RE: GET READY FOR MurphyMount Stewart, (not literally) and they already have them. Close, but no cigar or socially acceptable equivalent.
As far as 50 ppb, it depends on the soil profile, erosion and rainfall rates, sample depth, and typical anomaly threshold in the area, as well as the particular soil sample preparation and lab analysis technique. >20 ppb Au is the anomalous threshold in many areas. A few >1000 ppb screamers would have been nice, true. Compare to the published soil geochem maps by UW for comparison. The line spacing was not very dense, so that leaves a lot of room for things to slip between the cracks. You could squeeze a decent mine into 300 meters if the grade was good enough.
Not that I own any of this anyways.