I have a long-running campaign, and I'm looking to try this mod with it. It seems like existing ore patches will turn depleted just fine, though old depleted patches will obviously no longer exist since the game deleted them prior to the save. However, the mod tells me that I need to use "high powered drills" to mine deeper resources, yet I have neither a research nor a building called anything of the sort. Am I doing something wrong?

Oops. That's a relic from an old version. Tier 2 and tier 3 ores used to require their own drills. But I changed that and simply made mining slower. You can use your own mining drill mod if you like. I'm partial to the Uranium drills in Schalls Alien Tech.

When adding to an existing game, the mod takes a snapshot of all ores on the map as the mod is loaded and acts as if that's how the map was generated.

Ah, gotcha :) Yeah, both the short text blurb and the long-form description describe "high-powered drills" and I found a "mod highlight" video from 2019 which showed T2 and T3 drills in the research tree, so that confused me. Good to know, and I prefer this design myself.

Also good to know on using with existing save files. I obviously don't expect your mod to know where Ore existed previously but has been mined out, since I'm pretty sure that's not stored IN the save file. Doing it only for currently-existing ores as though that's how the map was generated is a good way of handling it. Thank you kindly for the explanation.

Actually, related question: if I trigger your mod in an existing save game AND THEN discover new ore fields, would those also be reduced in quantity like the mod is supposed to do to a newly-generated map? I'm using Train World, so I'm reliant on large, dependable ore fields :)

Yes, when the mod is added, all existing resources and new resources are reduced in their amount. The first tier of prospecting slightly increases the total resource amount over vanilla, and the second tier greatly increases it.

Got it! Thank you kindly for the explanation.