Standard replicators are able to replicate mundane materials and smaller not-too-complex machines. At one point, under the influence of a Cardassian anti-riot program, the replicators in DS9 are magically able to produce something like a self-targetting automatic phaser gun.
Normally, for more complex tasks, such as "building a powerplant" or "making major parts of a starship", very special and rare "industrial" replicators are needed. Apparently, an entire planet normally doesn't have more than half a dozen of these, and they are valuable enough for super secret security measures so the Maquis won't steal them (which they do anyway).
In either case, replication is the process of turning energy into matter.
In addition to their main power supply and thrust, the self-replicating mines contain a standard photon torpedo warhead, which means that they are able to release a considerable amount of energy (which is "gone" after the explosion) from a matter/antimatter reaction. The energy, and of course the antimatter must come from somewhere (regardless of the energy needed, can a replicator replicate antimatter at all?).
It seems improbable (if not impossible) that self-replicating mines could work at all. If you were able to replicate an energy cell containing the same amount of energy as the original one plus a considerable amount of matter/antimatter plus some other stuff, like a cloaking device then you would have the most perfect perpetuum mobile imaginable.