Thats a whole nasty can o worms.
If you confiscate the equipment you CAN be charged for theft-not very likely but you could.
If you find the equipment on your claim you can legally remove it but should place an add in a local paper advising of removal and storage,and appropriate fees for such.
This establishes that you did NOT “intend to permanantly deprive” ownership of equipment,thereby satisfying the law on theft.
All your left with is “unlawful posession”.
Need to speak to a lawyer about this part.
The other problem is that claims are on rivers-surprise surprise(mostly anyway) and ANYONE is allowed access to rivers under queens chain-as long as it is accessable from public property or from the river itself.
This means that people have the LEGAL RIGHT to be on your claim,but not for the purpose of mining.
Tramping,camping,hiking ,or just general sightseeing is someathing you cannot stop.
There are a few exceptions where the claim also has access rights too.
Another approach is that the equipment is abandoned on your claim and you are entitled to posession,after a few minor hurdles(see above on establishing lack of intent)
The final way is to just DESTROY and remove the equipment without being seen-the onus of proof is on the other party and without witnesses youre in the clear.
The case in court would be something like "well mr cods wallop,you claim you had commercial gold mining equipment in operation in an area YOU had no legal right to be operating in,you left said equipment in the area unattended and upon return to the area could not locate said equipment.
You did not observe anyone with said equipment,or remove said equipment and NOBODY has admitted removing said equipment.