Module 8 Overview

Module 8 Overview

Fewer than 10% of the mines in the United States are underground mines. Given a choice, we’d always choose to mine by a surface mining method, as surface mining is less expensive than underground. Unfortunately, we don’t usually have a choice! Certain commodities are found predominantly deep beneath the Earth’s surface – too deep to consider surface mining; and notable examples include gold, lead, molybdenum, platinum, potash, trona, salt, silver, and zinc. Other commodities are commonly mined on the surface, but because of their value, they are deep mined as well; and notable examples include diamonds, metallurgical & thermal coal and copper. In recent years, a third reason for going underground has emerged: the commodity is located in a suburban or urban environment, and local zoning ordinances preclude a surface mining operation. We are seeing this primarily with limestone. Finally, as time passes, the reserves that are easiest to exploit have been mined. Increasingly, we are having to mine deeper and deeper, and under more adverse conditions. The following article from the Wall Street Journal illustrates this well: "Mining a Mile Down: 175 Degrees, 600 Gallons of Water a Minute." Can you imagine mining under such conditions? It is a great engineering challenge, and we will see more and more of this!

The development of an underground mine follows a similar process to initial stages of surface mine development. A site has to be prepared, office buildings, shops, warehouses, and mineral processing facilities need to be constructed. And as with surface mine development, the timing of the infrastructure will minimize any premature upfront cash expenditures. The significant difference between surface and underground development is access to the orebody. This is usually easy to accomplish in surface mining because the orebody is close to the surface and often it is only necessary to remove vegetation, the soil layers, and a modest amount of overburden. By contrast, accessing a deep orebody can take considerable time, effort, and money. In many cases, we can access and begin mining a surface deposit within weeks, whereas it might take several months of even a year or more to access a deep deposit.

Learning Outcomes

At the successful completion of this module, you should be able to:

• demonstrate knowledge of the four types of openings used to access an ore body for underground mining, and specifically:
  • when each would be selected, i.e., the pros and cons,
  • where they would be located, and
  • the materials handling options for each type of opening after the mine is in production;
• demonstrate knowledge of the process / unit operations for developing shafts, slopes, drifts, and box cuts, including the type of equipment used;
• define, and/or draw & label as appropriate, the basic terms used to describe underground mining methods and activities - specifically, the common deposit and spatial, directional, and excavation terms (see text pp 79-83 for listing and definitions);
• sketch a generalized underground metal mine, for the purpose of illustrating the basic infrastructure of such a mine;
• name the three classes of underground mining methods, and describe the distinguishing characteristic of each class;
• demonstrate an understanding of the conditions under which one method would be selected over another. Describe the “defining” or “distinguishing” characteristics of each method;
• describe and sketch the essential elements of three major unsupported methods: room and pillar, a.k.a. stope and pillar, shrinkage stoping, and sublevel stoping. Name some commodities mined by these methods;
• draw a typical room and pillar coal mine layout showing mains, submains, and panel entries;
• describe the sequence of development and production for each method; identify typical equipment utilized for the associated unit operations; additionally:
  • for the room and pillar method, describe conventional, continuous, and longwall mining,
  • for shrinkage stoping, describe the more popular variant known as VCR,
  • for sublevel stoping, describe the variant known as bighole stoping;
• describe and sketch the essential elements of the major supported method known as cut and fill. Explain what is meant by drift and fill, undercut and fill, and overhand cut and fill;
• describe the sequence of development and production for the cut and fill method; identify typical equipment utilized for the unit operations and auxiliary operations;
• explain the concept of the historical methods of square-set stoping and stull stoping, and in what very limited circumstances they might be applied today. Describe how cut and fill mining can be used in conjunction with another primary mining method to increase the extraction ratio;
• describe and sketch the essential elements of the major caving methods known as sublevel caving and block caving, as well as another important caving method known as longwall mining (for coal and noncoal).