"Certainly it is possible that the rock is simply denser due to the increased pressure, but that may not be the sole reason."

This is not the case. The density is slightly higher at depth, but negligibly so. Further, once the drill bit cuts the core, the pressure is relieved and the density due to pressure abates.

Now, on to some interesting questions. Is this report of higher density accurate? Does this imply or hint at higher metal content? What do the geologists here have to say?