definition is sometimes a requirement for discovery...
You lost me there. By definition, defining an orebody cannot occur until one is discovered.
Of course ore grade matters, whether it is shallow or deep. Not all porphyry or skarn deposits survive the exploration phase, or the feasibility study stage. Most don't, in fact. Some porphyry systems give you a bunch of pyrite and little else. Some skarns give you a bunch of garnet, hematite, or calc-silicate minerals and no metals.
Maybe what you mean is that you are interpreting "discovery" to mean proof of an economic orebody, in which case you do need definition to be completed sufficiently to allow for that.
There is probably an ACME definition of discovery, but off the top of my head, I see the word "discovery" to mean uncovering sufficient evidence that an economic orebody is a reasonable possibility. For example, a drillhole with 200 feet averaging 0.4% copper is a "discovery", IMO. Is it proof of an economic orebody - no, not necessarily. It takes many other holes with reasonably good results, plus a positive feasibility study to confirm an economic orebody.
Market Data 
Markets 
