Mining_Methods_UnderGround_Mining - Mining and Blasting

longhole open stoping has contributed
to a lower production cost, but the fill
adds expense. However, because the
method does not normally require pillars,
no rock is sterilized when mining
the secondary stopes. These savings
offset the fill costs, and 800,000 t is
added to the ore reserves.
CMS surveys on the first two primary
stopes in Bu 450 showed that
drilling and blasting had followed the
ore boundaries according to plan.
Paste fill
Hydraulic fill was introduced to Zinkgruvan
in the early 1970s when the new
mill was built, and was used successfully
for many years. However, during
the transition to sub-level open stoping,
difficulties arose in sealing the open
stopes when using hydraulic fill. The
bulkheads could not be sealed against
the cracked rock in the draw points, and
there was also seepage through cracked
pillars. Because of the difficulties of
managing the fill, certain stopes have
not been filled, as the risk of fill collapsing
is greater than the chances of
a hanging wall collapsing in the open
stopes.
Alternatives that were studied included
hydraulic fill, with cement for about
50% solidity; paste fill, with cement for
70-76% solidity; and high-density fill,
with cement for greater than 76% solidity.
Paste fill with cement was selected
for longhole open stoping with primary
and secondary stopes. Investments
required in the paste plant, and for pipe
installations underground, reached
about 45 million SEK. Golder Paste
Technology, together with Zinkgruvan
personnel, handled the design, construction
and building.
Stope design criteria
The design of stope sizes was based on
the developed levels in the Burkland
ore. The paste fill is horizontally transported
1.4 km in order to reach these
stopes, so has to be pumpable. The fill
also has to have a minimum strength
of 0.35 Mpa, to handle a free-standing
height of 40 m.
The uni-axial pressure test and pumpability
test resulted in the specifications
Rocket Boomer M2 C developing the sublevels.
Paste fill specifications
for paste fill in the two orebodies shown
in the table above.
zinkgruVan, Sweden
Nygruvan Burkland
Primary stope 4 % cement 6 % cement
Secondary stope 1.5 % cement 2 % cement
Slump 150-180 mm 200-250 mm
Plan of stope extraction level.
Ore shaft
Ventilation
P
S
Ore outline
Waste shaft
Paste fill is transported to the 350 m-
level of the mine through two boreholes,
underground mining methods 55
Ramp
P
S
P
Ore drive
S
Transport drift
P
P=Primary
S=Secondary
S
Footwall drive
P