[nlitnd1]

I am proceeding on the premise that the amount of free gold to be found in stream beds and washes is inversely proportional to the particle size. This is supported by my own observations, having dredged professionally for three years in the Motherlode and by the observations of an acquaintance who confirmed my observations down to the micron level.
What he discovered is that particles in this size range accumulate not at depth but rather at the surface of a wash, with the highest concentration in the first 4in of sand. Apparently, the sand acts as a filtering medium and as the water soaks into the river bed the gold particles are accumulated. Particles of this size will remain in suspension indefinitely and to my knowledge can only be captured through filtration or electrolysis.
The task is to identify and successfully apply a leach to this surface sand. The prime nominee appears to be sodium thiosulfate for the following reasons.
1.   Cost is lower than any other known leach
2.   Is amenable to continuous or batch process
3.   Has a proven track record for the dissolution of micron gold
4.   Operates efficiently in the PH range of 9-10
5.   Is reportedly compatible with electrowinning in either continuous or batch mode
6.   Non toxic
7.   Operates aggressively at 80 deg. F

After several unsuccessful attempts at a batch leach extraction utilizing 50 gal barrels I decided to test the solution on filings from a gold crown tooth extraction. After several days immersion in solution I could not detect any change in the filings.

Question- Are the filings too large to be noticeably affected?
                   Are the alloyed metals interfering? Thiosulfate is known to dissolve only the topmost rungs of the electrical ladder. Gold, silver and platinum group.