Here's an interesting look at resource developement from the Ekati Diamond Mine perspective (remote mine north of Yellowknife).
A kimberlite pipe known as the Jay Pipe was to be developed. The resource had contained diamonds of between 7-10 billion dollars worth (10-12 years mine life). Permitting was compete and the EA was competed and accepted. Mining was clear to proceed.
The pipe required a Dike to compete and was reasonably capital intensive from a construction, stripping and operational perspective. The Ekati mine however contains all mining and processing equipment since it was an operational mine and if fact is still in operations. Only limited facilities would have to be constructed and all personnel were trained and in place.
Despite the value of the resource, it was determined to be uneconomic to mine. It actually had a post-tax NPV of postive 610 million, however considering cost escalation and project contingency was deemed uneconomic.
The project was abandoned even though permitting and EA were complete and construction was authorized to start.
A somewhat similar story to the Nico deposit. A great deposit, but uneconomical to mine in the North. Consider that this was a mine in full operation versus a mine that still has to be fully built and staffed. Lots of risk for investors.