May not be the best way to work out the viabilty of an individual resource stock. Best to start with the AUD price that gets a unit of production onto the market with a viable profit margin. The small gold explorer, Dioro, estimated the figure for it was AUD550. At about AUD532, Doro is a bit behind the eightball.
For AUZ, the aspiring nickel producer, it's budget AUD price per ton is 15500. At 0.80 AUD/USD that's about USD12400. Ni closed at about USD14700/ton on friday so AUZ is still well ahead. In fact about AUD3000/ton at the present dollar rate.
When I look at a small resource stock that is how I would approach it (also making sure there were not too many shares on issue and a viable resource had been delineated,which of course implies mining is in the planning stages. Penny "dreds" with less than this are pure gambles).
