SA regs are pretty vague, so long as you backfill your holes, do not destroy vegetation, and leave the area as you found it, you should be fine. Remember, it is only fossicking, so no need to to dig the hell out of an area taking more than your fair share, the authorities may deem that as procuring minerals per fininacial gain, which is not permitted. There are a few mineral localities around the Mount Crawford area, but unfortunately many have been obliterated by people who can't help themselves, and try to take the whole lot - one Beryl locality comes to mind.
Also remember it is an offence to fossick without a paid permit from the forestry headquarters, if not attended, enveloped are provided for the money, and permit sheets/pens are on hand.
Sailors Gully still comes up with some good Schorl Tourmaline crystals, about 3/4 the way up the gully on the left side, last time I was up there I grabbed a couple. You do find random good quality quartz crystal around the place, even quartz with rutile crystals in them have been found in the area. The crystal you found could have shed off from anywhere, but probably not too far from where you found it judging by how fresh it looks. Some of shafts in the area may have also intersected some vughs that contained good crystals, so they may shed from some of the workings.
If you don't already have the map of the mineral localities, here is a google link to the map pdf at the top of the search page:
http://www.google.com.au/search?q=m...tIH4Dw&ved=0CAcQ_AUoAA&biw=1280&bih=800&dpr=1