I've been out mining the last couple of nights and there's plenty of minerals on alpha for a solo miner, but no, I couldn't mine AFK, I acutally had to actively retarget and think; which was a pleasant break from running transport missions.
The mineral field I was on could have easily been depleted in 2 hours with 4 Rivelers. I did about 5% of the field and got about .8 M ore with only the bot bonus's. With the proper extensions, at level 5 only, would have been 20% more, roughly 1M ore. The entire field then will produce 20 M ore in about 2.5-3 hours.
While scanning I also found another field of a different ore within 3000 m of the previous field, I estimate that field would produce about 42 M ore in the same amount of time with 4 Rivlers.
* I specify Rivilers because it requires a dedicated industrialist to reach lvl 8 to even drive it
The next fields are likely to be further, but there's no spot more than 4000 km from a teleport on alpha.
Mineral fields now are larger with fewer cycles per stack. The total maxium amount of ore per field was reduced as was the recovery time, resulting in overall less ore per Island; with Beta levels being higher.
My personal experience mining pre patch on alpha -
I didn't need to area geoscan because my corp had already found the ore spots. I didn't need to tile scan because the whole thing was red. I would roll up in an Argano, target a spot, and empty my cargo about every 10 mins (Later with a termis it was every 5 minutes). I would sit there for hours and watch a movie or two, changing targets 3 or 4 times. I didn't put any skills into yeild, just enough EP to keep the termis AP stable. The remaining EP I spent on production lines.
The volume of ore we were gathering on alpha made 'effciency' meaningless in the production of assualts and ewar (no one was making mechs at the time).
As we progressed into Mech production, most of our miners also moved into Termis's, as well as our PVP players' mining alts. We still could not deplete a 'red' field of material on alpha; but only our dedicated production characters produced mechs, off spec producers like me just did ammo and charges.
We moved all operations to Beta Islands, including mining. Here we ran into logistical issues with combat coverage, roaming pressure based on time zones. Miners weren't able to mine, and there was nothing else for them to do, so they stopped logging in. We moved islands, which made it safer, but by that time the exodus from the game had already begun, and we just ran out of miners and production stopped.
At no time did we ever have any type of challenge with the minerals, just the logistics of getting them.
There is now a challenge with mining, the need to supervise your bot while mining, but finding and recovering the ore is still just a matter of logistics.
The current global amount of ore is about to change with the addition of 6 new Islands. There's a difference between a Challenge and Risk, mining should be challenging just as PVP is risky. Mining directors are going to establish the most productive means of gathering ore, previously that was putting as many bodies on the field as possible without regard to skill, now just putting bodies on the field is wasting ore and is less productive then putting fewer skilled agents on it. I also appreciate the fact that I don't have to sit there for 6 hours a night all week anymore because the field still has ore.
Yes, it is more difficult now to make NIC at mining, but as pointed out in the 'cast and by Syndic, people want to buy ore. You just have to dedicate your character to the task to make it productive; which is absolutely no different than any other role in the game.
and then the people that wanna sleep and give the stations away.. go back to alpha to produce :>
2 ways of doing it, and more fun pvp 
