I have plenty of mods that add new ores (FTB Industrial Contraptions, Mekanism, Thermal, etc.), and all of them mask the natural iron ore chance to appear, making it extremely rare to find (commonly copper is very abundant but has no significant use (for example Create Crafts & Additions or Additional Blocks give copper a set of tools)), or gold has no use either.

Edit: Title is supposed to say "make iron ore a little more common"

Unless they are actually changing the vanilla ore definitions they won't change the chance to spawn.

Except maybe that it will try to spawn and find other ore blocks (which are not "ore replaceable") occupy the spaces instead of stone, deep slate, etc.

 

If you make your own datapack: https://minecraft.fandom.com/wiki/Data_pack

you can replace the definitions yourself and change how the veins generate.

e.g. how many veins it tries to spawn per chunk:

https://github.com/misode/mcmeta/blob/6770559daf160f81f38a8d8a6e1558498efed37f/data/minecraft/worldgen/placed_feature/ore_iron_middle.json#L6

or how large the veins should be:

https://github.com/misode/mcmeta/blob/6770559daf160f81f38a8d8a6e1558498efed37f/data/minecraft/worldgen/configured_feature/ore_iron.json#L5

It could also be other worldgen is adding things that are not "ore replaceable", e.g. some other type of stone?

28 minutes ago, warjort said:

If you make your own datapack: https://minecraft.fandom.com/wiki/Data_pack

you can replace the definitions yourself and change how the veins generate.

Honestly, Datapacks and mods don't go well. Unless they're a way to change something from a mod, i don't like having to drag-drop a dp folder every time i have to make a world.

Why don't they go well? Mods are datapacks too.

You could use a mod like this: https://www.curseforge.com/minecraft/mc-mods/drp-global-datapack

or I believe kubejs also adds a folder to be used as a resource/datapack https://wiki.latvian.dev/books/kubejs/page/loading-assets-and-data (old docs)

or you could just make your own mod that is little more than whatever worldgen files you want to modify.