If this is the same thread about the sand with microscopic gold posted elsewhere, I think there are many considerations that need to be made before jumping into this. First being access to the beach to work on this material on a scale that will be required. Second is if the gold is detected and quantified to be worthwhile, aqua regia is a very expensive way to go and leaves you with a waste to process.
I think that if a dissolve in AR yielded a positive stannous test, the next step would be to drop all of the solids and filter them and do an assay fusion and cupellation to quantify the gold content.
Only then, when you are analytically convinced there is a payable lode there will the discussion of best leach methods be addressed. Cyanide is a viable option but not in a public space. Is this your land to work on or will this be a bucket full at night type process?