Types of Mines
The two types of mines commonly in use are placer mines and underground mines.
Placer Mines
Placer mining involves a pan or sluice to sift gravel, dirt, sand, and water from a flowing stream or river. This technique is most commonly employed above ground, but can be conducted below. Placer mining is a relatively simple operation requiring little equipment. At the basic level, the only requirements are a character with a shallow pan and a great deal of patience.
Placer mines collect mineral deposits from underground veins eroded by water and tumbled downstream. Finally deposited in the streambed, the miner harvests them from the water. Only mineral wealth, eroded from deposits, collects along the streambed. Since erosion is slow, placer mining is much less profitable than deep mining.
Placer mines do not yield profitable amounts of copper, iron, mithral, or gemstones. Characters who have discovered gold, silver, or platinum may try to mine the deposits. Underground mines are required for all other metals and gems. To calculate the value of placer mines, determine the quality and then roll 1d4 and multiply by 10. This is the percentage of its top value the mine will yield. For example, if a gold mine could yield 100 gp per week, a placer mine will yield only 10 to 40 gp per week.
Tunnel Mines
Operating an underground, or tunnel, mine requires a great deal more work than placer mines, but the potential for wealth is much greater. Underground mining tunnels into the earth, searching for veins of ore and gem-encrusted rock that is removed and the minerals and gems then extracted.
Excavating a Tunnel Mine
Excavating a tunnel is hard work and time consuming. The rates for excavating by the various races follow. Rates are in cubic feet, per miner, per eight-hour day.
Mining Rates Table
| Race of Miner | Very Soft Rock | Soft Rock | Hard Rock |
|---|---|---|---|
| Gnoll/Halfling/Human | 75 | 50 | 25 |
| Gnome/Kobold | 80 | 60 | 30 |
| Goblin/Orc | 85 | 65 | 30 |
| Dwarf/Hobgoblin | 90 | 70 | 35 |
| Ogre | 150 | 100 | 50 |
| Hill Giant | 250 | 150 | 75 |
| Fire Giant/Frost Giant | 300 | 200 | 100 |
| Stone Giant | 500 | 350 | 175 |
Mineral Vein Direction Table
| D4 Roll | Vein Runs |
|---|---|
| 1 | North-South |
| 2 | East-West |
| 3 | Northeast-Southwest |
| 4 | Northwest-Southeast |
Vein Path Alteration Table
| D10 Roll | Change |
|---|---|
| 1-2 | Steep descent |
| 3-4 | Shallow descent |
| 5 | Curves right (10-60 degrees) |
| 6 | Curves left (10-60 degrees) |
| 7 | Continues straight\ |
| 8 | Shallow ascent* |
| 9 | Steep ascent* |
| 10 | Vein ends |
* If the mine starts on the surface, the first time this is rolled it is treated as descent rather than ascent.
Miners who wish to continue working the mine must follow the vein, even if it goes in a direction they do not wish to follow. If the path of the vein takes a course that makes it impossible to follow, such as emerging into thin air through a cliff face, that particular course of the mine has run out. If the vein ends in both directions, the mine is played out. This rule takes priority over the Duration of Mining Site rules.
In unusual circumstances, say a tunnel that ends at a cliff which overlooks a gorge, miners may try to pick up the vein again on the other side. The DM must decide how likely that vein is to continue, depending on the situation.
Shoring a Tunnel
A tunnel mine must be supported, or shored, with wood or stone pillars. Otherwise, sections of the tunnel will almost certainly cave in. Shoring can be done by characters with Mining, Carpentry, or Stonemasonry proficiencies.
Each 10-foot section of tunnel requires two side and one ceiling brace, each at least 1 foot thick. If the tunnel is 10 feet wide and 10 feet high, each brace uses 30 feet of bracing material. Each shoring brace requires four hours to build.
Playing Out a Mine
Mines contain finite amounts of mineral wealth. Sometimes, this amount is enough to keep miners busy for generations. More frequently the mine plays out after a period of intensive mining.
To determine the length of time a mine will produce before depletion, roll 1d100 at the start of the mining operation. The result is the number of weeks the mine can be worked. If the result was doubles (11, 22, 33, etc.), the mine has a much longer duration. Roll 1d100 again, the result is the additional number of months the mine will produce. Add this figure to the number of weeks set by the first roll. If the second roll is also doubles, roll 1d100 a third time, the result is the number of additional years the mine is will operate. Further doubles rolls are treated as tens of years, hundreds of years, and so on.
For the sake of convenience, treat each month as four weeks and each year as 48 weeks or 12 months when totaling up the mine's longevity. Please note that a "week" is the amount of work that one dwarf can perform in a week. If 12 dwarves are engaged in excavating a mine, 12 weeks of the mine's lifetime are used up for each week of operation.
If the mine is a placer mine, disregard any doubles rolls for the duration of the find. A placer mine is always depleted after 1d100 hours of work.
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