3. INTRODUCTION
Commercially available machines excavate rock
primarily with high compressive forces that crush
the material at the rock-bit interface. Cutting hard
rock with such machines requires excessively large
forces. Bits wear and break rapidly under these
conditions.
Conventional methods includes the concept of
fracturing rock in tension during excavation.
Thermal methods present an alternate way to
induce tensile stresses in the rock as a primary
excavation technique.
4. PRINCIPLE OF WORKING
One such development is Microwave heating.
Microwave heating can fragment hard rock. It can
also weaken rock to improve other mining or
secondary breakage methods. Microwaves can
penetrate rock and, as electromagnetic energy is
converted to heat by rapid vibration of molecules at
a location inside the rock, can create a thermal
inclusion (hot spot) inside the rock. The hot rock
then expands according to its specific thermal
expansion, whereas the surrounding cool rock does
not. The resulting swelling of the hot spot inside the
rock causes tensile stresses in the surrounding
rock, eventually fragmenting it.
5. HISTORICAL BACKGROUND
Mining with heat dates to the earliest prehistoric
societies. The first hard-rock metal miners in this
country mined copper from northern Michigan 2000
years ago. Their technique was simple; they built
fires in mine pits. When the surrounding rock was
hot, they doused it with cold water. They then beat
the fractured ore with mauls to free it.
6. MECHANISM
Using a burner powered by diesel fuel, the intense heat
created within the vein shatters the rock containing the
precious metal contents, into small fragments. The ore
bearing vein is directly extracted, greatly reducing the dilution
factor and the inefficiencies associated with traditional mining
methods which extract large amounts of waste rock. With this
method, it's now possible to extract a narrow mining corridor
with widths of 30 cm to 1 metre.
3 to 6 inch pilot holes drilled into the vein with conventional
drill
Thermal Fragmentation (burner operating at 1800 ° C) is
inserted and spalls the rock, quickly increasing the diameter of
the hole to 30 - 90 cm
Extraction of ore in 0 - 13 mm fragments
Break leftover rock between fragmented holes to recover
remaining ore
7.
8. Spalling: When a solid body is subjected to intense thermal
action then it got mechanical ejection of pieces and that’s called
spalling.
Spalling occurs in rocks with low thermal conductivity as
temperature stress which arises due to the non uniform heating
gets concentrated owing to low thermal conductivity.
9.
10.
11.
12.
13. Aspects of Thermal Mining
High grade narrow vein deposits
To reduce dilution Thermal method of Mining.
To extract a narrow mineralized corridor, 30 cm to 1 meter wide.
Inserting a strong burner powered by diesel fuel and air into a pilot hole
previously drilled directly into the vein, a thermal reaction occurs spalling the
rock and enlarging the hole to 30-100 cm in diameter.
Resulting in 400% - 500% less dilution when compared to conventional mining
methods.
Reduces the environmental affects of mining operations since much smaller
quantities of rock are displaced, stockpiled, and treated using chemical agents.
For large scale operations, the mining method increases mining reserves, lowers
the cost per ounce, and increases the total profitability of existing mine
operations.
Lowers costs and risks of developing and mining small scale deposits, requiring
less investment capital, shortening the payback period, thus reducing the
14. Thermal fragmentation mining method
Strong burner powered by diesel fuel, is inserted into a 5 - 6 inch pilot
hole drilled into the vein using a conventional drill.
Burner spalls the rock, quickly increasing the diameter of the hole to
30 - 100 cm and producing rock fragments 0 - 13 mm in size.
The leftover rock between fragmented holes is broken loose using soft
explosives and a narrow mining corridor with widths of 30 cm to 1 meter
is thus extracted.
Since the waste walls are left intact, the dilution factor and the
inefficiencies associated with traditional mining methods are greatly
reduced
15. The Burner
Powered by diesel fuel and compressed air and generates temperatures up to 1800°C in
the combustion chamber.
The Fragmented Rock
The spalling process produces rock fragments 0 - 13 mm in size.
Drift Development and Stope Layout
Drift development is performed directly into the ore at intervals of 15 to 20 metres in
accordance with the geology of the ore body. Using a re-suing method, the ore is
blasted and recovered 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 and enlarged by way of thermal fragmentation.
16. Ore Extraction: Selective and Continuous
The thermal fragmentation mining Method allows for selective ore extraction; high grade
sections can be prioritized and extracted first.
Furthermore, thermal fragmentation is a continuous mining method; it uses no
explosives and is operated in a continuous chain, with one person first drilling a pilot
hole, followed by a second who enlarges it by way of thermal fragmentation.
Reducing Environmental Impact
Mine development is performed directly into ore resulting in less waste rock being
extracted and displaced into large piles at the surface. By solely extracting the mineralized
zone, only the necessary excavations are made.
Fewer tonnes need to be processed at the mill to extract the precious metals. The quantity
of chemical agents needed in the process is greatly reduced. Furthermore, the quantity of
energy needed to process the ore is also greatly diminished since less rock is sent to the
mill.
The space needed to host the mine site is greatly reduced, the alterations to the landscape
are significantly diminished, and the result is a cleaner and more responsible approach to
mine operations.
17. Productivity
The work group required to operate 1thermal fragmentation unit consists of a 2
person team (1thermal fragmentation operator, 1 drilling operator).
Furthermore, since less rock needs to be mucked, and hauled from the stope,
fewer personnel are needed for handling the ore.
The method reduces the personnel needed for mine operations by 30 -50% when
compared to conventional mine operations.
Mechanization and Employee Safety
Each unit is completely mechanized, reducing the risk of injuries and strain caused
by manual manipulation of heavy equipment. The operator stands at a safe
distance from the mining stope, virtually eliminating the risk of flying debris and
falling loose rock from the waste walls.
Each unit is equipped with sensors capable of identify the presence of 7 harmful
gases (such as carbon monoxide, sulphides, etc.), important safety measures when
mining in an underground environment.
18. THERMAL FRAGMENTATION METHOD IN
GREATER DETAIL
Until recently, the use of chemical explosives was the
only effective way of breaking hard rock. An
innovative approach, consisting in thermal
fragmentation, is currently in operation.
The technology utilizes the heat generated by a
powerful burner, powered by diesel fuel and air, to
create a thermal stress and break the rock. The
thermal reaction allows for the enlargement of 15cm
to 90cm holes by breaking the rock in a spalling
effect. This technology has been used in Russia for
over 40 years in large-scale open pits for the drilling of
large blast holes. Use of this technology in selective
ore extraction is a definitive plus for gold properties
that would otherwise be uneconomical using existing
mining methods.
19. The new approach to thermal fragmentation consists in
the enlargement of a 15-cm hole previously drilled with a
long hole drill. A strong burner, powered by diesel fuel
and air, is inserted in the hole, lowered to the bottom
and lighted. The heat generated raises the in-hole
temperature up to 1800°C. This creates thermal
stresses that spall the rock. In simple terms, spalling is
considered as a form of decrepitation caused by an
unequal expansion of rock crystals that overcomes
molecule cohesion. The broken material produced
during this process ranges in size from fine-grained to 4
cm. A portion of the material is ejected out of the hole as
burning progresses and the rest can either be blown out
of the hole by compressed air or aspirated.
25. APPLICABILITY
It is used to excavate rock with greater than 20,000
psi (140,000-kPa) compressive strength using
continuous mechanical machines.
Innovative mining method for narrow vein deposits.
26. ADVANTAGES OF THERMAL
FRAGMENTATION
Significantly reduces dilution.
Lessens the impact on the environment.
Used for the extraction of narrow ore deposit
