I recently had the occasion to sit and talk to an independent gold miner. This fellow had spend many seasons in the Yukon doing placer mining and had a few useful things to say about it.
In my friends experience the Alaskan placer mining season is very short- just 100 days or 2400 hours per year. In that time you have to get your operation in place and process enough gravel and sediment through the sluices or centrifuge to isolate enough gold to make the process profitable. Sluicing and centrifugation are just forms of classification and your system must be able to separate gold particles in a manner consistant with the particle size range prevalent in the claim.
It is not uncommon for gold to be heavily represented in the 400 mesh range, or ca 0.037 mm particle size. In the old days, miners recovered fine particulate gold using amalgamation. Some large operations like Ashanti Gold in Cripple Creek use cyanide heap leaching to isolate the fines.
Sluicing operations in Alaska require considerable cash input and preparation. Sluicing generates considerable suspended solid and turbidity in the streams and the EPA, BLM, and wildlife agencies will have to be satisfied that the environmental impact is understood and minimized. Permitting is therefore a major hurdle for potential sluicing operations beyond the small scale.
My friend said that continuous centrifugation was necessary to capture the 400 mesh gold fines in the district he worked. As the capital equipment requirements increase, the volume of sediment to be classified must be scaled up to bring a satisfactory return on investment. Manpower and ancillary equipment requirements increase correspondingly. Soon you have a camp to maintain, payroll, and a crew to feed. In remote locations, air cargo transport is necessary to bring in the machinery and supplies. There is no Home Depot down the road to supply duct tape. Just like on a trip to Mars, you have to anticipate all needs and haul it in ahead of time.
A modest mining effort soon becomes a large logistics and financing problem. It’s a wonder that anybody still does this kind of thing. But, yet, they do.