That makes complete sense, if we remember that this is supposed to be volcanic in nature. Since the earth's crust, at the time the deposit was formed, was several miles thick, it is (in my uneducated opinion) unlikely that the motherlode(s) are going to be near the surface, at least to a point where we have drilled. Most of the exciting finds have been open at depth, which I do not find surprising.

Nevertheless, this is exciting stuff, and it means that the real value for this entire area will be unknown for quite some time yet.