Judging by the billions in shareholder value lost by miners in the past few decades, selling out is clearly not an easy decision.

Edison Investment Research analyst Charles Gibson has picked the spot for investors to get in and out, in a presentation at Mining Journal Select London.

Using as an example Australian explorer Sirius Resources, which was bought out by Independence Group in 2015, he showed that getting on board when a company hinted at a big resource could be a winning move.

"If you didn't get into these shares within the first 10 weeks of that (A6c per share) hole (in 2012), on average you made zero money," he said.

Sirius skyrocketed to $5 a share (US$5.25 at the time) in 2013 after it demonstrated the promise of the Nova deposit, but those who bought in after that point did not make major gains, Gibson said.

"This company is fantastically successful: they announced a resource, they announced another resource, they got it in to production successfully, but if you got in after the jump, you wouldn't have made any money at all."

Using Edison's invented ideal junior gold company NonSuch Gold, Gibson said buying before the prefeasibility study was released or before it was turned into a bankable study was the best way to go.

"In the first four years, you're probably going to get a negative return …. [but] you're going to get two big positive returns for your studies. That's as you go from scoping to prefeasibilty, prefeasibility to bankable and you're going to lose money in financing and you're going to make money again as you go into development," he said.

"Once you're in production, your returns are pretty boring."

There is some difference between the Australian, Canadian and London markets in this regard - Gibson says London is more optimistic about future resources than the colonials - and also between metals.

But the Gibson rule could save investors from waiting until financing stumbles to get out of a middling miner.