­tem in 2018. We must find the right cus­tomer for it.”

The new drilling sys­tem, which is known as the blind shaft bor­ing sys­tem, is a com­bi­na­tion of three proven sys­tems de­vel­oped by the com­pany: a pi­lot drill that drills an ini­tial nar­row shaft, a rais­ing bore that widens the shaft and a hoist­ing sys­tem that re­moves ma­te­rial from the shaft.

The sys­tem sinks a shaft at a rate of 7m a day. In shafts sunk with ex­plo­sives, progress is no more than 3m a day.

Ac­cord­ing to a fi­nan­cial model, a 2km deep shaft costs about R9.4 bil­lion to sink and takes at least three years to build, but with the blind shaft bor­ing sys­tem, the shaft will be sunk within 18 months, bring­ing a sav­ing of R2.8 bil­lion.

It will cost be­tween R400 mil­lion and R800 mil­lion to build the sys­tem.

It is op­er­ated by four to six work­ers. For main­te­nance, about eight work­ers are re­quired.

For the con­ven­tional The pi­lot drill is a con­ven­tional drill with a di­am­e­ter of 4.8m, which drills a pi­lot shaft. It uses a sludge-wa­ter tech­nique where the bor­ing head is un­der wa­ter and grinds the rock into sludge.

The drill shaft is hol­low and the sludge is pumped up through it to a fil­ter plant above the bor­ing head, where the wa­ter and the crushed rock are sep­a­rated.

The wa­ter is re­turned to the bor­ing head, but the crushed rock is hoisted out of the shaft.

About 20m above the bor­ing head is a ream­ing head that reams the pi­lot shaft wider in a dry con­di­tion with the same tech­nique that large drilling con­trac­tors have for a long time used to widen pi­lot holes in rock.

The reamer is at­tached to a raised borer an­chored down­ward and is moved by hy­draulic arms fixed in the nar­rower pi­lot shaft.

The reamer widens the 4.8m pi­lot shaft so that the di­am­e­ter of the fi­nal shaft can be be­tween 10m and 14m wide.

That’s wide enough for any min­ing ac­tiv­ity, from ven­ti­la­tion to trans­port­ing peo­ple, ma­chines and ore.

The waste rock the reamer bores from the shaft walls is caught in a bunker and trans­ported out of the shaft.

The sys­tem weighs about 1 500 tons and is sus­pended into the shaft by a sturdy hoist­ing sys­tem above ground. ex­plo­sives method, about 40 work­ers are used to drill holes for the ex­plo­sives and hoist loose rock from the shaft.

In ad­di­tion, con­ven­tional shaft sink­ing is the most dan­ger­ous work in an un­der­ground mine.

“Yes, it pro­vides less jobs, but when you con­sider how many mines could so far not be opened be­cause it was un­af­ford­able and will now per­haps in fact be opened, the tech­nol­ogy does cre­ate jobs,” Germishuys said.

The sys­tem weighs a5out 1 500 tons ani hangs from a solii lift sys­tem con­nectei to rig­ging a5ove grouni, which iesce­nis into the grouni Waste rock is loaiei into a 5ucket ani pullei out of the shaft The en­larger wi­iens the 4.8m pi­lot shaft so that the fi­nal iiam­e­ter can 5e any­thing from 10m to 14m. This is wiie enough for any min­ing ac­tiv­ity – from ven­ti­la­tion to the trans­port of peo­ple, ma­chin­ery ani ore The ir­ill’s axis is hol­low so that silt can 5e pumpei through it to the sur­face into a fil­tra­tion sys­tem that sep­a­rates the wa­ter ani crushei rock. Wa­ter is then pumpei 5ack iown to the chuck A con­ven­tional pi­lot ir­ill with a iiam­e­ter of 4.8m ir­ills a pi­lot shaft. It uses a silt-wa­ter tech­nique that en­sures the chuck is unier­wa­ter ani the rock it is ir­illing is millei into silt

65m

85m

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