Mining engineering applies to the evaluation of a mineral resource to determine whether it can be mined technically and profitably or not. It includes the detailed study of reserve estimation, mining methods evaluation, processing technique analysis, capital and operating cost determination and impacts on the local populations and their environment.
A feasibility study can be considered in three stages: identification, prefeasibility and detailed feasibility studies. The three stages are similar in terms of scope and content. The difference is in the degree of detail, of accuracy, time and costs required to perform the studies.
The project is known by research of mineral maps, academic geological reports or local, state, and national geological reports. Other sources of information include property assays, well drilling logs, and local word of mouth. A preliminary study evaluates if the project can be of interest and what are the steps required to forward. Government award exploration permits - of given surface areas - to mining companies for a duration of 2-3 years. This enables the company to undertake exploration work on site to estimate reserves. Based on this the next steps can be undertaken.
This is the step that determines if a detailed study is required or not. It is done on the basis of estimation by a small group of technical individuals with an accuracy within 20 - 30%.
This is the most detailed study to evaluate whether to proceed with the project. It is the basis for capital estimation and provides budget figures for the project. It requires a significant amount of formal engineering work and accurate within 10 - 15%. Detailed feasibility studies are also called "definitive feasibility report (DFR)" or "Bankable feasibility report" (BFS). This because they permit to obtain financing from stakeholders and banks, both national and international. Feasibility reports are the trade of specialized consulting companies known to stakeholders, mining companies and financial institutions4. Their reputation is derived from dealing with multi-mineral mining projects over the world.
1. Geology and Resource: This is the step where drilling and sampling works is performed. Various methods are available for drilling based on the soil and mineral properties. The drill samples are prepared for the assay in order to determine the minimum, maximum and average ore grade and these figures are used to make the reserves estimation. The drilling and sampling procedure are based on guidelines for certification accepted in the mining community. These are the SAMREC and JORC codes for Code for "Reporting of Exploration Results, Mineral Resources and Ore Reserves" 1&2 .
2. Mine design and Mineable Reserve: This is the step where most economic way of mining is developed. Mine planning, model development, operation models and cost analysis are performed and thus the mineable reserve is estimated based on the economy. The major steps for the mine development are mine access (surface/underground), conveying system (especially in UG mines), backfill requirement, ore haulage, ventilation, Material top size etc.
Then the mining equipment selection is preformed and justified against the performance and economy.
The next major stage in mine development is the disposal of overburden generated.
3. Metallurgy and process facility: This is the major backbone of the project development structure. Sampling must be carefully carried out to ensure that the samples used in the metallurgical testwork are real representative of the whole ore body. Some major characteristics of the ore body is determined prior to the development of the plant design which includes Grinding work indices, feed size, settling characteristics, filtration characteristics etc.
Metallurgical testwork are performed in order to determine the amenability of the given ore to different concentration technologies. The major processes that are looked at are:
When these tests are completed, based on the test results the basic material flowsheet is developed. And then the equipment selection and plant layout figures are generated.
These data are used to estimate the amount and grade of concentrate, middling and tailings that are used to search potential customers and revenue earned.
4. Tailings disposal: In the case when the tailings can't be sold, the tailing disposal system plays a crucial role in order to get the mine permit. Mostly the tailings didn't place any major challenges. But, if the tailings have hazardous or toxic materials like cyanide, mercury etc. in it, then the disposal system must be effective in order to reduce the harmful effect on the environment and society.
5. Infrastructure development: This section includes the civil and major earthworks required to start the production. The office, labs, storage units, plant buildings, mining equipment shelters etc. are included in the infrastructure.
6. Power supply: Determining the power source, power line distribution, total power required and the power cost are the major things to be looked into in this step.
7. Water: Most of the plant process are water based, so, the estimation of water requirement plays an important role in the feasibility studies. Then based on the water demand water source, and its cost are evaluated.
8. Environmental impacts: For a project to be permitted by any government, an environmental clearance is required. In order to get the clearance, the environmental impacts need to be studied. The important aspects are acid mine drainage, cyanide management, and other toxic material controls (Arsenic, mercury, sulfur etc.)
9. Other key parameters: Support facilities, maintenance, transport cost of man and material, labor cost, site access (road facility or construction, fly in fly out, marine etc.), social impacts are also need to be studied.
10. Cost estimation: Based on the entire above-mentioned steps, capital and operating cost for each unit is estimated. It included all the costs for mine equipment, process equipment, construction costs etc.
11. Financial Evaluation: This is the stage where the project is evaluated based on the economy. The total cost and expenses are looked against the expected revenue gained from the selling of final products and by-products.
The key financial indicators examined to determine the viability of the project include Net Present Value (NPV) and the Internal Rate of Return (IRR). Annual cash flow need to be estimated over the entire life of the project, from construction to reclamation phase, based on upfront capital expenditures, mine and mill operating costs, employee wages and sales revenue.
12. Sensitivity Analysis: A sensitivity analysis is s then carried out to determine the impact of variation in metal price, operating cost, metal recovery, metal grade, and capital cost on the overall project NPV and IRR values. In doing sensitivity studies, one must be aware of the following main reasons for failure of feasibility studies at any of the above phases3:
The viability of a mine project is established by all these stages; and if based on these considerations, the project is deemed feasible, confidence is established5and financing can be obtained, the next stage of actual implementation can go ahead.
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Mis en ligne le 01/08/2014
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