Safe Mine Design and Mining Methods-smallscale.

Table of ContentsNTRODUCTION........................................................................................................................................1

MINING TERMINOLOGY...........................................................................................................................1

STAGES IN THE LIFE OF A MINE...............................................................................................................4

Prospecting..............................................................................................................................................4

Exploration..............................................................................................................................................4

Development...........................................................................................................................................4

Exploitation.............................................................................................................................................5

Reclamation.............................................................................................................................................5

UNIT OPERATIONS OF MINING................................................................................................................6

Underground Mining...............................................................................................................................8

UNDERGROUND MINING TERMINOLOGY................................................................................................8

Basic problems in underground operations.............................................................................................9

Means of access and egress...................................................................................................................10

Ground control in underground excavations.........................................................................................22

Natural support (room-and-pillar mining).............................................................................................23

Artificial support....................................................................................................................................26

Underground mining methods..............................................................................................................29

unsupported methods...........................................................................................................................30

Supported mining methods...................................................................................................................31

SURFACE MINING..................................................................................................................................33

Surface Mining methods........................................................................................................................34

Conical pit (Open pit) Mining.................................................................................................................35

Open Pit Terminology............................................................................................................................36

Placer and Placer Mining.......................................................................................................................40

Placer Mining Methods.........................................................................................................................41

Hydraulic Mining...................................................................................................................................43

SAFE MINE DESIGN AND MINING METHODS FOR SMALL SCALE MINING.

NTRODUCTION.

MINING TERMINOLOGYThere are many terms and expressions unique to mining that characterize the field and identify the user

of such terms as a ‘‘mining person.’’ The student of mining is thus advised to become familiar with all

the terms used in mining, particularly those that are peculiar to either mines or minerals. Most of the

mining terminology is introduced in the sections of this book where they are most applicable. Some

general terms are best defined at the outset; these are outlined here.

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

Some terms distinguish various types of mined minerals. Geologically, one can distinguish the following

mineral categories:

Mineral: a naturally occurring inorganic element or compound having an orderly internal structure and a

characteristic chemical composition, crystal form, and physical properties

Rock: any naturally formed aggregate of one or more types of mineral particles

Bedded Deposit - An ore deposit of tabular form that lies horizontally or only slightly inclined to the

horizontal, and is commonly parallel to the stratification of the enclosing rocks.

Country Rock/Host Rock - The rock in which the ore deposit is enclosed. It is the general mass of

adjacent rock as distinguished from that of a vein, or lode.

Dip - The angle at which a bed, stratum or vein is inclined from the horizontal.

Exploration - The work involved in gaining knowledge of the size, shape, position and value of an ore

body.

Fault - A discontinuity between two portions of the earth's surface that have moved relative to each

other. A fault is a failure surface and is evidence of severe earth stresses.

Foot Wall - The wall or rock under a vein. It is called the floor in bedded deposits.


Hanging Wall - The wall or rock on the upper side of an inclined vein. It is called the roof in bedded

deposits.

Outcrop - Commonly considered as the surface exposure of a mineral deposit. However, the uppermost

part of a mineral deposit may be covered with soil or overburden and thus the outcrop may be hidden.

Vein - A mineralized zone having a more or less regular development in length, width and depth to give

it a tabular form and commonly inclined at a considerable angle to the horizontal. The term lode is

commonly used synonymously for vein.

Economic differences in the nature of mineral deposits is evident in the following terms:

Ore: a mineral deposit that has sufficient utility and value to be mined at a profit.

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.

A further subdivision of the types of minerals mined by humankind is also common. These terms are

often used in the industry to differentiate between the fuels, metals, and nonmetallic minerals. The

following are the most common terms used in this differentiation:

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

radioactive minerals (uranium, thorium, and radium).

Nonmetallic minerals (also known as industrial minerals): the nonfuel mineral ores that are not

associated with the production of metals. These include 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, coalbed methane, gilsonite, and tar sands.

It should be noted that the mining engineer is associated with the extraction of nearly all these mineral

resources.


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.

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, the run-of-mine material is generally cleaned or

concentrated. This preparation or beneficiation of the mineral into a higher-quality 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.

Professionally, 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, already defined, 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 he or she may share those

duties 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.


STAGES IN THE LIFE OF A MINEThe 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 to 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 laws regulating the 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 in a book entitled Our Common Future (World

Commission on Environment and Development,1987 ) as ‘‘development that meets the needs of the

present without compromising the ability of future generations to meet their own needs.’’

ProspectingProspecting, the first stage in the utilization of a mineral deposit, is the search for ores or other valuable

minerals (coal or nonmetallics). Because 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

ExplorationThe 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 more refined than those used in

prospecting. The line of demarcation between prospecting and exploration is not sharp; in fact, a

distinction may not be possible in some cases. Exploration generally shifts to surface and subsurface

locations, using a variety of measurements to obtain a more positive picture of the extent and grade of

the ore body.


DevelopmentIn the third stage, development, the work of opening a mineral deposit for exploitation is performed.

With it begins the actual mining of the deposit, now called the ore. Access to the deposit must be gained

either (1) by stripping the overburden, which is the soil and/or rock covering the deposit, to expose the

near-surface ore for mining or (2) by excavating openings from the surface to access more deeply buried

deposits to prepare for underground mining.

In either case, certain preliminary development work, such as acquiring water and mineral rights, buying

surface lands, arranging for financing, and preparing permit applications and an environmental impact

statement (EIS), will generally be required before any development takes 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 disposal areas, offices, and other 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.

ExploitationExploitation, 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 is 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. Surface mining includes mechanical excavation methods such as open pit and

open cast (strip mining), and aqueous methods such as placer and solution mining. Underground mining

is usually classified in three categories of methods: unsupported, supported, and caving.

ReclamationThe final stage in the operation of most mines is reclamation, the process of closing a mine and

recontouring, revegetating, and restoring the water and land values. The best time to begin the

reclamation process of a mine is before the first excavations are initiated. In other words, mine planning

engineers should plan the mine so that the reclamation process is considered and the overall cost of


mining plus reclamation is minimized, not just the cost of mining itself. The new philosophy in the

mining industry is sustainability, that is the meeting of economic and environmental needs of the

present while enhancing the ability of future generations to meet their own needs (National Mining

Association,1998 ). In planning for the reclamation of any given mine, there are many concerns that

must be addressed. The first of these is the safety of the mine site, particularly if the area is open to the

general public. The removal of office buildings, processing facilities, transportation equipment, utilities,

and other surface structures must generally be accomplished. The mining company is then required to

seal all mine shafts, adits, and other openings that may present physical hazards. Any existing highwalls

or other geologic structures may require mitigation to prevent injuries or death due to geologic failures.

The second major issue to be addressed during reclamation of a mine site is restoration of the land

surface, the water quality, and the waste disposal areas so that long-term water pollution, soil erosion,

dust generation, or vegetation problems do not occur. The restoration of native plants is often a very

important part of this process, as the plants help build a stable soil structure and naturalize the area. It

may be necessary to carefully place any rock or tailings with acid-producing properties in locations

where rainfall has little effect on the material and acid production is minimized. The same may be true

of certain of the heavy metals that pollute streams. Planning of the waste dumps, tailings ponds, and

other disturbed areas will help prevent pollution problems, but remediation work may also be necessary

to complete the reclamation stage of mining and satisfy the regulatory agencies.

The final concern of the mine planning engineer may be the subsequent use of the land after mining is

completed. Old mine sites have been converted to wildlife refuges, shopping malls, golf courses,

airports, lakes, underground storage facilities, real estate developments, solid waste disposal areas, and

other uses that can benefit society. By planning the mine for a subsequent development, mine planners

can enhance the value of the mined land and help convert it to a use that the public will consider

favorable. The successful completion of the reclamation of a mine will enhance public opinion of the

mining industry and keep the mining company in the good graces of the regulatory agencies.

The fifth stage of the mine is thus of paramount importance and should be planned at the earliest

possible time in the life of the mine.


UNIT OPERATIONS OF MININGDuring the development and exploitation stages of mining when natural materials are extracted from

the earth, remarkably similar unit operations are normally employed. The unit operations of mining are

the basic steps used to produce mineral from the deposit, and the auxiliary operations that are used to

support them. The steps contributing directly to mineral extraction are production operations, which

constitute the production cycle of operations. The ancillary steps that support the production cycle are

termed auxiliary operations.

The production cycle employs unit operations that are normally grouped into rock breakage and

materials handling. Breakage generally consists of drilling and blasting, and materials handling

encompasses loading or excavation and haulage (horizontal transport) and sometimes hoisting (vertical

or inclined transport). Thus, the basic production cycle consists of these unit operations:

Production cycle= drill + blast + load + haul

Although production operations tend to be separate and cyclic in nature, the trend in modern mining

and tunneling is to eliminate or combine functions and to increase continuity of extraction. For example,

in coal and other soft rock mines, continuous miners break and load the mineral to eliminate drilling and

blasting; boring machines perform the same tasks in medium-hard rock.

The cycle of operations in surface and underground mining differs primarily by the scale of the

equipment. Specialized machines have evolved to meet the unique needs of the two regimes.


Underground Mining.

UNDERGROUND MINING TERMINOLOGY.Adit - A horizontal or nearly horizontal passage driven from the surface for the working of a

mine. If driven through the hill or mountain to the surface on the opposite side it would be a

tunnel.

Shaft - A vertical or inclined excavation in a mine extending downwards from the surface. A

shaft is provided with a hoisting apparatus at the top for handling men, rock and supplies, or it

may be used only in connection with ventilation operations.

Collar - The term applied to the timbering around the mouth or top of a shaft.

Crosscut - A horizontal opening driven across the course of a vein or in general across the

direction of the main workings.

Drift - A horizontal opening in or near an ore body and parallel to the course of the vein or long

dimension of the ore body.

Tunnel - A horizontal or nearly horizontal underground passage that is open to the atmosphere

at both ends. The term is loosely applied in many cases to an adit.

General

Recovery of mineral from 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 functions are normally required to

support the series of operations which comprise the complete mining process.

A suitable design of underground excavations within the mineral body, and in the rock mass

adjacent to it, is critical in assuring an efficient and safe mining performance.

The geometry of the mineral body and its rock mechanical properties should be, as far as

possible, known.


Mistakes in the choice of mine design and mining method may severely jeopardize productivity

and safety and may also lastingly sterilise mineral reserves, i.e. render it impossible for

extraction.

An inexperienced mine operator / owner should, therefore, seek advice from competent miners

when selecting an appropriate mine design and mining method which correspond to the

condition of the mineral deposit.

Basic problems in underground operationsAccess to the underground deposit is commonly provided by a single adit/shaft. No alternative

mean of egress from working faces to the surface is available. Thus miners may be trapped

underground in case the only available underground opening will collapse.

Depending upon the geometry of the mineral body, underground excavations are often

randomly generated and are either very narrow or of great extension. Confined and narrow

passage ways and production openings make winning and hauling operations as well as

travelling of persons difficult and inefficient.

Excessive large unsupported underground excavations are prone to roof falls and uncontrolled

rock movement. Heavy roof falls frequently endanger miners and often result in abandonment

of working faces.

Structural support is seldom provided. Even vital underground excavations such as mine

adits/shafts in potentially unstable ground are insufficiently supported.

Basic requirements for a safe and successful underground mine are:

• Providing and maintaining structurally stable means of access and egress (at least two for

every working block / mining area).

• Providing and maintaining stable underground excavations and working faces which are to be

kept open for as long as necessary.


Means of access and egressSmall-scale mining activities often commence with open casting on outcropping mineral

deposits or at the bottom of a surface mine which has arrived at the limit of economic depth.

Depending upon the nature and location of mineral deposits access to them is provided by

inclined or vertical shafts (placer and coal deposits) or by adits - horizontal or nearly horizontal

passages - driven from the surface (hard rock gold or fluorspar mining).

Means of access from surface to underground are often located on steep unconsolidated slopes

or on high walls (even overhanging) and are thus endangered by ground fall, landslide or cliff

collapse. Such incidents may result in a complete obstruction of the mine access, trapping

miners underground.

As far as practicable any mine entrance or outlet should not be located at potentially unstable

and steep walls or slopes, and under no circumstances beneath overhanging walls.


The overall slope angle should, in the long term, not exceed 70° in strong competent rock and

45° in weathered rock, soil or gravel.

Fissures, fractures or cleavages dipping towards the mine entrance require special attention, in

particular when wet. Such dangers may be minimized by applying a benching (terraced) system

during open casting.

Where this is not provided, mine entrances or outlets should be so constructed or secured as to

prevent any loose ground or wet material from falling or sliding towards or into the mine

opening which may result in a complete obstruction of it.

Structural support should be installed at the mine mouth (collaring), so designed that the mine

mouth reaches out of the danger zone of ground falls or wall collapses.

The support could consist of sturdy timber sets or waste/sand filled bags which should be

tightly set around the mine mouth.


All surface and seepage water should be channelled in such way as to prevent it from running

into the mine opening. Wet rock, in particular when fractured or decomposed is less stable than

dry rock.

Shafts or inclined mine adits are often several tens of meters deep and their entrances are not

guarded. There is a high risk that a mine worker or member of the public could fall in.

Therefore, the surface entrance to every mine shaft and every other inclined entrance should

be securely fenced or otherwise barricaded to prevent unauthorized entry and unintentional

fall in. Clear warning signs indicating “area of danger” should be posted.


Shafts driven into loose ground are often insufficiently or not supported causing ground fall into

the shaft due to degrading material around the mine mouth and in the shaft itself.

There is a high risk that such shafts may be obstructed or miners injured by falling material.

Complete shaft collapses are also not uncommon.


Any entrance of a vertical or inclined mine shaft should be effectively collared, by using

timbering or sand bags, to secure the shaft against dislodging loose ground.


Shafts or other adits which are to be used for the full life of the mine and in which miners

frequently travel into and out of the mine should be adequately lined by timbering (e.g. full

cribbing or timber sets), in particular when they are driven into unstable ground.

Many serious accidents happen in small-scale underground mining operations due to the fact

that only one mean of access or egress is provided. A mine adit or shaft may collapse or be

obstructed, subsequently trapping miners underground who cannot escape from the mine.

Therefore, it is a primary requirement to provide every underground mine as soon as

practicable with an alternative mean of access/egress to ensure that miners can escape safely

from the mine in case that one of them becomes impassable.

Except for the duration of development work the mine operator/owner should ensure that

there are at least two outlets providing at all times two separate exits to the surface.

For the development of a mine, two means of access into the mineral deposit should be driven

simultaneously and as soon as possible interconnected before continuing with production

headings / working faces.


As far as practicable, mine outlets should be so separated that anything which happens to any

of them will not affect the safety of the other. They should be located at least 50 metres apart

from each other.

No mining should take place in the vicinity of mine shafts or adits along their whole length. To

ensure their stability, safety pillars of adequate size and strength should be kept in place.

Mineworkers often have to use difficult means of access to travel to and from their work places

underground (e.g. climbing or walking through steep and narrow underground excavations

where there may be a danger of slipping or falling).


Any mine shaft exceeding an inclination of 45 degrees from the horizontal should be provided

with fixed stairs or a ladder way.


Every mean of access or egress, which is regularly used for the travelling of mine workers to or

from their working places in the mine, should be in such height and width as to allow ease of

travelling (not less than 1.7 m high and 1 m wide).

Sufficient clearance is also necessary to facilitate:

• the installation of ventilation equipment, such as air ducting;

• the use of means of support;

• material transport and mineral haulage;

• the rescue of injured persons ( e.g. use of a stretcher).


If ever feasible and practicable, mineral haulage should be performed mechanically. Manually

operated windlasses or compressed air powered small hoists may be used.


Every mine where there are personnel hoisting shafts more than 5 metres deep should be

provided at all times with a hoisting apparatus (e.g. winch, windlass) by which persons

employed below ground have readily available a mean of egress in an emergency.


Ground control in underground excavationsWorkers in underground stone mines have a high rate of injuries and fatalities caused by falls of

rock blocks from the roof or rib isolated by discontinuities or as a result of mining activities.

Underground excavations in good solid strata (as typical for most small-scale mines operating in

hard rock gold or fluorspar deposits) are normally stable and do not require structural support,

provided that:

• the open roof span between the host rock medium or pillars is not too wide;

• the adjacent strata is not weakened by excessive fractures / joints and natural faulting; and

• the rock is not destroyed by careless winning methods, such as careless blasting operations.

In less stable broken or weathered ground with frequent jointing and poor rock quality

structural strata control is critical in assuring the stability of underground excavations.

Adequately arranged pillars in a regular grid array or efficient means of artificial support should

be used.

Different methods of support may be applied to control/limit ground movement into mine

excavations, e.g.:

• Natural support methods, such as mineral / waste pillars

• Artificial support methods, such as timber sets, props, waste filled bags, etc.

A critical factor is the time for which underground openings are to be kept open. Main

underground roadways or means of access to the mine require radically different supports to

those at working faces where the roof may be allowed to collapse (in a controlled manner) a

few days after the mineral has been extracted.


Natural support (room-and-pillar mining)The objective of room-and-pillar mining methods is to extract the mineral as completely as

possible, leaving mineral/waste as pillars to support the roof, without jeopardising working

conditions or safety.

It is applicable to relatively flat-lying stratiform or lenticular mineral bodies, although the

method can accommodate a mineral dip up to 30°.

To ensure the integrity of any vital shaft or adit of a mine, a part of the strata should be left in

place as a safety pillar of such size as to provide adequate protection for them.

A safety pillar of mineral layer should be left along the intersection of a mineral deposit and

host rock, unless such bedrock is adequately strong and solid.


Along the boundary between different mining areas/working blocks a mineral layer of adequate

size should be left as a safety pillar. This is also important to reduce the danger of any inrush of

water/mud or outburst of gas from old workings into the active mine area.

Drives and working faces in solid rock would be stable provided about 30-40% of the mined

areas are remaining as pillars. The open span of the roof between pillars or the host rock

medium should be so designed as ground condition warrant and pillars should be of sufficient

size to safely support the roof (The open roof span should not exceed 5 metres in flat and

medium dip).

In less stable ground, such as pay gravel or coal deposits, pillars left as support should be not

less than 50 % and up to 75 % of the mined area. The open span of the roof between pillars or

the host rock medium should not exceed 2 metres (1m in pay-gravel).


Pillars should never be randomly “robbed” or reduced, since the immediate roof may be liable

to collapse, either during robbing or shortly thereafter.


Since personnel operate continuously under exposed roof spans, close observation of the

performance of roof and pillars is required and dangerous conditions should be immediately

corrected .

Artificial supportThe operator/owner of every mine where ground support is necessary should ensure that

support of suitable material is provided and readily available for use. If for any reason the

necessary support material is not available and the working place presents a hazard, the work

at such place should be stopped.

Timber sets or props, waste filled bags, chocks (square sets of timber packed with rock), or

other suitable means of support should be installed immediately after the roof has been

exposed and poor ground conditions indicate that it is necessary.

Vital underground excavations, such as mine shafts or adits should be structurally supported by

regular timber sets (every 1 or 1,5 m), especially when they are driven into loose ground.

So called chock-support may be used at working faces of greater extension or where supporting

pillars are being recovered.


Any means of support should be of adequate strength, be securely set on proper foundation

and blocked/wedged as to achieve a tight fit to the exposed ground.

Any damaged, loosened or dislodged means of support which creates a hazard to persons

should be repaired or replaced prior to any work or travel in the affected area.


Any roof or rib in underground excavations where persons normally travel or perform work

should be regularly examined for cracks or other signs of stress or weakness, in particular:

• prior to commencing any work;

• immediately after blasting;

• as ground conditions warrant.

Where the undercutting of a working face is essential, a sufficient means of support (e.g. sturdy

wooden props) should be properly installed to prevent overhanging material from collapsing.

Under no circumstances should any working face be worked in a way that causes

unsupported overhanging or undercutting.


Where ever loose ground at any underground excavation could create a danger to persons, it

should be scaled down or supported in a safe manner before other work or travel proceeds in

the affected area.

Scaling bars should be of such a length and design that will allow the removal of loose material

without exposing the person performing this task to injury.

Scaling should be carried out from a location which will not endanger persons by falling

material.

Underground mining methods.Underground methods—unsupported, supported, and caving—are differentiated by the type of

wall and roof supports used, the configuration and size of production openings, and the

direction in which mining operations progress.


unsupported methodsUsed to extract mineral deposits that are roughly tabular (plus flat or steeply dipping) and are

generally associated with strong ore and surrounding rock.

These methods are termed unsupported because they do not use any artificial pillars to assist in

the support of the openings. However, generous amounts of roof bolting and localized support

measures are often used. Room-and-pillar mining is the most common unsupported method

used primarily for flat-lying seams or bedded deposits like coal, trona, limestone, and salt.

Support of the roof is provided by natural pillars of the mineral that are left standing in a

systematic pattern.


Sublevel stoping provides sublevels from which vertical slices are blasted. In this manner, the

stope is mined horizontally from one end to the other.

Supported mining methods Are often used in mines with weak rock structure.

Cut-and-fill stoping

This is the most common of these methods and is used primarily in steeply dipping metal

deposits. The cut-and-fill method is practiced both in the overhand (upward) and in the

underhand (downward) directions. As each horizontal slice is taken, the voids are filled with a

variety of fill types to support the walls. The fill can be rock waste, tailings, cemented tailings, or

other suitable materials. Cut-and-fill mining is one of the more popular methods used for vein

deposits and has recently grown in use.


SURFACE MINING.Advantages of surface mining over underground mining.

Higher productivity.

Greater concentration of all operations and simplified management of men and

machines.

Greater output per mine.

Lower capital cost per annual tonne mined.

Lower operating cost per tonne.

Possibility of moving a higher ration of waste to mineral and the exploitation of lower

grade reserves.

Greater geological certainty.

Less limitation on size and weight of machines.

Simpler auxiliary operations and services.

Increased recovery of mineral and less dilutions.

Greater reserves available for mining.

Simplified planning and control

Increased safety (working environment).

High grade control.

Flexibility of operations.


Disadvantages.

The main disadvantages of surfacing mining are due to adverse climate conditions and thec

effect on the environment.

Rainfall, snow, fog, sever heat or cold result in a drop in efficiency of labour and

machines.

Large open pit mines require large areas of land for mining and spoil heaps which are

lost at least temporarily, to agriculture.

For night working large areas must be illuminated.

Where operations start from the outcrop the weathered zone might yield a low grade

product for example coking coal may be oxidized.

Surface Mining methods.The main mining methods may be classified as follows:

Conical pit mining.

Strip mining.

Terrace mining.


Conical pit (Open pit) Mining.The picture below shows a conical pit mine.


Open Pit Terminology.

Bench-a ledge that forms a single level of operation above which mineral or waste materials are

mined back to a bench face. The mineral or waste is removed in successive layers, each of

which is a bench. Several benches may be in operation simultaneously in different parts of, and

at different elevations in the open pit mine.

Bench height-vertical distance between the highest point (crest) of a bench and the lowest

(toe) of the bench. The bench height is normally governed by:

The specifications of operating machines, such as drills and shovels,

Government mining regulations.

Bench slope- the angle, measured in degrees between the horizontal and an imaginary line

joining the crest and the toe of the bench.

Pit limits- the vertical and lateral extent to which the open pit mine may be economically

conducted. Factors controlling the limits of the pit are:


The cost of removing overburden and waste material vs the minable value of the ore ( is

usually the prime factor.)

Existing surface infrastructure such as town ships rivers etc.

Berm- a horizontal shelf or ledge within the pit wall slope that is left for stability of the slope

and safety reasons.

Overall pit slope angle- is the angle at which the wall of an open pit stands, as measured

between the horizontal and imaginary line joining the top bench crest with the bottom bench

toe.

Haul road- it’s a road that provides access for haul-trucks to move from surface to the bottom

of the pit. This will save for the duration of the open pit mine. Below is a picture of a haul road.


Types of haul road systems:

A spiral system is an arrangement whereby the road is arranged spirally along the

perimeter walls of the pit so that the gradient of the road is more or less uniform from

the top to the bottom of the pit.

A zigzag or switchback is an arrangement in which the road surmounts the steep

gradient of the pit wall by zigzagging, generally on footwall side of the pit.


Placer and Placer Mining.Placer mining (Alluvial mining) - It is an aqueous extraction method intended for the recovery of

heavy minerals from placer or alluvial deposits, using water to excavate, transport, and

concentrate the mineral.

Placers are defined as deposits detrital material with the valuable mineral liberated and

recoverable as discrete grains. They usually occur as unconsolidated sediments, but a certain

amount of induration can be present. With the passage of time, undisturbed, unconsolidated

sediments consolidate through physical and chemical process, becoming consolidated rocks.

Placers are formed by weathering processes that liberate and concentrate some valuable

portion of the rock relatively closer to the surface. They occur at that stage of the rock forming

cycle between weathering and reconsolidation into sedimentary rock where the matrix can be

excavated readily and the desired mineral can be concentrated to point where it has a relatively

high value with little expense, that is, without incorporating processes like flotation or crushing.

Examples of Placer deposits.

Stream or fluvial placer-formed by running water that transport away the lighter

material more rapidly than heavier materials, thus concentrating them.

Wind-formed or eolian placers- formed by the action of wind removing lighter material.

Beach placers- formed by shore wave action, sometimes acting on preexisting or

currently forming stream placers.

Off-shore marine placers- formed by bottom current and wave action on preexisting

placers or mineralized bedrock sea level.


Placer Mining Methods.Hand Mining.

The simplest and probably the earliest mining and recovery method is panning, where material

thought to contain valuable heavy mineral is scooped into a pan and covered with water. The pan

is shaken to get the heavier particles to settle toward the bottom and swirled to wash the lighter

particles over the side.

Coarser light particles are brushed out of the pan by hand, and coarser heavier particles are saved

by hand picking. This settling, washing and picking process continues until there is a satisfactory

concentration of the desired heavy mineral in the bottom of the pan. The picture below shos a

pan used for gold panning operations.

Dredging.

Once a placer operation reaches the scale where a larger plant is warranted, a hydraulic or

dredging plant can be set up. Dredges operate either on:

Land, in which case they float on self constructed pond in the mineral bearing stream or plain.

Sea-going dredges which work in a lake or offshore.

A dredge consists of:


A floating hull with a mining control system.

Excavating and lifting mechanism.

Beneficiation circuits.

Waste-disposal systems.

All designed to work as a unit.

Cutter-Suction dredge.

Made up of a series of cutting arms rotating in a basket about a suction intake. This cutter head

is generally toothed and is swung back and forth through the bank ahead of the dredge. It can

operate with a treatment plant in a separate vessel or on land. the cutter-suction dredge with

transport (trailing dredge) is much used in Japan and Europe to recover sand and gravel

offshore.


The rotating arms break up the bank material, slurrying it so it can be drawn into the dredge

suction. The rotating cutter head is more efficient at cutting and slurrying material for the pump

intake when swing in one direction than the other.

The pump of the suction cutter brings relatively large amounts of water to the surface for the

mineral processing plant, and the feed to the processing plant must dewatered before the

material is distributed to most kinds of mineral recovery machinery.

Hydraulic Mining.Hydraulic mining, or hydraulicking, is a form of mining that uses high-pressure jets of water to

dislodge rock material or move sediment. In the placer mining of gold or tin, the resulting

water-sediment slurry is directed through sluice boxes to remove the gold.

Hydraulic mining encompasses the following three distinct modes of operation:

Hydraulicking- the process of breaking up and suspending the subject material into a

slurry.

Sluicing- the process of moving the slurry.

Educing- the process of introducing the slurry into a contained circuit.

Hydraulic mining is generally understood to be the application of these applications when open

to the atmosphere. If applied to similar materials underwater the process becomes one of

dredging.

Hydraulicking.

This is the breaking up of material at a mine face with energy in a stream of water, and

peptizing the material into a slurry.

The pressures utilized vary in practice from gravity flow down a slope to mega pascals or bars,

ranging from unraveling a bank of silt having no cohesion to breaking up consolidated rock. Any

particular material requires a specific energy for slurrification. This can be supplied in numerous

combinations of water quantity and pressure, producing different slurry densities.


The principal hydraulicking machine element continues to be the traditional giant or monitor, a

water connon developed from a simple nozzle on the end of a hose. Below is a picture of the

giant or monitor.

The picture below shows hydraulicking operation.

Sluicing.

This is the movement of slurry that may proceed by gravity alone for several kilometers or

require frequent or even continuous water or energy addition to move more kilometers.

Most mining operations use the hydraulicking monitor for sluicing, but may use a separate

monitor. In nearly all instances sluicing detracts from mine productivity and objectionably

reduces slurry density. The flow of slurry is hampered by unfavorable gradients and by dilution

with low energy water. Thus the sluicing path should be as short as possible, and water addition


and pond formation should be minimized. An adequate sluicing gradient should always be

maintained, which favors a short sluice run. The picture below shows a sluicing box.

Educing.

This is the lifting or pumping of slurry from its sluicing delivery point into a contained or

enclosed circuit.

Hydraulic mining is possible without educing but normally employs pumps, less frequently

eductors (water-jet-pumps), and rarely hydraulic elevators. These devices have physical

constraints that limit the maximum particle sizes they can handle. This usually requires that

they be used with screening apparatus.


The eductor is frequently moved to keep up with the face, thereby keeping sluicing and educing

ponds to a minimum. In turn, the short sluicing path prevents the low-pH water from migrating

through the tailing pile and contaminating ground water.


Safe Mine Design and Mining Methods-smallscale.

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Transcript of Safe Mine Design and Mining Methods-smallscale.