Mining_Methods_UnderGround_Mining - Mining and Blasting

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