I have no problem about nickel and copper being economic to process. Where I do not know and it is basicly because it is fundamentaly a nickel mine possibility, is the economics/chemistry of processing these multiple metals. If you optimize for nickel than some and perhaps all of the other metal extraction processes take a penalty.

My history is gold/silver/copper mines, little with base metals.

Let me use an example. If you have a pure nickel mine then you would extract say 90 percent of the metal in the ore. If you add copper to the ore and process for both then your nickel percentage is likely to go down to 88 percent and copper at 75 percent. ( Pure copper might be 90 percent also.) If you now add palladium or some other metal to the ore then nickel and copper percentage again is likely to decrese further.

My point is that eventually you reach a point where the dollar loss from extracting nickel or copper is not offset by the gain of another metal. Hence that other metal may not be economically practical to process for.

Seen it often with precious metal mines, I suppose with other metals is of little difference.

That is why we have feasability studies to determine best combination for top value.