This mod adds 'dense' versions of ore blocks that will drop 3x the items that regular ore will. It generates about 1-10 dense blocks per chunk (replacing already generated ores). for an overall increase in ores of about 5%.
The textures for the dense ores are dynamically generated from the base ores texture and the equivalent 'stone' texture. This means that you won't need to create a new texture for your texture packs (although you can create one anyway if you're not happy with the way it looks) .
In addition new ores can be added through the config system, details of which plus examples can be found of the github. Please note that this is intended primarily for modpack developers and as such is not recommended for basic users.