"...implied that the most copper and highest grades were at a depth of around 5,000..."

If I recall correctly, that was an interpretation from Ztem remote sensing. However, J. Briscoe later informed us that Ztem does not reveal skarn//CDR (carbonate replacement deposit). His geophysical analysis suggested skarn/CDR was near the surface at Hay Mountain, where he found copper oxide exposed in surface rocks—quartz and marble—suggesting a near-surface source he thought could be as close as 200 feet below. 

Again, the difference is that Ztem suggests a copper porphyry at depth, perhaps about 5,000 feet, while skarn/CDR showings may be nearer the surface if one drills the right location.