I disagree. Phelps Dodge, being the best in the business at copper ore smelting, did not let a "lil of this or that" slip by. They had the best metallurgical engineers of the time working on their process to extract every penny of value, including the gold. To think they would let any appreciable amount gold slip by in the slag is ludicrous. They were profit driven, just like any other mining company, and they did not let stuff slip through, or heads would roll.
Also, and I have said this before - the direct smelting ore that was processed in Clarkdale, never ran half an ounce per ton in gold. Maybe a tenth of that (0.050 oz/ton gold). There is no reason to think that a waste product would somehow have ten times as much gold as the original ores. That is also ludicrous, but the fine folks at SRCH would like investors to believe that lie because it is the basis for their scam.
What's in the slag - the usual iron, silicon, magnesium, some sulfur, etc. Maybe some detectable gold, probably not, I have not seen any reliable assays (and certainly not from SRCH). Probably a little copper too, but not much of that either. Again, the old-time smelters were pretty damn effective - they were not dumping valuable minerals out as slag.
What's in it for Luxor? Maybe discounted stock in lieu of cash? That's how it usually works with toxic financiers.