Ore spawning randomly underground when mined

The only solution i have been able to find which is still maintained is Ore Respawn which is a bukkit plugin which changes the mined ore to Bedrock and then after a configurable amount of time it will turn it back to the original ore.

I understand this is not an ideal solution as 1. bedrock is annoying and 2. players could remember where diamond was and just get unlimited.

The config is good and allows you to choose which ores or blocks this applies to, and the creater is looking to change the bedrock replacement.

Link

Another idea which doesn't affect generation is the OreGenerator Plugin which gives cobblestone generators a chance to spawn Ores.

Link

And last but not least. My favourite solution is to create a multiworld server using the MultiWorld Plugin

Have a world for mining then regenerate this world every day or week. even with a dif seed to make it interesting. That way the main world isn't an issue, Just make sure no one builds in the ore world.
You can even make this have better ore gen and make it a rich world that way.

A command-based option that also requires WorldEdit (assuming that WorldEdit commands can be run from command blocks), would be running 3 command blocks on a not-too-fast clock. Let's say you want ore to repopulate in the quader from (-1000, 0, -1000) to (1000, 100, 1000) with coal and iron ore at a frequecy of 10% each and diamond ore at a frequency of 3%, assuming you have all chunks within this area loaded. Then the commands, run shortly after one another, are:

1) //pos1 -1000 0 -1000

2) //pos2 1000 100 1000

3) //replace stone 77%stone,10%coal_ore,10%iron_ore,3%doamond_ore

Set them up as a normal command block chain: Set the first command block on "Unconditional" and "Needs Redstone" and lead the clock output to it. Then, chain the other 2 command blocks to it with "Conditional" and "Always Active". (Assuming you use 1.9 or higher, otherwise still put the clock to the first one, but then place a comparator leading out of it into the second one and another comparator out of the second one into the third one, since 1.8 had no native command block chaining yet so you have to implement it manually using comparators.)

If you use MCEdit, you can mark chunks for repopulation (note: this is different from regenerating the chunk). This cause the game to re-generate all of the ores, as well as re-grow trees. The good thing is that ores only appear where stone used to be, so dug out areas won't fill back up again, and you'll can get new ores in an older world. Downside is that it also makes new water pockets, so you could end up with water in your underground areas.