Oraxen doesn't natively support ores generation, instead you can use world generators like IrisWorldGenerator, EpicWorldGenerator or RealisticWorldGenerator.
For most custom world generators you need to find your custom block data. This can be achieved using any minecraft version on a server running Oraxen. Just place your block (you can get it from the oraxen inventory of give it to yourself through a command) and press F3 while looking at the block you want to add.
A noteblock based custom block
A mushroom based custom block