As outlined in previous RBA work on the topic, a significant share of the very large increase in investment in resource projects has been funded through foreign direct investment in the form of retained earnings.5 To the extent that resource companies have also used external funding sources, they have generally accessed offshore debt markets directly, rather than obtain funds through the domestic banking sector.6  reflects the fact that Australian banks have higher credit ratings than most other banks, proving attractive to customers whose mandates are rating constrained.
Another contributing factor is that the Australian banking sector can raise US dollar deposits from customers who do not have direct access to the US Federal Reserve and then deposit the funds at the Fed and earn the (small) spread. One might expect this activity to decline when US interest rates move away from zero.