An unusual combination - a trout dam and informal miners which you might see bagging paydirt at the outlet from the trout dam.
The cache is a nano, and should be easy to find.
NB: The Slaaihoek Pass road goes all the way through to Vygeboom Dam. Maps don't show the road past the mine, but it's there. Just turn sharp right onto the dirt road just before the security point at the mine entrance, and follow your GPS to the caches.