This would greatly change the dynamics of smelting and smithing, though. While in a fort without fuel (in this case wood) a fort must rely on other things or outside sources, this would allow all forts to be able to smelt equally. Also, a metal like adamantium which is in limited supply always, is not something you want to lose a single bar of, but would leave a fort with less overall because the rates of occurence, I am pretty sure, aren;t easily modifiable...
And... I don't know that one can make things be created more densely. You can make the occurences larger, though. Change in the matgloss_stone_mineral (where the ores are) the specific environment in which it is generated.
For example:
[ENVIRONMENT_SPEC:SANDSTONE:VEIN:100]
changes to
[ENVIRONMENT_SPEC:SANDSTONE:CLUSTER:100]
An example of a vein in the current way is something like the normal metals, like a copper vein, gold vein, and such. Things that spawn in clusters are, as an example, Magnetite, Olivine, and Microcline... Other options are CLUSTER_SMALL which is the size of a normal gem cluster, and CLUSTER_ONE which is an individual crystal. I don't think there's any others, or at least I haven't seen them, though it would be cool if there were.