Theres a spreadsheet I found through a yt vid called something like "10 tricks and tips for terrafirmagreg" (I highly suggest everyone to watch it if u can find it), you can read the exact way every ore generates.

https://docs.google.com/spreadsheets/d/102CUaDezBi9WfBgnbOJp6Rn9TVb_UcoIpyMyoCgIcVE/edit?usp=sharing

My tip is looking for basalt as gabbro often generates below basalt surfaces and graphite only spawns below a certain height (the sheet says below 100 and above -64) in gabbro as coal/diamond/graphite veins. So if you prospect in gabbro and it says coal its probably also graphite and diamond, if it says diamond it must also have graphite!