Lesson 4.3: Mining Methods
Lesson 4.3: Mining Methods
We are going to identify the various mining methods in this lesson, and then we are going to look at the factors that affect our selection of a method. Later in the course, we will study the methods in more detail, but at this stage, we want to understand why a particular method would be identified in the feasibility study.
Classification of Mining Methods
We will use a traditional taxonomy to classify the mining methods. At the top level, mining methods are either surface or underground. The difference rests solely with where we access the orebody: are we accessing it from the surface or is it too deep beneath the surface, such that we can only economically access it from underground?
4.3.1: Surface Mining Methods
4.3.1: Surface Mining Methods
Surface mining methods are traditionally divided into two classes: mechanical and aqueous. Mechanical methods rely on breaking the ore by mechanical means, and aqueous methods rely on the use of water or another solvent, e.g., an acid, to break down the ore and facilitate its removal.
Mechanical Methods
Open pit mining
This type of mining is used for near-surface deposits, primarily metal and nonmetal. The overburden is hauled away to a waste area and a large pit is excavated into the orebody. The depth of the pit is increased by removing material in successive benches. A few examples of commodities mined by this method would include iron and diamonds.
Open cast mining
Open cast mining is also known as strip mining and is used for bedded deposits, and most commonly for coal. Although it is similar to open pit mining, the distinguishing characteristic is that the overburden is not hauled away to waste dumps; but rather, it is immediately cast directly into the adjacent mined-out cut. There are two important sub methods for open cast mining. One is known as area mining, and is applicable when the terrain is relatively flat; and the other is contour mining, better suited for mountains regions. A few examples of commodities mined by this method include coal and phosphate.
Quarrying
Quarrying is a method of extracting dimension stone. The term dimension stone encompasses certain stone products used for architectural purposes such as granite countertops, marble flooring, and monuments, among a few others. The goal in the mining of these products is to remove large slabs that can be cut and machined to exacting architectural applications. Unlike open pit mining in which benching is required to prevent failure of the sides or pit slopes, the high strength and competency of the rock mass in quarries is such that vertical walls of 1000’ or more can be excavated. Now that I’ve given you the classical mining engineering definition of quarrying, you should be aware that just about everybody uses this word, "quarry" to describe any open pit operation in stone! Oh well… A few examples of commodities mined by this method include Georgia marble and Vermont granite.
Auger mining
This is a method to recover additional coal from under the highwall of a contour mine, when the ultimate stripping ratio has been achieved in open cast operations. It is sometimes referred to as secondary mining because it is done after the open cast mine has reached an economic limit.
Aqueous Methods
Hydraulic mining
Hydraulic mining is used for a limited class of deposits that are characterized as loosely consolidated, such as placer-type deposits. A high-pressure water canon is used to dislodge the deposit, and the resulting solution is either pumped to a processing plant or a gravity separation is performed at the mine site using something like a sluice. A few examples of commodities mined by this method include gold and kaolin.
Dredging
This method is used for underwater recovery of loosely consolidated materials using a floating mining machine known as a dredge. In some cases, the deposits are naturally underwater, while in others the area is flooded, creating an artificial lake on which the dredge operates. A few examples of commodities mined by this method include sand and gravel.
Solution mining
Solution mining is used to recover deep deposits that would be uneconomical using underground methods, but only if the ore can be easily dissolved by a solvent. In this method, holes are drilled from the surface into the deposit. A solvent is pumped down one hole, and the resulting solution with the dissolved mineral is pumped out another hole. This solute or pregnant liquor, as it is often known, is processed to extract the mineral of interest. In some cases, only one hole is used, but the hole has an inner and outer section to separate the in-going solvent from the out-coming solute. Water, acid, and steam are common solvents. A few examples of commodities mined by this method include uranium and sulfur.
Heap leaching
Heap leaching was used many years ago as a method to recover very low percentages of metal remaining in the tailings from mineral processing plants. Large piles, i.e., heaps, of the tailings of low-grade ore were created, a solvent was allowed to drip and percolate down through the heap, and then the pregnant liquor was recovered and processed. In this fashion, it is a secondary method. In recent years, it has been used with increasing frequency to recover high-value metals such as gold from very low-grade ores. A few examples of commodities mined by this method include copper and gold.
4.3.2: Underground Mining Methods
4.3.2: Underground Mining Methods
Underground mining methods become necessary when the stripping ratio becomes uneconomical, or occasionally when the surface use of the land would prohibit surface mining. Underground methods are traditionally broken into three classes: unsupported, supported, and caving methods. These classes reflect the competency of the orebody and host rock more than anything else. If you excavate an underground opening in the ore or the rock, is the opening stable -- i.e., will it remain open for an extended period, or will it begin to fall in? If it is unstable, i.e., the surrounding ore or rock breaks up and falls into the opening, how much support would be required to keep the opening from caving in? The answers to these questions lead us to choose mining methods from one of the three classes. Unsupported methods require the addition of minimal artificial supports to secure a stable opening, whereas the supported methods require the addition of major support to keep the openings from caving in. Finally, the third class is, at first glance, counterintuitive: in general our goal is to create stable openings underground for obvious reasons, but the methods in this class will only work if the host rock or orebody will cave easily under its own weight -- the caving methods actually depend on this caving action to function safely and productively!
Unsupported Methods
Room and Pillar mining
This method of mining is used to recover bedded deposits that are horizontal or nearly horizontal when the orebody and the surrounding rock are reasonably competent. Parallel openings are mined in the ore, i.e., rooms, and blocks of ore, i.e., pillars, are left in place to support the overlying strata. Other than the pillars, little artificial support is required and often consists of bolts placed into the overlying strata to pin the layers together, making them behave like a strong laminated beam. A few examples of commodities mined by this method would include coal, lead, limestone, and salt. Historically, if the pillars were irregular in size and placement, which is more likely to occur in certain metal and nonmetal deposits, this method was known as stope and pillar, rather than room and pillar. You will still hear the word stope and pillar being used, but the distinction is now largely irrelevant. This method accounts for the vast majority of all underground mining in the U.S., and likely the world. Watch this video (2:58) created by Caterpillar showing the use of their equipment in room and pillar mining.
In room and pillar mining, the coal seam is mined in a checkerboard style, leaving pillars of coal to support the roof which allows for instant coal access with a relatively low invest, compared to long wall mining, however only utilizes the coal reserves between 50 and 75 percent. It is a mining method of its own right as well as the supporting technology to develop roadways. In order to prepare the coal face for a long wall operation, in room and pillar mining continuity is the key to profit. From the continuous miner to the continuous flow of material, the coal is cut by a continuous miner which delivers the product to haulers. They bring the product to feeder breaker units that prepare and deliver it onto the belt system while feeder breakers are moved only occasionally, the other equipment is in constant motion, so maneuverability, cableless operation, and maximum load capacities are vital. With a full range of battery or diesel-powered vehicles, caterpillar has an answer to every challenge in room and pillar mining. It all starts at the coal face with the right cutting technology. Today's continuous miners are designed to cut at highest efficiency while keeping dust levels to a minimum with water sprays and dust collectors. They are available for operations from as low as 70 centimeters up to a maximum of five meters. From production to the delivery point, it's just a question of volume and velocity. That's easy physics for our range of utility vehicles. Being equipped with rubber tires and an industry-leading capacity, they keep the circulation of product and material at a healthy and profitable level. The roof bolter, follows production on its tail to create a safe mining environment. Driving the bolts into the roof in a safe and efficient way, is most important in this real hands-on job, therefore ergonomic controls and easy material access are one of the most important features in our roof bolters. The scoops multi-purpose contoured bucket will carry equipment, serve as a multi-tool, or clean roadways and feeder sections. Extended battery life and a dual motor option make it versatile yet powerful. The scoop has often been called the miners Swiss Army knife. As a matter of fact it is a real workhorse too.
Shrinkage stoping
Shrinkage stoping is used to recover steeply dipping orebodies when the ore and host rock are reasonably competent. A stope, i.e., a large section of the mine where active production is occurring, is mined, but the broken ore is not removed, but rather is left in place to support the walls of the stope until the time when all of the broken ore will be removed. Since rock swells, i.e., increases in volume when it is broken, it is necessary to draw off some of the broken ore as the stope is progressively mined. The name of this method derives from this drawing off or shrinkage of the stope. A modern and important variant of this method is known as vertical crater retreat (VCR) mining. A few examples of commodities mined by this method include iron and palladium. Watch this video (3:01) created by Atlas Copco demonstrating sublevel stoping mining method.
Open stoping
This type of mining is used to recover steeply dipping orebodies in competent rock. The ore is removed from the stope as soon as it is mined. Sublevel stoping and big-hole stoping are the important variants in use today. A few examples of commodities mined by this method include iron and lead/zinc.
Supported Methods
Supported methods historically included cut and fill stoping, stull stoping, and square set stoping. However, the last two are no longer used due to their extreme cost. We’ll confine our discussion to cut and fill stoping.
Cut and fill
Cut and fill is used to recover ore from weaker strength materials, in which the openings will not remain stable after the ore is removed, and the overlying strata cannot be allowed to cave. A slice of the orebody is mined and immediately after the ore is removed, backfill is placed into the opening to support the ore above. The next slice is removed, the cut is then backfilled, and the process repeats. As you might imagine, this is a very expensive method to use, and consequently, it would be used only for the recovery of high value ores. An example of a commodity mined by this method is gold. Watch this video (2:58) created by Altas Copco on Cut and Fill mining method.
Cut and fill mining is a favorite choice for steeply dipping, and sometimes irregular or bodies, and preferred by mines that require the capability of selective mining and adaptability to variations in the rock mass. It is generally referred to as a small-scale mining method. Mining is carried out in horizontal slices along the ore body where the bottom slice is mine first. The excavated area is then backfilled and production continues upwards. Each production level is accomplished by drifting until the entire slice has been mined. The slice is then backfilled and the fill becomes the working platform from which the next level is mined. Backslashing is done for providing access to the upper slices within the stope. When a stope is completed, a new access drift from the ramp is created to continue the production within the upper stope. One of the advantages with cut and fill mining is the possibility to reuse waste for backfill material such as tailings sand from the processing plant or waste rock from development. To mine the ore in one of the slices, we first need to drill blast holes. The next steps are charging and blasting the ore and then ventilate the toxic blast fumes. The ore is then mucked out and dumped into an ore pass or on to a truck. Before continuing with the next round, the rock needs to be reinforced. How this is done is decided by the mind for each individual situation. The mining continues until the entire slice of the ore has been mined. Since the mining can be tailored to suit the shape of the ore body, it is possible to minimize dilution of waste rock. To get access to more production points, a second entrance can be opened at another level in the ore body and excavated in parallel. The equipment used for mining the ore is usually the same as what is used for development. As the ore body is mined, the Rock stresses increase in the pillar above the mined area. Cut and fill mining is regarded as a low productivity mining method, but the advantage is high selectivity with good ore recovery and low dilution.
Caving methods
Caving methods include block caving, sublevel caving, and longwall mining. For emphasis, allow me to repeat what I said earlier: caving methods are used in settings where the ore or the host rock is so weak that it cannot support its own weight for any period of time; the methods only work if the rock or the ore will readily cave under its own weight.
Block caving
This method is used in weak and massive orebodies, in which the ore is undercut, and then as the broken ore is removed the remainder of the orebody collapses into this void, and as more ore is withdrawn, the caving continues. Typically the host rock is fairly strong, although ultimately it tends to cave into the void created from removing the ore. The fracturing and caving often break through to the surface. Watch this video (3:16) created by Atlas Copco on Block Caving Mining Method
Block caving is a large-scale mining method that allows for huge volumes of rock to be extracted efficiently. However the development time before production starts is longer compared to other mining methods. By drawing rock from the extraction level in the lower part of the mine, a gap is created. Absence of support for the overlying rock mass together with rock stress and gravity will cause the rock mass to cave. This minimizes drilling and blasting of ore but required the ore body to be large enough and the rock conditions to be favorable for natural breakage. To draw the first pieces of rock, to create this gap, the rock mass in the lower part of the ore body needs to be broken down into smaller pieces. To achieve this an undercut level is developed and blasted. Below, an extraction level is developed where or will be extracted throughout the life of that production area. Draw bells are created between undercut and extraction levels and become passages for caved rock. To avoid misfires, accurate drilling is crucial. Substantial rock reinforcement such as steel arches, sprayed concrete, cable bolts, rock bolts, steel mesh and straps are usually required due to several factors associated with block caving including extreme rock stress changes and a long production period. Rock is loaded from the draw points and can be dumped into ore passes connected to a haulage level or directly into a crusher. A variety of transportation methods can be employed for transporting ore to surface. The fragmentation of the ore and the crushing requirements are key factors influencing the choice of a method. The extraction of ore will sooner or later cause the surrounding rock to caves resulting in subsidence on the surface. Provided the rock breaks successfully and the ore can be extracted evenly at desired draw points, block caving is a high productivity method with low operating cost that allows a high degree of mechanization and capability of automation.
Sublevel caving
This type of caving is used in strong and massive orebodies in which the host rock is very weak and quickly caves into the void created by removing the core. As in block caving, the cave will ultimately reach the surface. Watch this video (3:05) created by Atlas Copco on sublevel caving mining methods.
Sublevel caving is a large-scale mining method suitable for large or bodies with a steep dip and a rock mass where the host rock in the hanging wall will fracture under controlled conditions, therefore the infrastructure is always placed on the footwall side. Mining starts at the top of the ore body and progresses downwards in a safe sequence. It is a productive mining method where all of the ore is fragmented by blasting and the host rock in the hanging wall of the ore body caves. Once the production drifts have been excavated and reinforced, the opening raised and long hole drilling in ring patterns are completed. Minimizing hole deviation when drilling is crucial as it will affect the fragmentation of the blasted ore and therefore also affect the flow of the caving rock mass. Rock is loaded from the cave front after each blasted ring. In order to control dilution of waste rock in the cave, loading a predetermined extraction percentage of rock is done. Or if there is a significant difference in density between ore and waste rock, bucket weighing can be utilized for dilution control. When loading from the cave front, it is important for the productivity to keep the roads maintained in a good condition. Dumping the ore into or passes connected to the haulage level is an efficient way of transporting rock from the production points to the crusher. Each sub level features a systematic layout with drifts across the or body. Activities in the parallel production drifts are performed simultaneously in order to maintain a good process in the mine. Due to caving of waste rock into the Blasted ore, a certain degree of or loss and waste rock dilution comes with the method. Caving will sooner or later also cause subsidence on the surface. Sublevel caving is a productive large-scale mining method that enables safe and efficient use of mining equipment with good mine planning, there are also great opportunities for automation.
Longwall mining
Longwall mining is a type of caving, applied to a horizontal tabular deposit such as coal. While block and sublevel caving are essentially vertically advancing metal mining methods, longwall mining is applied to relatively thin and flat-lying deposits – most often coal, but occasionally an industrial mineral such as trona. The coal seam is extracted completely between the access roads, and then as mining retreats, the overlying strata caves into the void left by removing the coal. Watch this video (5:31) created by Clearcut Mining Solutions showing logwall mining method.
This animation is intended to demonstrate how a typical underground long war mind may be developed. The mind depicted uses the retreat line while mining method and is intended to be schematic only. The design of the mind has been simplified with clarity and the design and features presented by no means indicative of all long-haul operations. Thumbwheel mining is a method used to extract coal from scenes where surface mining is not viable. In this example. the shallow dipping coal seam shown is to be extracted using longwall mining techniques. The seam is four meters thick and is overlain by around 80 to 100 meters of overburden. The thickness of the seam is constant over the coal deposit. As a guide the proposed development of the mine has shown over line the same. As can be seen the majority of the development is kept within the scene to minimize costs. The first step in the development of a longwall mine is to provide access from the surface to the coal seam below. This can be achieved in several ways. However, in this case a decline is used. On the surface, a portal is driven down at around 10 degrees into the ground. This forms the start of the decline. The decline consists of two roads, one for the conveyor that will transport coal out of the mine, and the other for general access and fresh air intake. The decline continues from the portal down into the coal seam. The coal conveyor will be installed. Only after the conveyor Drive is nolonger needed for development access. Once the decline has been finished, the development of the main headings can commence. The main headings are shown in green. The main headings near the portal consist of six roads 35 meters apart and 5 meters wide by 3 and a half meters tall. These roads are joined by cross cuts every 75 meters or so. This pattern leaves behind a series of pillars that are used to support the roof in the roads. The main heading service a major transport routes for workers, equipment, coal, and ventilation throughout the mine. Further from the portal, where traffic will be less the number of roads in the main headings may reduce. The ventilation shaft, which is shown in blue will be sunk early in the mines development, the shaft serves as an exit rate for exhaust air out at the mine. The main headings will not be completely developed at the start of the mine life, but instead will be developed only as far as is needed as to provide access to the areas that are currently being mind. The areas that have been mined out are shown in mottled white. In longwall mining, the coal is mined in longwall panels. The longwall panels shown here are 300 meters wide by 2 kilometers long by 3 and a half meters tall. In this example, the heart of the longwall panel is a full height of the seam being mined, however other factors such as coal quality at different levels in the seam and the size of mining equipment may also influence the height selected. The length and width of the longwall panel may be restricted by stability of the ground in a region, by severe faulting, or by the ability of the roof to cave. From a recovery and productivity aspect, the panel should be as wide and as long as possible. The way the coal in these longwall panels is mined is covered in another animation, however at this stage it is important to realize that the sheer equipment used to extract the coal from the longwall panel will move from the rear to the front of the panel taking slices off the 300 meter working face as it proceeds. The working face is the name given to the side of the longwall panel that is currently being mined. As this example uses retreat mining, access must be obtained to the rear of the longwall panel prior to mining. This is achieved by the construction of gate roads either side of the panel. The gate roads consists of two drifts running the length of the longwall panel connected by cut throughs. Again, this leaves pillars of coal called chain pillars to support these openings. The gate road next to the previously mined longwall panel is called the tailgate while the other is called the main gate. The tailgate of the current panel was the main gate of the previous. At the start of the block of longwall panels, both gate roads have to be developed, however as in this case, the previous longwall panel has already been developed and only the main gate must be driven. At the rear of the longwall panel, a starter drift is also excavated. The starter drift defines the working face and provides a space for the sheer and other equipment to be installed. At the other end of the panel, a barrier pillar is left behind this pillar will not be extracted and serves to support the main headings the pillar protects the main headings from the high stresses associated with the caving of overlying rock that occurs when the longwall panel has being mined. It is desirable for development to be around two or three longwall panels ahead of the panel currently being mined. Although this may be difficult to achieve in reality. This is done for several reasons; one, production is not slowed by development; two, methane in the longwall panels is allowed to diffuse out before mine it begins, and three so that as soon as one long will panel has finished being mined, the equipment can be moved to the next without being delayed. If development occurs too far ahead of mining however, there will be increased costs associated with the maintenance of the gate road openings.
Our goal in attempting to classify mining methods is to make it easier to learn the methods, because methods in a given class tend to work best in similar circumstances. Similarly, there tend to be just a few factors that differentiate the methods. By examining the classification scheme, we make it easier to remember the methods and the characteristics under which they can or cannot be used. It’s also useful to note that there is nothing sacred about the choice of a method. If five years down the road the characteristics of the deposit are changing, then another method will be employed. There are examples of mines utilizing three different mining methods over a 15-year period, as they adapt the mining method to the evolving geological conditions. Sometimes, one method is employed as the primary mining method, but another is used on retreat to recover pillars, for example. We’ll look at some of those cases later as well.
4.3.3: Why Do We Choose One Method over Another?
4.3.3: Why Do We Choose One Method over Another?
There are many factors that can affect the choice of a mining method. However, a relatively small number of them will dictate the choice. The others may affect the layout of that method, or other details, but rarely do they eliminate a method from consideration or drive the selection of a method. Let’s take a look at a comprehensive set of factors and understand what they mean. Then, we’ll step back, take a deep breath, and see how uncomplicated it can really be! Here is a comprehensive list with a few annotations to indicate the significance of the factor.
Spatial characteristics of the deposit
These factors play a dominant role in the choice of a mining method because they largely decide the choice between surface and underground mining, affect the production rate, and determine the method of materials handling and the layout of the mine in the ore body.
- size (especially height, thickness, and overall dimensions)
- shape (tabular, lenticular, massive, or irregular)
- attitude (inclination or dip)
- depth (mean and extreme values, stripping ratio)
- regularity of the ore boundaries
- existence of previous mining
Geologic and hydrologic conditions
Geologic characteristics of the ore and surrounding country rock influence method selection, especially choices between selective and nonselective methods, and ground support requirements for underground mines. Hydrology affects drainage and pumping requirements, both surface and underground. Mineralogy governs solution mining, mineral processing, and smelting requirements.
- mineralogy and petrography (e.g., sulfides vs. oxides in copper)
- chemical composition (primary and secondary minerals)
- deposit structure (folds, faults, discontinuities, intrusions)
- planes of weakness (joints, fractures, shear zones, cleavage in minerals, cleat in coal)
- uniformity of grade
- alteration and weathered zones
- existence of strata gases
Geotechnical (soil and rock mechanics) properties
The mechanical properties of ore and waste are key factors in selecting the equipment in a surface mine and selecting the class of methods (unsupported, supported, and caving) if underground.
- elastic properties (strength, modulus of elasticity, Poisson's ratio, etc.)
- plastic or viscoelastic behavior (flow, creep)
- state of stress (pre-mining, post-mining)
- rock mass rating (overall ability of openings to stand unsupported or with support)
- other physical properties affecting competence (specific gravity, voids, porosity, permeability, moisture content, etc.)
Economic considerations
Ultimately, economics determines whether a mining method should be chosen, because economic factors affect output, investment, cash flow, payback period, and profit.
- reserves (tonnage and grade)
- production rate (output per unit time)
- mine life (total operating period for development and exploitation)
- productivity (tons /employee hour)
- comparative mining costs of suitable methods
- comparative capital costs of suitable methods
Technological factors
The best match between the natural conditions and the mining method is sought. Specific methods may be excluded because of their adverse effects on subsequent operations (e.g., processing, smelting, environmental problems, etc.).
- recovery (proportion of the ore that is extracted)
- dilution (amount of waste that must be produced with the ore)
- flexibility of the method to changing conditions
- selectivity of the method (ability to extract ore and leave waste)
- concentration or dispersion of workings
- ability to mechanize and automate
- capital and labor intensities
Safety, Health, Environmental concerns
The physical, social, political, and economic climate must be considered and will, on occasion, require that a mining method be rejected because of these concerns. The impact of one mining method over another method on the environment must be considered. Similarly, the ability to provide the highest level of safety and health with one method as compared to a competing method must be considered.
- ground control to maintain integrity of openings
- subsidence, or caving effects at the surface; or affect on groundwater system
- atmospheric control (ventilation, air quality control, heat and humidity control)
- availability of suitable waste disposal areas
- workforce (availability, training, living, community conditions)
- comparative safety conditions of the suitable mining methods
4.3.4: Putting it into Perspective
4.3.4: Putting it into Perspective
So there you have it – the 37 factors that will influence your choice of a mining method… but how and when? Fortunately, this all reduces to a few major drivers.
First is depth...
If I know the depth of the deposit and the thickness of the overburden, I can do a few calculations and decide whether it is most likely going to be a surface or an underground mine. With this one factor, I’ve excluded or included half of the mining methods. Here, our decision tree has to split based on surface or underground. Let’s go down the surface path first.
If it’s a near-surface deposit, then tell me if it's metal, nonmetal, or coal deposit. If it’s a noncoal deposit, then open pit is likely. If it’s coal, then open cast is likely.
If it’s coal, then tell me about the topography. If it is flat lying, area mining is likely. If it is mountainous, then contour mining is the better choice.
On the other hand, if it is a low-grade and deep deposit, then solution mining will be considered if the mineral is one that is known to be recoverable with solution mining methods.
If the deposit is dimension stone, then I know it is going to be a quarry operation.
Ok, so what if an underground method is indicated?
The process is not quite as simple as for narrowing the field of surface methods, but almost so. Let’s go down that path and see.
First, I’d like to know about the attitude. Is the deposit horizontal or nearly so? If so, I’ve excluded several of the underground methods, e.g., shrinkage stoping and open stoping. On the other hand, if it is steeply pitching, I can eliminate room and pillar.
Next, I’d like to know about the competency of the host rock and the deposit. That will further narrow the field of potential methods.
This will all become clearer...
After we’ve studied the methods in more detail, this will become clearer. At this time, I am simply trying to make the process of selecting a method seem less intimidating. Sure, all of the 37 factors that I listed earlier are relevant, and that will become apparent by the end of the course. The ones with the greatest effect, in general, are:
- depth;
- surface features (especially for, but not limited to surface methods);
- attitude, shape, and size (extent);
- geotechnical characteristics of the orebody and the host rock;
- grade and uniformity;
- production requirements.
If these are the factors that essentially drive the selection process, then why do we bother listing the others? You will be in a stronger position to answer this at the end of the semester, but let me make a few remarks now, to give you a better feel for the relevance of the other factors, and why you should learn them!
- Safety considerations, as well as productivity, are responsible for the preference of vertical crater retreat mining rather than shrinkage stoping.
- Selectivity will be important for high grade ores in which the precious metal is concentrated in narrow veins or bands.
- Presence of discontinuities could nix the use of one caving method, but be largely irrelevant for a different caving method.
Lesson 4.3 Summary
Lesson 4.3 Summary
In this lesson, we’ve introduced the different mining methods used to exploit mineral deposits. We’ve characterized them into broad categories of underground and surface. Within each category, we established classes of methods, and then we identified the individual mining methods belonging to each class. We saw that a class represented a few specific characteristics of the deposit, and as such the methods in that class are well suited for deposits with those characteristics.
The choice of a specific mining method may require consideration of several factors, and we looked at six groups of factors totaling 37 in all. Although any of these factors can affect the selection of a mining method, a small set of the 37 have a disproportionate effect on the choice, and we identified those.
You will develop a better understanding of the details of the mining methods and the many factors that affect the choice of the method as we work through this course. Despite the lack of detail at this stage, you will find the material covered in this lesson to be quite useful as we continue into the remaining modules.
Regardless of which method we use, it is likely that the similar unit and auxiliary operations will be used during exploitation. The equipment itself may be very different, but the operations are similar from an engineering perspective. We’ll take a look at this in the next module.