Writing about Mines in your Fictional Universe: A Geology Introduction
Hello! I'm Bird, and I am here to guide you on a journey about different mines that exist, what materials are being mined, what those materials might be mined for, and what rocks/what processes might make these areas mineable. I will also touch briefly on the idea of gem quality, the commonness of the material, and what these things might look like fresh out of the dirt!
First things first, lets talk about the what types of things we might want to mine for in a fictional universe! There are a lot of things that are used daily that require mining, but there are a few that I see written about the most: Gold, Gemstones, Iron, and Coal. I personally would love to see this idea expanded on a bit, so lets talk about some mines that would definitely be necessary but overlooked! First one is pretty easy, glass! those beautiful stained glass windows are useless if no one is mining quartz to be made to glass, and I imagine it would be quite a profitable business seeing as glass, in general, was a luxury in ye olden times. The next thing we need to address is Abrasives! want to sand and polish stone and metal? Want to sharpen your blades for battle? May I introduce you to abrasive minerals! garnet, corundum (Ruby and Sapphire), and yes, diamond! Why are we using such beautiful gemstones to polish other things? Simple, even if you are to find a deposit of these gemstones (garnet being one of the more common ones) most of the time they are inclusion rich, ridiculously small, an undesirable color, or all three of these.
Finding gemstones that are good quality is hard, your character will not stumble upon it, pick up the rock and immediately know if the location is good enough to mine gemstones. If you are determined to make it a gemstone mine, have your character hold the mineral up to the sun/a light source and let them be able to see light coming through, though it is considerably thick.
Moving into metal mining! Metal mining is both easier and more complicated to write! Why is it complicated? Because unless it is gold or silver you are unlikely to see the desired metal itself. Why is it easy? welllll, I am going to try to make it easy. First things first, a lot of metals are chromaphores, this means that when the element is present, it will influence the color! Copper is an excellent example of this, old pennies oxidize and turn blue/teal/green, so do most rocks bearing copper! Looking for iron? It will probably stain the rocks dingy and brownish red. Things to note: copper and iron can be found in mineable amounts together! If you do this, iron will be present in the form of pyrite, or fool's gold, this has a nice cubic shape and can be described as such, the copper will typically leave a teal residue or veining across the rock, which in this case will almost exclusively be black to dark gray (Its basalt) but it can be found as the mineral chalcopyrite also (looks like fool's gold but it doesn't make cute crystals). Malachite is also a copper ore, in my experience I have never seen malachite from a mine that has looked like some of the stuff I have seen in gem shops, azurite (A darker blue mineral) can be present also, but again, these are usually very fine grained and would not be able to be used as jewelry, but obviously, in some places it must happen, just much less frequently.
Another thing I will briefly mention is that, if you are writing about metals remember that these metals will require a smelting process to extract a pure metal, this usually requires some other material (For iron, it is charcoal). Also remember alloys! Most useable metals are a mix of different metals to make them harder. This even includes gold jewelry. Last comment about metals, a very interesting plot for a fictional universe would be the use of lead. Lead ore was a hot commodity before we knew it was toxic, the side effects (Being nuts) could really create some tension.
Lastly in terms of mined material, I will briefly mention coal and stone in general just to say, coal is a sedimentary rock, distinctly different from the typical environments necessary to form most gemstones and heavy metal deposits (Yes, there are exceptions). Coal is dark black/gray, which is quite uncommon for sedimentary rocks which tend to range from reds/tans/browns/grays. When coal is lifted it will feel much lighter than you anticipate, which is the polar opposite of what happens when you lift a metal rich rock, which will feel immensely heavy. Finally, Coal will not turn into diamonds in nature, diamonds need mantle pressures and temperatures to form, there will be no diamonds under a coal mine unless there was a mantle derived eruption that got covered in a swamp, that became coal and as they dug they exposed the kimberlite pipe (I mention this because I just read this in a story and it hurt my feelings). Finally, If you want to write about a mine that is definitely necessary but want the content to be pretty low-maintenance, but profitable for whoever owns it, owning a granite/marble/ or really any desirable stone quarry would be perfect.
Now I will move onto what kind of mining exists today, I will not talk about every exclusive mine, but I will talk about ones that are common that are on my radar. First up, the one everyone talks about in books, underground mining. Underground mining is used when you are getting the material from the 'primary'/original source. The rock is rich in copper? Lets mine said rock. However, mining underground is the most dangerous form of mining, there can easily be a lack of oxygen because of insufficient ventilation (That's why people will carry something with an open flame when going into abandoned mines; if the flame goes out there is not enough oxygen and you have to turn back). There can also be lots of collapses due to overhead rocks, enough said. Cave mining is primarily done when the amount of rock above the deposit is too great to strip mine.
Now lets talk about strip mining! Strip mining is when you just mine on the surface, and dig deeper and deeper into the ground to obtain your desired resource whether it be stone, coal, gemstones, or anything else. It truly is less glamorous, but it is safer than digging a tunnel. That said it has its own issues, sure the oxygen is good, and you don't have to worry about the rocks collapsing over your head, but oh wait, the rocks can collapse over your head. Landslides can occur due to the over steepening of sides, excessive rainfall, and most importantly, old faults or planes of weakness that happen to be facing towards the mine (the diagram will help this make sense). Both of these types of mines can also create ecological damage, which can be mitigated nowadays, but then maybe not so much. Namely acid mine drainage, I will not talk much on the effects but a quick google search will give you plenty of information that might be useful for writing.
Now both of these are trying to mine a targeted rock, but sometimes its best to let nature do the work so we can do less. Diamonds, gold, corundum (rubies/sapphires), and garnets all have one thing in common. They are dense! So when erosion happens, and that sediment makes its way into a river, everything will separate based on its density. This is just because faster moving water can hold heavier sediments, and slower moving water will drop those heavy sediments leaving only the lighter sediments within the water. Lots of places that mine the things listed above will pan/sieve in active rivers and streams, or they can surface mine where rivers and streams used to be! These are called placer deposits. There is one setback though, the gemstones will not be perfect crystal shaped, they will be rounded due to being thrown around in a river (like beach glass). These are sapphires, but they have been rounded over time in the river.
Final thoughts, writing about a mine can seem nerve-racking, intimidating, or just something that you want to briefly mention and move on from, but truly I think going into the weeds could really add something to a story! Even if stories are slightly inaccurate about information, I am still 100x more excited to see it mentioned in more detail than to see it as a sentence. Besides it is fantasy, it doesn't always have to be exactly like earth.
