Mining along a river

Number one rule: you don't want to build your mine so that you have to fight the river as well as the earth. Start it well away from the water (preferably in a spot where high water is unlikely to drown your mine). And don't dig so that your mine breaches the riverbed.

If you mean to mine right at the edge of the river, I think that if it's a deep mine you just do as above, start in a dry place and dig till you hit your seam without making a hole in the river. Or if you're digging too close to the surface for that, just bring in the heavy equipment and earth movers and shift the lot to a place it can be processed. Contemporary mining tech can cut a mountain down to size, this should be no trouble if it's worth the investment.

I don't know if there's a close correlation between water table and rivers. I suspect not necessarily.

Common problems will vary depending on the specifics of the scenario, but they will probably center around maintaining a safe mining environment -- no cave-ins or collapses, breathable air, no explosions, no floods, etc. Water is a big problem -- even if you're not digging below the water table per se, you can have trouble with underground streams, springs, pools, etc., as well as water seeping down from the surface -- or pouring down through natural shafts. Depends on the terrain. Heat is a big problem in deep mines - it affects equipment as well as people, and mitigating it is costly. The economics of the mine are important too: if the operators are concerned for the welfare of the miners or consider them expendable, or if the mine is a cooperative community endeavor vs an evil empire extracting resources from the conquered, practices and conditions (& the chances for destructive accidents/"accidents") will be very different.

ETA: If you haven't decided what the mine is mining for, you may want to read up on the geology around different mineral deposits so you can figure out what's likely to be found in the type of place you want to write about. Minerals & ores aren't scattered about randomly -- each kind tends to occur in certain types of places, and some are often found in close proximity to each other, because of the geological processes that left them there. As a writer, you can either start with the terrain & the kind of mine you want and find an ore that fits it, or vice versa.

A lot of diamonds are mined as detrital material in stream gravels. Similar placer deposits of gold and platinum. You process the gravel through sluices and filters of various kinds. No real digging involved.

If you're talking about a diamond pipe, the remnant throat of an ancient volcano, and the river is running alongside or over the top of it, you want the diamonds badly enough? You divert the river. And have a lot of real good pumps.

caw

Is it an alluvial mine or a hard rock mine? It is not unusual to mine alluvial deposits beside rivers, and it is fairly simple.

They could be harvesting pearls, some of which grow in mussels that reside in certain rivers, or something like jade, which also comes from river rocks. This way it makes sense for your complex to be right on the river.

Too many variables. You'd need either to know what you're mining for, or what kind of river you're mining along. Geology or geography, you need to pick one, or the choices are too wide.
For example, there's a ton of information about mining gold along the Fraser River in B.C. Along the broad, earth banked edges, along the narrow, fast-flowing canyons? On behalf of a big mining company with money for all the best equipment, Or a couple of guys with patched-together basics? Are the rules and regulations strictly enforced, or can the miners do as they please? How are relations with any locals?

Nianne said:

Is the water table usually really close to the surface near a river.

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As a technical addendum, the surface of just about any river is the water table, where it breaks the land surface. Lakes, likewise. In the subsurface, porous soil has a zone of aeration (where air and water both occupy the pore spaces) and a lower zone of saturation, where water fills all pore spaces. The boundary of those two zones, which can move up or down, according to weather and climate, is the "water table".

caw

Caissons.

Jeff

Nianne said:

Thank you all for the replies!

Too many variables? Okay, hmm.

The river is subterranean. I'm not sure how much that necessarily implies about the geology of its bed. Can you have a soft-banked river underground, or are underground rivers pretty much only found along basalt formations and other hard surfaces?

I was picturing a relatively straight stretch of huge, deep, slow river in the middle of a very big cavern. I'm okay with this being implausible or impossible, but I need to know how much so it is.

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Most underground rivers on Earth are through limestone; although they could go through other soluble rocks, but the banks would be mostly stone with gravel banks here and there. If you can imagine a long, straight, slow stretch, then it is plausible.

There's also going to be a completely implausible amount of life (flora and fauna) along the edges of the river (fantasy story, and all that), all of it previously unknown to science. So, there could conceivably be a fair amount of local 'earth' built up in the area.

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Have you read the Center of the Earth series by Edgar Rice Burroughs? If not, then read it. You can put in anything that you want.

The material they're mining needs to be something that's literally never been seen before. Something so gorgeous it immediately commands astronomical prices. (Unobtanium, anyone?) I'm thinking that means it probably has a relatively recent biological origin -- some unique kind of limestone or excreted mineral that's built up into deep banks along the edges of the river?

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You are creating a different place, so anything that you dream up in the way of minerals would be plausible, but jade and diamonds are often found in alluvial deposits, and jade can look quite nice. Emeralds, rubies, and other hard gems are also found in alluvial deposits.

There are no local humans, and the operators can pretty much do whatever they want. They can get all the financing they want, but one thing that does concern me is how do they get their mining equipment to the site. They might be severely constrained in terms of the sheer tonnage of equipment they can bring.

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Wouldn't enslaving the pocals be more colorful? Those stones are going to be so valuable that you could even pay the miners.

At the same time, I do need this to be an operation that’s going to have significant impact on the local ecology. Nothing so simple as panning for gold. I need an installation big enough that an eco-terrorist would think about blowing it up in order to save the fantastic fauna, which really is in jeopardy of being wiped out.

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Read up on sluicing. It is primitive but effective and efficient. Diamonds and jade are considerably denser than most stones, and the other hard gems may also be.

Oh, and the water is toxic to humans.

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So they'll have to haul in water?

Nianne said:

You are a gem! How had I not thought of that?! Yes, they will have to port in water somehow.

And electricity.

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You might also have them filter the poison out of the water. I would imagine that there was some soluble poison in some of the rocks that it flows by. That even happens on Earth, but the concentration seldom gets so high that it is dangerous, except Rio Tinto in Spain.

If there's flowing water and a generator, then there is electricity.

Nianne said:

The only 'center of the earth' novel I've read is Jules Verne's. I was planning to grab a half dozen contemporary fantasy novels to read after I bang out a rough draft of this one; I will make sure Edgar Rice Burroughs is on the list.

Any other fiction suggestions?

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It's been a while since I read any ERB. He did some clever things in his center of the Earth series, but I always preferred the Venus series.