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40d:Exploratory mining
Exploratory mining is the process of mining large areas in order to locate resources such as gems, metal ores and other types of rock. It is also used, to a lesser extent, to find the locations of hidden underground features such as chasms, underground rivers, magma and adamantine. The most straightforward method is to mark a large rectangular area for digging. Unfortunately, this method is also the least efficient. More efficient digging patterns involve digging out a smaller percentage of the stone in a given area, but still revealing a large percentage of the stone. These patterns are compromises, which depend on factors that will be described in this article. Note that exploratory mining is the process dedicated solely to discovery of resources and features. The digging process is usually separated, and not discussed here in great detail. The cheating counterpart to exploratory mining is the infamous reveal tool.
Factors in exploratory mining
These are the factors we shall consider for each digging pattern. Knowing them and deciding on their priority will help you find the most suitable pattern. Most of the factors are represented by numbers, obtained by dividing two quantities. Others are more subjective.
Labor
Labor is the amount of work that goes into the digging process. Exploratory mining is a work intensive process, capable of straining even a large fortress, but the work that goes into different patterns varies greatly. A fortress with a large supply of skilled miners can afford to consider labor low priority. The labor factor is the fraction of stone dug out of an area, and as such, it's a percentage, between 0 and 100%.
Scarcity
Scarcity is the amount of desired material present in the rock layer. It's theoretically represented by the fraction of desired material in the soil layer, but one can seldom state it accurately or even estimate it. Scarcity is determined by the types of materials you're after. Single tiles are the scarcest, followed by small clusters, veins and large clusters. For the classification of your desired material, see the gem and stone articles. Underground features are about as scarce as large clusters.
If you are after the precious gems: diamond, sapphire and ruby, you will see that these can be found only in kimberlite (diamonds) and bauxite (sapphires and rubies) respectively. So you only need to use one of the lower-visibility methods to find the veins of kimberlite in a gabbro layer or the large clusters of bauxite in sedimentary layers respectively, and then dig those out using one of the patterns that reveals every tile.
In short, if the sought-after material is scarce, you want high visibility; if plentiful, covering a larger area, lower visibility methods will work.
Visibility
Visibility is the amount of tiles that you reveal in the digging process. Excavated tiles are always visible, and so are the tiles immediately adjacent to them, including diagonals. The purpose of exploratory mining is to make a single tile of the desired material visible, allowing you to switch to conventional digging and extract it and similar material connected to it. Visibility is represented by the fraction of visible tiles in the excavated area. Perfect visibility is not always a priority - it tends to decrease in importance as the size of the target increases, because there are fewer tiles that need to be dug out for the target stone to be found.
With some patterns, it's possible to start with lower visibility, and then "fill in" for more complete visibility in the areas you wish to concentrate on.
To better understand this, see veins and clusters.
Re-usability
Exploratory mining leaves behind a monotonous, repeating underground landscape of shafts or tunnels. The excavated level may be hard to reuse for habitation, storage or industry without additional digging and significant rebuilding efforts that leave behind inferior walls that cannot be engraved. Re-usability is subjective, and it depends on the desired layout. Re-usability is represented by the largest room size achievable by digging into the solid rock left behind without rebuilding any walls. Re-usability is a priority for a small fortress.
Resource Distribution
Ore
Ore occurs in three forms, depending on the kind:
- Large cluster: An oval that occupies nearly half of a 48x48 block, area-wise. Only one appears per block.
- Vein: A sinuous line of the material crosses the block. Multiple veins can occur in the same block. They usually cross each other, or one dead ends into the other if they do.
- Small cluster: A sprinkle of 3 to 9 adjacent tiles. Multiple small clusters of different materials may be in the same block.
Gems
Gems also occur in small clusters, or as a single tile.
Patterns
Patterns are represented by a unit tile. This unit tile is repeated throughout the area intended for excavation to create the desired pattern. Each pattern is analyzed with the above factors in mind.
Key: ░ = Not mined, not visible ▒ = Not mined, visible (wall) . = Mined (floor) x = Mined (shaft)
Hollow
All tiles are excavated.
- Labor: 100% of the tiles are excavated.
- Scarcity: Any scarcity. If it exists in the layer, it will be found.
- Visibility: 100% of the tiles are visible, obviously.
- Reusability: Approaches zero, except for mass storage. Any design other than a large hall requires reconstruction.
- Bottom line: Hollowing wastes labor like there's no tomorrow, but integrates extraction into the exploratory mining process. Use only if you have a lot of labor to spare, really need huge amounts of stone and don't mind the reconstruction required to make the hollow area habitable.
Rows
- Labor: 1/3 (~33%) of the tiles are excavated.
- Scarcity: Any scarcity. Clusters as small as a single tile are revealed.
- Visibility: 100%.
- Reusability: Very low. The long corridors aren't very useful, and can only be expanded to long, wide corridors.
- Bottom line: This method achieves the same visibility as hollowing out, but using a mere third of the labor. Ideal for hunting single-tile gems. As an added bonus, it is more efficient than a 3×3 design.
Diagonal
- Labor: 20% of the tiles are excavated.
- Scarcity: Any scarcity. Clusters as small as a single tile are revealed.
- Visibility: 100%.
- Reusability: With a bit of imagination you can build nice 3x3 rooms
- Bottom line: This method is 2nd most efficient of those with 100% visibility. This one doesn't use other levels to move from one spot to another but is annoying to designate.
Mine shafts, grid of every 3 tiles
- Labor: 11.1% of the tiles are excavated (1/9).
- Scarcity: Any scarcity. Clusters as small as a single tile are revealed.
- Visibility: 100%.
- Reusability: It's easy to make into square rooms of various sizes, the stairways can be removed and used as doorways, or just carved out as part of the rooms.
- Bottom line: You'll need to clear part of one layer above it to get it started (use one of the other methods to cover the area), but this method is the most efficient for those with 100% visibility, and has a great reuse value. Real dwarves' choice! It takes a lot of keypressing to designate, here is a ahk script to save your fingers. For a discussion on optimizing travel times through mineshafts, see here.
- See also: Mineshaft stitching
Pinwheel Shafts
- Labor: In this example about 17.3% of the tiles are being excavated..
- Scarcity: All except single-tile small clusters.
- Visibility: 96.6%.
- Reusability: Workshops can be easily fitted into the unmined 3x3 areas.
- Bottom line: Very similar to Mine Shafts, but you can replace the up/down stairways with a mixture of up stairs and down stairs, eliminating the chance that one of your dwarves will slip and fall all the way down the shaft.
7×7 blocks
- Labor: 15/64 (~23%) of the tiles are excavated.
- Scarcity: Veins and up, as the large 5X5 space left in each unit tile can easily conceal a small cluster.
- Visibility: 39/64 (~61%) of the tiles are visible.
- Reusability: Medium. The 7×7 blocks can easily be converted into 5×5 rooms, suitable for individual rooms, storage or workshops. Optionally, it can be converted into a grid of connected 7x7 rooms, if you center each room on a crossroad. Easily converted into a more thorough 3×3 block patten by digging through the large blocks.
- Bottom line: This is a low-labor method great for vein-hunting. The low labor cost puts you in a position to invest more and get better coverage if desired.
15×15 blocks
- Labor: 31/256 (~12%) of the tiles are excavated.
- Scarcity: Large clusters and up, as the large 13×13 space left in each unit tile can easily conceal quite a lot. Unless you have particularly bad luck you should also find all veins, but there is no guarantee.
- Visibility: 87/256 (34%) of the tiles are visible.
- Reusability: High. A 15×15 block of solid rock is extremely versatile when it comes to interior design. It's easily converted into a 7×7 block design, which may be further converted into a 3×3 block design.
- Bottom line: This method is preferable when you are low on labor or when you're after an underground feature. It can easily accommodate parts of your fort, or serve as the precursor for a more thorough search.
Mine Shafts on a 6-, 9-, 12- or 15-grid
- Labor: from under 3% (1/36) for the 6-grid to less than 0.5% for the 15 grid (1/225).
- Scarcity: Large clusters and up (as above), and magma pipes, magma pools, and underground pools. Underground rivers only guaranteed with the 6 grid, but a wider grid could start and easily get lucky.
- Visibility: extremely low.
- Reusability: High. Any area often needs a set of stairs (or more than one) leading up/down, and these would be the start of them.
- Bottom line: This method is used only when you are looking for a large underground feature, or getting a feel for the various rock layers, or just hoping to get lucky with little effort. Grids larger than 15 may start to miss even large features such as large clusters and pools, but can be used for identifying stone layers, and can always be filled back in later with shafts on a tighter grid. (see "searching for undergound water & magma, below)
- With any grid pattern, a (much) wider version could be used to start and to locate specific stone layers/areas, and then filled in later in a tighter pattern where you want if you're not lucky the first pass. If you plan to use the 3-grid pattern (for a 100% tile reveal) later, create your grid with intervals that are a multiple of "3". If you are only looking for veins, features or just don't care, then do as you will.
Searching for underground water & magma
While a lot of fun, underground features can be both difficult to find and dangerous to the unprepared, being as they are full of hostile creatures.
Magma is a rough circle usually about 20 tiles or more in diameter - a 12 grid is guaranteed to find one, a 15 is very unlikely to miss. Magnetite (an iron ore) is found in sedimentary layers in large clusters that are even bigger and even easier to find. Underground rivers are often only 5 tiles wide, damp stone included, and so the 6-grid may be necessary to find those.
If you noted where these features were located before embark, on the local map, that helps immensely. Each of these areas is 48 tiles across, and any feature such as a pool, pipe or river is enclosed completely within that area. Digging a single shaft for large features in the exact center pays off most of the time.
Digging
Underground features are a lot larger than veins and small clusters, so the 15x15 block method is more than sufficient to find them. If you dig tunnels rather than shafts, you only need to dig every 3rd z-level out as even the shortest feature, a cave river, can be discovered on any one of the 3 levels it influences with "warm" or "damp" stone, as shown in the side profiles below.
Over the top Reveals Hits damp Hits damp Underneath
(misses) (hits) (hits) (hits) (misses)
_______o## ######## ######### ######### ######### # Unmined stone
### ##### ___o ## #### ### #### ### #### ### ~ Water
###~~##### ####~~## __o#~~### ####~~### ####~~### _ Floor of the tunnel
########## ######## ######### ___o##### ######### o Miner
########## ######## ######### ######### _______o#
Once you encounter warm or damp stone you want to back off a couple of squares and dig an up staircase. On this new z-level dig another tunnel to where you just found damp/warm stone. Depending on how tall the feature was and whereabouts you hit it, you may need to repeat this approach. Eventually your miner will reach a z-level where he can safely dig all the way through to the "surface" of the feature.
Obsidian caps
Even when a magma pipe reaches the surface it can freeze over in cold climates, or may simply stop just short of surface. In theses case it will have a obsidian cap over it, which is easier to find: just search for any hills or mountainsides that have a circular chunk missing and/or a grey circle of stone (example on the right).