G'day Chimpy,
Been out there a few times and It's a great experience. Corona Station is just off the main road and you have to pretty well go strait past it to access the field. They were real helpful last time we went but it was a few years back. Their main concern was you close the gates, especially the old rickety wooden gate half away in.
We found Amethyst Hill was flogged to death and not worth persevering with, but Long Valley produced heaps of "Loose" crystals for us. The western side where they mark "Smokeys" has more amethyst than you may think. Plates are not easy to find as you need at least a few days to open a reasonable size hole to expose them. Greens are scarcer than hens teeth.
Best way to find pockets of "Loose" crystals is to check out the sides of the many small trenches along the side of the hills. You will find certain sections have small crystals scattered in the overburden. When you find these sections just re-open the trench and you should be able to follow the run.
If you've only got a day don't bother trying to start a new trench, They're very hit and miss. I'd take a decent pick as well as a good shovel and a 1/4" sieve, as they certainly don't jump out of the trenches by themselves. If you hit a pocket you can fill a litre bottle quite quick and they tumble up to make some handsome gems. Best of luck and I"m sure you will enjoy the digging and the spectacular scenery.
Cheers Wal