Mining_Methods_UnderGround_Mining - Mining and Blasting
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