Your comment - 'I think they should bring the tax in, but gradually,and progressively over a decade or so,and put all that extra money in to mending this country', ignores the fact that commodities booms are cyclical and in a decade the chance is that the high prices are gone and only Tier 1 mines are still operating.
This is why exploration in times of high prices allows for new resources to be found, that hopefully have low operating costs and can survive the lower prices in the future. You only have to look at the past to see these cycles.
