I wouldn't get too specific in the wording of what equipment to include i.e. sluice, highbanker, etc.
I would bring it back to the original intent of the legislation and that was to stop people bringing in a bloody big D9 and ripping up the place without having a mining claim / lease.
I would reword it as follows:
Definition of Heavy Machinery:
Heavy Machinery refers to heavy-duty vehicles, specially designed for executing construction tasks, most frequently ones involving earthwork operations. They are also known as, heavy machines, heavy trucks, construction equipment, engineering equipment, heavy vehicles, or heavy hydraulics. They usually comprise five equipment systems: implement, traction, structure, power train, control and information. Heavy Machinery functions through the mechanical advantage of a simple machine, the ratio between input force applied and force exerted is multiplied. Currently most heavy machinery employ hydraulic drives as a primary source of motion.
Permitted tools and extent of diggings
Hand tools such as picks, shovels, hammers, sieves, shakers, electronic detectors and other traditional hand tools can be used.
No heavy machinery is permitted.
38 Use of heavy machinery etc. prohibited
A person fossicking under a licence must not use heavy machinery to fossick.
Maximum penalty400 penalty units.
Can't make it any clearer than that.