RE: I bot ARG other than DNTI don't think they're really comparable. Candente is an explorer with no cashflow, where investors are essentially betting that someone will find the deposit attractive enough to buy them out.
Amerigo is a somewhat unique copper producer, since there aren't really any public companies with a similar production model. At least for me, the attraction here is not the potential for a buy-out (as I don't think one will happen), but the cash-flow potential if copper prices stay high. The current depressed price likely reflects fear of an economic slowdown and hence lower copper prices.
Chile does come with a smaller risk-premium than Peru at the moment, but do be aware that Amerigo still owns 5 million Candente shares, so they do have some indirect exposure to Peru.
Also, Amerigo is certainly not one of the world's larger copper producers. They do happen to get their raw material from a very large mine (ie. El Teniente's tailings), but that's not quite the same.