I always play with block durability on 25%, and do a loooooot of mining.
In a17, it's best to just do boulders until you have an auger. Once you have that, dig every gravel spot you can find in any biome. My world has tons of tiny holes because of all the ore prospecting I've done. Most of the time you will get sand, rocks, and iron. It is uncommon to find lead, nitrate, and coal in the gravel you dig up. This is true of any biome, I know it says iron is the dominant ore of forest, but it's a dirty lie. It's the dominant ore of EVERY biome. Sooo much iron is why it's hard to find the others. But keep trying... Dig every little gravel spot (which can be hard to see in some biomes like burnt) and eventually you will find one of the other ore types. Many times an iron deposit can segway into other ore types too, so dig multiple gravel spots in the same general area, if you found iron there first.
Great.
Now follow that gravel patch! Don't go straight down, follow the gravel. You at times might loose the trail, so dig a layer or 2 of stone as another user here said.
Eventually you will find that ore patch.
With an auger this ends up being better then mining boulders. You can extract vast quantities of potassium\coal\lead from just finding one of these deposits. You will also occasionally find a treasure deposit too which gives gold\silver\diamond. The experience gain from this is faster then doing anything else in game atm, even if you don't have an auger. Okay, I suppose you COULD do a lil better, on bloodmoons with molotovs, but that is only once a week, and mining is 24\7.
You will generally find more potassium in snow\wasteland and coal in burnt, but for the most part you can find enough of everything but oil, in any biome. I often don't need to make mines in every biome, just forest and desert.
Shale can be annoying to find, you just have to be really persistent. With auger it's super easy to find, tearing huge long tunnels in minutes, I would advise going pretty deep for best results. There are times I had to make tunnels over 2km long to find something, to give you an idea. Branching tunnels around 500m would probably be a saner way to do this heh.
Just 1 shale deposit is enough oil to probably cover you for the entire game, including grinding levels with auger to lvl 200.
Overall I feel no change was made from A16 vs A17 for underground mining, though I finally found gem deposits in A17, which I honestly can't remember ever finding before in previous alphas.
It's sad how boring (get it?) mining is right now. I really wish tnt was used for it instead. Tearing humongous holes and leaving the proper amount of ores to vacuum up after and finally also giving you the proper amount of xp... but instead you get almost nothing and it makes small holes. Actual mining in real life is done with EXPLOSIVES not ice augers, and it's soo much more fun and cool then this game makes it out to be.
Anyhoot, happy ore hunting! May you find lots of gold in them thar hills!