Mining_Methods_UnderGround_Mining - Mining and Blasting

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