Lava can range in temperature from 700-1200 degrees, according to wikipedia (don't knock my source, I'm a cs major not geology). Charcoal burns at 1100. Tapping magma directly out of a volcano would almost certainly be hot enough to work up to bronze, maybe even iron, assuming some non-human technology.
I'm interested in how exactly you intend to avoid dying from the convection or for that matter, how you plan to pump the magma without it ruining your equipment. Then there's the poisonous gases. Volcano lairs tend to fall short of OSHA compliance
Then there's the question of whether magma heats up when you pump oxygen into it, allowing it to surpass the melting point of useful metals. As you can see, charcoal falls short of iron melting point by several hundred degrees
I spoke of iron ore I might point out. Steel does require coal but iron ore doesn't for some reason. Carbon is needed to separate the oxygen from the iron oxide, also known as rust
Fair enough. The game also doesn't try to take into account the toxic gasses from running a charcoal forge indoors, CO and CO2 are less toxic but no less deadly in closed spaces like mineshafts. Presumably Toady simply hasn't gotten around to dealing with toxic gasses. Since dwarves can already work metal with magma, we can assume this is one of those areas where the game diverges from 1400's technology.
Oh yea, and the temperatures I gave earlier were incorrect. 700-1200 is the temperature of lava, molten rock that's been exposed to colder surface air. Magma, or subsurface molten rock, can break 2400 degrees, presuming you can find a way to survive that type of heat long enough to work the metal (which can presumably be done, as dwarves do it already) it's enough to work iron.
An argument can be made for requiring charcoal for smelting. Since most ores are bound to oxygen or sulfur, charcoal is used irl as a reducing agent. However, the argument should be made on the basis of charcoal being required for smelting, not that magma doesn't have the heat required.
Aside from that, peat could probably be used to fuel a forge if you processed it like charcoal, as could petrochemicals if they were ever implemented.
Cough up a historical precedent. Peat would have certainly seen use if it works, shouldn't be too difficult
Eh, I'll concede this point. While it's possible peat could be refined into a charcoal-like carbon density, it would be beyond 1400's level technology. It might be good enough to work up to bronze though, and with the new metal properties coming out in the next version that may not be such bad thing. And no, I don't want an infinite supply, I was thinking of mining peat being similar to mining out lignite or coal where it leaves a chunk of peat behind based on the miners skill that could be processed into something. Same thing goes with sand, though I would rather mining sand require wooden or stone supports and leave behind sand piles that have to be gathered in bags (possibly yielding multiple bags of sand, which could either be made into glass or disposed of).
Peat could also, in theory, be used as a reducer in a magma smelter. Again, I'm not sure if this is even possible, but it's something to consider. With heat from magma and carbon from peat, it may be possible to separate the metal from it's impurities.