This mod only works with a vanilla minecraft_server.1.8.jar server. It might not be compatible with any other mods, but it can be used with customized world presets.
1. Open minecraft_server.1.8.jar with WinRAR (or something similar) and drag the three .class files into it, overwriting if prompted.
2. Place the veins.csv file in your server folder, next to minecraft_server.1.8.jar.
Then restart your server. The new ore spawning will only happen in chunks generated after you installed the mod.
HOW IT WORKS:
The mod essentially adds some code to the chunk generator to override the default ore spawning. It loads the vein settings from veins.csv when you start the server. You can customize veins.csv however you want. It is capable of generating ore just like vanilla minecraft does, or far more interesting things. You can add as many "veins" or "layers" of ore as you want each with 20 settings to control different aspects of it. See veins.xlsx for some notes.
Here's an example preset that tries to be similar to vanilla but with the ore sometimes in clusters of varying sizes rather than distributed completely randomly/evenly as in vanilla.
I made this mod because I want more interesting distributions of ore to mine. I want to hit ore and have that indicate that maybe there is more nearby, but without certainty. I want to have various mines at any elevation in the map, rather than always going to level 12 to mine. This mod can achieve all these goals for me. I'm sharing it in the hope that others will customize it in interesting ways that maybe I can reuse, since there are too many possibilities for me to figure them all out on my own.
Back up your world before using this just in case. My apologies if the documentation isn't very good, this is a beta and I'm mainly sharing it so other modders can mess with it and make something interesting.
Feel free to modify and/or redistribute any part of my work and/or use it in your own mods. Credit is nice but not required.