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Mining_Methods_UnderGround_Mining - Mining and Blasting

Mining_Methods_UnderGround_Mining - Mining and Blasting

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MOunT iSa, auSTralia<br />

Drilling sublevel<br />

General view of sublevel stoping at Mount Isa copper mine.<br />

drilling is possible for hole lengths of<br />

over 50 m. Flexibility of use is promoted<br />

by the modular construction of<br />

the rigs so that, for example, the feed<br />

positioning system can be combined in<br />

different ways to obtain the required<br />

hole positions <strong>and</strong> directions. Types<br />

of drilling that can be h<strong>and</strong>led include<br />

bench drilling, fan drilling within a 90degree<br />

sector, 360-degree ring drilling,<br />

<strong>and</strong> parallel hole drilling.<br />

The Simba H4353, for example, is<br />

an all-hydraulic unit for large-scale ope-<br />

rations, carrying out 90-degree fan<br />

drilling, 360-degree ring drilling, or<br />

parallel hole drilling at 1.5 m intervals.<br />

The feed beam can be inclined 20<br />

degrees forward <strong>and</strong> 80 degrees backwards.<br />

The hole diameter range is 89-<br />

127 mm, to a maximum recommended<br />

hole depth of 51 m. Drilling control is<br />

automatic, using the Atlas Copco COP<br />

4050 rock drill.<br />

ANFO is the main explosive, mixed<br />

on site. It is not uncommon for it to be<br />

used to blast 100,000 t in a single firing.<br />

The broken ore falls to the bottom of the<br />

Cutoff slot<br />

Drawpoint<br />

Drilling pattern<br />

Cutoff raise<br />

Broken ore<br />

stope, <strong>and</strong> is extracted at the drawpoints<br />

by diesel-powered LHD wheel loaders<br />

with a 6.1 cu m bucket capacity. Then<br />

the ore is either tipped directly into<br />

the passes to feed the crusher or, if the<br />

stope is a long way from the crusher,<br />

into articulated haulage trucks. After<br />

crushing, the ore is sent via a 1.6 km<br />

cable belt to the U62 hoisting system,<br />

where 36 t skips take it to the surface.<br />

Mount Isa aims at 100% extraction<br />

so, in this method, pillars between<br />

blocks also need to be recovered. To<br />

achieve this, open ore stopes are filled<br />

with a cement-based slurry <strong>and</strong>/or rock<br />

mixture. The slurry is a mixture of Port-<br />

l<strong>and</strong> cement <strong>and</strong> concentrator tailings,<br />

whilst the rock is sourced from surface<br />

stockpiles, from the heavy media<br />

rejects from the lead concentrator, or<br />

slag waste from the copper smelter.<br />

The mixture sets into a hard, rock-like<br />

formation, providing a stable face to<br />

enable extraction of the adjacent ore<br />

pillar.<br />

Over half of the site’s production dril-<br />

ling units are Atlas Copco Simba rigs.<br />

As well as these, Atlas Copco Boomer<br />

rigs are used for rockbolting. At Mount<br />

Isa, in total, there are 27 drill rigs for de-<br />

velopment <strong>and</strong> rockbolting, 17 production<br />

drill rigs, 33 LHD loaders, 16<br />

articulated dump trucks for longer haulage,<br />

<strong>and</strong> seven raise drills.<br />

zinc-lead-silver extraction<br />

Panel stoping <strong>and</strong> bench stoping are<br />

used in the zinc-lead-silver mine,<br />

although sublevel open stoping has<br />

been introduced as well, where suitable.<br />

Whereas bench stoping involves<br />

mining the orebody longitudinally, panel<br />

stoping involves mining the orebody<br />

transversely. Panel stoping is still an<br />

open stoping method, <strong>and</strong> was considered<br />

more efficient for mining the wider<br />

orebodies at George Fischer. Bench<br />

stoping is still the preferred method for<br />

the mine’s narrow orebodies.<br />

Prior to the current benching method<br />

being introduced in 1992-93, cut-<strong>and</strong>-<br />

fill was used. In the cut-<strong>and</strong>-fill method,<br />

a horizontal slice of ore up to 4 m-high<br />

is extracted from the length of the ore-<br />

body. Although very selective in highgrade<br />

ores, the method is also expensive.<br />

Benching was introduced as a safer<br />

<strong>and</strong> more efficient method. The cut<strong>and</strong>-fill<br />

method requires a lot of ground<br />

support, as miners work in the orebody<br />

itself. With open stoping, workers are<br />

positioned outside the orebody, in a much<br />

safer working environment. Despite the<br />

larger open void, benching is more cost<br />

effective as less support is required,<br />

<strong>and</strong> the ore can be extracted more efficiently.<br />

In benching, horizontal tunnels, or<br />

‘sill drives’, are driven the length of the<br />

orebody at regular vertical intervals.<br />

The distance between sill drives depends<br />

on local ground conditions, <strong>and</strong> is ty-<br />

pically 15 m. Blast holes are drilled<br />

vertically down from one sill drive to<br />

the lower sill drive. Starting at one end<br />

of the bench, a row of holes is blasted<br />

to remove the rock between the two<br />

sill drives. The broken ore drops to the<br />

bottom of the orebody, <strong>and</strong> is removed<br />

by LHD to the orepass. It is necessary<br />

for the loader to go inside the stope to<br />

remove the ore, so fill is progressively<br />

introduced to the cavity to add stability<br />

102 underground mining methods

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