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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zinkgruVan, Sweden<br />
Changing systems at zinkgruvan<br />
Partners in<br />
production<br />
Zinkgruvan <strong>Mining</strong>, Sweden’s third<br />
largest mining company, is owned<br />
<strong>and</strong> operated by Lundin <strong>Mining</strong><br />
Group. Zinkgruvan <strong>Mining</strong> produces<br />
zinc concentrate (55% Zn) <strong>and</strong><br />
lead concentrate (73% Pb <strong>and</strong><br />
l,400 g/t Ag) <strong>and</strong> ships to smelters<br />
in northern Europe. The mine<br />
has been continuously in produc-<br />
tion since 1857, <strong>and</strong> ore output<br />
in 2006 was 787,000 t, together<br />
with around 250,000 t from waste<br />
development. Average zinc grades<br />
were high at 10.3%, whereas lead<br />
grades fell to 4.6%, <strong>and</strong> silver to<br />
93 g/t. For 2007, ore production<br />
is planned at 850,000 t, <strong>and</strong> a pro-<br />
ject to increase reserves is underway.<br />
Zinkgruvan ore reserves total<br />
11.2 million t, containing 9.3%<br />
zinc, 4.3% lead <strong>and</strong> 107 g/t silver,<br />
equivalent to approximately 15<br />
years of production. Added to<br />
this, discovered in the 1990s, is a<br />
copper mineralization of 3.5 million<br />
t containing 3.1% copper <strong>and</strong><br />
49 g/t silver.<br />
Production is obtained from<br />
open stopes where, following<br />
difficulties with seepage from<br />
hydraulic fill when rock quality<br />
diminished, the mine now uses<br />
paste fill. Rather than deepen<br />
the main hoisting shaft, the main<br />
ramp access was developed be-<br />
low the 800 m level <strong>and</strong> will bot-<br />
tom out at 1,100 m under present<br />
plans. Key to Zinkgruvan production<br />
efforts is equipment sup-<br />
plied by Atlas Copco, which includes<br />
four Simba production<br />
drill rigs, three Rocket Boomers<br />
<strong>and</strong> two Boltec rigs, together<br />
with long-term maintenance <strong>and</strong><br />
consumable supply contracts.<br />
Methodology<br />
Until the mid-1980s, upwards cut <strong>and</strong><br />
fill was the dominant mining method.<br />
However, when mining began at the 650<br />
m-level in Nygruvan, the first problems<br />
with rock stress occurred, resulting in<br />
the need for increased rock reinforcement.<br />
Longhole drilling with Simba M4 C in the Burkl<strong>and</strong> stopes.<br />
When mining reached the 566 mlevel,<br />
a borehole camera survey revealed<br />
a roof split 6 m above the stopes, causing<br />
ab<strong>and</strong>onment of cut <strong>and</strong> fill methods<br />
on safety grounds.<br />
Benching methods were introduced,<br />
<strong>and</strong> have been under constant development<br />
since, primarily because of high<br />
rock stress. Using benching, no working<br />
place need be developed wider than 7 m.<br />
Over the years, benching has developed<br />
from longitudinal bench <strong>and</strong> fill.<br />
The mined out bench is backfilled with<br />
hydraulic fill before mining the next<br />
bench above. Vertical pillars in the ore<br />
are left to stabilize the surrounding rock.<br />
Open stoping<br />
Development continued towards sublevel<br />
open stoping, which is a larger<br />
scale stoping method than longitudinal<br />
bench <strong>and</strong> fill, with improved rock<br />
stress.<br />
Sub-level open stoping as a production<br />
method worked excellently in<br />
Nygruvan, where the country rock is<br />
of extremely good quality. The ore is<br />
homogeneous, with distinct ore boundaries<br />
where dip in the ore is greater than<br />
75 degrees. The open room that is<br />
formed after the stope is mucked has<br />
height measurements of up to 70 m,<br />
width of 15 m, <strong>and</strong> a length of 50 m.<br />
After mucking is completed, the drawpoints<br />
are sealed with bulkheads, <strong>and</strong><br />
filled with hydraulic fill.<br />
In the mid-1990s, the Burkl<strong>and</strong> orebody<br />
was developed. Rock quality <strong>and</strong><br />
ore geometry were different compared<br />
to earlier orebodies, <strong>and</strong> a project was<br />
initiated to utilize a modified sub-level<br />
open stoping method for orebodies with<br />
weaker hanging walls, but retaining the<br />
advantages of the stoping method.<br />
In this method, open stopes have the<br />
approximate dimensions 40 m-high x<br />
50 m-long, <strong>and</strong> the orebody width up<br />
to 30 m. Pillars up to 10 m-thick are<br />
left between every stope to support the<br />
hanging wall, so some 16% of the ore<br />
is utilized as pillars. After the first stope<br />
underground mining methods 53