If I was a hedge fund that could use significant leverage, I think I would be quite happy shorting BHP and putting the money in Australian bonds of similar maturity.
That arb is also bet on the relative value of the Australian dollar versus the US dollar or perhaps a bet on the relative inflation/interest rates of the two countries. So you would also need to hedge out that risk or hope it goes the right way.
ij
It is astonishing what foolish things one can temporarily believe if one thinks too long alone ... where it is often impossible to bring one's ideas to a conclusive test either formal or experimental. J.M. Keynes