Underground
Mining
Lesson 10
Objectives:
a) Students will examine the baseline plan
for a POGO mine in Alaska.
b) Students will summmarize the mine planning
process.
Underground Mine Planning
The planning process will, in general move
through four steps, irrespective of the design phase: baseline
assessment, reserve determination, premine planning, and subsystem
design.
BASELINE ASSESSMENT
Baseline assessment of all available data
precedes any planning efforts. It is a comprehensive initial
review of all available information on the potential reserve
or mine from geographic, geologic, environmental, technical,
and economic standpoints. An example: the geologic location of
a resource would have a great influence on the economics and
may dictate the mining method due to the equipment and power
availability, labor availability, and skills level, supplies
transport, etc. Negative aspects of the location of a mine may
be overcome by the value of the resource but many problems such
as permitting, environmental, or geographic issues may need to
be overcome before it can become a profitable mine.
Geologic Factors
The geologic model is only an interpretation
of the actual conditions based on the skill of geologists and
the economic backing available to do thorough testing . Constant
testing and drilling is done as the project moves through the
design phases. The data collected dictates the changes that effect
the geologic model.
Two approaches can be used to handle the
uncertainty in the geologic model in mine planning efforts based
on risk:
1) accept the geology and develop the plan
accordingly
2) acknowledge the uncertainty in the geologic
model and direct the planning effort to assure sufficient subsystem
flexibility to accommodate any potential impact.
Environmental Factors
Today designing a mine requires planning
for environmental protection and reclamation from the very beginning.
Potential negative impacts can be minimized by including in the
planning:
1) cost of environmental protection rather
than trying to find a remedy for reclamation.
2) good community relations as negative
publicity may have severe economic consequences
The planning
process requires at least a minimum of baseline environmental
data.
1) overburden analysis
2) soil surveys identifying topsoil and
subsoil
3) hydrolic studies
4) determination of characteristics of
surface and ground water
5) vegetation and existing land use surveys
6) air quality analyses
7) wildlife surveys
8) archeological surveys
**********More About EIS in
Chapter 11************
Geographic and Economic Factors
There are a number of geographic and economic
factors to be considered in the baseline assessment. The location
of a reserve with respect to transportation for equipment and
shipment of the products, climate, labor force availability and
skills, and power availability.
Other factors may influence the method
of mining:
1) high labor costs
2) skill level
3) equipment availability
Economic factors that influence plan design
are:
1) political and tax environment
2) stability of the present government
3) availability of replacement equipment
and supplies
RESERVE DETERMINATION
The characteristics of a reserve are as
crucial as the reserve magnitude or grade: the depth, inclination,
geometry, type and properties of host and deposit rocks, quality,
etc. and play a key role in the design.
Criteria
A mineral deposit or resource can only
be classified as an ore body only when it can be mined at a profit.
The planning and design attempts to identify the method to make
this possible. Demand of the ore body and mining technology can
affect the future of a project. As more knowledge is gained about
the resource, the plan must include provisions for revisions
such as:
1) technological advances
2) market or demand
3) depletion
4) new geographic factors
Data Presentation
Data is usually presented in a matrix form
with one side presenting the degree of certainty of existence
or an ore or mineral and the other side indicates the recovery
viability. The use of computers offers huge masses of summary
that often is overwhelming when trying to present data. The effective
graphics of computers though, can often create a visual presentation
that is easier to present data than a matrix.
Mathematical Methods
To estimate the reserve involves taking
point data and transferring the data to block or grids for calculation
purposes. Mapping involves using the determination of the of
sample point coordinates to determine boundaries. Block size
in terms of length and width may be defined on the basis of geologic
structure, deposit variability, and data spacing or quality forecasting
requirements. Mapping the block data is critical to the planning
and design.
PREMISE PLANNING
The mine plan constantly evolves as the
mine process changes physical characteristics. Engineering science
and technology are constantly evolving while the mine is locked
into the physical framework. An interesting fact is that equipment
changes with time but the basic design of the mine remains the
same. This is most obvious in comparing existing and newer mines.
The only way to obtain accurate cost forecasts
for the project is to develop a life-of-the-mine plan for the
reserve block. This must include the reclamation and final land
use plan. There are limitless factors that go into mine planning.
Following is a list of concerns
for underground mining:
1) Regulatory and Legal Factors
Permits and approvals may be at the federal,
state, local, or regional level. These are subject to continual
revision or reinterpretation requiring ongoing review of the
mine plan. Review leases to insure that the mineral and surface
rights are available.
Compliance plans include:
1) mine layout with projections
2) strata/roof control plan
3) ventilation plan
4) fan stoppage plan
5) dust control plan
6) medical / emergency evacuation plan
7) fire control/mine evacuation plan
8) escapee map/plan.
2) Geologic/ Geotechnical Factors
Depending on the mining methods under consideration,
many geologic and geotechnical factors must be considered. The
economics usually favor extraction of the best grade materials
or the lowest mining cost areas to maximize the return on investments
and shorten payback period. While the immediate extraction of
the best grade materials enhances immediate finances it can compromise
designs.
3) Environmental Factors
The impact on the environment must be considered
from the beginning of the plan design. The impacts to the environments
can include; noise, aesthetics, air quality, water discharge
and run off. The environment must remain within regulation during
the initial data gathering to the reclamation process.
Reclamation plans include; drainage control,
segregation of waste material, erosion and sediment control,
solid waste disposal, regrading and restoration of waste and
mine areas. The plan must include the effects of the mine subsidence,
vibration ( induced by transportation, mining, processing or
subsidence) and impact on surface water. The environmental items
often dictate the economics and viability of the mine.
4) Technical Factors
The technical areas of the plan are the
most extensive. It takes into consideration the regulations,
geologic, and and environmental factors to develop each part
of the plan. The layout of the mine is determined by the size
and shape of the reserve. After the ore deposit is mapped, access
development for the reserve area is figured into the plan. The
size of the reserves determines the kinds of access and the number
of access portals needed. Access can be vertical shafts, inclined
slopes, and drifts or horizontal entries. The larger the reserve,
the more complicated the plan becomes.
Surface Facilities
The productivity and the reserve size determine
the size and placement of facilities. Consideration must be made
for access, extraction, removal, and storage of the ore, the
physical needs of the work force, and the operational needs of
the facility. Land acquisition for disposal areas, dust, noise,
safety, and layout are other design considerations.
Physical Factors
Isopach mapping is used to determine the
reserve depth and develop the best mine layout. The plan lays
out the number of benches and designates the portion of the reserve
that will best meet the needs of the market. Economics drive
the design to gain the most profit from the mine while still
maintaining plans for reclamation.
The sequence of the extraction can be important
to maximize the the reserve recovery. The mine may have multiple
seams being extracted at once or only a single vein. The plan
will take this into consideration and plan for the most efficient
method of recovery. Poor mining conditions must be factored into
the analysis to account for changes in productivity rates and
mine costs.
Equipment
The equipment needed is determined by the
dimensions and the hardness of the mineral deposit. Other factors
that need to be considered are production rates, seam or working
height, and property extent. Ventilation, size constraints, regulations,
and floor pressures may impact the choice of diesel-or electric-powered
equipment. The floor condition plays a a big part in the equipment
needed.
Desired product size also determines the
equipment selection. Some equipment is for fine-particle generation
and some is for a courser product.
Schedules for equipment overhaul should
be developed to assure productivity rates. New equipment purchase
should consider the incorporation of new technology as it becomes
available.
Support Systems/ Infrastructure
As the development of the mine progresses
the mine entries, drifts, and levels become part of the infrastructure.
All parts of the system must be evaluated for capacity and availability
. The systems are built in a series so that if one of the systems
fails the whole system is halted until systems are corrected.
A series system design is usually used to keep costs low as many
systems are parallel or redundant. They are designed to be as
maintenance free as possible.
Transportation
Transportation encompasses provisions for the movement of materials,
personnel and equipment into and out of the mine. Supplies, workers,
equipment must be transported in a timely manner to maintain
the planned production. One of the main transportation plans
include moving the mined material from the face to the processing
facility. A successful mine design will have a smooth transportation
flow.
Manpower
Staffing of the system is a function of the required production
level. Typically the manpower level is inversely related to the
relative level of capital spending but related to the reserve
size. Adequate personnel must be provided to allow the system
to function properly. Personnel includes the supervisory work
force as well.
Consideration must be made for support staff levels such as administration,
engineering, financial staff. The centralization of the the support
personnel may be more effective if centrally located depending
on particular circumstances. The physical location of the mine
must be considered also.
Mine Power
The electrical power needs of the mine depends on the mine productive
capacity and the mineral processing requirements. The availability
of necessary power in the area will determine if the mine will
produce it's own power. The power distribution system needs to
be adequate to provide support for the life of the mine. It must
be easily maintained and reliable.
Safeguards must be in place and adequate backup capacity must
be available when needed.
In many mine areas, backup systems are being designed where different
forms of power are being utilized, including solar. radio transmitters,
methane power generation and hydroelectric power.
Communications can be wired or wireless and include data and
voice transmissions. Backup systems for communication are also
very important to consider. Timely and accurate documentation
of the mining system status can be delivered all over the world
to provide for efficient mine production.
Water
Various mine systems need the water for cooling , dust suppression,
fire fighting,, processing, and personnel needs. If adequate
local water supply is not available, the plan design must include
a water system to meet all the potable and process water. Wells
may have to be drilled.
Ventilation
After most of the other factors are laid out the ventilation
is designed to provide the mine's life support system. The first
consideration is providing clean respirable air to the workers.
The dilution of contaminants is next. In other cases air can
used to cool also.
Mine layout is dramatically impacted by the ventilation system.
Proper airflow requires proper sizing , location and numbers
of airways. Minimum and maximum velocities, and quantities are
often specified by regulations and mine condition.
5) Mine Closing and Reclamation
After the deposit has been completely mined,
the mine area must be cleaned up and returned to approximately
it 's original condition. Permits require bonds to be set for
protection against not completing this reclamation. Funds are
allocated to cover this process from the onset of the mine. Much
of the reclamation process begin with the first breaking of the
ground. Openings are sealed, pits filled and revegetated, and
the structures removed. We will cover more on the reclamation
process in Chapter 15.
References**This article was adapted from
George W.Luxbacher and Richard T. Kline. SME Mining
Engineering Handbook, 2nd Edition, Volume 2. (Littleton,
Colorado: Society for Mining, Metallurgy, and Exploration,
Inc., 1992), pp. 1543-1549.
Mine Plant Layout
Mine planning layout is a general term
for describing the process of configuring a complex and often
expensive portion of an underground mine. This encompasses the
placement of all development facilities such as buildings and
structures, machinery, pipelines, power lines, equipment, cables
ponds, roads, rails and other auxiliary works needed to support
any underground mine activities. Mine plan layout is the design
for integrating all structures, systems or activities, required
to support the mine for economic gain.
The decisions are influenced by a number
of major factors namely, depth of cover, location with respect
to the reserve perimeter or ore body, surface topography, proximity
to contract services, power and water, locations of railroads
and market destinations, geological structure, proximity to population
centers, regulatory and environmental constraints, and ease of
of access by personnel.
Mine plant layout is divided into three
major subcategories: surface, shaft and underground plant. The
surface plant commenced at the entrance to the property to the
mine opening site.This is generally seen in the form of roads,
fencing, drainage, and runoff ditches, lighting/power lines,
and other items needed to provide the site with materials and
services.
The shaft plant subcategory begins at the
shaft of the collar and consists of the airways and pumps, piping,
water collection structures, communication and power lines, transportation
systems and the components between the surface and the underground
workings. This is generally seen in the form of roads, fencing,
drainage, and runoff ditches, lighting/power lines, and other
items needed to provide the site with materials and services.
The shaft plant layout encompasses all of the equipment, buildings,
yards and controls needed to service the mine.
The underground mine plant would include,
but not be limited to, ventilation, drainage, transportation,
supply and materials handling, mine power and communications.
There is a difference between designing
the plants for large and small mines. The three basic parameters
are duration of the underground facility, the profit expected
from the mine, and the needs of the mine for auxiliary services.
As a rule of thumb, the mines with a life longer than ten years
need a more detailed plan and thorough mine plant engineering.
Smaller mines that have a life of 3-5 years need a portable surface
plant, little or no shaft plant, and a very basic underground
plant layout.
Guidelines for Basic Plant Layout
1. Primary mine and preparation facilities
should be designed to last the life of the mine unless other
circumstances (economics, safety, regulations, etc.) dictate
a change.
2. Size of the stockpile areas, mine supply
yard capacity, bathhouse space, and throughout of the facilities
should reflect the expected maximum design of the mining operations.
Limitations to this guideline include space, topography, and
climate.
3. Primary design components such as power,
water, and access routes should reflect the most recent available
technologies. Mine power 20 years ago was thought to be adequate
at 440 V for primary machinery. Today the new trend is 950 V
.
4. The shaft plan design should reflect
sufficient flexibility in the placement of piping, cables, machinery,
and wires to allow individual repair or replacement without significantly
impacting any other component.
5. Shaft plant systems should be designed
for the life of the mine unless circumstances dictate otherwise.
Secondary guidelines are concerned with the interdependence of the mine
plant stems. Secondary guidelines are used during the second
stages mine plant layout after the initial design is determined.
There are three secondary design guidelines:
1. Competing uses for primary resources
such as power and water should be designed to compliment each
other. An example is where a thermal dryer fan motor comes on
in the plant the lights should not dim or production machinery
slow down.
2. The layout of any system should consider
built in safety systems so that it can function without problems
and that any failure won't cause other separate system failures.
3. The plan layout should, to the greatest
extent possible, minimize any waste or inefficiency in repetitive
operations between systems.
The final set, tertiary guidelines, is
directed toward the layout of systems when competing regulatory
agencies, outside oraganizations, and other unforeseen circumstances
compel a change in the design. These instances generally occur
when competing uses for natural resources are regulated by governmental
actions based on law. They are set apart from other guidelines
because they do not impact the design layout until the design
itself is under review by external authorities such as state,
federal , environmental or safety agencies, and the general public.
These guidelines are summarized as follows:
1. To the greatest extent possible, input
from the agencies or outside organizations should be gathered
early in the design process. The environmental permit may not
be submitted until the end of the design process but as much
input as possible needs to be gathered from the outside agencies
and general public in the beginning of the process. Public comment
sessions are a necessary ingredient to good public relations
and acceptance of the mine plan layout.
2. In public debates or public meetings
over technical design issues, "facts speak louder than words".
For the mining engineer, this means being prepared with correct
and completed data, and the facts should be stressed against
emotional arguments. To be effective with the "facts",
the engineer must be able to break the number down to clear charts,
graphs and tables.
3. Acceptable alternative solutions should
be developed for those items within the design layout that may
represent points of contention between various groups. These
alternatives may serve to avoid costly delays or redesign problems
later in the project design or construction phases.
4. Keep design parameters conforming to
known standards to aid in maintaining effective project design.
For example, in the US, electrical installations should reflect
current National Electrical Code Standards as well as local utility
construction standards, if necessary. Mine materials should conform
to US Bureau of Mine published standards as ASTM standards or
any other governmental agencies. Health and occupation standards
need to be met at the onset to avoid costly design changes or
expensive construction changes after completion.
References:
**This article was adapted from Scott G
Britton, Mine Plant Layout. SME Mining Engineering Handbook,
2nd Edition, Volume 2. (Littleton, Colorado:
Society for Mining, Metallurgy, and Exploration, Inc., 1992),
pp. 1572-1579.
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