au dollar could reach 1976 level of $1.40, page-2

Interesting argument - but if many Australian mines became marginal and were mothballed due to high AUD, this would also constrain the supply, which would in turn drive the price up further (in a free market)

If other high demand commodities were marginal as well, and mines were mothballed, export would drop, demand for the AUD would drop and the market would find a balance.