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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caving in primary rock. Currently, two<br />
forms of panel caving are in use: stan-<br />
dard panel caving as applied in the<br />
Teniente 4 Sur Sector; <strong>and</strong> panel<br />
caving with pre-undercut as used in the<br />
Esmeralda Sector.<br />
exploitation sequence<br />
The panel caving exploitation sequence<br />
initially used involved development<br />
<strong>and</strong> construction of production levels,<br />
undercutting at the undercut level, <strong>and</strong><br />
ore extraction. However, the dynamic<br />
caving fronts, under high stress conditions<br />
of 40-60 Mpa, resulted in substantial<br />
damage to the infrastructure.<br />
Indeed, extraction in El Teniente Sub<br />
6 Sector had to be stopped in March,<br />
1992 after several rockbursts caused<br />
fatal accidents, reflecting the low level<br />
of knowledge at the time about mining<br />
in primary rock.<br />
Between June, 1994 <strong>and</strong> August, 1997,<br />
El Teniente carried out experimental<br />
mining in a pilot area of 12,000 sq m.<br />
This process was closely monitored, <strong>and</strong><br />
the data served as the basis for a full<br />
geomechanical study. From September,<br />
1997 to June, 1998, during the preoperational<br />
phase, it was realized that<br />
it was necessary to research the relationship<br />
between seismic potential,<br />
undercutting speed <strong>and</strong> the mining of<br />
new areas. Because of this, <strong>and</strong> for the<br />
first time since the 1992 production<br />
freeze, El Teniente carried out preparatory<br />
work in a 6,000 sq m area using<br />
simultaneous production techniques.<br />
The test succeeded, with no significant<br />
rockbursts, thus proving the relationship<br />
between seismicity <strong>and</strong> caving<br />
speed. Indeed, it is now recognized that<br />
the uncontrolled seismicity induced by<br />
the mining extraction rate of advance<br />
of the caving face <strong>and</strong> extraction speed<br />
has been the main cause of damage to<br />
the tunnels <strong>and</strong> infrastructure on the<br />
lower levels.<br />
Nowadays, there are variables incorporated<br />
into the mining design <strong>and</strong> planning<br />
concept to control the excess of<br />
seismic activity, not only improving the<br />
working conditions on the production<br />
level, but also increasing productivity.<br />
During the pre-operational phase, over<br />
2 million t were removed from Teniente<br />
Sub 6, with only two small rockbursts.<br />
Panel caving with pre-undercut at Esmeralda.<br />
esmeralda pre-undercut<br />
Following on from the studies <strong>and</strong> controlled<br />
tests, El Teniente introduced a<br />
variation of its conventional panel caving<br />
undercut sequence. Known as<br />
pre-undercut, it essentially consists of<br />
developing the production level behind<br />
the undercut, rather than the more<br />
typical method where the production<br />
development is carried in parallel with<br />
the undercut ahead of the caving face.<br />
The pre-undercut achieves a better redistribution<br />
of the stresses ahead of the<br />
production development, resulting in<br />
less damage <strong>and</strong> improved safety.<br />
Although the pre-undercut variant<br />
had been tested in some small sectors of<br />
the mine, it was first used on an industrial<br />
scale in the new Esmeralda sector.<br />
Occupying a total area of 714,000 sq<br />
m, Esmeralda is located at 2,210 m asl<br />
within the El Teniente deposit, bounded<br />
el TenienTe, CHile<br />
on the west by the Braden breccia pipe,<br />
<strong>and</strong> in the north by El Teniente Sub 6<br />
Sector, <strong>and</strong> is below the Teniente 4 Sur<br />
Sector. Lithologically, it occurs mainly<br />
in <strong>and</strong>esite, <strong>and</strong> contains a total mineral<br />
reserve of 365 million t, with an average<br />
grade of 1.01% of copper <strong>and</strong> 0.024%<br />
of molybdenum. The total investment<br />
for Esmeralda was US$205.6 million,<br />
with conceptual engineering <strong>and</strong> design<br />
initiated in 1992, <strong>and</strong> caving starting in<br />
August, 1996. Ore production started in<br />
September, 1997, <strong>and</strong> has built up from<br />
an average of 4,000 t/day in 1998 to<br />
19,500 t/day in 2001, <strong>and</strong> full production<br />
of 45,000 t/day from 2005.<br />
Caving at Esmeralda was achieved<br />
with 16,800 sq m of available production<br />
undercut, once a problem of 'support<br />
points' was solved. These formed<br />
above the apex of the crown pillar, <strong>and</strong><br />
reduced the interaction between draw-<br />
points, making the flow of ore from<br />
underground mining methods 85