Mercury won't effect your sluice box if you frequently clean out the concentrates like as a bare minimum daily.
I have heard of it attacking the aluminium if concentrates are left in your sluice for extended time period like a few days or more
though i have never seen that myself.
The anti mining activists have been successful in portraying a myth that there is like litres of liquid mercury laying about in
stream sediments, but in reality its not that common, occasionally some of your gold will be partly coated in it.
I once panned some liquid mercury droplets in a creek? I suspect somebody had been experimenting with it, as it
was at least 1km downstream of the nearest old gold battery site.
Mercury lost during old mining would have been heavily dispersed by floods since, not saying it does not exist as fish flesh samples
confirm widespread effects.Finding large quantities would be very rare.