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