-
7/30/2019 2010CIMPaperV1
1/9
THERMAL FRAGMENTATION: REDUCING MINING WIDTH WHEN
EXTRACTINGNARROW PRECIOUS METAL VEINS
Donald Brisebois and Jean-Philippe Brisebois
Rocmec Mining, Canada
ABSTRACT
The mining of high-grade, narrow vein deposits is an important
field of activity in the precious
metal mining sector. The principle factor that has undermined
the profitability and effectiveness
of mining such ore zones is the substantial dilution that occurs
when blasting with explosivesduring extraction.
In order to minimise dilution, the Thermal Fragmentation Mining
Method enables the operatorto extract a narrow mineralised
corridor, 50 cm to 1 metre wide (according to the width of the
vein), between two sub-level drifts. By inserting a strong
burner powered by diesel fuel andcompressed air into a pilot hole
previously drilled directly into the vein, a thermal reaction
iscreated, spalling the rock and enlarging the hole to 80 cm in
diameter. The remaining ore
between the thermal holes is broken loose using low powered
explosives, leaving the waste
walls intact. This patented method produces highly concentrated
ore, resulting in 400% - 500%less dilution when compared to
conventional mining methods.
The mining method reduces the environmental affects of mining
operations since much smallerquantities of rock are displaced,
stockpiled, and treated using chemical agents. The fully
mechanised equipment operated by a 2-person team (1 thermal
fragmentation operator, 1
drilling operator) maximises the effectiveness of skilled
personnel, and increases productivity
and safety.
The Thermal Fragmentation is currently employed in 3 mining
operations in North America.
-
7/30/2019 2010CIMPaperV1
2/9
INTRODUCTION
The mining of high-grade, narrow vein deposits is a predominant
field of activity in the preciousmetal sector. These types of
deposits are located throughout the globe and have a
significantpresence in mining operations. The principle factor that
has undermined the profitability andeffectiveness of mining such
ore zones is the substantial dilution that occurs when blasting
withexplosives during extraction and the low productivity
associated with todays common extraction
methods. The Thermal Fragmentation Mining Method has been
conceived to mine a narrowmineralised corridor in a productive and
cost efficient manner in order to solve these particularchallenges.
The following describes this mining method in depth and outlines
its successes inimproving the extraction process of such ore
bodies.
DESCRIPTION OF TECHNOLOGY
A strong burner powered by diesel fuel is inserted into a 152 mm
pilot hole drilled into the vein(Figure 1) using a conventional
longhole drill. The burner spalls the rock quickly, increasing
thediameter of the hole to 30 - 80 cm (Figure 2) producing rock
fragments 0 - 13 mm in size. Theleftover rock between fragmented
holes is broken loose using soft explosives and a narrowmining
corridor with widths of 30 cm to 1 metre is thus extracted (Figure
3). Since the wastewalls are left intact, the dilution factor and
the inefficiencies associated with traditional miningmethods are
greatly reduced.
Figure 1: The Method (Creating the Opening)
Figure 2: Fragmented Hole (60 cm Wide)
-
7/30/2019 2010CIMPaperV1
3/9
Figure 3: Stope (80 cm Wide)
THE BURNER
The burner (Figure 4), powered by diesel fuel and compressed
air, creates a thermal cushion ofhot air in the pilot hole, which
produces a thermal stress when coming in contact with the rock.The
temperature difference between the heat cushion and the mass of
rock causes the rock toshatter in a similar manner as putting a
cold glass in hot water. A spalling effect occurs (Calmanand
Rolseth, 1968), and the rock is scaled off the hole walls and
broken loose by thecompressed air.
Figure 4: The Burner
-
7/30/2019 2010CIMPaperV1
4/9
THE FRAGMENTED ROCK
The process of fragmenting the rock is optimal in hard, dense
rock. The spalling processproduces rock fragments 0 - 13 mm in
size. Figure 5 illustrates the size of the fragmented ore.The
finely fragmented ore requires no crushing before entering the
milling circuit and can bemore efficiently transported since it
consumes less space than ore in larger pieces.
Figure 5: The Fragmented Rock
TONNAGE COMPARISON WITH ALTERNATIVE METHOD
The method produces highly concentrated ore, resulting in 400% -
500% less dilution whencompared to conventional mining methods.
Table 1 below compares the quantity of rockextracted when mining a
50 cm-wide vein using the thermal fragmentation mining method
asopposed to a shrinkage mining method.
Table 1: Tonnage calculation; comparing thermal fragmentation
and shrinkage methods
Tonnage Calculation
(40 m by 20 m Ore Block)
Thermal Fragmentation Shrinkage
Width in situ (m) 0.5 0.5
Mining Width Final Result 0.5 1.8
Planned Dilution 0 % 260 %
Height (m) 20 20
Length (m) 40 40
Density 2.8 2.8
Total Volume (t) 1120 4032
The table above shows approximately 4 times less rock needs to
be mined for the equivalentmineralised content. This method of
extraction allows mine operators to solely extractmineralised
zones, thus significantly reducing dilution factors and optimising
mine operations asa result. The technology enables the operator to
mine ounces and not tonnes.
-
7/30/2019 2010CIMPaperV1
5/9
DRIFT DEVELOPMENT AND STOPE LAYOUT
Drift development is performed directly into the ore at
intervals of 15 to 20 metres (Figure 6) inaccordance with the
geology of the ore body. Using a re-suing method, the ore is
blasted andrecovered in the first cut, then the waste is blasted
and hauled away in the second cut.
Following the creation of two sub-level drifts, a pilot hole is
drilled between the two levels andenlarged by way of thermal
fragmentation. The unit is designed to operate in a
compactunderground environment, in a drift as small as 1.8 m wide
by 2.8 m high (Figure 7). The
company also produces a unit measuring 0.8 m wide by 2.1 m high,
which is capable of workingin smaller sublevels.
Figure 6: Stope Layout
Figure 7: Equipment Dimensions
Mining Width: 50cmTotal: 1062 Tonnes
-
7/30/2019 2010CIMPaperV1
6/9
OTHER APPLICATIONS - DROP RAISING
The thermal fragmentation equipment is also used to create the
centre cut in traditional dropraising. The burner can enlarge a 152
mm pre-drilled pilot hole into an 80 cm cut on a 20 meterdistance
in approximately 4 hours total. By creating this large centre cut
quickly and efficiently,larger sections can be blasted with minimal
vibrations (Figure 8), thus avoiding damage to thesurrounding rock
(Figure 9). The number of blast holes needed and explosives are
reduced andthe risk of freezing the raise is minimised.
Figure 8: Thermal Cut (80cm) with blast hole
Figure 9: Drop Raise (20 m x 0.9m x 1.2m)
ENVIRONMENTAL IMPACT ANALYSIS
There is a growing need to develop sustainable mining methods
that minimise theenvironmental footprint left behind by mining
operations. While developing the Thermal
Fragmentation Mining Method, important efforts were made to
address and reduce theenvironmental effects that mine operations
have on the surrounding areas. Using the method,mine development is
performed directly into ore, resulting in less waste rock being
extractedand displaced to the surface. By solely extracting the
mineralised zone, only the necessaryexcavations are made. As shown
in Table 1 above, 4 times less rock needs to be mined for
theequivalent mineral content.
-
7/30/2019 2010CIMPaperV1
7/9
As a result of less rock being mined, fewer tonnes need to be
processed at the mill to extractthe precious metals. The quantity
of chemical agents needed in the process is greatly reducedand the
quantity of energy needed to process the ore is also greatly
diminished. The reducedquantity of energy for hauling and
processing the ore results in fewer greenhouse gases beingemitted.
The mining residue that remains once the precious metal contents
are removed is 4times less abundant, using the example above,
meaning much smaller tailing areas need to beconstructed,
maintained, and rehabilitated once mining operations have ceased.
The spaceneeded to host the mine site is greatly reduced, the
alterations to the landscape are significantlydiminished, and the
result is a cleaner and more responsible approach to mine
operations.
PRODUCTIVITY AND SAFETY
The shortage of skilled personnel in the mining community has
made it essential to find ways toincrease productivity per worker
while improving working conditions in order to attract and
retainskilled miners.
PRODUCTIVITY
The work group required to operate 1 thermal fragmentation unit
consists of a 2 person team (1thermal fragmentation operator, 1
drilling operator). Table 2 shows the time needed to extractan ore
block using the thermal fragmentation mining method in comparison
to using a shrinkagemining method.
Table 2: Tonnage calculation; comparing thermal fragmentation
and shrinkage methods
Tonnage Calculation
(40 m by 20 m Ore Block)
Thermal Fragmentation Shrinkage
Width in situ (m) 0.5 0.5
Mining Width Final Result 0.5 1.8
Planned Dilution 0 % 260 %
Height (m) 20 20
Length (m) 40 40
Density 2.8 2.8
Total Volume (t) 1120 4032
Number of Personel 2 2
Productivity per 12 hrs Shift (t) 30 30
Tonnes Extracted per 24 hrs 60 120
Days Required to Extract Ore Block 18.7 33.6
The table above demonstrates that for the equivalent amount of
mineral content, it takesapproximately half the time to mine the
ore zone using the thermal fragmentation miningmethod than when
using a shrinkage mining method. Furthermore, since less rock needs
to bemucked and hauled from the stope, fewer personnel are needed
for handling the ore.
MECHANISATION AND EMPLOYEE SAFETY
Each unit is completely mechanised, reducing the risk of
injuries and strain caused by manualmanipulation of heavy
equipment. The operator stands at a safe distance from the
stope,
virtually eliminating the risk of flying debris and falling
loose rock from the waste walls.Furthermore, unlike shrinkage
mining methods, smaller excavations are made (0.5 m comparedto 2 m)
so the occurrence of falling loose rock is greatly diminished.
-
7/30/2019 2010CIMPaperV1
8/9
ECONOMIC ANALYSIS
By rendering a greater number of narrow, mineralised zones that
are economical to extract, themining method has the potential to
convert a substantial portion of the mineral resources of
anoperating company into mineral reserves. A large number of mines
currently in operation todaycontain narrow, precious metal veins
throughout the ore body, but unless these veins are ofsignificant
width (usually 1 m or greater) or very high grade they are often
overlooked. As themine operator develops the zones to be extracted,
high grade, narrow ore bodies are often
uncovered, but not extracted since it is uneconomical to mine
such ore bodies usingconventional mining methods (shrinkage, long
hole, room and pillar, etc.) Table 3 belowdemonstrates the cost
savings per ounce of using the thermal fragmentation mining method
incomparison to the long-hole method. The study was done by
Canadian Institute of Mining using2001 exchange rate figures.
Table 3: Estimate cost comparison between underground thermal
fragmentation and long hole
Tonnage calculated on the basis of a 60
m by 60 m reserve block
Thermal drilling 3024 t Long-hole drilling 3024 t
Grade in situ (g/t) 35.00 35.00
Width in situ (cm) 30 30
Minimum width (cm) 30 140
Planned dilution 0% 367%Geological reserves 3024 14 112
Reserve grade (g/t) 35.00 7.50
Mining
Wall dilution 5% 35%
Stope recovery 79% 90%
Ore development 544 2540
Planned mining reserve 1961 14 606
Grade (g/t) 33.25 4.88
Mill recovery 96% 96%
Produced ounces 2013 2198
Thermal Drilling Long-hole Drilling
Unit Cost $/M Total Cost $/M Unit Cost $/M Total Cost $/M
Development
Drifts 1000.00 180 000.00 1000.00 180 000.00
Subdrifts 1000.00 120 000.00 1000.00 120 000.00
Raises 1000.00 60 000.00 1000.00 120 000.00
Drawpoint 1000.00 1000.00 60 000.00
Mining cost ($/t) 113.50 222 600.00 19.00 277 516.00
Mucking 8.00 15 690.00 4.00 58 424.00
Transportation 12.00 23 535.00 6.00 87 636.00
Milling 16.00 31 380.00 20.00 292 122.00
Environment 2.00 3922.00 2.00 29 212.00
Backfilling 5.00 73 030.00
Total 657 127.00 1 297 940.00
$ per tonne 335.06 88.86
$ per ounce 326.49 590.59
US$ per ounce 0.65 212.22 383.88
-
7/30/2019 2010CIMPaperV1
9/9
As the analysis above shows, it is approximately 45% less costly
to mine a narrow vein orebody using the thermal fragmentation
mining method than using a conventional mining method.Overall
profitability of mine operations is increased since more precious
metals can beeconomically mined for the same level of development
expenditures.
CONCLUSION
Many variations and adjustments have been made to conventional
methods of mining narrowprecious metal veins, but the serious
shortfalls brought upon by dilution remain. The
ThermalFragmentation Mining Method is a new and innovative way of
mining narrow vein ore bodiesand a foremost solution to solving the
problem of ore dilution by reducing it by a factor of 4 to 1.It
uses a unique tool, a powerful burner, to mine with precision, a
narrow mineralised corridor inan effective and productive manner.
The technology is positioned to meet the growingchallenges of
skilled labour shortages, tougher environmental guidelines, and the
depletion oftraditional large scale ore deposits mined using
conventional methods. As the technologycontinues to develop and
spread through the mining community, the objective remains
tooptimise the productivity and profitability of mining narrow,
high-grade, precious metal orebodies and to make a substantial,
lasting contribution to this sector of activity.
REFERENCES
Canadian Institute of Mining. (2003). Thermal rock fragmentation
Applications in narrow-vein extraction. Vol 96, #1071. CIM
Bulletin, Canada. pp. 66-71.[1]
Calaman J.J, Rolseth H.C., (1968). Surface Mining First Edition.
Chapter 6.4 Society forMining Metallurgy and Exploration Inc.,
Colorado, USA p.325-337. [2]
