[DevBlog: Scanning & Mining]

I am really liking what I am hearing about the development of this game and what you're trying to do with it. A few tweaks or alternatives to consider did come to mind: 
 

"...they are generated via our procedural algorithms together with the planet as voxel blobs."

Might I suggest that you might save on front-loaded data here? I think you could save the procedural generation until a player actually scans, although you could save again on processing by tying the new procedural generation to what has already been generated. More on that later... 

 

"They will be spread on the planets based on rarity and how important they actually are in crafting recipes..."

I think this should be partly randomized but related to the type of planet. You ARE basing the generation of planets on things like the type of their star, distance from the star, type of planetary system... right? Some things that are very useful should be very common, if they are useful only in bulk. Think of iron vs rare-earth semi-conductors. But there should be surprises, and options -- different minerals useful for similar things, but with drawbacks and advantages, according to their properties -- making refining, smelting/alloying and crafting all the more valuable and interesting, and an actual intellectual challenge, not just a matter of following pre-made recipes. It will also mean that the usefulness and value of various minerals will vary. You could also make some rare ones useful for other purposes, like maintaining health and treating diseases (or being poisonous?). Ooh, think of radioactive materials, or "radiant energy" rocks, both very useful for fueling and weapons but dangerous to extract and process? Maybe getting ahead here. 

 

"Each biome will have a set of typical resources associated with it, so prospecting starts by “knowing your biomes” ... [chart indicating rarity = depth]

 I don't think rarity should relate simply to depth. If something is really rare, it will be hard to obtain at any depth. It would be more interesting to have a few of those, plus some things that are fairly common and very useful, but only found in small, scattered deposits at great depth.   As I was saying, generate what's in the ground based on the ground that has been generated. I would not go by biomes, per se, except for some surface and near-surface minerals. Base the generation of minerals on the geological forms -- rivers or dry canyons, basins (lakes, oceans, dry), plains, hills, foothills, mountains. Players will learn (NOT be told, except by other players, forums, wiki) that certain minerals can be found only in or at a certain distance from these features. The kinds/qualities of the minerals should be generated based on some logical relationship to where they are, e.g. harder minerals found at greater depth, or maybe where rivers/canyons cut through mountains.  This is natural and will allow for the quick generation of mineral deposits on-demand/scanning, without having to load up lots of data in each planet to begin with.