I’ve been doing quite a bit of research into Thomas Edison’s 1882 patent (U.S. Patent No. 263,131) for placing magnets underneath a gold sluice.
The idea was pretty ingenious, using the magnetite/black sand flowing through the sluice. The material would build up in ridges above the magnets, essentially creating its own renewable riffles, and those black-sand riffles would help catch the gold.
I’ve searched for evidence of this type of magnetic sluice actually being used during the old hydraulic-mining era—not just in California, but also looking at mining history from places such as Australia and New Zealand.
So far, I haven’t found a photograph or historical record that conclusively proves that Edison’s exact under-the-sluice design was put into regular operation at a hydraulic mine.
The closest lead I’ve found is the old Cherokee hydraulic mining operation near Oroville, California. Edison and Frank McLaughlin were involved with experiments at the Cherokee Hydraulic Mine involving the black sands and tailings from that area around 1879–1881, immediately before Edison filed his magnetic-sluice patent in June 1881.
Unfortunately, the timing couldn’t have been much worse. Hydraulic mining in California was already coming under increasing legal attack because of the enormous amount of debris being dumped into the rivers. Edison’s California mining work and the development of his magnetic sluice occurred right around the same period that injunctions and, soon afterward, major court restrictions began shutting down large-scale hydraulic mining in certain areas.
So it’s entirely possible that the hydraulic mines and their black sands helped inspire Edison’s idea, but the industry he designed it for was beginning to disappear before the invention had much opportunity to be commercially developed.
I’m still looking for the real smoking gun: an old photograph, mining report, newspaper article, engineering journal, or mine record from anywhere in the world showing magnets mounted underneath a working hydraulic-era sluice.
It doesn’t have to be Edison’s system or even connected with Edison. If anybody knows of an old hydraulic or placer operation anywhere—California, Alaska, Canada, Australia, New Zealand, China, Russia, etc.—that used magnets underneath the sluice to create magnetic black-sand riffles, I’d really like to see it. The same system has been patented in other countries from 1901 to present.
