Print9.2.4: Prevalence of Underground Mining Methods
The actual number of underground mines will fluctuate somewhat year-to-year, as a few close and a few open. In recent years, there has been a more significant shift in the number, as several underground coal mines closed due to market conditions. Even though the actual numbers will vary, the proportions are relatively stable. For the purposes of this illustration, we will use underground mines in the U.S., and I’ll round up the number slightly for ease of comparison. There are approximately 600 underground mines in the U.S. Of those, approximately 400 are coal and approximately 200 are noncoal. The noncoal includes metals, industrial minerals, and stone mines.
Every one of the 400 coal mines utilizes the room and pillar method, neglecting the 2 or 3 underground anthracite mines that employ a hybrid method. All of the other underground mining methods are distributed among the 200 noncoal mines. Let’s look at that group in more detail.
| Unsupported Methods | Supported Methods | Caving Methods |
|---|---|---|
| Room and Pillar (150) | Cut and Fill (including sub-methods/variations (23) | Block Caving (2) |
| Shrinkage Stoping (2) | Sublevel Caving (0) | |
| Open Stoping (including sub-methods/variations) (18) | Longwall (all of the longwalls, coal and noncoal, are in mines that use room and pillar for the development of the panels) |
The disproportionate number of room and pillar mines is quite noteworthy. Roughly 75% of the underground noncoal mines employ this method. If you add the coal mines into the mix, roughly 90% of all underground mines are using the room and pillar method. Let me ask you a question. If you were to become an expert in the design of one mining method, which would you choose? Well, certainly your career options would be much better if you chose room and pillar! This is not to say that you don’t need to learn about the other methods! You do!!! However, in our curriculum, we do emphasize this method more than the others, and now you know why!
Let’s look at the commodities mined by the three most prevalent methods: room and pillar, cut and fill, and open stoping; as well as the two rarely used methods (in this country) of shrinkage stoping and block caving.
| Method | Commodity | Number |
|---|---|---|
| Room and Pillar | Limestone & Gypsum | 105 |
| Salt | 16 | |
| Lead/Zinc | 12 | |
| Trona | 5 | |
| Potash | 4 | |
| Silver/Gold | 3 | |
| Copper | 1 | |
| Open Stoping | Gold | 9 |
| Zinc | 7 | |
| Nickel | 1 | |
| Platinum | 1 | |
| Shrinkage Stoping | Gold | 2 |
| Cut & Fill | Gold | 19 |
| Silver | 2 | |
| Platinum | 2 | |
| Block Caving | Molybdenum | 2 |
Please be aware that not all commodities are accounted for in this table. There are additional industrial minerals mined by an underground method, which are not accounted for in this data. Despite the very small discrepancies in the totals, the data illustrates accurately the prevalence of the mining methods by commodity.
Review your knowledge of Module 9 terms by engaging with the interactive activities.