INTRODUCTION TO MINING TECH.
MPE 105
ND1 MINERAL AND PETROLEUM RESOURCES ENGINEERING.
FEDPOLYNEK!
1.0 MINING AND MINING TECHNOLOGY
Mining Technology is the art and science applied to the process of mining and operation of mines as
well as the processing of the minerals for the benefit of mankind.
Mining is the activity, occupation and industry concerned with extraction of valuable minerals or other
geological materials from the Earth, usually from an ore body, lode, vein, seam, reef or placer deposit.
These deposits form a mineralized package that is of economic interest to the miner. Ores recovered in
the process of mining include metals, coal, oil-shale, gemstones, limestone, chalk, dimension
stones, rock salt, potash, gravel, and clay. Mining is required to obtain any material that cannot be
grown through agricultural processes, or feasibly created artificially in a laboratory or factory. Mining
in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or
even water.
Mining of stones and metal has been a human activity since pre-historic times. Modern mining
processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine,
extraction of the desired materials, and final reclamation of the land after the mine is closed.
Since mining may also involve recovery of elements of minerals insitu as in leaching, mining activities
includes processing of ores. Thus, Mining in its broadest context encompasses the extraction of any
naturally occurring mineral substances – solid, liquid, and gas – from the earth or other heavenly
bodies.
A Mine is therefore an excavation made in the earth be it surface, underground or underwater for the
purpose of extracting minerals.
Figure 1.1: (a) Surface Mine
(b) Underground Mine
1.1 MINING’S CONTRIBUTION TO CIVILIZATION
Mining may well have been the second of humankind’s earliest endeavors granted that
agriculture was the first. The two industries ranked together as the primary or basic industries of
early civilization. Little has changed in the importance of these industries since the beginning of
civilization. If we consider fishing and lumbering as part of agriculture and oil and gas
production as part of mining then agriculture and mining continue to supply all the basic
resources used by modern civilization.
From prehistoric times to the present, mining has played an important part in human existence
(Madigan, 1981). Here the term mining is used in its broadest context as encompassing the
extraction of any naturally occurring mineral substances — solid, liquid, and gas — from the
earth or other heavenly bodies for utilitarian purposes. The most prominent of these uses for
minerals are identified in Table 1.
The history of mining is fascinating and it parallels the history of civilization, with many
important cultural eras associated with and identified by various minerals or their derivatives: The
Stone Age (prior to 4000
1780
B.C.E.),
B.C.E),
the Bronze Age (4000 to 5000
B.C.E.),
the Iron Age (1500
B.C.E.
to
the Steel Age (1780 to 1945), and the Nuclear Age (1945 to the present). Many
milestones in human history — Marco Polo’s journey to China, Vasco da Gama’s voyages to
Africa and India, Columbus’s discovery of the New World, and the modern gold rushes that led to
the settlement of California, Alaska, South Africa, Australia, and the Canadian Klondike were
achieved with minerals providing a major incentive (Rickard,1932). Other interesting aspects of
mining and metallurgical
history can be found by referring to the historical record provided
by Gregory (1980), Raymond (1984), and Lacy and Lacy (1992).
Table 1.1: Historic Uses of Minerals
Need or Use
Tools and utensils
Weapons
Ornaments and decoration
Currency
Structures and devices
Energy
Machinery
Electronics
Nuclear fission
Purpose
Food, shelter
Hunting, defense, warfare
Jewelry, cosmetics, dye
Monetary exchange
Shelter, transport
Heat, power
Industry
Computers, communications
Power, warfare
Age
Prehistoric
Prehistoric
Ancient
Early
Early
Medieval
Modern
Modern
Modern
The abundance of minerals also provides a method of creating wealth. Minerals can be marketed
on the open market, enabling the countries that possess them to obtain valuable currency from
countries that do not.
This generally results in the minerals-rich countries being the great
civilizations of the world while the countries that lack these resources generally suffer from a lower
standard of living.
The ability to use mineral resources as a means of creating wealth opens the possibility that a given
country or countries will attempt to control the entire market in a particular mineral, that is, to
create an economic cartel in that mineral. In 1973, the Organization of Petroleum Exporting
Countries (OPEC) attempted to control oil prices in a bold maneuver to obtain windfall profits
from the oil they produced. Although successful in the short run, the cartel eventually lost
effectiveness because of increased oil production elsewhere and difficulty in controlling its o wn
member countries. For a few years, OPEC was successful at regulating petroleum prices in an
awesome display of the value of possessing and producing some of the world’s most valuable
minerals. Other cartels have likewise been attempted.
However, the greater freedom in
international trade now makes such an attempt less likely to succeed.
1.2
HISTORY OF MINING IN NIGERIA
The history of mining in Nigeria dates back to the pre-colonial era when indigenes mined clay to make
bricks for building houses and several pottery wares for domestic water storage and cooking pots. The
pottery wares were also used for several decorative purposes. Beads made from stones and rock
broken with the application of heat also found uses in homes and local presses. Although there was
evidence of organized mining in parts of Nigeria before the colonial days, the history of modern
mining in the country began during the colonial era with the discovery and exploitation of cassarite
and colombite in the Jos Plateau, coal in Enugu, Gold around Ilesha Osun state and few other minerals.
The British colonial government created the Mineral Survey of the Northern Protectorates in 1903
with the Southern Protectorates following soon after. Nigeria started major production of coal, tin and
columbite by the 1940s. In 1956 when oil was discovered, the mineral industries suffered when the
focus shifted to mining oil. In the 1960s the Civil War led to expat mining experts leaving the country
and mines being abandoned. Mining regulations drastically changed and productivity declined. In the
late 1990s the government started selling government-owned mining companies to private investors.
The Nigerian Mining Cadastre Office manages all the Nigerian mining licenses and mining rights of
mine locations. They are a subsidiary of the Ministry of Mines and Steel Development of the Federal
Republic of Nigeria; an institution that formulates policy, provides information on mining potential
and production, regulates operations and generate revenue for the government. Other departments of
MMSD includes Mines inspectorate, Geological Survey of Nigeria, Artisanal and Small-scale mining
and mining environment. Despite massive mineral wealth, the Nigerian mining industry is vastly
underdeveloped and only accounts for 0.3% of the country’s GDP – and this due to oil resources. The
underdevelopment is resulting in Nigeria having to import processed minerals, even though it could be
locally produced
Coal, Lignite and Coke Mining in Nigeria
Coal was first discovered in 1909 and the industry thrived for some years before the Civil War. Prior to
the mining industry’s privatization, the Nigerian Coal Corporation held the monopoly on mining,
processing and selling coal, lignite and coke products. Despite the war ending in the 1970s the coal
industry did not recover. Attempts to mechanize the industry in the 1970s and 1980s failed and were
ultimately abandoned
Gold Mining in Nigeria
Abundant gold deposits exist in Northern Nigeria in Anka, Maru, Malele, Tsohon, Osun, Birnin,
Gwari-Kwaga, Bin Yauri, Gurmana and Iperindo. Production started in 1913 and peaked in the 1930s
before declining during the war. Mines were abandoned and like the coal industry, the gold mining
industry also didn’t recover. Although there are no large-scale gold mining operations in Nigeria
currently, there is some small-scale gold mining done by artists. The leading gold miners in Nigeria are
a family from Anka called Alye.
Iron Ore Mining in Nigeria
The purest deposits of iron ore in Nigeria is in Itakpe in the Kogi State. As one of the operational
mining industries in Nigeria, the country is exploring exporting iron ore in excess of domestic
requirements. The government of Nigeria has also invested in iron ore operations in Guinea.
Uranium Mining in Nigeria
The British Geological Survey recently discovered several major uranium deposits in Adamawa State,
Plateau State, Taraba State, Cross River State, Kano State and Bauchi State. The existing uranium
mining assets are being liquidated as in 2016. It is not known whether the recent discoveries will be
further explored.
Wolframite, Columbite, Tantalite and Bitumen Mining
Despite abundant deposits, only small-scale mining is done on these minerals.
1.3 ADVANCEMENTS IN MINING TECHNOLOGY
As one of humanity’s earliest endeavors and certainly one of its first organized industries mining has
an ancient and venerable history (Gregory,1980). To understand modern mining practices, it is
useful to trace the evolution of mining technology, which paralleled human evolution and the
advance of civilization.
Mining in its simplest form began with Paleolithic humans some 450,000 years ago, evidenced by
the flint implements that have been found with the bones of early humans from the Old Stone Age
(Lewis and Clark,1964). Our ancestors extracted pieces from loose masses of flint or from easily
accessed outcrops and using crude methods of chipping the flint, shaped them into tools and
weapons. By the New Stone Age, humans had progressed to underground mining in systematic
openings 2 to 3 ft (0.6 to 0.9 m) in height and more than 30 ft (9 m) in depth (Stoces,1954).
However, the o l d e s t known underground mine, a hematite mine at Bomvu Ridge, Swaziland
(Gregory,1980), is from the Old S t o n e A g e and believed to be about 40,000 years old. Early
m i n e r s employed crude methods of ground control, ventilation, haulage, hoisting, lighting, and
rock breakage. Nonetheless, mines attained depths of 800 ft (250 m) by early Egyptian times.
Metallic minerals also attracted the attention of prehistoric humans. Initially, metals were used in
their native form, probably obtained by washing river gravel in placer deposits. With the advent
of the Bronze and Iron Ages, however, humans discovered smelting and learned to reduce ores into
pure metals or alloys, which greatly improved their ability to use these metals.
The first challenge for early miners was to break the ore and loosen it from the surrounding rock
mass. Often, their crude tools made of bone, wood, and stone were no match for the harder rock,
unless the rock contained crevices or cracks that c o u l d be opened by wedging or prying. As a
result, they soon devised a revolutionary technique called fire setting, whereby they first heated the
rock to expand it and then doused it with cold water to contract and break it. This was one of the
first great advances in the science of rock breakage and had a greater impact than any other
discovery until dynamite was invented by Alfred Nobel in 1867.
Mining technology, like t h a t of all industry, languished during the Dark Ages. Notably, a
political d e v e l o p m e n t
in 1185 improved the s t a nd i n g of mining and the status of miners,
when the bishop of Trent granted a charter to miners in his domain. It gave miners legal as well
as social rights, including the right to stake mineral claims. A milestone in the history of mining,
the edict has had long-term consequences that persist to this day.
The greatest i m p a c t o n the need for and use of minerals, however, was provided by the
Industrial Revolution at the close of the eighteenth century. Along with the soaring demand f o r
minerals came spectacular improvements in mining technology, especially in scientific concepts and
mechanization, that have continued to this day.
During t h e last two centuries, there has been great progres s i n mining technology in m a n y
different a r e a s . Such p r o g r e s s is of ten m a d e in a n evolutionary rather than a revolutionary
manner. Yet every once in a while, a revolutionary discovery comes along and changes the
process of mining profoundly. During the nineteenth century, the invention of dynamite was the
most important advance. In the twentieth century, the invention of continuous mining equipment,
which extracts the softer minerals like coal without the use of explosives, was perhaps t h e most
notable of these accomplishments. The first continuous miner was tested in about 1 9 4 0 , with its
usefulness greatly enhanced by the development of tungsten carbide inserts in 1945 by McKenna
Metals
Company (now K e n n a m e t a l ). By 1950 the c o n t i n u o u s miner h a d started to
replace other coal mining methods. The era of mechanized mining had begun.
It is not possible to chronicle all of the developments that made mining what it is today. A more
complete chronology of the important events is outlined in Table 2. It has been prepared using the
m a n y references. A more comprehensive list of the crucial events in the development of mining
technology.
Table 1.2: Chronological Development of Mining Technology
Date
Event
450,000 B.C.E.
First mining (at surface), by Paleolithic humans for stone implements.
40,000
Surface mining progresses underground, in Swaziland, Africa.
30,000
Fired clay pots used in Czechoslovakia.
18,000
Possible use of gold and copper in native form.
5000
Fire setting, used by Egyptians to break rock.
4000
Early use of fabricated metals; start of Bronze Age.
3400
First recorded mining, of turquoise by Egyptians in Sinai.
3000
Probable first smelting, of copper with coal by Chinese; first use of iron implements by Egyptians.
2000
Earliest known gold artifacts in New World, in Peru.
1000
Steel used by Greeks.
100 C.E.
Thriving Roman mining industry.
122
Coal used by Romans in present-day United Kingdom.
1185
Edict by bishop of Trent gives rights to miners.
1524
First recorded mining in New World, by Spaniards in Cuba.
1550
First use of lift pump, at Joa c himstal, C z ec hos l ov a k i a .
1556
First mining technical work, De Re Metallica, published in Germany by Georgius Agricola.
1585
Discovery of iron ore in North America, in North Carolina.
1600s
Mining commences in eastern United States (iron, coal, lead, gold).
1627
Explosives first used in European mines,in Hungary (possible prior use in China).
1646
First blast furnace installed in North America, in Massachusetts.
1716
First school of mines established, at J oa c h im s ta l, Cz ec hos lov ak i a .
1780
Beginning of Industrial Revolution; pumps are first modern machines used in mines.
1800s
Mining progresses in United States; gold rushes help open the West.
1815
Sir Humphrey Davy invents miner’s safety lamp in England.
1855
Bessemer steel process first used, in England.
1867
Dynamite inv ent ed by Nobel, applied to mining.
1903
Era of mechanization and mass production opens in U.S. mining with development of first low-grade copper
porphyry in U t a h; although the first modern mine was an open pit, subsequent operations were underground
as well.
1940
First continuous miner initiates the era of mining without explosives.
1945
Tungsten carbide bits developed by McKenna Metals Company (now Kennametal).
[
It should be noted that the mining engineer is associated with the extraction of nearly all these
mineral resources. However, the production of petroleum and n a t u r a l gas has e v o l v e d into
a sepa rate industry with a specialized technology o f its own.
The essence of mining in extracting mineral wealth from the earth is to drive an excavation or
excavations from the surface to the mineral deposit. Normally, these openings into the earth are
meant to allow personnel to enter into the underground deposit. However, boreholes are at times
used to extract the mineral values from the earth. These fields of boreholes are also called mines,
as they are the means to mine a mineral deposit, even if no one enters into the geologic realm of
the deposit. Note that when the economic profitability of a mineral deposit has been established
with some confidence, ore or ore deposit is preferred as the descriptive term for the mineral
occurrence. However, coal and industrial mineral deposits are often not so designated, even if their
profitability has been firmly established. If the excavation used for mining is entirely open or
operated from the surface, it is termed a surface mine. If the excavation consists of openings for
human entry below the earth’s surface, it is called an underground mine. The details of the
procedure, layout, and equipment used in the mine distinguish the mining method. This is
determined by the geologic, physical, environmental, economic, and legal circumstances
that
pertain to the ore deposit being mined.
Mining is never properly done in isolation, nor is it an entity in itself. It is preceded by geologic
investigations that locate the deposit and economic analyses that prove it financially feasible.
Following extraction of the fuel, industrial mineral or metallic ore, and the run-of-mine material is
generally cleaned or concentrated. This preparation or beneficiation of the mineral into a higherquality product is termed mineral processing. The mineral products so produced may then undergo
further concentration, refinement, or fabrication during conversion, smelting, or refining to provide
consumer products. The end step in converting a mineral material into a useful product is
marketing.
The fields of endeavor associated with the mineral industries are linked to the phase or stage in
which an activity occurs. Locating and exploring a mineral deposit fall in the general province of
geology and the earth sciences. Mining engineering encompasses the proving (with the geologist),
planning, developing, and exploiting of a mineral deposit.
The mining engineer may also be
involved with the closure and reclamation of the mine property, although it is a shared duty with
those in the environmental fields. The fields of processing, refining, and fabricating are assigned to
metallurgy, although there is often some overlap in the mineral processing area with mining
engineering.
1.4 MINING/ GEOLOGICAL TERMINOLOGY
Mine: an excavation made in the earth to extract minerals
Mining: the activity, occupation, and industry concerned with the extraction of minerals
Mining engineering: the practice of applying engineering principles to the development,
planning, operation, closure, and reclamation of mines.
Mineral: a naturally o c c u r r i n g inorgani c element or compound having an orderly
internal
structure
and a cha rac teris tic chemical c o m p o s i t i o n , crystal form, and
physical properties.
Metallic ores: those ores of the ferrous metals (iron, manganese, molybdenum, and tungsten),
the base metals (copper, lead, zinc, and tin), the precious metals (gold, silver, the platinum
group metals), and the radio-active minerals (uranium, thorium, and radium).
Nonmetallic minerals (also known as industrial minerals): the nonfuel mineral ores that is
not associated with the production of metals, mined for their commercial values and used in
the industries based on their physical and chemical properties. These include gypsum, kaolin,
phosphate, potash, halite, trona, sand, gravel, limestone, sulfur, and many others.
Fossil fuels (also known as mineral fuels): the organic mineral substances that can be utilized
as fuels, such as coal, petroleum, natural gas, coal bed methane, gilsonite, and tar sands.
Rock: any naturally formed aggregate of one or more types of mineral particles.
Ore: a mineral deposit that has sufficient utility and value to be mined at a profit under the
present economic condition.
Gangue: the valueless mineral particles within an ore deposit that must be discarded.
Waste: the material associated with an ore deposit that must be mined to get at the ore and
must then be discarded. Gangue is a particular type of waste.
Ore: Ore is a mineral deposit that can be worked or mined for profit under the present or existing
economic condition.
Ore Shoot: the portion of the ore structure that carries sufficient valuable minerals to be profitable
to mine. i.e part of most concentration.
Lode: A mineral deposit consisting of a zone of veins, veinlets, disseminations, or planar breccias.
Outcrop: Is the part of the mineral deposit that appears on the surface of the ground.
Overburden: soil or rock lying on top of the bedrock or ore deposit.
Ore grade: the concentration of valuable minerals present in the ore deposit.
Cut-off grade: The lowest grade of mineralized material that qualifies as ore in a given deposit;
rock of the lowest assay included in an ore estimate.
Stripping ratio: The unit amount of spoil or overburden that must be removed to gain access to a
unit amount of ore or mineral material, generally expressed in cubic meters of overburden to
raw tons of mineral material.
Bedded deposit: A formation that shows successive beds, layers, or strata owing to the manner in
which it was formed.
Massive bedding: Very thick homogeneous stratification in sedimentary rocks.
Folds: A curve or bend of a planar structure such as rock strata, bedding planes, foliation, or
cleavage.
Fault: A fracture or a fracture zone in crustal rocks along which there has been displacement of the
two sides relative to one another parallel to the fracture.
Placer: A deposit of sand or gravel that contains particles of gold, ilmenite, gemstones, or other
heavy minerals of value. The common types are stream gravels and beach sands.
Bench: The horizontal step or floor along which coal, ore, stone, or overburden is worked or
quarried.
Shaft: A vertical or inclined opening extending downwards from the surface which serves as a
principal opening to the deposit underground.
Prospecting: searching for the minerals
Exploration: It’s all the activities involved in knowing more details about a mineral deposit e.g size,
shape, grade, tonnage e.t.c.
Development: It is the activity which involves clearing bushes, construction of access roads,
infrastructure e.t.c that will help in easy exploitation.
Exploitation: is the actual extraction of the minerals.
Prospecting lease: It is a document that gives the right to prospect mineral deposits.
Stope: An excavation from which ore has been removed in a series of steps.
Cross-cut: A small passageway driven at right angles to the main entry to connect it with a parallel
entry or air course or A tunnel driven at an angle to the dip of the strata to connect different
seams or workings.
Foot-wall: The underlying side of a fault, orebody, or mine working.
Hanging wall: is the upper part of a stope or the overlying side of an orebody, fault, or mine
working.
Adit: A horizontal opening into a deposit with an access but no exit.
Tunnel: A horizontal opening into a deposit with both access and exit.
Deposit: accumulation of ore or other valuable earth material in sufficient extent and degree of
concentration
Figure 1.2. Cross section of a mineral deposit
Figure 1.3a. A typical mine
b. Features of an Open pit Mine
1.5 STAGES IN THE LIFE OF A MINE
The overall sequence of activities in modern mining is often compared with the five stages in the
life of a mine: prospecting, exploration, development, exploitation, and reclamation. Prospecting
and exploration, precursors to actual mining are linked and sometimes combined. Geologists and
mining engineers often share responsibility for these two stages geologists more involved with the
former, mining engineers more with the latter. Likewise, development and exploitation are closely
related stages; they are usually considered to constitute mining proper and are the main province
of the mining engineer. Reclamation has been added t o these stages since the first edition, to
reflect the times. Closure and reclamation of the mine site has become a necessary part of the
mine life cycle because of the demands of society for a cleaner environment and stricter l a w s
regulating t h e abandonment of a mine. The overall process of developing a mine with the future
uses of the land in mind is termed sustainable development. This concept was defined as
‘‘development that meets the needs of the present without compromising the ability of future
generations to meet their own needs.’’ (United Nations General Asssembly, 1987).
Figure 1.4: Mine operation cycle.
Prospecting
Prospecting is the search for ores or other v a l u a b l e mi ne ral s . Mineral deposits may be located
either at or below the surface of the earth, both direct and indirect prospecting techniques are
employed.
The direct method of discovery normally limited to surface deposits, consists of visual
examination of either the exposure (outcrop) of the deposit or the loose fragments (float) that have
weathered away from the outcrop.
The indirect search for hidden mineral deposits is geophysics, the science of detecting anomalies
using physical measurements of gravitational, seismic, magnetic, electrical, electromagnetic, and
radiometric variables of the earth. The methods are applied from the air, using a irc raft a n d
s a t e l l i t e s ; on the surface of the earth; a nd beneath the earth, using methods that probe below
the topography. Geochemistry, the quantitative analysis of soil, rock, and water samples, and
geobotany, the analysis of plant g r o w t h p a t t e r n s , can also be employed as prospecting tools.
Exploration
The second stage in the life of a mine, exploration, determines as accurately as possible the size
and value of a mineral deposit, utilizing techniques similar to but m o r e r e fi n e d t h a n t h o s e
u s e d in prospecting. Exploration generally s hifts to s u rf a ce and subsurface locations, using a
variety of measurements to obtain a more positive picture of the extent and grade of the ore body.
Representative samples may be subjected to chemical, metallurgical, X ray, spectrographic, or
radiometric evaluation techniques that are meant to enhance the investigator’s knowledge of the
mineral deposit. The evaluated samples enable the geologist or mining engineer to calculate the
tonnage and grade, or richness, of the mineral deposit. Th e mining costs, t h e recoverable
valuable m i n era ls , the environmental costs, accessibility, and other foreseeable factors a r e
f u r t he r e s t i ma t e d in an effort to reach a conclusion about the profitability of the mineral deposit.
Development
In the third stage, development, the work of opening a mineral deposit for exploitation is performed.
With it begins the actual mining of the O r e / deposit. Access to the deposit must be gained either
by stripping the overburden, which is the soil and/or rock covering the deposit, to expose the
near-surface ore for mining or by excavating openings from the surface to access more deeply
buried deposits to prepare for underground mining.
Certain preliminary development w o r k , such as acquiring water and mineral rights, buying
surface
lands, arranging for
financing, and preparing p e r m i t applications
and an
environmental impact statement (EIS), will generally be required b e f o r e any development
t a k e s place. When these steps have been achieved, the provision of a number of requirements
access roads, power sources, mineral transportation systems, mineral processing facilities, waste
d i s p o s a l a r e a s , offices, and o t h e r
support
facilities must precede actual mining in most
cases. Stripping of the overburden will then proceed if the minerals are to be mined at the
surface. Development for underground mining is generally more complex and expensive. It
requires careful planning and layout of access openings for efficient mining, safety, and
permanence.
Exploitation
Exploitation, the fourth stage of mining, is associated with the actual recovery of minerals from
the earth in quantity. Although development may continue, the emphasis in the production stage
is on production. Usually only enough development i s done prior to exploitation to ensure that
production , once started, can continue uninterrupted throughout the life of the mine.
The mining method selected for exploitation is determined mainly by the characteristics of the
mineral deposit and the limits imposed by safety, technology, environmental concerns, and
economics. Geologic conditions, such as the dip, shape, and strength of the ore and the
surrounding rock, play a key role in selecting the method. Traditional exploitation methods fall
into two broad categories based on locale: surface or underground.\
Reclamation
Reclamation, the final stage of the life of a mine, is the process of restoring land that has
been mined to a natural or economically usable state. Although the process of mine reclamation
occurs once mining is completed, the planning of mine reclamation activities occurs prior to a mine
being permitted or started. Mine reclamation creates useful landscapes that meet a variety of goals
ranging from the restoration of productive ecosystems to the creation of industrial and municipal
resources. The approach to mine reclamation can either be forestry or holistic reclamation technique.
2.0 PROSPECTING AND EXPLORATION
2.1
PROSPECTING
Prospecting is the first stage of the geological analysis of a territory. It is the physical search
for minerals, fossils, precious metals or mineral specimens. The small-scale search for and collection of
minerals, fossils and gemstones for recreational, tourist, or educational purposes is known
as fossicking.
Prospecting is a small-scale form of mineral exploration. In searching for valuable minerals, the
traditional prospector relied primarily on the direct observation of mineralization in outcrops,
sediments, and soil. Although direct observation is still widely practiced, the modern prospector also
employs a combination of geologic, geophysical, and geochemical tools to provide indirect indications
for reducing the search radius. The object of modern techniques is to find anomalies—i.e., differences
between what is observed at a particular location and what would normally be expected.
In some areas a prospector must also make claims, meaning they must erect posts with the appropriate
placards on all four corners of a desired land they wish to prospect and register this claim before they
may take samples. In other areas publicly held lands are open to prospecting without staking a mining
claim.
2.2
EXPLORATION
Exploration is the process of searching for economic deposits of minerals, coal, oil or gas (petroleum).
Information gathered during exploration is used to assess the location, size and quality of the deposit to
determine if it can be economically recovered. Exploration is initially conducted over wide areas and
becomes more focused where potential resources are identified.
Once a discovery has been made, the property containing a deposit, called the prospect, is explored to
determine some of the more important characteristics of the deposit. Among these are its size, shape,
orientation in space, and location with respect to the surface, as well as the mineral quality and quality
distribution and the quantities of these different qualities.
The purpose of exploration is to search for a significant deposit that is economically feasible to extract,
process and sell. Before any resource exploration can be conducted by any explorer or company, they
must have an approved exploration license in place from the Mine Cadastre Office (MCO) or the
licensing bodies of the nation/state. Exploration license conditions can vary depending on the type of
resource and include conditions to minimize impacts caused. A security deposit lodgement is required
before any exploration activities take place. Exploration does not guarantee that mining will occur in a
given area.
2.2.1 STEPS OF THE MINERAL EXPLORATION PROCESS
1. Exploration Strategy: Where do you choose to explore? There are two basic strategies:
(a) Working from the known: Deposits tend to form in clusters in prolific belts, and exploration occurs
outward from known mineralization.
(b) Working from the unknown: If you review all available information, prospective areas with
potential for discoveries can be identified.
2. Prospecting: In this stage, boots are now on the ground – and it’s time to explore the backwoods for
showings. Prospectors will stake claims, map outcrops and showings, and search for indicator minerals.
The goal of the prospecting stage is to end the earliest piece of the exploration puzzle: the clue that
there is something much bigger beneath.
3. Early-Stage Exploration: Congrats, you’ve found something interesting – and now it’s time to ramp
up exploration efforts! This is where the amount of data and sophistication picks up. In this stage,
companies are using existing maps and historical data, geophysics, ground truthing, geochemistry, and
trenching to try and identify drill targets.
4. The “Truth Machine”: Geologists don’t call the drill a “truth machine” for nothing. If you’re target
hits, you’re in business. If your target misses, it’s time to go back a step and set new ones.
5. Discovery: Eureka! You’ve found something. Now it’s time to see how far the mineralization goes!
Once you have enough information, you can get an official resource estimate. This data is another
puzzle piece that will be crucial as you advance your discovery.
6. De-risking: Even at the best of times, mining can be expensive, risky, and tricky. That’s why your
investors and backers will want you to source even more data – it’ll allow you to see a clearer picture
of the deposit, and help your team see how it could take shape as a mine.
At this stage, drilling, metallurgical tests, environmental assessments, 3d models, and mine designs are
used to increase confidence in the project. Preliminary Economic Assessment (PEA) is carried out to
assess the potential economic outcomes of a mine. Then after, they may conduct an in-depth Feasibility
Study to help make a production decision.
7. Final Steps: By this point, you may have all the puzzle pieces – a clear vision of the deposit and its
potential to make decision. it’s time to make a production decision, construct the mine, and start
commercial production. But the data doesn’t stop there – at these later stages, even more data gets
created and it can help you make better decision
2.3
METHODS OF PROSPECTING AND EXPLORATION
The techniques for prospecting into Geological, Geochemical, Geophysical method.
GEOLOGICAL METHOD: is the detailed examination of out crops of ore deposits or ore fragments
and precise mapping of geological formation and its structures in the field (surface or near the surface).
it covers geological fieldwork and the laboratory studies directed to the discovery of workable mineral
concentrations. This method employs study of natural features in search for mineral deposits. When
indicator minerals i.e. “minerals species that directly show the presence of a specific type of
mineralization” are found in the deposit; it signifies proximity to the such mineralization. Example:
Presence of gahnite (ZnAl2O4) in the sediments, it indicates proximity to Zinc mineralization.
GEOPHYSICAL METHOD: Geophysical is a natural science that studies the physical process and
properties of mineral deposits or geological features concealed beneath the earth surface. In general, the
buried deposit or geological features must possess one or more physical properties different from the
surrounding so as to cause a measurable anomaly. Geophysical tools often operate above the ground
from aircraft or helicopters fitted with multisensors (airborne geophysical survey), or on the ground in
general (ground based geophysical survey). Geophysical studies are always quantitative relating to
actual measurements based on the variation of response pattern or contrast of propagating waves
passing through a non-homogeneous medium. The propagation parameters include seismicity, density,
magnetic susceptibility, natural remanent magnetization, electrical conductivity, resistivity, dielectric
permittivity, magnetic permeability, seismic wave velocity, electromagnetic and radiometric radiance.
The propagating wave reflects and refracts at the interface of rock types, structure, stratigraphic
formation, and the presence of mineralization, water, oil, and gas. The measures of variation are with
respect to either position of the objects, such as strength of magnetic field along a profile, or function of
time, like the propagation of seismic waves.
TABLE 2. 1: Geophysical Surveying Methods with Parameters and Properties of Deposits
Method
Measured Parameters
Seismic
Travel time of reflected
and refracted seismic
waves
Gravity (measuring
variation in Earth’s
gravitational fiel d)
Gravity
Magnetic
Operative Physical
Property
Density and elastic
mode
Velocity, acoustic
Density contrast
between the
surrounding host rocks
Suitable D e p o s i t Type
Coal, oil and gas, groundwater, layered
sedimentary ba sin, Ni-Cu-PGE in
volcanic basal flows
Massive sulfides, chromite, Ni-CuPGE, salt domes, barite, kimberlite
pipes, concealed basins
Measuring spatial
variation in Earth’s
magnetic field
Magnetic susceptibility
Magnetite-, ilmenite, pyrrhotiterich sulfides, Ni-Cu-PGE
1. Resistivity
Earth’s resistance
Electrical conductivity
Groundwater, sulfide, Ni-Cu-PGE
2. Induced
potential
Polarization voltage/frequency
development of ground
resistance
Electrical capacitance
Large sulfide dissemination, Ni-CuPGE, graphite
3. Self-potential
Electrical potential
Electrical conductivity
Sulfide veins, graphite, ground
water, Ni-Cu-PGE
Electromagnetic
Response to
electromagnetic radiation
Electrical conductivity
and inductance
Sulfide, Cr=Ni-Cu-PGE ore, graphite
Radiometric
Gamma radiation
Gamma ray
Thorium, uranium, radium
Borehole
Downhole probe
All types
Continuity of sulfide, Ni-Cr-Cu-PGE
in strike and depth
Electrical
geophysics and
mise-à-la-masse
1.
Seismic survey: A geophysical prospecting method based on the fact that the speeds of
transmission of shock waves through the Earth vary with the elastic constants and the densities of the
rocks through which the waves pass. The survey works on the mode of propagation of waves in elastic
media; more precisely, travel in rock media. The subsurface unit is assumed to be homogeneous and
isotropic to simplify wave propagation resulting in basic interpretation of the measured effects at the
plane of discontinuity. A seismic wave is initiated by firing an explosive charge (or by equivalent
artificial sources) at a known point (the shot point); records are made of the travel times taken for
selected seismic waves to arrive at sensitive recorders (geophones). There are two main subdivisions of
seismic operations: the reflection method and the refraction method. The seismic method has been
applied to a lesser extent to elucidate mining problems, partly due to its high cost. The seismic survey
can explain subsurface discontinuities, layering, and probable rocks/structures. It is suitable for the
investigation of coal, oil and gas, groundwater, and massive metallic deposits.
Figure 2.1: Seismic survey
2.
Gravity Survey: The gravity survey investigates variation (gravity anomalies) in Earth’s
gravitational field generated by differences in density between subsurface rocks. A gravimeter (absolute
or relative) measures the gravity field to determine variations in rock density in the Earth's crust. These
surveys are sensitive enough to detect small variations in the field, and thus can interpret and map the
locations of different rocks or geological formations which have contrasting densities. Ground-based
gravity surveys require a geophysical technician to take gravity measurements at set intervals of
distance and record the precise height at each location. Access to the recording sites can be by vehicle
or helicopter, depending upon remoteness. Sometimes gravity is measured from the air by a special
gravimeter housed in an aircraft. Density variation is induced by the presence of a causative body such
as salt domes, granite plutons, sedimentary basins, heavy minerals like chromite and manganese, and
faults and folds within the surrounding subsurface rocks. The size of the anomalies primarily depends
on the difference in density between host rocks and causative body, their geometrical form, and depth
of occurrence. The method is capable of being surveyed from the ground, air, and in a marine
environment.
Newton’s law of universal gravitation states that a particle attracts every other particle in the universe
using a force “F” that is directly proportional to the product of their masses (m1 and m2) and
inversely proportional to the square of the distance (r) between their centers.
Therefore, F α m1m2, Fα 1/r2
F = (G.m1m2)/(r2)
G = (F.r2)/(m1m2)
TABLE 2.2: Densities of Common Rocks and Minerals
Rocks
Density
(103 kg/m3)
Minerals
Density
(103 kg/m3)
Alluvium
1.96-2.00
Cassiterite
6.80-7.10
Amphibolite
2.79-3.14
Chalcopyrite
3.90-4.10
Anorthosite
2.61-2.75
Chromite
4.30-4.80
Basalt
2.70-3.20
Coal
1.11-1.51
Clay
1.63-2.60
Galena
7.40-7.60
Dolomite
2.28-2.90
Gabbro
2.85-3.12
Gypsum
2.30-2.80
Gneiss
2.61-2.99
Hematite
5.10
Granite
2.52-2.75
Magnetite
4.90-5.20
Limestone
2.60-2.80
Mercury
native
13.60
Peridotite
3.10-3.40
Platinum
naive
14.00-19.00
Quartzite
2.60-2.70
Pyrite
4.90-5.20
Rhyolite
2.40-2.60
Pyrrhotite
4.50-4.80
Sandstone
2.05-2.55
Silver native
10.10-11.10
Schist
2.50-2.90
Sphalerite
4.10-4.30
Shale
2.06-2.66
Quartz
2.59-2.65
3.
Enrollment
Gold native in
19.30
Magnetic Survey: Magnetic surveys measure the variations of the Earth's magnetic field due to
the presence of magnetic minerals. The investigation of subsurface geology based on anomalies in the
geomagnetic field resulting from varying magnetic properties of underlying rocks and minerals is the
basic principle of magnetic survey. These surveys are sensitive enough to detect subtle variations in the
abundance of magnetic minerals. These surveys are typically undertaken from a low altitude aircraft or
helicopter survey or by a geophysical technician on foot carrying a magnetometer and a sensor on a
pole. They are most often used in metallic mineral exploration.
The magnetic susceptibility of rocks depends mainly on the proportion of rock-forming minerals. The
most common rock types are either nonmagnetic or very feebly magnetic. Rocks develop a
susceptibility to magnetism with a higher proportion of magnetic minerals like magnetite, ilmenite, and
pyrrhotite. Mafic/ultramafic rocks are usually more magnetic due to higher content of magnetite than
acidic igneous rocks. Metamorphic rocks vary in magnetic property. Sedimentary rocks in general are
nonmagnetic unless locally enriched with magnetite, ilmenite, and pyrrhotite-magnetite-bearing sulfide
deposits.
4.
Electrical survey: Geoelectrical methods of mineral investigation depend on the properties of
conductivity and resistivity of subsurface rock mass to passing electric current. Methods include either
introduction of artificially generated current through ground or the use of a naturally occurring
electrical field within Earth. The current is propagated through a pair of electrodes connected to the
transmitter terminal. The resulting ground potential distribution is mapped by using another pair of
electrodes connected to a sensitive voltmeter. The potential distribution and lines of electrical flux can
be measured by the magnitude of current introduced and the variation in the receiving electrodes in a
homogeneous subsurface. The current deflects and distorts the normal potential in inhomogeneous
conditions in the presence of electrically conductive or resistive objects. The better conductive
causative mineral bodies are massive sulfide deposits, graphite-rich beds, and fractured/altered zones
with confined water containing dissolved salts and clay. Massive quartz veins are highly resistive to
current flow.
Three different types of geoelectrical methods are in use based on the type of current sources and
response to subsurface rocks: resistivity, induced potential and self-potential.
Electrical Resistivity method: It is the measure of the potential difference from an artificially generated
electric current introduced into the ground. Deviations from the background pattern of potential
differences indicate heterogeneities and the presence of anomalous objects in the subsurface.
Resistivity is one of the extremely variable physical properties of rocks and minerals. Certain minerals,
native metals, and graphite conduct electricity via the passage of electrons. Most rock forming minerals
are insulator. Hard compact rocks are usually bad conductors of electricity. The electric current is
carried through a rock by the passage of ions in pore waters. Porosity and degree of saturation govern
the resistivity of rocks. Resistivity increases as porosity decreases. It can either be vertical electrical
sounding or constant separation traversing.
Induced Polarization method: Induced polarization is an imaging technique that identifies electrical
chargeability of subsurface materials (orebodies). The electrochemical voltage does not drop to zero
instantly when externally applied direct current, connected through a standard four-electrode resistivity
spread, is switched off abruptly. The voltage dissipates gradually to zero after many seconds with a
large initial decrease. Similarly, the initial voltage jumps at initial supply of D.C and a slow increment
take place over a time before the steady-state value is reached. The ground acts as a capacitor, storing
electrical charge and becomes electrically polarized. The measurement of a decaying voltage over a
certain time interval is known as a time-domain induced potential survey.
Self-potential or spontaneous polarization: is based on natural potential differences resulting from
electrochemical reactions in the subsurface. The process is unique because it is passive, nonintrusive,
and does not require the application of an electric current. The causative body has to exist partially
close to the water table to form a zone of oxidation. The electrolytes in the pore fluids undergo
oxidation and release electrons that move upward through the orebody. The released electrons cause
reduction of electrolytes at the top of the orebody. An electronic circuit is thus created in the orebody
so that the top of the body acts as a negative terminal. The self-potential anomaly is invariably centrally
negative over metallic ore deposits.
Figure 2.2: Geophysical interpretation of self-potential, induced potential, and resistivity survey
5.
Electromagnetic Survey: An electromagnetic survey is based on the response of the earth to
the propagated electromagnetic fields composed of an alternating electric intensity and magnetizing
force. A primary or inducing field is generated by passing an alternating current through a coil (loop of
wire called a transmitter coil) placed over the ground. The primary field spreads out in space, both
above and below the ground, and can be detected with minor reduction in amplitude by a suitable
receiving coil in the case of a homogeneous subsurface. However, in the presence of a conducting
body; the magnetic component of an electromagnetic field penetrating the ground induces alternating
currents or eddy currents to flow within the conductor. Eddy currents generate their own secondary
electromagnetic field distorting the primary field. The receiver will respond to the result of arriving
primary and secondary fields so that the response differs in phase, amplitude, and direction. These
differences between transmitted and received electromagnetic fields reveal the presence of a conductor
and provide information on its geometry and electrical properties. Its application is not limited to
i.
locating abandoned mineshafts, crown pillars, and mine subsidence features.
ii.
Identifying bedrock and mineralization discontinuities.
iii.
Defining past landfill sites.
iv.
Mapping of soil types, land utilization, and land drainage patterns.
Figure 2.3: Conceptual diagram of electromagnetic induction processing system generating eddy
currents in subsurface conductive mass
6.
Radiometric survey: it detects and maps natural radioactive emanations (g-rays) from rocks
and soils., which are continuously being emitted by the decomposition of some common naturally
occurring radiogenic minerals. Generally, most gamma rays emanate from 30 cm above the rock or
soil, which can be detected by airborne surveys, or on surface rocks using a hand-held spectrometer.
The surveys focus on recording the amounts of isotopes of potassium, thorium, and uranium. The
common radioactive minerals are uraninite (238U), monazite (Ce, La, Nd, and Th), thorianite (232Th),
rubidium (87Rb) in granite-pegmatite, feldspar (40K), muscovite, sylvite in acid igneous rocks, and
radiocarbon (14C). Heat generated by radioactive disintegration controls the thermal conditions within
Earth. The rate of radioactive decay of some natural elements acts as a powerful means of dating the
geological time of rock formation (geochronology). Exploration for these minerals by radiometric
survey became important due to the demand for nuclear fuels and detection of associated
nonradioactive deposits, e.g., titanium and zircon. These surveys are most often used in metallic and
industrial mineral exploration.
Some isotopes are unstable and disintegrate spontaneously to generate other elements. Radioactivity
means disintegration of atomic nuclei by emission of energy and particles of mass. The byproducts of
radioactive disintegrations are in various combinations of a-particles of helium nuclei, b-particles of
electrons emitted by splitting of neutrons, and g-rays of pure electromagnetic radiation.
7.
Borehole logging:
Principle of well logging: Boreholes are drilled to study subsurface geology along the path of a hole.
The information helps to interpret a 3D picture of the area. Shallow noncore holes are excavated by
reverse-circulation drills in which rock fragments are blown out of the hole by air pressure. Deeper
holes are sunk by rotary drills with cutting units and tungsten-carbide or diamond bits. The drill-hole
provides non-coring cutting fragments flushed by drilling fluids (mud), and solid core using a core
barrel and water circulation. In the case of core drilling the recovered cores are logged for lithology,
mineralization, and structure. In noncore excavation and high core loss, information along the depth
can be obtained by the geophysical methods of down-the-hole geophysical survey or wire-line logging
using various sensors.
Mise-a`-la-Masse: meaning “excitation of the mass” in French, is a variation of an electrical resistivity
survey by enhancement of sufficient resistivity contrast between the host rock and the sulfide ore
compared to a conventional survey. It is a post-discovery method with definite knowledge of existing
sulfide mineralization. The interpreted equipotential maps are good indicators of continuity of
mineralization in strike, dip, shape, and interconnectivity between numbers of intersections.
Figure 2.4: Electrode configurations in a mise-à-la-masse survey with one current electrode located in a
borehole passing through a sulfide orebody and the other on the surface/another borehole to complete
the circuit. Both the potential electrodes are located on the surface.
GEOCHEMICAL PROSPECTING: geochemistry deals with the enrichment or depletion of certain
chemical elements in the vicinity of mineral deposits. It is the search for anomalies is based on the
systematic measurement of trace elements or chemically influenced properties. Samples of soils, lake
sediments and water, glacial deposits, rocks, vegetation and humus, animal tissues, microorganisms,
gases and air, and particulates are collected and tested so that unusual concentrations can be identified.
The main aim of carrying out geochemical sampling is to identify areas where there appears to be an
anomalous amount of the target mineral being sought, or of minerals which are known to be associated
with the target. Large areas can be covered at an initial stage by a regional sampling program which
would then be followed up by a more localized survey over anomalous areas. In all instances where
geochemical surveying is proposed, the locations of the samples are supplied to the Geological Survey
prior to the survey being carried out. If any of the locations are within a designated area or considered
likely to have a detrimental impact on a designated area, restrictions may be placed on the timing of the
activity or permission to carry out the activity can be refused.
Geochemical prospecting can be broadly classified into types depending on stages of the survey, nature
of the terrain, surface weathering, climate, and signals associated with mineralization, type of analytical
instrumentation available, and time and cost permissible for the program
1.
Soil sampling: Pedogeochemical survey is also known as soil survey. The soil is the
unconsolidated weathering product. It generally lies on or close to its source of formation such as
residual soil. It may be transported over large distances forming alluvial soil. The soil survey is widely
used in geochemical exploration and often yields successful results. The anomalous enrichment of
indicator elements from an underlying mineralization source is likely to occur due to secondary
dispersion in the overlying soil, weathered profile, and groundwater during the process of weathering
and leaching. The dispersion (is the natural process of outward movement of certain metallic elements
from a source) of elements spreads outward forming a larger exploration target than the actual size of
the orebody. it is carried out by individual or teams of people. Samples of a few hundred grams up to 5
– 10kg are collected using hand held auger for the small samples and spade for the larger ones. Auger
method is low impact and the ground can be left with no visible signs of disturbance. Larger samples
are collected from a dug pit.
Surveys are usually carried out over a rectangular grid which will vary in density depending on the
confidence of the target location, or along a transect. The area covered could be very large for regional
work or down to less than a few km for detailed/follow-up surveys.
Figure 2.5: Soil horizons showing dispersion halo.
Primary dispersion halos refer to a geochemical envelope, which is an expression of alteration and
zoning conditions surrounding metalliferous deposits while Secondary dispersion halos are the
dispersed remnants of mineralization caused long after deposit formation by surface processes of
chemical and physical weathering and redistribution of primary patterns.
2.
Stream sediment sampling: Samples are collected from as near the middle of the stream as
possible. It is based on the chemical analysis of samples of an active stream sediment from drainage
course Approximately 50 grams of material is normally taken but larger samples may be required
depending on method used and target. Where heavy metal mineralization is being targeted, samples are
collected as close to the bedrock as possible. This may require digging down through the overlying
material. The sediment is wet sieved through mesh screens to the required size and put in paper sample
bags for drying. Sample density is low (1 per Km2 or less) for regional surveys, increasing in density
for reconnaissance and follow-up studies.
Figure 2.6: Sediment sample collection.
Site selection for stream sediment sampling has the potential to be disruptive. Access is required to
the stream bed and the sediment must be disturbed to collect the samples. However, sampling is very
short term and generally only carried out in low order streams. Sampling is not permitted in streams
where it is considered that it will have a significant detrimental effect on protected species.
3.
Hydrogeochemical survey: Groundwater occurs in dug wells, springs, and boreholes
indicating better potential in exploration geochemistry, particularly if it is acidic (low pH) to dissolve
and transport metal elements like Cu, Pb, Zn, Mo, Sn, S,U, Ni, and Co caused by chemical
weathering, oxidation, and leaching. Surface water from streams, rivers, and oceans has less
dissolving power and fine-grained sediment adsorb much of the metal carried by water. Samples from
stream water and sediments are collected simultaneously for analysis.
The water samples are easy to collect. About a liter of water is collected in a special quality container.
Solubility of metals reduces with an increase of pH from 4 to 7. Therefore, pH is recorded at the time
of sample collection. Suspended solids are filtered before analysis. The elemental value changes with
time and season. It is desirable to analyze samples within 48 h of collection.
4.
Drift or Till Geochemical Survey: Drift prospecting is a broad term for sediments created,
transported, and deposited under the influence of the moving ice of glaciers particularly in steep
mountain terrain. The various sizes of rock fragments travel longer distances to form drift sequences.
The size and shape of mineralized boulders along with stream sediments reveal the extent of
transportation and to trace back the source of the parent deposit a few kilometers away at higher
elevation. The deposits are classified as glaciofluvial gravels and sands, silts and clays, and till or
moraine. Till is a favored sample medium for locating mineral deposits in glaciated terrain.
5.
Vegetation Survey: A vegetation survey can broadly be grouped namely geobotany and
biogeochemistry. The vegetation survey will receive prominence as an exploration guide for the future
as much of the world’s mineral resources are hidden beneath vegetation (Colin, 2007).
Geobotany: Plants usually respond to the geological environment in which they grow, and may show
characteristic changes with respect to form, size, color, growth rate, and toxic effects. Geobotany uses
these environmental variations. It includes a survey to recognize the presence or absence of specific
plant populations in a location, and is critically associated with particular elements.
Biogeochemical: Biogeochemistry encompasses the collection and chemical analysis of whole plants,
selected parts, and humus. The mobilized elements dissolve and enrich in soils during chemical
weathering. As plants and trees grow, these dissolved elements, including metals, from soil are
extracted by roots that act as a sampling agent. The elements migrate to various parts of the tree, such
as roots, trunk, stem, and finally to leaves. The cycle is complete with leaves falling to the ground
enriching the humus in metals
2.3
CONCEPTS OF GEOLOGICAL ANOMALY
This is a property of a geological body or complex bodies with obvious different composition, structure
or order of genesis as compared with the surrounding circumstances or a significant departure from the
normal pattern of a background value.
Figure 2.7: Anomaly of a copper deposit
2.3.1 FACTORS THAT INFLUENCE THE INTENSITY, SPREAD AND SIZE OF ANOMALY
1. Mobility power of elements in the physical and chemical milieu.
2. Depth of primary mineralization.
3. Wet and dry tropical climate.
4. Shape and size of mineralization.
5. Permeability, porosity, and mineralogical composition of host rock.
6. Local and regional topography.
7. Hydrologic regime.
8. Nature of weathered profile.
9. Tectonic movements.
10. Sampling media and density.
11. Precision and accuracy of the analytical procedure.
2.3.2 TYPES OF ANOMALY
1.
Geological Anomaly: this is the variation in the insitu formation of a particular location
compared to its surrounding.
2.
Geochemical Anomaly: the area where geochemical properties differ from the considered
normal and which may have resulted in the mineralization.
3.
Geophysical Anomaly: the area where the geophysical properties differ from the surrounding
areas and which may be the result of mineralization.
2.4
SAMPLING
Sampling is the process of taking a small portion of a finite part of a statistical population or only an
adjacent portion of the object under assessment to gain information on the whole body. The value of a
sample depends on the volume or quantity of material represented and the degree of accuracy. The
sampling objects in geological perspectives are granite hill, limestone deposit, alluvial soil, weathered
profile, beach sand, polymetallic nodules, mineral occurrences, drill core, well water, oil, and gas.
The sample interval and quantity will depend on homogeneity or complexity of minerals under search.
The “unit” of sample size, i.e., millimeter (mm), centimeter (cm), meter (m), feet (f), gram (g),
kilogram (kg), pound (lb), and liter (L), must be specified in particular to make it significant. The unit is
needed for precise computation of the average grade conventional and statistical method.
2.4.1 ASSUMPTIONS IN SAMPLING
i.
The sample is representative of a certain volume of the whole material.
ii.
The sample represent a known volume.
iii.
A certain degree of accuracy was maintained during sampling.
2.4.2 SAMPLING EQUIPMENTS
Samples are collected by various suitable and convenient methods and means without compromising
quality and reproducibility. The equipment used in sampling is either conventional tools or drilling
techniques.
Conventional tools: Conventional sampling tools are the hammer and chisel to collect rock chips.
Spades, shovels, and mechanized loaders are preferred to signify large volumes of sample material. The
other supporting tools are compass, Global Positioning System, handheld X-ray fluorescence (XRF)
analyzer, and camera.
Drilling Techniques: The search for deep-seated orebody, petroleum, and gas reservoirs was
unthinkable without efficient drill machines that can collect samples at depths of 2000 m. The drilling
techniques are essentially based on three motions: percussive, rotary, and a combined effect of
percussive and rotary. The various drill types are Percussion drilling, Percussive cum rotary drilling,
Auger drilling, Diamond drilling, Wire-line drilling, Reverse circulation drilling, Air-core drilling,
Sonic drilling, Directional drilling.
2.4.3 TYPES OF MINERAL SAMPLING
Mineral sampling is divided into four major types namely chemical, mineralogical, technical and
technological.
Chemical sampling: is the situation where samples are acquired for assaying and evaluating the
valuable and gangue in the ore deposit. It is used to determine the amount of useful composition and
harmful impurities in the deposits of metallic and nonmetallic minerals.
Mineralogical sampling: this is the sampling to get the various grades of the useful minerals in the
formation or ore body.
Technical sampling: It is used in analyzing minerals whose value depends on such mechanical and
physical properties as strength, resistance to compression, wear under friction, flexibility, resistance to
fire, resistance to aggressive chemical substances, and electrical conductivity.
Technological sampling: is the collection of samples for the study of technological properties of the
raw material made in the course of its beneficiation and processing. It is used in testing a mineral’s
concentration, capacity for melting or used on unprocessed form.
2.4.4 GEOLOGY SAMPLING GUIDES
Regardless of the types of sampling used, the process of sapling incorporates a series of steps which
may be carried out.
i.
Reconnaissance of the lands: a preliminary inspection of the lands to get relevant information
i.e size, shape and general characteristics of the deposit to prepare plan/map of the area for
planning and design.
ii.
Sampling:
iii.
Sample processing
iv.
Data processing
v.
Evaluation of results.
2.4.5 METHODS OF SAMPLING
Sampling methods vary from simple sampling on the exposures to sophisticated drilling methods; the
methods of sampling are generally done on the Surface or Underground.
Channel sampling: is suitable for uniformly distributed mineralization in the form of veins, stringers,
and disseminations. Sampling is performed by the cutting of channels across a mineralized body in
fresh surface exposures or underground mine workings, such as the mine face, walls, and roof. The area
is cleaned to remove dust, dirt, slime, and soluble salts by any of three processes. These are washing
with a hose pipe (air/water) or scrubbing with a stiff brush or by chipping of the outer part of rocks to
smoothen the sampling face. A linear horizontal channel is cut between two marked lines at a uniform
width and depth. The width is between 5 and 10 cm at a depth of 1 and 2 mm. Sample length varies
depending on variation in mineralization.
Figure 2.8: Channel sampling
Chip Sampling: is the collection of rock chips from a given geological unit. Chipping fragments of 12cm by 1-2 cm size covering the entire surface exposure, underground mine face, walls, and roof in a
regular grid interval of 25 cm x 25 cm. Chip sampling is more suitable when mineralization is
irregularly distributed or disseminated, and is not easily recognized by eye. The area is cleaned before
sample cutting. The sampler chips off fragments by hammer and a pointed chisel.
Figure 2.9: Chip sampling in irregular vein-type.
Bulk Sampling: A bulk sample comprises a large volume of material (100-1000 tonnes) representing
all metal grades and mineral distributions of an entire orebody. Samples are collected from different
parts of stockpiles generated from surface trial pits, underground cross-cuts, and run-of-mine ore of
regular production. The best collection equipment is shovels to handle huge volumes. Total material is
mixed thoroughly to reduce heterogeneity. Samples are used for developing beneficiation flowsheets
for optimum reagent consumption and maximizing recovery efficiency.
Grab Sampling: Grab sampling is performed at any stage of exploration, and more so during mine
production for a quick approximation of run-of-mine grade. The samples are randomly picked up from
loose broken material from outcrops, pits, trenches, mine workings, stope drawpoints, mine cars, load
shipments, and all types of stockpiles. Good care should be taken to avoid inclusion of any foreign
objects like wood, iron pieces, nails, masonry, and plastics.
Drilling or sludge sampling: the drill samples are obtained when drilling is undertaken on any
material. The crushed or core samples pass through the drill bit into the drill pipe to be received at the
surface; here by representing different depths position in the hole.
Other sampling methods are Soil sampling, Trenching, Stack sampling, ocean bed sampling, muck
sampling (broken samples from mine face/stope), car sampling and alluvial placer sampling.
3.0 DEVELOPMENT, EXPLOITATION AND MINE CLOSURE
3.1
MINE DEVELOPMENT
Mine Development means the location, opening and development of mines and all activities necessary,
expedient, conducive or incidental thereto including without limitation pre-stripping and the removal
and disposal of over-burden and waste. Recovery of mineral from surface or subsurface rock involves
the development of physical access to the mineralized zone, liberation of the ore from the enclosing
host rock and transport of this material to the mine surface. Excavations of various shapes, sizes,
orientations and duty functions are required to support the series of operations which comprise the
complete mining process. Mine development work is performed to open a mineral deposit for
exploitation by either stripping overburden for near surface deposits or excavating openings for deeply
buried deposits to prepare for underground mines. Mine developing to recover deposit can be through
open pit, stripping, box cut and benching for surface mine and broadly shaft sinking, adits and
inclines/declines.
Mine development may involve many activities such as:
•
The preparation of the mine site by clearing trees and blasting rock
•
The construction of mining facilities such as head frames, administration buildings or
mechanical shops
•
The creation of infrastructure such as power lines and substations, roads or water lines
Requirements
Before beginning development, certain requirements must be met. These requirements include:
•
Submitting a Notice of Project Status to the Mine Cadastre Office.
•
Consulting with all required parties.
•
Filing a closure plan with accompanying financial assurance and achieving certification.
•
Acquire all required permits/approvals from ministries, agencies and government organizations
3.1.1 FACTOR INFLUENCING THE METHODS OF DEVELOPMENT.
1. Size of Deposit: Minerals which aren’t of high value have to occur in large quantities for them to be
mined so that it will be a possible to recover mining costs and make a profit.
2.
Ore grade as determined by drilling: is defined as the tonnage to the valuable mineral to that of
the tonnage of the ore body. Minerals of high value will be mined even if they occur in small quantities
because once sold, it will be possible to offset mining costs and make a profit but deposits with low
mineral content are rarely worked on except if the mineral in them is rare e.g. uranium.
3.
Dip and strike: this refer to the orientation or attitude of the geological feature. The strike line
represents the intersection of the feature to the horizontal plane while dip acute angle of descent of
tilted bed relative to the horizontal plane.
4.
Fault and fold: while Fold is the subjection of geological feature to compressional forces the
bend the body either upward or downward.
5.
Water bearing strata: the presence of underground layer of aquifer or water body overlying or
overlain by the rock/ore body.
6.
Available Fund: is the amount of money or capital available to carry out the mine development
and exploitation.
7.
Topography and Climatic condition: Topography, a function of location, affects cost of
development and operation of a surface mine. Geographic location establishes climate and the
condition of remoteness from or proximity to civilization and its developed facilities such as
transportation systems, power supply, labour pool, manufacturing and supply services, and specialty
repair shops.
8.
Projected production rate: is a preapproved contract or plan on the amount of ore to be mined
per day/week/month/annum until the life of the mine is reached.
9.
Environmental concerns: is the consideration of the harm of the mining operation on the
biophysical environment. EIA is normally carried out to determine the extent of damage before miners
can be approved to carryout development and exploitation.
10.
Safety concern: safety is an essential component of any healthy workplace. Mines in particular
are hazardous environment with a large-scale environmental damage and loss of life thus making mine
safety an ever-present concern to ensure smooth running of the mining project.
11.
Mining Method: the choice of mining method either surface or underground determines the
extent of mine development in terms of accessing and recovering the valuables.
3.2
EXPLOITATION OF MINERALS
The exploitation
of
natural
resources is
the
extraction
or
wining
and
use
of natural
resources for economic growth sometimes with a negative connotation of accompanying environmental
degradation. It started to emerge on an industrial scale in the 19th century as the extraction and
processing of raw materials (such as in mining, steam power, and machinery) developed much further
than it had in preindustrial areas. During the 20th century, energy consumption rapidly increased.
Natural resources are not limitless and its excessive consumption gave rise to the following
consequences; Deforestation, Desertification, Extinction of species, Forced migration, Soil erosion, Oil
depletion, Ozone depletion, Greenhouse gas increase, Extreme energy, Water pollution, Natural
hazard/Natural disaster, and Metals and minerals depletion. The methods of mineral exploitation are
Surface and Underground approach.
3.2.1 FACTORS AFFECTING EXPLOITATION OF MINERAL RESOURCES AROUND THE WORLD.
The possession of minerals cannot decide the prosperity of a country; because existence of a mineral
ore is no guaranteeing that it will be exploited. Often, they are found in such a small proportion as to be
almost unavailable and, hence, not useful for man. Before a mineral can be worked it must be
ascertained whether its value is greater than the costs of working, transporting and concentrating the
ore.
The main factors influencing their exploitation are as follows:
Richness or Grade an economic value of the Ore:
The abundance or otherwise the absence of minerals determines in a large measure their commercial
exploitation. Ores vary in its metal content. Generally, the higher-grade ores are more economic to
work, not only because they yield large amount of metal but also because their higher metal content
makes them easier and cheaper to smelt. Minerals of high value such as gold, diamonds, copper,
uranium, can often be mined at very high cost, because they are in great demand and fetch high prices.
Production cost:
Extraction costs depend on the type of mining system selected, the level of mechanization, mine life,
and many other factors. This makes selecting the best system for a given deposit a complex process.
For example, deposits outcropping at the surface may initially be mined as open pits, but at a certain
depth the decision to switch to underground mining may have to be made. Even then, the overall cost
per ton of ore delivered to the processing plant would be significantly higher than from the open pit; to
pay for these extra costs, the grade of the underground ore would have to be correspondingly higher.
Competition from other sources:
The strive for excellence and supremacy can’t be denied in a thriving industry. The goals of the
extraction company remain the same but it cannot be shared. Hence, rivalry and contest for improved
productivity at minimum process input is very important factor to be considered in the development of
the mine.
Size of Deposit:
The size of deposit is important because mining requires a large amount of expensive equipment. It will
not be worthwhile to provide such equipment to work a deposit which will run out in some months.
Small- scale working is only profitable for precious minerals. Sometimes, small deposits may be
worked out profitably where transport cost is low.
Method of Mining:
The method of mining depends on the mode of occurrence of the ores. The open-cast mining is the
cheapest, while shaft mines are very expensive. The cost of mining also depends on the scale of
operations. If the mining has been done at a large scale, the capital and running costs can be offset.
Accessibility:
The accessibility of a region where the particular mineral deposit occurs is of great significance. The
terrain and climate determine accessibility which helps or hinders the mining operations.
Transportation Facilities:
For a successful mining, transportation facilities are very essential. Not only for the mining but it is also
necessary for mined ores to be transported at the sites of their use. Ores are relatively bulky and heavy.
They are thus costly to transport and the shorter the distance to be covered the better. The deposits
having coastal location or located near industrial sites have an advantage over those far inland.
Stage of Industrial Development:
The stage of industrialization of a country is the general index of the exploitation of her mineral wealth.
In fact, mineral exploitation is cumulative in the industrial cycle. The vast mineral resources of China,
India and Brazil almost remained neglected till they marched on the path of industrial development.
Technology:
Technological changes pertaining to mining methods, manufacturing processes and the like may
change once worthless deposits are converted into esteemed commercial ores. The technique of
geological survey has now been changed. With the help of remote sensing techniques, one is able to
estimate the reserves of mineral resources of a region. Other technological changes have changed the
pattern of exploitation of mineral resources.
Cheap labour supply:
In general, when labour market is dominated by one employer the demand for labour is less. There is
tendency that the wage rate in such location will be lower and gives room to consider manual practice
in the development work.
Economic system and tariff policies are notable.
It is important to determine the extent and nature of national and local laws and regulations, Land and
other necessary rights should be checked, such as water use rights and the ability to acquire auxiliary
land for plant site, roads, tailings disposal ground etc.
3.2.2 ENVIRONMENTAL EFFECT OF MINERAL EXPLOITATION
(a) Mining is hazardous occupation:
•
This occupation involves several health risks; dusts produced during mining operation are
injurious to health and cause lung diseases.
•
Extraction of some toxic or radioactive minerals leads to life threatening hazards.
•
Dynamite explosion during mining is very risky as fumes produced are extremely poisonous.
•
Underground mining is more hazardous than surface mining as there are more chances if
accidents like roof falls, flooding Increasing demand for high grade minerals has compelled
miners to carry out more extraction of minerals, which require more energy sources and
produce large amount of waste materials.
(b) Wastage of upper soil layer and vegetation:
Surface mining results in the complete destruction of upper soil layer and vegetation. After extraction,
the wastes are dumped in an area which destroys the total surface and vegetation.
(c) Environmental problems:
Over exploitation of mineral resources resulted in many environmental problems like:
•
Conversion of productive land into mining and industrial areas.
•
Mining and extraction process are one of the sources of air, water and land pollution.
•
Mining involves huge consumption of energy resources like coal, petroleum, natural gas etc.
which are in-turn non-renewable sources of energy.
•
Surface mining directly degrades the fertile soil surface thus effect ecology and climate if that
particular area.
3.3
MINE CLOSURE/RECLAMATION
Mine closure is the process of temporarily or permanently shutting down mining operation once the
mineral resources at the working mine is exhausted or the operation is no longer profitable. Mining is a
temporary activity, with its operation lasting years to several decades. Before mining permit are
granted, the mine closure plan is required by the regulatory agencies and it must demonstrate that the
site will not pose threat to the health of the environment or society in the future. In most cases, financial
assurance is required by the agencies as a guarantee that the funds required by mine closure will be
available in the event the company is unable to complete closure as planned.
Mine closure process is carried out in the following steps; Shut-down (reduction of labour/early
retirement), Decommissioning (demolishing or repurposing building & dissembling of facilities and
equipment), Reclamation/Remediation (Returning the land and water course to an acceptable standard),
and Post-closure monitoring program (assess the effectiveness of the reclamation measures and identify
corrective action in its event.
4.0 MINING METHODS
The method of mining is unique for each different size and each shape of orebody. Mineral
deposits differ in the shape and orientation of an orebody, the strength of the ore and surrounding rock,
and the type of mineral distribution. These geological features influence the selection of a mining
method and the plan for the ore development. Operating mines vary in size from small underground
mines (with production under 100 tonnes of mineral a day) to large open pits excavating tens of
thousands of tonnes of ore a day. The simple aim in selecting and implementing a particular mine plan
is always to mine a mineral deposit so that profit is maximized given the unique characteristics of the
deposit and its location, current market prices for the mined mineral, and the limits imposed by safety,
economy, environment. Mining method is generally classified into Surface and underground mining.
FACTORS THAT INFLUENCE MINE METHOD SELECTION
•
Distance of ore to the surface
•
Host rock and ore strength
•
Ore characteristics and nature of mineralization (Shape, size, regularity and continuity, Strike,
dip and thickness)
4.1
•
Stripping ratio (overburden and/or waste removed to ore ratio)
•
Possibility to minimize internal and external dilution and ore loss
•
Availability of infrastructures
•
Cost of mining and mineral dressing
•
Production target and resource
•
Value of primary, associated commodities and value
METHODS OF MINING
4.1.1 SURFACE MINING METHODS
Surface mining methods are defined as any excavation that commences from the natural surface and does
not require the construction of a tunnel or shaft. Surface mining is comparatively much cheaper than
underground methods. It covers about 70% of global mineral production. The first choice of hard rock
mining is adopting surface mine techniques, if the orebody is exposed or exists near to the surface. If a
mineral deposit lies close to the surface, of sufficiently big size, and its overburden is not too thick,
surface mining (an open-pit mine) can be the most suitable method to extract the ore. Underground
mining methods are appropriate to that part of the orebody where open-pit operation is uneconomic due
to high overburden to ore ratio. Surface mining is the exploitation method in which minerals are mined
from the surface. Surface methods are classified as aqueous mining which involves use of water for
extraction such as placer and solution mining or mechanical mining including Open-pit mining,
Quarrying, Strip mining and Auger mining.
ADVANTAGES OF SURFACE MINING
•
It is cheaper
•
It offers high level of recovery of the valuable ore deposit.
•
It is relatively safer.
•
It encourages the use of large-scale mining equipment hence offer higher production rate.
DISADVANTAGES OF SURFACE MINING
•
Depth limit; limited economic depth to which mining can take place.
•
Large-scale surface disturbance.
•
Large waste proportion of waste to ore.
•
Affected by climatic condition.
•
High Visibility
Mechanical Extraction Methods
The mechanical extraction involves mechanical processes to obtain minerals from the earth. There are
four mechanical extraction methods namely open pit mining, quarrying of dimension stone, open cast
mining, and auger mining. In open pit mining, a thick deposit is mined in benches or steps. However,
a comparatively thin deposit may be excavated from a single face as in the case of quarrying, augering
and open cast mining. In the case of these methods, a large capital investment is necessary, however,
they can provide high productivity, low operating costs, and satisfactory safety conditions.
Prior to or during mining, it is necessary to remove any overburden by a stripping operation. In
open cast (or strip) mining, overburden is removed by casting into mined-out areas, and mineral is
excavated in consecutive operations. Open pit or open cast mining is used to mine a mineral deposit
close to the earth’s surface that is of low stripping ratio, shows large extension, and is fairly uniform. It
should be noted here that a stripping ratio of 3 to1 means that there is thrice as much waste rock
mined as mineral (ore, coal, etc.).
Quarrying is a highly specialized small-scale method, slow and the costliest of all mining methods.
It is a special type of open-pit mining used to produce aggregates and dimension stone products where
rock joint fractures are infrequent, and, therefore, the bench faces are vertical. Lack of fractures often
permits near-vertical highwalls that can approach up to 300 m.
Augering is employed to recover coal from the highwall at the pit limit. This method is also
specialized but involves low costs. Open pit and open cast methods can be widely and variably
applied.
They use a conventional mining cycle of operations to extract mineral: rock breakage is achieved by
drilling and blasting, which precedes the material handling operations of excavation and haulage.
Aqueous Extraction Methods
The aqueous extraction methods must be provided with the access to water or an aqueous mixture
during mining and processing. It recovers the valuable mineral by jetting, slurrying, melting or
dissolving. There are of two types of these methods: (1) placer mining methods and (2) solution
mining methods.
Placer mining is used to mine mineral deposits that are not consolidated, such as sand, gravel or
alluvium in which a valuable heavy mineral exists freely. Valuable heavy minerals such as diamonds,
native gold, native platinum, and titanium can be found in placer form. There are possible two methods
for placer mining: hydraulicking and dredging. Hydraulicking (hydraulic mining) uses a high-pressure
stream of water to undercut and force an exposed bank to fall down while Dredging utilizes floating
vessels from which the ore minerals are extracted mechanically or hydraulically. Since the waste
material is usually lighter than the valuable heavy mineral to be extracted, this mineral can be removed
from water-base slurry by concentration in both methods.
Solution mining employs in situ techniques and surface techniques. Salt wells, uranium dissolution,
and the Frasch process to melt sulphur are examples of the in-situ techniques.
4.1.2 UNDERGROUND MINING METHODS
Underground mining is defined as mineral exploitation in which extraction operations are performed
under the earth’s surface. To select a proper mining method, one should know if ground support is
necessary or not, and determine its appropriate type, extent, and form. Moreover, they should design
an appropriate opening arrangement and extraction sequence to follow the size, volume, depth, shape
and orientation of the mineral deposit. Ground support plays crucial role in underground excavation,
hence, underground extraction methods are classified with regard to the extent of support used as
unsupported (self-supported), supported, and caving, with individual methods distinguished according
to the type of wall and roof supports utilized, the configuration of production openings, and the
direction in which mining operations advance.
ADVANTAGES OF UNDERGROUND MINING
•
As compared to surface mining, it allows a mine operation to be largely hidden.
•
Mining operation are limited only by the depth allowable in developmental work.
•
It encourages the use of old mine-out stope as a repository of waste blasted rock.
•
It produces very little waste and mill tailing hereby causing less damage to the environment.
DISADVANTAGES OF UNDERGROUND MINING
•
Pillar need to left in place to safeguard the safety and structure of haulages and drives.
•
It is applicable for high grade ore and is not suitable to low grade ore.
•
High mining cost per ton of ore and low production rate.
•
Low degree of safety in the mine.
Unsupported (Self-Supported) Methods
The unsupported class embraces self-supporting methods, which do not need any major artificial
system of support to carry the load comprised of both the weight of the overburden and any stresses in
the rock caused by tectonic forces (this load is called superincumbent load). It is applicable where the
walls of the openings and natural pillars are of sufficient strength to carry this load instead although
miners may help them along with bolts and screens. They may use rock or roof bolts or light structural
sets of timber or steel unless such artificial support impacts on the load-carrying ability of the natural
original structure. Unsupported (self-supported) methods are used to extract mineral deposits that are
tabular, flat or steeply dipping, and are surrounded by competent wall rock. There are five methods in
this class namely room and pillar mining, stope and pillar mining, shrinkage stoping, sublevel stoping,
and vertical crater retreat (VCR) mining.
Supported Methods
The supported methods of underground mining are those that need significant amounts of artificial
support to maintain stability in exploitation openings and systematic ground control over the entire
mine. Supported methods are applied when unsupported and caving ones cannot be. Support systems
for production workings are able to control wall closure and ground movements. Pillars and backfill are
used for supporting. However, backfill is the most satisfactory form of support because it is able to
support the superincumbent load almost entirely without yielding. Heavy support systems may
involve timber stulls and cribs, timber or steel sets and trusses, as well as steel jacks, arches, props,
chocks, shields, and canopies. Steel is stronger and yields less than timber, which is not sometimes
desirable. Moreover, timber is more flexible, workable and easy to install, and more economical. The
supported mining methods are designed for extraction of rock varying in competency from moderate to
incompetent. There are three methods of this type; the cut and filling stoping, stull stoping and square
stoping.
Caving Methods
Caving methods involve induced, controlled, huge caving of the ore body, the overlying rock, or both,
simultaneous with and crucial to mining performance. This type of mining precedes unavoidable
eventual subsidence of surface. There are three major caving methods are longwall mining, sublevel
caving, and block caving. Longwall mining is used in tabular, horizontal deposits, mainly coal; the
others are used for inclined, vertical, or massive deposits, metallic or nonmetallic. They are the
cheapest mining methods.
5.0 ROCK DRILLING PRINCIPLE, EQUIPMENTS AND APPLICATION
5.1
ROCK DRILLING
“Drilling or boring is a prime operation in the excavation technology without which exploration,
development, exploitation and liquidation of mineral deposits could not succeed.” It is operation to dig
out or excavate ground and dispose-off the spoil during mining, and tunneling operations. These
operations are mandatory during any phase of mine-life i.e. development, exploitation (or stoping) and
liquidation, in order to mine out a deposit by the application of any of the mining methods in practice.
These basic operations can be grouped into two classes: dislodging rock from the rock massif or deposit
which is known as primary breaking, and handling of material so generated. In any production cycle
these unit operations need to be carried out but apart from these operations some ancillary activities are
also carried out, and these are referred as the auxiliary operations.
Production cycle during Tunneling (or mine development) = shot hole drilling + blasting +
mucking + hauling + hoisting (optional)
Similarly, Production cycle during stoping operations in mines, or Large excavations in civil and
construction projects = blasthole drilling + blasting + mucking + hauling + hoisting (optional)
Term cycle implies that the mining and tunneling operations are cyclic or repetitive in nature but efforts are
being made to make the process continuous where the mineral/rock/ground after breaking moves
without interruption. Truly speaking this should be the ultimate aim but we are far away from such a
system. Number of techniques can fragment the rock but the prominent amongst them is drilling and
blasting.
5.1.1 PRIMARY ROCK BREAKING
Detaching the large rock mass from its parent deposit is known as rock breakage. Since prehistoric time
man devised several ways to achieve this task and he made the greatest technological advance in mining
history when eventually he discovered explosive and used it for rock breaking purposes. Application of
explosive in the rock is carried out by means of drilling holes, which are known as shot holes, blastholes
or big blastholes depending upon their length and diameter. Holes of small diameter (32–45 mm) and
short length (upto 3 m) are termed as shot holes, and they are drilled during tunneling and drivage work in
mines. The blastholes are longer (exceeding 3 m to 40 m or so) and larger in diameter (exceeding 45 mm to
75 mm or so), and that are drilled as cut-holes in tunnels and drives, and in the stopes. Besides their use in
surface mines, recently use of very large diameter (exceeding 75 mm) long holes, known as big blastholes,
have begun for the raising and stoping operations in underground mines too.
5.1.2
MECHANICS OF ROCK PENETRATION
Using the drills, the rock is attacked mechanically, either by percussive, rotary actions and a combination
(rotary-percussion) of these two methods are also used. The resulting action of the bit in each case is
almost similar i.e. crushing and chipping; what differs mainly is that the crushing action predominates in
percussion drilling and chipping action in the rotary drilling, and a hybrid action in the combination of
the two systems.
Percussive drilling: in this setting, the boring tool strikes the face and breaks the rock under the bit
during the interval between each strike the drill string turns through a small angle.
Rotary drilling: the boring tools rotates along the axis which coincides with the axis of the borehole and
at the same time supplies energy to the bit by rotating action and thrust.
Rotary-Percussive drilling: this method combines the principle of percussion and rotary drilling, where
periodical blows are struck against the rotary the rotating tool.
Based on this logic, drills are manufactured as based on several layout and operating medium.
TOP-HAMMER DRILL
In this system the top-hammer’s piston hits the shank adapter and creates a shock wave, which is
transmitted through the drill string to the bit. The energy is discharged against the bottom of the hole
and the surface of the rock is crushed into drill cuttings. These cuttings are in turn transported up the
hole by means of flushing air that is supplied through the flushing hole in the drill string. As the drill
is rotated the whole bottom area is worked upon.
DOWN-THE-HOLE (DTH) DRILL
In this system the down-the-hole hammer and its impact mechanism operate down the hole. The piston
strikes directly on the bit, and no energy is lost through joints in the drill string. The drill tubes
(rods, steels) convey compressed air to the impact mechanism and transmit rotation torque and feed
force. The exhaust air blows the holes and cleans it and carries the cuttings up the hole. DTH drills
differ from the conventional drills by virtue of placement of the drill in the drill string. The DTH drill
follows immediately behind the bit into the hole, rather than remaining on the feed as with the
ordinary drifters and jackhammers. Thus, no energy is dissipated through the steel or couplings, and
the penetration rate is nearly constant, regardless the depth of the hole.
ROTARY DRILL
Rotary crushing is a drilling method, which was originally used for drilling oil wells, but it is now days
also employed for the blast hole drilling in large open pits and hard species of rocks. It is used for a
rock having the compressive strength up to 5000 bars (72,500 psi). In rotary drilling energy is
transmitted via drill rod, which rotates at the same time as the drill bit is forced down by high feed
force. All rotary drilling requires high feed pressure and slow rotation. The relationship between these
two parameters varies with the type of rock. In soft formations low pressure and higher rotation rate
and vice versa, are the logics usually followed.
AUGUR DRILL
The augur drill is the simplest type of rotary drill in which a hallow-stem augur is rotated into the
ground without mud or flushing. The continuous-flight augurs convey the cuttings continuously to the
surface. This also works on the rotary cutting principle.
5.1.3 OPERATING COMPONENTS OF THE DRILLING SYSTEM
There are four main functional components of a drilling system:
The drill: it acts as prime mover converting the original form of energy that could be fluid, pneumatic
or electric into the mechanical energy to actuate the system.
The rod (or drill steel, stem or pipe): it transmits the energy from prime mover to the bit or applicator.
The bit: it is the applicator of energy attacking the rock mechanically to achieve penetration.
The circulation fluid: it cleans the hole, cools the bit, and at times stabilizes the hole. It supports the
penetration through removal of cuttings. Air, water or sometimes mud can be used for this purpose. It
flushes the cuttings as per the principle of the flushing velocities.
5.1.4 MATERIAL HANDLING IN DRILLING PROCESS
Materials handling involves the relocation of materials when a hole is drilled or excavated. The current
practice of materials handling depends on the type of hole being constructed (e.g., wells, mine shafts, or
tunnels); the site conditions; and the size, orientation, and length of the hole. In general, materials must
be transported from the bit face to the surface and from the surface to disposal. Materials handling
limits the rate of hole advance when materials cannot be transported to the surface as rapidly as they
are mined or when they cannot be moved from the surface to a disposal area as rapidly as they are
brought to the surface. Surface disposal problems often relate to environmental problems associated
with toxic materials (liquids or solids).
Screw augers: this augers’ helical screw ensure continuous remove solids from the hole to the surface
and subsequently disposed of the work space.
Buckets and bailers: Its application is rare in recent time. It allows water and solids to fill a tube that is
periodically retrieved and emptied.
Air Flushing: it's the chipping removal process where air serve as the fluid for cutting removal.
Water/Mud Flushing: It is the use of water or drill mud to carry cutting to the surface for separation and
disposal.
The fluid is picked up by the pump, circulated through the surface piping, and sent down the inside the
drill pipe and drill collars, where it exits the bit and entrains the drilled cuttings. The fluid carries the
cuttings to the surface for separation and disposal. The behavior of the cuttings in the circulating fluid
depends on fluid rheology; the different behaviors of the fluid help determine the degree of difficulty in
removing the cuttings from the hole. The ability to use fluids to transmit solids depends on fluid
properties such as density, viscosity, and velocity.
Note: Removal of cutting helps to maintain machine efficiency and reduce continuous grinding and regrinding of rock particles during drilling Operation.
5.1.5 DRILLING ACCESSORIES
To achieve the drilling of a hole some drilling accessories are required apart from rock drill. These are
integral drill steels, extension rods, shank adapters, sleeve couplings and bits.
EXTENSION DRILL STEELS
Threaded rods can be joined together to form a string, which can be used to drill long holes (longer than
the length of one rod). These rods have male threads and they are coupled to other with the use of
couplings having internal female threads. There are two types of rods: (i) shank rods – these are the
rods with an integral shank and a bit end. (ii) Full section extension rods – they can be round or
hexagonal having threads at both ends.
BITS
It is a part of the drilling equipment that performs the crushing work. The part of the bit in contact with
the rock is made of cemented carbide. The threaded rod is normally screwed into the bit until it bottoms.
The impact energy is then transmitted between the end of the rod and the thread bottom of the bit.
Types of drill bit
Mining and well drilling bits typically feature a threaded connection for attachment to a drill or drill
string and a hollow body through which drill fluids are circulated. Drill fluids are required to clear drill
cuttings, cool the bit, and stabilize the borehole wall. Types of well drilling bits include the following:
Tri-cone or roller bits contain three toothed cones, each with a journal angle pitched towards the bit’s
primary axis. The teeth of each cone mesh against one another to bore through solid earth. The bit is
driven by the weight-on-bit (WOB) while being pulled by the rotary action of the drill bit head.
Button bits are fixed-head bits that have conical or chisel bit inserts aligned in a matrix about the drill
bit head. The head configuration of the bit may be convex, concave, or flat. Button bits with
polycrystalline diamond compact (PDC) inserts may be referred to as PDC bits and are commonly used
in directional drilling operations.
Cross bits and chisel bits are fixed-head bits that have hardened steel or carbide blades. Chisel bits are
defined by a single blade while cross bits contain two or more blades that cross at the center of the bit.
The blades are typically tapered down toward the cutting surface.
Anchor bits are commonly used in coal mining operations to drill pilot holes for the insertion of roof
bolts. The roof bolts function to support roof rock and prevent cave-ins. Anchor bits are typically fixedhead winged bits and offer fast cutting action for drilling bore holes up to several feet long, ranging
from a half-inch to an inch or more.
5.1.6 SELECTION OF DRILL
Drill selection for a particular application is based on the technological and cost factors. It is considered
that the lower cost is obtainable in soft rock with rotary drag-bit drilling, in medium and hard rock with
rotary roller-bit and rotary-percussion drilling, and in very hard rock with percussion drilling. Use of
percussive drills is very common in underground metalliferous mines and tunnels. In surface mines
both types of drills have applications depending upon the rock types.
Drilling efficiency can be measured by taking into consideration the following parameters:
•
By the manner in which the drilling tool i.e. the drill acts upon the hole bottom (percussive,
rotary or rotary percussive)
•
The forces and the rate with which the drilling tools act upon the hole bottom
•
Hole diameter and its depth
•
The method and speed with which the drilling cuttings are removed from the hole.
These factors determine a type of drill required to suit a particular type of rock, as drillabilty of rocks
differs widely.
6.0 MINING EXPLOSIVE AND ACCESORRIES
6.1
INTRODUCTION TO MINING EXPLOSIVES
An explosive is a substance or mixture of substances, which with the application of a suitable stimulus,
such as shock, impact, heat, friction, ignition, spark etc., undergoes an instantaneous chemical
transformation into enormous volume of gases having high temperature, heat energy and pressure. This,
in turn, causes disturbance in the surroundings that may be solid, liquid, gas or their combination. The
disturbance in the air causes air blast and this is heard as a loud bang. The disturbance in the solid
structure results in its shattering and demolition. During wartime this property is utilized for destruction
purposes but the same is used for dislodging, breaking or fragmentation of the rocks for quarrying,
mining, tunneling, or excavation works in our day- to-day life. The energy released by an explosive
does the following operations:
6.2
•
Rock fragmentation
•
Rock displacement
•
Seismic vibrations
•
Air blast (heard as loud bang).
THEORY OF EXPLOSIVES
A general theory of explosives is that the detonation of the explosives charge causes a high-velocity
shock wave and a tremendous release of gas. The shock wave cracks and crushes the rock near the
explosives and creates thousands of cracks in the rock. These cracks are then filled with the expanding
gases that cracks until the gas pressure is too weak to expand the cracks any further, or are vented from
the rock. An explosive has four basic characteristics:
a) It is a chemical compound or mixture ignited by heat, shock, impact, friction, or a combination of
these conditions.
b) Upon ignition, it decom- poses rapidly in a detonation.
c) There is a rapid release of heat and large quantities of high-pressure gases that expand rapidly with
sufficient force to overcome confining forces.
d) The energy released by the detonation of explosives produces four basic effects; (a) rock
fragmentation; (b) rock displacement; (c) ground vibration; and (d) air blast.
The ingredients in explosives manufactured are classified as:
Explosive bases (Sensitizers). An explosive base is a solid or a liquid which, upon application or heat or
shock, breaks down very rapidly into gaseous products, with an accompanying release of heat energy.
Nitroglycerine (NG), Trinitrotoluene (TNT), Nitro-starch, aluminium are examples.
Combustibles. A combustible combine with excess oxygen in an explosive to achieve oxygen balance, to
prevent the formation of nitrous oxides (toxic fumes), and to lower the heat of the explosion.
Oxygen carriers. Oxygen carriers assure complete oxidation of the carbon in the explosive mixture,
which inhibits the formation of carbon monoxide. The oxygen carriers assist in preventing a lowering of
the exploding temperature. A lower heat of explosion means a lower energy output and thereby less
efficient blasting. Examples are AN, Sodium nitrate, Calcium carbonate etc.
Antacids. Antacids are added to an explosive compound to increase its long-term storage life, and to
reduce the acidic value of the explosive base, particularly nitroglycerin (NG).
Absorbents. Absorbents are used in dynamite to hold the explosive base from exudation, seepage, and
settlement to the bottom of the cartridge or container. Sawdust, rice hulls, nut shells, and wood meal are
often used as absorbents.
Antifreeze. Antifreeze is used to lower the freezing point of the explosive.
6.2.1 DETONATION AND DEFLAGRATION
When an explosive is initiated, it undergoes chemical decomposition. This decomposition is selfpropagating exothermic reaction, which is known as an explosion. The gases of this explosion with an
elevated temperature are compressed at a high pressure. This sudden rise in temperature and pressure
from ambient conditions results into a shock or detonation waves traveling through the unreacted
explosive charge. Thus, detonation is the process of propagation of the shock waves through an
explosive charge. The velocity of detonation is in the range of 1500 to 9000 m/sec. well above the speed
of sound. Deflagration is the process of burning with extremely rapid rate the explosive’s ingredients,
but this rate or speed of burning, is well below the speed of sound.
Figure 6.1 (a) Conceptual diagrams – Detonation and deflagration phenomenon.
6.3
BLASTING PROPERTIES OF EXPLOSIVES
Each explosive has certain specific properties or the characteristics. Its ingredients such as nitroglycerin
and ammonium nitrate contents have direct influence on some of its properties such as resistance to
water, detonation velocity, costs etc. Given below are some of the important proper- ties, which
influence the ultimate choice of an explosive.
1.
STRENGTH: It is the energy released/unit weight (known as weight strength); or per unit
volume (known as bulk strength) of an explosive. It Is often expressed relative to ANFO at 100% i.e.
taking ANFO as standard. High strength is needed to shatter the hard rocks but use of high strength
explosive in the soft; weak and fractured rocks will be wastage of the excessive energy imparted by
these explosives. Strength of an explosive is measured by:
•
Shock generated (VOD and speed of chemical reaction)
•
Gas volume
•
Energy
•
Detonation pressure
•
Explosion temperature
Velocity of detonation (VOD): is the measure of the shattering effect of an explosive i.e the measure of the
speed at which the detonation wave travels through the column of the explosive. It changes with change
in diameter and density of explosives. ‘Dautriche’, electronic or Hess method or tests can measure VOD.
Gas volume: Larger the gas volume of an explosive is the extent of throw obtained. If throw is to be
minimized its ingredients should be adjusted to get minimum volume of gas and maximum heat output.
‘Ballistic Mortar’ test and ‘Trauzl block’ test generally measure it.
Energy: The oxygen balance and reactive ingredients determines the energy output of an explosive.
This energy represents the temperature of explosion and hence the maximum work that can be done
by an explosive is indicated by this value.
Explosion temperature: This parameter is calculated based on the thermodynamic data of the
ingredients. In coal mines a balancing of explosion temperature and the gas volume play an important
role. If explosion temperature exceeds 1000°C it can make the methane atmosphere inconducive i.e.
mixture of air & methane can catch fire and explode.
2.
DETONATION VELOCITY: It is the velocity with which the detonation waves move through a
column of explosives. The detonation velocity is affected by factors such as Explosive type, Diameter,
Confinement, Temperature and Priming. The explosive’s detonation velocity ranges from 1500–6700
m/sec.
3.
DENSITY: The density of an explosive may be expressed in terms of specific gravity. Specific
gravity is the ratio of the density of the explosive to the density of water under standard conditions. The
specific gravity of commercial explosives ranges from 0.6 to 1.7 g/cc. For free running explosives, the
density is often specified. A dense explosive release more energy/unit volume, hence it is useful for the
hard and denser strata. For any explosive there is a critical density, above which, it cannot reliably
detonate.
4.
WATER RESISTANT: is the ability of any explosive to resist water without losing sensitivity or
efficiency. ANFO is poor water-resistant. Slurries are good water-resistant.
5.
FUME CHARACTERISTICS: Ideally, detonation of a commercial explosive produces water
vapor, carbon dioxide, and nitrogen. In addition, undesirable poisonous gases such as carbon monoxide
and nitrogen oxides are usually formed. These gases are known as fumes, and the fume class of an
explosive indicates the nature and quantity of the undesirable gases formed during detonation. Better
ratings are given to explosives producing smaller amounts of fumes. For open work, fumes are not usually
an important factor; in confined spaces, however, the fume rating of an explosive is important. In any
case, the blaster should ensure that everyone stays away from fumes generated in a shot. Carbon
monoxide gradually destroys the brain and central nervous system, and nitrogen oxides immediately
form nitric acid in the lungs.
6.
OXYGEN BALANCE: A proper balance of these ingredients is essential to minimize production
of the toxic (poisonous) gases, e.g. an excess of oxygen produces such as nitric oxides, nitrogen peroxide
and deficiency of oxygen result in the production of carbon monoxide. Also, such an imbalance effects
the energy generation. reactions as under:
7.
COMPLETION OF REACTION: Achieving a complete reaction at the required speed during
blasting is the next important factor, for example if a carbon atom is not oxidized to carbon dioxide but
carbon monoxide, the production of energy comes down by 75% of the expected energy, as shown below.
Similarly, formation of oxides of nitrogen involves the absorption of energy.
The last two equation won’t only produce lower energy but also yield toxic gases. In ANFO explosive
if moisture content exceeds 1%, it not only causes caking of ANFO but also makes the reaction
incomplete.
8.
DETONATION PRESSURE: is the shock wave pressure that is built ahead of reaction zone.
Higher the detonation pressure, higher would be the brisance capability (i.e. the ability to break or
shatter rock by shock or impact). Its value varies from 10 to 140 KB. rock, a lower pressure is
sufficient. Detonation pressures of explosives range from 10 to over 140 Kilobars (l Kilobar = 14,504
psi). Due to this property a primer having higher detonation pressure should be selected. Given below is
the mathematical relation to express this parameter:
Where as: p = detonation pressure in kilobars (KB)
ρ = explosive density in g/c.c
v
velocity of detonation in m/sec.
Above the critical density, detonation pressure is zero, as the cartridge does not explode
9.
CRITICAL DIAMETER: is the minimum diameter of a charge, below which the detonation does
not proceed, resulting in misfire. The detonation wave tends to fall or fade when diameter of explosive
charge decreases. At lower diameter even if the explosive is sensitive, the reaction in the cartridge may
be incomplete.
10.
SENSITIVITY: It is measured as the explosive’s propagation property to bridge a gap between
two consecutive cartridges or a column of an explosive charge e.g. if a cartridge is cut into two halves,
and the resultant pieces are kept apart. By initiating one of them, with how much gap the other will be
able to accept the propagation wave, if blasted unconfined in a paper tube.
11.
SHELF LIFE: Shelf lives of various products described are listed in their respective tables. For
most explosives products, a shelf life of one year is recommended, although satisfactory performance can
be expected from most products two, three, and even four years later. Consult the appropriate
manufacturer to determine shelf life ratings beyond one year. NPS-65 mandates a maximum shelfstorage of two years.
6.4
CLASSIFICATION OF EXPLOSIVES
Explosives have wide applications in mining and tunneling operations to carryout rock fragmentation
for the differing conditions; hence, a wide range of this product is available. Given below is the general
classification of explosives.
Low Explosives: Low explosives deflagrate rather than detonate. Their reaction velocities are 2000 to
less than 3000 feet per second. Black powder is a good example. These materials normally have little
water resistance, are highly flammable, sensitive to a No. 6 strength blasting cap, and have a heaving action
during blasting. Low explosives generally do not fragment rock as well as high explosives.
High Explosives: A high explosive is any chemical mixture that detonates with a reaction velocity over
5000 feet per second. The reaction can be initiated by a No. 8 strength blasting cap (i.e., high explosives
are
1. Straight Dynamite - Nitroglycerin in an absorbent, with velocities between 10,000 and 20,000 feet
per second. This dynamite is the most sensitive of all commercial explosives. The weight strength
is the actual percentage of nitroglycerin in the cartridge. This explosive has poor fumes, good
water resistance, and poor cohesion.
2. Ammonia Dynamite - This is similar to straight dynamite except that ammonium and/or sodium
nitrate and various carbonaceous fuels are substituted for a portion of the nitroglycerin. There
are three subclasses of ammonia dynamite:
High Density: This product has a detonation velocity of 8000 to 13,000 feet per second, good
water resistance, and fair to good fumes.
Low Density: This product has detonation velocities between 7,000 and 11,000 feet per second,
fair to good fumes and fair to poor water resistance.
Permissible Types: These products are similar to the low- density ammonia dynamites except
that they contain cooling salts such as sodium chloride. This material usually has good fumes and
fair to poor water resistance.
3. Gelatin Dynamite - Contains nitroglycerin gelled with nitrocellulose, and various absorbent filler
mate- rials. Forms a soupy to rubber-like mixture which is water-resistant.
(a) Straight Gelatin - Has a detonation velocity of 13,000 to 23,000 feet per second. Varieties
with strength rating above 60 percent have poor fume characteristics. Water resistance is
excellent and material is very cohesive.
(b) Ammonia or Special Gelatins - Similar in composition to straight gelatin except that some of
the nitroglycerin is replaced with ammonium and sodium nitrates and carbonaceous fuels. Has a
detonation velocity between 10,000 and 23,000 feet per second. Water resistance is good.
4. Semi-gelatin Dynamite - A combination of ammonia gelatin and ammonia dynamite, with lower
strength than gelatin, yet has good water resistance. Velocities between 10,000 and 15,000 feet
per second. Fume rating is good.
6.4.1 SELECTION OF EXPLOSIVES
There have been many systems developed to rate the strength or power or an explosive. Although these
systems work, it is still not clear as to whether or not the information is useful to the field blaster. There
are many reasons for choosing an explosive. These reasons range from the specifications of the product,
the price, availability, and reliability. Whatever the reason for selection, the blaster should consider the
following properties:
• Velocity
• Sensitivity
• Gas or Pressure Release
6.5
•
Water Resistance
•
Fume Quality
EXPLOSIVE INITIATING DEVICES/SYSTEMS
Any explosive needs stimuli like shocking, friction or flaming for it to blast, or the reaction to initiate in
it. The devices used to carry-out these operations are known as initiating devices. Initiators are devices
with high explosives that create detonation or burning when given an adequately big electrical or
mechanical impulse. A system of explosives and other devices contain initiators that are used to begin
detonation of all other components of a system. Initiation systems are electric or non-electric, and
consist of blasting caps, safety fuse, detonating cord, or non-electric shock tubes.
Electric blasting caps are the most popular method of initiation. An internal-connecting bridgewire
is heated by electrical energy sent through copper or iron legwires. This process ignites a cap-sensitive
explosive by detonating a high-explosive base charge. The electric blasting caps can be made with an
instantaneous (no delay train) time of initiation, or with time delays in milliseconds used in delayed
blasting. There are long or short-period delays. The application of time delays improves rock
fragmentation and the monitoring of ground vibrations. Caps can be energized with AC power lines
and capacitor-discharge DC power sources.
Nonelectric initiation systems contain a cap similar to that of electric cap, however in order to
initiate the cap, they are linked to plastic tubing or a transmission line that carries shock or heat (an
initiation). The energy source in the tubing is either a gas or mixture of an internal coating of special
explosive. Nonelectric tubing is not applied in underground coal or gassy mines since the initiation
produces an open flame, and hence is hazardous. Nonelectric systems enable one to design blasts with a
greater number of holes than in the case of traditional electric blasting.
NOTE: If explosives are to be used to break rock, they and blasting devices have to be properly chosen,
the borehole patterns, loading characteristics, and delay blasting sequence must be carefully designed,
and ground vibration, airblast, and fly rock have to be controlled properly.
6.6
USE, HANDLING, TRANSPORTATION AND STORAGE OF EXPLOSIVES
Explosive is a commodity that cannot be allowed to handle by anyone else than an authorized person by
the government, as it requires, a special skill for its handling, use, transfer and storage, apart from the
security reasons. Proper accountability is kept at any stage, right from receiving from the manufacturer up
to its end use, to avoid any pilferage. Explosive is very sensitive to shock, impact, jolt, friction, ignition,
spark or tampering. Hence the important guide-line is that, all precautions must be taken against all these
factors during its storage, transportation, handling and use. To safeguard against all these dangers, every
country has its own rules and regulations. One will find that these regulations have been formulated by
taking into consideration of these guidelines.
Figure 6.2 Design of Explosive Magazine and Explosive mixing plant
Magazine
It is a place where an explosive is stored. It is constructed using specified specifications by the safety
authority of any country and need to comply with certain basic design considerations. It should be
located in an isolated and remote area. May be an area surrounded by hills etc. or by artificially created
earth mounds. The electric overhead lines should be at least 91 m (300 ft. or as specified by the safety
authority) away. In general, the following guidelines are followed while constructing a magazine:
●
Roof should be leak proof and the floor damp proof. Dimensions should be chosen as per the
capacity.
● The doors and window should be of sufficient strength and constructed by fitting inner lining of wood.
No iron nail, hinge etc. should be used. All hinges, locks etc. should be made of brass or any nonferrous material such as copper, bronze etc. The idea is that any material that can produce spark should
not be used as a tool or construction material in the direct contact with the explosive. All doors should
open outwards.
● Magazine must be fitted with an effective lightening conductor system and all iron and steel used in
the construction of doors etc. should be properly bonded and earthen. Earthling should be checked
periodically.
● Provision for water and fire extinguishers should be made.
● ‘Z’ type of ventilators should be provided near the floor and roof in the walls.
● Detonators must be stored in a separate annex, which can be accessed separately.
Wall between explosive and detonator compartments should not be less than 0.9 m
(3 ft.) thick (or as specified by the safety authority).
● All detonators, explosive containers and fuse box etc. should be stored on wooden benches.
● Magazines should be fenced properly from all sides.
● Provision for its guarding by watchmen, round the clock, in rotation must be made.
Only authorized person should access the magazine.
Special vans are used to transport explosives. Containers of special design are used to transport
explosives from the magazine to underground up to its place of use. Usually these explosive containers
are kept in a special underground station, known as ‘Reserve Station’ before carrying them to the face.
The blaster transports detonators separately.
6.7
BLASTING MECHANICS
Upon detonation, explosives affect rock by various interrelated means. While the following discussion
simplifies a complex and (in some aspects) largely theoretical subject, it should provide a basic grasp of
blast mechanics. The same mechanisms apply to whatever material is being blasted (wood, concrete,
steel, soil, ice, etc.); however, results are highly dependent on material integrity. As a result, this
discussion will con- sider only monolithic bedrock in order to avoid confusion.
1. Detonation Shock Wave
Upon initiation, the detonation (explosive oxidation) zone proceeds down the column of explosive at the
product's detonation velocity. At the front of this detonation zone, an energy pulse or “shock wave” is
generated and transmitted to the adjacent rock; any air space between the explosive and the rock
absorbs wave energy and reduces its effect on the rock. The shock wave travels outward as a
compression wave in all directions from the borehole, moving at or near detonation velocity. The rock
immediately surrounding the borehole is crushed to some extent, dependent on how much the force of
the wave exceeds the compression strength of the rock. The force of the wave overcomes the elastic
limits of the rock, causing it to bend outward and crack.
2. Shock Wave Reflection
At this point, the result of the blast will only be very large wedge-shaped blocks, still interlocked.
However, when the shock wave reaches a free face, the outward-bending compressive force releases,
and the wave is reflected back into the rock as a tension wave. The speed of the shock wave has been
slowed somewhat, and its energy lowered, but if the distance from the borehole to the free face is not
too great, it still carries enough force to overcome the tensile strength of the rock. The reflected tension
wave causes lateral cracking in the rock between the radial cracks, creating “fragmentation.” If there is
no free face, such as behind the borehole, there will be no wave reflection and no lateral cracking. A point
to remember is that any break in rock continuity will act as a free face; a crack or weather seam is as
good as a quarry face in this regard.
3. Gas Pressure and Rock Movement
Upon detonation, along with the shock wave, the solid explosive is instantly converted to
superheated gas that is trying to occupy a space 10,000 to 20,000 times its original solid volume, and
exerting a pressure that can exceed 1.5 million psi. Without this gas pressure, the fractured rock would
not move and would remain interlocked. The fractured rock mass has a certain inertia which the gas
pressure must initially overcome to start rock movement. Thus, there is “hesitation” between detonation
and the start of rock movement, lasting roughly one millisecond per foot of distance between the
borehole and the free face. Once inertia is overcome, the rock moves outward away from the borehole,
although smaller fragments can move faster and be shot out as flyrock.
Figure 6.3 Mechanics of blasting
6.8
HOLE PATTERNS
Hole array is the arrangement of blastholes (both in plan and section). The basic blasthole arrays are
single-row, square, or rectangular and staggered arrays. Irregular arrays are also used to take in irregular
areas at the edge of a regular array. The term SPACING denotes the lateral distance on centers between
holes in a row. The BURDEN is the distance from a single row to the face of the excavation, or
between rows in the usual case where rows are fired in sequence.
Figure 6.4.1: Square or rectangular pattern
Figure 6.4.2: Staggered pattern
Figure 6.4.3 Single-line
6.8.1 DELAY PATTERNS
Delay patterns, and varying the hole array to fit natural excavation topography, allow for more
efficient use of the explosive energy in the blast. Benches may be designed and carried forth with
more than one face so that simple blasting patterns can be used to remove the rock.
Figure 6.5.1: Typical bench cut with two free faces and fired with one delay per row.
Figure 6.5.1 indicates that the direction of throw of the blasted rock can be controlled by varying the
delay pattern. The rock will move forward normally to the rows of holes. If the holes are fired in
oblique rows as in Figure 8-5, the rock mass would be thrown to the right during blasting.
Figure 6.5.2: Direction of throw of blasted rock
6.8.2 POWDER FACTOR
Powder factor can be expressed as a quantity of rock broken by a unit weight of explosives. Or,
alternatively, it can be the amount of explosives required to break a unit measure of rock. The powder
factor is a relationship between how much rock is broken and how much explosive is used to break it.
It can serve as an indicator of how hard the rock is, the cost of the explosives needed, and a guide to
planning a shot. Since rock strenght is usually measured in pounds, there are several possible
combinations that can express the powder factor.
Powder Factor = Tons of rock (or cubic yards) per pounds of explosive.
Normal range = 4 to 7
Shallow holes = 1 to 2
External loads = .3
Cubic/Tons of Rock = Powder Factor
lbs of Explosives
The higher the powder factor, the lighter the load. Lower powder factor means more explosives will be
required to achieve desired fragmentation.
Example:
1.5 tons = PF of 6
.25lbs
7.0 PRIMING OF EXPLOSIVE AND BLASTING DESIGN
Priming a charge is simply positioning a suitable primer within a charge or column of explosives. The
object is to provide the primary-initiating explosion needed to detonate the main charge efficiently. When
the primer is the first cartridge or one of the first cartridges to be loaded into the borehole, it is called
bottom priming. In this cartridge, the explosive end of the blasting cap must be pointed toward the collar
of the borehole. Regardless of where the primer is placed in a column of explosives, the explosive end
of the cap should ideally be pointed toward the main column of explosives.
Bottom priming is generally considered a safer practice than placing the primer at the collar. The
most important reason for this is less chance of misfires, and there is also less chance of the primer being
dislodged, cut off, or blown from the hole when multiple-hole delay blasting is being used.
Top priming is the positioning of primer cartridge toward the top of the collar. The advantages of top
priming are to keep the primer from becoming immersed in water at the bottom of wet holes, to keep the
primer high (more accessible) in the hole if it misfires and needs to be reprimed and reduced length fuse,
detonating cord, or leg wires.
When priming blasting agents with holes up to 2 1/2 inches in diameter, a full cartridge of high
velocity explosives like 60 percent ammonia gelatin, gels, slurries, or cast primers with a blasting cap, is a
sufficient charge. For larger holes, the priming requires much more care, especially if the hole is wet or
decked charges are used. A small quantity of a high-velocity primer is better than a large amount of a
lower velocity primer. The detonating velocity of the primer must be greater than or equal to the
detonating velocity of the agent for efficient detonation.
The objective of the primer is to achieve a stable detonation. Neither over-priming or under- priming
the agent is desirable. The diameter of the primer must be larger than the critical diameter of the explosive.
Every explosive has a certain critical diameter below which detonation will not propagate beyond the
primer point.
The problem of determining how many primers to use and where to locate primers in an explosive
column is a difficult one. Too many unnecessary primers add to the cost of blasting, while too few
primers rob the blast’s efficiency. Basically, the primers must be located so that the detonation travels
through the entire powder column before any of the gas and pressure is vented. In a shallow hole with a
short explosive column, only one primer would be needed. However, as the hole depth increases, the time
required for the entire powder column to detonate increases correspondingly. The requirement for
additional primers is determined by the amount of burden and stemming which confines the gases and
pressures. The following equation gives the maximum hole depth when the borehole is bottom primed:
H = 2.5 x Ve x B + T
Vr
Where:
H =
Ve =
Vr =
B =
T =
hole depth
velocity of the explosive
velocity of the rock
burden
stemming
As an example, assume the burden for a shot is 11 feet, the stemming is 9 feet, the velocity of the
explosive is 11,000 feet per second, and the velocity of the rock is 20,000 feet per second. What should be
the maximum hole depth for this type of shot?
H = 2.5 x Ve x B + T
Vr
H = 2.5 x 11,000 x 11 + 9
20,000
H = 15.13 + 9
H = 24.13 feet.
This equation indicates that if the borehole depth is greater than 24.13 feet, we need an additional
primer in the column. As long as the borehole is less than 24.13 feet, one primer located at the bottom of
the column will suffice.
When the boreholes are subdrilled, the equation becomes more complicated:
H = 2.5 x Ve x (B² + J²)½ + T
Vr
Where:
J = subdrilled distance
Example: Burden = 13 feet
Stemming = 10 feet
Subdrilling = 4 feet
Velocity of ANFO = 12,000 ft/sec
Velocity of limestone = 16,400 ft/sec
What is the maximum hole depth that should be used with a single primer?
7.1
LOADING, TAMPING, AND STEMMING
LOADING is the process of placing an explosive charge, complete with primer, into a drilled,
punched, or dug hole. Before loading, it is required to test the hole with a pole or measuring tape to
confirm that it is the desired depth and to ensure that there are no obstructions or rough spots which
might interfere with loading. The driller serves as the blaster’s eyes and the two must work together.
When loading, remember that the wrapper, or shell, on a primer cartridge should never be slit, or
tamped.
TAMPING is the compacting of the charge in the borehole to ensure that there are no breaks in the
continuity of the column and to increase the density of the charges, as well as fill all available borehole
space. A non-sparking pole should be used for tamping. Primer charges should be lowered or pushed
carefully into place. Sometimes cartridges may be tamped sufficiently by merely pressing down firmly
with the pole. Never tamp vigorously or continue to tamp after the explosives have filled-out to the walls of
the hole. Throughout the loading and tamping operation, great care must be taken to guard against
damaging or sharply kinking fuse, lead tubes of non-electric blasting caps, or leg wires of electric
blasting caps leading to the primer charge.
STEMMING is packing an inert material, such as gravel, sand, or drill cuttings, on top of the charge to the
top of the borehole. When loading a borehole, the blaster must always leave space for adequate
stemming and the explosive should not extend to the collar of the borehole. Stemming does more than
confine the explosive. It also protects the loaded explosives from accidental ignition or detonation. In
the stemming operation, a small quantity of stemming should be care- fully and gently pressed over the
charge. The remainder of the stemming should be progressively added and firmly tamped into the hole.
Ideally, stemming should be packed so that it is at least as solid as the surrounding earth.
The height or depth of the stemming depends on various factors ranging from the power of explosives,
burden, spacing, and material being blasted to material being used as the stemming. The stemming must
occur in an amount sufficient to confine the gases released by the explosives long enough for the gases to
do their work to prevent blowout. In solid rock, the stemming should be equal to the burden.
However, when blasting rock that is not solid, rock that has seams, cracks, and crevices, and laminated
layers, the amount of stemming should be decreased according to this formula:
Stemming = .7 x Burden
7.2
DELAY PRIMERS
Non-electric down-the-hole delay priming allows distribution of large amounts of explosives in many
small decks or charges in the overburden. This results in a level of shock and vibration below the legal
level, even though the same amount of explosives is used. The charges are simply detonated at different
time intervals. Normally, to set off a sequence of blasts at different levels within a single hole, several
blasting caps are placed down the hole, with explosives packed at the desired levels separated by
stemming material. The complexity of many wires extending out of the hole creates the possibility of
attaching wrong wires to the firing system.
With the delay primer, however, decks may be initiated starting at the top, the bottom, or the middle of
the burden, simply by choosing the right timing inserts. The delay primer consists of two parts (1) the
main explosive charge and (2) a delay insert that are joined at the time the hole is loaded. The main
explosive charge is cast into a molded plastic container that has a detonating cord tunnel on the side and a
sensor well and a cap well at the one closed end. The other end is open.
When the downline is initiated at the surface by a blasting cap or detonating cord, the propagation wave
travels through the cord at over 23,000 feet per second. When the wave passes through one of the cord
tunnels, it activates the sensor of the delay insert. This starts the delay column burning at a prescribed
rate toward the blasting cap in the primer. When the cap is initiated, it explodes, initiating the primer.