Guidlines for selecting mining methods for underground mining
- 1. GUIDELINES FOR SELECTING A MINING METHOD In some cases, the conditions around an ore deposit may be quite distinctive, and they may dictate one particular method or the immediate exclusion of other methods. Under such circumstances, the selection of the method is limited to adapting and refining the general method to the particular orebody. In other cases, the conditions may favor the application of several methods, which then must be compared and evaluated. In either case, the planning and evaluation of the mining method, together with a preliminary selection of equipment, is a task requiring careful study and consideration. Once the plans are set and development begins, it is extremely difficult and costly to change to an alternative method. In most cases, only minor alterations can be made. The emphasis on careful skilled engineering is underlined by the time factor. A project started today will require several years to reach production, and it is expected to produce ore for many years after that. Although the basic principles of a mining method can be expected to remain the same, rapid developments are being made in the machinery and its utilization, making the ore extraction process more efficient. Up-to-date knowledge of the latest developments in mining techniques and a feeling for future trends are necessary to design a successful project. General Considerations
- 2. GUIDELINES FOR SELECTING A MINING METHOD It is advisable to incorporate features that allow flexibility and growth in the mining system. Looking at mines that were developed only a few decades ago, difficulties now are found with the limitations of shaft dimensions, ventilation systems, etc. Many mines no longer can accommodate the increasing dimensions of new mining machines and the voluminous exhaust gases emitted by those machines. The process of selecting a mining method begins with a compilation and evaluation of the facts already known about the ore deposit. The available information can vary within wide limits, from observations made through core drilling of a recently explored mineralization to the extension of an orebody that is well known from previous underground mining. Under all circumstances, effective evaluation of the mining methods depends upon the information available. Rarely it is possible to do more than a preliminary study from core drilling observations and other surface investigations. Information from actual underground workings can suffice for a final development plan, so a combination of surface investigation and detailed studies of underground conditions is necessary to avoid mistakes in the early stages of mine development. General Considerations
- 3. GUIDELINES FOR SELECTING A MINING METHOD Figure illustrates surface drilling complemented by underground drifting and drilling. In this case, drifts, shafts, and other underground workings are engineered for use in the future production stage of the mine. New orebodies are most likely to be found in the immediate proximity of existing mines or in the same mineral-bearing region. Valuable information can be obtained from studies of mines already in operation. General Considerations
- 4. GUIDELINES FOR SELECTING A MINING METHOD Dip: The dip of the orebody is a factor influencing the mining method. Normally, the dip is classified as; steep > 50o medium 20o - 50o flat < 20o Geological Conditions
- 5. GUIDELINES FOR SELECTING A MINING METHOD Rock Strength: The characterization of rock as weak or strong is a very subjective matter; what might be considered strong rock in a coal mine could be viewed quite differently in a hard-rock mining environment. Core samples do give a general geological picture of the type of rock that can be expected in the hanging wall, the footwall, and the ore itself. Geological Conditions Another observation that can be made from the core samples is the percentage of the core length that is recovered. For a strong rock, the recovery should be approximately 90% of the core length. In another system, recording the lengths of individual pieces of the core may prove meaningful.
- 6. GUIDELINES FOR SELECTING A MINING METHOD Span Limits : In any mining system, the rock strength determines the limits for the sizes of the spans that can be excavated, either without support or with a particular method of support. If the span is too large, working conditions become unsafe, and caving may occur. To counteract potential misshapes, the size of the underground openings must be decreased. Reliable predictions can be made only as a result of actual underground investigation. However, the results of geological mapping and exploration drilling, compiled with other information, usually suffice to decide between open stoping or a filling method. The rock strength is one of the parameters used for the detailed layout of the particular method chosen. Geological Conditions
- 7. GUIDELINES FOR SELECTING A MINING METHOD Only the mineralization that can be exploited commercially to yield a profit for the mining enterprise is classified as ore. Anything else is just rock, even though minor metal contents can be given a certain value. Calculating the ore reserves assumes that mining costs are known, at least approximately, during the evaluation of borehole loggings and other observations. However, for a new prospect, the operational costs for mining can be left as a fairly rough estimation; the primary question is whether the potential tonnage and grade of the ore can justify the investment necessary to undertake a mining operation. This calls for a financial analysis adapted to the particular project. Normally, the boundaries of a mineralization are not distinct. Borehole logging may show areas with occasional high metal values, surrounded by scattered sections with lower grades and by barren rock. To define and map an orebody, it is necessary to establish a cutoff grade that represents the lowest grade (or combination of grades) at which the mineralized rock qualifies as ore. By applying different cutoff grades to the outlines of the orebodies, varying tonnages and average grades can be identified. Ore Reserves and Grades
- 8. GUIDELINES FOR SELECTING A MINING METHOD Outlining a small high-grade orebody indicates a mining operation of very modest size, where the investment in plant operations and equipment is minimized. Square-set mining, combined with labor-intensive vein mining, would be adequate in Case A. In Case B, the ore reserves are sufficient to justify a mine of more normal size. Cut-and-fill mining or sublevel stoping appear to be appropriate for the situation, but further careful study is required to select the most feasible system. Case C indicates the feasibility of large-scale mining, with high productivity and low operational costs. Block caving would be indicated in this case. Ore Reserves and Grades
- 9. GUIDELINES FOR SELECTING A MINING METHOD Quite complex and needs experts In general, Profit/Deficit = Income-Expense (TL/t) INCOME Market price of commodity*production rate EXPENSES 1) CAPEX : Capital Expenses Main Investments (Equipment, preperations, etc) 2) OPEX : Operational Expenses Labor, Energy, Process, Maintenance Renew investments 3) Other costs Taxes (Credit, governmental) Royalty Depreciation Depletion : the exhaustion of raw materials within a region Economic Evaluation
- 10. GUIDELINES FOR SELECTING A MINING METHOD In selecting a mining method, the anticipated cost of mining exerts a major influence. However, there are considerations other than simply finding the least costly procedure of excavating the rock. The characteristics and advantages of different mining methods also must be considered. For example, a method known to require more labor than another may allow selective mining, thus producing ore of a higher grade and yielding a more valuable product. This reasoning can be supported by an example where sublevel stoping is compared to cut-and-fill mining. Mining Costs and Ore Values
- 11. GUIDELINES FOR SELECTING A MINING METHOD Productivity in mining has become synonymous with mechanization, replacing manual labor with powerful machines. Over the last few decades, a tremendous development has taken place, rationalizing underground mining methods with the introduction of new machinery of increasing sizes and capacities. Mining methods and underground working have adjusted to accommodate the new equipment. The application of mining methods has shifted toward increasing mechanization where conditions are favorable for the use of heavy machines. Productivity and Mechanization Machine Considerations. Mechanization means that the majority of the underground work is accomplished by machines. In principle, the capacity of a machine is related to its size, so it is advantageous to select the Iargest units possible. However, there are Iimitations to the choice. Another factor is the capacity that can be utilized effectively. Often, underground workings are at different vertical elevations or are otherwise separated from each other, leaving no practical way of transferring a machine from one location to another quickly. The peak capacity of a machine is of no importance when it cannot be utilized effectively with a minimum of non- productive time.
- 12. GUIDELINES FOR SELECTING A MINING METHOD Mine Considerations. Productive mechanization is related closely to achieving high utilization, that is, operating machines with as few and as short interruptions as possible. This is best achieved by using a mining method with several working locations, within easy reach of each other, combined with mobile equipment that can shuttle from one location to another. Room-and-pillar mining is a typical example of a method allowing complete mechanization. Equipment can travel or nearly level roadways that are arranged for the best possible access to the working locations. Sublevel caving is equally favorable, with a Iarge number of working faces on the same level. With sublevel caving, there is the additional advantage of being able to drill, blast, and muck without sequencing these operations in a perfect cycle. Block caving may be considered favorable, although the production process is not as mechanically controlled as in other methods; boulders and hangups can disturb the regular flow of ore. Sublevel stoping, in turn, is an example of a method where production operations are concentrated into a few locations. In terms of mechanization, room-and-pillar and sublevel caving have a slight advantage over block caving and sublevel stoping. Block caving and sublevel stoping both require extensive development according to special plans and schedules before any production actually begins. Productivity and Mechanization
- 13. GUIDELINES FOR SELECTING A MINING METHOD Efficiency Considerations. A common basis for comparing the efficiency of mining operations calculates the ton-per-worker shift ratio. This is the output from the mine per working shift, divided by the number of underground workers; it also includes the labor not directly involved in ore production. Table lists some representative ton-per-worker shift ratios for the different mining methods. The high ends of the ranges indicate mining operations where conditions are entirely favorable and equipment capacities are fully utilized. Productivity and Mechanization
- 14. GUIDELINES FOR SELECTING A MINING METHOD Mining techniques have become totally dependent upon machines of various types. Selecting a machine for a given type of work and matching its capacity to the required output have become two of the most important tasks in mine planning and evaluation. Drilling Equipment. The fundamental operations in hard-rock mining are drilling, blasting, and removing the broken rock from the stoping area. The drilling operation is intended to produce a hole in the rock, into which the explosive is deposited. Mining Equipment and Productivity
- 17. GUIDELINES FOR SELECTING A MINING METHOD Loading and Transport Equipment. Although the drilling system is related to a specific mining method, loading and transport are not. The selection of equipment should entail an integration and optimization of both loading and transport operations, mostly related to the transport distance and the required capacity. The LHD technique is an integrated loading and transport operation. Its capacity always must be related to the transport distance. For crosscut loading and for loading into trucks, transportation is handled by separate carriers, which must be matched to the size of the loader. Mining Equipment and Productivity