Wrong. Funny, a writer from a gold producing state should know better.
The mercury, being very dense, will find its way to the lowest point in the stream-bed. eventually it will work its way down to bed-rock where it will stratify, along with gold, lead, silver, platinum, iron and other dense metals.
While dredging for gold in North Georgia and the Carolinas I have personally removed (dredged up) ounces of liquid mercury from stream beds where it has lain, undisturbed, since at least the 1850s. These creeks and rivers are home to many species of fish, none of which are suffering from mercury poisoning.