Note: Descriptions are shown in the official language in which they were submitted.
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THERMAL ROCK FRAGMENTATION APPLICATION
IN NARROW VEIN EXTRACTION
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to ore extraction and, more
particularly, to thermal fragmentation mining for extracting ore from narrow-
veins.
Description of the Prior Art
For many years, mine operators have worked on various ways to
mechanize mining. They have succeeded in many cases where the ore volume
was sufficient to justify the high capital costs of equipment and the required
infrastructures. Narrow-vein deposits, for their part, presented a greater
challenge
in terms of mechanization. Selective mining methods, such as shrinkage, were
replaced by using a mechanized long-hole mining method. Despite all. the
efforts
put into place, success stories remain rare. The difficulty in controlling
wall
stability following blast vibrations often resulted in high dilution,
preventing
narrow-veins extraction from being economically viable. Indeed, veins of small
cross-section have in the past been uneconomical to mine since with the
current
mining methods a small vein necessitates the removal of a large quantity of
waste
rock on either sides of the vein. A large quantity of ore must then be
processed to
retrieve the small quantity of desired minerals.
Therefore, a great number of known narrow veins of
mineralization are not presently mined since mining of such minerals is not
economically viable due to the limitations of the present mining methods.
SUMMARY OF THE INVENTION
It is therefore an aim of the present invention to provide a new ore
extracting process for allowing narrow veins of mineralization to be mined
profitably.
It is a further aim of the present invention to provide a new and
efficient mining approach for extracting ore from narrow-veins.
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It is a still further aim of the present invention to optimize ore
recuperation.
It is a further aim of the present invention to provide a new
narrow-vein ore extraction process by which dilution from the walls of the
vein is
minimal.
Therefore, in accordance with the present invention, there is
provided a method for extracting ore from an ore vein deposit, comprising the
steps of a) establishing the location of the rock walls bordering the ore vein
deposit, b) causing the ore comprised between the rock walls to span into
fragments, and c) retrieving the fragments.
In accordance with a further general aspect of the present
invention there is provided a process for extracting ore from a vein having
opposed sidewalk, comprising the steps of a) drilling pilot holes directly in
the
vein at specific intervals therealong, b) using thermal fragmentation,
enlarging the
pilot holes until the vein is fragmented, and c) recuperating the fragmented
ore
along the vein.
In accordance with a further general aspect of the present
invention, there is provided a free-blast mining method for extracting ore
from a
vein having opposed sidewalk, comprising the steps of: locating the vein and
determining the extent thereof, b) moving the burner at a controlled rate of
travel
between the sidewalls of the vein to cause the ore comprised in the vein to
span
into fragments, and c) retrieving the fragments.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the nature of the invention,
reference will now be made to the accompanying drawings, showing by way .of
illustration a preferred embodiment thereof, and in which:
Fig. 1 is a schematic comparison between a long-hole mining
method and a thermal fragmentation mining concept in accordance with a
preferred embodiment of the present invention;
Fig. 2 is a schematic top plan view of an ore vein illustrating how
the ore can be recuperated by thermal rock fragmentation;
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Fig. 3 is a schematic elevation view showing a surface excavation
design that can be used when the narrow vein is extracted by thermal
fragmentation;
Fig. 4 is a schematic perspective view of a narrow vein in the
S process of being grooved out by thermal fragmentation in accordance with a
further embodiment of the present invention; and
Fig. 5 is a schematic side elevation view illustrating a thermal
fragmentation channeling operation carned out for extracting ore from a narrow
vein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It is a problem in the field of mining to economically extract high
grade materials, such as gold, platinum, copper or other precious materials,
from
a narrow vein of mineralization. A narrow vein of mineralization is normally
not
commercially mined because the return in volume of useable mineral for the
amount of ore removed and the amount of labor required to remove the ore
render
it uneconomical to retrieve the desired minerals in a narrow vein application.
As
will be seen hereinafter, the present invention provides a solution to that
particular problem by significantly minimizing the dilution of the precious
mineral into the surrounding waste rock during the extraction operation.
Unlike conventional mining methods which require that a great
amount of commercially worthless rock (barren) be removed on either side of
the
vein due to the utilization of explosive charges, the present free-blast
mining
method provides for the removal of the true value only, i.e. the extraction of
the
mineral deposit from the surrounding environment. This may be readily
appreciated from Fig. 1 which shows a schematic comparison between the
dilution associated with a conventional mining method and the present thermal
fragmentation mining method. More particularly, according to the conventional
long-hole mining method, blastholes 10 are drilled in the vein 12 and on
either
side thereof. Each blasthole 10 is filled with an explosive charge, such as
dynamite, and the region in the vicinity of the blastholes 10 is fragmented by
the
explosive power of the charge. This results in the formation of a large trench
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which extends laterally outwardly of the vein sidewalk 16 along all the length
of
vein 12. For instance, in the case of a vein having a 30 cm (12 inches) width,
a
trench of 140 cm (55 inches) in width will have to be blasted. This implies a
dilution of about SS cm (22 inches) on each side of the vein 12 throughout the
length thereof. That is to say that the amount of waste or commercially
worthless
material that has to be mined is significantly greater than the amount of
material
comprised between the vein sidewalk 16. The ratio is about 6 tonnes of
commercially worthless matter for 1 tonne of desired mineral.
In contrast, according to the present invention, pilot holes 18 (not
blastholes) are defined directly in the vein 12 and subsequently enlarged or
reamed by thermal fragmentation to the vein sidewalk 16, thereby avoiding
dilution of the ore body contained in the vein in the commercially worthless
matter located outwardly of the vein sidewalls 16. The trench can be kept as
narrow as possible. This permits to extract 1 tonne of the desired mineral for
2
tonnes of gangue.
According to a preferred mode of extraction of the present
invention, a first series 20 of three pilot holes 22, 24 and 26 are drilled
directly
into the vein 12 at predetermined longitudinal intervals, as shown in Fig 2.
The
intervals are determined by the width of the vein 12. For a vein having a 12
inches (30 cm) width, the pilot holes are preferably of about 6 inches (15 cm)
in
diameter and spaced by a distance of about 21 inches (53 cm). Each pilot hole
is
between 40 feet (12 m) to 60 feet (18 m) deep and substantially center
relative to
a central axis of the vein 12. The broken material produced is recuperated and
subsequently processed to separate the mineralized material from the barren.
The next step consists in the verification of the pilot holes 22, 24
and 26. In order to make sure that the pilot holes 22, 24 and 26 are in the
vein 12,
a conventional in-the-hole device (not shown) is used to locate the vein 12.
Once
the ore is located in the pilot holes 22, 24 and 26, thermal fragmentation is
started
to enlarge each pilot hole to the sidewalk 16 of the vein 12. In practice, it
is
understood that the pilot holes 22, 24 and 26 might in some instances be
thermally reamed to a location which is located slightly outwardly of the
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sidewalls 16 of the vein 12, as shown in dotted lines in Fig. 2. Each pilot
hole. is
enlarged by lowering a strong burner (not shown), powered by diesel fuel and
air,
into the hole and by igniting it. The burner could also be provided in the
form of a
plasma torch, especially in underground mining operations. The heat generated
by
the burner raises the temperature in the hole up to 1800° C. This
creates thermal
stresses that spall the rock. In simple terms, spalling is considered to be a
form of
decrepitation caused by an unequal expansion of rock crystals which overcomes
molecule cohesion. The broken or fragmented material produced during this
process ranges in size from fine grain to 4 cm (1.6 inch).
The first three pilot holes 22, 24 and 26 are preferably individually
enlarged along all the length thereof from bottom to top in a predetermined
sequence starting with the first hole 22, the third hole 26 and the second
hole 24.
The broken material produced during the thermal fragmentation operation of the
first and third holes 22 and 26 is preferably left in the holes to act as a
thermal
1 S barrier for preventing heat from escaping from the second hole 24 when the
pillars of material separating the second hole 24 from the first hole 22 and
the
second hole 24 from the third hole 26 start to become fragmented, thereby
allowing heat to pass from the second hole 24 to the first and the third holes
22
and 26. By leaving the fragmented material in the holes until the thermal
fragmentation is fully completed in the adjacent hole, significant saving can
be
made in term of thermal energy consumption. As shown in dotted lines in Fig.
2,
the second hole 24 is enlarged to a greater extent than the first and third
holes 22
and 26 so as to completely fragment the pillar between the first and second
holes
22 and 24 and the pillar between the second and third holes 24 and 26.
Thereafter, a second 'series 28 of pilot holes, comprising two
longitudinally spaced-apart holes 30 and 32, are drilled directly in the vein
12 at
the downstream end of the first series 20. The second pilot hole 32 of the
second
series 28 is first enlarged by thermal fragmentation followed by the first
pilot hole
30. As for the first series 20, the fragmented material produced during the
thermal
fragmentation performed in each hole is preferably left in the hole and the
first
pilot 30 is enlarged to a greater extent than adjacent holes 26 and 32. As a
general
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rule, the holes which are enlarged to a large size are always comprised
between
two pairs of pilot holes which have already been enlarged. As represented by
reference numeral 34 further pairs of longitudinally spaced-apart pilot holes
36
and 38 are subsequently drilled and enlarged until the end of the vein 12 is
reached.
Once the vein 12 has been fragmented on all the length thereof or
along a sufficient portion thereof, the fragmented material is recuperated as
by
aspiration.
For deep veins extending more than 60 feet (18 m) deep into the
surrounding strata, the waste rock surrounding the veins can be blasted after
the
ore contained in the first 60 feet (18 m) deep or so of the veins has been
recovered as per the way described hereinbefore. In this way, the ore body of
the
vein can be fragmented and retrieved on another 60 feet (18 m) deep by
repeating
the above described steps from the new excavated bench level. It is understood
that the 60 feet (18m) deep is dictated by the limits of the drilling
equipment and
is only given for illustrative purposes.
As shown in Fig. 3, for a three-bench extraction of narrow veins,
the stripping ratio is much less when using the thermal fragmentation mining
concept. Because of the small size of the mobile equipment (the burner), the
final
pit shape can be kept as narrow as possible. This provides significant mining
cost
reduction. It is also advantageous in that it contributes to minimize dilution
by
avoiding stripping of waste.
The second bench level 40 is formed by blasting the waste rock 42
surrounding the vein 12 after the ore body comprised in the first 60 feet (18
m)
deep of the vein 12 has been retrieved from the first or surface level. After,
the
second bench level 40 has been excavated, the mining equipment, including the
drill and the burner, is moved onto the platform of the second bench level 40
and
pilot holes are drilled and enlarged by thermal fragmentation as per the way
described hereinbefore. The fragmented material is retrieved as by aspiration
and
the site is further excavated to form a third bench level 44 to permit
retrieval of
the remaining deepest portion of the vein 12.
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The above described thermal fragmentation mining method can be
adapted to either surface or underground mining.
According to a further general aspect of the present invention,
thermal fragmentation is used to carry out a channeling operation directly
into the
ore vein deposit to proceed with the extraction of the ore body from the
surrounding waste rock without having to drill pilot holes into the vein.
As shown in Fig. 4, the ore vein 12 is first localized and a vertical
face 46 at one end of the vein 12 is exposed as by excavation. Then, a
vertical
channel is cut in the exposed vertical face 46 between the rock walls 16
bordering
the ore vein deposit. The vertical channel is obtained by directing the flame
generated by the burner against the exposed vertical face and by moving the,
burner vertically and sideways at a controlled rate of travel between the
sidewalk
16 of the vein 12 to cause the ore comprised in the vein 12 to span into
fragments. ~ The motion of the burner is confined within the boundaries of the
vein, as indicated by arrows 48 and 50. The groove is gradually deepened by
continuously re-adjusting the distance between the burner and the bottom of
the
groove. This distance is herein referred to as the "stand-off distance" and is
substantially maintained constant through out the process. To do so, the
burner
could be mounted on a telescopic mast. Once the telescopic mast has been
deployed to its fully extended position, the fragmented material is retrieved
as by
aspiration, the burner is withdrawn from the groove and the vertical face 46
is
blasted to expose a new vertical rock face from where it will be possible to
continue the channeling operation of the vein 12. These steps are repeated
until
the ore vein 12 has been completely extracted.
Fig. S illustrates the adaptation of the above-described spallation
channeling technique to an underground vein deposit. As for conventional
underground mining operations, the ore vein 12 is sandwiched between top and
bottom galleries 52 and 54. Access to the galleries 52 and 54 is provided by a
vertical hole 56. The burner 58 is preferably mounted on a robot 60 lowered
into
the vertical hole 56. The robot 60 is adapted to vertically displace the
burner 58
between the top and bottom galleries 52 and 54 and sideways between the
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sidewalk of the vein 12. The heat generated by the burner 58 causes the ore
body
forming the vein 12 to span into chips. As the groove is being formed in the
work
face, the robot 58 advances further into the groove so as to maintain the
burner 58
at a substantially constant stand-off distance from the bottom of the vertical
groove. Aspiration is conducted to retrieve the chips from the groove. Once
the
groove has been deepen by a predetermined distance, a second vertical hole
(not
shown) is defined and the channeling process is repeated from this new hole.
By
so repeating the above-described steps, the ore vein can be completely
extracted,
while avoiding undesired stripping of the surrounding waste rock. In this way,
only the true value is extracted.
In summary, numerous advantages can be anticipated when
looking at the present ore vein extracting process: In conventional selective
mining, a portion of waste rock has to be included in the mineable reserves to
allow sufficient space for equipment and workers. As illustrated in Fig. 1, by
using the thermal fragmentation mining concept, the portion of waste rock to
be
excavated is minimal. Therefore, significant savings related to ore handling,
ore
treatment and environmental control can be realized.
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