What is the metallurgical/mining origin for Dwarven ingots? As far as I know, the only way to get them is by melting down Dwemer artifacts. I always expect to find a great Dwemer mining complex somewhere.

I think they're some manner of alloy whose metallurgical formula is lost with the Dwemer.

Tonal Architecture.

ESO gives us some dwarven ore stuff, but I like to think its just a cheap way to manufacture a material that looks similar to what the Dwemer use, without it actually being the same thing.

This was addressed by one of the Loremasters:

Ah, okay. Good to see I was spot on in my assumption.

That's a good explanation, though I still like my idea that the Dwemer used tonal architecture to make certain mineral deposits into the same metal in order to increase productivity.

Given the spiders animunculi sometimes carry ore, I can't help but wonder if they somehow convert it into more dwarven metal.

That's sort of my speculation on it as well for the most part.

Dwemer Metal is Dwemer Body and Spirit fused through Tonal Architecture.

I believe that only applies to Numidium's golden skin.

The "golden skin" is a metaphor, like the golden fleece of Jason and the Argonauts was a metaphor. In both cases it is a means to refer to the bridge between the mundane and the divine.

Numidium was made of Dwemer metal, which uses souls as a component. Many souls were sacrificed to create Numidium. Perhaps they used the souls of slaves or animals for works of lesser importance.

Slaves or an entire race, willing the profane into the sacred required the Heart of Lorkhan and Kagrenac's Tools. It was the apex of Dwemer achievement, not some common process required for literally everything the entire Dwemer civilization built that wasn't carved from stone.

The disappearance of the Dwemer was pretty much solved in Morrowind, it stated that the Dwemer as a race literally became Numidium, at least if you believe what Yagrum tells you after bringing him two books. I feel the Dwemer becoming the Brass-skin could be a metaphor but they certainly became Numidium.

Hah....you assume or remeber him saying that.What he actually says is:

"By refreshing my memory with "Divine Metaphysics," I believe I can explain. The Dwemer were not unified in their thinking. Kagrenac and his tonal architects, among them Bthuand Mzahnch, believed they could improve the Dwemer race. Others argued that the attempt would be too great a risk. The war with Nerevar and the Dunmer may have led Kagrenac to carry out his experiments prematurely. Although this book argues that nothing disastrous could result, the disappearance of my race argues otherwise."

"Lord Kagrenac, the foremost arcane philosopher and magecrafter of my era, devised tools to shape mythopoeic forces, intending to transcend the limits of Dwemer mortality. However, in reviewing his formulae, some logicians argued that side effects were unpredictable, and errors might be catastrophic. I think Kagrenac might have succeeded in granting our race eternal life, with unforeseen consequences -- such as wholesale displacement to an Outer Realm. Or he may have erred, and utterly destroyed our race."

Or is there another dialog where he says what you claim he does?

i'm disappointed that radac stungnthumz had absolutely nothing to say about the disappearance, or yagrum. that would've been a golden opportunity. or talk to any of the dwarven ghosts really.

the dwemer were destroyed if the undistrubed ashpiles are anything to go by.

^^Not Yagrum, but Baladas.

The two quotes don't quite actually come into conflict a great deal, save Yargrum's Outer Realms comment. The Mer's sorta out of his mind though, so there's that. Coupled with previous exposition and dev comments, the latter seems to be the "correct" explanation. Interestingly enough, Yag will not elaborate on Divine Metaphysics, which details the Numidum's part in the whole thing, which is sort of damning in of itself.

Apparently, Bthuand Mzahnch could not foresee the risk of the Chimer preventing Numidium from ever receiving its heart. Well either that, or the Tonal Architects' overall plan had a huge, unresolved hole in it.

Their bodies were destroyed, at least. Their souls are believed to have become Numidium in a process that I believe may be similar to how Alduin empowers himself by devouring the souls of fallen Nords.

Well, Bthuand strikes me as the guy running around saying "Come on guys, trust us! We got facts and stuff to back it up!", and we can't be sure of how many Dwemer actually bought into Kragenec's whole spiel.