Surface Mining andUnderground Mining

Dr. BUN Kim NgunI4 - GGG

Introduction of Mining Engineering

Stage of Mining Prospecting and Exploration

Stage of Mining Development and Exploitation

Unit Operations of Mining

Surface Mine Development

Surface Mining Method Mechanical Extraction

Surface Mining Method Aqueous Extraction

The major purposes of development are to provideaccess to the ore deposit, permitting entry of theminers, equipment, supplies, power, water andventilating air, as well as egress for the mineral beingmined and the waste produced. (Development isthe work of opening a mineral deposit forexploitation).

Involved in development are all steps necessary tobring a mine into full scheduled production. Theseinclude planning, design, construction and otherphases.

Development activities commence duringexploration stage and feasibility study economicanalysis, land acquisition, selection of miningmethod, preliminary financing, excavation ofopening.

In surface mine, access to an ore body overlain bywaste is gained by stripping the overburden (which isplaced on disposal dumps and subsequently must bereclaimed).

In an underground mine, small sized openings aredriven from the surface to intersect the ore body andeventually to connect with large exploitationopenings.

Because mainly waste material is involved indevelopment stage, little income accrues during theexcavation of development openings (any oreencountered is generally stockpiled until the minegoes into production).

Other purposes of development are related topreparatory work, facilities, personnel, and services thesupport the mining and mineral processing.

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Following a successful exploration program and prior todeveloping a mineral property, consideration of varietyof influencing factors is necessary.

These factors can be divided in three categories:

- Locational Factors- Natural and Geologic Factors- Social Economic Political Environmental Factors

1. Locational factor: Ore bodies are located where youfound them and not always in the most advantageoussettings.

Variables affected by location:(a) Ease of transport of the mineral products and supplies.(b) Availability of labor and support services (housing,

educational and recreational facilities).(c) Operational (and psychological) impacts of climate

and weather.(d) Employees satisfaction with their lifestyle.

2. Natural and Geological factors: This will affect manykey aspects of mine development, especially accessopenings and surface plant location.

The most important factors in this category will include:(a) Topography(b) Spatial relations (size, shape, attitude, depth, etc) of

the ore body.(c) Rock mechanics properties (strength, modulus of

elasticity, hardness, abrasiveness, etc).(d) Chemical and metallurgical properties of the ore that

affect processing and smelting.

3. Social economic-political Environment Factors: Most of thetime out of control of the mining company, a number ofvariables can exercise a disproportionate influence onboth the development and operation of a mine. Theirinfluence may be difficult to predict ahead of time.

Factor:(a) Demographics and occupational skills of the local

population.(b) Means of financing and marketing (determines the scale

and continuity of operation)(c) Political stability of host country (less developed countries

constitute a high rick for foreign investors)(d) Environmental legislation(e) Government aids, government restrictions, and taxes on

mineral enterprises.

The steps generally carried out during mine developmentfor both surface and underground mines include thefollowing:

1. Adoption of a feasibility report as a planningdocument, subject to modification as the project isdeveloped and mined.

2. Confirmation of the mining method(s) and generalsequence of mining (initial choice of equipment typesand size of the workforce may also be made at thispoint).

3. Arrangement of financing, based on confirmation ofore reserves and cost estimates by independentconsultants.

4. Acquisition of land and mineral rights as needed.

5. Filing of environmental impact statement, obtainingthe mining permit and posting of bonds subject toboth federal and state statutes, as applicable.

6. Provision of surface access, transportation,communication, and power supply to the mine site.

7. Planning and construction of the surface plant,including all support and service facilities andadministrative offices.

8. Erection of the mineral processing plant, if required,and ore-handling and shipment facilities, andpreparation of stockpiling and waste disposalfacilities.

9. Acquisition of mining equipment for developmentand exploitation.

10. Construction of the main openings to the ore bodyin underground mining or advanced stripping insurface mining to provide direct access to the orezone.

11. Construction of the underground facilities (orepasses, crusher stations, transport systems, etc) orthe surface installations (crusher station, waterhandling system, maintenance garages, etc) toinitiate production.

12. Recruitment and training of the labor force andprovision of general support services (housing,transportation, educational needs, medicalservices, consumer goods, etc.) as necessary.

The Several of these steps may be conductedsimultaneously; other may be added because ofspecial needs (e.g. taking on partners, negotiatingshipping and sales agreement etc.) and some may beomitted (e.g. land acquisition if completed duringexploration).

To ensure that all development tasks are completed ontime, careful scheduling is normally required.

Mining land may be applied on land selected from theProspecting Permit/License (Prospecting/ExplorationLicense for the new legislation).

The alienated land can also be acquired and beconverted to mining land.

Since the land belongs to the state , all applicationsmust be made to the State government.

Environmental issues are governed by theEnvironmental Quality Act. Mining is regarded as aprescribed activity, whereby Environmental ImpactAssessment (EIA) report has to be submitted to the DOEbefore the application is being considered by the landoffice.

Any mining venture must consider this EIA as cost as thereport has to be prepared by a consultant.

Mining is considered a high-risk industry for investmentpurpose speculative venture.

Financing of Mining Ventures:

In financing a mining venture, the developing companymust both decide on and arrange a means offinancing. Factors to consider are terms of the landacquisition agreement (lease, purchase, etc),marketing arrangements (long-term contracts arealmost a necessity), time to repay any loan incurred(preferably the same as the life of the mine, risk factor ofthe venture (set by lending agencies), a politicalclimate of the host country and the possible operationof the mine as a joint venture with another company.

Funds become available when developmentexpenditures begin and continue at a rate to matchspending, until the mine generates sufficient revenues tocover operating expenses.

Financing of Mining Ventures:

In financing a mining venture, the developing companymust both decide on and arrange a means of financ .

Financing of Mining Ventures:

Alternative forms of financing popularly used to developmines are as follows:

- Loan from commercial banks, and private investmentsources trust funds, insurance companies or foreign firms.

- Issues of securities, stocks and bonds, through investmenthouses or banks (a form of internally generated financingthat avoids borrowing secured by collateral).

- Rental of equipment by leasing firms (avoid debtfinancing, but limited in application).

- Government loads world bank or International MonetaryFund for projects in Third world countries, etc.

Implementation of the Mine Development Plan:

Once financing is secured, speed is now essence.Interest costs on any borrowed money begin to accrueimmediately and will continue through the life of themine.

Changes in the original feasibility report are to beexpected, too many changes can be costly toimplement in terms of both time and money.

Implementation of the Mine Development Plan:

Because of the complexity of mine construction, thescheduling and coordination of task is best done byapplying operation research technique such as CPM The completion time can only be shortened byrearranging or improving individual task times.

Every effort is made to get the mine into production atthe earliest possible moment the strategy minimizedfront-end expenditures to realize an early cash flow fromoperations.

Implementation of the Mine Development Plan:

In the construction phase, one decision looms as criticaland must precede all others, and that is selection of theplant site. Three group of factors require consideration:

- Economic : outside access, surface rights, labour andliving conditions, power supply, water rights, means oftransportation, government restrictions, building costs andcontracts.

- Terrains : Space availability, topography, climate, weatherexposure, drainage and vulnerability to natural disasters

- Environmental : air, water, soil and waste pollution,reclamation, subsidence, noise, blasting damage,beneficiation and public relations.

Implementation of the Mine Development Plan:

The first principle in selecting the plant site and overalllayout is to locate facilities in close proximity to ore bodyand main mine openings without interfering with eachother or with mine operation.

The second principle is to avoid having relocate parts ofthe plant because of expansion or competition forspace with other facilities, encroachment by the mineitself, or subsidence of underground workings.

Without production of ore at a substantial, sustainedrate, there can be no opportunity for a mining ventureto succeed.

Exploitation is the work of recovering mineral from theearth in economic amounts and delivering it to shippingor processing facilities on the surface.

The method chosen for exploitation distinguishes thefinal stage in the life of mine.

Selection of the mining method is crucial for exploitationprocess and probably the key engineering decisionmade also in mine development.

Factors to be considered in selection for mining method:

1. Spatial characteristics of the deposit:These factors will decide the choice between surfaceand underground mining method, affect theproduction rate and will determine the method ofmaterials handling and the layout of the mine in theore body.

i. Size (especially height, thickness and overall dimensions)ii. Shape (tabular, lenticular, massive or irregular)iii. Attitude (inclination or dip)iv. Depth (mean and extreme values, stripping ratio)v. Regularity of the ore boundariesvi. Existence of previous mining

2. Geological and hydrological conditions:

The geologic characteristics of both the mineraldeposit and adjacent country rock (host material)influence method selection, especially choicesbetween selective and nonselective methods andextent of support required for ground andunderground control.Hydrology affects drainage and pumpingrequirements, both surface and underground.Mineralogy governs mineral processing requirement.

2. Geological and hydrological conditions:

i. Mineralogy and petrographyii. Chemical composition (primary and secondary

minerals)iii. Planes of weakness (joins, fractures, shear zone,

cleavage in minerals)iv. Uniformity of gradev. Alteration and weathered zonesvi. Existence of strata gases

3. Geotechnical properties:The mechanical properties of ore and waste are keyfactors in selecting the equipment in a surface mineand selecting the class of methods (unsupported,supported and caving) if underground.

i. Elastic properties ( modulus of elasticity, Poissons ratio,etc.)

ii. Mechanical strengthiii. State of stress (premining, postmining, original, modified

by mining)iv. Rock mass rating (overall ability of opening to stand

unsupported or with support)v. Other physical properties (SG, porosity, permeability,

moisture content, etc.)

4. Economic consideration:Ultimately, economics determines whether a miningmethod should be chosen, because economic factorsaffect output, investment, cash flow, payback periodand profit.

i. Reserves (tonnage and grade)ii. Production rate (output per unit time)iii. Life of mine (total operating period for development

and exploitation)iv. Productivity (tonne/employee/hour)v. Comparative mining costs of suitable methodsvi. Comparative capital costs of suitable method.

5. Technological factors:The best match between the natural conditions andthe mining method is sought.

i. Recovery (proportion of the ore that is extracted)ii. Dilution (amount of waste that must be produced with

the ore)iii. Flexibility of the method to changing conditionsiv. Selectivity of the method (ability to extract ore and

leave waste)v. Concentration or dispersion of workingsvi. Ability to mechanize and automatevii.Capital and labor intensities

Automatic locomotives are being used to handle500Mt per train on the new main level. (Kiruna Iron OreMine)

Remote control of trains on the 1045m level from the controlcentre (Kiruna Iron Ore Mine, Sweden)

6. Environmental concerns:Physical environment including social-political-economic climate is involved.

i. Ground control to maintain integrity of openingsii. Subsidence, or caving effects at the surfaceiii. Atmosphere control (ventilation, air quality control, heat

and humidity control)iv. Availability of suitable waste disposal areasv. Workforce (availability, training, health and safety, living,

community conditions)vi. Comparative safety conditions of the suitable mining

methods

Kiruna Iron Ore Mine, Sweden

With an ore body 4kmlong, 80m wide andreaching a depth of2km, LKABs Kiruna isthe worlds largest,most modernunderground iron oremine. Since miningbegan here over 100years ago, LKAB hasproduced over 950Mtof ore, yet only one-third of the originalore body has beenextracted. Theoperation employs1,800 people, ofwhom 400 work in themine.

The basic objective in selecting a method to mine aparticular mineral deposit is to design an exploitationsystem that is the most suitable under actualcircumstances.

Engineering evaluation is carried on at three level:- Conceptual study the physical characteristics andoutput quantities of a number of mining methods,layouts and systems are assessed.- Engineering study the preceding concepts arequantified and compared, resulting in firm designs andcosts.- Detailed design study drawings and specifications forconstruction for the preferred method are prepared.The result is a final engineering report on whichinvestment decisions, equipment purchases and aconstruction schedule are based.

Once a decision on mining method is made, anddevelopment and exploitation get underway, it isextremely difficult to alter the plans or change toanother method

1. Mine Management

When the exploitation stage of the mine begins, theorganization of its management and workforce shouldbe complete.

The management structure employed by most miningcompanies is a staff-and-line organization.

The Line activities are those normally considered to beprimary functions of the organization such asoperations (mining, processing, and smelting) sales,finance and exploration.

1. Mine Management (ctd)

Staff activities are those functions that support theproduction activities of the company.

The staff groups do not have authority to direct anyaspect of the line functions but report do the generalmanager.

2. Mine Cost

The sum of all the cost associated with bringing a mineinto production through the stages of prospecting,exploration, development, exploitation andreclamation is called the direct mining cost.

If calculated on a gross basis, it is a total cost;if on a unit ($/ton or $/tonne), it is a unit cost.

Indirect mining cost is an overhead that usuallyincludes allowance of 5% to 10% for administration,engineering and other itemized services.

2. Mine Cost (ctd)

Overall mining cost = direct cost + indirect cost

Overall production cost = Overall mining cost +Processing, smelting,

transportation, etc

Stage/(ProjectName)

Procedure Time Cost/Unit Cost

1. Prospecting(Mineral deposit)

Precursors to Mining

Search for orea. Prospecting methods

Direct: physical geologyIndirect: geophysical,

geochemicalb. Locate favourable loci

(maps, literature,old mines)

c. Air: aerial photographyairborne geophysics,satellite

d. Surface: groundgeophysics, geology

e. Spot anomaly, analyse,evaluate

1 3 years $0.20 10 million or$0.05 - $1.00/ton($0.05 1.10/tonne)

Stage/(Project Name)

Procedure Time Cost/Unit Cost

2. Exploration(Ore body)

Precursors to Mining

Defining extent and value ofore(examination/evaluation)

a. Sample (drilling andexcavation), assay, test.

b. Estimate tonnage andgrade.

c. Valuate deposit (Hoskoldformula or discountmethod: present value =income - cost

Feasibility study: makedecision to abandon ordevelop

2 5 years $1 - $15 million or$0.20 - $1.50/ton($0.22 -$1.65/tonne)

Stage/(Project Name)

Procedure Time Cost/Unit Cost

4. Exploitation(Mine)

5. Reclamation(Real estate)

Mining Proper

Large scale production of orea. Factors in choice of method:

geological, geographical,economical,environmental,societal safety.

b. Types of mining methodssurface: open pit, open castetcUnderground: blastholestoping, sublevel stoping,room and pillar, bolck cavingetc

c. Monitor cost and economicpayback (3 10 yr)

Post Mining

Restoration of sitea. Removal of plant and

buildingsb. Reclamation of waste and

tailings dumpsc. Monitoring of discharges

10 - 30 years

1 10 years

$5 - $75 million or$2.00 - $150/ton($2.20 - $165/tonne)

$1 - $20 million$0.20 - $4.00/ton($0.22 4.40/tonne)

Determination of costs is important for the miningengineer and experience and research will assist inthe task.

Cost fluctuate unpredictably over time with priceinflation, changes in labor rates and technologicalprogress.

In alluvial deposit the cheapest method is dredgingbut large areas are required to cover up for the highinitial capital costs.

Estimate the unit profit in mining that its processing a0.60% copper ore deposit. Selling price of copperin the concentrate is $1.63/kg and overall unitcosts are $7.50/tonne. Overall recovery is 92%

Also calculate the cutoff grade for the copperdeposit.

Value = Grade X Recovery X Price= 0.0060 X 0.92 X 1.63 X 1000kg/tonne= $9.00/tonne

Profit = Value Cost= 9.00 7.50 = $ 1.50 / tonne

Cutoff grade = Cost / (Price X Recovery)= 7.50/ (1.63 X 0.92) = 5 kg / tonne= 5kg/tonne / 1000kg/tonne= 0.5%

Calculate the cutoff grade (in percent ) for aniron deposit, given the following: Iron ore price $82.67 / tonne, 100% Fe Total Production Cost $ 24.61 / tonne Recovery 95%