Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02466114 2004-05-03
CONTINUOUS EXTRACTION OF UNDERGROUND NARROW-VEIN METAL-BEARING
DEPOSITS BY THERMAL ROCK FRAGMENTATION
Field of the Invention
The present invention relates to a method for extracting minerals from a
narrow-vein
mining deposit through utilization of a thermal-induced rock fragmentation to
channel out the
mineralization.
Background of the Invention
Exploitation of narrow-vain deposits represents great challenges. Highly
selective
mining methods for this type of exploitation are associated With high
operational constraints that
interfere with mechanization. Conventional methods require a substantial
amount of skilled
manpower, which is becoming a scarce commodity. High operational costs results
in the
profitability of these deposits to be rather risky. In order to ensure the
survival of this type of
exploitation, it is crucial to develop innovative equipment and mining
methods.
The mineral inventory of a mining operation is classified into reserves and
resources,
reserves being the economically mineable part. Resources involve a level of
geological
knowledge that is usually insufficient to enable an appropriate economic
evaluation or, in some
cases, the estimated grade is lower than the economic grade.
In recent years, the long-hole mining method has been used in soave narrow-
vein ore
mining operations. Such a method is not always suitable to the operation
conditions.
Implementation of the method involves large blasts that damage the rock mass
with several
fractures that cause rock face instability resulting in frequent fall of waste
rock. This waste
mixes up with the broken ore and adds to the planned dilution in reserve
estimate. Like the ore,
this waste rock must be mucked and processed, significantly increasing
operation costs.
SUMMARY OF THE INVENTION
One aspect of the present invention relates to a method for extracting
minerals from a
narrow-vein deposit. Location of the vein and determination of the extent
thereof forms the
boundaries of the stope. Access to the stope is prepared by excavating an
upper drift and a
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CA 02466114 2004-05-03
lower drift to form a panel therebetween. Equipment and a burner are installed
from the upper
drift. The burner is moved along a panel surface in a predetermined pattern,
while spalled rock
chips from the panel surface are collected at the lower drift. By providing
highly selective
extraction of ore, thermal fragmentation allows for substantial savings on ore
transportation, ore
processing and on the environmental level by reducing the generated waste
volume.
Another aspect of the invention relates to a method of extracting minerals
from narrow-
vein deposit including the step of ascertaining the extent of the vein and
establishing an
extraction zone of material, which extends beyond the extent of the vein. A
surface of the
extraction zone is then exposed after which a source of heat is provided,
capable of inducing
thermal fragmentation of the material in the extraction zone. The source of
heat is moved across
the surface while maintaining sufficient proximity to cause thermal
fragmentation of the material
on the surface. The fragmented material is collected.
Another aspect of this invention includes the use of a plasma torch for
extraction of
narrow-vein mineral deposits. The plasma torch is moved across a surface of
the deposit, in a
sweeping movement, at a rate which, while maintaining sufficient proximity of
the plasma torch
with the surface of the deposit, induces thermal fragmentation to a layer of
the deposit.
BRIEF DESCRIPTION OF THE DRAWINGS
The following description will be more readily understood with reference to
the drawings
in which a preferred embodiment of the invention is illustrated.
Figure lA is an elevational view of a cross-section of a stope, with Figure 1B
being a
plan view thereof, showing a first phase of the operation;
Figure 2A is an elevational of a cross-section of a stope, with Figure 2B
being a plan
view thereof, showing a second phase of the operation;
Figure 3A is an elevational of a cross-section of a stope, with Figure 3B
being a plan
view thereof, showing a third phase of the operation;
Figure 4A is an elevational view of a cross-section of a stope, with Figure 4B
being a
plan view thereof, showing a fourth phase of the operation;
Figure 5A is an elevational view of a cross-section of a stope, with Figure SB
being a
plan view thereof, showing a fifth phase of the operation; and
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Figures 6A and 6B are schematic diagrams in plan view comparing thermal torch
fragmentation method versus the prior art long-hole mining method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A mining method generally consists of four distinct steps: drilling, blasting,
mucking,
and transport of the ore to the shaft for hoisting to the surface. The
application of the method
described herein enables a reduction in the required number of steps; drilling
and blasting being
replaced by a single step of continuous rock fragmentation.
The present invention provides a method of using a burner to exploit
underground
narrow-vein metalliferous deposits by thermal fragmentation, through sweeping
in a sequence
across the height and width of the vein. Most of the items or equipment
required to perform the
method are in common usage in mining operations, except for the plasma torch
equipment and a
vacuum system to draw off the ore. A plasma torch is used as the source of
heat by which
thermal fragmentation or spalling of a surface layer of the deposit is
induced. While other types
of burners could be utilized, plasma torches are preferred as they do not
produce the emissions
that combustible fuel torches do. Plasma torches produce intense heat and the
higher rate of
heating expedites the thermal fragmentation process. The intense heat,
however, necessitates the
movement of the torch in a sweeping pattern to avoid localized fusion of the
rock.
Figures lA and 1B illustrate the general arrangement of a standard stope 10.
In a first
phase, cross-cuts 12,13 are developed to access the upper and lower levels of
a mineralized
block 14. These accesses 12,13 are planned to intercept mineralization at the
block centre 16,
thus separating the stope 10 in two. From the upper and lower accesses 12,13,
upper and lower
drifts 18,20 are developed in the ore. The plan view of Figure 1B shows the
stope accesses
12,13 leading to the drifts 18,20. These drifts 18,20 represent the upper and
lower limits of the
stope 10 to be processed. Preferably, the maximum distance on either side of
the stope access is
limited to 50 meters, which will ensure proper efficiency of the vacuum
devices and plasma
torch. One skilled in the art would appreciate the distance may vary according
to the limitations
of different equipment.
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After the stope accesses 12,13 and drifts 18,20 arecompleted , a~ service
raise 22 is
excavated at the block centre 16. The main purpose of the raise 22 is to
enable workers to access
sub-levels, transport equipment and to supply required ventilation, water, air
and electric lines.
From the service raise 22, a sub-level 24 is preferably excavated to reduce
the vertical
mining distance in order to easily follow the mineralization, which is
generally not rectilinear
over long distances.Slot raises 26,28 are also developed at each stope
extremity to allow initial
installation of the plasma torch equipment (not shown in Figures lA and 1B).
Finally, small
openings 30 are preferably excavated in the upper and lower stope cross-cuts
accesses for the
installation of the vacuum device and the equipment required to operate the
plasma torch. The
final arrangement of the various drifts and raises results in the mineral
block 14 being sectioned
into a plurality of panels 32.
Preliminary tests that were performed on granite blocks demonstrated that rock
is broken
into small chips or fragments by moving a plasma torch along the rock surface.
This rock-
fraeturing through thermal fragmentation occurs as a result of thermal shock
created by the
plasma torch flame on contact with the rock surface. The generated chips have
a dimension that
is usually less than 2 cm.
As shown in Figures 2A and 2B, burner equipment 34 is installed from the sub-
level 24
or from the drift located above the section to be extracted. During
fragmentation, the burner 36
is moved from top to bottom in a back-and-forth movement, as well as from left
to right between
the sidewalk of the panel. When the spalling efficiency diminishes, a
mechanism associated
with the equipment 34 brings the burner 36 closer to the rock face 38. Once
the mechanism
reaches a maximum extension, all of the equipment 34 is brought closer to the
face 38 and
spalling continues. Preferably the burner 36 is moved at a controlled rate
through a
predetermined pattern.
As indicated above, the preferred embodiment of the stope 10 is separated into
four
panels 32 and each panel 32 is extracted consecutively in a predetermined
sequence. After the
extraction of a panel 32 as shown in Figure 3A, an opening is created between
two drifts or, in
the case of Figure 3A, between the lower drift 20 and the sub-level 24;
consequently, it will be
impossible to travel in the lower drift. Thus, extraction should begin in the
lower panels 32a,
32b and then move upward.
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As the burner 36 sweeps along the rock face 38, the rock chips 42 are
extracted. Since
this mining method is directed towards a highly selective ore extraction, the
excavated rock
volume is low while the grade of the rock is high. The low rock volume
produced to be handle
enables a simple mucking system to be implemented at a low cost. An example of
such a system
is shown in Figures 2A and 2B which uses a metal container 44 that can hold up
to 8 tons of ore.
The container 44 is positioned directly under the work face 38 at the base of
the opening 40 to
recover the falling rock fragments 42. The winch 52 hoists the container to
follow the mining
process. Afterwards, the accumulated ore is vacuumed by the vacuum system 46
through
vacuum hoses 48 into a mine car 50.. It is suggestible to perform mucking
twice per work shift,
thereby eliminating the requirement of having a full-time employee on mucking
operations.
The mining sequence of the preferred stope embodiment is shown in Figures 2A
to 5A.
Firstly, the plasma torch equipment 34 is installed in the sub-level 24 above
panel 32a, as shown
in Figure 2A. The ore container 44 and the winch S2 are installed in the lower
drift. The
vacuum system 46 is located in the lower stope access 13 and a hose 48 of
sufficient length is
used to vacuum the accumulated ore from inside the container 44. The burner 34
is moved
across the rock surface 38 in a repetitive sweeping movement to remove
successive layers of
rock 38, while the container 44 is moved in unison with the burner equipment
34 to continuously
catch the falling rock fragments 42. Preferably, not the entire panel 32a is
removed so as to
leave a supporting pillar 54 (see Figure 3B). Once panel 32a is complete, the
equipment 34 is
transferred to the opposite lower panel 32b for use in a similar arrangement,
as shown in Figure
3B.
In order to extract upper panels 32c, 32d, the plasma torch equipment 34 is
mobilized in
the upper drift 18 and the mucking equipment is installed in the sub-level 24,
as shown in
Figures 4A and 5A. However, the opening 40 created during the extraction
phases, as shown in
Figures 2A and 3A, extends through the sub-level floor an approximate width of
45 cm, as
shown in Figure 6A. Therefore, workers should be secured during their
displacement, such as by
securely tying themselves to a lifeline. Furthermore, depending on ground
conditions,
construction of a floor could be required to block access to the opening.
CA 02466114 2004-05-03
The vacuum system 46 remains in the lower access 13 throughout the extraction
of the
stopel0 and the suction hose 48 is extended as required. As mentioned
previously, the service
raise 22 or slot raises 26,28 are used to move equipment inside the stope I0.
The application of the thermal fragmentation method with a burner or plasma
torch
allows for high selectivity, the possibility of mechanization, continuous
mining, immediate ore
recovery, and elimination of the use of explosives. Figure 6A shows that the
opening 40 formed
with the present thermal fragmentation method is 4 times smaller than the
opening 60 formed
through traditional long-hole mining with explosives as seen in Figure 6B,
therefore much less
waste 62 is generated. The boundaries of the extraction zone 64 for the
thermal fragmentation
method, shown by dotted lines 66 in Figure 6A, which extend beyond the
ascertained width 68 of
the vein 70, can be much narrower than the required extraction zone 74 for the
long hole blasting
method, shown by dotted lines 76 in Figure 6B, which extend significantly
beyond the
ascertained width 78 of the vein 80, thus leading to greater amount of waste
62 in the mined ore.
Furthermore, after the extraction, the walls 82 have more stability than walls
84 that have
been massively fractured, as through long-hole blasting methods. Mineral
recovery is
immediate, as compared to conventional methods in which the mineral may remain
underground
in inventory for a period of time, sometimes being non-recoverable due to
stope instability,
which results in significant financial loss.
As shown in Table l, selective mining allows for a substantial reduction in
extracted
tonnage. A smaller volume of rocks for handling and processing directly
impacts operation
costs. Moreover, a continuous penetration in the rock allows dynamic
readjustment of the
extraction in order to stay inside the mineralized zone and consequently avoid
dilution from
mining.
The method of the present invention allows fox continuous extraction since the
process
do not generate large amount of gas compared with the explosives. A 7-day work
schedule is
therefore possible, rather than the typical 5-day work schedule currently
employed in narrow-
vein mines. Such a work schedule would increase annual production, thereby
decreasing indirect
operational and depreciation costs.
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Table 1 - Comparison of thermal fragmentation with plasma torch and long-hole
mining
methnri~
Calculated Tonnage based Thermal Long-hole
on a reserve
block of 100 m by 45 m Fragmentation
Grade in situ (ozls.ton) 1.70 1.70
Width in situ (cm) 30 30
OYe development
Development tonnage (s.ton)6 506 8 130
Development grade (oz/s.ton)0.22 0.22
Mining
Geological reserves (s.ton)3 166 2 965
Grade of geological reserves1.70 1.70
(g/t)
Minimum width (cm) 45 180
Planned dilution 50% 500%
Walls dilution 0% 35%
Stope recovery 95% 85!
Planned mining reserves 4 511 20 413
(s.ton)
Mined grade 1.13 0.21
Mill recovery 95% 95%
Produced ounces (stope 6 220 5 757
and
develo ment
Thermal fragmentation Long-hole
Unit cost Total Unit cost Total
$ls.ton $ $ls.ton $
_ 354 252 462 889
Development
Mining cost ($It) 5$-~~ 262 564 19.00 387 852
,
Mucking 5.00 22 557 4.00 81 653
Transport to mill (stope) 24 813 5.50 112 273
5.50
Transport to mill 5 35 785 5.50 44 714
50
.
(development)
Milling (stope) 10.37 46 783 12.20 249 042
Milling (development) 12.2079 377 12.20 99 183
TOTAL 826131 1 437 607
CAN$ per short ton 74.98 50.37
CAN$ per ounce 132.82 249.71
x "' .r(1:~5~:. .. 8~1: . v6z2.~31,
Ext~erimental Setup
A test case was conducted by elaborating a mining concept using thermal rock
fragmentation with a plasma torch to mine extremely narrow veins. The test
case was developed
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according to commonly found stope dimensions in mining operations. A stope
height of 45
meters was selected, which corresponds to the standard distance between two
levels. For
equipment operational reasons, the maximum length was fixed to 100 meters.
Table 2 lists the
details of development of the scope.
Table 2 - Details of developments
Width Height Length
(m) (m) (m)
Upper access 2.7 2.7 10
Lower access 2.7 2.7 10
Upper ore drift 2.4 2.4 100
Lower ore drift 2.4 2.4 100
Service raise 2.4 2.4 40
-
_ -- 2.4 2.4 98
Sub-level
Slot raises 1.8 1.8 76
Excavation for plasma torch 3.0 2.4 4.5
equipment
3.0 2.7 4.5
Excavation for vacuum
One skilled in the art will appreciate that variations in the number of panels
is possible.
As an example, excavation could be performed in a single lowex panel 1 or 2
without forming or
expanding to the upper panels 3 or 4.
Another variation exists in the sweeping of the burner. The burner can, be
swept from left
to right or right to left, while progressing from the top of the stope panel
to the bottom.
Alternatively, sweeping can occur from top to bottom, while progressing from
left to right or
right to left. The pattern and rate of motion of the burner/plasma torch will
be dependent on
several factors, including but not limited to the physical dimensions of the
deposit, the
composition of the deposit, variations in the deposit, desired fragmentation
rate/volume, type and
output of the burner/plasma torch, etc. The rate and pattern can be
predetermined through
theoretical considerations and/or empirical evaluation of test samples. The
rate and pattern can
also be adapted dynamically during the process to ensure optimization of
fragmentation.
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Optimization does not necessarily mean increased fragment size, as fragment
size can have an
affect on the removal process in the case of vacuum removal, for example, or
on subsequent
processing steps. Volumetric removal rate (yield) is typically a better
indicator of efficiency.
Another embodiment of the present invention provides for automatic operation
of the
equipment. Thus, the operator can safely remain in a workplace outside of the
stope, while the
automatic equipment operates within the stope. Cameras can be used to monitor
progress.
Furthermore, automatic detection of surface edges could be employed, further
reducing input
required from an external operator and eliminating the need for cameras. In
such an automatic
system, the burner could be provided on a platform extending up from the floor
of the lower
drift.
While there has been shown and described herein a method for continuous
extraction of
deposits in narrow-vein mining applications, it will be appreciated that
various modifications and
or substitutions may be made thereto without departing from the spirit and
scope of the
invention.
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